JP2017049117A - Dimension measurement device and reference optical path length scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dimension measurement device and a reference optical path length scanning device that can shorten a measurement time with a measurement velocity improved, and enhance measurement accuracy, and further can expand a scanning range of reference light.SOLUTION: A dimension measurement device 10 of an embodiment is configured to use a ball lens 24 as a reference mirror; move the ball lens 24 along a round movement trajectory; and change an optical path length of reference light 58. Even when the ball lens 24 changes its position along the round movement trajectory, a pose of an incidence surface relative to the reference light 58 remains unchanged. Thus, the ball lens 24 is configured to totally reflect the incident reference light 58 in a direction opposite an incidence direction of the reference light 58 regardless of a movement position.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a dimension measuring apparatus and a reference optical path length scanning apparatus, and more particularly to a dimension measuring apparatus and a reference optical path length scanning apparatus that measure the dimension of an object to be measured using the principle of low coherence interferometry. Note that the present invention does not exclude application to coherent interference.

  Patent Documents 1 and 2 disclose scanning-type white light interferometry using the principle of low coherence interference as a method for accurately measuring the dimension (surface height) of an object to be measured in a non-contact manner.

  White interferometry uses a white light source with a broad spectrum and a short coherent length. That is, the white light emitted from the white light source is divided into measurement light and reference light, the measured light is irradiated onto the object to be measured, and the divided reference light is irradiated onto the reference mirror. Then, interference fringes are formed by causing interference between the measurement light reflected by the object to be measured and the reference light reflected by the reference mirror, and based on the interference fringes, the dimensions of the object to be measured at the position irradiated with the measurement light are measured. To do.

  The interference fringes are formed when the optical path length of the measurement light and the optical path length of the reference light are substantially equal, and the amplitude of the interference fringes becomes maximum when the optical path lengths match. Therefore, the dimension of the measurement object is measured by moving the reference mirror, scanning the optical path length of the reference light, and measuring the optical path length of the reference light when the amplitude of the interference fringes is maximized. According to the white light interferometry, the dimension of the object to be measured can be measured with nanometer accuracy by accurately scanning the optical path length of the reference light.

  By the way, Patent Document 1 discloses a reference optical path length scanning device in which a plurality of corner cube prisms as reference mirrors are installed on a rotary table. According to this reference optical path length scanning device, the corner cube prism moves at high speed along a circular movement locus by rotating the rotary table at high speed, so that the optical path length of the reference light can be scanned at high speed. . This improves the measurement speed.

  When the measurement range of the dimension is wide, the movement range of the reference mirror is also widened, but the measurement time can be shortened by using the reference optical path length scanning device. The comparison of the measurement time is a comparison with a device in which the reference mirror is moved by a linear motion device such as a ball screw device.

JP 2009-222705 A JP 2010-43954 A

  By the way, in the reference optical path length scanning device that directly irradiates the corner cube prism 2 arranged on the turntable 1 with the reference light 5 from the optical fiber 3 through the lens 4 as shown in FIG. Since the attitude of the corner cube prism 2 (the direction of the incident surface 2A with respect to the reference light 5) changes with the rotation shown, there is a problem that the measurement accuracy decreases.

  That is, the incident angle of the reference light 5 with respect to the incident surface 2A of the corner cube prism 2 changes with the rotation of the turntable 1 from the position of the incident angle 0 degrees of the corner cube prism 2 indicated by the solid line. That is, the incident angle of the reference light 5 with respect to the incident surface 2A of the corner cube prism 2 indicated by a two-dot chain line is larger than the incident angle 0 degrees of the corner cube prism 2 indicated by a solid line. As a result, the light receiving area of the reference light 5 on the incident surface 2A is reduced, so that the amount of the reference light 5 incident on the corner cube prism 2 is reduced. As a result, since the light intensity of the reference light 5 that interferes with the measurement light is lowered, there is a problem that the measurement accuracy is lowered.

  In order to solve such a problem, only the reference light when the corner cube prism moves within the range of the rotation angle in the vicinity including the incident angle of 0 degrees is extracted, and the reference light interferes with the measurement light. However, in this case, there is a problem that the scanning range of the reference light 5 becomes narrow and the measurement range becomes narrow.

  In FIG. 13, reference numeral 6 indicates a rotation axis of the rotary table 1, reference numeral 7 indicates a reflecting mirror that reflects the reference light 5 emitted from the corner cube prism 2 to the corner cube prism 2, and reference numeral 8 indicates a corner. A circular movement locus of the cube prism 2 is shown.

  The present invention has been made in view of such circumstances, and can improve the measurement speed, shorten the measurement time, improve the measurement accuracy, and expand the scanning range of the reference light. It is an object to provide a measuring device and a reference optical path length scanning device.

  According to one aspect of the present invention, in order to achieve the object of the present invention, a light source that emits white light, a light dividing unit that divides the white light into measurement light and reference light, and a measurement light to be measured A measuring light irradiating means for irradiating an object; a rotating member that rotates about a rotation axis; and a ball lens that is disposed on the rotating member and reflects the reference light incident thereon, and rotates by rotating the rotating member Reference light path length scanning means for changing the position of the ball lens with respect to the optical axis direction of the reference light by rotating a ball lens having a refractive index of 2 around the axis, and the measurement light and the ball lens reflected by the object to be measured A dimension measuring apparatus comprising: a light detecting means for detecting interference light combined with the reference light reflected by the light; and an arithmetic means for calculating a dimension of the object to be measured based on the interference light detected by the light detecting means. provide.

  According to the aspect of the dimension measuring apparatus of the present invention, the white light emitted from the light source is divided into the measurement light and the reference light by the light dividing means, and the measurement light and the reference light are emitted from the light dividing means. The measurement light emitted is applied to the object to be measured by the measurement light irradiation means, and the emitted reference light is applied to the ball lens. Then, the measurement light reflected or scattered on the surface of the object to be measured and the reference light reflected by the ball lens are combined by the light splitting means, and the interference light is detected by the light detection means. Then, the calculation means calculates the dimension of the object to be measured based on the interference light detected by the light detection means.

  One aspect of the present invention uses a ball lens having a refractive index of 2 as a reference mirror, and rotates the ball lens by a rotating member to change the position of the ball lens with respect to the optical axis direction of the reference light. The optical path length of the reference light is scanned. Even if the position of the ball lens changes along a circular movement locus centering on the rotation axis, the attitude of the incident surface with respect to the reference light does not change. Therefore, the ball lens reflects the incident reference light in a direction opposite to the incident direction of the reference light regardless of the rotational position.

  Therefore, according to one embodiment of the present invention, the measurement speed can be improved and the measurement time can be shortened, the measurement accuracy can be improved, and the scanning range of the reference light can be expanded.

  In addition, according to one embodiment of the present invention, the intensity unevenness of the reference light reflected by the ball lens can be suppressed, so that the measurement accuracy is further improved.

  Furthermore, according to one aspect of the present invention, the ball lens can be downsized due to the expansion of the scanning range of the reference light, so that the reference optical path length scanning unit can be downsized.

  Furthermore, according to one aspect of the present invention, since a ball lens having a lower air resistance than that of a corner cube prism is used, the moving speed of the ball lens can be increased. Therefore, the measurement speed is further improved.

  In one embodiment of the present invention, it is preferable that a plurality of ball lenses be arranged along a circumferential direction around the rotation axis of the rotation member.

  According to one embodiment of the present invention, the ball lens can be easily moved along a circular locus by rotating the rotating member around the rotation axis. Also, the measurement speed is improved by arranging a plurality of ball lenses.

  In one embodiment of the present invention, it is preferable that a light reflection film is provided on a reflection surface of a ball lens having a refractive index of 2 that reflects reference light.

  According to one aspect of the present invention, the reference light incident on the ball lens can be reflected as effectively as possible. Thereby, scanning accuracy and measurement accuracy are further improved.

  In one embodiment of the present invention, an etalon (a ball lens in this case may have a refractive index smaller than 2) is preferably provided between the light source and the light splitting unit.

  According to one embodiment of the present invention, white light can be generated as intensity-modulated light by an etalon, so that an effective optical path length of reference light that interferes with measurement light can be increased.

  In order to achieve the object of the present invention, an aspect of the present invention provides a reference optical path length scanning device that scans the optical path length of the reference light out of the measurement light and the reference light divided by the light dividing means. A rotating member that is rotated about the center, and a ball lens that is disposed on the rotating member and reflects the reference light incident thereon. The reference is obtained by rotating the rotating member and rotating the ball lens about the rotation axis. Provided is a reference optical path length scanning device for changing a position of a ball lens with respect to an optical axis direction of light.

  According to the reference optical path length scanning device of one aspect of the present invention, since the ball lens is used as the reference mirror that scans the reference light, the measurement speed can be improved, the measurement time can be shortened, and the measurement accuracy can be improved. In addition, the scanning range of the reference light can be expanded.

  According to the dimension measuring apparatus and the reference optical path length scanning apparatus of the present invention, since the ball lens is used as the reference mirror, the measurement speed can be improved and the measurement time can be shortened, and the measurement accuracy can be improved. The scanning range can be expanded.

The block diagram of the dimension measuring apparatus of embodiment with which the dimension measuring apparatus of this invention was applied Side view showing a configuration example of a resonator Graph showing an example of the transmission characteristics of a resonator Diagram showing an example of the transmission characteristics of a resonator FIG. 4 is a diagram showing the frequency indicating the transmittance peak in the transmission characteristics of the resonator shown in FIG. 4 based on “frequency-electric field”. Explanatory drawing showing the optical path where the reflected light from the ball lens returns to the optical fiber Enlarged view of the ball lens Enlarged view of a ball lens with a reflective coating on the reflective surface of the ball lens Flow chart showing the operation of the dimension measuring device (A) is a graph showing the change in the light intensity of the ball lens with respect to the rotation angle of the rotary table, (B) is a graph showing the change in the light intensity of the corner cube prism with respect to the rotation angle of the rotary table. Explanatory drawing with multiple ball lenses arranged on a rotary table Explanatory drawing which showed the optical path of reflected light at the time of arranging a plurality of ball lenses on a turntable Explanatory drawing of the reference optical path length scanning device which directly irradiates the reference light toward the corner cube prism arranged on the rotary table

  Hereinafter, preferred embodiments of a dimension measuring device and a reference optical path length scanning device according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram of a dimension measuring apparatus 10 according to an embodiment to which a dimension measuring apparatus and a reference optical path length scanning apparatus of the present invention are applied.

[Dimension measuring device 10]
The dimension measuring apparatus 10 includes a broad spectrum light source (hereinafter abbreviated as “light source”) 12, a resonator (etalon) 14, a circulator 16, a beam splitter (light splitting means) 18, and an object scanning optical system (measurement light irradiation means). 20

  Further, the dimension measuring apparatus 10 includes a reference optical path length scanning device (reference optical path length scanning means) 22 having a ball lens 24 as a reference mirror, a detector (light detection means) 26, a frequency type amplifier 28, and a controller (calculation means). 30 and optical fibers 32, 34, 36, 38, 40, 42.

  In the dimension measuring apparatus 10, white light emitted from the light source 12 enters the resonator 14 via the optical fiber 32. The resonator 14 has a discrete light transmission band with respect to the frequency of light, receives white light from the light source 12, generates intensity-modulated light 15 having a specific optical frequency component, and emits only the intensity-modulated light 15. . The resonator 14 will be described later (see FIGS. 2 to 5).

  The intensity modulated light 15 emitted from the resonator 14 enters the beam splitter 18 through the optical fiber 34, the circulator 16, and the optical fiber 36.

  The intensity-modulated light 15 is split by the beam splitter 18 into measurement light that travels toward the measurement object scanning optical system 20 and reference light that travels toward the reference optical path length scanning device 22 and then is emitted in the respective directions.

  The measurement light emitted from the beam splitter 18 enters the measurement object scanning optical system 20 via the optical fiber 38 and forms an image on the measurement point on the surface of the measurement object 44 by the lens 46 of the measurement object scanning optical system 20. Is done. Then, the measurement light reflected or scattered at the measurement point is returned to the beam splitter 18 via the measurement object scanning optical system 20 and the optical fiber 38.

  On the other hand, the reference light emitted from the beam splitter 18 enters the reference optical path length scanning device 22 through the optical fiber 40, and enters the ball lens 24 through the collimator lens 48 of the reference optical path length scanning device 22. Then, the reference light reflected by the ball lens 24 (hereinafter also referred to as reflected light) is returned to the beam splitter 18 via the collimator lens 48 and the optical fiber 40.

  Here, reference numeral 58 indicates reference light incident on the ball lens 24, and reference numeral 60 indicates reflected light reflected by the ball lens 24. In the specification, the reference light 58 and the reflected light 60 may be described separately, but the reflected light 60 is a part of the reference light 58.

  On the other hand, the measurement light and the reference light returned to the beam splitter 18 are combined by the beam splitter 18 and then enter the detector 26 via the optical fiber 36, the circulator 16, and the optical fiber 42.

  Hereinafter, each part of the dimension measuring apparatus 10 will be described in detail.

<Light source 12>
The light source 12 is a white light source having a short coherent length and capable of emitting light having a broad wavelength. As the light source 12, for example, an LED (Light Emitting Diode), an SLD (Super Luminescence Diode), a halogen lamp, or an optical frequency comb (however, when an optical frequency comb is used, the length of the etalon and the repetition frequency of the intensity-modulated light must match. You can use it). The center wavelength of the light emitted from the light source 12 can be set to 750 nm, 1300 nm, 1550 nm, and the like, for example.

<Resonator 14>
FIG. 2 is a side view showing the configuration of the resonator 14.

  The resonator 14 is a Fabry-Perot etalon with a fixed inter-interference distance, and includes a pair of reflection plates 14A and 14B that are arranged apart from each other, and a reflection region 14C between the reflection plates 14A and 14B. Have.

  The reflection plate 14A transmits white light from the light source 12, but reflects light from the reflection plate 14B. On the other hand, the reflection plate 14B transmits only the intensity-modulated light 15 having a specific optical frequency component and reflects light components in other frequency bands.

  The reflection area 14C is an area where incident light repeats reflection between the reflection plate 14A and the reflection plate 14B, and elements constituting the reflection area 14C are not particularly limited. For example, the resonator 14 in which the reflection area 14C is made of air is called an air gap etalon, and the resonator 14 in which the reflection area 14C is made of a solid such as quartz is called a solid etalon.

  When white light from the light source 12 enters the reflection area 14C from the reflection plate 14A, the incident light repeatedly reflects between the reflection plate 14A and the reflection plate 14B, and a specific wavelength component (frequency component) is strengthened by the interference effect. Then, the light passes through the reflection plate 14B and is emitted from the resonator 14. The characteristic of the intensity-modulated light 15 emitted from the resonator 14 is specified by FSR (Free Spectral Range) and finesse (FSR / Full width at half maximum: Finesse).

  FIG. 3 is a graph illustrating an example of the transmission characteristics of the resonator 14. The horizontal axis in FIG. 3 indicates the fringe order (m, m + 1, m + 2), and the vertical axis indicates the transmittance of the resonator 14.

  The interval between adjacent light transmission bands with respect to frequency is constant. That is, the characteristics of the resonator 14 are determined based on the FSR representing the transmission band interval of the resonator 14 and the FWHM which is the full width at half maximum of the transmission peak. Finesse is an index indicating the degree of sharpness of interference fringes.

  FIG. 4 is a diagram illustrating an example of the transmission characteristics of the resonator 14, where the horizontal axis represents frequency and the vertical axis represents transmittance. As shown in FIG. 4, the frequency indicating the transmittance peak appears discretely. The interval between adjacent transmittance peaks is determined based on the FSR.

  FIG. 5 is a diagram showing the frequency indicating the transmittance peak in the transmission characteristics of the resonator 14 shown in FIG. 4 based on “frequency-electric field”.

The resonator 14 according to the embodiment generates and emits the intensity modulated light 15 having “f _rep ” of 15 GHz. Therefore, the dimension measuring apparatus 10 of the embodiment uses the periodicity of the intensity-modulated light 15 from the resonator 14 to obtain the same effect as the measurement using the optical comb, that is, the reference light that interferes with the measurement light. An effective optical path length can be increased.

<Beam splitter 18>
The beam splitter 18 in FIG. 1 divides the intensity-modulated light 15 incident through the optical fiber 36 into measurement light emitted to the optical fiber 38 and reference light emitted to the optical fiber 40. Further, the beam splitter 18 combines the measurement light returned via the optical fiber 38 and the reference light returned via the optical fiber 40, and outputs the resultant light to the optical fiber 36. For example, various known optical couplers having such a function can be used as the beam splitter 18.

<Measurement Scanning Optical System 20>
The measurement object scanning optical system 20 forms an image of the measurement light emitted from the optical fiber 38 at an arbitrary measurement point on the surface of the measurement object 44 via the lens 46. Then, the measurement object scanning optical system 20 collects the measurement light reflected or scattered at the measurement point and makes the measurement light incident on the optical fiber 38. For this purpose, the measuring object scanning optical system 20 includes a lens 46, a scanning mirror (not shown), and an actuator (not shown) for driving the scanning mirror. The actuator adjusts the direction of the reflecting surface of the scanning mirror according to the control signal received from the controller 30.

  Further, the measurement object scanning optical system 20 is provided with a translucent reflecting plate 50 for creating a zero point signal RS in the controller 30. Since the reflecting plate 50 is disposed at a position having the same length as the reference optical path length, an interference fringe having an optical path difference of 0 is formed by the detector 26. Note that the symbol TS is a target signal.

<Reference Optical Path Length Scanning Device 22>
The reference optical path length scanning device 22 is configured such that the reference light emitted from the optical fiber 40 enters the optical fiber 40 again after passing through a predetermined optical path. Then, the reference optical path length scanning device 22 scans the optical path length of the optical path, and adjusts the optical path difference between the optical path length of the measurement light and the optical path length of the reference light.

  For this purpose, the reference optical path length scanning device 22 includes a ball lens 24, a disk-shaped rotary table (rotary member) 54 having a rotary shaft 52 at the center, and a motor 56 that rotates the rotary table 54 via the rotary shaft 52. . The rotation shaft 52 is arranged in a direction orthogonal to the light beam of the reference light 58 in the plan view of FIG.

  The rotating table 54 is rotated at a constant rotational speed in the direction indicated by the arrow A by the motor 56 during the measurement operation. For example, the rotary table 54 is rotated at 5000 rpm during the measurement operation. When the rotation speed of the turntable 54 is set to 5000 rpm, the frequency of 15 GHz corresponds to 10 mm in length. Therefore, the scanning length is required to be 10 mm or more. A ball lens 24 that scans the reference light 58 is disposed on the upper surface of the rotary table 54.

<Ball Lens 24>
The ball lens 24 moves (rotates) along a circular movement locus when the rotary table 54 is rotated. Since the position of the ball lens 24 with respect to the optical axis direction of the reference light 58 is changed by the rotation operation of the rotary table 54, the optical path length of the reference light is scanned. The movement amount of the ball lens 24 is calculated by the controller 30 based on the rotation radius and rotation angle of the ball lens 24.

  FIG. 6 is an explanatory diagram showing an optical path in which reflected light (reference light) 60 from the ball lens 24 having a refractive index of about 2.0 returns to the optical fiber 40 through the collimator lens 48. Note that the refractive index of the ball lens 24 is preferably 1.9 to 2.1, and more preferably 1.95 to 2.05.

  As shown in the enlarged view of FIG. 7, the ball lens 24 having a refractive index of 2 has a spherical incident surface 24A on which the reference light 58 emitted from the beam splitter 18 (see FIG. 1) is incident, and the incident surface 24A. And a spherical reflecting surface 24B that reflects the reference light 58 incident from the incident surface 24A toward the incident surface 24A. Further, when the refractive index is 2, the reference light 58 incident from the incident surface 24A is collected at one point of the reflecting surface 24B and reflected by the reflecting surface 24B. At this time, the reflected light 60 reflected by the reflecting surface 24B is reflected in a direction opposite to the incident direction of the reference light 58.

  That is, by using the ball lens 24 as a reflecting mirror, the incident angle of the reference light 58 incident on the incident surface 24A of the ball lens 24 is not affected by the movement position of the ball lens 24. In addition, a light amount substantially equal to the light amount incident from the incident surface 24A can be reflected by the reflecting surface 24B.

  Accordingly, the scanning range is expanded as compared with a conventional dimension measuring apparatus using a corner cube prism as a reflecting mirror.

  Further, since the ball lens 24 is a sphere, the air resistance received by the ball lens 24 when the rotary table 54 rotates is smaller than that of the beam splitter. Thereby, since the vibration of the rotary table 54 resulting from air resistance can be suppressed, highly accurate scanning is attained.

  FIG. 8 is an enlarged view of the ball lens 24, and is an explanation in which a reflective coating (light reflecting film) 62 such as gold plating is applied to the surface of the reflecting surface 24B of the ball lens 24 near the condensing point. Since the reference light 58 that has reached the reflecting surface 24B is reflected to the maximum by the reflection coat 62, the reference light 58 that has reached the reflecting surface 24B can be used to the maximum extent possible.

<Detector 26>
The detector 26 in FIG. 1 outputs the detected light quantity as an electrical signal. For example, a semiconductor detection element such as a photodiode, a CCD (Charge Coupled Device), or a C-MOS (Complementary Metal Oxide Semiconductor) is used as the detector 26. The detector 26 samples at predetermined time intervals, and converts the detected light amount at each sampling time into an electrical signal. Further, the detector 26 is electrically connected to the controller 30 via the frequency type amplifier 28, and sequentially transmits the electric signal to the controller 30.

  Here, when optical interference occurs due to the interference light in which the reference light and the measurement light are combined, the optical path difference of the light changes according to the movement of the ball lens 24. The electrical signal to be changed also varies. Further, since the position of the ball lens 24 changes with the rotation of the rotary table 54, the position changes with time. Therefore, the interference fringes are observed in the temporal change of the electrical signal output from the detector 26.

<Optical fibers 32-42>
The optical fibers 32 to 42 are disposed between the light source 12, the resonator 14, the circulator 16, the beam splitter 18, the measurement object scanning optical system 20, the reference optical path length scanning device 22, and the detector 26. Is transmitted. Various known optical fibers can be used as the optical fibers 32 to 42, but it is preferable that the transmission loss is as small as possible with respect to the wavelength of the light emitted from the light source 12.

<Controller 30>
The controller 30 is configured by a so-called PC (Personal Computer), an arithmetic device such as a CPU (Central Processing Unit), a semiconductor memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory), a magnetic disk, an optical disk, and the like. A storage device including these reading devices, a communication device including software such as electronic circuits and device drivers configured based on communication standards such as RS232C and Ethernet (registered trademark), and a CPU stored in the storage device A program to be executed.

  Then, the controller 30 calculates the height of the measurement point of the object to be measured 44 by measuring the optical path length of the reference light from the light amount detected by the detector 26.

  Moreover, the controller 30 is electrically connected to each part of the dimension measuring apparatus 10, and performs overall control thereof.

  Further, the controller 30 calculates the movement amount of the ball lens 24 based on the rotation radius and rotation angle of the ball lens 24, and calculates the optical path length of the reference light based on the movement amount. And the controller 30 calculates the dimension (surface height) of the to-be-measured object 44 based on the interference fringe produced according to the optical path difference of reference light and measurement light.

[Operation of Dimension Measuring Device 10]
FIG. 9 is a flowchart showing the operation of the dimension measuring apparatus 10 when measuring the dimension of the DUT 44. The operation of the dimension measuring apparatus 10 is controlled by the controller 30.

  As a preliminary preparation, a reference product having a known dimension is installed in the dimension measuring device 10, and the position PR of the ball lens 24 corresponding to the maximum value of the interference fringe amplitude when the reference surface is irradiated with the measurement light is calculated. It is stored in the storage device of the controller 30.

  When the measurement operation is started, the controller 30 controls the motor 56 to rotate the rotary table 54 at a predetermined rotational speed (for example, 5000 rpm) (step S101).

  Next, the actuator of the measurement object scanning optical system 20 is controlled to adjust the direction of the scanning mirror so that the measurement light forms a spot at an arbitrary measurement point of the measurement object 44 (step S102).

  Next, an interference fringe generated according to the difference between the optical path length of the measurement light and the optical path length of the reference light 58 is detected by the detector 26 (step S103). The detector 26 transmits an electrical signal corresponding to the interference fringe to the controller 30.

  Next, the controller 30 correlates the electrical signal received from the detector 26 with the position of the ball lens 24 (step S104).

  Then, the controller 30 measures the time at which the amplitude of the periodic vibration of the electrical signal is maximized, that is, the time TP at which the amplitude of the interference fringe is maximized, and calculates the position PP of the ball lens 24 at the time TP. (Step S105).

  Thereafter, the controller 30 calculates the optical path difference of the reference light 58 corresponding to the difference between the position PP of the ball lens 24 obtained in step S105 and the position PR of the ball lens 24 similarly obtained with respect to the reference plane. Is calculated (step S106).

  And the controller 30 calculates the surface height of the to-be-measured object 44 in a measurement position by adding the optical path difference to the surface height of a reference surface (step S107).

  Then, the controller 30 repeatedly performs the processes of steps S101 to S107 described above, and measures the surface height at each point on the surface of the measurement object 44 for each measurement light irradiation position.

  By the way, in the dimension measuring apparatus 10 including the resonator 14, the intensity-modulated light 15 (see FIGS. 4 and 5) is applied to the object to be measured 44 and the ball lens 24. The measurable range is expanded as compared with a general dimension measuring device irradiated on the lens 24.

  That is, the measurable range of the dimension measuring apparatus 10 using the intensity-modulated optical signal emitted from the resonator 14 is determined according to the FSR of the resonator 14 (see FIG. 3). Specifically, “the position of the object 44 to be measured where the optical path length of the measurement light and the optical path length of the reference light are equal (which can be measured by a dimension measurement apparatus using general low-coherence light that does not include the resonator 14 ( (Hereinafter also referred to as “zero point position”) ”and“ N × nD (where “N” represents an integer of 1 or more, “n” represents the refractive index of the reflection region 14C of the etalon 14) from the zero point position, “D” represents the distance between the reflective coat 14A and the reflective coat 14B of the etalon 14) ”, and the position at a distance can be measured.

Therefore, according to the dimension measuring apparatus 10, “L = (L ₀ + N × nd (where“ L ₀ ”represents the zero point position,“ N ”represents an integer of 0 or more, and“ n ”represents the etalon 14. It represents the refractive index of the reflective area 14C, and “d” represents the distance between the reflective coat 14A and the reflective coat 14B of the etalon 14) ”, and can be measured at discrete positions L. The discrete positions L indicate positions that are separated from the zero point position L _{0 of the} object to be measured 44 by “N × nd” in the direction in which the intensity-modulated light 15 is directed to the object to be measured 44.

〔effect〕
The dimension measuring apparatus 10 according to the embodiment scans the reference light 58 in a short time by the ball lens 24 by scanning the reference light 58 and rotating the rotary table 54 for scanning the optical path of the reference light 58. Can do. Further, the optical path length of the reference light 58 can be greatly scanned in a short time. As a result, the dimension measuring apparatus 10 can improve the measurement speed and shorten the measurement time, improve the measurement accuracy, and expand the scanning range of the reference light.

  Further, the dimension measuring device 10 and the reference optical path length scanning device 22 of the embodiment use the ball lens 24 as a reference mirror, and move the ball lens 24 along a circular movement locus so that the optical path length of the reference light 58 is increased. Scanning.

  Even if the position of the ball lens 24 changes along the circular movement locus, the attitude of the incident surface with respect to the reference light 58 does not change. Therefore, the ball lens 24 reflects the incident reference light 58 in a direction opposite to the incident direction of the reference light 58 regardless of the moved position. Due to the above characteristics of the ball lens 24, the following effects can be obtained.

  FIG. 10A is a graph showing changes in the light intensity of the ball lens 24 with respect to the rotation angle of the turntable 54. Here, FIG. 10B will be described with reference to FIG. 13. FIG. 10B is a graph showing a change in light intensity of the corner cube prism 2 with respect to the rotation angle of the turntable 1. is there.

  10A and 10B, the horizontal axis indicates the rotation angle of the rotary table, and the vertical axis indicates the light intensity.

  The light intensity on the vertical axis indicates the light intensity of the reflected light 60 reflected by the reflecting surface 24B of the ball lens 24 in FIG. 10A, and is reflected by the reflecting surface of the corner cube prism 2 in FIG. 10B. Refers to the light intensity of reflected light. Further, the angle at which the light intensity is maximum is set to a rotation angle of 0 degrees, and the light intensity when rotated in the ± direction with respect to the light intensity at the rotation angle of 0 degrees is shown as a relative value.

  As shown in FIG. 10A, the light intensity of the reflected light 60 reflected by the reflecting surface 24B of the ball lens 24 is maximum within a rotation range of −40 to +40 degrees without being influenced by the rotation angle of the rotary table. The value was maintained.

  On the other hand, as shown in FIG. 10B, the light intensity of the reflected light reflected by the reflecting surface of the corner cube prism 2 decreased as the rotation angle of the rotary table increased. In addition, at the rotation position of −40 to +40 degrees, the light intensity decreased by 20% or more.

  Therefore, according to the dimension measuring apparatus 10 of the embodiment, the measurement speed can be improved and the measurement time can be shortened, the measurement accuracy can be improved, and the scanning range of the reference light can be expanded.

  Moreover, according to the dimension measuring apparatus 10, since the intensity nonuniformity of the reference light 58 reflected by the ball lens 24 can be suppressed, the measurement accuracy is further improved.

  Further, according to the dimension measuring device 10, the ball lens 24 can be downsized due to the expansion of the scanning range of the reference light 58, so that the reference optical path length scanning device 22 can be downsized. It was. Specifically, a small ball lens 24 having a diameter of 5 to 10 mm could be applied.

  Furthermore, according to the dimension measuring apparatus 10, since the spherical ball lens 24 having a small air resistance is used as compared with the corner cube prism 2 which is a three-sided mirror, the moving speed of the ball lens 24 can be increased. . Therefore, the measurement speed was further improved.

  When the rotation speed of the rotary table is increased, the rotary table vibrates due to air resistance, causing measurement errors. For this reason, the corner cube prism 2 cannot increase the rotation speed. On the other hand, in the case of the ball lens 24, the rotation speed could be increased 3 to 5 times compared to the case of the corner cube prism 2.

  Further, as shown in FIG. 8, a reflective coat 62 is applied to the reflective surface 24B of the ball lens 24.

  Therefore, according to the dimension measuring apparatus 10, the reference light incident on the ball lens 24 can be reflected to the maximum extent. Thereby, the scanning accuracy and the measurement accuracy are further improved.

  FIG. 11 is a plan view in which a plurality of ball lenses 24 are arranged along the circumferential direction around the rotation shaft 52 of the turntable 54. Six ball lenses 24 are arranged at equal intervals at positions on a concentric circle S centering on the rotation shaft 52 of the rotary table 54.

  FIG. 12 is a diagram showing two ball lenses 24 extracted from the six ball lenses 24 shown in FIG. 11, and an explanation showing the optical path of the reflected light 60 of the two ball lenses 24. FIG.

  As shown in FIG. 12, even when two ball lenses 24 having different positions exist in the light beam of the reference light 58, the incident angle of the reference light 58 incident on the incident surface 24A of the ball lenses 24 changes. do not do. Even if the movement position of the ball lens 24 changes, the ball lens 24 can reflect a light amount substantially equal to the incident light amount within the luminous flux of the reference light 58.

  When a plurality of ball lenses 24 are arranged on the rotary table 54, the controller 30 calculates the optical path length of the reference light as follows.

  A rotary encoder (not shown) is attached to the rotary shaft 52 of the rotary table 54, and the rotation angle information output from the rotary encoder is associated with the position of each ball lens 24. Then, the controller 30 identifies the reflected light 60 reflected from which position of the plurality of ball lenses 24 based on the rotation angle information output from the rotary encoder.

  Then, the controller 30 specifies the ball lens 24 that reflects the reflected light 60 at that time based on the rotation angle information from the rotary encoder that is output when the interference fringes are formed. The optical path length of the reference light is calculated based on the position. By arranging a plurality of ball lenses 24 in this manner, the reference light 58 can be scanned at high speed.

  DESCRIPTION OF SYMBOLS 10 ... Dimension measuring apparatus, 12 ... Light source, 14 ... Resonator, 15 ... Intensity modulation light, 16 ... Circulator, 18 ... Beam splitter, 20 ... Measuring object scanning optical system, 22 ... Reference optical path length scanning apparatus, 24 ... Ball lens , 24A ... incidence surface, 24B ... reflection surface, 26 ... detector, 28 ... frequency amplifier, 30 ... controller, 32, 34, 36, 38, 40, 42 ... optical fiber, 44 ... object to be measured, 46 ... lens 48 ... Collimator lens, 50 ... Reflector, 52 ... Rotating shaft, 54 ... Rotating table, 56 ... Motor, 58 ... Reference light, 60 ... Reflected light, 62 ... Reflective coating

Claims (5)

A light source that emits white light;
A light splitting means for splitting the white light into measurement light and reference light and emitting them;
Measuring light irradiation means for irradiating the object to be measured with the measurement light
A rotating member that rotates about a rotation axis; and a ball lens that is disposed on the rotation member and reflects the reference light incident thereon. The ball is rotated about the rotation axis by rotating the rotation member. A reference optical path length scanning unit that changes a position of the ball lens with respect to an optical axis direction of the reference light by rotating a lens;
Light detection means for detecting interference light in which the measurement light reflected by the object to be measured and the reference light reflected by the ball lens are combined;
A calculation means for calculating a dimension of the object to be measured based on the interference light detected by the light detection means;
A dimension measuring device comprising:   The dimension measuring device according to claim 1, wherein a plurality of the ball lenses are arranged along a circumferential direction around the rotation axis of the rotating member.   The dimension measuring apparatus according to claim 1, wherein a light reflection film is provided on a reflection surface of the ball lens that reflects the reference light.   The dimension measuring apparatus according to claim 1, wherein an etalon is provided between the light source and the light splitting unit. In the reference optical path length scanning device that scans the optical path length of the reference light among the measurement light and the reference light divided by the light dividing means,
A rotating member that rotates about a rotation axis; and a ball lens that is disposed on the rotation member and reflects the reference light incident thereon. The ball is rotated about the rotation axis by rotating the rotation member. A reference optical path length scanning device that changes a position of a ball lens with respect to an optical axis direction of the reference light by rotating the lens.

Images