Hi Ruilin,

You could try to set your mask aligner to proximity mode, if currently
set to contact mode, albeit at the cost of poorer resolution. But, if
your layer is relatiuvely thick, which I am guessing is the case as it
appears to have excess solvent, then resolution and side-wall profile
will not be too good anyway. Do some trials at different proximity
gaps, and compare resolution results to those when using pressure or
vacuum contact.

Other things you could try are i) increasing your soft-bake time, at
lower temperature and/or ii) conducting all baking operations on a
hotplate, to drive off solvent from the surface, and avoiding the
formation of a "dry skin" as often happens during oven baking.

Good luck, and remember: SU-8 is more art than science. You have to
put in the time to get the best process for your application, and
eventual processes are often not easily transferrable (hence the part
about art)

Regards,

Michael Larsson


> From: "郑瑞麟(Ruilin Zheng)" 
> To: mems-talk@memsnet.org
> Date: Tue, 21 Oct 2008 19:22:36 +0800
> Subject: [mems-talk] SU-8 layer stick to mask after exposure
> Hello, everyone,
>
> I met a problem in SU-8 process recently, the SU-8 layer stick to the mask
> after exposure.
> I rarely have this problem before. Two weeks ago, I applied an Omega UV
> filter for the exposure step to filter out short wavelength UV light.
> And this problem appear every time during exposure.
> At first I think it may be caused by insufficient soft-bake dose, but after
> I tried to prolong the baking time and use higher temperature, SU-8 layer
> still sticked to the mask.
> Does anyone have some ideas about this problem? Please help me out.
>
> By the way, the photoresist is SU-8 2150 by microchem, will be expired at
> Dec,2008.