Dry release of metal structures in oxygen plasma: process characterization and optimization

Abstract

A surface micromachining fabrication scheme suitable for fabrication of free-standing metallic structures is presented. The technique is based on using conventional photoresist as a sacrificial layer, on which a metal structural layer is evaporated and patterned. The resulting structures are subsequently dry released in an isotropic oxygen plasma. For the HPR504 and HiPR6517 photoresists, a lateral underetching rate (at a power of 1000 W) of up to 1 was obtained. Structures with lateral dimensions of at least up to can be released as no etch-rate saturation for underetching beyond 20 m was observed. The process has been tested using Al as a structural layer, but any metal that can be evaporated or sputtered can be used. The presented dry-release technique is fully compatible with standard silicon IC processing and can be applied as a post-processing module. The technique eliminates any sticking problem and simplifies processing as compared to wet-etching release.