JPH05126603A - Grating interferometer - Google Patents

Abstract

(57) [Abstract] [Purpose] A grating interferometer using the principle of optical heterodyne to prevent deterioration of accuracy due to fluctuations in wavelength difference between two wavelengths of light. [Structure] After allowing two-wavelength light to enter the diffraction grating 9 once,
The corner cubes 10 and 10 ′ re-enter each of the outgoing diffracted lights into the diffraction grating 9 in the direction opposite to the outgoing direction, and
Diffraction of the same order is performed multiple times to combine and interfere, and the detector 12 detects the beat signal. By doing so, the final outgoing angle of the outgoing light from the diffraction grating 9 becomes constant regardless of the wavelength difference variation of the two-wavelength light, and the variation of the combined state is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for obtaining movement information of an object with high accuracy using a diffraction grating.
INDUSTRIAL APPLICABILITY The present invention is particularly well applied to the semiconductor industry, measuring and processing machines requiring high precision, industrial robot fields, and the like.

[0002]

2. Description of the Related Art With the high integration of semiconductor ICs and LSIs,
The miniaturization of integrated circuit patterns has progressed year by year, and the performance of exposure apparatuses for semiconductor manufacturing has been improved accordingly. In particular, the alignment of the mask and the wafer is an important factor for improving the performance, but in recent alignment, it is required to have alignment accuracy of the order of 10 nm. Further, there is an increasing demand for higher precision of the shape of the projection lens system used in the exposure apparatus.

On the other hand, the density of compact disks, laser disks, optical memories, and magnetic disk memories has been increasing more and more, and the shape accuracy and positioning accuracy required for mechanical parts and optical parts used for them have become higher year by year. Along with this, the accuracy of machining position and the like of these industrial machines have become severer year by year. Especially, the shape accuracy of optical parts is 1
The order of 0 nm is being demanded.

Taking length measurement as an example, pure mechanical rulers, vernier calipers, micrometer, etc. have long been known.
So-called precision measurement, which has a problem of accuracy of submicron,
In the area of processing, these tools are useless. recent years,
The length measurement technology that uses light not only enables objective and speedy measurement by photoelectrically converting light and performing electrical processing, but also enables highly accurate measurement.

As an example, there is known an optical wave interferometer with a wavelength of laser light as a reference. Although the resolution of this length measuring device is on the order of 1 nm, the accuracy (stability) cannot sufficiently meet the current level of precision measurement processing requiring the order of 10 nm. This is because the wavelength of the light wave propagating in air is
This is because it is not stable due to air turbulence and the accuracy (stability) of the length measurement value is reduced.

Therefore, as a means for compensating for this drawback of the optical wave interferometer, a length meter based on an optical scale is known. It is known that, in this scale reference method, a grating interferometer-type length measuring device using the grating pitch of the grating as a reference can obtain a resolution of the order of 10 nm.

Regarding the basic principle of this lattice interference, for example, optical technology contact (Vol. 23, No. 1, p.
2, 1985), and therefore omitted here.

In this case, the reference diffraction grating 9 is shown in FIG.
As shown in (1), the grating 9g is made at a pitch of 1 micron order using a mechanical ruling engine, laser beam scanning exposure, electron beam or photolithography based on glass, metal or ceramic.

Light is incident on this diffraction grating, and the generated diffracted light is transmitted through analyzers having different polarization directions of 45 ° and received respectively. As a result, sinusoidal signals with different 90 ° phases, which vibrate sinusoidally with the displacement of the diffraction grating, are obtained.

A procedure for converting two electric signals having a phase difference of 90 ° into electric pulses will be described with reference to FIG.

The sine waves of (a) and (b) are compared with a predetermined threshold value, and the waveform is shaped into a rectangular wave as shown in (c) and (d). By capturing the rising and falling edges of this rectangular wave, a pulse signal is generated as shown in (e).

By counting this pulse signal, the phase change of the light wave can be detected, and the movement amount of the diffraction grating corresponding to the optical scale can be detected.

On the other hand, there is a limit in the electrical division method for reading the displacement of the scale with higher resolution.

Therefore, an example is known in which the optical heterodyne method is applied to the grating interference method.

The optical heterodyne method is to detect the beat of two light waves having an electrically detectable frequency difference of several MHz by a detector and detect the phase of the signal with high accuracy.

FIG. 7 shows an example in which such an optical heterodyne method is applied to the grating interference method. A typical example of such a system is shown in Japanese Patent Laid-Open No. 62-274216. GL is a HeNe Zeeman laser 2
Wavelength orthogonal polarization light source, HM is a half mirror, GS is a diffraction grating integrated with a moving body, M1, M2 and M3 are mirrors,
PBS is a polarizing beam splitter, PL1 and PL2 are polarizing plates, D1 and D2 are detectors, and LA is a phase detector. The laser light flux from the Zeeman light source shares the optical axis, the polarization planes are orthogonal to each other, and the frequency difference is 100 KHz-2M.
It is composed of two luminous fluxes different in Hz, and this luminous flux passes through the half mirror HM, is reflected by the mirror M1, and is vertically incident on the diffraction grating GS. There, the luminous flux is diffracted by GS, and the diffracted light is divided into two luminous fluxes having different signs. At this time, in accordance with the principle of lattice interference, the phase of the light beam diffracting in the traveling direction is advanced, and the phase of the light beam diffracting in the opposite direction to the traveling direction is delayed. Each diffracted light is a mirror M2,
It is reflected by M3 and enters the polarization beam splitter PBS. The polarization beam splitter reflects P-polarized light and transmits S-polarized light. Two-wavelength light beams with different polarization planes from the Zeeman laser are combined by this PBS, and after the polarization planes are aligned by the polarizing plate PL2, they become beat signals and are detected by the detector D2. On the other hand, the light reflected by the half mirror HM has its polarization plane aligned by the polarizing plate PL1 and then becomes a reference beat signal which is detected by the detector D1. This detector D1,
The output from D2 is incident on the phase detector LA, where the phase difference between the beat signals is detected. For details of the principle of optical heterodyne, see, for example, Optical Volume 9, No. 5 (1980, 10
The explanation is omitted here.

[0017]

By the way, the configuration of the conventional system is a system in which two first-order diffracted lights having different signs are directly interfered with each other. This means that not only can optical resolution be doubled,
There is a problem that the length measurement value is affected by the fluctuation of the two wavelengths forming the optical heterodyne.

Now, the two wavelengths of heterodyne are λο, λο
When + Δλ, the fluctuation of Δλ becomes a problem among the fluctuations of the two wavelengths of λο and Δλ.

For example, it is well known that, as the light source means for optical heterodyne, an acousto-optical element (AO) is used in addition to the Zeeman laser as in the above-mentioned conventional example.

AO has the following effects by propagating ultrasonic waves inside the glass.

That is, the diffraction grating is formed by the refractive index difference generated by the density of the ultrasonic waves. Further, this diffraction grating advances in the direction perpendicular to the wavefront. The light flux that crosses there causes Ramanus or Bragg diffraction and undergoes Doppler shift.

Therefore, the shifted wavelength fluctuates due to the instability of the frequency of the driver for driving the ultrasonic wave propagated to the AO, the temperature dependence of the propagation speed of the ultrasonic wave of the AO itself, and the like. This becomes a serious problem for measurement on the nm order.

It is generally known that Δλ fluctuates not only in the AO system but also in the dual wavelength system using the Seman laser.

Returning to the conventional example of FIG. 7, the adverse effect of the fluctuation of Δλ will be described. The fluctuation of Δλ becomes the fluctuation of the diffraction angle of the light beam from the diffraction grating, and the fluctuation of the other does not change.
In the interference with the light ray of ο, the incident positions on the beam splitter PBS are displaced from each other, the multiplexing is defective, the light intensity varies, and the electrical phase signal corresponding to this light intensity is affected.

This will be described in detail. In such an optical system, the arrangement and angles of the mirrors M2 and M3 are set with respect to the diffraction angle determined by the grating pitch of the diffraction grating and the wavelength of light, and both light beams are well combined by the polarization beam splitter PBS. A beat signal that interferes with each other and causes a phase change in the detector D2 due to the displacement of the diffraction grating is obtained. When Δλ fluctuates here, the wavelength of one light beam fluctuates and the diffraction angle changes, so that the polarization beam splitter P
The incident position on the BS changes significantly. On the other hand, the incident position of the other light beam on the polarization beam splitter PBS does not change. Therefore, both are polarized beam splitter PBS
The upper incident positions deviate from each other so that they do not combine well, interference becomes poor, and the S / N ratio of the beat signal decreases, resulting in a decrease in length measurement accuracy.

As described above, in the grating interferometer by the optical heterodyne method, there is a problem that a new error factor such as a variation of Δλ, that is, a variation between two wavelengths has a significant influence on the measurement value. It was

In view of the above-mentioned drawbacks of the conventional example, it is an object of the present invention to provide a grating interference measurement in which a detection error caused by a fluctuation between two wavelengths is prevented.

[0028]

In order to achieve the above object, the present invention provides a light generating means for generating two types of light having different wavelengths and a diffraction grating for relatively detecting displacement information. Illumination means for entering the light from the light generating means,
Deflecting means for arranging the light paths of the incident light and the outgoing light to be the same or parallel and arranged to deflect the diffracted light emitted from the incident diffraction grating in the direction of the diffraction grating; The light deflected by the deflecting means re-enters the diffraction grating, interferes with the diffracted light generated and is received to generate a beat signal corresponding to the two types of light, and a light detecting means of the beat signal. Displacement detecting means for detecting relative displacement information of the diffraction grating by phase change is provided. Further, the present invention includes a light generating means for generating two kinds of light having different wavelengths, and an illumination means for making the light from the light generating means incident on a diffraction grating for relatively detecting displacement information. , Diffracted light emitted from the diffraction grating to which the two kinds of light have been incident is deflected in the direction of the diffraction grating and incident on the diffraction grating to finally form diffracted light diffracted an even number of times. For arranging deflecting means for changing the directions of the incident light and the outgoing light by making the optical paths of the incident light and the outgoing light the same or parallel to each other, the even-numbered diffracted light is interfered and received to generate a beat signal corresponding to the two kinds of light. A light detecting means and a displacement detecting means for detecting relative displacement information of the diffraction grating by the phase change of the beat signal are provided.

[0029]

As a result, the final exit angle of the light flux from the diffraction grating does not fluctuate, the change of the combined state is suppressed, and the S / N ratio is not easily influenced by the wavelength difference fluctuation, and a high measurement accuracy is always obtained. I can do things.

[0030]

FIG. 1 shows a first embodiment according to the present invention. In the figure, 1 is a semiconductor laser (LD) which is a coherent light source, 2 is a collimator lens for converting a divergent light beam into a parallel light beam, and 4 and 4'reflect S polarized light and P
Polarization beam splitter that transmits polarized light, 5,
5'and 11 are mirrors for changing the direction of the light flux, 3,
3'is an AO modulator that shifts (shifts) the frequency of the light from the LD. When the transmitted light flux passes through the AO modulator,
It is known that the first-order diffracted light causes a frequency shift of the same frequency as the drive frequency of the AO modulator.

6 is an aperture for removing unnecessary diffracted light generated by the AO modulator, 7 is a half mirror for splitting a part of the light beam, 8, 8 ', 8 ",
8 '''is a polarizing plate for aligning the vibration directions of the wavefronts and causing interference, 9 is a diffraction grating as a reference of the amount of movement, 10 and 10' do not change the direction of incident light, and The corner cube, 12, 12 'are photoelectric conversion detectors capable of detecting strong and weak signals of MHz light, 13 is a phase detection circuit for detecting the phase difference of the sine wave signals from 12, 12', and 14 is the same. A counter circuit for detecting the counter difference of the sine wave signal, 15 is a circuit 13, 14
This is an arithmetic circuit that calculates the amount of movement of the diffraction grating 9 based on the amount of detection from.

Next, the operation will be described.

L with the plane of polarization set to 45 ° with respect to the plane of the paper
The light flux from D1 is made into a parallel light flux by the collimator 2 and divided into two directions by the polarization beam splitter 4. The P-polarized component is transmitted, and the AO modulator 3 shifts the frequency of the first-order diffracted light. On the other hand, the S-polarized component reflected by the polarization beam splitter 4 is the AO modulator 3 '.
Similarly, frequency shift is caused by. However, the frequency shift amount at this time is different from that of the AO modulator 3. The respective light fluxes are reflected by the mirrors 5 and 5 ', combined by the polarization beam splitter 4', and only the respective first-order diffracted lights pass through the aperture 6. The AO modulators 3 and 3'are reflected at 7 when the drive frequency difference is set to, for example, 1 MHz,
The light flux whose polarization planes are aligned in 8 is 1M in 12 detectors.
A beat signal of Hz can be obtained. This is used as a reference beat signal.

The luminous flux transmitted through the half mirror 7 is reflected by the mirror 1.
It is reflected at 1 and enters the diffraction grating 9 perpendicularly. The light beams diffracted by the diffraction grating, that is, the + nth-order light and the −nth-order light (n is an arbitrary natural number, for example, 1) are respectively in the corner cube 1.
Go to 0, 10 '. The light beams traveling to the respective corner cubes are overlapped with S-polarized light and P-polarized light having a frequency difference of 1 MHz, but since the polarization directions are 90 °, they can be separated by the polarizing plates 8'and 8 ". That is, for example, 8 '
Transmits S-polarized light and 8 ″ transmits P-polarized light.

When the diffraction grating 9 moves, it undergoes a frequency shift according to the amount of movement. For example, if the grating spacing (pitch) is moved in the left-right direction in the drawing of FIG. 1, the light flux toward the corner cube 10 is delayed in phase by one wavelength and the frequency is lowered. On the other hand, the luminous flux heading for the corner cube 10 'has a phase that advances by one wavelength and an increase in frequency.

Here, the corner cubes 10 and 1 are further added.
When the ± n-th order diffracted light returned from 0 ′ is re-incident on the diffraction grating 9, the + n-th order light by the re-diffraction of the + n-th order light and the −n-th order by the re-diffraction of the −n-th order light. The light undergoes the same frequency (phase) shift in the direction in which each light flux undergoes the first frequency (phase) shift. Therefore, each light beam has a frequency (phase) of two wavelengths.
Since the shifts occur in the opposite directions, a frequency (phase) shift of four wavelengths is eventually generated between the respective light fluxes. The two light fluxes are combined and emitted from the diffraction grating.

The light fluxes returning from the corner cubes 10 and 10 'and combined by the diffraction grating 9 are parallel to each other, and after passing through the same optical path, are bent by the mirror 11 and have their polarization planes aligned by the polarizing plate 8'''. It is detected by the detector 12. The beat signal here is shifted at a phase four times that of a signal with n = 1 and the movement pitch of the diffraction grating being one cycle. This phase shift amount is roughly determined by counting the period difference (coarse detection) between the two signals by the counter circuit by using the 1 MHz signal from the detector 12 'as a reference signal and counting the period difference between the two signals. The fine phase (fine detection) inside is detected by finely detecting the phase difference between both signals by the phase detection circuit. As a result, the moving distance detection circuit 15 can detect in a range with a resolution of 1 nm (grating pitch of 1.6 μm) and a grating length, for example, several tens mm.

Here, let us consider a case where the wavelength difference between the two light fluxes fluctuates and one wavelength changes as described above. This light beam changes the diffraction angle of the first diffraction and changes the emission angle from the diffraction grating 9, but reenters the diffraction grating 9 at the same incident angle as the emission angle changed by the corner cube. The diffraction angle of the re-incident light also changes, but the incident angle changes by canceling the change, so that the exit angle of the re-diffracted light beam is constant. Therefore, after the re-diffraction of the two light beams, the two beams are kept parallel to each other, and the combined state can be largely prevented from being changed as compared with the case where the diffraction angle is changed.

As described above, even if the difference between the two wavelengths fluctuates due to the configuration of the present apparatus, the beat signal obtained is hardly affected, and the measurement with a high S / N ratio becomes possible.

The second embodiment is shown in FIG. In the first embodiment, the grating as the movement reference is the transmission type diffraction grating, but in this embodiment, the reflection type diffraction grating 9'is used.
Hereinafter, the same members as those in FIG. 1 are denoted by the same reference numerals. This apparatus also has a configuration in which the diffraction is performed twice as in the first embodiment which is a transmission type. This structure is more compact because the optical components are arranged on one side of the diffraction grating and is easy to use on a stage or the like. The other structure, operation, and action are similar to those of the first embodiment, and the description thereof will be omitted.

A third embodiment is shown in FIG. It is an example in which the principle of the present invention is applied to a rotary encoder. That is, the diffraction grating 9 ″ is arranged in a circle around the rotation axis SP, and the measured value is obtained as the rotational movement amount of the diffraction grating 9 ″. In this device, in addition to this, half mirror 7
The transmitted light of is separated by the polarization beam splitter 21 into polarization directions (that is, by frequency) and is incident on the diffraction grating separately, which is different from the above-described embodiment.
The reflected light (S polarized light) of the polarization beam splitter 21 is λ / 4.
Circularly polarized light passes through the plate 22, is reflected by the mirror 23, and enters the diffraction grating 9 ″. Here, the + nth-order transmitted diffraction light is emitted. The + n-th order diffracted light is reversed in direction by the cat's eye optical system 10 ″ while keeping the traveling direction of the light as it is. In this way, the light returned from the cat's eye optical system 10 '' is re-incident on the diffraction grating and diffracted. Of the transmitted diffracted light, the + n-th order light (light diffracted twice + n-th order) travels backward in the same or parallel optical path as the optical path before entering the diffraction grating 9 ″ for the first time, and passes through the mirror. It is incident on the λ / 4 plate 22 via 23. Here, this time, it is converted into P-polarized light, emitted, and transmitted through the polarization beam splitter 21. Similarly, a light beam (P-polarized light) of the light from the half mirror 7 which is transmitted through the polarization beam splitter 21 is circularly polarized by the λ / 4 plate 22 ′, reaches the diffraction grating 9 ″ from the mirror 23 ′, and is diffracted. The −n-order diffracted light from the grating 9 ″ is reversely traveled by the cat's eye optical system 10 ″ ″ and re-incident, and at the time of re-diffraction −
The n-th order diffracted light (twice-light diffracted at the n-th order) is mirror-2.
After passing through 3 ′, it is S-polarized by the λ / 4 plate 22 ′ and reflected by the polarization beam splitter 21. Both light fluxes are diffracted twice by the diffraction grating in this manner, and then the polarization beam splitter 21
Are combined, and the analyzer 8 '''extracts only the 45 ° components of each other and receives them by the detector 12 to obtain a beat signal. The electrical system after that is the same as that of the above-mentioned embodiment and is omitted. Further, the other configurations and operations are the same as those in the above-mentioned embodiment, and the description thereof will be omitted. Also in this embodiment, the emission angle of the light flux finally emitted from the diffraction grating does not change even if the wavelength difference between the two wavelength lights changes, and the polarization beam splitter 2
Between the incident positions of the two light fluxes on one surface, the occurrence of deviation is significantly suppressed as compared with the case where the emission angle finally changes. This enables more accurate detection than before.

FIG. 4 shows a fourth embodiment in which optical heterodyne is used in a structure for performing diffraction four times. That is, by modifying the apparatus of FIG. 1 into the following form, it is possible to interfere the light beams diffracted four times by the diffraction grating. The transmitted light from the half mirror 7 reaches a point P1 on the diffraction grating 9. The + n-order light from the point P1 passes through the optical path L11, and enters the corner cube C11.
And then reenters the point P2 on the diffraction grating. The + nth-order light from the point P2 (the twice-diffracted light) passes through the optical path L21 and is transmitted by the polarizing plate 8 ″ to the P.I. Only one of the components of S (provisionally P) passes and re-enters the point P4 on the diffraction grating through the corner cube CC3. + N-order light from point P4 (3
The (diffracted light) passes through the optical path L31, reaches the point P6 on the diffraction grating through the corner cube CC1 again. The + n-order light (four times diffracted light) from the point P6 is emitted from the half mirror 7 to the point P1.
Travels parallel and opposite to the optical path to. Similarly, point P
The -nth-order light (1st-order diffraction) from 1 passes through the optical path and L12 via the corner cube CC2 and the point P3, and the -nth-order light (2nd-order diffraction) from the point P3 passes through the optical path L22 and forms a corner. Cube CC4, polarizing plate 8'for passing S component, point P5
-Nth order light (three times diffraction) from point P5 via optical path L
After passing through 32, it reaches the point P6 through the corner cube CC2, and the −n-order light (fourth diffraction) from the point P6 also travels from the half mirror 7 in the direction parallel and opposite to the optical path of the point P1. In this way, the 4th + nth-order diffracted light flux and the 4th-nth-order diffracted light multiplexed at the point 6 pass through the mirror M and the analyzer 8 ″ ″ extracts mutual 45 ° components. , And they are detected by the detector 12. The electrical system is the same as that of the above-mentioned embodiment and will not be described. In this example, since n = 1 and the optical sensitivity is optically eight times the grating pitch, the sensitivity is twice as high as that of the first embodiment and 0.5 under the same conditions.
It can be expected with a resolution of nm. Also in this example, the final emission angle from the diffraction grating is always constant and parallel to each other without being influenced by the variation of the wavelength difference between the two wavelength lights, and the combined state is significantly larger than when the final emission angle changes. Can be suppressed.

In this way, when light is repeatedly incident on the diffraction grating and diffracted by the means for changing the direction of the light such as the corner cube without changing the direction of the light, the number of times of diffraction of one light beam is an even number. By doing so, the above-mentioned effect of suppressing the fluctuation of the multiplexing state can be obtained.

FIG. 8 shows a fifth embodiment of the present invention. The present invention is a modification of the second embodiment. The points different from the second embodiment will be described below. Light emitted from the aperture 6 is separated by the polarization beam splitter 31 into polarization directions (that is, frequencies). The transmitted light (here, P-polarized light) enters the point P _A on the diffraction grating through the mirror 32. The + nth-order diffracted light from the point P _A is retreated by the corner cube 10 and enters the point P _B on the diffraction grating. And + n from the point P _B
The next diffracted light (twice diffracted) travels in parallel and in the opposite direction to the optical path from the mirror 32 to the point P _A and travels to the polarization beam splitter 33.
Incident on and transmitted through. On the other hand, -n-order diffracted light from the point P _A is likewise reached the point P _C through the corner cube 10 ', -n th order diffracted light from the point P _C (2 times diffraction), the mirror 32
From the point P _A to the point P _A , and travels in the opposite direction to the polarization beam splitter 33 ′ and is transmitted therethrough. Here, the reflected light of the polarization beam splitter 31 (here, S-polarized light) enters the half mirror 34 through the corner cube 10 ″ for optical path length adjustment, and the reflected light of the half mirror 34 enters the polarization beam splitter 33. Further, the transmitted light passes through the mirror 35, enters and is reflected by the polarization beam splitter 33 ', and is combined with the above-mentioned diffracted light in the same optical path length. The combined and interfered light is detected by the detectors 12 and 12 ', and the beat signal corresponding to each is detected. Since the phases of the beat signals are shifted from each other by 4 cycles when the diffraction grating 9'moves by 1 pitch, a fine phase difference is detected by the phase detection circuit 13 using the beat signals, and the counter circuit is used. 1 in 14
By counting the phase difference for each cycle, the moving distance calculation circuit 15 can detect the relative displacement amount of the diffraction grating in a wide range with high accuracy.

Also in this embodiment, the final exit angle of the P-polarized light from the diffraction grating does not change even if the wavelength changes (the S-polarized light has a constant optical path regardless of the wavelength).
Similar to the above, it is possible to suppress the fluctuation of the combined state.

[0046]

As described above, in the grating interferometer using the optical heterodyne, the resolution can be improved not only by diffracting and interfering the light flux at least twice or more even times. The accuracy can be improved,
Performance can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a second embodiment of the present invention.

FIG. 3 is a schematic diagram of a third embodiment of the present invention.

FIG. 4 is a schematic diagram of a fourth embodiment of the present invention.

FIG. 5 is a diagram showing an example of a diffraction grating.

FIG. 6 is a graph for explaining electric pulse conversion.

FIG. 7 is an explanatory diagram of a conventional example.

FIG. 8 is a schematic view of a fifth embodiment of the present invention.

[Explanation of symbols]

 1 Coherent light source 3, 3'AO modulator 4, 4'Polarizing beam splitter 9 Diffraction grating 8, 8 ', 8 "' Polarizing plate 12, 12 'Optical detector 13 Phase detection circuit 15 Moving distance calculation circuit

Claims (2)

[Claims] 1. A light generating means for generating two types of light having different wavelengths, and an illuminating means for allowing light from the light generating means to enter a diffraction grating for relatively detecting displacement information. Arranged so as to deflect the diffracted light emitted from the diffraction grating to which the light is incident, in the direction of the diffraction grating,
The deflecting means for changing the directions of the incident light and the outgoing light by making the optical paths the same or parallel, and the diffracted light generated by the light deflected by the deflecting means re-incident on the diffraction grating are received by interfering with each other. Grating having a light detecting means for generating a beat signal corresponding to the light and a displacement detecting means for detecting relative displacement information of the diffraction grating by a phase change of the beat signal. Interferometer. 2. A light generating means for generating two kinds of light having different wavelengths, and an illuminating means for making light from the light generating means incident on a diffraction grating for relatively detecting displacement information. , Diffracted light emitted from the diffraction grating to which the two kinds of light have been incident is deflected in the direction of the diffraction grating and incident on the diffraction grating to finally form diffracted light diffracted an even number of times. For arranging deflecting means for changing the directions of the incident light and the outgoing light by making the optical paths of the incident light and the outgoing light the same or parallel to each other, the even-numbered diffracted light is interfered and received to generate a beat signal corresponding to the two kinds of light. A grating interference measuring apparatus comprising: a light detecting unit; and a displacement detecting unit for detecting relative displacement information of the diffraction grating based on a phase change of the beat signal.