SURFACE SILICON-DEUTERIUM BOND-ENERGY FROM GAS-PHASE EQUILIBRATION

The bond. strength of deuterium (D) to the surface of silicon was determined to be 2.67 +/- 0.1 eV from measurements of the amount of D on the surface in equilibrium with D2 gas at various pressures. This was done by measuring the amount of D on surfaces of closed internal microcavities using nuclear reaction analysis. The binding of D to a silicon surface is significantly weaker than the Si-H bond in silane which has been assumed in the past to indicate the strength of the surface Si-H bond. The fact that the Si-D bond strength is comparable to the activation energy for thermal desorption of H from Si suggests a possible reaction path for desorption in which the first and rate-determining step is the dissociation of a Si-H bond followed by the exothermic reaction between the released H atom and a second Si-H to form a H-2 molecule and two Si- dangling bonds. Our result also gives a value of 1.8 eV for the activation energy for dissociative adsorption of D2 on silicon. The number of bond sites is comparable to the number of Si atoms on the cavity surfaces calculated from the total cavity surface area determined by TEM.