This paper describes the deposition by light-stimulated breakdown of gallium and indium on borosilicate glass, gallium arsenide and indium phosphide substrates, from precursors whose ultraviolet (uv) spectra have recently been reported. Some preliminary work on the deposition of indium phosphide is also reported, using an indium-phosphorus complex whose uv spectrum is also given.

Thin (< 1.2 μpm) Ge and Si films have been grown with rates up to 3.6 μm/hr by laser-induced chemical vapor deposition (LCVD) on a variety of substrates. Germanium films grown on amorphous SiO2 (quartz) by photodissociating GeH4 in He at 248 nm (KrF laser) exhibit grain sizes of 0.3 – 0.5 μm that increase only slightly up to the pryolytic threshold for GeH4 (280°C). On (100) NaCl, however, Ge films grown at a substrate temperature of 120°C are expitaxial. The activation energy for the LCVD growth of Ge films (from GeH4) on SiO2 is measured to be 85 ± 20 meV which suggests that germanium is arriving at the substrate in atomic form. The wavelength and intensity dependence of the initial film growth rate supports the conclusion that this process is photolytic and is initiated by the absorption of a single photon.

Stimulated growth of single crystalline GaAs has been obtained by irradiation of (100) oriented GaAs substrates inside an MOCVD reactor with a pulsed Nd-YAG laser.

Process temperatures have been varied between 540°C and 360°C. In the non-irradiated areas, below 480°C substrate temperature the growth rate decreases rapidly, whereas in the irradiated part of the substrate epitaxial layers could be grown in the whole temperature range investigated. Below 450°C, the growth is reaction limited.

Some results on hydrogenated amorphous silicon growth by CO2 laser photodissociation of silane are reported. A 100 W CW CO2 laser was used as the excitation source. A horizontal configuration was adopted, where the laser beam is sent parallel to the substrate surface inside a flux reactor, and its energy is used to excite and dissociate the silane molecules flowing near the solid surface. The laser has no direct heating effect on the substrate, which is independently heated by an oven.

The photoproduced radicals by interacting with the surface grow a film at a rate strongly depending on silane pressure, substrate temperature and laser intensity. This experimental configuration allows depositions on large areas, owing to the large number of reactant molecules involved in the photochemical process. Moreover, material can be produced with a continuously variable hydrogen content, since the substrate temperature required for obtaining depositions can be as low as room temperature and adjusted independently of the other process parameters.

The film properties are similar to those of the glow discharge deposited material. The film amorphousness and the hydrogen presence either in monohydride and dihydride groups are evidenced by x-ray patterns and ir spectra. Results on the electrical and optical properties are also reported.

Metal, dielectric and semiconductor films have been deposited by laser chemical vapor deposition (LCVD) using both pulsed and cw laser sources on a variety of substrates. For LCVD on substrates such as quartz, the deposition was monitored optically in both transmission and reflection using a collinear visible laser and the depositing CO2 laser. Deposition initiation and rate were correlated with irradiation conditions, the laser generated surface temperature, and the changing optical properties of the filmpsubstrate during deposition. Single crystallites of W greater than 100 pm tall were deposited using a Kr laser on Si substrates.

The deposition of a-Si:H by means of CO2 laser-induced pyrolysis of silane gas is described. Deposition rates were found to increase with increasing silane flow rate, reactor pressure, laser power and substrate temperature. Spin density decreased and both optical gap, and hydrogen content increased with decreasing substrate temperature. Electrical conductivities are reported.

UV excimer lasers have been used to dope semiconductors by a one–step process in which the laser serves both to release dopant atoms from a parent molecule and to melt the surface, allowing incorporation of dopant atoms by liquid state diffusion. The technique has been used to dope Si, GaAs, and InP. Shallow junctions formed by the technique have been fabricated into efficient Si and GaAs solar cells.

Dopant patterns of 250-nm linewidth have been written in silicon by localized heating with a cw laser beam, and then transferred into positive and negative surface-relief patterns by preferential etching. The tightly focused beam both generates free dopant atoms and simultaneously promotes solidstate diffusion into the substrate. Because of the nonlinear dependence of diffusion rates on temperature, the linewidths of the patterns are substantially narrower than those of both the temperature and the laser-beam profiles on tile surface. In addition, an enhancement is observed in diffusion rates under the strong thermal gradients associated with highly localized heating.

UV laser photochemical dissociation and laser enchanced thermal dissociation have been used to generate free metal dopant species from a variety of organometallic molecules near a semiconductor substrate surface. Simultaneous laser annealing via a localised melt phase allows diffusion driven implantation of the metal atoms and subsequent electrical activation in the regrowing material. High levels of dopant concentration and activation are readily achieved in this way.

Results will be presented on doping of silicon by boron using an ArF laser. These will include data on junction depths, number density and carrier density as a function of depth and interpretation of the data in terms of calculated temperature profiles.

The possibility of tailoring junction characteristics by control of laser and gas flow parameters will be considered with preliminary experimental data.

Phase transformation occuring upon CW laser irradiating through optical fiber polymetallic, multilayered films deposited on insulating substrates is shown to provide a simple and versatile way to optically micro-print predetermined patterns. The technique allows both further reduction to the Rayleigh limit and simultaneous multiplication of the patterns.

Laser irradiation of a solid surface under an oxidizing ambient gas can activate localized, heterogeneous chemical reactions which modify the surface. Under suitable conditions, the laser initiates a reactive plasma near the gas/solid interface. This plasma mechanism is proposed as the basis for a new surface chemical technique which we denote laser-pulsed plasma chemistry (LPPC). LPPC experiments on niobium metal under one atmosphere of oxygen employed a pulsed CO2 laser and displayed single-pulse, self-limiting, oxide growth. Product oxide thickness increased with optical intensity. Surface layer thickness and chemical composition were determined for oxide layers between 1 nm and 5 nm thick using x-ray photoelectron spectroscopy (XPS or ESCA). Composition of these niobium oxide (Nb2O5−δ) surfaces was similar to the composition produced by RF plasma oxidation, but the valence defect, δ, for LPPC oxides was approximately two to five times lower. At high laser intensity (≥4 × 106 W/cm2), direct optical heating or plasma-mediated thermal coupling to the solid activates interdiffusion at the oxide/metal interface.

Microscopic metal patterns may be produced on p-type semiconductors using a maskless photoelectrochemical procedure in which electroplating is induced by minority carriers in illuminated portions of a semiconductor electrode. Resolution exceeding l0μ has been achieved for deposits of Au on p-GaAs and Cu on p-Si. “Electroless” imaging and negative photoelectrochemical imaging are also discussed.

Electronic surface states in semiconductors often lie between the valence and conduction bands and give rise to charge densities confined to the surface region. Laser radiation of frequency less than the energy gap can excite electrons from delocalized valence band states to these localized surface states leading to large changes in the charge distribution at the surface. Selective enhancement of adsorption/desorption processes involving ionic or polar adspecies can result from such a charge redistribution. Using a onedimensional model for silicon, the cross-section for the laser-induced electronic transition to surface states is shown to be large. The interaction energy of an adspecies with the surface changes significantly with direct excitation of surface states in a semiconductor. For a one-dimensional metal, however, direct transitions between bulk and surface states are not allowed, but phonon-mediated transitions coupled with laser radiation lead to substantial charge transfer as for semiconductors.

We describe the oxidation of 1000 Å thick metal films on glass substrates when exposed to a scanning laser beam. For Cd and Cu films optical spectroscopy shows an energy gap of 2.45 eV and 2 eV respectively, in agreement with published data for CdO and Cu2O. We measure the power threshold for complete oxidation in a single scan and deduce the maximum temperature, which is inconsistent with thermal oxidation data but corresponds to the m.p. of the metals. We point out the important contribution of the heat of formation to the temperature balance and demonstrate that in the case of Al this effect is sufficient to destroy any oxide formed.