A new frontside-release etch-diffusion process for the fabrication of thick Si microstructures

A new frontside-release etch-diffusion process has been developed to create released single crystal Si microstructures without the need for wafer bonding. This frontside-release process is simple and requires only a single mask. A deep dry etch is used to define the structures, followed by a short boron diffusion to convert them to p⁺⁺ Si. A short etch in ethylenediamine pyrocatechol is then used to undercut and release the structures from the frontside of the Si wafer. The structures are isolated from the substrate using a reverse biased p ⁺⁺/n junction. Since the structures have a high aspect ratio, beams longer than 600 μm can be released without sticking to the substrate. Resonant microstructures have been fabricated using this process and their resonant frequency has been measured