JP2008309638A - Dimension measuring device and dimension measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dimension measuring device and dimension measuring method capable of measuring the measuring object dimension of an object to be measured in a short time. <P>SOLUTION: This dimension measuring device 1 comprises a first interferometer 3 for dividing the light from a white light source 2 into a first light flux and second light flux going to the object to be measured and causing the first optical path difference corresponding to the measuring object dimension of the object between the first light flux and the second light flux, a second interferometer 4 for dividing the light flux coming from the first interferometer 3 into a third light flux going to a reference mirror 43 and a fourth light flux going to a moving mirror 44 movable along the optical path, and causing the second optical path difference between the third light flux and the fourth light flux, a detector 5 for receiving the third and fourth light fluxes and detecting an interference signal, and a controller 6 for estimating the peak of the interference signal to the object by fitting the master characteristic curve previously determined about the master of the object to an interference signal group acquired at a plurality of sampling points of the moving mirror 44, and determining the measuring object dimension from the second optical path difference corresponding to the peak. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dimension measuring apparatus and a dimension measuring method, and more particularly to a dimension measuring apparatus and a dimension measuring method using white interference.

  Conventionally, a method using the principle of white interference has been proposed as a method for accurately measuring the dimension or surface roughness of a processed part in a non-contact manner. For example, a measuring apparatus that measures the flange back of a digital camera using white light interference is known (see Patent Document 1). In the measuring apparatus described in Patent Document 1, light emitted from a white light source is divided into a first optical path and a second optical path by a beam splitter. And the light which went to the 1st optical path is reflected by the reference mirror for length measurement which can move along a 1st optical path. On the other hand, the light traveling toward the second optical path is reflected by an image sensor of the camera fixedly attached to a reference plane that can come into contact with the flange of the camera. The light reflected by the reference mirror and the image sensor is united by a beam splitter and detected by a detector. Here, by moving the reference mirror along the first optical path, the maximum amount of white interference fringes of the light passing through the first optical path and the light passing through the second optical path, that is, the white interference becomes a peak. The position of the reference mirror is detected. Based on the position of the reference mirror, the length from the flange to the image sensor is detected.

  Thus, in order to accurately determine the measurement target dimension of the object to be measured using white interference, it is necessary to accurately determine the peak position of the interference fringes. Therefore, when measuring the interference fringes, it is necessary to change the optical path difference between the two optical paths little by little to acquire the interference signal. For example, in the measurement apparatus described above, the period of the interference fringes is approximately ½ of the center wavelength of light emitted from the white light source with respect to the position of the reference mirror. It is necessary to acquire the interference signal while moving the reference mirror at intervals of 4 or less. However, if an interference signal is acquired at such a very short sampling interval, the measurement time per time becomes very long. Therefore, assuming the characteristic function corresponding to the envelope of the interference signal, the shape of the measurement target surface can be measured in a short time by measuring only a sufficient number of interference signals to determine the peak position of the specific function. A method has been developed (see Patent Document 2).

JP 2005-115149 A JP 2001-66122 A

  However, for example, when a measuring device using the principle of white interference is introduced into the product inspection process to measure the measurement target dimension of the object to be measured, it is required to inspect a large number of products in a short time. Therefore, the shorter the time required for one measurement, the better.

  In view of the above problems, an object of the present invention is to provide a dimension measuring apparatus and a dimension measuring method capable of measuring a measurement target dimension of an object to be measured in a short time in dimension measurement using white interference. .

According to one embodiment of the present invention, a dimension measuring device for measuring a dimension of an object to be measured is provided. Such a dimension measuring apparatus splits a white light source and light emitted from the white light source into a first light beam and a second light beam directed to the object to be measured, and reflects the first light beam on the object to be measured. A first interferometer that generates a first optical path difference corresponding to the measurement target dimension of the object to be measured between the two light beams and emits the first light beam and the second light beam according to one light beam; A second interferometer having a reference mirror whose position is fixed and a movable mirror movable along the optical path, wherein the light beam emitted from the first interferometer is directed to the reference mirror. And a second interferometer for branching into a fourth light beam traveling toward the movable mirror to generate a second optical path difference between the third light beam and the fourth light beam, and the third light beam and the fourth light beam. Is detected, an interference signal generated when the first optical path difference and the second optical path difference are substantially equal is detected, and a signal corresponding to the interference signal is output. A detector and a storage unit storing a master characteristic curve representing a period and amplitude variation of an interference signal obtained from the interference signal detected for the reference measurement object, using the reference measurement object as the measurement object; A controller for obtaining a measurement target dimension of the object to be measured;
The controller includes an interference signal acquisition unit that acquires, as a sample interference signal group, interference signals at a plurality of sampling points related to the position of the moving mirror, and a sample interference signal by fitting a master characteristic curve to the sample interference signal group. A peak estimation unit that estimates the peak of the master characteristic curve when the group and the master characteristic curve are the best match, and a peak estimation unit that estimates the peak of the interference signal for the object to be measured; and a mobile mirror that corresponds to the peak estimated by the peak estimation unit And a dimension determining unit that calculates a measurement target dimension by calculating a second optical path difference with respect to the position.

According to another embodiment of the present invention, a dimension measuring device for measuring a dimension of an object to be measured is provided. The dimension measuring apparatus is a first interferometer having a white light source, a reference mirror whose position is fixed, and a movable mirror movable along the optical path, and the light emitted from the white light source is converted into the reference mirror. A first interferometer for branching into a first light beam directed toward the second light beam and a second light beam directed toward the movable mirror to produce a first optical path difference between the first light beam and the second light beam; The first light beam and the second light beam emitted from one interferometer are branched into a third light beam and a fourth light beam that are directed to the object to be measured, and the third light beam is reflected by the object to be measured. A second interferometer that causes a second optical path difference corresponding to the measurement target dimension of the object to be measured between the four light beams and emits the third light beam and the fourth light beam according to one light beam. , Receiving the third light flux and the fourth light flux, detecting an interference signal generated when the first optical path difference and the second optical path difference are substantially equal, A master characteristic curve that represents the fluctuation and period of the interference signal obtained from the interference signal detected for the reference measurement object using the detector that outputs the corresponding signal and the reference measurement object as the measurement object A storage unit that stores the data and a controller that calculates the measurement target dimensions of the object to be measured are included.
The controller includes an interference signal acquisition unit that acquires, as a sample interference signal group, interference signals at a plurality of sampling points related to the position of the moving mirror, and a sample interference signal by fitting a master characteristic curve to the sample interference signal group. A peak estimation unit that estimates the peak of the master characteristic curve when the group and the master characteristic curve are the best match, and a peak estimation unit that estimates the peak of the interference signal for the object to be measured; and a mobile mirror that corresponds to the peak estimated by the peak estimation unit A dimension determining unit for calculating a measurement target dimension by calculating a first optical path difference with respect to the position;

  According to still another embodiment of the present invention, a dimension measuring device for measuring a dimension of an object to be measured is provided. The dimension measuring apparatus is an interferometer having a white light source and a movable mirror that can move along the optical path, and the light emitted from the white light source is directed to the first light beam and the movable mirror that are directed to the object to be measured. An interferometer that branches into a second light beam and reflects the first light beam by the object to be measured to cause an optical path difference between the first light beam and the second light beam, and a first light emitted from the interferometer And the second light flux are received, an interference signal generated when the optical path length for the first light flux and the optical path length for the second light flux are substantially equal is detected, and a signal corresponding to the interference signal is output. A detector and a storage unit storing a master characteristic curve representing a period and amplitude variation of an interference signal obtained from the interference signal detected for the reference measurement object, using the reference measurement object as the measurement object; A controller for obtaining a measurement target dimension of the object to be measured; The controller includes an interference signal acquisition unit that acquires, as a sample interference signal group, interference signals at a plurality of sampling points related to the position of the moving mirror, and a sample interference signal by fitting a master characteristic curve to the sample interference signal group. A peak estimation unit that estimates the peak of the master characteristic curve when the group and the master characteristic curve are the best match, and a peak estimation unit that estimates the peak of the interference signal for the object to be measured; and a mobile mirror that corresponds to the peak estimated by the peak estimation unit A dimension determining unit that obtains a measurement target dimension of the object to be measured by calculating a difference between the position and a predetermined reference position of the movable mirror.

  Further, according to the present invention, the sampling interval between adjacent sampling points among the plurality of sampling points is set so as not to be substantially an integral multiple of 1/4 of the center wavelength of the light emitted from the white light source. It is preferable.

According to still another embodiment of the present invention, the light emitted from the white light source is branched into a first light beam and a second light beam that are directed toward the object to be measured, and the first light beam is divided by the object to be measured. A first optical path difference corresponding to the measurement target dimension of the object to be measured is generated between the reflected light and the second light flux, and the first light flux and the second light flux are emitted in accordance with one light flux. The interferometer, a reference mirror whose position is fixed, and a movable mirror movable along the optical path, and directs the light beam emitted from the first interferometer to the reference mirror A second interferometer for branching into a third light flux and a fourth light flux directed toward the movable mirror to produce a second optical path difference between the third light flux and the fourth light flux; An interference signal generated when the first light path difference and the second light path difference are approximately equal is detected by receiving the light beam and the fourth light beam, and a signal corresponding to the interference signal is detected. That stores a master characteristic curve representing a period and amplitude variation of an interference signal obtained from an interference signal detected for the reference measurement object. There is provided a method for measuring a dimension of an object to be measured in a measurement system having a section.
According to the dimension measuring method, the interference signal at a plurality of sampling points related to the position of the movable mirror is obtained as a sample interference signal group, and a master characteristic curve is fitted to the sample interference signal group to obtain a sample interference signal group. Estimating the peak of the master characteristic curve when the master characteristic curve and the master characteristic curve are the best match, and the second optical path difference with respect to the position of the movable mirror corresponding to the estimated peak And calculating a measurement target dimension by calculating.
In each of the above embodiments, the white light source is not limited to a light source that emits light in a broad band in the visible light range, but a light source that emits light in a certain wavelength band with a predetermined wavelength as a center wavelength.

  ADVANTAGE OF THE INVENTION According to this invention, it became possible to provide the dimension measuring apparatus and dimension measuring method which can measure the measuring object dimension of a to-be-measured object in a short time in the dimension measurement using white interference.

Hereinafter, embodiments in which the present invention is applied to an inner diameter measuring device that measures the inner diameter of a cylindrical object to be measured, such as a ring gauge and a cylinder, will be described with reference to the drawings.
An inner diameter measuring apparatus to which the present invention is applied causes light from a white light source to enter a first interferometer, and the first interferometer generates two light beams having an optical path difference corresponding to the inner diameter of the object to be measured. . The two light beams are incident on the second interferometer, and the light beams are divided and interfered with each other in two optical paths that generate an optical path difference substantially equal to the optical path difference, thereby generating white interference fringes. Then, the inner diameter of the object to be measured is obtained by detecting the maximum signal value of the white interference fringe with a detector and measuring the optical path difference between the two optical paths of the second interferometer. At that time, the inner diameter measuring device obtains a master characteristic curve representing the period and amplitude fluctuation of the interference signal in advance from the interference signal acquired for the master which is the reference product of the object to be measured, and the master characteristic curve is relatively small. The interference signal group acquired at several sampling points is fitted to estimate the peak of the interference signal with respect to the object to be measured. Then, the inner diameter dimension of the object to be measured is obtained based on the estimated peak.

  FIG. 1 is a diagram showing a schematic configuration of an inner diameter measuring apparatus 1 to which the present invention is applied. The inner diameter measuring device 1 includes a white light source 2, a first interferometer 3 that generates an optical path difference corresponding to twice the inner diameter of the object to be measured, and an optical path difference generated by the first interferometer 3. A second interferometer 4 that generates a white interference fringe by generating an optical path difference, a detector 5 that detects the interference fringe generated by the second interferometer 4, and a control method for each part and detection of the interference fringe. A controller 6 is provided for determining the inner diameter of the measurement object. Further, the inner diameter measuring device 1 includes an optical fiber 7 that transmits light from the white light source 2 to the first interferometer 3 and an optical fiber 8 that transmits light emitted from the first interferometer 3 to the second interferometer. Have.

  The white light source 2 is a light source that has a short coherence length and can emit light having a broad wavelength. As the white light source 2, for example, an LED, an SLD (super luminescent diode), an SOA (Semiconductor Optical Amplifier) light source, an ASE (Amplified Spontaneous Emission) light source, or the like can be used. The center wavelength of the light emitted from the white light source 2 can be set to 750 nm, 1300 nm, 1550 nm, and the like, for example. In the present embodiment, an infrared LED having a center wavelength of 1550 nm is used as the white light source 2.

  FIG. 2 shows a schematic configuration diagram of the first interferometer 3. In the first interferometer 3, two light beams B 1 and B 2 having an optical path difference corresponding to twice the inner diameter of the DUT 10 arranged on the XYZ stage 36 are generated. For this purpose, in the first interferometer 3, the light incident from the white light source 2 through the first optical fiber 7 is converted into parallel light by the collimator lens 31, and the first position for adjusting the output position with respect to the incident parallel light is adjusted. To the wedge prism 32. Then, the light emitted from the wedge prism 32 is incident on a beam splitter 33 disposed substantially at the center of the inner diameter of the DUT 10. The incident light is reflected by the beam splitter 33 and branched into a light beam traveling toward the inner surface S1 of the DUT 10 and a light beam B2 that passes through the beam splitter 33 and travels straight. The light beam traveling toward the inner surface S1 of the device under test 10 returns to the beam splitter 33 after being reflected by the inner surface S1 of the device under test 10. A part of the light beam returned to the beam splitter 33 passes through the beam splitter 33 and travels to the inner surface S2 opposite to the inner surface S1 of the DUT 10. Then, the light beam directed toward S2 is reflected by the inner surface S2 and returns to the beam splitter 33 again. A part of the light beam returned to the beam splitter 33 is reflected by the beam splitter 33. This light beam is called B1. The light beam B1 and the light beam B2 are emitted together when emitted from the beam splitter 33. The light beam B1 and the light beam B2 are emitted from the beam splitter 33, then enter the second wedge prism 34 for position adjustment, and the position is adjusted so as to enter the condenser lens 35. Then, the light beam B 1 and the light beam B 2 are collected through the condensing lens 35, exit from the first interferometer 3, and enter the optical fiber 8.

  At this time, since the light beam B1 emitted from the first interferometer 3 reciprocates between the inner surfaces S1 and S2 of the object to be measured 10, if the inner diameter of the object to be measured 10 is D, the light beam B1 and the light beam B2 2D, a 2D optical path difference occurs. A light beam B 1 and a light beam B 2 having a 2D optical path difference are incident on the second interferometer 4 through the optical fiber 8.

  Note that the XYZ stage 36 has an axial direction of the device under test 10 (that is, a direction parallel to the light beam B2), a direction parallel to the light beam B1 and a direction perpendicular to the light beam B1 within a cylindrical cross section orthogonal to the axial direction of the device under test 10. It can be moved in three directions, and is driven by the stage controller 37. The stage controller 37 is electrically connected to the controller 6 and is controlled by the controller 6.

  FIG. 3 shows a schematic configuration diagram of the second interferometer 4. The light beams B1 and B2 emitted from the optical fiber 8 pass through the collimator lens 41 of the second interferometer 4 and become parallel light. Then, the light enters the beam splitter 42. The light beams B1 and B2 are reflected by the beam splitter 42 and branched into light beams B11 and B21 that travel toward the first optical path, and light beams B12 and B22 that pass through the beam splitter 42 and travel toward the second optical path. A light beam B11 represents a light beam that travels to the first optical path of the second interferometer 4 among the light beams B1 emitted from the first interferometer 3, and the light beam B21 emitted from the first interferometer 3. Of the light beam B2, the light beam traveling toward the first optical path of the second interferometer 4 is represented. Similarly, a light beam B12 represents a light beam that travels to the second optical path of the second interferometer 4 among the light beams B1 emitted from the first interferometer 3, and a light beam B22 is emitted from the first interferometer 3. Of the measured light beams B2, the light beams traveling toward the second optical path of the second interferometer 4 are represented.

  A reference mirror 43 whose position is fixed is installed in the first optical path. The light beams B <b> 11 and B <b> 21 going to the first optical path are reflected by the reference mirror 43 and return to the beam splitter 42, and part of the light passes through the beam splitter 42 and goes to the detector 5. On the other hand, a movable mirror 44 that is movable along the optical path is provided in the second optical path. Then, the light beams B12 and B22 traveling toward the second optical path are reflected by the moving mirror 44 and returned to the beam splitter 42. A part of the light beams B12 and B22 are reflected by the beam splitter 42 and travel to the detector 5 together with B11 and B21.

The movable mirror 44 is attached to the support member 45. The movable mirror 44 and the support member 45 are installed on a piezo fine movement stage 46 that can finely adjust the position of the movable mirror 44 although the movement range is narrow. The movable mirror 44 and the support member 45 are installed on a coarse movement stage 47 that, together with the piezo fine movement stage 46, has a relatively large movement range and roughly determines the position of the movement mirror 44. The piezo fine movement stage 46 and the coarse movement stage 47 are electrically connected to the piezo controller 51 and the stage controller 52, respectively. Then, the piezo fine movement stage 46 and the coarse movement stage 47 move the movable mirror 44 along the second optical path based on control signals from the piezo controller 51 and the stage controller 52.
If the interference signal is continuously measured during the movement while moving the movable mirror 44, the piezo fine movement stage 46 and the piezo controller 51 may be omitted.

  A corner cube 48 is attached to the back surface of the support member 45. Further, an interferometer 49 for measuring the position of the movable mirror 44 is installed behind the support member 45 (that is, on the opposite side of the beam splitter 42 with the support member 45 as the center). The position measurement interferometer 49 is irradiated to the corner cube 48, reflected by the corner cube 48 and returned to the position measurement interferometer 49, and interference observed between the reference light and the reference light. The amount of movement of the movable mirror 44 can be measured by counting the number of moving stripes.

The detector 5 outputs the detected light quantity as an electrical signal. As the detector 5, for example, a semiconductor detection element such as a photodiode, CCD, or C-MOS can be used. In this embodiment, a detector in which CCD elements are arranged in a two-dimensional array is used as the detector 5.
The detector 5 is electrically connected to the controller 6 and transmits an electrical signal corresponding to the detected light amount to the controller 6.

FIG. 4 shows a functional block diagram of the controller 6.
The controller 6 is configured by a so-called PC, and is in accordance with a storage unit 61 including an electrically rewritable nonvolatile memory, a magnetic disk, an optical disk, and a reading device thereof, and communication standards such as RS232C and Ethernet (registered trademark). The communication unit 62 includes software such as the configured electronic circuit and device driver.
Further, the controller 6 is a detector at any sampling point of the movable mirror 44 as a functional module realized by a CPU, ROM, RAM and its peripheral circuits (not shown) and a computer program executed on the CPU. The interference signal is acquired from the interference signal acquisition unit 63, which is a sample interference signal group by associating the acquired interference signal with the position of the sampling point, and the interference signal acquisition unit 63 acquires the interference signal from the interference signal acquisition unit 63. A peak estimation unit 64 that estimates the peak of the signal, a dimension determination unit 65 that calculates the inner diameter D of the DUT 10 from the position of the movable mirror 44 corresponding to the estimated peak of the interference signal, and each part and position of the controller 6 Measurement interferometer 49, piezo controller 51, stage controller 52, detector 5, etc. And a control unit 66 for controlling the devices connected to over La 6.

Hereinafter, an operation for measuring the inner diameter of the DUT 10 by the inner diameter measuring apparatus 1 will be described.
Since the light from the white light source 2 has a short coherence length, interference fringes are generated only when the optical path differences are substantially equal. Here, the distance from the beam splitter 42 to the reference mirror 43 in the first optical path of the second interferometer 4 is L1, and the distance from the beam splitter 42 to the moving mirror 44 in the second optical path is L2. If there is, an optical path difference of 2 (L2−L1) is generated between the third light flux and the fourth light flux (where L2> L1). At this time, if (L2−L1) and D are equal, the first interferometer 3 uses the first interferometer 4 out of the light beams B1 reflected by the inner surfaces S1 and S2 of the DUT 10. The optical path difference between the light beam B11 passing through the optical path and the light beam B2 passing through the beam splitter 33 in the first interferometer 3 and the light beam B22 passing through the second optical path in the second interferometer 4 is 0. It becomes. Therefore, the maximum interference signal can be observed. Then, as the difference between (L2−L1) and D increases, the magnitude of the interference signal decreases rapidly. Therefore, the inner diameter D of the DUT 10 can be obtained by measuring (L2-L1) when the interference signal becomes maximum, that is, when the interference signal reaches a peak.

  Further, when the moving mirror 44 is brought closer to the beam splitter 42, the optical path difference 2 (L1-L2) generated between the third light flux and the fourth light flux is twice the inner diameter D of the DUT 10. Interference fringes can be observed even at equal points (however, L1> L2). In this case, among the light beams B1 reflected by the inner surfaces S1 and S2 of the object to be measured 10 in the first interferometer 3, the light beams B12 that have passed through the second optical path in the second interferometer 4 and the first This is because, in the second interferometer 4, the optical path difference between the light beam B 2 that has passed through the beam splitter 33 in the interferometer 3 and the light beam B 21 that has passed through the first optical path becomes zero. Therefore, the difference between the position of the moving mirror 44 at which the interference signal generated between the light beams B11 and B22 is maximized and the position of the moving mirror 44 at which the interference signal generated between the light beams B12 and B21 is maximized. By dividing by 2, the inner diameter D of the DUT 10 can be obtained.

  However, in order to accurately obtain the position of the movable mirror 44 at which the interference signal peaks, as described above, it is necessary to acquire the interference signal while moving the movable mirror 44 at a very short sampling interval. . In this embodiment, assuming that the center wavelength of the light emitted from the white light source 2 is λ, the optical path difference between the light beam B11 and the light beam B22 varies by λ when the moving mirror 44 is moved by λ / 2. Is approximately λ / 2. In consideration of the sampling theorem, the sampling pitch must be at least half the period of the interference fringes. In this embodiment, since the center wavelength of the light emitted from the white light source 2 is 1550 nm, the sampling pitch must be 387 nm or less. Thus, if an interference signal is acquired at a very short sampling pitch, a long time is required for each measurement.

  Here, if the surface accuracy and measurement conditions of the inner surfaces S1 and S2 of the object to be measured 10 are substantially the same, the period and amplitude of the interference signal are substantially the same even if the inner diameter D is slightly different. Only the position of the movable mirror 44 where the peak of the interference signal is observed varies according to the inner diameter D. Therefore, a master characteristic that accurately represents the interference signal cycle and amplitude fluctuation by acquiring an interference signal in advance while moving the movable mirror 44 at a sufficiently small sampling pitch with respect to a master that is a reference product of the DUT 10. Find the curve. And when measuring the internal diameter D of the to-be-measured object 10, said master characteristic curve with respect to the interference signal group about several sampling points acquired while moving the movable mirror 44 with a comparatively big sampling pitch. Can be used to estimate the peak of the interference signal for the DUT 10.

FIG. 5 is a diagram showing how fitting is performed while shifting the master characteristic curve obtained for the master with respect to the interference signal at each sampling point obtained for the DUT 10 with respect to the position of the movable mirror 44. In FIG. 5, the horizontal axis represents the position of the movable mirror 44, and the vertical axis represents the interference signal intensity. Each point 501 to 509 represents the interference signal intensity at each sampling point obtained for the DUT 10. A solid line 520 and a broken line 530 are master characteristic curves. The solid line 520 and the broken line 530 change the position of the master characteristic curve with respect to the position of the movable mirror 44.
As shown in FIG. 5, the interference signals 501 to 509 at the respective sampling points are in good agreement with the master characteristic curve indicated by the solid line 520, but are greatly deviated from the master characteristic curve indicated by the broken line 530. In this way, if the position of the master characteristic curve is shifted little by little with respect to each sampling point, the interference signals 501 to 509 coincide well at a certain point. Since the master characteristic curve indicated by the solid line 520 that matches well with the interference signals 501 to 509 is considered to well represent the behavior of the interference signal of the DUT 10, the peak position of the master characteristic curve indicated by the solid line 520 the X _P, it can be estimated that the peak position of the interference signal measured for the DUT.

FIG. 6 shows an operation flowchart of the inner diameter measuring apparatus 1 when measuring the inner diameter D of the DUT 10.
First, as a preliminary preparation, an interference signal is acquired for the master of the DUT 10 while moving the movable mirror 44 at a sufficiently small sampling pitch, and the master represents the fluctuation of the interference signal with respect to the period of the interference signal and the position change of the movable mirror 44. A characteristic curve is obtained and stored in the storage unit 61. The sampling pitch is set to ¼ or less (in this embodiment, 387 nm or less) of the center wavelength of the light emitted from the white light source 2. The obtained master characteristic curve is stored in the storage unit 61 as a one-dimensional array in which interference signal values acquired at each sampling point are stored in order from the sampling point closer to the beam splitter 42. The interference signal value between the sampling points may be obtained by a known interpolation method such as linear interpolation or cubic spline interpolation, and may be included in the array storing the master characteristic curve.
Further, the maximum value of the interference signal, that is, the peak of the interference signal is obtained from the master characteristic curve. Then, the position corresponding to the peak is converted into the distance from the position of the movable mirror 44 corresponding to the first element of the array and stored in the storage unit 61.

Further, the sampling pitch for the position of the movable mirror 44 when the interference signal is acquired for the DUT 10 is determined. This sampling pitch can be set wider than the sampling pitch when the interference signal is acquired for the master in order to acquire the master characteristic curve. For example, in the present embodiment, the sampling pitch is basically a value obtained by dividing the range of the position of the movable mirror 44 where the interference fringes are observed into eight equally in the master characteristic curve. However, the sampling pitch is set so that the interference signals acquired for all sampling points are not near the center of the amplitude (that is, the output signal of the detector 5 when no interference signal is observed). Is preferred. As described above, when the center wavelength of the light emitted from the white light source 2 is λ, the period of the interference fringes is λ / 2. Therefore, if the sampling pitch is set to an integral multiple of λ / 4, the interference signal acquired for each sampling point may be substantially constant in some cases. In such a case, it is difficult to fit the master characteristic curve with high accuracy to the interference signal group at each sampling point. Therefore, when the sampling pitch determined as described above is substantially equal to an integral multiple of λ / 4, a value obtained by adding a certain correction value α to the sampling pitch is again set as the sampling pitch. The correction value α can be a value other than an integral multiple of λ / 4, such as λ / 6, λ / 7, and λ / 8.
The range of the position of the movable mirror 44 where the interference fringes are observed can be set to a range where the output signal from the detector 5 is equal to or greater than a predetermined threshold. The predetermined threshold is, for example, the substantially maximum value S _max of the output signal from the detector 5 when the interference fringe is measured in advance in a state where the DUT 10 is not disposed on the first interferometer 3. The output signal value S ₀ from the detector 5 in a state where it is not detected can be S ₀ + (S _max −S ₀ ) / 4. Alternatively, the position range described above may be a range in which an increase / decrease in the output signal from the detector 5 can be observed with a period of approximately ½ of the center wavelength of the white light source 2 as the moving mirror 44 moves.

The method for determining the sampling pitch is not limited to the above. The number of sampling points may be increased or decreased depending on the required accuracy of dimension measurement and the required processing speed. For example, as described above, a value obtained by dividing the position range of the movable mirror 44 where the interference fringes are observed into eight equal parts may be used as the sampling pitch, and a value obtained by dividing ten parts or five may be used as the sampling pitch. . Further, the sampling pitch may be fixedly determined as a value other than an integral multiple of λ / 4 based on the center wavelength λ from the white light source 2.
The determined sampling pitch is stored in the storage unit 61.

When the measurement is started, first, as an initialization procedure, the reference position of the movable mirror 44, that is, the movable mirror 44 in which the optical path difference between the first optical path and the second optical path of the second interferometer 4 becomes zero. Is determined (step S101). Therefore, the position where the object to be measured 10 is not installed in the first interferometer 3 of the inner diameter measuring device 1 and the interference fringe is detected by the second interferometer 4 is obtained. At this time, since there is no light beam reflected by the inner surface of the DUT 10, all the light beams emitted from the first interferometer 3 are B2. Therefore, in the second interferometer 4, the difference between the distance L1 from the beam splitter 42 to the reference mirror 43 in the first optical path and the distance L2 from the beam splitter 42 to the moving mirror 44 in the second optical path is zero. When the interference signal is maximized. Therefore, the controller 66 of the controller 6 drives the piezo fine movement stage 46 through the piezo controller 51 to move the movable mirror 44. Then, the interference signal acquisition unit 63 of the controller 6 observes the light amount detected by the detector 5 at a plurality of measurement points, and finds the position where the detected light amount is maximum, that is, the interference signal is maximum. Then, the maximum value of the output signal value, that is, the maximum value of the interference signal is obtained. Controller 6, the position of the movable mirror 44 when the interfering signal becomes maximum value, received from the position measurement interferometer 49, as a position X ₀ of the L1 = L2, the storage unit 61 of the controller 6 .

  Next, the DUT 10 is installed on the first interferometer 3 of the inner diameter measuring device 1. At this time, as described above, the white interference fringes are observed only at a position where the inner diameter D of the DUT 10 and (L2−L1) are substantially equal. Therefore, the control unit 66 of the controller 6 drives the coarse movement stage 47 through the stage controller 52 to retract the movable mirror 44 of the second interferometer 4 by a distance substantially equal to the inner diameter D of the object to be measured 10. Thereafter, the control unit 66 of the controller 6 acquires the sampling pitch from the storage unit 61. Then, similarly to the above, the control unit 66 drives the piezo fine movement stage 46 through the piezo controller 51 and moves the movable mirror 44 by the sampling pitch. Further, the interference signal acquisition unit 63 of the controller 66 acquires a signal value corresponding to the light amount detected by the detector 5 at each sampling point, that is, an interference signal value (step S102).

When the interference signal value at each sampling point is acquired, the peak estimation unit 64 of the controller 6 reads the master characteristic curve from the storage unit 61 (step S103). Then, the peak estimation unit 64 performs fitting between the interference signal value group acquired at each sampling point and the master characteristic curve while shifting the position of the master characteristic curve relative to each sampling point to obtain the best match. The position of the master characteristic curve to be obtained is obtained (step S104). Specifically, the peak estimation unit 64 obtains a sum of squares of errors representing a deviation amount between the interference signal group and the master characteristic curve in order to evaluate the degree of coincidence when the master characteristic curve is arranged at a predetermined position. For this purpose, the peak estimation unit 64 uses one point of the sampling point as a reference point, and associates the reference point with any element of the array in which the master characteristic curve is stored (hereinafter referred to as master array). For example, the sampling point having the largest acquired interference signal value among the sampling points is set as the reference point. The reference point is made to correspond to the first element of the master array. Then, the square value of the difference between the interference signal at the reference point and the interference signal stored in the corresponding element in the master array (hereinafter referred to as the master signal) is calculated. Similarly, for the other sampling points, the master signal of the corresponding element (that is, the element whose distance from the element corresponding to the reference point is equal to the distance from the sampling point of interest to the reference point) is obtained from the master array. Obtain a square value of the difference between the interference signal and the master signal. When the square value of the difference between the interference signal and the master signal is obtained for all the sampling points, the peak estimation unit 64 sums them up and sums them to calculate the error square sum ess that represents the amount of deviation between the interference signal group and the master characteristic curve. seek _1.

Next, in order to evaluate the degree of coincidence when the position of the master characteristic curve is shifted from the predetermined position with respect to the interference signal group, the peak estimation unit 64 sets the elements of the array corresponding to the reference point. While shifting one by one, the same process as described above is performed to obtain error square sums ess _{2 to} ess _n (n is a natural number of 2 or more). Then, the calculated error square sums ess _{1 to} ess _n are compared to determine the minimum value of the error square sum. The element number of the array corresponding to the reference point when the error sum of squares is minimum represents the position of the master characteristic curve that most closely matches the interference signal value group acquired for each sampling point.
The fitting method is not limited to the above. For example, fitting is performed by estimating a curve that passes through the interference signal value acquired for each sampling point, performing a cross-correlation operation with the master characteristic curve, and determining the position of the master characteristic curve when the correlation value is highest. May be performed. Furthermore, other fitting methods may be used.

When the position of the master characteristic curve that most closely matches the interference signal value group acquired for each sampling point is obtained, the peak estimation unit 64 calculates the peak of the interference signal measured for the DUT 10 based on the position. The position is estimated and the position is obtained (step S105). Specifically, the peak estimation unit 64 obtains the distance from the position in the master characteristic curve corresponding to the reference point to the peak position of the interference signal in the master characteristic curve when the error sum of squares is minimized. The distance is calculated from the peak position of the master characteristic curve read from the storage unit 61 (expressed by the distance from the position corresponding to the first element as described above) from the element corresponding to the reference point and the master array. It is calculated by subtracting the corresponding distance between the first elements. A value obtained by adding the distance from the position in the master characteristic curve corresponding to the reference point to the peak position to the position of the movable mirror 44 at the reference point is set as the peak position X _p of the interference fringes of the DUT 10.

When the peak position X _p of the interference fringes is estimated, the dimension determining unit 64 of the controller 6 reads the position X ₀ of the movable mirror 44 when L1 = L2 from the storage unit 61 and sets the value of X _p −X ₀ . The calculated value of the inner diameter D of the device under test 10 is obtained (step S106).

  When acquiring the interference signal, the controller 6 stops the moving mirror 44 at each sampling point for a predetermined time in order to remove noise due to air turbulence or the like, and corresponds to the light amount detected by the detector 5 during that time. An interference signal may be obtained by averaging the signal over time. Since the noise component becomes almost zero by time averaging, the interference signal can be accurately obtained by obtaining the interference signal as described above.

  Further, in the first interferometer 3, when the position of the beam splitter 33 does not exactly coincide with the center of the inner diameter of the device under test 10, the light beam B 1 is shifted from the diameter of the inner diameter of the device under test 10. The measured value is not accurate. In order to solve the problem, the measurement of the inner diameter is repeated by shifting the positional relationship between the beam splitter 33 and the DUT 10 in the direction perpendicular to the light beam B1 within the cylindrical cross section orthogonal to the axial direction of the DUT 10. Then, the value at which the obtained measurement value is maximum is taken as the inner diameter of the DUT 10.

  Therefore, once the controller 6 obtains the measured value of the inner diameter by the above procedure, it stores it in the storage unit 61. Next, the controller 6 transmits a control signal to the stage controller 37 of the first interferometer 3 to drive the XYZ stage 36, and the measured object 10 is changed to the light beam B1 by a predetermined amount (for example, 0.1 μm). It is moved in a direction perpendicular to the direction. Then, the inner diameter is measured again to obtain a measured value. The obtained measurement value is compared with the measurement value stored in the storage unit 61 of the controller 6. If the newly obtained measurement value is larger than the stored measurement value, the measurement value stored in the storage unit 61 is updated with the newly obtained measurement value. Thereafter, the DUT 10 is moved again in the same direction, and the measurement of the inner diameter is repeated. And when the measured value memorize | stored in the memory | storage part 61 becomes more than the newly measured value, let the measured value memorize | stored in the memory | storage part 61 be the internal diameter D of the to-be-measured object 10. FIG.

On the other hand, when the measured value of the inner diameter measured first is equal to or larger than the measured value measured next, the controller 6 moves the DUT 10 in the direction opposite to the direction in which the measured object 10 is first moved. Then, the measurement is repeated in the same manner as described above, and when the measured value stored in the storage unit 61 becomes equal to or greater than the newly measured value, the measured value stored in the storage unit 61 is used as the measured object 10. The inner diameter D of
In this way, by searching for the maximum measured value of the inner diameter D while changing the positional relationship between the object to be measured 10 and the beam splitter 33, the inner diameter measuring apparatus 1 accurately sets the beam splitter 33 to the center of the object to be measured 10. Since the inner diameter measurement result in the state of being placed in the position can be obtained, the inner diameter of the DUT 10 can be measured with high accuracy.

Instead of measuring the reference position X ₀ of the movable mirror 44 in step S101, the movable mirror 44 is moved closer to the beam splitter 42 than the reference mirror 43, and the interference signal generated between the light beams B12 and B21 is maximized. The position X _p ′ of the movable mirror 44 may be obtained by performing the same process as in steps S102 to S105. Then, a value of (X _p −X _p ′) / 2 is calculated, and the value may be used as the inner diameter D of the DUT 10. The intensity of the interference signal observed at the reference position X ₀ is greatly different from the intensity of the interference signal observed at the position X _p . On the other hand, the interference signal observed at the position X _p and the interference signal observed at the position X _p ′ have substantially the same intensity. Therefore, when the measured value of the inner diameter of the DUT 10 is obtained based on the difference between the position X _p and the position X _p ′, the measured inner diameter value is obtained based on the difference between the reference position X ₀ and the position X _p. Since the change in the output signal with respect to the change in the amount of light received by the detector 5 can be increased, the position of the movable mirror 44 where the interference signal becomes the maximum value can be specified more accurately.

  As described above, the inner diameter measuring apparatus 1 to which the present invention is applied obtains a master characteristic curve representing the period and amplitude variation of the interference signal in advance from the interference signal acquired for the master of the device under test 10, and actually When measuring the inner diameter of the object to be measured 10, the master characteristic curve is fitted to the interference signal group obtained at a rough sampling pitch with respect to the position of the movable mirror 44 to estimate the peak position of the interference signal. To do. Therefore, it is possible to accurately estimate the position of the peak of the interference signal only by acquiring the interference signal with respect to a relatively small number of sampling points, so that the time required for one measurement can be shortened.

  In addition, this invention is not limited to said embodiment. For example, the device under test is not limited to a cylindrical one. The measuring apparatus of the above embodiment can be applied as it is when measuring the distance between two opposing surfaces of an object to be measured. In the measurement apparatus of the above embodiment, the second interferometer may be a Fizeau interferometer.

The present invention can also be applied to a configuration in which only one Michelson interferometer is used as in the measurement apparatus described in Patent Document 1.
FIG. 7 shows a schematic configuration diagram of a configuration of the dimension measuring apparatus 11 that uses only one Michelson interferometer. In this configuration, the measurement light emitted from the white light source 12 is converted into a first light beam directed to the object to be measured 10 ′ by the beam splitter 13 and a second light beam directed to the movable mirror 14 movable along the optical path. To divide. Then, the first light beam reflected by the object to be measured 10 ′ and the second light reflected by the moving mirror 14 are converted into one light beam again by the beam splitter 13, and the interference signal is detected by the detector 15. . The signal output from the detector 15 is transmitted to the controller 16. The controller 16 has the same configuration as the controller 6 in the above embodiment. Further, similarly to the above-described embodiment, the storage unit of the controller 16 stores a master characteristic curve obtained from an interference signal acquired for a master that is a reference product of the device under test 10 ′.
When measuring the DUT 10 ′, the controller 16 moves the movable mirror 14 with a relatively coarse sampling pitch, and acquires an interference signal at each sampling point. Then, the controller 16 estimates the peak of the interference signal by fitting a master characteristic curve to the interference signal group at each sampling point. Then, it is estimated that the optical path difference between the first light flux and the second light flux becomes zero at the position X _p of the movable mirror 14 corresponding to the peak. Finally, by calculating the difference between the reference position X ₀ of the movable mirror 14 predetermined in relation to the measured object 10 ′ and the obtained position X _p of the movable mirror 14, the measured object 10 ′ Determine the dimensions (eg surface height, etc.).

Furthermore, in the embodiment using two interferometers, the white light source arranged on the first interferometer 3 side and the detector arranged on the second interferometer 4 side may be interchanged. . In this case, two light beams having an optical path difference corresponding to the measurement target dimension of the object to be measured are generated in advance on the second interferometer 4 side, and these light beams are sent to the first interferometer 3 side through the optical fiber. In the first interferometer 3, the received two light beams are further divided into a light beam reflected by the inner surfaces S 1 and S 2 of the object to be measured 10 and two light beams traveling straight through the beam splitter 33, and one of them. The white interference fringes are observed by detecting with a detector. Also in this case, the measured value of the inner diameter D of the DUT 10 can be obtained by measuring the optical path difference generated on the second interferometer 4 side.
As described above, various modifications can be made within the scope of the present invention according to the embodiment to be implemented.

It is a schematic block diagram of the internal diameter measuring apparatus to which this invention is applied. It is a schematic block diagram of the 1st interferometer which comprises an internal diameter measuring apparatus. It is a schematic block diagram of the 2nd interferometer which comprises an internal diameter measuring apparatus. It is a functional block diagram of the controller of an internal diameter measuring device. It is a figure which shows a mode that the interference characteristic in each sampling point of a to-be-measured object and the master characteristic curve of the interference signal calculated | required about the master are fitted. It is an operation | movement flowchart of an internal diameter measuring apparatus. It is a schematic block diagram of the dimension measuring apparatus by other embodiment to which this invention is applied.

Explanation of symbols

1 Inner Diameter Measuring Device (Dimension Measuring Device)
DESCRIPTION OF SYMBOLS 11 Size measuring apparatus 10, 10 'Measured object 2,12 White light source 3,4 Interferometer 5,15 Detector 6,16 Controller 31,41 Collimator lens 32,34 Wedge prism 33,42,13 Beam splitter 35 Condensing Lens 36 XYZ stage 37 Stage controller 43 Reference mirror 44, 14 Moving mirror 45 Support member 46 Piezo fine movement stage 47 Coarse movement stage 48 Corner cube 49 Position measurement interferometer 51 Piezo controller 52 Stage controller 61 Storage section 62 Communication section 63 Interference signal Acquisition unit 64 Peak estimation unit 65 Dimension determination unit 66 Control unit 7, 8 Optical fiber

Claims (5)

A dimension measuring device for measuring a dimension of an object to be measured,
A white light source,
The light emitted from the white light source is branched into a first light beam and a second light beam that are directed toward the object to be measured, and the first light beam is reflected by the object to be measured, and the second light beam A first interferometer that causes a first optical path difference corresponding to a measurement target dimension of the object to be measured to emit the first light flux and the second light flux in accordance with one light flux;
A second interferometer having a reference mirror having a fixed position and a movable mirror movable along the optical path, wherein a light beam emitted from the first interferometer is directed to the reference mirror. A second interferometer for branching into a light beam and a fourth light beam directed to the movable mirror to produce a second optical path difference between the third light beam and the fourth light beam;
The third light beam and the fourth light beam are received, an interference signal generated when the first optical path difference and the second optical path difference are substantially equal is detected, and a signal corresponding to the interference signal is output. A detector to
A storage unit storing a master characteristic curve representing a period and amplitude variation of an interference signal obtained from the interference signal detected for the reference measurement object using a reference measurement object as the measurement object;
A controller for obtaining a measurement target dimension of the object to be measured,
An interference signal acquisition unit that acquires the interference signals at a plurality of sampling points related to the position of the movable mirror as a sample interference signal group;
The master characteristic curve is fitted to the sample interference signal group, and the peak of the master characteristic curve when the sample interference signal group and the master characteristic curve most closely match is determined as an interference with the object to be measured. A peak estimator for estimating a signal peak;
A dimension determining unit for obtaining the measurement target dimension by calculating the second optical path difference with respect to the position of the movable mirror corresponding to the peak estimated by the peak estimating unit;
A controller having
A dimension measuring apparatus comprising: A dimension measuring device for measuring a dimension of an object to be measured,
A white light source,
A first interferometer having a reference mirror having a fixed position and a movable mirror movable along an optical path, wherein the light emitted from the white light source is directed to the reference mirror; A first interferometer for branching into a second light beam directed toward the movable mirror and causing a first optical path difference between the first light beam and the second light beam;
The first light beam and the second light beam emitted from the first interferometer are branched into a third light beam and a fourth light beam that are directed toward the object to be measured, and the third light beam is divided into the measured light. A second optical path difference corresponding to the measurement object size of the object to be measured is generated between the fourth light flux and the fourth light flux, and the third light flux and the fourth light flux are combined into one light flux. A second interferometer that emits together,
The third light beam and the fourth light beam are received, an interference signal generated when the first optical path difference and the second optical path difference are substantially equal is detected, and a signal corresponding to the interference signal is output. A detector to
A storage unit storing a master characteristic curve representing a period and amplitude variation of an interference signal obtained from the interference signal detected for the reference measurement object using a reference measurement object as the measurement object;
A controller for obtaining a measurement target dimension of the object to be measured,
An interference signal acquisition unit that acquires the interference signals at a plurality of sampling points related to the position of the movable mirror as a sample interference signal group;
The master characteristic curve is fitted to the sample interference signal group, and the peak of the master characteristic curve when the sample interference signal group and the master characteristic curve most closely match is determined as an interference with the object to be measured. A peak estimator for estimating a signal peak;
A dimension determining unit for obtaining the measurement target dimension by calculating the first optical path difference with respect to the position of the movable mirror corresponding to the peak estimated by the peak estimating unit;
A controller having
A dimension measuring apparatus comprising: A dimension measuring device for measuring a dimension of an object to be measured,
A white light source,
An interferometer having a movable mirror movable along an optical path, wherein the light emitted from the white light source is branched into a first light beam directed toward the object to be measured and a second light beam directed toward the movable mirror. An interferometer that reflects the first light beam by the object to be measured to generate an optical path difference between the first light beam and the second light beam;
An interference signal generated when the first light flux and the second light flux emitted from the interferometer are received, and an optical path length for the first light flux is substantially equal to an optical path length for the second light flux. A detector for detecting and outputting a signal corresponding to the interference signal;
A storage unit storing a master characteristic curve representing a period and amplitude variation of an interference signal obtained from the interference signal detected for the reference measurement object using a reference measurement object as the measurement object;
A controller for obtaining a measurement target dimension of the object to be measured,
An interference signal acquisition unit that acquires the interference signals at a plurality of sampling points related to the position of the movable mirror as a sample interference signal group;
The master characteristic curve is fitted to the sample interference signal group, and the peak of the master characteristic curve when the sample interference signal group and the master characteristic curve most closely match is determined as an interference with the object to be measured. A peak estimator for estimating a signal peak;
A dimension determining unit for obtaining the measurement target dimension by calculating a difference between the position of the movable mirror corresponding to the peak estimated by the peak estimating unit and a predetermined reference position of the movable mirror;
A controller having
A dimension measuring apparatus comprising:   The sampling interval between adjacent sampling points of the plurality of sampling points is set so as not to be an approximately integer multiple of 1/4 of the center wavelength of light emitted from the white light source. The dimension measuring device according to any one of the above. The light emitted from the white light source is branched into a first light beam and a second light beam that are directed to the object to be measured, and the first light beam is reflected by the object to be measured and is between the second light beam and the second light beam. A first interferometer that generates a first optical path difference corresponding to a measurement target dimension of the object to be measured and emits the first light beam and the second light beam according to one light beam, and a position are fixed. A second interferometer having a reference mirror and a movable mirror movable along the optical path, wherein the light beam emitted from the first interferometer is a third light beam directed to the reference mirror; A second interferometer for branching into a fourth light beam directed toward the movable mirror and causing a second optical path difference between the third light beam and the fourth light beam; and the third light beam; An interference signal generated when the fourth light beam is received and the first optical path difference and the second optical path difference are substantially equal is detected, and a signal corresponding to the interference signal is detected. And a master characteristic curve representing a period and amplitude variation of an interference signal obtained from the interference signal detected for the reference measurement object, and a reference measurement object as the measurement object A measuring method for measuring a dimension of an object to be measured in a measuring system having a storage unit,
Obtaining the interference signals at a plurality of sampling points relating to the position of the movable mirror as a sample interference signal group;
The master characteristic curve is fitted to the sample interference signal group, and the peak of the master characteristic curve when the sample interference signal group and the master characteristic curve most closely match is determined as an interference with the object to be measured. Estimating a signal peak;
Obtaining the measurement target dimension by calculating the second optical path difference with respect to the position of the movable mirror corresponding to the estimated peak;
A dimension measuring method characterized by comprising:

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