High aspect ratio deep silicon etching

This paper reports an improved deep reactive ion etching (DRIE) process for ultra high aspect ratio silicon trenches with reduced undercut. By ramping process pressure, etch power, and switching time, we are able to produce 5.7 μm trenches with an aspect ratio of 70 and 3 μm trenches with an aspect ratio of 97. We reduce undercut by half by adjusting the length and pressure of the passivation step.