Hi Ruilin,

Well keeping your SU-8 in a small bottle in the fridge is not
detrimental per se, but it could cause problems if you were to open
the still cold bottle in a humid environment. This would cause water
condensation to contaminate your sample. I don't think condensation is
the source of the stiction problem, however. On the contrary,
contamination usually degrades SU-8 / substrate adhesion.

In your case, you have a thick resist layer, with some parts (most
probably the outer rim) thicker, and thus less dry, than others after
the soft bake. Try to incorporate an edge-bead removal program in your
spin profile, or increasepre-bake time or temperature to dry off even
the thickest regions. These are the only things I can suggest.

If you stil get stiction, then play around with the contact mode. Try
proximity instead of vacuum or pressure contact.

p.s. also perform a "pihrana" on the mask plate. It must be pretty gooey by now.

Good luck.

Regards,

Michael Larsson

> ---------- Forwarded message ----------
> From: "郑瑞麟(Ruilin Zheng)" 
> To: "General MEMS discussion" 
> Date: Wed, 22 Oct 2008 09:18:50 +0800
> Subject: Re: [mems-talk] SU-8 layer stick to mask after exposure
> Hi,
> Thank you all for the advice!
>
> I checked my hotplate, and I think it works ok, because I found that the the
> SU-8 layer shrunk a lot and the edge of silicon wafer appeared after
> soft-bake, when I used higher soft-bake dose.
> The exposure dose should be reduced than that without Omega UV filter, but I
> also tried to increase the exposure time by 40%.
> The problem has not been solved yet.
> Can this problem have something to do with the photoresist itself?
> The SU-8 I am using is stored in a small bottle ( sealed but not very well )
> instead of the original bottle, and put in the refrigerator (several degree
> above zero) for over two months.