Oxygen plasma treatment was performed on the excimer laser annealed poly-Si surface, followed by gate oxide deposition with low pressure chemical vapor deposition (LPCVD) in order to control the threshold voltage of excimer laser annealed poly-Si thin film transistors (TFTs).

Threshold voltages of n-channel TFTs increase from 0.4 to 2.8 V by varying the treatment time from 0 to 7 min. It is shown the effective charge density increased toward negative direction with increase of the treatment time.

In addition to the increase of threshold voltage, the oxygen plasma treatment on the Si surface led to an increase in the deposition rate of LPCVD oxide films with an apparent reduction of carbon around the interface between gate insulator and poly-Si film after oxygen plasma treatment.

A study of laser annealing of a-SiC:H films was carried out in order to obtain poly-SiC films. First, a-SiC:H films were fabricated at temperatures ranging from 30 to 400 °C. All these films show amorphous structure before the annealing process. After annealing by a single pulse of 248 nm laser, films show poly-SiC structure. The pulse energies used for these anneals varied from 30 to 300 mJ/pulse. After exposing to a laser pulse, the a-SiC:H films melt and recrystallize forming poly-SiC structure. In addition to this process, a fraction of the film is observed to be vaporized. This vaporized fraction depends on the original film composition, hardness and the laser pulse-energy. Electrical resistivity of the films before the annealing process lies in the region of 1015 Ωcm. This resistivity drops drastically after the annealing process.

Structural transformations induced in amorphous Ge films by picosecond laser pulses are studied by means of Raman spectroscopy and their dependence on parameters like the pulse fluence or the thermal conductivity of the substrate are analyzed. A correlation length model is used for studying the crystallization process, while the average bond angle distortion is used for determining the state of relaxation of the amorphous phase. Silicon and glass substrates are compared.

The state of relaxation of amorphous Ge films has been modified upon melting and rapid solification induced by irradiation with ps laser pulses. The material obtained upon irradiation with fluences sligthly above the melting threshold is less relaxed than the as-deposited one (de-relaxation process). For larger fluences the results obtained suggest that the degree of relaxation is related to the supercooling achieved prior solidification.

Effects of ultraviolet (UV) laser irradiation on the local crystal structure have been investigated for amorphous Ti-O thin films sputtered on ST-cut quartz substrates. The irradiation was conducted with a pulsed KrF excimer laser of 248nm in wavelength. There were few changes in the optical transmission spectra of the films before and after the irradiation. The crystal structure of the films was characterized by electron diffraction, XPS and EXAFS analyses. The results obtained from these analyses suggest the films gradually crystallize to a TiO2 crystal with the rutile type structure by the increasing of the laser pulses.

In this paper, we report on a new excimer-laser crystallization (ELC) method that is highly effective in extending the super-lateral growth (SLG) distance and which does not involve any preheating of the substrate. The technique utilizes bi-directional irradiation of a dual layer Si film stack (separated by an oxide layer) deposited on a quartz wafer. The top layer is irradiated with a projection system which transfers a mask image in order to produce grain-boundary-location-controlled (GLC) regions, and the bottom layer, upon irradiation with a uniform beam, acts as a medium that favorably affects the thermal evolution of the top layer. The technique is effective and attractive in that the heating is spatially and temporally localized in an optimal manner. The thermal environment required for extending the SLG distance, as is induced by the melting and solidification of the bottom layer, is physically regulated by the melting temperature of Si, and the enthalpy difference between liquid and solid can be used to initially store and subsequently release heat. Using the method, we were able to attain GLC regions with widths up to 10 μm in 1000-Å Si films without any substrate heating. We elaborate on the applicability of the method to various artificially controlled super-lateral growth (ACSLG) techniques, and discuss process optimization by means of varying the multilayer configuration.

Based on the artificially controlled super-lateral growth approach, we have developed a novel excimer-laser-based high-substrate-temperature method for producing single-crystal Si islands on SiO2. By irradiating a photolithographically preconfigured sample, complete melting of an Si film is induced only at precisely predesignated locations within patterned and physically isolated islands. An intentionally incompletely melted section within each island initiates lateral growth of crystalline grains. A “bottleneck” portion of the island permits only one of the laterally growing grains to propagate into the main portion of the island. The low nucleation-to-growth-rate ratios that are attainable with high substrate temperatures (1000–1200 °C) can lead to nearly unlimited lateral growth distances; with a proper combination of the substrate temperature and the island dimension, the main area of an island—up to 50×50 μm2 in area—is readily converted into a large single-crystal region.

We have developed a two-dimensional numerical model of excimer-laser melting and solidification that properly takes into account the non-equilibrium and transient nature of the process. The model incorporates a novel explicit finite difference scheme for efficiently solving the heat conduction equation and an algorithm that incorporates the interface response function for properly simulating the evolution of phase domains. The model provides space- and time-resolved information regarding the thermal profile and phase domains from which nearly all of the important solidification details can be extracted (e.g., interface location, solidification velocity, interfacial undercooling, etc.). For the simple partial-melting-and-vertical-regrowth scenario, results from the model converge with the results from the well-established one-dimensional model. As a result of its two-dimensional and non-equilibrium formulation, which also respects the amorphous and inert nature of the underlying oxide surface, the model is unique in its capability for properly simulating those solidification scenarios that involve extensive lateral growth of solids, as for example those behind the super-lateral growth phenomenon and various artificially controlled super-lateral growth processes.

Thin films of gold, copper and iron deposited on silica were driven into the substrate by a laser pulse. This transport takes place only when the irradiation is performed at a laser energy density of 0.7 J/cm2 or lower. Cross sectional transmission electron microscopy (TEM) of the irradiated specimens reveals two distinctive stages in the encapsulation process. In the first, the film melts and clusters into small particles and in the second one the particles are driven into the substrate by the laser pulse. The particle size of encapsulated metal varies from 5 to 50 nm. Selected area diffraction of the large particles and lattice fringe images of the smaller particles reveal pure metals, e.g., gold, copper or iron. Titanium films laser irradiated are not encapsulated in silica; instead, these films react with silica forming an amorphous compound. Apparently, one of the conditions required for encapsulation is that the metal should not react with the substrate material. On subsequent irradiation at a laser energy density of 1.5 J/cm2, ablation of silica partially exposes the metallic particles. Strong bonding between a new film deposited after irradiation and the substrate is obtained because these particles anchor the freshly deposited film. Anchoring is clearly revealed by cross sectional TEM. The mechanisms of encapsulation are discussed using results from TEM and adhesion testing.

Laser-induced chemical etching of Ti in phosphoric acid has been investigated using cw Nd:YAG (1.064 μιm) and Argon lasers (514 nm) operating in the fundamental Gaussian mode. Two different regions of etching were observed, which are separated by a characteristic threshold value of the laser power and ascribed to melting of the metal. Below the threshold an exponential dependence of etch rates on laser power suggest a thermally activated etching mechanism. Time-resolved measurements indicate in this region the dissolution of the passivation layer followed by surface etching of the metal grains. After laser illumination an immediate repassivation of the re-cooled surface stops the etch reaction.

The formation of periodic patterns on fullerite thin film surfaces is observed after irradiation with a pulsed Nd:Yag laser (1064 nm). C60 disruption and subsequent coalescence of the fragments take place, resulting in the formation of carbon nanotubes and polyhedral hollow graphitic particles. The effects of irradiation have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman scattering.

We report a systematic study of laser-controlled etching behaviors of AlxGa1−xAs epitaxial layers (x from 0 to 0.5) by varying parameters such as laser power, beam scanning speed, beam duty cycle, number of scans and different doping types and concentrations. The laser source was an argon ion laser emitting at 514.5 n-type layers were found to be significantly higher than those for p-type layers. Generally, higher etch rates were observed for layers with higher aluminium mole fraction. The etch rate was found to increase at an exponential rate with the laser power for CW beam, but this increase became linear when a chopped laser beam was used. The dependence of etch rates on different conditions can be largely accounted for by the differences in the built-in electric field at the surface as well as differences in the laser-induced local temperature rise in the layers.

The removal of particles as small as 0.1 μm was achieved using a pulsed CO2 laser to induce the explosive vaporization of condensed water. The surfaces used were hydrophilic oxidized silicon. The contaminant particles were 0.1 μm alumina, 0.1-0.2 μm fumed silica, and 0.1 μm polystyrene latex; their zeta potentials in water vary from positive to negative. The effect of the laser beam energy flux on the cleaning efficiency was thoroughly investigated. It was varied between 0.5 and 3 J/cm2. Whatever the nature of the contaminants, the cleaning process was characterized by an upper limit, the surface damage threshold energy density, determined to be 1.5 J/cm2. If the removal efficiency drops for the lowest beam energy flux, i.e., 0.5 J/cm2, and 0.1 μmAl2O3 particles, no single, sharp removal threshold was observed. Another parameter of importance investigated was the thickness of the condensed water. It was varied by changing the time of exposure of the substrate surface to water vapor before laser irradiation, the vapor flow being fixed to 4700 ml/min. Exposure times ranging from 1.5 to 2.5 s were evaluated to be the most effective.

Light emitting silicon has been prepared by Ar laser (514.5 nm) induced stain etching and Nd:YAG impulse (532 nm) laser irradiation in air. Photoluminescence (PL), IR and XPS spectra have been studied. The intensity and position of the PL depend on the power or the energy and the duration of laser beam treatment during the etching. Correlation between the PL and chemical bonding is discussed.

Laser-assisted dry etching ablation (LADEA) has been reviewed with an emphasis on its applicability for the microstructuring of III-V semiconductor compounds. The method is based on the application of an excimer laser ( λ= 308 nm) for pulsed heating of a wafer which is placed in a stream of Cl2/He gas. Both the products of chemical reaction and the depth to which a laser-induced reaction takes place depend on laser fluence. This makes possible the ablation of a well defined volume of the material. Little or no structural damage to the surface is observed because ablation is carried out with laser fluences below those required to melt the matrix material. The laser fluence dependence of the etch rate indicates that the process is primarily temperature driven with a characteristic energy for desorption. We have investigated LADEA as a method for in-situ processing of III-V semiconductors and the fabrication of nanostructures. An atomic force microscopy study has shown that atomically smooth surfaces can be obtained if the etch rate is near 1/2 atomic layer per laser pulse. The lateral resolution of LADEA has been found to be at least 20 nm. This, as well as the results of in-situ photoluminescence and Auger electron spectroscopy measurements, indicate that LADEA can be used for the direct (photoresist-free) fabrication of high quality microstructures and, ultimately, for the nanostructuring of III-V semiconductor compounds.

The surfaces of Al2O3 and AlN are modified by pulsed-laser irradiation This modification promotes the deposition of copper when the irradiated substrates are immersed in an electroless bath. In this paper the nature of the surface modification is analyzed using results from Auger Emission Spectroscopy (AES) and Cross Sectional Transmission Electron Microscopy (XTEM). During irradiation AlN thermally decomposes leaving a discontinuous metallic film on the surface. A film of Al2O3 is detected at the surface of the irradiated AlN substrate, much thicker when the irradiation is performed in an oxidizing atmosphere than when done in a reducing one. Nanoparticles of metallic aluminum are generated during laser irradiation of Al2O3 in a reducing atmosphere. When the irradiation of Al2O3 is performed in an oxidizing atmosphere, regions containing aluminum or substoichiometric alumina are detected by AES. It is concluded that the presence of metallic aluminum is the main reason why electroless deposition can occur in both AlN and Al2O3. Deposition kinetics are completely consistent with this conclusion. It is very likely that also substoichiometric alumina helps to catalyze the electroless deposition.

Sintered aluminium nitride ceramic is most attractive for applications in modern electronic packaging, due to its high thermal conductivity and its high electrical resistivity. Among the sintering additives which are mentioned in the literature, Y2O3 is used most often as sintering accelerator and densificator for AlN commercial ceramics.

Since excimer lasers have recently proved to be efficient in ceramic processing for industry, the effects of excimer laser irradiation on sintered Y2O3;rdoped AlN ceramic have been studied in this work. Raman spectroscopy, low-angle X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray analysis are used for characterizing both the initial and processed materials. The results reveal that yttrium-containing phases which are present at the AlN grain boundaries play an essential role in coupling the (λ =248nm) excimer laser beam with sintered material. Moreover, the laser-induced decomposition of these pre-existing complex phases and the subsequent spinel-like formation upon autocatalytic copper (or nickel) deposition are associated with (and explain) the excellent adhesion of the so-formed metal layer onto the ceramic substrate.

Excimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V, high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy. Hardness and modulus were not significantly affected by the treatment, but friction in dry sliding against an alumina pin was reduced. The reduction was small but persistent for multiply melted and resolidified surfaces. These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately 1,000 cycles, indicating wear-through of the modified surface. The observed properties will be discussed in terms of the excimer laser modification process and the microstructure and composition of the resulting surfaces.

This paper deals with a well known puzzling observation that wetting in some instances is improved by a chemical reaction between a liquid and a solid substrate in laser processing while in other systems just the opposite effect takes place. Here, contact angles of liquid Al on SiO2 and liquid Ti on Al2O3 are reported and some results of laser melt injection of SiO2 particles into molten Al.The surface and interface structures were explored by scanning electron microscopy and energy dispersive X-ray spectrometry. According to the experimental observations, it appears that the volume change of ceramic substrates during reaction plays a key role in the effect of chemical reaction on wetting.

Photochemical resistless etching was carried out by using a Xe2* excimer lamp and a KrF excimer laser. The decomposition method with Xe2* excimer lamp increases the decomposition efficiency by 100 times than that of using ArF excimer laser and etchant gas, CHClF2. Xe2* excimer lamp irradiation allowed decomposition of CHClF2 gas to produce CF2 radical with a small quantity of gas. The CF2 radical was polymerized to form fluorocarbon layer on the SiO2 substrate. Simultaneously, circuit patterned KrF excimer laser was vertically irradiated the fluorocarbon layer on the substrate for resistless etching. The etching depth was about 1,000Â.