Hi William,

If e-beam litho and PMMA is your only option, you may try depositing your
substrate with Cr or Mo and use PMMA as a mask to wet etch either of these
metals. Then use one of these metals as a mask for your chlorine-based
etching process. If you are using pure RIE process at room temperature and
moderate pressure of 50 - 200 mTorr, Cl radicals do not form volatile
products with Mo or Cr, according to their vapour pressure data. Let's try
and let us know how it goes. Some member here said BCl3/Cl2 plasma also
eat Cr, but as many knows that RIE is all dependent on process conditions.
Afterall, if DC bias is high enough, everything etches (by sputtering),
isn't it?


Yours sincerely,

Isaac Chan
University of Waterloo