JP5936399B2 - Position detection device - Google Patents

Description

  The present invention relates to a displacement detection device that detects a displacement of a surface to be measured by a non-contact sensor using measurement light emitted from a light source, and more particularly to a technique for detecting a displacement in a vertical direction of 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.

Japanese Patent Laid-Open No. 5-89480

  However, in the displacement detection device described in Patent Document 1, the objective lens is moved up and down in the optical axis direction by a drive mechanism such as an actuator using a magnet and a coil. Therefore, the mechanical response frequency of the vertical movement of the objective lens is limited by the structure and mass of the actuator. As a result, with the displacement detection device, it was difficult to measure the object to be measured that vibrates at high speed. In addition, while the detection point can be narrowed down, there is a problem that a large error occurs due to the influence of a foreign object on the object to be measured and a fine shape change close to the beam shape, and the use conditions are limited. .

  Furthermore, when the object to be measured has a laminated structure, it is very difficult to apply focus servo to any layer from among them, and stable measurement is impossible.

  Therefore, in view of the conventional problems as described above, an object of the present invention is to provide a displacement detection device capable of detecting a displacement in a height direction of a member to be measured with high accuracy and capable of performing stable measurement at high speed. There is to do.

  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 apparatus, which is a light source that emits measurement light, a first light beam that is object light that causes the measurement light emitted from the light source to enter a member to be measured, and reference light. A light beam splitting unit that splits the light beam into a second light beam; and diffracting the first light beam split by the light beam splitting unit and reflected by the surface to be measured of the member to be measured. A diffraction grating that is incident again on the measurement surface of the member to be measured, a reflection unit that reflects the second light beam divided by the light beam dividing unit, a first light beam divided by the light beam dividing unit, and a first light beam An optical path length adjusting means for adjusting an optical path length of at least one of the two light beams, the first light beam diffracted by the diffraction grating and reflected again by the surface to be measured, and the light beam reflected by the reflecting unit. Second light Based on the intensity of the interference light received by the light receiving unit, the light receiving unit that receives the interference light of the first light beam and the second light beam superimposed by the light beam combining unit, Relative position information output means for outputting displacement information in the height direction of the surface to be measured, and the grating vector of the diffraction grating is disposed substantially perpendicular to the surface to be measured of the member to be measured, Even if the member is displaced in the height direction, the optical path length of the first light flux is always maintained at a constant distance .

  In the displacement detection device according to the present invention, the optical path length adjusting means includes an optical path length of the first light beam from the light beam splitting unit to the light beam coupling unit via the diffraction grating, and the second light beam. The optical path length adjustment range includes a coincident point with the optical path length from the light beam splitting unit to the light beam coupling unit through the reflecting unit.

  In the displacement detection device according to the present invention, the optical path length adjusting means may adjust the optical path length of the light beam passing through the optical prism by moving the optical prism, for example.

  In the displacement detection apparatus according to the present invention, for example, the diffraction grating is a reflection type diffraction grating, and the optical path length adjusting means moves the diffraction grating in the optical axis direction of the incident light beam to thereby change the optical path length. Can be adjusted.

  Furthermore, in the displacement detection device according to the present invention, the optical path length adjusting means adjusts the optical path length by moving a reflecting mirror that reflects the first light beam, the second light beam, or both, for example. can do.

  According to the present invention, the optical path length adjusting means is used to change the optical path length of at least one of the first light beam that is the object light incident on the member to be measured divided by the light beam dividing unit or the second light beam that is the reference light. By adjusting, it is possible to detect the displacement in the height direction of the member to be measured that is laminated with high accuracy, and to perform stable measurement at high speed.

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 optical path length adjustment means with which the said displacement detection apparatus was equipped. 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 side view which shows typically the structure of the to-be-measured member which has the multilayer to-be-measured surface measured by the said displacement detection apparatus. FIG. 3 is a side view schematically showing the displacement detection device. 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 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. 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 block diagram which shows the other structural example of the displacement detection apparatus to which this invention is applied. 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.

  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.

  This displacement detection device 100 uses a diffraction grating 14 to detect a displacement in the vertical direction (measurement direction Z) of the measurement target surface 1a of the measurement target member 1 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 L0 emitted from the light source 10 into two light beams L1 and L2, a diffraction grating 14, a reflecting mirror 18, and the member to be measured. A relative position detector 20 is provided for optically detecting the relative position in the measurement direction Z based on the measurement light L1 reflected by one measured surface 1a.

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

  When a light source having a short coherence distance is used as the light source 10, as the coherence distance becomes shorter, noise due to unnecessary stray light interference can be prevented, and highly accurate measurement can be performed. Therefore, it is desirable to use a light source having a short coherence distance as much as possible.

  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 1 to be measured through the first phase plate 13, and the second light beam L2 is used as reference light as the second phase plate 15 and the optical path length adjusting prism. The reflection mirror 18 is irradiated through 17a. 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 15 are each composed of a quarter wavelength plate or the like.

  Here, as shown in FIG. 2, the optical path length adjusting prism 17a is moved by the movable portion 17b in a direction perpendicular to the optical axis of the second light beam L2 incident as the reference light, thereby causing the second light beam It functions as an optical path length adjusting means for changing the optical path length of L2. A stage or a piezo element is used for the movable part 17b.

  The optical path length adjusting means 17 including the optical path length adjusting prism 17a and the movable portion 17b is provided in the optical path of the second light beam L2 from the light beam splitting unit 12 to the diffraction grating 14, thereby reducing the optical path length of the second light beam L2. Can be adjusted arbitrarily.

  Thereby, the measurement target surface 1a of the measurement target member 1 whose surface is covered with a protective film such as transparent glass, and the boundary surfaces 1A, 1B,... Of each layer of the measurement target member 1 formed of a multilayer film as shown in FIG. .. Even when 1N is the measured surface 1a, the measured surface 1a that satisfies the condition of L2 = L1 can be detected. Furthermore, since the coherence distance of the light source 10 is short, only the boundary surface of the layer that satisfies the condition of L2 = L1 can be selected and detected as the measured surface 1a.

  Here, a mirror or the like is generally used as the member 1 to be measured, but the surface to be measured 1a of the member 1 to be measured whose surface is covered with a protective film such as transparent glass or a multilayer film as shown in FIG. When the boundary surfaces 1A, 1B,... 1N of the respective layers of the measured member 1 are the measured surface 1a, the surface of the measured member 1 without the protective film is the measured surface 1a and the optical path length Therefore, with a light source having a short coherence distance, even if an interference signal is obtained with the reflected light from the surface 1s, an interference signal with the reflected light from the boundary surfaces 1A, 1B,. Absent.

  Examples of the member to be measured 1 formed of a multilayer film having the measurement surfaces 1a as the boundary surfaces 1A, 1B,... 1N of the layers include a multilayer film and a semiconductor wafer.

  In the case of surface reflection, since the optical path lengths A = A ′ and B = B ′ are always equal to each other due to the variation of the member 1 to be measured, the first light flux L1 and the second light flux L2 once. If the lengths are adjusted equally, detection can be performed stably as long as the refractive index of the medium in the optical path of the first light beam L1 does not change. On the other hand, in the case of the surface reflection and the refractive index n in the stacked medium, even if A = A ′, the inside of the medium satisfies B <B ′, so that a difference occurs in the optical path length. Therefore, in order to detect the surface of each layer, as shown in FIGS. 4A and 4B, it is necessary to adjust the second light flux L2 so as to match the optical path length of each first light flux L1. There is.

  The optical path length adjusting means 17 by the optical path length adjusting prism 17a and the movable portion 17b serves to eliminate the difference in optical path length and select and detect the surface of each layer.

  The optical path length adjusting unit 17 includes an optical path length from the light beam splitting unit 12 to the light beam coupling unit 12 via the diffraction grating 14 in the first light beam L1 that is object light, and a second light beam that is reference light. It has an optical path length adjustment range including a coincident point with the optical path length from the light beam splitting section 12 at L2 to the light beam coupling section 12 via the diffraction grating 14.

  In this displacement detection device 100, the incident angle of the second light beam L2 on the diffraction grating 14 is changed by rotating the reflecting mirror 18 in conjunction with the adjustment of the second light beam L2 by the optical path length adjusting means 17. I try not to.

  In this displacement detection apparatus 100, the diffraction grating 14 is a reflective diffraction grating that reflects and diffracts incident light.

  Then, the member to be measured 1 reflects the first light beam L1 diffracted by the diffraction grating 14 and returns it to the light beam splitting unit 12 again. The diffraction grating 14 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 14 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 14 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 14 is arranged in the range of 90 ° to ± 2 ° with respect to the measurement surface 1a of the member 1 to be measured, the displacement detection device 100 is used for low-precision measurement of a machine tool or the like Is enough.

  Also, the first light beam L1 incident on the diffraction grating 14 is reflected and diffracted by the diffraction grating 14. The grating pitch Λ of the diffraction grating 14 is set so that the diffraction angle is substantially equal to the incident angle to the diffraction grating 14. That is, the grating pitch Λ of the diffraction grating 14 is preferably set 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 14 is disposed at a right angle to the measured surface 1a of the member 1 to be measured, the incident angle to the diffraction grating 14 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 14 and diffracted and incident again on the measured surface 1a of the measured member 1. It is reflected by the surface to be measured 1a and overlaps with the optical path when entering the diffraction grating. As a result, the first light beam L1 diffracted by the diffraction grating 14 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.

  For example, a diffraction grating having a structure as shown in the side view of FIG. 5 is used as the diffraction grating 14.

  The diffraction grating 14 includes so-called blazed diffraction gratings 14A and 14B in which the cross-sectional shape of the groove is formed in a sawtooth shape. According to this diffraction grating 14, the diffraction of the first light beam L 1 that is object light reflected by the measurement surface 1 a of the member 1 to be measured and the second light beam L 2 that is reference light reflected by the reflecting mirror 18. Efficiency can be increased and signal noise can be reduced.

  As shown in FIG. 1, the reflecting mirror 18 reflects the second light beam L <b> 2 split by the light beam splitting unit 12 to the diffraction grating 14. The reflecting mirror 18 is provided at a position facing the member to be measured 1 with the diffraction grating 14 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 14 are arranged so that the angle formed by the reflecting surface of the reflecting mirror 18 and the diffraction surface of the diffraction grating 14 is approximately 90 °.

  Further, the reflecting mirror 18 reflects the second light beam L2 diffracted by the diffraction grating 14 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 14 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 14 in the first light beam L1 is equal to the optical path length from the light beam splitting unit 12 to the diffraction grating 14 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 14 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 14. As a result, the optical path when being diffracted by the diffraction grating 14 and entering the reflecting surface of the reflecting mirror 18 again overlaps the optical path when being reflected by the reflecting mirror 18 and entering the diffraction grating 14.

  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 14 and the beam splitting unit 12 from the beam splitting unit 12 to the beam splitting unit 12 through the reflecting mirror 18 and the diffraction grating 14. 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 equal, even if there is a wavelength variation of the light source 10 due to changes in atmospheric pressure, humidity, or temperature, the first light beam L1 and the second light beam The influence which L2 receives can be made equal. 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.

  Further, as shown in FIG. 6, 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.

  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 14, 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 measurement surface 1a of the measurement target member 1 moves from the diffraction position T1 of the diffraction grating 14 to the diffraction position T2. Here, since the diffraction grating 14 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 14 is z that is twice that when the member 1 to be measured is moved.

  Further, since the diffraction grating 14 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 14 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. 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 periods of the interference light intensity of the first light beam L1 and the second light beam L2 have 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.

  Here, in the displacement detection device 100, the optical path length adjusting means 17 by the optical path length adjusting prism 17a and the movable portion 17b is provided in the optical path of the second light beam L2 from the light beam splitting unit 12 to the diffraction grating 14, thereby providing the first. Although the optical path length of the second light beam L2 can be arbitrarily adjusted, the optical path length adjusting means by the optical path length adjusting prism 17a and the movable portion 17b in the optical path of the first light beam L1 from the light beam splitting unit 12 to the diffraction grating 14. By providing 17, the optical path length of the first light beam L1 may be adjusted.

  Further, as in the displacement detection device 100A shown in FIG. 8, the reflecting mirror 18 that reflects the second light beam L2 that is the reference light is disposed perpendicular to the optical axis of the second light beam L2, and the movable unit 17A performs the above operation. An optical path length adjusting means for adjusting the optical path length of the second light beam L2 by moving the reflecting mirror 18 in the optical axis direction of the second light beam L2 may be provided. In this case, the optical path length adjusting means includes the optical path length from the light beam splitting unit 12 to the light beam coupling unit 12 through the diffraction grating 14 in the first light beam L1 that is the object light, and the second light beam that is the reference light. The optical path length adjustment range including the coincidence point with the optical path length from the light beam splitting section 12 to the light beam coupling section 12 through the reflecting mirror 18 in the light beam L2 is assumed. A stage or a piezo element is used for the movable portion 17A.

  Further, like the displacement detection device 100B shown in FIG. 9, the reflective diffraction grating 14A that diffracts the first light beam L1 that is object light and the reflective diffraction grating that diffracts the second light beam L2 that is reference light. 14B is arranged separately, and one or both of the diffraction grating 14A and the diffraction grating 14B are moved by the movable portions 17A and 17B in the direction X perpendicular to the measurement direction Z of the surface to be measured 1a. An optical path length adjusting unit that adjusts the optical path length of one or both of the second light beams L2 may be provided. In the displacement detection device 100B, the diffraction grating 14A and the diffraction grating 14B are previously measured in the measurement direction so that the optical path lengths of the first light beam L1 and the second light beam L2 can be matched within the adjustment range by the optical path length adjusting means. They are shifted in the direction X perpendicular to Z.

  A stage, a leaf spring, and a piezo element are used for the movable parts 17A and 17B. The movable parts 17A and 17B may be moved by adjusting the temperature and utilizing the temperature expansion of the object.

  In the displacement detection devices 100A and 100B, components common to the displacement detection device 100 are denoted by the same reference numerals in the drawing, and redundant description is omitted.

  Further, 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 14. The relative position information in the measurement direction Z of the measured surface 1a is output from the relative position information output unit 20B based on the light detection output obtained by the light receiving unit 20A. As shown in FIG. 5, the light receiving unit 20A that receives the measurement light L1 reflected by the measurement surface 1a of the member 1 to be measured via the transmission diffraction grating 14C is provided, and is based on the light detection output obtained by the light reception unit 20A. The relative position information of the measurement surface 1a in the measurement direction Z can also be applied to a displacement detection device 100C that outputs the relative position information output unit 20B.

  That is, similarly to the displacement detection device 100, the displacement detection device 100C shown in FIG. 10 detects the displacement of the measurement surface 1a of the measurement target member 1 that can move relative to 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 the absolute position in the measurement direction Z based on the measurement light L1 reflected by the measurement target surface 1a of the member to be measured 1 and the diffraction grating 14C of the mold, the reflection mirror 18, the return reflection mirror block 19 The relative position detector 20 and the absolute position detector 30 are optically detected.

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

  In this displacement detection apparatus 100C, the measurement light L0 emitted from the light source 10 is collimated by the lens 11A and is incident on the light beam splitting unit 12 as parallel light. The first light beam L1 that is object light by the light beam splitting unit 12 and the reference The light is divided into a second light beam L2 that is light.

  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 enters the transmissive diffraction grating 14C.

  The diffraction grating 14C is a transmission type diffraction grating that transmits and diffracts incident light.

  That is, in the displacement detection device 100C, the transmission type diffraction grating 14C is provided instead of the reflection type diffraction grating 18 in the displacement detection device 100.

  The first light beam L1 incident on the transmission type diffraction grating 14C is transmitted through the transmission type diffraction grating 14C and diffracted once, and the first light beam L1 on the measurement surface 1a of the member 1 to be measured is 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 14C passes through the transmission type diffraction grating 14C and enters the light receiving unit 31 of the absolute position detection unit 30.

  The second light beam L2 split by the light beam splitting unit 12 is incident on the reflecting mirror 18 via the second phase plate 15 and the optical path length adjusting prism 17a, and the member 1 to be measured 1 passes through the reflecting mirror 18. Is incident on the first irradiation spot Sc1 on the measured surface 1a, reflected by the measured surface 1a, and incident on the transmissive diffraction grating 14C.

  Then, the second light beam L2 incident on the transmission type diffraction grating 14C passes through the transmission type diffraction grating 14C 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.

  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 14C. 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 via the grating 14C.

  In this displacement detection device 100C, the return reflector block 19 is arranged so that the optical path length of the first light beam L1 is equal to the optical path length of the second light beam L2. Further, the return reflector block 19 can be moved by the movable portion 17C in the measurement direction Z of the measurement target surface 1a of the measurement target member 1. A stage, a leaf spring, and a piezo element are used for the movable portion 17C. Further, the temperature of the movable portion 17C may be adjusted and moved using the temperature expansion of the object.

  In other words, the displacement detecting device 100C moves the return reflector block 19 in the measurement direction Z of the measurement target surface 1a of the member 1 to be measured by the movable portion 17C, so that the first light flux L1 and the second light flux. Optical path length adjusting means for adjusting the optical path length of L2 is provided. In this displacement detection device 100C, the optical path length adjusting means adjusts the optical path length of the first light beam L1 and the optical path length of the second light beam L2, thereby providing a reflection surface on which the member 1 to be measured is laminated. In addition, the optical path length is adjusted to the first light beam L1 from the boundary surface of each layer, and the boundary surface to be measured can be selected and detected.

  In the displacement detection device 100C, the relative position detection unit 20 uses 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 100C, the transmissive diffraction grating 14C is disposed substantially perpendicular to the measured 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 14C is preferably set so that the diffraction angle is substantially equal to the incident angle to the diffraction grating 14C. That is, as described above, the grating pitch Λ of the diffraction grating 14C is expressed by the following equation 2 when the first incident angle 1a of the measured surface 1a of the member 1 to be measured is θ1, the second incident angle θ2 and the wavelength λ: 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 14C 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 14C. 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 14C.

  That is, the Bragg condition can be satisfied, and the diffracted light diffracted by the diffraction grating 14C 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 14C 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 14C is incident again on the first irradiation spot Pc1 on the measurement target surface 1a of the measurement target member 1 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 14C to the diffraction position T2. Further, the first light beam L1 diffracted for the first time by the diffraction grating 14C moves from the second irradiation spot Pd1 on the measurement target surface 1a of the member 1 to be measured to the second irradiation spot Pd2.

  Here, the diffraction grating 14C is disposed substantially perpendicular to the surface 1a to be measured 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 moving on the diffraction grating 14C is z that is twice that when the member 1 to be measured is moved.

  Further, the diffraction grating 14C is disposed substantially at right angles 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 14C 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 the displacement detection device 100C, 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 represents the amount of movement of the first light beam L1 on the diffraction grating 14C. 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 14C. 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 apparatus 100C, when the grating pitch of the diffraction grating 14C and the grating pitch of the diffraction grating 14 in the displacement detection apparatus 100 are the same, the resolution can be doubled compared to the displacement detection apparatus 100.

  For example, when the grating pitch Λ of the diffraction grating 14C 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 14C are set to 45 °, the measured surface 1a of the measured member 1 is in the height direction. When moved by 0.5515 μm, the first light beam L1 moves on the diffraction grating 14C 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 100C, the first light beam L1 is irradiated to two places of the first irradiation spot Pc1 and the second irradiation spot Pd1 on the measured surface 1a of the measured member 1 with one 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.

  1, 1A, 1B, 1C, 1D, 1E member to be measured, 1a surface to be measured, 2 substrate, 3 reflective film, 10 light source, 11 lens, 12 beam splitting part, 13, 16 phase plate, 14, 14A, 14B, 14C diffraction grating, 17 optical path length adjusting means, 17a optical path length adjusting prism, 17b, 17A, 17B, 17C movable part, 18 reflecting mirror, 19 return reflecting mirror block, 19A, 19B reflecting surface, 20 relative position detecting part, 20A Light receiving unit, 20B relative position information output unit, 21 condenser lens, 22 half mirror, 23, 25 polarizing beam splitter, 24, 223 phase plate, 26-29 light receiving element, 61a, 61b differential amplifier, 62a, 62b first A / D converter, 63 waveform correction processing unit, 64 incremental signal generator, 100, 100A, 100B, 100C Position detecting device

Claims (5)

A light source that emits measurement light;
A light beam splitting unit that splits the measurement light emitted from the light source into a first light beam that becomes object light that enters the member to be measured, and a second light beam that becomes reference light;
The first light beam divided by the light beam splitting unit and reflected by the surface to be measured of the member to be measured is diffracted, and the diffracted first light beam is incident again on the surface to be measured of the member to be measured. A diffraction grating,
A reflecting portion that reflects the second light flux divided by the light flux splitting portion;
An optical path length adjusting means for adjusting an optical path length of at least one of the first light beam and the second light beam divided by the light beam dividing unit;
A first light beam diffracted by the diffraction grating and reflected again by the surface to be measured; a light beam coupling unit that superimposes the second light beam reflected by the reflection unit; A light receiving portion for receiving interference light of the first light flux and the second light flux,
Relative position information output means for outputting displacement information in the height direction of the surface to be measured based on the interference light intensity received by the light receiving unit;
Equipped with a,
The grating vector of the diffraction grating is arranged substantially perpendicular to the surface to be measured of the member to be measured, and the optical path length of the first light beam is always constant even when the member to be measured is displaced in the height direction. A displacement detection device characterized by being maintained at a distance of .   The optical path length adjusting means includes an optical path length from the light beam splitting unit in the first light beam to the light beam coupling unit through the diffraction grating, and a light beam splitting unit to the reflection unit in the second light beam. The displacement detection device according to claim 1, further comprising: an optical path length adjustment range including a coincidence point with an optical path length until the light beam coupling unit returns to the light beam coupling unit.   The displacement detection device according to claim 1, wherein the optical path length adjusting unit adjusts an optical path length of a light beam passing through the optical prism by moving the optical prism. The diffraction grating is a reflective diffraction grating;
The displacement detection device according to claim 1, wherein the optical path length adjusting unit adjusts the optical path length by moving the diffraction grating in an optical axis direction of an incident light beam.   The displacement detection device according to claim 1, wherein the optical path length adjusting unit adjusts the optical path length by moving a reflecting mirror that reflects the first light beam, the second light beam, or both.