CN104048597B - Self adaptation common light path grating interferometer and its implementation - Google Patents

Abstract

An adaptive common optical path grating interferometer, including: a grating scale with relative motion, a corner cube prism, a mirror, a mirror, a position-sensitive detector, a polarization beam splitter, a linearly polarized light source, and a PZT for driving the mirror A micro-displacement driver, a data acquisition and processing and control unit, a polarization phase-shift interference photoelectric detection unit or a dual-frequency heterodyne interference photoelectric detection unit. The present invention adopts the self-adaptive method of controlling the corner cube prism or reflector based on the position feedback of the diffractive light spot to ensure the complete common optical path characteristics of the dynamic grating interferometer, thereby eliminating the influence of the optical path caused by the relative movement error of the grating scale body, thereby obtaining high precision and resolution.

Description

Adaptive Common Optical Path Grating Interferometer and Its Realization Method

technical field

The invention relates to an optical measuring instrument, in particular to an adaptive common optical path grating interferometer and its realization method.

Background technique

The grating interferometer is the core of the high-precision grating ruler measurement system (the grating pitch is generally less than 10 microns), which determines its accuracy and resolution. The high-precision grating ruler measurement system consists of a grating ruler body, a mounting fixture, a reading head based on a grating interferometer, a signal controller and a display, and its function is to measure high-precision displacement. Widely used in machine tool processing control, wafer processing and cutting, integrated circuit lithography equipment, semiconductor testing, robot systems, aerospace, scientific research, military and other fields.

The high-precision grating ruler measurement system is not only one of the most basic modern automatic measuring instruments, but also one of the important guarantees for high precision and high quality in modern processing, production and scientific research. Especially in the fields of 20nm/14nm integrated circuit lithography equipment, nano/subnanometer scientific research, aerospace, scientific research, military and other fields, there is a demand for higher precision and resolution for high-precision grating ruler measurement systems.

Compared with the high-precision laser interferometer, although the grating scale measurement system based on the grating interferometer has the advantage of being insensitive to the environment, due to the influence of the motion error between the reading head and the grating scale body of the grating scale measurement system, it is still difficult Achieve the same high precision and resolution.

Canon of Japan proposed US5038032, US5146085, US4912320 and other patents, and IBM of the United States proposed patent US5442172, all trying to solve the above-mentioned problem of motion error influence. ZYGO of the United States also applied for many novel grating interferometer patents, such as US8300233B2, US0194824A1, US0114061A1, to obtain Higher accuracy and resolution. However, the technical solutions represented by the above all have the following problem: no real complete common-optical path interferometer design is adopted. Therefore, the influence of the optical path of the above-mentioned motion error cannot be eliminated, but its influence can only be alleviated. Further, Wu from Tamkang University in Taiwan proposed a quasi-common optical path grating interferometer [Sensors and Actuators A: Physical, 193:69-78, 2013] to obtain better performance. This proves that designing a grating interferometer with a common optical path is an effective way to eliminate the influence of the above-mentioned motion errors and obtain high precision and resolution.

Contents of the invention

The purpose of the present invention is to propose a complete common optical path grating interferometer on the basis of previous technical solutions and research results, and further adopt an adaptive method to realize its dynamic common optical path, so as to eliminate the influence of the above-mentioned motion error, thereby obtaining higher Accuracy and Resolution.

Technical solution of the present invention is as follows:

An adaptive common optical path grating interferometer is characterized in that it includes: a grating scale with relative motion, a corner cube, a reflector, a mirror, a position-sensitive detector, a first polarizing beam splitter, a linearly polarized light source, and a PZT micro-displacement driver, data acquisition and processing and control unit, interference photoelectric detection unit for driving the above mirror,

① The polarized beam emitted by the linearly polarized light source is divided into transmitted S light and reflected P light by the first polarizing beam splitter, and the P light is reflected by the mirror and then diffracted by the relative moving grating ruler (m>=1) order diffracted light incident corner cube, the ±m (m>=1) order diffracted light incident corner cone after the described S light is reflected by the mirror and then diffracted by the relative motion grating ruler Prism, the P light and S light reflected by the corner cube prism respectively enter the optical path of the other party, and generate a Doppler frequency shift of ±2m times respectively, and finally the two optical paths generate a Doppler frequency shift difference of 4m times, and in The first polarized beam splitter is emitted in the same direction and orthogonally polarized, forming a complete common optical path, which is incident on the interference photodetection unit, and the output terminal of the interference photodetection unit is connected to the data acquisition unit. and processing and control unit inputs,

②The position-sensitive detector is arranged in the direction of the reverse transmitted light of the mirror to detect the light point change of the grating scale diffracted light, and the output terminal of the position-sensitive detector is connected to the data acquisition and processing and The input terminal of the control unit, the output terminal of the data acquisition and processing and control unit is connected to the control terminal of the PZT micro-displacement driver, and the PZT micro-displacement driver drives the reflector or the corner cube to change the orientation of the incident and outgoing light rays .

The interference photodetection unit is a polarization phase-shift interference photodetection unit or a dual-frequency heterodyne interference photodetection unit.

The polarization phase-shifting interference photodetection unit is composed of a quarter-wave plate, a non-polarizing beam splitter, a second polarizing beam splitter, a third polarizing beam splitter, a first detector, a second detector, a third detector and a fourth detector.

The dual-frequency heterodyne interference photodetection unit is composed of a first polarizing beam splitter, a non-polarizing beam splitter, a first analyzer placed at 45 degrees of orthogonal polarization and a corresponding fifth detector, and an orthogonal polarization It consists of the second analyzer placed at 45 degrees and the corresponding sixth detector.

The linearly polarized light source is a light emitting diode, a laser diode, a solid light source or a gas light source; a single-frequency laser or a dual-frequency orthogonally polarized laser.

The PZT micro-displacement driver can also be replaced by MEMS or electrostatic, or planar micro-motor.

The grating scale is an ordinary grating scale or a blazed grating scale, and the grating scale is a reflection type grating scale or a transmission type grating scale.

The position sensitive detector is PSD or detector array, or CCD detector, or CMOS.

The corner cube prism is either a right-angle prism or a mirror assembly cube.

The data acquisition, processing and control unit is composed of a data acquisition card, a motion control card and an industrial computer.

The adaptive realization method of described self-adaptive common optical path grating interferometer is characterized in that the method comprises the steps:

①Initialization: The statically adjusted grating interferometer is in a state of complete common optical path, and the grating ruler has no movement. The data acquisition, processing and control unit collects the light spot position of the light diffracted by the grating ruler on the position-sensitive detector as the target reference position, And set the threshold of the difference from the target reference position;

② During work, the data acquisition and processing and control unit collects the spot position of the light diffracted by the grating ruler on the position-sensitive detector, and calculates the difference between the spot position and the target reference position; if the position difference If it is less than or equal to the set threshold, go to step ④; if the position difference is greater than the set threshold, go to step ③;

③The data acquisition, processing and control unit feeds back the position difference to the PZT micro-displacement driver in real time, drives the mirror or the corner cube to move, and adjusts the light spot to a situation where there is no movement and the light spot is completely in common with the optical path The target reference position of , go to step ②;

④ The data collection and processing and control unit synchronously collects the data of the interference photoelectric detection unit, calculates the relative displacement of the corresponding grating ruler, and outputs it at the output end of the data collection and processing and control unit.

Technical effect of the present invention:

The invention adopts an adaptive method to realize the dynamic common optical path of the grating interferometer, which can eliminate the influence of the motion error of the grating ruler, thereby obtaining higher precision and resolution.

Description of drawings

Fig. 1 is an optical path diagram of an embodiment in which a single three-dimensional PZT micro-displacement device is used to drive a mirror to realize an adaptive common optical path grating interferometer.

Fig. 2 is an optical path diagram of an embodiment in which two three-dimensional PZT micro-displacement devices respectively drive two mirrors to realize an adaptive common optical path grating interferometer.

Fig. 3 is an optical path diagram of an embodiment in which a single three-dimensional PZT micro-displacement device is used to drive a corner cube to realize an adaptive common optical path grating interferometer.

Fig. 4 is an optical path diagram of an embodiment using dual-frequency heterodyne interferometry in Fig. 3 .

detailed description

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

1. Embodiment 1. Figure 1.

The laser 8 emits linearly polarized light, which is divided into P light and S light by the first polarizing beam splitter 7, and enters the diffraction grating 1 through the mirror 3 and the mirror 4 respectively, and is diffracted by the diffraction grating 1 (set as ±1-order light The direction of the two diffracted lights of ) is perpendicular to the diffraction grating 1, and after being reflected by the corner cube prism 2, the P light and the S light respectively enter the respective optical paths of the other party (S light and P light), forming a complete common optical path, and then pass through the first polarization Beam splitter 7 emerges as orthogonal linearly polarized light, which enters the dotted line frame by non-polarizing beam splitter 10, quarter wave plate 9, second polarizing beam splitter 12, third polarizing beam splitter 15 and the first A polarization phase-shift interference photoelectric detection unit (hereinafter referred to as A) composed of a detector 11, a second detector 13, a third detector 14, and a fourth detector 16 forms four detection signals with a phase shift of 90°, and then passes The data acquisition, processing and control unit calculates the phase information corresponding to the position of the diffraction grating 1 by phase-shift interferometry (Optical Shop Testing[M], John Wiley&Sons, 2007, Chapter14, p547), and finally converts it into corresponding displacement information and outputs it .

The above solution has optical 4 subdivision features and is not thermally sensitive. It has a certain ability to resist rotation (yaw), roll (roll), translation (stand off), and side shift (offset), but it will still be limited for the pursuit of higher precision and resolution.

In order to better eliminate the influence of all motion errors of the grating scale, the following method is adopted: a certain amount of S light is leaked at the mirror 4, and the position-sensitive detector 6 is used to detect the position of the light spot in real time; and at the mirror 3, The mirror 3 is driven by a three-dimensional PZT micro-displacement device 5 . When the diffraction grating scale 1 moves, if there is a motion error, it will cause the diffracted light to move, degrade the characteristics of the common optical path, and cause the light spot on the position sensitive detector 6 to move. Data acquisition and processing and control unit 17 (hereinafter referred to as B in the figure) feeds back the movement amount to the three-dimensional PZT micro-displacement device at the reflector 3, and drives it dynamically so that the light point on the position-sensitive detector 6 returns to the common position. Light spot on the optical path (the actual processing is less than the target reference position difference threshold, that is, the light spot movement threshold). The data acquisition and processing and control unit 17 synchronously collects the data of the above-mentioned polarization phase shift interference photoelectric detection unit, calculates the relative displacement of the corresponding grating scale, and outputs it at the output end of the data acquisition and processing and control unit 17 . Thus, an adaptive dynamic common optical path grating interferometer can be guaranteed to eliminate the influence of all motion errors of the grating scale. Higher accuracy and resolution can thus be achieved. In the above solution, the data acquisition and processing and control unit 17 is composed of a data acquisition card, a motion control card and an industrial computer.

2. Embodiment 2. Figure 2.

The difference from Fig. 1 is that two position-sensitive detectors 6-1 (ie, 6 in the original Fig. 1) and 6-2 are respectively used as the position-sensitive detection feedback for light spot movement. Two three-dimensional PZT micro-displacement devices are respectively used to drive the mirrors 4 and 3 (the mirror 3 in the original figure 1 is changed to a mirror) to control the adaptive optical path and the common optical path. A in the figure is the polarization phase-shift interference photoelectric detection unit in the dotted line box in FIG. 1 , and B is the data acquisition, processing and control unit 17 in FIG. 1 . In the figure, the control line of the PZT micro-displacement device is not marked.

3. Embodiment 3. Figure 3.

Two position-sensitive detectors 6-1 (ie, 6 in the original figure 1) and 6-2 are respectively used as the position-sensitive detection feedback for light spot movement. The transflector 4 and the transflector 3 (the reflector 3 is changed into the transflector in the original figure 1) are fixed. A three-dimensional PZT micro-displacement device 5 drives the corner cube prism 2 to control the adaptive optical path and the common optical path. A in the figure is the polarization phase-shift interference photodetection unit within the dotted line box in FIG. 1 , and B is the data acquisition, processing and control unit 17 . In the figure, the control line of the PZT micro-displacement device is not marked.

4. Embodiment 4. Figure 4.

If a dual-frequency orthogonally polarized laser is used as a light source, the corresponding photoelectric signal detection and processing uses dual-frequency heterodyne interferometry instead of the above-mentioned polarization phase-shifting interferometry. Take Figure 3 as an example for modification, and other above-mentioned cases can be modified accordingly.

Dual-frequency orthogonally polarized laser 8 emits linearly polarized light, which is split into two beams of light by a non-polarizing beam splitter 18, and one beam is received by a detector 22 through an analyzer 19 placed at an orthogonal polarization of 45 degrees as a reference beam; One beam is divided into P light and S light by the first polarizing beam splitter 7, and passes through the mirror 4 and the mirror 3 respectively (the mirror 3 in the original figure 1 is changed to a mirror) and enters the diffraction grating 1, and the diffraction grating After the diffraction of ruler 1 (set as ±1st order light), the direction of the two diffracted lights is perpendicular to the diffraction grating 1, and after being reflected by the corner cube prism 2, the P light and the S light respectively enter the respective optical paths of the other side (S light and P light) , forming a complete common optical path, and then output as orthogonal linearly polarized light through the first polarizing beam splitter 7, and receive it by the detector 21 through the analyzer 20 placed at 45 degrees of orthogonal polarization. Two channels of photoelectric signals are input to the data acquisition and processing and control unit B, and then the phase corresponding to the position of the diffraction grating scale 1 is calculated by dual-frequency heterodyne interferometry (Optical Shop Testing [M], John Wiley & Sons, 2007, Chapter 14, p640). Information, and finally converted into corresponding displacement information and output. The corresponding adaptive optical path common optical path control is the same as Case 3. In the figure, the control line of the PZT micro-displacement device is not marked. By the non-polarizing beam splitter 18, the first polarizing beam splitter 7, the first analyzer 19 placed at 45 degrees of orthogonal polarization and the corresponding fifth detector 22, the second analyzer placed at 45 degrees of orthogonal polarization The polarizer 20 and the corresponding sixth detector 21 form a dual-frequency heterodyne interference photodetection unit. Data acquisition and processing and control unit B is composed of data acquisition card, motion control card and industrial computer.

In the above cases, the grating scale can also be transmissive; when the transmissive type is used, the corner cube prism is placed as a mirror image relative to the reflective grating scale, and the reflective grating scale is also replaced by the transmissive grating scale.

Claims (11)

1. An adaptive common optical path grating interferometer, comprising: a grating ruler (1), a corner cube (2), a reflector (3), a mirror (4), and a position-sensitive detector (6) for relative motion , a first polarizing beam splitter (7), a linearly polarized light source (8), a PZT micro-displacement driver for driving the corner cube (2) or mirror (3) or mirror (4), data Acquisition and processing and control unit, interference photoelectric detection unit, characterized in that: ① The polarized light beam emitted by the linearly polarized light source (8) is divided into transmitted S light and reflected P light through the first polarizing beam splitter (7), and the P light is reflected by the reflector (3) and then passed through The ±m-order diffracted light after the diffraction of the relative motion grating scale (1) is incident on the corner cube prism (2), wherein m>=1, and the said S light passes through the relative motion grating after being reflected by the transflector (4) The ±m (m>=1) order diffracted light after the diffraction of the ruler (1) is incident on the corner cube (2), and the P light and the S light respectively enter the other party's optical path through the reflection output of the corner cube (2), and generate are respectively ±2m times Doppler frequency shift, and finally the two optical paths produce a 4m times Doppler frequency shift difference, and exit the orthogonal polarization state in the same direction at the first polarization beam splitter (7), forming a complete A common optical path, the complete common optical path is incident on the interference photodetection unit, the output end of the interference photoelectric detection unit is connected to the input end of the data acquisition and processing and control unit, ②The position-sensitive detector (6) is arranged in the direction of the reverse transmitted light of the mirror (4) to detect the change of the light spot of the grating scale diffracted light, and the output terminal of the position-sensitive detector (6) Connect the input end of the data acquisition and processing and control unit, the output end of the data acquisition and processing and control unit is connected to the control end of the PZT micro-displacement driver, and the PZT micro-displacement driver drives the reflector or pyramid Prisms to change the orientation of incoming and outgoing light rays. 2. The adaptive common optical path grating interferometer according to claim 1, characterized in that the interference photodetection unit is a polarization phase shift interference photodetection unit or a dual-frequency heterodyne interference photodetection unit. 3. adaptive common optical path grating interferometer according to claim 2, is characterized in that described polarization phase-shifting interference photodetection unit is made of quarter-wave plate (9), non-polarization beam splitter (10), The second polarization beam splitter (12), the third polarization beam splitter (15) and the first detector (11), the second detector (13), the third detector (14), the fourth detector (16 )composition. 4. adaptive common optical path grating interferometer according to claim 2, is characterized in that described dual-frequency heterodyne interference photodetection unit is made of first polarization beam splitter (7), non-polarization beam splitter (18) , the first analyzer (19) placed at 45 degrees of orthogonal polarization and the corresponding fifth detector (22), the second analyzer (20) placed at 45 degrees of orthogonal polarization and the corresponding sixth detector Device (21) is formed. 5. The adaptive common optical path grating interferometer according to claim 1, wherein said linearly polarized light source is light emitting diode, laser diode, solid light source or gas light source; single-frequency laser or dual-frequency orthogonally polarized of lasers. 6. The adaptive common optical path grating interferometer according to claim 1, characterized in that said PZT micro-displacement driver can also be replaced by MEMS or electrostatic, or planar micro-motor. 7. The self-adaptive common optical path grating interferometer according to claim 1, characterized in that said grating ruler is a common grating ruler or a blazed grating ruler, and said grating ruler is a reflection type grating ruler or a transmission type grating ruler. 8. The adaptive common optical path grating interferometer according to claim 1, characterized in that said position-sensitive detector is a PSD or a detector array, or a CCD detector, or a CMOS. 9. The self-adaptive common optical path grating interferometer according to claim 1, characterized in that the corner cube is either a rectangular prism or a reflective mirror assembly cube. 10. The adaptive common optical path grating interferometer according to any one of claims 1 to 9, characterized in that the data acquisition, processing and control unit is composed of a data acquisition card, a motion control card and an industrial computer. 11. the self-adaptive realization method of self-adaptive common optical path grating interferometer claimed in claim 1, it is characterized in that the method comprises the steps: ①Initialization: The statically adjusted grating interferometer is in a state of complete common optical path, the grating ruler (1) has no movement, and the data acquisition and processing and control unit described above collects the light diffracted by the grating ruler (1) on the position-sensitive detector (6) The spot position of the target is used as the target reference position, and the threshold value of the difference from the target reference position is set; ② During work, the data acquisition and processing and control unit collects the light spot position of the grating ruler diffracted light on the position sensitive detector (6), and calculates the difference between the light spot position and the target reference position; if the If the position difference is less than or equal to the set threshold, go to step ④; if the position difference is greater than the set threshold, go to step ③; ③The data acquisition and processing and control unit feeds back the position difference to the PZT micro-displacement driver in real time, drives the reflector (3) or the corner cube (2) to move, and adjusts the light spot to zero For the reference position of the target in the case of complete common light path during motion, go to step ②; ④ The data collection and processing and control unit synchronously collects the data of the interference photoelectric detection unit, calculates the relative displacement of the corresponding grating ruler, and outputs it at the output end of the data collection and processing and control unit.