On Tue, Feb 20, 1996 10:46:26 AM at Jim Folta wrote:
>My problem is that the photoresist tends to recede from the edges of the
>tops of the mesas. It seems that high surface tension of photoresist on
the
>silicon nitride coated surface causes the already thin resist to draw back

>from the edge. I use DMSO vapor adhesion promoter. The receding effect
occurs
>for both spin-coating, and dip coating with thinned resist. Do you know if

>this surface tension effect occurs on oxide surfaces as well?
We have observed the same problem with both spin vs dip coating (thinned)
methods, on oxide surfaces, after using HMDS prep. And I agree -- this is a
fluid mechanics problem. The problem occurs mainly during the hard bake.
Apparently the resist (Shipley 1808, 21%, which we have also used after
diluting to 10% and even 5%) becomes liquid enough during a hard bake at 135
degrees C to reflow. And reflow it does, away from the trench edge. The
edge-reflow problem is certainly reduced by lowering the hard bake temperature
to 110 degrees C, but then come increased problems with the wafer sticking to
the mask plate after alignment and exposure. This is a situation where we'd
like to try a mask aligner that makes a softer contact during exposure --
unfortunately we do not have such an aligner.

Has anyone had success with using a low hard bake temperature (110 degrees C or
less, Shipley 1800 series resist) and avoiding problems with the wafer sticking
to the mask plate after alignment and exposure?

Perry Skeath