Etching a semiconductor material and automatically stopping same

Abstract

There is disclosed a method of etching a semiconductor substrate having a region heavily doped with N type impurity atoms spaced from one surface thereof. The one surface of the substrate is masked with an oxide layer or the like and openings are formed in this layer to expose surface areas of the substrate. The substrate is exposed to a refractory metal hexafluoride at elevated temperature whereby the hexafluoride and the exposed substrate material react such that the refractory metal replaces the substrate material until the metal reaches the heavily doped region. This region substantially stops the reaction. Depending on the semiconductor device being made, the refractory metal can then be etched in an etchant that does not react with the semiconductor material to form a moat of uniform depth, or it can be left in place.