KINETICS OF THE REACTIONS OF INTRINSIC AND PHOSPHORUS DOPED POLYCRYSTALLINE SILICON WITH MOLECULAR CHLORINE

The reactions of molecular chlorine with intrinsic and phosphorous doped polycrystalline silicon have been studied as a function of pressure and temperature. In the pressure range from 0.25-30 Torr the etch rate for these two materials was found to be given by the following rate laws: etch rate (intrinsic) = 10(9.6 +/- 0.5) nm min-1 Torr-1/2 exp[(-116 +/- 7 kJ/mol)/RT] (Cl2 pressure)1/2; etch rate (n-type) = 10(8.2 +/- 0.2) nm min-1 Torr-1/2 exp [(-82 +/- 3 kJ/mol)/RT] (Cl2 pressure)1/2-10(7.1 +/- 0.9) nm min-1 exp[(-77 +/- 12 kJ/mol)/RT]. Such a rate law is shown to be consistent with a mechanism for the reaction in which the molecular chlorine is dissociatively adsorbed on the surface of the silicon, and the reaction of this adsorbed atom provides the rate controlling step for the process. Doping of the silicon with phosphorus is found to increase the etch rate by lowering both the preexponential factor and the activation energy for the process.