Two-DOF (degree of freedom) heterodyne grating interferometer displacement measurement system

Abstract

A two-DOF (degree of freedom) heterodyne grating interferometer displacement measurement system comprises a two-frequency laser, a grating interferometer, a measuring grating, a receiver, and an electronic signal processing part. The grating interferometer comprises a polarizing beam splitter, a reference grating and a refraction element. The measurement system measures displacement according to optical grating diffraction, optical Doppler Effect and optical beat frequency principle. A two-frequency laser beam emitted by the two-frequency laser enter the grating interferometer and the measuring grating before two light signals are output to the receiver, and the signals are sent to the electronic signal processing part. When the grating interferometer is in two-DOF linear relative motion with the measuring grating, the system can output two linear displacements. The measurement system allows for sub-nano or higher resolution and precision, and can measure two linear displacements simultaneously. The measurement system has the advantages of insensitivity to environment, high measurement precision, small size, light weight and the like, and after the measurement system is used as a lithography machine ultra-precision workpiece bench position measurement system, comprehensive performances of a workpiece bench can be improved.

Description

technical field [0001] The invention relates to a grating measurement system, in particular to a two-degree-of-freedom heterodyne grating interferometer measurement system used 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 is common for general industrial applications. [0003] The lithography machine in semiconductor...

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Problems solved by technology

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

U.S. Patent Publication No. US2011 / 0255096A1 (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 the displacement measurement, which can measure the horizontal and vertical displacements simultaneously, but the structure is complex; US Patent Document Publication No. US2011 / 0096334A1 (publication date April 28, 2011) discloses a heterodyne interferometer, the interferometer The grating is used as the objective mirror in the instrument, but the interferometer can only realize 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", Japanese scholar GAOWEI proposed a single encoder using the principle of diffraction interference. Frequency 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 literature 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

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