ADSORPTION AND DESORPTION-KINETICS FOR SICL4 ON SI(111)7X7

The adsorption and desorption kinetics for SiCl4 on Si (111)7x7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. TPD experiments monitored SiCl 2 as the desorption product at approximately 950 K using a heating rate of β=9 K/s. SiCl2 was also observed as the desorption product in the LITD yield at all surface coverages. LITD measurements determined the initial reactive sticking coefficient (S0) of SiCl4 on Si(111)7x7 versus surface temperature. The sticking coefficient was observed to decrease with surface temperature from S0≈0.18 at 160 K to S0≈0.03 at 600 K. TPD experiments revealed that the chlorine surface coverage saturated after large SiCl4 exposures and the saturation coverage was independent of surface temperature. Isothermal LITD studies enabled the surface chlorine coverage to be monitored as a function of time during SiCl2 desorption. These studies revealed second-order desorption kinetics for SiCl2 with a desorption activation barrier of Ed=67±5 kcal/mol and preexponential of νd = 3.2x100±0.1 cm2/s. Experiments with preadsorbed hydrogen demonstrated that the initial sticking coefficient of SiCl4 was reduced as a function of increasing hydrogen coverage. This behavior indicated that the adsorption of SiCl4 on Si(111)7x7 requires free surface dangling bonds. LITD techniques were also used to study the surface diffusion of the chlorine on Si(111)7x7 after SiCl4 adsorption. No evidence of significant surface chlorine mobility (D≤2x10-11 cm2/s) was found for surface temperatures as high as 825 K. © 1990 American Institute of Physics.