Galvanic corrosion induced degredation of tensile properties in micromachined polycrystalline silicon

Immersion of polycrystalline silicon in hydrofluoric acid-based solutions is often utilized in microsystem fabrication to liberate mechanical structures. The authors demonstrate, using microfabricated tensile specimens, that such etching can cause a catastrophic reduction in tensile strength and elastic modulus in silicon galvanically coupled to a metallic layer, such as commonly used gold. Galvanically corroded silicon exhibits grain-boundary attack leading to intergranular fracture and/or generalized material removal. The severity of damage and corresponding losses in strength and modulus depend on etch duration and etch chemistry. In contrast, without a metallic layer, uncorroded silicon fails transgranularly and independent of etch duration or chemistry.