MEMS deep-RIE fabrication process and device characterization

Abstract

The notching and stiction problem, which widely exists in silicon on insulator (SOI) microstructure fabrication, were resolved in this study. In this paper, a new plasma trench technique that is based on the deep reactive ion etching (DRIE) process is proposed. In this modified process, the deep reactive ion etching (RIE) was divided into several steps, where conformal plasma enhanced chemical vapor deposition (PECVD) oxide coating, and directional oxide etch back were employed to prevent the notching effect and the reactive ion etching (RIE) lag effect is also improved. Therefore, the microstructures regardless of the feature sizes could be realized. The stiction problem is eliminated by using dry chemical release replacing wet release in this approach, where the notching effect is used. The notching or footing effect was exploited for attaining the lateral etch following the deployment of the anisotropic plasma etching of the inductively coupled plasma (ICP). This method was proven useful for both the uniform and non-uniform feature designs. With this novel process, the high aspect ratio beams can be obtained. The thickness of the silicon layer is 75 μm, while the depth of the beams is 70 μum where the 5 μm silicon was etched to suspend the movable beams. The aspect ratio is as high as 35. Trenches with very different widths of 2.5 μm and 35 μm are also achieved at the same time.