Hi YiYi,

For your application, vacuum contact lithography and Cr mask may be the
best approach to obtain your resolution. But one concern is that your 2-um
squares will be 45deg "tilted" from your intended design due to the
Fraunhofer diffraction pattern of your UV light source through a square
aperture. Please consult with any textbook on Fourier optics for the
physics of this diffraction pattern. I have seen this effect based on my
experiments. My suggestion is that your Cr mask design should try both
your intended square array design and another one with your squares tilted
45deg to compensate for the possibility of this effect.

Or they can be degenerated into circular holes depending on
the contrast of your resist and your hardbake condition (don't do 120C
hardbake if you don't want your resist to reflow). Also, the more the gap
between your mask and your resist, the higher the tendency to get circular
holes.


Yours sincerely,

Isaac Chan, Ph.D.
University of Waterloo

On Wed, 18 May 2005, Yi Zhao wrote:

> I want to pattern 2 micron holes array (center to center distance for
> neighboring holes is 4 micron) on 8 micron thick AZ4620. I prefer a near
> vertical sidewall profile of the resist. Does any one has experience on
> it, or any suggestion?