Decomposition mechanisms of SiHx species on Si(100)-(2×1) for x=2, 3, and 4

Silane adsorption at a surface temperature of 150 K and the surface decomposition of SiH3 and SiH2 have been investigated on the Si(100)-(2×1) surface using static secondary ion mass spectrometry (SSIMS) and temperature programmed desorption (TPD). Silane dissociatively chemisorbs at 150 K to form SiH3 and H. At saturation, the combined coverage of these two is approximately 0.4 groups/1st layer Si atom (0.2 SiH4 adsorbed/1st layer Si atom). Using SiH4, the surface coverage of SiH3 species is varied, and the coverage-dependant kinetics of SiH3 decomposition are examined using temperature programmed SSIMS. Changes in SiH4 exposure and source of SiH3 (di- vs monosilane) cause changes in surface SiH3 stability. The stability changes are interpreted as due to blocking of empty sites (dangling bonds, db) required for SiH3 decomposition to SiH2 and H. It is shown here that the decomposition temperature of SiH3 can vary from 200 to 600 K, depending on the dangling bond coverage (θdb). Subsequently, evidence for a coverage dependant change in the decomposition mechanism of SiH2 is presented. Two mechanisms for SiH2 decomposition are experimentally distinguished, and competition of these is governed by θdb. We conclude that both the mechanism and rate of decomposition of surface SiH3 and SiH2 are dependant on the local surface environment near these species.