We have been trying to release a 0.2 micron thick layer of polyimide
over a silicon frame with a diameter of 100 - 500 microns. The layers
from top to bottom are metal 0.1 microns thick (Al or Cr) unpatterned,
polyimide, silicon dioxide (0.5- 1 microns), and a 300 micron thick
wafer. The etching is done by DRIE with the oxide as a stop layer. We
notice cracking in the metal layer after release. Has anyone had this
problem? Any suggestions will be appreciated.

Thanks in advance,
   Mike Martin
   U. of Louisville