Dear all,

Recently, I am working on a two layer SU-8 structure. All the process are
followed with the suggested procedures. However, the problem appeared when I
try to look for the alignment mark, after I have spin coated and prebaked
the second layer of SU-8, it is difficult to locate the first layer exposed
features.

First layer thickness : 3.7um
Second layer thickness : 17 - 20um

I found that it is extremely difficult to locate the first layer pattern
under the microscope after I have coated the second layer, despite it can be
seen be naked eye.... Sometimes if there are some defect or bump in the 2nd
layer above the alignment mark, then it can be seen clearly. However, it  is
a random process and will affect my pattern. Are there any ways to improve
the visiblity of the alignment mark after I have coated the 2nd layer?
Thanks.

Regards,

Bill

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