We have built and tested a laser induced desorption (LID), electron impact ionization, time-of-flight (TOF) mass spectrometer (MS) designed to nondestructively identify and measure adsorbed contaminants on critical surfaces for the microelectronics and optics industries. The LID-TOFMS combines the capability of a TOF mass spectrometer to measure all the desorbed molecules from a single laser shot with an infrared Er:YAG laser (2.94 micron), which is not strongly absorbed by many transparent optical materials but is strongly absorbed by water, the most common adsorbed surface contaminant, to yield surface composition as a function of position on the sample. The LID-TOFMS was calibrated using an oxalic acid film on a polished stainless steel plate, which also contained adsorbed water. Contaminants on CaF₂ surfaces measured by LID-TOFMS include water and hydrocarbons. Desorbed molecules decrease with increasing irradiations at a fixed laser fluence, suggesting that the surface is being cleaned.

Ablation dynamics of fused silica by multiwavelength excitation process using F₂ and KrF excimer laser has been investigated by energy analyzed mass spectrometry of ablated species. The number of Si ion generated by multiwavelength excitation process corresponds to that by single-F₂ laser ablation and to approximately 2.1 times larger than that by single-KrF excimer laser ablation. In addition, kinetic energy distribution of Si⁺ ablated by multiwavelength excitation process shows almost same as that by single-F₂ laser ablation. We regard that absorption of KrF excimer laser by excited state generated by F₂ laser (excited-state absorption: ESA) causes similar electron excitation process to single-F₂ laser irradiation, resulting in enhancement of Si ion with higher kinetic energy and then in high-quality ablation.

Shorter life time cycles of products, increasing workpiece variety and declining lot sizes demand for a closed processing chain which enables the economic production of variable products in the future. A new type of manufacturing concept for the production of the 21^st century is lined out by the design of an "Autonomous Production Cell." Applied to and designed for manufacturing with laser radiation this concept shows completely new ways in comparison to former manufacturing procedures. The manufacturing processes in the Autonomous Production Cell start with a production oriented design and planning of the manufacturing procedure is including sensor controlled processing of the workpieces with integrated quality management. The quality management detects failures in the manufacturing procedure and allows back-coupling to any preceding step by means of a multistage cascaded production controller. In comparison to former concepts the user is at all times integrated into the manufacturing procedure. The user can add his own competence and creativity. At the same time he is being relieved by routine work and gets adequate help by the system in corresponding situations. The design of the components of the Autonomous Production Cell (design and planning tools, networking of sensors and actuators, user interface, etc.) has been performed as general as possible. This offers the possibility to transfer this concept with countable efforts to all the manufacturing with laser radiation such as welding, cutting, surface treatment, freeforming, rapid prototyping, etc.

The research and development of the optical system described was due in part to the virtual stalemate of current microvia dirlling technology within the High Density Interconnect market. The desire by industry to acquire faster processes for drilling microvias led to our research in the utilization of hybrid optical systems, where standard refractive and computer generated diffractive optics could be meshed to create a system that would out perform the current technology in the marketplace. The outcome of this work is covered in the following paper and will, at the outset, briefly cover the targeted market segment for which the beam delivery system was developed, as well as its general capabilities. The paper will cover the basic architecture and technology behind the laser optical beam delivery system, as well as the unique components that make up the assembly. Each of the optical elements within the system will be briefly described, and the CGH elements will be briefly explained, including a description of the software used. The laser beam characteristics at several points along the beam delivery will be discussed, as well as the final image formed at the target plane where the microvia is drilled. Specific performance details will be shared with regards to component efficiency, i.e. diffraction efficiency losses, as well as total system performance throughout the beam line. The final section will cover materials processing, including the remarkable process rate increases and microvia hole quality achieved.

Using an innovative approach based on Yb:fiber amplifiers and pre-shaped pulsed diode seeders, a unique laser source with tunable pulse duration and rectangular pulse shape has been developed. Based on the patented use of multimode fibers with single-mode output, the resultant system provides pulses adjustable between 4 and 20 ns duration with sharp rise times of < 1.5 ns, at a repetition rate of up to 20 kHz. The output pulse energy of > 15 microJoules can be maintained over the full tuning range. The high-quality output beam is coupled into a polarization-maintaining, single-mode delivery fiber for ease of integration into an application. With this "tailorable" pulse design, control of laser energy deposition in very confined laser interaction zones (by pulse shape), and of its dosage (by pulse duration) can be optimized by the user and adjusted in real-time from the laser controller in response to measured structural changes. Results of machining of materials such as Si, Cr on glass and drilling of Cu/Pl/Cu are presented, showing the unique capability of this laser and its advantageous use to ablate, structure, repair, or trim very small areas (down to sub-micron size) without damaging or influencing the underlying and/or neighboring structures.

High beam quality is one of the most important properties for micro material processing with lasers. It facilitates slight focus diameters and due to high Raleigh length even at strong focusing drilling of holes with high aspect ratio. Together with high average output powers it allows fast processes with high quality. Another important point is the wavelength of the laser radiation. Many materials e.g. diamond or silicon show no sufficient absorption at fundamental wavelength of Nd based solid-state laser sources. Frequency conversation to the second and fourth harmonic allows the efficient processing of these materials. At least flexible pulse peak power and repetition rate is necessary to optimize the process. Three laser systems which fulfill these requirements are investigated. A pulsed pumped Nd:YAG System which delivers an average output power of 315 W with M² = 2.6 at the fudamental wavelength and 124 W at the second harmonic. Another pulsed pumped System based on Nd:YAG with an average output power up to 125 W with M² = 2.2 at the fundamental wavelength, 49.5 W at the second harmonic and 4.75 W at 266 nm. Due to its active Q-switch the pulse peak power of this system is variable in a wide range. Furthermore, a continuously pumped amplifier arrangement with nearly diffraction limited output of 120 W average power has been achieved at 10 kHz repetition rate.

Silicon is the standard material for the production of integrated circuits and one of the most important substrates for micro systems technology. It can be produced with an extraordinarily high purity, homogeneity and crystal perfection. Today, laser processing of silicon is becoming increasingly more interesting. This can be partly attributed to the evolution of frequency-converted solid state lasers which emit visible or ultraviolet radiation that is readily absorbed by silicon. Another reason for the growing interest in laser processing of silicon devices is that conventional technologies are approaching their limits. Especially laser cutting of thin silicon wafers as an alternative to mechanical sawing represents a very promising option for industrial applications. This paper shows current research results on laser processing of silicon. Besides laser cutting and ablation with frequency-tripled Nd:YAG lasers and Ti:Sapphire femtosecond lasers, laser welding of silicon with millisecond pulses is a focus of the presented work. When welding Si, the brittle behavior of the material usually leads to thermally induced cracks. These cracks do typically not occur when cutting with short and ultrashort pulsed lasers. A controlled heating of the work piece can prevent cracks during welding with millisecond pulses as well. Together with laser cutting and welding, laser adjustment of silicon components by ultrashort pulse ablation of pre-stressed layer systems, which is also described in this paper, is another promising approach for high precision manufacturing of silicon micro devices.

Cutting of thin material, c.f. stencils, stents and thin wafers, is an important market for laser machining. Traditionally this task is performed using flash-lamp pumped, free-running Nd:YAG lasers. Using the water-jet guided laser technology, we experienced that the use of Q-switched lasers leads to superior results while cutting a variety of thin materials. In this technique, the laser is conducted to the work piece by total internal reflection in a thin stable water-jet, comparable to the core of an optical fiber. Utilizing this system, we obtain burr-free, slightly tapered cuts at the same speed as the classical laser cutting and without distinguishable heat affected zone. The main difference is, except the water-jet usage, the pulse duration which is approximately 400 ns instead of 20 to 200 μs in the case of free running lasers. Up to 40'000 high quality apertures per hour can be achieved in stencil mask cutting with the new system. We will compare qualitatively the two possibilities: conventional laser cutting with free-running lasers and water-jet guided laser cutting with Q-switched lasers. The results will be discussed in terms of the different physical effects involved in the material removal upon both methods. In particular the importance of molten material expulsion by the water-jet will be pointed out and compared to the action of the assist-gas. The mentioned effects show that the combination of short pulse laser and water-jet will be beneficial for the production of a wide range of precision parts.

The incessantly growing demands for higher speed of the wireless telecommunications and more compact devices require using of thin compound semiconductor wafers. The dicing is the very last process of the wafer manufacturing. At this stage the IC pattern is completely built up and the wafer has the highest value. Therefore, the goal of the singulation process is to provide the highest possible throughput. The conventional saw techniques "struggle" at their speed limits, while the conventional laser is not an appropriate dicing tool due to the strong thermal effect and big heat affected zones. The water-jet guided laser technology provides cool laser dicing since the laser is coupled in a fine stable water-jet and conducted to the work piece by means of total internal reflection like through an optical fiber, as the relatively low water pressure (10 - 30 MPa) of the tiny jet with diameter 40 - 100 μm results in a negligible force on the sample. This technology provides higher cutting speeds and burr-free kerf quality. By means of the Laser MicroJet, wafers as thin as 25 μm could be diced in streets of 50 μm width, with almost 100% wafer throughput. Here we compare the water-jet guided laser cutting with conventional techniques for dicing of thin semiconductor wafers. The results for Silicon and GaAs/Ge wafers are discussed in terms of speed, kerf quality and die fracture strength.

We are going to present a new technology for laser machining of silicon developed at the Laser Institute of Mittweida by a suggestion and in cooperation with the Technical University of Chemnitz, Department of Electrical Engineering and Information Technology. It allows the laser induced bending of microstructural silicon elements prepared by anisotropic wet etching. Bending of the element toward the incident laser beam occurs as a result of the laser induced thermal stresses in the material. We investigated the influence of various process parameters on the bending angle. There is only a small range of laser power to generate bendings in silicon. We will show a variety of examples including multiple and also continuous bendings. There are several essential advantages compared to conventional bending technologies: Laser bending is a contactless process without using additional tools or external forces. Because of the local laser treatment the heat flux to neighbouring material can be minimized so that the technology is suitable for machining of already finished microsystems. This new technology opens up a new field of applications in microsystem technologies. It is possible to generate a clip-chip-mechanism to clip a chip in a holder. Other examples are the exact positioning of optical mirrors or other components, the production of electrostatic drives and sliding chips for micro optical benches.

Fabrication and characteristics of two-dimensional (2D) and three-dimensional (3D) periodic structures, recorded in the bulk of SU8 photoresist film by multiple-beam interference is described. Multiple beams (up to nine) were generated by a diffractive beam splitter. Recording was performed by ultrashort laser pulses with temporal width of 140 fs (FVWM) and central wavelength of 800 nm, derived from a Ti:sapphire laser. Intensity-dependent photomodification of the photoresist was due to single-photon as well as multi-photon (two and three) absorption. After the development, the exposed resist films contained free-standing 2D and 3D periodic dielectric structures with unexposed exposed regions removed by the development. Detailed examination of the samples has revealed close resemblance between their structure and the light intensity distributions in the multiple-beam interference fields, expected from the numerical calculations. Quality of the samples recorded by a single-photon absorption was lower than that of other samples, in particular due to poor development quality. The microfabrication method used in this work appears to be a suitable for obtaining photonic crystal templates.

Ultrashort pulse or femtosecond laser materials processing is an emerging technology that potentially can produce substantial cost savings in the manufacture of a wide variety of Navy systems. A laser micromachining testbed facility utilizing two industrial laser systems, a Ti:Sapphire laser capable of producing pulses of less than 150 femtoseconds and a frequency tripled Nd:YLF laser (351 nm, approximately 50 nsec pulsewidth) has been established at the Electro Optics Center (EOC). The testbed provides the EOC with a facility for feasibility testing of laser micromachining applications and a resource for workforce training. In addition, the testbed provides a unique capability of evaluating ultrashort [150 fs, long wavelength (775 nm)] pulses versus longer pulse, short wavelength (351 nm), high photon energy pulses for micromachining applications. Comparison of processing by the femtosecond and uv solid state laser will reveal the optimal processing for an intended application where throughput, stability and quality of the process can be assessed.

Femtosecond laser processing is a promising new technology for the fabrication of micro-scale components from engineering materials, such as metals. In the femtosecond time regime, the ablation process is nearly a solid to vapor transition, thereby providing access to cut smaller features. Sandia National Laboratories has constructed a femtosecond laser microfabrication system to study the ability to produce microscale components in metals and glasses. In this paper, we will report on our initial studies to understand the metal ablation process with respect to manufacturing process parameters. With this understanding, we will show that femtosecond laser processing can fabricate complex components with fine feature detail and clean surfaces. A key finding in this work is the substantial effect of layer decrement on resulting recast material deposition when processing in air.

We have been working on the tailored ablation processing of advanced materials using femtosecond lasers. Here we would like to focus on the femtosecond laser processing tailored for hydroxyapatite. Hydroxyapatite is a key material of human tooth and human bone. The human bone is made of hydroxyapatite oriented along the collagen. The micromachining of human bone is highly required for medicine. The medical issue is how to preserve the chemical property of the laser-ablated surface. By use of pulsewidth tunable femtosecond laser (50fs - 2ps, 1.5mJ, 1kpps), we compared the relative content of calcium and phosphorus. The relative content of calcium and phosphorus is kept unchanged before and after laser ablation. For these medical applications, the intense femtosecond laser delivery through optical fibers is required. It is theoretically shown that it is possible to deliver the 900 fs pulses of 0.1 mJ/pulse through a 1 m-lohng graded index fiber with a 200 μm core diameter if the fiber has the optimum refractive index profile. We therefore conclude that graded index multimode fibers give better spatial distributions of the output transverse mode than hollow fibers or step index multimode fibers, and can deliver larger pulse energy than single mode fibers.

Femtosecond pulsed laser induced phase transition in iron was investigated using electron backscatter diffraction pattern (EBSP) analyzing system in this study. Mirror polished surface of single crystalline iron (purity: 99.99%) was irradiated by femtosecond pulsed laser (wavelength: 800 nm, pulse width: 120 fs, fluence: 2.5 J/cm², intensity: 1.6x10¹³ W/cm², number of pulses: 2000 pulses) in argon atmosphere. Electron beam irradiated the mirror polished vertical section by using colloidal silica under the bottom of the laser irradiated part, and the electron backscatter diffraction pattern was analyzed to determine the crystalline structure. ε phase of hcp structure found to exist around 4 μm deeper from the bottom. γ phase of fcc structure was not detected. This result shows the shock induced by femtosecond pulsed laser irradiation causes the α ↔ ε phase transition. It is suggested that this experimental method has a potential to investigate the existence and its crystalline structure of high pressure and high temperature phase of iron (β phase).

Laser assisted nanofabrication for surface nanopatterning is investigated. To overcome the limitation of light wavelength, pulsed lasers were applied to combine with atomic force microscope (AFM) and nanoparticle self-assembled mask to achieve sub-30 nm patterning on the metallic surfaces. The mechanisms of the formation of nanostructure patterns are discussed. Progress on numerical simulation and physical modeling of laser assisted nanofabrication has been demonstrated. The method of AFM tip or particle enhanced laser irradiation allows the study of field enhancement effects as well as its potential applications for nanolithography.

A cone microstructure has been used as a template to generate nanotips and to promote nanoparticle alignment. A quasi-periodic array of nanotips is produced when the laser-induced cone microstructure is subject to chemical etching due to tapering of the cone tips. Nanoparticles can be produced on the surface of a silicon specimen by irradiating it in the presence of an inert gas atmosphere. The backscattered material that is re-deposited on the substrate, upon irradiation at fluences close to the melting threshold, is composed of a thin film intermixed with extremely small nanoparticles. Further irradiation promotes film clustering and nanoparticle formation. In the presence of cones, the nanoparticles become aligned into straight and long (~1 mm) lines whose spacing is close to the laser wavelength. This result suggested an ordering mechanism similar to that occurring for laser-induced periodic surface structures. The relation between nanoparticle line spacing and angle of incidence of the radiation supported this similarity. Nanoparticle ordering also was promoted by laser-enhanced chemical vapor deposition (LCVD) using polarized light, when a laser-induced periodic surface nanostructure was present in the substrate.

A line of periodic dot structure was fabricated on and inside materials by laser-induced modification with interfered femtosecond laser beams split by a diffractive optics. In addition, dot matrix and comb structures were fabricated with transportation of a sample at arbitrary speeds. These structures worked as transmission and reflection gratings. In addition, nanowires were fabricated by peeling the comb structure. Dot matrix was also formed by a single shot of laser ablation with four interfering beams.

One of the most straightforward methods possible is presented and investigated to form thin film GaAs. The film was deposited on unheated glass in vacuum (10^-6 Torr) by the ablation from a GaAs wafer with the emission of a pulsed Nd:YAG laser (532 nm, 6 ns, 10 Hz). The photoluminescence, photocurrent, transmission and micro-Raman measurements of the films demonstrate that films with promising optoelectronic properties have been formed. Most importantly, from the viewpoint of light emitting and optoelectronic device production, the films show photoluminescence of comparable intensity with the bulk material without emissions owing to impurities, although the films show a rather flat absorption edge which indicates tail states. The observed photocurrent was in the μA/W range driven by rather moderate electric fields on the order of 100 V/cm. Concerning the material quality, the films have an extremely smooth surface as demonstrated with scanning electron microscopy. Grown GaAs films on glass substrates were amorphous evidenced by X-ray diffraction measurements, however, micro-Raman measurements showed crystalline phonon modes, suggesting that localized crystalline structure might co-exist in amorphous GaAs films.

Emerging applications in the microelectronics industry impose special manufacturing requirements that are not well addressed by conventional manufacturing techniques. On the other hand, advances in laser technology, optics and beam steering combined with a better understanding of laser-material interaction make laser micromachining a viable, attractive, cost-effective and in some cases enabling technology to support these applications. This paper reviews some of the emerging applications in the microelectronics industry that are well served by laser micromachining and discusses the advancements in lasers, optics and beam steering that enable cost effective laser micromachining. It also discusses some open issues that are the subject of current and future research.

A facility for rapid prototyping of MEMS devices is crucial for the development of novel miniaturized components in all sectors of high-tech industry, e.g. telecommunications, information technology, micro-optics and aerospace. To overcome the disadvantages of existing techniques in terms of cost and flexibility, a new approach has been taken to provide a tool for rapid prototyping and small-scale production: Complex CAD/CAM software has been developed that automatically generates the tool paths according to a CAD drawing of the MEMS device. As laser ablation is a much more complicated process than mechanical machining, for which such software has already been in use for many years, the generation of these tool paths relies not only on geometric considerations, but also on a sophisticated simulation module taking into account various material and laser parameters and micro-effects. The following laser machining options have been implemented: cutting, hole drilling, slot cutting, 2D area clearing, pocketing and 2½D surface machining. Once the tool paths are available, a post processor translates this information into CNC commands that control a scanner head. This scanner head then guides the beam of a UV solid-state laser to machine the desired structure by direct laser ablation.

Liquid crystal polymer (LCP) is a new and innovative material being used as an alternative to polyimide in the flexible circuit industry. LCP has many intrinsic benefits over polyimide including lower moisture absorption and improved dimensional stability. However, LCP is very resistant to chemical milling or etching. As a result, other methods for processing the material are being investigated including laser micromachining. In this paper, three frequency converted diode-pumped solid-state (DPSS) Nd:YVO₄ lasers at 355 nm were used to micromachine a LCP film and a copper/LCP laminate. Of them, two are Q-switched lasers operating in the nanosecond regime and the other a mode-locked laser in the picosecond regime. The Q-switched lasers can be operated at pulse repetition rates of 1 to 300 kHz while the mode-locked system is operated at 80 MHz. The micromachining experiments consisted of cutting the 50 μm thick LCP film, cutting the 18 μm thick copper on the film, and drilling micro-vias through both the copper coating and the film substrate. The laser/material interactions and processing speeds were studied and compared. The results show that, compared to polyimide film of the same thickness, LCP film can be more efficiently processed by laser micromachining. In addition, each laser has a unique advantage in processing LCP based flexible circuit materials. The Q-switched lasers are more capable of processing the copper coating while the mode-locked laser can cut LCP film faster with the smallest kerf width.

Laser micromachining of n-type silicon wafer was studied using femtosecond laser operating at 400 and 800 nm wavelengths. The fundamental wavelength was used to fabricate a diaphragm of 4 mm diameter using a computer controlled galvo head. The laser pulsewidth was 110 fs, repetition rate of 1 kHz, and maximum average power of 2 W. The experiments were done in air and in vacuum environment. The samples were examined with optical microscope and surface profilometer. Experiments were also done with doubling the laser beam frequency using LBO crystal to get 400 nm wavelength. Using a 10 nm resolution stage, high numerical aperture microscope objective, we were able to fabricate 235 nm wide lines with 600 nm depth.

A new field in laser processing is opened by this method of modifying the optical properties, i.e. the refractive index, absorption- and scattering-coefficient, inside the material. Focusing ultra short laser pulses inside the transparent media allows to control and modify their optical properties. This is referred to as nik-engineering, 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 even on a microscopic scale. New results in nik-engineering obtained in our application laboratory are presented using different optical materials. The results in laser nik-engineering of photo-chromic glass using ultra short laser pulses at a wavelength of 800 nm are presented to the best of our knowledge for the first time. We discuss the results and the possibilities of nik-engineering and consider the technological relevance with respect to decorative work, micro-tagging, and other functional structures.

Excimer laser ablation at 193 nm is used for the generation of a surface relief structure on fused silica with the aim to fabricate diffractive optical phase elements to be applied for efficient laser materials processing. Though there are several problems to achieve high aspect ratio material removal at this laser wavelength (193 nm) in a scarcely absorbing material (fused silica), ablation of sub-μm depth, as it is needed to generate the appropriate phase delays of diffractive phase elements (DPE) for UV-applications, is possible without cracking. Applying a machining process corresponding to a bitmapped DPE design generated by an Iterative Fourier Transform Algorithm (IFTA), the fused silica surface is patterned on a 128 x 128 pixel² area with a pixel size of 12.5 x 12.5 μm². The step height of this two level DPE has to be adapted to the combination of the wavelength, at which the element will be applied, and the refractive indices of the DPE-material and the environment. The example DPE is designed as a 10 x 10 focus raster generator for a UV-femtosecond laser operating at 248 nm. Using this DPE in combination with a 25x Schwarzschild objective, the parallel drilling of micron sized holes in stainless steel and other metals is demonstrated.

Laser processing using a multiple visible and UV wavelength copper laser source is presented with particular emphasis on photonic and microelectronic applications. Visible micromachining of ceramics and diamond are discussed in addition to UV micromachining/microfabrication of germanium doped silica, sapphire and kapton.

A phenomenon of a strong irreversible variation of the refractive index (Δn approximately equals - 0.2) in a subsurface layer of the lithium niobate crystal has been observed. The effect arises under the strong absorption of high-power radiation with wavelength 248 nm of KrF excimer laser. The characteristics of the subsurface photorefractive effect (SPRE) were identified by using the data on measurements of the reflection coefficient of a crystal and of the diffraction efficiency of a recorded phase grating. About 40% of niobium and oxygen atoms has been found to be displaced from the lattice points in the 350 ± 50 angstrom subsurface layer. This phenomenon was used for creation of some integrated optics elements.

A new single step direct-write photomask process has been proposed by using Bi/In bimetallic thermal resist which turns almost transparent with high energy laser exposure. The Bi over In metallic films, each layer approximately 40 nm thick, were DC-sputtered onto quartz mask plate substrates in a single pump-down chamber. Before laser exposure the Bi/In had 2.91 Optical Density. Bi/In is a bimetallic thermal resist and hence shows near wavelength invariance exposure sensitivity from Near IR to UV light. For Bi/In exposure, up to 0.9 W Argon laser (514 nm) beam was focused by an f = 50 mm lens to a 10 micron spot. When writing a mask the Bi/In coated sample was placed on a computer-controlled high accuracy X-Y table and the pattern was raster-scanned by the laser at 10 mm/sec. After exposure the Bi/In film became nearly transparent (0.26 OD) at I-line (365 nm) wavelength, and remained conductive. Bi/In photomasks have been used together with a standard mask aligner to pattern the oxide and Al layer during the manufacturing of test solar cell devices in the lab. Experiments also showed that annealing the as-deposited films at 90°C before laser exposure increase the Bi/In transparency.

Laser-induced backside wet etching of silica glass plates was performed by the excitation of a pure toluene solution with a ns-pulsed KrF excimer laser at 248 nm. Well-defined grid micropattern was fabricated without debris and microcrack around the etched area. To understand the etching mechanism, the formation and propagation of shockwave and bubble were monitored by time-resolved optical microscopy at the interface between the silica glass and the toluene solution after laser irradiation. Transient high-pressure as well as high-temperature generated by UV laser irradiation plays a key role in the etching process.

During the last decade, diode-pumped TEM₀₀ mode solid state lasers have gained widespread application in micromachining of dielectrics and metals. Commercial systems with output powers of up to 40W at 1064nm, 20W at 532nm, 15W at 355nm and 2W at 266nm, repetition rates of up to 400kHz and pulse durations between 10ns and 100ns are now being used in numerous micromachining applications. In addition, industrial applications of modelocked lasers are starting to emerge. This paper will give an overview of the state-of the art of diode-pumped TEM₀₀ mode solid state lasers and their applications in micromachining.

To meet the industry's demand for reducing machine cycle lengths concerning laser-drilling a Nd:YAG Master-Oscillator Power-Amplifier (MOPA)-system was developed at the LMTB-laboratories that emits high-power peak-pulses at excellent beam-quality. Presently, the output power of the oscillator (10W@1064nm) with a beam-quality of M²=1.3 is amplified to 95W@1064nm with M²=2.3 and a single pulse energy up to 500mJ. The pulse duration can be varied between 26 and 230ns. On account of the excellent beam quality, frequency conversion resulted in 49W@532nm and 4.8@266nm. The MOPA-System is used for laser micro drilling experiments into metals and ceramics where the influence of the beam quality on the geometrical shape of the hole is investigated and compared with applications conducted with similar laser systems. Additionally means in optimizing the drilling process such as burr-minimizing and melt-reduction were introduced. Furthermore, experiments using tapered drilling technique are undertaken. A maximum aspect ratio of 1:200 in stainless steel was obtained.

Dielectric sensors with smallest electrode structures are used to monitor several technical applications. Thus, durable substrate materials are essential for the exploitation of the sensors in hostile process environment. Here, ceramics and different glasses show ideal material properties, but are difficult-to-machine in the micrometer range. UV-laser beam sources are well suited for an economic manufacturing of micro-structures in these brittle materials. Especially, advanced laser tools like excimer- and frequency converted solid-state lasers show excellent machining results. This paper presents the development of new laser based production techniques and innovative process chains for the fabrication of distinctive electrode structures in high stable materials. Two different machining concepts are shown. A conductive Indium Tin-Oxide (ITO) layer with a thickness of about 600nm has been structured with a KrF excimer laser (λ = 248 nm, H = 5 J/cm²), without damaging the underlying borosilicate glass substrate. The dimension of the electrodes and insulation channels of the sensor are as small as 50μm. For the second approach of manufacturing a dielectric sensor, aluminum oxide as a bulk substrate materials has been machined with the same laser type. No thermal damage was observed by an operating fluence H = 20 J/cm². The obtained extreme durable embedded-electrode-type sensor can completed by filling the cavity with conductive material by standard electroplating techniques. For the manufacturing process, a high flexible NC-controlled machining concept is presented, which allows a time and pulse minimized fabrication as well as an optimization of the surface quality of the micro-sensor, including a process optimization via simulation.

In this paper we show that a femtosecond laser enables us to form true three-dimensional microstructures embedded in a photosensitive glass Foturan for lab.-on-chip applications. The Foturan glass has superior properties on transparency, hardness, chemical and thermal resistances, and biological compatibility. After exposure to the tightly focused laser beam, latent images are written inside the glass. Modified regions are developed by a post baking process and then preferentially etched away in an ultrasonic solution of 10% hydrofluoric acid in water. By use of this technique, we fabricated various true 3D microstructures including microfluidic components and micro-optics inside the Foturan glass. However, the microchannel fabricated inside glass by scanning focal spot of a femtosecond laser perpendicularly to the direction of laser propagation gets an elliptical shape with a cross section of large aspect ratio, owing essentially to a longitudinal distribution of the focal spot produced by an objective lens with numerical aperture of 0.46. We demonstrate that the aspect ratio can be effectively improved by use of a slit-assisted irradiation method. Lastly, we show that 3D micro-optics are fabricated inside the Foturan glass, which enhances the function of lab.-on-chip.

We discuss laser fabrication of microstructures in photoetchable glass-ceramics, FOTURAN. A KrF excimer laser (λ = 248 nm, τ = 25 ns) is used for surface micromachining, and a femtosecond laser (λ = 800 nm, τ = 80 fs) is used for fabricating three-dimensional structures. Other aspects of the machining, such as the fluence and crystallization depth resulting from these two methods are presented. A detailed analysis of the absorption process of both lasers in FOTURAN is discussed.

Microfluidic channels on borosilicate glass are machined using femtosecond lasers. The morphology of the ablated surface is studied using scanning microscopy. The results show micron scale features inside the channels. The formation mechanism of these features is investigated by additional experiments accompanied by a theoretical analysis of the thermal and fluid processes involved in the ultrafast laser ablation process. These studies indicate the existence of a very thin melting zone on glass and suggest that the surface morphology is formed by the plasma pressure-driven fluid motion of the melting zone during the ablation process.

In the microscopic world the need of functional prototypes increases, e.g. as a precondition for a mould insert fabrication for micro-injection moulding. In this work the direct fabrication of prototypes made from polymers with an accuracy down to the micrometer range will be presented. For this purpose the direct patterning or modification of polymers with UV-laser radiation is performed for applications in fluidic and micro-optics. Different UV laser sources such as excimer and frequency-multiplied Nd:YAG were used. In the case of complex designs for fluidic applications it is powerful to use Nd:YAG laser radiation as patterning tool because of their high laser repetition rates: CAD data from complex fluidic designs were transmitted directly via CAM module into the polymeric surface. Because of the very small laser pulse duration of about 400-500 ps the thermal-induced damage during ablation decreases significantly. Process parameters, ablation rates and attainable surface qualities for capillary-electrophoreses chips will be presented. With the aid of a motorised aperture or a rotating mask system, excimer laser radiation is used to enable a well defined patterning of grooves with sharp edges and smooth sidewalls. The direct ablation of polymethylmethacrylate (PMMA), as well as the laser induced modification of the polymeric chemistry is used for the preparation of passive integrated-optical waveguides. Two types of concepts of waveguides are discussed: 1. Laser patterned grooves are filled with index matched materials which leads either to an increase or a decrease of the refractive index relative to pure PMMA. 2. Localised laser-induced polymer modification leads immediately to an integrated waveguide with higher refractive index. Both types of waveguides-concepts are characterised by their optical properties, which will be discussed in detail.

Highly accurate resistances can be made by iteratively laser inducing 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. These laser tuned microdevices have been electrically characterized and their current-voltage (I-V) behaviors are linear at low voltages and sublinear at higher voltages where carrier mobility is affected by the presence of high fields. Considering that the microdevice is a one dimensional trap less n+ υ n+ structure, we have developed a theoretical current-voltage equation that satisfies these experimental results.

This paper describes a new growth method of ZnO nanorods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nanostructured-ZnO thin films. Under an optimized deposition conditions, ZnO nanoroods 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 nanorods under an optical excitation at 355 nm, indicating a high quality of the crystal.

The early stage of optical damae caused by F₂ laser irradiation on the wide bandgap fluoride crystal, CaF₂, is investigated and compared with the case of ArF laser irradiation. Besides a blue emission band due to self-trapped exciton, sharp emission lines appear and grow at a fluence of about 2 J cm^-2, showing the initiation of the optical damage and growth of plume from the F₂-laser-irradiated surface of CaF₂. There exist cracks and melted structures on the laser-damaged surface, which are caused by thermal stress and vaporization due to laser absorption and following local heating.

Results of semiconductor laser crystallization of a-Si:H on transparent conducting fluoride doped tin oxide coated glass are discussed. A-Si:H films were prepared by plasma enhanced chemical vapor deposition. Laser crystallized films of a-Si:H were characterized by X-ray diffraction and optical microscopy. Semiconductor laser crystallization process as compared to well-established excimer laser offers low cost large area technology for solar cell, display and other applications. Longer wavelength of diode lasers (805 nm) allows light to penetrate deeper in the films for crystallization of thicker films required for enhanced light absorption.

Surface relief type gratings for input laser coupling were fabricated on the PLD deposited 2 at.%Nd:GGG thin film optical waveguide by femtosecond laser interferometric processing. The morphology and coupling efficiency were experimentally evaluated. A clear periodic structure with a fringe period of approximately 800 nm and height of approximately 100 nm was obtained for a surface relief type grating induced on the target surface with a fluence of 0.92 Jcm^-2. The coupling efficiency of an 808 nm-centered laser diode pumping light into the 1.35 μm thick film was measured as a function of the incident angle. Three coupling peaks were observed at 57°, 65° and 77°, each being the coupling to the TE₀, TE₁ and TE₂ modes respectively. Each peak had a large FWHM and a maximum coupling efficiency was 3%.

We have studied femtosecond laser ablation characteristics of LiNbO₃ for the first time. LiNbO₃ is ferroelectric material with large optical nonlinearity and Pockels effect. The femtosecond laser ablation is very useful to fabricate various optical devices including the optical modulator and the tunable optical filter for optical communication systems because the thermal damage around the irradiated area is small due to the short pulse width, and the sub-wavelength structures may be formed by the multi-photon excitation. In our experiments, the femtosecond Ti:Sapphire laser system (Energy 0.14 mJ/pulse, Wavelength 800 nm, Pulse duration 60 fs, Repetition rate 1 kHz) based on the chirped-pulse amplification (CPA) technique was used. The aperture with a diameter of 5 mm was imaged onto the LiNbO₃ surface by the objective lens in the air. We observed ablation holes by the scanning electron microscope and the profilometer. We have found no damage around the holes and the clear boundary between ablated area and non-ablated area was observed. Those features are very useful for precise material processing. The bottom face of the holes was relatively flat. The etching rate was 0.93 micrometer/pulse and proportional to the number of the laser pulse. The results showed that the femtosecond laser ablation is an innovative tool for manufacturing LiNbO₃-based optical devices.

With a loosely focused femtosecond laser, refractive index change is induced in silica glass without any scanning process. By decrease numerical aperture of the incident laser, the induction of irregular structure can be avoided such as clacks and spatial splitting of the induced refractive index change region. We demonstrate controlling of the refractive index change by optimizing the numerical aperture and input energy and input pulsewidth and laser shot number. A new method of fabrication of photonic devices in silica glass is proposed.

Chrome-on-quartz optics serve multi-functions including high-resolution masks for UV lithography. At the next node down, F₂-laser lithography demands alternate high-transparency substrates such as wide-bandgap CaF₂. We present here a direct-write method of F₂-laser ablation for selective removal of 110-nm thick chrome films on CaF₂ and SiO₂ (fused silica) substrates. Laser-processing parameters are presented for micropatterning of the chrome film with minimal damage to the underlying substrates. Damage thresholds, ablations rates, incubation processes, and surface morphology of the chrome and CaF₂ are described together with methods that reduce ablation debris and collateral damage. Laser-patterned masks are tested in a 157-nm optical projection system at 30-mJ/cm² fluence for sub-micron laser structuring of glass and other materials.

In order to attempt the direct laser marking for ROM media like a compact disk for identification, various laser heating was carried out against a thin metallic film in the transparent medium. As heat sources for the processing, a semiconductor laser excitation YAG laser (532 nm wavelength of second harmonic, max 150 mW), semiconductor lasers (780 nm, up to 2 W), and an Ar ion laser (514.5 nm, max 2000 mW), etc. were used. The media under consideration on laser marking is an aluminum thin film reflector layer, which was sandwiched between a polycarbonate (PC) of 1.2 mm and a protection film of 5 μm thickness. The aluminum thin film (Al) is 100 nm in thickness. The obtained laser marking sizes were less than 1 μm and were evaluated using SEM and AFM. The observation samples inside a transparency resin were obtained by tearing off a protection film, and the surfaces of the bared PC and protection film were examined. The surface conditions and cross sections of laser-marking area were observed. It seems that the heated aluminum thin film were melted and a hole arose. Then a cavity was not observed from SEM cross-section observation in the marking area. It became clear that the holes were filled with PC by SEM and AFM observation. These results indicate the possibility of heat localization at the Al-PC interface and also significant heat penetration into the PC substrate itself.

The melted area is found on the surface ablated by nanosecond and picosecond laser pulses. However, the heat effect is little on the ablated surface in the case of femtosecond laser due to non-thermal ablation process. Heat-affected zone of metallic bulk crystal ablated with femtosecond Ti:sapphire laser pulses is experimentally studied. As a result of XRD (X-ray diffraction) measurements, the XRD peak signal of the area ablated with Ti:sapphire laser becomes smaller than that of the crystalline metal sample. While the crystallinity of the metal sample is crystalline before the laser ablation, the crystallinity in the ablated area is partially changed into the amorphous form. Because the residual pulse energy that is not used for the ablation process remains, leading to the formation of thin layer of melt phase. The melt layer is abruptly cooled down not to be re-crystallized, but to transform into the amorphous form. It is evident that the area ablated with femtosecond laser is changed into the amorphous metal. Additionally XRD measurements and AR⁺ etching are performed alternately to measure the thickness of the amorphous layer. In the case of iron, the thickness is measured to be 1 μm approximately, therefore heat-affected zone is quite small.

The investigation of laser induced forward transfer (LIFT) process using femtosecond pulsed laser comparing with that using excimer laser is reported. Ni thin film of several hundreds of nanometer thickness, which is deposited on fused silica substrate, was irradiated by single pulse of KrF excimer laser (wavelength: 248 nm, pulse width: 30 ns) or femtosecond pulsed laser (wavelength: 800 nm, pulse width: 120 fs), and transferred to a Si acceptor substrate. It is shown that laser beam profile affected the removal of thin film. It is revealed that adhesion of particles was inhibited using femtosecond pulsed laser in comparison with the case of excimer LIFT process.

Experimental results obtained in study of spontaneous UV radiation source based on high-current pulsed discharge in xenon developed for irradiation of diamond crystal to convert it into conductive state are presented. It is shown that at the pressure of about 450 Torr radiation of Xe lines predominate in UV range of discharge radiation spectrum. The part of radiation energy in the range of 200 - 250 nm with respect to the radiation energy of the whole range recorded (200 - 650 nm) may reach 50%. The maximum density of radiation power was 185 kW/cm². At pressure increasing up to 1200 Torr, the part of thermal radiation increases too. In this case the part of radiation energy in the range of 200 - 250 nm does not exceed 20%.

Industrial manufacturing with the aid of laser technology has found many applications in the microelectronics industry during the last three decades. At Philips the main application fields are laser spot welding and marking. Several novel fields are strongly coming up due to the high demands in the microelectronics and (flat) display industry that cannot be met with conventional technologies. In this paper we give an overview of the present status of laser technology in electronics manufacturing and of innovative developments for new applications in microelectronics and photonics.

Current product development showing an ever shrinking physical volume is asking for new, reliable joining technologies. Laser beam technologies conceal innovative solutions to overcome limitations of conventional joining technologies. Laser beam welding of thermoplastics offers several process technical advantages. The joining energy is fed contact-less into the joining area, avoiding mechanical stress and thermal load to the joining partners. The energy is supplied spatially (seam width on the order of 100 μm) and timely (interaction time on the order of ms) very well defined. Different process strategies are possible leading to flexibility, product adapted irradiation, short process times and high quality weld seams as well as to high integration abilities and automation potentials. During the joining process no vibration, no thermal stress, no particle release takes place. Therefore, destruction of mechanically and electronically highly sensitive components, such as microelectronics, is avoided. The work place pollution is neglectable compared to other joining technologies, such as gluing (fume) or ultrasonic welding (noise, pieces of fluff). Not only micro-components can be welded in a reproducible way but also macro-components while obtaining a hermetic sealing with good optical appearance. In this publication firstly, an overview concerning process technical basis, aspects and challenges is given. Next, results concerning laser penetration welding of polymers using high power diode lasers are presented, while comparing contour and simultaneous welding by experimental results and the on-line process monitoring.

Laser beam soldering (LBS) is a non-standard manufacturing process for electronic packaging and interconnection technology today. Due to the actual trend towards complex and cost intensive products, LBS gains more attention for certain applications in this field. For mass production in automotive applications a fully automated and temperature controlled LBS process was developed. The achieved results are discussed with respect to quality, reliability and process efficiency and compared to established micro flame (hydrogen) soldering technology. The development of the LBS process is presented. The process window is optimized using High Speed Video Imaging. Temperature signals are logged by means of pyrometry. The processed parts are evaluated with metallographical assessment of solder joint quality. Especially cross sections reveal the fine grained structure and the shape of the meniscus of the solder joints. The reliability is proven using shear strength tests and thermally induced strain cycles. Conclusively, LBS is a stable, reproducible process for applications requiring controlled and locally restricted heat input. The thermal and mechanical stress is reduced in comparison to conventional techniques.

Conventional joining techniques like press fitting or crimping require the application of mechanical forces to the parts which, in combination with the tolerances of both parts to be joined, lead to imprecision and poor tensile strength. In contrast, laser beam micro welding provides consistent joining and high flexibility and it acts as an alternative as long as press fitting, crimping, screwing or gluing are not capable of batch production. Different parts and even different metals can be joined in a non-contact process at feed rates of up to 60 m/min and with weld seam lengths from 0.6 mm to 15.7 mm. Due to the low energy input, typically 1 J to 6 J, a weld width as small as 50 μm and a weld depth as small as 20 μm have been attained. This results in low distortion of the joined watch components. Since the first applications of laser beam micro welding of watch components showed promising results, the process has further been enhanced using the SHADOW technique. Aspects of the technique such as tensile strength, geometry and precision of the weld seam as well as the acceptance amongst the -mostly conservative- watch manufacturers have been improved.

In present-day industry, particularly in the area of microelectronics packaging and assembly, there is a strong demand for highly reliable, miniature joints of thin copper parts. Laser welding could be the perfect solution for making such joints if this process were not highly sensitive to various parameters, such as the reflectivity of the copper workpiece, the gap between the product parts to be welded, and laser-power density. The robustness of the process is further limited because two important product properties (reflectivity and heat conductivity) change strongly during welding. An investigation has been performed to increase the robustness by means of real-time feedback control, based on several parameters that are monitored simultaneously during the process. It is shown how this drastically decreases the influence of the above-mentioned variations with "heat conduction" welds. The control algorithm was based on an approximate model of the (non-linear) welding process. In addition, it is shown how adaptive feedforward control is required to cope with the limited response time of the system. Finally, some remarks are made on experiences iterative learning control. This investigation was part of the European co-operation project SLAPS, performed within the framework of the IMS/Brite-Euram III program. The support from the European Commission and the IMS regional offices is gratefully acknowledged.

Nd:YAG solid-state lasers have been integrated in many seam welding applications. They provide a good ability of integration into existing manufacturing sequences and allow its easy automation. Appropriate process monitoring systems are needed to decrease necessary user intervention, to ensure a high machine availability and to realize a zero defect production. In the electronics industry, laser spot welding techniques using pulsed Nd:YAG-lasers have been established in mass production applications, for example in manufacturing of electron gun components for TV monitor tubes over the last 25 years. They require different strategies and methods for process monitoring systems. Apart from these integrated laser spot welding applications, there is a current demand for new technologies to join micro components onto 3-dimensional (3-D) circuit substrates and to connect electrical plugs. In recent years, laser spot joining techniques have emerged as a viable option for packaging electrical and mechanical microparts, such as surface mounted devices (SMDs) and casings. Under most conditions, laser spot welding provides more durability as well as thermal and mechanical stability compared to traditional packaging techniques, such as simultaneous soldering. Additionally, under less ideal conditions, the packaging quality can be inconsistent, resulting in the need for optimization and monitoring of the weld parameters under different conditions. In order to achieve a stable process during packaging of electrical components despite their weak absorption of laser radiation and different surface qualities, a process monitoring system should be needed.

"Laser Droplet Welding" is an innovative joining technology. The welding is realised by a laser generated liquid metal droplet which is deposited onto the parts to be joined. The raw material is a metal wire. In conventional laser welding a gap between the parts worsens the quality of the laser welded joint substantially. Contrarily a droplet offers sufficient material to bridge gaps. Even different gap sizes can be bridged by a suitable selection of the droplet size. A further advantage is the controllable heat transfer, only given by the heat content of a single drop that is sufficient to produce a high-temperature weld. The droplet heating provides the opportunity to weld small devices, thin coatings and even heat sensitive components without negative influence on their mechanical and electrical function. It is also possible to interconnect different materials by the addition of material supplied in form of drops. With the Laser Droplet Weld it is furthermore possible to join high reflective materials. This article describes the process and the system technology as well as achieved results. It will mainly focus on the droplet detachment which influences the complete process, e.g. the heat quantity or weld splashes.

The theoretical criterion defining the threshold pulse energy and beam intensity required for melt ejection is proposed. The results of numerical simulation present dependencies of the threshold pulse energy and beam intensity as functions of laser pulse duration and beam radius. The experimental verification of proposed criterion is described and the comparison of theoretical predictions and measurements is presented. The criterion is applied for simulation of laser drilling metal foil with thickness in the range 25 μm - 125 μm using laser beam with 12 μm beam radius and pulse durations 10 ns and 100 ns. The computational results are used to interpret the results of experimental study of laser drilling of 125 μm aluminum foil using a single mode beam of a XeCl laser performed at the Nederlands Centrum voor Laser Research (NCLR) and the University of Twente. Additional results on Nd:YAG spot welds in pure Ni are also presented.

Ceramic and crystalline wafer substrates are widely used in microelectronics. The individual choice is based on their thermal, optical and mechanical properties. For a variety of applications high quality laser micro processing of these materials, i.e. the generation of blind and through holes, grooves and even complex three dimensional micro structures, is gaining in importance. The department of applied laser technologies of the LMTB GmbH has conducted extensive studies on the versatility of q-switch Nd:YAG laser systems for the micro structuring of ceramic and crystalline wafer substrates that differ strongly in their optical and mechanical properties, such as Al₂O₃, AlN, sapphire, Si and SiC. This paper discusses the laser material micro machining results in respect to the laser parameters used to optimize the micro processing quality and speed for the different materials.

μFor drilling fused silica, mechanical techniques like with diamond drills, ultrasonic machining, sand blasting or water jet machining are used. Also chemical techniques like laser assisted wet etching or thermal drilling with CO₂-lasers are established. As an extension of these technologies, the drilling of micro-holes in fused silica with VUV laser radiation is presented here. The high absorption of the 157 nm radiation emitted by the F₂ excimer laser and the short pulse duration lead to a material ablation with minimised impact on the surrounding material. Contrary to CO₂-laser drilling, a molten and solidified phase around the bore can thus be avoided. The high photon energy of 7.9 eV requires either high purity nitrogen flushing or operation in vacuum, which also effects the processing results. Depending on the required precision, the laser can be used for percussion drilling as well as for excimer laser trepanning, by applying rotating masks. Rotating masks are especially used for high aspect ratio drilling with well defined edges and minimised debris. The technology is suitable particularly for holes with a diameter below 200 μm down to some microns in substrates with less than 200 μm thickness, that can not be achieved with mechanical methods. Drilling times in 200 μm fused silica substrates are in the range of ten seconds, which is sufficient to compete with conventional methods while providing similar or even better accuracy.

Each electronic chip is packaged in order to connect the integrated circuit and the printed circuit board. In consequence high-speed singulation of packages is an important step in the manufacturing process of electronic devices. The widely used technique of abrasive sawing encounters problems due to the combination of different materials used in packages such as copper and mold compound. The sawing blade rapidly blunts because of the copper adhering to the saw blade and covering the diamonds. In fact, the abrasive saw, well adapted to silicon wafer sawing, has problems to adapt to package materials. It has already been shown that the water jet guided laser can be used for efficient high quality singulation of leadframe based packages. In this technique a low-pressure water jet guides the laser beam like an optical fiber, providing efficient cooling of the cutting kerf at exactly the point that was heated during the laser pulse. We present new cutting results using a frequency doubled Nd:YAG laser with 100 W average power, and the combination setup for generating a 200 W green laser beam. The timing between the two lasers can be precisely controlled.

New branch in optoelectronics and photonics -- integrated optical circuits as a part of hybrid optical devices and the problems of coupling efficiency in optical interconnections (OI) -- is discussed. General approach to optical circuits analysis and adjustment based on classical optics is presented. The means to improve OI light efficiency in two regions -- far-field (Fraunhofer diffraction zone) free space and near-field (Fresnel diffraction zone) vicinity of micro-optical devices are proposed. New optical elements for OI -- fiber-end mounted microlenses, their design, computer simulation and fabrication technique are considered.

Excimer lasers were demonstrated to be effective tools in (1) engraving ceramics and polymers, (2) changing irreversibly the surface chemistry of the irradiated material, and (3) restricting these effects to specific areas of interest. In so doing, excimer laser irradiation does open new routes to functionalizing the surface of such diverse and difficult materials, allowing them to be utilized in given applications. In this paper, it is demonstrated how the above three potentialities of excimer laser surface irradiation may be put into practice in producing application-specific metallic tracks onto either sintered ceramics or polymeric materials. To this end, the accent is deliberately put here on the photochemical aspect of this irradiation process. The latter is responsible for modifying the surface stoichiometry and/or structure of irradiated ceramics and silicone rubbers and also, of some of the solid additives which combine to polymers to form so-called thermoplastics. An important consequence of this changing surface chemistry resides in the possibility for decorating the processed surfaces with metal via an electro less technique, thus establishing the ground for a novel metallization process that is presented and examplified.

The delamination of a thin film heterostructure by selective absorption of pulsed laser energy at a buried interface enables the transfer of the thin film heterostructure from its growth substrate to virtually any receptor substrate without significant heating of material outside the interaction zone. By combining this "laser lift-off" process with low-temperature bonding methods, disparate classes of materials can be intimately integrated without exceeding the thermal budget of the least robust of the materials to be integrated. Furthermore, heterostructures that can be grown by epitaxy on one substrate can be transferred intact, without significant deterioration in crystal quality, to a receptor substrate that enhances the performance or functionality of the heterostructure in a device or microsystem. In this paper, applications of laser lift-off in the packaging and integration of light-emitting GaN devices are highlighted. Transfer of these devices from their sapphire growth substrates to thermally and electrically conductive receptor substrates is shown to result in improved device performance through the reduction of thermal and electrical series resistances, and by the improvement in optical design enabled by access to both sides of the heterostructure. Continued development of laser lift-off packaging has the potential to reduce manufacturing costs and complexity as well through the elimination of the sapphire dicing step. Finally, the application of the LLO technique to the assembly of functionally-enhanced microsystems is illustrated with the example of an integrated fluorescence detection microsystem.

The use of direct-write techniques in the design and manufacture of interconnects and antennas offers some unique advantages for the development of next generation commercial and defense microelectronic systems. Using a laser forward transfer technique, we have demonstrated the ability to rapidly prototype interconnects and various antenna designs. This laser direct-write process is compatible with a broad class of materials such as metals and electronic ceramics and its capable of depositing patterns of any of these materials over non-planar surfaces in a conformal manner. The laser direct-write process is computer controlled so as to allow any given design to be easily modified and adapted to a particular application. To illustrate the potential of this technique, examples of metal lines on laser micromachined polyimide substrates for interconnect applications, are discussed and evaluated. In addition, examples of simple planar and conformal antennas are provided to demonstrate how this technique can influence current and future microelectronic device applications.

Possibilities of the control of the size and size distribution of the colloidal gold particles produced by the 110-fs laser ablation from a gold plate in aqueous environment are studied. Compared to pure deionized water, significant reduction of the mean size and size dispersion of the produced particles was observed when the ablation was performed in aqueous solutions of cyclodextrins (CDs), while the efficiency of the size reduction depended on the concentration and type of the CD (α-CD, β-CD or γ-CD). In particular, ablation at 10 mM of β-CD led to a production of 2-2.4 nm particles with narrow size distribution of less than 1-1.5 FWHM, which were very stable under aerobic conditions without any protective agent present. In the UV-vis spectrum, the gold nanoparticles exhibited an absorption band at 520 nm due to the generation of plasmon resonances. The fabricated particles are of importance for biosensing applications.

A semi-continuous process for the synthesis of fullerenes is described. This novel process incorporated a carbon powder feed system in combination with a continuous-wave CO₂ laser irradiation source. The carbon powder contained no fullerenes but did contain graphite crystals and amorphous carbons of selected particle sizes (5, 10, or 20 μm), and selected irregular or spherical particle shapes. The method was successfully used to deposit C₆₀ and C₇₀ powders and films continuously. Laser irradiation of the carbon powder produced an observable laser plume. The experimental results and mechanism for the process are discussed.

Laser manipulation technique was applied to patterning of single nanoparticles onto a substrate one by one in solution at room temperature. Individual polymer nanoparticles were optically manipulated to the surface of glass substrate in ethylene glycol solution of acrylamide, N,N'-methylenebis(acrylamide), and commercial radical photoinitiator. An ultra violet (UV) laser beam was focused to the nanoparticle, which led to generation of sub-μm sized acrylamide gel around the particle. The polymer nanoparticles were incorporated into the polymerized gel and fixed onto the substrate. A single gold nanoparticle was optically trapped and moved to the surface of the glass substrate in ethylene glycol. Additional irradiation of the UV laser light induced transient melting of the particle, resulting in its adhesion to the substrate. By the use of the present methods, arrangement of individual polymer and gold nanoparticles on any pattern was achieved.

Germanium wafer surface is modified by a technique of CO₂-laser induced air breakdown processing, which was recently introduced and used to produce photoluminescent Si-based nanostructured layers. Structural and optical properties of the Ge-based layers, formed under the irradiation spot as a result of the processing, are characterized by different techniques (SEM, XPS, FTIR, XRD, and PL). It has been found that the layers present a porous structure, containing nanoscale holes, and consist of Ge nanocrystals embedded into GeO₂ matrices. They exhibited strong photoluminescence (PL) in the green range (2.2 eV), which was attributed to defects in GeO₂ matrix due to the presence of Ge-O modes with some OH vibration in the FTIR spectra. The layers are of importance for local patterning of nanostructures on semiconductors.

Absorption spectra of Ni nanoparticles in silica glass (SiO₂) fabricated by negative-ion implantation of 60 keV Ni to 4x10¹⁶ ions/cm² were determined from three sets of spectra, i.e., transmittance, reflectance of implanted-surface side and that of rear-surface side, of the same samples, to exclude incoherent multiple reflection (ICMR) due to substrates. Although the absorption spectrum of as-implanted state is smeared with defect absorption, two absorption bands at 3.3 and 6.0 eV due to Ni nanoparticles are observed after annealing at 800°C in vacuum. However, a predicted peak energy from a criterion for surface plasmon resonance (SPR), ε_m'(ω) + 2 ε_d'(ω) = 0, was in 2.8 eV, far away from the observed peaks. Another criterion, (ε_m' + 2ε_d')² + (ε_m'')² = minimum, gives the peak energy of 5.9 eV. From decomposition of the dielectric constants into free- and bound-electron contributions, we conclude that the 3.3 eV peak is SPR-like, although the contribution of the bound-electrons to the 3.3 eV peak is not small. Size dependence also supports the assignment of the 3.3 eV peak. The large contribution of the bound electrons is due to a nature of the partially filled 3d orbitals of Ni. This is contrast to the closed 3d orbitals of Cu, and probably is the origin of the broad peak width.

In this paper we discuss three optical methods for in situ characterization of single wall carbon nanotube (SWNT) growth by laser vaporization at elevated temperatures: optical absorption spectroscopy, optical incandescence, and light scattering. Optical absorption spectroscopy was successfully used to estimate the size of carbon nanoparticles and to monitor the atomic metal catalyst in the propagating laser ablation plume. These measurements indicate that the aggregation rate of carbon nanoparticles increases rapidly at lower oven processing temperatures. The second method, incandescence, was applied to measure the particle temperature within the propagating plume at different times after ablation. The third approach, imaging of the plume using Rayleigh scattered light, was used to monitor the ejected material inside the hot furnace as well as to observe the plume when it exits the furnace, i.e., in the cold zone of a quartz tube reactor. We demonstrated that Rayleigh scattering imaging combined with TEM analysis of the produced material was very useful for controlling the length of SWNTs and estimation of the growth rates. A general picture of SWNT growth by laser vaporization based on in situ diagnostics of ejected material at different times after ablation is discussed.

The first thin-film single-wall carbon nanotube (SWNT) composites synthesized by pulsed laser deposition (PLD) are reported. Ultrahard, transparent, pure-carbon, electrically-insulating, amorphous diamond thin films were deposited by PLD as scratch-resistant, encapsulating matrices for disperse, electrically conductive mats of SWNT bundles. In situ resistance measurements of the mats during PLD, as well as ex situ Raman spectroscopy, I-V measurements, spectroscopic ellipsometry, and field emission scanning electron microscopy, are used to understand the interaction between the SWNT and the highly energetic (approximately 100 eV) carbon species responsible for the formation of the amorphous diamond thin film. The results indicate that a large fraction of SWNT within the bundles survive the energetic bombardment from the PLD plume, preserving the metallic behavior of the interconnected nanotube mat, although with higher resistance. Amorphous diamond film thicknesses of only 50 nm protect the SWNT against wear, providing scratch hardness up to 25 GPa in an optically transmissive, all-carbon thin film composite.

Regular and tidy periodic structures hae been directly induced on glasses using a CW CO₂ laser beam with linear polarization. It is experimentally shown that precise periodic structures with the period of several microns can be formed by means of well-set laser parameters. The orientation of the periodic structures formed is the same as that of the laser polarization no matter what the scanning direction is. The occurrence of periodic structures is very sensitive to laser power level and scanning velocity. To obtain appropriate periodic patterns, a combined condition of laser energy and scanning velocity must be satisfied. The period, width and height of the structures are dependent on processing parameters. An interesting phenomenon is that the period decreases with increasing scanning velocity. Permanent relieves with periods, widths and heights varied with the laser parameters are also studied.

Iron-carbon composite nanopowders have been synthesized by the CO₂ laser pyrolysis of gas-phase reactants. The experimental device allows for a very low reaction time and a rapid freezing that creates nanoscale-condensed particles. Iron pentacarbonyl and ethylene-acetylene mixtures were used as iron and carbon precursors. In a two-steps experiment, the reaction products may present themselves as iron-based nanoparticles dispersed in a carbon matrix. By a careful control of experimental parameters and radiation geometries we demonstrate the feasibility of an efficient and well-controlled, single-step technique for the production of iron-based nano-cores embedded in carbon layers. Highly dispersed nanoparticles, narrow size distributions and particles with about 4.5 - 6 nm mean diameters were obtained. Electron microscopy and Raman spectroscopy were used in order to analyze the structure and composition of the obtained nanopowders as well as their Soxhlet residue.