ATOMIC H-ABSTRACTION OF SURFACE-H ON SI - AN ELEY-RIDEAL MECHANISM

The abstraction kinetics for atomic hydrogen (H-at) removal of chemiso rbed D and atomic deuterium (D-at) removal of chemisorbed H are studie d on single crystal Si surfaces. The surface H and D coverages are mea sured in real time by mass analyzing the recoiled H+ and D+ ion signal s. On both Si(100) and Si(111) surfaces, the abstraction reactions are efficient, and have very low activation energies similar or equal to 0.5-1 kcal/mol. For abstraction from surfaces containing only monohydr ide species, the abstraction reaction probability is similar or equal to 0.36 times the adsorption rate of H-at or D-at. For the same H-at a nd D-at exposures, the reaction rates for H-at removal of adsorbed D a nd D-at removal of adsorbed H are nearly identical. All observations a re consistent with a generalized Eley-Rideal abstraction mechanism, an d a two-dimensional quantum-mechanical model is used to calculate reac tion probabilities for these reactions. According to the model, the ac tivation energies are due to enhanced abstraction rates from excited v ibrational states of the adsorbed Si-H or Si-D bond. With SiH2 and SiH 3 species present on the surface, the removal rate of H using D-at is decelerated, suggesting that the higher hydrides have a lower cross se ction for abstraction.