Anisotropic etching rates in TMAH solutions of different Si crystallographic orientation as a function of film stress

Based on our previous experience in microelectronic device fabrication, we made a test process run to investigate the influence of the stress of the different multilayer films such as SiO2 and Si3N4 as masking material which are commonly used in MEMS fabrication processes. The stress of the films was measured by using a profilometer. We evaluated the different structures using anisotropic TMAH etching with different concentrations and temperatures to demonstrate the influence of the thin film stress on the etching rate of different crystallographic orientation. Optical miscroscope was used to measure both the underatching rate, the etch depth and the inclination angle. Morphology and surface roughness were studied by using a SEM. The results of our investigation demonstrate that it exists a significative influence of the superficial masking layer stress on the etching behaviour. This has to be taken in consideration in order to get a better control in wet etching processes.