Anisotropic reactive ion etching in silicon, using a graphite electrode

Monocrystalline silicon is etched in a simple reactive ion etching system with mixtures of SF,, Ar and H-2 to obtain deep trenches. A graphite electrode is used to increase the anisotropy of the etching processes. The effect of varying flow, pressure and power levels on etch rate and anisotropy has been studied. Addition of Ar to SF6 results in an increase of ion bombardment of the graphite electrode. This will increase the carbon content in the plasma. Using Ar additions, wall slopes of approximately 60 degrees are obtained; without Ar the etching is almost perfectly isotropic. Addition of H-2 to the SF6-Ar mixtures will decrease the free fluorine content in the plasma. This will decrease the etch rate and increase the anisotropy of the process. Anisotropic etching has been achieved and 30 mu m deep vertical trenches have been etched to obtain micromechanical structures. (C) 1998 Elsevier Science S.A.