Hello Bill,

what I usually do is to wipe the keys with the acetone. As the first layer
is already after PEB and cross-linked it withstands the solvent quite well,
the second layer is easy to dissolve. I use at least two swabs for one key,
first removing the SU8 in wider area around the key and second to remove
residues from inner part.

Of course this can be done only if keys are far enough from the product, or
you have to sacrifice some products close by.

Common way to avoid this issue completely is to use the substrate which
already contains the alignment keys (e.g. in metal) and align both SU8
layers to it.

With best regards,

Daniel



Daniel Figura

smartfabgroupT Company

process consulting . data processing . fab software

Phone: +421 944 45 26 86

E-mail: [email protected], Web: www.smartfabgroup.com



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-----Original Message-----
From: [email protected]
[mailto:[email protected]] On
Behalf Of [email protected]
Sent: Thursday, May 15, 2014 15:32
To: [email protected]; [email protected]
Subject: [mems-talk] ??: Alignment problem with Multilayer SU-8 fabrication

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


------ ????------
???: Gareth Jenkins
??: ??, 2014?5?15? 8:30
???: General MEMS discussion;
??: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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