It sounds like the isotropic nature of the wet etch is undercutting the
resist enough to make it lift off.  You may have to add a CD bias to your
mask of about 2 um (so a 4 um printed line will create a 2 um line post
etch) or use an anisotropic plasma etch.


Eric Miller
Laboratory Manager
Washington Technology Center
Ph:  206 616-3855
www.watechcenter.org


-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Jukka.Viheriala@orc.tut.fi
Sent: Thursday, August 12, 2004 7:58 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] 2um Al line etching using PR as a mask

Hello,

I have been trying to wet etch 300 nm thick Al layer using 2um wide PR
stripe. However I have problems width adhesion of resist to aluminum. PR
stripe seems to peal of when I'm etching.

I have been using following process.

1.    Spin HDMS on wafer (no I can't use vapor prime)
2.    Spin 1um thick AZ6612 on wafer
3.    Soft bake 2 min @ 110 C on hotplate
4.    Exposure
5.    Develop
6.    Hard bake 3 minutes in oven. 120 C.
7.    Etch with wet etchant

I have tried
HCl:H20 1:2 => very non uniform etching + Resist was removed
BOE => Resist was removed
HF:H2O2:H2O 1:1:20 => Resist was removed
H3PO4:HNO3:CH3COOH:H2O 4:1:4:1 => Resist was removed

Does anyone have good solutions. I know that I can grow SiN on Al and use
that as an etch mask or use dry etching but these steps make process more
complicated and I'm designing fast test process to test epi-wafers.

-Jukka Viheriala



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