A boron etch-stop assisted lateral silicon etching process for improved high-aspect-ratio silicon micromachining and its applications

High-aspect-ratio micromachining (HARM) developed in recent years has made many devices more versatile compared to the surface micromachining process, but it has also met some challenges which have not occurred before. Those issues made many restrictions on HARM structure design, including structure thickness/width limitations, anchor-induced design problems, thickness uniformity and sidewall conductivity problems, which are discussed in this paper. Accordingly, we propose a novel boron etch-stop assisted lateral silicon etching (BELST) process which employs the (111) wafer process and heavy boron diffusion. Many design constraints have been reduced through some delicate designs of the BELST process. Furthermore, the process is capable of various applications, and has been applied in fabricating a dual mass-spring resonator and a micro vibrating gyroscope in this work. In summary, the developed BELST process can possess most existing merits as well as reducing many design constraints in the existing HARM process, and is expected to contribute in making HARM more competitive and convenient.