Gas-phase etching of sacrificial oxides using anhydrous HF and CH 3OH

One of the major issues in surface micromachining is process-induced failures of overhanged microstructures, after sacrificial removal. This failure process consists of temporary deformation due to capillary force and permanent stiction of the deformed microstructures to substrate due to the residue product. In order to alleviate this failure, some researchers have investigated the use of low surface-tension liquids, temporary support, sublimation of the final liquid or supercritical method. These conventional methods, however, are complicated liable to plasma damage during PR ashing, or require careful handling of the samples in rinse liquid. In this paper, we present a newly developed anhydrous HF gas-phase etching (GPE) technology for the removal of sacrificial TEOS (tetraethylorthosilicate) oxide. In order to minimize the capillary force of gas-liquid interface and residue product, methanol of low vapor pressure was employed as a catalyst instead of water vapor. The proposed process features simplicity, virtually no capillary forces and even compatibility with IC process as well. The effectiveness of HF GPE with methanol was verified by successfully fabricating the polysilicon cantilevers up to 1000 um in length with no stiction. The etch rate of HF GPE was 10-15 um/hr for the sacrificial TEOS oxide of 0.1-2 um channel height