Hi,

Thank you all for the great information provided.

Our UV lamp is not designed for lithography. It is simply an adjustable UV
source for polymerization without any lenses to collimate the light. We measured
intensity of the UV source and it is good for SU-8 exposure.

However, we also observed thicker shadows along side walls for tall features
than short features under profilometer, indicating a larger slope of walls for
tall features.

In addition, when the features are tall, small rater patterns cannot be well
separated, forming grooves between them. This is not like T-topping, but it is
the opposite.

The T-topping may be caused by the excessive absorption of DUV or i-line while
the reverse pattern is more likely to be caused by either the collimation of the
light or the contact between the mask the substrate.

Since I can ensure a fairly good vacuum and direct contact between the mask the
substrate, I believe that the problem lie in the collimation of the light.

I do not think I can modify the setup of our UV light by adding a front lens,
but I　will see if I can select rays which are in certain direction and block
others. This can reduce the intensity but maybe I can increase the exposure
time.


One more questions, is this sloped side wall issue a common problem for people
using soft masks (plastic masks)?


Any suggestions are appreciated.

Cheers


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