The establishment of a fabrication technique for surface-micromachined sensor devices constructed from polycrystalline silicon thin films is in urgent need for the production of resonating microsensor devices with higher performance and integration at lower cost. The method of controlling the stress condition needed to the polycrystalline silicon thin films is studied. It is found that a procedure of post-annealing process after deposition of amorphous silicon thin films from disilane gas is suitable for obtaining the tensile stress state of polycrystalline silicon thin films for use in doubly-supported-beam structures. To prevent a bending of cantilever beam caused by the non-uniform stress distribution in the surface normal direction, we analyzed the stress distribution in the films using a newly developed method. The stress distribution was proved to be influenced by the substrate condition, surface condition, and phosphorus doping. According to these results, some methods to restrict the bending are designed. One of the methods is to eliminate the surface layer with strong tensile stress from the polycrystalline silicon thin film. Another is to induce a tensile stress increase in a localized layer by the post-annealing after oxygen ion implantation, which acts as a counter balance to compensate a bending momentum. These results prove their effectiveness in the restriction of the bending to the extent acceptable for a sensor operation.
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