Protective coatings in harsh environments

The chemical stability of different coatings for micromechanical sensors is investigated. The coatings included are standard passivation layers in the IC industry: silicon oxide, silicon nitride and silicon carbide. The corrosion rates of these materials are tested in water based media with varying pH values and temperatures. Homogenous corrosion is observed yielding etch rates up to 1000 Angstrom h(-1) for silicon oxide, 70 Angstrom h(-1) for silicon nitride and 2.6 Angstrom h(-1) for silicon carbide at 140 degrees C in potassium hydroxide.