ISOTHERMAL H-2 DESORPTION-KINETICS FROM SI(100)2X1 - DEPENDENCE ON DISILANE AND ATOMIC-HYDROGEN PRECURSORS

Isothermal H2 desorption kinetics from the Si(100)2 x 1 surface were s tudied using laser-induced thermal desorption (LITD) techniques. Disil ane (Si2H6) and atomich hydrogen were used as the hydrogen precursors. Atomic hydrogen deposits only hydrogen adatoms and H2 subsequently de sorbs from a nearly atomically flat Si(100)2 x 1 surface. Disilane dep osits both hydrogen and silicon adatoms that may produce an atomically rough Si(100) surface. This surface roughening with silicon adatoms s imulates silicon chemical vapor deposition and may affect the H2 desor ption kinetics. The isothermal LITD studies revealed first-order H2 de sorption kinetics for both precursors. An activation barrier of E(d) = 57.2 +/- 2.6 kcal/mol and a pre-exponential factor of nu(d) = 2.21 x 10(15 +/- 1) s-1 were measured for the atomic hydrogen precursor. An a ctivation barrier of E(d) = 54.3 +/- 2.3 kcal/mol and a pre-exponentia l factor of nu(d) = 2.32 x 10(14 +/- 1) s-1 were determined for the di silane precursor. Within the experimental error, the isothermal H2 des orption kinetics were not significantly affected by the hydrogen sourc e. The similar desorption kinetics are attributed to the surface mobil ity of the silicon adatoms deposited with disilane. The silicon adatom s can either diffuse to nearby step edges or form Si(100)2 x 1 islands on the underlying Si(100)2 x 1 surface. The first-order H2 desorption kinetics are explained by the concerted desorption of H2 from two hyd rogen atoms prepaired on the same silicon dimer on the Si(100)2 1 surf ace.