Design approach and comparison of projection cameras for EUV lithography

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This paper presents an approach that uses implicitly defined optical surfaces for designing imaging and illumination systems. In the standard aspheric optical surface, consisting of a conic with an evenorder polynomial, the surface sagitta (sag), z, is defined explicitly as a function of the coordinates x and y. This standard aspheric surface is deemed useful for describing surfaces with small departures from a conic surface. However, optical surfaces with large departures from a conic are sometimes useful for current applications, such as null certification, conformal domes and windows, luminaires, and condenser design. The approach in this paper, which uses implicitly defined surfaces to describe highly aspheric surfaces, can be more general and easier to use for some situations. The sag z of an implicit surface is not defined directly, as it is in an explicit surface. Instead, it is defined indirectly in a more general form, as a function of x, y, and z. Because implicit functions have a more general form than explicit functions, they can better describe a variety of surfaces that cannot be easily described using the standard explicit aspheric surface. We show some examples of current interest.

Section: The Use Of a Z-polynomial Aspheric Mirror In A Cassegrain-tymentioning

confidence: 97%

Use of implicitly defined optical surfaces for the design of imaging and illumination systems

Lerner

Sasián

2000

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“…A n ρ n ; (15) where c is the curvature of the base sphere, r is the radial coordinate, and ρ is the normalized radial coordinate of which normalization radius is indicated in Table 4. To meet the specification, even-order aspherical terms up to 12th order are needed.…”

Section: Design With Even-order Aspherical Termsmentioning

confidence: 99%

Aberration properties of odd-order surfaces in optical design

Tanabe

Shibuya

2016

Abstract. We theoretically represent the effectiveness of the odd-order surface for optical designs via an aberration theory. The theory employs an expression of the odd-order surface with aberration coefficients, which are derived by power-series expansion of wavefront aberration with respect to the coordinates of optical surfaces. This expression allows us to understand the aberration characteristics of odd-order surfaces. By applying this aberration theory to the design of extreme ultraviolet lithography optics, we show that odd-order surfaces are effective in reducing higher-order aberrations with fewer coefficients than even-order surfaces do. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

“…Lerner et al applied y −ȳ design diagram to obtain initial solutions. 6 However, the applicability of this method to the objective systems, which have more than four reflective mirrors, requires further study. Bal et al and Bociort et al proposed a design method based on a paraxial approximation model and initial configurations were designed via exhaustive searching of all the independent variables.…”

Section: Introductionmentioning

confidence: 99%

Grouping design method with real ray tracing model for extreme ultraviolet lithographic objective

Cao

Liu

2013

Abstract. Choosing an adequate initial design for optimization plays an important role in obtaining high-quality extreme ultraviolet (EUV) lithographic objectives. A grouping design method with real ray tracing model is developed to acquire initial configurations of high numerical aperture (NA) objective for EUV lithography. In this method, the objective system is first divided into three mirror groups. The initial parameters of each mirror group are then determined by real ray calculation under design constraints. Finally, the three mirror groups are connected directly into a feasible initial system. Due to real ray calculation, the discrepancy of the ray path induced by paraxial approximation and the exhaustive search of variables is avoided in a high-NA objective design. In addition, the incidence angles on reflective mirrors can be controlled in the design of each group, which makes the initial configuration suited to further optimization and compatible multilayer design. An NA 0.33 six-mirror EUV lithographic objective is designed as an example to implement this method.