How thick are the washers?  Have you tried exposing without using the washers at
all (i.e., contact exposure)?

Prof. Jeffrey P. Wolinski
Department of Physics
Grove City College

Voice: 724-458-2201
Fax: 724-458-2181

-----Original Message-----
From: [email protected] [mailto:mems-talk-
[email protected]] On Behalf Of Dimitar Dimitrov
Sent: Tuesday, July 08, 2014 01:26 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Unremoved SU-8 after exposure

Thank you,

The imprinter is kind of strange. The lamp is at the bottom. 20 cm above is a
vacuum chamber. The bottom of the chamber is quartz 1/2 inches width. I put the
mask over the quartz. The Si wafer is upside down so SU-8 is facing the lamp.
Two washers are separating the mask with wafer.

Do you think that the quartz is scattering the light and the distance between
the mask and film is enough to allow it to expose everything?

I never thought of this.


-----Original Message-----
From: [email protected] on behalf of
Andrew Sarangan
Sent: Mon 7/7/2014 7:21 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Unremoved SU-8 after exposure

My guess is you are getting exposure due to scattered light from the back side
of the wafer (since you are using pyrex).  SU8 is very transparent to UV. I use
a second wafer on the back side painted with a mat black paint.

On Mon, Jul 7, 2014 at 1:25 PM, Dimitar Dimitrov 
wrote:
>
> Hello,
>
> I am graduate student in Brooklyn College and I am trying to reinvent the
whole MEMS procedure as I do not have any professional help. My science adviser
is from another field.
>
> I am having difficulties with the developing of SU-8 2025. Here is what I am
doing:
>
> I am spin - coating 4 inch Si or Pyrex wafer to 50 - 60 um thin film
> Pre - baking at 96 degrees for 15 min Sometimes instead I am putting
> the wafer in the vacuum chamber of my UV imprinter. The vacuum is taking away
the solvent and clear most of the bubbles.
> UV exposure with a hand made Imprinter: Xenon lamp 22kV at 10 microsec.
pulses. Three 30 seconds exposures with couple of seconds pause.
> UV lamp creates heat so the wafer is let for 2 - 3 min to relax.
> Post bake of 15 min at 95 degrees.
>
> Developing by tenderly shaking the wafer in a vessel with Propylene glycol
monomethyl ether forever.
>
> The result is that I clearly can see my pattern as exposed SU-8 is yelowish
but the unexposed parts are not removed and form thin film with the exposed
part.
> Less exposure leads to removing all of the polymer.
> (This is happening even without any mask but the pattern is formed by
> metal structure that divides 4 inch wafer into several smaller
> regions.)
>
> Can anybody figure out what is my mistake?
>
> Thank you
> Dimitar Dimitrov
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