Comment stsetch SNF 2010-03-23 09:40:45: Problem with DEEP when using holder

nharjee at snf.stanford.edu nharjee at snf.stanford.edu
Tue Mar 23 09:40:45 PDT 2010


This problem is likely related to the backside He issues that Elmer is currently debugging, but provides some more information to help you decide whether to use the tool. I etched >350 um wide trenches through 400 um of handle silicon stopping on buried oxide. During the etch, backside He pressure was ~8.5 Torr and leak rate was high at ~5 sccm. Total silicon exposure was ~5% of the wafer. At the end of the etch, the features were ~14 um larger in all directions than the lithographically defined size. Looking at cross-section, the etch profile is straight for the first ~50 um of etching, but blows out thereafter at an angle of ~2.5 deg from the vertical. In this anomalous region, the even scalloping characteristic of DRIE is lost. Poor backside cooling may be the issue, as it would reduce the polymer dep rate on the sidewalls. If you would like to see SEMs, please let me know.




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