Optical interferometric characterization of membrane curvature in boron doped Si microstructures

Optical interferometry has been applied to determine the membrane curvature of p++Si beams. Clamped-clamped Si beams and cantilevered beams were fabricated with an etch- diffusion process and a dissolved wafer process and characterized. This measurement technique allows for very precise measurement of the bending of released Si beams due to stress, thus small height variations due to membrane curvature in clamped-clamped beams can be resolved. Cantilevered beams were found to bend more due to stress as length increased and width decreased. Thicker beams also showed less bending due to stresses due to their increased stiffness. A 6.0 micrometer thick cantilevered beam had a deflection of 12.4 micrometer due to stress, while a 36.7 micrometer thick beam had a deflection of only 0.2 micrometer. Beams fabricated using a dissolved wafer process with a 12 h B diffusion were found to bend the same amount as those fabricated using an etch- diffusion process with a 4 h diffusion. Using the deep etch- shallow diffusion process, resonating elements that are 20 micrometer long, 4 micrometer wide, and 28 micrometer thick were found to be perfectly flat without any bending.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.