Laser irradiation at 193 nm of multilayered Cl2 on an Si wafer cooled to 100 K leads to both photodissociation of Cl2 and formation of photoetching products.

We have investigated the reactions of neutral fluorocarbon fragments, generated by laser photolysis of suitable precursors, with single-crystal silicon and thermally deposited silicon oxide surfaces. CF3 free radicals are generated by infrared multiple-photon dissociation of C2F6. While CF3 undergoes dissociative chemisorption on Si, it adsorbs very little on annealed SiO2 surfaces, and even on ion-damaged oxide surfaces, CF3 adsorbs but does not undergo transfer of fluorine from the fluorocarbon to surface silicon atoms. CF2, produced by excimer-laser photolysis of C2F4, is adsorbed on SiO2 surfaces. As with CF3, no transfer of fluorine from carbon to silicon is observed, even after argon-ion sputtering or ultraviolet irradiation of the surface. These measurements have been extended to NF3; this species chemisorbs and dissociates on a silicon surface, but even a monolayer of oxide is sufficient to block this process. A simple model based on the relative strengths of C-F, N-F, Si-F, Si-C, Si-O, and Si-N bonds appears to account for the observed behavior of CF3, CF2, and NF3 species on silicon and silicon oxide surfaces. In other cases, however, a barrier appears to be implicated in the chemisorption process.

Resistless photoetching of SiC was performed by using XeF and KrF excimer laser beams. In this method, ClF3 gas was used for etchant. C1F3 gas has a unique absorption band in the range of 300- 430 nm. The strongest absorption band corresponds to the wavelength of the XeF laser (350 nm). So C1F3 gas is decomposed effectively. On the other hand, the absorption factor of SiC is about 30% in the range of 200-400 nm, and the bonding energy of SiC is lower than the photon energy of the KrF laser beam. For these reasons, it is possible to cut the bond of SiC directly. Thus, two laser beams were used. Fluence of the KrF laser beam was 200 mJ/cm2, of the XeF, 50 mJ/cm2. Total flow rates through the cell were 0.05 1/min. We can fabricated the etched feature of reticle pattern by reductive projection. Line and space was 10 μm and etching rate was 50Å/pulse.

The results of CW frequency-doubled argon-ion laser etching and pulsed excimer laser etching of lithium niobate (LiNbO3) are compared. Argon-ion laser etching occurs in the presence of Cl2 at laser intensities of 1.1 MW/cm2 or higher. The 257 nm laser beam with up to 25 mW power is focused to a 1.5 μm diameter spot and scanned at speeds of 10 μm/s or less. Excimer laser etching is done at 248 nm (KrF) with the laser beam focused onto the sample with cylindrical optics. Trenches <20 μm wide and several millimeters long are produced by ablating the target and without scanning the beam. Excimer laser etching of lithium niobate has been attempted in the presence of C12, O2, N2, H2 or air. Excellent results are obtained with air as the etching medium.

A quartz crystal microbalance (QCM) has been used to study the 248 nm laser-induced etching of nickel by Br2. The experiment consists of focusing a pulsed UV laser beam at normal incidence onto the surface of a quartz crystal coated with 1μm of polycrystalline nickel. Absolute etch rates of nickel, in terms of mass removed per unit time, are determined from the integrated sensitivity function of the 6Mhz crystals used in this work. The dependence of the etch rate on Br2 pressure and laser fluence was measured. The kinetic data obtained from these measurements show that the mechanism of the etching process is dominated by the formation and the subsequent removal of a NixBry monolayer.

Maskless etching of the composite structure of Mn-Zn ferrite and sendust (Fe-Si-Al alloy) was performed by focused argon-ion-laser irradiation in a CCl4 atmosphere and aqueous solutions. Only a mixture of KOH and NaOH aqueous solutions was found to smoothly etch the composite structure by thermochemical reaction using laser irradiation. A maximum etching rate of 14 μm/sec was obtained for sendust-on-ferrite substrates.

Maskless etching of single crystalline Mn-Zn ferrite in an H3PO4 aqueous solution by Ar+ laser irradiation has been investigated to obtain high etching rates and aspect-ratios of etched grooves. The etching processes have been found to be photochemical in a low laser power region and thermochemical in a high laser power region. High etching rates of up to 340 pm/s and an aspect-ratio of 50 for slab structures have been achieved. Periodic ripple structures have been observed under specific etching conditions due to the local surface melting.

Laser ablation using focussed excimner light has been found to be an effective technique for the direct, maskless patterning of High Tc superconductor films. The apparatus used in the work consists of an adjustable aperture which is illuminated by a 193 nm excimer laser beam. The aperture is imaged by a microscope onto the substrate into an area as large as 200 × 200 to an area as small as 2 × 2 square microns. The superconductor films are placed on a 0.5 micron resolution, computer controlled x-y stage. Laser fluences up to 5 J/cm2 and repetition rates of 10 Hz were found to be sufficient to ablate (pattern) the High Tc films with no apparent effect on their superconducting properties as evidenced by the films′ resistance as a function of temperature (R vs T) before and after patterning.

The technique and apparatus are flexible enough to allow patterning across entire substrates and/or the definition of isolated features as small as one micron. To date, the technique has been successfully used to pattern a wide variety of films (based on material and thickness), to fabricate transmission lines several millimeters long, to pattern superconducting quantum interference devices (SQUIDs) which operate at liquid nitrogen temperatures, and to study the behavior of individual grain boundaries within films.

A very high pressure-sampling mass spectrometer has been used to identify the vapor transport species and determine the thermochemistry and kinetics of laser-induced plumes produced from graphite and superconducting composition YBa2Cu3Ox targets (x = 6.5 to 7). An electron impact ion source was used for the ionization and detection of neutral plume species. The plumes initially contain -1 atm (1 atm = 101.325 kPa) of neutral and charged atomic and molecular species in a vacuum of <10−7 atm. Time resolved mass spectra were obtained with graphite targets for the neutral plume species Cn (n = 1-9) for varying laser fluence, laser-surface interaction geometry, vapor plume-sampling geometry, and target surface morphology. Relatively low abundance charged species C1+, C2+, C3+, and impurities Na+ and K+ were also observed in the laser-induced plume.

Mass spectra obtained with superconducting YBa2Cu3Ox targets showed a variety of species in the laser-induced plumes including both neutral and ionic Y, Ba, and Cu. In addition, molecular species such as O2, BaO, CuO+, YO and bimetallics (BaCu, YCu) were observed.

At laser threshold fluences near ion product formation, we have measured the ejected ion kinetic-energy distributions from the UV laser ablation of crystalline aluminum and silver targets. The mean kinetic energy is found to be hyperthermal.

Dynamical characteristics of laser desorption and chemical processes in Group IV elements have been investigated by means of space/time resolved optical spectrometry in micrometers and nanoseconds scale on the light emitted from desorbed particles. The results suggest that desorbed atoms are coagulated in the form of large size clusters in a few ns after laser excitation. These clusters subsequently decompose into their ultimate forms of monomers. This interpretation is consistent with the conclusion drawn from our time-of-flight analysis of decomposition in 100 ns time scale.

Pulsed laser irradiation at 248 nm can ablate Si atoms from an Si wafer. The mechanism of this photoablation has been examined by laser-induced fluorescence analysis of the Si products. The Si atoms are measured to leave the wafer surface with averaged translational energy of 2.5 kcal/mol. The distribution of translational energy is well described by the theoretical model for non-cascade ablation processes.

Experiments on the ablation of undoped polytetrafluoroethylene (teflon), monocrystalline sodium chloride (NaCl) and polymethyl-methacrylate (PMMA) with 300 fs uv excimer laser pulses at 248 nm are reported. In contrast to standard 16 ns excimer laser pulses, these ultrashort pulses ablate essentially uv-transparent materials, heretofore not accessible to clean ablation, with good edge quality and no signs of thermal damage, with removal rates are on the order of one micrometer per pulse.

We examine effects resulting from the irradiation of glassy sodium trisilicate (Na2O 3SiO2) with 248 nm excimer laser light at fluences from 1–5 J/cm2. We observe a threshold for the onset of etching of the surface at 3 J/cm2. We present SEM images of the resulting surface topography under etching conditions as well as recent measurements of the particle emission and photon emission from atoms leaving the surface region. A clear correlation is observed between this etching threshold and a) onset of emission of fast excited neutrals, as well as b) the appearance of atomic Na D resonance radiation emitted from particles up to several cm from the surface. We also present identifiction of the emitted positive ions.

A study of laser-induced reactive evaporation-condensation is presented. This considers coevaporation of metallic, and non-metallic species, by a cw carbon dioxide laser beam, within a reducing environment (98.5% hydrogen, 1.5% methane). A heated W filament placed in proximity of the laser beam-substrate interaction zone produces W for deposition via chemical vapor transport reactions. Composite thin films of a W matrix containing amorphous silica fibers have been deposited on nickel alloy substrates. These films form at rates of about 1 micron/sec, and are found to be adherent to the substrates. The diameter of the fibers is between 25 nm and 120 nm, depending on the interaction time. Various analytical techniques have been employed to characterize as-synthesized layers. Mechanisms of this process are discussed.

Tactile sensors and ultrasonic transducers based on the piezoelectric properties of polyvinyledene difluoride, PVF2, usually take the form of thin 10 - 110 μm polymer films coated on one or both sides with a metallic film. Electrode patterns are usually fabricated by photolithography that requires a 90 °C baking process which may harm the piezoelectric properties of the PVF2 film. We have developed an alternate method, based on direct patterning with a XeCl laser, yielding complex patterns of lines as narrow as 20 μm which are better than those fabricated by photolithography. The metallic film is ablated on both sides of the polymer while maintaining the intrinsic properties of the PVF2. The ablation mechanism is investigated using transmission optical, scanning electron, and scanning acoustic microscope images. The performance of an ultrasonic transducer fabricated with this technique is described.

The dependance on the pulse width of the ultraviolet laser ablation and etching of poly(methyl methacrylate) was examined using 40-100 ns pulses. These pulses were created by stitching together two identical pulses, each of 40 ns half-width, which were separated by a set time interval from 0 to 380 ns. The etch depth/pulse is sensitive to the pulse width and, therefore, the power density in this polymer.

The response of PMMA to etching by pairs of pulses suggests that short-lived species which may be electronic states (e.g., triplets) and/or radicals play an important role in the ablation. The shape of the pulse was also found to influence the etch depth/pulse.

The etching of polyimide by these extended pulses shows trends that are opposite to those observed in poly(methyl methacrylate). In this instance the shielding of the latter portion of the incoming pulse by the products that are ablated by the front portion is probably a serious effect.

The ionic products from excimer laser photoablation (λ = 308 nm) of polyimide (Kapton) film have been studied as a function of fluence. Large ion masses up to about 900 a.m.u. are easily observed, the mass distribution depending strongly on the fluence. Velocities of the emitted particles lie between 1400 and 10000 ms−1, again dependent on the fluence. A mechanism to explain the high velocities is suggested consisting of ionisation of the surface polymer molecules followed by a Coulomb explosion combined with expansion of the high density gas formed by the photoablation.

The reaction of oxygen with silicon induced by intense photon beams at different wavelengths is described. We find different enhancement rates applying to UV and visible radiation, which can be as high as 400% for thin film growth at low temperatures. Often, however, they can be so small that they may be completely overshadowed at high temperatures by the rapid oxidation rates arising from thermal contributions. By using UV radiation projected through a mask to induce low temperature photonic oxidation of silicon, we have grown directly patterned oxide structures dispensing with the need for conventional photolithographic etching.

We have investigated the formation of polycrystalline TiN and amorphous TiNxOy films using laser physical (LPVD) and laser chemical (LCVD) vapor deposition techniques. The LPVD method involved the ablation of a TiN hot pressed pellet and Ti in the presence of nitrogen plasma using nanosecond XeCl excimer laser pulses (wavelength 308nm, pulse duration 45×10−9 seconds, and energy density ∼4-5 Jcm−2). The films were polycrystalline (average grain size ∼100Å) with face-centered-cubic structure and lattice constant of 4.25Å. The average grain size remained constant as the substrate temperature ranged from 25 to 550°C. In the LCVD method, a pulsed CO2 laser beam was used to crack TiCl4 and NH3 and form TiN films. Amorphous TiNxOy films were formed under poor vacuum conditions in the LPVD techniques. These amorphous TiNxOy films often exhibited explosive recrystallization with characteristic star patterns. Resistivity and microhardness measurements were made on these films and these results have been correlated with microstructure and chemical composition.