Adsorption and decomposition of trichlorosilane and trichlorogermane on porous silicon and Si(100)2×1 surfaces

Abstract

The adsorption and decomposition of trichlorosilane (SiHCl3) and trichlorogermane (GeHCl3) on silicon surfaces were studied using Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption investigations. The FTIR transmission spectroscopy experiments were performed in situ in an ultrahigh vacuum chamber on high surface area porous silicon samples. The FTIR spectra revealed that SiHCl3 dissociatively adsorbed at 200 K and formed SiH, SiClx, ClSiH, and Cl2SiH surface species. The presence of ClxSiH species indicated incomplete decomposition of SiHCl3 upon adsorption at 200 K. GeHCl3 also dissociatively adsorbed at 200 K and formed SiH and SiClx species. The absence of an infrared absorption in the Ge–H stretching region suggests complete transfer of hydrogen from Ge to surface Si atoms at 200 K. The thermal stabilities of the surface species were then studied with annealing experiments. The ClxSiH species deposited by SiHCl3 exposure at 200 K decomposed between 200 and 590 K and formed additional SiH and SiCl species. The SiClx (x=2 or 3) species deposited by either GeHCl3 or SiHCl3 dissociative adsorption converted to silicon monochloride species between 200 and 600 K. The SiH surface species subsequently decreased at temperatures between 680 and 780 K as H2 desorbed from the silicon surface. FTIR spectroscopy was also utilized to monitor the adsorption of SiHCl3 and GeHCl3 on porous silicon at different surface temperatures. These adsorption studies were in agreement with the thermal annealing experiments. Temperature programmed desorption (TPD) studies were performed following saturation SiHCl3 and GeHCl3 exposures on Si(100)2×1. After SiHCl3 adsorption, the only desorption species were H2, HCl, and SiCl2, and they were observed at 810, 850, and 970 K, respectively. Following GeHCl3 adsorption, the TPD experiments monitored H2, HCl, SiCl2, and Ge at 810, 850, 950, and 1200 K, respectively. The adsorption kinetics of SiHCl3 and GeHCl3 were also measured on Si(100)2×1 and initial reactive sticking coefficients of S0≊.019 for SiHCl3 and S0≊1 for GeHCl3 were determined at 500 K. These experiments provide insight into the surface chemistry of chlorosilanes and chlorogermanes during Si, Ge, and Si1−xGex chemical vapor deposition on silicon surfaces.