This PDF file contains the front matter associated with SPIE Proceedings Volume 7202, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing

A lab-on-a-chip (LOC) is a device that incorporates in a single substrate the functionalities of a biological laboratory, i.e. a network of fluidic channels, reservoirs, valves, pumps and sensors, all with micrometer dimensions. Its main advantages are the possibility of working with small samples quantities (from nano- to picoliters), high sensitivity, speed of analysis and the possibility of measurement automation and standardization. They are becoming the most powerful tools of analytical chemistry with a broad application in life sciences, biotechnology and drug development. The next technological challenge of LOCs is direct on-chip integration of photonic functionalities for sensing of biomolecules flowing in the microchannels. Ultrafast laser processing of the bulk of a dielectric material is a very flexible and simple method to produce photonic devices inside microfluidic chips for capillary electrophoresis (CE) or chemical microreactors. By taking advantage of the unique three-dimensional capabilities of this fabrication technique, more complex functionalities, such as splitters or Mach-Zehnder interferometers, can be implemented. In this work we report on the use of femtosecond laser pulses to fabricate photonic devices (as waveguides, splitters and interferometers) inside commercial CE chips, without affecting the manufacturing procedure of the microfluidic part of the device. The fabrication of single waveguides intersecting the channels allows one to perform absorption or Laser Induced Fluorescence (LIF) sensing of the molecules separated inside the microchannels. Waveguide splitters are used for multipoint excitation of the microfluidic channel for parallel or higher sensitivity measurements. Finally, Mach-Zehnder interferometers are used for label-free sensing of the samples flowing in the microfluidic channels by means of refractive index changes detection.

Laser based solder bumping is a highly flexible and fast approach for flux-free soldering of micro-optical components in complex 3D geometries with localized and time restricted energy input. Solder joints provide superior mechanical strength, higher radiation stability, humidity resistance and a good thermal and electrical conductivity compared to adhesive bonding. Due to the good long term stability solder joints are feasible for the integration of optical, mechanical, electronic, and MEMS/MOEMS devices in multi functional hybrid optical assemblies. Comparative studies of solder bumping of optical components with sputtered thin film metallization on platforms made of Alumina (Al₂O₃) and Low Temperature Cofired Ceramics (LTCC) with both Au and AgPd thick film metallization were carried out using design of experiment methods (DoE). The influence of the system parameters, laser pulse energy and duration, distance, incidence angle and nitrogen pressure on targeting accuracy and bond strength were evaluated. The jetting of liquid solder spheres within a localized nitrogen atmosphere improves wetting on the respective wetting surfaces and simplifies the joining process due to integration of solder alloy preform handling and reflowing, thus showing great potential for a high degree of automation.

For mounting FAC lenses to diode lasers a new technology is introduced. Solder jet ball bumping is demonstrated to have the potential to replace conventional mounting technologies like adhesive bonding. The advantage of this method is a thermally and mechanically stable connection of micro optics and laser without drawbacks of outgasing and sensitivity to UV. The reached accuracy is within the range of one micrometer.

High power fiber laser assemblies require monolithic joining technologies for low loss, mechanically stable and reliable spliced component interconnection. In contrast to conventional heat sources for splicing a carbon dioxide laser heats optical fibers and end caps only by radiation. The advantages of laser heating, e.g. precisely defined areas of laser impact and high process purity, meet the goals for high power applications. Requirements and challenges like tensile strength, centricity and reproducibility while using the splicing technology for a production line will be shown on behalf of a special developed CO₂ laser splicing device, splicing experiments and respective results.

The requirement for microwiring technology by a wet process has significantly increased recently toward the achievement of printable and flexible electronics. We have developed the metal microwiring with a resolution higher than 1 μm by the laser direct writing technique using Ag and Cu nano-particle-dispersed films as precursors. The technique was applied to the microwiring on a flexible and transparent polymer film. The metallization is caused in a micro-region by focused laser beam, which reduces the thermal damage of the flexible polymer substrate during the metallization process. The laser direct writing technique is based on the efficient and fast conversion of photon energy to thermal energy by direct excitation of the plasmon absorption of a metal nano-particle, which provides Cu microwiring with a low resistivity owing to the inhibition of the surface oxidation of the Cu nano-particle.

The material development of improved lithium ion batteries will play an important role in future mobile applications and energy storage systems. Electrode materials made of nano-composited materials are expected to improve battery lifetime and will lead to an enhancement of lithium diffusion and thus improve battery capacity and cyclability. In this study, research was conducted to further improve the electrochemical properties of thin film cathodes by increasing the surface to volume ratio and thereby the lithium intercalation rate. Cathode materials were synthesised by r.f. magnetron sputtering of LiCoO₂ targets in a pure argon plasma. LiCoO₂ films 3 μm thick and with a grain size of 10 to 500 nm were deposited on silicon and stainless steel substrates. The deposition parameters (argon pressure, substrate bias) were varied to create stoichiometric films with controlled nano-crystalline texture and morphology. During laser-assisted surface treatment, cone-shaped periodic surface structures were produced. For this purpose high repetition excimer laser radiation at wavelengths of 193 nm and 248 nm and with short laser pulse widths (4-6 ns) were used. Structure sizes varied with laser and processing parameters, e.g. laser fluences, pulse number, wavelength and processing gas. Laser annealing in air or furnace annealing in a controlled argon/oxygen environment were then used to create the high temperature phase of LiCoO₂ (HT-LiCoO₂). The sputtered films were studied with Raman spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction to determine their stoichiometry and crystallinity before and after laser treatment. The development of HT-LiCoO₂ and also the formation of a Co₃O₄ phase were discussed. By means of electrochemical cycling, the performance of the manufactured films was investigated.

Controlled growth of self-aligned single-walled carbon nanotubes (SWNTs) was realized using optical near-field effects in a laser-assisted chemical vapor deposition (LCVD) process. Electronic devices containing ultrashort suspended SWNT channels were successfully fabricated at relatively low substrate temperatures. According to the numerical simulations using High Frequency Structure Simulator (HFSS), significant local-heating enhancement occurred at electrode tip apexes under laser irradiation, which was about ten times higher than the rest part of the electrodes. Experimental results revealed that the localized heating enhancement at the electrode tip apexes significantly stimulates the growth of SWNTs at a significantly reduced substrate temperature compared with the conventional LCVD process. The near-field enhancement dependence on metallic film thickness and laser polarization was investigated through numerical simulation using HFSS, which provided a guideline for further optimization of maximum near-field enhancement. This technique suggests a viable laser-based strategy for fabricating SWNT-based devices at relatively low substrate temperatures in a precisely controlled manner using the nanoscale optical near-field effects, which paves the way for the mass production of SWNT-based devices using expanded laser beams.

In order to develop a multifunctional material, a laser induced process was applied to change the properties of a glass-ceramic by introducing a second phase into the surface. Localized melting of the ceramic and/or a melting of a preplaced powder layer was achieved by the application of laser energy. After solidification a composite with new properties was developed. The characteristic feature of the process is the option of a local modification, which is restricted to the substrate surface and can be controlled by adjustment of the laser parameters. Accordingly modified areas with different geometries and with a complex multiphase microstructure could be fabricated, while the ceramic bulk remains in its original state. Sintered LTCC-substrates (Low Temperature Co-fired Ceramic) were modified with powders metal-oxides (WO₃, CuO) with nanosized particles. Powders of metals (Cu, Ni) were used too. Cladding layers located at the top of the substrate or layers with a thickness up to several hundred microns, which were embedded into the substrate surface, could be fabricated. The properties of the laser modified regions differ significantly from that of the LTCC-substrate. The obtained structures offer modified mechanical, thermophysical and electrical properties. In particular an enhanced thermal conductivity could be detected. The electrical resistivity of the laser modified tracks widely varied depending on the process parameters and the powder. Tracks made with CuO- and WO₃-powders show a negative temperature coefficient for electrical resistance, i.e. it decreases with increasing temperature, which is typical for semiconductors.

A multiscale model is developed to study to the femtosecond laser single pulse and pulse train processing of the metal films. In our model, molecular dynamics simulation combined with the improved two-temperature model is employed in the ablation area and the improved two-temperature model is applied in heat-affected zone. This paper extends the improved two-temperature model to describe higher laser fluences processing by introducing the phase change. The phase change mechanisms of the non-equilibrium thermal melting and vaporization are both analyzed, which has a strong impact on the lattice temperature evaluation. The model can simulate phase change process of gold with higher accuracy. It is demonstrated that the pulse train could improve the fabrication accuracy, repeatability, and controllability.

With ever more stringent requirements regarding the quality of laser-supported production processes, measuring techniques for comprehensive characterization of laser beams and beam delivery optics are rapidly gaining importance. Of particular interest is precise knowledge regarding the beam profile, the beam propagation characteristics, and the wavefront. The latter describes the local direction of energy flux and carries detailed information about the beam aberrations, including intrinsic ones as well as those introduced by optical elements along the beam path. In this paper we give an overview of the status and current developments in the field of laser beam characterization. Examples from industrial applications are given, including the diagnostics of 193 nm excimer lasers. Along with a description of measuring procedures according to ISO standards, emphasis is placed on diagnostics based on Hartmann-Shack wavefront sensors. From the wavefront and the simultaneously recorded near-field profile beam parameters such as diameter, divergence, and M² can be evaluated in real-time. In addition, the approach also accomplishes prediction of the propagation behavior of the radiation field.

Laser-induced breakdown spectroscopy (LIBS) with spatial confinement and LIBS combined with laser-induced fluorescence (LIF) have been investigated to improve the detection sensitivity and selectivity of LIBS. An obvious enhancement in the emission intensity of Al atomic lines was observed when a cylindrical wall was placed to spatially confine the plasma plumes. The maximum enhancement factor for the emission intensity of Al atomic lines was measured to be around 10. Assuming local thermodynamic equilibrium conditions, the plasma temperatures are estimated to be in the range from 4000 to 5800 K. It shows that the plasma temperature increased by around 1000 K when the cylindrical confinement was applied. Fast imaging of the laser-induced Al plasmas shows that the plasmas were compressed into a smaller volume with a pipe presented. LIBS-LIF has been investigated to overcome the matrix effects in LIBS for the detection of trace uranium in solids. A wavelength-tunable laser with an optical parametric oscillator was used to resonantly excite the uranium atoms and ions within the plasma plumes generated by a Q-switched Nd:YAG laser. Both atomic and ionic lines can be selected to detect their fluorescence lines. A uranium concentration of 462 ppm in a glass sample can be detected using this technique at an excitation wavelength of 385.96 nm for resonant excitation of U II and a fluorescence line wavelength of 409.01 nm from U II. The mechanism of spatial confinement effects and the influence of relevant operational parameters of LIBS-LIF are discussed.

Scanning Tunneling Microscope (STM) based Tip-enhanced Raman Spectroscopy (TERS) was used to map Single-walled Carbon Nanotubes (SWCNTs) dispersed on silicon surfaces. A software program developed with Labview platform was used to perform the mapping. STM tips made of gold (Au) were fabricated by electrochemical etching and employed in our TERS system to realize nanoscale spatial resolutions and obtain enhanced signals. Mapping of the SWCNTs was also performed using a micro-Raman system. It was found that the SWCNTs could be well resolved by the TERS system but could not be resolved by the micro-Raman system. Further analysis shows that, the ultimate resolution of the TERS system can reach around 30 nm, while the micro-Raman system shows a resolution around 5 μm.

We have developed a novel debris-free in-air laser dicing technology, which is expected to give less failure of MEMS devices and hence improves yields. Our technology combines two processes: a dicing guide fabrication and a wafer separation process. The first process is internal transformation using a nanosecond Nd:YVO₄ laser with high repetition rate and/or a pulsed fiber laser with 200ns pulsewidth. The laser pulses are focused inside the MEMS wafer without surface ablation. In order to make cross-sectional internal transformation, the laser beam is scanned several times with defocusing. The laser scanning speed per each scanning is 100-700 mm/sec depending on the layer material, the machining time is much faster than the conventional blade dicing. The second process is non-contact separation by thermally-induced crack propagation using a CO₂ laser or mechanical separation by bending stress. In the each separation process, the internal transformation fabricated in the first process worked well as the guide of separation, and the processed wafer was diced with low stress. This dicing technology was applied for 4-inch MEMS wafers, e.g. pressure sensors, etc., and the sensor chips were separated without mechanical damages.

The cleaving process has the potential to replace the dicing of thin wafers. Its inherent advantages are no mechanical forces to the substrate, no material losses, and high edge quality. In order to determine the fundamental mechanisms leading to a reliable cleaving process the complex interaction of wavelength and temperature dependent absorption, heat transfer, material elongation and finally crack formation is theoretically described and experimentally verified. A successful process observed if sufficient thermal stress can be generated to induce a crack and if no surface deformation occurs due to overheating. Most relevant parameters determining the process window are irradiated power, cutting speed, and focus spot size. The results of these parameter variations are presented. Accuracy and reproducibility is demonstrated by cleaving stripes of different widths fulfilling the requirements of the electronic packaging industry. In the third section the influence of the crystalline orientation is investigated. As a result mono-crystalline silicon exhibits an anisotropic behaviour when changing the cutting direction whereas for polycrystalline substrates a permanent change of the crystal structure is found at the grain boundary. Finally, the obtainable edge quality is presented briefly, which leads to higher sample strengths compared to conventional laser and mechanical processes.

Today's complexity in packaging of MEMS and BioMEMS requires advanced joining techniques that take the specific package integration for each device into account. Current focus on reducing investment and operating costs for device packaging require a flexible and reliable joining approach for similar and dissimilar materials such as metals, polymers, glass and silicon to manage increasing system complexity. Depending on the application, packaged devices must fulfill tough requirements regarding strength, thermal stress, fatigue and hermeticity and long-term stability. This research is focused on laser microjoining of polyimide and PEEK polymers to metals such as nitinol, chromium and titanium using fiber laser. Our earlier investigations have demonstrated the potential of this unique joining technique, which successfully addresses the existing microjoining challenges including high precision, localized processing capability and biocompatibility. Our current study further defines the key processing parameters for joining novel dissimilar material combinations based on the characterization of such laser joints by means of mechanical failure tests and the bond area analysis using optical microscope, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results compare operating windows for generating quality bonds for different material joining configurations. They also provide an initial approach to characterize laser-fabricated microjoints that can be potentially used for the optimization of the design process of devices utilizing these materials. Potential packaging applications include microsystems used for chemical or biological assays (lab-on-a-chip), implantable devices used for pressure or temperature sensing, neural stimulation and drug delivery.

This paper presents an alternative adhesive bonding system which is able to join very small parts as well as relatively large parts with high accuracy requirements. The main advantages are the possibility to apply small volumes, to preapply the adhesive with a temporarily delayed joining procedure and extremely short set cycles. The center of micro joining develops suitable joining techniques on the basis of non-viscous adhesive systems (hot melts). The process development focuses on the suitability for automation, process times and the applicability of batch processes. The article discusses certain hot melt application techniques that are suitable for batch production e. g. the laser-sintering of hot melt powder, presents an adapted assembly system and shows an example of an automated assembly process for hot melt coated micro components. Therefore, using hot melts can be a technologically and economically interesting alternative for the assembly and packaging of MEMS.

In electrical connections with enameled copper wires, isolation material residue can be found in the solder area when the coating is not stripped. This residue can lead to mechanical and electrical problems. In electronic devices and MEMS, quality requirements increase with rising thermal requirements for electrical contacts made from enameled copper wire. Examples for this exist in the area of automotive electronics, consumer electronics and in the field of machine design. Typical products with electrical connecting which use enameled wires include: micro-phones and speakers (especially for mobile phones), coil forms, small transformers, relays, clock coils, and so on. Due to increasing thermal and electrical requirements, the manufacturer of enameled wires continuously develops new isolating materials for the improvement of isolation classes, thermal resistance, etc. When using current bonding and solder processes, there exist problems for contacting enameled copper wire with these insulation layers. Therefore the Institute of Joining and Welding, Department Micro Joining developed a laser based solder process with which enamels copper wires can enable high quality electrical connections without a preceding stripping process.

Laser interference lithography is applied to fabricate large-area plasmonic nanostructures. This approach has the advantages of being non-contact process in air and able to achieve large-area and maskless nanolithography at a high speed with low system investment. Single layer Au or Ag noble metallic thin film and Ag/Au, Ag/Ni or Au/Ni bimetallic layer thin films are patterned into nano-dot, nano-rod and nano-nut arrays by laser interference lithography. Plasmonic effects of the fabricated metallic nanostructures are studied. Tunable and multi-peak surface plasmon resonances of these nanostructures can be obtained, which have potential applications in solar cells, bio-sensing and photonic circuits.

Interference exposure using a deep-UV laser in combination with dry etching is instrumental in manufacturing subwavelength patterns used at visible wavelengths. For well resolved patterns, interference fringes must be held still during exposure to achieve a high fringe contrast. Two-beam interference exposure requires a lot of space and equipment to build stable optics and produce patterns on an industrial scale. On the other hand, hologram mask exposure is theoretically far more robust in unfavorable surrounding conditions since a resist layer is placed directly beneath the mask. To produce good-quality resist patterns by using hologram masks, two issues need to be addressed. First, light reflections occurring at interfaces between the mask, the air gap and the resist need to be reduced to secure a high uniformity of exposure intensity. Second, only two diffraction beams should be generated to make an interference field with a high fringe visibility. What mask configurations should be chosen depends on what patterns are to be made. The best answer to produce sub-100-nm patterns is using a hologram mask in Bragg geometry and filling the air gap with a high-index liquid.

UV lasers are well-established sources for a wide variety of micro-machining applications. The small wavelength makes them ideal for processing of small features or to modify thin surfaces. Especially short pulse UV lasers are ideal for ablation of various materials, e. g., polyimide, parylene, PMMA, copper, gold and diamond. Furthermore these lasers are used for silicon annealing and patterning of fine circuitries to various substrates. The demand for smaller feature sizes of micro-mechanical and micro-electronic devices set new requirements in regard to resolution, throughput and overall cost efficiency of the process. In this paper, high-power excimer laser micro-machining and annealing relevant applications will be presented and discussed.

When the frequency, pulse width, the beam profile, and energy density of the laser were controlled, then irradiated onto the silicon wafer with a beam of 15μm diameter or less, we observed that convex dot with a height of 100-300 nano- meters was formed. [1] The laser energy density through which the convex dot was formed was below 3.8J/cm². In the semiconductor excitation laser, the pulse width was 40nsec-150nsec; the wavelength was 532 nm. [2]We developed equipment by using convex dots that was able to form 2D minute code of 16x16 dots in 100μm x100μm area in each IC chip on the silicon wafer without particle generation .

Laser double pulses offer interesting opportunities to increase the ablation performance of ultra short laser pulses. In recent published and performed experiments we have presented an optical setup that covers delay times from some picosecond up to 20 ns as well as first experimental results of ablating aluminium and silicon. In this paper we present further results of especially interesting time domains for both materials. The ablation efficiency on silicon with inter pulse delays from 6.3 ns to 15 ns was investigated. In this range the double pulse effect was mainly depending on the fluency. The double pulse efficiency increase is connected with a higher thermal impact on the work piece. The change of delay and repetition rate has no influence on the ablation efficiency for both single and double pulses. The experiments on aluminium concentrated on the pulse delays of 50 ps to 400 ps. The ablation depth per pulse is lower than for single pulse ablation in this range. Double pulse efficiency decreases up to a pulse delay of 150 ps.

Laser processes have penetrated into the crystalline silicon solar cell production market some time ago already, but are still far from reaching the status they probably will achieve one day. As the largest fraction of state-of-the-art production lines still produces conventional screen-printed aluminum back surface field (Al-BSF) cells, the applicability of lasers is currently limited mainly to the process step of laser edge isolation, while only a few other companies use lasers for groove formation (fabrication of laser grooved buried contact solar cells) or via hole drilling. Due to the contactless nature as well as the possibility to process a wide variety of materials with fine structures, lasers can be used for a vast field of production steps like ablating, melting and soldering different materials. Within this paper several applications of laser processes within the fabrication of various next-generation silicon solar cell structures are presented. These processes are for example laser via hole drilling, which is inevitable for MWT and EWT (metal and emitter wrap through) solar cells, LFC (laser-fired contacts) as a fast and easy approach for the production of passivated emitter and rear solar cells as well as laser ablation of dielectric layers and laser doping which offer the chance for industrial production of several different high efficiency solar cell structures.

Structuring and patterning of thin layer via selective laser ablation is one of the key technologies in production of display and photovoltaic. Concurrently, there are two ablation processes used in production of thin film solar cells: Scribing via selective ablation and edge isolation via deletion. The common laser beams have circular cross section. Furthermore, the most currently lasers of high beam quality have Gaussian beam profile. Because of threshold behaviour Gaussian beam profile is not favourable for ablation process. On the other side there are emerging laser concepts which deliver rectangular or saqure top-hat beams with high beam quality. In this paper we will discuss the fundamentals of ablation processes with circular Gaussian beams, one dimensional top-hat beams and two dimensional square top-hat beams. The major issues will be the energy efficiency of the process and the area over filling aspect for the different beam profiles. The corresponding experimental results will be presented.

In this paper we present an original approach to estimate the heat affected zone in laser scribing processes for photovoltaic applications. We used high resolution IR-VIS Fourier transform spectrometry at micro-scale level for measuring the refractive index variations at different distances from the scribed line, and discussing then the results obtained for a-Si:H layers irradiated in different conditions that reproduce standard interconnection parameters. In order to properly assess the induced damage by the laser process, these results are compared with measurements of the crystalline state of the material using micro-Raman techniques. Additionally, the authors give details about how this technique could be used to feedback the laser process parametrization in monolithic interconnection of thin film photovoltaic devices based on a-Si:H.

The main goal in PV research is a significant reduction of Watt-peak costs of PV systems and thus of solar cells. Innovative cell concepts including robust and reasonable process technologies are necessary to provide highest efficiencies and low process complexity. Laser technology with its excellent features for material machining offers many opportunities to make economical manufacturing processes feasible for solar cell production. To benefit from these advantages of laser technology the knowledge of methods for a relevant process characterization is required. This paper reviews experimental investigations of laser processes concerning laser related machining of silicon for PV application. The processes of interest are laser ablation of diffusion barriers and passivating dielectric layers from silicon surfaces to realize local contact openings. The impact of important laser source parameters, such as pulse energy, pulse duration and laser wavelength, on a silicon substrate in terms of crystal damage is investigated by means of contactless charge carrier lifetime measurements. From these measurements important conclusions can be drawn considering the final solar cell performance. This paper describes the extraction of relevant electrical parameters of laser treated silicon wafers like local saturation current densities deduced from lifetime measurements. These investigations allow the evaluation of different laser sources for the high-efficiency approach.

High power laser sources are used in various production tools for microelectronic products and solar cells, including the applications annealing, lithography, edge isolation as well as dicing and patterning. Besides the right choice of the laser source suitable high performance optics for generating the appropriate beam profile and intensity distribution are of high importance for the right processing speed, quality and yield. For industrial applications equally important is an adequate understanding of the physics of the light-matter interaction behind the process. In advance simulations of the tool performance can minimize technical and financial risk as well as lead times for prototyping and introduction into series production. LIMO has developed its own software founded on the Maxwell equations taking into account all important physical aspects of the laser based process: the light source, the beam shaping optical system and the light-matter interaction. Based on this knowledge together with a unique free-form micro-lens array production technology and patented micro-optics beam shaping designs a number of novel solar cell production tool sub-systems have been built. The basic functionalities, design principles and performance results are presented with a special emphasis on resilience, cost reduction and process reliability.