Hi, all

Recently faced a strange problem during photoresist cleaning. I used
AZ7220 to pattern electrode, the bake temperature for all is 95-100C.
Because the pattern is broken during development, I clean the AZ 7220
with acetone for 5-10 mins which not completely remove the
photoresist. Then I went through the Piranha 1:1 at room temperature
for 20mins. However, there is still some pink color (in microscope)
residual left in my DRIE etched pattern bottom.

The strange thing is that I used all possible photoresit remove
methods. But these pink color residual still left there with no
visually removal at all. The methods I tried are:
Prinha 3:1 (H2SO4:H2O2) for 30mins
Resist remover RR2 for 20-30mins at 110C
Remover PG for 20mins at 50C
Even O2 plasma 100W 10sccm for 10mins.

What probably you guys think this pink color layer is? and How can
remove it completely with any possible method?

Btw, I measured this thin pink layer is around  200nm thick.

Thank you very much!

Steven