It is indeed aweful! Some thoughts.

1. I don't know what the thickness of your resist is. However, I would lower
the exposure and go with a longer develop time. Selectivity goes up when the
driving force of a reaction is less. It is a universal principle whether
etching or adding halogens to alkanes. I would do a small DOE.

Also, what feature size are you resolving? If you are trying to do features
smaller than your resolution, you are going to have poor edge features. The
light from one edge is "bleeding" through to the other edge.

2. If #1 doesn't fix it, I think 54 deg. is fairly bad even for a poor
process, it might be your exposure tool. Suss is fairly good and fairly
helpful on technical help. HOWEVER, before you call them, collect some data.

A. Run a resolution mask and see what the resolution of your process is
across the wafer. Also, check edge sharpness of different size features.
Make sure the mask has X & Y features.
B. Check that the coatings on the inside of the optical chambers haven't all
peeled off and you are dealing with scattered light.
C. Check that your lens and other optical surfaces aren't fogged or cracked.

D. Check that your soft contact is really a soft contact. Put a wafer in the
tool, load a blank mask, and then illuminate it with monochromatic green
light and see your fringe pattern. This might involve using an extension
mirror.

Suss can help you with interpreting the resolution mask results.

Ed Sebesta
Secretary of Texas MEMS organizing committee.


-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Andrea Mazzolari
Sent: Sunday, January 17, 2010 7:20 AM
To: General MEMS discussion
Subject: [mems-talk] S1813 vertical sidewalls


Hi All,

i need to pattern S1813 with vertical sidewalls, but at the present time i
get an angle of about 54 deg. Awful... My maskaligner is an old karl suss.

Here is my procedure:
-spinning of S1813
-soft bake 3 min at 115 deg
-photolitography in contact mode (150mJ)
-development in MF319 (about 45 seconds)
-hard bake 15 min at 115.

Any suggestion to improve the sidewall angle ?

Best regards,
Andrea