I used to use a phase contrast microscope to align layers.
Once I found the alignment marks under the microscope, I would manually
scratch the resist with a scalpel (which needs a steady hand). Then I could
align the second layer to the scratches on the mask aligner.


On 14 May 2014 17:14, Bill Chow  wrote:

> 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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