We have utilized an ArF excimer laser in a projection imaging geometry to etch GaAs layers grown in situ within a molecular beam epitaxy (MBE) system. Clean epitaxial surfaces were prepared using standard MBE growth procedures, then etched in a second chamber isolated by a gate valve. We report studies of the etching dependence on pulse rate (0.2 Hz to 150 Hz) and chlorine pressure (10−6, 10−4, and 5×10−3 Torr). We discuss the etching mechanism in terms of previous studies of the reaction between GaAs surfaces and molecular chlorine under high vacuum conditions. We show that the pulse rate and Cl2 pressure dependencies of the etching can be explained by the progress of the reaction at the instant of pulse exposure. Etch morphology is found to vary with the repetition rate, with the smoothest surfaces obtained at low repetition rates. We discuss the implications of the results in the context of in situ thin layer processing and epitaxial overgrowth.

The use of lasers in the doping of semiconductors has been investigated extensively these last years both for photovoltaic and microelectronic applications. In this work, doping of single-crystal silicon in BCl3 ambients using a pulsed UV laser has been studied as a function of laser wavelength and fluence in order to investigate the effects of photochemical decomposition of the BCl3 gas and the effects of thermal decomposition of adsorbed layers on the doping process. Different parameters involved in the process (laser energy density, number of pulses per frame, BCl3 gas pressure) were investigated. The electrical characteristics of the doped layers were discussed.

Boron doping of single crystal silicon using an argon fluoride excimer laser with diborane gas has been performed. Diborane gas has an absorption at 193nm, which leads to gas phase photodecomposition of the diborane. Utilizing the photolyic effect, we obtained high surface concentration and ultrashallow junctions of 5×1020 cm−3 and 0.1 µm, respectively. The photolytic effect enhances the incorporation of the dopant species.

A focused argon ion laser (514 nm) beam has been used for patterning superconducting lines of YBa2Cu3O7–δ using films prepared from metal trifluoroacetate solution precursors. A stoichiometric mixture of the precursors is dissolved in methanol, and the solution is spun on yttria-stabilized zirconia substrate to form a film. The film is patterned by irradiating in selected areas by direct laser writing to convert the irradiated layers to an intermediate fluoride state, the nonirradiated areas being unchanged. The nonirradiated areas are then dissolved away, leaving a pattern of the fluoride material. This patterned layer is converted to the superconducting oxide in a subsequent high temperature step involving reaction with water vapor.

In a rapid thermal processing system working at a total pressure of a few Torr, we have obtained selective epitaxial growth of silicon at temperatures as low as 650°C. When using SiH2Cl2 (DCS) as the reactive gas, no addition of HCl is needed. Nevertheless, using SiH4 below 950°C a small amount of HCl should be added.

Some kinetic aspects of the two systems, DCS/HCI/H2 and SiH4/HCl/H2, are presented and discussed. For the DCS system, we show that the rate-limiting reactions are slightly different from those commonly accepted in the literature, where the results are from systems working at atmospheric pressure or in the 20-100 Torr range.

Our model is based on the main decomposition of DCS, SiH2Cl→SiHCl + HCl, instead of the widely accepted reaction SiH2Cl2→SiCl2 + H2. This is the main reason why no extra HCl is required in the DCS/H2 system to obtain full selectivity from above 1000°C down to 650°C.

A laser-generated plasma source of monochromatized soft x-rays has been used to study the x-ray lithographic resist properties of poly(cyclohexylmethylsilane-co-dimethylsilane). X-ray absorption spectra near the SiL2,3 edge of unexposed samples were measured to guide the choice of exposure photon energy. We find that poly(cyclohexyl-methylsilane-co-dimethylsilane) exhibits positive tone at x-ray energies near 105 eV (Si 2p resonance), a sensitivity of 1000 mJ/cm2 and a contrast of 1.5. Sensitivity is found to increase markedly when exposed samples are held in air before development. Using simple wire mesh masks, estimates of the minimum achievable linewidth have been made.

In the Laser Chemistry Group's program aimed at understanding the basic mechanisms involved in the fabrication and characterization of integrated circuits, we have converted an infrared laser-based, thick film trimming technique, which is over 15 years old, to UV light. It is known that excimer lasers can be used for microfabrication of semiconductors and ceramics. Much cleaner ablations than those obtainable with the infrared lasers have been demonstrated in a large variety of materials. This, together with the fact that excimers with repetition rates over 1 kHz are presently on the market, leads us to propose that better accuracies and smaller drifts, should be achievable using excimer laser-based thick film hybrid circuit trimming. Results of XeCl laser trimming of over four hundred resistors, including temperature coefficient of resistance measurements and life tests at elevated temperatures, demonstrate that UV trimming is a factor of 10 better than the presently used infrared process.

The evolution of the excimer laser from a research tool in the 1970's to the industrial models of the 1980's has opened up numerous applications in semiconductor manufacturing, materials processing, and biological and medical research. Present production-capable, computercontrolled excimer systems with handling equipment enabling efficient automation can now operate for up to 50 million shots before undergoing scheduled maintenance, with fluences remaining within ±10% in most cases. Thus, although many uses for the excimer laser are still researchoriented, production applications are rapidly emerging.