HI,


I am getting trouble to patterning Si3N4. The Wafers are coated by LPCVD
Si3N4(2000A, SQI), or Low-stress LPCVD Si3N4(1 micron, Stanford).

My problem is that the nitride can not be etched perfectly by using RIE
with CF4(200mtorr, 200W, 15 sccm). I did for 2 min, 5 min, 10 min, 20 min,
30 min (of course Shipley1813 can not survive more than 10 min,
I patterned twice for 20 min and 30 min etching). However, the nitride
seems still stay on the Si wafer. The color is showing Si but KOH does not
etch the wafer.
After the longer dry etch(>10min) KOH start to etch Si, not yet perfect.
Some area can not be etched.
I am etching from backside of the wafers(unpolished).

I think 2000A or 1 micron LPCVD Si3N4 is standard for micromachining, but
I can not get good etched surface.

I used to use 600A(Wafernet Inc.) LPCVD Si3N4, and had no problem to
pattern and etch them(2 min dry etch was enough on both sides of wafer).

Does anyone can suggest any help?
Is long dry etch forms any protect layer(i.e. polymerizzation)?


Thank you for your help.


============================================
Kiyotaka Mori (Graduate Student)

Dept.of Materials and Nuclear Engineering,
BLDG.090,
University of Maryland at College Park,
College Park, MD 20742
Tel: 301-405-5229
Fax: 301-314-9467
E-mail: mori@eng.umd.edu
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