Laser assisted particle removal (LAPR) is a novel technique capable of removing particulate contamination from solid surfaces. LAPR uses an energy transfer medium which preferentially absorbs into capillary spaces under and around the particles on the contaminated substrate. Laser irradiation causes explosive evaporation of the energy transfer medium via absorption into the energy transfer medium itself or the substrate/particle system with subsequent conductive heat transfer. The explosive force propels particles off the substrate much like a small rocket engine. In our experiments, LAPR was used to remove 9.5 micrometers Al2O3, 5 micrometers Al2O3, and 1 micrometers polystyrene particles from Si surfaces at the wavelengths of 10.6 micrometers and 9.6 micrometers using water as the energy transfer medium. At these wavelengths the laser energy is absorbed predominantly in the water. Laser removal thresholds (J/cm2) were obtained using a degenerate threshold model. The temperature rise in the energy transfer medium was estimated, suggesting that superheating of the absorbed water is a reasonable mechanism for LAPR.

Pulsed laser heating of a surface is shown to be a promising new approach for effective cleaning of small particulate contaminations. Various versions of such a technique of laser cleaning is possible, depending on where the laser irradiation is absorbed and whether a thin film is deposited on the surface to enhance the cleaning. We have observed that laser cleaning with the highest efficiency can be achieved by choosing a laser wavelength (typically ultraviolet) that is strongly absorbed by the surface, and by pulse-depositing a water film of thickness on the order of microns on the surface momentarily before the pulse laser irradiation. This permits the effective removal of particles smaller than approximately equals 20 micrometers , down to as small as 0.1 micrometers , from a solid surface, using a modest ultraviolet laser fluence of approximately equals 0.1 J/cm2.

Excimer laser ablation of multi-layered films was studied using the photoacoustic mirage effect technique. Layered systems of a polymer-metal-SiO2 type was investigated for various metals between 0.5 and 2 J/cm2. Significant changes in the deflection signal were found when the ablation passed the interface between subsequent layers. This effect can be used to distinguish between different materials and is therefore suited for an in situ control of pulsed laser processing.

248 nm excimer laser ablation of a polyurethane polymer is shown to proceed efficiently and with a surprising lack of post-ablation surface debris. The absorption spectrum of this material displays a strong increase in absorbance beginning at 260 nm and extending to shorter wavelengths, whereas a relatively weak absorption for longer wavelengths accounts for the inability of 308 nm excimer radiation to cause efficient ablation. Ablation rate versus incident fluence data were obtained by both conventional stylus profilometry and the higher precision quartz-crystal microbalance (QCM) method. The data from both methods were in agreement, although the QCM technique provided far more detail of the threshold region. Interestingly, near 35 mJ/cm2 incident fluence, a pronounced increase in the slope of the rate versus fluence curve appears. This is suggestive of a mechanistic change from a lower to higher efficiency ablation regime. Applying a conventional Beer's Law analysis of rate versus In(fluence) yields a straight line that agrees well with the data up to 300 mJ/cm2. In face, the absorption coefficient derived from the slope of this curve is within 4% of the experimentally determined low-level value.

Fully integrated excimer laser mask macro and microprojectors and application workstations that produce on the workpiece illumination uniformities as low as +/-5% with overall energy throughput efficiencies of up to 70% are described.

Up to now, copper vapor lasers (CVLs) have been mainly applied in the field of nuclear fuel enrichment, as illumination sources, in short time photography and in medical applications. Due to their interesting characteristics (short pulse duration, high repetition rate) these lasers might also become useful in the field of materials processing. In this paper recent investigations on the drilling behavior of different metals with a CVL are reported. Fine drilled holes in thin metal sheets with minimized heat affected zones could be obtained. Microscopical investigations were used to characterize the influence of different substrates and processing conditions.

Rapid manufacturing of free-form solid objects from CAD designs can be accomplished by the process of Selective Laser Sintering (SLSTM) introduced by DTM Corp. Prototype construction by the process of Selective Laser Sintering consists of slicing a prototype CAD design into multiple layers, and building a prototype by selectively sintering corresponding layers of powdered material and thermally fusing all the layers to make the final part. Selective sintering on a given powder layer involves delivering thermal energy to the powder in localized spots that are dictated by the corresponding layer of the sliced CAD representation of the part. The localized thermal energy delivery results in localized powder sintering which causes a solidification of the powder that matches the corresponding layer of the sliced CAD design. The powder layer thickness and the thermal energy delivery are matched so that the thermal penetration causes binding of each layer to the previous one. A powder feeding mechanism provides the successive powder layers as required, and an oven chamber is used to bring the powder to a preset thermal level to minimize the localized thermal energy delivery required for local sintering to occur. The incremental localized thermal energy is delivered by a scanned CO2 laser beam.

In previous work we examined the particle emissions and changes in the surface topography of sodium trisilicate glass (Na2O(DOT)3SiO2) accompanying exposure to pulsed 248 nm excimer laser light. This material ablates readily over a wide range of fluences (> 2.6 J/cm2) after a fixed number of preliminary laser pulses (an incubation effect). The effectiveness of laser bombardment in removing material is strongly dependent on defects produced by high fluence 248 nm radiation. We show a dramatic synergism in the ablation process at sub-threshold and near-threshold fluences by simultaneous bombardment of the glass surface with 0.5 - 2 keV electrons and laser pulses. Similar results are obtained on single crystal NaCl, LiF, and UV grade fused silica. We attribute this effect to surface defects produced by the electron beam. A model is discussed involving surface and near-surface defects created by the electron beam which allow for single photon excitations of electrons to the conduction band and subsequent free-electron/laser heating. Preliminary results with MgO suggest that certain impurities can have the opposite effect by trapping electrons at defects from which single photon absorption does not yield conduction band electrons. This reduction in laser-material coupling may occur despite enhanced absorption at the laser wavelength. Thus the effectiveness of defects in enhancing laser-material interactions depends strongly on their ability to provide high cross section excitations to the conduction band. The potential of these effects in the control of laser-material interactions in optical materials and in laser processing of materials is discussed.

The behavior of the reflectivity of a Si single crystal during irradiation with two successive Nd:YAG pulses is investigated with ns resolution. The first pulse melts the surface, and therefore the reflection coefficient increases to the value of the metallic liquid at the melting temperature. Upon further heating of the surface with the second pulse, we observe a decrease of the reflection coefficient, resulting from the temperature dependent dielectric function of the molten Si. The largest decrease in the reflectivity that could be reached before damaging the surface amounted to 9% for both wavelengths 633 nm and 488 nm.

Due to imprecisions in the deposition process, linear semiconductors require post-production circuit adjustment. Lasers are used to adjust (or trim) thin film resistors to precise electrical performance specifications. The effect of coherent laser beam interference in multilayer structure on thin film resistor trimming has been well documented. As the layer structure becomes more and more complex, the difficulty in determining the interference effect on the trimming results becomes greater. To assist the circuit designer and laser trimmer user, a simplified multilayer thin-film resistor interference model and a universal software program have been developed. Several verifications have been made of customer designs using the model and software programs. While the model gives the user a clear picture of the physics of the interference effect, the software provides a precise recommendation for layer structuring that results in maximum laser absorption into the resistor.

Defect characterization of epitaxial silicon films grown on lightly boron-doped Si (100) substrates by low temperature photo-enhanced chemical vapor deposition (PCVD) using 193 nm ArF excimer laser dissociation of Si2H6 in an ultra-high-vacuum (3 X 10-9 Torr) chamber is discussed. A factorial design of experiments was used to investigate the dependence of crystallinity and growth rate on laser intensity, Si2H6 partial pressure, substrate temperature, and substrate-to-laser-beam distance. PCVD of Si was achieved in two ways: with the laser passing parallel to the substrate or directly incident on it. For parallel laser incidence, epitaxial films were achieved at temperatures as low as 250 degree(s)C with controllable deposition rates of 0.5 approximately equals 4 angstroms/min. using photon flux densities of 1015 photons/pulse.cm2, and Si2H6 partial pressure of 20 mTorr. The growth rates were observed to be linearly dependent on laser power. For direct laser incidence, single crystal films with a growth rate of approximately equals 20 angstroms/min. were obtained at a photon flux density of 7 X 1014 photons/pulse.cm2 at 300 degree(s)C and 20 mTorr Si2H6 partial pressure. The growth rate were found to be linearly dependent on photon flux density also. The crystallinity was studied by in situ reflection high energy electron diffraction (RHEED), and selected area electron diffraction in a transmission electron microscope (TEM), and defects such as stacking faults and dislocation loops were investigated by TEM and dilute Schimmel etching/Nomarski microscopy.

Low temperature silicon epitaxy has been achieved at substrate temperatures ranging from 250 degree(s)C to 350 degree(s)C using the 193 nm output of ArF excimer laser to generate reactive growth precursors by photolytic decomposition of Si2H6. Growth rate dependencies on substrate temperature, Si2H6 partial pressure, laser photon flux density, and beam-to-substrate distance are presented. A simple expression for the growth rate as a function of process parameters can be obtained by considering the single-photon absorption rate of Si2H6 at the ArF excimer laser wavelength of 193 nm, and the gas kinetic transport of the resulting photofragments to the substrate surface. With the beam tangentially positioned approximately 1 mm from the substrate, a large percentage (7 +/- 1%) of the silicon available from the excited Si2H6 contributes to film formation. As the beam is moved away from the substrate, the chemical reaction rate of the growth precursors becomes significant with respect to the diffusion rate and the growth rate is observed to decrease. By tilting the laser beam to provide a normally incident component striking the substrate surface, the dangling bond density of the surface can be increased by photon assisted H desorption and growth rates are observed to increase. At substrate temperatures less than 400 degree(s)C, the growth rate is weakly dependent on temperatures with an activation energy of approximately equals 0.05 eV, whereas for temperatures above 400 degree(s)C, film deposition becomes dominated by pyrolytic decomposition of Si2H6 with an activation energy of approximately equals 1.2 eV.

A new approach to drilling GaAs substrate vias in a production environment is described. Rapid drilling of vias in thinned wafers has been achieved with a frequency doubled Nd:YAG laser. A description of the equipment, laser parameters, and process is given. Production results are also shown.

Laser chemical vapor deposition (LCVD) of gold has been used to repair 'open' defect on high-end multi-chip packaging modules. The ability to repair metallurgical features of less than 25 micrometers width was readily accomplished and electrical resistances are comparable to resistances of unrepaired nets of identical geometry. The reliability of LCVD repairs was monitored after thermal processing, T&H and electrical stressing. The ability to repair 'open' defects in the thin-film redistribution (TFR) layer of the module has facilitated testing of designs early in the development process.

A process for fast personalization of multi-chip modules has been developed. Multilayer substrates with an incomplete top layer are prefabricated. Substrates are personalized within a few hours, using a frequency doubled Nd:YAG laser. 50 ns pulses with a pulse energy of 0.3 mJ are used for cutting. The same laser is also used for the direct writing of spot links, by decomposition of copper formate films with pulses of only 0.2 (mu) J at a repetition rate of 100 kHz. A detailed description of the applied copper formate technology is presented here.

Lasers are being used for a wide range of applications in the microelectronics and packaging industries in such diverse applications as etching, film deposition, repair of open circuits and short circuits, machining and trimming of components, and heating of solder connections. In these applications, the laser radiation is primarily used as a heat source, to melt, ablate, or otherwise alter a material through a thermal process. The use of a laser under these conditions can often lead to damage to the surrounding layers or underlayers, which is particularly important when the laser is not well controlled and when the surrounding layers are thermally sensitive. The development of high-performance wiring for greater wiring density and smaller signal propagation delays has placed greater emphasis on the control of laser-initiated thermal processes. The thin film metal patterns produced in IBM's packaging programs can be used in a wide variety of metal/insulator structures. Although the metallurgies are typically copper based, the choice of insulator materials can vary, with structures produced with both inorganic (glasses and ceramics) and organic (polymers) dielectrics. Several laser-based technologies have been developed at IBM, establishing the capability to modify fine line circuit patterns on the range of packaging materials. These modification techniques, either to repair defects created during the manufacturing process or to restructure the circuit for design and performance reasons, can be achieved with the proper control of the laser conditions. This ability to control the laser/material interaction, with the goal of successfully modifying the circuit without adversely affecting the integrity of the dielectric will be discussed. The applications of these techniques to IBM's thin film packaging will be described, with specific focus on the two technologies recently introduced for the manufacture of East Fishkill's new high end packaging products.

ICs interconnection networks can be locally modified using a tightly focused laser beam to induce chemical reactions on the circuit surface. Owing to the precursor used, conductors and insulators can either be etched or deposited within the laser spot. Bertin & Co. have recently developed a line of laser-assisted tools dedicated to VLSI prototypes rewiring. This paper summarizes the tests performed on various technology devices from major IC manufacturers: IBM, STM, and Texas Instruments. The different repair steps and results of the characterization tests are presented.

A laser heating process was used to form structures which facilitate tape automated bonding (TAB). Uniform metal spheroids were created by melting the end of each TAB conductor intended for connection to the terminal pads of an integrated circuit (IC). A fully automated laser tool designed and built to fabricate these structures is described. Results for ICs bonded using this technology are presented.

The conventional thermo-compression bonding processes for bonding tape-automated-bonding (TAB) leadframes to silicon die has inherent reliability drawbacks due to the high pressures and temperatures necessary to produce a good metallurgical joint. Whether tin- or gold-plated tape is used, the bonding process can cause damage to the underlying structure of the device which results in device failures. The use of a laser source for inner lead bonding (ILB) has the advantage of providing a very localized temperature input to the bonding site with minimal contact force. The resulting mechanical stresses on the device are consequently low and the overall temperature extreme to which the device is subjected is similarly low. Advanced Micro Devices, Inc., has undertaken a program to qualify a gold/tin laser bonded ILB process as a viable manufacturing alternative to thermo-compression bonding. The initial evaluation has defined thresholds for laser input energy necessary to produce a good fillet around the TAB beam and a void-free interface. This is the first necessary step to provide the degree of gold/tin alloying necessary to prevent Kirkendall voiding during subsequent high temperature storage. Among the parameters critical to the bonding process is the wafer bump surface topography. The quality of the bonding process has been monitored using bond strength data and visual examination before and after high temperature storage and temperature cycling tests. The test samples used were 154 and 160 lead production TAB tape and device designs with approximately equals 200 (mu) lead pitch and a 410 lead experimental tape with 102 (mu) lead pitch.

Up to now, lasers have been well established in the field of materials processing for cutting, welding, and surface treatments. Recently, lasers in the medium power range have been of increasing interest in the production of electronic components. Higher integration density of electronic circuits demands improved mounting technology. Due to the reduced contact area of modern surface mounted packages, more sophisticated soldering systems are required to ensure product quality. Standard reflow soldering techniques may damage thermally sensitive devices, and mechanical tensions in the solder joints will occur, due to different thermal expansion coefficients. These problems can be avoided using a laser, as the amount of heat induced into the component is very small. Another advantage is the step-wise heat input resulting in a minimal overall thermal loading of the device and the possibility to control individually the heatflow for each solderjoint. In some applications lasers are the only reasonable tool, e.g., repairing printed circuit boards (PCB) produced in surface mounting technology or soldering of three dimensional PCBs. To improve quality and productivity of laser soldering tools, the time required for melting and wetting has to be minimized in the same manner as defective solder joints should be detected online. There are some commercial laser soldering systems available, using different types of process control, e.g., pyrometrical temperature measurement, detection of the reflected laser beam energy, or evaluating the sound emission while melting the solder with a pulsed laser. To obtain certain time- temperature curves, an analogous regulation of the beam power is required. Therefore a pyrometer offers the best approach to get optimal thermal input, even if the measurement is difficult due to complex geometry and unknown emissivity of the surface. This paper outlines the behavior of the solder paste under irradiation of different wavelengths and the possibility of controlling the solder process via the above mentioned setup.

The drive towards miniaturization in electronics assembly has produced new devices with small lead pitch and high lead count which are difficult to bond reliably to substrates using conventional mass soldering technology. Micro-soldering using lasers has the potential to solve many of the problems involved. The results of Nd:YAG laser soldering trials on a ceramic chip with Kovar leads spaced at 0.025 in. are described. The results are compared with the predictions of a detailed finite-element thermal model of the systems and also with real-time thermocouple measurements of the temperature reached at specific locations during the soldering step. Implications for future work in this area are discussed.

In this paper, the ablation processes were investigated using light deflection spectroscopy as a detection method. The cumulative effect of PMMA near the ablation threshold was studied in detail, and the cutting-edge quality of photoablation was improved to some extent by a nitrogen gas stream.

The problem of tracking very small semiconductor products with a bar code is easily overcome by the use of the matrix symbol, which is a unique two-dimensional symbol that is the most space efficient method of packing binary data. It is both machine written and machine read to provide the utmost in accuracy and repeatability. The number of data cells can either be expanded or contracted to handle the required information and in addition can contain parity and error correcting codes. Semiconductor chips, wafers, substrates, modules and even masks can all be laser marked with this symbol and quickly read at any later stage of the manufacturing process. This unique symbol is computer generated by a software algorithm which creates the data cells and data frame which are laser etched on the product. On-line product identification yields immediate benefits in manufacturing such as inventory control, proper mating of parts, proper selection of test programs, quality control, etc. Use of a very small unique machine readable symbol now permits these benefits to be extended to miniature parts in an automated high speed manufacturing line.

Among the newly developed techniques for thin film processing and semiconductor device fabrication, the excimer laser is one of the most promising and powerful due to its usefulness for rapid thermal processing and surface microstructure modification. To date, its applications in microelectronics include deep UV lithography, metal deposition and reflow, process monitoring and diagnostics, laser repairing, and thin film processing including high temperature superconductor material synthesis and laser enhanced chemical vapor deposition (CVD). In this paper, the status of semiconductor device metallization using excimers laser will be reviewed, and recent development in texturization of polycrystalline silicon thin films, silicide formation, and maskless patterning using excimer lasers will be presented.

High-Ta superconducting Bi-Sr-Ca-Cu-O films on single crystal silicon substrates were prepared by laser induced plasma deposition. The stoichiometric change of cation concentrations of sintered target material to the thin film using a Nd-YAG and an excimer laser for the deposition is compared. Laser ionization and spark source mass spectrometry (SSMS and LIMS) were applied for the trace and cluster analysis of YBa2Cu3O and Bi-Sr-Ca-Cu-O ceramics.