Etch stop materials for release by vapor HF etching

The integrity of various materials upon exposure to vapor HF etching was investigated. Whereas silicon nitride did not withstand the vapor HF, it was found that Al2O3 and AlF3 are fully inert, thus both are suitable etch stop materials. In addition, the reflectance of Al in the ultraviolet range was measured, and found to be unaltered by the etchant. The thickness of AlSiCu also remained the same. All materials are suitable for use in CMOS MEMS microsystems.