I am fabricating PDMS waveguides by soft lithography using silicon mold chips which I structure in clean room.
I face two problems :
Firstly, after dicing the wafer in the clean room, there are millions of micro sized silicon wafer particles which deposit in the waveguide cavities. How can I clean them up?
I tried ultrasonic in DI water, it works good enough (not absolutely good), but ultrasonic also breaks off the C4F8 anti stiction layer which is necessary to good demolding.
Secondly, after pouring the PDMS onto the silicon wafer mold and curing the PDMS, the wafer has to be cleaved and peeled off from the PDMS layer. this again leaves behind lots of silicon particles which stick to the cured PDMS. I tried cleaning the PDMS structures with Isopropanol or with DI water in ultrasonic, but the silicon particles just won't leave the PDMS. What can I use to clean up the small particles sticking to the PDMS?
Thank you .
Can't you deposit a protection layer on top of your structure before dicing -- e.g. a photoresist layer? This will sound a bit silly, but can't you remove the PDMS before cleaving the wafer?
yeah...so the photoresist protection layer method i am already trying..and working on it. only fear is what will happen to the C4F8 layer, which is extremely important to have intact, after the acetone bath treatment.
And regarding removing the PDMS before cleaving, well that is exactly the problem. the design and requirements are such that it becomes imperative to cleave the wafer first and then remove the PDMS. it is required because not complete part of the chip (silicon wafer chip) has to be removed but only half of it...and the other half is required to be sticking to the PDMS. So yeah can't go around that.
Maybe it would be wise to reformulate the flow in order to prevent dicing with PDMS added before cleavage. As mentioned before a sacrificial protective layer would be wise. You can try to manually add a weak tape film (ex: Scotch, ...) around sensitive PDMS and then break. Else, before ultrasonic in DI water, you can try to glue and peel particles with tape.
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