In-situ monitoring and study of sacrificial layer SiO ₂ etching

An instrument was installed to in-situ monitor the etching process of the sacrificial layer SiO ₂ using hydrofluoric acid (HF), which is influenced by such factors as temperature, composition and concentration of the etchant, sacrificial material, residual stresses of the material, etc. A variety of test structures were designed to investigate the influence of the different structures on etching process. And the effects of these factors on etching rate and etching results were discussed and analyzed in detail. In the experiment, the reaction limitation phase and the diffusion limitation phase during the etching process were observed, which demonstrate that diffusion rate of HF becomes the dominant factor for the etching rate after long-time etching. Furthermore, the phenomena of concave etching front and circular etching patterns was accompanied by the etching process. Stress profile and difference in hydrophobicity between materials might be the reasons for these phenomena. The method, instrument, experimental results and conclusions in this paper are valuable for MEMS sacrificial layer release process.