Dissolution of silicon and junction delineation in silicon by the CrO 3-HF-H 2O system

Abstract

The dissolution of single crystal silicon by aqueous solutions of hydrofluoric acid and chromium (VI) oxide was studied as a function of the resistivity of silicon and the composition of the etchant. In the concentration range under study, the dissolution rate is dependent on the resistivity of the silicon. The dissolution process is controlled by the chemical reaction rather than by the diffusion of chemical species; the rate of the chemical reaction is limited by the supply of carriers at the silicon surface. When the etchant was 2 M in chromium (VI) oxide, the dissolution rate of silicon of a given resistivity is second order with respect to hydrogen fluoride, suggesting that the formation of bivalent silicon is probably the rate-determining step of the chemical reaction. An aqueous solution of hydrofluoric acid and chromium (VI) oxide can be used for delineating electrical junctions and revealing certain resistivity variations in silicon. A technique for this purpose is described and applied to multilayer silicon specimens. The relative etch rates of the various layers depend on resistivity somewhat differently from isolated specimens of similar resistivities, presumably