JP2013186114A - Position detection device - Google Patents

Abstract

In an incremental displacement detection device, when detecting a displacement of a surface to be measured of a member to be measured that is relatively movable in a direction perpendicular to a measurement direction, based on measurement light reflected by the surface to be measured, Without moving in the vertical direction, the absolute position can be detected at high speed and the origin can be returned.
A relative position and an absolute position in the measurement direction Z are optically determined based on measurement light L1 reflected by a measurement surface 1a of a measurement target 1 movable in a direction X perpendicular to the measurement direction Z. And an absolute position detection region 4 for moving the optical axis of the measurement light L1 at the end in the movement direction X of the member 1 to be measured. The absolute position detection unit 30 performs absolute position detection by moving the optical axis of the measurement light L1 in the absolute position detection region 4 and returns position information obtained by the relative position detection unit 30.
[Selection] Figure 1

Description

  The present invention relates to a displacement detection device that detects a displacement of a surface to be measured of a member to be measured that is relatively movable in a direction perpendicular to a measurement direction based on measurement light reflected by the surface to be measured.

  Conventionally, a displacement detection device using light has been widely used as a device for measuring the displacement and shape of a surface to be measured in a non-contact manner. As a typical example, there is a method of irradiating a surface to be measured with a laser beam and detecting a change in position of reflected light with a PSD (Position Sensitive Device). However, this method has a problem in that it is easily affected by the inclination of the surface to be measured, the sensitivity is low, and the measurement resolution decreases when the measurement range is expanded.

  On the other hand, there is a method using a Michelson interferometer with the surface to be measured as a mirror surface. This method has a wide detection range and excellent linearity. However, when the measurement range is widened, the method receives a change in the wavelength of the light source and a change in the refractive index of the air.

  On the other hand, the light emitted from the light source is condensed on the surface to be measured by the objective lens, and the reflected light reflected by the surface to be measured is condensed by the astigmatic optical element and incident on the light receiving element, and then focused by the astigmatism method. Generate an error signal. Then, the servo mechanism is driven using the focus error signal, and the objective lens is displaced so that the focal position of the objective lens becomes the surface to be measured. At this time, there is a method of detecting the displacement of the surface to be measured by reading a scale of a linear scale that is integrally attached to the objective lens via a connecting member (for example, see Patent Document 1). This method has an advantage that it is difficult to receive a change in the inclination of the surface to be measured, and a large measurement range can be measured with high resolution.

  In the displacement detection device disclosed in Patent Document 1, in order to increase the accuracy of displacement detection, the numerical aperture (NA: Numerical Aperture) of the objective lens is increased to reduce the beam diameter focused on the surface to be measured. ing. For example, when the beam diameter formed on the surface to be measured is about 2 μm, the detection accuracy of the linear scale is about several nm to several hundred nm.

  In addition, in the displacement detection method, as in the displacement detection device disclosed in Patent Document 1, a single-scale lattice pattern and an origin pattern are provided on the main scale, and the detection position is set to a single scale with reference to the origin. As shown in the incremental type that detects the amount of displacement from the number of repetitions of the periodic signal formed by the interaction between the lattices and the displacement detection device disclosed in Patent Document 2, binary code patterns are provided on a plurality of tracks. There is an absolute type that detects the position by reading the code of the provided main scale.

  In the incremental type, in order to detect the origin pattern at the time of restart, it is necessary to perform the origin return operation by reciprocating the main scale once at most. On the other hand, in the absolute type, since the code indicating the absolute position can be read without moving the main scale at the time of restarting, no home return operation is required.

Japanese Patent Laid-Open No. 5-89480 JP 2002-139352 A

  As described above, in the incremental type displacement detection device that needs to perform the origin return operation by reciprocating the main scale at most once in order to detect the origin pattern at the time of restart, the displacement and shape of the measurement surface of the member to be measured When the measured member is out of the detection range, the absolute position cannot be reproduced by the relative position detection unit.Therefore, the origin return process for obtaining the absolute position must be performed using the absolute position detection unit. I must. For this reason, the operation of moving the object to be measured once in the vertical direction and acquiring the absolute position becomes unnecessary, and wasteful measurement time is generated.

  In view of the above-described conventional problems, an object of the present invention is to provide an incremental displacement detection device that detects the displacement of a surface to be measured of a member to be measured that is relatively movable in a direction perpendicular to the measurement direction. An object of the present invention is to detect the absolute position at a high speed and return to the origin without performing a moving operation in the height direction when detecting based on the measurement light reflected by the measurement surface.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

  That is, the present invention is a displacement detection device that detects a displacement of a measurement target surface of a measurement target member movable in a direction perpendicular to a measurement direction based on measurement light reflected by the measurement target surface. A relative position detector and an absolute position detector for optically detecting the relative position and the absolute position in the measurement direction based on the measurement light reflected by the measurement surface of the member to be measured, and the movement of the member to be measured An absolute position detection region for moving the optical axis of the measurement light at the end of the direction, and the absolute position detection unit detects the absolute position by moving the optical axis of the measurement light in the absolute position detection region. And the position information obtained by the relative position detector is restored.

  In the displacement detection device according to the present invention, the optical axis of the measurement light may be moved in the absolute position detection region by, for example, an inclined reflecting surface.

  Moreover, the displacement detection apparatus according to the present invention can move the optical axis of the measurement light in the absolute position detection region by changing the refractive index, for example.

  In the displacement detection device according to the present invention, the optical axis of the measurement light can be moved by, for example, a diffraction grating in the absolute position detection region.

  Further, in the displacement detection device according to the present invention, the relative position detection unit includes, for example, a light receiving unit that receives measurement light reflected by a measurement surface of the measurement target member via a reflective diffraction grating, The relative position information of the measurement surface in the measurement direction can be output based on the light detection output obtained by the light receiving unit.

  Further, in the displacement detection device according to the present invention, the relative position detection unit includes, for example, a light receiving unit that receives measurement light reflected by a measurement surface of the measurement target member via a transmission diffraction grating, The relative position information of the measurement surface in the measurement direction can be output based on the light detection output obtained by the light receiving unit.

  In the displacement detection apparatus according to the present invention, the absolute position detection unit includes, for example, a two-divided light receiving unit that receives measurement light reflected in the absolute position detection region, and the light obtained by the two-divided light receiving unit. Based on the detection output, absolute position information of the measurement surface in the measurement direction can be output.

  Further, in the displacement detection device according to the present invention, the absolute position detection unit includes, for example, a four-divided light reception unit that receives measurement light reflected in the absolute position detection region via an astigmatism generation unit, Based on the light detection output obtained by the four-divided light receiving unit, the absolute position information of the measurement surface in the measurement direction can be output.

  According to the present invention, by having the absolute position detection region that moves the optical axis of the measurement light at the end in the moving direction of the member to be measured, the absolute position detection unit allows the light of the measurement light in the absolute position detection region. The absolute position can be detected by moving the shaft, and the position information obtained by the relative position detector can be restored, and the displacement of the measured surface of the measured member movable in the direction perpendicular to the measuring direction In the displacement detection device that detects based on the measurement light reflected by the surface to be measured, when the member to be measured is out of the detection range, the absolute position can be set at a high speed only by returning the member to be measured to the detection range. Detect and return to origin.

It is a block diagram which shows the structural example of the displacement detection apparatus to which this invention is applied. It is a side view which shows typically the structural example of the reflection type diffraction grating with which the said displacement detection apparatus was equipped. It is a block diagram which shows the structure of the relative position information output part in the relative position information detection part with which the said displacement detection apparatus was equipped. It is a block diagram which shows the structure of the absolute position information detection part with which the said displacement detection apparatus was equipped. It is a wave form diagram which shows the waveform of the absolute position signal obtained by the said absolute position information detection part. It is a side view which shows typically the structural example of the to-be-measured member which has the absolute position information area which moves the optical axis of measurement light with the inclined reflective surface in the said displacement detection apparatus. It is a figure which shows typically the relationship between the irradiation spot on the to-be-measured surface of the 1st light beam irradiated to the to-be-measured surface of the to-be-measured member in the said displacement detection apparatus, and the diffraction position on a diffraction grating. The side view which shows typically the other structural examples (A), (B), (C) of the to-be-measured member which has the absolute position information area which moves the optical axis of measurement light with the inclined reflective surface in the said displacement detection apparatus. It is. It is a side view which shows typically the other structural example of the to-be-measured member which has the absolute position information area which moves the optical axis of measurement light by the change of the refractive index in the said displacement detection apparatus. It is a side view which shows typically the other structural example of the to-be-measured member which has the absolute position information area which moves the optical axis of measurement light using the diffracted light by the diffraction grating in the said displacement detection apparatus. It is a side view which shows typically the diffracted light by the diffraction grating in the said absolute position information area. It is a side view which shows typically the movement of the optical axis of the measurement light using the diffracted light by the diffraction grating in the said absolute position information area. It is a figure which shows the change of the zero cross position of the absolute position signal obtained by the said absolute position information detection part. It is a block diagram which shows the other structural example of the displacement detection apparatus to which this invention is applied. FIG. 4 is a side view schematically showing a state of reflection of a first light beam irradiated on a measurement target surface of a measurement target member and diffraction by a transmission type diffraction grating in the displacement detection device. It is a block diagram which shows the other structural example of the displacement detection apparatus to which this invention is applied. It is a top view which shows the structure of the 4-part light-receiving part with which the light-receiving part of the absolute position information detection part in the said displacement detection apparatus is equipped. It is a figure which shows an example of the irradiation image by the 1st light beam irradiated to the 4-part light-receiving part of the said light-receiving part via the astigmatism generation part in the said displacement detection apparatus. It is a characteristic view which shows the characteristic of the focus error signal detected by the absolute position information detection part in the said displacement detection apparatus.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
The present invention is applied to, for example, a displacement detection apparatus 100 configured as shown in the block diagram of FIG.

  The displacement detection device 100 detects the displacement of the measurement target surface 1a of the measurement target member 1 that can move relative to the direction X perpendicular to the measurement direction Z based on the measurement light L1 reflected by the measurement target surface 1a. A light source 10, a light beam splitting unit 12 that splits the measurement light L 0 emitted from the light source 10 into two light beams L 1 and L 2, a diffraction grating 15, a reflecting mirror 18, and the member to be measured 1. A relative position detector 20 and an absolute position detector 30 for optically detecting the relative position and the absolute position in the measurement direction Z based on the measurement light L1 reflected by the surface to be measured 1a.

  Examples of the light source 10 include a semiconductor laser diode, a super luminescence diode, a gas laser, a solid-state laser, and a light emitting diode.

  When a light source having a long coherence distance is used as the light source 10, the tilt tolerance is widened because the light source 10 is not easily affected by the difference in the optical path length between the object light and the reference light due to the tilt of the measured surface 1a of the member 1 to be measured. Further, as the coherence distance of the light source 10 becomes shorter, noise due to unnecessary interference of stray light can be prevented, and highly accurate measurement can be performed.

  Further, when a single mode laser is used as the light source 10, it is desirable to control the temperature of the light source 10 in order to stabilize the wavelength. In addition, high-frequency superimposition or the like may be added to the light of the single mode laser to reduce the coherence of the light. Further, even when a multi-mode laser is used, by controlling the temperature of the light source 10 with a Peltier element or the like, noise due to unnecessary interference of stray light can be prevented and more stable measurement can be performed.

  The measurement light L0 emitted from the light source 10 is incident on the light beam splitting unit 12 via a lens 11 made of a collimator lens or the like. The lens 11 collimates the measurement light L0 emitted from the light source 10 into parallel light. Therefore, the measurement light L0 collimated into parallel light by the lens 11 is incident on the light beam splitting unit 12.

  The beam splitting unit 12 splits the collimated measurement light L0 into a first light beam L1 that is object light and a second light beam L2 that is reference light. The first light beam L1 is irradiated as object light on the member to be measured 1 via the first phase plate 13 and the objective lens 14, and the second light beam L2 is used as the reference light with the second phase plate 16 and The light is applied to the reflecting mirror 18 through the condenser lens 17. The light beam splitting unit 12 includes, for example, a polarization beam splitter that reflects s-polarized light and transmits p-polarized light in the measurement light L0 incident from the light source 10.

  In the light beam splitting unit 12, the measurement light L0 is split into a first light beam L1 and a second light beam L2, and the ratio of the light amount is measured when the member 1 to be measured 1 enters the light receiving unit 20A of the relative position detection unit 20. It is preferable to set the ratio so that the same amount of light is obtained on each of the side and the reflector 18 side.

  Further, a polarizing plate may be provided between the light source 10 and the light beam splitter 12. As a result, it is possible to remove leakage light and noise that are slightly present as polarization components orthogonal to each polarization.

  The first phase plate 13 and the second phase plate 16 are each composed of a quarter wavelength plate or the like.

  Furthermore, the objective lens 14 and the condensing lens 17 condense the first light beam L1 and the second light beam L2 into convergent light that converges on the diffraction grating 15.

  Thereby, the fall of the amplitude of the interference signal which arises when the measured surface 1a of the measured member 1 is tilted (tilted) can be suppressed. Further, the diameter of the beam irradiated on the measured surface 1a of the measured member 1 may be adjusted according to the purpose of use, such as condensing the light beam L2 on the measured surface 1a of the measured member 1.

  The member to be measured 1 reflects the first light beam L1 to the diffraction grating 15. In addition, as the member to be measured 1, a mirror or the like having the surface to be measured 1a as a mirror surface is used. A detailed configuration example of the member 1 to be measured will be described later.

  The diffraction grating 15 is a reflection type diffraction grating that reflects and diffracts incident light.

  Then, the member 1 to be measured reflects the first light beam L1 diffracted by the diffraction grating 15 and returns it to the light beam splitting unit 12 again. The diffraction grating 15 is substantially perpendicular to the measured surface 1a of the member 1 to be measured, that is, the angle formed by the diffraction surface of the diffraction grating 15 and the measured surface 1a of the member 1 to be measured is approximately 90 °. Has been placed.

  The accuracy with which the diffraction grating 15 is arranged with respect to the member 1 to be measured is variously set according to the measurement accuracy required for the displacement detection device 100. That is, when high accuracy is required for the displacement detection device 100, it is preferable to arrange the diffraction grating 18 in a range of 90 ° ± 0.5 ° with respect to the measured surface 1 a of the measured member 1. On the other hand, even when the diffraction grating 15 is disposed in the range of 90 ° to ± 2 ° with respect to the measured surface 1a of the member 1 to be measured, the displacement detection device 100 is used for low-accuracy measurement of a machine tool or the like. Is enough.

  Further, the first light beam L1 incident on the diffraction grating 15 is reflected and diffracted by the diffraction grating 15. The grating pitch Λ of the diffraction grating 15 is set so that the diffraction angle is substantially equal to the incident angle to the diffraction grating 15. That is, it is preferable to set the grating pitch Λ of the diffraction grating 15 to a value satisfying the following expression 1, where θ is the incident angle to the surface 1a to be measured and λ is the wavelength of light. As described above, since the diffraction grating 15 is arranged at a right angle to the measurement surface 1a of the member 1 to be measured, the incident angle to the diffraction grating 15 is π / 2−θ.

  Λ = λ / (2sin (π / 2−θ)) Equation 1

  Therefore, the first light beam L1 divided by the light beam splitting unit 12 is reflected by the diffraction grating 15 and diffracted and incident on the measured surface 1a of the measured member 1 again. It is reflected by the surface to be measured 1a and overlaps the optical path when entering the diffraction grating 15. As a result, the first light beam L1 diffracted by the diffraction grating 15 returns to the same point as the irradiation spot P1 irradiated from the light beam splitting unit 12 to the measured surface 1a of the measured member 1. Then, the first light beam L1 is reflected again by the measured surface 1a of the member 1 to be measured, and returns to the light beam dividing unit 12 through the same optical path as the light beam irradiated from the light beam dividing unit 12.

  As the diffraction grating 15, for example, a diffraction grating 15A having a structure as shown in the side view of FIG. 2 is used.

This diffraction grating 15A is a so-called blazed diffraction grating in which the cross-sectional shape of the groove is formed in a sawtooth shape. According to the diffraction grating 15A, diffraction of the first light beam L1 that is object light reflected by the measurement surface 1a of the member 1 to be measured and the second light beam L2 that is reference light reflected by the reflecting mirror 18 is performed. Efficiency can be increased and signal noise can be reduced.
Further, as shown in FIG. 1, the reflecting mirror 18 reflects the second light beam L <b> 2 divided by the light beam dividing unit 12 to the diffraction grating 15. The reflecting mirror 18 is provided at a position facing the member to be measured 1 with the diffraction grating 15 interposed therebetween. The reflecting surface of the reflecting mirror 18 is disposed substantially parallel to the measured surface 1 a of the measured member 1. Therefore, the reflecting mirror 18 and the diffraction grating 15 are arranged so that the angle formed by the reflecting surface of the reflecting mirror 18 and the diffraction surface of the diffraction grating 15 is approximately 90 °.

  The reflecting mirror 18 reflects the second light beam L2 diffracted by the diffraction grating 15 again and returns it to the light beam splitting unit 3. Note that the second light beam L2 reflected by the reflecting mirror 18 and diffracted by the diffraction grating 15 also passes through the same optical path as the light beam when irradiated from the light beam splitting unit 12, similarly to the first light beam L1. Return to the beam splitting unit 12.

  The reflecting mirror 18 is arranged so that the optical path length from the light beam splitting unit 12 to the diffraction grating 15 in the first light beam L1 is equal to the optical path length from the light beam splitting unit 12 to the diffraction grating 15 in the second light beam L2. Is done. By providing the reflecting mirror 18, it is possible to easily adjust the optical path length of the first light beam L1, the optical path length of the second light beam L2, and the angle of the optical axis when manufacturing the displacement detecting device 100. . As a result, the light source 10 can be made less susceptible to wavelength fluctuations due to changes in atmospheric pressure, humidity, and temperature.

  As described above, the reflecting surface of the reflecting mirror 18 and the diffractive surface of the diffraction grating 15 are preferably arranged at substantially right angles, similarly to the relationship between the measured surface 1a of the measured member 1 and the diffraction grating 15. Thereby, the optical path when it is diffracted by the diffraction grating 15 and again enters the reflecting surface of the reflecting mirror 18 is overlapped with the optical path when it is reflected by the reflecting mirror 18 and enters the diffraction grating 15.

  Further, the light beam splitting unit 12 superimposes the first light beam L1 and the second light beam L2 reflected and returned from the member to be measured 1 and the reflecting mirror 18, and irradiates the light receiving unit 20A of the relative position detecting unit 20 with each other. To do. That is, the light beam splitting unit 12 in the displacement detection device 100 serves as a light beam splitting unit that splits the measurement light L0 into the first light beam L1 and the second light beam L2, and the first light beam L1 and the second light beam. It has a role as a light beam coupling part for superimposing L2.

  Here, the length from the beam splitting unit 12 to the beam splitting unit 12 via the member 1 to be measured and the diffraction grating 15 and the beam splitting unit 12 from the beam splitting unit 12 through the reflecting mirror 18 and the diffraction grating 15 to the beam splitting unit 12. The length until returning is set to be approximately equal. That is, since the optical path lengths of the first light beam L1 and the second light beam L2 are set to be equal, even if there is a wavelength variation of the light source due to changes in atmospheric pressure, humidity, or temperature, the first light beam L1 and the second light beam L2 Can be equally affected. As a result, there is no need to perform atmospheric pressure correction, humidity correction, and temperature correction, and stable measurement can be performed regardless of the surrounding environment.

  The relative position detection unit 20 includes a light receiving unit 20A and a relative position information output unit 20B.

  The light receiving unit 20A of the relative position detecting unit 20 is condensed by the condensing lens 21 on which the first light beam L1 and the second light beam L2 superimposed by the light beam dividing unit 12 are incident, and the light is collected by the condensing lens 21. A first mirror L1 and a second beam L2, that is, a half mirror 22 that splits incident light, a first polarization beam splitter 23 on which incident light split by the half mirror 22 is incident, and the half mirror 22 A second polarization beam splitter 25 is provided on which the divided incident light is incident via a light receiving side phase plate 24 made of, for example, a quarter wavelength plate.

  The first polarizing beam splitter 23 and the second polarizing beam splitter 25 reflect the interference light having the s-polarized component and transmit the interference light having the p-polarized component, so that the first light beam L1 and the second light beam L2 are transmitted. The interference light with the light beam L2 is split.

  The first polarizing beam splitter 23 is arranged so that the polarization direction of the incident light beam is inclined 45 degrees with respect to the incident surface. A first light receiving element 26 and a second light receiving element 27 are provided on the light exit side of the first polarizing beam splitter 23. A third light receiving element 28 and a fourth light receiving element 29 are provided on the light exit side of the second polarizing beam splitter 25.

  Also, as shown in FIG. 3, the relative position information output unit 20B of the relative position detection unit 20 includes a first differential amplifier 61a, a second differential amplifier 61b, and a first A / D converter 62a. A second A / D converter 62b, a waveform correction processing unit 63, and an incremental signal generator 64.

  In the first differential amplifier 61a, the first light receiving element 26 and the second light receiving element 27 of the light receiving unit 20A are connected to the input end, and the second A / D converter 62b is connected to the output end. . In the second differential amplifier 61b, the third light receiving element 28 and the fourth light receiving element 29 of the light receiving unit 20A are connected to the input end, and the second A / D converter 62b is connected to the output end. ing. The first A / D converter 62 a and the second A / D converter 62 b are connected to the waveform correction processing unit 63. The waveform correction processing unit 63 is connected to an incremental signal generator 64.

  As shown in FIG. 1, the absolute position detection unit 30 includes a light receiving unit 31 provided so as to face the diffraction grating 15 and an absolute position information output unit 32 connected to the light receiving unit 31.

  The light receiving unit 31 of the absolute position detecting unit 30 receives reflected light (0th order light) reflected from the diffraction grating surface of the first light beam L1 incident on the diffraction grating 15.

  For example, as shown in FIG. 4, the light receiving unit 31 includes a two-divided light receiving unit having a fifth light receiving element 31A and a sixth light receiving element 31B.

  The two-divided light receiving unit 31 includes the fifth light receiving element 31A and the first light receiving element 31A along the direction in which the beam spot of reflected light moves (shifts) when the measured surface 1a of the measured member 1 is displaced in the height direction. Six light receiving elements 31B are arranged side by side. The fifth light receiving element 31 </ b> A and the sixth light receiving element 31 </ b> B are connected to a differential comparator 32 </ b> A constituting the absolute position information output unit 32.

  The light receiving unit 31 of the absolute position detecting unit 30 converts the light detected by the fifth light receiving element 31A and the sixth light receiving element 31B into electric energy (photoelectric conversion) to generate an output signal, and performs differential comparison. Output to the device 32A.

  When the measured surface 1a of the measured member 1 is displaced in the height direction, the reflected light of the first light beam L1 shifts from, for example, the fifth light receiving element 31A to the sixth light receiving element 31B. Then, when the photoelectrically converted signal is passed through the differential comparator 32A, a change in signal output as shown in FIG. 5 is obtained. The absolute position in the height direction of the measured surface 1a of the member 1 to be measured can be detected by comparing the relative position information with the zero cross position in the change in signal output shown in FIG. 5 as an absolute position.

  Here, the member 1 to be measured in the displacement detection apparatus 100 will be described.

  In general, a mirror or the like is used as the member to be measured 1 that reflects light from the light source 10. As shown in FIG. 6, the member 1 to be measured has a substrate 2 and a reflective film 3 laminated on the substrate 2. The reflective film 3 is processed extremely flat. Further, it is possible to detect a more accurate displacement in the height direction by flattening the surface. Furthermore, the reflective film 3 may reflect only a specific wavelength including the wavelength of the measurement light L1.

  In the displacement detection device 100, the member 1 to be measured has an absolute position detection region 4 in which inclined reflecting surfaces 4A for moving the optical axis of the measurement light L1 are formed at both ends in the moving direction.

  The absolute position detection unit 30 in the displacement detection apparatus 100 performs absolute position detection by moving the optical axis of the measurement light L1 by the inclined reflecting surface 4A in the absolute position detection region 4 of the member 1 to be measured. be able to.

  In the displacement detection device 100 having such a configuration, the first light beam L1 and the second light beam L2 that are superimposed by the light beam splitting unit 12 and incident on the light receiving unit 20A of the relative position detection unit 20 are the first polarized light. Each of the beam splitters 23 has a p-polarized component and an s-polarized component. Therefore, the first light beam L1 and the second light beam L2 that have passed through the first polarizing beam splitter 23 interfere with each other in polarized light having the same polarization direction. Therefore, the first light beam L1 and the second light beam L2 can be caused to interfere with each other by the first polarization beam splitter 23.

  Similarly, in the first light beam L1 and the second light beam L2 reflected by the first polarization beam splitter 23, polarized light having the same polarization direction interferes with the first polarization beam splitter 23. For this reason, the first polarization beam splitter 23 can cause interference.

  The interference light with the first light beam L1 and the second light beam L2 reflected by the first polarization beam splitter 23 is received by the first light receiving element 26. Further, the interference light with the first light beam L1 and the second light beam L2 transmitted through the first polarization beam splitter 23 is received by the second light receiving element 27. Here, the signals photoelectrically converted by the first light receiving element 26 and the second light receiving element 27 are signals having a phase difference of 180 degrees.

  Accordingly, an interference signal of Acos (Kz + δ) is obtained by the first light receiving element 26 and the second light receiving element 27. A is the amplitude of interference, and K is the wave number represented by 2π / Λ. Z represents the amount of movement of the first light beam L1 on the diffraction grating 15, and δ represents the initial phase. Λ is the pitch of the grating in the diffraction grating 4.

  Here, as shown in FIG. 7, when the member 1 to be measured moves by z / 2 in the height direction, the first light beam L1 irradiated on the surface to be measured 1a of the member 1 to be measured is emitted from the irradiation spot P1. Move to the irradiation spot P2. Further, the first light beam L1 reflected by the measured surface 1a of the measured member 1 moves from the diffraction position T1 of the diffraction grating 15 to the diffraction position T2. Here, since the diffraction grating 15 is disposed substantially perpendicular to the measurement surface 1a of the member 1 to be measured, the distance between the diffraction position T1 and the diffraction position T2 is the distance between the irradiation spot P1 and the irradiation spot P2. Double z. That is, the amount of movement of the first light beam L1 that moves on the diffraction grating 15 is z that is twice that when the member 1 to be measured is moved.

  Further, since the diffraction grating 15 is disposed substantially perpendicular to the measurement surface 1a of the member 1 to be measured, even if the member 1 to be measured is displaced in the height direction, the distance between P2 and T2 and P2 Since the distance between -P1 and T1 is constant, it can be seen that the optical path length of the first light beam L1 is always constant. That is, the wavelength of the first light beam L1 does not change. When the member 1 to be measured is displaced in the height direction, only the position incident on the diffraction grating 15 changes.

  Therefore, the phase of Kz is added to the diffracted first light beam L1. That is, when the member 1 to be measured moves by z / 2 with respect to the height direction, the first light beam L1 moves by z on the diffraction grating 15. Therefore, the first light beam L1 is added with the phase of Kz, and the first light receiving element 26 and the second light receiving element 27 receive the interference light that causes the light of one period to be bright and dark.

  Here, the interference signal obtained by the first light receiving element 26 and the second light receiving element 27 does not include a component related to the wavelength of the light source 10. Therefore, even if the light source wavelength varies due to changes in atmospheric pressure, humidity, and temperature, the interference intensity is not affected.

  On the other hand, the light beam La transmitted through the half mirror 22 is incident on the second polarization beam splitter 25 via the light receiving side phase plate 24. The light beam La composed of the first light beam L1 and the second light beam L2, which are linearly polarized light whose polarization directions are different from each other by 90 degrees, is transmitted through the light receiving side phase plate 24 and becomes circularly polarized light in the opposite directions. Since the circularly polarized light in the opposite directions are on the same optical path, the circularly polarized light becomes linearly polarized light by being superimposed, and is incident on the second polarization beam splitter 25.

  The s-polarized component of this linearly polarized light is reflected by the second polarization beam splitter 25 and received by the third light receiving element 28. The p-polarized component passes through the second polarizing beam splitter 25 and is received by the fourth light receiving element 29.

  As described above, the linearly polarized light incident on the second polarizing beam splitter 25 is generated by superimposing the circularly polarized light in the opposite directions. Then, the polarization direction of the linearly polarized light incident on the second polarization beam splitter 25 is rotated by 1/2 when the member 1 to be measured moves by Λ / 2 in the height direction. Accordingly, the third light receiving element 28 and the fourth light receiving element 29 can similarly obtain an interference signal of Acos (Kz + δ ′). δ 'is an initial phase.

  Further, the signals photoelectrically converted by the third light receiving element 28 and the fourth light receiving element 29 have a phase difference of 180 degrees.

  In this displacement detection apparatus 100, the second polarization beam splitter 26 that divides the light beam received by the third light receiving element 28 and the fourth light receiving element 29 with respect to the first polarizing beam splitter 23 is 45. It is tilted. For this reason, the signals obtained in the third light receiving element 28 and the fourth light receiving element 29 are 90 degrees out of phase with the signals obtained in the first light receiving element 26 and the second light receiving element 27.

  Therefore, for example, a signal obtained by the first light receiving element 26 and the second light receiving element 27 is used as a sin signal, and a signal obtained by the third light receiving element 28 and the fourth light receiving element 29 is used as a cosine signal. Can be obtained.

  Signals obtained by these light receiving elements 26 to 29 are calculated by the relative position information output unit 20B, and the displacement amount of the measured surface 1a is counted.

  In the relative position information output unit 20B, first, the first differential amplifier 61a differentially amplifies signals obtained by the first light receiving element 26 and the second light receiving element 27 of the light receiving unit 20A with phases different from each other by 180 degrees. The DC component of the interference signal is canceled.

  This signal is A / D converted by the first A / D converter 62a, and the signal amplitude, offset, and phase are corrected by the waveform correction processing unit 63. This signal is output from the incremental signal generator 64 as an A-phase incremental signal, for example.

  Similarly, the signals obtained by the third light receiving element 35 and the fourth light receiving element 36 are differentially amplified by the second differential amplifier 61b and A / D by the second A / D converter 62b. Converted. Then, the signal amplitude, offset, and phase are corrected by the waveform correction processing unit 63 and output from the incremental signal generator 64 as a B phase incremental signal that is 90 degrees different from the A phase.

  The two-phase incremental signal obtained in this way is discriminated forward / reversely by a pulse discriminating circuit (not shown) or the like, whereby the amount of displacement in the height direction of the measured surface 1a of the member 1 to be measured becomes positive in the positive direction. Whether it is negative or negative can be detected.

  Further, by counting the number of pulses of the incremental signal with a counter (not shown), it is possible to measure how many of the above-mentioned periods the interference light intensity of the first light beam L1 and the second light beam L2 has changed. Thereby, the amount of displacement of the measured surface 1a of the measured member 1 is detected.

  Note that the relative position information output from the relative position information output unit 20B in the displacement detection apparatus 100 may be the above-described two-phase incremental signal, or a signal including the displacement amount and the displacement direction calculated therefrom. May be.

  The displacement detection apparatus 100 has the absolute position detection region 4 in which the inclined reflection surfaces 4A for moving the optical axis of the measurement light L1 are formed at both ends in the movement direction X of the member 1 to be measured. The detection unit 30 can perform absolute position detection by moving the optical axis of the measurement light L1 in the absolute position detection region 4, and when the member 1 to be measured is out of the detection range, the measurement target is measured. By simply returning the member 1 to the detection range, the absolute position can be detected at high speed, and the relative position information obtained by the relative position information detection unit 20 can be reset or preset to return to the origin.

  Here, when it is necessary to make the surface of the member 1 to be measured flat, for example, as shown in the member 1A to be measured shown in FIG. By sealing the absolute position detection region 4 in which the optical axis of the measuring light L1 is moved by the reflecting surface 4A with a light-transmitting member 5, it can be made flat.

  Further, as shown in a member to be measured 1B shown in FIG. 8B, the member to be measured includes an absolute position detection region 4 in which the optical axis of the measuring light L1 is moved by the inclined reflecting surfaces 4A at both ends of the member to be measured 1. A flat surface can be obtained by sealing the entire measurement surface 1 a with a light-transmitting member 5.

  Further, the inclined direction may be reversed by the inclined reflecting surfaces 4A formed in the absolute position detection regions 4 at both ends of the member 1 to be measured, as in the member 1C to be measured shown in FIG. Further, the sloped reflecting surface 4B may be formed in the absolute position detection regions 4 at both ends.

  Further, the absolute position detection regions 4 at both ends in the movement direction X of the member to be measured 1 may be any region having a function of moving the optical axis of the measurement light L1, and the member to be measured 1D shown in FIG. As described above, the absolute position detection regions 4D having a function of moving the optical axis of the measurement light L1 by changing the refractive index can be provided at both ends of the movement direction X of the member 1 to be measured.

  In this way, the absolute position detection region 4D having the function of moving the optical axis of the measurement light L1 by the change in the refractive index has a configuration in which the refractive index of the seal member at the edge portion of the member to be measured is different from the other portions, It can be set as the area | region which gave the change to the refractive index distribution of the glass by an ion exchange method.

  Further, the absolute position detection region 4 having a function of moving the optical axis of the measurement light L1 is, for example, light of the measurement light L1 using diffracted light by a diffraction grating as in the member to be measured 1E shown in FIG. The axis can be moved.

  Like the member to be measured 1E, an absolute position detection region 4E in which a diffraction grating 4e is arranged on the outer periphery of the member to be measured is provided.

  In this member to be measured 1E, as shown in FIG. 11, when the measurement light L1 is incident on the outer peripheral absolute position detection region 4E, diffracted light L12 is obtained in addition to the reflected light L11 of the measurement light L1. The diffraction angle θ12 of the diffracted light L12 is given by sin θ11 + sin θ12 = nλ / d, where n is the order, λ is the incident wavelength, and d is the grating pitch.

  Therefore, in this displacement detection apparatus 100, the reflected light L11 is incident on the fifth light receiving element 31A and the diffracted light L12 is incident on the sixth light receiving element 31B. If the reflected light on the diffraction grating 1e of the member to be measured 1E is L11 <L12, the fifth light receiving element 31A and the sixth light receiving element 31B obtained by the differential comparator 32A The differential output is zero-crossed at the boundary between the partial absolute position detection region 4E where the diffraction grating 1e of the member to be measured 1E is disposed and the part where there is no diffraction grating.

  That is, since the reflected light L11 is incident on the fifth light receiving element 31A at θ1, the zero cross position x varies depending on the position in the z direction, as shown in FIGS. By acquiring the correlation between the zero cross position x and the z position in advance, the z position can be determined from the amount of deviation of the zero cross position x using the zero cross signal as a trigger.

  In the displacement detection apparatus 100, the relative position information detection unit 20 includes a light receiving unit 20A that receives the measurement light L1 reflected by the measurement surface 1a of the measurement target member 1 through the reflective diffraction grating 18. Based on the light detection output obtained by the light receiving unit 20A, the relative position information of the measurement surface 1a in the measurement direction Z is output from the relative position information output unit 20B. For example, the displacement detection shown in FIG. Like the apparatus 100A, a light receiving unit 20A that receives the measurement light L1 reflected by the measurement surface 1a of the member 1 to be measured through the transmission diffraction grating 15A is provided, and the light detection output obtained by the light reception unit 20A is obtained. Based on this, the relative position information of the measurement surface 1a in the measurement direction Z can be output from the relative position information output unit 20B.

  That is, similarly to the displacement detection device 100, the displacement detection device 100A shown in FIG. 14 detects the displacement of the measurement surface 1a of the measurement target member 1 that can be relatively moved in the direction X perpendicular to the measurement direction Z. Detecting based on the measurement light L1 reflected by the surface 1a, the light source 10, the light beam splitting unit 12 for dividing the measurement light L0 emitted from the light source 10 into two light beams L1 and L2, and transmission The relative position and absolute position in the measurement direction Z are determined based on the measurement light L1 reflected by the measurement target surface 1a of the member under measurement 1 and the diffraction grating 15A of the mold, the reflection mirror 18, the return reflection mirror block 19, and A relative position detector 20 and an absolute position detector 30 for optically detecting the position are provided.

  In addition, in this displacement detection apparatus 100A, about the component which is common in the said displacement detection apparatus 100, the same code | symbol is attached | subjected in the figure and the overlapping description is abbreviate | omitted.

  In this displacement detection device 100A, the measurement light L0 emitted from the light source 10 is incident on the light beam splitting unit 12 as convergent light by the lens 11A, and the light beam splitting unit 12 uses the first light beam L1 that is object light and the reference light. It is divided into a certain second light beam L2.

  The first light beam L1 divided by the light beam splitting unit 12 is incident on the first irradiation spot Pc1 on the measured surface 1a of the member 1 to be measured via the first phase plate 13, and the measured surface 1a. The light is reflected and incident on the transmissive diffraction grating 15A.

  The diffraction grating 15A is a transmissive diffraction grating that transmits and diffracts incident light.

  In this displacement detection device 100A, the transmission type diffraction grating 15A is provided in place of the reflection type diffraction grating 18 in the displacement detection device 100.

  Then, the first light beam L1 incident on the transmission type diffraction grating 15A passes through the transmission type diffraction grating 15A and is diffracted once, and the first light beam L1 on the measurement surface 1a of the member 1 to be measured is obtained. The incident light enters a second irradiation spot Pd1 different from the first irradiation spot Pc1, is reflected by the surface to be measured 1a, and is incident on the first reflecting surface 19A of the return reflector block 19.

Further, the first light beam L1 incident on the transmission type diffraction grating 15A passes through the transmission type diffraction grating 15A and enters the light receiving unit 31 of the absolute position detection unit 30.
In the absolute position detection unit 30, the first light beam L1 that is transmitted through the transmission type diffraction grating 15A and incident thereon is received by the light receiving unit 31, and the fifth light receiving element 31A and the sixth light receiving element 31B perform photoelectric conversion. Based on the detection signal obtained by conversion, the zero cross position of the differential output obtained by the differential comparator 32A is set as an absolute position and compared with relative position information to thereby measure the height of the measured surface 1a of the measured member 1 Absolute position detection in direction Z is performed.

  The second light beam L2 divided by the light beam splitting unit 12 is incident on the reflecting mirror 18 through the second phase plate 16, and the measured surface 1a of the member 1 to be measured is passed through the reflecting mirror 18. The light enters the first irradiation spot Sc1, is reflected by the surface to be measured 1a, and enters the transmissive diffraction grating 15A.

  Then, the second light beam L2 incident on the transmission type diffraction grating 15A passes through the transmission type diffraction grating 15A and is diffracted once, so that the first irradiation on the reflection surface of the reflection mirror 18 is performed. The incident light enters a second irradiation spot Sd1 different from the spot Sc1, is reflected by the reflecting surface, and is incident on the second reflecting surface 19B of the return reflector block 19.

  Here, in the lens 11A, the first light beam L1 and the second light beam L2 divided by the light beam dividing unit 12 are the first reflection surface 19A and the second reflection surface 19B of the return reflector block 19, respectively. The measurement light L0 emitted from the light source 10 is caused to enter the light beam splitting unit 12 as converged light so as to converge at the light receiving unit 31 of the absolute position detection unit 30.

  The return reflecting mirror block 19 is a substantially triangular mirror having a first reflecting surface 19A and a second reflecting surface 19B. The first reflecting surface 19A is connected to the surface to be measured 1a of the member to be measured 1 along the same optical path as when the first light beam L1 reflected and incident on the surface to be measured 1a of the member to be measured 1 is reflected. The light is returned to the light beam splitter 12 through the transmission type diffraction grating 15A. Further, the second reflecting surface 19B reflects the reflecting surface of the reflecting mirror 18 and the transmission type diffraction in the same optical path as when the second light beam L2 reflected and incident on the reflecting surface of the reflecting mirror 18 is reflected. It returns to the light beam splitting unit 12 through the grating 15A.

  In the displacement detection apparatus 100A, the relative position detection unit 20 converts the superimposed first light beam L1 and second light beam L2 reflected from the member 1 to be measured and the reflecting mirror 18 and returned to the light beam splitting unit 3. The light receiving unit 20A receives the relative position information in the measurement direction Z of the surface to be measured 1a based on the light detection output obtained by the light receiving unit 20A in the same manner as the displacement detection device 100. Output from the output unit 20B.

  Here, in this displacement detection apparatus 100A, the transmissive diffraction grating 15A is disposed substantially perpendicular to the measurement surface 1a of the member 1 to be measured, and as shown in FIG. The first light beam L1 incident on the first irradiation spot Pc1 at the incident angle θ1 is incident at the incident angle π / 2−θ1. Furthermore, the first light beam L1 is incident on the second irradiation spot Pd1 on the measured surface 1a of the measured member 1 at an incident angle θ2.

  The grating pitch Λ of the diffraction grating 15A is preferably set so that the diffraction angle is substantially equal to the incident angle to the diffraction grating 15A. That is, as described above, the grating pitch Λ of the diffraction grating 15A is given by the following equation 2 where θ1 is the first incident angle of the measured surface 1a of the member 1 to be measured, θ2 is the second incident angle, and the wavelength λ is: Meet.

  Λ = nλ / (sin (π / 2−θ1) + sin (π / 2−θ2)) Equation 2

  Note that n is a positive order.

  When the incident angle to the diffraction grating 15A is equal to the diffraction angle, the first irradiation spot Pc1 and the second irradiation spot Pd1 can be configured symmetrically with respect to the diffraction grating 15A. Equation 2 can be expressed by the following Equation 3.

  2Λsin θ = nλ Equation 3

  Is the incident angle and diffraction angle of the diffraction grating 15A.

  That is, the Bragg condition can be satisfied, and the diffracted light diffracted by the diffraction grating 15A can be strengthened.

  Further, the first light beam L1 incident on the measured surface 1a of the measured member 1 at an angle θ2 is reflected by the measured surface 1a of the measured member 1, and the first reflecting surface 19A of the return reflector block 19 is reflected. , Is reflected by the first reflecting surface 19A, follows the same optical path as the going, and again enters the second irradiation spot Pd1 of the measured surface 1a of the measured member 1 at an incident angle θ2.

  Further, the first light beam L1 reflected by the measured surface 1a of the measured member 1 is incident again on the diffraction grating 15A at an angle π / 2−θ2. The second diffraction in the first light beam L1 is diffracted at the diffraction angle π / 2−θ1 under the condition of Equation 1. Then, the first light beam L1 diffracted by the diffraction grating 15A is incident on the first irradiation spot Pc1 of the measured surface 1a of the measured member 1 again at an incident angle θ1. Therefore, the optical path of the returned first light beam L1 reflected by the measured surface 1a of the member 1 to be measured overlaps the optical path of the first light beam L1 that is split by the light beam splitting unit 12.

  When the measured surface 1a of the measured member 1 moves by z / 2 in the height direction, the first light beam L1 irradiated on the measured surface 1a of the measured member 1 is emitted from the first irradiated spot Pc1. Move to the first irradiation spot Pc2. Further, the first light beam L1 reflected by the first irradiation spots Pc1 and Pc2 on the measured surface 1a of the measured member 1 moves from the diffraction position T1 of the diffraction grating 15A to the diffraction position T2. Further, the first light beam L1 diffracted for the first time by the diffraction grating 15A moves from the second irradiation spot Pd1 on the measured surface 1a of the measured member 1 to the second irradiated spot Pd2.

  Here, the diffraction grating 15A is arranged at a substantially right angle to the measurement surface 1a of the member 1 to be measured, and the distance between the diffraction position T1 and the diffraction position T2 is the first irradiation spot Pc1 and the first irradiation. Z is twice the interval between the spots Pc2. That is, the amount of movement of the first light beam L1 that moves on the diffraction grating 15A is z that is twice that when the member 1 to be measured is moved.

  In addition, the diffraction grating 15A is disposed substantially perpendicular to the measurement surface 1a of the member 1 to be measured, and the optical path length of the first light beam L1 is the same even if the member 1 to be measured is displaced in the height direction. Always constant. That is, the wavelength of the first light beam L1 does not change. When the member 1 to be measured is displaced in the height direction, only the position incident on the diffraction grating 15A changes.

  Note that the second light beam L2 applied to the reflecting mirror 18 is the same as the first light beam L1, and thus the description thereof is omitted.

  In this displacement detection apparatus 100A, the first light beam L1 is diffracted twice. Therefore, a phase of 2 Kz is added to the first light beam L1 diffracted twice. K is a wave number represented by 2π / Λ. Z indicates the amount of movement of the first light beam L1 on the diffraction grating 15A. That is, when the member 1 to be measured moves by z / 2 with respect to the height direction, the first light beam L1 moves by twice z on the diffraction grating 15A. Further, by diffracting twice, a phase of 2 Kz is added to the first light beam L1, and interference light that causes light and darkness of light for two periods is received by the light receiving unit 20A of the relative position detection unit 20.

  That is, the first light receiving element 26 and the second light receiving element 27 of the light receiving unit 20A can obtain an interference signal of Acos (2 Kz + δ). Further, the third light receiving element 28 and the fourth light receiving element 29 can obtain an interference signal of Acos (2 Kz + δ ′).

  Therefore, in this displacement detection device 100A, when the grating pitch of the diffraction grating 15A and the grating pitch of the diffraction grating 15 in the displacement detection device 100 are the same, the resolution can be doubled compared to the displacement detection device 100.

  For example, when the grating pitch Λ of the diffraction grating 15A is set to 0.5515 μm, the wavelength λ is set to 780 nm, and the incident angle and the diffraction angle of the diffraction grating 15A are set to 45 °, the measured surface 1a of the measured member 1 is set in the height direction. When moved by 0.5515 μm, the first light beam L1 moves on the diffraction grating 15A twice as much as 0.5515 μm, that is, by two pitches. Further, since the first light beam L1 is diffracted twice, the light intensity of four times can be obtained by the light receiving unit 20A of the relative position detecting unit 20. That is, one period of the obtained signal is 0.5515 μm / 4 = 0.1379 μm.

  Further, in this displacement detection apparatus 100A, the first light beam L1 is irradiated to two locations of the first irradiation spot Pc1 and the second irradiation spot Pd1 on the measured surface 1a of the measured member 1 with a single optical system. Therefore, the measurement point can be canceled with a single optical system.

  Further, with the configuration as described above, even if the measurement surface 1a of the member 1 to be measured is tilted, it is tilted depending on when the first irradiation spot Pc1 is irradiated and when the second irradiation spot Pd1 is irradiated. Can be countered. Therefore, it is difficult for the optical path length of the first light beam L1 to change, and the difference between the optical path length of the first light beam L1 and the optical path length of the second light beam L2 can be reduced.

  Also in this displacement detection apparatus 100A, when the member to be measured 1 having the absolute position detection region 4 for moving the optical axis of the measurement light L1 at both ends in the movement direction X is out of the detection range, the member to be measured 1 Is returned to the detection range, the absolute position information detected by the relative position information detection unit 30 can be used to reset or preset the relative position information obtained by the relative position information detection unit 20 to return to the origin.

  Further, in the displacement detection devices 100 and 100A, the relative position is detected using the absolute position information detected by the absolute position detection unit 30 including the two-divided light receiving unit 31 having the fifth light receiving element 31A and the sixth light receiving element 31B. Although the relative position information obtained by the position information detection unit 20 is reset or preset to return to the origin, the present invention is not limited to the displacement detection devices 100 and 100A. For example, as shown in FIG. Like the displacement detection apparatus 200, the present invention can also be applied to a displacement detection apparatus using an astigmatism method.

  The displacement detection device 200 shown in FIG. 16 detects the displacement of the measured surface 1a of the measured member 1 that can be relatively moved in the direction X perpendicular to the measurement direction Z, like the displacement detection devices 100 and 100A. A light source 210 and a light beam splitter 212 for dividing the measurement light L0 emitted from the light source 210 into two light beams L1 and L2, which are detected based on the measurement light L1 reflected by the measurement surface 1a; Relative position detection unit 220 for optically detecting the relative position and absolute position in the measurement direction Z based on the reflecting mirror 217 and the measurement light L1 reflected by the measurement surface 1a of the member 1 to be measured, and absolute position detection The astigmatism generation unit 240 is provided between the light beam splitting unit 212 and the relative position detection unit 220 and the absolute position detection unit 230.

  In the displacement detection device 200, the light source 210 is constituted by, for example, a semiconductor laser diode, a super luminescence diode, a light emitting diode, or the like. As will be described later, in the displacement detection device 200, measurement is performed using the interference light of the measurement light from the light source 210. Therefore, the longer the coherence distance of the measurement light emitted from the light source 210 is, the wider the measurement range is. Become.

  The measurement light L0 emitted from the light source 210 is incident on the light beam splitting unit 212 through a lens 211 made of a collimator lens or the like. The lens 211 collimates the measurement light L0 emitted from the light source 210 into parallel light.

  The light beam splitting unit 212 splits the collimated measurement light L0 into a first light beam L1 that is object light and a second light beam L2 that is reference light. The first light beam L1 is irradiated as object light to the member 1 to be measured through the first phase plate 213 and the objective lens 214, and the second light beam L2 is used as the reference light with the second phase plate 215 and The light is applied to the reflecting mirror 217 via the condenser lens 216. The light beam splitting unit 212 includes, for example, a polarization beam splitter that reflects s-polarized light and transmits p-polarized light in the measurement light L0 incident from the light source 210.

  The p-polarized first light beam L1 that has passed through the light beam splitting section 212 becomes circularly polarized light by passing through the first phase plate 213 such as a quarter-wave plate, and the object lens 1 to be measured is measured by the objective lens 214. It is condensed on the surface 1a. The higher the NA value of the objective lens 214, the higher the resolution. Conversely, the lower the NA value, the wider the measurement range of the surface to be measured 1a.

  The first light beam L1 collected by the objective lens 214 does not necessarily have to be imaged on the measurement surface 1a. By shifting the imaging position from the surface to be measured 1a and increasing the spot diameter on the surface to be measured 1a, it is possible to reduce the influence of the measurement error due to the surface roughness of the surface to be measured 1a and foreign matter.

  In the displacement detection device 200, the objective lens 214 is fixed.

  Therefore, in this displacement detection device 200, the position where the first light beam L1 is imaged by the objective lens 214 does not vary regardless of the unevenness of the measured surface 1a. For this reason, it can be used as a reference point for obtaining the absolute displacement of the non-measurement surface 1a.

  The first light beam L1 incident on the surface to be measured 1a as object light is reflected by the surface to be measured 1a and again enters the first phase plate 213 such as a quarter-wave plate via the objective lens 214. Is done.

  That is, since the second phase plate 215 such as a quarter-wave plate is disposed on the optical path between the first light beam splitting section 212 and the measured surface 1a of the measured member 1, the object light The first light beam L1 incident on the surface to be measured 1a is transmitted through the first phase plate 213 twice on the forward path toward the surface to be measured 1a and on the return path to the first light beam splitting section 212. The direction is rotated 90 degrees to become s-polarized light. Then, the first light beam L 1 that has become s-polarized light is reflected by the first light beam splitting unit 212 and is incident on the astigmatism generation unit 240.

  The second light beam L2 incident on the reflecting mirror 217 as the reference light is reflected by the reflecting mirror 217 and passes through the condenser lens 216 again to form a second phase plate 215 such as a quarter wavelength plate. Is incident on.

  That is, since the second phase plate 215 such as a quarter-wave plate is disposed on the optical path between the first light beam splitter 212 and the reflecting mirror 217, the second light beam L2 is reflected. By passing through the second phase plate 215 twice on the forward path toward the mirror 217 and on the return path returning to the first light beam splitting section 212, the polarization direction is rotated 90 degrees to become p-polarized light. Then, the second light beam L <b> 2 that has become p-polarized light passes through the first light beam splitting unit 212 and enters the astigmatism generation unit 240.

  The optical path length from the first light beam splitting unit 212 to the reflecting mirror 217 and the focal point position of the first light beam L1 by the objective lens 214 from the first light beam splitting unit 212, that is, the reference point for measuring the absolute displacement. The optical path lengths are preferably equal.

  Thereby, even if there is a wavelength variation of the light source due to changes in atmospheric pressure, humidity, and temperature, it is possible to equalize the effects of the first light beam L1 and the second light beam L2. Therefore, the interference light intensity of the first light beam L1 and the second light beam L2 received by the light receiving unit 220A of the relative position information detection unit 220 can be stabilized regardless of the surrounding environment, and more accurate measurement can be performed. Can do.

  The light beam splitting unit 212 superimposes the first light beam L1 and the second light beam L2 reflected and returned from the member to be measured 1 and the reflecting mirror 217, and enters the astigmatism generation unit 240.

  In this displacement detection device 200, the astigmatism generation unit 240 divides the incident light from the light beam splitting unit 212, that is, the first light beam L 1 and the second light beam L 2 that are superimposed and incident by the light beam splitting unit 212. Astigmatism is generated in the light beam that is divided into directions and is incident on the light receiving unit 221 of the relative position information detecting unit 220 and the light receiving unit 231 of the absolute position information detecting unit 230 and incident on the light receiving unit 231 of the absolute position information detecting unit 230. And includes a condenser lens 241, a beam splitter 242, and a polarizing plate 243.

  In the astigmatism generation unit 240, incident light condensed by the condensing lens 241, that is, the first light beam L 1 and the second light beam L 2 are reflected by the beam splitter 242 and received by the relative position information detection unit 220. The light enters the portion 220A. Further, the incident light transmitted through the beam splitter 242, that is, the first light beam L 1 and the second light beam L 2 are reflected light from the measured surface 1 a of the measured member 1 by transmitting through the polarizing plate 243. Only the first light beam L1 is incident on the light receiving unit 231 of the absolute position information detecting unit 230.

  That is, the polarizing plate 243 is disposed on the optical path of the first light beam L1 and the second light beam L2 that have passed through the beam splitter 242 of the astigmatism generation unit 240, and transmits only the first light beam L1. As a result, only the first light beam L1 that is the reflected light from the measurement surface 1a of the DUT 1 is extracted, the offset light amount is removed, and the light is incident on the light receiving unit 231 of the absolute position information detection unit 230.

  In the astigmatism generation unit 240, astigmatism is generated in the first light beam L 1 incident on the light receiving unit 231 of the absolute position information detection unit 230 by passing through the beam splitter 242.

  Although astigmatism may be generated by arranging a cylindrical lens, in this astigmatism generation unit 240, the beam splitter 242 splits the light beam in two directions and simultaneously generates astigmatism. This is preferable because the score can be reduced.

  In addition, by forming, for example, a chromium film or a dielectric multilayer film on the polarizing plate 243, the function of the astigmatism generation unit 240 as the beam splitter 242 can be combined. In this case, since the operations of the beam splitter 242 and the polarizing plate 243 are realized by one component, the number of components can be reduced.

  In the displacement detection device 200, the relative position information detection unit 220 includes a light receiving unit 220A and a relative position information output unit 220B.

  The light receiving unit 220A of the relative position information detection unit 220 includes a half mirror 221 that divides the first light beam L1 and the second light beam L2 reflected by the beam splitter 242 of the astigmatism generation unit 240 into two light beams, The first polarization beam splitter 222 that divides the first light beam L1 and the second light beam L2 divided by the half mirror 221 and the incident light divided by the half mirror 221 are composed of, for example, a quarter wavelength plate. A second polarization beam splitter 224 that is incident through the phase plate 223 is provided.

  The first polarizing beam splitter 222 and the second polarizing beam splitter 224 reflect the interference light having the s-polarized component and transmit the interference light having the p-polarized component, so that the first light beam L1 and the second light beam L2 are transmitted. The interference light with the light beam L2 is split.

  The first polarizing beam splitter 222 is arranged so that the polarization direction of the incident light beam is inclined 45 degrees with respect to the incident surface. A first light receiving element 226 and a second light receiving element 227 are provided on the light exit side of the first polarizing beam splitter 222. A third light receiving element 228 and a fourth light receiving element 229 are provided on the light exit side of the second polarizing beam splitter 224.

In the light receiving unit 220A of the relative position information detecting unit 220, the first light beam L1 and the second light beam L2 incident on the half mirror 221 are both divided.
The first polarization beam splitter 222 on which the first light beam L1 and the second light beam L2 transmitted through the half mirror 221 are incident is polarized light of the first light beam L1 and the second light beam L2 whose polarization directions are different from each other by 90 degrees. The direction is inclined so that the polarization direction is inclined by 45 degrees with respect to the incident surface of the first polarizing beam splitter 222. Thus, both the first light beam L1 and the second light beam L2 have a p-polarized component and an s-polarized component with respect to the first polarizing beam splitter 222, respectively. Accordingly, the first light beam L1 and the second light beam L2 that have passed through the first polarizing beam splitter 222 become, for example, p-polarized light having the same polarization direction, and thus the first light beam L1 and the second light beam L2 Can be made to interfere.
Similarly, the first light beam L1 and the second light beam L2 reflected by the first polarizing beam splitter 222 are s-polarized light with respect to the first polarizing beam splitter 222 and have the same polarization direction. So you can make it interfere.

  The interference light with the first light beam L1 and the second light beam L2 transmitted through the first polarization beam splitter 222 is received by the first light receiving element 226. The interference light with the first light beam L1 and the second light beam L2 reflected by the first polarizing beam splitter 222 is received by the second light receiving element 227.

  In addition, signals that are photoelectrically converted by the first light receiving element 226 and the second light receiving element 227 are signals that are 180 degrees out of phase.

  In the first light receiving element 226 and the second light receiving element 227, an interference signal of Acos (Kz + δ) is obtained. A is the amplitude of interference, K is the wave number represented by 2π / Λ, and Λ is the wavelength of the measurement light L 0 emitted from the light source 210.

  Z is the amount of change in the optical path length of the first light beam L1 reflected by the measurement surface 1a of the member 1 to be measured, which varies depending on the shape of the measurement surface 1a.

  Since the reflecting mirror 217 is fixed, the optical path length of the second light beam L2 does not change.

  Therefore, in the first light receiving element 226 and the second light receiving element 227, the light intensity of one cycle is generated every time the optical path length of the first light flux changes by Λ / 2 according to the shape of the surface to be measured 1a. Interference light is received.

  On the other hand, the first light beam L1 and the second light beam L2 reflected by the half mirror 221 are incident on a phase plate 223 such as a quarter-wave plate. The first light beam L 1 and the second light beam L 2, which are linearly polarized light whose polarization directions are different from each other by 90 degrees, pass through the phase plate 223, and thus become circularly polarized lights that are opposite to each other. Since the circularly polarized light in the opposite directions are on the same optical path, the circularly polarized light becomes linearly polarized light by being superimposed, and is incident on the second polarization beam splitter 224.

  The s-polarized component of this linearly polarized light is reflected by the second polarizing beam splitter 224 and received by the third light receiving element 228. Further, the p-polarized light component passes through the second polarization beam splitter 224 and is received by the fourth light receiving element 229.

  As described above, the linearly polarized light incident on the second polarizing beam splitter 224 is generated by superimposing the circularly polarized light in the opposite directions. Therefore, when the optical path length of the first light beam L1 changes and the phase of the first light beam L1 and the second light beam L2 shifts, the polarization direction of the superimposed linearly polarized light rotates.

  The polarization direction of the linearly polarized light incident on the second polarization beam splitter 224 is 180 degrees, that is, 1 when the optical path length of the first light beam L1 changes by Λ / 2 when the member 1 to be measured moves in the height direction. Rotate twice.

  Therefore, the third light receiving element 228 and the fourth light receiving element 229 receive the interference light that causes the light of one period to be bright and dark each time the optical path length of the first light beam L1 changes by Λ / 2. A signal photoelectrically converted by the third light receiving element 228 and the fourth light receiving element 229 is represented by Acos (Kz + δ ′). δ 'is an initial phase. Further, the signals photoelectrically converted by the third light receiving element 28 and the fourth light receiving element 29 have a phase difference of 180 degrees.

  An interference signal represented by Acos (Kz + δ ′) is obtained by photoelectrically converting the interference light. δ 'is an initial phase.

  In the light receiving unit 220A of the relative position information detecting unit 220, the third polarization beam splitter 222 that splits the light beam received by the first light receiving element 226 and the second light receiving element 227 is compared with the third polarizing beam splitter 222. The second polarization beam splitter 224 that divides the light beam received by the light receiving element 228 and the fourth light receiving element 229 is disposed with an inclination of 45 degrees. For this reason, the signals obtained in the third light receiving element 227 and the fourth light receiving element 228 are 90 degrees out of phase with the signals obtained in the first light receiving element 226 and the second light receiving element 227.

  Therefore, for example, a signal obtained by the first light receiving element 226 and the second light receiving element 227 is used as a sin signal, and a signal obtained by the third light receiving element 228 and the fourth light receiving element 229 is used as a cosine signal. Can be obtained.

  The signals obtained by these light receiving elements 226 to 229 are calculated by the relative position information output unit 220B, and the displacement amount of the measured surface 1a is counted.

  The relative position information output unit 220B is configured similarly to the relative position information output unit 20B provided in the relative position information detection unit 220 in the displacement detection apparatus 100.

  In the relative position information output unit 220B, the signals obtained by the first light receiving element 226 and the second light receiving element 227 differing in phase from each other by 180 degrees are differentially amplified by a differential amplifier to cancel the DC component of the interference signal. Then, A / D conversion is performed by the A / D converter, the signal amplitude, the offset, and the phase are corrected by the waveform correction processing unit, and the signal is output from the incremental signal generator as an A-phase incremental signal, for example. Similarly, the signals obtained by the third light receiving element 228 and the fourth light receiving element 229 are A / D converted by an A / D converter after being differentially amplified by a differential amplifier, and a waveform correction processing unit Thus, the signal amplitude, offset, and phase are corrected, and an incremental signal generator outputs a B phase incremental signal that is 90 degrees out of phase with the A phase.

  The two-phase incremental signal obtained in this way is discriminated forward or backward by a pulse discriminating circuit or the like (not shown), whereby the amount of displacement in the height direction of the surface to be measured 1a is positive or negative. It can be detected.

  Further, by counting the phase change of the incremental signal in unit time with a counter (not shown), it is possible to measure how many of the above-mentioned periods the interference light intensity between the first light beam and the second light beam has changed. Therefore, the amount of displacement in the height direction of the surface to be measured 1a is thus detected.

  Note that the relative position information output from the relative position information output unit 220B may be the above-described two-phase incremental signal, or a signal including the displacement amount and the displacement direction calculated therefrom.

  In this displacement detection device 200, the absolute position information detection unit 230 includes a light receiving unit 231 and an absolute position information output unit 232.

  As shown in FIG. 17, the light receiving unit 231 of the absolute position information detecting unit 230 includes a four-divided light receiving unit having four light receiving elements, that is, fifth to eighth light receiving elements 231A, 231B, 231C, and 231D.

  The outer shape of the spot of the second light beam L1 formed on the four-divided light receiving portion 231 changes depending on the position of the surface to be measured 1a in the height direction.

  That is, since the astigmatism is given to the first light beam L1 incident on the four-divided light receiving unit 231 by the astigmatism generation unit 240, for example, the first light beam L1 irradiated onto the measured surface 1a. Is on the upper side of the measured surface 1a, as shown in FIG. 18A, the spot A1 of the first light beam L1 on the four-divided light receiving portion 231 has an elliptical shape.

  Further, when the focal point of the first light beam L1 irradiated on the measured surface 1a is on the measured surface 1a, for example, as shown in FIG. 18B, the spot A2 is substantially circular. .

  Further, when the focus of the first light beam L1 irradiated on the measurement surface 1a is below the measurement surface 1a, as shown in FIG. 18C, the spot A3 is the spot A1. The major axis direction is an ellipse rotated 90 degrees.

  Assuming that output signals output from the fifth to eighth light receiving elements 231A, 231B, 231C, and 231D are A, B, C, and D in order from the light receiving element 231A, respectively, the first irradiated on the measured surface 1a. The focus error signal SFE indicating the deviation of the light beam L1 from the focal position is expressed by the following equation (4).

      SFE = (A + C) − (B + D) Equation 4

  FIG. 19 shows the characteristics of the focus error signal obtained by this equation 4. The horizontal axis is the position in the height direction of the measured surface 1a, and the vertical axis is the focus error signal.

  As shown at point B, for example, when the focal point of the second light beam irradiated onto the measurement target surface 1a is on the measurement target surface 1a, the focus error signal becomes zero.

  In the displacement detection apparatus 200, since the objective lens 214 is fixed as described above, the focal position of the first light beam L1 irradiated onto the surface to be measured 1a is constant. Therefore, the height of the measured surface 1a when the focus error signal becomes zero is always the same, and the position where the focus error signal becomes zero can be used as a reference point in displacement detection.

  The calculation unit for obtaining the focus error signal may be built in the light receiving unit 231 or may be provided in the absolute position information output unit 232. The absolute position information output unit 232 A / D converts the focus error signal and outputs a value.

  A light scatterer such as cloudy glass may be disposed on the optical path between the astigmatism generator 240 and the light receiver 231 of the absolute position detector 230. Thereby, a uniform light intensity distribution is obtained in a cross section perpendicular to the optical axis direction of the first light beam L1 incident on the light receiving unit 231. Therefore, it is possible to suppress the detection of minute scratches or foreign matters on the surface to be measured 1a, and the influence of the surface roughness is reduced, so that the average height of the surface to be measured 1a can be measured. .

  Further, when such a light scatterer is vibrated at, for example, 1 KHz or more and the scattering direction is changed variously, the speckles on the light receiving elements 41 to 44 are averaged and the speckle contrast is reduced.

  In addition, an aperture having a predetermined aperture shape is disposed on the optical path of the first light beam L1 between the objective lens 214 and the light receiving unit 231 of the absolute position detecting unit 230, and the objective lens is set at a specific incident angle and incident position. The reflected light from the surface to be measured 1a that re-enters 214 may be blocked. Thereby, it is possible to prevent the diffracted light due to the foreign matter or the unevenness on the measured surface 1a from being received by the light receiving unit 231 as stray light.

  In addition, the light receiving elements in the relative position detection unit 220 and the absolute position detection unit 230 may receive interference light or light with astigmatism using an optical fiber. By using an optical fiber, it is possible to arrange these light receiving elements at locations away from the optical system of the displacement detection device 200.

  Therefore, by arranging the light receiving element in the vicinity of the absolute position information output unit 50 and the relative position information output unit 60, the electric communication distance from the light receiving element to these output units can be shortened, and the response speed can be improved.

  As described above, in the displacement detection device 200, the measurement light L0 emitted from the light source 210 is divided into two light beams L1 and L2, and the first light beam L1 is incident on the measured surface 1a of the member 1 to be measured. The second light beam L2 is incident on the reflecting mirror 217.

  Then, the absolute position information is detected by obtaining the focus error signal using the reflected light from the measured surface 1a, and the interference light between the reflected light from the fixed reflecting mirror 217 and the reflected light from the measured surface 1a. Relative position information is obtained.

  Since the intensity of the interference light periodically changes in accordance with the amount of displacement of the measured surface 1a, the linearity of the signal can be ensured by using the change in the intensity of the interference light as a scale. Since the period of intensity change of the interference light is determined by the wavelength of the light, it can be used as an accurate and fine scale.

  Further, the reference point of the scale obtained by the change in the intensity of the interference light can be obtained from the focus error signal obtained by the reflected light from the surface to be measured 1a.

  Therefore, in the displacement detection device 200, for example, the displacement can be accurately detected by counting the pulses generated by the relative position information output unit 220B, that is, the phase information with reference to the position where the focus error signal becomes zero.

  In this displacement detection device 200, the absolute position serving as the reference point is acquired from the focus error signal, so the objective lens 214 is fixed, and it is not necessary to move the objective lens 214 up and down following the surface to be measured 1a. Therefore, a driving mechanism for driving the objective lens 214 is not required, and generation of heat is suppressed. Further, there are no restrictions on the use conditions depending on the response frequency of the drive mechanism.

  In this displacement detection apparatus 200 as well, when the member to be measured 1 having the absolute position detection region 4 that moves the optical axis of the measurement light L1 at both ends in the movement direction X is out of the detection range, the measurement is performed. By simply returning the member 1 to the detection range, the absolute position information detected by the absolute position information detecting unit 230 can be used to reset or preset the relative position information obtained by the relative position information detecting unit 220 to return to the origin. it can.

  1, 1A, 1B, 1C, 1D, 1E member to be measured, 1a surface to be measured, 2 substrate, 3 reflective film, 4, 4D, 4E absolute position detection region, 4A, 4B reflective surface, 4e diffraction grating, 5 light transmission Member, 10, 210 light source, 11, 211 lens, 12, 212 beam splitting part, 13, 16, 213, 215 phase plate, 14, 214 objective lens, 15, 15A diffraction grating, 17, 216 condenser lens , 18, 217 reflector, 19 return reflector block, 19A, 19B reflecting surface, 20, 220 relative position detector, 20A, 220A light receiver, 20B, 220B relative position information output unit, 21, 241 condenser lens, 22, 221 Half mirror, 23, 25, 222, 224 Polarizing beam splitter, 24, 223 Phase plate, 26-29, 226-229 Element, 30, 230 Absolute position detection unit, 31,231 Light receiving unit, 31A, 31B, 231A to 231D Light receiving element, 32, 232 Absolute position information output unit, 32A Differential comparator, 61a, 61b Differential amplifier, 62a, 62b First A / D converter, 63 Waveform correction processing unit, 64 Incremental signal generator, 100, 100A, 200 Displacement detection device, 240 Astigmatism generation unit, 241 Condensing lens, 242 Beam splitter, 243 Polarizing plate

Claims (8)

A displacement detection device that detects a displacement of a measured surface of a measured member that is relatively movable in a direction perpendicular to a measurement direction based on measurement light reflected by the measured surface,
A relative position detector and an absolute position detector for optically detecting the relative position and the absolute position in the measurement direction based on the measurement light reflected by the measurement surface of the member to be measured;
An absolute position detection region for moving the optical axis of the measurement light at an end in the moving direction of the member to be measured;
The absolute position detection unit performs absolute position detection by moving the optical axis of the measurement light in the absolute position detection region, and returns position information obtained by the relative position detection unit. Detection device.   The displacement detection apparatus according to claim 1, wherein an optical axis of the measurement light is moved by an inclined reflecting surface in the absolute position detection region.   The displacement detection apparatus according to claim 1, wherein an optical axis of the measurement light is moved by a change in refractive index in the absolute position detection region.   The displacement detection apparatus according to claim 1, wherein an optical axis of the measurement light is moved by a diffraction grating in the absolute position detection region.   The relative position detection unit includes a light receiving unit that receives measurement light reflected by the surface to be measured of the member to be measured via a reflective diffraction grating, and based on a light detection output obtained by the light receiving unit. 5. The displacement detection device according to claim 1, wherein relative position information of the measurement surface in the measurement direction is output.   The relative position detection unit includes a light receiving unit that receives measurement light reflected by the surface to be measured of the member to be measured through a transmission diffraction grating, and based on a light detection output obtained by the light receiving unit. 5. The displacement detection device according to claim 1, wherein relative position information of the measurement surface in the measurement direction is output.   The absolute position detection unit includes a two-divided light receiving unit that receives measurement light reflected in the absolute position detection region, and the measurement direction of the surface to be measured based on a light detection output obtained by the two-divided light receiving unit. 5. The displacement detection apparatus according to claim 1, wherein the absolute position information is output.   The absolute position detection unit includes a four-divided light receiving unit that receives measurement light reflected in the absolute position detection region via an astigmatism generation unit, and is based on a light detection output obtained by the four-divided light receiving unit. The displacement detection apparatus according to claim 2, wherein absolute position information of the measurement surface in the measurement direction is output.