Abstract
We have developed a novel technique of sacrificial layer etching for micro electro mechanical systems (MEMS). Our technique uses vapor of hydrofluoric acid (HF) to etch sacrificial silicon oxide and to make freestanding silicon microstructures. The advantages of this technique are: (1) no subsequent water rinse is needed, (2) freestanding silicon microstructures can be successfully released without sticking to the substrate, (3) equipment for our vapor phase HF etching simply consists of Teflon beakers only. Conditions for the technique have been optimized by estimating etching rate with test patterns made of silicon-on-insulator (SOI) wafers and by observing water droplets condensation on the sample surface with thermally oxidized silicon chips. By this technique we have successfully obtained freestanding microstructures of SOI wafers. Microcantilevers of as long as 5000 µm (a 5-µm-wide, 10-µm-thick, and 5000-µm-long cantilever over a 0.6-µm-gap) have been successfully released without adhering to the base substrate or contacting the neighboring cantilevers. We have also fabricated and actuated electrostatic comb-drive actuators of 60 and 200 comb pairs to demonstrate high processing yield of our nonstick releasing technique.