A new ultra-hard etch-stop layer for high precision micromachining

In the present work we describe a high-precision fabrication method for silicon micromachining based on a newly developed epitaxial etch-stop. This etch-stop, composed of a silicon-germanium alloy with no boron doping, outperforms traditional boron-doped etch stops in several important and fundamental ways. Etch selectivities in a variety of standard etchants compare favorably with those obtained using high-concentration boron diffused and epitaxial layers. Microstructural analysis of the new etch-stop layer demonstrates a significant reduction in defect density relative to boron-doped counterparts. Tuning fork gyroscopes built with the new etch-stop show build dimensions comparable to those fabricated with conventional methods. We propose a band structure model for the etch-stop mechanism that mimics the hole-injection phenomenon often invoked for boron doping, and conclude with a brief discussion of the advantages of this new fabrication technology.