This happened to me once, and I traced it to temperature overshoot of
the oven. You may want to check your hotplate temperature with an
accurate thermocouple.


On Fri, Jul 19, 2013 at 2:58 PM, hamed khoojinian  wrote:
> Hello all,
>
> I am new to lithography so I apologize if questions are excessively
> ignorant.
>
> I am having trouble hard baking thick film of AZ4620. I am spinning on
> ~20um twice. My 40um of AZ4620 exposes and develops well, but on hard
> baking on hotplate the pattern is lost immediately as the PR reflows into a
> dome. This PR will be dry etched (so it will see high heat eventually).
>
> Hard baking:
> I am hardbaking 40-60um of AZ4620 at 90C for 30min (reflows in under
> 10min).
> I tried ramping 20-50C, holding overnight. Little rounding at edges, but a
> two days later it had reflowed even more.
>
> Other resists have had some problems, but I am still trying out new resists
> (right now i'm on 4903, and two negative resists).
>
> So can someone give me some guidelines on how to hard bake 4620 so I won't
> have to change the process much? I'm very confused because I thought the Tg
> for 4620 was not this low, and because I do single spins of 4620 (~10-15um)
> and hardbake at 90C without reflow! Why would thicker application drop the
> Tg so much?
>
> Should I try exposing post development to UV to crosslink the top before
> hard baking? Would that inhibit solvent evaporation too much? "Low and
> Slow" bake over 3 days? Or just give up on 4620... (any AZ class PR that
> would work here?)
>
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