Dear Isaac,

I have a very similar problem here. I used RIE to etchback a layer of
TEOS(@695 degree) oxide with CHF3/CH4/Ar mixture to expose the underlying
layer of amorphous silicon. Then I found my TMAH can't etch the amorphous
silicon.  The same amouphous Si without TEOS oxide deposition and RIE
etchback, can be etched in TMAH perfectly.  From the RIE etch rate, I am
pretty sure there is no TEOS oxide left on the exposed a-Si.  I am guessing
there is polymer residue on the amouphous silicon. I've tried O2 ozone PR
asher following by 10 minutes in Piranha to remove them, but it didn't work.
Do you have any suggestion to deal with these tough residue? More O2 plasma?


Best Regards,

Yenchun Lee
Department of Physics
National Tsing Hua University
Taiwan