Illumination system with freeform fly’s eye to generate pixelated pupil prescribed by source-mask optimization in extreme ultraviolet lithography

Abstract

Abstract. Source-mask optimization (SMO) has emerged as a key technique for 7-nm node and beyond in extreme ultraviolet (EUV) lithography. The pupil required by SMO is usually pixelated, with a free choice of intensity per pixel. However, due to the discrete nature of the EUV illumination system, pupil intensity in current EUV SMO must also be discretized. An illumination system with a freeform fly's eye that is able to generate the pixelated pupil is proposed. Clear apertures of the field facets in the fly's eye are different from each other so that the intensity of each pixel on the pupil can meet the requirements of SMO. Each of the field facets is constructed with a freeform surface to get the required arc-shaped illuminated area on the reticle. A method integrated with a numerical method and an optimization process is used to design the freeform surface of the field facets. The simulation result of the design for a prescribed freeform pixelated pupil shows that the uniformity on the reticle is 96.4%, and the pupil intensity error is approximated to be 0.035. The results indicate that the system is effective in generating the required freeform pixelated pupil and reducing the restrictions imposed on the SMO process in EUV lithography.

Investigation of spline approximation approach of surface data for synthesis of high-efficient beam shapers

“…The use of freeform surfaces in modern optical systems makes possible to increase the efficiency of wavefront conversion and/or reduce the number of components in the system without losing the quality of beam shaping [1]. Moreover, optical freeforms are applied in various fields -from lithography to space technologies [2,3]. The development of technologies for the production and control of aspheric surfaces, coupled with the advent of new manufacturing methods and materials as well as the development of computer modeling, has ensured an increased demand for high-performance systems including the freeform components.…”

The Inverse Optimization of an Optical Lithographic Source with a Hybrid Genetic Algorithm

“…Several resolution enhancement technologies (RETs) for the attainment of high-quality aerial image have been proposed [8][9][10]. In these methods, pixelated source optimization (SO), which is an inverse optimization method, can efficiently promote the performance in optical lithographic imaging [11][12][13]. This can be achieved with mathematical and algorithmic approaches, which can inversely optimize the intensity distribution of an optical lithographic source according to aerial image or resistance pattern.…”

“…The genetic algorithm (GA), which is a typical example of a heuristic approach, has been widely employed as a key tool for achieving the optimization of complex models in Freeform illuminations, which can be created with a set of micromirror arrays, have been developed to provide more degrees of freedom for regulating the illumination shape in optical lithography [11,14,15]. In a pixelated source model, changes in intensity of the pixels can indicate the mirror flip angle, where a pixel represents a unit mirror.…”