David,

Can you say a bit more about the process and equipment that you are using?  What
is your exposure dose (mJ/cm2)?  Are you using hot plates that are made for
photoresist processing or lab hot plates?  Have you characterized the
temperature uniformity of the hot plate?  of the substrate on the hot plate?
When you say full strength TMAH developer, what is the %-age of the TMAH in
developer, for example, 2.25%?

What I have found in general is that the PEB is a the most critical parameter,
and PAB perhaps just a bit less so, but also important.  If there is a non-
uniformity in the hot plate temperature, or if the surface is not machined flat
and you are not using a vacuum to hold the substrate, the substrate temperature
will vary and this will cause process non-uniformity.  Similarly, if your
substrate has poor thermal characteristics, additional attention must be paid to
be sure the resist-coated surface reaches the required temperature.  You mention
a 7x7" area, so if your substrate is not round, you may be getting resist on the
back side, again causing poor thermal contact with the hot plate and non-uniform
temperature transfer.  I think the process latitude should not be that narrow.

Brad Cantos
brad.cantos@holage.com
http://holage.com




On 10 May 2010, at 2:07 PM, David Casale wrote:

> I have recently been using NR9-1500PY resist from Futurrex for lift-off
> metallization and wanted to see if anyone else has the same experience
> that I am having with the resist. I am using a Bachur upright exposure
> unit with near UV exposure, vacuum contact printing, and hotplates for
> the PAB and PEB. I have been developing using full strength TMAH based
> developer. My experience thus far is that the process latitude is very
> small for getting the resist to work properly. I have noticed a
> significant difference in the amount of undercut based on exposure and
> develop times, and a also occasionally the resist just seems completely
> over exposed and unable to develop at all. I also notice quite a bit of
> variation in the amount of undercut over a 7"X7" area. I am just curious
> if I am missing something in my process control that is common, or if
> this is just the nature of using this type of LOR.
>
> Sincerely,
>
> David Casale
> R&D Engineer
> www.maxlevy.com 
> Max Levy Autograph
> 2710 Commerce Way
> Philadelphia, PA 19154 USA
> tel: 215-842-3675