Extension of discussion with Ravi on lift off.  The objective is to
produce a resist pattern where the dimensional control is easy and there
is a reverse angle on the resist side wall.  This ensures the deposited
metal does not stick to the side wall.  There are many ways to achieve
this. 1)  Ignore and use very thick resist.  2) Use chlorobenzene which
swells the top of the resist to create an overhang.  3) Use 2 resist
layers the top layer creates an overhang.  4) Use an ammonia reversal
technique that neutralizes the first exposure.  Then use a controlled
flood exposure that allows the resist profile to adopt a reverse slope.
In my experience +22 degrees to -22 degrees is practical.  A lot of
users aim for vertical to create maximum Critical dimension control.
Most lift off users aim for -22 degrees.  Dimensions down to .08 microns
and resist thicknesses up to 40 microns are practical.  Contact me for
more information and or technical papers.

Bill Moffat, CEO
Yield Engineering Systems, Inc.
2185 Oakland Rd., San Jose, CA  95131
(408) 954-8353

cell 408 590 4577
bmoffat@yieldengineering.com
www.yieldengineering.com

-----Original Message-----

On 1/15/07, Ravi Shankar  wrote:
>
> Hi all,
>
>    I need to use lift-off process for my device fabrication.. So far
> we haven't standardised lift-off process in our lab. We are suing
> S1813 and HNR 120 photoresists... Is it possible to achieve lift-off
> process with these low thickness photoresists? Can any one suggest
> recipe for lift-off process.. suggestions will be highly appreciated.