Measurement of Residual Stress-Induced Bending Moment of P⁺ Silicon Films

Abstract

This paper presents results from measurements of residual stress-induced bending moment of heavily-boron-doped (p⁺) silicon films. Microfabricated free-standing cantilever beams of p⁺ silicon were fabricated by using anisotropie etching of (100) silicon wafers in ethylene-diamine and pyrocatechol. The p⁺ etch stops forming the cantilevers were created by diffusion from a solid source at 1125°C for one and two hour time durations. The nonuniform residual stress distribution through the thickness of the p⁺ silicon cantilevers resulted in a deflection of the beams. The as-diffused p⁺ silicon films had a residual stress distribution through the film thickness which resulted in negative bending moments. Thermal oxidation subsequent to the diffusion step modified the residual stresses near the top surface or, perhaps, plastically deformed the near surface region of the p⁺ thin film. As a result, thermally oxidized p⁺ silicon films exhibited a positive bending moment. Measurements of the deflection curves of the beams in conjunction with beam theory were used to calculate the residual stress-induced bending moments.