Xiao Qiang,
Your aspect ratio is 2.5 with wide separations between holes, so it should
be very doable. If you use commercially-made Cr mask, I have no doubt
about the sharpness of mask patterns. I don't know what kind of profile
you get from your experiment and how vertical you want, but something to
try is to use vacuum contact to minimize the gap. Trade-off of course is
mask and resist damage due to surface particulates. The way you calculate
your dose is right. You really have to try out which dose is the best for
your case. The recommended dose just give you a target to start with. If I
remember correctly, the manufacturer used projection printer to
characterize dose values. There are numerical aperture and depth of focus
to controls the overall resist profile. You don't have these parameters to
concern with. I don't use their recommended dose but I know I am not going
to try 10 mJ/cm2 or 10,000 mJ/cm2 either. You can read my article on my
approach to thick resist lithography optimization:
I. Chan and A. Nathan, "Thick Film Resist Lithography for a-Si:H Devices
with High Topography and Long Dry Etch Processes," J. Vac. Sci. Technol.
A, vol. 22, pp. 1048-1053, May 2004.
Feel free to ask if you have further questions. Best of luck in your
process.
Regards,
Isaac Chan, Ph.D.
On Fri, 6 Oct 2006, Zhang Xiao Qiang wrote:
> Hi, Isaac
>
> For my case, the thickness is 15 um. I am using hard contact mode and Cr
> mask. I am sure that the profile in mask is very sharp. What I am trying
> to do is process 6 um hole array with space of 20 um.
>
> Do you calculate the dose of print like this? For my MA8 aligner, the
> H-line is 405 nm and 10 mw/cm2, so for 1600 mw/cm2 I shall expose 160 s.
> Is it correct?
>
> My softbake time is too long if you compare with the recommended recipe
> of AZ P4620. Do you think it is proper?