FTIR studies of water and ammonia decomposition on silicon surfaces

Fourier transform infrared (FTIR) transmission spectroscopy was used to monitor the decomposition of H2O (D2O) and NH3 (ND3) on silicon surfaces. Experiments were performed in-situ in an ultra-high vacuum (UHV) chamber using high surface area poroussilicon samples. The FTIR spectra revealed that H2O dissociates upon adsorption at 300K to form SiH and SiOH surface species. NH3 also dissociates upon adsorption at 300 K to form SiH and SiNH2 species. Silicon samples with saturation exposures of H2O and NH3 were progressively annealed from 300 K to 860 K. The FTIR spectra of an H2O-saturated silicon surface revealed that the SiOH species decomposed to form a silicon oxide species and additional surface hydrogen between 460 K and 580 K. Likewise, the SiNH2 species decomposed between 540 K and 660 K to produce silicon nitride and additional surface hydrogen. In both cases, the SiH surface species decreased as H2 desorption from the silicon surface was observed above 700 K.