Hi,

I have compiled all the responses regarding compatibility of Al,
Cr, and Pt in TMAH as following. I appreciate all the suggestions.

Li Shi

Date: Mon, 31 May 1999 13:27:30 -0700 (PDT)
From: Matthew Hills 
To: [email protected]
Subject: Re: Does TMAH attack Al, Cr, or Pt?

TMAH can attack Al.

It can be used for silicon etching if dopants are added to passivate
the aluminum.  see:
  http://transducers.stanford.edu/stl/Publications/PDF-files/ErnoThesis.pdf

TMAH is present in developer and even in the low concentrations there will
do some etching of the aluminum.  In the presence of other metals this
etching can be dramatically enhanced.  (exposed Ti and Aluminum is a bad
combination, for instance...)

Matt

Date: Tue, 1 Jun 1999 07:19:41 -0700
From: Linda Whittelsey 
To: Li Shi 
Subject: RE: Does TMAH attack Al, Cr, or Pt?

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Dilute TMAH will attack Al, but not Cr or Pt.  People often use TMAH based
developers such as AZ300MIF as an Al etchant.  AZ makes a positive developer
that will not attack Al (Simply called AZ 1:1 Developer)I am not sure if
more concentrated TMAH will attack Cr.  About the only thing that will
attack Pt is Aqua Regia.

Date: Tue, 01 Jun 1999 12:58:10 -0700
From: tim slater 
To: Li Shi 
Subject: Re: Does TMAH attack Al, Cr, or Pt?

platinum and chrome aer OK indefinitely, but the material the chrome is
deposited on will maybe be affected.  aluminum is REPORTEDLY ok after a
sufficient amount of aluminum is dissolved into the TMAH bath, but i've
never verified that experimentally myself (as you may know, sometimes other
researchers' results are not as useful as they seem from journal paper!).
i think you have to dissolve a lot of aluminum into the bath.  suggest you
avoid aluminum if at all possible.

cheers, have fun!

Tim

Date: Sat, 05 Jun 1999 19:50:29 +0100
From: Tom Rust 
To: Li Shi , [email protected]
Subject: Re: Does TMAH attack Al, Cr, or Pt?

Li Shi wrote:
>
> Could anyone tell me whether TMAH attacks Al, Cr, or Pt? THanks.
>
> Li Shi
>
>
TMAH does etch Al. Ever wonder why there are faint etch marks in Al
layers after you've stripped resist from misaligned wafers? The TMAH in
the developer.
--
Tom Rust
Nanochip Inc
Box 13249

Date: Tue, 8 Jun 1999 08:54:45 -0400
From: [email protected]
To: [email protected]
Subject: Re: Does TMAH attack Al, Cr, or Pt?




From:  Robert Antaki@MITEL on 06/08/99 08:54 AM
>From what I recall of my master's
TMAH at about 25% and around 80C etches Al and Cr.  It does no etch Pt.
I heard of additives that reduce dramatically Al etching, but I don't know
the details.
Some is linked to predissolved Silicon in the TMAH.

regards,
Robert  Antaki

Date: Tue, 8 Jun 1999 17:20:37 -0500
From: [email protected]
To: [email protected]
Subject: Pt,Cr,Al and TMAH

Hello,

I have not tried TMAH with Pt, Cr, or Al but I have some information which
might be of interest to you.

First,  I have worked with Pt lines on sensors and I don't think that TMAH
would attack it since EDP and KOH do not significantly attack the metal.
If TMAH does attack the metal then let me know since the only other wet
etchant for Pt is aqua regia at 90 C.

Cr's compatibility with TMAH I do not know.

There are several papers which discuss how to keep TMAH from attacking
Aluminum.  The first papers used powdered silicon then this migrated to the
Aluminum.  The first papers used powdered silicon then this migrated to the
addition of chemicals to replace the powdered silicon.  You may find it
hard to get a combination which doesn't attack silicon while giving a good
siicon bulk etch.  If you are only removing poly from filled trenches or
something than you should be fine.