Recently much research on fabrication of polymer micro structures has been carried out. One of the main advantages of using polymer in micro structure fabrication is the easiness of applying replication processes for mass production. A micro stamping process applying heat and pressure, also referred to as hot embossing lithography, can replicate micro-structures on polymer surfaces. By reforming thermoplastics, many micro features can be transferred directly to polymer surfaces. The micro stamping consists of two main steps: a stamp fabrication step and a replication step. Until now, metal or silicon stamps have been used. In this work, photo-etchable glass-ceramic micro stamps are used, which are micro-machined using an excimer laser processing technique. With the laser process, a glass-ceramic stamp can be fabricated quickly and precisely. In addition, a micro stamping device has been designed and developed for this process. Polyvinylchloride (PVC) is used as the replicating polymer because it has a low glass transition temperature (65 C) and good formability. Many micro structures such as micro channels have been produced. The advantages and the limits of using glass-ceramics stamps and stamping with the PVC material are discussed.

To correlate femtosecond laser beams in wide region and achieve laser ablation, beam correlators based on coherent optical system were developed. By processing thin films using the systems, uniformly spaced and nano-sized structures were generated. The generated structures were nanohole, grating, nanobump, bead on bump, standing bead. The shape of the structure changed on changing the laser fluence, the number of beams, and the correlation parameters. By peeling the structures, nano-sized materials such as nanomesh and nanobelt were generated.

Two-dimesional (2D) lattices of microspheres formed by self-assembly from colloidal solutions have been used for laser-induced surface patterning by ablation, etching, deposition, and surface modification. The imaging properties of microspheres and the related intensity- and temperature-distributions on nearby substrates are studied and compared with experimental results on the deposition of Pd from aqueous solutions of PdCl₂ in NH₃.

Carbon nanocomposites consist of thermoset and thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This new and innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, Nd:YAG and Nd:YVO₄ solid-state lasers were used to micromachine carbon nanocomposite thermoplastic materials. Experimentation was completed to compare the ability to laser micromachine carbon nanomaterial, carbon black, and unfilled polyurethane. The experimentation studied the relationship between repetition rate, travel speed, and material removal rate. The processing consisted of cutting channels into the materials using an Nd:YVO₄ laser at 1064, 532, and 355 nm wavelengths. The material removal rate and groove width were quantified for all wavelengths and compared versus the experimental variables. Trials were also completed on laser machining deep channels using an Nd:YAG laser and polyetheretherketone (PEEK) filled with carbon black and carbon nanofiber. The results of the experimentation show similar material removal rates for carbon black and carbon nanofiber filled polyurethane. The PEEK material exhibited high aspect ratio channels with both carbon black and carbon nanofiber fillers. Laser micromachining of polymers whcih were previously unmachinable using infra-red has been demonstrated.

Laser beam sources emitting pulses with durations in the regime between nano- and femtoseconds are winning more and more importance for processing optical and semiconductor materials. Beneath lithography, etching and coating, laser technology is necessary to support the production of innovative electronic and optical devices. Finest structures, cuts and drillings can be manufactured in a high variety of materials like silicon, glasses but also in composite materials like polymers. In this paper a survey on a number of laser based processes for microelectronic and optoelectronic manufacturing is presented. With regard to this context effects and material interactions are discussed and attached to different laser beam sources. The quality of processes as well as their economical meaning from perspective of laser technology is evaluated. An overview about machining and actual trends for ns-, upcoming ps- and fs-laser technology are presented.

On the fast growing market of precision micro-machining of metals lasers do not only compete with other methods of structuring. There is also strong competition among different laser-processing strategies and, especially, among laser sources with different pulse duration. A comprehensive study of laser micro-machining with nanosecond, picosecond, and femtosecond laser pulses will be presented with a focus on fundamental aspects of the processes and on their practical consequences. An analysis will be given of the potential or the limitations of these laser processes with respect to their industrial application.

Laser micromachining of semiconductor materials such as silicon and sapphire has attracted more and more attention in recent years. High precision laser cutting and drilling processes have been successfully used in semiconductor, photonics, optoelectronics, and microelectromechanical system (MEMS) industries for applications including wafer dicing, scribing, direct via forming, and three-dimensional structuring. In the current study, Q-switched diode-pumped solid-state (DPSS) lasers have been used to scribe grooves on silicon wafer substrates at different pulsewidths (10 and 32 ns), pulse repetition rates (30, 40, and 50 kHz), focal lengths (100 and 53 mm), and wavelengths (355 and 266 nm). Experimental results have been compared between different laser parameters including pulsewidth, power level, pulse repetition rate, and wavelength. It has been found that at the same average power and same repetition rate, the grooves scribed by the longer pulsewidth laser are deeper, while the shorter pulsewidth laser produces better quality cuts. However, the same short pulsewidth laser can produce deeper grooves by increasing its repetition rate and power. Moreover, given the same laser parameters, the shorter focal length objective produces deeper grooves than the longer focal length one but it does not reduce the feature size proportionally due to the complications induced by debris and recast materials. Finally, with the same optical set-up and laser output parameters, it appears that the 266 nm laser does not provide obvious advantage when compared to the 355 nm laser in these particular silicon scribing experiments. The implications of these results are also discussed.

Femtosecond laser micromachining of silicon offers the potential to realize precision components with minimal thermal damage. In this work, an assessment of the damage observed in bulk silicon during femtosecond laser micromachining is presented. The different analysis methods used to determine the structural and chemical changes to wafer grade silicon is first described. The analysis is at or above the ablation threshold - defined as the point where laser induced crystalline- damage is first observed for 1 kHz laser pulses, of 150 fs duration, at a wavelength of 775nm. Structural analysis is based upon electron and optical microscopies, with different sample preparation techniques being used to reveal the micro-machined structure. A key feature of the work presented here is the high-resolution Scanning Transmission Electron Microscope (STEM) images of the laser-machined structures. Below the ablation threshold, electrical experiments were performed with silicon under femtosecond laser excitation to provide a direct method for determining the accumulation of damage to the silicon lattice. Based on this analysis, it will be shown that laser machining of silicon with femtosecond pulses can produce features with minimal thermal damage, although lattice damage created by mechanical stresses and the deposition of ablated material both limit the extent to which this can be achieved, particularly at high aspect ratios.

The femtosecond laser ablation of gold in aqueous solution has been used to produce colloidal gold nanoparticles. We consider the effect of size reduction through the use of aqueous cyclodextrin (α-CD, β-CD or γ-CD) solutions. Both the size reduction and the colloid stability depend on the type of CD, with the smallest, almost monodispersed and extremely stable particles prepared with β-CD, followed by slightly larger ones fabricated in γ-CD and α-CD. Several studies were carried out to elucidate the nature of the interaction between the gold and CDs. In particular, we studied the influence of pH on the size distribution and the electric charge of the gold particles surface. We examined the gold surface composition and determined the nature of the chemical groups on the gold. This enabled us to develop a model of chemical interactions between the gold and the CDs, which includes both a hydrophobic interaction of the Au⁰ with the interior cavity of the CD and a hydrogen bonding of -O^- groups, on the partially oxidized gold surface, with -OH groups of the CDs. These nanoparticles are of importance in biosensing applications.

Post-growth selective-area laser tuning of quantum well infrared photo-detector (QWIP) material has been investigated as a possible route towards the fabrication of a multicolor low-cost focal plane array device. The method takes advantage of the infrared laser for inducing local temperature of a semiconductor wafer that leads to a spatially selective quantum well intermixing (QWI) process. The wafer consisting of 30-pairs of 6 nm GaAs quantum wells and 35 nm Al_0.31Ga_0.69As barriers was irradiated by a fast scanning CW Nd:YAG laser beam projecting a total of 12 lines spaced at 0.8 mm. For the chosen pattern, writing scheme and a total power delivered to the sample, a material has been fabricated with 12-regions of distinctly different bandgaps in the range of 790 to 830 nm. Preliminary calculations predict reasonably well the laser-induced temperature profile achieved with a stationary laser beam. However, a more advanced model needs to be developed in order to describe temperature profiles induced with a fast scanning laser beam.

A new field in laser processing is opened by a laser-induced modification of the optical properties, i.e. the refractive index, absorption- and scattering-coefficient, inside transparent materials, preferentially optical glasses. Ultra short laser pulses are capable of inducing these modifications without cracking or even melting the glass matrix. The femtosecond and in some cases even picosecond laser technology allows to control and modify the optical properties in the bulk on a sub-µm scale. This is referred to as nik-engineering ^TM, relating the experimental technique to changes of the complex refractive index (n + ik). Three dimensional patterns of the (n + ik) modifications can be achieved in the subsurface region on a microscopic scale. The technical potential for optical applications is challenging and on the verge to be exploited. New results on nik-engineering using ultra-short laser pulses at a wavelength of 800 nm was investigated for special glasses with semi-conductive nano-particles, i.e. photo-chromic and GG/RG filter glasses. This paper discusses the laser-induced optical modification inside these glasses for different laser fluence and shot numbers, addressing also the possible technological relevance of these effects in respect to decorative work, micro-tagging, and other functional structures.

Surface micro-structuring of fused silica glass plates was performed by single-shot irradiation with a single-mode laser beam from a diode-pumped solid state UV laser at 355 nm. Well-defined micropattern without debris and microcrack formations around the etched area was fabricated by laser ablation with a focused laser-beam in the ambient air. The time-resolved optical emission spectra of plume were measured to elucidate the ablation behavior of silica glass induced by nanosecond-pulsed laser irradiation at 355 nm where absorption of silica glass is negligibly small. This method is suitable for rapid prototyping of surface microstructuing without a clean room environment.

A new laser mask projection technique, Synchronised Image Scanning (SIS), has been developed for the efficient fabrication of dense arrays of repeating microstructures on large area substrates. This paper details the technique and provides specific examples of the type of structures that can be produced. SIS is a laser micro-machining technique where the information for the ablation of a specific 3D feature is stored as a linear array on a chrome-on-quartz mask. The feature is then written by synchronised motion and laser firing, such that the firing frequency of the laser corresponds to the spatial pitch of the features. This requires highly accurate laser triggering with low-jitter signals, and accurate stages with high resolution encoders. An add-in for CAD software has been developed to generate the mask pattern efficiently and error-free, using the 3D designs. SIS allows for major improvements in the accuracy and speed with which 3D patterns can be created over large areas by laser ablation. Feature sizes down to a few microns can be produced with excellent surface quality. Large areas of microstructures have wide ranging applications in many areas. One example is the machining of large polymer master panels for electroforming to produce moulds for replication of display enhancement films.

The 157nm F2-laser drives strong and precisely controllable interactions with fused silica, the most widely used material for bulk optics, optical fibers, and planar optical circuits. Precise excisions of 10 to 40 nm depth are available that meet the requirements for generating efficient visible and ultraviolet diffractive optical elements (DOE). F2-laser radiation was applied in combination with beam homogenization optics and high-precision computer controlled motion stages to shape 16-level DOE devices on bulk glasses and optical fiber facets. A 128×128 pixel DOE was fabricated and characterized. Each level had distinguishable spacing of ~140 nm and surface roughness of ~38 nm. The far-field pattern when illuminated with a HeNe laser agreed well with the simulation results by an Iterative Fourier Transform Algorithm (ITFA). Improvements to increase the 1st order diffraction efficiency of 22% are offered.

In optical communication there are systems requiring a parallel transmission of several high bit rate data channels based on singlemode fibers. Especially for a free space transmission within such a system a precise collimation of the parallel channels is necessary to guarantee a low loss system. For this purpose compact two dimensional fiber collimator arrays can be used. A main quality characteristic for this arrays is the pointing accuracy, the angular deviation of the collimated beams to a theoretical optical axis. The angular deviation is caused by a lateral offset of the fiber axes to the axes of the corresponding micro lens. To minimize this offset we developed and analyzed an actor geometry for a fiber array which allows a laser based micro alignment of the fibers to the micro lenses. An alignment accuracy within submicrons can be realized which guarantees a pointing accuracy below 0.01 degrees. In this paper we demonstrate some important results of the FEM based analyzes to show the influence of different laser parameters for optimizing the alignment procedure and to minimize alignment time. Experimental results confirm the actor behavior calculated in the FE analyzes and demonstrate the qualification of laser based micro alignment of fibers for the assembly of highly precise two dimensional fiber collimator arrays.

Direct UV-writing is an ideal technique for rapid prototyping and small batch fabrication of integrated optical circuits. Based on the refractive index increase of a glass from exposure to a tightly focused UV beam. The translation of this beam relative to a suitable substrate allows the definition of 2-d waveguide structures such as s-bends and power couplers without the need for subsequent processing. Our alternative technique, Direct Grating Writing retains the advantages of Direct UV writing for channel definition but allowing both the grating and channel structure to be formed in the same process. Using this new technique, we present the fabrication of conventional channel waveguides and Bragg channel waveguides. We demonstrate the independence of the Bragg grating strength from the strength of the channel waveguide, the sensitivity of this process as a characterization technique, and the ability to use this technique to fabricate more complex 2-D structures for integrated optical circuits. We finally present the fabrication of a range of gratings spanning the entire wavelength span commonly used for optical communication with no change in the equipment.

Using femtosecond laser pulses it is possible to produce true three-dimensional photonic structures in different glasses and crystalline media. This direct writing process offers great flexibility, however, it has the drawback of a comparatively slow processing speed. In this presentation we will demonstrate a possibility to overcome this limitation. Based on a fiber based CPA system producing 300 fs pulses with pulse energies of up to 1 μJ and repetition rates in the MHz range we fabricated low loss waveguides (propagation losses 0.5 dB/cm) inside silicate glasses at high writing speeds up to 100 mm/s, limited only by the positioning system. The achieved refractive index changes are > 0.01. The influence of the processing parameters (writing speed, pulse energy) on the induced changes and the waveguiding properties will be discussed in detail.

We present the fabrication of waveguides in optical materials using a femtosecond laser. The direct laser writing technique has the unique advantage of allowing volume structures to be fabricated. We investigate several writing schemes in non-oxide glasses and characterize the photo-induced modifications of the optical properties. These changes are linked to structural changes in the glass matrix, as revealed by Raman spectroscopy.

We demonstrated a simple chromatic dispersion reduction method of 3-dimensional (3D) patterning of femtosecond pulses using a multi-level phase type diffractive optical element (DOE) and a focusing objective lens. Our method increases flexibility of femtosecond laser microprocessing. With appropriate focal length of the DOE and distance between the DOE and the focusing lens, large chromatic dispersion of the DOE resulting from spectral bandwidth of a femtosecond pulse can be reduced, and 3D focusing pattern of femtosecond pulse can be obtained not only controlled in focal plane but also in focal depth. The method was verified through optical and processing experiments with laser pulses of 400 fs duration and of 40 nm bandwidth. The focal length of the DOE and the objective lens was 1600 mm and 10 mm, respectively. Partially periodical structure of focusing points was formed at designed position and its focal depth were much smaller than that focused with only the DOE. By irradiating the constructed beam, microstructure was formed precisely inside SiO₂ glass. The processed points are clearly separated each other with a separation of 5 mm and the spot sizes were almost same as those irradiated without the DOE.

The index of refraction of most glasses can be permanently changed by exposure to femtosecond laser pulses. This effect allows for the fabrication of various two-dimensional or three-dimensional light guiding structures. Passive and active optical devices have been manufactured using this femtosecond direct-write technique. A closely related technique has recently been demonstrated to manufacture three-dimensional microfluidic networks. We describe recent work at Translume and RPI in femtosecond direct write to produce devices which incorporate on a single glass chip optical network with microfluidic network.

Three-dimensional (3-D) microstructuring of photostructurable glass is demonstrated by using femtosecond (fs) laser for Lab.-on-chip, in other words, micro total analysis system (μ-TAS), application. The fs laser direct-write process followed by a thermal treatment and chemical etching in a HF aqueous solution produces true 3-D hollow microstructures embedded in the photostructurable glass. This technique is applied for manufacturing a microfluidic structure inside the glass. Mixing of two kinds of aqueous solutions is demonstrated in the fabricated structure. A freely movable microplate is also fabricated inside glass to control a stream of reagents in the microfluidics. To give additional functions to the fabricated microfluidics, selective metal plating of the glass i s performed by the fs laser irradiation in an electroless plating solution. This paper also discusses the mechanism of photostructurable glass modification by the fs laser.

This paper presents the results of recent efforts to improve the biocompatibility and integration of implantable bioMEMS devices. Laser micro-grooves and micro-grids were irradiated onto silicon surfaces using ultraviolet lasers. The micro-textured surfaces were then coated with nano-scale layers of titanium to promote improved biocompatibility. The micro-groove geometries have been shown to promote contact guidance, which leads to reduced scar tissue formation. In contrast, smooth surfaces result in random cell orientations and the increased possibility of scar tissue formation. The nature of the cellular attachment and adhesion to the coated/uncoated micro-textured surfaces was elucidated by the visualization of the cells through scanning electron microscopy. Finally, the implications of the results are discussed for integration of silicon-based microelectronics and sensors into biological systems.

As features and dimensions become smaller, traditional laser processing in semiconductor industry are hitting its limitations due to the thermal effects inherited in long pulse processing. Ultrafast lasers become more reliable and are available commercially. However, their industrial applications, though very desirable due to their non-thermal nature processing, are only limited to those with high value added. Current status of ultrafast laser applications in semiconductor industry is reviewed. Shortcomings of current commercial systems are analyzed. Requirements for ultrafast laser based production system and future direction are discussed.

Thin sections of single-crystal sapphire are favored as substrates for the epitaxial deposition of gallium nitride and other III-V and II-VI thin films used in the fabrication of electro-optic devices such as blue-green LEDs and laser diodes. Due to difficulties commonly encountered in cutting this hard material, alternatives to traditional mechanical processing techniques are of particular interest. This paper reviews a recent study characterizing the scribing of sapphire using the tightly focused output of an ultraviolet wavelength pulsed solid-state laser.

The generation of debris is critical in the future application of laser technology in IC, MEMS, MOEMS manufacture. Re-deposition of debris is also critical in optimising throughput of multi-pass laser ablative processes. In this study, the debris formed in laser micromachining of wafer grade silicon is investigated. Details of the laser workstation, based on a UV DPSS laser, will be presented and the development of real time diagnostic capabilities and off-line techniques will then be described. A real time imaging capability has been used to monitor plasma and shock front propagation with nanosecond resolution. The detection system is also used to monitor spectral emission of debris and micron-sized particulate ejected from the silicon surface. Emission spectroscopy of the laser ablated silicon in the plasma show spectral features that are characteristic of atomic and molecular species on timescales of nanoseconds and microseconds, respectively, after the laser pulse. Off-line characterisation techniques have focused on investigating the distribution and chemical composition of entrapped particulate. A number of novel experimental configurations for particulate entrapment, both adjacent to and remote from the laser-ablated surface, will be described. EDX results indicate that debris generated in air is composed principally of oxygen and silicon. Additional SEM results indicate that the particulate size grows through aggregation and depends on the environment in which they are generated.

The water jet guided laser technology (laser Microjet®) has been developed since 10 years now and is used for several applications in the semiconductor industry. In this unique laser cutting technique, a thin stable water jet is used as a waveguide for a high-power Nd:YAG laser, that may be frequency doubled or tripled. This presentation gives an overview of the semiconductor machining applications of this technique and relates the different applications to alternative techniques and the different functions of the water jet. The water jet cools the sample when the laser is not emitting, it expels the melt very efficiently, and it avoids that the few generated particles can attach to the wafer surface. The strengths of Laser Microjet® machining are free shape cutting and cutting of thin wafers. In free shape cutting the system leads to much better results in terms of fracture strength and process simplicity than the classical laser cutting methods. In thin wafer cutting astonishing cutting speeds are obtained at very good cut quality (200 mm/s in 50 micron thick wafers). Due to the free shape cutting possibilities drilling and slotting with aspect ratios of up to 5 is also possible resulting in the same edge quality as standard cutting.

Highly accurate resistances can be made by iterative laser-induced local diffusion of dopants from the drain and source of a gateless field effect transistor into its channel, thereby forming an electrical link between two adjacent p-n junction diodes. In this paper we present a complete modeling, which permits to obtain the device characteristics from process parameters. Three-dimensional (3D) temperature calculations are performed from heat diffusion equation using an apparent heat capacity formulation. Melted region determinations are satisfactory compared with in-situ real-time optical measurements of the melted region behavior. Then 3D dopant diffusion profiles are calculated using Fick’s diffusion equation. Finally electronic characteristics are obtained from the new tube multiplexing algorithm for computing the I-V characteristic and the device differential resistance. Numerical simulations using our software are satisfactory compared with experimental I-V measurements.

CO₂ laser drilling of the resin coated copper (RCC) layers of laminated circuit boards has been investigated at different fluence levels. The threshold fluence for copper layer drilling is found to be 570 Jcm^-2 for 5μm and 1500 Jcm^-2 for 12μm copper thickness, using laser pulses in the 10 μs and 20 μs FWHM respectively. Undercut in the resin layer is found to primarily depend on the amount of excess energy in the pulse tail. Methods to reduce the pulse decay time have been investigated, giving smaller diameter breakthrough holes close to threshold, which should aid the control of hole drilling in RCC. High-speed videography has been used to verify the observations of post-processing analysis.

As the most efficient UV laser sources excimer lasers are unique tools for the various fields of material processing. Essentially, the tight process windows fuel the need for better dose control during laser illumination and hence the demand for high repetition rate excimer lasers operating at comparably low pulse energies of only some 10 mJ. Compact, flexible excimer lasers offering high repetition rate-low energy and low cost of ownership pave the way to efficient mask writing and wafer inspection systems for chip manufacturing as well as to efficient testing of optical materials. Utilizing micro-mirror arrays, high-repetition rate-low energy excimer lasers are ideal for flexible direct-write material processing approaches e.g., in laser marking or cleaning. Moreover, medical applications such as refractive eye surgery currently using up to 200 Hz repetition rate will benefit from high-repetition rate excimer lasers offering reduced treatment times with excimer laser based systems with 500 Hz and even 1000 Hz in the near future.

The Global Positioning System (GPS) has become a mature technology and is continually being applied in new and more demanding applications. A current effort in this area is the development of compact, durable but lightweight GPS antennas on conformal surfaces for handheld devices. Because modeling the electromagnetic performance of these antennas is often difficult, prototypes are typically built, measured and redesigned in an iterative process. We demonstrate the fabrication of a GPS conformal antenna under ambient-temperature conditions using a combination of laser micromachining and/or laser direct-write processes. The electromagnetic behavior of the antennas is then characterized and the design of the antenna structures is further optimized. Pattern simulations and input impedance measurements of the antenna are presented that demonstrate the usefulness and success of the iterative process made possible with this fabrication technique

The experimental characterization of fatigue crack initiation and growth of structural materials can be very expensive and time consuming. Fatigue specimens are typically controlled by a single dominant defect and several specimens are needed to examine the fatigue response for each loading condition of interest. Time and expense add up as millions of load cycles are sometimes required to initiate a crack, and replicate tests are necessary to characterize the inherent statistical nature of fatigue. In order to improve the efficiency of experimentation, we are developing laser-based techniques to produce fatigue test samples with arrays of defects. Controlled arrays of oval shaped micro-defects are laser-micromachined in titanium alloy (Ti-6Al-4V). Crack initiation from the individual defects in the arrays is monitored using a DC potential drop technique. Results indicate the utility of this approach in multiplying the amount of fatigue data generated per specimen-test. The new fatigue test approach is applicable to a wide range of material systems and initial defect structures.

Laser-Induced Forward Transfer (LIFT) of aluminum films was performed using a 7 ns Nd:YAG laser operating at 1064 nm. Aluminum films of 200 nm and 1 micron thickness were supported on glass substrates prior to transfer. Films were irradiated at the interface between the film and donor substrate using contact and non-contact configurations. Direct contact occurred between film and acceptor in contact mode, and non-contact mode used a gap of the order of tens of micrometers. Three transfer regimes were observed in contact mode- 1) single droplets or a ring-like structure with dimensions similar to or smaller than the laser spot size at low fluences, and 2) localized material transfer near the center of the laser spot above a threshold value of laser fluence, and 3) spattered material spreading outside of the laser spot. In non-contact mode at fluences below the contact mode spatter threshold, the transferred spot consisted of small droplets until reaching the spatter regime. The ring structure in contact mode is interpreted in terms of flow of molten aluminum resulting from Marangoni flow. The LIFT process observed in non-contact mode is interpreted in terms of evaporation at low fluences and phase explosion at high fluences.

A critical review of pulsed laser micromachining of Indium Tin Oxide (ITO) films on glass substrates is presented. The thermal mechanisms responsible for ITO micromachining are discussed, including the roles of melting, thermo-capillary flow of molten ITO, and vaporization. The importance of flexible displays now motivates research of ITO on flexible polymer substrates. Experimental results of Nd:YAG micromachining of ITO on PET substrates are presented. The results show distinct differences from the case of glass substrates. Ablated sections have complete ITO removal with little damage to the PET substrate. The edges of the ablated sections have no melt ridge build-up as seen on glass substrates. Results are interpreted in terms of the thermal and mechanical properties of the film and substrate.

Bilayer thermal resist Sn/In films have been found to be promising analogue direct-write photomask materials. The bimetallic films turn to be more transparent after a laser exposure which raises the films above the eutectic temperature. Laser converted layers are oxidized to a controlled extent, depending on the laser exposure energy. The exposure causes a change of absorption at 365nm from 3OD to 0.22OD. The thermal resist shows near wavelength invariance from IR to UV. The Sn/In films, each layer ~40 nm thick, were DC-sputtered onto glass slides or quartz substrates. To make grayscale photomasks the samples are placed on a computer-controlled high accuracy X-Y table. The computer takes a bitmap gray-scale pattern as the input and modulates an optical shutter, which in turn, controls the actual power of a CW Argon laser (514 nm) beam applied to the thermal resist according to the gray-scale value. Sn/In photomasks have been used together with a standard mask aligner to successfully make 3D patterns on Shipley SPR2FX-1.3 photoresist. CF4/O2 plasma etching has been used to transfer the 3D patterns to SiO₂ substrates. XRD analysis shows that laser power determines the extent of oxidation of the metal films.

The dynamics of the laser induced plasma during pulsed laser deposition of BaTiO₃ thin films is studied theoretically and experimentally and related to the resulting film properties. The expansion of the laser induced plasma is modelled taking inelastic collisions between ablated particles and processing gas particles into account. The predictions of the model are in agreement with data from high speed photography of the plasma emission. Pulsed laser deposition with KrF excimer laser radiation (wavelength 248nm, pulse duration 20 ns) is used to grow dense, transparent, amorphous, poly-crystalline and single crystalline erbium doped BaTiO3 thin films for photonic applications. Visible emission due to up-conversion luminescence (wavelength 528 nm and 548 nm) under excitation with diode laser radiation at a wavelength of 970-985 nm is investigated as a function of the erbium concentration of 1-46 mol % and structural film properties. The dielectric films are micro machined to form optical wave guiding structures using Ti:sapphire laser radiation (wavelength 810 nm, pulse duration 63-150 fs) by scanning the focussed laser beam relatively to the sample.

Laser processing techniques, such as laser direct-write (LDW) and laser sintering, have been used to deposit mesoporous nanocrystalline TiO₂ (nc-TiO₂) films for use in dye-sensitized solar cells. LDW enables the fabrication of conformal structures containing metals, ceramics, polymers and composites on rigid and flexible substrates without the use of masks or additional patterning techniques. The transferred material maintains a porous, high surface area structure that is ideally suited for dye-sensitized solar cells. In this experiment, a pulsed UV laser (355nm) is used to forward transfer a paste of commercial TiO₂ nanopowder (P25) onto transparent conducting electrodes on flexible polyethyleneterephthalate (PET) and rigid glass substrates. For the cells based on flexible PET substrates, the transferred TiO₂ layers were sintered using an in-situ laser to improve electron paths without damaging PET substrates. In this paper, we demonstrate the use of laser processing techniques to produce nc-TiO₂ films (~10 μm thickness) on glass for use in dye-sensitized solar cells (V_oc = 690 mV, J_sc = 8.7 mA/cm₂, ff = 0.67, η = 4.0 % at 100 mW/cm²). This work was supported by the Office of Naval Research.

This paper describes a new growth method of ZnO nano-rods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nano-structured-ZnO thin films. Under an optimized deposition conditions, ZnO nano-rods with a diameter of about 300 nm and 6 μm in length have been synthesized without any catalyst by nanoparticle assisted laser ablation deposition. The laser action was observed in the nano-rods under an optical excitation at 355 nm, indicating a high quality of the crystal.

Hetero-pairing of thin-film GaAs on Si is of considerable interest for novel applications in optoelectronics. However, the formation of high-quality GaAs is difficult and requires expensive top technologies such as molecular beam epitaxy (MBE) and related methods. In general, MBE forms high-quality epitaxial layers but is not capable of the straightforward formation of GaAs on Si because of the 4.1% lattice mismatch between both materials. We have developed and explored the possibilities of pulsed-laser deposition (PLD) for the formation of GaAs films on (100) n-type Si substrates. The films have been produced in vacuum (10^-6 torr) employing the fundamental (1064 nm), second (532 nm), and third (355 nm) harmonic emission of a Nd:YAG laser with a repetition rate of 10 Hz and a pulse duration of 6 ns. The laser was focused on (100) p-type (10¹⁹ cm^-3) GaAs wafers with an energy fluence of 0.79-0.84 J/cm². During the deposition, the substrate was not heated. The current-voltage characteristic of the samples showed rectification, i.e., the doping of the GaAs target was successfully maintained in the PLD film and a diode was formed in conjunction with the oppositely doped Si substrate. The observation of photocurrent without bias is an additional proof that an operating junction was achieved. The crystallographic quality of the films was checked by x-ray analysis and revealed that the films show [111]-oriented crystalline parts. The realization of GaAs/Si photodiodes reveals the potential of PLD to be used for the monolithic integration of GaAs photonic devices with Si circuits.

We have analyzed the drilling process with femtosecond laser on the silicon surface in order to investigate a degree of thermal effect during the dicing process of the very thin silicon substrate (thickness: 50 μm). Femtosecond laser pulse (E = 30~500 μJ/pulse, τ = 150~200 fs, λ = 780nm, f = 10 Hz) was focused on the silicon substrate using a lens with a focal length of 100 mm. An image-intensified CCD camera with a high-speed gate of 5 ns was utilized to take images of drilled hole during the processing. As a result, the rise time for increasing diameter of the holes was changed at energy between 180 and 350 μJ/pulse. The width of the molten walls around the hole became wider under the conditions where the rise time became longer. So, it is said that we can estimate the degree of the thermal effect qualitatively by analyzing the rise time. These knowledge is thought to be very important and useful for developing the dicing technique of thin silicon wafers by femtosecond lasers.

We present theoretical calculations and experimental measurements of silicon micromachining rates, efficiency of laser pulse utilization, and morphology changes under UV nanosecond pulses with intensities ranging from 0.5 GW/cm² to 150 GW/cm². Three distinct irradiance regimes are identified based on laser intensity. At low intensity, proper gas dynamics and ablation vapor plume kinetics are taken into account in our theoretical modeling. At medium high intensity, we incorporate the proper plasma dynamics, and predict the effects of the laser generated vapor plasma and the electron hole plasma on the laser-matter interaction. At even higher intensity, we attribute the observed increased ablation rate to energy re-radiation from the laser heated hot plasma, the strong shock wave, and the accompanied strong shock wave heating effects. Experimentally measured data in these regimes agree well with our calculations, without changing parameters in the calculations used for the three regimes. Our results can be applied toward quantitatively characterize the behavior of ablation results under different laser parameters to achieve optimal results for micromachining of slots and vias on silicon wafers.

Dicing of semiconductor wafers is an example of an application requiring a processing quality superior to what can be achieved using classical laser techniques. For this reason, sawing the wafers with a diamond-edged blade has been developed into a high-tech process, that guarantees good and reliable cuts for Silicon wafers of more than 300 microns thickness. Today, wafer thickness is getting thinner; down to 50 microns and also more brittle III-V compound semiconductors are used more frequently. On these thin wafers; the laser begins again to compete with the diamond saw, because of laser cutting-quality and cutting-speed, are increasing with decreasing wafer thickness. Conventional laser cutting however has the disadvantages of debris deposition on the wafer surface, weak chip fracture strength because of heat induced micro cracks. An elegant way to overcome these problems is to opt for the water-jet guided laser technology. In this technique the laser is conducted to the work piece by total internal reflection in a 'hair-thin' stable water-jet, comparable to an optical fiber. The water jet guided laser technique was developed originally in order to reduce the heat affected zone near the cut, but in fact the absence of beam divergence and the efficient melt xpulsion are also important advantages. In this presentation we will give an overview on today’s state of the art in dicing thin wafers, especially compound semiconductor wafers, using the water-jet guided laser technology.

Laser ablation using diode pumped solid state lasers shows great potential for a wide range of micromachining applications. We have been using a frequency quadrupled Nd:VO₄ laser (266 nm wavelength), with a pulse duration < 30 ns, to ablate a sol-gel Ormocer material. With a pulse energy of around 20 μJ, and a focal spot of the order of 10 μm diameter, single pulses were found to produce craters a few microns in depth and ~10 μm in diameter. A study of the variation of the crater profile with pulse energy and angle of incidence to the surface has enabled the development of an efficient method to simulate the ablation for a series of consecutive shots constituting a toolpath. Multiple pulses with varying degrees of overlap were simulated, and compared with experiment. Results show that the model accurately predicts the profiles of trenches and pocketed surfaces given parameters obtained from a single crater machined at normal incidence. The "self calibrating" feature of our approach significantly reduces the number of input parameters required for adequate simulations. In particular, it does not require knowledge of the beam profile or material ablation curve. The simplicity and practicality of the method make it promising for use in an industrial environment.

BaTiO₃ thin films have been grown on Si(100) substrate by KrF pulsed-laser deposition (PLD). The influence of substrate temperature and background oxygen pressure on the chemical composition and crystal structure of BaTiO₃ films was studied. The films were characterized by X-ray diffraction (XRD), UV/VIS/NIR spectrometer, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In our experiments, the BaTiO₃ films with uniform grains were produced at O₂ pressure range of 10-30 mTorr and a substrate temperature of 600°C-620°C. At lower substrate temperature, the XRD patterns of the films displayed weaker peaks with wider FWHM and the AFM images showed grain boundary defects and numerous holes. The compositional analysis performed by XPS indicated that almost stoichiometric 1:1:3 composition BaTiO₃ films were grown by PLD at optimized deposition parameters. The excessive oxygen resulted in the formation of other molecules for the film development. The additional XRD peaks of the films were observed when O₂ pressure was increased.

This paper proposes a robust discrete time Kalman filter (RDKF) for the dynamic compensation of nonlinearity in a homodyne laser interferometer for high-precision displacement measurement and in real-time. The interferometer system is modeled to reduce the calculation of the estimator. A regulator is applied to improve the robustness of the system. An estimator based on dynamic modeling and a zero regulator of the system was designed by the authors of this study. For real measurement, the experimental results show that the proposed interferometer system can be applied to high precision displacement measurement in real-time.

A spectrally tunable VCSEL (vertical cavity surface-emitting laser) was used as part of sensing hardware for measurements of the radial-integrated gas temperature inside an inductively coupled plasma reactor. The data were obtained by profiling the Doppler-broadened absorption of metastable Ar atoms at 763.51 nm in argon and argon/nitrogen plasmas (3, 45, and 90% N2 in Ar) at pressure 0.5-70 Pa and inductive power of 100 and 300 W. The results were compared to rotational temperature derived from the N₂ emission at the (0,0) transition of the C³Π_u-B³Π_g system. The differences in integrated rotational and Doppler temperatures were attributed to non-uniform spatial distributions of both temperature and thermometric species (Ar* and N₂*) that varied depending on conditions. A two-dimensional, two-temperature fluid plasma simulation was employed to explain these differences. This work should facilitate further development of a miniature sensor for non-intrusive acquisition of data (temperature and densities of multiple plasma species) during micro- and nano-fabrication plasma processing, thus enabling the diagnostic-assisted continuous optimization and advanced control over the processes. Such sensors would also enable tracking the origins and pathways of damaging contaminants, thereby providing real-time feedback for adjustment of processes. Our work serves as an example of how two line-of-sight integrated temperatures derived from different thermometric species make it possible to characterize the radial non-uniformity of the plasma.

There are many phenomena that occur during laser radiation interaction with solids, one of them is hardening. In a broad sense of this word, it is a way to keep or to "froze" the high temperature structure of materials after being melted. Maybe the case of glass-ceramics laser hardening is one of the most impressive. Because the high temperature structure induced by laser radiation acting on these materials is mostly amorphous (the structure consists of 70-80% or even more glass phase)- keeping this structure means to save at room temperature optical properties of appeared glass, first of all -transmission, dispersion and very often optical force. Many aspects of the mentioned phenomenon were discussed in previous papers qualitatively [1, 2, 3]. In this paper we present quantitative data about rates of heating-cooling and corresponding changes in typical glass-ceramics such as cracking, amorphization, and reverse crystallization. The next aim of the paper is to illustrate changes in structural, chemical, mechanical, and optical properties due to laser radiation interaction with glass-ceramics. Thus, we demonstrated a way how to develop new materials with the use of laser modification of glass-ceramics.

High power single mode fiber lasers are an excellent tool for micro cutting applications. In order to manage the heat input into the material most micro cutting applications require pulsed operation of the laser. Temporal pulse shaping is a proven and enabling technology for many laser welding applications with flash lamp pumped lasers where typical pulse lengths are in the order of 0.1 to 10 ms. The excellent controllability of diode pumped fiber lasers enables pulse shaping during the cutting process with laser pulse length typically less then 0.1 ms. For laser micro cutting applications a small kerf width with small HAZ and good surface finish define the quality of the process. This paper shows the influence of the laser pulse shape on the cutting quality in stainless steel with diode pumped fiber lasers.

Laser processing has large potential in the packaging of integrated circuits (IC). It can be used in many applications such as laser cleaning of IC mold tools, laser deflash to remove mold flash from heat sinks and lead wires of IC packages, laser singulation of BGA (ball grid array) and CSP (chip scale packages), laser reflow of solder ball on GBA, laser peeling for CSP, laser marking on packages and on Si wafers. Laser nanoimprinting of self-assembled nanoparticles has been recently developed to fabricate hemispherical cavity arrays on semiconductor surfaces. This process has the potential applications in fabrication and packaging of photonic devices such as waveguides and optical interconnections. During the implementation of all these applications, laser parameters, material issues, throughput, yield, reliability and monitoring techniques have to be taken into account. Monitoring of laser-induced plasma and laser induced acoustic wave has been used to understand and to control the processes involved in these applications. Numerical simulations can provide useful information on process analysis and optimization.

This paper deals with basic investigations in order to control the laser spot micro welding process when packaging electronic components onto three dimensional molded interconnect devices (3-D MID) or flexible printed circuit boards. A wide range of experiments has been carried out for both successful and fail welds. Typical failures appearing during welding are either damage of the circuit board due to overpower or loss of connection between the welded components due to gap formation between the leads of the component and the circuit board. The optical radiation emitted from the process was firstly measured off-axially and co-axially with a spectrometer. To aid the spectrometric analysis, an optical sensor based on a silicon photo diode and an appropriate optical filter was applied for detecting the emitted radiation. The signal was acquired, analyzed, and saved using a dedicated software program. Changes in the detected radiation due to different weld conditions were evaluated. Moreover, the weld quality was investigated by Scanning Electron Microscope (SEM) measurements and cross-sectional analysis. A correlation has been found between the signal course and the weld quality. Primarily, there are three relevant signal phases (high peak, flat stage, and small peak) appearing during the weld. Any changes in the characteristic signal during these process phases can be used to predict the quality of the welds.

The results of a study of a single 200 femtosecond laser pulse interaction with thick stainless steel and HgCdTe samples are reported. The threshold pulse energies required to produce sample surface melting are measured. The melt dynamics, material removal rate and evolution of surface morphology were observed for different pulse energies and number of laser pulses. It was observed that, similarly to long laser pulse interaction, a layer of melt can be produced at the sample surface. Increase of laser pulse energy results in melt ejection in the radial direction toward the periphery of the interaction zone resembling evaporation recoil melt removal typical for laser interaction in range from nanosecond to cw. The removal of material from stainless steel sample was observed to be highly nonuniform. The columnar structures were observed on the surface of stainless steel samples. The period of these structures is dependent on laser pulse energy and number of pulses. The observed melting threshold is compared with the theoretical prediction obtained using two-temperature model.

Micro-joining and hermetic sealing of dissimilar and biocompatible materials is a critical issue for a broad spectrum of products such as micro-electronics, micro-optical and biomedical products and devices. Today, biocompatible titanium is widely applied as a material for orthopedic implants as well as for the encapsulation of implantable devices such as pacemakers, defibrillators, and neural stimulator devices. Laser joining is the process of choice to hermetically seal such devices. Laser joining is a contact-free process, therefore minimizing mechanical load on the parts to be joined and the controlled heat input decreases the potential for thermal damage to the highly sensitive components. Laser joining also offers flexibility, shorter processing time and higher quality. However, novel biomedical products, in particular implantable microsystems currently under development, pose new challenges to the assembly and packaging process based on the higher level of integration, the small size of the device's features, and the type of materials and material combinations. In addition to metals, devices will also include glass, ceramic and polymers as biocompatible building materials that must be reliably joined in similar and dissimilar combinations. Since adhesives often lack long-term stability or do not meet biocompatibility requirements, new joining techniques are needed to address these joining challenges. Localized laser joining provides promising developments in this area. This paper describes the latest achievements in micro-joining of metallic and non-metallic materials with laser radiation. The focus is on material combinations of metal-polymer, polymer-glass, metal-glass and metal-ceramic using CO₂, Nd:YAG and diode laser radiation. The potential for applications in the biomedical sector will be demonstrated.

Carbon nanocomposites consist of thermoset or thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This new and innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, direct diode and Nd:YAG solid-state lasers were used to transmission weld -carbon nanocomposite materials. The experimentation was focused on exploiting the infrared absorbing characteristics of the carbon nanocomposites. Polyetheretherketone (PEEK) based polymer was used in the initial experimentation to quantify weld strength. The experimentation included a complete analysis of the transmission characteristics of the base polymer at 810 nm and 1,064 nm wavelengths, an optical microscope view of the weld cross-section, and transmission welding experimentation. The transmission welding experimentation studied the relationship between average power, travel speed, and weld peel strength. A micro-channel welding experiment was also completed using a polycarbonate (PC) based polymer. The experimentation qualified the minimum feature size that could be joined. The resulsts show that the carbon nanocomposites can be welded in a similar way to carbon black filled materials. The carbon nanocomposites exhibited higher peel strengths at lower average laser power at both 810 and 1064 nm. The carbon nanocomposite material exhibited a unique characteristic of being able to be machined and welded by the same laser wavelength.

Indispensable in laser-processing applications is an accurate and efficient delivery of light energy to process points. For mass production, multi-beam parallel processing is a must to gain high throughput. Diffractive optics is a competitive and cost-effective solution to achieve these goals. A diffractive optical element (DOE) is able to offer various light-control functions such as focusing, splitting and shaping according to the user’s requests. These elements can be utilized in a compact and convenient optical system. Thus laser-processing technologies using diffractive optics can be easily brought into manufacturing settings. We present four laser-based processes, each of which adopts diffractive optics in a distinctive way. They are 1) laser drilling of silicon wafers using a diffractive array illuminator to form microcavities for inkjet printers, 2) laser cutting of metal films using a diffractive focusator to produce liquid-crystal display panels for mobile phones, 3) laser soldering of quartz oscillators using a diffractive beam duplicator onto printed circuits set in wristwatches, and 4) laser sealing of packages using diffraction patterns to house electronic components therein. Some of these processes are at work routinely in our manufacturing plants.