An etch release for a MEMS device on a substrate includes etching the substrate with an etchant vapor and a wetting vapor. A thermal bake of the MEMS device, after the etch release may be used to volatilize residues. A supercritical fluid may also be used to remove residual contaminants. The combination of the etchant vapor, such as HF, and the wetting vapor, such as an alcohol vapor, improves the uniformity of the etch undercut on the substrate.