Ques: Develop Resist on thin metal films

Anthony Flannery afflannery at comcast.net
Tue Jun 1 15:53:53 PDT 2004

You have learned the painful lesson of a galvanic reaction. The etching
of Al in contact with Pt is so violent in LDD26W it generates gas and
blows out the sidewalls of your resist. 
This is caused by the work function difference between the two metals.
The Pt "biases" the Al and drives its etching. 
Short answer - you can't do it. 
Long answer - it will be very difficult. If you can completely isolate
the Pt from the developer you can possible pattern them on the same
wafer with the same resist, but the Pt must be COMPLETELY isolated
(nothing around the edge). If they have to be in contact and exposed, it
may be possible to find a developer chemistry that does not attack the
Al, but it probably won't be with this resist. You will have to
experiment with other resists - I would suggest switching to a negative
Good luck. I've always thought there is a very very good paper waiting
to be written on using galvanic interaction to selectively control
etching in MEMS. Maybe for my next PhD :)
Tony Flannery

-----Original Message-----
From: Abhijit Pethe [mailto:pethe at stanford.edu] 
Sent: Tuesday, June 01, 2004 12:22 PM
To: svgdev at snf.stanford.edu
Cc: innotec at snf.stanford.edu
Subject: Ques: Develop Resist on thin metal films



Has anyone seen the developer attack thin metal films on the developer
track? My process involves deposition of thin Pt/Al film in the Innotec.


Pt: 300A

Al: 700A

Base Pressure: 3e-7

I did a bake in the Yes oven followed by 1mm 3612 resist followed by
exposure. When I put the wafers through the standard developer track
LDD26W (Prog. 3), I notice metal peeling from those wafers. During the
develop program I did notice some reaction on the wafers. Has anyone
seen this before?


I would appreciate any help on this topic.





Abhijit Jayant Pethe

PhD Candidate

Department of Electrical Engineering

Stanford University, CA 

Phone :(O)(650)-725-3608; (C) (650)-387-6435

e-mail:  <mailto:pethe at stanford.edu> pethe at stanford.edu


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