Surface micromachining of chip-edge silicon microcantilevers using xenon difluoride etching of silicon-on-insulator

Abstract

We demonstrate a straightforward surface micromachining process for the rapid prototyping of thin ‘chip-edge’ silicon microcantilevers protruding from the edge of a silicon-on-insulator (SOI) chip. The process uses a single photolithographic mask—with xenon difluoride used to both pattern the silicon microcantilevers and release them by etching part of the underlying silicon wafer. During the release step, the silicon microcantilevers are protected from the xenon difluoride by a combination of photoresist and buried silicon dioxide. The use of common microfabrication materials (SOI and positive photoresist) and chemicals (buffered hydrofluoric acid and xenon difluoride), along with a maximum process temperature of 100 °C, makes for a generic, soft micromachining process which is—in principle—compatible with preserving the integrity of any pre-patterned circuitry present on the silicon microcantilever top surface. Doppler vibrometry measurements of the silicon microcantilevers reveal a well-defined resonant frequency and a quality factor comparable with that of similar silicon microcantilevers fabricated using other means. Our enabling technological process allows the rapid prototyping of chip-edge silicon microcantilevers—potentially integrating sensitive circuitry for novel probe technologies—by avoiding the relatively cumbersome, expensive, and potentially circuit-damaging front-to-back processing/deep etching combination.