JP5342178B2 - Shape measuring apparatus and shape measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape measuring apparatus and its shape measuring method which can accurately measure the surface shape of a glossy surface in a short time. <P>SOLUTION: The shape measuring apparatus 1 includes an imaging section 25 for picking up surface images of a sample 15 put on a sample stand 16 for a microscope, a piezoelectric drive controller which moves an imaging optical system relatively to the sample 15 periodically along the optical axis of the imaging optical system of the imaging section 25, and stores and outputs amounts of travel, a two-beam interference objective lens 14 which laps intensity unevenness of reflected light from the surface of the sample 15 reflecting the unevenness of the surface of the sample 15 over the surface image, and a controlling processor 27 for acquiring the surface shape of the sample 15 by calculating a relative height of the surface of the sample 15, on the basis of a travel distance value at which a degree of focusing of a plurality of surface images picked up by the imaging section 25 for picking up the surface images over which the intensity unevenness of the reflected light is lapped over with the objective lens 14 becomes maximum, among the travel distance values of the imaging section 25 output from the piezoelectric drive controller. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a shape measuring apparatus that calculates the surface height of an object to be measured by using an optical microscope and obtains the surface shape of the object to be measured, and a shape measuring method thereof.

Various devices have been proposed in the past as devices for calculating the surface height of an object to be measured using an optical microscope, and there is a device disclosed in Patent Document 1 as an example. The shape measuring apparatus 500 disclosed in Patent Document 1 will be briefly described with reference to FIG. 9. The microscope objective lens 540 is continuously predetermined by the piezo drive device 530 at a rate of, for example, 15 times per second. Are scanned back and forth in the direction along the optical axis of the microscope. While reciprocally scanning in this manner, the image of the sample 550 formed by the microscope objective lens 540 is picked up by the high-speed camera 510 at a rate of one piece per 1/900 second and converted into a digital signal. The data is output to the control processor 590. The control processor 590 calculates the degree of focus (degree of focus) for each pixel of the input image, and for each pixel within one cycle from the upper limit position to the lower limit position in the direction along the optical axis of the microscope. The position in the optical axis direction where the highest degree of focus is detected is determined as the relative height of that point. According to the shape measuring apparatus 500 having such a configuration, the surface shape of the object to be measured can be measured in a relatively short time.
Japanese Patent No. 3737483

  By the way, for example, a polished surface such as a polished metal surface or glass surface may have fine cutting marks of about 10 μm that cannot be seen with the human eye in focus. When the shape measuring device 500 is used to measure the shape of such a cut mark (surface shape of the glossy surface) in a short time, the S / N ratio (used for measurement) of the image signal used for the measurement is measured. For example, as shown in FIG. 8A, it is difficult to accurately measure the shape of a fine cutting mark of about 10 μm.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a shape measuring apparatus and a shape measuring method thereof that can accurately measure the surface shape of a glossy surface in a short time.

In order to achieve such an object, a shape measuring device according to the present invention is provided along an optical axis of an imaging unit that captures a surface image of an object to be measured placed on a stage, and an imaging optical system of the imaging unit. The imaging optical system is reciprocally moved relative to the object to be measured, a movement control unit that stores and outputs a movement amount, and the reflected light and the reference light from the surface of the object to be measured are overlapped, An interference fringe generation optical system that generates interference fringes reflecting the irregularities on the surface of the object to be measured, and the interference fringes included by the image pickup unit while reciprocally moving the imaging optical system relative to the object to be measured. A surface image is picked up, and a movement amount when the maximum degree of focus is obtained in each of the reciprocal relative movements for each predetermined area of the imaging surface constituting the image pickup unit, and is obtained for each of the reciprocal relative movements. Based on a plurality of said movement amounts Configured with a, a calculation section for the every predetermined area and calculates the relative height of the surface of the object to be measured determine the surface shape of the object to be measured.

Further, in the above-described shape measuring apparatus, the calculating unit, by Rukoto determined focus degree based on the second derivative value of the signal intensity detected by the pixels constituting the imaging surface, the maximum degree of focus It is preferable to calculate the relative height of the surface of the object to be measured for each of the pixels, by obtaining the amount of movement when the value is obtained .

In the above-described shape measuring apparatus, it is preferable that the stage can support the object to be measured such that a surface to be measured of the object to be measured is inclined with respect to the optical axis of the imaging optical system. Further, in the above-described shape measuring apparatus, a configuration in which a mask formed so that a plurality of small holes are regularly arranged may be arranged on the reference surface of the interference fringe generating optical system.

Here, in the above-described shape measuring apparatus, it is preferable that the calculation unit stores a movement amount when the maximum degree of focus is obtained in each of the reciprocating relative movement cycles .

Moreover, in the above-described shape measuring apparatus, it is also preferable that the calculation unit take an arithmetic average of relative heights at which the degree of focus is not less than a predetermined threshold for each pixel constituting the imaging surface .

Furthermore, in the above-described shape measuring apparatus, the calculation unit applies a probability density function to the appearance frequency distribution of the relative height that achieves a degree of focus equal to or greater than a predetermined threshold for each pixel constituting the imaging surface, so that the probability is maximum. The structure which calculates | requires the relative height to become may be sufficient. In the shape measuring apparatus described above, the probability density function is preferably a normal distribution.

Further, in the above-described shape measuring apparatus, the calculation unit approximates the vicinity of the maximum frequency of the appearance frequency distribution of the relative height that achieves a focusing degree equal to or greater than a predetermined threshold for each pixel constituting the imaging surface by a quadratic curve. In addition, a configuration for obtaining the relative height at which the maximum frequency is obtained is also preferable.

In the shape measuring method according to the present invention, the shape measuring device configured as described above is used to capture an image by the imaging unit while moving the imaging optical system relative to the object to be measured by the movement control unit. When obtaining the surface shape of the object to be measured by calculating the relative height of the surface of the object to be measured based on the degree of focus obtained based on the plurality of surface images obtained The unit captures the surface image including the interference fringes generated by the interference fringe generation optical system and superimposed on the surface image.

  According to the present invention, the surface shape of the glossy surface can be accurately measured in a short time.

  Examples 1 and 2 as preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic diagram of a shape measuring apparatus 1 according to a first embodiment to which the present invention is applied. The configuration of the shape measuring apparatus 1 will be described with reference to FIG. The shape measuring apparatus 1 mainly includes an imaging unit 25, a microscope body 26, and a control processor 27. The microscope main body 26 mainly includes a microscope sample stage 16, a microscope base 18, and an inclined plate 20, and the inclined plate 20 is placed on the upper surface of the microscope sample stage 16. Therefore, for example, the measurement surface (upper surface) of the sample 15 which is a glossy surface is imaged by placing the measurement object, for example, a substantially rectangular parallelepiped sample 15 on the upper surface of the inclined plate 20 and performing the measurement. Measurement can be performed in a state of being inclined with respect to the optical axis of the imaging optical system constituting the unit 25.

  The imaging unit 25 is mainly composed of a high-speed camera 11, a microscope barrel device 12, a piezo drive device 13, a two-beam interference objective lens 14, and a microscope illumination device 17. The microscope illumination device 17 includes a light source 17a that emits illumination light and a beam splitter 17b. As shown in FIG. 2, the two-beam interference objective lens 14 is mainly composed of a beam splitter 31, a reference surface bright field objective lens 32, a reference surface 33, and an object bright field objective lens 34. Exemplifies a linique type interference optical system. The microscope barrel device 12 is configured to include an imaging lens (not shown) therein, and forms interference image light including interference fringes on the imaging surface of the high-speed camera 11 as will be described later. The high-speed camera 11 is configured to be able to capture images at a rate of, for example, 1/900 seconds, and converts the captured image into a digital signal and outputs the digital signal to a high-speed image processor 42 described later. (See FIG. 3).

  The piezo driving device 13 is configured by using a piezo element whose volume changes by changing the applied voltage. In this embodiment, the piezo driving device 13 can continuously reciprocate a predetermined width at a rate of 15 times per second, for example. It has become. Since the piezo driving device 13 is attached to the upper end portion of the two-beam interference objective lens 14, the two-beam interference objective lens 14 is driven by the imaging optical that constitutes the imaging unit 25 when the piezo driving device 13 is driven. It is reciprocated in the direction along the optical axis of the system (vertical direction in FIG. 1). Further, the piezo drive device 13 is connected to a piezo drive control device 41, which will be described later, and the drive is controlled (see FIG. 3). As shown in FIG. 3, the control processor 27 is mainly composed of a piezo drive control device 41, a high-speed image processor 42, and a control computer 43, and detailed operations thereof will be described later.

  Although the constituent parts of the shape measuring apparatus 1 have been described above, the measurement method for measuring the surface shape of the measurement surface of the sample 15 using the shape measuring apparatus 1 will be described together with the operation of each constituent part. To do. First, the illumination light emitted from the light source 17a and reflected by the beam splitter 17b reaches the beam splitter 31 in the two-beam interference objective lens 14 (see FIGS. 1 and 2). The illumination light is split by the beam splitter 31, one passing through the object bright field objective lens 34 and irradiating the measurement surface of the sample 15, and the other passing through the reference plane bright field objective lens 32. Then, the reference surface 33 is irradiated. The illumination light reflected on the measurement surface of the sample 15 and the reference surface 33 is overlapped again by the beam splitter 31 to generate interference fringes, and the interference image light including the interference fringes is emitted from the high-speed camera 11. An image is formed on the imaging surface.

  At the time of the measurement, since the piezo drive device 13 is continuously reciprocated by the piezo drive control device 41, the two-beam interference objective lens 14 (the bright field objective lens 34 for the object) is moved to each position. The interference image light in this state is imaged on the imaging surface of the high-speed camera 11. In this embodiment, since the high-speed camera 11 is used, it is possible to reliably capture an image at each moving position with respect to driving of the piezo driving device 13. Here, since the interference fringes are generated based on the phase difference (optical path difference) between the reflected light from the measurement surface of the sample 15 and the reflected light from the reference surface 33, the interference fringes are included as follows. By calculating the image, it is possible to determine the surface shape by measuring the relative height of the measurement surface of the sample 15.

  Therefore, a method for obtaining the shape of the measurement surface by measuring the relative height of the measurement surface of the sample 15 in the control processor 27 will be described with reference to the following four measurement methods (measurement methods 1 to 4).

(Measurement method 1)
First, as shown in FIG. 3, the high-speed image processor 42 continuously outputs an operation signal for moving the piezo drive device 13 by a predetermined scanning distance to the piezo drive control device 41, and this operation. In synchronization with the output of the signal, an image captured by the high-speed camera 11 and converted into a digital signal is input. By doing so, the high-speed image processor 42 can store the movement distance information along the optical axis direction of the imaging optical system constituting the imaging unit 25 and the image at each movement position. . Further, the high-speed image processor 42 outputs an operation signal to the piezo drive control device 41 to drive the piezo drive device 13 continuously and cyclically within a predetermined scanning width.

  Then, the high speed image processor 42 calculates the degree of focus for each pixel of the input image. At this time, as a technique for obtaining the degree of focus, it can be obtained by using a secondary differential value (change rate of the signal intensity of the pixel) or a variance value. In this embodiment, the secondary differential value is used. Yes. Note that the degree of focus of a pixel can be obtained by using, for example, a filter (Laplacian filter) based on a secondary differential value using information of surrounding pixels.

  Furthermore, the high-speed image processor 42 generates the original height image 42a and the focus degree image 42b at a rate of one sheet while the piezo drive device 13 circulates up and down once based on each input information. Each of them is output to the control computer 43. The original height image 42a is a value stored by the high-speed image processor 42 that is determined to be closest to the true height obtained during one cycle of vertical movement for each pixel. The degree image 42b stores the degree of focus of each pixel for each pixel.

  The control computer 43 inputs a plurality of original height images 42a and a plurality of focus degree images 42b obtained within a predetermined period, and calculates a height image closer to the true height image. Here, the calculation method of the height image in the control computer 43 will be specifically described with reference to the graph shown in FIG. The vertical axis in FIG. 4 (a) represents the degree of focus, and the horizontal axis represents time. Each plot in the graph of FIG. 4 (a) is the above-mentioned focus degree image that is output in one cycle. A value for one pixel arbitrarily extracted from among them is shown. In addition, the vertical axis in FIG. 4B represents height, and the horizontal axis represents time, and each plot in the graph of FIG. 4B represents the height image that is output in one cycle. The values for one pixel arbitrarily extracted from these are shown, and for convenience of explanation, FIG. 4 (a) and FIG. 4 (b) are shown for the same pixel. At this time, the time point indicating the maximum degree of focus within a predetermined period, for example, the height of the plot 61 indicating the height in the plot 51 is determined as the relative height of the pixel.

  By performing the above calculation for all the pixels and determining the relative heights of all the pixels, a height image 43a (surface shape of the measurement surface of the sample 15) closer to the true height image is obtained. Can be sought. Then, by outputting the obtained height image 43 a to, for example, the monitor 44 shown in FIG. 3, the surface shape of the measurement surface of the sample 15 can be observed by the monitor 44.

(Measurement method 2)
Since the measurement method 2 is the same as the measurement method 1 described above up to the process of creating the above-described FIG. 4A and FIG. 4B in the control computer 43, the measurement method 1 and The description of the same part is omitted, and the part different from the measuring method 1 will be mainly described. As described above, the control computer 43 inputs the plurality of original height images 42a and the focus degree images 42b obtained within a predetermined period, so that the control computer 43 receives, for example, FIG. Assume that the graph shown in 4 (b) is created. Here, in FIG. 4A, for example, the height of the plot in which the degree of focus greater than or equal to the predetermined threshold value 52 is detected (for example, plots 61, 62a, 62b, 62c, 62d, 62e in FIG. 4B). 62f, 62g) is determined to determine the relative height of the pixel. The height image 43a can be obtained by performing the above calculation for all the pixels and determining the relative heights of all the pixels.

(Measurement method 3)
Since the measuring method 3 is the same as the measuring method 1 described above until the process shown in FIGS. 4A and 4B is created in the control computer 43, the measuring method 1 and The description of the same part is omitted, and the part different from the measuring method 1 will be mainly described. As described above, the control computer 43 inputs the plurality of original height images 42a and the focus degree images 42b obtained within a predetermined period, so that the control computer 43 receives, for example, FIG. Assume that the graph shown in 4 (b) is created.

  Here, in FIG. 4A, for example, the height of the plot in which the degree of focus greater than or equal to the predetermined threshold value 52 is detected (for example, plots 61, 62a, 62b, 62c, 62d, 62e in FIG. 4B). 62f, 62g), as shown in FIG. 5, the vertical axis indicates the height and the horizontal axis indicates the appearance frequency, and an appearance frequency distribution for each section 71 having a predetermined height is created. Then, by applying a probability density function (for example, normal distribution 72) to the created appearance frequency distribution, a height (for example, height 71a shown in FIG. 5) that gives the maximum appearance frequency in the normal distribution 72 is obtained. The relative height of the pixel is determined. The height image 43a can be obtained by performing the above calculation for all the pixels and determining the relative heights of all the pixels.

(Measurement method 4)
In the measurement method 3 described above, the configuration using the normal distribution 72 is an example, and a probability density function other than the normal distribution 72 can be applied to the appearance frequency distribution. Therefore, in the measurement method 4, a case where a quadratic curve is used as the probability density function will be described with reference to FIG. The measurement method 4 is the same as the measurement method 3 described above until the process of creating the appearance frequency distribution for each section 71 shown in FIG. A description will be omitted, focusing on the differences from the measurement method 3.

  For example, it is assumed that the appearance frequency distribution shown in FIG. 6 is created as described above. Then, among the appearance frequency distributions shown in FIG. 6, the frequency distribution showing the maximum appearance frequency (for example, the height value of the hatched frequency distribution 81 in FIG. 6) is designated as the center. A quadratic curve 83 is applied to the appearance frequency value distribution in the section (for example, section 82 shown in FIG. 6), and the relative height of the pixel is determined as the height giving the maximum appearance frequency at that time. The height image 43a can be obtained by performing the above calculation for all the pixels and determining the relative heights of all the pixels.

  In the shape measuring apparatus 1, when the piezo driving device 13 is driven and the two-beam interference objective lens 14 is repeatedly reciprocated, interference fringes appear when the focal plane passes through the measurement surface of the sample 15 for each pixel. However, in all cases that pass through the measurement surface of the sample 15, a sufficiently high degree of focus cannot be detected for each pixel. In particular, when the measurement surface of the sample 15 is a glossy surface, the S / N ratio of the image signal used for the measurement (the density of the image used for the measurement) is extremely low, which is necessary for accurately measuring the surface shape. In some cases, a sufficiently high degree of focus cannot be detected. In such a case, by using any one of the above-described measurement methods 1 to 4 in the shape measuring apparatus 1, only the effective focus degree (image signal in which the surface shape is faithfully reflected) is used for each pixel. Thus, the relative height and the surface shape can be obtained. For example, in the conventional shape measuring apparatus 500, it is difficult to accurately measure the shape of a fine cutting mark of about 10 μm as described above (see FIG. 8A), but according to the present invention. According to the shape measuring apparatus 1, it becomes possible to measure a cutting trace of about 10 μm clearly (see FIG. 8B). 8A and 8B show the results when the same field of view of the same glossy surface is measured.

  If the sample 15 is placed on the upper surface of the microscope sample stage 16 without using the inclined plate 20, the optical axis of the imaging optical system constituting the imaging unit 25 is substantially orthogonal to the measurement surface of the sample 15. There is a case. In such a case, the width and interval of the interference fringes become too large with respect to the size of the pixel, and the secondary differential value for each pixel becomes small, which is necessary for accurately measuring the surface shape. A sufficiently high degree of focus may not be detected. Therefore, as shown in Example 1 described above, the measurement is performed with the sample 15 placed on the upper surface of the inclined plate 20 and positioned obliquely with respect to the optical axis of the imaging optical system. The width and interval can be reduced, and a sufficiently high degree of focus can be detected. Therefore, it is possible to accurately measure the shape of a fine cutting mark of, for example, about 10 μm formed on the measurement surface of the sample 15.

  A schematic diagram of a shape measuring apparatus 2 according to a second embodiment to which the present invention is applied is shown in FIG. This shape measuring apparatus 2 is substantially the same in configuration as the shape measuring apparatus 1 according to the first embodiment, and the same parts as the shape measuring apparatus 1 are denoted by the same reference numerals and description thereof is omitted. However, it demonstrates centering on a different part from the shape measuring apparatus 1. FIG. The shape measuring device 2 removes the inclined plate 20 provided in the above-described shape measuring device 1, and the mask 35 shown in FIG. 7 is attached to the reference surface 33 of the two-beam interference objective lens 14 shown in FIG. It has a configuration. A plurality of through holes 35 a having a diameter of about 2 μm are formed on the entire surface of the mask 35 with a distance of about 2.5 μm from each other.

  In the shape measuring apparatus 2 configured as described above, the illumination light is reflected at the portion of the reference surface 33 where the through hole 35a is formed, but the portion of the mask 35 where the through hole 35a is not formed (in FIG. 7). In the portion (shown in black), the illumination light is not reflected. Therefore, when the illumination light reflected from the measurement surface of the sample 15 and the reference surface 33 is superimposed again by the beam splitter 31 and an interference fringe is generated, the illumination light from the reference surface 33 is formed with a through hole 35a. Since the illumination light is only from the portion, an interference fringe disappearing region (light and shade pattern) is formed in the interference fringe. By forming the interference fringe disappearing region, the S / N ratio of the image signal used for measurement can be increased.

  Then, the interference image light including the interference fringe in which such an interference fringe disappearing region is formed is imaged on the imaging surface of the high-speed camera 11 and, similarly to the shape measuring apparatus 1, the measurement method described above. By using any one of 1 to 4, the relative height of the measurement surface of the sample 15 is obtained. At this time, an interference fringe disappearing region is formed in the interference fringes, so that the image used for measurement can be shaded and sufficiently high as required to accurately measure the surface shape. The degree of focus can be detected. Therefore, it is possible to accurately measure a fine shape of, for example, about 0.1 μm or less formed on the measurement surface that has become a glossy surface. For this reason, even when the sample 15 is placed on the inclined plate 20 as in the above-described shape measuring device 1, the measurement by the shape measuring device 2, for example, part of the measurement surface constitutes the imaging unit 25. This is effective when it is substantially orthogonal to the optical axis of the imaging optical system.

  As described above, according to the shape measuring apparatus according to the present invention, the surface shape of the glossy surface can be accurately measured in a short time. Furthermore, it is possible to greatly improve the efficiency of material development and contribute to speeding up the geometrical inspection of materials.

  In the above-described embodiment, the configuration using the two-beam interference optical system is exemplified as a method for generating the interference fringes. However, the configuration is not limited to this configuration. For example, a configuration in which the interference fringes are generated using the differential interference optical system may be used. Furthermore, a configuration in which interference fringes are generated using a fringe projection method may be used.

  The present invention as described above is not limited to the above-described embodiment, and can be appropriately improved as long as it does not depart from the gist of the present invention.

It is the schematic which showed the shape measuring apparatus which concerns on this invention. It is the schematic which showed the structure of the two-beam interference objective lens. It is the block diagram which showed the structure of the shape measuring apparatus which concerns on this invention. It is a graph for demonstrating the measuring methods 1 and 2, Comprising: (a) shows the relationship between a focus degree and time, (b) has shown the relationship between height and time. It is a graph for demonstrating the measuring method 3, Comprising: The relationship between height and appearance frequency is shown. It is a graph for demonstrating the measuring method 4, Comprising: The relationship between height and appearance frequency is shown. It is the figure which showed the mask used for the shape measuring apparatus which concerns on Example 2 of this invention. It is a figure which shows the result of having measured the surface shape of a glossy surface, Comprising: When (a) is measured using the conventional shape measuring apparatus, (b) is the case where it measures using the shape measuring apparatus based on this invention. Show. It is the schematic which showed the conventional shape measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shape measuring apparatus 14 Two-beam interference objective lens (Optical system which produces unevenness of reflected light intensity)
15 Sample (object to be measured)
16 Microscope sample stage (stage)
25 Imaging unit 27 Control processor (calculation unit)
35 Mask 35a Through hole (small hole)
41 Piezo drive control device (movement control unit)

Claims (10)

An imaging unit that captures a surface image of the object to be measured placed on the stage;
A movement control unit that reciprocally moves the imaging optical system relative to the object to be measured along the optical axis of the imaging optical system of the imaging unit, and stores and outputs a movement amount;
An interference fringe generating optical system for generating interference fringes reflecting the unevenness of the surface of the object to be measured by overlapping the reflected light from the surface of the object to be measured and the reference light ;
While the imaging optical system is reciprocally moved relative to the object to be measured, the imaging unit captures the surface image including the interference fringes, and the reciprocating relative is performed for each predetermined region of the imaging surface constituting the imaging unit. The amount of movement when the maximum degree of focus is obtained in each of the movements is obtained, and the surface relative to the surface of the object to be measured is determined for each predetermined region based on the plurality of movement amounts obtained for each of the reciprocal relative movements. A shape measuring apparatus comprising: a calculating unit that calculates a surface shape of the object to be measured by calculating a height. The arithmetic unit, by Rukoto determined focus degree based on the second derivative value of the signal intensity detected by the pixels constituting the imaging surface, determine the amount of movement when the maximum degree of focus is obtained 2. The shape measuring apparatus according to claim 1 , wherein a relative height of the surface of the object to be measured is calculated for each of the pixels . The shape according to claim 1, wherein the stage can support the object to be measured such that a surface to be measured of the object to be measured is inclined with respect to an optical axis of the imaging optical system. measuring device.   The shape measuring apparatus according to claim 1, wherein a mask formed so that a plurality of small holes are regularly arranged is arranged on a reference surface of the interference fringe generating optical system. 5. The shape measuring apparatus according to claim 1 , wherein the calculation unit stores a movement amount when a maximum in-focus degree is obtained in each of the reciprocating relative movement cycles . The arithmetic unit, the shape of claimed in any one of 5, characterized in that taking the arithmetic mean of the relative height of a predetermined threshold value or more focus degree for each pixel constituting the imaging surface measuring device. The calculation unit applies a probability density function to an appearance frequency distribution of a relative height that achieves a degree of focus equal to or greater than a predetermined threshold for each pixel constituting the imaging surface, and obtains a relative height that maximizes the probability. shape measuring apparatus according to any one of claims 1 to 5, wherein.   The shape measuring apparatus according to claim 7, wherein the probability density function is a normal distribution. The calculation unit approximates the vicinity of the maximum frequency of the appearance frequency distribution of the relative height that is a focus degree equal to or greater than a predetermined threshold for each pixel constituting the imaging surface by a quadratic curve, and calculates the relative height that is the maximum frequency. shape measuring apparatus according to claim 1, any one of 5, wherein the determination. A shape measuring method performed using the shape measuring apparatus according to any one of claims 1 to 9,
While moving the imaging optical system relative to the object to be measured by the movement control unit, based on the degree of focus obtained based on a plurality of the surface images obtained by the imaging unit. When calculating the surface height of the object to be measured by calculating the relative height of the surface of the object to be measured,
The shape measurement method, wherein the imaging unit captures the surface image including the interference fringes generated by the interference fringe generation optical system and superimposed on the surface image.