JP7493960B2 - Shape measuring device and shape measuring method - Google Patents

Description

The present invention relates to a shape measuring device and a shape measuring method.

Conventionally, shape measuring devices that measure the shape of a measurement object are known. For example, Patent Document 1 discloses a shape measuring device that uses a Fizeau interferometer.

Figure 9 is a diagram showing an example of the configuration of a shape measuring device using a Fizeau-type interferometer 100. The interferometer 100 expands the irradiation range of the laser light emitted from the laser 101 to the field of view size of the interferometer using an optical system using lenses 102 and 105, irradiates the reference surface 106 and the measurement object W, and causes the reference light, which is reflected light from the reference surface 106 and the measurement object W, and the measurement light to interfere with each other. The interferometer 100 then uses the imaging lens 107 to form an image of the interference light on the image sensor surface of the camera 108 at a predetermined magnification. The shape measuring device 110 measures the relative shape of the measurement surface with respect to the reference surface by analyzing the interference fringes reflected in the image data generated by the image sensor.

JP 2007-333428 A

The feature of the interferometer 100 is that it can measure with high precision the shape of a large surface determined by the magnification or reduction optical system consisting of lenses 102 and 105, the magnification of the imaging lens 107, and the size of the image sensor of the camera 108, using the wavelength of the light source as a ruler.

The range of the measurement surface corresponding to one pixel of the imaging element (hereinafter also referred to as pixel size), which corresponds to the lateral resolution when measuring the shape, is determined by the sizes of the imaging elements of lens 102, lens 105, imaging lens 107, and camera 108. In an interferometer, as the range of the measurement surface included in the image data generated by the imaging element becomes larger (as the field of view becomes larger), the pixel size also becomes larger and the lateral resolution becomes lower, but it has the advantage of being able to measure a wide area with nanometer accuracy.

Interferometer 100 also has the disadvantage that the tolerance range for the inclination angle of the measurement surface is extremely low. This is because if there is unevenness on the measurement surface within the pixel size corresponding to one pixel of the imaging element, the amplitude of the light and dark signals of the interference fringes corresponding to the unevenness of the object surface decreases due to the integration of interference intensities with different phases.

This drawback becomes more pronounced the larger the pixel size corresponding to one pixel of the imaging element becomes. In other words, the wider the field of view of the interferometer, the larger the pixel size corresponding to one pixel of the imaging element becomes, and the narrower the allowable range of the tilt angle of the measurement surface becomes. For this reason, in an interferometer with a wide field of view, it is necessary to accurately position and adjust the measurement target within a very limited narrow angle range.

In addition, since a curved surface can be locally thought of as a two-dimensional collection of inclined planes, the narrow tolerance range for the inclination angle of the measurement surface means that only a very limited number of objects can be measured, where the deviation between the shape of the measurement object and the reference surface is extremely small. In other words, if the reference surface is a flat standard, only measurement objects with a very flat surface can be measured, and if it is a spherical standard, only measurement objects with a small difference in radius of curvature from the standard can be measured.

In other words, conventional measurement devices using interferometers receive interference intensity using a camera with a single pixel size, which means that the tolerance range for the tilt angle of the measurement surface is extremely narrow, meaning that only objects with shapes that have a small deviation from the reference surface can be measured.

Therefore, the present invention has been made in consideration of these points, and aims to provide a shape measuring device that can measure the shape of a measurement object that has a large shape deviation from a reference surface.

The shape measuring device according to the first aspect of the present invention is a shape measuring device that measures the shape of a measurement object based on the result of interference between a reference light serving as a measurement standard in an interferometer and a measurement light generated by reflection or transmission from the measurement object, and has an image acquisition unit that acquires a first captured image composed of a plurality of pixels having a pixel size of a first pixel size that indicates the range of the measurement surface of the measurement object corresponding to one pixel, and a second captured image composed of a plurality of pixels having a pixel size of a second pixel size different from the first pixel size, and a shape measuring unit that measures the shape of the measurement object based on a first pixel value of a pixel in the first captured image and a second pixel value of a pixel in the second captured image that correspond to the same position of the measurement object.

The image acquisition unit may acquire the first captured image and the second captured image generated by the imaging element by changing the magnification of an imaging lens that focuses the reference light and the measurement light on the imaging element in the interferometer.

The image acquisition unit may acquire the first captured image generated by a first imaging element provided in the interferometer, and may also acquire the second captured image generated by a second imaging element provided in the interferometer and different from the first imaging element.

The shape measurement unit may unify the coordinate system corresponding to the first captured image and the coordinate system corresponding to the second captured image into the same coordinate system by performing coordinate conversion or data complementation of at least one of the first captured image and the second captured image, and measure the shape of the measurement object based on the first pixel value of a pixel in the first captured image and the second pixel value of a pixel in the second captured image after unification.

The shape measurement unit may measure the shape and amplitude value of the interference fringes of the measurement object based on the first pixel value of a pixel in the first captured image, and measure the shape and amplitude value of the interference fringes of the measurement object based on the second pixel value of a pixel in the second captured image, select a relatively higher amplitude value from the amplitude value of the interference fringes corresponding to the first pixel value corresponding to the same position of the measurement object and the amplitude value of the interference fringes corresponding to the second pixel value, and measure the shape of the measurement object by treating the measurement results of the measurement object corresponding to the selected amplitude value at each of the multiple positions as information indicating the shape of the measurement object.

The shape measurement unit may measure the shape and amplitude value of the interference fringes of the measurement object based on the first pixel value of a pixel in the first captured image, and measure the shape and amplitude value of the interference fringes of the measurement object based on the second pixel value of a pixel in the second captured image, and measure the shape of the measurement object by combining the measurement result based on the first pixel value and the measurement result based on the second pixel value corresponding to the same position of the measurement object based on the amplitude value of the interference fringes corresponding to the first pixel value corresponding to the same position of the measurement object and the amplitude value of the interference fringes corresponding to the second pixel value.

The shape measurement unit may measure the shape of the measurement object by combining the measurement result based on the first pixel value of a pixel in the first captured image corresponding to the same position of the measurement object and the measurement result based on the second pixel value of a pixel in the second captured image such that the measurement result corresponding to a relatively large amplitude value of the interference fringes is strongly reflected.

A shape measurement method according to a second aspect of the present invention includes the steps of acquiring a first captured image composed of a plurality of pixels, each having a pixel size of a first pixel size, which indicates the range of the measurement surface of the measurement object corresponding to one pixel, and a second captured image composed of a plurality of pixels, each having a pixel size of a second pixel size different from the first pixel size, executed by a computer that measures the shape of the measurement object based on the result of interference between a reference light serving as a measurement standard in an interferometer and a measurement light generated by reflection or transmission from the measurement object, and measuring the shape of the measurement object based on a first pixel value of a pixel in the first captured image and a second pixel value of a pixel in the second captured image, which correspond to the same position of the measurement object.

The present invention has the effect of being able to measure the shape of a measurement object that has a large shape deviation from a reference surface.

FIG. 1 is a diagram showing a configuration of a measurement system according to an embodiment of the present invention. 13 is a graph showing the amplitude of the interference fringes shown in formula (4) when the wavelength of the emitted light is 633 nm and the pixel size is 20 μm. 13 is a graph showing the calculation results of the amplitude of the interference fringes shown in equation (4) when the pixel size is changed. FIG. 2 is a diagram showing a configuration of a shape measuring device. FIG. 4 is a diagram showing the height of a measurement object at each position. 11A and 11B are diagrams showing the measurement results of the object to be measured by the shape measuring unit. 10 is a flowchart showing a process flow in a shape measuring unit. FIG. 13 is a diagram showing another configuration of the shape measuring device. FIG. 1 is a diagram showing an example of the configuration of a shape measuring apparatus using a Fizeau interferometer.

[Configuration of measurement system S]
FIG. 1 is a diagram showing the configuration of a measurement system S according to this embodiment.
The measurement system S includes an interferometer 10 and a shape measuring device 20 .

The interferometer 10 is, for example, a Fizeau interferometer, and includes a light source 11, a lens 12, a pinhole 13, a beam splitter 14, a lens 15, a reference surface 16, an imaging lens 17, and a camera 18. Note that in this embodiment, the interferometer 10 is a Fizeau interferometer, but is not limited to this and may be another interferometer.

The light source 11 is, for example, a laser light source, and emits laser light as emitted light.
The lens 12 collects the light emitted from the light source 11. The collected light is incident on the pinhole 13. The light emitted from the pinhole 13 passes through a beam splitter 14 and is incident on the lens 15. The lens 15 is, for example, a collimator lens, and converts the incident light into parallel light. The parallel light is incident on a reference surface 16.

A part of the parallel light is reflected by the reference surface 16 and enters the beam splitter 14 as a reference light. Another part of the parallel light passes through the reference surface 16 and is reflected by the measurement object W. The parallel light reflected by the measurement object W passes through the lens 15 and enters the beam splitter 14 as a measurement light. The reference light and the measurement light have different optical path differences, so they interfere with each other and become interference light that generates light and dark fringes. The interference light enters the imaging lens 17 via the beam splitter 14. The interference light that enters the imaging lens 17 forms an image and enters the camera 18. The camera 18 is equipped with an image sensor and generates image data showing the interference fringes generated by the interference light. The generated image data is output to the shape measurement device 20. Here, it is assumed that the center position in the optical axis direction of the imaging lens 17 and the center position in the optical axis direction of the image sensor of the camera 18 coincide with each other.

The shape measuring device 20 measures the shape of the measurement object W based on the results of interference between the reference light, which serves as the measurement standard in the interferometer 10, and the measurement light generated by reflection or transmission from the measurement object W. The shape measuring device 20 acquires image data output from the camera 18, and measures the relative shape of the measurement surface of the measurement object W with respect to the reference surface 16 by analyzing the interference fringes reflected in the acquired image data.

In explaining the shape measuring device 20 according to this embodiment, the relationship between the tilt angle, interference fringes, and pixel size on the measurement surface of the measurement target W will be explained. The pixel size indicates the range of the measurement surface that corresponds to one pixel of the image sensor of the camera 18.

The interference fringes generated by the interference light between the measurement light and the reference light when a coherent light beam is irradiated onto the measurement surface of the measurement object W tilted at an angle θ are expressed by a one-dimensional model. The brightness of the interference fringes is generated by the optical path length difference 2h(x) between the reference surface 16 and the measurement surface of the measurement object W, and is expressed by the following formula (1). A(x) is a component corresponding to the amplitude of the interference fringes, and B(x) is a component corresponding to the bias of the interference fringes.

When the measurement surface of the measurement object W is an ideal plane and the ideal plane is inclined at an angle θ to cause interference, the height h(x) of the measurement surface in the x-direction can be expressed as a function of the angle θ including a constant D, as shown in the following equation (2).

Next, if the pixel size indicating the range of the measurement surface corresponding to one pixel of the imaging element of the camera 18 is d, the interference intensity at one pixel of the imaging element is the value obtained by integrating equation (1) with respect to d, as shown in equation (3).

Equation (3) is modified based on equations (1) and (2). For simplicity, the bias component of the interference fringes included in equation (1) and the constant term D shown in equation (2) are omitted, and only the amplitude term corresponding to the signal component in the interference measurement is calculated and expanded for equation (3). Equation (3) can be modified as shown in equation (4) below.

As shown in formula (4), the interference fringes generated by position X are amplitude modulated by a sinc function with parameters of pixel size d, tilt angle θ of the measurement surface of the measurement object W, and wavelength λ of the light emitted from the light source 11. Due to the nature of the sinc function, the amplitude of the interference fringes generated by position X becomes smaller as 2d tan(θ)/λ approaches an integer other than 0, and becomes 0 when 2d tan(θ)/λ becomes an integer other than 0. The fact that the amplitude of the interference fringes is 0 indicates that the interference fringes do not change with respect to the height difference on the measurement surface of the measurement object W, and therefore, at position X where the amplitude becomes 0, it means that the height difference on the measurement surface cannot be measured. In addition, when |2d tan(θ)/λ|>1, the interference fringes appear again, but due to the nature of the sinc function, the peak amplitude of the interference fringes becomes a smaller value than when θ=0.

Figure 2 is a graph of the amplitude of the interference fringes shown in equation (4) when the wavelength λ of the emitted light is 633 nm and the pixel size d is 20 μm. In Figure 2, the horizontal axis indicates the tilt angle θ, and the vertical axis indicates the amplitude of the interference fringes (absolute value of the sinc function). As shown in Figure 2, the amplitude of the interference fringes attenuates as the tilt angle θ increases, and becomes nearly zero when the tilt angle θ becomes 0.91°. Thereafter, the amplitude of the interference fringes increases once as the tilt angle θ increases, before attenuating again to zero. The amplitude of the interference fringes increases once, before attenuating again to zero, repeating this periodic fluctuation and converging to zero.

In equation (4), the sinc function that determines the value of the amplitude of the interference fringes has the pixel size d as a variable. Therefore, by changing the pixel size d, it is possible to change the period of increase and decrease in the amplitude of the interference fringes relative to the inclination angle θ of the measurement surface of the measurement object W. Figure 3 is a graph showing the calculation results of the amplitude of the interference fringes shown in equation (4) when the pixel size d is changed.

In FIG. 3, the amplitude of the interference fringes when the pixel size d is 20 μm is shown by a solid line, and the amplitude of the interference fringes when the pixel size d is 16 μm is shown by a dashed line. The wavelength λ of the emitted light is 633 nm, the same as in the example shown in FIG. 2.

As shown in FIG. 3, it can be seen that the period of increase and decrease in the amplitude of the interference fringes when the pixel size d is 20 μm is different from the period of increase and decrease in the amplitude of the interference fringes when the pixel size d is 16 μm. For example, when the tilt angle θ is 0.91°, the amplitude of the interference fringes is nearly 0 when the pixel size d is 20 μm, but the amplitude of the interference fringes is 0.178 when the pixel size d is 16 μm. Therefore, when two measurement results with different pixel sizes are combined, even for a tilt angle θ where the amplitude of the interference fringes is 0 in one measurement result and the height difference on the measurement surface is unmeasurable, the height difference on the measurement surface can be measured by using the other measurement result, and the tilt angle θ can be measured.

The shape measuring device 20 according to this embodiment therefore takes into account the relationship between the inclination angle, interference fringes and pixel size on the measurement surface of the measurement object W, and acquires a first captured image and a second captured image with different pixel sizes. The shape measuring device 20 then measures the shape of the measurement object W based on a first pixel value of a pixel in the first captured image and a second pixel value of a pixel in the second captured image that correspond to the same position on the measurement object W.

In this way, for a position in the first captured image where the amplitude of the interference fringes is zero and the height difference on the measurement surface is unmeasurable, the height difference on the measurement surface corresponding to that position in the second captured image can be measured. Thus, the shape measuring device 20 can measure the shape of the measurement object W having a large shape deviation from the reference surface. Furthermore, since the measurement system S has a wider allowable inclination angle when arranging the measurement surface of the measurement object W, the measurement object W can be easily arranged with lower accuracy than before, and usability can be improved compared to the conventional measurement system S. Furthermore, since the measurement system S has a wider allowable inclination angle when arranging the measurement surface of the measurement object W, the measurement system S can measure the shape even if the measurement object W has a free-form surface with local undulations.

[Configuration of shape measuring device 20]
Next, a description will be given of the configuration of the shape measuring device 20. Fig. 4 is a diagram showing the configuration of the shape measuring device 20. The shape measuring device 20 is a computer including a storage unit 21 and a control unit 22.

The storage unit 21 is, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory). The storage unit 21 stores various programs for causing the shape measurement device 20 to function. The storage unit 21 stores programs for causing the control unit 22 to function as an image acquisition unit 221 and a shape measurement unit 222.

The control unit 22 is, for example, a CPU (Central Processing Unit). The control unit 22 controls functions related to the shape measurement device 20 by executing various programs stored in the memory unit 21. The control unit 22 functions as an image acquisition unit 221 and a shape measurement unit 222 by executing the programs stored in the memory unit 21.

The image acquisition unit 221 acquires a first captured image composed of a plurality of pixels having a first pixel size, the pixel size indicating the range of the measurement surface of the measurement object W corresponding to one pixel, and a second captured image composed of a plurality of pixels having a second pixel size different from the first pixel size.

Specifically, the image acquisition unit 221 acquires the first and second captured images generated by the imaging element of the camera 18 in the interferometer 10 by changing the magnification of the imaging lens 17 that focuses the reference light and the measurement light on the imaging element.

More specifically, the image acquisition unit 221 acquires a first captured image using an imaging lens 17 with a first imaging magnification M1 in the interferometer 10. In order to analyze the phase of the interference fringes using the phase shift method, the image acquisition unit 221 acquires a plurality of first captured images while shifting the reference surface 16 in the optical axis direction by a predetermined amount. Similarly, the image acquisition unit 221 acquires a second captured image using an imaging lens 17 with a second imaging magnification M2 in the interferometer 10. The image acquisition unit 221 acquires a plurality of second captured images while shifting the reference surface 16 in the optical axis direction by a predetermined amount, in the same manner as when acquiring a plurality of first captured images.

The shape measurement unit 222 measures the shape of the measurement object W based on a first pixel value of a pixel in the first captured image and a second pixel value of a pixel in the second captured image that correspond to the same position of the measurement object W.

Specifically, first, the shape measurement unit 222 performs coordinate conversion on at least one of the first captured image and the second captured image, thereby unifying the coordinate system corresponding to the first captured image and the coordinate system corresponding to the second captured image into the same coordinate system.

For example, the center position of the first captured image and the center position of the second captured image correspond to the same position on the measurement object W. The shape measurement unit 222 calculates the magnification ratio of the imaging range of the measurement object W corresponding to the second captured image relative to the imaging range of the measurement object W corresponding to the first captured image based on the magnification ratio and focal length of the imaging lens 17 when the first captured image was acquired and the magnification ratio and focal length of the imaging lens 17 when the second captured image was acquired. Based on the calculated magnification ratio, the shape measurement unit 222 performs coordinate conversion of at least one of the first captured image and the second captured image so that the positions of the measurement object W corresponding to the same coordinates in the first captured image and the second captured image are the same.

Then, the shape measuring unit 222 measures the shape of the measurement object W based on the first pixel value of the pixel in the first captured image and the second pixel value of the pixel in the second captured image after the coordinate system has been unified. The shape measuring unit 222 measures the relative height difference of the measurement object W, which indicates the shape of the measurement object W, based on the first pixel value of the pixel in the first captured image, and measures the relative height difference of the measurement object W based on the second pixel value of the pixel in the second captured image.

First, the shape measuring unit 222 calculates the phase Φ(x, y) of the pixel at each coordinate (x, y) indicated by the first image information and the second image information by inputting the intensity information I(x, y) of the interference fringes, which is the pixel value of the pixel at each coordinate (x, y) indicated by the plurality of first image information and the plurality of second image information acquired while shifting the reference surface 16, into the following formula (5). In addition, in formula (5), j is an index value indicating whether the calculated result corresponds to the first image information or the second image information. j=1 corresponds to the first image information, and j=2 corresponds to the second image information. n indicates the number of times the reference surface 16 is shifted at one coordinate (x, y).

The shape measuring unit 222 performs a phase unwrap (connection) process on each phase Φ(x, y) of each coordinate (x, y) indicated by the first image information, calculated by equation (5), to convert the phase Φ of each coordinate (x, y) into a measurement value m ₁ (x, y) indicating a relative height difference in the measurement object W. The phase unwrap process is a process of smoothly connecting phases under the premise that the phase difference between adjacent pixels is 2π or less. Similarly, the shape measuring unit 222 performs a phase unwrap process on each phase Φ(x, y) of each coordinate (x, y) indicated by the second image information, calculated by equation (5), to convert the phase Φ of each coordinate (x, y) into a measurement value m ₂ (x, y) of the measurement object W at each coordinate (x, y).

The shape measuring unit 222 measures the amplitude value of the interference fringes based on the first pixel value of the pixel in the first captured image, and measures the amplitude value of the interference fringes based on the second pixel value of the pixel in the second captured image. For example, the shape measuring unit 222 calculates the amplitude A(x, y) of the pixel at each coordinate (x, y) indicated by the first image information and the second image information by inputting the intensity information I(x, y) of the interference fringes at each coordinate (x, y) indicated by the plurality of first image information and the plurality of second image information into the following formula (6).

The shape measurement unit 222 selects the relatively higher amplitude value from among the amplitude value of the interference fringes corresponding to the first pixel value and the amplitude value of the interference fringes corresponding to the second pixel value, both of which correspond to the same position on the measurement object W. The shape measurement unit 222 measures the shape of the measurement object W based on the measurement results of the measurement object W corresponding to the selected amplitude values at each of the multiple positions.

Below is shown an example of measurement of the measurement object W. FIG. 5 is a diagram showing the height at each position of the measurement object W. The measurement object W is assumed to be a spherical object. FIG. 6 is a diagram showing the measurement results of the measurement object W by the shape measurement unit 222. FIG. 6(a) shows the measurement results of the measurement object W based on the first image information, and FIG. 6(b) shows the measurement results of the measurement object W based on the second image information.

When the measurement target W has a spherical shape, the tilt angle increases continuously from the center toward the periphery. Therefore, for each of the first pixel size corresponding to the first image information and the second pixel size corresponding to the second image information, the amplitude of the interference fringes becomes close to 0 at a specific position on the circumference (specific tilt angle) when the sphere is viewed from above, making it impossible to measure. In the measurement results shown in FIG. 6(a), it can be confirmed that measurements are impossible at positions x1, x2, x3, x4, x5, and x6. In contrast, in the measurement results shown in FIG. 6(b), it can be confirmed that measurements are possible at positions x1 to x6 that are impossible to measure in FIG. 6(a), and that measurements are impossible at positions other than these positions.

In the example shown in Fig. 6, since the amplitude _A2 (x,y) is greater than the amplitude _A1 (x,y) in the vicinity of positions x1, x2, x3, x4, x5, and x6, the shape measurement unit 222 selects the measurement value _m2 (x,y) in the vicinity of these positions x1 to x6. In this manner, the shape measurement unit 222 can complement the positions x1, x2, x3, x4, x5, and x6 that cannot be measured in the measurement result shown in Fig. 6(a) with the measurement result shown in Fig. 6(b), so that even for a spherical measurement target W with a large shape deviation, it is possible to continuously measure up to the portion with a large tilt angle.

In the example shown in FIG. 3, the measurement results when the pixel size is 20 μm become unmeasurable at an inclination angle of about 1°. However, by using the measurement results when the pixel size is 20 μm and the measurement results when the pixel size is 16 μm, no unmeasurable locations arise even at inclination angles of 3° or more, and the shape of the measurement target W can be measured continuously.

[Processing flow]
Next, a description will be given of the flow of processing in the shape measuring unit 222. FIG.

First, the image acquisition unit 221 acquires a first captured image, which is an image captured when an imaging lens 17 having a first imaging magnification M1 is used in the interferometer 10, and also acquires a second captured image, which is an image captured when an imaging lens 17 having a second imaging magnification M2 is used (S1, S2).
Next, the shape measuring section 222 unifies the coordinate system corresponding to the first captured image and the coordinate system corresponding to the second captured image into the same coordinate system (S3).

Next, the shape measurement unit 222 calculates a measurement value m ₁ (x, y) indicating the relative elevation difference of the measured object W at each coordinate (x, y) based on the first pixel value of the pixel in the first captured image, and calculates a measurement value m ₂ (x, y) based on the second pixel value of the pixel in the second captured image (S4).

Next, the shape measuring unit 222 measures the amplitude A ₁ (x, y) of the interference fringes at each coordinate (x, y) based on the first pixel value of the pixel in the first captured image, and measures the amplitude A ₂ (x, y) of the interference fringes at each coordinate (x, y) based on the second pixel value of the pixel in the second captured image (S5). Note that the processes of S4 and S5 do not have to be performed in the order shown in FIG. 7, and S4 may be performed after S5.

Next, the shape measurement unit 222 selects either the measurement value m1(x,y) or the measurement value _m2 (x,y) based on the amplitude _A1 (x,y) of the interference fringes corresponding to the first pixel value and the amplitude _A2 (x,y) of the interference fringes corresponding to the _second pixel value at each coordinate (x,y) corresponding to the same position on the measurement object W (S6). This completes the measurement of the shape of the measurement object W.

[Modification 1]
In the above description, the shape measuring unit 222 measures the shape of the measurement object W by selecting a measurement result with a relatively large corresponding amplitude value from among the measurement results corresponding to the same position, but this is not limited to this. The shape measuring unit 222 may measure the shape of the measurement object W by combining a measurement result based on the first pixel value and a measurement result based on the second pixel value, which correspond to the same position of the measurement object W, based on an amplitude value of interference fringes corresponding to a first pixel value and an amplitude value of interference fringes corresponding to a second pixel value, which correspond to the same position of the measurement object W.

In this case, the shape measurement unit 222 calculates a composite value m synth (x, y) by combining the measurement value m ₁ (x, y), which is a measurement result based on the first pixel value of a pixel in the first captured image corresponding to the same position of the measurement object W, and the measurement value m ₂ (x, y), which is a measurement result based on the second _pixel value of a _pixel in the second captured image, so that the measurement value corresponding to the relatively large amplitude value of _the interference fringes is strongly reflected.

Specifically, the shape measuring unit 222 calculates a weighted average of the measurement values m ₁ (x, y) and m ₂ (x, y) based on the amplitudes A ₁ (x, y) and A ₂ (x, y) to calculate a composite value m _synth (x, y) as shown in the following formula (7). In this way, the shape measuring unit 222 can accurately measure the shape of the measurement target W based on the two measurement results.

[Modification 2]
In addition, after performing phase unwrapping processing, the shape measuring unit 222 measures the shape of the measurement object W by selecting, from among heights corresponding to the same position, a height whose corresponding amplitude value is relatively large, but this is not limited to this.

As described above, phase unwrapping is a process that smoothly connects phases between adjacent pixels under the assumption that the phase difference is 2π or less. For example, as shown in FIG. 6(a), if there is an unmeasurable area between area a1 and area a2, and shape continuity cannot be ensured in that area at a phase of 2π (λ/2) or less, it becomes difficult to determine the relationship in height between areas a1 and a2 and connect the phase.

Therefore, the shape measurement unit 222 may calculate the measurement value m 1 (x, y), the measurement value m ₂ (x, y), the amplitude A 1 (x, y), and the amplitude A ₂ (x, y) while performing phase unwrapping processing for each of the first pixel value corresponding to the pixel of the first captured image and the _second pixel value corresponding to the pixel of the _second captured image in order from a reference position (for example, the center position of the captured image). Then, at a position where one of the measurement values m ₁ (x, y) and the measurement value m ₂ (x, y) becomes unmeasurable, the shape measurement unit 222 may complement the measurement value at the unmeasurable position by using the measurement value at the other position. In this way, even if the continuity of the shape at a phase of 2π or less cannot be ensured in one unmeasurable region, the measurement result of the other can be used to complement and measure the shape of the measurement target W.

[Modification 3]
Further, the image acquisition unit 221 acquires the first captured image and the second captured image generated by the imaging element of the camera 18, but the present invention is not limited thereto, and the first captured image and the second captured image generated by the imaging elements of the two cameras may be acquired. Fig. 8 is a diagram showing another configuration example of the measurement system S according to the present embodiment. In the measurement system S shown in Fig. 8, the interferometer 10 includes a first imaging lens 17A and a second imaging lens 17B instead of the imaging lens 17 shown in Fig. 1, a first camera 18A and a second camera 18B instead of the camera 18, and a beam splitter 19. The magnifications of the first imaging lens 17A and the second imaging lens 17B are different from each other.

The beam splitter 19 causes a portion of the reference light and measurement light incident via the beam splitter 14 to be incident on the first imaging lens 17A, and causes another portion of the reference light and measurement light to be incident on the second imaging lens 17B. The reference light and measurement light that have passed through the first imaging lens 17A are incident on the first camera 18A, and the reference light and measurement light that have passed through the second imaging lens 17B are incident on the second camera 18B. The first camera 18A has a first imaging element with a first resolution, and the second camera 18B has a second imaging element with a second resolution that is, for example, the same as the first resolution. The first imaging element generates a first captured image and outputs it to the shape measurement device 20. The second imaging element generates a second captured image and outputs it to the shape measurement device 20.

The image acquisition unit 221 acquires a first captured image generated by a first imaging element of a first camera 18A provided in the interferometer 10, and acquires a second captured image generated by a second imaging element of a second camera 18B provided in the interferometer 10. In this way, the shape measurement device 20 can acquire two captured images with different pixel sizes at once.

[Modification 4]
In addition, the shape measuring unit 222 unifies the coordinate system corresponding to the first captured image and the coordinate system corresponding to the second captured image into the same coordinate system by performing coordinate conversion, but this is not limited to this. The shape measuring unit 222 may unify the coordinate system corresponding to the first captured image and the coordinate system corresponding to the second captured image into the same coordinate system by performing data complementation of at least one of the first captured image and the second captured image. In this case, for example, the shape measuring unit 222 enlarges or reduces at least one of the first captured image and the second captured image based on the calculated magnification ratio so that the positions of the measurement target W corresponding to the same coordinates in the first captured image and the second captured image are the same.

In addition, the shape measurement unit 222 calculates the magnification ratio of the imaging range of the measurement object W corresponding to the second captured image relative to the imaging range of the measurement object W corresponding to the first captured image, but this is not limited to this. Information indicating the magnification ratio may be stored in advance in the storage unit 21, and the shape measurement unit 222 may determine the magnification ratio by referring to the information.

[Effects of this embodiment]
As described above, the shape measuring device 20 according to this embodiment acquires a first captured image composed of a plurality of pixels having a first pixel size, each pixel size indicating the range of the measurement surface of the measurement object W corresponding to one pixel, and a second captured image composed of a plurality of pixels having a second pixel size different from the first pixel size, and measures the shape of the measurement object W based on a first pixel value of a pixel in the first captured image and a second pixel value of a pixel in the second captured image corresponding to the same position of the measurement object W. In this way, the shape measuring device 20 can measure the shape of the measurement object W having a large shape deviation from the reference surface 16.

Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination also has the effect of the original embodiment.

REFERENCE SIGNS LIST 10 Interferometer 11 Light source 12 Lens 13 Pinhole 14 Beam splitter 15 Lens 16 Reference surface 17 Imaging lens 18 Camera 19 Beam splitter 20 Shape measuring device 21 Memory unit 22 Control unit 221 Image acquisition unit 222 Shape measuring unit S Measurement system

Claims (10)

A shape measuring apparatus for measuring a shape of a measurement object based on a result of interference between a reference light serving as a measurement reference in an interferometer and a measurement light generated by reflection or transmission from the measurement object, comprising:
an image acquisition unit that acquires a first captured image configured with a plurality of pixels, each of which has a first pixel size indicating a range of a measurement surface of the measurement object corresponding to one pixel, and a second captured image configured with a plurality of pixels, each of which has a second pixel size different from the first pixel size;
a shape measuring unit that measures a shape of the measurement object and a first amplitude value as an amplitude value of interference fringes at each of a plurality of positions based on a first pixel value that is a pixel value of a pixel in the first captured image , and measures a second amplitude value of the shape of the measurement object and an amplitude value of interference fringes at each of the plurality of positions based on a second pixel value that is a pixel value of a pixel in the second captured image, selects a relatively higher amplitude value from the first amplitude value and the second amplitude value at each of the plurality of positions, and measures the measurement result of the measurement object corresponding to the selected amplitude value at each of the plurality of positions as information indicating the shape of the measurement object, thereby measuring the shape of the measurement object;
A shape measuring device having a A shape measuring apparatus for measuring a shape of a measurement object based on a result of interference between a reference light serving as a measurement reference in an interferometer and a measurement light generated by reflection or transmission from the measurement object, comprising:
an image acquisition unit that acquires a first captured image configured with a plurality of pixels having a first pixel size, the pixel size indicating a range of a measurement surface of the measurement object corresponding to one pixel, and a second captured image configured with a plurality of pixels having a second pixel size different from the first pixel size;
a shape measuring unit that measures a first amplitude value that is an amplitude value of interference fringes of the measurement object at each of a plurality of positions based on a first pixel value that is a pixel value of a pixel in the first captured image, measures a first measurement value that indicates a shape of the measurement object based on the first amplitude value, measures a second amplitude value that is an amplitude value of interference fringes of the measurement object at each of the plurality of positions based on a second pixel value that is a pixel value of a pixel in the second captured image, measures a second measurement value that indicates the shape of the measurement object based on the second amplitude value, and replaces, among the first measurement values corresponding to each of the plurality of positions, the first measurement value corresponding to a position where the first amplitude value could not be measured with the second measurement value corresponding to that position, or replaces, among the first measurement values corresponding to each of the plurality of positions, the first measurement value corresponding to a position where the first amplitude value corresponding to the first measurement value is smaller than the second amplitude value with the second measurement value, and measures the measurement values corresponding to each of the plurality of positions after replacement as information indicating the shape of the measurement object;
A shape measuring device having a A shape measuring apparatus for measuring a shape of a measurement object based on a result of interference between a reference light serving as a measurement reference in an interferometer and a measurement light generated by reflection or transmission from the measurement object, comprising:
an image acquisition unit that acquires a first captured image configured with a plurality of pixels having a first pixel size, the pixel size of which indicates a range of a measurement surface of the measurement object corresponding to one pixel, and a second captured image configured with a plurality of pixels having a second pixel size different from the first pixel size;
a shape measuring unit that measures a first amplitude value as an amplitude value of a shape and interference fringes of the measurement object at each of a plurality of positions based on a first pixel value that is a pixel value of a pixel in the first captured image, and measures a second amplitude value as an amplitude value of the shape and interference fringes of the measurement object at each of the plurality of positions based on a second pixel value that is a pixel value of a pixel in the second captured image, and measures a shape of the measurement object by combining a measurement result based on the first pixel value and a measurement result based on the second pixel value that correspond to the same position of the measurement object based on the first amplitude value and the second amplitude value at each of the plurality of positions;
A shape measuring device having a the shape measuring unit measures the shape of the measurement object by combining a measurement result based on the first pixel value and a measurement result based on the second pixel value of a pixel in the first captured image corresponding to the same position of the measurement object such that a measurement result corresponding to a relatively large amplitude value of the interference fringes is strongly reflected out of the measurement result based on the first pixel value of a pixel in the first captured image and the measurement result based on the second pixel value of a pixel in the second captured image corresponding to the same position of the measurement object.
The shape measuring apparatus according to claim 3 . the image acquisition unit acquires the first captured image and the second captured image generated by the imaging element by changing a magnification of an imaging lens that images the reference light and the measurement light on the imaging element in the interferometer.
The shape measuring apparatus according to any one of claims 1 to 4 . the image acquisition unit acquires the first captured image generated by a first imaging element provided in the interferometer, and acquires the second captured image generated by a second imaging element provided in the interferometer and different from the first imaging element;
The shape measuring apparatus according to any one of claims 1 to 4 . the shape measuring unit unifies a coordinate system corresponding to the first captured image and a coordinate system corresponding to the second captured image into an identical coordinate system by performing coordinate conversion or data complementation on at least one of the first captured image and the second captured image, and measures the shape of the measurement object based on the first pixel value of a pixel in the first captured image and the second pixel value of a pixel in the second captured image after unification.
The shape measuring apparatus according to any one of claims 1 to 6 . A computer executes a process for measuring the shape of a measurement object based on the interference result between a reference light serving as a measurement reference in an interferometer and a measurement light generated by reflection or transmission from the measurement object.
acquiring a first captured image including a plurality of pixels having a first pixel size, the first pixel size indicating a range of a measurement surface of the measurement object corresponding to one pixel, and a second captured image including a plurality of pixels having a second pixel size different from the first pixel size;
a step of measuring a shape of the measurement object and a first amplitude value as an amplitude value of interference fringes at each of a plurality of positions based on a first pixel value which is a pixel value of a pixel in the first captured image, and measuring a second amplitude value of the shape of the measurement object and an amplitude value of interference fringes at each of the plurality of positions based on a second pixel value which is a pixel value of a pixel in the second captured image, selecting a relatively higher amplitude value from the first amplitude value and the second amplitude value at each of the plurality of positions, and using the measurement result of the measurement object corresponding to the selected amplitude value at each of the plurality of positions as information indicating the shape of the measurement object, thereby measuring the shape of the measurement object;
A shape measurement method comprising the steps of: A computer executes a process for measuring the shape of a measurement object based on the result of interference between a reference light serving as a measurement reference in an interferometer and a measurement light generated by reflection or transmission from the measurement object.
acquiring a first captured image including a plurality of pixels having a first pixel size, the first pixel size indicating a range of a measurement surface of the measurement object corresponding to one pixel, and a second captured image including a plurality of pixels having a second pixel size different from the first pixel size;
a step of measuring a first amplitude value which is an amplitude value of interference fringes of the measurement object at each of a plurality of positions based on a first pixel value which is a pixel value of a pixel in the first captured image, measuring a first measurement value indicative of a shape of the measurement object based on the first amplitude value, measuring a second amplitude value which is an amplitude value of interference fringes of the measurement object at each of the plurality of positions based on a second pixel value which is a pixel value of a pixel in the second captured image, measuring a second measurement value indicative of the shape of the measurement object based on the second amplitude value, replacing, among the first measurement values corresponding to each of the plurality of positions, the first measurement value corresponding to a position where the first amplitude value could not be measured with the second measurement value corresponding to that position, or replacing, among the first measurement values corresponding to each of the plurality of positions, the first measurement value corresponding to a position where the first amplitude value corresponding to the first measurement value is smaller than the second amplitude value with the second measurement value, and using the measurement values corresponding to each of the plurality of positions after the replacement as information indicative of the shape of the measurement object, thereby measuring the shape of the measurement object;
A shape measurement method comprising the steps of: A computer executes a process for measuring the shape of a measurement object based on the result of interference between a reference light serving as a measurement reference in an interferometer and a measurement light generated by reflection or transmission from the measurement object.
acquiring a first captured image including a plurality of pixels having a first pixel size, the first pixel size indicating a range of a measurement surface of the measurement object corresponding to one pixel, and a second captured image including a plurality of pixels having a second pixel size different from the first pixel size;
measuring a first amplitude value as an amplitude value of a shape and interference fringes of the object at each of a plurality of positions based on a first pixel value which is a pixel value of a pixel in the first captured image, and measuring a second amplitude value as an amplitude value of the shape and interference fringes of the object at each of the plurality of positions based on a second pixel value which is a pixel value of a pixel in the second captured image, and measuring a shape of the object by combining a measurement result based on the first pixel value and a measurement result based on the second pixel value which correspond to the same position of the object at each of the plurality of positions based on the first amplitude value and the second amplitude value;
A shape measurement method comprising the steps of:

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