Comment wbsilicide SNF 2010-11-23 21:06:25: Wrong mix in bath or water addition???

dkozak at dkozak at
Tue Nov 23 21:06:25 PST 2010

Using 9:1 Sulfuric acid: hydrogen peroxide bath today to strip resist:
The bath was changed only one day before, and liquid level was slighlty above the full mark (looked OK).  
After heating the bath to 120 degrees, put in my cassette with four wafers, covered with 7 um SPR 220-7 resist.  
two cycles of 20 min each FAILED TO STRIP RESIST!!! (a spray with acetone does more).  
Had to dump a little of liquid and pour some Hydrogen peroxide to replenish.  After that, PR was stripped in 5 seconds.
Either the change of bath was done to wrong concentrations, or people who did not want to replenish hydrogen peroxide just added water to the bath.   
I would expect some evaporation of peroxide after a day, so the liquid should not have been at above full level.  So, latter hypothesis is the more likely one.  

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