Hi Robert
We at ETH have a STS RIE/ICP system. I did some Si deep etches (ca 300micron)
using diamond as stop layer but didn't notice
any problems. Plasma exposed diamond aerea was abot 2 cmsquare per sample and we
etched 5 samples.
 So I think the carbon from the diamond cannot be the main reason of the
problem.
Greetings
Stefan