A STUDY OF RESIDUAL-STRESS DISTRIBUTION THROUGH THE THICKNESS OF P(+) SILICON FILMS

This paper investigates the effect of thermal oxidation on the residual stress distribution through the thickness of heavily boron-doped (p+) silicon films. The deflection of p+ silicon cantilever beams due to residual stress variation through the film thickness is studied for as-diffused and thermally oxidized films. Cantilevers of as-diffused p+ silicon films display a positive curvature (or a negative bending moment), signified by bending up of the beams. Thermal oxidation of the films prior to cantilever fabrication by anisotropic etching modifies the residual stresses in the p+ film, specially in the near-surface region (i.e., the top 0.3 to 0.5 mum for the oxidation times used here), and can result in beams with a negative curvature even when the oxide is removed from the p+ silicon cantilever surface subsequent to cantilever fabrication. Excluding the near-surface region, for the diffusion and oxidation times studied, the residual stress distribution through the remainder of the p+ silicon film thickness is such that a positive curvature of the cantilevers results even when oxidation is performed.