Reaction kinetics of GeCl 4 on Si(111)7 × 7

Abstract

GeCl 4 may be useful for the deposition of germanium or the growth of Si 1− x Ge x heterostructures on silicon surfaces. To explore the interaction of GeCl 4 with silicon surfaces, the adsorption and desorption kinetics on Si(111)7 × 7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Following GeCl 4 adsorption, TPD experiments monitored SiCl 2 and atomic Ge as the desorption species at approximately 920 and 1200 K, respectively. SiCl 2 was also observed at all coverages in LITD product yields. The SiCl 2 desorption products indicate that the incoming chlorine atoms on GeCl 4 transfer from Ge to the silicon surface. TPD experiments following multiple GeCl 4 adsorption/desorption cycles also monitored GeCl 2 desorption at ~ 875 K. LITD measurements were used to determine the initial reactive sticking coefficient of GeCl 4 on Si(111)7 × 7. The initial sticking coefficient was larger than previously measured sticking coefficients for chlorosilanes and alkylsilanes on Si(111)7 × 7. The sticking coefficient was S 0 ≈ 1.0 at 150 K and decreased to S 0 ≈ 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 GeCl 4 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 SiCl 2 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 × 10 4±0.2 cm 2/ s. These measured surface reaction kinetics for GeCl 4 on Si(111)7 × 7 should help to determine the conditions for atomic layer growth of Ge or Si 1− x Ge x on silicon surfaces.