how large is your mark? How thick is the resist? How thick is your first
layer?

yutchow2@gapps.cityu.edu.hk 于2014年5月15日星期四写道：

> Thanks for your suggestion. Unfortunately， I don't have phase contrast
> microscope. In addition, the first layer structure was not clear to see and
> difficult to observe both the alignment mark on the first layer and on the
> mask clearly at the same time. Are there any usual practice to locate and
> align the second layer with high accuracy? I am using Karl Suss MA6. Thanks.
>
> Regards,
>
> Bill
>
>
> ------ 原有訊息------
> 寄件者： Gareth Jenkins
> 日期: 週四, 2014年5月15日 8:30
> 收件者： General MEMS discussion;
> 主旨：Re: [mems-talk] Alignment problem with Multilayer SU-8 fabrication
>
> 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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