Displacement measurement system of two-degree-of-freedom heterodyne grating interferometer based on optical double-range method

Abstract

A two-freedom heterodyne grating interferometer displacement measuring system based on the optical octave method comprises a two-frequency laser, a grating interferometer, a measuring grating and a photovoltaic conversion unit. The grating interferometer comprises a polarization splitting prism, a reference grating and a refraction element. On the basis of optical grating diffraction, optical Doppler and the optical beat frequency principle, the measuring system realizes displacement measurement. Laser of the double-frequency laser enters the grating interferometer and the measuring grating, and then two paths of optical signals are output to the photovoltaic conversion unit. When the interferometer and the measuring grating are in two-freedom linear relative motion, the system can output two linear displacements. The measuring system realizes optical octave through the second diffraction principle, improves resolution, can realize sub-nanometer and even higher resolution, and can measure two linear displacements at the same time. The two-freedom heterodyne grating interferometer displacement measuring system has the advantages of being insensitive to environments, high in measuring precision, small in size, light in weight and the like, and can improve the performance of a workpiece table when used as a lithography machine ultra-precise workpiece table displacement measuring system.

Description

technical field [0001] The invention relates to a displacement measurement system of a two-degree-of-freedom heterodyne grating interferometer based on an optical multiplier method, in particular to a two-degree-of-freedom heterodyne grating interferometer measurement system for displacement measurement of a workpiece table of a lithography machine. Background technique [0002] As a typical displacement sensor, the grating measurement system is widely used in many electromechanical equipment. The measurement principle of the grating measurement system is mainly based on the Moiré fringe principle and the diffraction interference principle. As a well-developed displacement sensor, the grating measurement system based on the Moiré fringe principle has become the first choice for displacement measurement of many electromechanical equipment due to its long measuring range, low cost, and easy installation and adjustment, but the accuracy is usually on the order of microns, which...

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[0005] US Patent Documents US7,102,729 B2 (published on August 4, 2005), US7,483,120 B2 (published on November 15, 2007), US7,940,392 B2 (published on December 24, 2009), published No. US2010 / 0321665 A1 (published on December 23, 2010) discloses a planar grating measurement system and layout scheme applied to the ultra-precision workpiece table of a lithography machine. The measurement system mainly uses a one-dimensional or two-dimensional planar grating Cooperate with the reading head to measure the horizontal large-stroke displacement of the workpiece table, and use sensors such as eddy current or interferometer for vertical displacement measurement, but the application of various sensors limits the measurement accuracy of the workpiece table

US patent document US7,864,336 B2 (published on January 4, 2011) discloses a grating interferometer measurement system applied to an ultra-precision workpiece table of a lithography machine. The system utilizes the Littrow conditional grating reflection of two reading heads to realize Displacement measurement, but requires many components and large volume, and the measurement accuracy is limited due to the calculation through the results of two reading heads

U.S. Patent Publication No. US2011 / 0255096 A1 (published on October 20, 2011) discloses a grating measurement system applied to an ultra-precision workpiece stage of a lithography machine. The measurement system also uses a one-dimensional or two-dimensional grating with a specific The reading head realizes displacement measurement, and can carry out horizontal direction and vertical displacement measurement simultaneously, but the structure is complicated; U.S. Patent Literature Publication No. US2011 / 0096334 A1 (publication date: April 28, 2011) discloses a heterodyne interferometer, The interferometer uses a grating as the objective mirror, but the interferometer can only achieve one-dimensional measurement

In the research paper "Design and construction of a two-degree-of-freedom linear encoder for nanometric measurement of stage position and straightness. Precision Engineering 34 (2010) 145-155", the Japanese scholar GAOWEI proposed a single-frequency encoder using the principle of diffraction interference Two-dimensional grating measurement system, which can realize horizontal and vertical displacement measurement at the same time, but due to the use of single-frequency laser, the measurement signal is susceptible to interference and the accuracy is difficult to guarantee

Chinese patent document application numbers 201210449244.9 (application date November 09, 2012) and 201210448734.7 (application date November 09, 2012) respectively disclose a heterodyne grating interferometer measurement system, and the readings in the two interferometer measurement systems The head structure uses a quarter-wave plate to change the polarization state of the beam, the optical structure is complex, and the non-ideality of the optical components will lead to measurement errors

In addition, Chinese Patent Literature Publication Nos. CN103307986A (disclosure date: September 18, 2013) and CN103322927A (disclosure date: September 18, 2013) respectively disclose a heterodyne grating interferometer measurement system. The structure of the reading head adopts the optical path design of two subdivisions, which leads to the deficiency of low resolution

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