Larger than specification Raith Circles on Photonic Crystals
jwc at snf.stanford.edu
Wed Nov 24 11:47:11 PST 2004
In my thinking about your problem with Larger than specification Raith
Circles in your ZEP-520-12 exposures, I think I have come up with
several reasons for the results you showed to me last week! I would
like you to consider the following factors and make some exposure test
over the holiday period.
Check your single pixel line dose and the area step parameter. If your
SPL line dose is too high you will get much larger SPL dimensions. That
coupled with a very small area step which would exacerbate this effect
and in my thinking could lead you to the results you showed me. (Raith
circles with diameters nearly 50% larger than specified in GDS file.)
Please do an exposure test on your substrates and expose at DF 0.7,
0.75, 0.8 of the SPL dose you determine to just clear a SPL with a
matrix of area steps on the order of 20, 30, and 35 nm. This should
likely get you back into the right size specification for your Photonic
Crystal patterns. My ZEP-520 optimized dose for SPL's is 90 - 120 uC/cm
on Si substrates at 10 kV using the 20 um aperture
With the pitches you are using (~ 500 - 500 nm?) you will experience
some contribution for exposure proximity effects and to adjust for this
you would need to reduce your exposure dose while evaluating CD
dimension, in this case the diameter of your Photonic Crystals.
The only other significant factor could be if there exist a decided
offset in the backscatter response of your quartz substrates. In the
past I would have increased my dose slightly when writing on my
substrates but in your case it is better to carefully evaluate and
determine your actual 'dose to clear' on your substrates. You may find
that the 10 kV 'dose to clear' is in the 30 - 35 uC/cm^2 regime instead
of the normal 40 uC/cm^2 we typically employ for Silicon substrates.
(reference ZEP -520 resist Thickness ~240 nm.)
I have not had a chance to get any feedback from RAITH in this
concern.. I do hope to speak with Michael Kahl and Joe Klingfus with
RAITH after the Thanksgiving holiday on this and a number of
application issues and questions.
Thank you for your support!
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