Hi Nidhi,

Only a suggestion to your first problem. If there is Cr diffusion it should
probably appear under an optical microscope. Edges should give you a clear
idea. My thoughts are that you might have had a fine layer of undeveloped
resist and the etchant is not reaching the Chrome layer. A simple experiment
may prove it. Take two dummy PDMS pieces, do the process exactly the same
and instead of a photomask patterning, flood expose them. Later develop one
sample in your developer and strip another sample. Now check with the Chrome
etchant. I would prefer using resist strippers like 1165 but even acetone
may work. If both of them behave the same way then it is probably thermal
treatment that is the culprit.

At that point, I think you would be better off spinning the resist and
leaving it overnight at room temperature. But that is for the next set of
experiments.

I would look for other suggestions from the group too.

FYI, Shipley resists contain PFOS (which is carcinogenic) and are being
eliminated from usage in big companies.

Thanks,
Pavan

On Wed, Jun 17, 2009 at 2:12 PM, nidhi maheshwari wrote:

> Dear All,
>
> This is with reference to my earlier question on metallization on
> PDMS. Few problems which I am still facing with regards to
> metallization on PDMS are as follows-
>
> 1) I have only a Chrome layer (~20nm) onto PDMS. For patterning this
> layer, I spin coat positive resist (Shipley S1813) and pre-bake
> (keeping the pre-bake temperature to as low as 45C). When I try to
> etch chrome, the layer of chrome remains intact, i.e. to say there is
> no etching even after 30mins in etchant (ceric ammonium nitrate
> +acetic acid mix). While the sample of chrome on PDMS which is not
> patterned gets etched easily. Can it be some kind of diffusion of
> chrome in PDMS while pre-bake of resist which is not allowing it to
> get etched?
>
> 2) Gold film on PDMS once etched in KI+I2+water mix imparts a reddish
> colour to PDMS. The colour is of etchant and it is not removed even
> after sonication in acetone and water. Is it due to the etchant
> getting adsorbed by PDMS? Will it change the properties of PDMS?
>
> Apart from the above queries I would also like to know has anyone ever
> tried patterning PPR onto PDMS say for a lift-off process? I have
> tried spinning PPR directly on PDMS and also spinning HMDS first and
> then PPR. In both the cases PPR is not sticking to PDMS. Can someone
> please suggest some way by which I can spinh coat uniform layer of PPR
> onto PDMS.
>
> Thanks and warm regards,
> Nidhi