Polycrystalline Silicon Micromechanical Beams

Using the conventional MOS planar process, miniature cantilever and doubly supported mechanical beams are fabricated from polycrystalline silicon. Poly-Si micromechanical beams having thicknesses of 230 nm to 2.3 microns and separated by 550 nm to 3.5 microns from the substrate are made in a wide range of lengths and widths. Two static mechanical properties are investigated: the dependences of maximum free-standing length and beam deflection on the thickness of the beam. By annealing the poly-Si prior to beam formation, both of these properties are improved. Nonuniform internal stress in the poly-Si is apparently responsible for the beam deflection.