Hai,

    The pictures obviously show that it has been overexposed.
I would suggest 30sec is more than enough for 20um...
Make sure you are using Filter to remove lower wavelength's, because at
lower wavelength's, SU 8 will obsorb UV light and its gives some
unexpected results.

If you want a paper regarding exposure optimzation, mail me I will send
you as Attachment.

Regards,

Riyaz Pasha Shaik

>
> > From: "Christoph Friese" 
> To: 
> Date: Thu, 29 Sep 2005 12:54:27 +0200
> Subject: [mems-talk] SU-8 over-exposure
>
> Hello,
>
> I'm working on SU-8 2010 for layers with a thickness of about 20µm on
> Pyrex.
>
> I exposed these layers with 120sec, 60sec and 30sec (with 9mW/cm2) and
> I'm
> observing some kind of overexposure (extrem with 120sec and nearly
> invisible
>
> at 30sec).
>
> [Pictures at http://www.imtek.de/micro-optics/SU8/SU8_2010_Exp.jpg]
>
> All three wafers are treated the same way, except the exposure dose.
> Could
> someone tell me what is exactly happening in the areas between the
> tines?
>
> Is this kind of a diffusion of the activated acid or just internal
> reflections
> between the substrate (Pyrex) and the mask?