Mr. Lidong Wei Profile

Lidong Wei

at Beijing Institute of Technology

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Proceedings Article | 21 November 2014 Paper

Design of chirped fly’s eye uniformizer for ArF lithography illumination system

Lei Xiao, Yanqiu Li, Lidong Wei

Proceedings Volume 9296, 92960P (2014) https://doi.org/10.1117/12.2072433

KEYWORDS: Eye, Lithographic illumination, Reticles, Lithography, Speckle, Speckle pattern, Cylindrical lenses, Optical components, Geometrical optics, Diffusers

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Fly’s eye uniformizer is the key part of ArF lithography illumination system, whose main function is to illuminate the reticle uniformly. Due to the periodic structure of regular fly’s eye uniformizer and the high coherence of the ArF laser, the output intensity distribution is modulated with equidistant sharp intensity peaks (interference speckle pattern) which disturbed the uniformity on the reticle. In this paper, we design a chirped fly’s eye uniformizer which consists of chirped fly’s eye and a condenser for illumination system in ArF lithography system. The chirped fly’s eye consists of individually shaped micro-lenses defined by a parametric description which can be derived completely from analytical functions. The micro-lenses with different thicknesses in the chirped fly’s eye have a function of delaying the optical path which reducing the laser coherence and speckle pattern on the reticle. Detailed design process of the chirped fly’s eye uniformizer for numerical aperture (NA) 0.75 lithography illumination system is presented. Light intensity distribution on reticle produced by regular and chirped fly’s eye uniformizer are analyzed and compared by the method of wave optics, and the results show that chirped can restrain sharp intensity peaks efficiently. Furthermore, the chirped fly’s eye uniformizer has been traced in LightTools software under conventional and annual illumination modes, and the non-uniformity of the non-scan and scan direction on the reticle reached 0.75% and 1.24% respectively. The simulation results show that the chirped fly’s eye uniformizer can provide high illumination uniformity and reduce the speckle pattern efficiently without additional elements.

Proceedings Article | 5 November 2014 Paper

Design of freeform illumination sources with arbitrary polarization for immersion lithography

Lidong Wei, Yanqiu Li, Ke Liu

Proceedings Volume 9272, 927221 (2014) https://doi.org/10.1117/12.2177846

KEYWORDS: Polarization, Mirrors, Wave plates, Light, Lithographic illumination, Immersion lithography, Microlens array, Microlens, Relays, Modulation

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Polarized illumination and source mask optimization (SMO) are two prominent resolution enhancement technologies (RETs) in immersion lithography. Recently, source-mask-polarization optimization (SMPO) has been developed to support photolithographic process shrinks, which shows that the illumination system with arbitrary intensity and polarization distribution of light in the pupil is emergency. In this paper, we propose a unique illumination system design to match the target SMPO source and meet the requirement of immersion lithography at 45-16 nm node. In our designed illumination system, the adjustable λ/2 wave plates and mirror array are introduced to produce arbitrary intensity and polarization distribution of light in the pupil. The three λ/2 wave plates are designed to that can move freely in certain planes perpendicular to the optical path. To produce target SMPO sources, the positions of thousands spots reflected by adjustable mirrors array are firstly designed and optimized to approximate the target intensity distribution in the pupil corresponding to unpolarized light. Then the target polarization states in all the spots are obtained in the pupil by designing and optimizing the relative positions of the three wave plates. Compared with prior design method, our design results show that the intensity distribution and polarization state of all spots in the pupil match the target SMPO source accurately and efficiently with lower intensity lost.

Proceedings Article | 18 December 2012 Paper

Detailed illuminator design for full-field ArF lithography system with a method based on the fly's eye

Lidong Wei, Yanqiu Li, Lihui Liu

Proceedings Volume 8550, 855032 (2012) https://doi.org/10.1117/12.980911

KEYWORDS: Fiber optic illuminators, Eye, Lithography, Diffractive optical elements, Reticles, Zoom lenses, Relays, Lithographic illumination, Lens design, Axicons

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Lithography is the key technology to semiconductor manufacture. With the rapid improvement of projection lens and resolution enhancement technique (RET), the essence of the illuminator can never be overestimated in the lithography system. However, due to various and complex components and the fact that fewer design methods were proposed in the papers compared with those of the projection lens, a detailed design method for the illuminator is needed. This paper introduces the detailed design process for the illuminator in a NA 0.75 lithography system on 90nm node. The exposure field at the reticle plane is 104mm×42mm. The illuminator mainly consists of three parts: the beam shaping unit, the uniformizer and the relay lens. In order to construct the matching relationship among the various components in the illuminator, a design method based on the fly’s eye, which is the core and starting point, has been proposed. This method has been successfully used in small field lithography system. With this method, the matching relationship in the illuminator can be determined easily, and the illumination NA and size are guaranteed simultaneously. Furthermore, the detailed design for some key issues in the illuminator is given: the diffractive optical element (DOE), zoom lens and axicon are used together to generate different sources in the entrance pupil of the projection lens; the condenser design; and 1X relay with two cylinder lenses to achieve trapezoid intensity distribution in the scan direction. A demonstration simulation result is given, and the uniformity of the non-scan and scan direction reached 1.2% and 1.7% respectively under all illumination modes. The result showed good performance and the requirements of the lithography tools have been met.

Proceedings Article | 16 October 2012 Paper

Illuminator design for small field ArF lithography system

Lidong Wei, Yanqiu Li, Ke Liu, Xiaolin Liu

Proceedings Volume 8416, 84160I (2012) https://doi.org/10.1117/12.978289

KEYWORDS: Fiber optic illuminators, Eye, Lithography, Reticles, Beam shaping, Excimer lasers, Spherical lenses, Lithographic illumination, 193nm lithography, Tolerancing

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Design and development of small field ArF lithography system can achieve the prospective studies and key technologies for industrial lithography with low cost. An illuminator has been designed for the ArF projection lens which has a specification of 0.75 numerical aperture (NA), 70μm×70μm image field and x40 reduction ratio. The illuminator consists of 3 parts: fly’s eye, condenser lens and beam shaping unit. A design method based on the fly’s eye, which is the core and starting point, has been proposed. At first, the basic structure of fly’s eye has to be determined. Then the first order of the condenser, such as focal length and the diameter of the stop can be derived when both the field size and illumination NA are guaranteed. At last, the stop diameter is used as the goal of the beam profile exiting from the beam shaping unit. Thus the initial parameters and relationship between various units in the illuminator can be determined. This method can also be used in full field system design. The NA of the illuminator (NA _ILL ) in the reticle space is 0.01875 and the illuminated area is 4mm×4mm. The telecentric degree is smaller than 6mrad, which guaranteed that the exit pupil of the illuminator match the entrance pupil of projection lens well. The illumination uniformity can reach 1.125% RMS (Root-Mean-Square) over the reticle with LightTools^TM. The results show that all the parameters meet the requirements of the small field ArF lithography system.

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