Reaction of H2S with Si(100)

The dissociative adsorption of H2S on Si(100) and the subsequent desorption of hydrogen from and diffusion of sulfur into the same surface have been i nvestigated using temperature-programmed desorption (TPD) and Auger electro n spectroscopy (AES). Desorption of hydrogen occurred at 546 OC from surfac es exposed to H2S at temperatures ranging from -145 to 425 degrees C; an ad ditional H-2 desorption channel at 433 degrees C was seen for the -145 degr ees C case. A comparison of this behavior with desorption from atomic-hydro gen-dosed Si(100) indicated that these features are due to the desorption o f surface monohydride and dihydride species, respectively. In the TPD studi es, the surface was saturated by 0.5 ML of H2S fur all substrate exposure t emperatures. No desorption feature attributable to sulfur-related species w as observed for any of the surface conditions. However, AES measurements re vealed a sharp decrease in the concentration of sulfur at the surface over the temperature range of 525-625 degrees C, indicating that H-2 desorption is accompanied by diffusion of sulfur into the Si crystal. The exponential decay of the sticking coefficient derived from the coverage dependence of t he H2S adsorption at 25 degrees C is consistent with a two-step model for t he adsorption kinetics.