JP5414197B2 - Displacement detector - Google Patents

Description

  The present invention relates to a displacement detection device that detects a displacement between an objective lens and a surface to be measured using an optical astigmatism method. Specifically, the optical achromatic member is disposed on at least one of the optical path between the light source and the objective lens and between the objective lens and the light receiving element, thereby causing the wavelength variation of the emitted light emitted from the light source. It corrects chromatic aberration.

  Conventionally, displacement detectors have been widely used as devices for measuring the displacement and shape of a surface to be measured. In the displacement detection device, the laser light emitted from the light source of the non-contact sensor is condensed on the surface to be measured via the objective lens, and a focus error signal is generated by the astigmatism method from the reflected light reflected by the surface to be measured. Then, using this focus error signal, servo is applied to move and adjust the focal position of the objective lens, and the scale to be measured is read by reading the scale of the linear scale integrally attached to the objective lens via the connecting member The displacement of is detected.

  However, the above-described displacement detection device has a problem in that high linearity of the focus error signal itself is poor and thus high detection accuracy cannot be obtained. Therefore, Patent Document 1 proposes a displacement detection apparatus that outputs a calibrated output signal corresponding to a focus error signal of a non-contact sensor from a calibration table.

Japanese Patent Laid-Open No. 5-89480

  However, in the general displacement detection device including the above-mentioned Patent Document 1, when the displacement detection device is turned on and the displacement measurement of the surface to be measured is started, the temperature of the light source rises and the laser light emitted from the light source Wavelength will fluctuate. Further, the temperature of the light source varies due to a change in the temperature around the displacement detection device, and the wavelength of the laser light also varies. Since the refractive index of the light passing through the objective lens differs depending on the wavelength, this also shifts the focal position of the objective lens. As a result, the conventional displacement detection apparatus has a problem that chromatic aberration is greatly affected, and the displacement of the surface to be measured cannot be detected with high stability and high accuracy.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a displacement detection device that detects the displacement of the surface to be measured with high stability and high accuracy regardless of the wavelength variation of the light source. There is.

The displacement detection device according to the present invention solves the above-described problem, and a light source, an objective lens that condenses the light emitted from the light source on the surface to be measured, and the surface to be measured by the objective lens. An astigmatism generating lens that collects and diverges the reflected light that is collected and reflected by the surface to be measured, and generates a focus error signal based on the reflected light that is collected by the astigmatism generating lens, and an objective lens A non-contact sensor having a light receiving element for detecting displacement information based on the focal position of the lens, a control unit for adjusting the focal position of the objective lens based on the displacement information detected by the light receiving element, and a connecting member to the objective lens A displacement scale measuring unit that measures the amount of displacement of the linear scale when the focal position of the objective lens is adjusted by the control unit. At least one light path and between the objective lens and the light receiving element of the figure, the optical achromatic member of correcting chromatic aberration caused by the wavelength variation of the emitted light emitted from the light source is disposed.
Moreover, it has the housing | casing which accommodates a non-contact sensor, and the movable part which consists of a linear scale attached to the objective lens and the said objective lens via the connection member. The movable portion is provided so as to be movable with respect to the housing . The non-contact sensor further includes a collimating lens that is disposed between the light source and the objective lens and converts the light beam of the emitted light emitted from the light source into parallel light. Optical achromatic member is fixed to the housing, Ru is disposed in the optical path of the emitted light is converted into parallel light by a collimator lens. Further, the optical achromatic member is formed by bonding a first glass material having a first refractive index and a second glass material having a second refractive index different from the first refractive index, and a collimating lens. The end surface on the side and the end surface on the objective lens side are flat surfaces.

  In the displacement detection device of the present invention, when an optical achromatic member is disposed on the optical path between the light source and the objective lens, the emitted light emitted from the light source is incident on the optical achromatic member. The optical achromatic member corrects the focal position shift caused by the wavelength variation of the emitted light. Thereby, since the emitted light whose focal position is corrected is collected on the surface to be measured, the influence of chromatic aberration can be suppressed.

  Further, when an optical achromatic member is disposed on the optical path between the objective lens and the light receiving element, the reflected light reflected by the surface to be measured is incident on the optical achromatic member. In the optical achromatic member, the deviation of the focal position caused by the wavelength variation of the emitted light or reflected light is corrected. As a result, the reflected light whose focal position is corrected is collected on the light receiving element, so that the influence of chromatic aberration can be suppressed.

  The control unit adjusts the focal position of the objective lens based on the displacement information detected by the light receiving element. The displacement amount measuring unit measures the displacement amount of the objective lens when the focal position of the objective lens is adjusted by the control unit.

  According to the present invention, by disposing the optical achromatic member on the optical path, it is possible to correct the focal position shift due to wavelength variation. Thereby, chromatic aberration caused by the lens on the optical path including the objective lens can be corrected, and the displacement of the surface to be measured can be detected with high stability and high accuracy.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a block configuration example of a displacement detection device 10 according to an embodiment of the present invention. As shown in FIG. 1, the displacement detection apparatus 10 includes a non-contact sensor 100A, a control unit 200, a servo control unit 210, an actuator 300, a displacement amount measurement unit 400, a signal processing unit 404, and a display unit 140. With. In FIG. 1, the configuration of the non-contact sensor 100A is simplified for convenience.

  FIG. 2 is a perspective view showing a configuration example of the non-contact sensor 100A. As shown in FIG. 2, the non-contact sensor 100A includes a light source 102, a collimating lens 104, a polarizing beam splitter 108, a first achromatic lens 150A, a second achromatic lens 150B, and a λ / 4 plate. 110, a mirror 112, an objective lens 114, an astigmatism lens 118, a light receiving element 120, and a housing (chassis) 180.

  The housing 180 houses the light source 102, the collimating lens 104, the polarizing beam splitter 108, the first achromatic lens 150A, the second achromatic lens 150B, the astigmatism lens 118, and the light receiving element 120. . An opening 132 for allowing the emitted light L that has passed through the first achromatic lens 150 </ b> A to pass to the λ / 4 plate 110 side is formed in the lower portion of the housing 180.

  The light source 102 is composed of, for example, a semiconductor laser diode, a super luminescence diode, a light emitting diode, or the like, and emits an emitted light L such as a laser beam toward the collimating lens 104. The collimating lens 104 converts the emitted light L emitted from the light source 102 into parallel light. The emitted light L converted into parallel light is incident on the polarization beam splitter 108. The polarization beam splitter 108 transmits the emitted light L that has passed through the collimating lens 104 and makes it incident on the first achromatic lens 150A.

  The first achromatic lens 150 </ b> A is an example of an optical achromatic member, and corrects chromatic aberration caused by wavelength variation due to a temperature change of the light source 102. The objective lens constituting the first achromatic lens 150A has a small radius of curvature and a large chromatic aberration, and the combination of glass materials is limited. Therefore, it is difficult to design the lens. Therefore, in the present embodiment, as shown in FIG. 2, the first color is provided between the polarizing beam splitter 108 and the λ / 4 plate 110 and between the polarizing beam splitter 108 and the astigmatism lens 118, respectively. The lens design is facilitated by arranging the achromatic lens 150A and the second achromatic lens 150B.

  The first achromatic lens 150A may be integrated with the objective lens 114, but in order to reduce the mass of the movable part including the objective lens 114 as much as possible, the first achromatic lens 150A is removed from the objective lens 114. Is preferably separated. Therefore, in the present embodiment, the first achromatic lens 150A is attached and fixed to the support portion 182 (see FIG. 3) of the front wall surface 180a of the housing 180, for example.

  FIG. 3 is a diagram illustrating the fixed portion 600 and the movable portion 700 of the non-contact sensor 100A. The light source 102 is held at a predetermined position by support portions 188 and 188 provided in the housing 180. The collimating lens 104 is held at a predetermined position by support portions 186 and 186 provided in the housing 180. The polarization beam splitter 108 is held at a predetermined position by support portions 184 and 184 provided in the housing 180. The first achromatic lens 150 </ b> A is held at a predetermined position by support portions 182 and 182 provided in the housing 180. In this example, the light source 102, the collimating lens 104, the polarization beam splitter 108, the first achromatic lens 150 </ b> A, and the housing 180 are referred to as a fixing unit 600.

  On the other hand, the objective lens 114 and the linear scale 408 coupled to each other via the coupling member 500 are provided to be movable by driving the actuator 300. In this example, the objective lens 114, the linear scale 408, and the connecting member 500 are referred to as a movable portion 700.

  Thus, in the present embodiment, the first achromatic lens 150A is attached to the housing 180 and is provided separately from the objective lens 114 of the movable unit 700. Thereby, the mass of the movable part 700 can be lowered, and the movable part 700 can operate stably and accurately.

  FIG. 4A is a diagram illustrating a configuration example of the first achromatic lens 150A. The first achromatic lens 150A is disposed between the polarization beam splitter 108 and the λ / 4 plate 110 and in the emitted light L converted into parallel light by the collimating lens 104 (see FIG. 2). . The first achromatic lens 150A is configured by bonding a convex lens 152 having a refractive index (first refractive index) Na and a concave lens 154 having a refractive index (second refractive index) Nb. The end surface 152a on the light source 102 side of the convex lens 152 and the end surface 154a on the objective lens 114 side of the concave lens 154 are each processed flat. Thus, when the wavelength is the center wavelength, the first achromatic lens 150A functions as a parallel plate instead of a lens, and chromatic aberration can be effectively suppressed.

  Here, the refractive index difference between the convex lens 152 and the concave lens 154 is preferably set to 0.01 or less, for example. This is because when the wavelength of the emitted light L emitted from the light source 102 is the center wavelength, the difference in the glass material between the two convex lenses 152 and the concave lens 154 does not appear if the difference in refractive index is made small. This is because there is no refraction at the point, and the same behavior as when a single lens is used can be obtained.

  The ratio of the Abbe number (νa / νb) between the Abbe number νa of the convex lens 152 and the Abbe number νb of the concave lens 154 is preferably 1.7 or more. This is because even if the wavelength slightly varies, the refractive index difference generated between the two convex lenses 152 and the concave lens 154 changes greatly, and the bonded surface can function as a lens. As a result, by selecting the radius of curvature of the bonded surface, it is possible to set the focal length of the entire bonded lens due to wavelength variation to be constant.

  Returning to FIG. 2, the emitted light L that has passed through the first achromatic lens 150 </ b> A is incident on the λ / 4 plate 110. The λ / 4 plate 110 converts the incident light L that is incident linearly polarized light into right-handed circularly polarized light. The emitted light L that has passed through the λ / 4 plate 110 is reflected by the mirror 112 toward the surface to be measured TG and is incident on the objective lens 114.

  The objective lens 114 is an optical element including a lens having a predetermined numerical aperture, and is provided so as to be movable in conjunction with the linear scale 408 by the actuator 300. The emitted light L incident on the objective lens 114 is condensed on the measurement surface TG.

  The emitted light L condensed on the measurement surface TG is reflected by the measurement surface TG. The reflected light Lr reflected by the surface to be measured TG passes through the objective lens 114, is reflected by the mirror 112, and enters the λ / 4 plate 110.

  The λ / 4 plate 110 further rotates the reflected light, which is incident polarized light rightward, to the right, and converts it into reflected light Lr composed of linearly polarized light that is shifted from the emitted light L by ½ wavelength. The reflected light Lr that has passed through the λ / 4 plate 110 passes through the first achromatic lens 150A and is incident on the polarization beam splitter 108 again.

  The polarized beam splitter 108 reflects the reflected light Lr toward the second achromatic lens 150B because the incident reflected light Lr is shifted by ½ wavelength with respect to the emitted light L. The reflected light Lr reflected by the polarizing beam splitter 108 enters the second achromatic lens 150B.

  The second achromatic lens 150B is disposed between the polarization beam splitter 108 and the astigmatism lens 118, and corrects chromatic aberration of the reflected light Lr reflected by the polarization beam splitter 108. FIG. 4B is a diagram illustrating a configuration example of the second achromatic lens 150B. The second achromatic lens 150B is configured by bonding a convex lens 152 having a refractive index (first refractive index) Na and a concave lens 154 having a refractive index (second refractive index) Nb. On the light receiving element 120 side, unlike the objective lens 114, the aberration is not so important. Therefore, the end surface 152a side of the convex lens 152 and the end surface 154a side of the concave lens 154 are not processed flat. Of course, the end surfaces 152a and 154a may be processed as described above. The other refractive index, refractive index difference, Abbe number, and Abbe number ratio are the same as those in the first achromatic lens 150A described above. The reflected light Lr whose chromatic aberration is corrected by the second achromatic lens 150B enters the astigmatism lens 118.

  The astigmatism generating lens 118 has a shape obtained by dividing a cylinder into two in the axial direction, and collects and diverges light in a section having a curvature, and transmits light as it is in a plane section. The reflected light Lr incident on the astigmatism lens 118 is condensed on the light receiving element 120.

  The light receiving element 120 generates a focus error signal SFE based on the reflected light Lr collected by the astigmatism lens 118 and supplies the focus error signal SFE to the servo control unit 210. The light receiving element 120 is configured by a four-divided diode. 5A to 5C are diagrams illustrating the beam diameter of the reflected light Lr collected on the four-divided diode. When the surface to be measured TG is at the focal length f1 (see FIG. 1) of the objective lens 114, the condensed light becomes a circular light spot LR as shown in FIG. Further, when the objective lens 114 moves away from the measurement target surface TG from the focal length f1, as shown in FIG. 5B, an elliptical light spot LRx spreading laterally is obtained, and when the objective lens 114 approaches the focal length f1, As shown in FIG. 5C, an elliptical light spot LRy spreads vertically.

Here, if the output signals output from each of the divided photodiodes are A, B, C, and D, the focus error signal SFE representing the deviation of the focal length f1 is given by the following equation (1).
SFE = (A + C)-(B + D) (1)
At this time, the focus error signal SFE given by the above equation (1) has characteristics as shown in the graph of FIG. In the characteristics shown in FIG. 6, when the origin O is the in-focus position and the distance between the objective lens 114 and the measured surface TG is d, the focal distance f1 and the distance (focal position) d are equal at the origin O. Become.

  Returning to FIG. 1, the servo control unit 210 adjusts the focal position of the objective lens 114 based on the focus error signal SFE output from the light receiving element 120. The servo control unit 210 includes a servo amplifier (not shown) and a comparison circuit. The servo amplifier amplifies the supplied focus error signal SFE and supplies it to the comparison circuit. The comparison circuit compares a preset reference value with the focus error signal SFE. The reference value is set within a range in which an error from the focal length f1 can be allowed, and is stored in the ROM of the comparison circuit, for example. As a result of comparing the reference value and the focus error signal SFE, the servo controller 210 determines that the focus error signal SFE has a zero value when the value of the focus error signal SFE exceeds the allowable range of the reference value. Signal) Sd is generated and supplied to the actuator 300.

  The actuator 300 includes a movable coil 302, a permanent magnet 304, and a connecting member 500. The upper end portion of the connecting member 500 is attached to the lower portion of the movable coil 302. The objective lens 114 is attached and fixed to the lower end portion of the connecting member 500. The movable coil 302 moves the connecting member 500 in the directions of arrows D1 and D2 so that the focus error signal SFE has a zero value according to the drive signal Sd supplied by the servo control unit 210. In conjunction with this movement, the objective lens 114 integrally attached to the connecting member 500 is also moved in the directions of the arrows D1 and D2, and the distance d between the objective lens 114 and the measured surface TG is always the focal length f1 of the objective lens 114. The feedback control is performed so that the value becomes equal to. The actuator 300 may be attached in the vicinity of the objective lens 114 as shown in FIG.

  Since a voice coil motor is used as the actuator 300, the linearity with respect to the displacement of the surface to be measured TG is high. This is because the voice coil motor is a motor that is linearly displaced with respect to the current supplied to the movable coil 302. Therefore, the displacement amount can be easily detected by measuring the current supplied to the movable coil 302. The actuator 300 is not limited to a voice coil motor, and may be replaced with a DC servo motor, a stepping motor, a piezoelectric element, or the like.

  The displacement measuring unit 400 includes a linear scale 408 and a lattice interferometer 402. The linear scale 408 is formed with a scale (light-shielding pattern) 406 made of, for example, chromium at a predetermined pitch, and is attached and fixed at a predetermined position of the connecting member 500. The linear scale 408 is provided with an origin 410 at a substantially central position of the scale 406. Here, the scale 406 of the linear scale 408 is attached on the extension line Oa of the optical axis Lo of the objective lens 114. In other words, the linear scale 408 is arranged coaxially (in-line) with respect to the optical axis Lo of the objective lens 114. As the linear scale 408, for example, an optical scale (hologram scale) in which light interference fringes are recorded as a scale 406 can be used. In place of the optical scale, a magnetic scale or a capacitive scale may be used.

  The grating interferometer 402 is fixed to the housing 180 (see FIG. 2), reads the value of the scale 406 of the linear scale 408, generates a scale read signal Sv, and supplies the generated scale read signal Sv to the signal processing unit 404. To do. When the surface to be measured TG is displaced, the objective lens 114 and the linear scale 408 are displaced by the same distance in the same direction so as to maintain the focal length f1, so that the lattice interferometer 402 indicates the displacement amount on the scale of the linear scale 408. Read from 406. The grating interferometer 402 can be moved in the vertical direction of the extension line Oa of the optical axis Lo and in the directions of the arrows D1 and D2, and can be fixed to the housing 180 or the like at the moved position. .

  The signal processing unit 404 calculates the amount of displacement of the measurement surface TG based on the scale reading signal Sv output from the grating interferometer 402. Then, the signal processing unit 404 performs predetermined image signal processing based on the control signal Ss from the control unit 200, generates an image signal Si based on the calculated displacement amount, and outputs the image signal Si to the display unit 140. The image signal Si generated by the signal processing unit 404 may be stored in a data logger (not shown).

  The display unit 140 includes, for example, an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), or an EL (Electro Luminescence). The display unit 140 performs display based on the image signal Si output from the signal processing unit 404, and displays the displacement of the measurement target surface TG on the screen of the display unit 140. Thereby, automatic measurement can be easily performed.

  The control unit 200 controls operations of the servo control unit 210 and the signal processing unit 404, and includes, for example, a CPU (Central Processing Unit), a ROM (Read-Only Memory), and a RAM (Random Access Memory). .

  As described above, according to the present embodiment, the first achromatic lens 150A is disposed on the optical path between the polarizing beam splitter 108 and the λ / 4 plate 110, and the astigmatism with the polarizing beam splitter 108 is also reduced. By disposing the second achromatic lens 150B on the optical path to the adult lens 118, it is possible to correct the focal length shift due to the wavelength variation of the emitted light L and the reflected light Lr. Thereby, chromatic aberration caused by the lens on the optical path including the objective lens 114 can be corrected, and the displacement of the measurement surface TG can be detected with high stability and high accuracy.

  Further, since the first achromatic lens 150A is fixed to the housing 180 and is provided separately from the objective lens 114, the movable portion 700 including the objective lens 114 can be reduced in weight. Thereby, the movable part 700 can be operated stably and accurately, and the displacement of the surface to be measured TG can be detected with high accuracy.

  In addition, the displacement obtained by the above-described displacement detection device 10 is such that the linear scale 408 that is moved integrally with the objective lens 114 is arranged coaxially with the optical axis Lo of the objective lens 114, so-called in-line. Therefore, Abbe error does not occur. For this reason, since the displacement amount of the linear scale 408 and the displacement amount of the objective lens 114 correspond to 1: 1, the displacement amount can be detected with extremely high accuracy.

  Moreover, if it is within the detection range of the linear scale 408 (full scale of the scale 406), a wide detection range can be obtained without impairing the detection accuracy.

  Further, since feedback control is used, no measurement error occurs even if the sensitivity of the focus error signal SFE changes due to the reflectance of the surface to be measured TG, and errors due to variations and drifts in the elements of the servo system and the actuator 300 occur. This eliminates the need for adjustment and calibration, and enables stable detection over a long period of time.

  Furthermore, by forming the origin 410 on the linear scale 408, there is an advantage that the amount of displacement of the measured surface TG can be detected with the position of the origin 410 as the reference position.

[Second Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the component which is common in the displacement detection apparatus 10 demonstrated in 1st Embodiment mentioned above, and the non-contact sensor 100A, and detailed description is abbreviate | omitted.

  FIG. 7 is a diagram illustrating a configuration example of a non-contact sensor 100B according to the second embodiment of the present invention. As shown in FIG. 7, the non-contact sensor 100B includes a light source 102, a collimating lens 104, a polarizing beam splitter 108, a first achromatic lens 150A, a second achromatic lens 150B, and a λ / 4 plate. 110, a mirror 112, an objective lens 114, an astigmatism lens 118, and a light receiving element 120. Note that the housing 180 is omitted for convenience.

  The first achromatic lens 150 </ b> A is an example of an optical achromatic member, and corrects chromatic aberration caused by wavelength variation due to a temperature change of the light source 102. The first achromatic lens 150 </ b> A is disposed between the collimating lens 104 and the polarization beam splitter 108 and in the parallel light converted by the collimating lens 104. The first achromatic lens 150A is configured by bonding a convex lens 152 and a concave lens 154, and the end surface 152a of the convex lens 152 on the light source 102 side and the end surface 154a of the concave lens 154 on the objective lens 114 side are each processed into a flat shape. (See FIG. 4A).

  The second achromatic lens 150B is disposed between the polarization beam splitter 108 and the astigmatism lens 118, and corrects chromatic aberration of the reflected light Lr reflected by the polarization beam splitter 108. The configuration of the second achromatic lens 150B is the same as that of the above-described second achromatic lens 150B (see FIG. 4B).

  Also according to the present embodiment, the same effects as those of the first embodiment can be obtained. That is, in the present embodiment, the first achromatic lens 150A is disposed on the optical path between the collimating lens 104 and the polarizing beam splitter 108, and the light between the polarizing beam splitter 108 and the astigmatism lens 118 is light. A second achromatic lens 150B is disposed on the road. Thereby, chromatic aberration caused by the lens on the optical path including the objective lens 114 can be corrected, and the displacement of the measurement surface TG can be detected with high stability and high accuracy.

[Third Embodiment]
Hereinafter, the present embodiment will be described with reference to the drawings. In the first and second embodiments, the first and second achromatic lenses 150A and 150B are used as the optical achromatic member. In this embodiment, a diffractive optical element is used as the optical achromatic member. The difference is that 160 is used. In addition, the same code | symbol is attached | subjected to the component which is common in the displacement detection apparatus 10 demonstrated in 1st Embodiment mentioned above, and the non-contact sensor 100A, and detailed description is abbreviate | omitted.

  FIG. 8 is a diagram illustrating a configuration example of a non-contact sensor 100C according to the third embodiment of the present invention. As shown in FIG. 8, the non-contact sensor 100C includes a light source 102, a collimating lens 104, a polarizing beam splitter 108, a diffractive optical element 160, a λ / 4 plate 110, a mirror 112, and a first objective. It has a lens 114, a second objective lens 116, an astigmatism lens 118, and a light receiving element 120. Note that the housing 180 is omitted for convenience.

  The diffractive optical element 160 is an example of an optical achromatic member, and corrects chromatic aberration caused by wavelength variation due to a temperature change of the light source 102. In this example, the first and second Fresnel zone plates 160A and 160B are used as an example of the diffractive optical element 160.

  FIGS. 9A and 9B are diagrams showing a configuration example of the first Fresnel zone plate 160A. The first Fresnel zone plate 160 </ b> A is disposed between the collimating lens 104 and the polarization beam splitter 108 and in the emitted light L converted into parallel light by the collimating lens 104. The first Fresnel zone plate 160A is configured by forming ring-shaped irregularities on a glass substrate.

Here, as shown in FIG. 9B, when the boundary of the k-th annular zone from the center of the first Fresnel zone plate 160A (annular zone) is rk and the wavelength of the light used is λ. The focal length of the first Fresnel zone plate 160A is given by the following equation (2).
Ff = rk ² / kλ (2)

The depth h of the concave portion of the annular zone is given by the following formula (3).
h = 0.5λ / (n−1) (3)
n is the optical refractive index of the substrate material used for the first Fresnel zone plate 160A.

At this time, when the wavelength changes by δλ, the focal length change amount δFf is given by the following equation (4).
δFf = − (δλ / λ) Ff (4)
That is, when the wavelength is shifted by δλ, the focal length is shortened in proportion. Therefore, since the focal length is shortened when the wavelength is shifted in the longer direction, the chromatic aberration can be effectively corrected by using the first Fresnel zone plate 160A.

  The second Fresnel zone plate 160B is disposed between the polarizing beam splitter 108 and the second objective lens 116. The second Fresnel zone plate 160B has the same configuration as the first Fresnel zone plate 160A described above.

  When the first and second Fresnel zone plates 160A and 160B described above are used, the diffraction efficiency is 41%, for example. In order to further improve the diffraction efficiency, other diffractive optical elements 160 can be used in addition to the first and second Fresnel zone plates 160A and 160B.

  10A to 10C are diagrams showing a configuration example of another diffractive optical element 160. FIG. As another diffractive optical element 160, a multistage Fresnel zone plate 160C as shown in FIG. 10A or a blazed Fresnel zone plate 160D as shown in FIG. 10B can be used. Furthermore, as another diffractive optical element 160, as shown in FIG. 10C, a Fresnel lens 160E whose spatial frequency is modulated from the center toward the outside can also be used.

  According to the present embodiment, the diffraction efficiency can be improved as compared with the case where the first and second Fresnel zone plates 160A and 160B are used.

[Fourth Embodiment]
Hereinafter, the present embodiment will be described with reference to the drawings. The present embodiment is different from the first embodiment in that the diffractive optical element 160 is disposed only at one location between the first objective lens 114 and the light receiving element 120. In addition, the same code | symbol is attached | subjected to the component which is common in the displacement detection apparatus 10 demonstrated in 1st Embodiment mentioned above, and the non-contact sensor 100A, and detailed description is abbreviate | omitted.

  FIG. 11 is a diagram illustrating a configuration example of a non-contact sensor 100D according to the fourth embodiment of the present invention. As shown in FIG. 11, the non-contact sensor 100D includes a light source 102, a collimating lens 104, a polarizing beam splitter 108, a diffractive optical element 160, a λ / 4 plate 110, a mirror 112, and a first objective. It has a lens 114, a second objective lens 116, an astigmatism lens 118, and a light receiving element 120. Note that the housing 180 is omitted for convenience.

  The diffractive optical element 160 is an example of an optical achromatic member. In this example, a Fresnel zone plate 160F is used as an example of the diffractive optical element 160. The Fresnel zone plate 160F has the same configuration as the first and second Fresnel zone plates 160A and 160B described above. In addition to the Fresnel zone plate 160F, the multistage Fresnel zone plate 160C, the blazed Fresnel zone plate 160D, and the Fresnel lens 160E may be used.

  The Fresnel zone plate 160F is disposed between the polarizing beam splitter 108 and the second objective lens 116. The Fresnel zone plate 160F has an absolute value larger than that of the lens by an order of magnitude, and has a function opposite to that of the lens. That is, when the wavelength of the lens is shifted in the longer direction, the focal length becomes longer, whereas in a diffractive optical element such as the Fresnel zone plate 160F, the focal length is shifted in the shorter direction. Here, since the light beam (reflected light Lr) that has passed through the optical elements such as the collimator lens 104, the polarization beam splitter 108, and the first objective lens 114 arrives on the light receiving element 120 side, the influence of wavelength fluctuations appears greatly. Therefore, in this embodiment, the Fresnel zone plate 160F is disposed between the polarization beam splitter 108 on the light receiving element 120 side and the second objective lens 116, thereby effectively correcting chromatic aberration. Can do.

  It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention.

  For example, the actuator 300 is not limited to a voice coil motor, and may be replaced with a DC servo motor, a stepping motor, a piezoelectric element, or the like.

  In the first embodiment, the astigmatism method is used to obtain the focus error signal SFE. However, the present invention is not limited to this, and a critical angle method, a knife edge method, or the like may be used instead. In either method, since the focus error signal SFE is controlled so as to have a zero value, the displacement can be detected with high accuracy even if the reflectance of the surface TG to be measured is different.

  Further, the detection optical system including the light source 102, the polarization beam splitter 108, the mirror 112, and the light receiving element 120 is attached to the connecting member 500 so as to move integrally with the objective lens (first objective lens) 114. You may comprise and you may fix to the housing | casing 180. FIG. By configuring so as to move integrally with the objective lens 114, the displacement detection range is expanded to the full scale of the linear scale 408. When fixed to the housing 180, that is, when configured in a distributed type, the actuator 300 can be made relatively small, and the weight of the displacement detection device 10 including the objective lens 114 can be reduced. it can. This makes it possible to detect the displacement amount at a higher speed.

It is a figure which shows the structure of the displacement detection apparatus which concerns on the 1st Embodiment of this invention. It is a perspective view which shows the structure of a non-contact sensor part. It is a figure which shows the stationary part and movable part of a non-contact sensor. It is a figure which shows the structure of the 1st and 2nd achromatic lens. It is a figure which shows the light reception operation | movement of a light receiving element. It is a figure which shows the characteristic of a focus error signal. It is a perspective view which shows the structure of the non-contact sensor part which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the structure of the non-contact sensor part which concerns on the 3rd Embodiment of this invention. It is a figure which shows the structure of a diffraction type optical element (the 1). It is a figure which shows the structure of a diffraction type optical element (the 2). It is a perspective view which shows the structure of the non-contact sensor part which concerns on the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Displacement detection apparatus, 100A, 100B, 100C, 100D ... Non-contact sensor, 102 ... Light source, 104 ... Collimating lens, 114 ... Objective lens, 120 ... Light receiving element, 150A ... first achromatic lens, 150B ... second achromatic lens, 152 ... convex lens, 152a ... end surface, 154 ... concave lens, 154a ... end surface, 160 ... diffraction Type optical element, 160A ... first Fresnel zone plate, 160B ... second Fresnel zone plate, 160D ... blazed Fresnel zone plate, 160E ... Fresnel lens, 180 ... housing, 210 ... servo control unit, 400 ... displacement measuring unit, 402 ... lattice interferometer, 408 ... linear scale, SFE ... Focus error signal

Claims (3)

A light source, an objective lens that condenses the light emitted from the light source on the surface to be measured, and condenses the reflected light that is condensed on the surface to be measured by the objective lens and reflected by the surface to be measured. An astigmatism generating lens that diverges; and a light receiving element that generates a focus error signal based on reflected light collected by the astigmatism generation lens and detects displacement information based on a focal position of the objective lens. A non-contact sensor;
A control unit for adjusting the focal position of the objective lens based on the displacement information detected by the light receiving element;
A displacement scale measuring unit having a linear scale attached to the objective lens via a connecting member, and measuring the displacement amount of the linear scale when the focal position of the objective lens is adjusted by the control unit; With
An optical color that corrects chromatic aberration caused by wavelength variation of the emitted light emitted from the light source on at least one of the optical path between the light source and the objective lens and between the objective lens and the light receiving element. An eraser is placed,
A housing for housing the non-contact sensor;
A movable part comprising the objective lens and the linear scale attached to the objective lens via a connecting member;
The movable part is provided to be movable with respect to the housing,
The non-contact sensor is
A collimating lens that is disposed between the light source and the objective lens, and converts the luminous flux of the emitted light emitted from the light source into parallel light;
The optical achromatic member is
The first glass material having the first refractive index is different from the first refractive index, which is fixed in the casing and arranged in the optical path of the emitted light converted into parallel light by the collimating lens. A displacement detection device comprising a second glass material having a second refractive index bonded together, and an end surface on the collimating lens side and an end surface on the objective lens side being flat . The refractive index difference between the first glass material and the second glass material is 0.01 or less, and the ratio between the Abbe number of the first glass material and the Abbe number of the second glass material is 1.7 or more. Item 2. The displacement detection device according to Item 1. The displacement detection device according to claim 1, wherein the optical achromatic member is constituted by a diffractive optical element.