[mems-talk] un-steep wall for AZ 4620

[Brubaker Chad]

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: c.brubaker at EVGroup.com, www.EVGroup.com


-----Original Message-----
From: mems-talk-bounces at memsnet.org [mailto:mems-talk-bounces at memsnet.org] On Behalf Of Zhang Xiao Qiang
Sent: Wednesday, September 13, 2006 6:11 AM
To: mems-talk at memsnet.org
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 at 70C and 2min at 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 at 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?