Influence of masking layer stress on anisotropic silicon etching in TMAH solutions

Nowadays MEMS device fabrication requires an accurate knowledge of the silicon etching parameters. We studied the relation between thin film masking layers residual stress and the orientation dependence of the silicon etching rate using TMAH solutions. In particular we focused on widely used masking films such as SiO2 and Si3N4. Dedicated test structures were designed, fabricated and tested. We found an influence of the masking layer residual stress on the silicon etching rate anisotropy and a lower value of anisotropy for higher stressed structures.