Adsorption and desorption kinetics for SiH2Cl2 on Si(111) 7×7

Abstract

The adsorption and desorption kinetics for dichlorosilane (SiH2Cl2) on Si(111) 7×7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The TPD experiments monitored H2, HCl, and SiCl2 desorption products at 810, 850, and 1000 K, respectively. H2, HCl, and SiCl2 desorption products were also observed in the LITD yield at all surface coverages. In agreement with the TPD studies, linear ramp LITD experiments monitored the disappearance of the H2, HCl, and SiCl2 LITD signals at 810, 850, and 1000 K. LITD measurements determined the initial reactive sticking coefficient (S0) of SiH2Cl2 on Si(111) 7×7 versus surface temperature. The sticking coefficient was S0≊0.36 at temperatures from 150 to 200 K. Above 200 K, the sticking coefficient decreased to S0≊0.10 at 350 K and S0≊0.0025 at 850 K. The temperature-dependent sticking coefficient was consistent with a precursor-mediated adsorption model. As a function of surface coverage following SiH2Cl2 exposure, TPD studies observed that the HCl desorption yield decreased relative to the H2 and SiCl2 desorption yields. These results indicated that when more hydrogen desorbs as H2 at higher coverages, the remaining chlorine is forced to desorb as SiCl2. TPD experiments also determined that the surface chlorine coverage saturated and was independent of surface temperature after large SiH2Cl2 exposures on Si(111) 7×7. Epitaxial growth of silicon by dichlorosilane chemical vapor deposition can be predicted using the measured adsorption and desorption kinetics for dichlorosilane on Si(111) 7×7. When these kinetics are employed together with incident SiH2Cl2 fluxes, very good agreement is observed between predicted and measured silicon growth rates.