Dear Avinash,
Ion milling works very well for non active structure. Since it is a physical
process (momentum transfer) the underlying material is prone to severe
surface damage. Cooling your sample goes a long way to minimizing the damage
to your photoresist.

I have used many resists, most with good results. One item to look for is
the formation of slag. Slag is a combination of the milled materials and the
resist. It usually forms on the sidewall of the milled feature. If an
insulator is going to be put on then the slag will be a problem. There are
some ways to deal with it. What type of miller do you have access to? What
is your substrate?

Sincerely,
Tom Wester

ProcessTek , PO Box 315 , Lynnfield, MA 01940
tel 781-595-1355 , fax 781-595-9582 , tom_wester@ieee.org

-----Original Message-----
From: askane@west.raytheon.com 
To: MEMS@ISI.EDU 
Date: Friday, February 19, 1999 2:13 PM
Subject: Ion Milling as an Alternative to Wet/Dry Etching of Aluminum


>     Hello everyone,
>
>     I'm currently working on process development for a multilayer
>     microwave integrated circuit. My final metallization layer is
>     aluminum, and I would like to minimize undercutting, so I am
>     considering a Barium Chloride type of dry etching procedure,
>
>     However, I recently learned about the ion-milling technique. It claims
>     to have virtually no undercut, and high yields. A careful choice of
>     photoresist must be made as the process generates much heat.
>
>     Anyone have any experience with ion milling? I would appreciate a list
>     of references, and some advice as to if this process is suitable for
>     microwave integrated circuits. I've already consulted the Jan '85
>     paper from Microwaves and RF.
>
>     Thanks in advance,
>
>     Avinash Kane
>     Raytheon Systems Company
>     Solid State Microwave
>     Fullerton, California
>     askane@west.raytheon.com
>
>
>