Device for three-dimensional shape measurement and a method for three-dimensional shape measurement

Abstract

Providing a device and method for three-dimensional shape measurement that are capable of reducing the time and labor required by an examiner and easily improving the measurement accuracy of a three-dimensional shape of a surface to be measured. The device for three-dimensional shape measurement comprises: an interference objective lens including an interference unit configured to separate a portion of the measurement light emitted by a light source unit as reference light and to generate multiplexed light of the measurement light returning from the surface to be measured and the reference light returning from a reference surface; and an objective lens configured to cause the measurement light to focus onto the surface to be measured.a scanning unit configured to cause the interference objective lens to scan in a scanning direction that is parallel to an optical axis of the objective lens relative to the surface to be measured; an image acquisition unit configured to repeatedly capture an image of the multiplexed light produced by the interference unit and to output a plurality of captured images, including interference fringes, during scanning by the scanning unit; and a first signal processing unit configured to calculate the sharpness of each pixel of the plurality of captured images output by the image acquisition unit and to calculate the three-dimensional shape of the surface to be measured based on a result of comparing the sharpness of each pixel at the same coordinate of the plurality of captured images.

Description

Technical area

[0001] The subject matter disclosed herein relates to a three-dimensional shape measuring apparatus and a three-dimensional shape measuring method that measure a three-dimensional shape of a surface to be measured using a focal point method. State of the art

[0002] A device for three-dimensional shape measurement is known which optically measures three-dimensional shapes, such as fully focused images, surface shapes and surface roughness shapes of a surface to be measured of a measuring object according to a focal point method (focus variation scheme (FV)) (see PTL 1 and PTL 2).

[0003] The three-dimensional shape measurement device using the FV scheme includes a drive mechanism, a microscope equipped with a camera, and a control device. The drive mechanism causes the microscope to scan in a scanning direction (height direction). While the drive mechanism causes the microscope to scan, the camera continuously captures images of a surface to be measured to obtain a plurality of captured images. The control device measures the three-dimensional shape of the surface to be measured based on a result of calculating the sharpness of each captured image and comparing the sharpness of each pixel at the same coordinate of each captured image.

[0004] Three-dimensional shape measurement using the FV scheme has the advantage of being suitable for three-dimensional shape measurement of inclined surfaces and enabling high-speed measurement compared to three-dimensional shape measurement using a white light interference scheme (WLI). On the other hand, three-dimensional shape measurement using the FV scheme has the disadvantage of having lower resolution in the height direction of a surface to be measured and also being unable to measure a surface to be measured, such as a mirror surface, which has fewer changes in luminance compared to three-dimensional shape measurement using the WLI scheme.

[0005] PTL 1 discloses a surface shape detection device used in a case where three-dimensional shape measurement of a mirror-like surface to be measured is performed according to the FV scheme, in which patterns such as texture patterns are projected onto the surface to be measured. The surface shape detection device improves the contrast of the surface to be measured by projecting the texture patterns onto the surface to be measured, thereby improving the measurement accuracy of the three-dimensional shape of the surface to be measured.

[0006] PTL 2 discloses a shape measuring device comprising optical means, a scanning stage, interference light generation means, an image pickup unit, and a light-shielding plate. The optical means, whose depth of field is equal to or smaller than the measurement accuracy of a three-dimensional shape of a surface to be measured, directs measurement light downward onto the surface to be measured and also directs incident light upward. The scanning stage scans the surface to be measured in a scanning direction (height direction). The interference light generation means generates reference light that interferes with the incident light. The image pickup unit captures an image of the "incident light" or "interference light between the incident light and the reference light."The light-shielding plate is insertable and removable into a beam path of the reference light, allowing switching between the acquisition of an image of the incident light and the acquisition of an image of the interference light by an image acquisition unit. In the shape measuring device in Patent 2, the image acquisition unit acquires an image of the interference light when measuring the three-dimensional shape of an inclined surface to be measured according to the FV scheme. As a result, the contrast of an acquired image is enhanced by the interference fringes contained in the image acquired by the image acquisition unit, thus improving the measurement accuracy of the three-dimensional shape of the surface to be measured. List of citationsPatent literature PTL 1 Japanese Patent Application, Laid-Open No. 6-010675 PTL 2 Japanese Patent Application, Laid-Open No. 10-68616 Summary of the inventionTechnical problem

[0007] Incidentally, the surface shape detection device described in Patent 1 requires a projection system to be provided in the microscope to project texture patterns onto the surface to be measured, although it may not be possible to provide the projection system depending on the type (structure) of the microscope. Therefore, the method described in Patent 1 cannot easily improve the measurement accuracy of the three-dimensional shape of the surface to be measured.

[0008] In the shape measuring device described in PTL 2, it is necessary to provide the means for generating interference light and the light-shielding plate in the microscope, although it may not be possible to provide the means for generating interference light and the light-shielding plate depending on the type (structure) of the microscope. Therefore, the method described in PTL 2 cannot easily improve the measurement accuracy of the three-dimensional shape of the surface to be measured. Another problem with the shape measuring device described in PTL 2 is that an examiner must insert and remove the light-shielding plate, which is troublesome. In addition, in the shape measuring device described in PTL 2, it is necessary to provide optical means having a depth of field equal to or smaller than the measurement accuracy of the three-dimensional shape of the surface to be measured.

[0009] An object of the subject matter disclosed herein, which has been created in view of these circumstances, is to provide a three-dimensional shape measuring apparatus and a three-dimensional shape measuring method capable of reducing the time and labor of an examiner and easily improving the measurement accuracy of the three-dimensional shape of a surface to be measured. Solution to the problem

[0010] To achieve the object of the subject matter disclosed herein, a three-dimensional shape measurement apparatus configured to measure a three-dimensional shape of a surface to be measured by a focal point method comprises: a light source unit configured to emit measurement light; an interference objective lens including an interference unit configured to separate a portion of the measurement light emitted from the light source unit as reference light, emit the measurement light onto the surface to be measured, emit the reference light onto a reference surface, and generate multiplexed light of the measurement light returning from the surface to be measured and the reference light returning from the reference surface; and an objective lens configured to cause the measurement light to focus on the surface to be measured;a scanning unit configured to cause the interference objective lens to scan in a scanning direction parallel to an optical axis of the objective lens relative to the surface to be measured; an image pickup unit configured to repeatedly capture an image of the multiplexed light generated by the interference unit and output a plurality of captured images including interference fringes during scanning by the scanning unit; and a first signal processing unit configured to calculate the sharpness of each pixel of the plurality of captured images output by the image pickup unit and calculate the three-dimensional shape of the surface to be measured based on a result of comparing the sharpness of each pixel on the same coordinate of the plurality of captured images.

[0011] Since the three-dimensional shape measurement device is easily applicable to existing fixtures, it is possible to easily improve the measurement accuracy of the three-dimensional shape of a surface W to be measured and further reduce the time and labor required for the examiner to insert and remove the light-shielding plate.

[0012] In the three-dimensional shape measurement device according to another aspect of the subject matter disclosed herein, the path length of the measurement light is equal to the path length of the reference light when an optical path length of the measurement light between the interference unit and the surface to be measured is set as the path length of the measurement light, and an optical path length of the reference light between the interference unit and the reference surface is set as the path length of the reference light. In this way, the intensity of the interference fringes in the captured image can be increased, and the contrast of the surface to be measured in the captured image can be further improved.

[0013] The three-dimensional shape measurement device according to yet another aspect of the subject matter disclosed herein comprises: a second signal processing unit configured to calculate height information of the surface to be measured for each pixel to calculate the three-dimensional shape of the surface to be measured based on luminance values ​​for each pixel on the same coordinate of the plurality of captured images output by the image capturing unit; a first evaluation value calculation unit configured to calculate an evaluation value of a calculation result of the first signal processing unit and an evaluation value of a calculation result of the second signal processing unit;and a determination unit configured to determine a calculation result of the three-dimensional shape of the surface to be measured from the calculation result of the first signal processing unit or the calculation result of the second signal processing unit, whichever has a higher evaluation value based on the calculation results of the first evaluation value calculation unit. In this way, measurements according to the FV scheme and the WLI scheme can be performed in one measurement (sampling) operation.

[0014] The three-dimensional shape measurement device according to yet another aspect of the subject matter disclosed herein comprises: a second signal processing unit configured to calculate height information of the surface to be measured for each pixel to calculate the three-dimensional shape of the surface to be measured based on luminance values ​​for each pixel on the same coordinate of the plurality of captured images output by the image capturing unit; a second evaluation value calculation unit configured to calculate an evaluation value of a calculation result of the first signal processing unit and an evaluation value of a calculation result of the second signal processing unit for each pixel;and an integration unit configured to generate an integrated three-dimensional shape of the surface to be measured by selecting, for each pixel, the calculation result of the first signal processing unit or the calculation result of the second signal processing unit, whichever has a higher evaluation value based on the calculation results of the second evaluation value calculation unit. This makes it possible to achieve both the advantage of measurement according to the FV scheme and the advantage of measurement according to the WLI scheme.

[0015] In the three-dimensional shape measuring apparatus according to another aspect of the subject matter disclosed herein, the evaluation value is a signal-to-noise ratio.

[0016] In the three-dimensional shape measuring apparatus according to yet another aspect of the subject matter disclosed herein, the scanning unit causes a microscope including the interference objective lens and the image pickup unit to scan relative to the surface to be measured.

[0017] To achieve the object of the subject matter disclosed herein, a three-dimensional shape measurement method that measures a three-dimensional shape of a surface to be measured by a focal point method comprises: an emission step of emitting measurement light; an interference step of separating a part of the measurement light emitted in the emission step as a reference light, emitting the measurement light onto the surface to be measured, emitting the reference light onto a reference surface, and generating multiplexed light of the measurement light returning from the surface to be measured and the reference light returning from the reference surface;a scanning step of causing an interference objective lens including an interference unit that performs the interference step and an objective lens that causes the measurement light to focus on the surface to be measured to scan in a scanning direction that is parallel to an optical axis of the objective lens relative to the surface to be measured; an image capturing step of repeatedly capturing an image of the multiplexed light generated in the interference step and outputting a plurality of captured images including interference fringes during the scanning step; and a signal processing step of calculating the sharpness of each pixel of the plurality of captured images output in the image capturing step and calculating the three-dimensional shape of the surface to be measured based on a result of comparing the sharpness of each pixel on the same coordinate of the plurality of captured images. Advantageous effects of the invention

[0018] The subject matter disclosed herein can reduce the time and effort required by an examiner and easily improve the measurement accuracy of the three-dimensional shape of a surface to be measured. Short description of the drawings Fig. 1 is a schematic view of a three-dimensional shape measuring apparatus of a first embodiment. Fig. Figure 2 shows an example of an image taken by a camera of a surface to be measured. Fig. 3 is a functional block diagram of a control device of the first embodiment. Fig. 4 is an explanatory diagram for describing the calculation of a three-dimensional shape of the surface to be measured by a signal processing unit. Fig. 5 is a flowchart showing the processing procedure of measuring the three-dimensional shape of the surface to be measured by the three-dimensional shape measuring apparatus of the first embodiment.

[0019] A reference number 6A of the Fig. Fig. 6 is a front view of a captured image obtained in a comparative example using an observation lens in the measurement according to an FV scheme, and a reference numeral 6B of the Fig. 6 is an enlarged view of a given focus calculation area in the captured image.

[0020] A reference number 7A of the Fig. Fig. 7 is a front view of a captured image obtained in a present example by using an interference objective lens in the measurement according to the FV scheme, and a reference numeral 7B of the Fig. 7 is an enlarged view of a given focus calculation area in the captured image. Fig. 8 is an explanatory diagram showing an example of a shape of the optical plane surface, which is the three-dimensional shape of an optical plane surface measured in the comparative example. Fig. 9 is an explanatory diagram showing an example of a shape of the optical plane surface, which is the three-dimensional shape of an optical plane surface measured in the present example. Fig. 10 is a diagram showing a comparison between a cross-sectional curve of the optical plane surface based on the shape of the optical plane surface in the comparative example and a cross-sectional curve of the optical plane surface based on the shape of the optical plane surface in the present example. Fig. 11 is an explanatory diagram showing an example of a shape of the ball bearing surface, which is the three-dimensional shape of a ball bearing surface measured in the comparative example. Fig. 12 is an explanatory diagram showing an example of a shape of the ball bearing surface, which is the three-dimensional shape of a ball bearing surface measured in the present example. Fig. 13 is a diagram showing a comparison between a cross-sectional curve of the ball bearing surface based on the shape of the ball bearing surface in the comparative example and a cross-sectional curve of the ball bearing surface based on the shape of the ball bearing surface in the present example. Fig. 14 is a diagram showing a cross-sectional curve of an optical plane surface measured in the first embodiment. Fig. 15 is a functional block diagram of a control device for a three-dimensional shape measurement apparatus of a second embodiment. Fig. 16 is a flowchart showing the processing procedure of measuring the three-dimensional shape of a surface to be measured by the three-dimensional shape measuring apparatus of the second embodiment. Fig. 17 is a functional block diagram of a control device for a three-dimensional shape measurement apparatus of a third embodiment. Fig. 18 is a flowchart showing the processing procedure of measuring the three-dimensional shape of a surface to be measured by the three-dimensional shape measuring apparatus of the third embodiment. Description of the embodimentsFirst embodiment

[0021] The Fig. Figure 1 is a schematic view of a three-dimensional shape measuring device 9 of a first embodiment. The X and Y directions of the mutually orthogonal X, Y, and Z directions in the drawing are directions parallel to a horizontal direction, and the Z direction is a direction parallel to a vertical direction.

[0022] As in the Fig. 1, the three-dimensional shape measuring device 9 measures a three-dimensional shape of a surface W to be measured using an FV (Focal Point Method) scheme. The three-dimensional shape measuring device 9 essentially comprises a microscope 10, a drive mechanism 12, a scale 14, and a control device 16.

[0023] The microscope 10 includes 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, the beam splitter 22, the imaging lens 32, and the camera 34 are arranged in this order along the Z direction above the surface W to be measured. Furthermore, the light source unit 20 is arranged at a position facing the beam splitter 22 in the X direction (may also be the Y direction).

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

[0025] A half mirror, for example, is used as the beam splitter 22. The beam splitter 22 reflects a portion of the measurement light L1 incident from the light source unit 20 toward the interference objective lens 24 to a lower side in the Z direction. Furthermore, the beam splitter 22 transmits a portion of the multiplexed light L3 incident from the interference objective lens 24, which will be described later, to the upper side in the Z direction and emits the multiplexed light L3 toward the imaging lens 32.

[0026] The interference objective lens 24 is detachably mounted on a commonly known objective lens holder (such as a turret) of the microscope 10, instead of an objective lens for bright field observation (hereinafter abbreviated as observation lens) used in general FV measurement. The interference objective lens 24, which is a Michelson lens, includes 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 this order along the Z direction above the surface W to be measured, and the reference surface 24c is arranged at a position facing the beam splitter 24b in the X direction (may also be the Y direction).

[0027] The objective lens 24a has a focusing function and causes the measuring light L1 incident from the beam splitter 22 to focus on the surface W to be measured by the beam splitter 24b.

[0028] As a beam splitter 24b, which corresponds to an interference unit of the subject matter disclosed here, a half mirror, for example, is used. The beam splitter 24b splits a portion of the measurement light L1 incident from the objective lens 24a as a reference light L2, passes the remaining measurement light L1 through, and emits the remaining measurement light L1 onto the surface W to be measured, and emits the reference light L2 onto the reference surface 24c. Reference numeral D1 in the drawing indicates a path length of the measurement light, which is an optical path length of the measurement light L1 between the beam splitter 24b and the surface W to be measured. The measurement light L1 that has passed through the beam splitter 24b is irradiated onto the surface W to be measured, then reflected by the surface W to be measured, and returns to the beam splitter 24b.

[0029] For example, a reflecting mirror is used as the reference surface 24c, and the reference surface 24c reflects the reference light L2 incident from the beam splitter 24b toward the beam splitter 24b. A position of the reference surface 24c in the X direction can be manually adjusted using a reference surface position adjustment mechanism 25.

[0030] The reference surface position adjustment mechanism 25, which is, for example, a screw-type fine adjustment mechanism, adjusts the position of the reference surface 24c in the X direction by operation by an operator. This enables adjustment of a reference light path length D2, which is an optical path length of the reference light L2 between the beam splitter 24b and the reference surface 24c. Here, the position of the reference surface 24c in the X direction is adjusted by the reference surface position adjustment mechanism 25 such that the path length of the reference light D2 is equal to (including approximately equal to) the path length D1 of the measurement light while the objective lens 24a focuses on the surface W to be measured.The method for adjusting the X-direction position of the reference surface 24c is not particularly limited, and an automatic adjusting mechanism using a publicly known actuator, a temperature adjusting mechanism (heater and temperature sensor) that reversibly thermally deforms the holder 24d (reference surface containing portion 24d2) as described later, or the like may be used.

[0031] The beam splitter 24b generates the multiplexed light L3 of 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 the multiplexed light L3 toward the objective lens 24a on the top side in the Z direction. The multiplexed light L3 passes through the objective lens 24a and the beam splitter 22 and is incident on the imaging lens 32. The multiplexed light L3, which is interference light of the measurement light L1 and the reference light L2, contains interference fringes 37 (see the Fig. 2). When the objective lens 24a focuses on the surface W to be measured, the path length D1 of the measuring light is equal to the path length D2 of the reference light, as described above, and therefore the intensity of the interference fringes 37 contained in the multiplexed light L3 becomes stronger.

[0032] The holder 24d is formed of a metal material such as brass. The holder 24d includes a lens barrel 24d1 and a reference surface-containing portion 24d2. The lens barrel 24d1 is cylindrical and extends in the Z direction, and contains (holds) the objective lens 24a and the beam splitter 24b. The reference surface-containing portion 24d2 is cylindrical and extends in the X direction from a position where the lens barrel 24d1 holds the beam splitter 24b and contains the reference surface 24c. As described above, the position of the reference surface 24c in the X direction can be manually adjusted using the reference surface position adjustment mechanism 25.

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

[0034] The camera 34, which corresponds to an image pickup unit of the presently disclosed subject matter, includes a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) type imaging element (not shown). The camera 34 captures an image of the multiplexed light L3 formed by the imaging lens 32 on the imaging surface of the imaging element, performs signal processing on an image signal of the multiplexed light L3 obtained by the imaging, and outputs the captured image 36.

[0035] The Fig. Figure 2 shows an example of the captured image 36 of the surface W to be measured, which was captured by the camera 34. Here, the description is given using an optical plane surface (mirror surface) as an example of the surface W to be measured. As shown in the Fig. 2, the multiplexed light L3 contains the interference fringes 37 as described above when the objective lens 24a is focused on the surface W to be measured, and therefore the captured image 36 also contains the interference fringes 37. As a result, the contrast of the surface W to be measured in the captured image 36 can be improved even if the surface W to be measured is a mirror surface (in this case, an optical plane surface).

[0036] Back to Fig. 1: The drive mechanism 12 corresponds to a scanning unit of the subject matter disclosed here. The drive mechanism 12 is composed of various types of actuators, such as a well-known linear motor or a motor drive mechanism, and supports the microscope 10 so that it is movable in the Z direction, which is a scanning direction. The drive mechanism 12 causes the microscope 10 to scan along the Z direction, that is, the direction parallel to an optical axis of the objective lens 24a, under the control of the controller 16. This enables a change in the path length D1 of the measuring light when measuring the three-dimensional shape of the surface W to be measured.

[0037] The drive mechanism 12 only needs to be capable of causing the microscope 10 to scan in the Z direction relative to the surface W to be measured, and may, for example, cause the surface W to be measured (support portion supporting the surface W to be measured) to scan in the Z direction.

[0038] For example, a linear scale is used as the scale 14, which is a position detection sensor that detects the position of the microscope 10 in the Z direction. The scale 14 repeatedly detects the position of the microscope 10 in the Z direction and repeatedly outputs the position detection result to the controller 16.

[0039] The control device 16 comprehensively controls the operation of measuring the three-dimensional shape of the surface W to be measured by the microscope 10, the calculation of the three-dimensional shape of the surface W to be measured, and the like according to an input operation to an operation unit 17. The control device 16 includes an arithmetic circuit composed of various types of processors, memories, and the like.The various types of processors include a central processing unit (CPU), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), a programmable logic device (e.g., a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and field programmable gate array (FPGA)), and the like. Various types of functions of the control device 16 may be implemented by one processor or by a plurality of processors of the same type or different types.

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

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

[0043] The Fig. Fig. 4 is an explanatory diagram for describing the calculation of a three-dimensional shape of the surface W to be measured by a signal processing unit 102. In the Fig. 4, each pixel is expressed in a checkered pattern (checkerboard pattern) to facilitate the discrimination of each pixel in the respective captured images 36.

[0044] The signal processing unit 102 corresponds to a first signal processing unit of the subject matter disclosed herein. The signal processing unit 102 acquires the captured image 36 output by the camera 34 each time the camera 34 acquires the image of the multiplexed light L3. Next, the signal processing unit 102 calculates the sharpness (contrast, image clarity) for each pixel of the respective captured images 36 acquired by the camera 34. For example, the signal processing unit 102 sets a pixel for calculating sharpness as the target pixel 104 and calculates the sharpness according to a well-known method based on a luminance value of the target pixel 104 and a luminance value of each pixel within a sharpness calculation range 106 with the target pixel 104 as a reference.The signal processing unit 102 calculates the sharpness of each pixel in the respective captured images 36 by repeatedly performing processing steps to calculate the sharpness for all pixels in the respective captured images 36.

[0045] After calculating the sharpness, the signal processing unit 102 compares the sharpness of each pixel on the same coordinate (each pixel of the imaging element of the camera 34) of the respective captured images 36, as indicated by a straight line ZL in the drawing, and determines the position in the Z direction where the sharpness becomes maximum for each pixel on the same coordinate. The signal processing unit 102 then determines the focal point position of the camera 34 for the surface W to be measured for each pixel on the same coordinate to calculate the three-dimensional shape (height distribution) of the surface W to be measured. Calculating the three-dimensional shape of the surface W to be measured using the FV scheme is a well-known technique (see PTL 1), and therefore, a detailed description is omitted here. Functionality of the first embodiment

[0046] The Fig. 5 is a flowchart showing the processing flow of measuring the three-dimensional shape of the surface W to be measured by the three-dimensional shape measuring device 9 of the first embodiment according to the three-dimensional shape measurement method of the subject matter disclosed herein. The interference objective lens 24 is mounted on the microscope 10 in advance. The position of the reference surface 24c in the X direction is adjusted in advance so that the path length D2 of the reference light becomes equal to the path length D1 of the measurement light in a state where the objective lens 24a is focused on the surface W to be measured.

[0047] As in the Fig. 5, the operator sets the surface W to be measured, which is a measurement object, on the microscope 10 and operates the operation unit 17 to perform the operation of starting the measurement of the three-dimensional shape of the surface W to be measured (step S1). When the measurement start operation is executed, the measurement control unit 100 of the control device 16 starts emitting the measurement light L1 from the light source unit 20 (corresponding to an emission step of the subject matter disclosed herein). As a result, the multiplexed light L3, which consists of the measurement light L1 reflected by the surface W to be measured and the reference light L2 reflected by the reference surface 24c and includes the interference fringes 37, is incident on the camera 34 (corresponding to an interference step of the subject matter disclosed herein).The measurement control unit 100 then controls the drive mechanism 12 to cause the microscope 10 to start scanning in the Z direction (step S3, corresponding to a scanning step of the subject matter disclosed herein).

[0048] Furthermore, the measurement control unit 100 causes the camera 34 to repeatedly capture the image of the multiplexed light L3 based on the detection result of the position of the microscope 10 in the Z direction by the scale 14 each time the microscope 10 moves a certain distance in the Z direction (step S4, NO in step S5 and step S6, corresponds to an image capturing step of the presently disclosed subject matter). Accordingly, during scanning by the microscope 10, the captured image 36 is repeatedly input from the camera 34 to the signal processing unit 102, and the signal processing unit 102 repeatedly acquires the captured image 36.

[0049] A reference number 6A in the Fig. Fig. 6 is a front view of the captured image 36 obtained in a comparative example using the observation lens in the measurement according to the FV scheme (hereinafter abbreviated as comparative example), and a reference numeral 6B in the Fig. 6 is an enlarged view of a given focus calculation area 106 in the captured image 36. A reference number 7A in the Fig. Fig. 7 is a front view of the captured image 36 obtained in the present example using the interference objective lens 24 in the measurement according to the FV scheme (hereinafter abbreviated as the present example), and a reference numeral 7B in the Fig. 7 is an enlarged view of the given focus calculation area 106 in the captured image 36.

[0050] The Fig. 6 and Fig. The surface W to be measured indicated in Figure 7 is an optical plane surface, i.e. a mirror surface. As indicated by the reference numerals 6A and 6B in the Fig. 6, in the comparative example, the camera 34 captures the image of the measurement light L1 returned from the surface to be measured W through the observation lens, that is, the image of the returned light that does not include the interference fringes 37, and therefore, the interference fringes 37 in the captured image 36 are not generated on the surface to be measured W. Thus, in the comparative example, the contrast of the surface to be measured W in the captured image 36 decreases, and the contrast within the focus calculation area 106 also decreases.

[0051] In contrast, in the present example, as shown in reference numerals 7A and 7B, the Fig. 7, the camera 34 captures the image of the surface W to be measured through the interference objective lens 24, that is, the image of the multiplexed light L3 including the interference fringes 37, resulting in the generation of the interference fringes 37 on the surface W to be measured in the captured image 36. Therefore, in the present example, the contrast of the surface W to be measured in the captured image 36 is enhanced, and the contrast within the sharpness calculation area 106 is also enhanced.

[0052] Back to the Fig. 5: When the scanning of the microscope 10 ends (YES in step S5), as shown in the Fig. 4, the signal processing unit 102 repeatedly sets the target pixel 104 and the sharpness calculation area 106, and repeatedly calculates the sharpness for all pixels of the respective captured images 36. Next, the signal processing unit 102 compares the sharpness of each pixel on the same coordinate of the respective captured images 36 and determines the position in the Z direction at which the sharpness becomes maximum for each pixel on the same coordinate, so that the focal point position of the camera 34 for the surface W to be measured is determined for each pixel on the same coordinate. In this way, the signal processing unit 102 calculates the three-dimensional shape (height distribution) of the surface W to be measured (step S7, corresponding to a signal processing step of the subject matter disclosed herein).

[0053] In the following, the measurement result of the three-dimensional shape of the surface W to be measured in the present example is compared with the measurement result of the three-dimensional shape of the surface W to be measured in the comparison example.

[0054] The Fig. Fig. 8 is an explanatory diagram showing an example of a shape 150A of the optical plane surface, which is the three-dimensional shape of an optical plane surface measured in the comparative example. Fig. Fig. 9 is an explanatory diagram showing an example of a shape 150B of the optical plane surface, which is the three-dimensional shape of an optical plane surface measured in the present example. Fig. 10 is a diagram showing a comparison between a cross-sectional curve of the optical plane surface based on the shape 150A of the optical plane surface in the comparative example and a cross-sectional curve of the optical plane surface based on the shape 150B of the optical plane surface in the present example. "LATERAL POSITION" in the Fig. 10 indicates the position on a given straight line along the optical plane, and “HEIGHT POSITION” in the Fig. 10 indicates a height position of the optical plane surface in the Z direction on the given straight line (this also applies to the later described Fig. 14).

[0055] As in the Fig. 8 to 10, in the comparative example, when the surface W to be measured is an optical flat surface (mirror surface), the shape 150A of the optical flat surface becomes noisy, and the three-dimensional shape of the surface W to be measured becomes difficult to measure. In contrast, in the present example, even when the surface W to be measured is an optical flat surface (mirror surface), the generation of noise on the shape 150B of the optical flat surface is suppressed, so that the three-dimensional shape measurement of the surface W to be measured becomes possible.

[0056] The Fig. Fig. 11 is an explanatory diagram showing an example of a shape 154A of the ball bearing surface, which is the three-dimensional shape of a ball bearing surface measured in the comparative example. Fig. Fig. 12 is an explanatory diagram showing an example of a shape 154B of the ball bearing surface, which is the three-dimensional shape of a ball bearing surface measured in the present example. Fig. 13 is a diagram showing a comparison between a cross-sectional curve of the ball bearing surface based on the shape 154A of the ball bearing surface in the comparative example and a cross-sectional curve of the ball bearing surface based on the shape 154B of the ball bearing surface in the present example. "LATERAL POSITION" in the Fig. 13 indicates the position on a given curve along the ball bearing surface, and “HEIGHT POSITION” indicates a height position of the optical plane surface on the given curve.

[0057] As in the Fig. As shown in Figures 11 to 13, the resolution of the shape 154A of the ball bearing surface in the height direction is approximately 10 µm in the comparative example when the surface W to be measured is a ball bearing surface, while the resolution of the shape 154B of the ball bearing surface in the height direction in the present example is approximately 1 µm. This shows that the resolution of the three-dimensional shape of the surface W to be measured can be made higher in the present example than in the comparative example.

[0058] Thus, in the present example, the contrast of the surface W to be measured (focus calculation area 106) in the captured image 36 is improved by generating the interference fringes 37 on the surface W to be measured in the captured image 36 by the interference objective lens 24, so that the measurement sensitivity and resolution of the three-dimensional shape of the surface W to be measured are improved. Therefore, the measurement accuracy of the three-dimensional shape of the surface W to be measured is improved in the present example. Moreover, compared with the texture pattern described in PTL 1, the interference fringes 37 show a larger change in luminance when the microscope 10 is caused to scan in the Z direction, and therefore the measurement sensitivity and resolution of the three-dimensional shape of the surface W to be measured are further improved, that is, the measurement accuracy of the three-dimensional shape is further improved.

[0059] Furthermore, since the three-dimensional shape of the surface W to be measured is measured according to the FV scheme in this example, it is possible to improve the measurement accuracy of the three-dimensional shape of the surface W to be measured while performing a high-speed measurement according to the FV scheme. For example, in the case of performing the three-dimensional shape measurement, the Fig. 11 and Fig. 12, the measurement time according to the FV scheme is 5 seconds, which corresponds to about 1 / 3 of the measurement time of the WLI method, which is 16 seconds.

[0060] Thus, in the first embodiment, the measurement accuracy of the three-dimensional shape of the surface W to be measured is improved by simply providing the interference objective lens 24 in the microscope 10, thereby eliminating the need to provide the texture pattern projection system described in PTL 1 in the microscope 10 or the interference light generation means and the light-shielding plate described in PTL 2 in the microscope 10. As a result, the subject matter disclosed herein is also easily applicable to existing three-dimensional shape measurement devices (microscopes) employing the FV scheme, thereby making it possible to easily improve the measurement accuracy of the three-dimensional shape of the surface W to be measured.Furthermore, in the first embodiment, an examiner does not need to insert or remove the light-shielding plate as described in Patent Application Publication No. 2, thus reducing the examiner's time and labor. As a result, the first embodiment can reduce the examiner's time and labor and easily improve the measurement accuracy of the three-dimensional shape of the surface W to be measured.

[0061] In the shape measuring device described in PTL 2, the depth of field of the objective lens is set to be equal to or smaller than the measurement accuracy of the three-dimensional shape of the surface W to be measured, although in the first embodiment, it is not necessary to set the depth of field of the objective lens 24a to be equal to or smaller than the measurement accuracy of the three-dimensional shape of the surface W to be measured.

[0062] Specifically, when a numerical aperture (NA) of the objective lens 24a is, for example, 0.3 and a wavelength of the measurement light L1 is, for example, 0.53 µm, a depth of field of the objective lens 24a is given by “Depth of field = wavelength / (2 × NA 2 )] = 2.94 µm“ On the other hand, as shown in the Fig. 14, in the three-dimensional shape measurement result of the optical plane surface (surface to be measured (W) in the first embodiment, peak-to-peak (PP) is 0.4 µm or less. Accordingly, in the first embodiment, it is not necessary to set the depth of field of the objective lens 24a to be equal to or smaller than the measurement accuracy of the three-dimensional shape of the surface to be measured W. Here, the Fig. 14 is a diagram showing a cross-sectional curve of an optical plane surface measured in the first embodiment. Second embodiment

[0063] The Fig. 15 is a functional block diagram of a control device 16 for a three-dimensional shape measuring device 9 of a second embodiment. The three-dimensional shape measuring device 9 of the first embodiment calculates only the three-dimensional shape of the surface W to be measured according to the FV scheme based on the captured images 36 obtained during scanning of the microscope 10. In contrast, the three-dimensional shape measuring device 9 of the second embodiment calculates the three-dimensional shape of the surface W to be measured according to two types of schemes: the FV scheme and the WLI scheme simultaneously (or may be sequentially) based on the captured images 36 obtained during scanning of the microscope 10, and compares the three-dimensional shape calculation results with the two schemes to select the result with the better signal-to-noise ratio (S / N ratio).

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

[0065] The first signal processing unit 102A, which is the same as the signal processing unit 102 in the first embodiment, calculates the three-dimensional shape of the surface W to be measured according to the FV scheme based on the captured images 36 output by the camera 34 during scanning of the microscope 10.

[0066] The second signal processing unit 102B calculates the three-dimensional shape of the surface W to be measured according to the WLI scheme based on the captured images 36 output by the camera 34 during scanning of the microscope 10. Specifically, the second signal processing unit 102B compares luminance values ​​for each pixel on the same coordinate in the respective captured images 36. Next, the second signal processing unit 102B determines a position in the Z direction at which the luminance value for each pixel on the same coordinate of the respective captured images 36 becomes maximum to calculate height information of the surface W to be measured for each pixel on the same coordinate. In this way, the three-dimensional shape (height distribution) of the surface W to be measured is calculated.The calculation of the three-dimensional shape of the surface to be measured W using the WLI scheme is also a well-known technique (see, for example, Japanese Patent Application Laid-Open No. 2017-106860), and therefore a detailed description is omitted here.

[0067] The S / N ratio calculation unit 102C, which corresponds to a first evaluation value calculation unit of the subject matter disclosed herein, calculates an S / N ratio of the calculation result of the three-dimensional shape of the surface W to be measured by the first signal processing unit 102A and an S / N ratio of the calculation result of the three-dimensional shape of the surface W to be measured by the second signal processing unit 102B. The S / N ratio is an example of the evaluation value of the subject matter disclosed herein, and since a calculation method of the S / N ratio is a well-known technology, a detailed description is omitted here (see, for example, Japanese Patent Application Laid-Open No. 2021-33525).

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

[0069] The Fig. Fig. 16 is a flowchart showing the processing flow of the three-dimensional shape measurement of the surface W to be measured by the three-dimensional shape measuring device 9 of the second embodiment. As shown in the Fig. 16, the processing from step S1 to step S6 is essentially the same as the processing in the Fig. 5, and therefore a specific description is omitted here.

[0070] When the scanning of the microscope 10 ends (YES in step S5), the first signal processing unit 102A calculates the sharpness for each pixel of the captured images 36 input from the camera 34 (step S7A). Next, the first signal processing unit 102A calculates the three-dimensional shape of the surface W to be measured, as in the case of the signal processing unit 102 in the first embodiment, based on the result of the sharpness comparison for each pixel at the same coordinate of the respective captured images 36 (step S8A).

[0071] Furthermore, the second signal processing unit 102B acquires the luminance values ​​for each pixel of the captured images 36 input from the camera 34 (step S7B). The second signal processing unit 102B then determines a position in the Z direction at which the luminance values ​​for each pixel on the same coordinate of the respective captured images 36 become maximum, and calculates height information of the surface W to be measured for each pixel on the same coordinate to calculate the three-dimensional shape of the surface W to be measured (step S8B).

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

[0073] When the calculation of the S / N ratios by the S / N ratio calculation unit 102C is completed, the determination unit 102D determines the result with the higher S / N ratio from the three-dimensional shape calculation result by the first signal processing unit 102A and the three-dimensional shape calculation result by the second signal processing unit 102B as the measurement result of the three-dimensional shape of the surface W to be measured (step S10). In this way, the determination unit 102D determines the three-dimensional shape calculation result by the first signal processing unit 102A as the measurement result of the three-dimensional shape of the surface W to be measured when the surface W to be measured is a surface suitable for the FV scheme, such as a steep inclined surface.Conversely, the determination unit 102D determines the calculation result of the three-dimensional shape by the second signal processing unit 102B as the measurement result of the three-dimensional shape of the surface W to be measured when the surface W to be measured is suitable for the WLI scheme, such as a mirror surface, or a surface requiring high resolution in the Z direction (height direction) (such as a ball bearing surface).

[0074] Thus, in the second embodiment, it becomes possible to perform the measurement according to the FV scheme and the WLI scheme in one measurement operation (scanning the microscope 10) by simultaneously calculating the three-dimensional shape of the surface W to be measured according to the FV scheme and the WLI scheme based on the captured images 36 obtained during scanning of the microscope 10, and comparing the calculation results of the three-dimensional shape according to the two schemes to select the result with the better S / N ratio. This allows the three-dimensional shape of the surface W to be measured that is not suitable for measurement according to the WLI scheme, such as a steep inclined surface, to be measured according to the FV scheme, while the three-dimensional shape of the surface W to be measured that is not suitable for measurement according to the FV scheme, such as a mirror surface, to be measured according to the WLI scheme. Third embodiment

[0075] The Fig. 17 is a functional block diagram of a control device 16 for a three-dimensional shape measuring device 9 of a third embodiment. The three-dimensional shape measuring device 9 of the second embodiment simultaneously calculates the three-dimensional shape of the surface W to be measured according to the FV scheme and the WLI scheme, and compares the three-dimensional shape calculation results by the two schemes to select the result with the better S / N ratio. In contrast, the three-dimensional shape measuring device 9 of the third embodiment calculates an integrated three-dimensional shape of the surface W to be measured based on the three-dimensional shape calculation results by the two types of schemes.

[0076] As in the Fig. As shown in Fig. 17, the three-dimensional shape measuring device 9 of the third embodiment has substantially the same configuration as the three-dimensional shape measuring device 9 of the second embodiment, except that the control device 16 functions as the "S / N ratio calculating unit 102E and the integrating unit 102F" instead of the "S / N ratio calculating unit 102C and the determining unit 102D." Thus, functions or components that are the same as in the respective embodiments are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0077] The Fig. Fig. 18 is a flowchart showing the processing flow of measuring the three-dimensional shape of the surface W to be measured by the three-dimensional shape measuring device 9 of the third embodiment. As shown in Fig. Fig. 18, the processing from step S1 to steps S8A and S8B is basically the same as the processing in the Fig. 16, and therefore a detailed description is omitted here.

[0078] The S / N ratio calculation unit 102E corresponds to a second evaluation value calculation unit of the subject matter disclosed herein. After processing steps S8A and S8B, the S / N ratio calculation unit 102E calculates an S / N ratio of the three-dimensional shape calculation result of the first signal processing unit 102A (step S9A1) and also calculates an S / N ratio of the three-dimensional shape calculation result of the second signal processing unit 102B (step S9B1) for each pixel of the respective captured images 36 (for each pixel of the imaging element of the camera 34). Since a calculation method of the S / N ratio for each pixel is also a well-known technology, a detailed description will be omitted here (see, for example, Japanese Patent Application 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 in the first signal processing unit 102A and the S / N ratio of the three-dimensional shape calculation result in the second signal processing unit 102B for each pixel described above to select the result with a higher S / N ratio (step S10A). The integration unit 102F then integrates the calculation results of the three-dimensional shape selected for each pixel to generate an integrated three-dimensional shape of the surface W to be measured (step S11A).

[0080] Thus, in the third embodiment, the integrated three-dimensional shape of the surface W to be measured is generated based on the result of selecting the result with a higher S / N ratio from the results of the three-dimensional shape calculation in the first signal processing unit 102A and the second signal processing unit 102B for each pixel, making it possible to obtain both the advantage of measurement according to the FV scheme and the advantage of measurement according to the WLI scheme. As a result, it is possible to perform a highly accurate measurement of the three-dimensional shape of the surface W to be measured, which is a mixture of a steep inclined surface that can be measured with high accuracy according to the FV scheme and a mirror surface that can be measured with high accuracy according to the WLI scheme. Other

[0081] While in the second and third embodiments, the S / N ratio was described as an example as the evaluation value of the result of the three-dimensional shape calculation, evaluation values ​​other than the S / N ratio may also be used as long as the evaluation values ​​can be used as an index of the measurement accuracy of the three-dimensional shape of the surface W to be measured.

[0082] Although in each of the embodiments, the Michelson interference objective lens 24 is provided in the microscope 10, it is possible to provide various well-known interference objective lenses, such as Mirau and Linnik interference objective lenses.

[0083] While in each of the embodiments the drive mechanism 12 causes the microscope 10 to scan in the Z direction, a scanning target is not particularly limited as long as the interference objective lens 24 can at least be caused to scan in the Z direction relative to the surface W to be measured. List of reference symbols 9 Device for three-dimensional shape measurement 10 Microscope 12 Drive mechanism 14 scale 16 Control device 17 Control unit 20 light source unit 22 beam splitters 24 Interference objective lens 24a objective lens 24b beam splitter 24c reference surface 24d holder 24d1 lens barrel 24d2 section containing the reference surface 25 Mechanism for adjusting the position of the reference surface 32 imaging lens 34 Camera 36 captured 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 unit 102D Determination unit 102E N-ratio calculation unit 102F Integration Unit 104 target pixels 106 Focus calculation area 150A, 150B Shape of the optical plane surface 154A, 154B Shape of the ball bearing surface D1 Path length of the measuring light D2 Path length of the reference light L1 measuring light L2 reference light L3 Multiplex light W surface to be measured QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 6-010675

[0006] JP 10-68616

[0006] WO 2017-106860

[0066] JP 2021-33525

[0067] JP 2007-68597

[0078]

Claims

[1] A three-dimensional shape measuring device configured to measure a three-dimensional shape of a surface to be measured by a focal point method, comprising: a light source unit configured to emit measurement light; an interference objective lens including an interference unit configured to separate a portion of the measurement light emitted from the light source unit as a reference light, emit the measurement light onto the surface to be measured, emit the reference light onto a reference surface, and generate multiplexed light of the measurement light returning from the surface to be measured and the reference light returning from the reference surface, and an objective lens configured to cause the measurement light to focus on the surface to be measured; a scanning unit configured to cause the interference objective lens to scan in a scanning direction parallel to an optical axis of the objective lens relative to the surface to be measured; an image pickup unit configured to repeatedly pick up an image of the multiplexed light generated by the interference unit and to output a plurality of picked up images including interference fringes during scanning by the scanning unit; and a first signal processing unit configured to calculate the sharpness of each pixel of the plurality of captured images output by the image capturing unit and to calculate the three-dimensional shape of the surface to be measured based on a result of comparing the sharpness of each pixel on the same coordinate of the plurality of captured images. [2] The three-dimensional shape measuring device according to claim 1, wherein when an optical path length of the measuring light between the interference unit and the surface to be measured is set as a path length of the measuring light and an optical path length of the reference light between the interference unit and the reference surface is set as a path length of the reference light, the path length of the measuring light is equal to the path length of the reference light. [3] The three-dimensional shape measuring device according to claim 1 or 2, comprising: a second signal processing unit configured to calculate height information of the surface to be measured for each pixel to calculate the three-dimensional shape of the surface to be measured based on luminance values ​​for each pixel on the same coordinate of the plurality of captured images output from the image capturing unit; a first evaluation value calculation unit configured to calculate an evaluation value of a calculation result of the first signal processing unit and an evaluation value of a calculation result of the second signal processing unit; and a determination unit configured to determine a calculation result of the three-dimensional shape of the surface to be measured from the calculation result of the first signal processing unit or the calculation result of the second signal processing unit, whichever has a higher evaluation value based on the calculation results of the first evaluation value calculation unit. [4] The three-dimensional shape measuring device according to claim 1 or 2, comprising: a second signal processing unit configured to calculate height information of the surface to be measured for each pixel to calculate the three-dimensional shape of the surface to be measured based on luminance values ​​for each pixel on the same coordinate of the plurality of captured images output from the image capturing unit; a second evaluation value calculation unit configured to calculate an evaluation value of a calculation result of the first signal processing unit and an evaluation value of a calculation result of the second signal processing unit; and an integration unit configured to generate an integrated three-dimensional shape of the surface to be measured by selecting, for each pixel, the calculation result of the first signal processing unit or the calculation result of the second signal processing unit, whichever has a higher evaluation value based on the calculation results of the second evaluation value calculation unit. [5] The three-dimensional shape measuring device according to claim 3 or 4, wherein the evaluation value is a signal-to-noise ratio. [6] The three-dimensional shape measuring apparatus according to any one of claims 1 to 5, wherein the scanning unit causes a microscope including the interference objective lens and the image pickup unit to scan relative to the surface to be measured. [7] A method for three-dimensional shape measurement which measures a three-dimensional shape of a surface to be measured by a focal point method, comprising: an emission step of emitting measuring light; an interference step of separating a part of the measurement light emitted in the emission step as a reference light, emitting the measurement light onto the surface to be measured, emitting the reference light onto a reference surface, and generating multiplexed light of the measurement light returning from the surface to be measured and the reference light returning from the reference surface; a scanning step of causing an interference objective lens including an interference unit that performs the interference step and an objective lens that causes the measurement light to focus on the surface to be measured to scan in a scanning direction that is parallel to an optical axis of the objective lens relative to the surface to be measured; an image capturing step of repeatedly capturing an image of the multiplexed light generated in the interference step and outputting a plurality of captured images including interference fringes during the scanning step; and a signal processing step of calculating the sharpness of each pixel of the plurality of captured images output in the image capturing step, and calculating the three-dimensional shape of the surface to be measured based on a result of comparing the sharpness of each pixel on the same coordinate of the plurality of captured images.

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