I use a fairly ordinary lab hotplate (no programmable ramping) and allow
it to heat from room temperature and also allow it to ramp with the
hotplate from 65 to 95C. It takes a minute or two between temperatures.
If your heating is quicker is probably isn't a big problem so long as it
is fairly uniform and doesn't overshoot excessively.
With thinner layers ramping is less critical and also the soft bake is
much less critical than the post exposure bake. I think the most
important step is to allow it to cool slowly with the hotplate after the
post exposure bake.
I heard something about using a Petri dish as well but don't know how
much it helps. I think something was said about it reflecting heat back
onto the wafer as well which somehow help
Gareth


Peng Li (Paul) wrote:
> Hey Mike,
>
> That sounds a nice idea! I have a question though. Do you heat the wafer
> gradually from room temperature to 65C or you just heat it directly at 65C
> after spincoating? The same question can also be applied to the 65C to 95C
> situation.
>
> Our hotplate heats up very quickly, I have to do ramped heating manually.
> This give me a hard time. What kind of hotplate are you using?
>
> I also read that covering a Petri dish on the wafer during softbaking may
> also helpful, as this prevent the surface from drying too quickly.