Hi Ping,
I agree with Bob, you are likely getting some sputtering of your mask
layer followed by micromasking. Do you have a capacitive or inductive
RIE? Can you monitor the DC bias of your plasma?
Here's some things to try:
1) Change masking layer
2) Sounds like you're having problems with reproducability that is
ultimately effecting the DC bias of the plasma, i.e. ions are acquiring
enough energy to sputter the aluminum. First, be sure your electrode
temperature (the chiller) is not below room temperature. A cold
electrode will condense water vapor and change the plasma chemistry.
This effect MIGHT explain why your second sample looked much better.
Second, run an oxygen plasma at high power density and high pressure
(say 200-400 mTorr) before you begin your process. This will remove all
organic contamination.
3) If you still have problems reduce the ion energy by either
increasing the process pressure or decreasing the power.
Good luck,
Mike
>>> [email protected] 10/8/2003 2:34:13 PM >>>
Hi All,
We had very serious problems with RIE grass when we were etching
chips.
In the chip, we used Al as mask for 7um SiO2 anisotropic RIE etch (CHF3
and
O2) and we tried to put the chip on steel plate, Si wafer or quartz to
avoid
the RIE grass. But there is not much difference.
And we found that if we etch 2 chips in sequence, then the first chip
etched
has much grass, but the second one is very clean. Recently, there was
leak
in the RIE system and we fixed it, but etching chips in sequence to
avoid
grass doesn't work and the result seems much worse than before. Does
anyone
have any idea about why we can get a better result for the 2nd chip
(all the
parameters are same) and why it doesn't work after fixing the machine?
Also if we just etch 1 chip, sometimes it has lots of grass, but
sometimes
it has less grass and is acceptable (open area without Al mask has
more
grass than small gaps). The result is not stable, and varies without
reason.
Does anyone have idea about this? Cleaning the system doesn't seem to
help
much.
Last, because the system is not reliable and produces grass without
forewarning, is there any kind of method that can tell if the RIE
system is
good to run? I mean, is there a method that can test if we will get
grass in
the etched chip before we etch it except using our chips for the test
every
time, because the number of chips is limited and we don't want to
waste
them.
And do you have any good idea about avoiding the RIE grass?
Thanks a lot for your help.
Jiaping
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