Quinghong,

I have successfully used image reversal on 4-6µm of resist (Shipley
SPR220 series) to lift off 2µm of evaporated Au in a pilot-production
mode.  As you have noted, the bilayer resists are unstable and I have
found the results to be difficult to repeat consistently with thick
layers.  The advantages of single layer image reversal is that it is a
very mature process, and it has excellent latitude for exposure and
development, especially if you are patterning isolated lines or pads.
On the negative side, you need to generate masks that are opposite
polarity, you need a specialized oven that provides ammonia atmosphere
for the image reversal step that typically takes 1 hour, and a flood
exposure step is required.  There is at least one contributor to this
forum (Bill Moffat) who has offered to do samples in the past.

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

LinkedIn: http://www.linkedin.com/in/bradcantos


On Feb 9, 2009, at 10:47 AM, Qinghong Du wrote:

> Hi
>
> I am looking for bilayer PR lithography to generate undercut for 2um
> Au lift-off process. Anyone can sugguest some solutions? Currently I
> use OCG825 and AZ5214E bilayer PR, but it is not very stable.
>
> Thank you for your help.
>
> Qinghong
> DiCon Fiberoptics, Inc.