Isothermal H2 desorption kinetics from Si(100) 2 × 1: dependence on disilane and atomic hydrogen precursors

Isothermal H2 desorption kinetics from the Si(100)2 × 1 surface were studied using laser-induced thermal desorption (LITD) techniques. Disilane (Si2H6) and atomic hydrogen were used as the hydrogen precursors. Atomic hydrogen deposits only hydrogen adatoms and H2 subsequently desorbs from a nearly atomically flat Si(100)2 × 1 surface. Disilane deposits both hydrogen and silicon adatoms that may produce an atomically rough Si(100) surface. This surface roughening with silicon adatoms simulates silicon chemical vapor deposition and may affect the H2 desorption kinetics. The isothermal LITD studies revealed first-order H2 desorption kinetics for both precursors. An activation barrier of Ed = 57.2 ± 2.6 kcal/mol and a pre-exponential factor of vd = 2.21 × 1015±1 s-1 were measured for the atomic hydrogen precursor. An activation barrier of Ed = 54.3 ± 2.3 kcal/mol and a pre-exponential factor of vd = 2.32 × 1014±1 s-1 were determined for the disilane precursor. Within the experimental error, the isothermal H2 desorption kinetics were not significantly affected by the hydrogen source. The similar desorption kinetics are attributed to the surface mobility of the silicon adatoms deposited with disilane. The silicon adatoms can either diffuse to nearby step edges or form Si(100)2 × 1 islands on the underlying Si(100)2 × 1 surface. The first-order H2 desorption kinetics are explained by the concerted desorption of H2 from two hydrogen atoms prepaired on the same silicon dimer on the Si(100)2 × 1 surface.