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