Micromechanical structures in amorphous silicon

The dependence of the residual stress of amorphous silicon on deposition parameters and annealing was examined in order to develop an all low temperature, micromechanical structure fabrication process. The amorphous silicon was deposited from silane in a parallel plate, plasma enhanced CVD system. The as-deposited films are 1 mu m thick and have compressive residual stress. Thermal annealing dramatically reduced the stress and produced tensile films at temperatures as low as 400 degrees C. The stress in amorphous silicon is believed to depend upon the hydrogen content, which is dramatically changed during annealing at temperatures greater than 350 degrees C. Cantilever beams and bridges were fabricated using surface micromachining techniques, with amorphous silicon as the structural material and aluminum as the spacer layer. This process, with maximum temperature of 400 degrees C, enables one to fabricate silicon micromechanical components directly on top of completed integrated circuits.<
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