Pablo,
Coat the wafer with positive resist, expose with a mask that has openings
where you want the holes in the aluminum. Do not develop. Put in an ammonia
atmosphere at 90 degrees C for an hour. This will diffuse through the resist
and neutralize the acid in the exposed areas, without hurting the sensitizer in
the unexposed resist. Now flood expose, at 2.5 times the exposure intensity of
the first exposure and develop. The main field of resist will develop away
leaving pillars where you first exposed. The side walls of the pillars will be
at a reverse angle of 22 degrees to the normal. Now put down aluminum and the
aluminum will not coat the side walls of the resist pillars because of the
reverse angle. Now ultrasonic agitation in acetone will remove the resist and
lift off the aluminum on top of the resist. A large sheet of aluminum with
defined holes and no etching. Think resolution better than your exposure unit
and simple consistency. I am attaching 3 papers on reversal techniques. Let me
know if I can help doing demonstrations on your wafers. Bill
-----Original Message-----
From: Pablo Bianucci [mailto:[email protected]]
Sent: Wednesday, February 12, 2003 7:55 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Etching holes in aluminum
Hi Bill!
On Tue, Feb 11, 2003 at 08:18:59AM -0800, Bill Moffat wrote:
> It may be that lift off is a better answer. I have seen a reverse
> picture sub micron 0.5 micron pillars 1.2 micron high used for a
> lost contact process. I have also seen 800 Angstrom lines and
> spaces using image reversal and lift off. If you think this can
> help let me know. Bill Moffat
I have never been exposed to image reversal techniques. How do they work?
If lift off is possible, that would be very convenient!
Thanks a lot for your help!
Bye & Good Luck!
Pablo B.
>
> -----Original Message-----
> From: Pablo B [mailto:[email protected]]
> Sent: Monday, February 10, 2003 3:18 PM
> To: MEMS-talk
> Subject: [mems-talk] Etching holes in aluminum
>
>
> Hi!
>
> We need to etch some submicron holes in an Aluminum
> layer over GaAs. The holes would be patterned on PMMA
> using e-beam lithography. Is there any wet chemical
> etchant that will etch away the Al leaving holes of
> reasonable quality? Is reactive ion etching the only
> way?
>
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