CHARACTERIZATION OF ANHYDROUS HF GAS-PHASE ETCHING WITH CH3OH FOR SACRIFICIAL OXIDE REMOVAL

One of the major issues in surface micromachining is process-induced f ailures of freestanding microstructures after the removal of sacrifici al layers. This failure process consists of temporary deformation due to capillary force during drying and permanent stiction of the deforme d microstructures to the substrate due to the residual product. In ord er to alleviate this failure, some researchers have investigated the u se of low-surface-tension liquids, temporary support, sublimation of t he final liquid, or the supercritical method. In this paper, we presen t the characteristics of newly developed anhydrous HF (hydrogen fluori de) gas-phase etching (GPE) technology to remove sacrificial TEOS (tet raethylorthosilicate) oxide. In order to minimize the capillary force of the gas-liquid interface and residual product, methanol of low vapo r pressure and low surface tension is employed as a catalyst instead o f water vapor. The effectiveness of HF GPE with methanol is verified b y successfully fabricating polysilicon cantilevers up to 1000 mu m in length with no stiction using photothermal radiometry. The etch rate i s 10-15 mu m h(-1) for sacrificial TEOS oxide, and shows little deviat ion for a one-dimensional microchannel of 0.1-2 mu m height. (C) 1998 Elsevier Science S.A.