Projectors

August 27, 2023 - A catadioptric VUV photolithography projector, submittewww.spiedigitallibrary.org/conference-proceedings-of-spie/5962/59620Y/Catadioptric-projection-lenses-for-immersion-lithography/10.1117/12.625199.short d by Professor Jose Sasian

Jose's contribution is a catadioptric photolithography system, as described in US Patent Application #20030058421A1, example 1; the figure below shows a schematic.   Note that the object field is decentered from the optical axis, enabling fold mirrors at two intermediate image planes.  Several SPIE papers nicely describe the need for such systems, as well as their implementation.  An important design feature is the use of a poorly-corrected intermediate  image plane to balance aberrations across this intermediate image. 

The posted design claims excellent color correction, due in part to the use of calcium fluoride lens elements.  The +- 1pm bandwidth sounds tiny when compared to photographic applications, but is quite broad for photolithographic sources.  I posted the file as a lens archive (.zar) file to include the index of refraction near the disclosed 157nm wavelength.  I pulled these values from published data, then corrected the index of the intermediate spaces to bring focus to the disclosed image distance.

The model also illustrates balancing of aberrations across the image planes.  The figures below show the surface-by-surface contributions to the Seidel wavefront terms for axial color (W020) and spherical aberration (W040).  The intermediate image planes are at surfaces 20 and 32  On the W020 plot, notice that the contributions are small or positive in this surface range; outside of this range, notice that the contributions are generally small or negative.  Similarly, on the W040 plot, notice that the contributions are generally small or negative in the S20-32 range, while the contributions are small or positive outisde this range.

February 28. 2015:  12 new projectors submitted by Steve Eckhardt   

        Most of these files are assigned to U.S. Precision Lens (USPL), which, as an independent manufacturer of TV projection lenses, filed many patents.  It later became part of Corning, then 3M.  Projector lenses are often good starting points for telecentric designs; I find the USPL designs to be less helpful because of their heavy use of aspheres.

September 15. 2014:  24 Projector design files posted   

I’ve uploaded several files today:

- Twelve designs for conference room projectors.  I’ve found these designs to be useful reference points for telecentric systems.  The designs generally have a little zoom, with surprisingly complex motion of the elements through zoom.

- Five cinematography projectors.  Image quality is excellent; and, as with most cinematography lenses, color correction is excellent.  Notice that one design is anamorphic.

- Two projectors for photolithography.  Most patented photolith systems are so complex that they don’t seem too instructive.  An obvious exception to this is the original patent for the Offner relay system, a 1:1 projector using just two mirrors.

- Four designs of overhead projectors.  None of the models is typical, in that all four elements instead of the typical three.  One has an unusually large field of view, enabling projection without keystone distortion.  I’m surprised by the relatively poor image quality, although the poor imaging could be due to inaccuracies in the published design example rather than the design capability.

Two of these projector models are based on patents from important court cases regarding lens design.  U.S. Patent #3,126,786 was the subject of 3M vs. Projection Optics, and U.S. Patent 3,748,015 was the subject of PerkinElmer vs. ComputerVision.  Both court cases covered tricky issues on obviousness and prior art regarding lens design; Joseph Gortych wrote an excellent review of this issue in Optics and Photonics News, titled “Lens Design Patents: The view from court space.”

Do you see something interesting in these files?  Share your insight in the Comments section.  Do you have lens design files you’d like to share?  Please participate in building the site.

Listing of design files: