HYDROGEN DESORPTION RATE AND SURFACE HYDROGEN COVERAGE DURING ISOTHERMAL ANNEALING FOR SI2H6-ADSORBED SI(100) SURFACES

The hydrogen desorption kinetics were investigated from the viewpoint of hydrogen-unoccupied site distributed on Si2H6-adsorbed Si(100) surfaces during isothermal annealing. The surface electronic state due to Si dimer-dangling bonds was observed in situ by ultraviolet photoelectron spectroscopy. The hydrogen desorption was found to be a first-order reaction with an small activation energy of 21.9 kcal/mol, in comparison to the value obtained by thermal desorption spectroscopy (TDS), 47-58 kcal/mol. To interpret this discrepancy, we proposed a desorption reaction model, in which H-2 formation from a paired monohydride on a dimer, which proceeds dominantly during isothermal desorption, is disturbed by dimer Si-Si bond breaking due to rapid temperature elevating in TDS, and therefore an additional energy for hydrogen to hop between resultant isolated monohydrides and form dihydride, 34.5 +/- 4.6 kcal/mol, is necessary in TDS for H-2 desorption.