I would like to fabricate the above "sacrificial" stamp, spin coat soft silicone on it and afterwards dissolve the PMMA it with acetone/IPO, so that the silicone has 2um diameter/15um holes in it. If anyone can think of some other material that could be used for this purpose, I am open to any suggestion.
We use SU-8 photoresist to make casting masters for PDMS. To get holes, you'll need to constrain the top of the PDMS so that you'll displace it from the top of your posts. Otherwise, you will have a thin membrane on one side of your posts. If you silanize the casting master, you should be able to remove the PDMS by careful pealing. 15 micron PDMS is tricky to handle. I usually do my peal in an IPA bath to keep the PDMS from sticking to it's self. You may also want to look into PVA. It is water soluble and works great as a sacrificial layer that doesn't require organics that make PDMS swell.
Check our lab website, you will find plenty of pillar structures:
http://pi.is.mpg.de/
PMMA will be hard to expose that deep with anything but x-rays. For photolithography SU-8 is a way to go, except you will not be able to dissolve it, so you will have to follow the route Ron described above.
It is possible with nanoindentation lithography. Please find attached file for more details.
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