Adsorption and decomposition of dichlorosilane on porous silicon surfaces

Abstract

The adsorption and decomposition of dichlorosilane (SiH2Cl2) on silicon surfaces were studied using Fourier transform infrared (FTIR) transmission spectroscopy. These FTIR studies were conducted in situ in an ultrahigh vacuum chamber using high surface area, porous silicon samples. The FTIR spectra of porous silicon following saturation SiH2Cl2 exposures at 200 K revealed the presence of primarily dihydride (SiH2) and monochloride (SiCl) surface species. These surfaces species are consistent with an adsorption mechanism involving Si–Cl bond breakage, i.e., SiH2Cl2 (g)+2Si*→Si*–SiH2Cl+Si*–Cl. The stability of these surface species was then examined as a function of annealing temperature. The infrared absorbance for the SiH2 scissors mode decreased as the temperature was raised from 300 to 660 K. Concurrently, the absorbance increased for the SiH monohydride stretch. These spectral changes indicated that the dihydride (SiH2) species were converted to monohydride (SiH) species. Above 660 K, the SiH species disappeared concurrently with H2 desorption from the silicon surface. The uptake of dichlorosilane on porous silicon was also monitored as a function of substrate temperature. These experiments confirmed that SiH2 is the major surface hydride species following SiH2Cl2 adsorption at low temperatures. These studies of dichlorosilane adsorption and decomposition on silicon surfaces should help to clarify the mechanism of silicon chemical vapor deposition and atomic layer epitaxy with dichloro- silane.