KINETICS OF THE REACTION OF MOLECULAR BROMINE WITH DOPED POLYCRYSTALLINE SILICON

The reactions of molecular bromine with phosphorus-doped polycrystalline silicon have been studied as a function of pressure and temperature. In the pressure range from 0.5 to 30 torr and at temperatures between 360 and 410-degrees-C, the etch rate was found to be half order in the pressure of Br2, confirming earlier observations on the reaction of intrinsic silicon with molecular bromine. The experimental rate law is shown to be consistent with a mechanism for the reaction in which the gaseous Br2 is adsorbed on the surface and then dissociated, with both steps occurring reversibly. By comparing these results with the rate constants for the etching of intrinsic silicon, we find an enhancement factor of over 125 can easily be achieved with moderate phosphorus doping levels. Such enhancements with doping are found to be attributable principally to a decrease in the activation energy for the reaction.