Specific Process Knowledge/Etch/DRIE-Pegasus/FAQ/Potasi

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Question

We have had several requests on etches that produce sloped (app. 80 degrees) sidewalls with low roughness. Where should I start?

Answer

This type of etching is very dependent on the feature size, open area, required depth etc etc. In general, BOSCH processing is not suitable for this type of profile; before the profile is brought in anywhere close to the 80deg there will be grass issues in the sidewall. In almost all cases, achieving ~80deg or "positive" profile can be achieved only by significantly undercutting the mask, where the final base width of the etched structure will be ~same as the initial mask opening. The downside of this approach (aside from the loss of CD at the opening) is the "overhang" - this is what we call the local bowing at the top of the structure. This overhang is worse where species transport is most limited....i.e. small trenches or vias will suffer more than large trench openings. Most of the work we have experience with is based around ~50um vias to a depth of ~100um or trenches of ~200um width. Process approaches differ significantly for these different features.