Deep lateral anhydrous HF/methanol etching for MEMS release processes

As demonstrated earlier, gas-phase etching of sacrificial oxide with a vapor mixture of anhydrous HF (AHF) and methanol (CH3OH) offers a clean, stiction-free, effective etching technique for microelectro-mechanical systems (MEMS) release. The use of AHF/methanol process in MEMS release operations is explored in the deep lateral etching of patterned silicon-on-insulator (SOI) substrates using a 200 mm multiwafer commercial module, which assures adequate process throughput. It was determined that highly selective, with respect to both Si and Si3N4, etching of SiO2 can be accomplished by controlling pressure and wafer temperature. It was also observed that the vertical etch rates for both the AHF/methanol and the HF: H2O solution was higher than the rates of lateral etches in confined geometries. Furthermore, the AHF/methanol and 1: 10 HF: H2O etch chemistries were directly compared in releasing silicon cantilevers up to 500 mu m in length and a significantly faster, stiction-free process was observed in the former case. Adequate process reproducibility from wafer to wafer as well uniformity across the wafer was demonstrated. c 2008 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.2959177]