[Libre-silicon-devel] OK. That happened (Funding)

Staf Verhaegen staf at fibraservi.eu
Fri Dec 18 10:31:45 CET 2020

Ferenc Éger schreef op vr 18-12-2020 om 02:50 [+0100]:
>     Hello Everyone,
>     I recently elaborated further on the optical considerations of
>       the uLED reticle topic. I put the results into the maskless
> litho
>       repo as usual:
> https://redmine.libresilicon.com/projects/maskless-lithography/repository/43/revisions/master/entry/uLED_optics
>     Please find errors in it...

Nice work, I agree that when using a LED matrix array it corresponds
with handling each point as independent light source (this contrary to
the use of micro-mirrors where off-axis would still be possible). It
thus corresponds to optimization of the optics for what in lithography
is called isolated features. What does stay the same is that
optimization of the lens NA is a trade-off between DOF (depth-of-focus) 
and resolution + sensitivity to light intensity variation.
The light intensity variation is caused by difference in intensity
between different LEDs, the variation in intensity of a single LED over
time and the non-uniform intensity over the field of the lens system.
The first could in theory be corrected by varying the on-time of
different LEDs although then the resolution in time has to be higher
than the total 'amount' of the light in the minimum period.
The focus variation is determined by the quality of your leveling
system, the flatness of the top surface you want to image on and the
non-uniformity of focus over the field of the lens system.
In lithography this is verified experimentally by looking at so called
focus-exposure (FE) matrices. This optimization can be done on a built
system although money can be saved by elimating the need for high-NA
from the start. The cost of lens sytem increases with increasing field
size and increasing NA.


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