Etching Burried Oxide at the Bottom of High Aspect Ratio Structures

Plasma based dry etching is a key process widely used in micro-fabrication today. In this article, we look at the challenges involved in the anisotropic etching of buried SiO2 layers at the bottom of high aspect ratio structures on SOI wafers. We present our etch results that show the limitations of using a process with radio frequency (RF) substrate bias. This is followed by results obtained with a newly developed dielectric etch process based on a pulsed low frequency (LF) bias which makes it possible to etch through even relatively thick buried oxide layers. Finally we present an application in which this newly developed process was used.