Ned,

That should work, although you might experience some undercutting of the
aluminum due to the galvanic coupling of the Cr with the Al. There is no way
to determine how much undercut will occur except experimentally. You might
also experience some undercut of the Cr when you inititially pattern it
depending on your Al surface area relative to the photoresist covering the
Cr. That could be non-uniform depending on how long the etch continues
before completion.

----- Original Message -----
From: "Ned Flanders" 
To: "General MEMS discussion" 
Sent: Tuesday, January 03, 2012 6:30 AM
Subject: [mems-talk] Chromium as a mask for wet etching of aluminum


> Hey all,
>
>
> this may sound a bit weird, but I have my reasons: I need to wet-etch
> (phosphoric acid as enchant) an aluminum wafer. I must use an
> inorganic mask for the purpose, but my favorite would be chromium:
> deposit a thin layer of chromium on my aluminum wafer, pattern it with
> ceric ammonium nitrate and then etch the aluminum with phosphoric
> acid. I need to etch some 100 um of aluminum.
>
> The big problem I have is, I don't know whether there will be some
> electrochemical effects that would prevent either of the etching
> processes. Let me know before I go and waste several hours in a futile
> attempt.
>
>
> By the way, happy and fruitful New Year - good health and successful
> experiments going forward!
>
>
> m