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 investigated using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Desorption of hydrogen occurred at 546 OC from surfaces exposed to H2S at temperatures ranging from -145 to 425 degrees C; an additional H-2 desorption channel at 433 degrees C was seen for the -145 degrees C case. A comparison of this behavior with desorption from atomic-hydrogen-dosed Si(100) indicated that these features are due to the desorption of surface monohydride and dihydride species, respectively. In the TPD studies, the surface was saturated by 0.5 ML of H2S fur all substrate exposure temperatures. No desorption feature attributable to sulfur-related species was observed for any of the surface conditions. However, AES measurements revealed 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 the H2S adsorption at 25 degrees C is consistent with a two-step model for the adsorption kinetics.