Three-dimensional shape measuring device and three-dimensional shape measuring method

Abstract

To provide a three-dimensional shape measuring device and a three-dimensional shape measuring method capable of reducing time and effort for an examiner and easily improving measuring accuracy of a three-dimensional shape of a surface to be measured.SOLUTION: A three-dimensional shape measuring device comprises: an interference objective lens including an interference section which splits a portion of measurement light emitted by a light source section from the measurement light as reference light, and generates a combined light beam of the measurement light returning from a surface to be measured and the reference light returning from a reference surface, and an objective lens which condenses the measurement light onto the surface to be measured; a scanning section which causes the interference objective lens to relatively scan in a scanning direction parallel to an optical axis of the objective lens, relative to the surface to be measured; an imaging section which repeatedly images the combined light beam generated by the interference section, during scanning by the scanning section, and outputs a plurality of captured images containing interference fringes; and a first signal processing section which calculates a degree of focus for each pixel in the plurality of captured images output from the imaging section, and calculates a three-dimensional shape of the surface to be measured on the basis of a result obtained by comparing the degree of focus for each pixel having the same coordinates in the plurality of captured images.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a three-dimensional shape measurement apparatus and a three-dimensional shape measurement method for measuring the three-dimensional shape of a measurement surface by a focus variation method.

Background Art

[0002] There is known a three-dimensional shape measurement apparatus that optically measures three-dimensional shapes such as the full focus image, surface shape, and surface roughness shape of a measurement surface of a measurement object by a focus variation method [Focus Variation (FV) method] (see Patent Document 1 and Patent Document 2).

[0003] The FV method three-dimensional shape measurement apparatus includes a drive mechanism, a microscope provided with a camera, and a control device. The drive mechanism scans the microscope along a scanning direction (height direction). The camera continuously captures the measurement surface while the microscope is being scanned by the drive mechanism to acquire a plurality of captured images. The control device calculates the focus degree of each captured image and measures the three-dimensional shape of the measurement surface based on the result of comparing the focus degrees of pixels at the same coordinates of each captured image.

[0004] Such three-dimensional shape measurement by the FV method has the advantages of being suitable for measuring the three-dimensional shape of an inclined surface and enabling high-speed measurement as compared with three-dimensional shape measurement by the white light interferometry (WLI) method. On the other hand, three-dimensional shape measurement by the FV method has the disadvantages that the height direction resolution of the measurement surface is lower and that it is impossible to measure a measurement surface with little luminance variation such as a mirror surface, as compared with three-dimensional shape measurement by the WLI method.

[0005] Patent Document 1 discloses a surface shape detection device that projects a pattern, such as a texture pattern, onto a mirror-like surface to be measured when performing three-dimensional shape measurement of the surface using the FV method. This surface shape detection device improves the accuracy of measuring the three-dimensional shape of the surface to be measured by projecting a texture pattern onto the surface to be measured and improving the contrast of the surface.

[0006] Patent Document 2 discloses a shape measuring device comprising an optical means, a scanning stage, an interference light generating means, an imaging unit, and a light-shielding plate. The optical means has a depth of focus less than or equal to the measurement accuracy of the three-dimensional shape of the surface to be measured, and guides measurement light to the surface to be measured below and reflected light upward. The scanning stage scans the surface to be measured along the scanning direction (height direction). The interference light generating means generates a reference light that interferes with the reflected light. The imaging unit captures the "reflected light" or "the interference light of this reflected light and the reference light." The light-shielding plate is detachably provided in the optical path of the reference light and switches between capturing reflected light and capturing interference light by the imaging unit. In the shape measuring device described in Patent Document 2, when measuring the three-dimensional shape of a slanted surface to be measured using the FV method, the imaging unit captures interference light. As a result, the contrast of the captured image is improved by the interference fringes contained in the captured image captured by the imaging unit, thereby improving the measurement accuracy of the three-dimensional shape of the surface to be measured. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 6-010675 [Patent Document 2] Japanese Patent Application Publication No. 10-68616 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the surface shape detection device described in Patent Document 1 requires a projection system to be installed in the microscope to project a texture pattern onto the surface to be measured, and depending on the type (structure) of the microscope, it may not be possible to install such a projection system. For this reason, the method described in Patent Document 1 cannot easily improve the measurement accuracy of the three-dimensional shape of the surface to be measured.

[0009] The shape measuring device described in Patent Document 2 requires the installation of an interference light generating means and a light-shielding plate in the microscope, but depending on the type (structure) of the microscope, it may not be possible to install the interference light generating means and the light-shielding plate. For this reason, even with the method described in Patent Document 2, it is not possible to easily improve the measurement accuracy of the three-dimensional shape of the surface to be measured. Furthermore, the shape measuring device described in Patent Document 2 requires the examiner to insert and remove the light-shielding plate, which is time-consuming. In addition, the shape measuring device described in Patent Document 2 requires the installation of an optical means having a depth of focus less than or equal to the measurement accuracy of the three-dimensional shape of the surface to be measured.

[0010] This invention has been made in view of these circumstances, and aims to provide a three-dimensional shape measuring device and a three-dimensional shape measuring method that can reduce the workload of the examiner and easily improve the measurement accuracy of the three-dimensional shape of the surface to be measured. [Means for solving the problem]

[0011] A three-dimensional shape measuring device for achieving the object of the present invention is a three-dimensional shape measuring device for measuring the three-dimensional shape of a surface to be measured by the focus method, comprising: a light source unit that emits measurement light; an interference unit that splits a portion of the measurement light emitted from the light source unit as reference light, emits the measurement light onto the surface to be measured and emits the reference light onto the reference surface, and generates a combined wave light of the measurement light returning from the surface to be measured and the reference light returning from the reference surface; an objective lens that focuses the measurement light onto the surface to be measured; a scanning unit that scans the interference objective lens relative to the surface to be measured along a scanning direction parallel to the optical axis of the objective lens; an imaging unit that repeatedly images the combined wave light generated by the interference unit during scanning by the scanning unit and outputs a plurality of imaged images including interference fringes; and a first signal processing unit that calculates the degree of focus for each pixel of the plurality of imaged images output from the imaging unit and calculates the three-dimensional shape of the surface to be measured based on the result of comparing the degree of focus for each pixel at the same coordinate of the plurality of imaged images.

[0012] This three-dimensional shape measuring device can be easily applied to existing devices, thus easily improving the measurement accuracy of the three-dimensional shape of the surface W to be measured, and further reducing the effort required for the examiner to insert and remove the light-shielding plate.

[0013] In a three-dimensional shape measuring apparatus according to another aspect of the present invention, when the optical path length of the measurement light between the interference zone and the surface to be measured is defined as the measurement optical path length, and the optical path length of the reference light between the interference zone and the reference surface is defined as the reference optical path length, the measurement optical path length and the reference optical path length are the same. This increases the intensity of interference fringes in the captured image and further improves the contrast of the surface to be measured in the captured image.

[0014] In another aspect of the present invention, a three-dimensional shape measuring device comprises: a second signal processing unit that calculates the height information of the surface to be measured for each pixel based on the brightness value of each pixel at the same coordinate of a plurality of captured images output from an imaging unit to calculate the three-dimensional shape of the surface to be measured; a first evaluation value calculation unit that calculates an evaluation value of the calculation result of the first signal processing unit and an evaluation value of the calculation result of the second signal processing unit; and a determination unit that, based on the calculation result of the first evaluation value calculation unit, determines the higher of the evaluation values ​​of the calculation result of the first signal processing unit and the calculation result of the second signal processing unit as the calculation result of the three-dimensional shape of the surface to be measured. This makes it possible to perform FV method and WLI method measurements in a single measurement operation (scan).

[0015] In another aspect of the present invention, a three-dimensional shape measuring device comprises: a second signal processing unit that calculates the height information of the surface to be measured for each pixel based on the brightness value of each pixel at the same coordinate of a plurality of captured images output from an imaging unit, and calculates the three-dimensional shape of the surface to be measured; a second evaluation value calculation unit that calculates an evaluation value of the calculation result of the first signal processing unit and an evaluation value of the calculation result of the second signal processing unit for each pixel; and an integration unit that, based on the calculation result of the second evaluation value calculation unit, selects the higher evaluation value from the calculation result of the first signal processing unit and the calculation result of the second signal processing unit for each pixel to generate an integrated three-dimensional shape of the surface to be measured. This makes it possible to combine the advantages of FV method measurement and WLI method measurement.

[0016] In another aspect of the present invention, a three-dimensional shape measuring device is defined as the signal-to-noise ratio.

[0017] In a three-dimensional shape measuring apparatus according to another aspect of the present invention, the scanning unit scans a microscope, which includes an interference objective lens and an imaging unit, relative to the surface to be measured.

[0018] A three-dimensional shape measurement method for achieving the object of the present invention is a three-dimensional shape measurement method for measuring the three-dimensional shape of a measurement surface by a focus synthesis method. In the method, an emission step of emitting measurement light, a splitting step of splitting a part of the measurement light from the measurement light emitted in the emission step as reference light, emitting the measurement light to the measurement surface and emitting the reference light to a reference surface, and generating interference light of the measurement light returning from the measurement surface and the reference light returning from the reference surface; a scanning step of relatively scanning an interference objective lens including an interference unit that performs the interference step and an objective lens that condenses the measurement light on the measurement surface along a scanning direction parallel to the optical axis of the objective lens; an imaging step of repeatedly imaging the interference light generated in the interference step during the scanning step and outputting a plurality of imaging images including interference fringes; and a signal processing step of calculating the focus degree for each pixel of the plurality of imaging images output in the imaging step and calculating the three-dimensional shape of the measurement surface based on the result of comparing the focus degrees for each pixel of the same coordinates of the plurality of imaging images.

Effect of the Invention

[0019] The present invention can reduce the labor of an inspector and easily improve the measurement accuracy of the three-dimensional shape of the measurement surface.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic diagram of a three-dimensional shape measurement device according to the first embodiment. [Figure 2] It is a diagram showing an example of an imaging image of a measurement surface imaged by a camera. [Figure 3] It is a functional block diagram of a control device according to the first embodiment. [Figure 4] It is an explanatory diagram for explaining the calculation of the three-dimensional shape of the measurement surface by a signal processing unit. [Figure 5] It is a flowchart showing the flow of a measurement process of the three-dimensional shape of a measurement surface by a three-dimensional shape measurement device according to the first embodiment. [Figure 6]Reference numeral 6A is a front view of a captured image obtained in a comparative example using an observation lens in FV method measurement, and reference numeral 6B is an enlarged view in which an arbitrary focus calculation range within the captured image is enlarged. [Figure 7] Reference numeral 7A is a front view of a captured image obtained in this embodiment using an interference objective lens in FV method measurement, and reference numeral 7B is an enlarged view in which an arbitrary focus calculation range within the captured image is enlarged. [Figure 8] It is an explanatory diagram showing an example of an optical flat surface shape which is a three-dimensional shape of an optical flat surface measured in a comparative example. [Figure 9] It is an explanatory diagram showing an example of an optical flat surface shape which is a three-dimensional shape of an optical flat surface measured in this embodiment. [Figure 10] It is a graph comparing a cross-sectional curve of an optical flat surface based on the optical flat surface shape of a comparative example and a cross-sectional curve of an optical flat surface based on the optical flat surface shape of this embodiment. [Figure 11] It is an explanatory diagram showing an example of a ball bearing surface shape which is a three-dimensional shape of a ball bearing surface measured in a comparative example. [Figure 12] It is an explanatory diagram showing an example of a ball bearing surface shape which is a three-dimensional shape of a ball bearing surface measured in this embodiment. [Figure 13] It is a graph comparing a cross-sectional curve of a ball bearing surface based on the ball bearing surface shape of a comparative example and a cross-sectional curve of a ball bearing surface based on the ball bearing surface shape of this embodiment. [Figure 14] It is a graph showing a cross-sectional curve of an optical flat surface measured in the first embodiment. [Figure 15] It is a functional block diagram of a control device of a three-dimensional shape measuring apparatus according to the second embodiment. [Figure 16] It is a flowchart showing the flow of measurement processing of the three-dimensional shape of a measured surface by the three-dimensional shape measuring apparatus according to the second embodiment. [Figure 17]This is a functional block diagram of the control device for the three-dimensional shape measuring device according to the third embodiment. [Figure 18] This flowchart shows the flow of the measurement process for the three-dimensional shape of a surface to be measured using the three-dimensional shape measuring device of the third embodiment. [Modes for carrying out the invention]

[0021] [First Embodiment] Figure 1 is a schematic diagram of the three-dimensional shape measuring device 9 according to the first embodiment. In the figure, among the mutually orthogonal XYZ directions, the XY direction is parallel to the horizontal direction, and the Z direction is parallel to the vertical direction.

[0022] As shown in Figure 1, the three-dimensional shape measuring device 9 performs three-dimensional shape measurement of the surface to be measured W using the FV method (focusing method). This three-dimensional shape measuring device 9 comprises, broadly speaking, a microscope 10, a drive mechanism 12, a scale 14, and a control device 16.

[0023] The microscope 10 comprises a light source unit 20, a beam splitter 22, an interference objective lens 24, an imaging lens 32, and a camera 34. The interference objective lens 24, beam splitter 22, imaging lens 32, and camera 34 are arranged in that order along the Z-direction upward from the surface W to be measured. The light source unit 20 is positioned opposite the beam splitter 22 in the X-direction (or Y-direction).

[0024] The light source unit 20, under the control of the control device 16, emits a parallel beam of white light (low coherence light with little coherence) as measurement light L1 toward the beam splitter 22. The light source unit 20, although not shown in the figures, includes a light source capable of emitting measurement light L1, such as a light-emitting diode, semiconductor laser, halogen lamp, and high-intensity discharge lamp, and a collector lens that converts the measurement light L1 emitted from this light source into a parallel beam.

[0025] The beam splitter 22 is, for example, a half-mirror. The beam splitter 22 reflects a portion of the measurement light L1 incident from the light source 20 toward the interference objective lens 24 on the lower side in the Z direction. The beam splitter 22 also transmits a portion of the combined light L3, described later, incident from the interference objective lens 24 toward the upper side in the Z direction, and emits this combined light L3 toward the imaging lens 32.

[0026] The interference objective lens 24 is detachably held in a known objective lens holder (such as a revolving nosepiece) of the microscope 10, instead of the bright-field observation objective lens (hereinafter abbreviated as observation lens) used in general FV method measurements. This interference objective lens 24 is of the Michelson type and comprises an objective lens 24a, a beam splitter 24b, a reference surface 24c, and a holder 24d. The beam splitter 24b and the objective lens 24a are arranged in order along the Z-direction upward from the measurement surface W, and the reference surface 24c is positioned opposite the beam splitter 24b in the X-direction (or Y-direction).

[0027] The objective lens 24a has a focusing function, and focuses the measurement light L1 incident from the beam splitter 22 onto the surface to be measured W through the beam splitter 24b.

[0028] The beam splitter 24b corresponds to the interference section of the present invention, and for example, a half mirror is used. The beam splitter 24b splits a portion of the measurement light L1 incident from the objective lens 24a into reference light L2, transmits the remaining measurement light L1 to the surface to be measured W, and reflects the reference light L2 toward the reference surface 24c. In the figure, the symbol D1 indicates the measurement optical path length, which is the optical path length of the measurement light L1 between the beam splitter 24b and the surface to be measured W. The measurement light L1 that has passed through the beam splitter 24b is irradiated onto the surface to be measured W, and then reflected by the surface to be measured W and returns to the beam splitter 24b.

[0029] The reference plane 24c, for example, uses a reflective mirror to reflect the reference light L2 incident from the beam splitter 24b back towards the beam splitter 24b. The position of this reference plane 24c in the X direction can be manually adjusted by the reference plane position adjustment mechanism 25.

[0030] The reference plane position adjustment mechanism 25 is, for example, a screw-type fine adjustment mechanism that adjusts the X-direction position of the reference plane 24c in response to input from the operator. This makes it possible to adjust the reference optical path length D2, which is the optical path length of the reference light L2 between the beam splitter 24b and the reference plane 24c. Here, the X-direction position of the reference plane 24c is adjusted by the reference plane position adjustment mechanism 25 so that the reference optical path length D2 matches (or approximately matches) the measured optical path length D1 when the objective lens 24a is focused on the surface W to be measured. The method for adjusting the X-direction position of the reference plane 24c is not particularly limited, and an automatic adjustment mechanism using a known actuator, or a temperature adjustment mechanism (heater and temperature sensor) that reversibly thermally deforms the holder 24d (reference plane storage section 24d2) described later may be used.

[0031] The beam splitter 24b generates a combined beam L3 from the measurement light L1 returning from the surface to be measured W and the reference light L2 returning from the reference surface 24c, and emits this combined beam L3 toward the objective lens 24a on the upper side in the Z direction. This combined beam L3 passes through the objective lens 24a and the beam splitter 22 and enters the imaging lens 32. The combined beam L3 is the interference light of the measurement light L1 and the reference light L2 and contains interference fringes 37 (see Figure 2). Furthermore, when the objective lens 24a is focused on the surface to be measured W, the measurement light path length D1 and the reference light path length D2 coincide as described above, so the intensity of the interference fringes 37 contained in the combined beam L3 becomes stronger.

[0032] The holder 24d is made of a metal material such as brass. This holder 24d comprises a lens barrel 24d1 and a reference surface housing section 24d2. The lens barrel 24d1 is formed in a cylindrical shape extending in the Z direction and houses (holds) the objective lens 24a and the beam splitter 24b. The reference surface housing section 24d2 is formed in a cylindrical shape extending in the X direction from the holding position of the beam splitter 24b in the lens barrel 24d1 and houses the reference surface 24c. As previously described, the position of the reference surface 24c in the X direction can be manually adjusted by the reference surface position adjustment mechanism 25.

[0033] The imaging lens 32 images the multiplexed light L3 incident from the beam splitter 22 onto the imaging plane of the camera 34 (not shown in the figure). Specifically, the imaging lens 32 images a point on the focal plane of the objective lens 24a as an image point on the imaging plane of the camera 34.

[0034] Camera 34 corresponds to the imaging unit of the present invention and, although not shown in the figures, is equipped with a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) type image sensor. Camera 34 captures the combined wave light L3 that is imaged on the imaging surface of the image sensor by the imaging lens 32, and processes the imaging signal of the combined wave light L3 obtained by this imaging to output an imaged image 36.

[0035] Figure 2 shows an example of an image 36 of the surface to be measured W captured by the camera 34. Here, we will explain using an optical flat surface (mirror surface) as an example of the surface to be measured W. As shown in Figure 2, when the objective lens 24a is in focus on the surface to be measured W, interference fringes 37 are included in the combined light L3 as described above, and therefore interference fringes 37 are also included in the image 36. As a result, even if the surface to be measured W is a mirror surface (in this case, an optical flat surface), the contrast of the surface to be measured W in this image 36 can be improved.

[0036] Returning to Figure 1, the drive mechanism 12 corresponds to the scanning unit of the present invention. The drive mechanism 12 is composed of various actuators, such as a known linear motor or motor drive mechanism, and holds the microscope 10 so that it can move in the scanning direction, the Z direction. Under the control of the control device 16, the drive mechanism 12 scans the microscope 10 along the Z direction, that is, a direction parallel to the optical axis of the objective lens 24a. This makes it possible to change the measurement optical path length D1 when measuring the three-dimensional shape of the surface to be measured W.

[0037] The drive mechanism 12 only needs to be capable of scanning the microscope 10 relative to the surface to be measured W in the Z direction; for example, it may scan the surface to be measured W (the support part that supports the surface to be measured W) in the Z direction.

[0038] Scale 14 is a position detection sensor that detects the Z-direction position of the microscope 10, and a linear scale is used, for example. This scale 14 repeatedly detects the Z-direction position of the microscope 10 and repeatedly outputs the position detection result to the control device 16.

[0039] The control device 16 comprehensively controls the measurement operation of the three-dimensional shape of the surface W to be measured by the microscope 10, and the calculation of the three-dimensional shape of the surface W to be measured, in response to input operations to the operation unit 17. This control device 16 is equipped with an arithmetic circuit composed of various processors and memory. Various processors include CPUs (Central Processing Units), GPUs (Graphics Processing Units), ASICs (Application Specific Integrated Circuits), and programmable logic devices [e.g., SPLDs (Simple Programmable Logic Devices), CPLDs (Complex Programmable Logic Devices), and FPGAs (Field Programmable Gate Arrays)]. The various functions of the control device 16 may be implemented by a single processor, or by multiple processors of the same or different types.

[0040] Figure 3 is a functional block diagram of the control device 16 of the first embodiment. As shown in Figure 3, the control device 16 is connected to various parts of the microscope 10 (light source unit 20 and camera 34), the drive mechanism 12, the scale 14, and the operation unit 17.

[0041] The control device 16 functions as a measurement control unit 100 and a signal processing unit 102 by executing a control program (not shown) read from a storage unit (not shown).

[0042] The measurement control unit 100 controls the drive mechanism 12, the light source unit 20, and the camera 34 to perform three-dimensional shape measurement of the surface to be measured W using the FV method. Specifically, after starting the emission of measurement light L1 from the light source unit 20, the measurement control unit 100 controls the drive mechanism 12 to scan the microscope 10 in the Z direction. Furthermore, while the drive mechanism 12 is scanning the microscope 10 in the Z direction, the measurement control unit 100, based on the detection result of the Z-direction position of the microscope 10 by the scale 14, repeatedly causes the camera 34 to capture multiplexed light L3 and output the captured image 36 to the control device 16 each time the microscope 10 moves by a certain pitch in the Z direction.

[0043] Figure 4 is an explanatory diagram illustrating the calculation of the three-dimensional shape of the surface W to be measured by the signal processing unit 102. In Figure 4, each pixel is represented in a checkerboard pattern to facilitate the distinction between each pixel in each captured image 36.

[0044] The signal processing unit 102 corresponds to the first signal processing unit of the present invention. This signal processing unit 102 acquires the captured image 36 output from the camera 34 each time the camera 34 captures multiplexed light L3. Next, the signal processing unit 102 calculates the degree of focus (contrast, sharpness) for each pixel of each captured image 36 acquired from the camera 34. For example, the signal processing unit 102 designates the pixel for which the degree of focus is calculated as the focus pixel 104, and calculates the degree of focus using a known method based on the brightness value of this focus pixel 104 and the brightness values ​​of each pixel within the degree of focus calculation range 106 based on the focus pixel 104. The signal processing unit 102 calculates the degree of focus for each pixel of each captured image 36 by repeatedly performing the degree of focus calculation process for all pixels of each captured image 36.

[0045] After calculating the degree of focus, the signal processing unit 102 compares the degree of focus for each pixel at the same coordinate in each captured image 36 (each pixel of the image sensor of the camera 34) as shown by the straight line ZL in the figure, and determines the Z-direction position where the degree of focus is maximized for each pixel at the same coordinate. Then, the signal processing unit 102 calculates the three-dimensional shape (height distribution) of the surface to be measured W by determining the focal position of the camera 34 with respect to the surface to be measured W for each pixel at the same coordinate. Note that the calculation of the three-dimensional shape of the surface to be measured W using the FV method is also a known technique (see Patent Document 1 above), so a detailed explanation is omitted here.

[0046] [Operation of the First Embodiment] Figure 5 is a flowchart showing the flow of the measurement process for the three-dimensional shape of a surface to be measured W by the three-dimensional shape measuring device 9 of the first embodiment of the three-dimensional shape measurement method of the present invention. Note that an interference objective lens 24 is pre-mounted on the microscope 10. Furthermore, the X-direction position of the reference surface 24c is pre-adjusted so that the reference optical path length D2 matches the measurement optical path length D1 when the objective lens 24a is focused on the surface to be measured W.

[0047] As shown in Figure 5, the operator sets the surface to be measured W in the microscope 10 and operates the control unit 17 to start measuring the three-dimensional shape of the surface to be measured W (step S1). Once this measurement start operation is performed, the measurement control unit 100 of the control device 16 starts emitting measurement light L1 from the light source unit 20 (corresponding to the emission step of the present invention). As a result, the combined light L3 of the measurement light L1 reflected from the surface to be measured W and the reference light L2 reflected from the reference surface 24c, and which includes interference fringes 37, is incident on the camera 34 (corresponding to the interference step of the present invention). Then, the measurement control unit 100 controls the drive mechanism 12 to start scanning the microscope 10 in the Z direction (step S3, corresponding to the scanning step of the present invention).

[0048] Furthermore, based on the detection result of the Z-direction position of the microscope 10 by the scale 14, the measurement control unit 100 repeatedly causes the camera 34 to capture multiplexed light L3 each time the microscope 10 moves by a certain pitch in the Z direction (corresponding to NO in steps S4 and S5, step S6, and the imaging step of the present invention). As a result, while the microscope 10 is being scanned, the captured image 36 is repeatedly input from the camera 34 to the signal processing unit 102, and the signal processing unit 102 repeatedly performs the acquisition of the captured image 36.

[0049] In Figure 6, reference numeral 6A is a front view of the image 36 obtained in a comparative example (hereinafter referred to as the comparative example) using an observation lens in the FV method measurement, and reference numeral 6B is an enlarged view of an arbitrary focus calculation range 106 within the image 36. In Figure 7, reference numeral 7A is a front view of the image 36 obtained in this embodiment (hereinafter referred to as the embodiment) using an interference objective lens 24 in the FV method measurement, and reference numeral 7B is an enlarged view of an arbitrary focus calculation range 106 within the image 36. Note that the surface to be measured W shown in Figures 6 and 7 is an optical flat surface, i.e., a mirror surface.

[0050] As shown by reference numerals 6A and 6B in Figure 6, in the comparative example, the camera 34 captures the reflected light of the measurement light L1 from the surface to be measured W through the observation lens, that is, it captures the reflected light that does not contain interference fringes 37, so no interference fringes 37 are generated on the surface to be measured W in the captured image 36. For this reason, in the comparative example, the contrast of the surface to be measured W in the captured image 36 decreases, and consequently, the contrast within the focus calculation range 106 also decreases.

[0051] In contrast, as shown by reference numerals 7A and 7B in Figure 7, in this embodiment, the camera 34 images the surface to be measured W through the interference objective lens 24, that is, it images the combined wave light L3 including interference fringes 37, so that interference fringes 37 are generated on the surface to be measured W in the captured image 36. As a result, in this embodiment, the contrast of the surface to be measured W in the captured image 36 is improved, and consequently the contrast within the focus calculation range 106 is also improved.

[0052] Returning to Figure 5, once the scanning of the microscope 10 is complete (YES in step S5), the signal processing unit 102 repeatedly performs the following for all pixels of each captured image 36, as shown in Figure 4: setting the pixel of interest 104 and the focus calculation range 106, and calculating the focus. Next, the signal processing unit 102 compares the focus of each pixel at the same coordinate in each captured image 36 and determines the Z-direction position where the focus is maximized for each pixel at the same coordinate, thereby determining the focal position of the camera 34 relative to the surface to be measured W for each pixel at the same coordinate. As a result, the signal processing unit 102 calculates the three-dimensional shape (height distribution) of the surface to be measured W (step S7, corresponding to the signal processing step of the present invention).

[0053] Below, we compare the measurement results of the three-dimensional shape of the surface W to be measured in this embodiment with the measurement results of the three-dimensional shape of the surface W to be measured in the comparative example.

[0054] Figure 8 is an explanatory diagram showing an example of optical flat surface shape 150A, which is the three-dimensional shape of the optical flat surface measured in the comparative example. Figure 9 is an explanatory diagram showing an example of optical flat surface shape 150B, which is the three-dimensional shape of the optical flat surface measured in this embodiment. Figure 10 is a graph comparing the cross-sectional curve of the optical flat surface based on optical flat surface shape 150A of the comparative example and the cross-sectional curve of the optical flat surface based on optical flat surface shape 150B of this embodiment. In Figure 10, "lateral position" indicates a position on an arbitrary straight line along the optical flat surface, and "height position" indicates the height position in the Z direction of the optical flat surface on this arbitrary straight line (the same applies to Figure 14 described later).

[0055] As shown in Figures 8 to 10, in the comparative example, when the surface W to be measured is an optical flat surface (mirror surface), the noise in the optical flat surface shape 150A increases, making it difficult to measure the three-dimensional shape of the surface W to be measured. In contrast, in this embodiment, even if the surface W to be measured is an optical flat surface (mirror surface), the generation of noise in the optical flat surface shape 150B is suppressed, making it possible to measure the three-dimensional shape of the surface W to be measured.

[0056] Figure 11 is an explanatory diagram showing an example of the ball bearing surface shape 154A, which is the three-dimensional shape of the ball bearing surface measured in the comparative example. Figure 12 is an explanatory diagram showing an example of the ball bearing surface shape 154B, which is the three-dimensional shape of the ball bearing surface measured in this embodiment. Figure 13 is a graph comparing the cross-sectional curve of the ball bearing surface based on the ball bearing surface shape 154A of the comparative example and the cross-sectional curve of the ball bearing surface based on the ball bearing surface shape 154B of this embodiment. In Figure 13, "lateral position" indicates the position on an arbitrary curve along the ball bearing surface, and "height position" indicates the height position of the optical flat surface on this arbitrary curve.

[0057] As shown in Figures 11 to 13, when the surface W to be measured is the surface of a ball bearing, the resolution in the height direction of the ball bearing surface shape 154A is about 10 μm in the comparative example, whereas in this embodiment, the resolution in the height direction of the ball bearing surface shape 154B is about 1 μm. Therefore, in this embodiment, the resolution of the three-dimensional shape of the surface W to be measured can be improved compared to the comparative example.

[0058] In this embodiment, the interference objective lens 24 generates interference fringes 37 on the surface to be measured W in the captured image 36, thereby improving the contrast of the surface to be measured W (focus calculation range 106) in the captured image 36. As a result, the measurement sensitivity and resolution of the three-dimensional shape of the surface to be measured W are improved. Therefore, in this embodiment, the measurement accuracy of the three-dimensional shape of the surface to be measured W is improved. Furthermore, compared to the texture pattern described in Patent Document 1, the interference fringes 37 exhibit a larger change in brightness when the microscope 10 is scanned in the Z direction, thus further improving the measurement sensitivity and resolution of the three-dimensional shape of the surface to be measured W, i.e., further improving the measurement accuracy of the three-dimensional shape.

[0059] Furthermore, in this embodiment, since the three-dimensional shape measurement of the surface W to be measured is performed using the FV method, it is possible to improve the measurement accuracy of the three-dimensional shape of the surface W to be measured while performing high-speed measurement using the FV method. For example, when performing three-dimensional shape measurement of the ball bearing surface shown in Figures 11 and 12, the measurement time using the FV method is 5 seconds, which is about 1 / 3 of the measurement time of 16 seconds using the WLI method.

[0060] As described above, in the first embodiment, the measurement accuracy of the three-dimensional shape of the surface to be measured is improved simply by providing an interference objective lens 24 to the microscope 10. Therefore, it is not necessary to provide the texture pattern projection system described in Patent Document 1 to the microscope 10, or the interference light generating means and light shielding plate described in Patent Document 2 to the microscope 10. As a result, the present invention can be easily applied to existing FV type three-dimensional shape measuring devices (microscopes), and the measurement accuracy of the three-dimensional shape of the surface to be measured can be easily improved. Furthermore, in the first embodiment, the examiner does not need to insert or remove the light shielding plate as described in Patent Document 2, thus reducing the examiner's workload. As a result, in the first embodiment, the examiner's workload can be reduced and the measurement accuracy of the three-dimensional shape of the surface to be measured can be easily improved.

[0061] Furthermore, in the shape measuring device described in Patent Document 2, the depth of focus of the objective lens is set to be less than or equal to the measurement accuracy of the three-dimensional shape of the surface to be measured W. However, in the first embodiment, it is not necessary to set the depth of focus of the objective lens 24a to be less than or equal to the measurement accuracy of the three-dimensional shape of the surface to be measured W.

[0062] Specifically, if the numerical aperture (NA) of the objective lens 24a is, for example, 0.3, and the wavelength of the measurement light L1 is, for example, 0.53 μm, then the depth of focus of the objective lens 24a is given by: Depth of focus = [Wavelength / (2 × NA] 2 This is expressed as )] = 2.94 μm. On the other hand, as shown in Figure 14, in the three-dimensional shape measurement results of the optical flat surface (surface W to be measured) in the first embodiment, the PP (Peak-to-Peak) is 0.4 μm or less. Therefore, in the first embodiment, it is not necessary to set the depth of focus of the objective lens 24a to be less than or equal to the measurement accuracy of the three-dimensional shape of the surface W to be measured. Figure 14 is a graph showing the cross-sectional curve of the optical flat surface measured in the first embodiment.

[0063] [Second Embodiment] Figure 15 is a functional block diagram of the control device 16 of the three-dimensional shape measuring device 9 of the second embodiment. The three-dimensional shape measuring device 9 of the first embodiment performs only three-dimensional shape calculation of the surface to be measured W using the FV method based on a plurality of captured images 36 obtained during scanning of the microscope 10. In contrast, the three-dimensional shape measuring device 9 of the second embodiment performs three-dimensional shape calculation of the surface to be measured W using two types of methods, the FV method and the WLI method, simultaneously (or sequentially) based on a plurality of captured images 36 obtained during scanning of the microscope 10, and compares the three-dimensional shape calculation results of the two types to select the one with the better signal-to-noise ratio (S / N ratio).

[0064] The three-dimensional shape measuring device 9 of the second embodiment has basically the same configuration as the three-dimensional shape measuring device 9 of the first embodiment, except that the control device 16 functions as a first signal processing unit 102A, a second signal processing unit 102B, an S / N ratio calculation unit 102C, and a determination unit 102D. For this reason, components that are functionally or structurally identical to those of the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0065] The first signal processing unit 102A is the same as the signal processing unit 102 in the first embodiment described above, and performs three-dimensional shape calculation of the surface to be measured W in the FV method based on a plurality of captured images 36 output from the camera 34 while the microscope 10 is scanning.

[0066] The second signal processing unit 102B performs a three-dimensional shape calculation of the surface to be measured W using the WLI method, based on multiple captured images 36 output from the camera 34 while the microscope 10 is scanning. Specifically, the second signal processing unit 102B compares the brightness values ​​of each pixel at the same coordinate in each captured image 36. Next, the second signal processing unit 102B calculates the height information of the surface to be measured W for each pixel at the same coordinate by determining the Z-direction position where the brightness value is maximized for each pixel at the same coordinate. This calculates the three-dimensional shape (height distribution) of the surface to be measured W. Note that the calculation of the three-dimensional shape of the surface to be measured W using the WLI method is also a known technique (see, for example, Japanese Patent Application Publication No. 2017-106860), so a detailed explanation is omitted here.

[0067] The S / N ratio calculation unit 102C corresponds to the first evaluation value calculation unit of the present invention, and calculates the S / N ratio of the three-dimensional shape calculation result of the surface to be measured W by the first signal processing unit 102A and the S / N ratio of the three-dimensional shape calculation result of the surface to be measured W by the second signal processing unit 102B, respectively. Note that the S / N ratio is an example of an evaluation value of the present invention, and the method for calculating the S / N ratio is publicly known, so a detailed explanation is omitted here (see, for example, Japanese Patent Application Publication No. 2021-33525).

[0068] The determination unit 102D compares the S / N ratio of the three-dimensional shape calculation result of the surface W to be measured by the first signal processing unit 102A and the S / N ratio of the three-dimensional shape calculation result of the surface W to be measured by the second signal processing unit 102B, based on the calculation result of the S / N ratio calculation unit 102C. Then, the determination unit 102D determines the one with the higher S / N ratio between the three-dimensional shape calculation result of the first signal processing unit 102A and the three-dimensional shape calculation result of the second signal processing unit 102B as the three-dimensional shape measurement result of the surface W to be measured.

[0069] Figure 16 is a flowchart showing the flow of the measurement process for the three-dimensional shape of the surface to be measured W by the three-dimensional shape measuring device 9 of the second embodiment. As shown in Figure 16, the processes from step S1 to step S6 are basically the same as those of the first embodiment shown in Figure 5, so a detailed explanation is omitted here.

[0070] When scanning by the microscope 10 is completed (YES in step S5), the first signal processing unit 102A calculates the degree of focus for each pixel of the multiple captured images 36 input from the camera 34 (step S7A). Next, based on the results of comparing the degree of focus for each pixel at the same coordinate in each captured image 36, the first signal processing unit 102A calculates the three-dimensional shape of the surface to be measured W, similar to the signal processing unit 102 of the first embodiment (step S8A).

[0071] Furthermore, the second signal processing unit 102B detects the brightness value for each pixel of the multiple captured images 36 input from the camera 34 (step S7B). Next, the second signal processing unit 102B determines the Z-direction position where the brightness value is maximized for each pixel at the same coordinate in each captured image 36, and calculates the height information of the surface to be measured W for each pixel at the same coordinate, thereby calculating the three-dimensional shape of the surface to be measured W (step S8B).

[0072] Then, the S / N ratio calculation unit 102C calculates the S / N ratio of the three-dimensional shape calculation result of the surface W to be measured by the first signal processing unit 102A and the S / N ratio of the three-dimensional shape calculation result of the surface W to be measured by the second signal processing unit 102B (step S9).

[0073] Once the S / N ratio calculation by the S / N ratio calculation unit 102C is completed, the determination unit 102D determines the result of the three-dimensional shape calculation of the surface to be measured W, whichever has the higher S / N ratio between the result of the three-dimensional shape calculation of the first signal processing unit 102A and the result of the three-dimensional shape calculation of the second signal processing unit 102B (step S10). As a result, if the surface to be measured W is a surface suitable for the FV method, such as a steep slope, the determination unit 102D determines the result of the three-dimensional shape calculation of the first signal processing unit 102A as the result of the three-dimensional shape measurement of the surface to be measured W. Conversely, if the surface to be measured W is a surface suitable for the WLI method, such as a mirror surface or a surface requiring high resolution in the Z direction (height direction) (such as a ball bearing surface), the determination unit 102D determines the result of the three-dimensional shape calculation of the second signal processing unit 102B as the result of the three-dimensional shape measurement of the surface to be measured W.

[0074] As described above, in the second embodiment, three-dimensional shape calculations of the surface to be measured W using the FV method and the WLI method are performed simultaneously based on multiple imaging images 36 obtained during scanning of the microscope 10. By comparing the three-dimensional shape calculation results of the two methods and selecting the one with a better signal-to-noise ratio, it is possible to perform measurements using both the FV method and the WLI method in a single measurement operation (scanning of the microscope 10). As a result, three-dimensional shape measurements can be performed using the FV method for surfaces to be measured W such as steep slopes that are unsuitable for WLI measurement, and conversely, three-dimensional shape measurements can be performed using the WLI method for surfaces to be measured W such as mirrors that are unsuitable for FV measurement.

[0075] [Third Embodiment] Figure 17 is a functional block diagram of the control device 16 of the three-dimensional shape measuring device 9 of the third embodiment. In the three-dimensional shape measuring device 9 of the second embodiment described above, three-dimensional shape calculations of the surface to be measured W are performed simultaneously using the FV method and the WLI method, and the results of the three-dimensional shape calculations of the two methods are compared to select the one with the better signal-to-noise ratio. In contrast, the three-dimensional shape measuring device 9 of the third embodiment calculates the integrated three-dimensional shape of the surface to be measured W based on the results of the three-dimensional shape calculations of the two methods.

[0076] As shown in Figure 17, the three-dimensional shape measuring device 9 of the third embodiment has basically the same configuration as the three-dimensional shape measuring device 9 of the second embodiment, except that the control device 16 functions as an "S / N ratio calculation unit 102E and integration unit 102F" instead of an "S / N ratio calculation unit 102C and determination unit 102D". For this reason, components that are functionally or structurally identical to those in each of the above embodiments are denoted by the same reference numerals and their descriptions are omitted.

[0077] Figure 18 is a flowchart showing the flow of the measurement process for the three-dimensional shape of the surface to be measured W by the three-dimensional shape measuring device 9 of the third embodiment. As shown in Figure 18, the processes from step S1 to steps S8A and S8B are basically the same as those of the second embodiment shown in Figure 16, so a detailed explanation is omitted here.

[0078] The S / N ratio calculation unit 102E corresponds to the second evaluation value calculation unit of the present invention. After processing in steps S8A and S8B, the S / N ratio calculation unit 102E calculates the S / N ratio of the three-dimensional shape calculation result of the first signal processing unit 102A for each pixel of each captured image 36 (each pixel of the image sensor of the camera 34) (step S9A1), and also calculates the S / N ratio of the three-dimensional shape calculation result of the second signal processing unit 102B (step S9B1). Note that the method for calculating the S / N ratio for each pixel is also known technology, so a detailed explanation is omitted here (see, for example, Japanese Patent Application Publication No. 2007-68597).

[0079] Based on the calculation results of the S / N ratio calculation unit 102E, the integration unit 102F compares the S / N ratio of the three-dimensional shape calculation result of the first signal processing unit 102A with the S / N ratio of the three-dimensional shape calculation result of the second signal processing unit 102B for each pixel, and selects the one with the higher S / N ratio (step S10A). Then, the integration unit 102F integrates the three-dimensional shape calculation results selected for each pixel to generate the integrated three-dimensional shape of the surface to be measured W (step S11A).

[0080] As described above, in the third embodiment, the integrated three-dimensional shape of the surface W to be measured is generated for each pixel based on the selection of the result of the three-dimensional shape calculation between the first signal processing unit 102A and the second signal processing unit 102B, which has a higher S / N ratio. This makes it possible to achieve both the advantages of the FV method and the WLI method of measurement. As a result, the three-dimensional shape of the surface W to be measured, which contains a mixture of steep slopes that can be measured with high accuracy using the FV method and mirrored surfaces that can be measured with high accuracy using the WLI method, can be measured with high accuracy.

[0081] [others] In the second and third embodiments described above, the signal-to-noise ratio (S / N ratio) was used as an example of an evaluation value for the three-dimensional shape calculation result. However, any evaluation value other than the S / N ratio may be used as an indicator of the measurement accuracy of the three-dimensional shape of the surface W being measured.

[0082] In each of the above embodiments, the microscope 10 is equipped with a Michelson-type interference objective lens 24, but various known interference objective lenses such as Mirau-type or Linnick-type may also be provided.

[0083] In each of the above embodiments, the microscope 10 is scanned in the Z direction by the drive mechanism 12, but the object to be scanned is not particularly limited as long as at least the interference objective lens 24 can be scanned relative to the surface to be measured W in the Z direction. [Explanation of symbols]

[0084] 9 Three-dimensional shape measuring device 10 Microscopes 12 Drive mechanism 1 / 14 scale 16 Control device 17 Control section 20 Light source section 22 Beam Splitter 24 Interferometric objective lenses 24a objective lens 24b Beam Splitter 24c reference plane 24d holder 24d1 lens barrel 24d2 Reference surface storage compartment 25 Reference plane position adjustment mechanism 32 imaging lenses 34 Cameras 36 Acquired Images 37 Interference fringes 100 Measurement Control Unit 102 Signal Processing Unit 102A First Signal Processing Unit 102B Second Signal Processing Unit 102C N ratio calculation section 102D Decision Section 102E N ratio calculation section 102F Integration Department 104 pixels of interest 106 Focus Calculation Range 150A, 150B Optical flat surface shape 154A, 154B Ball bearing surface shape D1 Measurement optical path length D2 Reference optical path length L1 Measurement light L2 Reference Light L3 combined light W Surface to be measured

Claims

1. In a three-dimensional shape measuring device that measures the three-dimensional shape of a surface to be measured using the focus method, A light source unit that emits measurement light, An interference objective lens comprising: an interference unit that splits a portion of the measurement light emitted from the light source unit into a reference light, emits the measurement light onto the surface to be measured and emits the reference light onto the reference surface, and generates a combined wave of the measurement light returning from the surface to be measured and the reference light returning from the reference surface; and an objective lens that focuses the measurement light onto the surface to be measured; A scanning unit that scans the interference objective lens relative to the surface to be measured along a scanning direction parallel to the optical axis of the objective lens, During scanning by the scanning unit, the imaging unit repeatedly captures the multiplexed light generated by the interference unit and outputs a plurality of captured images including interference fringes. A first signal processing unit calculates the degree of focus for each pixel of a plurality of captured images output from the imaging unit, and calculates the three-dimensional shape of the surface to be measured based on the result of comparing the degree of focus for each pixel at the same coordinate of the plurality of captured images, A second signal processing unit calculates the height information of the surface to be measured for each pixel based on the brightness values ​​of each pixel at the same coordinate in a plurality of captured images output from the imaging unit, and calculates the three-dimensional shape of the surface to be measured. An evaluation value calculation unit that calculates the evaluation value of the calculation result of the first signal processing unit and the evaluation value of the calculation result of the second signal processing unit, Based on the calculation results of the evaluation value calculation unit, a determination unit determines the higher of the calculation results of the first signal processing unit and the calculation results of the second signal processing unit as the calculation result for the three-dimensional shape of the surface to be measured, A three-dimensional shape measuring device equipped with the following features.

2. The three-dimensional shape measuring apparatus according to claim 1, wherein when the optical path length of the measurement light between the interference portion and the surface to be measured is defined as the measurement optical path length, and the optical path length of the reference light between the interference portion and the reference surface is defined as the reference optical path length, the measurement optical path length and the reference optical path length are the same.

3. The three-dimensional shape measuring device according to claim 1 or 2, wherein the evaluation value is the signal-to-noise ratio.

4. The three-dimensional shape measuring apparatus according to any one of claims 1 to 3, wherein the scanning unit scans the microscope, including the interference objective lens and the imaging unit, relative to the surface to be measured.

5. In a three-dimensional shape measurement method for measuring the three-dimensional shape of a surface to be measured using the focus method, An emission step in which measurement light is emitted, Interference step: A part of the measurement light emitted in the emission step is separated from the measurement light to be used as reference light, the measurement light is emitted to the surface to be measured and the reference light is emitted to the reference surface, thereby generating a combined wave of the measurement light returning from the surface to be measured and the reference light returning from the reference surface. A scanning step involves scanning an interference objective lens, which includes an interference unit for performing the interference step and an objective lens for focusing the measurement light onto the surface to be measured, relative to the surface to be measured along a scanning direction parallel to the optical axis of the objective lens. During the scanning step, the multiplexed light generated in the interference step is repeatedly captured to output a plurality of captured images including interference fringes; A first signal processing step calculates the degree of focus for each pixel of the multiple captured images output in the imaging step, and calculates the three-dimensional shape of the surface to be measured based on the result of comparing the degree of focus for each pixel at the same coordinate of the multiple captured images, A second signal processing step calculates the three-dimensional shape of the surface to be measured by calculating the height information of the surface to be measured for each pixel based on the brightness values ​​of each pixel at the same coordinate of the multiple captured images output in the imaging step, An evaluation value calculation step that calculates the evaluation value of the calculation result of the first signal processing step and the evaluation value of the calculation result of the second signal processing step, A determination step in which, based on the calculation result of the evaluation value calculation step, the higher of the calculation result of the first signal processing step and the calculation result of the second signal processing step is determined as the calculation result of the three-dimensional shape of the surface to be measured, A three-dimensional shape measurement method having the following characteristics.

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