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

The bond. strength of deuterium (D) to the surface of silicon was dete rmined to be 2.67 +/- 0.1 eV from measurements of the amount of D on t he surface in equilibrium with D2 gas at various pressures. This was d one by measuring the amount of D on surfaces of closed internal microc avities using nuclear reaction analysis. The binding of D to a silicon surface is significantly weaker than the Si-H bond in silane which ha s 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 acti vation energy for thermal desorption of H from Si suggests a possible reaction path for desorption in which the first and rate-determining s tep is the dissociation of a Si-H bond followed by the exothermic reac tion between the released H atom and a second Si-H to form a H-2 molec ule and two Si- dangling bonds. Our result also gives a value of 1.8 e V for the activation energy for dissociative adsorption of D2 on silic on. The number of bond sites is comparable to the number of Si atoms o n the cavity surfaces calculated from the total cavity surface area de termined by TEM.