Tomoyuki Matsuyama

Nikon projection lens update

This paper describes various kinds of technological improvements in ArF projection lenses for success in very low-k1 and high NA lithography. This paper covers optical design, lens manufacturing, aberration characterization, aberration manipulation, flare control, and linear polarizing illumination. Actual lens performance of the Nikon NSR-S307E (0.85NA ArF Optics) is also reviewed.

Microlithographic lens for DUV scanner

This paper describes several kinds of new technologies introduced into the latest microlithographic lens system for Nikons DUV (Deep Ultra Violet) scanner.

High-NA and low-residual-aberration projection lens for DUV scanner

This paper describes several kinds of new technologies, which are introduced into newly developed 0.78 NA ArF projection lens for Nikons latest DUV scanner, the NSR- S306C. A new lens configuration for an ArF projection system is obtained as a result of a minute survey of the space of the aspheric optical design. The new configuration uses fewer elements and less volume of calcium fluoride (CaF2) than a conventional type. Lens mounting performance and its stability is another key issue to realizing a high performance imaging system, because lens element deformation due to lens mounting degrades imaging performance severely. Reduction of the number of the elements of a new optical design can increase room for the opto-mechanical system. Even complicated mechanisms, such as kinematic lens mounting, can fit in the space. A pure kinematic lens mounting is developed for the new ArF projection lens system to minimize lens deformation due to lens mounting. The same mechanism is applied to the positioning scheme of a lens element for high precision lens adjustment. Simultaneous use of the new lens positioning system and a lens controller can perform high precision and rather complex lens fine-tuning. Intrinsic birefringence of calcium fluoride (CaF2) is a new item, which is a hot issue in F2 optics. Even for ArF projection lens system, the intrinsic birefringence is one of the most critical issues in terms of impact upon lens performance. Special treatment is required to avoid the degradation of imaging performance due to the intrinsic birefringence effects. Resist image comparison between an ArF lens with the treatment and that without is reviewed. Finally, actual lens performance is shown.

Immersion Lithography Ready for 45 nm Manufacturing and Beyond

Enhanced resolution capability, defined in Rayleighs criterion as: R = (k1*lambda)/NA (1); where R = minimum resolution, lambda = exposure wavelength, and k1 = process dependent factor is the key motivation for the transition to immersion lithography, and the continued push for higher numerical apertures (NA). Regardless of the imaging enhancements made possible by immersion lithography though, this technology would not have been implemented in volume manufacturing if two potential showstoppers identified early on, overlay and defectivity performance, were not successfully overcome. Fortunately, intense collaboration between scanner and track suppliers, resist vendors, and IC manufacturers has yielded significant progress in the critical areas of immersion defectivity and overlay. As a result, immersion lithography is experiencing rapid adoption into mainstream semiconductor manufacturing. Hyper-NA immersion scanners, such as the Nikon NSR-S609B (NA=1.07), began shipping in early 2006 for use in 55 nm production and 45 nm process development. These systems are already being used successfully for 56 nm NAND flash manufacturing. Aggressive industry integration continues, and scanners such as the NSR-S610C (NA=1.30) are fully capable of delivering the critical performance metrics required for 45 nm half-pitch production and beyond. Current areas of industry investigation now focus on the feasibility and practicality of extending immersion lithography to 32 nm applications using new lens and resist materials, as well as exploring alternative immersion fluids to push immersion lithography as far as possible.

Improving lens performance through the most recent lens manufacturing process

A continuous demand for finer and finer exposed patterns is pushing the k1 factor down to 0.4 or below, which is very close to its theoretical limit. The low-k1 lithography requires high NA and small residual aberration of a deep ultra-violet (DUV) projection lens system. The amount of aberration of current projection lens is less than design residual value of the lens in a decade ago. A lot of designers’ efforts are put into optical design and opt-mechanical design of the projection lens to meet lithography requirements. However, technological innovations in manufacturing process are also needed for the realization of a state of the art projection lens. In some cases, manufacturing process is rather essential for the final lens performance improvement. This paper shows the most recent lens manufacturing process in Nikon. In addition to the manufacturing process itself, some supporting technologies in the manufacturing process are also reviewed.

Impact of realistic source shape and flexibility on source mask optimization

Abstract. Source mask optimization (SMO) is widely used to make state-of-the-art semiconductor devices in high-volume manufacturing. To realize mature SMO solutions in production, the Intelligent Illuminator, which is an illumination system on a Nikon scanner, is useful because it can provide generation of freeform sources with high fidelity to the target. Proteus SMO, which employs co-optimization method and an insertion of validation with mask three-dimensional effect and resist properties for an accurate prediction of wafer printing, can take into account the properties of Intelligent Illuminator. We investigate an impact of the source properties on the SMO to pattern of a static random access memory. Quality of a source made on the scanner compared to the SMO target is evaluated with in-situ measurement and aerial image simulation using its measurement data. Furthermore, we discuss an evaluation of a universality of the source to use it in multiple scanners with a validation and with estimated value of scanner errors.

Analysis of imaging performance degradation

The wavefront aberration that is generally represented with Zernike polynomials is an approximate representation. The reasons are that, in actual optics, the wavefront has such frequency component that cannot be represented with Zernike polynomials. Moreover, it can never be scalar or monochromatic. Instead, it must be vector and polychromatic. Higher frequency component beyond Zernike representation could cause a local flare that will be observed in the surrounding area of nominally bright patterns. Vector aspect of light leads to imaging degradation combined with birefringence of the material. Even with a narrowed spectral bandwidth of excimer lasers, chromatic aberration could be a factor that impacts imaging performance. Lateral, rather than axial, chromatic aberration can be critical because it is influential to CD uniformity across the field. This paper describes the factors that deteriorate imaging performance based on Nikon’s optics, and finally concludes hat our optics is well balanced among these factors.

An aberration control of projection optics for multi-patterning lithography

In order to realize further improvement of productivity of semiconductor manufacturing, higher throughput and better imaging performance are required for the exposure tool. Therefore, aberration control of the projection lens is becoming more and more important not only for cool status performance but also heating status. In this paper, we show the improvements of cool status lens aberration, including scalar wavefront performance and polarization aberration performance. We also discuss various techniques for controlling thermal aberrations including reduction of heat in the lens, simulation, compensating knob, and adjusting method with actual imaging performance data during heating and cooling.

Tolerancing analysis of customized illumination for practical applications of source and mask optimization

Due to the extremely small process window in the 32nm feature generation and beyond, it is necessary to implement active techniques that can expand the process window and robustness of the imaging against various kinds of imaging parameters. Source & Mask Optimization (SMO) 1 is a promising candidate for such techniques. Although many applications of SMO are expected, tolerancing and specifications for aggressively customized illuminators have not been discussed yet. In this paper we are going to study tolerancing of a freeform pupilgram which is a solution of SMO. We propose Zernike intensity/distortion modulation method to express pupilgram errors. This method may be effective for tolerancing analysis and defining the specifications for freeform illumination. Furthermore, this method is can be applied to OPE matching of free form illumination source.

Catadioptric lens development for DUV and VUV projection optics

According to the International Technology Roadmap for Semiconductors (ITRS), the 65nm technology node is forecast to appear in 2007. In this paper, we propose two specifications for the projection optics at 65nm nodes. The one is over 1.0 numerical aperture (NA) at 193nm lithography by liquid immersion. The other is 0.85 NA at 157nm lithography. Since it almost impossible for traditional dioptric optics to realize these specifications, catadioptric is supposedly the leading optics for an extreme optical lithography, like 65nm node. Described in the paper are feasibility study for catadioptric optics, and our assembly strategy. Emphasis is placed on our selection methodology among a variety of catadioptric configurations.