August 27, 2023: Catadioprtric VUV photolithography projector submitted by Jose Sasian

Jose has taught has taught a generation of lens designers at U. of Arizona.

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 outside this range. 

February 7. 2021:  9 new designs posted from Braat & Török's Imaging Optics

        Joseph Braat provided explanatory test:

"The design 7.79 is an f - theta  scanning objective (Imaging Optics, page 524), with the following specifications: f =1.25 mm, NA=0.42,  λ = 785 nm, lens material for all five elements is the Schott SF6 glass (refractive index 1.785). The parallel incident laser beam is deflected by a spinning mirror polygon that deflects the beam over an angular range of 2x22deg with respect to the axial direction. The position of the focused image point should be a linear function of the deflection angle, the proportionality factor being the focal distance of 1.25 mm of the system. The image field is perfectly flat such that the laser beam is sharply focused everywhere on the scan line of almost 1 mm long. The number of Rayleigh-resolved image points NR on the field diagonal of 960 um is approximately 850.                  

"Design 7.81 is an all-mirror achromatic projection system (Imaging Optics, page 527), for microlithography (Offner system). The specifications are: f  is almost infinitely large (22.2 m), doubly telecentric system with diaphragm on the central smaller mirror, NA=0.15, typical operating wavelength is λ  = 365 nm (spectral i line of the Hg-spectrum). Construction length is 1 meter. Well-corrected ring field, centred off-axis at 150.2 mm, ring width is 1 mm. The number NR measured over the ring width of 1 mm is 670 ( λ = 365 nm).

"Design 7.86a is a monochromatic water-immersion projection lens (Imaging Optics, page 534), patented by the Carl Zeiss company (Oberkochen): US 7969663 (Dodoc, Ulrich, Rostalski; 2011).  The specifications are:  f =158 mm, NA=1.10, field diameter is 28 mm, magnification  = -0.25,  λ = 193 nm (argon fluoride excimer laser), construction length is 1028 mm, telecentric at the image side. The system shows the pronounced bulges and constrictions that are typical for refraction-only projection systems. The system has a very low level of aberration, including field curvature and distortion. This very high imaging quality has been achieved with the aid of 13 aspheric surfaces. The number NR measured over the field diameter of 28 mm is 260000.

"Design 7.86b is a historic design (Braat, 1985) for the h-line of a Hg-source,  λ  = 405 ± 4 nm (Imaging Optics, page 534),. Further specifications: f =77 mm, NA=0.38, magnification = -0.20, field diameter is 20 mm, construction length is 602 mm, telecentric at the image side. The system shows the bulges and constrictions that are typical for refraction-only projection systems. The number NR on the field diameter of 20 mm is 30000.

"Design 7.89a is a 6-mirror projection system operating at the extreme ultraviolet (EUV) wavelength of λ  = 13.4 nm (Imaging Optics, page 538). All mirror surfaces are aspheric, with symmetry of revolution. Further specifications are f =245 mm, NA=0.20, magnification = -0.25, ring field running from 35.5 to 37.5 mm off-axis. Construction length is 1007 mm, telecentric at the image side. US patent 6396067 (Braat; 2002).  The number NR measured over the ring width of 2 mm is approximately 50000.

"Design 7.89c is also a 6-mirror system operating at the extreme ultraviolet (EUV) wavelength of  λ = 13.4 nm (Imaging Optics, page 538). All mirror surfaces are aspheric and show symmetry of revolution. Further specifications are f' = -326 mm, NA=0.25, magnification +0.25, ring field running from 29.0 to 31.0 mm off-axis. Construction length is 1486 mm, telecentric at the image side. US patent 7199922 (Mann, Ulrich, Hudyma; 2007). The number NR measured over the ring width of 2 mm is approximately 60000.

"Design 7.94 is an 8-mirror system (Imaging Optics, page 542), operating at the extreme ultraviolet (EUV) wavelength of λ  = 13.4 nm (all mirror surfaces are aspheric and show symmetric of revolution). Further specifications are f' = -236 mm, NA=0.40, magnification +0.25, ring field running from 26.3 to 27.6 mm off-axis. Construction length is 839 mm, telecentric at the image side. European patent EP1199590 A1 (Mann, Seitz, Ulrich; 2002). The number NR measured over the ring width of 1.3 mm is approximately 64000.

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; a lot of the skill has been retained at Greenlight Optics.  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 use 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.”

Summary of designs

Design files