Hi Xiong, everybody
Etching photoresist off as a sacrificial layer is not a trivial task. You
cannot remove it using wet developer or solvents, as capillary forces will pull
the mirrors down onto the underlying surface. You can do it using dry etching,
which avoids the capillary problem, but there are other things to watch. You
need a dry etch system which can etch isotropically (not RIE, as this is
anisotropic), with soft pump-down and vent (to avoid turbulence when small
fragile structures are around). The rate of sideways etching is often quite
low, so you will need holes in the mirror surface to avoid ridiculously long
etch times. The size of holes will determine the spacing. A reasonable amount
would be 2 micron diameter holes on 10 micron pitch.
As the photoresist is removed, so the thermal contact to the mirror becomes
worse. This means that the mirror will heat up due to energy from the plasma
and may bend. This could be your biggest problem if flatness is critical.
Hope this helps. You can find information on similar MEMS applications at
either http://www.oxfordplasma.de or http://www.oxford-instruments.com/pt/.
Best regards,
Martin
Mr. Martin Walker, Senior Applications Engineer
Oxford Instruments Plasma Technology
North End, Yatton, Bristol, BS49 4AP, UK
Tel. +44 1934 837031 Fax. +44 1934 837001
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