Projection lenses for high resolution lithography have high NA and work at small wavelengths. In the wavelength regime of VUV (e.g. 193nm), there is a very limited number of optical glasses available, namely fused silica and calcium fluoride. The latter is very expensive and used only sparely, leading to limited possibilities for chromatic correction. In addition to catadioptric approaches, another way to deal with chromatic aberrations is the use of diffractive optical elements (DOEs). They have negative dispersion coupled with positive power and they do not contribute to the Petzval sum. Moreover, it is easy to integrate an aspherical functionality into the structure of the DOE. Usually a DOE is placed close to the aperture stop to correct axial color. The stop of a lithographic projection lens often is located at the largest diameter, causing some serious fabrication difficulties for the DOE. For this reason a class of lenses with intermediate image is of interest. Here, the accessible conjugate of the aperture stop enhances the possibilities to arrange the stop and the DOE. This allows a convenient tradeoff between fabrication challenges and aberration correcting properties. We present different lens designs that take advantage of the named properties of DOEs at high numerical aperture.
Projection lenses for high resolution lithography have high NA and work at small wavelengths. In the wavelength regime of VUV (e.g. 193nm), there is a very limited number of optical glasses available, namely fused silica and calcium fluoride. The latter is very expensive and used only sparely, leading to limited possibilities for chromatic correction. In addition to catadioptric approaches, another way to deal with chromatic aberrations is the use of diffractive optical elements (DOEs). They have negative dispersion coupled with positive power and they do not contribute to the Petzval sum. Moreover, it is easy to integrate an aspherical functionality into the structure of the DOE. Usually a DOE is placed close to the aperture stop to correct axial color. The stop of a lithographic projection lens often is located at the largest diameter, causing some serious fabrication difficulties for the DOE. For this reason a class of lenses with intermediate image is of interest. Here, the accessible conjugate of the aperture stop enhances the possibilities to arrange the stop and the DOE. This allows a convenient tradeoff between fabrication challenges and aberration correcting properties. We present different lens designs that take advantage of the named properties of DOEs at high numerical aperture.
Recently, the development of high NA lenses for immersion lithography turned from dioptric concepts to catadioptric design forms. The introduction of mirrors involves the new challenge to deal with the inevitable obscuration of either field or pupil. We review the strategies used in this regard for microlithography, while focussing on the two most favored ones, folded and inline concepts. Although the vignetting situation is more complicated for inline systems, we report progress in this field of optical design yielding similar system performance for inline and folded designs. Since inline optical systems are much easier to realize, these are the concept of choice.
Advanced dioptric projection lenses from Carl Zeiss are used in some of the world's most advanced deep ultraviolet projection lithography systems. These lenses provide a resolution of better than 100 nm across the entire field of view with a level of aberration control that maximizes critical dimension uniformity and lithographic process latitude. These dioptric projection lenses are currently being used for critical layer device patterning for a wide array of complex logic, memory, and application specific integrated circuits. Zeiss' involvement in the development of ultraviolet lenses goes back to the year 1902, more than 100 years ago, when von Rohr calculated the first monochromatic ultraviolet microobjectives for ultra-high-resolution microphotography using a line-narrowed source. The modern dioptric projection lenses for lithography are influenced by the collective experience in the field of microscopy, and the more recent experience with early step-and-repeat lenses. We discuss some of the foundations of modern dioptric designs in the context of this history, demonstrating that rapid synthesis of designs is possible using combinations of monochromatic microscope objectives and early step-and-repeat lenses from the 1970s. The problems associated with ultrahigh numerical aperture objectives are discussed. Specifically, it is demonstrated that aspheres can be used effectively to reduce the volume of full field projection lenses, making the mechanical implementation of a 0.90 NA lens feasible in production. Several contemporary dioptric projection lens designs are reviewed in detail. The extension of these designs to numerical apertures greater than 1.0 using immersion techniques is demonstrated. These immersion lenses give the potential for 40-nm resolution.
Advanced dioptric projection lenses from Carl Zeiss are used in some of the world's most advanced deep ultraviolet projection lithography systems. These lenses provide a resolution of better than 100 nm across the entire field of view with a level of aberration control that maximizes critical dimension uniformity and lithographic process latitude. These dioptric projection lenses are currently being used for critical layer device patterning for a wide array of complex logic, memory, and application specific integrated circuits.
Zeiss' involvement in the develop of ultraviolet lenses goes back to the year 1902, exactly 100 years ago, when Moritz von Rohr calculated the first monochromatic ultraviolet micro-objectives for ultra-high resolution microphotography using a line-narrowed source. The modern dioptric projection lenses for lithography are influenced by the collective experience in the field of microscopy, and the more recent experience with early step-and-repeat lenses. This paper discusses some of the foundations of modern dioptric designs in the context of this history, demonstrating that rapid synthesis of designs is possbile using combinations of monochromatic microscope objectives and early step-and-repeat lenses from the 1970's. The problems associated with ultra high numerical aperture objectives are discussed. Specifically, it is demonstrated that aspheres can be used effective to reduce the volume of full field projection lenses, making the mechanical implementation of a 0.90 NA lens feasible in production. Several contemporary dioptric projection lens designs are reviewed in detail. The extension of these designs to numerical apertures greater than 1.0 using immersion techniques is demonstrated. These immersion lenses give the potential for 40 nm resolution.
Spectral devices are frequently using holographic diffraction gratings as dispersing elements. The trend in developing such devices is going toward rather small and compact ones, which use CCD-detectors. Very useful for these purposes are imaging concave gratings. They realize an essential progress by the combination of dispersion with imaging properties. Mostly their imaging properties are priorly used in a single plane only. This means, a small area around the center point of the entrance slit is taken into account only in the performance of the grating. We have investigated some possibilities to design gratings with high spectral as well as high spatial resolution. The influence of several grating parameters on spectral and spatial resolution properties is discussed and ways to find new application possibilities by variation of chosen parameters are shown. Which improvements could be reached with the help of further optical surfaces are discussed.
The design, production, and evaluation of a polychromator with high spectral resolution are discussed. In the example of using it in environmental monitoring some aspects of the designing process are shown. Some useful tools, such as spot diagrams and lineprofiles, to evaluate the performance of a grating are shown. As a part of this designing process the use of surface contouring is discussed. Some results of the performance are presented.
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