Orientation-dependent plasma etch rates of single crystal silicon for dry etcher parts

We have evaluated the orientation dependence of plasma etch rates for single crystal silicon using SF6/Ar and CF4/Ar/O-2 chemical gases in an inductively coupled plasma dry etcher. Etch rates for different crystal orientations having various surface conditions were measured. The results indicate that the <111> crystal lattice orientation is etched at a lower rate than the <100> orientation. The dependence of the silicon etch rate on the crystal orientation is derived from differences in the local neighborhood of the exposed surface atoms, such as number of neighbors, dangling bond, and surface bond. Finishing the silicon parts with mirror-finish polishing results in surfaces with a very thin subsurface damage layer that exhibits a lower plasma etch rate. This compares to the much thicker damage layer caused by abrasive machining of the surface during grinding steps, and to the portion of this that remains, after polishing.