Modeling of photochemical vapor deposition of epitaxial silicon using an ArF excimer laser

摘要

Abstract: Low temperature silicon epitaxy has been achieved at substrate temperatures ranging from 250$DGR@C to 350$DGR@C using the 193 nm output of ArF excimer laser to generate reactive growth precursors by photolytic decomposition of Si$-2$/H$-6$/. Growth rate dependencies on substrate temperature, Si$-2$/H$-6$/ partial pressure, laser photon flux density, and beam-to-substrate distance are presented. A simple expression for the growth rate as a function of process parameters can be obtained by considering the single-photon absorption rate of Si$-2$/H$-6$/ at the ArF excimer laser wavelength of 193 nm, and the gas kinetic transport of the resulting photofragments to the substrate surface. With the beam tangentially positioned approximately 1 mm from the substrate, a large percentage (7 $POM 1%) of the silicon available from the excited Si$-2$/H$-6$/ contributes to film formation. As the beam is moved away from the substrate, the chemical reaction rate of the growth precursors becomes significant with respect to the diffusion rate and the growth rate is observed to decrease. By tilting the laser beam to provide a normally incident component striking the substrate surface, the dangling bond density of the surface can be increased by photon assisted H desorption and growth rates are observed to increase. At substrate temperatures less than 400$DGR@C, the growth rate is weakly dependent on temperatures with an activation energy of $APEQ 0.05 eV, whereas for temperatures above 400$DGR@C, film deposition becomes dominated by pyrolytic decomposition of Si$-2$/H$-6$/ with an activation energy of $APEQ 1.2 eV.!23