An Analysis of Beam Deflections in Poly-SiGe Cantilevers

A predictive model for the deflection and profile of poly-SiGe beams for different thicknesses and geometries was evaluated. This model combines experimental data and finite element analysis (FEA). The structure employed to derivate the stress gradient and to calibrate and test the FEA calculations is a cantilever beam with dimensions of 1 mm length, 100 mum width and 10 mum thickness. The stress gradient of the film is obtained by measuring the deflection of the cantilevers with different etch depths. The deflection of the beam was calculated initially using a 2D plane stress model. The influence of the clamping region on the deflection was studied by using a perfect clamped beam and compared with a beam clamped only at the bottom clamp interface. In the second case a "tilt" effect near the anchor was observed due to the average stress in the unreleased thin film. FEM has been successfully applied to calculate the deflection of SiGe cantilever beams. Extra information like the stress distribution after releasing, the effect of Poisson's ratio on the curvature of the beam and the effect of clamping on the deflection was investigated