Amorphous fluoropolymer protective coatings for front-side MEMS releasing by hydrofluoric acid vapor etching

摘要

Vapor-phase hydrofluoric acid (HF) sacrificial layer etching is frequently used in the microelectrome-chanical systems (MEMS) industry because it allows freestanding microstructures to be released without sticking to the substrate and does not require time-consuming and expensive deep reactive-ion etching (DRIE) processes. However, due to process complexity and limited protectable duration in previous work, an effective surface protecting method by using easily coated and removed films is still under development. In this work, we present a novel approach of spinning an amorphous fluoropolymer coating to protect the microstructures of the passivation layer and metal electrodes from HF vapor attack. The HF-resistant capability of the amorphous fluoropolymer is assessed, and the results demonstrate that the proposed method has advantages of lower cost and easier processing compared with the complicated process used for fabricating inorganic films. Through the use of a post-bake temperature lower than 220 ℃ within a single additional process that lasts for less than 2 h, an amorphous fluoropolymer coating can be treated and coated in a protective layer thinner than 4 urn that can withstand an HF vapor etching application period of longer than 30 min. Using this method, we successfully fabricated a target MEMS device with front-side release by HF vapor etching in which the remaining microstructures were well protected.