I casted PDMS on a silicon wafer that was partially silanized. I can remove most parts of the PDMS (especially where there is no pattern on the wafer) but PDMS is stuck in some parts of the wafer. How can I completely remove PDMS without damaging the wafer? I can't fabricate another wafer, so I'm looking for a very safe removal process.
Hi Reza,
Are the features on your wafer made of silicon i.e. etched etc or are they formed using a patterned resist for example?
If the features are silicon then you should be able to use sulfuric acid followed by a general wafer clean.
Adam
Hi Adam.
The photoresist is completely removed so the features are just SiO2. Does sulfuric acid damage the wafer? because I think PDMS should be immersed in sulfuric acid (96%) for 24 hours to be dissolved.
Hi Reza,
I'm fairly sure that sulphuric acid doesn't etch SiO2, at least at an appreciable rate.
In our lab we O2 plasma bond pdms to our substrates (glass or Si) and to release the substrate we immerse in concentrated sulphuric acid, for us it loosens the pdms to allow us to pull the pdms fragments off. The acid also turns a brown colour after this.
I cannot confirm that microscopic pdms doesn't exist on the substrates, SEM would be needed. But no residues are seen microscopically.
After removing we immerse in sulphuric acid and then clean the substrates.
Adam
If I remember approximately 5 - 10 minutes however as the sulphuric shouldn't etch the SiO2 then time shouldn't be a problem. However, if your substrate is valuable then I would check ensure with the literature that your features won't be etched away as I'm not sure of your feature sizes.
Adam
Hi Timothy, I just did what you suggested. First, I coated my wafer with pluronic F-127. Then I performed every thing you said. PDMS didn't break apart while I was trying to peel it but some micron sized PDMS around sharp corners are still in the wafer.
Adam,
I immersed the wafer in sulfuric acid for 10 minutes. It dissolves PDMS but a new problem happened. When I tried to pull out the wafer, some PDMS from acid solution coated the wafer again. I used 100 ml sulfuric acid for a 10 cm wafer.
Do you think cleaning the residue of PDMS with piranha solution is possible?
Dear All,
Thanks for helping me with your suggestions. I thoroughly cleaned the wafer today. I washed it with sulfuric acid as Adam said to reduce PDMS contamination, then cleaned it with piranha solution for 20 minutes. Then I washed it with DI running water. PDMS peeled off in contact with water. I repeated this procedure one more time to ensure no PDMS residue is remained on the wafer.
Again, thanks for your help.
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