An ambient composed of hydrogen (≥ 95%), carbon dioxide (0.5–5%), and silicon tetrabromide (0.1–1%) will deposit a film of silica on a substrate heated to 800°–850°C. The process has particular application for coating germanium for high‐speed planar device technology; it is useful for silicon also. The reaction may be carried out immediately after epitaxial germanium deposition in the same equipment.