DIETHYLSILANE ON SILICON SURFACES - ADSORPTION AND DECOMPOSITION KINETICS

The adsorption and decomposition kinetics of diethylsilane (DES), (CH3 CH2)2 SiH2, 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 x 7 decreased versus surface temperature from S0 almost-equal-to 1.7 x 10(-3) at 200 K to S0 almost-equal-to 4 x 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 x 7. The ethylene desorption and growth of hydrogen coverage during ethyl group decomposition were consistent with a beta-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 x 7 as a function of time following DES exposures. The first-order decomposition kinetics were E(d) = 36 kcal/mol and nu(d) = 2.7 x 10(9) s-1. These decomposition kinetics suggest that the silicon surface catalyzes the beta-hydride elimination reaction.