The photochemical growth of polycrystalline and amorphous Ge films on SiO2, GaAs and NaCl by photodissociating GeH4 with excimer laser radiation in parallel geometry is reported. For substrate temperatures (TS) below the pyrolytic threshold for GeH4 (553 K), two distinct regions of film growth are observed. In the 425< TS < 553 K range, the ultraviolet (UV) laser “seeds” the reactor with Ge2H6 which readily pyrolyzes at the surface, forming several monolayers of Ge which subsequently catalyze the pyrolysis of GeH4. The activation energy (Ea) in this region is the same as that for the normal CVD growth of Ge from GeH4 (Ea = 0.9 eV). If, however, the laser is pulsed throughout the film growth run, Ea falls by a factor of at least 2 and growth is observed for TS as low as 300 K. In this laser sustained region, film growth ceases in the absence of UV laser radiation. These results clearly demonstrate the ability of a UV laser to alter the reactor chemistry and dictate the species responsible for film growth.

We compare, in this study, the photoassisted processes for silicon deposition using both a low pressure mercury lamp and an ArF excimer laser for the specific case where the SiH4 gas is sealed in the reaction chamber.

We present an experimental study and modelling of gas phase and surface processes involved in mercury-sensitized decomposition of SiH4, leading to hydrogenated amorphous silicon (a-Si:H) film deposition in a parallel plate reactor. The total surface reaction proabability β and the sticking probability s of SiH3 on a growing a-Si:H film are determined in the 40° – 350°C temperature domain. At 100°C β ≈ 0.1 ± 0.01 whereas s ≈ β/4 which reveals an intense radical recombination on the surface. Both β and s increase as a function of temperature. At 350°C β reaches 0.21±0.01. These results are interpreted by a precursor state model for SiH3 adsorption.

Amorphous silicon films were deposited by using silane molecular beams excited either by ArF laser beams or heated tungsten wires. Reaction mechanisms are discussed on the basis of the dependence of deposition rates on substrate temperature and, in the case of the heated-wire method, on wire temperature.

Atomic layer epitaxy (ALE) of GaAs by pulsed laser metal organic vapor phase epitaxy is reported. Suspension of Ga deposition at 100% coverage is an essential part of the growth mechanism for ideal ALE. This is achieved by a photo-catalytic decomposition of adsorbed trimethylgallium (TMG). Selective enhancement of the decomposition rate for adsorbed TMG on As, with no enhancement for that on Ga is the main reason for suspension of Ga deposition at 100% coverage. A decomposition rate for TMG on As which is about 100 times faster than that on Ga is estimated from a comparison between theory and experiment.

The growth of GaAs thin films from the excimer laser photolysis of trimethylarsine (TMAs) and trimethylgallium (TMGa) at 193 nm is reported. Scanning electron microscopy (SEM), electron channeling, Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM), and Auger electron spectroscopy (AES) were used to characterize the films. Incident laser fluences on the surface of 0.096–0.115 J/cm2 lead to carbon desorption, adatom mobility, transient annealing and hence epitaxial growth. However, TEM micrographs also revealed the growth of GaAs twins along the <110> direction in a novel periodic fashion, with a spacing equal to that of the ArF excimer laser wavelength (193 nm). Time-resolved mass spectrometry, used to determine gas-phase photolysis products created during the deposition process, showed that AsCH3 and higher gallium-alkyls are significant products which transport As and Ga to the surface.

Laser-assisted deposition of GaAs, AlAs and [AIGa]As thin films on Ge(100) substrates from trimethylgallium-trimethylarsenic and trimethylaluminumtrimethylarsenic Lewis acid-base adduct source materials is reported. A parametric study has been performed in which reactive gas pressure, substrate temperature, laser fluence, laser wavelength (248 nm or 193 nm). and orientation of the laser beam with respect to the substrate have been varied. In the case of irradiation parallel to the substrate, stoichiometric films of GaAs and [AIGa]As have been obtained. The data suggest that for irradiation perpendicular to the substrate a competition exists between desorption and photodeposition, which adversely affects film stoichiometry under the conditions studied.

An Ar+ ion laser has been used for direct writing of GaAs and GaAsP single crystal films on thermally biased GaAs substrates. Multiple scanning of the laser beam at speeds in the range 100–200 μm/s at carefully selected growth conditions resulted in single crystalline selectively deposited films. Photoluminescence indicates that these deposited films have optical properties that are comparable with the conventionally (MOCVD) grown material.Laser beam irradiation has been used to form a superlattice (SL) structure which has been demonstrated in the GaAsP-GaAs system. When a GaAs substrate is exposed to fluxes of AsH3, PH3 and TMG at 500°C, only GaAs will be deposited because of the insufficient cracking of PH3. However, localized laser heating results in GaAsP deposition. A GaAsP-GaAs superlattice with a period of about 400 Å has been synthesized. This laser induced technique can thus have potential applications in the generation of abrupt interfaces without the use of shutters as in MBE or gas switching as in MOCVD.

Room-temperature, optically-induced oxidation of the gallium arsenide surface has been studied with laser radiation of different wavelengths. It was found that deep-ultraviolet light is much more effective in enhancing oxidation than near-ultraviolet or visible light. The growth rate of the oxide was also found to be drastically increased by the presence of chemisorbed water molecules on the surface.

This paper describes the optical and electrical properties of silicon oxide thin films produced using a novel photoenhanced deposition technique. Since there is no damage to the growing film surface from energetic ions, this process has the potential to produce better semiconductor/insulator interfaces than those grown using conventional RF glow discharge techniques. The deposition system is comprised of a windowless nitrogen discharge lamp contained within the reaction vessel. This unified approach allows the low wavelength UV light from the lamp to couple directly into the reaction gases without attenuation by a window material or the need for mercury sensitisation. Thin films of silicon oxide have been deposited onto single crystal silicon wafer substrates from a nitrous oxide/monosilane reaction gas mixture. The deposition rate and physical properties of films produced in this way are comparable to those of high quality insulator films deposited by plasma enhanced CVD techniques. The results of electrical tests indicate that this material could be used as a low temperature deposited insulator for thin film devices.

Silicon nitride and oxide films have been formed using a photo-CVD apparatus with a microwave-excited VUV lamp. The lamp used was a D2 lamp or a rare gas resonance line lamp such as Xe and Kr. For the nitride film deposited at 320 °C, the BHF etching rate of the film, 40–70Å/min, is lower by less than one-tenth than that deposited using a conventional low-pressure Hg lamp, indicating formation of a high density film. The deposition rate has been enhanced dramatically from 13Å/min to 100Å/min by incorporating the photo-ionization assisted effect, which is brought about by an ionization of a substrate surface and by ions formed by collisions of reactant gases with photoelectrons and photo-ionized ions. The BHF etching rate of the oxide film is considerably lower than those formed using a Hg lamp and excimer lasers, and is similar to that using conventional PE-CVD. Conformal step coverage has been obtained for both the silicon nitride and oxide films.

An alternative approach is described for the laser synthesis of silicon nitride layers using relatively innoccuous, non-pyrophoric reactants such as hexamethyltrisilazane. The pyrolysis process produces 2000 A particles of silicon nitride and the reaction mechanisms are invesigated using infrared spectroscopic analyses. The morphology of the deposited layer is critically dependent on process conditions due to considerable differences in the coupling efficiencies of the nitride deposit and the underlying metallic substrate. The existence of a laser-generated plasma above the metal is discussed in the light of microstructural features observed.

Oxidation of copper films is carried out using a cw argon ion laser. Time-resolved reflectance measurements during the reaction are performed at probe wavelengths of 632.8 and 514.5 nm. Strong temporal variations in reflectance are observed, and are attributed to interference within the growing oxide film. Measurements carried out as a function of laser power are complemented by Auger electron and scanning electron microscopy. A theoretical model of the system has been developed which treats its optical and thermal properties and the film growth process in an integrated way. The calculations highlight the intimate connection between the time dependence of the optical properties of the metal-metal oxide system and the film growth rate. The highly non-isothermal conditions which prevail account for the rapid rate of oxidation relative to furnace oxidation. Although both laser and furnace oxidation are thermal processes which obey a parabolic rate law, preliminary oxygen pressure dependence data indicate that they may not have the same rate determining step.

A uniform thin TiO2 film with the rutile structure which is usually made at higher than 700°C, can be formed at room temperature by the laser irradiation of adsorbed TiCl4 followed by oxidation and repeated cycles of this procedure on a silicon(100) single crystal surface. The laser irradiation to gaseous mixture of TiCl4 and oxygen from the direction parallel or perpendicular to the substrate, on the other hand, leads to the formation of a TiO2 film consisting of amorphous fine particles. The mechanism of the film formation is briefly discussed.

Nitridation and oxidation of titanium is achieved by pulsed laser irradiation of Ti immersed in liquid ammonia or water. Rutherford Backscattering Spectrometry shows that large amounts of nitrogen and oxygen can be incorporated in the metal surface to a depth of several 1000 Å. X-ray diffraction shows evidence of compound formation. Scanning Electron Microscopy reveals that initial surface texture is smoothed, and that stress induced cracks and holes may appear. Irradiation of Fe and Si immersed in various liquids shows that modification depends on which combination of solid and liquid is used. Influence of processing parameters such as laser-energy density and number of laser pulses on compound formation has been investigated. The process is viewed as a reactive solute incorporation in the laser melted surface layer, followed by compound formation.

Excimer laser induced rapid formation of nitride and oxide layers on beryllium samples immersed in liquid nitrogen and water, resp., has been studied. From Rutherford backscattering spectra the amounts of incorporated nitrogen and oxygen were determined. In addition, scanning electron microscopy was used to study the morphology of the irradiated surface and compound formation was confirmed by X-ray diffraction. Our results show that extremely rapid reaction takes place when the laser energy is sufficient to melt the beryllium surface. The amount of reaction is found to be proportional to both the energy density and the number of laser shots, until a nearly stoichiometric layer of Be3N2 or BeO is formed at the surface, at which point the reaction saturates. Growth rates on the order 20 nm per shot are deduced from the data, which is orders of magnitude higher than those achieved by conventional means.

Synthesis of diamond thin-films has been tried by an ArF excimer laser-induced chemical vapor deposition (LCVD) technique, using acetylene diluted with hydrogen as a source gas and a silicon wafer as a substrate. In these experiments, irradiation geometry, substrate temperature and laser power density were varied. Upon irradiation by a focused laser beam, deposition of diamond on substrates heated above 400°Cwas observed, and was confirmed by reflection electron diffraction (RED) photographs. Homogeneity of the diamond films was improved by irradiation parallel to the substrate. These facts suggest that the formation of diamond proceeds through multiple photon decomposition of the reactant gas, and that electronic excitation of gas phase rather than that of substrate or adsorbate layer is essential to form diamond.

The technique of ion beam deposition (IBD) is utilized to investigate low-energy, ion-induced damage on Si and Ge; to study reactive ion cleaning of Si and Ge; to fabricate amorphous isotopic heterostructures; and to fabricate and study the low-temperature epitaxial deposition of 74Ge on Ge(100), 30Si on Si(100), and 74Ge on Si(100). The techniques of ion scattering/channeling and cross-sectional TEM are combined to characterize the deposits.

Real-time spectroscopic phase modulated ellipsometry is used to study the influence of ion bombardment on the growth of plasma deposited amorphous silicon (a-Si:H). The influence of the relative ion flux impinging on the substrate is discussed by comparing a-Si:H films deposited in RF and multipole discharges. A nucleation process is observed in the early stage of the growth of a-Si:H deposited on chromium substrates. When the ion bombardment is strong (multipole plasma) a coalescence of the island structure is observed leading to the formation of a high density film with a smooth interface.

The influence of surface mobility on the growth of Ge films is studied as a function of preparation conditions. The positive ion bombardment during film deposition on chromium substrates is analyzed using an electrostatic analyzer. The dielectric functions of the films are measured over the range 1.7–4.5 eV using in-situ spectroscopic phase modulated ellipsometry (SPME). The spectra of microcrystalline germanium (μc-Ge) present a shoulder near 4.2 eV which corresponds to the E2. optical transition observed in single crystal germanium. For substrate temperatures greater than 150°C, a transition from a-Ge:H to μc-Ge appears when the ion kinetic energy exceeds a threshold energy Eth, around 120 eV. Eth decreases as a function of substrate temperature. The Eth value is found to be higher than the threshold value corresponding to the opposite transition, giving evidence of a substrate memory effect on the growth of μc-Ge. Kinetic ellipsometry measurements of the early stage of the μc-Ge deposition on chromium are accurately, modelled by microcrystalline nucleation at a 50 Å level. After 200 Å thickness, μc-Ge grows with an overlayer. The description of μc-Ge as a mixture of c-Ge, a-Ge:H and voids is discussed.