Diethylsilane on silicon surfaces: Adsorption and decomposition kinetics

Abstract

The adsorption and decomposition kinetics of diethylsilane (DES), (CH3CH2)2SiH2, on silicon surfaces were studied using laser-induced thermal desorption (LITD), temperature programmed desorption, and Fourier transform infrared (FTIR) spectroscopic techniques. LITD measurements determined that the initial reactive sticking coefficient of DES on Si(111) 7×7 decreased versus surface temperature from S0≊1.7×10−3 at 200 K to S0≊4×10−5 at 440 K. The temperature-dependent sticking coefficients suggested a precursor-mediated adsorption mechanism. FTIR studies on high surface area porous silicon surfaces indicated that DES adsorbs dissociatively at 300 K and produces SiH and SiC2H5 surface species. Annealing studies also revealed that the hydrogen coverage on porous silicon increased as the SiC2H5 surface species decomposed. CH2=CH2 and H2 were the observed desorption products at 700 and 810 K, respectively, following DES adsorption on Si(111) 7×7. The ethylene desorption and growth of hydrogen coverage during ethyl group decomposition were consistent with a β-hydride elimination mechanism for the SiC2H5 surface species, i.e., SiC2H5→SiH+CH2=CH2. Isothermal LITD studies monitored the decomposition kinetics of SiC2H5 on Si(111) 7×7 as a function of time following DES exposures. The first-order decomposition kinetics were Ed=36 kcal/mol and νd=2.7×109 s−1. These decomposition kinetics suggest that the silicon surface catalyzes the β-hydride elimination reaction.