Nikon Corporation

Nikon Research Corporation of America

Zhiqiang Liu

Eric Peter Goodwin

Goldie Goldstein

Yuki Terui

A position encoder for monitoring relative movement between a first object and a second object includes a grating that is coupled to the first object, and an image sensor assembly that is coupled to the second object. The image sensor includes a first image sensor; a second image sensor that is spaced apart from the first image sensor; an optical element that includes a first optical surface and a second optical surface that is spaced apart from the first optical surface; and an illumination system. The illumination system directs an illumination beam at the optical element to create (i) a first reference beam that is reflected by the first optical surface and directed at the first image sensor, (ii) a second reference beam that is reflected by the second optical surface and directed at the second image sensor, and (iii) a transmitted beam that is transmitted through the optical element and is directed at and impinges on the grating to create a first measurement beam that is diffracted by the grating and directed at the first image sensor, and a second measurement beam that is diffracted by the grating and directed at the second image sensor.

Two-dimensional position encoder

An optical system configured as part of optical metrology unit used to assess the operational status of a workpiece and, in a specific case, configured as an encoder head of a lithographic exposure tool. The optical system is devoid of a stand-alone optical corner-cubes and includes, instead, a single, imperfect or frustrated cuboid of optically-isotropic material that, in operation with the diffraction grating of the workpiece, simultaneously forms four interferometric signals for measuring x-, y, and z-positions of the workpiece grating relative to the optical system. Proposed system and method solve problems of (i) structural complexity of a conventional metrology unit for use in an exposure tool, (ii) burdensome alignment of the multitude of optical prisms in the process of forming such metrology unit, and (iii) cyclic non-linear errors associated with measurements involving conventional corner-cubes-based metrology units.

Optical system with a frustrated isotropic block

Methodology of measuring a position of a wafer with an encoder directing measurement beam(s) of light towards a wafer area that is being contemporaneously patterned in an exposure apparatus. The Abbe error of such measurement is minimized or even negated by combining the data from first and second measurement signals, one of which is defined as complementary, Abbe-error correcting measurement signal for which the induced Abbe error is either opposite to or at least different from the Abbe error corresponding to another, main measurement signal. The combination of the main and Abbe-error correcting signals is performed with a heterodyne interferometer employing a two-dimensional diffraction grating diffracting each of the measurement beams twice.

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Kanagawa-ken, Japan

Zhiqiang Liu