Doping and Crystallographic Effects in Cl-Atom Etching of Silicon.

Absolute rates for the intrinsic reaction between Cl atoms and surfaces of P-doped polycrystalline silicon, P-doped Si (100) and As, Sb-doped Si(111) substrates were measured for the first time as a function of dopant concentration and substrate temperature in a downstream reaction system. This study clearly shows when there is no ion bombardment, crystal orientation influences the Cl-Si reaction more than dopant concentration. Moreover, we have discovered that the the doping effect continues to influence the Si-Cl reaction rate even when silicon is lightly doped. Etch rate enhancements of heavily doped silicon over lightly doped silicon range from 30-300 depending on the surface type and temperature. In Cl source discharges, the doping effect has only been detected when n-type carrier densities are greater than ~ 10 sup (18) cm sup (-3), presumably because competing effects such as mild ion-induced etching are larger than the low chemical rates intrinsic to lightly doped silicon.