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Sputtered Silicon for Microstructures and Microcavities


 Sputtered silicon can be used to make released microstructures at temperatures compatible with prefabricated aluminum-metallized CMOS circuitry. The fabrication sequence is similar to LPCVD polysilicon processes and involves a wet release from an oxide sacrificial layer. This process was used to fabricate a variety of test structures, including cantilevers, combs, and spirals. During release of the structures porosity to HF was observed in films up to 5 μm thick. This porosity resulted in the formation of completely enclosed cavities formed beneath silicon membranes over oxide sacrificial layers, and may have implications for the packaging of released devices. Several properties of the sputtered silicon films were investigated, including their in-plane stress, strain gradient, film density, surface roughness, electrical resistivity, and permeability. The dependency of these properties on deposition power, pressure, and film thickness as well as the effects of low-temperature annealing were also investigated.