Proceedings Volume 4779

Advanced Characterization Techniques for Optical, Semiconductor, and Data Storage Components

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Proceedings Volume 4779

Advanced Characterization Techniques for Optical, Semiconductor, and Data Storage Components

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Volume Details

Date Published: 11 November 2002
Contents: 8 Sessions, 20 Papers, 0 Presentations
Conference: International Symposium on Optical Science and Technology 2002
Volume Number: 4779

Table of Contents

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Table of Contents

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  • Sub-Wavelength Metrology I
  • Sub-Wavelength Metrology II
  • Characterization in the VUV to X-Ray Regimes
  • Surface Defect, Roughness, and Scatter Analysis
  • Poster Session
  • Ellipsometry and Reflectometry
  • Optical Material and Thin-Film Characterization
  • Large Area and Wavefront Inspection
Sub-Wavelength Metrology I
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Sub-nm topography measurement by deflectometry: flatness standard and wafer nanotopography
Ralf D. Geckeler, Ingolf Weingaertner
Current demands of the semiconductor industry on the measurement accuracy in lithography have reached nanometer and even sub-nanometer levels. We have built a novel scanning facility based on ESAD (Extended Shear Angle Difference) deflectometry for the ultra-precise and traceable measurement of large near-flat and slightly curved optical surfaces. One primary application of the device is to establish the improved standard for straightness and flatness with sub-nanometer accuracy at PTB. Transfer standards then will allow optical devices, e.g., interferometers and wafer mappers, to be calibrated with high accuracy. The measurement principle is based on the analysis of differences between reflection angles obtained at surface points with large lateral displacements (shears). The ESAD principle minimizes error influences and in first order is independent of stage errors and whole-body movements of the specimen. ESAD scanning does not rely on external reference surfaces of matched topography and allows the accurate calibration of the angle measuring device. The measurands are directly traceable to the SI units of angle and length. We will report in detail on the new ESAD facility for the ultra-precise measurement of large (up to 500 mm in diameter) near-flat optical surfaces. We will present first measurements of a number of plane optical substrates with the device from various fields of application. The main error influences will be discussed, including the calibration of the high-resolution autocollimator used for angle measurement. Investigations into the repeatability, reproducibility and uncertainty of the topography measurement using the new facility at the sub-nanometer level will be presented.
Novel concept for the ultraprecise and fast measurement of the nanotopography of large wafers
Ingolf Weingaertner, Matthias Wurm, Ralf D. Geckeler, et al.
The measurement of the topography or the nanotopography of large wafers up to 450 mm in diameter with satisfactory lateral resolution and nanometer uncertainty is still an unsolved problem. The topography of wafers covers a relatively large measurement range as wafers have surfaces with a so-called "slightly unflat" topography which mostly exceeds the measurement capabilities of interferometers. For the ultraprecise and traceable measurement of the slope and topography of slightly unflat optical surfaces, a novel scanning deflectometry principle has been developed. An uncertainty of the topography in the nanometer range will be achieved, as this principle minimizes error influences and allows a highly precise calibration of the angle measuring device. The main goal is to use this principle for the ultraprecise measurement of the nanotopography of large wafers. The measurement principle is based on the analysis of differences of reflection angles obtained at surface points which are separated by large lateral shears. It does not rely on external reference surfaces of matched topography and in first and second order is independent of any stage errors and the whole-body motion of the specimen. The measurands are directly traced back to the base units of angle and length. The specific idea of wafer measurement is to combine rotational and linear scanning with the measurement of slope difference vectors and to arrive at an unambiguous solution for the topography and nanotopography. The equations with the slope difference vectors are solved to reconstruct the slope vectors, as newly developed mathematical algorithms allow the surface slope to be reconstructed from slope differences for two different shears. This is reached by applying natural extensions and shearing transfer functions by a mathematically exact method over the whole surface area. Further the differential equations for the slope vectors are solved to unambiguously reconstruct the topography. With this method it is possible to achieve nanometer uncertainty and at the same time a high lateral resolution, short measurement times and the possibility of mastering the large measurement range necessary for slightly unflat wafer surfaces.
Sub-Wavelength Metrology II
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Investigation of optical properties of injection-moulded subwavelength gratings
Surface reflections from optical transmission components are in many cases unwanted and cumbersome. Thin film coating is the conventional technique used for anti-reflection treatment of optical components. In recent years subwavelength gratings have been studied as a replacement for thin films. Subwavelength gratings are microstructures that can be formed on one or both sides of a substrate. Typically an optical component needs to be AR-coated on both sides. We have fabricated injection moulded subwavelength gratings superimposed upon a blazed grating structure in polycarbonate. The gratings are initially formed by electron-beam lithography and subsequently replicated using the same process which is used to manufacture standard plastic compact discs (CDs). There are several problems when trying to characterize a component such as a blazed transmittance grating. First of all there is the spread of internal reflections. Light that is reflected inside the substrate is shifted in lateral position due to the angle of the grating. We have thoroughly investigated the effects of decrease in grating efficiency due to internal reflections and also tried to minimize these effects by appropriately treating both sides of the plastic CD.
Characterization in the VUV to X-Ray Regimes
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Optical metrology in the VUV and EUV spectral range
Klaus R. Mann, Sebastian Kranzusch, G. Eckert, et al.
In order to improve the efficiency of optical components for microlithography, metrology for comprehensive characterization of DUV and VUV radiation and the related optics has been developed at Laser-Laboratorium Gottingen. The performance of optical components is assessed by measuring absorptance, scatter losses and damage thresholds during ArF and F2 laser irradiation. Absolute linear and non-linear absorption coefficients are determined by high-resolution laser calorimetry, which provides greatly enhanced accuracy as compared to transmissive measurements. This technique accomplishes also fast monitoring of laser induced degradation phenomena. The absorptance data are compared with the results of accompanying high-resolution laser-induced fluorescence measurements. For an assessment of the optical quality of DUV/VUV optics, a specially designed wavefront analyzer based on the Hartmann-Shack principle is employed. This device, which also allows accurate beam characterization of ArF and F2 laser in the near- and far-field, can be used as an alternative to interferometric measurements for "at wavelength" testing of optics, e.g. for on-line monitoring of compaction or lens heating in fused silica.
Surface Defect, Roughness, and Scatter Analysis
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Surface damage metrology: precision at low cost
Lionel R. Baker
This paper reviews the current status of methods for the inspection and measurement of damage, such as digs and scratches on high quality surfaces and reports on relevant ISO standards. A simple but precise low-cost approach for measuring imperfections and contamination on and within an optical system using a digital camera is described.
Large AFM scans with a nanometer coordinate measuring machine (NCMM)
With the increasing amount of applications in the field of nanotechnology there is a growing demand for a detailed inspection of surface areas of millimeter sizes. The geometry of silicon micro structures is as well of interest as the detection and shape characterization of defects on optical surfaces. It is state of the art to be able to measure topographies within 2 1/2 D with nanometer resolution by using scanning probe microscopes. So far they are usually restricted to area sizes of 100 square microns. Furthermore it is state of the art to build positioning systems covering several millimeters and resolving nanometers. Those systems are restricted in their positioning uncertainty, which can be estimated within several ten nanometers. Very few research labs and one or two industrial sites are involved in developments and investigations on combining large area positioning systems with atomic force probe heads. Systems being able to cover 6 decades (mm...nm) are highly sensitive to the choice of control parameters. We are investigating a prototype of such a system employing a calibration standard representing a lattice with 1 micron pitch width. Some "real life" semi conductor structures have been measured as well. Up to now the response of atomic force probe heads to the scanning motion of the table is not fully understood. The talk will reveal obstacles, their overcoming, and it will probe that realizing large area topography measurements with high resolution is possible. Futhermore, the need of strategies of selecting areas such that the amount of data can be handled in a reasonable way will be shown.
Measurement of the 100-nm NIST SRM 1963 by lase surface light scattering
Thomas A. Germer, George W. Mulholland, Jung Hyeun Kim, et al.
Accurate sizing of particles deposited on surfaces is important for the semiconductor, optical, and data storage industries. The recent availability of accurate light scattering models for non-ideal conditions enables the determination of particle size with a complete assessment of the measurement uncertainties. In this manuscript, we describe a light scattering measurement of the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1963 deposited onto a silicon wafer. The measurement was carried out using 441.6 nm, p-polarized light. The measurement yielded a value of 99.7 nm with an expanded uncertainty (95 % confidence limit) of 1.7 nm. The uncertainty is dominated by the reproducibility of the measurement. Uncertainties in the substrate optical properties, the thickness and optical properties of the substrate oxide, and the shape of the particle dominate the systematic uncertainty.
Performance limits of ARS sensor based on CMOS photodiode array
Measuring the light scatter back from a coherently illuminated surface is a powerful and fast measurement method to observe surfaces and its properties. It opens the possibility to measure integral surface topography constants, material properties, surface defects and contamination. In this paper the performance limits of the angle resolved light scatter sensor (ARS sensor) LARISSA (Large Dynamic Range Intelligent Scatter Sensor Approach) will be discussed and exemplified by using a technical application. In the first part of the paper the experimental setup of the ARS sensor LARISSA will be considered. In the second part of the paper the performance limitation of the ARS sensor LARISSA concerning particle detection will be derived based on simulation and measurement results. Finally a short overview is given about further development of the ARS sensor.
Poster Session
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Theoretical investigation for improvement of scanning a near-field optical microscope
A near-field optical microscope on the basis of two trapeziform metallic strips on the surface of a dielectric cone is investigated1. It is shown that such construction of a near-field probe significantly improved the optical efficiency of a near-field microscope. The field distribution in the vicinity of probe apex is investigated for this probe and for the usual SNOM probe. On the basis of mathematical simulation it was shown that this type of a near-field microscope is promising for use in optical information recording with pit length less than 200 nm and also for using as optical heating element in magnetic information recording. The construction of a near field microscope for information recording is proposed on the basis of this near-field microscope and a solid immersion lens2. The model of a near field strips probe with cleaved apex is proposed. A method of checking the distance between a probe and the surface on the basis of exciting mechanical vibration of cleaved apex by voltage step is offered. The oscillation amplitude and their attenuation are determined by measuring high-frequency electromagnetic oscillation, which are excited by oscillation of opposite charges at the apex of a probe. The investigation was carried out on the basis of a mathematical model and an experiment is needed for full investigation.
Ellipsometry and Reflectometry
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Design and Implementation of a rotationally symmetric ellipsometer
We report a unique scanning microellipsometer using a high numerical aperture lens to provide large-angle ellipsometric illumination and high spatial resolution. This microellipsometer is equivalent to a multi-channel rotating analyzer ellipsometer obeying rotational symmetry. The symmetry is realized by using a circularly polarized incident beam, a variable circular retarder and a rotational analyzer. This rotational symmetry offers better signal-to-noise ratio compared with the other microellipsometer techniques. Scanning ellipsometric measurement of surface relief with spatial resolution of 0.5 μm is performed with a NA of 0.8 illumination by use of a He-Ne laser source.
Far-infrared magneto-optic generalized ellipsometry determination of free-carrier parameters in semiconductor thin film structures
Tino Hofmann, Mathias Schubert, Craig M. Herzinger
In accord with the Drude model, the free-carrier contribution to the dielectric function at infrared wavelengths is proportional to the ratio of the free-carrier concentration N and the effective mass m, and the product of the optical mobility μ and m. Typical infrared optical experiments are therefore sensitive to the free-carrier mass, but determination of m from the measured dielectric function requires an independent experiment, such as an electrical Hall-effect measurement, which provides either N or μ. However, doped zincblende III-V-semiconductors exposed to a strong external magnetic field exhibit non-symmetric magneto-optical (MO) birefringence, which is inversely proportional to m. Therefore, if the spectral dependence of the MO dielectric function tensor is known, the parameters N, μ and m can be determined independently from optical measurements alone. Generalized Ellipsometry (GE) measures three complex-valued ratios of normalized Jones matrix elements, from which the individual tensor elements of the dielectric function of arbitrarily anisotropic materials in layered samples can be reconstructed. We present the application of GE at far-infrared (FIR) wavelengths for measurement of the FIR-MO-GE parameters, and determine the MO dielectric function of GaAs for wavelengths from 100 μm to 15 μm. We obtain the free electron mass and mobility results in excellent agreement with results obtained from Hall-effect and Shubnikov-de-Haas experiments. (F)IR-MO-GE may open up new avenues for non-destructive characterization of free-carrier properties in complex semiconductor heterostructures.
Reflectometry-based approaches for in-situ monitoring of etch depths in plasma etching processes
Vijayakumar C. Venugopal, Andrew J. Perry
Tighter control requirements for plasma etch processes drive the search for more accurate and robust methods for monitoring processes in situ. Conventional optical methods such as optical emission spectroscopy and interferometry, while easy to use, have their limitations especially in their ability to compensate for incoming material variations. As an alternative, we have successfully developed a broadband (UV-VIS-NIR) reflectometry-based approach for in situ monitoring of etch processes such as shallow trench isolation (STI) and recess etch processes. This approach enables us to estimate in real time the vertical dimensions of features of interest on patterned wafers. The approach has proven to be robust in that it works for a given application without modification for a variety of pattern densities and incoming material variations. It has proven to be easy to use in that there is minimal user/operator input required. We present results for a couple of applications that we have studied.
Optical Material and Thin-Film Characterization
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Simultaneous measurement of bulk absorption and fluorescence in fused silica upon ArF laser irradiation
Christian Muhlig, Siegfried Kufert, Wolfgang Triebel, et al.
A new setup was established to simultaneously record the bulk absorption of fused silica at 193 nm and its laser induced fluorescence (LIF). Bulk absorption coefficients in the 10-3/cm range are measured in a compact setup with small samples of 20 x 20 x 10 mm3 using an ArF pump laser and recording the ArF laser induced deflection (LID) of a diode probe laser beam. LIF is measured through an optical fiber coupled to an intensified gated CCD camera. Within the first few pulses of ArF laser irradiation the bulk absorption coefficient and LIF emission around 300 nm and 400 nm (oxygen deficient centers, ODC) decrease considerably, sometimes to a fraction of their initial values. In smoe fused silica samples additional fluorescence in teh green-yellow wavelength region is found. This fluorescence increases in a strongly nonlinear way with the fluence. Assuming fluorescence excitation by single photon absorption the observed behavior can be explained by saturation of the absorption transition which put limitations on the fluence applicable in the experiments. Summarizing the obtained results a measurement instruction for precise absorption measurements of fused silica at 193 nm laser irradiation is suggested and fused silica samples have been investigated concerning their dependence of the absorption coefficient on the fluence. The results, in combination with transmission measurements of 300 mm long fused silica samples, confirm the nonlinear increase of the absorption with increasing fluence.
Advanced industrial metrology used for qualification of high-quality optical materials
Axel Engel, Gerhard Westenberger, L. Bartelmess, et al.
Schott Glass is producing and developing the optical material for various specialized applications in photonics, optical and microlithography technology. In order to achieve the specifications several of metrology R&D activities have been done and hardware has been installed in the metrology labs. Today special diagnostics are available to qualify materials for the absolute refractive index, the transmissin, radiation durability and inner quality to ensure the quality of the produced materials. Methods used for this qualifications are minimum deviation, precision spectral photometer, in-situ transmission measurements using UV lasers and Rayleigh Scattering. The optical material quality requirements of such materials are extremely high and still increasing. Therefore further development and implementation of diagnostics have been iniatiated, e.g. Raman Scattering, fluorescence and refractive index measurements. We present the status of R&D activities for metrology, which is necessary to visualize the status and the improvement of the optical quality with the help of new and improved metrology.
Channel structures observed in natural diamonds, synthetic moissanite, and synthetic quartz
Taijin Lu, James E. Shigley, John I. Koivula
Internal growth and dissolution features are visual characteristics of some natural, synthetic, and treated gem materials. Open channels or need-like structures are occasionally observed in natural diamond, synthetic moissanite (SiC-6H), and chemically-etched synthetic colorless quartz. The distinguishing features among the channel structures in these materials are compared, and possible formation mechanisms of the channels associated with dislocations or dislocation bundles are discussed.
Multidomain genetic algorithm (MDGA) and its applications to thin film metrology
JingMin Leng, John J. Sidorowich, Jon L. Opsal
We have developed a new Multi-domain Genetic Algorithm (MDGA) as a tool for advanced recipe development and applied it to metrology based on X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE). In our MDGA approach, multiple data sets are examined with the output being an optimal set of parameters for robust and rapid measurements. The data sets usually span the expected range of variations likely to be encountered in a process to be monitored (e.g., the data sets correspond to different thickness but with the same density or dispersion).In one application involving XRR measurements, a set of Ti films with thickness of 200 Å was plasma treated for 0 sec, 10 sec, 30 sec, 50 sec, and 100 sec. Although it was expected that the plasma treated Ti film had a higher density than the non-treated Ti film, we found that the plasma treated Ti film had to be modeled as a two-layer film stack: the plasma treated Ti on top of a regular Ti. Without the MDGA, the densities of the top plasma treated Ti and the bottom Ti traded off since they are so close. With the MDGA, the densities of the top and bottom Ti films were regarded as global optimization parameters while the thickness and roughness of each layer were allowed to vary as local parameters. Our results show that the MDGA can clearly separate the plasma treated Ti from the untreated Ti film across the entire wafer set. On the other hand normal non-linear regression methods cannot distinguish the plasma treated Ti from the untreated Ti. In an application using SE measurement of a bottom anti-reflective coating (BARC) material, a linescan of 11 points across a 200mm wafer was measured with the thickness of the BARC film treated as a local parameter while the dispersion was treated as a set of global parameters. With the help of the MDGA, the dispersion modeling of the BARC film captured two main features at ~ 4.77 eV (260nm) and ~ 5.07 eV(235nm), as well as three small peaks at 3.16 eV(392nm), 3.37 eV (368nm) and 3.53 eV (351nm). In this way, the measured dispersion of the BARC film is more representative of the entire wafer than any dispersion developed from a single point measurement.
Ag-Sb-Te system for phase change optical data storage
Yagya Deva Sharma, Promod K. Bhatnagar
For phase change optical data storage, several chalcogenide-based materials have been reported and are expected to replace the conventional magnetic disk. In the present work, preparation and characterization of the chalcogenide allow Agx - Sb 2(1-x) - Te 3(1-x) with different composition (x = 0.16, 0.18 and 0.20) has been presented. Samples were prepared using melt quenching technique and the films were grown by thermal evaporation system. The crystallization process of Ag- Sb- Te material was studied using differential thermal analysis (DTA) and Optical analysis (Transmittance and reflectance) respectively. The films were studied for both cases: before and after annealing. The Differential thermal analysis curves were recorded for different compositions and Glass transition temperature (Tg), crystallization temperature (Tc) and melting temperature (Tm) have been obtained. It may also be concluded that Tg/Tm ratio is closer to required condition for phase change optical data storage material. Thermal and optical analysis shows that the Ag - Sb- Te material is a potential candidate for phase change optical data storage. The optimized composition has also been obtained.
Large Area and Wavefront Inspection
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Shack-Hartmann wavefront sensor precision and accuracy
Daniel R. Neal, James Copland, David A. Neal
The design of a wavefront sensor may be determined by the lenslet array and camera selection. There are numerous different applications for these sensors, requiring widely differing dynamic range and accuracy. Performance metrics are needed to evaluate candidate designs and to compare results. We have developed a standard methodology for measuring the repeatability, accuracy and dynamic range of different wavefront sensor designs, and have experimentally applied these metrics to a number of different sensors.
Application of Shack-Hartmann wavefront sensing technology to transmissive optic metrology
Human vision correction optics must be produced in quantity to be economical. At the same time every human eye is unique and requires a custom corrective solution. For this reason the vision industries need fast, versatile and accurate methodologies for characterizing optics for production and research. Current methods for measuring these optics generally yield a cubic spline taken from less than 10 points across the surface of the lens. As corrective optics have grown in complexity this has become inadequate. The Shack-Hartmann wavefront sensor is a device that measures phase and irradiance of light in a single snapshot using geometric properties of light. Advantages of the Shack-Hartmann sensor include small size, ruggedness, accuracy, and vibration insensitivity. This paper discusses a methodology for designing instruments based on Shack-Hartmann sensors. The method is then applied to the development of an instrument for accurate measurement of transmissive optics such as gradient bifocal spectacle lenses, progressive addition bifocal lenses, intrarocular devices, contact lenses, and human corneal tissue. In addition, this instrument may be configured to provide hundreds of points across the surface of the lens giving improved spatial resolution. Methods are explored for extending the dynamic range and accuracy to meet the expanding needs of the ophthalmic and optometric industries. Data is presented demonstrating the accuracy and repeatability of this technique for the target optics.
Research on quasi-digitizing interferometer for optical measurement
Mengchao Li, Gang Zheng, Baoxue Chen, et al.
In this paper, a Michelson form interferometer not only acts as a pure unit of measurement, but also as part of the digital encoder. When a normal beam splitter is taken place of the special one which made of photorefractive material, the orders of the diffraction correspond the path light intensity and its fringe. The out put field is shown as array form. Signal would be sent by optical fiber and all system is full optical with quasi-digitized code.