The use of ZnS as a sacrificial layer in the construction of PECVD SiNx self-supporting structures

The construction of freestanding microstructures requires the use of a sacrificial etch layer. Whilst SiO₂ is commonly employed as a sacrificial layer for LPCVD silicon nitride structures, we have found that it is incompatible with thin self-supporting membranes of PECVD silicon nitride. Specifically, when fabricating such self-supporting membranes the selectivity of the membrane to the SiO₂ etch is too low. This problem causes the membrane structure to be etched significantly during the long etch times required to release a device from the sacrificial layer. It is shown that by using ZnS as a sacrificial layer, thin self-supporting membrane microstructures formed from PECVD silicon nitride can be accomplished. This process allows integration of MEMs structures with semiconductors that are incompatible with high temperature processing