A Study On Silicon Wet Etching For MEMS

Because of its anisotropic etching in some high-pH etchants (EDP, KOH, H2N-NH2, NH40H, TMAH), single crystal silicon has found a wide application range including microelectroics, microoptics and micromechanical systems . With the increasing market of delicate and precise devices, production of smooth, defect-free silicon surface is essential. However, there appear inhomogeneity on the etched silicon surface. And there are some explanations for this. As to see, the hydrogen bubbles and silicate particles affect badly etched silicon surface roughness.To avoid the inhomogeneity on etched silicon surface, people have given all kinds of ways: addition of oxidizers to alkaline etchant, etching under anodic bias, adding alcohol or isopropyl alcohol into alkaline etchant, etching with ultrasonic agitation, et al. There few of reports about addition of surfactants in etchant for reducing the etched silicon surface roughness .This paper summarizes all kinds of models about silicon anisotropic etching, and puts forward some significative notions for the development of models.By the way of analyzing the solution's microstructure and particle density fluctuation in solution, we can conclude that the solution structure will change when the ingredients in solution and outside conditions will become different. At the same time, the characters of solution may change, which affects the etch results. This paper introduces the surfactant's characters and analyzes how the solution's properties will change after adding surfactant into solution. Through a lot of experiments, this paper mensurates the relationship between surface tension and the different non-ionic-surfactant concentrations in solution. We also study how pH-value of enchant affects the results. This paper has studied how KOH etchant with different concentration surfactant influences silicon etched surface and the idea is firstly stated that the concentration of surfactant in the enchant is higher than its cmc. The results have shown that roughness of etched Si surface decrease with increasing concentration (>cmc) of non-ionic surfactant. The method, that hydrogen peroxide (H2O2) is added into etchant, can eliminate the hydrogen bubbles at all. At last, the hydrogen peroxide's action during silicon etching is analyzed.