a question about RIE undercut.
I am using RIE to etch silicon(O2/CF4=5/50 sccm, pressure 50 m torr, power 300
W), wafer is SOI wafer, devise layer 230nm,100 direction
the mask is 100nm of Cr.
after etching , I use Cr etchant( bought from Transene company, LTD, type 1020)
to remove Cr mask.
It seems that there is a huge undercut around 100nm,
( I think so because the silicon bridge does not look sharp and flat, and
resistance is much bigger than expected)
I  etched only 230 nm deep, this is quite unresonable,
it looks like the side of the bridge was peeled off  a little bit.
there might be three possiblitis for this problem.
1. SOI wafer is not good.
2. RIE under cut( pressure has be set  very low already).
3. Cr etchant eat some silicon.
anyone have some idea of this problem and how to solve it.

thanks a lot
Yu Chen
[email protected]