There are a few things in your process that look a little off to me.
First, your spin time is pretty short. This, by itself, is not a problem.
However, it does tend to leave a greater amount of solvent within the film.
This leads to the second issue.
For the film thickness you are coating (~12µm), your bake is awfully low
temperature and very short. Keep the 70C bake (this helps prevent bubble
formation), but increase your final bake temperature to between 105ºC and 110ºC,
and increase your bake time to ~ 3-5 minutes. A bake plate with programmable
ramp proximity pins (such as that on the EVG100 series coaters) can help with
this process, eliminating the need for the two-temperature bake.
It sounds as if you may have too much solvent in the resist during
exposure/develop. This tends to make the un-exposed region more soluble in the
developer.
Your exposure also seems a little low, but I am more accustomed to broadband
exposures, so I can't be sure. As a test, try increasing your exposure dose by
~50%. If you are underexposed, it will make the exposed region less soluble
than it should be, requiring a more harsh developer, and a longer develop time.
This is requiring you to use a 1:3 dilution of AZ400K when, for a 12µm film, you
should be using 1:4. This, combined with the higher solvent content in the
film, can make your trench features (especially at the top region, where the
sidewall becomes exposed to the developer immediately) to widen.
Finally, I have never needed to use a post-exposure bake for AZP4620 - I don't
know the specific behavior of the material, but this may cause some lateral
diffusion of the photo-active compounds within the film.
Best Regards,
Chad Brubaker
EV Group invent * innovate * implement
Technology - Tel: 480.727.9635, Fax: 480.727.9700 e-mail:
[email protected], www.EVGroup.com
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Zhang Xiao Qiang
Sent: Wednesday, September 13, 2006 6:11 AM
To: [email protected]
Subject: [mems-talk] un-steep wall for AZ 4620
Dear all
I am trying to make the pattern size of few microns and the aspect
ration is 2:1 to 3:1 using AZ 4620. I found that it is difficult to get
the steep wall. The upper pattern is about 7-8 micron for designed 6
micron pattern after developing. My recipe is spin coating 20s+1600
rpm(about 12 micron), soft bake 1min@70C and 2min@100 C. leave the baked
samples for about one hour and then exposure 40 s using I line(365 nm,
10 mW/cm2). PEB 2 min@100 C. Develop for 2.5-3 min using AZ 400K : DI
water 3:1 developer.
Do you think I made any mistakes and the task is feasible?
