When patterning ITO, we used a mixture of (160mL) HCL and (40mL) Nitric at
45C (Aqua Regia).  Prior to this step it was important to anneal the film.
The anneal improved conductivity but it also improved the etch properties
substantially.  If the anneal was skipped, we experienced undercutting as
you've described.  At the time, i was using Shipley S1811 positive
photoresist, but I assume others would work fine.

With our recipe the "anneal" was simply 25 minutes in the oven before
lithography (~200C) but we also had reasonable results with a furnace anneal
or in-situ anneal after sputtering with lamps.

As another mentioned, you could also try a lift-off process.  It should work
fine for such a thin film and large features.

Hope this helps,
Alasdair

On Tue, Sep 13, 2011 at 10:18 PM, Yanhua Dai  wrote:

> Hi, All
>
> Does someone know how to pattern ITO/glass? The ITO film on the glass is
> about 30nm and the pattern feature is about 20um. I tried HCL and it removed
> ITO under resist. And does someone know recipe using photoresist as a mask?
>
> Thank you very much!
>
> Yanhua