Dear All,

I am trying to eatch through holes in 450 micron thicks wafer in STS
machine, but i am getting very rough surface(bubble type of shapes)
after some etching time.

I have SEM pics of through etched holes and trenches which I can
forward if you contact me directly.

Feature size diameter is 30-35 microns and total thickness of wafer is
450 microns.  Total process time is also very high 4 hrs 30 mins (etch
rate ~ 1.6 um/min)

Process parameters used are
Coil Power - 800 W,
Platen Power - 12 W
SF6 flow - 130 sccm
O2 - 13 sccm
C4F8 - 100 sccm
Etch /Passivation time - 13/7
APC - 75%

I am using 10 um AZ9260 as mask.

This very rough surface (bubble type shape ) are occuring at almost same
place and after some time.

Can anyone suggest me any idea why this strange thing is occuring and
any suggestions to overcome this problem.

I will be very thankful to any suggestions.

Thanks,
Pradeep Dixit
Research Student