JP2013033018A - Heterodyne laser interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heterodyne laser interferometer that accurately eliminates an influence of any dead path from a result of interferometry.SOLUTION: A heterodyne laser interferometer comprises a branching unit 80 that branches a beam from a heterodyne laser beam source 10 and generates a measurement beam B1 and a reference beam B2, a polarized beam splitter 30 that splits the measurement beam B1 and the reference beam B2, 1/4 wavelength plates 31 and 32 disposed on measurement paths LP1 and LP2, measuring mirrors 341 and 342 fixed to a movable measurement object 50 and irradiated with measurement beams B11 and B12, reflecting mirrors 411 and 412 arranged in the vicinities of the measuring mirrors 341 and 342 and irradiated with reference beams B21 and B22, and an arithmetic circuit 70 that calculates a displacement from two beat signals based on light with which the reflection light from the measurement mirrors 341 and 342 interfere and light with which reflection light from the reflecting mirrors 411 and 412. The branching unit 80 has adjusting means that performs adjustment by continuously varying the luminous quantity ratio between the measurement beam B1 and the reference beam B2.

Description

  The present invention relates to a movable part of a precision processing apparatus such as a heterodyne laser interferometer or an electron beam drawing apparatus that measures the displacement of an object to be measured using laser light used for processing and manufacturing of precision machines, semiconductors, optical disks and the like. More specifically, the present invention relates to a heterodyne laser interferometer that performs dead-path error correction.

  A typical method used for laser interferometry is a heterodyne laser interferometer that is highly accurate and stable.

FIG. 1 shows a typical configuration example of a conventional heterodyne laser interferometer.
The heterodyne laser light source 10 emits two linearly polarized outgoing beams having slightly different frequencies and orthogonal polarization planes. The beam emitted from the heterodyne laser light source 10 and branched by the beam splitter 20 converts the interference state into an electrical signal by the photodetector 21, and the beat signal is detected by the reference signal circuit 22.
On the other hand, the beam transmitted through the beam splitter 20 is split into a reference beam and a measurement beam by the polarization beam splitter 30.

The reference beam passes through the quarter-wave plate 31, is reflected by the reference mirror 33 whose position is fixed, and returns to the polarization beam splitter 30 through the quarter-wave plate 31.
The measurement beam passes through the quarter wavelength plate 32, is reflected by the movable measurement mirror 34, and returns to the polarization beam splitter 30 through the quarter wavelength plate 32.

Since the reference beam and the measurement beam reflected by the reference mirror 33 and the measurement mirror 34 pass through the quarter-wave plates 31 and 32 twice, respectively, the polarization plane is rotated, and the outgoing beam is separated from the polarization beam splitter 30, and the light The detector 35 converts the interference state into an electrical signal, and the measurement signal circuit 36 detects a beat signal. In many cases, the polarizing beam splitter 30 and the two quarter-wave plates 31 and 32 are integrated.
Subsequently, the outputs of the reference signal circuit 22 and the measurement signal circuit 36 are arithmetically processed by the arithmetic circuit 70.

  When the movable measurement mirror 34 mounted and fixed on the measurement object moves, the beat signal phase of the measurement signal circuit 36 changes, and the frequency is Doppler shifted in accordance with the speed. The movement distance can be measured by computing these based on the above.

  This moving distance is performed not by absolute value measurement but by relative value measurement, and the measurement value is reset to zero at an arbitrarily determined measurement origin (O). The difference in optical path length between the reference beam and the measurement beam at the measurement origin is a dead path.

  In general, it is difficult to make the dead path zero because of restrictions on the arrangement of the optical system. The laser light wavelength changes depending on the ambient temperature, humidity, and atmospheric pressure (known as Edren's equation), so the laser interferometry measurement value also changes, but the change in the dead path is separated from the measurement value. As a result, there is a problem that the moving distance measurement accuracy of the movable measuring mirror 34 is lowered.

Therefore, a method and an apparatus for reducing the influence of dead path have been proposed.
First, there is a method in which a design dead path amount is obtained in advance, a dead path amount change due to an environmental change is calculated, and an actual length measurement result including the dead path is corrected (see Patent Documents 1 and 2).
That is, the dead path length Ld is measured by some means (for example, a measure), the measurement result measured using laser interference is L, and the measured length is corrected by Edren's formula taking the sign dash into consideration for the environment such as temperature. As a result, the true moving distance La is obtained as La = L ′ − (Ld−Ld ′) (Patent Document 1).
It also has a detection unit for environmental conditions such as temperature, and the operator inputs the dead path length Cd (correctly the count value corresponding to the distance) to the input unit of the dead path so that correction by the Edren's formula is automatically performed. The true movement distance is C = Cp− (Cd−Cd ′) with respect to the measured movement distance Cp (Patent Document 2).

  However, in these conventional techniques, the dead path amount is obtained in advance, and the change in the dead path amount due to the environmental change is calculated to correct the length measurement result including the dead path. There was a problem that the accuracy of was low.

  In addition, the reference and measurement optical path is equipped with an expansion / contraction mechanism so that the distance between the reference mirror / measurement object and the polarization beam splitter can be increased / decreased, and based on the reference signal from the light source corresponding to dead path zero, the reference and measurement optical path An apparatus has been proposed in which the dead path itself is removed from the optical system by calculating the phase difference, expanding and contracting the length of the reference optical path, and actually adjusting the dead path length to zero (see Patent Document 3). ).

  However, with this conventional technology, the dead path amount is actually obtained to eliminate itself, but a necessary optical path expansion / contraction mechanism is necessary for this purpose, and it is difficult to realize it in terms of actual device mounting. There was a problem in terms of.

  In addition, a quarter wavelength plate of the reference optical path is partially inserted into the reference beam, a part of the surface of the quarter wavelength plate of the measurement optical path is used as a mirror and placed at the measurement origin, and the reference signal is the reference optical path. The measurement signal is generated by interference between the portion reflected from the reference mirror without passing through the quarter-wave plate and the portion reflected from the surface of the quarter-wave plate of the measurement optical path. Since it is generated by interference between the part reflected from the reference mirror and the part reflected by the quarter wavelength plate of the measurement optical path and reflected from the measurement mirror, the measurement of the dead path is performed with the reference signal. There has been proposed a device that performs position length measurement using a measurement signal and cancels a dead path amount change from a length measurement result of a measurement mirror (see Patent Document 4).

  However, in this conventional technique, the dead path amount change is offset by performing optical length measurement of the dead path portion together with the object, but it can be read that the position of the reference mirror is fixed. If the reference mirror is allowed to move and applied to the differential detection optical system, the position of the measurement optical path is reversed with respect to the optical axis between the two optical paths, so that the measurement optical path is aligned with the same straight line of the measurement mirror. However, it is necessary to shift the optical path, and there is a problem that an extra mechanism is required.

In laser interferometry, there is a method of improving resolution by using a reference optical path as a measurement optical path.
A typical configuration is shown in FIG. 2, in which a reference mirror 33 and a measurement mirror 34 are mounted on an object to be measured 50 with mirror surfaces facing each other in opposite directions.
The reference beam to the reference mirror 33 is guided from the quarter-wave plate 31 through three mirrors 51, 52, and 53 for changing the direction. The reference beam and the measurement beam are on the same straight line, and the mirror surfaces of the reference mirror 33 and the measurement mirror 34 are arranged to be perpendicular to the beam.

  Compared with the heterodyne laser interferometer of FIG. 1, the difference is that the mirror surface of the reference mirror 33 is mounted on the measuring object with the mirror surface of the measuring mirror 34 facing away from the straight line corresponding to the optical axis. ing. In this configuration, the optical path length is differentially detected and doubled with respect to the amount of movement of the measurement target in the optical axis direction, so that the resolution is doubled.

  Further, in such a differential detection optical system configuration, the functions of the reference mirror 33 and the measurement mirror 34 are exactly the same. However, in optical differential detection, it is necessary to configure an optical system that sandwiches the object to be measured. Therefore, the optical path is basically an unequal-length optical path with a moving amount added to the object to be measured, and the dead path is shown in FIG. It becomes larger than the normal optical system shown. For this reason, it is necessary to take measures to further suppress a decrease in measurement accuracy due to a dead path.

  In Patent Document 5, two measurement beams separated by a polarization beam splitter of a heterodyne laser interferometer are irradiated on the object to be measured from opposite directions on a virtual straight line, and the object to be measured is reflected by the reflected interference light. When measuring the displacement of the measurement object, the reflection mirror provided near the object to be measured reflects a part of the cross section of the two measurement beams irradiated to the object to be measured, and returns from the object to be measured that returns to the opposite direction as the same luminous flux. The reflected beam and the reflected beam from the reflecting mirror are divided into two parts after the polarizing beam splitter, and the beat signal of the reflected interference light from the object to be measured and the two-beat signal of the reflected interference light beat signal from the reflecting mirror The transition corresponding to the difference is calculated. Thereby, the former corresponds to the amount of displacement of the object to be measured including the dead path, and the latter corresponds to the amount of the dead path, so that the dead path amount can be eliminated by taking the difference.

  However, in this prior art, the influence of the dead path is eliminated by performing the optical length measurement of the dead path portion together with the object. However, the reflected light beam is physically divided into two parts, and further from the reflected light from the object and the reflection mirror. The light is selected by aperture restriction. For this reason, there is a problem that the amount of light reaching the photodetector relating to the beat signal is small, and the measurement accuracy is affected or the measurement cannot be performed depending on the reflectance of the target.

  The present invention has been made in view of the above problems in the prior art, and in a heterodyne laser interferometer that uses optical differential detection, it is possible to accurately eliminate the influence of a dead path from a length measurement result. An object is to provide a heterodyne laser interferometer.

  The present invention provided in order to solve the above-mentioned problems is a heterodyne laser interferometer for measuring the displacement of an object to be measured (movable measurement object 50), and directs the reflecting surfaces in opposite directions on a virtual straight line. Two measurement mirrors (measurement mirrors 341 and 342) fixed to the object to be measured, and a heterodyne laser that physically emits two linearly polarized laser beams with different polarization planes at different frequencies as one laser beam. A light source (heterodyne laser light source 10) and two physically separated parallel laser beams consisting of a measurement beam (measurement beam B1) and a reference beam (reference beam B2) by splitting the laser beam from the heterodyne laser light source And a polarization beam that splits the measurement beam and the reference beam from the splitter in two directions. Splitter (polarizing beam splitter 30) and a measurement beam (first measurement beam B11) and a reference beam (first reference beam B21) in one direction among the measurement beam and the reference beam divided in the two directions. The measurement beam (second measurement beam B12) and the reference beam (second reference beam B22) in the other direction are guided along the virtual straight line toward one of the two measurement mirrors (measurement mirror 341). Two measurement optical paths (measurement optical paths LP1 and LP2) guided to the other measurement mirror (measurement mirror 342) side along the virtual straight line, and two quarter-wave plates provided in the optical paths of the two measurement optical paths, respectively. (Quarter wave plates 31, 32) and two counter-waves which are disposed between the quarter wave plate and the measurement mirror for each of the two measurement optical paths and reflect the reference beam. The intensity of the measurement beam interference light (measurement beam interference light B1k) obtained by causing the measurement beams reflected by the mirrors (reflection mirrors 411 and 412) and the two measurement mirrors to interfere with each other by the polarization beam splitter is electrically A measurement beam light detector (light detector 35) to detect, a measurement beam measurement circuit (measurement signal circuit 36) that generates a beat signal from the output of the measurement beam light detector, and the two reflection mirrors. A reference beam light detector (light detector 37) for electrically detecting the intensity of reference beam interference light (reference beam interference light B2k) obtained by causing each of the reference beams to interfere with each other with the polarization beam splitter; and the reference beam light A reference beam measurement circuit (measurement signal circuit 38) for generating a beat signal from the output of the detector, and a beat signal generated by the measurement beam measurement circuit And an arithmetic circuit (arithmetic circuit 70) for calculating a displacement corresponding to a difference between beat signals generated by the reference beam measuring circuit, and the branching unit continuously calculates a light amount ratio between the measuring beam and the reference beam. The heterodyne laser interferometer is characterized by having an adjusting means for adjusting by changing it (FIGS. 3, 4, and 9).

  Further, the present invention provided to solve the above-mentioned problems is a heterodyne laser interferometer for measuring the displacement of the object to be measured (movable measurement object 50), wherein the reflecting surfaces of the heterodyne laser interferometers are arranged in opposite directions on a virtual straight line. A laser beam including two measurement mirrors (measurement mirrors 341 and 342) fixed to the object to be measured and two linearly polarized laser beams having polarization planes orthogonal to each other at different frequencies. A heterodyne laser light source (heterodyne laser light source 10) that is branched and emitted as two physically separated parallel laser beams consisting of a measurement beam (measurement beam B1) and a reference beam (reference beam B2), and the heterodyne laser light source Polarization beam splitter (polarization beam splitter 30) that splits the measurement beam and reference beam from the beam in two directions Among the measurement beam and the reference beam divided in the two directions, a measurement beam (first measurement beam B11) and a reference beam (first reference beam B21) in one direction are converted into the two directions along the virtual straight line. The measurement mirror is guided to one measurement mirror (measurement mirror 341), and the measurement beam in the other direction (second measurement beam B12) and the reference beam (second reference beam B22) are measured along the virtual straight line. Two measurement optical paths (measurement optical paths LP1, LP2) guided to the mirror (measurement mirror 342) side and two quarter wavelength plates (1/4 wavelength plates 31, 32) provided in the optical paths of the two measurement optical paths, respectively. ), Two reflection mirrors (reflection mirrors 411 and 412) that are arranged between the quarter-wave plate and the measurement mirror for each of the two measurement optical paths and reflect the reference beam, Measurement beam photodetector (photodetector) for electrically detecting the intensity of measurement beam interference light (measurement beam interference light B1k) obtained by causing the measurement beam reflected by two measurement mirrors to interfere with each other by the polarization beam splitter 35), a measurement beam measurement circuit (measurement signal circuit 36) for generating a beat signal from the output of the measurement beam photodetector, and the reference beams reflected by the two reflecting mirrors by the polarization beam splitter. A reference beam light detector (light detector 37) for electrically detecting the intensity of the interfered reference beam interference light (reference beam interference light B2k), and a reference for generating a beat signal from the output of the reference beam light detector Beam measurement circuit (measurement signal circuit 38), beat signal generated by the measurement beam measurement circuit, and beat generated by the reference beam measurement circuit An arithmetic circuit (arithmetic circuit 70) for calculating a displacement corresponding to the difference between the signals, wherein the heterodyne laser light source includes an adjusting unit that continuously adjusts a light amount ratio between the measurement beam and the reference beam. The heterodyne laser interferometer is characterized by having (FIGS. 5, 6, and 9).

  Further, the present invention provided to solve the above problem is a heterodyne laser interferometer that measures the displacement of an object to be measured (movable measurement object 50 (cylindrical object 50a)), and has a plane of polarization at different frequencies. A heterodyne laser light source (heterodyne laser light source 10) that physically emits two orthogonally linearly polarized laser beams as one laser beam, and a measurement beam (measurement beam B1) by splitting the laser beam from the heterodyne laser light source And a branching unit (branching unit 80) for generating two physically separated parallel laser beams consisting of a reference beam (reference beam B2), and a measuring beam and a reference beam from the branching unit are split in two directions. Polarization beam splitter (polarization beam splitter 30), measurement beam and reference beam divided in the two directions Among them, a measurement beam in one direction (first measurement beam B11) and a reference beam (first reference beam B21) are guided to one side of the object to be measured, and a measurement beam in the other direction (second measurement beam B12). And two measurement optical paths (measurement optical paths LP1 and LP2) for directing the reference beam (second reference beam B22) to the other side of the measurement object facing each other, and two optical paths provided in each of the two measurement optical paths A quarter-wave plate (quarter-wave plates 31, 32) and two reflections that are arranged between the quarter-wave plate and the object to be measured for each of the two measurement optical paths and reflect the reference beam. The intensity of the measurement beam interference light (measurement beam interference light B1k) obtained by causing the measurement beam reflected on both sides of the mirror (reflection mirrors 411 and 412) and the measurement object to interfere with each other by the polarization beam splitter. A measurement beam light detector (light detector 35) for detecting air; a measurement beam measurement circuit (measurement signal circuit 36) for generating a beat signal from the output of the measurement beam light detector; and the two reflecting mirrors. A reference beam photodetector (photodetector 37) for electrically detecting the intensity of the reference beam interference light (reference beam interference light B2k) obtained by causing each reflected reference beam to interfere with the polarization beam splitter; A reference beam measurement circuit (measurement signal circuit 38) that generates a beat signal from the output of the reference beam photodetector, and a difference between the beat signal generated by the measurement beam measurement circuit and the beat signal generated by the reference beam measurement circuit An arithmetic circuit (arithmetic circuit 70) for calculating a displacement corresponding to the above-mentioned, and the branching unit adjusts the light quantity ratio between the measurement beam and the reference beam by continuously changing the ratio. The heterodyne laser interferometer is characterized by having adjusting means for adjusting (FIG. 10).

  According to the heterodyne laser interferometer of the present invention, a measurement target is measured with an optical differential detection configuration, and at the same time, a reflection mirror is installed in a portion close to the measurement target, and a dead path is formed in a part of the measurement beam. Since the length measurement is also performed and the dead path value is removed from the final length measurement result, the influence of the dead path can be eliminated from the length measurement result even when the resolution is double. In addition, the measurement beam and the reference beam are physically separated parallel beams, and a beat signal photodetector can be used for each light quantity without beam splitting, so that measurement can be performed with high accuracy. At this time, since the light intensity ratio between the measurement beam and the reference beam can be continuously changed by the adjusting means, it becomes possible to set the optimum light intensity of the measurement beam for the measurement object, and the reliability of the measurement accuracy is improved. More improved. Thereby, it becomes possible to measure even a measurement object having a low reflectance.

It is a block diagram which shows the structural example 1 of the conventional heterodyne laser interferometer. It is a block diagram which shows the structural example 2 of the conventional heterodyne laser interferometer. It is a block diagram which shows the structure in 1st Embodiment of the heterodyne laser interference length measuring device which concerns on this invention. It is a block diagram which shows the structure in 2nd Embodiment of the heterodyne laser interference length measuring device which concerns on this invention. It is a block diagram which shows the structure in 3rd Embodiment of the heterodyne laser interference length measuring device which concerns on this invention. It is a block diagram which shows the structure in 4th Embodiment of the heterodyne laser interference length measuring device which concerns on this invention. It is the schematic which shows the reference example 1 of the adjustment means of the light quantity ratio of the measurement beam and reference beam in the heterodyne laser interferometer which concerns on this invention. It is the schematic which shows the reference example 2 of the adjustment means of the light quantity ratio of the measurement beam and reference beam in the heterodyne laser interferometer which concerns on this invention. It is the schematic which shows the structural example of the adjustment means of the light quantity ratio of the measurement beam and a reference beam in the heterodyne laser interferometer length measuring device which concerns on this invention. It is a block diagram which shows the structure in 5th Embodiment of the heterodyne laser interference length measuring device which concerns on this invention. (A) The cross-sectional schematic diagram which shows the cutting trace which arose on the surface of the cylindrical object, (b) The schematic diagram of the cylindrical object with a cutting trace. It is a schematic diagram which shows (a) the irradiation state of the X direction with respect to the cylindrical object of a measurement beam, (b) the irradiation state of the Y direction, and (c) the irradiation state of the X and Y directions.

The configuration of the heterodyne laser interferometer according to the present invention will be described below.
FIG. 3 is a block diagram showing the configuration of the first embodiment of the heterodyne laser interferometer according to the present invention.
As shown in FIG. 3, from the heterodyne laser light source 10, two linearly polarized outgoing beams having slightly different frequencies and orthogonal planes of polarization are physically emitted as one laser beam, followed by this one. Are split into two parallel measurement beams (B1) and a reference beam (B2) which are physically separated by a splitter 80. As the splitter 80, a combination of a non-polarizing beam splitter and a mirror can be used.

  The measurement beam (B1) and the reference beam (B2) output from the splitter 80 are incident on the polarization beam splitter 30, and are divided into two directions by the polarization beam splitter 30, respectively. Note that the measurement beam (B1) and the reference beam (B2) are incident on the polarization beam splitter 30 as two physically separated parallel laser beams, so that the measurement beam (B1) and the reference beam (B2) are at different positions (points) in the polarization beam splitter 30. Divided. That is, in the polarization beam splitter 30, the measurement beam (B1) is divided at the point P1, and the reference beam (B2) is divided at the point P2.

  At this time, the measurement beam (B1) is divided into a first measurement beam B11 and a second measurement beam B12, and the reference beam (B2) is divided into a first reference beam B21 and a second reference beam B22. Further, the first measurement beam B11 and the first reference beam B21 are beams reflected by the polarization beam splitter 30 and directed upward in the figure, and the second measurement beam B12 and the second reference beam B22 are polarization beams. The beam is transmitted through the splitter 30 and directed to the right in the figure. Further, the first measurement beam B11 and the first reference beam B21 pass through the measurement optical path LP1 while being in a parallel relationship that is physically separated from each other, and the second measurement beam B12 and the second reference beam B22 are The measurement light path LP2 passes through the parallel relationship in which the two are physically separated from each other.

  In the measurement optical path LP1, a quarter-wave plate 31 and mirrors 51, 52, and 53 are arranged, and the first measurement beam B11 and the first reference beam B21 are in a parallel relationship in which they are physically separated from each other. After being transmitted through the quarter-wave plate 31, the direction is changed by being reflected by the mirrors 51, 52, and 53, and is guided to the measurement mirror 341 side.

  Here, the first measurement beam B11 is reflected by the measurement mirror 341 as it is, then travels back along the measurement optical path LP1, and returns to the polarization beam splitter 30 via the quarter-wave plate 31. Further, the first reference beam B21 passes through the same optical path as the first measurement beam B11 up to the mirror 53 in the measurement optical path LP1, and is reflected by the reflection mirror 411 disposed at a predetermined position in front of the measurement mirror 341. From there, the measurement light path LP1 is traced back to the polarization beam splitter 30 via the quarter-wave plate 31.

  Note that the first measurement beam B11 reflected and returned returns to the point P1 where the measurement beam B1 incident from the branching device 80 is split in the polarization beam splitter 30. Further, the first reference beam B21 reflected and returned returns to the point P2 where the reference beam B2 incident from the branching device 80 is split in the polarization beam splitter 30. Therefore, the first measurement beam B 11 and the first reference beam B 21 that have been reflected back are incident on different positions (points) in the polarization beam splitter 30.

  In the measurement optical path LP2, a quarter wavelength plate 32 is disposed, and the second measurement beam B12 and the second reference beam B22 are maintained in a parallel relationship in which they are physically separated from each other. After passing through the four-wavelength plate 32, it is guided to the measurement mirror 342 side.

  Here, the second measurement beam B12 is reflected by the measurement mirror 342 as it is, then travels back along the measurement optical path LP2, and returns to the polarization beam splitter 30 via the quarter wavelength plate 32. Further, the second reference beam B22 passes through the measurement optical path LP2 through the same optical path as the second measurement beam B12, is reflected by the reflection mirror 412 disposed at a predetermined position before the measurement mirror 342, and from there, the measurement optical path It goes back to LP2 and returns to the polarizing beam splitter 30 via the quarter-wave plate 32.

  The second measurement beam B12 reflected and returned returns to the point P1 where the measurement beam B1 incident from the branching device 80 is split in the polarization beam splitter 30. Further, the second reference beam B22 reflected and returned returns to the point P2 where the reference beam B2 incident from the branching device 80 is split in the polarization beam splitter 30. Therefore, the second measurement beam B12 and the second reference beam B22 that have been reflected back are incident on different positions (points) in the polarization beam splitter 30, and the first measurement beam B11 that has been reflected back. And the second measurement beam B12 are incident on the polarization beam splitter 30 at the same position (point P1), and the first reference beam B21 and the second reference beam B22 that have been reflected back are the same position on the polarization beam splitter 30. It will enter (point P2).

  The polarizing beam splitter 30 and the two quarter-wave plates 31 and 32 may be integrated.

  In addition, the measurement optical path LP1 and the measurement optical path LP2 from the mirror 53 to the measurement mirror 341 are adjusted to form a straight line (virtual straight line), and the mirror surfaces (reflection surfaces) of the two measurement mirrors 341 and 342 are the measurement optical path LP1. , LP2 is installed and fixed to the movable measuring object 50 so as to be perpendicular to the optical axis of LP2 and facing the opposite direction.

  The reflection mirrors 411 and 412 are arranged with respect to the optical axes of the measurement optical paths LP1 and LP2 so as to reflect the first reference beam B21 and the second reference beam B22, respectively, and to go back the measurement optical paths LP1 and LP2. .

  Further, the reflection mirrors 411 and 412 are arranged as close to the measurement mirrors 341 and 342 as possible.

  As the measurement mirrors 341 and 342 and the reflection mirrors 411 and 412, use of a plane mirror or a corner cube can be considered. Alternatively, the measurement mirrors 341 and 342 may be configured such that the end surface itself of the movable measurement object is a reflection surface.

  In the measurement optical path LP1, the distance from the polarization beam splitter 30 to the measurement mirror 341 is MP1, and the distance DP1 from the polarization beam splitter 30 to the reflection mirror 411. In the measurement optical path LP2, the distance MP2 from the polarization beam splitter 30 to the measurement mirror 342. The distance from the polarizing beam splitter 30 to the reflection mirror 412 is DP2.

Here, the first measurement beam B11 that has exited from the polarization beam splitter 30, reflected by the measurement mirror 341, and returned to the polarization beam splitter 30 again passes through the quarter-wave plate 31 twice. The polarization beam splitter 30 is separated from the outgoing beam and passes through the polarization beam splitter 30 downward in the figure. Also, the second measurement beam B12 that has exited from the polarization beam splitter 30, reflected by the measurement mirror 342, and returned to the polarization beam splitter 30 again passes through the quarter-wave plate 32 twice, so that the polarization plane rotates. Then, the output beam is separated from the polarization beam splitter 30 and reflected by the polarization beam splitter 30 downward in the figure. At this time, in the polarization beam splitter 30, one measurement beam obtained by causing the first measurement beam B11 reflected and returned from the measurement mirror 341 and the second measurement beam B12 reflected and returned from the measurement mirror 342 to interfere with each other is measured. The beam interference light B1k is emitted downward in the figure.
Next, the measurement beam interference light B 1 k is bent by the mirror 60 and guided to the photodetector 35.

  The photodetector 35 converts the interference state (intensity) of the measurement beam interference light B1k into an electrical signal, and then the measurement signal circuit 36 generates a beat signal from the output signal of the photodetector 35. The beat signal of the measurement signal circuit 36 corresponds to the distance (MP1-MP2), which corresponds to the moving distance of the measurement target including the dead path amount in the differential detection optical system.

On the other hand, the first reference beam B21 that has exited from the polarizing beam splitter 30, reflected by the reflecting mirror 411, and returned to the polarizing beam splitter 30 again passes through the quarter-wave plate 31 twice, so that the plane of polarization rotates. The polarized beam splitter 30 separates the outgoing beam and transmits the polarized beam splitter 30 downward in the figure. Further, the second reference beam B22 that has exited from the polarizing beam splitter 30, reflected by the reflecting mirror 412, and returned to the polarizing beam splitter 30 again passes through the quarter wavelength plate 32 twice, so that the plane of polarization rotates. Then, the output beam is separated from the polarization beam splitter 30 and reflected by the polarization beam splitter 30 downward in the figure. At this time, in the polarizing beam splitter 30, one reference beam that interferes with the first reference beam B 21 that has been reflected by the reflecting mirror 411 and the second reference beam B 22 that has been reflected by the reflecting mirror 412 and returned. The beam interference light B2k is emitted downward in the figure. Further, the reference beam interference light B2k is emitted from the polarization beam splitter 30 while maintaining a physical relationship that is physically separated from the measurement beam interference light B1k.
Next, the reference beam interference light B <b> 2 k is bent by the mirror 61 and guided to the photodetector 37.

  The measurement beam interference light B1k and the reference beam interference light B2k are emitted from the polarization beam splitter 30 as two parallel beams that are physically separated from each other. Therefore, the measurement beam interference light B1k and the reference beam interference light B2k are emitted. Each can be simply guided to the photodetectors 35 and 37 as they are.

  The photodetector 37 converts the interference state (intensity) of the reference beam interference light B2k into an electrical signal, and then the measurement signal circuit 38 generates a beat signal from the output signal of the photodetector 37. The beat signal of the measurement signal circuit 38 corresponds to the distance (DP1-DP2), which corresponds to the dead path amount in the differential detection optical system.

  Next, the arithmetic circuit 70 receives the beat signal generated by the measurement signal circuit 36 and the beat signal generated by the measurement signal circuit 38 and calculates a displacement corresponding to the difference between the two. That is, since the measurement signal circuits 36 and 38 can electrically detect the moving distance of the measurement object including the dead path amount and the dead path amount, the arithmetic circuit 70 outputs the output signal of the measurement signal circuit 36 and the measurement signal circuit 38. The difference between the output signals ((MP1−MP2) − (DP1−DP2)) can be calculated to obtain the moving distance of the measurement object not including the dead path amount in the differential detection optical system.

  As a method of calculating the difference between the output signal of the measurement signal circuit 36 and the output signal of the measurement signal circuit 38 in the arithmetic circuit 70, the output signal of the measurement signal circuit 36 is used as a reference beat signal, and the beat signal of the measurement signal circuit 38 is used. The method of obtaining the difference between Alternatively, the reference signal circuit 22 (not shown in FIG. 3) described with reference to FIGS. 1 and 2 is used, and the output signals of the measurement signal circuit 36 and the measurement signal circuit 38 and the output signals of the reference signal circuit 22 are A method may be used in which a difference is obtained and data corresponding to (DP1-DP2) and (MP1-MP2) is actually calculated, and then the difference is calculated.

  The heterodyne laser interferometer of this embodiment can be applied to the measurement of the movement amount of a linear motion stage as an example. As a specific example, if it is applied to a precision linear motion stage for semiconductor, optical disk, and hard disk pattern fabrication, the stage movement can be measured with high accuracy without being affected by dead paths. It is possible to improve the accuracy of the production pattern.

Next, the configuration of the second embodiment of the heterodyne laser interferometer according to the present invention will be described.
FIG. 4 is a block diagram showing the configuration of the second embodiment of the heterodyne laser interferometer according to the present invention.
In this embodiment, compared to the heterodyne laser interferometer (first embodiment) of FIG. 3, the measurement mirrors 341 and 342 use the end face of the movable measuring object 50 as a reflection surface, and the measurement beam B11 and B12 are different in that they are provided with lenses 421 and 422 for condensing and irradiating the measurement mirrors 341 and 342, respectively, and the other parts are the same as those in FIG.

  By focusing the measurement beams B11 and B12 with the lenses 421 and 422, a measurement object that can take a measurement mirror area smaller than the beam diameter of the light source or a measurement object whose measurement mirror is a curved surface is used. Even measurement becomes possible.

  Further, it is preferable to place the reflecting surface on the incident surface of the lenses 421 and 422 as the positions of the reflecting mirrors 411 and 412 because the reflecting mirror interval can be maximized.

  In addition, the length measuring mechanism (method) of the movable measuring object 50 in the heterodyne laser interferometer of FIG. 4 condenses the measuring beams B11 and B12 by the lenses 421 and 422 and the end face of the movable measuring object 50 (measurement mirror). 341, 342) and the reflected light is passed through the lenses 421, 422 and returned to the polarization beam splitter 30, only the basic length measurement mechanism (method) is different from the first embodiment. Since it is the same as that of 1 embodiment, the description is abbreviate | omitted.

  In this example, the end face itself of the movable measuring object 50 is mirrored to form the measurement mirrors 341 and 342. However, independent measuring mirrors 341 and 342 are installed on the movable measuring object 50 and fixed as shown in FIG. It can be done.

  As an example, the heterodyne laser interferometer of this embodiment can be applied to the measurement of the amount of rotational shake of the rotary stage. As a specific example, if applied to a precision turntable for optical disk and hard disk pattern fabrication, the turntable rotational runout is measured with high accuracy without being affected by dead paths, so the amount of rotational deflection at the laser beam position for pattern fabrication It is possible to improve the accuracy, for example, by creating a track pattern with no wobbling.

Next, the configuration of the third embodiment of the heterodyne laser interferometer according to the present invention will be described.
FIG. 5 is a block diagram showing the configuration of the third embodiment of the heterodyne laser interferometer according to the present invention. This embodiment differs from the first embodiment (FIG. 3) in that the beam is split inside the heterodyne laser light source 10 and two beams are emitted.

  As shown in FIG. 5, in the heterodyne laser light source 10, two linearly polarized outgoing beams whose frequencies are slightly different from each other and whose polarization planes are orthogonal to each other are first physically generated as one beam, and then the branching device 80. Are branched into two parallel measurement beams (B1) and a reference beam (B2) and emitted to the outside. As the splitter 80, a combination of a non-polarizing beam splitter and a mirror can be used.

  The measurement beam (B1) and the reference beam (B2) emitted from the heterodyne laser light source 10 enter the polarization beam splitter 30, and are divided into two directions by the polarization beam splitter 30, respectively. Note that the measurement beam (B1) and the reference beam (B2) are incident on the polarization beam splitter 30 as two physically separated parallel laser beams, so that the measurement beam (B1) and the reference beam (B2) are at different positions (points) in the polarization beam splitter 30. Divided. That is, in the polarization beam splitter 30, the measurement beam (B1) is divided at the point P1, and the reference beam (B2) is divided at the point P2.

  At this time, the measurement beam (B1) is divided into a first measurement beam B11 and a second measurement beam B12, and the reference beam (B2) is divided into a first reference beam B21 and a second reference beam B22. Further, the first measurement beam B11 and the first reference beam B21 are beams reflected by the polarization beam splitter 30 and directed upward in the figure, and the second measurement beam B12 and the second reference beam B22 are polarization beams. The beam is transmitted through the splitter 30 and directed to the right in the figure. Further, the first measurement beam B11 and the first reference beam B21 pass through the measurement optical path LP1 while being in a parallel relationship that is physically separated from each other, and the second measurement beam B12 and the second reference beam B22 are The measurement light path LP2 passes through the parallel relationship in which the two are physically separated from each other.

  In the measurement optical path LP1, a quarter-wave plate 31 and mirrors 51, 52, and 53 are arranged, and the first measurement beam B11 and the first reference beam B21 are in a parallel relationship in which they are physically separated from each other. After being transmitted through the quarter-wave plate 31, the direction is changed by being reflected by the mirrors 51, 52, and 53, and is guided to the measurement mirror 341 side.

  Here, the first measurement beam B11 is reflected by the measurement mirror 341 as it is, then travels back along the measurement optical path LP1, and returns to the polarization beam splitter 30 via the quarter-wave plate 31. Further, the first reference beam B21 passes through the same optical path as the first measurement beam B11 up to the mirror 53 in the measurement optical path LP1, and is reflected by the reflection mirror 411 disposed at a predetermined position in front of the measurement mirror 341. From there, the measurement light path LP1 is traced back to the polarization beam splitter 30 via the quarter-wave plate 31.

  Note that the first measurement beam B11 reflected and returned returns to the point P1 where the measurement beam B1 incident from the branching device 80 is split in the polarization beam splitter 30. Further, the first reference beam B21 reflected and returned returns to the point P2 where the reference beam B2 incident from the branching device 80 is split in the polarization beam splitter 30. Therefore, the first measurement beam B 11 and the first reference beam B 21 that have been reflected back are incident on different positions (points) in the polarization beam splitter 30.

  In the measurement optical path LP2, a quarter wavelength plate 32 is disposed, and the second measurement beam B12 and the second reference beam B22 are maintained in a parallel relationship in which they are physically separated from each other. After passing through the four-wavelength plate 32, it is guided to the measurement mirror 342 side.

  Here, the second measurement beam B12 is reflected by the measurement mirror 342 as it is, then travels back along the measurement optical path LP2, and returns to the polarization beam splitter 30 via the quarter wavelength plate 32. Further, the second reference beam B22 passes through the measurement optical path LP2 through the same optical path as the second measurement beam B12, is reflected by the reflection mirror 412 disposed at a predetermined position before the measurement mirror 342, and from there, the measurement optical path It goes back to LP2 and returns to the polarizing beam splitter 30 via the quarter-wave plate 32.

  The second measurement beam B12 reflected and returned returns to the point P1 where the measurement beam B1 incident from the branching device 80 is split in the polarization beam splitter 30. Further, the second reference beam B22 reflected and returned returns to the point P2 where the reference beam B2 incident from the branching device 80 is split in the polarization beam splitter 30. Therefore, the second measurement beam B12 and the second reference beam B22 that have been reflected back are incident on different positions (points) in the polarization beam splitter 30, and the first measurement beam B11 that has been reflected back. And the second measurement beam B12 are incident on the polarization beam splitter 30 at the same position (point P1), and the first reference beam B21 and the second reference beam B22 that have been reflected back are the same position on the polarization beam splitter 30. It will enter (point P2).

  The polarizing beam splitter 30 and the two quarter-wave plates 31 and 32 may be integrated.

  In addition, the measurement optical path LP1 and the measurement optical path LP2 from the mirror 53 to the measurement mirror 341 are adjusted to form a straight line (virtual straight line), and the mirror surfaces (reflection surfaces) of the two measurement mirrors 341 and 342 are the measurement optical path LP1. , LP2 is installed and fixed to the movable measuring object 50 so as to be perpendicular to the optical axis of LP2 and facing the opposite direction.

  The reflection mirrors 411 and 412 are arranged with respect to the optical axes of the measurement optical paths LP1 and LP2 so as to reflect the first reference beam B21 and the second reference beam B22, respectively, and to go back the measurement optical paths LP1 and LP2. .

  Further, the reflection mirrors 411 and 412 are arranged as close to the measurement mirrors 341 and 342 as possible.

  As the measurement mirrors 341 and 342 and the reflection mirrors 411 and 412, use of a plane mirror or a corner cube can be considered. Alternatively, the measurement mirrors 341 and 342 may be configured such that the end surface itself of the movable measurement object is a reflection surface.

  In the measurement optical path LP1, the distance from the polarization beam splitter 30 to the measurement mirror 341 is MP1, and the distance DP1 from the polarization beam splitter 30 to the reflection mirror 411. In the measurement optical path LP2, the distance MP2 from the polarization beam splitter 30 to the measurement mirror 342. The distance from the polarizing beam splitter 30 to the reflection mirror 412 is DP2.

Here, the first measurement beam B11 that has exited from the polarization beam splitter 30, reflected by the measurement mirror 341, and returned to the polarization beam splitter 30 again passes through the quarter-wave plate 31 twice. The polarization beam splitter 30 is separated from the outgoing beam and passes through the polarization beam splitter 30 downward in the figure. Also, the second measurement beam B12 that has exited from the polarization beam splitter 30, reflected by the measurement mirror 342, and returned to the polarization beam splitter 30 again passes through the quarter-wave plate 32 twice, so that the polarization plane rotates. Then, the output beam is separated from the polarization beam splitter 30 and reflected by the polarization beam splitter 30 downward in the figure. At this time, in the polarization beam splitter 30, one measurement beam obtained by causing the first measurement beam B11 reflected and returned from the measurement mirror 341 and the second measurement beam B12 reflected and returned from the measurement mirror 342 to interfere with each other is measured. The beam interference light B1k is emitted downward in the figure.
Next, the measurement beam interference light B 1 k is bent by the mirror 60 and guided to the photodetector 35.

  The photodetector 35 converts the interference state (intensity) of the measurement beam interference light B1k into an electrical signal, and then the measurement signal circuit 36 generates a beat signal from the output signal of the photodetector 35. The beat signal of the measurement signal circuit 36 corresponds to the distance (MP1-MP2), which corresponds to the moving distance of the measurement target including the dead path amount in the differential detection optical system.

On the other hand, the first reference beam B21 that has exited from the polarizing beam splitter 30, reflected by the reflecting mirror 411, and returned to the polarizing beam splitter 30 again passes through the quarter-wave plate 31 twice, so that the plane of polarization rotates. The polarized beam splitter 30 separates the outgoing beam and transmits the polarized beam splitter 30 downward in the figure. Further, the second reference beam B22 that has exited from the polarizing beam splitter 30, reflected by the reflecting mirror 412, and returned to the polarizing beam splitter 30 again passes through the quarter wavelength plate 32 twice, so that the plane of polarization rotates. Then, the output beam is separated from the polarization beam splitter 30 and reflected by the polarization beam splitter 30 downward in the figure. At this time, in the polarizing beam splitter 30, one reference beam that interferes with the first reference beam B 21 that has been reflected by the reflecting mirror 411 and the second reference beam B 22 that has been reflected by the reflecting mirror 412 and returned. The beam interference light B2k is emitted downward in the figure. Further, the reference beam interference light B2k is emitted from the polarization beam splitter 30 while maintaining a physical relationship that is physically separated from the measurement beam interference light B1k.
Next, the reference beam interference light B <b> 2 k is bent by the mirror 61 and guided to the photodetector 37.

  The measurement beam interference light B1k and the reference beam interference light B2k are emitted from the polarization beam splitter 30 as two parallel beams that are physically separated from each other. Therefore, the measurement beam interference light B1k and the reference beam interference light B2k are emitted. Each can be simply guided to the photodetectors 35 and 37 as they are.

  The photodetector 37 converts the interference state (intensity) of the reference beam interference light B2k into an electrical signal, and then the measurement signal circuit 38 generates a beat signal from the output signal of the photodetector 37. The beat signal of the measurement signal circuit 38 corresponds to the distance (DP1-DP2), which corresponds to the dead path amount in the differential detection optical system.

  Next, the arithmetic circuit 70 receives the beat signal generated by the measurement signal circuit 36 and the beat signal generated by the measurement signal circuit 38 and calculates a displacement corresponding to the difference between the two. That is, since the measurement signal circuits 36 and 38 can electrically detect the moving distance of the measurement object including the dead path amount and the dead path amount, the arithmetic circuit 70 outputs the output signal of the measurement signal circuit 36 and the measurement signal circuit 38. The difference between the output signals ((MP1−MP2) − (DP1−DP2)) can be calculated to obtain the moving distance of the measurement object not including the dead path amount in the differential detection optical system.

  As a method of calculating the difference between the output signal of the measurement signal circuit 36 and the output signal of the measurement signal circuit 38 in the arithmetic circuit 70, the output signal of the measurement signal circuit 36 is used as a reference beat signal, and the beat signal of the measurement signal circuit 38 is used. The method of obtaining the difference between Alternatively, the reference signal circuit 22 (not shown in FIG. 5) described with reference to FIGS. 1 and 2 is used, and the output signals of the measurement signal circuit 36 and the measurement signal circuit 38 and the output signals of the reference signal circuit 22 are A method may be used in which a difference is obtained and data corresponding to (DP1-DP2) and (MP1-MP2) is actually calculated, and then the difference is calculated.

  The heterodyne laser interferometer of this embodiment can be applied to the measurement of the movement amount of a linear motion stage as an example. As a specific example, if it is applied to a precision linear motion stage for semiconductor, optical disk, and hard disk pattern fabrication, the stage movement can be measured with high accuracy without being affected by dead paths. It is possible to improve the accuracy of the production pattern. Since the parallel measurement beam and the reference beam that are physically separated from the heterodyne laser light source 10 are emitted, the first of the present invention can be used without installing an optical system for branching the measurement beam and the reference beam. The same effect as the embodiment can be obtained.

Next, the configuration of the heterodyne laser interferometer according to the fourth embodiment of the present invention will be described.
FIG. 6 is a block diagram showing the configuration of the heterodyne laser interferometer according to the fourth embodiment of the present invention.
In this embodiment, compared to the heterodyne laser interferometer (third embodiment) of FIG. 5, the measurement mirrors 341 and 342 use the end face of the movable measuring object 50 as a reflection surface, and the measurement beam B11 and B12 are different from each other in that they include lenses 421 and 422 for condensing and irradiating the measurement mirrors 341 and 342, respectively, and the other parts are the same as those in FIG.

  By focusing the measurement beams B11 and B12 with the lenses 421 and 422, a measurement object that can take a measurement mirror area smaller than the beam diameter of the light source or a measurement object whose measurement mirror is a curved surface is used. Even measurement becomes possible.

  Further, it is preferable to place the reflecting surface on the incident surface of the lenses 421 and 422 as the positions of the reflecting mirrors 411 and 412 because the reflecting mirror interval can be maximized.

  Further, the measuring mechanism (method) of the movable measuring object 50 in the heterodyne laser interferometer of FIG. 6 condenses the measuring beams B11 and B12 by the lenses 421 and 422, and the end face of the movable measuring object 50 (measurement mirror). 341, 342) and the reflected light is passed through the lenses 421, 422 and returned to the polarization beam splitter 30, only the basic length measurement mechanism (method) is different from the first embodiment. Since it is the same as that of 3 embodiment, the description is abbreviate | omitted.

  In this example, the end face itself of the movable measuring object 50 is mirrored to form the measuring mirrors 341 and 342. However, independent measuring mirrors 341 and 342 are installed on the movable measuring object 50 and fixed as shown in FIG. It can be done.

Here, the heterodyne laser interferometer shown in FIG. 3 to FIG. 6 has a light amount ratio adjusting means for the measurement beam B1 and the reference beam B2 in the branching unit 80.
For example, in the branching device 80, a plurality of non-polarizing beam splitters having different light intensity division ratios are prepared, and one of them is selected and arranged at a predetermined position, and includes a mirror prepared separately from the non-polarizing beam splitter. Two parallel beams (measurement beam B1 and reference beam B2) may be branched and generated from the beam incident on the non-polarizing beam splitter by the optical path.

  As a specific example, as shown in FIG. 7, a plurality of non-polarizing beam splitters (here, three non-polarizing beam splitters 811, 812, 813) having different light intensity division ratios are prepared, and rotation is used. There is a configuration in which one is selected and disposed at a predetermined position (the position of the non-polarizing beam splitter 812 in FIG. 7) and is combined with the fixed mirror 82 to form an optical path.

  Further, as shown in FIG. 8, a plurality of combinations of non-polarizing beam splitters and mirrors with different relative light intensity division ratios (here, non-polarizing beam splitter 811 and mirror 821, non-polarizing beam splitter 812 and 3 sets of mirror 822, non-polarizing beam splitter 813 and mirror 823) are prepared, and one set is selected from them by using rotation (the position of the pair of non-polarizing beam splitter 812 and mirror 822 in FIG. 8). There is a configuration in which the optical path is arranged.

  By doing so, the measurement light beam B1 and the reference beam B2 can be branched and simultaneously the light quantity ratio between them can be changed. If the reflectance of the measurement object (movable measurement object 50) is small, the measurement beam B1 Increasing the light amount ratio increases the amount of light reaching the light detector 35, and improves the measurement stability and accuracy compared to the case where the light amount ratio between the measurement beam B1 and the reference beam B2 is fixed (for example, 1: 1). It becomes possible to improve. This is particularly effective when the end surface of the movable measuring object 50 is a reflecting surface (measurement mirrors 341 and 342) as in the configuration shown in FIGS. In this case, the light amount of the reference beam B2 is relatively small. However, since the reference beam B2 is reflected by the reflection mirrors 411 and 412, the reflectivity is high, and there is usually a problem even if the reflected light amount is considerably reduced. do not become.

  By the way, since the adjustment means shown in FIGS. 7 and 8 is configured to select from a predetermined light quantity ratio between the plurality of measurement beams B1 and the reference beam B2, the light quantity ratio between the measurement beam B1 and the reference beam B2 can be adjusted. However, the adjustment is stepwise (discontinuous), and the measurement beam quantity may not always be optimal for the reflectance of the measurement target (movable measurement object 50). In addition, due to the structure of the apparatus, it is difficult to provide the adjustment means with many options (a plurality of fixed light amount ratios) of the light amount ratio between the measurement beam B1 and the reference beam B2, in which case the measurement accuracy and stability are somewhat Will remain lost.

  Therefore, in the present invention, the branching unit 80 includes an adjusting unit that continuously adjusts the light amount ratio between the measurement beam B1 and the reference beam B2. Specifically, the adjusting means includes a first polarization beam splitter (polarization beam splitter 911) for polarizing and separating an incident laser beam into a first beam (f1) and a second beam (f2), and the first , Two half-wave plates (1 / 2-wave plates 921, 922) for adjusting the polarization directions of the second beam, and the first beam with the polarization direction adjusted for the S-polarized component ( And a second polarization beam splitter (polarization beam splitter 913) that separates into a P-polarized component (↑) and an S-polarized component (◎) and a P-polarized component (↑). ) And the measurement beam B1 (or reference beam) by combining the S-polarized component of the first beam and the P-polarized component of the second beam. A fourth polarization beam splitter (polarization beam splitter 914), and a fifth polarization beam that combines the P polarization component of the first beam and the S polarization component of the second beam into one beam. A splitter (polarizing beam splitter 915) and a half-wave plate (1 /) that rotates the polarization direction of one beam from the fifth polarizing beam splitter by 90 degrees to form the reference beam B2 (or measurement beam) A two-wave plate 923).

FIG. 9 shows a configuration example of the adjusting means in the spectrometer 80 of the heterodyne laser interferometer of the present invention.
As shown in FIG. 9, the adjusting means is configured to split and generate two parallel beams (measurement beam B1 and reference beam B2) from the beam incident on the polarization beam splitter 911 using polarized light. Yes. In FIG. 9, reference numerals 911, 912, 913, 914, and 915 are polarization beam splitters, reference numerals 921, 922, and 923 are half-wave plates, and reference numerals 821, 822, and 823 are mirrors that bend the optical path. is there.

The adjusting means shown in FIG. 9 has the following optical functions.
That is, since the outgoing beam from the light source (heterodyne laser light source 10) is two linearly polarized outgoing beams whose polarization planes are orthogonal, the polarized beam splitter 911 separates the outgoing beam into the first beam f1 and the second beam f2. . At this time, the first beam f1 is an S-polarized component (represented by ◎ in the figure), and the second beam is a P-polarized component (represented by ↑ in the figure).

  Next, the first beam f1 is reflected by the mirror 821 and passes through the half-wave plate 922. The half-wave plate 922 is rotated by a predetermined angle to change the polarization direction of the first beam f1 to S-polarized light. As a result, the P-polarized light component is also generated in the beam f1 after passing through the half-wave plate 922. When the first beam f1 enters the polarization beam splitter 913 in this state, it is separated into an S-polarized component and a P-polarized component (the S-polarized component (）) is reflected and the P-polarized component (↑) is transmitted).

  Similarly, the second beam f2 passes through the half-wave plate 921, but by rotating the half-wave plate 921 by a predetermined angle and shifting the polarization direction of the second beam f2 from the P-polarized light, An S-polarized component is also generated in the beam f2 after passing through the half-wave plate 921. When the second beam f2 enters the polarization beam splitter 912 in this state, it is separated into an S-polarized component and a P-polarized component (S-polarized component (◎) is reflected and P-polarized component (↑) is transmitted).

  Next, the S polarization component (◎) of the first beam f1 separated by the polarization beam splitter 913 and the P polarization component (↑) of the second beam f2 separated by the polarization beam splitter 912 are the polarization beam splitter. At 914, it is combined as one beam and becomes a measurement beam B1.

  Similarly, the P-polarized component (↑) of the first beam f1 separated by the polarizing beam splitter 913 and the S-polarized component (◎) of the second beam f2 separated by the polarized beam splitter 912 are the polarized beam splitter. In 915, the beams are combined as one beam, and the polarization direction is rotated 90 degrees by the half-wave plate 923 to become the reference beam B2.

  In such an adjusting means, the light quantity ratio between the measurement beam B1 and the reference beam B2 is continuously changed between 0: 1 and 1: 0 in accordance with the rotation angle of the half-wave plates 921 and 922. It is possible to adjust.

  In this way, in the spectrometer 80, the measurement beam B1 and the reference beam B2 can be branched, and at the same time, the light quantity ratio between them can be continuously changed and adjusted. 50), it is possible to obtain an optimal measurement beam light amount, and further improve the reliability of measurement. For example, when the reflectance of the measurement target (movable measurement object 50) is small, the light amount reaching the photodetector 35 is increased by increasing the light amount ratio of the measurement beam B1, and the light amount ratio between the measurement beam B1 and the reference beam B2 It is possible to improve the stability and accuracy of measurement compared to the case where is fixed (for example, 1: 1). This is particularly effective when the end surface of the movable measuring object 50 is a reflecting surface (measurement mirrors 341 and 342) as in the configuration shown in FIGS.

  Next, the configuration of the fifth embodiment of the heterodyne laser interferometer according to the present invention will be described. Note that a description of the same points as in the first to fourth embodiments is omitted. FIG. 10 is a block diagram showing the configuration of the fifth embodiment of the heterodyne laser interferometer according to the present invention.

  In this embodiment, compared to the heterodyne laser interferometer (second embodiment) of FIG. 4, the measurement object (movable measurement object 50) is a cylindrical object 50a such as a rotary stage, and the measurement beam B11, B12 is different in that it includes lenses 431 and 432 for condensing B12 and irradiating the peripheral surfaces of the cylindrical object 50a (surfaces corresponding to the measurement mirrors 341 and 342), and other parts are the same as the configuration of FIG. It is.

  When a heterodyne laser interferometer is used to measure the rotational shake amount of the cylindrical object 50a, the measurement surface is, for example, the side surface of the turntable or the spindle shaft, and the rotating cylindrical object 50a is irradiated with the measurement beams B11 and B12. Become.

  Since the side surface of the cylindrical object 50a is a curved surface, as described in the second embodiment (FIG. 4) and the fourth embodiment (FIG. 6), the measurement beams B11 and B12 are narrowed by the lenses 431 and 432, respectively. However, depending on the size of the target curved surface, the beam spot size to be irradiated needs to be considerably reduced. In addition, although it is necessary to consider the relationship with the curvature radius of the to-be-measured surface, the beam spot size to be irradiated needs to be about several to several tens of microns when the diameter is less than 100 mm, for example.

  For such a beam spot size, the side surface (curved surface) of the cylindrical object 50a is a sufficiently polished smooth surface such as a mirror (for example, about λ / 10; λ is a laser wavelength of about 0.5 to 1 micron). If there is no problem if the side surface of the cylindrical object 50a is formed of a metal cutting surface or the like, for example, the cutting trace may not be negligible with respect to the beam spot size. For example, as shown in FIG. 11 (a), when the depth of the cutting trace (indicated by 50b in FIG. 11) is equal to or greater than the laser wavelength, the measurement beams B11 and B12 (50c in FIG. 11) are irradiated. The length measurement data fluctuates depending on where the cutting mark 50b hits or the overlap with the cutting mark 50b.

  As shown in FIG. 11B, in the case of measuring the displacement of the side surface of the rotating cylindrical object 50a, when the cylindrical object 50a is manufactured by metal cutting, the Y direction of the figure (circular cross-sectional circle of the cylinder) Although the cutting trace 50b remains in the vicinity of the plane including the cutting trace 50b, the cutting trace 50b is not formed completely in parallel, and meanders or partially disappears. Further, since the rotation of the cylindrical object 50a is also shaken, even if the measurement beams B11 and B12 are fixed, the measurement beam measurement beams B11 and B12 repeatedly traverse the cutting mark 50b during the rotation.

  Therefore, there is a problem that the length measurement data (interference state of the measurement beam interference light B1k) fluctuates due to the crossing of the cutting mark 50b on the side surface of the cylindrical object 50a, and the displacement measurement accuracy on the cylindrical side surface is lowered.

  It is assumed that the inventors of the present application measured displacement with a heterodyne laser interferometer while rotating a turntable with a diameter of 120 mm manufactured by cutting aluminum at 1200 rpm (the beam spot was narrowed down to a beam spot of about 10 microns). Drift components other than runout occurred. This is not limited to the cutting mark 50b of the cylindrical object 50a, and the same phenomenon can occur depending on the size even when the movable measuring object 50 has a scratch or a rough surface.

  Further, as described above, when the measurement object moves during the displacement measurement, generally, the irradiation position of the beam spot of the measurement beams B11 and B12 also moves, so that the beam spot crosses a cutting mark or a flaw.

  As described above, due to the presence of micro unevenness on the surface of the measurement object, the measurement data is subject to fluctuations, and the displacement measurement accuracy decreases despite the fact that the macro amount of displacement of the object curved surface is measured. Problem arises. If the curved surface to be measured can be polished to a mirror surface, the above problem can be solved, but micron-level curved surface polishing is technically difficult, and the shape, size, material, and workability are high. In many cases, it is difficult from the viewpoint of costs.

  Therefore, in this embodiment, as shown in FIGS. 12A and 12B, the measurement beams B11 and B12 are directed in one direction by using lenses 431 and 432 having a convergence action only in one direction (here, the Y direction). Only to converge. As the lenses 431 and 432, for example, cylindrical lenses can be used.

  The measurement beams B11 and B12 are converged only in the Y direction by the lenses 431 and 432, and condensed into a slit shape (indicated by 50c in FIG. 12) on the surface of the cylindrical object 50a as shown in FIG. Irradiate as

  The beam convergence direction is made to coincide with the curved surface direction (Y direction) of the cylindrical object 50a. When the curved surface is cut and manufactured, the cutting marks 50b extending in the Y direction are arranged in the X direction. However, the measurement beams B11 and B12 are not condensed in the X direction by the lenses 431 and 432, and thus the surface to be measured It is possible to have a sufficient size (usually about several millimeters) compared to the cutting traces 50b, scratches, and the like that are micro unevenness. For this reason, it is possible to average the influences of the cut marks 50b and scratches on the surface to be measured so as not to affect the displacement data accuracy. Further, since the measurement beams B11 and B12 are narrowed down in the Y direction, reflected light from the surface of the cylindrical object 50a can be obtained and the displacement of the curved surface can be measured.

  In the heterodyne laser interferometer of this embodiment, the measurement object (cylindrical object 50a) is irradiated using lenses (lenses 431 and 432) that converge the measurement beams B11 and B12 in only one direction, and the surface of the measurement object is irradiated. Irradiation is performed so as to be condensed into a slit shape. Therefore, even if the measurement target has a curved surface in only one direction, the focusing direction of the measurement beams B11 and B12 can be made to coincide with the curved surface direction of the measurement target, and the irradiated beam spot can be a non-curved surface of the measurement target. Since it can be long in the direction, it is possible to average the influence of fine irregularities on the surface of the measurement object and to measure the displacement with high accuracy.

  As described above, the heterodyne laser interferometer of this embodiment can also be applied to the measurement of the amount of rotational shake of a rotary stage or the like. For example, when applied to precision turntables for optical disk and hard disk pattern fabrication, the turntable rotational runout can be measured with high accuracy without being affected by dead paths, and the rotational runout amount is fed back to the laser beam position for pattern fabrication. Thus, it is possible to improve accuracy, for example, by creating a track pattern with no shake. Since the parallel measurement beam and the reference beam physically separated from the heterodyne laser light source 10 are emitted, the second embodiment of the present invention can be used without installing an optical system for branching the measurement beam and the reference beam. The same effect as the embodiment can be obtained.

  As described above, according to the heterodyne laser interferometer of the present invention, it is possible to reach the photodetector as it is without reducing the amount of light related to the beat signal of the measurement beam and the reference beam. Without being affected, it is possible to eliminate the influence of the dead path from the measurement result and obtain a highly accurate measurement result.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

10 Heterodyne laser light source 20 Beam splitter 21, 35, 37 Photo detector 22 Reference signal circuit 30, 911, 912, 913, 914, 915 Polarizing beam splitter 31, 32 1/4 wavelength plate 33 Reference mirror 34, 341, 342 Measurement Mirror 36, 38 Measurement signal circuit 50 Movable measurement object 50a Cylindrical object 50b Cutting mark 50c Beam spot 51, 52, 53, 60, 61 Mirror 70 Arithmetic circuit 80 Branch device 82, 821, 822, 823 Mirror 411, 412 Reflection mirror 421 , 422 Lens 431, 432 Lens 811, 812, 813 Non-polarizing beam splitter 921, 922, 923 Half-wave plate B1, B11, B12 Measurement beam B1k Measurement beam interference light B2, B21, B22 Reference beam B2k Reference beam interference Light DP1, DP2, MP1, MP2 Distance f1 First beam f2 Second beam LP1, LP2 Measurement optical path P1, P2

JP 06-058711 A Japanese Patent Application Laid-Open No. 09-287917 JP 2003-287403 A Japanese Patent Laid-Open No. 11-257915 JP 2007-327819 A

Claims (10)

A heterodyne laser interferometer that measures the displacement of an object to be measured,
Two measuring mirrors fixed on the object to be measured with their reflecting surfaces facing in opposite directions on a virtual straight line;
A heterodyne laser light source that physically emits two linearly polarized laser beams having different polarization planes at different frequencies as one laser beam;
A splitter for splitting the laser beam from the heterodyne laser source to generate two physically separated parallel laser beams consisting of a measurement beam and a reference beam;
A polarization beam splitter that splits the measurement beam and the reference beam from the splitter in two directions;
Among the measurement beam and the reference beam divided in the two directions, the measurement beam and the reference beam in one direction are guided to one measurement mirror side of the two measurement mirrors along the virtual straight line, and the measurement beam in the other direction and Two measurement optical paths for guiding the reference beam along the virtual straight line toward the other measurement mirror;
Two quarter-wave plates provided in the optical paths of the two measurement optical paths,
Two reflecting mirrors arranged between the quarter wave plate and the measuring mirror for each of the two measuring optical paths and reflecting the reference beam;
A measurement beam photodetector for electrically detecting the intensity of measurement beam interference light obtained by interfering the measurement beams reflected by the two measurement mirrors with the polarization beam splitter;
A measurement beam measurement circuit for generating a beat signal from the output of the measurement beam photodetector;
A reference beam photodetector for electrically detecting the intensity of the reference beam interference light obtained by causing the reference beam reflected by the two reflecting mirrors to interfere with each other by the polarization beam splitter;
A reference beam measurement circuit for generating a beat signal from the output of the reference beam photodetector;
An arithmetic circuit for calculating a displacement corresponding to a difference between the beat signal generated by the measurement beam measurement circuit and the beat signal generated by the reference beam measurement circuit;
With
The heterodyne laser interferometer is characterized in that the branching unit has adjusting means for continuously changing and adjusting a light amount ratio between the measurement beam and the reference beam.   The adjusting means adjusts the polarization direction of each of the first beam and the second beam, and a first polarization beam splitter that polarization-separates the incident laser beam into a first beam and a second beam. Two half-wave plates, a second polarization beam splitter that separates the first beam with the polarization direction adjusted into an S-polarization component and a P-polarization component, and a second beam with the polarization direction adjusted A third polarizing beam splitter that separates the S-polarized component and the P-polarized component, and a first polarized beam of the first beam and the P-polarized component of the second beam are combined to form the measurement beam or the reference beam. 4 polarization beam splitters, a fifth polarization beam splitter that combines the P polarization component of the first beam and the S polarization component of the second beam into one beam, and the fifth polarization beam splitter. The heterodyne laser interferometer according to claim 1, further comprising: a half-wave plate that rotates the polarization direction of one beam from the liter by 90 degrees to serve as the reference beam or the measurement beam. .   3. The apparatus according to claim 1, further comprising two lenses arranged between the reflection mirror and the measurement mirror for each of the two measurement optical paths, and condensing the measurement beam on a reflection surface of the measurement mirror. The described heterodyne laser interferometer. A heterodyne laser interferometer that measures the displacement of an object to be measured,
Two measuring mirrors fixed on the object to be measured with their reflecting surfaces facing in opposite directions on a virtual straight line;
A laser beam including two linearly polarized laser beams having orthogonal polarization planes at different frequencies is generated, and the laser beam is branched and emitted as two physically separated parallel laser beams consisting of a measurement beam and a reference beam. A heterodyne laser light source,
A polarizing beam splitter that splits the measurement beam and the reference beam from the heterodyne laser light source in two directions;
Among the measurement beam and the reference beam divided in the two directions, the measurement beam and the reference beam in one direction are guided to one measurement mirror side of the two measurement mirrors along the virtual straight line, and the measurement beam in the other direction and Two measurement optical paths for guiding the reference beam along the virtual straight line toward the other measurement mirror;
Two quarter-wave plates provided in the optical paths of the two measurement optical paths,
Two reflecting mirrors arranged between the quarter wave plate and the measuring mirror for each of the two measuring optical paths and reflecting the reference beam;
A measurement beam photodetector for electrically detecting the intensity of measurement beam interference light obtained by interfering the measurement beams reflected by the two measurement mirrors with the polarization beam splitter;
A measurement beam measurement circuit for generating a beat signal from the output of the measurement beam photodetector;
A reference beam photodetector for electrically detecting the intensity of the reference beam interference light obtained by causing the reference beam reflected by the two reflecting mirrors to interfere with each other by the polarization beam splitter;
A reference beam measurement circuit for generating a beat signal from the output of the reference beam photodetector;
An arithmetic circuit for calculating a displacement corresponding to a difference between the beat signal generated by the measurement beam measurement circuit and the beat signal generated by the reference beam measurement circuit;
With
The heterodyne laser light source has adjustment means for adjusting the light quantity ratio between the measurement beam and the reference beam by continuously changing the heterodyne laser light source.   The adjusting means adjusts the polarization direction of each of the first beam and the second beam, and a first polarization beam splitter that polarization-separates the incident laser beam into a first beam and a second beam. Two half-wave plates, a second polarization beam splitter that separates the first beam with the polarization direction adjusted into an S-polarization component and a P-polarization component, and a second beam with the polarization direction adjusted A third polarizing beam splitter that separates the S-polarized component and the P-polarized component, and a first polarized beam of the first beam and the P-polarized component of the second beam are combined to form the measurement beam or the reference beam. 4 polarization beam splitters, a fifth polarization beam splitter that combines the P polarization component of the first beam and the S polarization component of the second beam into one beam, and the fifth polarization beam splitter. The heterodyne laser interferometer according to claim 4, further comprising: a half-wave plate that rotates the polarization direction of one beam from the liter by 90 degrees to serve as the reference beam or the measurement beam. .   6. The apparatus according to claim 4, further comprising two lenses arranged between the reflection mirror and the measurement mirror for each of the two measurement optical paths, and condensing the measurement beam on a reflection surface of the measurement mirror. The described heterodyne laser interferometer.   The heterodyne laser interferometer according to any one of claims 1 to 6, wherein the measuring mirror has an end surface of the object to be measured as a reflecting surface. A heterodyne laser interferometer that measures the displacement of an object to be measured,
A heterodyne laser light source that physically emits two linearly polarized laser beams having different polarization planes at different frequencies as one laser beam;
A splitter for splitting the laser beam from the heterodyne laser source to generate two physically separated parallel laser beams consisting of a measurement beam and a reference beam;
A polarization beam splitter that splits the measurement beam and the reference beam from the splitter in two directions;
Of the measurement beam and the reference beam divided in the two directions, the measurement beam and the reference beam in one direction are guided to one side of the measurement object, and the measurement beam and the reference beam in the other direction are opposed to each other. Two measuring light paths leading to the other side;
Two quarter-wave plates provided in the optical paths of the two measurement optical paths,
Two reflecting mirrors arranged between the quarter-wave plate and the object to be measured for each of the two measuring optical paths, and reflecting the reference beam;
A measurement beam photodetector for electrically detecting the intensity of measurement beam interference light obtained by interfering the measurement beams reflected on both sides of the measurement object with the polarization beam splitter;
A measurement beam measurement circuit for generating a beat signal from the output of the measurement beam photodetector;
A reference beam photodetector for electrically detecting the intensity of the reference beam interference light obtained by causing the reference beam reflected by the two reflecting mirrors to interfere with each other by the polarization beam splitter;
A reference beam measurement circuit for generating a beat signal from the output of the reference beam photodetector;
An arithmetic circuit for calculating a displacement corresponding to a difference between the beat signal generated by the measurement beam measurement circuit and the beat signal generated by the reference beam measurement circuit;
With
The heterodyne laser interferometer is characterized in that the branching unit has adjusting means for continuously changing and adjusting a light amount ratio between the measurement beam and the reference beam.   2. The apparatus includes two lenses arranged between the reflection mirror and the object to be measured for each of the two measurement optical paths, and condensing the measurement beam in one direction to irradiate the object to be measured. Item 9. The heterodyne laser interferometer in accordance with Item 8.   The heterodyne laser interferometer according to any one of claims 1 to 9, wherein the polarization beam splitter includes the two quarter-wave plates in an integrated manner.

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