Characterization of anhydrous HF gas-phase etching with CH3OH for sacrificial oxide removal

Abstract

One of the major issues in surface micromachining is process-induced failures of freestanding microstructures after the removal of sacrificial layers. This failure process consists of temporary deformation due to capillary force during drying and permanent stiction of the deformed microstructures to the substrate due to the residual 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 the supercritical method. In this paper, we present the characteristics of newly developed anhydrous HF (hydrogen fluoride) gas-phase etching (GPE) technology to remove sacrificial TEOS (tetraethylorthosilicate) oxide. In order to minimize the capillary force of the gas-liquid interface and residual product, methanol of low vapor pressure and low surface tension is employed as a catalyst instead of water vapor. The effectiveness of HF GPE with methanol is verified by successfully fabricating polysilicon cantilevers up to 1000 mu m in length with no stiction using photothermal radiometry. The etch rate is 10-15 mu m h(-1) for sacrificial TEOS oxide, and shows little deviation for a one-dimensional microchannel of 0.1-2 mu m height. (C) 1998 Elsevier Science S.A.