H2O ADSORPTION-KINETICS ON SI(111)7X7 AND SI(111)7X7 MODIFIED BY LASER ANNEALING

The adsorption kinetics of H2O on Si(111)7X7 and Si(111)7X7 modified b y laser annealing were studied using laser-induced thermal desorption and temperature-programmed desorption techniques at temperatures betwe en 180 and 800 K. The laser-annealed Si(111)7X7 surface displayed an e nhanced initial reactive sticking coefficient for H2O compared with th e unmodified Si(111)7X7 surface. At 180 K, the initial reactive sticki ng coefficient was S-0=6.9X10(-1) on laser-anmealed Si(111)7X7 compare d with S-0=1.9X10(-2) on unmodified Si(111)7X7. This larger initial st icking coefficient is attributed to the creation of a more reactive su rface structure formed by the laser annealing process. At higher oxyge n coverages, the reactivity of the laser-annealed surface changed and displayed much slower H2O adsorption rates that were similar to the ki netics on Si(111)7X7. The decreasing initial reactive sticking coeffic ient versus increasing surface temperature suggested a precursor-media ted adsorption mechanism on both the Si(111)7X7 and laser-annealed Si( 111)7X7 surfaces. After long H2O exposures, the oxygen coverage satura ted at theta(0) approximate to 0.35 monolayers on Si(111)7X7 for tempe ratures between 300 and 700 K. At higher surface temperatures, the sat uration coverage increased prior to SiO desorption at temperatures abo ve 900 K. This increase was attributed to the creation of additional d angling bond adsorption sites following H-2 desorption at temperatures above 700 K. (C) 1995 American Vacuum Society.