Proceedings Volume 8679

Extreme Ultraviolet (EUV) Lithography IV

Patrick P. Naulleau
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Proceedings Volume 8679

Extreme Ultraviolet (EUV) Lithography IV

Patrick P. Naulleau
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 26 April 2013
Contents: 13 Sessions, 91 Papers, 0 Presentations
Conference: SPIE Advanced Lithography 2013
Volume Number: 8679

Table of Contents

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Table of Contents

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  • Front Matter: Volume 8679
  • Invited I
  • EUV Resists: Joint Session with Conferences 8679 and 8682
  • Sources
  • Mask I
  • Resist Outgassing
  • Optics and Metrology
  • OPC and Modeling
  • EUV Resists
  • High NA and Magnification
  • Mask II
  • Invited II
  • Poster Session
Front Matter: Volume 8679
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Front Matter: Volume 8679
This PDF file contains the front matter associated with SPIE Proceedings Volume 8679, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.
Invited I
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Effects of multilayer period on EUVL imaging for 2X node and beyond
In EUVL, major impacts on determining critical dimension (CD) are resist process, scanner finger print, and mask characteristics. Especially, reflective optics and its oblique incidence of light bring a number of restrictions in mask aspect. In this paper, we will present one of the main contributors for wafer CD performance, such as center wavelength (CW) of multilayer (ML) in EUVL mask. We evaluate wafer CDs in 27.5nmHP L/S, 30nmHP L/S, and 30nmHP contact patterns with NXE3100 by using masks with purposely off-targeted CW ranging from 13.4 to 13.7nm. Based on the results from the exposure experiments, we verify that the CW specification for NXE3100 is regarded as 13.53 ± 0.015nm at CWU=0.03nm to satisfy the wafer CD requirements. According to verified simulations, however, we suggest a new CW specification for NXE3300 with higher values considering wide illumination cone angle from larger numerical aperture (0.33NA). Moreover, simulations in different exposure conditions of NXE3300 with various patterns below 20nm node show that customized CW specification might be required depending on target layers and illumination conditions. We note that it is also important to adjust CW and CWU in final mask product considering realistic difficulties of fabrcation, resulting in universal CW specification.
Investigation of EUV pellicle feasibility
Luigi Scaccabarozzi, Dan Smith, Pedro Rizo Diago, et al.
EUV defectivity has been an important topic of investigation in past years. Today, the absence of a pellicle raises concerns for particle adders on reticle front side. A desire to improve defectivity on reticle front side via implementation of a pellicle could greatly assist in propelling EUV into high volume manufacturing. In this paper, we investigate a set of pellicle requirements and potential EUV pellicle materials. Further, we present experimental results of pellicle performance results and imaging results.
EUV resist materials design for 15nm half pitch and below
Hideaki Tsubaki, Shinji Tarutani, Naoki Inoue, et al.
Chemically amplified resist materials with a different sensitivity were prepared to investigate impact of sensitivity on resolution at 15 nm half-pitch (hp) using a EUV micro-field exposure tool (MET) at SEMATECH Berkeley. Sensitivity at least slower than 30 mJ/cm2 was required to resolve 15 nm hp patterns using current EUV resists. It is noteworthy that resolution of 15 nm hp was limited by not only pattern collapse but also pinching of patterns. The same tendency is observed in E-beam patterning at 20 nm hp. A strong relationship between pinching and sensitivity in E-beam exposure indicates contribution of photon-shot noise on the pinching. Clear correlation between diffusion length and pinching using the E-beam exposure indicates that acid diffusion is another contributor on the pinching. Bound PAG into polymer and molecular PAG with a big anchor group showed almost same character on pinching. Key conclusion here is even in a molecular PAG, we can control acid diffusion to achieve 15 nm hp resolution capability. Strategy to improve sensitivity is to utilize resist with high deprotection efficiency. Polymer with a low thermal activation energy on deprotection (low Ea polymer) was demonstrated as a key technology to achieve 15 nm hp resolution with a faster sensitivity below 26 mJ/cm2. Special rinse material was effective for reducing LWR by ~ 20%. Sensitivity dependency of outgassing have been systematically discussed at first. A good linear correlation between a cleanable outgassing amount and exposure energy strongly indicates tradeoff relationship between outgassing and sensitivity. Applying a new EUV topcoat to resist demonstrated reduction of outgassing from 7.39 nm to below 0.1 nm with maintaining resolution.
EUV Resists: Joint Session with Conferences 8679 and 8682
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Oxide nanoparticle EUV resists: toward understanding the mechanism of positive and negative tone patterning
Souvik Chakrabarty, Christine Ouyang, Marie Krysak, et al.
DUV, EUV and e-beam patterning of hybrid nanoparticle photoresists have been reported previously by Ober and coworkers. The present work explores the underlying mechanism that is responsible for the dual tone patterning capability of these photoresist materials. Spectroscopic results correlated with mass loss and dissolution studies suggest a ligand exchange mechanism responsible for altering the solubility between the exposed and unexposed regions.
Effect of leaving group design on EUV lithography performance
Owendi Ongayi, Vipul Jain, Suzanne M. Coley, et al.
In this paper, we will describe some of our efforts on various leaving group designs and their impacts on resist performance, mainly focusing on the leaving group polarity, activation energy and molecular volume. The EUV lithographic performances of the newly designed leaving groups are evaluated on a standard methacrylate polymer bound photoacid generator (PBP) platform. With our low activation energy and hydrophobic leaving group PBP, we report good line and space and contact hole performance using the Albany eMET and LBNL BMET tool.
Sources
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LPP-EUV light source development for high volume manufacturing lithography
Since 2002, we have been developing a CO2-Sn-LPP EUV light source, the most promising solution as the 13.5 nm high power (>200 W) light source for HVM EUV lithography. Because of its high efficiency, power scalability and spatial freedom around plasma, we believe that the CO2-Sn-LPP scheme is the most feasible candidate as the light source for EUVL. By now, our group has proposed several unique original technologies such as CO2 laser driven Sn plasma generation, double laser pulse shooting for higher Sn ionization rate and higher CE, Sn debris mitigation with a magnetic field, and a hybrid CO2 laser system that is a combination of a short pulse oscillator and commercial cw-CO2 amplifiers. The theoretical and experimental data have clearly demonstrated the advantage of combining a laser beam at a wavelength of the CO2 laser system with Sn plasma to achieve high CE from driver laser pulse energy to EUV in-band energy. Combination of CO2 laser power and droplet generator improvements on new EUV chamber (Proto-2) enables stable EUV emission. EUV burst operation data shows stable average 10.2W(clean power @ I/F) EUV emission and maximum 20.3W(clean power @ I/F) was demonstrated. For future HVM the maximum of 4.7% CE with a 20 μm droplet are demonstrated by ps pre-pulse LPP. Also reported 40kW CO2 laser development project cooperate with Mitsubishi electric.
Advances in computer simulations of LPP sources for EUV lithography
A. Hassanein, T. Sizyuk
Photon sources for extreme ultraviolet Lithography (EUVL) are still challenging problem to achieve high volume manufacture in the semiconductor industry. Currently EUVL community narrowed the research and developments to two directions: discharge produced plasma (DPP) assisted with trigger lasers and dual-pulse laser produced plasma (LPP) with mass-limited targets. Such complicated systems require extensive optimization to enhance the conversion efficiency (CE) and components lifetime and detail source optimization requires significant experimental and costly efforts. We used our HEIGHTS simulation package to study and optimize LPP sources and to make realistic predictions as well as benchmarking of key experimental results. HEIGHTS package includes 3-D detail description of various integrated physical processes involved in LPP and DPP devices. The models are extensively tested and benchmarked separately in each physics phase of laser/target interaction as well as in the entire integrated system without any parameters adjustments or fittings. We simulated LPP sources in full 3-D geometry using 10-50 μm tin droplet targets, as single droplets as well as distributed fragmented microdroplets with equivalent mass. We studied mass dependence, laser parameters efficiency, atomic and ionic debris generation, and optimization of EUV radiation output. Our modeling and simulation included all phases of laser target evolution: from laser/droplet interaction, energy deposition, target vaporization and fragmentation, ionization, plasma hydrodynamic expansion, thermal and radiation energy redistribution, and EUV photons collection as well as detail mapping of photons source location and size. We also predicted potential damage to the optical collection system from plasma energetic debris and the requirements for mitigating systems to reduce debris fluence. The debris effect on mirror collection system is analyzed using our 3-D ITMC-DYN Monte Carlo package. Modeling results were benchmarked against our CMUXE experimental studies for the in-band photons production and for debris and ions generation.
Lifetime and refurbishment of multilayer LPP collector mirrors
Torsten Feigl, Marco Perske, Hagen Pauer, et al.
The usable power of high-power EUV light sources at 13.5 nm and also the lifetime of source and collector optics are currently considered to be the largest challenges encountered during the transition of EUV lithography from the current beta-tool status to high-volume manufacturing. Fraunhofer IOF Jena has developed cost-effective refurbishment technologies of multilayer-based near normal incidence collector mirrors for high-power laser-produced plasma sources. Presently, the collector mirror lifetime exceeds 80 billion laser pulses which correspond to a lifetime of several months during continuous use of the source. Together with their partners Cymer is currently carrying out a focused program to improve the collector lifetime. New multilayer coatings together with new in-situ cleaning strategies during source operation are key technology development strategies to get closer to the ultimate target of about one year collector lifetime. The paper discusses different LPP collector refurbishment strategies and presents the recent status on collector refurbishment techniques.
Contamination concerns at the intermediate focus of an extreme ultraviolet light source
David N. Ruzic, John Sporre, Dan Elg, et al.
The emission of species that can chemically or physically alter the surface of post intermediate-focus optics will increase the cost of ownership of such an EUV lithography tool past the point of cost effectiveness. To address this concern, the Center for Plasma-Material Interactions has developed the Sn Intermediate Focus Flux Emission Detector (SNIFFED). The effects of increasing buffer gas, increasing pressure, and chosen buffer gas species will be presented. Furthermore the presence of a secondary plasma, generated by EUV light will be analyzed and exposed as a potential issue in the strive for a contaminant free intermediate focus.
Mask I
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Dressed-photon nanopolishing for extreme ultraviolet mask substrate defect mitigation
Ranganath Teki, Arun John Kadaksham, Frank Goodwin, et al.
Although the quality of extreme ultraviolet (EUV) mask substrates has improved by continuous refinement of the polishing processes, the yield of defect-free blanks is still very low. Dressed-photon nanopolishing (DPNP) is a novel vapor phase, photo-chemical, non-contact etching process that has been shown to locally smooth bumps and pits to below 1 nm in height/depth while not affecting the surface roughness. DPNP is based on the concept of a dressed photon, which is a quasi-particle in the optical near field of a surface that can couple with lattice phonons in nanometric regions (< 100 nm). When illuminated with light of a suitable wavelength, such coupled states are generated on a nanometrically rough material surface and impart sufficient energy to an etchant gas to enable its dissociation and etching in the rough regions only. DPNP can be the last polishing step on EUV substrates to eliminate any remnant pits and/or embedded particles on the surface to yield potentially defect-free substrates.
EUV mask defect analysis from mask to wafer printing
Yoonsuk Hyun, Kangjoon Seo, Kyuyoung Kim, et al.
ASML NXE3100 has been introduced for EUV Pre-Production, and ASML NXE3300 for High Volume Manufacturing will be installed from this year. EUV mask defect control is the one of the concerns for introducing EUVL to device manufacturing, for current EUV mask defect level is too high to accept for device volume production. EUV mask defects come from mask blank, mask process and mask handling. To have reduced mask defect level, quality control of blank mask, optimization of EUV mask process and improvement of EUV mask handling need to be ready. In this paper, we analyze printed defects exposed from EUV full field mask at NXE3100. For this analysis we trace mask defects from mask to wafer printing. From this we will show current EUV mask’s defect type and numbers. Acceptable defect type, size and numbers for device manufacturing with EUVL will be shown. Through investigating printing result of natural ML defects, realistic level of natural ML defects will be shown.
Defect printability comparing actinic printing with advanced simulation for EUV masks
Il-Yong Jang, Ranganath Teki, Vibhu Jindal, et al.
We describe the printability of native phase defects categorized by type and dimension using NXE3100 EUV scanner and DPS (Defect Printability Simulator) software developed by Luminescent Technologies. The critical dimension (CD) error on wafers simulated by the DPS is strongly affected by the geometry of the multilayer (ML) used as an input parameter for simulation. This finding is supported by cross section images of the ML acquired from transmission electron microscopy (TEM) showing that the diameter of the defect and geometry of the ML are closely related. Accordingly, the selection of the type of ML geometry seems to be important in the accuracy of defect printability simulation. The CD error simulated from the DPS using reconstructed ML geometry shows better correspondence with that measured on a wafer than conformal or smoothed ML geometry. The DPS software shows good simulation performance in predicting defect printability at 27nm HP node. This is verified by wafer printing and RCWA simulation.
EUV actinic blank inspection: from prototype to production
Anna Tchikoulaeva, Hiroki Miyai, Tomohiro Suzuki, et al.
The availability of actinic blank inspection is one of the key milestones for EUV lithography on the way to high volume manufacturing. Placed at the very beginning of the mask manufacturing flow, blank inspection delivers the most critical data set for the judgment of the initial blank quality and final mask performance. From all actinic metrology tools proposed and discussed over the last years, actinic blank inspection (ABI) tool is the first one to reach the pre-production status. In this paper we give an overview of EIDEC-Lasertec ABI program, provide a description of the system and share the most recent performance test results of the tool for 16 nm technology node.
Resist Outgassing
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Relationship between resist related outgassing and witness sample contamination in the NXE outgas qualification using electrons and EUV
EUV photoresists are considered as a potential source of optics contamination, since they introduce irradiation induced outgassing in the EUV vacuum environment. Therefore, before these resists can be used on e.g. ASML NXE:3100 or NXE:3300, they need to be tested in dedicated equipment according to a well-defined procedure, which is based on exposing a witness sample (WS) in the vicinity of a simultaneously exposed resist as it outgasses. Such an outgassing test infrastructure is available at many sites, but exposure modes on the witness sample and wafer can be significantly different, which potentially could lead to different test results. In this investigation, we first explored in more detail the relationship between resist outgassing as measured by RGA (Residual Gas Analysis) and the carbon growth obtained in the WS test. A good correlation was found by using a timeintegrated and mass-weighted sum of the RGA-measured mass peaks. Next, the impact of the resist exposure mode on the WS contamination result was investigated at imec, where the outgas test setup allows to expose the wafer with EUV irradiation as well as electrons in the same vacuum environment. It was found that minor differences observed in the WS test results, can be explained by adequate characterization of exposure intensity distribution and dose control. Finally the WS test results at imec from the different exposure modes were compared to the test results at NIST. The small differences in contamination that were observed could be explained by differences in test procedure, by using the time dependent RGA approach. From the combined work on outgassing measurements and WS contamination testing we have significantly improved our understanding of the relationship between outgassing and contamination processes induced by EUV photons and electrons. We have also demonstrated how to compare results obtained at different outgas testing sites, which is important in quantifying the potential risk to EUV device manufacturing posed by resist outgassing.
Resist outgassing contamination growth results using both photon and electron exposures
Gregory Denbeaux, Yudhishthir Kandel, Genevieve Kane, et al.
During exposure in an EUV scanner, photoresist and other materials coated on a wafer are known to outgas various species. As a requirement to pattern materials in an ASML NXE scanner, these materials need to be screened for outgassing and possible optics contamination. As part of the testing process, a resist-coated wafer is exposed in a vacuum chamber mimicking the conditions inside an EUV scanner. The resist exposure source can be either EUV photons or electron beam (e-beam). This presentation will cover the results to date on a SEMATECH program to study resist outgassing from both the commercial system from EUV Tech and a custom Resist Outgassing and Exposure (ROX) tool. The EUV Tech results reported will be based on electron exposures of the photoresist, and the ROX results reported will be based on EUV photon exposures of the photoresist. The results reported will cover both tools and the measurements of over 80 commercial photoresists.
Study of EUV outgassing spatial distribution toward witness plate in the EUV outgas tester
Yukiko Kikuchi, Eishi Shiobara, Hiroyuki Tanaka, et al.
In the experiments to evaluate outgassing of EUV resists, it was found that the amount of PAG anion and/or Fluorine observed on the witness sample (WS) was different for the variety of WS location and direction in the testing chamber. The XPS measurements showed there were about 10 times of Fluorine atoms on the WS which were put to face the exposing position of the resist on the wafer compared to that were put to turn the back on the wafer. As the Fluorine is the component of photo-acid-generator (PAG) of resists used in the experiments, it is thought that the PAG anion and/or its decomposed species have high sticking coefficient to the WS. The simulation was performed to understand the directivity of outgassing from the exposing point, using the Direct Simulation Monte Carlo (DSMC) method. The results indicated that the sticking coefficient of PAG anion is about 0.8, suggesting that the position and direction of WS in the chamber relative to the wafer strongly affects the amounts of deposition of the species having big sticking coefficients.
Balancing lithographic performance and resist outgassing in EUV resists
Shu-Hao Chang, Shu-Fang Chen, Ying-Yu Chen, et al.
Resolution (R), line-width roughness (L), and sensitivity (S) are three key indices describing the performance of a resist. When optimizing a resist to compromise the RLS trade-off in extreme-ultraviolet lithography, outgassing of the resist also needs to be considered, because it will cause deposition of cleanable and non-cleanable contaminants on the surface of the projection optics and reduce the throughput of the exposure tool. In this paper, the dependence of outgassing of a resist on its compositions, such as types of photo-acid generator, quencher, and acid liable group as well as their loadings are investigated systematically through a set of specially prepared resist samples. The outgassing of these samples is tested on EUVOM-9000 from Litho Tech Japan. The lithographic performances of these samples are also characterized on the ASML NXE3100. Directions for optimizing resist lithographic performance under the constraint of resist outgassing are proposed.
Optics and Metrology
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EUVL resist-based aberration metrology
Extreme Ultraviolet Lithography (EUVL) at 13.5 nm is currently the most promising technology for advanced integrated circuit (IC) manufacturing nodes. Since the wavelength for EUVL is an order of magnitude smaller than current optical lithography systems (193 nm), wavelength scaled tolerances on lens manufacturing must be tightened to avoid image distortion and contrast loss as these scale with wavelength. Therefore understanding the aberrations of an EUVL system both in idle and production conditions is paramount. This study aims to assess a photoresist based technique for capturing pupil information of EUVL systems that can be implemented during full system use. Several data sets have been collected on an ASML EUV Alpha-Demo Tool (ADT) using the latest Center for Nanoscale Science and Engineering (CNSE) baseline resist Shin-Etsu SEVR139. Various one-dimensional and two-dimensional binary structures were imaged and used for pupil extraction in conjunction with computational modeling and simulations. Results show a stable extracted aberration signature over several measurements. Results also show that the method is sensitive to sub-nm levels of aberration change.
In situ optical testing of exposure tools via localized wavefront curvature sensing
We present a new form of optical testing for exposure tools based on measuring localized wavefront curvature. In this method, offset monopole illumination is used to probe localized regions of the test optic pupil. Variations in curvature manifest as focus shifts, which are measured using a photodiode-based grating-on-grating contrast monitor, and the wavefront aberrations are reconstructed using a least-squares approach. This technique is attractive as it is independent of the numerical aperture of the system and does not require a CCD or a separate interferometer branch.
Application of phase shift focus monitor in EUVL process control
Both 90.9° and 180° phase shifts have been achieved using a new Phase Shift Mask (PSM) structure. This PSM is intended for use as a focus monitor. Both the EUV images of the focus monitor patterns on the new EUV PSM test mask, obtained from the SEMATECH/Berkeley Actinic Inspection Microscope (AIT), and the SEMATECH EUV Micro Exposure Tool (MET), shows that an alternating PSM EUV mask can be effectively used for EUVL focus monitoring.
OPC and Modeling
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EUV multilayer defect compensation (MDC) by absorber pattern modification, film deposition, and multilayer peeling techniques
Making a multilayer defect-free extreme ultraviolet (EUV) blank is not possible today, and is unlikely to happen in the next few years. The method proposed by Luminescent is to compensate effects of multilayer defects on images by modifying the absorber patterns. Progress in MDC is the subject of this paper. The multilayer growth model was calibrated using real data – the top layer profile captured by AFM and cross section captured by TEM for programmed defects with corresponding AIT images. Multilayer defect profiles on repair sites were recovered by applying inverse methods with the calibrated model to AFM surface scans. The recovered defect profiles were fed into the MDC engine to calculate modified absorber patterns that would compensate for the defects. Further, a new method to compensate for phase errors by depositing materials in addition to absorber modifications has been developed. Simulation studies using this new method will be presented in this paper. Different options of multilayer peeling for compensating phase error, especially for bump defect, are also evaluated through simulation.
Evaluation of methods to improve EUV OPC model accuracy
Several methods are evaluated to improve the accuracy of extreme ultraviolet (EUV) lithography OPC models by including additional physical effects which are not commonly used in deep ultraviolet (DUV) OPC. The primary additions to the model in this work are model based corrections for flare and two different corrections for mask shadowing effects, commonly referred to as HV bias. The quantitative, incremental, improvement from each of these additions is reported, and the resulting changes in tape-out flow and OPC runtime are discussed
Fast 3D thick mask model for full-chip EUVL simulations
Extreme ultraviolet lithography (EUVL) uses a 13.5nm exposure wavelength, all-reflective projection optics, and a reflective mask under an oblique illumination with a chief ray angle of about 6 degrees to print device patterns. This imaging configuration leads to many challenges related to 3D mask topography. In order to accurately predict and correct these problems, it is important to use a 3D mask model in full-chip EUVL applications such as optical proximity correction (OPC) and verifications. In this work, a fast approximate 3D mask model developed previously for full-chip deep ultraviolet (DUV) applications is extended and greatly enhanced for EUV applications and its accuracy is evaluated against a rigorous 3D mask model.
Process and proximity correction, and verification for extreme ultraviolet lithography
Gökhan Perçin, Huixiong Dai, Hsu-Ting Huang, et al.
Extreme ultra-violet (EUV) lithography has been planned for high-volume manufacturing (HVM) in 2014 for critical layers of advanced nodes in the semiconductor industry. Process and proximity correction (PPC) and verification is necessary in order to compensate various optical and other process effects in EUV lithography. Since the long-range flare, mask shadowing effect, and lens characteristics all vary throughout the whole mask range, position dependent PPC and verification may be needed for accurate mask pattern synthesis. In this paper, we will study the PPC accuracy. The PPC flow uses a single PPC kernel set and a full-mask flare map for long-range flare correction. The lithography model is calibrated in accordance with this PPC flow. The lithography model is used to perform full-mask correction for the 10nm node test chip mask for BEOL/FEOL short loop flow development. The optimized full-mask patterns were placed on the mask and printed using a 0.25 NA EUV scanner at various focus and dose conditions. Printed wafers were measured by a CD-SEM and compared to post-PPC verification results.
Modeling strategies for EUV mask multilayer defect dispositioning and repair
The paper describes a modeling approach, which enables systematic printing and compensation repair studies for multilayer defects on EUV-masks. The procedure combines an approximative model for the pre-optimization of required repair shapes with an accurate and efficient, fully rigorous modeling of the final repair shape. The obtained simulations results demonstrate the capabilities of compensation repair to reduce the impact of defects and confirm the eligibility of this technique as a valuable and important ingredient of a defect mitigation strategy for EUV masks.
EUV Resists
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Evaluation of EUV resist performance with interference lithography towards 11 nm half-pitch and beyond
Yasin Ekinci, Michaela Vockenhuber, Mohamad Hojeij, et al.
The performance of EUV resists is one of the main challenges for the cost-effectiveness and the introduction of EUV lithography into high-volume manufacturing. The EUV interference lithography (EUV-IL) is a simple and powerful technique to print periodic nanostructures with a resolution beyond the capabilities of other tools. In addition, the well-defined and pitch-independent aerial image of the EUV-IL provides further advantages for the analysis of resist performance. In this paper, we present evaluation of chemically-amplified resists (CAR) and inorganic resists using EUV-IL. We illustrate the performance of the tool through a reproducibility study of a baseline resist over the course of 16 months. A comparative study of the performance of different resists is presented with the aim of resolving patterns with CARs for 16 nm half-pitch (HP) and 11 nm HP. Critical dimension (CD) and line-edge roughness (LER) are evaluated as functions of dose for different process conditions. With a CAR with about 10 mJ/cm2 sensitivity, 18 nm L/S patterns are obtained with low LER and well-resolved patterns are achieved down to 16 nm HP. With another CAR of about 35 mJ/cm2 sensitivity, L/S patterns with low LER are demonstrated down to 14 nm HP. Resolved patterns are achieved down to 12 HP, demonstrating the capability of its potential towards 11 nm HP if pattern collapse mitigation can be successfully applied. With EUV-sensitive inorganic resists, patterning down to 8 nm has been realized. In summary, we show that resist platforms with reasonable sensitivities are already available for patterning at 16 nm HP, 11 nm HP, and beyond, although there is still significant progress is needed. We also show that with decreasing HP, pattern collapse becomes a crucial issue limiting the resolution and LER. Therefore resist stability, collapse mitigation, and etch resistance are some of the significant problems to be addressed in the development of resist platforms for future technology nodes.
Resist process applications to improve EUV patterning
Karen Petrillo, Kyoungyoung Cho, Alexander Friz, et al.
Roughness control is a key technical issue in extreme ultraviolet (EUV) lithography. It applies to both line and space (L/S) and contact hole (C/H) structures. Recently, SEMATECH and Tokyo Electron Limited (TEL) developed several track-based techniques, including developer optimization, FIRM™ (Finishing up by Improved Rinse Material), and smoothing to reduce structural roughness. The combination of these techniques improved line width roughness (LWR) about 25% from the 2011 baseline of 32 nm L/S. C/H structures were also tested with the combination process. This paper describes our latest L/S and C/H roughness performance post-lithography and postetch. A feasibility study of negative tone develop (NTD) resists for EUV is also included.
Development of molecular resist derivatives for EUV lithography
D. Patrick Green, Vipul Jain, Brad Bailey, et al.
As part of the continued effort of Dow's Electronic Materials business unit to generate novel resists for advanced semiconductor technologies, there has been a recent emphasis on the development of several new photoresists and ancillary platforms to enable EUV lithography. An important aspect for the success of EUV lithography is the development of photoresist materials that can meet the stringent requirements for Resolution, Line width roughness (LWR) and Sensitivity (RLS). While, a great portion of industrial research is focused on the development of polymeric resists like Polymer Bound PAGs (PBPs), small monodisperse organic molecules called molecular glasses (MGs) have gained increased attention over the past several years. If properly designed, MGs could possess physical properties that are very similar to polymeric resists while offering superior performance, specifically towards improving LWR. We have developed several MG resists based on calixarene cores that exhibit promising lithographic performance. We have continued to study the structure-property relationship of these materials with special emphasis on molecular architectures and design strategies for improved photoresist performance. In this paper, we summarize the promising lithographic performance of these MG resists that are considered as alternative choices to polymeric resists for enabling next generation lithography.
Relationship between stochastic effect and resist pattern defect in extreme ultraviolet lithography
With the approach of extreme ultraviolet (EUV) lithography to its realization, practical issues such as the defects of resist patterns have attracted attention. In this study, the defects of line-and-space resist patterns were investigated from the viewpoint of the stochastic effects of chemical reactions. The stochastic effect was expressed using the standard deviation σ of protected unit concentration. To eliminate bridges within ~7 μm length in the line direction, roughly 1-2σ difference is required between average protected unit concentration and dissolution point at the center of space. To eliminate line breaks and severe shrinkages within ~7 μm length in the line direction, roughly 1σ difference is required between average protected unit concentration and dissolution point at the center of resist line pattern.
EUV sensitive Si containing hard mask (Si-HM) for PTD and NTD process in EUVL
Wataru Shibayama, Shuhei Shigaki, Rikimaru Sakamoto, et al.
Tri-layer process is the one of the key technique both for the lithography and etching around Hp20nm patterning. In applying for tri-layer process, we are focusing on inorganic type under layer which mainly containing Si atoms. This Si type hard mask (Si-HM) can perform not only as the Lithography performance enhancement layer for fine pitch, but also as the etching hard mask against bottom layer (spin on carbon : SOC). In this paper, we propose our new Si-HM concepts to achieve high sensitivity, wide process window and good line edge roughness. The key point of our concepts is EUV sensitive unit in Si-HM. Our EUV sensitive unit strongly promotes acid generation from PAG of EUV photo resist. Especially, for EUV NTD lithography process, EUV sensitive unit can perform as the adhesion enhancer between Si-HM and photo resist at EUV exposed area. As this result, we could resolve 22nm L/S=1/1 pattern on the EUV sensitive Si-HM by EUV NTD process even in the condition which hp40nm was the resolution limit with HMDS treated Bare-Si / PR stack. Moreover, from the view point of etching hard mask, 30nm dense L/S pattern and 20nm semi iso line pattern could be transferred to SOC layer successfully. We will present our latest Si-HM performance specialized for EUV lithography.
High NA and Magnification
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Mask effects for high-NA EUV: impact of NA, chief-ray-angle, and reduction ratio
With higher NA (≫ 0.33) and increased chief-ray-angles, mask effects will significantly impact the overall scanner performance. We discuss these effects in detail, paying particular attention to the multilayer-absorber interaction, and show that there is a trade-off between image quality and reticle efficiency. We show that these mask effects for high NA can be solved by employing a reduction ratio <4X, and show several options for a high-NA optics. Carefully discussing the feasibility of these options is an important part of defining a high-NA EUV tool.
Considerations for high-numerical aperture EUV lithography
With numerical apertures > 0.4 there will be broad ranges of angles of incidence of light on masks for EUV systems with 4× lens reduction, leading to several undesirable consequences with current MoSi multilayers and tantalum-based absorbers. An option for reducing the range of incident angles is to increase the lens reduction, but this entails small field sizes with standard 6" mask form factors or necessitates the use of larger masks sizes. Small fields lead to a need for stitching or accepting substantially reduced throughput - a problem for a technology already challenged with respect to cost-of-ownership. The implementation of larger mask formats is straightforward but requires considerable investments in new tools for mask making. New absorbers may provide a solution for high-NA EUV lithography at 4× lens reduction, but much R&D is required to demonstrate that this approach will work.
Projection optics for extreme ultraviolet lithography (EUVL) micro-field exposure tools (METs) with a numerical aperture of 0.5
Holger Glatzel, Dominic Ashworth, Mark Bremer, et al.
In support of the Extreme Ultraviolet Lithography (EUVL) roadmap, a SEMATECH/CNSE joint program is under way to develop 13.5 mn R and D photolithography tools with small fields (micro-field exposure tools [METs]) and numerical apertures (NAs) of 0.5. The transmitted wavefront error of the two-mirror optical projection module (projection optics box [FOB]) is specified to less than 1 mn root mean square (RMS) over its 30 μm x 200 μm image field. Not accounting for scatter and flare losses, its Strehl ratio computes to 82%. Previously reported lithography modeling on this system [1] predicted a resolution of 11 mn with a k-factor of 0.41 and a resolution of 8 mn with extreme dipole illumination. The FOB's magnification (5X), track length, and mechanical interfaces match the currently installed 0.3 NA FOBs [2] [3] [6], so that significant changes to the current tool platforms and other adjacent modules will not be necessary. The distance between the reticle stage and the secondary mirror had to be significantly increased to make space available for the upgraded 0.5 NA illumination modules [1].
Mask 3D effects and compensation for high NA EUV lithography
Mask shadow compensation for EUV lithography has typically been performed using simple rule-based schemes during optical proximity correction (OPC). However, as feature sizes decrease, the required corrections get more complex as they become dependent on both feature size and type. Thus, OPC models that account for these 3D mask effects are becoming essential. These models become even more important for higher numerical aperture EUV systems due to larger angles of incidence on the mask and tighter process budgets for CD and overlay. This paper will focus on estimating these 3D mask effects and evaluate the extendibility of current available OPC models for some specific higher numerical aperture EUV systems. It is concluded that the current available 3D mask models are capturing the primary effects and it is believed that with further refinement they are likely extendable to meet the needs of future high-NA tools. Additionally, a combination of thinner mask absorber, tighter scanner focus control and/or larger optical magnification will likely be required to print sub-30nm pitch structures with higher numerical aperture EUV systems.
Mask II
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Commissioning an EUV mask microscope for lithography generations reaching 8 nm
Kenneth A. Goldberg, Iacopo Mochi, Markus Benk, et al.
The SEMATECH High-NA Actinic Reticle review Project (SHARP) is a synchrotron-based, EUV-wavelength microscope, dedicated to photomask imaging, now being commissioned at Lawrence Berkeley National Laboratory. In terms of throughput, resolution, coherence control, stability and ease of use, SHARP represents a significant advance over its predecessor, the SEMATECH Berkeley Actinic Inspection Tool (AIT), which was decommissioned in September 2012. SHARP utilizes several advanced technologies to achieve its design goals: including the first Fouriersynthesis illuminator on a zoneplate microscope, EUV MEMS mirrors, and high-efficiency freestanding zoneplate lenses with numerical aperture values up to 0.625 (4×). In its first week of operation, SHARP demonstrated approximately 150 times higher light throughput than AIT and a spatial resolution down to 55-nm half-pitch with 0.42 4×NA (i.e. the smallest feature size on our test mask.) This paper describes the current status of the tool commissioning and the performance metrics available at this early stage.
Experimental phase defect printability evaluation using a programmed phase defect in EUVL mask
Tsuneo Terasawa, Tsuyoshi Amano, Sunghyun Oh, et al.
Influence of phase defects on printed images of mask pattern was experimentally investigated by printing line patterns on wafer, with the line patterns’ half pitches of 26 nm ~ 22 nm. And the experimental results were compared with the simulation results. A test mask prepared for this experiment contained programmed phase defects of 100 nm ~ 34 nm in width and of around 1.9 nm ~1.5 nm in depth. The defects were arrayed in a way such that the pitch of the array would differ from the pitches of the absorber line pitches. Therefore, the phase defects were placed at different positions relative to those of the absorber line patterns. Mask patterns were printed on wafer using an exposure tool NXE:3100 with a numerical aperture (NA) of 0.25 and a reduction of 4X. To evaluate the printed patterns affected by the phase defects, dipole illumination was employed. The incident angle of mask illumination chief ray was 6 degrees and the direction of absorber line patterns on the mask was set parallel to the chief ray incident plane. The printed line patterns on wafer were evaluated; and the phase defect impacts on them were examined in terms of space width variation as measured by SEM. An influence of line edge roughness (LER) of the resist pattern did seem to appear in this experiment, it was difficult to analyze the critical dimension (CD) error with accuracy of better than 10 %. Although there happened to be a quantitative difference between the simulation and experimental results, the relative location dependence was quite noticeable and the effect of a phase defect was mitigated by covering the defect with an absorber pattern.
Challenges in EUV mask blank deposition for high volume manufacturing
EUVL requires high-yield, low defect density reflective mask blanks, a requirement which is considered one of the top two critical technology gaps for commercialization of the technology. At the SEMATECH Mask Blank Development Center (MBDC), research on defect reduction and yield improvement for EUV mask blanks is being pursued using the Veeco Nexus deposition tool. The defect performance of this tool is one of the factors limiting the availability of defect-free EUVL mask blanks. SEMATECH identified the key components in the ion beam deposition system that are currently impeding the reduction of defect density and the yield of EUV mask blanks. SEMATECH improved the defect performance of the champion blank with 12 defects above 45 nm which is a 36% improvement from the data reported last year for the champion blank (19 defects above 45 nm). The yield analysis on high quality mask blanks from ion beam deposition system is also presented. Substrate quality is currently the biggest source of mask blank defects, while high yield also requires complete elimination of large size defects from deposition. A roadmap to meet the required defectivity specification for EUV mask blanks is presented.
Extending Ru capping layer durability under physical force cleaning
Physical force wet cleaning technologies (MegaSonic & Droplet Spray) are considered the supreme challenge in 193i reticle cleaning due to smaller critical dimension, high feature aspect ratio, and sensitive interfaced fragile features. However this was not considered equally challenging in EUV masks. Recently, MegaSonic cavitation has been linked to Ru (capping layer) pitting issues; making the use of acoustic based cleaning questionable for EUVL reticles. Nevertheless, acoustic energy is necessary to remove particles trapped in deep and congested trenches. This strengthens the need to control the physical force energy within the damage free regime even further. In this study we have investigated method to control MegaSonic cavitation as well as established a link between pattern damage observed in optical mask and Ru pitting in EUV masks. Effect of different cleaning chemistries typically used in mask cleaning is compared with a new cleaning chemistry (referred to as chemical A). A new POR (Process of Record) based on chemical A is qualified and its effects on PRE, absorber CD and EUV-reflectivity are discussed.
Invited II
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ASML's NXE platform performance and volume introduction
Rudy Peeters, Sjoerd Lok, Erwin van Alphen, et al.
All six NXE:3100, 0.25 NA EUV exposure systems are in use at customer sites enabling device development and cycles of learning for early production work in all lithographic segments; Logic, DRAM, MPU, and FLASH memory. NXE EUV lithography has demonstrated imaging and overlay performance both at ASML and end-users that supports sub- 27nm device work. Dedicated chuck overlay performance of <2nm has been shown on all six NXE:3100 systems. The key remaining challenge is productivity, which translates to a cost-effective introduction of EUVL in high-volume manufacturing (HVM). High volume manufacturing of the devices and processes in development is expected to be done with the third generation EUV scanners - the NXE:3300B. The NXE:3300B utilizes an NA of 0.33 and is positioned at a resolution of 22nm which can be extended to 18nm with off-axis illumination. The subsystem performance is improved to support these imaging resolutions and overall productivity enhancements are integrated into the NXE platform consistent with 125 wph. Since EUV reticles currently do not use a pellicle, special attention is given to reticle-addeddefects performance in terms of system design and machine build including maintenance procedures. In this paper we will summarize key lithographic performance of the NXE:3100 and the NXE:3300B, the NXE platform improvements made from learning on NXE:3100 and the Alpha Demo Tool, current status of EUV sources and development for the high-power sources needed for HVM. Finally, the possibilities for EUV roadmap extension will be reviewed.
CO2/Sn LPP EUV sources for device development and HVM
Laser produced plasma (LPP) systems have been developed as the primary approach for use in EUV scanner light sources for optical imaging of circuit features at 20nm nodes and beyond. This paper provides a review of development progress and productization status for LPP extreme-ultra-violet (EUV) sources with performance goals targeted to meet specific requirements from ASML. We present the latest results on power generation and collector protection for sources in the field operating at 10W nominal power and in San Diego operating in MOPA (Master Oscillator Power Amplifier) Prepulse mode at higher powers. Semiconductor industry standards for reliability and source availability data are provided. In these proceedings we show results demonstrating validation of MOPA Prepulse operation at high dose-controlled power: 40 W average power with closed-loop active dose control meeting the requirement for dose stability, 55 W average power with closed-loop active dose control, and early collector protection tests to 4 billion pulses without loss of reflectivity.
Optics for ASML's NXE:3300B platform
Martin Lowisch, Peter Kuerz, Olaf Conradi, et al.
Shipping in 2013, the NXE:3300 is the second generation of ASML’s EUV exposure platform. We review the current status of EUV optics production for the NXE:3300 tools. Four customer systems of the StarlithTM3300 series have been delivered so far. These sets of optics are characterized by a numerical aperture of 0.33 as well as significantly lower flare and wave-front levels compared to the StarlithTM3100. Meanwhile imaging down to 14 nm node features was demonstrated with the StarlithTM3300 pilot optics. Starting with this generation we introduce a fully new illumination system which allows for setting changes without efficiency loss. In this paper we focus on mirror fabrication and at wavelength qualification results of the optical systems produced so far. We also give an outline of potential solutions for the next generation of EUVL optics using higher NA.
Through-focus EUV multilayer defect repair with nanomachining
Defects within the multilayer mirrors of EUV photomasks have been a leading challenge for EUV lithography for quite some time. By creating non-planar surfaces, they distort both the amplitude and phase of reflected light. Amplitude errors generally create a CD error on wafer, whereas phase errors tend to cause asymmetric printing through focus. Since defect-free mask blanks are not expected to be available for initial high volume EUV manufacturing, defect mitigation, compensation, and repair strategies are essential. This paper describes a technique to repair both the amplitude and phase effects of multilayer defects. For a bump defect, the phase effect (i.e. tilted Bossung curve behavior) is corrected by removing multilayer material in the vicinity of the defect. This creates a phase effect opposite to that of the defect and the two effects cancel. The amplitude error (i.e. CD error) caused by both the defect and by the phase repair is then corrected by modifying the surrounding absorber pattern. The repairs in this paper are performed by nanomachining with an AFM repair tool. The concept is validated by a combination of simulation and experimental studies with data from the Actinic Inspection Tool (AIT) at the Lawrence Berkeley National Laboratories, the EUV Alpha Demo Tool (ADT) in Albany, New York, and an AFM repair tool. The process for a complete multilayer repair is described using an example native defect repair. Encouraging results indicate that nanomachining is capable of creating the complex nano-scale three dimensional topographies required for the repair. Repair strategies for both bump and pit defects are addressed. Multiple simulation studies are used to understand the requirements for such a repair and what type of repairs may be possible.
Patterning challenges of EUV lithography for 1X-nm node DRAM and beyond
Tae-Seung Eom, Hong-Ik Kim, Choon-Ky Kang, et al.
In this paper, we will discuss patterning challenges of EUV lithography to apply 1xnm node DRAM. EUV lithography is positioned on essential stage because development stage for DRAM is going down sub-20nm technology node. It is time to decide how to make sub-20nm node DRAM. It will be the simplest and cost effective way to make device with matured EUVL. But in spite of world-wide effort to develop EUV lithography, the maturity of EUV technology is still lower than conventional ArF immersion lithography. So, DRAM manufacturers are considering several candidates such as DSA, DPT and MPT simultaneously. In addition, DRAM manufacturers are considering new cell layout and new memory also. For this study, we investigate process window and shadow effect across exposure field of sub-20nm node DRAM cell. We also performed an overlay matching experiment between 0.25NA EUV scanner and 1.35NA ArF immersion scanner. In addition, we will compare EUV lithography with ArF immersion DPT or SPT in view of patterning performance. Finally, we will discuss some technical issues to applying EUV lithography such as flare, resist LER, EUV OPC and illumination condition using 0.25NA EUV scanner.
Towards manufacturing a 10nm node device with complementary EUV lithography
Jan V. Hermans, Huixiong Dai, Ardavan Niroomand, et al.
For device manufacturing at the 10nm node (N10) and below, EUV lithography is one of the technology options to achieve the required resolution. Besides high throughput and extreme resolution, excellent wafer CD, overlay and defect control are also required. In this paper, we discuss two wafer CD uniformity issues, the effect of the reticle black border and photon shot noise. The readiness of EUV lithography for N10 will be discussed by showing on-product imaging and overlay performance of a self aligned via layer inserted with EUV lithography. EUV single patterning results will be discussed by comparing the imaging performance of our NXE:3100 cluster to the NXE:3300 at ASML. Last but not least, the extendibility of EUV lithography towards sub 10nm patterning will be discussed by demonstrating sub 10nm half pitch LS patterns with EUV single Self Aligned Double Patterning (SADP).
Poster Session
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Limitation of OAI + AttPSM in EUVL
Shinn-Sheng Yu, Yen-Cheng Lu, Chih-Tsung Shih, et al.
In extreme ultraviolet lithography (EUVL), the application of off-axis illumination (OAI) leads to degradation in aerial image contrast, resulting in an unacceptably high mask error enhancement factor as the pattern pitch becomes smaller, even if an attenuated phase-shifting mask (AttPSM) of optimized attenuation is employed. We show that this is an intrinsic problem of OAI and cannot be remedied by adopting a thinner absorber, a smaller chief ray angle of incidence at the object side, or a projection optics box with a higher numerical aperture. Based on simulation results using the best conditions for OAI, we may conclude that single-patterning EUVL will probably end at a technology node with the minimum pitch of 22 nm, unless we can come up with other innovative ways for performing EUVL imaging or designing and formulating resists with blurs less than 5 nm at reasonable exposure dose.
Experimental verification of EUV mask limitations at high numerical apertures
In this work, we use a high accuracy synchrotron-based reflectometer to experimentally determine the effects of angular bandwidth limitations on high NA EUV performance. We characterized mask blank and mask pattern diffraction performance as a function of illumination angle, scatter angle, and wavelength. A variety of pattern feature sizes ranging down to coded sizes of 11 nm (44 nm on the mask) are considered. A Rigorous Coupled-Wave Analysis (RCWA) model is calibrated against the experimental data to enable future model-based performance predictions. The model is optimized against the clearfield data and verified by predicting the mask pattern diffraction data. We thus have confirmed the degradation and asymmetry of diffraction orders at high AOI.
Homogeneity improvement of TiO2-SiO2 glass synthesized by the soot method and its evaluation using the ultrasonic measurement system
Masahiro Kawagishi, Junko Konishi, Masaaki Takata, et al.
TiO2-SiO2 glass is one of the leading candidates for optical elements of extreme ultraviolet lithography. TiO2-SiO2 glass synthesized by the soot method has shown striae related to inhomogeneity of TiO2 concentration formed in the planes perpendicular to soot growth direction in the synthesis process. It can induce CTE variation and localized surface roughness. Striae were characterized in three modes by polarization microscope. Such striae were improved with an improved gas condition and developing a modified material gas supply system. Specimen prepared from the improved TiO2-SiO2 glass was evaluated by a line-focus-beam ultrasonic material characterization system, using a surface-acoustic-wave mode. Improved glass had 43% striae level compared to conventional glass by birefringence measurement, 31% compared to conventional glass by the ultrasonic measurement. It was found that improved glass had good homogeneity to both directions perpendicular and parallel to striae plane.
Inspection and compositional analysis of sub-20 nm EUV mask blank defects by thin film decoration technique
V. Jindal, A. John, J. Harris-Jones, et al.
EUVL requires a high yield of low-defect density reflective mask blanks, one of the top two critical technology gaps for the commercialization of this technology. One of the major sources of mask blank defects is the top of the substrate due to substrate quality, cleaning residue, and handling- or storage-induced defects. SEMATECH’s current inspection tool, the Lasertec 7360, can detect defects down to 37 nm on quartz substrates in dense scan mode. Defects below 40 nm on these substrate are difficult to detect, which challenges the quantification and characterization, and hence the determination of defect sources. SEMATECH developed a thin film decoration technique to quantify sub-40 nm defects and analyze composition to pinpoint defect sources. The technique involves oblique angle deposition in an ion beam deposition system, which decorates the particle. The decoration of particles is optimized by depositing enough thin film so that defects can be detected by the Lasertec7360 and yet keeping the film thin enough to employ several metrology techniques to efficiently analyze defect composition. The challenges involved with the metrology of such embedded defects and the impact of oblique angle deposition will be discussed. A theoretical model of defect decoration that can successfully simulate the thin film deposition on top of the defects will be provided. The effect of angle, deposition rate, and deposition time to quantify the decoration effect will also be presented.
Propagation of surface topography of EUV blank substrate through multilayer and impact of phase defect structure on wafer image
Our recent study reveals that the propagation of a phase defect (PD) from an EUV mask substrate surface through a multilayer does not always propagate in a vertical direction. In this study, to fully understand the propagation model of PDs, two types of defects on a Qz substrate are prepared. One is space patterns fabricated by a mask patterning process followed by an etching giving a cross-sectional angle of 90 degrees. The others are AFM scratched space patterns with their cross-sectional angles as 30 and 60 degrees. After coating, a patterned Qz substrate with a multilayer, propagation of PDs through the multilayer was observed by a TEM. As a result, the TEM images clearly exhibited a tendency that originating from the Qz substrate while the PDs propagated through the multilayer their propagation path was inclined toward the center of the mask. A maximum inclination of this path was found to be 5.9 degrees at a distance of 93 mm away from the mask’s center. The impacts of the inclination angles on the printed images on wafer calculated using a simulator. A phase defect with an inclination angle of one degree corresponded to a positional shift of one nanometer on printed wafer image.
Modeling studies on alternative EUV mask concepts for higher NA
This paper investigates the performance of different mask options for sub-13 nm EUV-lithography with a 4x demagnification and an NA of 0.45. The considered mask options include standard binary masks, standard attenuated phase-shift masks, etched attenuated phase-shift masks and embedded-shifter phase-shift masks. The lithographic performance of these masks is investigated and optimized in terms of mask efficiency, NILS, DoF, OPC-performance and telecentricity errors. A multiobjective optimization technique is used to identify the most promising mask geometry parameters.
Low thermal expansion material (LTEM) cleaning and optimization for extreme ultraviolet (EUV) blank deposition
Arun John Kadaksham, Ranganath Teki, Milton Godwin, et al.
With the insertion of extreme ultraviolet lithography (EUVL) for high volume manufacturing (HVM) expected in the next few years, it is necessary to examine the performance of low thermal expansion materials (LTEMs) and assess industry readiness of EUV substrates. Owing to the high cost of LTEM, most of the development work so far has been done on fused silica substrates. Especially in developing cleaning technology prior to multilayer deposition, fused silica substrates have been used extensively, and defect trends and champion blank data have been reported using multilayer deposition data on fused silica substrates. In this paper, the response of LTEMs to cleaning processes prior to multilayer deposition is discussed. Cleaning processes discussed in this paper are developed using fused silica substrates and applied on LTEM substrates. The defectivity and properties of LTEM to fused silica are compared. Using the dense scan feature of the substrate inspection tool capable of detecting defects down to 35 nm SiO2 equivalent size and appropriate defect decoration techniques to decorate small defects on substrates to make them detectable, cleaning technologies that have the potential to meet high demands on LTEM for EUVL are developed and optimized.
Evaluation of novel projection electron microscopy (PEM) optics for EUV mask inspection
In order to achieve inspection sensitivity and a attainability for 1× node, a projection electron microscopy (PEM) system is employed that enables us to do high-speed/ high-resolution inspection that is not possible with the conventional DUV and EB inspection systems. By selecting a higher electron energy in imaging using Electron Optics (EO) exposure, and by applying a newly designed model to the basic PEM optics model, we have minimized the aberration in imaging that occurs when working with EO; and we have improved the related transmittance of such a system. The experimental result by showing designs for the improved transmittance, is obtained by making electron throughput measurement.
Registration accuracy improvement of fiducial mark on EUVL mask with MIRAI EUV ABI prototype
In order to mitigate phase defects on EUVL mask blanks, Fiducial Marks (FMs) should be located with high registration accuracy by the EUV Actinic Blank Inspection tool, the E-Beam (EB) writer, and other inspection tools. The proposed registration accuracy is less than 10 nm for each tools [1]. In our previous studies [2] and [3] we fabricated FMs by FIB etching, or resist exposure by the EB writer and etching process, and inspected those FMs by the EUV Actinic full-field mask Blank Inspection (ABI) prototype developed at MIRAI-Selete. The registration accuracy of those FMs with the MIRAI EUV ABI prototype were not enough due to a pixel size of 500 nm on the mask in order to achieve total less than 10 nm defect location accuracy on the EUVL mask blank. We studied the registration accuracy improvement of FM on the blank by the experiment with the MIRAI EUV ABI prototype to establish the phase defect mitigation method. In this experiment, we took some images of FMs by moving the mask stage of the MIRAI EUV ABI prototype by lengths of sub-pixels. And we analyzed registration accuracy of FM by stringing those images shifting sub-pixel. This method can achieve less than 2.5 nm FM registration accuracy by the conditions equal to or more than 4 times quasimagnification, trench detection, and 50% threshold level In this presentation, we will explain the experiment results of FM registration accuracy improvement on the EUVL mask with MIRAI EUV ABI prototype to establish the phase defect mitigation method.
Study on EUV mask defect inspection with hp 16nm node using simulated projection electron microscope images
According to an ITRS2012-Update the sensitivity requirement for EUV mask pattern inspection system is to be less than 18 nm for half pitch (hp) 16 nm node devices. The inspection sensitivity of extrusion and intrusion defects on hp 64 line-and-space patterned EUV mask was investigated using simulated projection electron microscope (PEM) image. The obtained defect images showed optimization of current density and image processing techniques were essential for the detection of defects. Extrusion and intrusion defects with 16 nm in size were detected on images formed by 3000 electrons per pixel. The landing energy also greatly influenced the defect detection efficiency. These influences were different for extrusion and intrusion defects. These results were in good agreement with experimentally obtained yield curves of the mask materials and the elevation angles of the defects. These results suggest that PEM technique has a potential to detect 16 nm size defects on hp 64 nm patterned EUV mask.
Development of 3D Monte Carlo simulations for predicting multilayer geometry of pit-type EUV defects
Robert F. Spivey, Ranganath Teki, T.-M. Lu
The EUV community has come to the conclusion that completely eliminating EUV mask defects will be nearly impossible in the near future. Instead the industry trend is to develop high performance optical simulations of the multilayer coating in order to compensate for the defects during manufacturing. In order for these simulations to be accurate the full multilayer structure of the EUV defect should be known. Currently there is no usable 3D method of simulating pit-type defects as they are relaxed during the energetic deposition of the Mo/Si multilayer. Current approximations used to model the defect's propagation are poor and have many shortcomings. Monte Carlo simulations of thin film growth are explored for this usage. They are validated using experimental data of a STEM cross section of a multilayer pit-type defect. Monte Carlo methods allow a full 3D representation of the system and have the advantage of great flexibility in deposition conditions and flux distributions. The Solid-on-Solid aggregation model is used to deposit particles onto initial substrate defects; this model does not allow overhanging particles, which replicates the smooth growth of ion-beam deposition well. Surface diffusion is simulated using Boltzmann statistics with activation energies of diffusion biased by local geometry. The growths are compared by observing the aspect ratio of the defect as a function of film thickness; the aspect ratio is defined as the depth of the defect divided by its full width at half maximum. Good fitting is observed for initial defect templates created from atomic force microscopy scans of observed initial defects. More rigorous tests of accuracy are also performed by comparing simulation predictions to AFM scans of the ending multilayer.
Effect of phase defect shape on ABI signal intensity and defect image intensity on wafer with simulation
In this paper, phase defect impact variation, which is caused by the characteristics of defect shapes, is verified by a simulation. Actinic blank inspection (ABI) signal intensity, and defect image intensity on wafer, affected by characteristics changes in the shape of the phase defect, was calculated. ABI signal intensity and defect image intensity on wafer did not remain constant even when the phase defect volume was fixed. According to this simulated result, defect side wall angle and defect volume (with tilted top surface) affected both intensities. When the impacts, caused by phase defect, on ABI signal intensity, and on defect image intensity on wafer, are monitored then shape of the phase defect should be taken into consideration for accurate estimation. Also, through this simulation, a relationship between ABI signal intensity and defect image intensity on wafer was confirmed. The impact variation (which is caused by defect shape change) for both intensities showed similar tendencies. Therefore, it is believed that ABI system is an effective way to capture harmful phase defects affecting the wafer intensity, even when there were defects with various shapes.
Mathematical model for calculating speckle contrast through focus
Rene A. Claus, Andrew R. Neureuther, Patrick P. Naulleau
The significantly reduced wavelength and the reflective nature of EUV masks causes phase variations resulting from roughness on the mask to result in intensity variations when the wafer is out of focus. These variations should be understood and modeled to control LER and device yield. A typical approach to modeling the effects of roughness is to image many masks using a thin mask simulator. These images can then be statistically analyzed to get the speckle properties. A model already exists that can relate speckle contrast to LER. This paper presents a method to compute the speckle image intensity using a single convolution with the roughness. This can be used to compute speckle through focus quickly. The presented technique takes into account defocus and the illumination coherence. It can be applied to phase roughness and amplitude roughness (reflectivity variations). In addition to speed improvements, the convolution kernel provides insights into the interaction of the source mask and mask roughness showing that, depending on the illumination coherence and defocus, not all roughness frequencies are attenuated equally.
Evaluating the effect of EUV multilayer buried defects on feature printability using a stochastic resist model
Extreme ultraviolet (EUV) lithography has a number of challenges not encountered in DUV lithography. One of these challenges is that the stochastic nature of resist exposure is much more pronounced at an exposure wavelength of 13.5 nm than 193 nm. This leads to line-edge roughness (LER) and impacts critical dimension uniformity. Another challenge is that the reflective multilayer (ML) in photomasks will likely have defects buried in the ML. The size and the location of these defects could affect feature printability. This paper aims to study these two new challenges using a comprehensive lithographic model that accounts for both the scattering of light due to ML defects and stochastic resist effects. This enables more accurate predictions of the process window which could lead to more robust defect compensation.
Effects of varying the parameters in witness-sample-based photoresist outgas testing: dependence of the carbon growth on pumping speed and the dose, time, and area of resist exposure
In this work, we discuss several parameters influencing extreme ultraviolet (EUV) resist qualification test results. The witness sample resist qualifications test is implemented on several different instruments world wide. The original protocol for the test developed by the tool manufacturer requires that a 300 mm wafer be exposed to a dose to clear in one hour. Also required is that the carbon contamination rate on the witness sample be mass limited, i.e., that the rate be saturated with respect to the EUV or e-beam intensity. Simple arguments have been presented in the past to show that the thickness of the carbon growth should be inversely proportional to the pumping speed and proportional to the area exposed if dose and duration were held constant. The present experiments demonstrate the real-life limitations of these arguments and provide validation to our area scaling procedure to equate test results done with 200 mm wafers to results expected for 300 mm wafers. In the process of studying the dependence of carbon growth on pumping speed, we encountered the important effect of increased partial pressure on the degree of intensity saturation.
Status of EUV reflectometry at PTB
Christian Laubis, Annett Barboutis, Martin Biel, et al.
With several pre-production EUV tools already in the field, the development of EUV Lithography has gained momentum and the first production tools are scheduled for delivery in 20131. Consequently, the demand for EUV radiometry has grown as well with respect to volume and variety of the measurement requirements. Building on almost two decades of experience, PTB offers a wide range of actinic EUV measurements, like reflectance and transmittance, to characterize optical elements and sensitivity measurements to characterize detection devices. Based on these core competences, new applied measurements can be offered. Diffusely scattered light can be used to assess surface roughness (PSD) in the otherwise difficult to measure spatial frequency region of 1 μm to 10 μm. PTB performs EUV metrology at two dedicated complementary beamlines covering the wavelength range from 0.65 nm to 30 nm with particularly well-collimated radiation and the range from 5 nm to 50 nm with higher radiant power, variable degree of polarization and adjustable spot size on the sample. Both beamlines are optimized to achieve temporally stable normalized radiant power and excellent wavelength reproducibility at high spectral purity with out-of-band radiation in the range of 10-3 relative, as a prerequisite for low measurement uncertainties and long-term reproducibility. We present an updated overview of our capabilities with a focus on the long-term stability of our instrumentation and methods.
Hartmann wavefront sensor for EUV radiation
K. Mann, B. Flöter, T. Mey, et al.
A compact Hartmann wavefront sensor specifically optimized for the EUV spectral range was developed in a cooperation of Laser-Laboratorium Göttingen and DESY / Hamburg. Primarily designed for optics adjustment and beam characterization of the free electron laser FLASH, the self-supporting device can also be used in combination with any other EUV radiation source, as e.g. for at-wavelength fine-tuning of EUVL beam line optics. Tests performed at FLASH and LCLS indicate an average wavefront measurement repeatability of λ/116 (wrms) at λ=13.5nm for the EUV Hartmann sensor. The device can be successfully employed for characterization of the unfocused FEL beam, as well as for fine-adjustment of EUV optics, as demonstrated for an ellipsoidal focusing mirror at beam-line BL2 of FLASH. The wavefront monitored behind this mirror provided information on typical misalignment effects such as astigmatism or coma. Improved alignment allowed for reduction of the wavefront rms (wrms) from 3.9nm to 1.5nm. Tests performed with LPP EUV sources indicate that the new sensor can also be used for actinic optics characterization and real-time fine-tuning of EUVL optics systems.
A reverse design method for EUV lithography illumination system
Qiuli Mei, Yanqiu Li, Fei Liu
Few design method for Extreme Ultraviolet (EUV) lithography illumination system has been proposed in the past years. In this paper, we developed a design method for the illuminator with all the components in the system designed in a reverse sequence. Some key issues about the design of relay system and the configuration of the fly’s eye will be discussed in detail. An illuminator for numerical aperture 0.3 lithography has been designed with the method developed in this paper. Design result shows the slit uniformity of the scanning energy distribution can reach 1.2% under 90-degree dipole illumination, 45-degree quadrupole illumination and annular illumination.
Patterning at 6.5 nm wavelength using interference lithography
Nassir Mojarad, Michaela Vockenhuber, Li Wang, et al.
We present the results of patterning chemically-amplified and inorganic resists at 6.5 nm wavelength using interference lithography. Well-resolved patterns down to 22 nm HP are obtained. Dose-dependent line-edge roughness and critical dimensions in the resolution range of 50-22 nm half-pitch are obtained using 13.5 and 6.5 nm wavelength. The performances of the resists are compared for both cases. Increased line-edge roughness is observed for patterning 6.5 nm compared to the patterning at 13.5 nm wavelength.
Simulation analysis of LER and dose tradeoffs for EUV resists with photo-decomposable quenchers
Suchit Bhattarai, Andrew R. Neureuther, Patrick P. Naulleau
The SuMMIT stochastic simulator has been used to conduct a simulation study of photo-decomposable quencher (PDQ) based EUV resists and performance comparison between PDQ resists and conventional quencher (regQ) resists analyzed from the standpoint of dose and LER metrics. The dose and LER Tradeoffs have been analyzed as a function of base loading, base diffusion lengths and relative deprotection/quenching rates. About 3.5% LER improvements with PDQ has been predicted at a dose of 15 mJ/cm2 with base loaded at 20% of PAG loading, for 25 nm half-pitch line-space patterns. Dose savings of 2 mJ/cm2 and LER improvement of 0.1 nm between regQ and PDQ resists are predicted with a base diffusion length equal to the acid diffusion length of 10 nm, and base loaded at 30% of PAG loading. Dose improvements of 1 mJ/cm2 for equal regQ and PDQ LERs of 3.5 nm is possible at a deprotection rate that is half as fast as the acid/base quenching rate of 10 nm3/s. Improvement in the deprotection gradient is found to be the dominant factor behind lower PDQ LERs, while the difference in deprotection noise between conventional quenchers and PDQs is found to be marginal.
Relation between sensitivity and resolution in polymer bound PAGs and polymer blend PAGs
Satoshi Enomoto, Tuan Nguyen Dang, Cong Que Dinh, et al.
Recently, polymer-bound PAGs (anion bound) are actively investigated as Extreme ultra violet (EUV) resist. Some experimental results showed, in case of shot diffusion length acid generator bounded polymer showed lower sensitivity comparing with long diffusion length acid generator. In our previous investigation, short diffusion length PAG reactivity is changed due to binding to polymer by pulse radiolysis method. However, shot diffusion PAG bound to polymer showed lower LWR than long diffusion length PAG. Therefore, acid diffusion length difference originate in PAG is important to resist performance. The diffusion length difference influence deprotection reaction in PEB process. In this paper, we evaluated polymer-bound PAGs and polymer blend PAGs by electron beam (EB) exposure tool employing various PEB temperature and PEB time to conform the influence of acid diffusion regulation about polymer-bound PAGs for resist performances. As the result, even if acid generator bound polymer applied as a resist, acid diffusion regulation isn’t so strict that acid can migrate in the polymer matrix during PEB.
Stochastic resist patterning simulation using attenuated PSM for EUV lithography
In EUV Lithography, mask shadowing effect and photon shot noise effect are the main sources of patterning limit, critical dimension (CD) non-uniformity and low imaging properties. In this paper, the patterning performance of a 6% attenuated phase shift mask (PSM) is valuated, and the results show that this can be used for half-pitch (hp) down to 14 nm with 0.33NA due to the improved stochastic patterning properties. The proposed PSM consists of 26.5 nm of TaN as an absorber layer and 14 nm of Mo as a phase shifter on 2.5 nm thick Ru capped Mo/Si multilayers. This structure has ~6% reflectivity at the absorber stack and 180° phase shift. The improved stochastic resist patterning properties of PSM were compared with those of conventional binary intensity mask (BIM) with a 70 nm-thick TaN absorber for the 14 ~ 22 nm line and space (L/S) 1:1 dense pattern with 0.33NA off-axis illumination conditions with a EUV generic resist model.
Quencher distribution engineering of out-of-band insensitive EUV resists: experiments and stochastic simulation
Shang-Chieh Chien, Shu-Hao Chang, Jui-Ching Wu, et al.
We investigated the effect of quencher type and loading concentration in OoB-insensitive EUV resists via actual exposure on the latest EUV scanner and stochastic simulation using Prolith. Model resist samples with two quencher types, conventional base type and photo-decomposable base type, at variant loading concentrations were prepared and tested. Basic indicators of lithographic performance, such as depth of focus, energy latitude, and line-width roughness were significantly improved by 80 nm, 8.4% and 25%, respectively along with a moderate increase of sensitivity (ca. 5mJ/cm2) under the optimized quencher condition. Meanwhile, we further quantitatively analysis the outgassing-induced contamination growth to realize the quencher distribution engineering effect on outgassing issue in EUV lithography. In addition, stochastic simulation for EUV resist featuring various types of quenchers provides certain correlation with the experimental results.
Prediction of resist sensitivity for 13.5-nm EUV and 6.x-nm EUV extension from sensitivity for EBL
Tomoko G. Oyama, Akihiro Oshima, Tuan Nguyen Dang, et al.
Extreme ultraviolet lithography (EUVL) at 13.5 nm will soon be applied in high-volume manufacturing of semiconductors, as a replacement to the ArF excimer laser immersion lithography. Recently, the potential application of exposure wavelengths of 6.x nm (particularly 6.6-6.8 nm) has been discussed as EUVL extension. The 6.x nm exposure source is currently under development, therefore screening of resists with conventional exposure tools will accelerate the selection or novel development of high sensitivity resists for 6.x nm EUVL. In the present study, the sensitivities of a chemically amplified (CA) resist (OEBR-CAP112) and non-CA resists (ZEP520A and poly(methyl methacrylate)) were evaluated with 30 keV and 75 keV electron beam lithography (EBL) tools. In terms of radiation chemistry, the obtained dose/sensitivities (μC cm-2) were converted into the absorbed doses (Gray; Gy = J kg-1). If EB- and EUV-induced chemical reactions are the same, the required absorbed doses for EB and EUV would be similar values. The sensitivities for EUV/soft X-rays including 6.x nm were predicted assuming the required absorbed doses in a resist would show similar values for both EB and EUV. We investigated precise sensitivities of the resists for EUV/soft X-rays including 6.7 nm using highly-monochromated synchrotron radiation. For both CA and non-CA resists, the predicted and experimentally obtained sensitivities agreed well with each other. These results suggested that almost the same chemical reactions are induced in resists for both EUVL and EBL. Hence, it was found that we can predict the resist sensitivities for EUV/soft X-rays at any exposure wavelength from the exposure results for EBL.
Study of LWR reduction and pattern collapse suppression for 16nm node EUV resists
Eishi Shiobara, Yukiko Kikuchi, Toshiro Itani
EUV lithography is the most promising future technology for manufacturing devices at and below 16-nm half-pitch node. However, line width roughness (LWR) and pattern collapse are major concerns in device manufacture. In this study, the ability of surfactant rinses to reduce LWR and suppress pattern collapse was investigated. Certain surfactant rinses achieved both. We analyzed the critical dimension (CD) variation of resist patterns during surfactant rinse by highspeed atomic force microscopy (HS-AFM). No significant swelling was observed during the rinse process. We also evaluated a smoothing process subsequent to rinsing; namely, the highly controllable post-bake process. Surfactant rinse followed by post-bake process further reduced LWR.
Reaction mechanisms of various chemically amplified EUV and EB resist
We synthesized three type polymers 1) Poly hydroxyl-styrene (PHS resist). 2) hydroxyl-styrene methacrylate copolymer (Hybrid resist). 3) methacrylic acid tertiary aliphatic esters copolymer (Methacrylate resist). These polymers have been used in ArF, KrF lithography. Recently, these resists have been investigated to employ for Extreme ultra violet (EUV) lithography because absorption of EUV doesn’t depend on the molecular structure. But EUV has very higher energy than ArF, KrF and it is exceed ionization potential of resist materials. Thus, polymer behavior under the EUV exposure is different from ArF, KrF exposure. For analyzing difference between ArF, KrF and EUV, we conducted to exposed resist materials (PHS, Hybrid, Methacrylate resist) using electron beam (EB) radiation source. As the results, we observed PHS resist showed crosslinking behavior less than 5μ C/cm2 , Hybrid resist showed cross-linking behavior more than 20μ C/cm2, Methacrylate resist showed moderate main chain scission behavior less than 20μ C/cm2 respectively.
Development of an atomic hydrogen system for treatment of EUV mask blanks
Tyler R. Mowll, Arun J. Kadaksham, Zachary R. Robinson, et al.
EUV masks and mask blanks pose new challenges for storing and cleaning, as the masks are designed to be pellicle-less. A ruthenium capping material is often used as an etch stop for mask making; however, it is readily oxidized by exposure to air and cleaning chemicals. It also gathers particles from the environment and cleaning solutions due to its adhesion properties. Oxidation of the Ru cap and underlying multilayers is undesirable since it reduces the EUV reflectivity of the masks and blanks. Similarly, particle contamination can result in defects in the transferred image. Therefore, it is important that a process be developed to reduce the oxidized Ru cap to its original pure state without exposing it to harsh chemicals that would further degrade the surface. Since atomic hydrogen has been shown to reduce ruthenium oxide, a high vacuum based atomic hydrogen dosing system has been developed that is used to determine the reduction rate of the surface region of EUV optics. The atomic hydrogen doser can also remove carbon species from the surface region by forming volatile hydrocarbon species. The chamber has a base pressure of 10-8 Torr and uses a tungsten filament to dissociate the molecular hydrogen. The mounting plate for the mask blanks is made from molybdenum, which has a relatively high thermal conductivity, and helps maintain a uniform substrate temperature distribution. Analysis of the reduction rate is achieved by performing angle-resolved XPS measurements before and after atomic hydrogen exposure. A 15 min exposure to atomic hydrogen with a hydrogen pressure of 10-4 Torr and 3.0 A of current through the tungsten filament was found to be sufficient to completely reduce the native ruthenium oxide.
Resist outgassing characterization based on the resist compositions and process
Norihiko Sugie, Toshiya Takahashi, Kazuhiro Katayama, et al.
For extreme ultraviolet (EUV) lithography, some critical issues concerning possible tool optics contamination due to resist outgassing remain to be resolved [1-4]. Before resists can be used on the ASML NXE:3100 and ASML NXE:3300 EUV scanners, they need to be tested in dedicated equipment and qualify according to the ASML NXE outgassing guidelines. In view of these guidelines, EIDEC has been working on an infrastructure set-up to enable resist outgassing testing. However, further investigations are still necessary to realize the application of the proposed outgassing evaluation method. Moreover, given the significant number of resists to be tested, fundamental studies to established concepts that reduce the number of resist outgassing tests are necessary. The application of these concepts focused on resist outgassing characterization based on resist composition and processes is presented. Moreover, a suggestion on how this fundamental information can be applied to reduce the total number of resist outgassing tests required for various EUV resists is discussed.
Collector optic in-situ Sn removal using hydrogen plasma
John R. Sporre, Dan Elg, David N. Ruzic, et al.
The presence of Sn on the collector optic of an extreme ultraviolet (EUV) light lithography tool continues to be a concern for source manufacturers. A mere nanometers deposition results in reduction of EUV light reflectivity to unacceptable levels. It has been shown previously that hydrogen radical etching of Sn provides a promising technique for in-situ cleaning of the collector optic. One concern in this technique is the redeposition by radicalized SnH4 breaking apart after making contact with a surface. To address this concern, large scale etching measurements were made using a metallic antenna as the substrate. Optimized etch rates approaching 7.5±1 nm/min have been achieved with a flow rate of 500 sccm at a pressure of 80 mTorr. The effect of variations in the Sn cleaning environment will be investigated with respect to temperature increases as well as air, oxygen, and methane contamination gasses. Furthermore, the effect of Sn located away from the cleaning location will also be presented.
Laser produced plasma EUV light source for EUVL patterning at 20nm node and beyond
This paper describes the development of a laser-produced-plasma (LPP) extreme-ultraviolet (EUV) source for advanced lithography applications in high volume manufacturing. EUV lithography is expected to succeed 193nm immersion double patterning technology for sub-20nm critical layer patterning. In this paper we discuss the most recent results from high power testing on our development systems in San Diego, and describe the requirements and technical challenges related to successful implementation of these technologies. Subsystem performance will be shown including the CO2 drive laser, droplet generation, laser-to-droplet targeting control, intermediate-focus (IF) metrology, out-of-band (OOB) radiation measurements and system use and experience. In addition, a multitude of smaller lab-scale experimental systems have also been constructed and tested..
Important processes in modeling and optimization of EUV lithography sources
T. Sizyuk, A. Hassanein
Laser produced plasma (LPP) sources for extreme ultraviolet (EUV) photons are currently based on using small liquid tin droplets as target that has advantages in generation of stable continuous targets at high repetition rate, larger photon collection angle, and reduced contamination and damage to optical mirror system from plasma debris and energetic particles. The ideal target is to generate a source of maximum EUV radiation output and collection in the 13.5 nm range with minimum atomic debris. Based on our predictions, the smallest efficient droplets are of diameters in the range of 20-30 μm. In this study we analyzed detail plasma evolution processes in LPP systems using small spherical tin targets to predict the optimum droplet size yielding maximum EUV output. We identified several important processes during laser-plasma interaction that can affect conditions for optimum EUV photons generation. The importance of accurate description of modeling these processes increases with the decrease in target size and its simulation domain.
Magnetic mitigation of debris for EUV sources
D. Elg, J. Sporre, D. Curreli, et al.
Extreme Ultraviolet (EUV) lithography sources expel high-energy ions and neutral particles, which degrade the quality of the collector optic. The mitigation of this debris is one of the main problems facing potential manufacturers of EUV sources. The use of magnetic fields to deflect ionic debris has been proposed and is investigated here. In this paper, we present a detailed computational model of magnetic mitigation, along with experimental results that confirm the correctness of the model. Using a strong permanent magnet, it is experimentally shown that, using high enough fields, magnetic mitigation can be a successful method of deflecting ionic debris from an EUV source. For example, through an orifice centered at 0° from the pinch, we saw a flux of 1.65×108 +/- 1.5×107 ions/(m2*pulse*eV) of 4keV ions without deflection and a negligible flux with deflection. With the orifice at a 35° angle from the pinch, a negligible 4keV flux was seen without deflection. However, with magnetic deflection, a 4keV flux of 1.03x108 +/- 9.4x106 ions/(m2*pulse*eV) were seen. The half-angle spread of the orifice was .047° with a tolerance of .008°.
Enhancing resolution with pupil filtering for projection printing systems with fixed or restricted illumination angular distribution
Greg McIntyre, Leon Teeuwen, Erik Sohmen, et al.
For projection printing imaging systems with fixed or restricted illumination modes, pupil filters may enhance imaging for select features by blocking rays of light that negatively contribute to imaging. A method to design pupil filters for the optimum printing of a select feature type and size is presented. With this method, a series of pupil filters have been developed and are being tested to enhance the resolution of the Albany Alpha Demo Tool (ADT, 0.25NA) in order to enable resist and process development at feature sizes relevant to the 10 and 7nm nodes. By only allowing light to propagate to the wafer that positively contributes to imaging, six filters have been custom designed to optimize printing of the following sub-resolution feature types and sizes: 22 and 19 nm HP lines, 24 and 21 nm HP contacts, and 27×22 nm HP rectangular contacts. Development and installation of enabling hardware on the scanner is complete, six filters have been manufactured and imaging in resist has validated the concept. Over 20% improvement in tool resolution has been achieved for 22nm HP lines, allowing resist process development for NXE3300 conditions on the ADT. This paper discusses the theory behind the filter designs, the experimental in-resist evaluations, and other aspects of the development, to include challenges caused by the filters with slit uniformity, stray light, and reticle alignment.
Roughness and variability in EUV lithography: Who is to blame? (part 1)
Process variability in today’s EUV lithography might be a showstopper for features below 27nm dimensions. At these feature sizes, electrical devices are influenced by quantum effects and thus have to face the discrete behavior of light and matter. More in general, lithography uncertainties arise from each lithographic element: the source, the photomask, the optical system, and the photoresist. In order to individually assess all the different contributions to the final resist roughness, a EUV mask with known absorber pattern variability was used to expose different resists at different process conditions. CD-SEM analyses were performed on both mask absorber and resist pattern and then used to build a stochastic resist model. In this first paper, we present a complete characterization of the root causes which are responsible of the CD nonuniformity for 27nm half-pitch dense contact-holes exposed with the ASML NXE:3100 scanner installed at imec. Using the same stochastic model, a simulated evaluation to quantify the possible impact of the different elements composing the lithographic process is performed at higher numerical aperture.
7nm node EUV predictive study of mask LER transference to wafer
D. Civay, E. Nash, U. Klostermann, et al.
The transition into smaller nodes has resulted in stringent CD tolerance requirements and the role of mask LER in that budget is not sufficiently understood. The critical variables associated with mask LER were explored with the goal of establishing mask requirements based on wafer requirements. A systematic study of the impact of mask LER correlation length (ξ), critical exponent (α) and standard deviation of the line edge (σ) on the printability of 7nm node line/space (L/S) and contact holes (CH) in extreme ultraviolet lithography has been simulated. An experimentally relevant range of the three mask LER variables was explored in these simulations. CDU and CER/LER were the primary metrics used to gauge printability and they were evaluated as a function of ξ, α and σ with stochastic simulations. A 45nm pitch was investigated to determine critical mask LER parameters that mark printability transition regions relevant to the 7nm node middle of line.
Silica aerogel can capture flying particles in EUV tools
Kazuya Ota, Jiro Inoue
A flying particle in a vacuum tool necessarily has a higher velocity than the critical velocity determined by the particle material and the surface material of chamber walls or tool structures. A flying particle loses kinetic energy at every collision with a surface and the velocity is reduced by about 10% a collision. When the velocity of the particle is below the critical velocity, the particle is captured by the surface at the next collision. We must catch the particles before they reach the reticle surface not protected by pellicle. It is a well-known fact that silica aerogels can capture stardust in space. Typical size of the stardust is a few tens of microns and the estimated velocity is a few tens of kilometers per second. On the other hand, typical size of particles in EUV tools is about 100 nm and the typical velocity is about a few hundreds of meters per second. The ratio of kinetic energy of the two is about 1:300,000,000,000. Can silica aerogels capture such low energy particles in the same way as stardust without bouncing the particles or generating debris? The question motivated us to evaluate the properties of silica aerogels in a vacuum; we evaluated the outgassing rate and the particle trapping performance of several aerogels with different densities, 0.012 - 0.19 g/cm3. We found that some aerogels captured more than 90% incident particles and the outgassing rate is sufficiently low for EUV tools.
Impact of EUV mask roughness on lithography performance
The influence of surface roughness of an EUV mask on wafer image has been thoroughly investigated by lithography simulation with the Monte Carlo method. Based on the power spectral density of the surface roughness of an actual mask, and based on a given random phase distribution, we have reconstructed a number of rough surfaces with various rms roughness values. We quantitatively estimated the impacts of these reconstructed rough surfaces on wafer images. Furthermore, we also investigated the influence of phase defects formed on the rough surfaces. We then did the process margin analysis that showed the specifications of the surface roughness.
Track processing optimizations for different EUV resist platforms: preparing for a NXE:3300 baseline process
Philippe Foubert, Koichi Matsunaga, Hideo Shite, et al.
To make sure a baseline process will be ready for the evaluation of the NXE:3300, imec evaluates promising new EUV resist materials with regards to imaging, process window and line width roughness (LWR) performance. From those screening evaluations, highest performing materials meeting dose sensitivity requirements are selected to be installed on the coat/develop track. This work details the process optimization results of the different selected resist platforms with regards to full wafer processing. Evaluations are executed on the ASML NXE:3100 equipped with a laser-assisted discharge produced plasma source from XTREME technologies, and interfaced to a TEL CLEAN TRACKTM LITHIUS ProTM -EUV.
Simulation-assisted layout biasing in EUV lithography and prediction of an optimum resist parameter space
Chandra Sarma, John Biafore, Kyoungyong Cho, et al.
This paper demonstrates a new simulation-based methodology for optimizing critical dimension (CD) bias for contact holes (CH) arrays using several different extreme ultraviolet (EUV) resists that were fully calibrated and verified with physical resist models. The bias for CH was optimized using local CD uniformity (CDU) 3-sigma as a cost function. The CD sigma variations of near-neighbor contact holes were simulated as a function of dose-to-size and mask bias, averaged over a large number of stochastic trials. There is a distinct bias for minimum CD sigma accompanied by an increase in the process window. The results are confirmed with wafer data. We will discuss the results in terms of EUV photon shot noise coupled with resist parameters. The simulation results will be used to predict a parameter space for EUV resist that can optimize line edge roughness (LER)/resolution/process window and CDU. Finally, various tradeoffs will be presented that will enable the process to perform in a high volume manufacturing environment.
Deep ultraviolet out-of-band characterization of EUVL scanners and resists
As Extreme Ultraviolet Lithography (EUVL) gets closer to production, an increasing interest is devoted to Deep Ultraviolet Out-of-Band (DUV OoB). In fact, EUV sources are known to emit a broad spectrum of wavelengths, among which DUV could potentially contribute to the exposure and degrade imaging performance. In this paper, the DUV/EUV ratio in pre-production (ASML NXE:3100) and alpha (ASML ADT) EUVL scanners is investigated. The OoB is quantified using a previously proposed methodology [1] based on the use of an aluminum-coated mask capable to provide quantitative in situ information on DUV/EUV ratio without disrupting the tool. The OoB sensitivity of an extensive set of resists is estimated in order to properly guide material development. The impact of OoB on imaging and on Intra-Field Critical Dimension Uniformity (IF CDU) is quantified using resists with large differences in OoB sensitivity. In addition, the impact of mask design on OoB is also investigated. The results indicated that it is in fact possible to reduce the OoB sensitivity of a resist (from 2.5 down to 0.3%) without compromising imaging performance and that tool OoB qualification and monitoring are critical in a production environment.
Investigation of coat-develop track system for EUV resist processing
EUV lithography (EUVL) is the leading candidate for the manufacture of devices with 1× nm node and beyond. However, many challenges remain for the industry to understand clearly and to overcome before EUVL will be ready for application in volume production. Efforts have been made to improve the various critical components of EUVL, such as light source, exposure tool, mask, resist material, and so on.[1,2] Among these, resist materials are considered as one of the most critical issues in realizing EUVL.[3,4] Coat-develop track system overcame several challenges for each traditional resist system (i.e. i-line, KrF ArF, and ArF immersion). EUV resist system requires ultra thin organic film coating.[5] The under-layer thickness is below 10nm and the resist thickness is about 40nm, however, in some cases film thickness is smaller than the diameter of particles on the substrate, even if the particle size is smaller than the detection limit of defect inspection tool. Also EUV resist patterning becomes extremely small pattern pitch. It leads the difficulty of CD control because the resist solubility in develop processing depends on resist type. Some resists were significantly swelled during develop process. Swelling depends on develop time and developer materials. That behavior on EUV resist system is becoming evident.[6] Furthermore, LWR improvement on track processing is required. During the conference, we will discuss how to coat the substrate with ultra thin film and how to control resist dissolution to improve CD uniformity and LWR. Additionally, we will show the latest lithographic results obtained with the novel application for EUV coat-develop track system.
Heat behavior of extreme-ultraviolet pellicle including mesh support
As is well known, a very short wavelength of 13.5 nm EUV is strongly absorbed by the most materials and this might cause huge heat deposition and as a result the pellicle deformation. Previously we have shown that the temperature rising of the thin pellicle membrane is minimal and cooling between the exposures is efficient enough so that we do not have to worry about the pellicle deformation. People still worry about the temperature rising of the mesh structure. We find that the cooling of the mesh was very slow and can pile up and damage the pellicle because thick (~ 50 μm) mesh structure has much larger mass compared to very thin (~ 50 nm) membrane. In order to see this heat behavior of the mesh, we intentionally increased the exposure time up to 2000 ms from normal 10 ms for Si, Zr, and Ni mesh. For the case of silicon mesh, the peak temperature rises up with the exposure time initially, but the temperature is not increased any more and is saturated even though more energy is deposited as the exposure time is increased. This result shows again that the heat pile up to pellicle including both membrane and mesh support can be managed and EUV pellicle can be used for EUV high volume manufacturing.
The need for EUV lithography at advanced technology for sustainable wafer cost
Arindam Mallik, Wim Vansumere, Julien Ryckaert, et al.
Extreme Ultra-Violet lithography (EUVL) is considered as the most promising candidate to replace optical lithography from the 14nm technology node onwards. EUVL has recently been supplanted by multiple patterning using existing 193nm immersion lithography tools for upcoming 14 nm technology node due to the current resolution limitations and production level efficiency restrictions. In this paper, a wafer cost model for technology node from 28nm down to 14nm has been developed. It identifies lithography module as the key component where innovation can be leveraged to reduce cost. The results presented in the paper reveal that wafer cost will be increased by 30% from 28nm to 20nm technology node. A 70% increase in wafer cost is foreseen during a transition from 20nm to 14nm node based on 193nm immersion lithography and multiple patterning. The cost analysis predicts a 30% wafer cost reduction by adapting EUVL at a 14 nm technology node compared to 193nm immersion technology (normalized to 28nm wafer cost). It proves that the readiness of EUVL is critical to keep scale the logic devices at the pace of Moore’s law without violating the scale of economics in semiconductor industry.
The study of novel PAG containing acid amplifier in EUV resist material
Hyun Sang Joo, Jin Ho Kim, Joon Hee Han, et al.
The minimum target specificatons of EUV resist material are the Resoultion ≤ 22nm half pitch L/S, Line Width Roughness ≤ 1.7nm, and Sensitivity 10mJ~15mJ[1]. The major pending issue of EUV resist is how to simultaneously achieve high sensitivity, high resolution and low LWR.[12] Especially, LWR[2] is the main issue among above RLS performances. Thus, we have measured acid diffusion length of blend type PAG and Polymer bound PAG in order to confirm the fact that the acid diffusion length of Polymer Bound PAG type is shorter than that of blend type PAG. With the results of these experiments, we could determine polymer bound PAG as polymer platform for EUV resist material. We have also researched about acid labile group to improve the sensitivity of EUV resist with introduction of various kinds of monomers and we have tried to develop novel acid amplifier to get a good acid yield. Additionally, we have also studied the effects of steric hinderance through diversifying the size of pendent group to make polymer of high performance. In this paper, we will discuss the results of these studies obtained by EUV tools.
Optimizing XPS tool performance for characterizing trace contamination elements for EUV resist outgas testing
Mihir Upadhyaya, Yudhishthir Kandel, Gregory Denbeaux, et al.
Extreme ultraviolet (EUV) resist outgassing is viewed as one of the factors to be considered in the research and development of EUV resists1-3. Resist outgassing in an EUV exposure tool system can lead to contaminated optics which can cause a decrease in EUV energy reaching the wafer surface, in turn leading to lower throughput. There is a program underway to measure the relative contamination rates from different resists following the ASML approved protocols for witness plate testing4. One of the important steps in this is measuring the residue on the optics after cleaning using X-ray photoelectron spectroscopy (XPS). Anything non-cleanable on the reflective optics could lead to its permanent degradation which is undesirable. Due to the number of resists being developed for EUV, there is a need for rapid testing and optimizing the XPS for throughput, precision and accuracy. In this paper, we discuss the role of XPS in quantification of species that adhere to the witness plate sample, which is a ruthenium-coated silicon wafer, as a result of the resist outgassing upon EUV exposure. XPS is a relatively slow spectroscopic technique when high accuracy in measurements is necessary, as is the requirement for our application. In this study we have attempted to optimize the various XPS parameters such as the beam power, beam spot size as well as the pass energy of the analyzer. We also studied the XPS anode degradation and the impact it has on the measurement accuracy.
Effect of cleaning on EUV masks
A major difference between EUV lithography and its conventional optical predecessors is the lack of a usable pellicle. No material has been found that is both transmissive at the EUV lithography wavelength of 13.5nm and that has sufficient structural integrity to serve as a pellicle. Therefore, during exposure to EUV light the mask is unprotected and accretes particles. This necessitates repeated cleanings of the mask, which raises concerns about changes in the mask induced by the cleaning process. It is only through metrology that these concerns can be addressed. This paper describes an optical characterization method to determine the effect of cleaning an EUV mask.