CN103604375A - Double frequency laser grating interference two-dimensional measurement method and system with optical aliasing resistance - Google Patents

Abstract

The anti-optical aliasing dual-frequency laser grating interference two-dimensional measurement method and system belong to the grating measurement technology; the system includes a laser, a grating interference mirror group, a photoelectric detection and signal processing unit, and the two beams output by the laser at the same time have different frequencies and are spaced apart. The laser beam is incident on the polarizing beam splitter in parallel, the first beam is reflected by the polarizing beam splitter and then enters the reference grating to form multi-order multi-beam reference diffracted beams, the second beam is transmitted by the polarizing beam splitter and then enters the measuring grating to form multiple beams Measuring the diffracted beam, the three beams in the reference diffracted beam are sequentially combined with the 0 and ±1 order beams in the measuring diffracted beam to form an optical beat frequency, and the two-dimensional relative motion information of the measuring grating is obtained through photoelectric detection and signal processing; the method The sum system eliminates the optical frequency aliasing, polarization state aliasing and the corresponding periodic nonlinear error caused by the incomplete traditional polarization splitting. It can improve its comprehensive performance when used in the ultra-precision workpiece stage position measurement system of lithography machine.

Description

Anti-aliasing dual-frequency laser grating interference two-dimensional measurement method and system

technical field

The invention relates to a grating measurement method and a measurement system, in particular to a dual-frequency laser grating interference two-dimensional measurement method and a measurement system.

Background technique

The lithography machine in semiconductor manufacturing equipment is the key equipment in the production of semiconductor chips. The ultra-precision workpiece stage is the core subsystem of the lithography machine, which is used to carry the mask plate and silicon wafer to complete the high-speed ultra-precision step-and-scan movement. Ultra-precision workpiece table has become the most representative type of ultra-precision motion system due to its high-speed, high-acceleration, large-stroke, ultra-precision, and multi-degree-of-freedom motion characteristics. In order to realize the above-mentioned movement, the ultra-precision workpiece table usually uses a dual-frequency laser interferometer measurement system to measure the multi-degree-of-freedom displacement of the ultra-precision workpiece table. However, with the continuous improvement of motion indicators such as measurement accuracy, measurement distance, and measurement speed, the dual-frequency laser interferometer has a series of problems such as environmental sensitivity, difficulty in improving measurement speed, space occupation, high price, and difficulty in designing, manufacturing and controlling the target workpiece table. The problem is difficult to meet the measurement needs.

In response to the above problems, major companies and research institutions in the field of ultra-precision measurement in the world have carried out a series of research, the research mainly focuses on the grating measurement system based on the principle of diffraction interference, and the research results have been disclosed in many patent papers. Holland ASML Company U.S. Patent US7,102,729B2 (disclosure date August 4, 2005), US7,483,120B2 (disclosure date November 15, 2007), US7,940,392B2 (disclosure date December 24, 2009) Japan), US2010/0321665A1 (public date 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 a one-dimensional or two-dimensional plane The grating cooperates with the reading head to measure the horizontal large-stroke displacement of the workpiece table, and height sensors such as eddy currents or interferometers are used to measure the displacement in the height direction, 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) of ZYGO Corporation of the United States discloses a grating measurement system applied to ultra-precision workpiece tables of lithography machines. The measurement system also uses one-dimensional or two-dimensional gratings. A specific reading head realizes displacement measurement, which can simultaneously measure horizontal and vertical displacements; Tsinghua University Chinese Patent CN102937411A (public date: February 20, 2013), Tsinghua University Chinese Patent CN102944176A (public date: February 27, 2013) Disclosed is a dual-frequency grating interferometer displacement measurement system for an ultra-precision workpiece table of a lithography machine. The measurement system replaces the measurement target reflector (pyramid) of a traditional dual-frequency laser interferometer with a grating to realize dual-frequency laser Grating interferometry can measure large horizontal travel displacement and vertical displacement at the same time, but because the dual-frequency laser is coaxial, it uses a polarization beam splitter to separate it into reference light and measurement light, and there is optical frequency aliasing caused by incomplete polarization splitting , polarization aliasing and the corresponding periodic nonlinear error problem. The Chinese patent CN102353327A of the University of National Defense Science and Technology of the Chinese People's Liberation Army (public date: February 15, 2013) discloses a dual-frequency laser grating interferometry method and measurement system. Light, reference light and measuring light are incident on the moving measuring grating at the same time, and the reference light and measuring light diffracted by the measuring grating merge to form an optical beat frequency, and the displacement of the moving grating is obtained by photoelectric detection and signal processing. This system can only realize one Dimensional measurement also has the problems of optical frequency aliasing, polarization state aliasing and corresponding periodic nonlinear errors caused by incomplete polarization splitting.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and to seek an anti-optical aliasing dual-frequency laser grating interferometry method and system. The measurement system can achieve sub-nanometer or even higher resolution and precision, and can Simultaneously measure horizontal displacement and vertical displacement. The measurement system is used for the displacement measurement of the ultra-precision workpiece table, which can effectively reduce the deficiency of the laser interferometer measurement system in the application of the ultra-precision workpiece table, and improve the performance of the ultra-precision workpiece table of the lithography machine.

The purpose of the present invention is achieved like this:

Anti-aliasing dual-frequency laser grating interference two-dimensional measurement method, the laser outputs two laser beams at the same time, wherein the first laser beam is at the first frequency, and the second laser beam is at the second frequency, the first laser beam and the The second laser beam is spatially separated and incident on a beam splitter in parallel, the first laser beam is reflected by the beam splitter to form a reference beam incident on the reference grating, and is diffracted by the reference grating to form multiple orders of multi-beam reference diffracted beams, the second A beam of laser light is transmitted through the beam splitter to form a measuring beam that is incident on the measuring grating, and is diffracted by the measuring grating to form multiple orders of measuring diffracted beams. The first, second, and third laser beams in the reference diffracted beams The first beam, the second beam, and the third laser beam in the measurement diffracted beam are combined in turn to form optical beat frequency interference, and the optical beat frequency signal is subjected to photoelectric detection and signal processing to obtain the two-dimensional relative motion information of the measuring grating.

Anti-aliasing dual-frequency laser grating interference two-dimensional measurement system, including a laser that can output two laser beams with different frequencies and a polarization beam splitter, one of which is transmitted to the polarization beam splitter through the first single-mode polarization-maintaining fiber The incident end of the first incident laser beam is formed, and the other laser beam is transmitted to the incident end of the polarization beam splitter through the second single-mode polarization-maintaining fiber to form the second incident laser beam, and the polarization state of the first incident laser beam is adjusted to make The first incident laser beam is reflected on the beam-splitting film surface of the polarization beam splitter to form a reference arm beam. On the optical path of the reference arm beam, a reference arm quarter-wave plate, a reference arm refraction element and a reference grating are sequentially arranged, and the reference arm beam Pass through the reference arm quarter-wave plate and the reference arm refraction element to the reference grating, the reference arm beam is diffracted and reflected by the reference grating to form (+1, 0) order beam, (+1, +1) order beam and (+1) order beam , -1) level beam, the (+1, 0) level beam, (+1, +1) level beam and (+1, -1) level beam are adjusted to the same beam direction as the reference arm after passing through the reference arm refraction element The arm beams are parallel and reversed, the (+1, 0) order beam, (+1, +1) order beam and (+1, -1) order beam return to the polarizing beam splitter through the reference arm quarter-wave plate , and through the spectroscopic film, the photodetector A, photodetector B and photodetector C are sequentially arranged on the transmitted light path through the spectroscopic film, and the (+1, +1) level beam is directed to the photodetector A , the (+1, 0) level beam shoots to the photodetector B, and the (+1, -1) level beam shoots to the photodetector C; the polarization state of the second incident laser beam is adjusted so that the second incident laser beam is polarized The beam of the measuring arm is transmitted through the surface of the spectroscopic film of the beam splitter, and the measuring arm quarter-wave plate, the measuring arm refraction element and the measuring grating are sequentially arranged on the optical path of the measuring arm beam, and the measuring arm beam passes through the measuring arm quarter-wave The refraction element of the measuring arm and the measuring arm shoots to the measuring grating, and the beam of the measuring arm is diffracted and reflected by the measuring grating to form 0-order beams, +1-order beams and -1-order beams, and the 0-order beams, +1-order beams and -1-order beams pass through After the refraction element of the measuring arm is adjusted, its beam direction is parallel and opposite to that of the measuring arm beam. The 0-order beam, +1-order beam and -1-order beam return to the polarization beam splitter through the quarter-wave plate of the measuring arm, and are polarized The reflection of the beam splitter forms beam B, beam A, and beam C respectively in sequence. The beam A merges with the (+1, +1) beam and shoots to the photodetector A, and the beam B merges with the (+1, 0) beam and shoots To the photodetector B, the light beam C merges with the (+1, -1) light beam and shoots to the photodetector C. The photodetectors A, B, and C convert the beat-frequency optical signal into an electrical signal, which is transmitted by a wire or an optical fiber They are respectively sent to the signal processing unit to complete the processing.

Compared with the prior art, the present invention has the advantages of:

(1) The dual-frequency laser beam output by the laser in the present invention is transmitted separately in space, and separately incident on the polarization beam splitter, eliminating the optical frequency aliasing caused by the incomplete splitting of the traditional coaxial dual-frequency laser by the polarization beam splitter , polarization aliasing and the corresponding periodic nonlinearity error;

(2) In the present invention, the dual-frequency laser is separately transmitted by two single-mode polarization-maintaining optical fibers, which is beneficial to the polarization state adjustment and optical path alignment of the dual-frequency laser;

(3) In the present invention, the 0th-order and symmetrical high-order diffracted light produced by the diffraction of the measuring grating form optical beat-frequency interference with the diffracted light of the reference grating respectively, and are measured simultaneously by three photodetectors, and the measuring grating can be accurately measured through signal processing The relative displacement in the two-dimensional plane does not require the laser to provide a separate beat frequency signal of the dual-frequency laser frequency difference, which reduces the number of optical components and simplifies the layout of the optical path.

Description of drawings

The accompanying drawing is a structural schematic diagram of an anti-optical aliasing dual-frequency laser grating interference two-dimensional measurement system.

In the figure: 1-laser; 2-the first single-mode polarization-maintaining fiber; 3-the second single-mode polarization-maintaining fiber; 4-polarization beam splitter; 5-reference arm quarter-wave plate; 6-reference arm Refractive element; 7-reference grating; 8-quarter-wave plate of measuring arm; 9-refractive element of measuring arm; 10-measuring grating; 11-photodetector A; 12-photodetector B; 13-photodetector C; 14-signal processing unit; 20-first incident laser beam; 21-reference arm beam; 22-(+1,+1) level beam; 23-(+1,0) level beam; 24-(ten 1 ,-1) level beam; 30-second incident laser beam; 31-measurement arm beam; 32-+1 level beam; 33-0 level beam; 34--1 level beam; B, C.

Detailed ways

The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Anti-aliasing dual-frequency laser grating interference two-dimensional measurement method, the laser outputs two laser beams at the same time, wherein the first laser beam is at the first frequency, and the second laser beam is at the second frequency, the first laser beam and the The second laser beam is spatially separated and incident on a beam splitter in parallel, the first laser beam is reflected by the beam splitter to form a reference beam incident on the reference grating, and is diffracted by the reference grating to form multiple orders of multi-beam reference diffracted beams, the second A beam of laser light is transmitted through the beam splitter to form a measuring beam that is incident on the measuring grating, and is diffracted by the measuring grating to form multiple orders of measuring diffracted beams. The first, second, and third laser beams in the reference diffracted beams The first beam, the second beam, and the third laser beam in the measurement diffracted beam are combined in turn to form optical beat frequency interference, and the optical beat frequency signal is subjected to photoelectric detection and signal processing to obtain the two-dimensional relative motion information of the measuring grating.

The anti-aliasing dual-frequency laser grating interference two-dimensional measurement system includes a laser 1 capable of outputting two laser beams of different frequencies and a polarization beam splitter 4, wherein one laser beam is transmitted to the The incident end of the polarization beam splitter 4 forms the first incident laser beam 20, and another laser beam is transmitted to the incident end of the polarization beam splitter 4 through the second single-mode polarization-maintaining optical fiber 3 to form the second incident laser beam 30, adjusting the first The polarization state of the incident laser beam 20 is such that the first incident laser beam 20 is reflected on the beam-splitting film surface of the polarization beam splitter 4 to form a reference arm beam 21, and the reference arm quarter wave is sequentially arranged on the optical path of the reference arm beam 21 Plate 5, reference arm refraction element 6 and reference grating 7, reference arm beam 21 passes through reference arm quarter-wave plate 5 and reference arm refraction element 6 and shoots to reference grating 7, reference arm beam 21 is formed by diffraction and reflection of reference grating 7 (+1,0) level beam 23, (+1,+1) level beam 22 and (+1,-1) level beam 24, the (+1,0) level beam 23, (+1,+1) ) level beam 22 and (+1, -1) level beam 24 after passing through the reference arm refraction element 6, the beam direction is adjusted to be parallel and opposite to the reference arm beam 21, (+1, 0) level beam 23, (+1 , +1) order light beam 22 and (+1,-1) order light beam 24 are returned to polarizing beam splitter 4 through reference arm quarter-wave plate 5 again, and pass through light-splitting film, pass through the transmitted light of light-splitting film A photodetector A11, a photodetector B12, and a photodetector C13 are sequentially arranged on the road, the (+1, +1)-level light beam 22 shoots to the photodetector A11, and the (+1, 0)-level light beam 23 shoots to the photodetector Device B12, (+1,-1) level light beam 24 shoots to photodetector C13; Adjust the polarization state of the second incident laser beam 30, make the second incident laser beam 30 transmit and form measurement Arm beam 31, the measurement arm quarter-wave plate 8, the measurement arm refraction element 9 and the measurement grating 10 are sequentially arranged on the optical path of the measurement arm beam 31, and the measurement arm beam 31 passes through the measurement arm quarter-wave plate 8 and The refraction element 9 of the measuring arm shoots towards the measuring grating 10, and the beam 31 of the measuring arm is diffracted and reflected by the measuring grating 10 to form a 0-order beam 33, a +1-order beam 32 and a -1-order beam 34, and the 0-order beam 33, +1-order beam 32 and -1 level beam 34 after passing through the measuring arm refraction element 9, the beam direction is adjusted to be parallel and opposite to the measuring arm beam 31, and the 0-level beam 33, +1 level beam 32 and -1 level beam 34 pass through the measuring arm 4 The one-half-wave plate 8 returns to the polarization beam splitter 4, and is reflected by the polarization beam splitter 4 to form beam B36, beam A35, and beam C37 respectively in turn, and the beam A35 merges with the (+1, +1) level beam 22 and shoots to the photoelectric Detector A11, light beam B36 and (+1, 0) level light beam 23 converge and shoot to photodetector B12, light beam C37 and (+1, -1) level light beam 24 converge and shoot to photodetector C13, described photodetector A11, B12, C13 convert the beat frequency optical signal The electrical signals are sent to the signal processing unit 14 by wires or optical fibers to complete processing.

An anti-optical aliasing dual-frequency laser grating interference two-dimensional measurement system, the reference grating 7 is a plane reflective two-dimensional orthogonal grating, and the measurement grating 10 is a plane reflective one-dimensional grating or a plane reflective two-dimensional orthogonal raster.

Anti-optical aliasing dual-frequency laser grating interference two-dimensional measurement system, the detection of the optical beat signal by the photodetectors A11, B12 and C13 can be directly detected by the photodetector or remotely detected by the fiber optic probe.

When the measuring grating 10 is stationary, the (+1, +1) level beam 22 and the beam A35, the (+1, 0) level beam 23 and the beam B36, the (+1, -1) level beam 24 and the beam C37 respectively form a measurement Optical beat frequency interference, the beat frequency is the difference between the frequency of the dual-frequency laser output by the laser 1, when the measuring grating 10 moves parallel to the beam 31 of the measuring arm, the 0-order beam 33 will generate a corresponding Doppler frequency shift, when measuring When the grating 10 moves perpendicular to the beam 31 of the measuring arm and at the same time perpendicular to the grating writing direction of the measuring grating 10, the +1-level beam 32 and the -1-level beam 34 will respectively produce Doppler frequency shifts of equal magnitude and opposite sign, which The optical beat frequency signals detected by the photodetectors A11, B12 and C13 are changed, and finally the signals received by the photodetectors A11, B12 and C13 are processed to accurately measure the relative displacement of the grating 10 on the two-dimensional plane.

Claims (4)

1. the double-frequency laser grating interference two-dimensional measurement method of an anti-optics aliasing, it is characterized in that laser instrument exports two bundle laser simultaneously, wherein beam of laser is first frequency, the second bundle laser is second frequency, described beam of laser and the second bundle laser are spatially separately and parallelly incide a spectroscope, beam of laser reflects to form reference beam through spectroscope and incides with reference to grating, by forming the inferior multi beam of a plurality of levels with reference to optical grating diffraction with reference to diffracted beam, the second bundle laser forms measuring beam through spectroscope transmission and incides measurement grating, by measuring optical grating diffraction, form the inferior multi beam measurement diffracted beam of a plurality of levels, describedly with reference to first in diffracted beam, restraint, the second bundle, three beams of laser Shu Yici respectively with the first bundle of measuring in diffracted beam, the second bundle, three beams of laser bundle correspondence is converged formation optical beat and is interfered, optical beat signal is processed the two-dimensional phase that obtains measuring grating to movable information through photodetection and signal.

2. the double-frequency laser grating interference two-dimensional measurement system of an anti-optics aliasing, the laser instrument (1) and the polarization spectroscope (4) that comprise exportable two bundle different frequency laser beam, the incident end that wherein beam of laser bundle transfers to polarization spectroscope (4) through first single-mode polarization maintaining fiber (2) forms the first incoming laser beam (20), the incident end that another bundle laser beam transfers to polarization spectroscope (4) through second single-mode polarization maintaining fiber (3) forms the second incoming laser beam (30), it is characterized in that adjusting the polarization state of the first incoming laser beam (20), make the first incoming laser beam (20) reflect to form reference arm light beam (21) at the light splitting face of polarization spectroscope (4), in the light path of described reference arm light beam (21), configure successively reference arm quarter-wave plate (5), reference arm dioptric element (6) and with reference to grating (7), reference arm light beam (21) process reference arm quarter-wave plate (5) and reference arm dioptric element (6) directive are with reference to grating (7), reference arm light beam (21) is through forming (+1 with reference to grating (7) diffraction reflection, 0) level light beam (23), (+1, 10) level light beam (22) and (+1,-1) level light beam (24), described (+1, 0) level light beam (23), (+1, + 1) level light beam (22) and (+1,-1) level light beam (24) its beam direction after reference arm dioptric element (6) is adjusted into parallel and reverse with reference arm light beam (21), (+1, 0) level light beam (23), (+1, + 1) level light beam (22) and (+1,-1) level light beam (24) turns back to polarization spectroscope (4) through reference arm quarter-wave plate (5) again, and through spectro-film, seeing through on the transmitted light path of spectro-film photodetector A (11) successively, photodetector B (12) and photodetector C (13), described (+1, + 1) level light beam (22) directive photodetector A (11), (+1, 0) level light beam (23) directive photodetector B (12), (+1,-1) level light beam (24) directive photodetector C (13), adjust the polarization state of the second incoming laser beam (30), make the second incoming laser beam (30) become gage beam light beam (31) at the light splitting face transmission of polarization spectroscope (4), allocating and measuring arm quarter-wave plate (8) successively in described gage beam light beam (31) light path, gage beam dioptric element (9) and measurement grating (10), gage beam light beam (31) is measured grating (10) through gage beam quarter-wave plate (8) and gage beam dioptric element (9) directive, gage beam light beam (31) forms 0 grade of light beam (33) through measuring grating (10) diffraction reflection, + 1 grade of light beam (32) and-1 grade of light beam (34), described 0 grade of light beam (33), + 1 grade of light beam (32) is adjusted into parallel and reverse with gage beam light beam (31) with-1 grade of light beam (34) its beam direction after gage beam dioptric element (9), 0 grade of light beam (33), + 1 grade of light beam (32) and-1 grade of light beam (34) pass through gage beam quarter-wave plate (8) again and turn back to polarization spectroscope (4), through polarization spectroscope (4) reflection, form respectively successively light beam B (36), light beam A (35), light beam C (37), described light beam A (35) and (+1, + 1) level light beam (22) converges directive photodetector A (11), light beam B (36) and (+1, 0) level light beam (23) converges directive photodetector B (12), light beam C (37) and (+1,-1) level light beam (24) converges directive photodetector C (13), described photodetector A, B, C (11, 12, 13) convert beat frequency light signal to electric signal, by wire or optical fiber, deliver to respectively signal processing unit (14) and complete processing.

3. the double-frequency laser grating interference two-dimensional measurement system of anti-optics aliasing according to claim 2, it is characterized in that described is flat reflective two-dimensional quadrature grating with reference to grating (7), and described measurement grating (10) is flat reflective one-dimensional grating or flat reflective two-dimensional quadrature grating.

4. the double-frequency laser grating interference two-dimensional measurement system of anti-optics aliasing according to claim 2, is characterized in that described photodetector A, B, C (11,12,13) can be by photodetector direct detections or by fibre-optical probe remote probe to the detection of optical beat signal.

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