JPH11183116A - Method and device for light wave interference measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow range-finding without interruption without zero-resetting even when the laser light on a measurement light path is blocked, and to constitute an interference optical system with ease at low cost. SOLUTION: A polarizing beam splitter 2 which slits the light of wavelength λ1 emitted from a laser light source 1 into a measurement light path and a reference light path, a reference reflection mirror 6 provided on the reference light path, a measurement reflection mirror 7 movably provided on the measurement light path, and photoelectric detector 9 for photodetecting interference light of reference and measurement light are provided. Here, the polarizing beam splitter 12 which splits the light of λ2(≠λ1) emitted from a laser light source 11 into two, an optical system 10 which deflects one of the split λ2 light toward the measurement deflection mirror 7, which becoming parallel to the measurement light path on the way of measurement light path, and a photoelectric detector 17 for photodetecting interference light between one light reflected on the measurement reflection mirror 7 and the other light are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interference measuring method and apparatus for measuring displacement of an object with high accuracy, and more particularly, to photolithography for manufacturing a semiconductor device, a liquid crystal display device, a thin film magnetic head and the like. The present invention relates to an optical interference measurement method and apparatus suitable as an ultra-precision positioning method and apparatus for a stage used in an exposure apparatus used in a process.

[0002]

2. Description of the Related Art In a photolithography process in a manufacturing process of a semiconductor device, a liquid crystal display device, or the like, a circuit pattern formed on a reticle or a mask (hereinafter, referred to as a reticle) is projected through a projection optical system onto a semiconductor wafer or glass plate. A projection exposure apparatus that performs projection exposure on a wafer is used. There are various types of projection exposure apparatuses. For example, in the case of manufacturing a semiconductor device, a wafer is step-and-stepped through a projection optical system having an image field capable of projecting the entire reticle circuit pattern at one time. A projection exposure apparatus that performs exposure in a repeat mode, or a one-dimensional scanning of a wafer while scanning a reticle one-dimensionally at a speed synchronized with the reticle.
There is an AND scan type projection exposure apparatus.

In the exposure operation of these projection exposure apparatuses, it is essential to accurately superimpose the image of the reticle pattern on the pattern formed on the wafer. Therefore, the reticle or wafer is placed on the XY plane. The X-Y stage capable of moving two-dimensionally is required to have high positioning accuracy. An optical interference measuring device is used to position the XY stage very precisely.

As this type of light wave interference measuring device, there is widely used a device which uses a helium-neon (He-Ne) gas laser whose frequency is stabilized as a light source and employs a heterodyne detection system (for example, manufactured by Hewlett-Packard Company, USA). Used.

Here, a conventional light wave interference measuring apparatus will be described with reference to FIG. In FIG. 7, a laser light source 1 emits a laser beam having a center wavelength λ1 and mutually orthogonal polarization directions having slightly different wavelengths. The laser beam emitted from this laser light source 1 is polarized beam splitter 40
And is separated into a measurement optical path and a reference optical path. In the polarization beam splitter 40, the light of the p-polarized component is transmitted and proceeds to the measurement optical path, becomes the measurement light converted into circularly polarized light by the quarter-wave plate 44, and the light of the s-polarized component is reflected by the polarization beam splitter 40. To the reference optical path, enters the mirror 3 and bends the optical path so as to be parallel to the measurement light.
The reference light is converted into circularly polarized light by the 波長 wavelength plate 42.

The reference light is a reference reflecting mirror (fixed mirror).
The measurement light is reflected at 6, and the measurement light is reflected at a measuring reflecting mirror (moving mirror) 7. Each reflected light is again a quarter-wave plate 4
2 and 44, the light is converted into linearly polarized light whose polarization direction is rotated by 90 ° with respect to the original polarization direction. 1
The measurement light transmitted through the 波長 wavelength plate 44 enters the polarization beam splitter 40 and is reflected by the polarization beam splitter 40 because the polarization direction is rotated by 90 ° from the beginning.

On the other hand, the reference light transmitted through the quarter-wave plate 42 is reflected by the mirror 3 and enters the polarization beam splitter 40. Similarly, since the polarization direction is rotated by 90 ° from the beginning, the polarization beam splitter 40 Through. Therefore, the reference light and the measurement light exit the polarization beam splitter 40 coaxially. The reference light and the measurement light pass through the dichroic mirror 48 and enter the polarizer 8. The polarization direction of the polarizer 8 is set to be inclined by 45 ° with respect to the reference light and the measurement light. Therefore, both lights transmitted through the polarizer 8 interfere with each other and are detected by the photoelectric detection element 9. The interference signal converted into an electric signal by the photoelectric detection element 9 is input to a phase meter (not shown) together with a reference signal obtained by directly interfering the laser beams of the p-polarized component and the s-polarized component inside the laser light source 1. Then, by integrating the amount of phase change of the measurement signal with respect to the reference signal, the displacement of the measurement reflecting mirror 7 can be known.

However, this type of light wave interference measuring apparatus (laser interferometer) integrates the relative displacement of the measuring reflecting mirror 7 mounted on a stage or the like with respect to the reference reflecting mirror 6 and the phase change of the interference signal. However, since the distance between the reference reflecting mirror 6 and the measuring reflecting mirror 7 cannot be determined directly, once the interferometer beam is interrupted, the position reference is lost. have. As is well known, it is possible to perform origin search (hereinafter, referred to as “origin search”) for providing a position reference using a photoelectric sensor or the like, but the accuracy is at most about μm.
In addition, there is a problem that the stage has to be moved to find the origin, and it takes a long time for measurement. Instead of the photoelectric sensor, a linear encoder may be installed in the guide portion of the stage, and the origin may be determined based on the measured value. In this case, it is not necessary to move the stage to find the origin, but this type of encoder has a problem that the absolute position accuracy in the stroke range of several tens of cm is at most about μm even though the measurement is reproducible. Can not be solved.

[0009]

Therefore, in order to solve the above-mentioned problem, a light wave interference measuring apparatus combined with another interferometer as shown in FIG. 7 is used. From the laser light source 11 of this other interferometer, a center wavelength λ2 different from the wavelength λ1,
A laser beam having two polarization directions is emitted. The laser beam emitted from the laser light source 11 is
The laser beam is bent at 5 and is incident on the dichroic mirror 46, is coaxial with the laser beam from the laser light source 1, is incident on the polarization beam splitter 40, and is separated into a measurement optical path and a reference optical path. In the polarization beam splitter 40,
The light of the p-polarized component is transmitted and proceeds to the measurement optical path, becomes the measurement light converted into circularly polarized light by the quarter-wave plate 44, and the light of the s-polarized component is reflected by the polarization beam splitter 40 and proceeds to the reference optical path, The light enters the mirror 3 and is bent so that its optical path becomes parallel to the measurement light, and becomes reference light converted into circularly polarized light by the 波長 wavelength plate 42.

The reference light is a reference reflecting mirror (fixed mirror).
The measurement light is reflected at 6, and the measurement light is reflected at a measuring reflecting mirror (moving mirror) 7. Each reflected light is again a quarter-wave plate 4
2 and 44, the light is converted into linearly polarized light whose polarization direction is rotated by 90 ° with respect to the original polarization direction. 1
The measurement light transmitted through the 波長 wavelength plate 44 enters the polarization beam splitter 40 and is reflected by the polarization beam splitter 40 because the polarization direction is rotated by 90 ° from the beginning.

On the other hand, the reference light transmitted through the quarter-wave plate 42 is reflected by the mirror 3 and enters the polarization beam splitter 40. Similarly, since the polarization direction is rotated by 90 ° from the beginning, the polarization beam splitter 40 Through. Accordingly, the reference light and the measurement light are coaxial, exit the polarization beam splitter 40, are reflected by the dichroic mirror 48, and enter the polarizer 16. The polarization direction of the polarizer 16 is set such that the polarization direction is inclined by 45 ° with respect to the reference light and the measurement light.
Therefore, both lights transmitted through the polarizer 16 interfere with each other and are detected by the photoelectric detection element 17. The interference signal converted into an electric signal by the photoelectric detection element 17 is input to a phase meter (not shown) together with a reference signal obtained by directly interfering the laser beams of the p-polarized component and the s-polarized component inside the laser light source 11. And
By integrating the amount of phase change of the measurement signal with respect to the reference signal, the displacement of the measurement reflecting mirror 7 can be known.

In this manner, a so-called absolute interferometer, which is a well-known technique, can be configured. For example, a laser light source 11
The wavelength λ2 may be varied and the wavelength may be swept, the phase change may be measured, and the difference between the optical path lengths of the reference optical path and the measurement optical path may be directly obtained. Absolute interference measurement within the wavelength may be performed.

However, in the above-described system in which the laser beams from both light sources are introduced into the same interference optical system using the two laser light sources as described above, and the measurement is performed by combining the displacement measurement and the absolute position measurement, Since it becomes necessary to form an interference optical system with the same system for light of another continuous wavelength or multiple wavelengths in addition to the light of the laser wavelength for length measurement, the polarization beam splitter 40 or the quarter-wave plate 42, It is essential that 44 is achromatic in a wide wavelength range. However, it is actually very difficult to form an optical element that is achromatic in such a wide wavelength range.
Further, even if it can be formed, there is a problem that high cost cannot be avoided.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light wave capable of continuously measuring the length without returning to the original point even if the laser beam in the measurement light path is interrupted, and which can easily form an interference optical system at low cost. An object of the present invention is to provide an interference measurement method and apparatus.

[0015]

SUMMARY OF THE INVENTION It is an object of the present invention to separate light having a wavelength λ1 into reference light and measurement light, reflect the reference light with a reference reflector provided on a reference optical path, and convert the measurement light into measurement light. It is reflected by a measuring reflector movably provided on the road, and the reflected reference light and the measuring light interfere with each other to measure a relative moving distance ΔL of the measuring reflector moved from the reference position with respect to the reference reflector. In the light wave interference measurement method, an optical path length difference L1 (= φ1 · λ1) between a reference optical path and a measurement optical path at a reference position.
/ M, where m is the number of turns of the optical path)
1 is measured, the light having the wavelength λ2 (≠ λ1) is further used, the light having the wavelength λ2 is separated into two lights, and one light is incident on the measuring light path in parallel from the middle of the measuring light path and reflected for measurement. The light reflected by the mirror is caused to interfere with one of the reflected light and the other light, so that an optical path length difference L2 between the optical path of one light and the optical path of the other light at the reference position (= φ2 / λ2 / m) The phase φ1 ′ based on the optical path length difference L1 + ΔL (= φ1 ′ · λ1 / m) between the reference optical path and the measurement optical path at the relative movement distance ΔL is measured, and one of the phases at the relative movement distance ΔL is measured. The optical path length difference L2 + ΔL (= φ2 ′ · λ) between the optical path of the light and the optical path of the other light
2 / m), and the phases φ1, φ
2. A light wave interference measurement method characterized in that a relative movement distance ΔL when light of wavelength λ1 is cut off is obtained based on 2, φ1 ′ and φ2 ′.

The relative movement distance ΔL is as follows: ΔL = ΔΦ · λs / m where ΔΦ = Φ′−Φ, Φ = φ2−φ1, Φ ′ = φ2′−φ1 ′ Synthetic wavelength λs = λ1 · λ2 // λ2−λ1 |

It is another object of the present invention to provide a light wave interference measuring method, wherein the wavelength λ3 (≠ λ1, ≠ λ2, | λ2-λ1 |>
| Λ3-λ2 |) is further used to separate the light of the wavelength λ3 into two, and one of the light is incident on the measurement optical path in the middle of the measurement optical path and reflected by the measurement reflector. The reflected one light and the other light are caused to interfere with each other, based on an optical path length difference L3 (= φ3 · λ3 / m) between the optical path of the one light and the optical path of the other light at the reference position. The phase φ3 is measured, and the optical path length difference L3 + ΔL (= φ3 ′ · λ3 /) between the optical path of the one light and the optical path of the other light at the relative movement distance ΔL.
m), the existence range of ΔL is determined based on the relatively wide synthetic wavelength λsW = λ2 · λ3 / | λ3-λ2 |, and then based on the narrower synthetic wavelength λs. And ΔL is obtained by the method.

[0018] Further, the object is to provide an optical wave interference measuring method, wherein the optical path difference L1 between the reference optical path and the measuring optical path at the reference position, and the optical path length difference L2 between the optical path of one light and the optical path of the other light. Are made substantially equal to each other.

Still another object of the present invention is to provide a light wave interference measuring method, comprising: an optical path length difference L1 between a reference optical path and a measurement optical path at a reference position; and an optical path length difference between one optical path and the other optical path. L2 and L1 >> L2 are achieved by a light wave interference measurement method.

The object is to provide a first light source for emitting a first light for measuring a displacement of an object, a first beam splitter for separating the first light into a measurement light path and a reference light path, and a reference light. A reference reflecting mirror provided on the road, a measuring reflecting mirror movably provided on the measuring optical path, and a second reflecting light receiving the interference light of the first light reflected by the reference reflecting mirror and the measuring reflecting mirror. In the optical interference measuring apparatus having the first light receiving section, the first
A second light source that emits a second light having a wavelength different from the wavelength of the second light, a second beam splitter that splits the second light into two, and a second light splitter that splits the second light into two. A first optical system for directing the one from the middle of the measurement optical path toward the measurement mirror in parallel with the measurement optical path, and a first optical system for receiving interference light between one of the lights reflected by the measurement mirror and the other light. This is achieved by a light wave interference measurement device further comprising two light receiving units.

The above object is also achieved in the above-mentioned optical interference measuring apparatus, wherein the first optical system further transmits the other of the second light,
From the middle of the reference light path, the light is directed toward the reference reflecting mirror in parallel with the reference light path, and the second light receiving unit reflects the second light reflected by the measurement reflecting mirror.
And an interference light between the other of the second light reflected by the reference reflecting mirror and the other of the second light reflected by the reference reflecting mirror.

Further, the above object is achieved by a light wave interference measuring apparatus, wherein the second light source is a tunable laser. Still another object of the present invention is to provide a light wave interference measuring apparatus, wherein the third light source that emits third light having a wavelength different from the wavelengths of the first and second lights and the third light are separated into two. A third beam splitter, a second optical system that directs one of the two split third lights to a measuring reflector in a direction parallel to the measuring optical path from the middle of the measuring optical path, and a measuring reflector. This is achieved by a light wave interference measurement device, further comprising a third light receiving unit that receives interference light between one of the reflected third lights and the other light.

The second optical system further directs the other of the third light from the middle of the reference optical path to the reference reflecting mirror in parallel with the reference optical path, and the third light receiving section includes a measuring reflecting mirror. An interference light between one of the third lights reflected by the reference light and the other of the third lights reflected by the reference reflecting mirror may be received. Further, the third beam splitter may be shared by the second beam splitter, and the second optical system may be shared by the first optical system.

Further, in the above-mentioned optical interference measuring apparatus,
The first light is composed of two lights having polarization directions perpendicular to each other and having slightly different frequencies, the first beam splitter is a polarization beam splitter, and has a wavelength on the measurement optical path and on the reference optical path, respectively. A plate is arranged, and the first optical system directs at least one of the second light beams from between the wave plate and the measurement reflector on the measurement optical path to the measurement reflector in parallel with the measurement optical path. May be arranged.

The first optical system has at least a second optical system.
May be arranged so as to direct the other of the lights from the wave plate on the reference optical path and the reference reflecting mirror toward the reference reflecting mirror in parallel with the reference optical path. Further, in the above-described optical interference measuring apparatus, the first to third light sources are wavelength stabilized lasers.

As described above, according to the present invention, at least the light-wave interferometer for measuring length using light of a predetermined wavelength and the light-wave interferometer using light of another wavelength different from the predetermined wavelength are used. The optical axes of the measuring beams of both interferometers are guided in parallel from the middle to the same measuring mirror, and the amount of movement of the measuring mirror within the combined wavelength of both interferometers is measured, and the phase change is counted. Even if the measuring light is cut off, the position of the measuring mirror from the origin can be measured within the composite wavelength with the resolution of the lightwave interferometer for length measurement. . Since the lightwave interferometer for length measurement and another lightwave interferometer using light of a different wavelength are configured to combine at least the optical axes of both measurement lights from the middle, Use an inexpensive element corresponding to a single wavelength as a polarization separation element (polarization beam splitter) that separates the optical path into a reference optical path and a measurement optical path, or a quarter-wave plate that rotates the polarization direction of the reference light or the measurement light. Will be able to do it.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, the basic principle of the optical interference measuring method according to the present invention will be described first. This light wave interference measurement method can be applied to all of the light wave interference measurement devices described in the first to sixth embodiments described below. First, it is assumed that the wavelength of the length measuring laser interferometer is λ1 and the wavelength of the additional wavelength laser interferometer to be added is λ2. Since the optical path length difference between the two interference optical systems is generally different, L1 and L2 are given as follows.

L1 = φ1 · λ1 / m (1) L2 = φ2 · λ2 / m (2)

Here, m is the number of turns of the optical path, and φ is the phase. Then, φ1 and φ2 when the measuring reflecting mirror is at the origin position P are stored. Next, assuming that the distance between PQ when the measuring reflector moves and is at the position of Q is ΔL,

L1 + ΔL = φ1 ′ · λ1 / m (3) L2 + ΔL = φ2 ′ · λ2 / m (4)

Therefore, if Φ = φ2−φ1 here,

ΔΦ = Φ′−Φ = (φ2′−φ1 ′) − (φ2−φ1) = mΔL (1 / λ2-1 / λ1) Therefore, the composite wavelength λs is expressed as λs = λ1 · λ2 / | λ2-λ1 .. (5), ΔL = ΔΦ · λs / m (6) where ΔΦ is the change amount of Φ.

That is, if it is known where the measuring reflector is located in the unit of λs / m, even if the beam is cut off, Φ ′ is measured again to obtain ΔΦ, thereby obtaining ΔL.
Can be requested. Since the measurement accuracy can be set within the range of λ1 / m as described later, ΔL can be finally obtained with the accuracy of the original length measuring laser interferometer.

Next, the accuracy of this measurement will be described in detail.
First, the error propagation rule is applied to equation (6). First, equation (6) is transformed using equation (5),

ΔL = ΔΦ · λs / m = {(φ2′−φ1 ′) − (φ2−φ1)} (λs /
m) From this, δ (ΔL) = 2 (δφ2 + δφ1) (λs / m) + ΔL · (λs / λ1) (δλ1 / λ1) + ΔL · (λs / λ2) (δλ2 / λ2) (7) . Here, from the equations (1) and (2), δφ1 = δ′φ1 + mL1 · δλ1 / λ1 ² δφ2 = δ′φ2 + mL2 · δλ2 / λ2 ²

Is as follows. The first term in each of the above equations represents an error in phase measurement, and the second term represents an error due to wavelength fluctuation. Substituting these equations into equation (7) gives

Δ (ΔL) = 2 (δ′φ2 + δ′φ1) (λs / m) + 2L1 · (λs / λ1) (δλ1 / λ1) + 2L2 · (λs / λ2) (δλ2 / λ2) + ΔL · (λs / m λ1) (δλ1 / λ1) + ΔL · (λs / λ2) (δλ2 / λ2) = 2 (δ′φ2 + δ′φ1) (λs / m) + (2L1 + ΔL) (λs / λ1) (δλ1 / λ1) + (2L2 + ΔL) ) (Λs / λ2) (δλ2 / λ2) Since ΔL is smaller than L1 or L2, δ (ΔL) = 2 (δ′φ1 + δ′φ2) (λs / m) + 2L1 (λs / λ1) (δλ1 / λ1) + 2L2 (λs / λ2) (δλ2 / λ2) (8)

The first term of the equation (8) represents the influence of the phase measurement error, and the second term represents the wavelength stability (δλ1) of the laser having the wavelength λ1.
/ Λ1), and the third term also indicates the effect of the wavelength stability of the laser having the wavelength λ2. The above conditions are:

Δ (ΔL) <λ1 / 2m (9)

Is represented by When this condition is met,
ΔL can be measured with the accuracy of the original length measuring laser interferometer.
As a specific example, 633 of He-Ne laser
When a 612 nm oscillation line of a He-Ne laser is similarly selected for nm and λ2, λs = 18.45 μm. here,
If the interferometer is a single-pass optical system, m = 2. L1 = 0.1 m and L2 = 0.1 m.
The phase measurement error is mainly determined by the resolution, but if measurement responsiveness is not required,

Δ′φ1 = δ′φ2 = 1/1024

The degree is easily realizable. Although the wavelength stability depends on the time interval of the measurement, if it is within about one hour, about δλ1 / λ1 = δλ2 / λ2 = 2E-9 can be achieved. Therefore,

2 (δ′φ1 + δ′φ2) (λs / m) = 36 nm 2L1 (λs / λ1) (δλ1 / λ1) = 11.7 nm 2L2 (λs / λ2) (δλ2 / λ2) = 12.1 nm . Therefore, Expression (9) can be satisfied.

Now, as an apparatus to which the above-described light wave interference measuring method of the present invention is applied, a light wave interference measuring apparatus according to the first embodiment of the present invention will be described with reference to FIG. In the present embodiment, a light wave interference measurement device having a configuration in which the optical path length differences L1 and L2 of the two interference optical systems are equal (L1 = L2) will be described.

In FIG. 1, a laser light source 1 has a center wavelength λ.
At 1, a laser beam having slightly different wavelengths and mutually orthogonal polarization directions is emitted. The laser beam emitted from the laser light source 1 enters the polarization beam splitter 2 and is split into a measurement optical path and a reference optical path. In the polarization beam splitter 2, the light of the p-polarized component is transmitted and proceeds to the measurement optical path, becomes the measurement light converted into circularly polarized light by the quarter-wave plate 5, and the light of the s-polarized component is reflected by the polarization beam splitter 2. Then, the light enters the mirror 3 and enters the mirror 3 so that the optical path is bent so as to be parallel to the measurement light, and becomes reference light converted into circularly polarized light by the quarter-wave plate 4.

The reference light and the measuring light pass through the dichroic mirror 10, and the reference light is a reference reflecting mirror (fixed mirror).
The measurement light is reflected at 6, and the measurement light is reflected at a measuring reflecting mirror (moving mirror) 7. Each reflected light is returned to the dichroic mirror 1 again.
After passing through 0, the light passes through quarter-wave plates 4 and 5, respectively, and is converted into linearly polarized light whose polarization direction is rotated by 90 ° with respect to the original polarization direction. The measurement light transmitted through the 波長 wavelength plate 5 enters the polarization beam splitter 2 and is reflected by the polarization beam splitter 2 because the polarization direction is rotated by 90 ° from the beginning.

On the other hand, the reference light transmitted through the 波長 wavelength plate 4 is reflected by the mirror 3 and is incident on the polarization beam splitter 2.
Similarly, since the polarization direction is rotated by 90 degrees from the beginning, the light passes through the polarization beam splitter 2. Therefore, the reference light and the measurement light are coaxial, exit the polarization beam splitter 2 and enter the polarizer 8. The polarizer 8 is set so that the polarization direction is inclined by 45 ° with respect to the reference light and the measurement light.
Both lights transmitted through the polarizer 8 interfere with each other and are detected by the photoelectric detection element 9. This interference signal (hereinafter referred to as a measurement signal) converted into an electric signal by the photoelectric detection element 9 is a reference signal obtained by directly interfering a laser beam of a p-polarized component and an s-polarized component inside the laser light source 1. Together with the phase change amount of the measurement signal with respect to the reference signal, the displacement of the measurement reflecting mirror 7 can be known. The laser interferometer system having the above configuration will be referred to as an interferometer A.

On the other hand, the laser light source 11 emits a laser beam having a center wavelength λ2 which is different from the wavelength λ1 and also has polarization directions orthogonal to each other and slightly different in wavelength. The laser beam emitted from the laser light source 11 enters the polarization beam splitter 12 and is split into a measurement optical path and a reference optical path. In the polarization beam splitter 12,
The light of the p-polarized component is transmitted and proceeds to the measurement optical path, becomes the measurement light converted into circularly polarized light by the quarter-wave plate 15, and the light of the s-polarized component is reflected by the polarization beam splitter 12 and proceeds to the reference optical path, The light enters the mirror 13 and is bent so that the optical path becomes parallel to the measurement light, and becomes reference light converted into circularly polarized light by the quarter-wave plate 14.

After the reference light and the measuring light are reflected by the dichroic mirror 10, the reference light is reflected by the reference reflecting mirror (fixed mirror) 6, and the measuring light is reflected by the measuring reflecting mirror (moving mirror) 7. After each reflected light is reflected by the dichroic mirror 10 again, the 光 wavelength plates 14 and 15
And the polarization direction is 90 ° with respect to the original polarization direction.
It is converted to rotated linearly polarized light. The measurement light transmitted through the 波長 wavelength plate 15 enters the polarization beam splitter 12 and is reflected by the polarization beam splitter 12 because the polarization direction is rotated by 90 ° from the beginning.

On the other hand, the reference light transmitted through the 波長 wavelength plate 14 is reflected by the mirror 13 and enters the polarization beam splitter 12. Similarly, since the polarization direction is rotated by 90 ° from the beginning, the polarization beam splitter 12 Through. Therefore, the reference light and the measurement light are coaxial and become the polarization beam splitter 12.
And enters the polarizer 16. The polarization direction of the polarizer 16 is set to be inclined by 45 ° with respect to the reference light and the measurement light. Therefore, both lights transmitted through the polarizer 16 interfere with each other and are detected by the photoelectric detection element 17. The interference signal (measurement signal) converted into an electric signal by the photoelectric detection element 17 is input to the phase meter 52 together with a reference signal obtained by causing the laser beams of the p-polarized component and the s-polarized component to directly interfere inside the laser light source 11. Then, by integrating the amount of phase change of the measurement signal with respect to the reference signal, the displacement of the measurement reflecting mirror 7 can be known. The laser interferometer system having the above configuration
I will call it.

Now, a brief description will be given of the process of finding the origin when the laser beam is cut off in the light wave interference measurement apparatus including the two sets of interferometers A and B as described above. First, the optical path length difference L1 between the reference optical path of the interferometer A and the measuring optical path when the measuring reflecting mirror 7 is at the reference position (origin position P).
(= Φ1 · λ1 / m, where the number of turns of the optical path is m = 2)
And a phase φ2 based on an optical path length difference L2 between the reference optical path and the measurement optical path of the interferometer B (= φ2 · λ2 / m, where the number of turns of the optical path m = 2) is measured in advance.
The difference φ2−φ1 is stored.

Assuming that the relative moving distance ΔL from the reference position of the measuring reflecting mirror 7 after the laser beam is cut off is within λs / 2, the reference optical path of the interferometer A and the measuring optical path at the relative moving distance ΔL are determined. Optical path length difference L1 + ΔL (= φ1 ′ · λ1 /
2) and a phase φ2 ′ based on an optical path length difference L2 + ΔL (= φ2 ′ · λ2 / 2) between the reference optical path and the measurement optical path of the interferometer B, and the difference φ2′−φ1 ′ is calculated. Ask.

By doing so, ΔΦ is obtained, while
Since the composite wavelength λs is also obtained from Expression (5), Expression (6)
Thus, the displacement ΔL from the position of the first origin search can be obtained. Note that the error analysis in the case of the present embodiment may be performed by setting L1 = L2 in Expression (8).

As described above, according to the optical interference measuring apparatus of the present embodiment, the interferometers A and B are used, and at least the optical axes of the measuring lights of the interferometers A and B are made parallel from the middle. And the amount of movement of the measuring reflector 7 within the combined wavelength of the two interferometers A and B can be measured without counting the phase change. Even if the measuring light is blocked, the position of the measuring reflecting mirror 7 from the origin can be determined within the combined wavelength with the resolution of the length measuring light wave interferometer. Since the length measuring interferometer A and the interferometer B are configured to combine at least the optical axes of the two measuring beams from the middle, the optical paths of the interferometers A and B are separated into a reference optical path and a measuring optical path. The device corresponding to only a single wavelength can be used for the polarization beam splitters 2 and 12 for performing the operation, or the quarter-wave plates 4, 5, 14, and 15 for rotating the polarization direction of the reference light and the measurement light. Can be constructed at low cost and easily.

Next, a schematic configuration of an optical interference measuring apparatus according to a second embodiment of the present invention will be described with reference to FIG.
In the present embodiment, the optical path length difference L between the two interference optical systems described above.
The case where L1 and L2 are different (L1 ≠ L2) will be described.

The configuration of the optical interference measuring apparatus according to the present embodiment is characterized in that a mirror system 18 is added to the optical path of the interferometer B of the optical interference measuring apparatus according to the first embodiment. 1 are the same in operation and function as in the first embodiment shown in FIG. 1, and therefore, are denoted by the same reference numerals as in FIG. 1 and will not be described. By adding a mirror system 18 having two mirrors to the optical path of the interferometer B as shown in FIG. 2, unlike the first embodiment, the optical path length differences L1 and L2 of the two interference optical systems are different. be able to. For example, the optical path length difference L2 of the interferometer B can be made extremely small by changing the arrangement of the two mirrors of the mirror system 18.

Thus, the polarization beam splitters 2 and 12 for separating the optical paths of the interferometers A and B into a reference optical path and a measurement optical path, or a quarter-wave plate 4 for rotating the polarization direction of the reference light and the measurement light. 5, 14, 15, etc., the elements corresponding to only a single wavelength can be used, and the wavelength stability of the laser light source 11 of the interferometer B is inferior to that of the laser light source 1 of the interferometer A. Even in such a case, high positioning accuracy can be maintained, as can be seen from Equation (8) of the error analysis in the lightwave interference measurement method of the present invention described above.

Next, an optical interference measuring apparatus according to a third embodiment of the present invention will be described with reference to FIG. In the configuration of the lightwave interference measurement device according to the present embodiment, the operation and function are the same as those of the lightwave interference measurement devices according to the first and second embodiments described with reference to FIGS. The components are denoted by the same reference numerals, and description thereof will be omitted. The light wave interference measuring apparatus according to the present embodiment is characterized in that a reference reflecting mirror (fixed mirror) 19 dedicated to interferometer B is provided separately from reference reflecting mirror 6 of interferometer A, as shown in FIG. Have. That is, the mirror 13 shown in FIGS. 1 and 2 is removed, and the reference light emitted from the laser light source 11 and reflected by the polarization beam splitter 12 is divided by 1 /
The light passes through the four-wavelength plate 14 and is reflected by the reference reflecting mirror 19 dedicated to the interferometer B.

Thus, as in the second embodiment, by adjusting the position of the reference reflecting mirror 19, the optical path length difference L2 of the interferometer B can be made extremely small. Therefore, according to the present embodiment, each interferometer A,
Polarization beam splitters 2 and 12 for separating the optical path of B into a reference optical path and a measurement optical path, or １ ／ wavelength plates 4, 5, 14, and 15 for rotating the polarization direction of the reference light and the measurement light to a single wavelength. And the wavelength stability of the laser light source 11 of the interferometer B is inferior to that of the laser light source 1 of the interferometer A.
High positioning accuracy can be maintained based on the error analysis expression (8) in the light wave interference measurement method of the present invention described above.

Next, a schematic configuration of an optical interference measuring apparatus according to a fourth embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 4, the light wave interference measuring apparatus according to the present embodiment includes an interferometer A and an interferometer B similar to those shown in FIG. 3 representing the third embodiment. A laser interferometer C of another wavelength different from the wavelength used in B is constructed, and the measuring light of the interferometer C is made coaxial from the middle of the measuring optical path of the interferometer A and made incident on the measuring reflecting mirror (moving mirror) 7. Is characterized by the fact that In the configuration of the optical interference measurement apparatus according to the present embodiment, the components of the optical interference measurement apparatus according to the third embodiment described with reference to FIG.
In the operation and function, the same components are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 4, the interferometer C has a center wavelength λ3
It has a laser light source 21 that emits a laser beam of (λ3 ≠ λ1, λ3 ≠ λ2). This laser beam also has mutually orthogonal polarization directions with slightly different wavelengths. The laser beam emitted from the laser light source 21 enters the polarization beam splitter 60 and is split into a measurement optical path and a reference optical path. In the polarization beam splitter 60,
The light of the p-polarized component is transmitted and proceeds to the measurement optical path, becomes reference light converted into circularly polarized light by the quarter-wave plate 62, and the light of the s-polarized component is reflected by the polarizing beam splitter 60 to 1 /
The measurement light is converted into circularly polarized light by the four-wavelength plate 64.

After passing through the quarter-wave plate 62, the reference light enters a reference reflecting mirror (fixed mirror) 68. Further, the measuring light is transmitted through the quarter-wave plate 64, then reflected by a dichroic mirror 66 provided in the middle of the measuring optical path of the interference system A, and is reflected coaxially with the measuring light of the interferometer A for measurement. Head to mirror 7.

The reference light reflected by the reference reflecting mirror 68 is again incident on the quarter-wave plate, and the polarization direction is 90 ° from the beginning.
The light becomes linearly polarized light rotated by degrees and is reflected by the polarization beam splitter 68. On the other hand, the measuring light reflected by the measuring reflecting mirror 7 is again reflected by the dichroic mirror 66,
The light passes through the 波長 wavelength plate 64 and is converted into linearly polarized light whose polarization direction is rotated by 90 ° with respect to the original polarization direction. The measurement light transmitted through the 波長 wavelength plate 64 enters the polarization beam splitter 60 and transmits through the polarization beam splitter 60 because the polarization direction is rotated by 90 ° from the beginning.

The reference light reflected by the polarization beam splitter 60 and the measurement light transmitted through the polarization beam splitter 60 are:
The light enters the polarizer 70 in a coaxial manner. The polarization direction of the polarizer 70 is set to be inclined by 45 ° with respect to the reference light and the measurement light. Therefore, both lights transmitted through the polarizer 70 interfere with each other and are detected by the photoelectric detection element 72. The interference signal (measurement signal) converted into an electric signal by the photoelectric detection element 72 is combined with a phase signal (not shown) together with a reference signal obtained by causing the laser beams of the p-polarized component and the s-polarized component to directly interfere within the laser light source 21. (Omitted), and by integrating the phase change amount of the measurement signal with respect to the reference signal, the displacement of the measurement reflecting mirror 7 can be known.

The electric signals detected by the interferometers A and B are also input to a phase meter (not shown) in the same manner as in the first to third embodiments. Required for the interferometer. In the present embodiment, the wavelength difference between the wavelengths λ2 and λ3 is
It is set smaller than the wavelength difference between 1 and λ2 or between λ1 and λ3. Therefore, the combined wavelength λ23 determined from the wavelengths λ2 and λ3 is longer than the combined wavelength λ12 determined from the wavelengths λ1 and λ2.
Therefore, in the lightwave interference measuring apparatus according to the present embodiment, first, the measuring reflecting mirror 7 is used in units of the composite wavelength λ23.
Is measured with a coarse measurement range but coarse resolution. Next, similarly to the third embodiment, the position of the measuring reflecting mirror 7 is precisely obtained using the signals of the interferometer A having the wavelength λ1 and the interferometer B having the wavelength λ2.

In order to determine the position of the measuring reflecting mirror 7 in two stages, the measuring reflecting mirror 7 divides the composite wavelength λ23 by the number m of reflected light paths (in this case, m = 2). Therefore, the optical interference measurement apparatus according to the present embodiment has a feature that the measurable range can be expanded as compared with the above-described first to third embodiments.

Next, an optical interference measuring apparatus according to a fifth embodiment of the present invention will be described with reference to FIG. The light wave interference measuring apparatus according to the present embodiment is similar to the fourth embodiment described with reference to FIG.
13 is a modification of the optical interference measurement apparatus according to the embodiment.
In the configuration of the light wave interference measurement device according to the present embodiment,
Components having the same functions and functions as those of the optical interference measuring apparatus according to the fourth embodiment described with reference to FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

The light wave interference measuring apparatus according to the present embodiment
As shown in FIG. 5, in addition to the length measuring interferometer A, two laser interferometers B and C having different wavelengths are formed, and their measurement light is transmitted to the fourth interferometer.
In the same manner as in the first embodiment, the light is incident coaxially from the middle of the measurement optical path of the interferometer A. The laser beam of wavelength λ2 emitted from the laser light source 11 of the interferometer B and the laser beam of wavelength λ3 emitted from the laser light source 21 of the interferometer C are made coaxial by the dichroic mirror 20 and enter the polarization beam splitter 120. As in the fourth embodiment, one of the two laser beams is transmitted through the quarter-wave plate 150, and then becomes coaxial with the measurement optical path of the interferometer A by the dichroic mirror 10 so that the reflection mirror for measurement is used. 7 and the other polarization component is １ ／
After passing through the wave plate 140, the light is transmitted to the reference reflecting mirror 19 common to the interferometers B and C.

The laser beams reflected by the reflecting mirrors are combined again by the polarizing beam splitter 120, and the beams of wavelengths λ2 and λ3 are separated by the reflection type diffraction grating as the wavelength splitting means 22, and the polarizers 16 , 70 cause the polarization components to interfere with each other, and the interference light is detected by the photoelectric detectors 17 and 72. The detected electric signal is input to a phase meter (not shown) as in the above-described embodiment, and the amount of phase change of the measurement signal with respect to the reference signal is obtained for each interferometer.

In this embodiment, as in the fourth embodiment, the wavelength difference between the wavelengths λ2 and λ3 is set smaller than the wavelength difference between the wavelengths λ1 and λ2 or between the wavelengths λ1 and λ3. Thus, the composite wavelength λ23 determined from the wavelengths λ2 and λ3 is longer than the composite wavelength λ12 determined from the wavelengths λ1 and λ2. Therefore, first, the position of the measuring reflecting mirror 7 is roughly determined using the combined wavelength λ23 as a unit. Then, the wavelength λ1
From the signals of the interferometer A and the interferometer B having the wavelength λ2, the position of the measuring reflecting mirror 7 can be accurately obtained.

In the present embodiment, similarly to the fourth embodiment, the position of the measuring reflecting mirror 7 is determined in two steps. =
It is only necessary to fall within the range divided by 2), and there is an advantage that the measurable range is expanded as compared with the first to third embodiments.

The polarization beam splitter 12 here
The 0 and quarter wave plates 140 and 150 have wavelengths λ2 and λ3
In both cases, it must be designed to have a predetermined optical performance. That is, these optical elements are achromatic at wavelengths λ2 and λ3. Further, the wavelength splitting means 22 does not necessarily have to be a reflection type diffraction grating, but may be, for example, a dispersion prism.

Next, an optical interference measuring apparatus according to a sixth embodiment of the present invention will be described with reference to FIG. The optical interference measuring apparatus according to the present embodiment employs a so-called absolute interferometer in which the laser light source of the interferometer B of the optical interference measuring apparatus according to the third embodiment shown in FIG. It is characterized by the following points. In the configuration of the lightwave interference measurement apparatus according to the present embodiment, the same reference numerals are given to the same components in operation and function as those of the lightwave interference measurement apparatus according to the third embodiment described with reference to FIG. The description is omitted here.

In this embodiment, as shown in FIG. 6, a tunable laser light source 31 is used for the interferometer B, and the wavelength is obtained by sweeping the wavelength of the laser beam output from the tunable laser light source 31. From the obtained phase change, the optical path length difference L2 of the interference system B is directly obtained. Based on this,
The origin can be determined with the measurement resolution of the interferometer A. Note that the polarization beam splitter 12 shown in FIG.
It is assumed that the 2 and 1/4 wavelength plates 142 and 152 are achromatized within the wavelength variable range of the wavelength variable laser light source 31.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-described embodiment, each interferometer of the light wave interference measuring apparatus measures an interference signal by a heterodyne method, but the present invention is not limited to this, and a homodyne method interferometer may be used. Of course it is good.

Further, in the above embodiment, the interferometer B which is made to enter the measurement optical path or the reference optical path of the interferometer A from the middle is used.
Alternatively, the measurement light and the reference light of the interferometer C are made coaxial with the measurement light and the reference light of the interferometer A so as to be incident on each reflecting mirror. However, the present invention is not limited to this. The beams may be shifted in parallel with each other, and no problem occurs as long as the condition of the above equation (9) is satisfied.

[0077]

As described above, according to the present invention, even if the measuring light is cut off, the position of the measuring reflecting mirror from the origin is determined within the composite wavelength with the resolution of the measuring light wave interferometer. Will be able to do it. Since the lightwave interferometer for length measurement and another lightwave interferometer using light of a different wavelength are configured to combine at least the optical axes of both measurement lights from the middle, Polarization separation element (polarization beam splitter) that separates the optical path into a reference optical path and a measurement optical path
Inexpensive elements corresponding to a single wavelength can be used for a quarter-wave plate or the like for rotating the polarization direction of reference light or measurement light.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a light wave interference measurement device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of a lightwave interference measurement device according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a schematic configuration of an optical interference measurement apparatus according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a schematic configuration of a light wave interference measurement device according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing a schematic configuration of a lightwave interference measurement device according to a fifth embodiment of the present invention.

FIG. 6 is a diagram showing a schematic configuration of a light wave interference measurement device according to a sixth embodiment of the present invention.

FIG. 7 is a diagram showing a schematic configuration of a conventional light wave interference measurement device.

[Explanation of symbols]

1, 11, 21 Laser light source 2, 12, 60, 120, 122 Polarizing beam splitter 4, 5, 14, 15, 140, 142, 150, 152
Quarter-wave plate 6, 19 Reflector for reference 7 Reflector for measurement 8, 16, 70 Polarizer 9, 17, 72 Photodetector 10, 20, 66 Dichroic mirror 22 Spectral unit 31 Wavelength variable laser light source 50, 52 Phase meter

Claims (14)

[Claims] 1. A light having a wavelength λ1 is separated into a reference light and a measurement light, the reference light is reflected by a reference mirror provided on a reference light path, and the measurement light is provided movably on the measurement light path. The reference light and the measurement light reflected by the measured measurement mirror, interfere with the reflected reference light and the measurement light, and move the measurement reflection mirror relative to the reference reflection mirror relative to the reference reflection mirror by moving from a reference position Δ
In the light wave interference measurement method for measuring L, a phase φ1 based on an optical path length difference L1 between the reference optical path and the measurement optical path at the reference position (= φ1 · λ1 / m, where m is the number of turns of the optical path). The light having the wavelength λ2 (≠ λ1) is further used to separate the light having the wavelength λ2 into two lights. The one light reflected by the reflecting mirror and the other light interfere with each other, and an optical path length difference L2 (= φ2) between the optical path of the one light and the optical path of the other light at the reference position. .Lambda.2 / m), and a phase .phi.1 'based on an optical path length difference L1 + .DELTA.L (= .phi.1' .. lambda.1 / m) between the reference optical path and the measurement optical path at the relative movement distance .DELTA.L, The optical path of the one light and the optical path of the other light at the relative movement distance ΔL Path length difference L2 + ΔL (= φ2 '· λ2 /
m), and measuring the relative movement distance ΔL when the light of the wavelength λ1 is cut off based on the phases φ1, φ2, φ1 ′, and φ2 ′. Interference measurement method. 2. The light wave interference measuring method according to claim 1, wherein the relative moving distance ΔL is ΔL = ΔΦ · λs / m, where ΔΦ = Φ′−Φ, Φ = φ2−φ1, Φ ′ = φ2 ′. −φ1 ′ A light wave interference measurement method characterized by being determined from the synthetic wavelength λs = λ1 · λ2 / | λ2-λ1 |. 3. The method of claim 1, wherein the wavelength λ3 (λ1, ≠ λ2, | λ2-λ1 |> | λ3-
λ2 |) is further used to separate the light having the wavelength λ3 into two, and one of the light is incident on the measurement optical path in the middle of the measurement optical path and is reflected by the measurement reflector. The reflected one light and the other light are caused to interfere with each other to make an optical path length difference L3 (= φ3 · λ3 / m) between the optical path of the one light and the optical path of the other light at the reference position. Phase φ
3 and the optical path length difference L3 + ΔL (= φ3 ′ · λ3 /) between the optical path of the one light and the optical path of the other light at the relative movement distance ΔL.
By measuring the phase φ3 ′ based on m), a relatively wide synthesized wavelength λsW = λ2 · λ3 / | λ3-λ
2. An optical interference measurement method, wherein an existence range of the ΔL is obtained based on 2 |, and then the ΔL is obtained based on the synthesized wavelength λs which is narrower. 4. The light wave interference measurement method according to claim 1, wherein an optical path length difference L1 between the reference optical path and the measurement optical path at the reference position, and an optical path of the one light. A light wave interference measurement method, wherein an optical path length difference L2 from the optical path of the other light is made substantially equal. 5. The light wave interference measurement method according to claim 1, wherein an optical path length difference L1 between the reference optical path and the measurement optical path at the reference position, and an optical path of the one light. An optical path interference measurement method, wherein an optical path length difference L2 from the optical path of the other light is L1 >> L2. 6. A first light source for emitting a first light for measuring a displacement of an object, a first beam splitter for separating the first light into a measurement light path and a reference light path, and the reference light A reference reflecting mirror provided on a road, a measuring reflecting mirror movably provided on the measuring optical path, and interference light of the first light reflected by the reference reflecting mirror and the measuring reflecting mirror A first light receiving unit that receives light, a second light source that emits second light having a wavelength different from the wavelength of the first light, and two light sources that emit the second light. A first beam splitter for splitting the second light into two beams; and a first optical system for directing one of the split second beams from the middle of the measurement optical path to the measurement reflector in parallel with the measurement optical path. And interference between the one light reflected by the measurement reflecting mirror and the other light A light wave interference measurement device, further comprising a second light receiving unit for receiving light. 7. The light wave interference measuring apparatus according to claim 6, wherein the first optical system further reflects the other of the second light from the middle of the reference optical path in parallel with the reference optical path. The second light receiving section is configured to reflect one of the second light reflected by the measurement reflecting mirror and the second light reflected by the reference reflecting mirror.
An interferometer for receiving an interference light with the other of the light beams. 8. The light wave interference measurement device according to claim 6, wherein the second light source is a wavelength tunable laser. 9. The light wave interference measuring apparatus according to claim 6, wherein a third light source that emits third light having a wavelength different from the wavelengths of the first and second lights, and the third light source. A third beam splitter for splitting the second light into two light beams, and one of the two third light beams split from the middle of the measurement light path to the measurement reflector in parallel with the measurement light path. A second optical system; and a third light receiving unit that receives interference light between one of the third lights reflected by the measurement reflecting mirror and the other light. Light wave interferometer. 10. The light wave interference measuring apparatus according to claim 9, wherein the second optical system further reflects the other of the third light from the middle of the reference light path in parallel with the reference light path. A third light-receiving unit, the third light-receiving unit reflecting one of the third light reflected by the measurement reflecting mirror and the third light reflected by the reference reflecting mirror;
An interferometer for receiving an interference light with the other of the light beams. 11. The optical interference measuring apparatus according to claim 9, wherein the third beam splitter is also used as the second beam splitter, and the second optical system is used as the first optical system. A light wave interference measurement device, which is also used. 12. The light wave interference measurement apparatus according to claim 6, wherein the first light is composed of two lights having polarization directions perpendicular to each other and having slightly different frequencies, The first beam splitter is a polarization beam splitter, and a wavelength plate is disposed on each of the measurement optical path and the reference optical path. The first optical system transmits at least one of the second light to the A light wave interference measurement device, which is arranged so as to be directed from the wave plate on the measurement optical path and the reflection mirror for measurement to the reflection mirror for measurement in parallel with the optical path for measurement. 13. The optical interference measuring apparatus according to claim 12, wherein the first optical system transmits at least the other of the second light between the wave plate on the reference optical path and the reference reflecting mirror. A light wave interference measuring apparatus, which is disposed so as to face the reference reflecting mirror in parallel with the reference optical path. 14. An optical interference measurement apparatus according to claim 6, wherein said first to third light sources are wavelength-stabilized lasers.