Those pink areas are definitely photoresist. It is important to remember
that PR will withstand HF, but only for short time. Try using BOE
(commercially available buffered oxide etch), or reduce concentration of
BHF(this will effect your etch rate). I do not know what is the
practical difference between BOE and self-made BHF, to tell you the
truth.

However, with films this thick (1um), dry etch is almost always a better
option than BHF etch. You can also try to use a hard mask.

Elina


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Z.,W.Y.(Lydia)
Sent: Tuesday, January 04, 2005 7:48 PM
To: General MEMS discussion
Cc: wez6@lehigh.edu
Subject: [mems-talk] Peel Off


Dear All,

When I etched my wafers using buffer HF(NH4F: HF=10:1), Sio2 was etched
away, however, lots of pink pieces dropped into solution. After DI water
resining and spinning dry, more and more pink pieces appeared and stuck
to the wafer. And large areas in wafer-frontside(suppose to be PR)
looked uniformly, i.e. some area look darker than others. The backside
sio2 removed compeletely.

I processed those wafers using the following step:
1) RCA clean silicon wafer and Wet-oxidize (~1 um)
2) O2 plasma etch the front side (for cleaning) [2 min, 300W, 300 mtorr]
3) Photolithagraphy (130C/1hr dehydration bake, 10 min HDMS vaper prime,
spin-coat PR[OCG825], 95C/30min softbake, exposure, develop, 130C/30min
hard bake)
4) BHF etch SiO2 for 17 min and DI risine and spin dry. (backside SiO2
has been etched away since no protection)

Are those pink pieces PR or SiO2? Any suggestions for possible reasons
or improvements are highly apperaciate.

Lydia

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