ArF Excimer Laser-Enhanced Photochemical Vapor Deposition of Homoepitaxial Silicon from Disilane

Abstract

AbstractThe 193 nm output of an ArF excimer laser has been used to selectively photodissociate Si2H6 to deposit homoepitaxial Si films in the temperature range of 250°C to 350°C. Photolytic decomposition of Si2H6 results in the generation and adsorption of growth precursors on a hydrogenated Si surface. A simple growth kinetic model has been developed based on the most likely primary photofragments upon single-photon absorption by Si2H6 at the ArF excimer laser wavelength of 193 nm, and gas kinetic transport of the resulting photofragments to the substrate surface. Growth rates are observed to vary linearly with laser beam power and Si2H6 partial pressure when the laser beam is tangentially positioned less than 0.5 mm from the Si substrate for Si2H6 partial pressures less than 40 mTorr, total chamber pressures of 600 mTorr, and laser beam photon flux densities less than 2×1016 photons/cm2.pulse. Under these conditions, gas-phase diffusion dominates over chemical reaction rates and laser beam absorption is in the optically thin limit. The model then reduces to a simple form that predicts a linear dependence of growth rate on Si2H6 partial pressure and gives an accurate estimate of the expected growth rate. The epitaxial films are specular, and appear to have very low defect density in terms of stacking faults, as determined by modified Schimmel etching and Nomarski microscopy, and dislocation loops as determined by TEM (less than 105 loops/cm2). The crystallinity has been confirmed both by in situ RHEED, where we see a (l×l) streaky pattern, as well as selected electron diffraction, which shows a (100) crystalline orientation.