Problem stsetch SNF 2010-11-01 20:55:59: Etch rate decreasing + grass

jcdoll at jcdoll at
Mon Nov 1 20:55:59 PDT 2010

I ran the standard DEEP recipe at the end of September and obtained an etch rate of 2um/min and no grass formed. In fact, the etch dominated the passivation so much that the sidewall angle was about 94 degrees (reentrant sidewall profile).
I ran the standard DEEP recipe again today and the etch rate is <1.5um/min (still etching the wafer, so it may be even lower) and grass slowly formed, covering the entire wafer by the 3.5hr mark.
Both runs were performed after running the same seasoning recipe (3min SF6 etchback, 10min O2 plasma and 20min switched gas along the lines of the standard UC Berkeley process). Wafers are 300um wide trenches with 10% exposed area, 7um thick photoresist on front and back, wafers in the Al holder. He cooling is steady at ~27.8 sccm.

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