With CHF3 RIE of SiO2 there is a tendency to leave what I call a phantom
film on the underlying silicon.  This can drive you nuts because it
looks like a thin oxide remaining.  A few years ago I read a study that
indicated that a fluorocarbon was left on the Si, under which was a
layer of fluorinated Si.  Damage to the Si extended as deep as a micron.
Adding oxygen to the CHF3 may reduce the amount of polymer left behind
at the expense of selectivity.

Roger Shile

-----Original Message-----

Subject: [mems-talk] About the RIE etch of SiO2

SiO2 film with a thickness of 2 micro is RIE etched, the etch parameters
are as
follows,
CHF3:30sccm
Pressure:6Pa
RF Power:300W
Etch mask:P.R.
the etch result shows that the etching rate biases at different etch
window size.
In order to improve the uniformity, the pressure is decreased to 2.6Pa
and the
flow rate of CHF3 is increased to 40sccm, and the etch was tried again.
The etch
result shows better uniformity but with another problem. Something
remained at the
bottom of the etch window, especially where near to the side wall of
etch window.
Would any body give me an explanation of this kind of phenomenon and
provide some
better advice to improve the etch uniformity of RIE? thanks