Hi Madhav,

Achieving good adhesion between Shipley resists and SiO2 is always a
challenge. You certainly have to ensure your wafer is sufficiently
dehydration baked, and you also need to include an HMDS vapour priming
step for your resist to stand any chance of remaining attached to the
wafer after development.

A few more points to note: your resist could be old or contaminated -
remember contamination could simply be in the form of moisture
absorption. Old resist usually has a lower solvent content, meaning a
shorter time may be required during soft bake.

Some quick changes to your process that could help improve adhesion:
1. Piranha followed by SC1 and SC2 cleaning steps;
2. dehydration bake @ 150 deg C in a (clean) convection oven for 30 mins;
3. Vapour priming step using HMDS;
4. Optional dehydration step @ 150 deg C in convection oven for 30
mins - HMDS is hydrolysed, and thus rendered useless (actually even
detrimental to adhesion), in the presence of moisture;
5. Spin resist soon after wafer cool-down;
6. Soft-bake @ 90 deg C in a convection oven - there is a school of
thought that the high-temp, short ramp profile can be too aggressive
for certain applications.

Good luck. Hope this helps a little.

Regards,

Michael Larsson, PhD


> Hi,
>       I am experiencing a problem in patterning on silicon-di-oxide
> wafers; I am using SHIPLEY 1818 resist to get a thickness of 2.5 micron; 6
> seconds of exposure time. After developing for 60 seconds, I observe, the
> resist layer peels off; leaving no patterns on the wafer. Also I had
> soft-baked the resist at 95 C for 2 minutes in hot-plate.
> This seems strange to me, as a month ago, I had successfully transferred
> the patterns on to silicon-di-oxide wafers.
> I am using mylar film masks.
> Please let me know, if any one had experienced similar problems before; and
> if so, could you let me know suggestions to solve ?
>
> Thanks
>
> Regards,
> Madhav Rao,
> Graduate student,
> University of Alabama.