Looking at the profile it looks like reflections. You see the cancellation
at the bottom etc. if this was diffusion, the line widening would have been
more uniform.

Shay

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Christoph Friese
Sent: Thursday, September 29, 2005 12:54 PM
To: [email protected]
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?