Kris
Bubbling in PR material, was really common in our lab. Especially,
az4620. As suggested by on reply, cleaning is very important, small
residual tent to trap the gas form exposure, which suppose to diffuse
through the PR in the atmosphere. You can also try 2 things that worked
pretty good for as.
1) degas your photoresit, we vacuum it, after each use.
2) increase your baking temp in 5C. be sure that you are still bellow
the crystal temp of the PR. if you pass this temp the PR will crack.

You can also try heating it up the pr material. We use a 3mm gap between
the Si and the hot plate for 1 min, before full contact backing.
I hope these is helpful for you
Giancarlo

Giancarlo Corti,
Graduate Student,  Mechanical Engineering
University of Idaho, POBox: 0902

----- Original Message -----
From: kris 
Date: Saturday, November 5, 2005 6:50 pm
Subject: [mems-talk] Bubbles in Photoresist
To: mems-talk@memsnet.org

> Hello All,
>
> I am following the following steps for AZP4903 recipe.
> I have bubbles problems
>
> [1]. Dehyrate Sio2 wafer at 150C.
> [2] Spin HMDS for 4000 r.p.m for 40 sec.
> [3] spin AZP4903 to shoot for the thickness of 15
> microns. Spin is usually done for longer periods of
> time to evaporate all the solvent in the photoresist.
> [4} Softbake the wafer from room temperature to 110C
> on contact hot plate. This takes almost 10 mins.
>
> when i expose the photoresist to the light(25mW/cm2).
> I have seen bubbles in the PR which were not observed
> during the softbaking step.
>
> Can anyone suggest me on this.