Oxidation Kinetics of Silicon Surfaces: Reactive Sticking Coefficient, Apparent Saturation Coverage and Effect of Surfac
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OXIDATION KINETICS OF SILICON SURFACES: REACTIVE STICKING COEFFICIENT, APPARENT SATURATION COVERAGE AND EFFECT OF SURFACE HYDROGEN
S.M. GEORGE, P. GUPTA, C.H. MAK AND P.A. COON Dept. of Chemistry, Stanford University, Stanford, Calif.
94305
ABSTRACT The kinetics of the initial oxidation of silicon surfaces by 02 were studied using laser-induced thermal ssorption (LITD), temperatureprogrammed desorption (TPD) and Fourier Transform Infrared (FTIR) spectroscopy. The LITD results showed that the oxidation of Si(lll)7x7 by 02 was characterized by two kinetic processes: an initial rapid oxygen uptake followed by a slower growth that asymptotically approached an apparent saturation oxygen coverage. The initial reactive sticking coefficient of 02 on Si(lll)7x7 decreased with surface temperature. In contrast, TPD experiments on Si(lll)7x7 and FTIR studies on porous silicon demonstrated that the apparent saturation oxygen coverage increased as a function of surface temperature. Experiments with preadsorbed hydrogen also revealed that silicon oxidation was inhibited as a function of increasing hydrogen coverage on the Si(lll)7x7 surface.
Introduction The reaction of oxygen with silicon surfaces is of great fundamental and technological interest. Not only is oxidation a model silicon surface reaction, but this reaction also produces dielectric isolation in silicon devices. As the dimensions of integrated circuitry are progressively reduced in the submicron regime, the understanding of this basic reaction becomes increasingly important. In the nanometer limit, surface-to-volume ratios are extremely high, and the kinetics of silicon surface oxidation are critical to comprehending and controlling this essential chemical processing step. In this study, we report on laser-induced thermal desorption (LITD),temperature programmed desorption (TPD) and Fourier Transform Infrared (FTIR) experiments that were used to investigate the kinetics of both the fast and slow steps in the oxygen adsorption process. These studies allowed the initial reactive sticking coefficient-of oxygen on the Si(lll)7x7 surface to be measured as a function of surface temperature. In addition, the kinetics of the slow adsorption step were studied on Si(lll)7x7 and porous silicon as a function of surface temperature. Moreover, in order to study the dependence of oxidation rate on surface dangling bond density, the initial reactive sticking coefficient and apparent saturation oxide coverage on Si(lll)7x7 were measured as a function of preadsorbed hydrogen. The experimental apparatus described in detail previously (UHV) chamber used for the LITD pump and a titanium sublimation
for LITD and FTIR experiments has been [1,2]. Briefly, the ultrahigh vacuum studies was pumped by a 300 i/sec ion pump. These pumps maintained background
Mat. Res. Som. Symp. Proc. Vol. 131. @1989 Materials Research Society
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This pressures of approximately 4x10"I Torr during these experiments. chamber was also equipped with a low energy electron diffraction (LEED) spectrometer,
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