Control of residual stress of polysilicon thin films by heavy doping in surface micromachining

Control of residual stress of polysilicon thin films for use in surface micromachining was experimentally studied. It was found that stress can be controlled by fairly heavy doping and subsequent annealing. Polysilicon films with lower than 50 ppm tensile and -50 ppm compressive strain were fabricated as measured from micromachined test structures. Very low tensile strains of less than 100 ppm were obtained with As/sup +/ implantation doses on the order of 1-3*10/sup 16/ cm/sup -2/ and annealing temperatures of 1050 degrees C. Strains as low as 15-30 ppm were achieved. The problem of sticking of structures to the substrate after wet etching of sacrificial oxide was observed and circumvented.<
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