Hello Penghui,

unfortunately, you did not describe your coating problem in detail, so it is
quite difficult to present good solutions how to improve your coating
results. But most of the coating problems I have seen so far are caused by
one or more of the following reasons:

Temperature problem:
If the resist and the substrate have different temperatures you will see a
circular nonuniformity after the coating, depending on the area where you
have dispensed the resist. The coater chuck is critical as well because a
temperature difference between chuck and substrate may lead to an image of
the chuck in the coated resist layer. To minimize this problem, make sure
that both, resist and substrate, have the same temperature, make also sure
that the spinner chuck is made of (or at least coated with) a material with
a low thermal conductivity.

Turbulences:
Depending on the design of your spinner bowl and the exhaust flow you may
have turbulent airflows above the wafer causing stochastically patterns in
the coated layer. Try to reduce the exhaust to see if the coating results
gets better, but be careful not to allow the solvent fumes escape from the
spinner bowl.

Skin on the dispensed resist:
Open resist tends to dry out quickly, producing a skin on the surface. When
dispensed onto the wafer, this skin may cause nonuniform coatings. If you
use a spin coater with an automatic dispense system, try to do a
pre-dispense before every coating process to have "fresh" resist on the
wafer only. If you dispense manually and directly from the bottle, you
should take care of closing the bottle tightly after each dispense.

Resist quality:
Old or contaminated resist may lead to weird coating results. Also resists
that have been stored at a too high temperature could make it impossible to
achieve a good uniformity. If you have access to another bottle of the same
resist type, do some tests with this material and see if the results are
different.

Surface defects on the substrate:
I expect you substrates to be perfectly flat and free of voids, but to
complete this list it is necessary to mention this point as well. Any
particle on the surface to be coated will cause striations (comets) in the
resist layer and thus a poor uniformity.

Please feel free to contact me directly if you have any further questions.

Best Regards,

Frank.


--------------------------------------------
SUSS MicroTec
Applications Center Europe
Frank Runkel
Schleissheimer Str. 90
85748 Garching
Germany
Fon     +49 89 32007 - 302
Fax     +49 89 32007 - 390
email   [email protected]



> --__--__--
>
> Message: 6
> Date: Thu, 4 Apr 2002 14:43:41 -0800 (PST)
> From: penghui zhao 
> To: [email protected]
> Subject: [mems-talk] uniform of resist on Platinum
> Reply-To: [email protected]
>
>  Hi, guys
>
> I have read letter son the web page, so I want you to help me with the
> nonuniformity. I met one problem when I spin resist on the Platinum, the
> resist is not uniform. I do not make it yet.The resist used is  S 1805
> photoresist containing: propylene glycol monomethyl either acetate, and
> the adhesion promoter is AP010 HMDS. Would you please give me some
> suggestions to solve this problem to get uniform spin coating?  Thanks a
> lot!
>
> Sincerely yours
>
> Penghui Zhao
>
> Deparment of Materils Science
>
> University of North Texas
> Yahoo! Tax Center - online filing with TurboTax
>
> --__--__--