Atomic layer epitaxy (ALE) of GaAs is achieved by metalorganic vapor phase epitaxy (MOVPE) under irradiation by Ar ion laser. The self-limiting mechanism for gallium deposition at one atomic layer on an arsenic atomic surface is realized by the site-selective decomposition of triethylgallium on the arsenic surface. A patterned growth of ALE is obtained by scanning a laser beam on a substrate.

Laser-induced epitaxial growth of GaP has been achieved using both pyrolytic and photolytic reactions. A focused beam from an argon ion laser operating at 514.5 nm was used to ‘direct-write’ epitaxial microstructures of GaP on silicon using a pyrolytic process. An ArF excimer laser has also been used to demonstrate homoepitaxy utilizing the photolytic process.

The laser induced photo-MOVPE (photolytic-metal organic vapour phase epitaxy) technique has been used to grow epitaxial films onto CdTe or GaAs substrates (with a 257nm frequency doubled Argon ion laser). The growth temperature was chosen to be below the normal pyrolysis temperature so that decomposition of the metal-organics will only occur within the illuminated parts of the substrate. A measure of enhancement of growth rate by UV illumination is the photo-enhancement factor which has been determined for CdTe deposits onto Si(100) substrates using the precursors dimethyl cadmium (Me2Te) together with either diethyl telluride (Et2Te) or dimethyl ditelluride (Me2Te2). For patterned epitaxial layers at 300°C, Et2Te was preferable to Me2Te2 because Et2Te was more stable, yielding a higher photo-enhancement factor. A 2-D array of CdTe mesas (60 × 60μm) has been deposited onto a GaAs (100) substrate. Using imaging SIMS (secondary ion mass spectrometry) the distribution of major elements and impurities have been studied.

Silicon lines are directly written using argon ion laser CVD. The thickness profile of the line has a Gaussian-like shape. The thickness profile is calculated with the model based on Arrhenius behavior. A good agreement is obtained.

The effective exposure time is used to analyze the direct writing process. Using it, the average growth rate is estimated to be about 100 times faster than that of conventional large area CVD with the activation energy of 2.4± 0.4eV.

We present in this paper a comparison of the photodissociation processes of SiH4 and Si2H6 under pulsed excimer laser at 193 nm. The experimental curves of the gas composition as a function of laser energy density show that the dissociation of Si2H6 results from both one and two-photon absorption whereas SiH4 only absorbs two photons. The deposition yield of Si2H6 has also been determined as a function of the number of laser pulses or initial pressure. These experimental results show the establishment of a stationary state in the gas phase and prove the existence of reverse reactions in the disilane kinetic model. The photodissociation of Si2H6 under UV laser excitation (193 nm) presents, therefore, similar properties to those of SiH4.

The viability of ammonia as a sensitiser for the epitaxial growth of Ge on GaAs by laser photochemical vapour deposition (LPVD) has been investigated. Specifically NH3/GeH4/He (0.8/5/95 sccm, 5.5 Torr total pressure) mixtures have been irradiated by a 193nm ArF excimer laser in parallel geometry for substrate temperatures, Ts<400°C. As evidenced by a dramatic acceleration in Ge film growth rate, the NH3 efficiently couples the laser radiation to the GeH4 precursor molecule. The microstructures of LPVD Ge films grown with and without NH3 have been examined by TEM, and the epitaxial nature of both types of films has been verified, although some subtle differences are noted. Chemical analysis of the deposited films has been carried out using Auger spectroscopy, X-ray photoelectron spectroscopy and secondary ion mass spectroscopy. Our results show that there is little or no nitrogen incorporation into the Ge films grown in the presence of NH3, and that hydrogen contamination in our films is minimal. The beneficial effect of NH3 on the growth rate of LPVD Ge films is attributed to the photolytic production of hydrogen atoms which efficiently decompose GeH4 by hydrogen abstraction collisions.

The synthesis of Ge-Se deposits has been demonstrated by using continuous wave CO2 laser excited reactions of GeC14 and Se2Cl2 precursors, each transported in an argon carrier gas. The deposited Ge-Se layers are rich in Ge with a composition of 70% of Ge and 30% of Se. Microstructural examinations reveal that the microstructure consists of amorphous Ge-Se particles ranging in diameter from 2000 Å to 7000 Å. Suggestions are made for the possible mechanisms that might occur during film deposition including, pyrolytic reactions, multiphoton dissociations, and Volmer-Weker film growth.

An experimental study of diamond formation by laser-induced chemical vapor deposition (CVD) technique using a gaseous mixture of H2 and CCl4 is reported. The laser used in this work is an ArF excimer laser which emits 80 - 200 mJ pulses with 20 ns duration. We have succeeded in obtaining thin films of diamond by the activation of hydrogen to enhance the removal of graphite and the production of CH radicals. Films obtained without the activation were composed of amorphous carbon and graphite. Hydrogen was activated by a microwave discharge tube or a hot tungsten filament. Films were characterized by Raman scattering and reflection electron diffraction. The diagnostic study using a visible optical emission spectroscope shows that the emission intensity ratio of CH to C2 radicals increases in the system with the activation.

Substrate temperature during deposition of hard carbon films by short pulse (40 nsec, FWHM) eximer (308 nm) laser ablation (∼1.25 × 108 W/cm2) of solid carbon affects the optical and mechnical properties of deposited films. Films deposited at 25° C are superior to those deposited at 500° C. Deposited films were charaterized by spectroscopic ellipsometry, microhardness, TEM, Raman and FT-IR techniques.

A ring shaped cold cathode electron gun provides a large area disc shaped vacuum ultraviolet (VUV) light source up to 20 cm in diameter. The windowless disc plasma is also a source of radical and excited atomic gas species. VUV photons, excited species, and radicals can all assist dissociation of CVD feedstock reactants via volume photo-absorption and sensitized atom-molecule collisions, respectively. In addition, the excited radical flux and VUV impingement on the film may also assist heterogeneous surface reactions and increase surface mobility of absorbed species. Thin films of aluminum nitride, Si3N4, and hydrogenated amorphous silicon have been deposited at temperatures between 100°C - 400°C. The deposited films show significant improvement over other photoassisted CVD processes in the film quality achieved, the substrate temperature required and the maximum deposition rates.

Mercury cadmium telluride epitaxial layers have been grown using methylallyltelluride (MATe), dimethylcadmium (DMCd), and elemental Hg. Using these precursors high quality films have been achieved over the temperature range of 200-300°C. Comparisons are made between UV photon-assisted and thermally deposited films. Composition, growth rate, and electrical properties are compared for the two processes under various parameter conditions. Properties of films deposited on various substrates including CdTe, GaAs, and GaAs/Si are also described.

The growth of high quality ZnSe by organometallic vapor phase epitaxy (OMVPE) has generally been hindered because of parasitic source pre-reactions or relatively high source decomposition temperatures. In this work, we have used vacuum ultraviolet photons generated by a disk-plasma lamp to assist the ZnSe growth process using diethylselenium and diethylzinc as source materials. This approach has resulted in satisfactory growth rates and high material quality at temperatures as low as 250°C, without the limitations of prereaction typically observed when H2Se is used for the selenium source material. In addition, the alkyl selenium compound offers advantages due to reduced toxicity compared to H2Se. This new, low-growth-temperature process thus offers the possibility of improved stoichiometry and impurity incorporation control as well as a reduced thermal effect on the underlying substrate during growth. At the same time, the advantages of excellent morphology and uniformity typically exhibited by the alkylbased growth processes are retained.

The adsorption and photoreactions of Mo(CO)6 coadsorbed with K on Si(111)7×7 at 90 K have been studied under ultra-high vacuum conditions. It is found that dissociative adsorption of Mo(CO)6 on the K preadsorbed surface occurs for coverages below a monolayer. A multilayer of physisorbed Mo(CO)6 molecules is formed on top of the monolayer. Under photon irradiation physisorbed Mo(CO)6 molecules are dissociated and CO desorption is observed. The photoreactions of Mo(CO)6 occur over a wide wavelength range from the UV to IR. In contrast, only UV radiation induces photoreactions of Mo(CO)6 on the K-free Si(111)7×7 surface. Evidently K opens a new channel for the photoreactions of Mo(CO)6 on the surface. A mechanism involving interactions between photogenerated charge carriers and the substrate-adsorbate complex is proposed.

Photodecomposition of trimethylaluminum (TMA) flowing with H2 on p-type Si under UV irradiation is shown to be exclusively a reaction confined to surface species. Thus photonucleation and photodeposition of Al on Si is controlled either by Si-H or Si-O and Si-OH bonds. In the regions where Si-O and Si-OH are present, Al-O forms, which inhibits Al deposition either directly or via the adsorption of C containing photoproducts. In the other regions where Si is H terminated, it is assumed that H2 adsorbs dissociatively on Al clusters, thus leading to the formation followed by the desorption of methane from the adsorbed phase. For this reason, Al thin films are C contamination free.

The polymerization of ethylene on surfaces sequentially dosed with TiC14 and trimethylaluminum was studied by Fourier transform infrared spectroscopy. The polymer film was observed in situ as a function of time and under the influence of 254-nm cw radiation. The rate of polymerization and the saturation thickness of the polyethylene are strongly dependent on the order of dosing and the partial pressures of the reactants that form the catalyst. UV enhancement of polymerization was demonstrated to occur through two separate photochemical channels: gas-phase photolysis of the reactants and solid-phase chemical transformation of a noncatalytic thin film.

When laser-driven etching of a semiconductor requires direct participation of photogenerated carriers, the etching quantum yield will be sensitive to the electronic properties of a specific semiconductor material. The band-gap energy of the semiconductor determines the minimum photon energy needed for carrier-driven etching since sub-gap photons do not generate free carriers. However, only those free carriers that reach the reacting surface contribute to etching and the ultimate carrier flux to the surface is controlled by more subtle electronic properties than the lowestenergy band gap. For example, the initial depth of carrier generation and the probability of carrier recombination between the point of generation and the surface profoundly influence the etching quantum yield. Appropriate manipulation of process parameters can provide additional reaction control based on such secondary electronic properties. Applications to selective dry etching of GaAs and related materials are discussed here.

The sensitivity of the laser-controlled aqueous etching to the optical and electrical properties of semiconductors was utilized during the etching of n-GaAs/n-AlGaAs multilayers to produce novel microstructures. Since this process is controlled by the transport of photogenerated holes to the semiconductor/solution interface, we found that the morphology of etched features is dependent on the bandgap and hole diffusion length of each layer within the heterostructure.

Photochemical etching of InP using a cw frequency doubled Ar+ laser is evaluated with a view to the production of optoelectronic device features. The diffusion-limited resolution of the unmodified etching process is discussed and a new method of etching high resolution grooves which utilises a native oxide coating is described. Grooves produced in this way have widths comparable to that of the laser beam.

UV laser photolysis of chlorine (λ = 350-360 nm) has been used to produce a microscopic atomic chlorine source. Crystalline silicon has been etched and deep, through-wafer vias have been fabricated. The etching process has been modeled and both theoretical and experimental results are given.

Si (100) samples have been irradiated with excimer laser pulses (λ = 308nm, pulsewidth =28ns) in a low pressure chlorine environment, at a fluence just enough to melt the surface. Time-of-flight spectra of the particles desorbed due to the laser irradiation have been measured as a function of effective chlorine pressure and desorption angle. Maxwell- Boltzmann distributions have been used to fit the measurements. The mean kinetic energy per particle increases with increasing chlorine pressure. Angular distributions of the desorbed particles are found to be cosine like at a chlorine coverage much less than a monolayer and sharply peaked along the surface normal at coverages on the order of a monolayer. Monte-Carlo simulations of the desorption process show that due to collisions between the desorbed particles the change in angular distribution can be explained. The increase in mean energy with increasing chlorine coverage however cannot be explained by gas phase collisions. A possible desorption process is suggested.