REACTION-KINETICS OF GECL4 ON SI(111)7X7

GeCl4 may be useful for the deposition of germanium or the growth of Si1-xGex heterostructures on silicon surfaces. To explore the interaction of GeCl4 with silicon surfaces, the adsorption and desorption kinetics on Si(111)7 x 7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Following GeCl4 adsorption, TPD experiments monitored SiCl2 and atomic Ge as the desorption species at approximately 920 and 1200 K, respectively. SiCl2 was also observed at all coverages in LITD product yields. The SiCl2 desorption products indicate that the incoming chlorine atoms on GeCl4 transfer from Ge to the silicon surface. TPD experiments following multiple GeCl4 adsorption/desorption cycles also monitored GeCl2 desorption at approximately 875 K. LITD measurements were used to determine the initial reactive sticking coefficient of GeCl4 on Si(111)7 x 7. The initial sticking coefficient was larger than previously measured sticking coefficients for chlorosilanes and alkylsilanes on Si(111)7 x 7. The sticking coefficient was S0 almost-equal-to 1.0 at 150 K and decreased to S0 almost-equal-to 0.1 at 700 K. The temperature dependence of the initial sticking coefficient was consistent with a precursor-mediated adsorption model. LITD measurements determined that the chlorine surface coverage saturated after large GeCl4 exposures and the saturation coverage was independent of surface temperature. This self-limiting behavior should be useful for the controlled deposition of germanium on silicon surfaces. Isothermal LITD studies of SiCl2 desorption revealed second-order kinetics with an activation barrier of E(d) = 81 +/- 3 kcal/mol and a preexponential factor of v(d) = 1.2 x 10(4 +/- 0.2) cm2/s. These measured surface reaction kinetics for GeCl4 on Si(111)7 x 7 should help to determine the conditions for atomic layer growth of Ge or Si1-xGex on silicon surfaces.