JP2021167786A - Flatness measuring device and method - Google Patents

Abstract

To reduce measurement time compared to conventional methods.SOLUTION: A flatness measuring device for measuring the flatness of a sample surface of a measurement sample includes: a grazing incidence interferometer that includes an optical member having a reference plane and forming an optical interferometer between the reference plane and the sample surface of the measurement sample, and a light source irradiating coherent light at an angle to the reference plane; a tilting member that tilts the sample surface in one direction relative to the reference plane; and a flatness calculation unit that calculates the flatness of the sample surface on the basis of interference fringes formed by the grazing incidence interferometer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a technique for measuring the flatness of a sample surface in a measurement sample using interference fringes.

When precisely measuring the flatness of the sample surface in the measurement sample, the sample surface is irradiated with interfering light such as laser light through the reference plane, and the reflected light of the sample surface and the reflected light of the reference plane cause optical interference. A method of generating interference fringes and measuring flatness is widely used. When the sample surface is a rough surface, for example, the oblique incident interferometer described in Patent Documents 1 and 2 is applied in order to improve the intensity of the reflected light from the measurement sample. Further, in the method using the oblique incident interferometer, since the light is obliquely irradiated to the measurement sample at the incident angle θ, the equivalent wavelength is λ / cos θ. Therefore, the sample surface is increased or decreased by increasing or decreasing the incident angle θ. The sensitivity of the interference fringes to the unevenness of the sample can be adjusted, and the dynamic range of measurement can be expanded.

Japanese Unexamined Patent Publication No. 2006-23263 Japanese Unexamined Patent Publication No. 2000-18912

Although not limited to the techniques described in Patent Documents 1 and 2, in the method using an optical interferometer, interference fringes composed of a bright region and a dark region are generated due to the unevenness of the sample surface. The approximate flatness of the sample surface can be evaluated by the interval between the bright regions (or dark regions) of the interference fringes. However, in order to quantify the flatness, the phase shift method described in Patent Document 1 is applied. In this phase shift method, it is necessary to acquire a plurality of images of interference fringes by changing the distance between the prism having the reference plane and the sample surface. Therefore, an increase in measurement time due to mechanical scanning such as prism movement becomes a problem.

The present invention has been made in view of the above problems, and provides a flatness measuring device and a method capable of shortening the measurement time as compared with the conventional case by obtaining flatness without moving the reference plane. The purpose is to do.

The flatness measuring device according to the first aspect of the present invention is
An optical member having a reference plane and forming an optical coherometer between the reference plane and the sample surface of the measurement sample, and an oblique incident interferometer provided with a light source unit that obliquely irradiates the reference plane with coherent light.
An inclined member that inclines the sample surface in one direction with respect to the reference plane,
It is provided with a flatness calculation unit for obtaining the flatness of the sample surface based on the interference fringes formed by the oblique incident interferometer.

The flatness measuring method according to the second aspect of the present invention is
Using an optical member having a reference plane and forming an optical coherometer between the reference plane and the sample surface of the measurement sample, and an oblique incident interferometer provided with a light source unit that obliquely irradiates the reference plane with coherent light. A flatness measuring method for determining the flatness of the sample surface.
A tilting step that tilts the sample surface in one direction with respect to the reference plane.
It includes a flatness calculation step for obtaining the flatness of the sample surface based on the interference fringes formed by the oblique incident interferometer.

According to the first aspect or the second aspect, since the sample surface is inclined in one direction with respect to the reference plane, it is possible to generate interference fringes in which the light and dark patterns are arranged in one direction. Compared to the interference fringes that occur when the sample surface is completely flat, when the sample surface has irregularities, the interference fringes change at the place where the irregularities exist. Therefore, the flatness of the sample surface is obtained based on the interference fringes. As described above, since the flatness of the sample surface is required without changing the distance between the reference plane and the sample surface by moving the reference plane, the measurement time can be shortened as compared with the conventional case.

In the first aspect, for example,
The tilting member may tilt the sample surface in one direction with respect to the reference plane so as to meet the spatial resolution required for the flatness.

In the second aspect, for example,
The tilting step may tilt the sample surface in one direction with respect to the reference plane so as to meet the spatial resolution required for the flatness.

In these embodiments, the spatial resolution of flatness depends on the spacing of the bright (or dark) regions of the interference fringes. On the other hand, the spacing between the bright (or dark) regions of the interference fringes depends on the angle of inclination of the sample plane with respect to the reference plane. Therefore, according to these aspects, the sample surface is inclined in one direction with respect to the reference plane so as to meet the spatial resolution required for flatness, so that the spatial resolution required for flatness can be satisfied. can.

In the first aspect, for example,
The flatness calculation unit obtains a spatial frequency spectrum from the interference fringes formed by the oblique incident interferometer, and obtains the phase of the interference fringes from a predetermined frequency range including the frequency component of the interference fringes in the spatial frequency spectrum. The flatness may be obtained from the obtained and the phase of the obtained interference fringes.

In the second aspect, for example,
In the flatness calculation step, the spatial frequency spectrum is obtained from the interference fringes formed by the oblique incident interferometer, and the phase of the interference fringes is obtained from a predetermined frequency range including the frequency component of the interference fringes in the spatial frequency spectrum. The flatness may be obtained from the obtained and the phase of the obtained interference fringes.

According to these aspects, since the phase of the interference fringes is obtained from a predetermined frequency range including the frequency component of the interference fringes in the spatial frequency spectrum, the phase calculation time can be further reduced.

According to the present invention, by obtaining the flatness without moving the reference plane, it is possible to shorten the measurement time as compared with the conventional case.

It is a block diagram which shows schematic structure of the flatness measuring apparatus in this embodiment. It is a figure which shows schematic structure of the oblique incident interferometer and the image pickup part. It is a figure which shows the image of the interference fringes imaged by the image pickup unit. It is a figure which shows the result of the Fourier transform schematicly. It is a figure which shows the result of the Fourier transform schematicly. It is a figure which shows the calculation result of a phase roughly. It is a flowchart which shows schematic operation procedure of the flatness measuring apparatus.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same reference numerals are used for the same components, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a block diagram schematically showing the configuration of a flatness measuring device 100 that executes the flatness measuring method in the present embodiment. FIG. 2 is a diagram schematically showing the configurations of the oblique incident interferometer 10 and the imaging unit 110.

As shown in FIG. 2, the oblique incident interferometer 10 includes a light source unit 105, first, second, and third optical systems L1, L2, L3, a mirror M1, an optical member P, and an inclined member 15. A measurement sample 20 having a sample surface 20S is placed on the inclined member 15. The measurement sample 20 is, for example, a donut-shaped disk in a plan view having a diameter of 120 mm.

The optical member P is an optical element having a reference plane and forming an optical interference meter between the reference plane and the sample surface 20S of the measurement sample 20. In the present embodiment, the optical member P is, for example, a triangular prism having an isosceles right triangle in cross section, more specifically, an isosceles right triangle in cross section, and its bottom surface is a reference plane 20P. One side surface connected to one side of the reference plane 20P is an incident surface 21P to which the coherent light emitted from the light source unit 105 is incident, and the other side surface connected to the other side of the reference plane 20P is an optical coherometer. The injection surface 22P emits the interference light generated by the interference of the coherent light.

The light source unit 105 is a device connected to the control circuit 130 (FIG. 1) and emits a laser beam having a predetermined wavelength as coherent light according to the control of the control circuit 130. The light source unit 105 includes, for example, a He-Ne laser device that emits a laser beam having a wavelength of 632.8 nm.

The imaging unit 110 is connected to the control circuit 130 (FIG. 1), and according to the control of the control circuit 130, interference fringes (interference) generated by an optical interferometer formed by the reference plane 20P and the sample surface 20S of the measurement sample 20. It is a device that captures an image of light). The image pickup unit 110 includes, for example, a digital camera having an image pickup element of a CCD type or CMOS type two-dimensional image sensor. The image (image data) of the interference fringes is output from the imaging unit 110 to the control circuit 130.

The tilting member 15 is a member that tilts the sample surface 20S of the measurement sample 20 in one direction DR with respect to the reference plane 20P of the optical member P. In the present embodiment, the inclined member 15 is, for example, a columnar member, and includes a mounting surface 15U on which the measurement sample 20 is placed and a lower surface 15D facing the mounting surface 15U. When the inclined member 15 is arranged so that the lower surface 15D is a horizontal plane parallel to the horizontal direction, the mounting surface 15U is formed so as to be inclined with respect to the lower surface 15D at an inclination angle θ in one direction DR. , The optical member so that the reference plane 20P of the optical member P is separated from the sample surface 20S of the measurement sample 20 and parallel to the lower surface 15D when the flat plate-shaped measurement sample 20 is placed on the mounting surface 15U. P is supported by a support member (not shown). Therefore, when the measurement sample 20 is placed on the mounting surface 15U, the tilting member 15 tilts the sample surface 20S in a unidirectional DR with respect to the reference plane 20P at an tilt angle θ. That is, the distance between the sample surface 20S and the reference plane 20P gradually increases from one end to the other end in the horizontal direction.

The phase at that position is calculated from the interval between the bright regions (or dark regions) of the interference fringes. Therefore, the spatial resolution depends on the interval between the bright regions (or dark regions) of the interference fringes, that is, the inclination angle θ. As described above, in the present embodiment, the inclination angle θ of the mounting surface 15U of the inclination member 15 is determined according to the spatial resolution required for the flatness measurement.

In these optical members P, the light source unit 105, and the image pickup unit 110, the light source unit 105 is the optical member P so that the interfering light emitted from the light source unit 105 is obliquely incident on the reference plane 20P at a predetermined incident angle. The imaging unit 110 is arranged so as to be in the specular reflection direction of the interfering light incident on the reference plane 20P.

Then, in the present embodiment, in order to reduce the size of the apparatus, a mirror M1 that bends the optical path is arranged in the optical path between the light source unit 105 and the optical member P, and an irradiation region (irradiation area) of interfering light is provided. In order to expand, the first optical system L1 is arranged in the optical path between the light source unit 105 and the mirror M1, and the second optical system L2 is arranged in the optical path between the mirror M1 and the optical member P. There is. The first optical system L1, the mirror M1, and the second optical system L2 constitute an illumination optical system that irradiates the reference plane 20P with coherent light emitted from the light source unit 105.

On the other hand, the third optical as a light receiving optical system that guides the interference light of the coherent light emitted from the ejection surface 22P of the optical member P to the imaging unit 110 in the optical path between the optical member P and the imaging unit 110. The system L3 is arranged so that its optical axis coincides with the optical axis of the imaging unit 110. The third optical system L3 is configured to include one or more lenses.

The first optical system L1 is an optical element that collects incident light, and includes one or a plurality of lenses. The mirror M1 is preferably a total reflection mirror, and is arranged at a position away from the first optical system L1 and the focal length of the first optical system L1. The second optical system L2 is an optical element that parallelizes incident light, and includes one or a plurality of lenses. The light source unit 105, the first optical system L1 and the second optical system L2 are arranged so that their optical axes coincide with each other.

The interfering light emitted from the light source unit 105 is incident on the first optical system L1, collected by the first optical system L1 at the focal distance, spreads, is incident on the mirror M1, and is reflected by the mirror M1. As a result, the optical path is bent toward the second optical system L2, is incident on the second optical system L2, becomes parallel light in the second optical system L2, and is incident on the optical member P via the incident surface 21P. The coherent light incident on the optical member P is obliquely incident on the reference plane 20P, a part of the light is reflected on the reference plane 20P, and the rest thereof is transmitted through the reference plane 20P and reflected on the sample surface 20S. The coherent light reflected on the reference plane 20P and the coherent light reflected on the sample surface 20S interfere with each other, and this coherent light is emitted from the optical member P via the ejection surface 22P, and is emitted from the optical member P via the ejection surface 22P. As an interference fringe image, the light is incident on the imaging unit 110.

In this example, the interference fringes are imaged by the imaging unit 110 by the third optical system L3. However, a screen is arranged after the ejection surface 22P, and the interference fringes obtained by the screen are imaged. It may be. In this case, there is an advantage that the aperture of the third optical system L3 can be made smaller than the size of the interference fringe image.

As shown in FIG. 1, the flatness measuring device 100 includes an oblique interferometer 10, an imaging unit 110, a display 115, an input unit 120, and a control circuit 130. The oblique incident interferometer 10 includes a light source unit 105. The control circuit 130 includes a memory 140, a central processing unit (CPU) 150, and peripheral circuits (not shown). The flatness measuring device 100 shown in FIG. 1 is provided, for example, in an inspection process of a factory that produces a measurement sample 20.

The memory 140 is composed of, for example, a semiconductor memory or the like. The memory 140 includes, for example, a read-only memory (ROM), a random access memory (RAM), an electrically erasable and rewritable ROM (EEPROM), and the like. The CPU 150 functions as the measurement control unit 151 and the flatness calculation unit 152 by operating according to the control program of the present embodiment stored in the memory 140, for example, the ROM. The flatness calculation unit 152 includes a Fourier transform calculation unit 161 and an inverse Fourier transform calculation unit 162.

The measurement control unit 151 controls the light source unit 105 to emit coherent light from the light source unit 105 to generate interference fringes. The measurement control unit 151 controls the imaging unit 110 to image the interference fringes and acquire the image data of the interference fringes. The flatness calculation unit 152 calculates the flatness of the sample surface 20S of the measurement sample 20 based on the image data of the interference fringes. Each function of the Fourier transform calculation unit 161 and the inverse Fourier transform calculation unit 162 will be described later.

The display 115 includes, for example, a liquid crystal display panel. The display 115 is controlled by the CPU 150 to display, for example, the flatness of the sample surface 20S.

The input unit 120 includes, for example, a mouse or a keyboard. When operated by the user, the input unit 120 outputs an operation signal indicating the operation content to the control circuit 130. When the display 115 is a touch panel display, the touch panel display may also serve as the input unit 120 instead of the mouse or keyboard.

FIG. 3 is a diagram showing an image of interference fringes captured by the imaging unit. 4 and 5 are diagrams schematically showing the results of the Fourier transform. FIG. 6 is a diagram schematically showing the calculation result of the phase. FIG. 7 is a flowchart schematically showing an operating procedure of the flatness measuring device. The operation of the flatness measuring device 100 will be described with reference to FIGS. 1 to 6 according to the flowchart of FIG. 7. For example, the operation of FIG. 7 is repeatedly executed in accordance with the transport timing of the measurement sample 20 that has been transported to the inspection process along the transport path of the factory.

In step S1000 of FIG. 7 (corresponding to an example of the tilt step), for example, the measurement sample 20 is placed on the mounting surface 15U of the tilt member 15, and the sample surface 20S of the measurement sample 20 is referred to the reference plane 20P of the optical member P. It is tilted at an inclination angle θ. For example, the measurement sample 20 may be placed on the mounting surface 15U of the tilting member 15 so that the operator or the robot arm does not come into contact with the optical member P.

In step S1005, the measurement control unit 151 controls the light source unit 105 to emit coherent light to generate interference fringes, and further controls the image pickup unit 110 to cause the image pickup unit 110 to image the entire sample surface 20S. And acquire the image of the interference fringes. The reflected light on the reference plane 20P of the optical member P and the reflected light on the sample surface 20S of the measurement sample 20 interfere with each other, and interference fringes corresponding to the difference in optical path lengths are generated. Further, as described above, the sample surface 20S of the measurement sample 20 is inclined with respect to the reference plane 20P of the optical member P in a unidirectional DR at an inclination angle θ. Therefore, as shown in FIG. 3, the imaging unit 110 acquires the interference fringe image 30 of the interference fringes in which the light and dark patterns are arranged in the one-way DR. The interference fringe image 30 is configured by alternately repeating linear bright regions 30a and linear dark regions 30b arranged in the one-way DR.

Compared to the interference fringes that occur when the sample surface 20S is completely flat, when the sample surface 20S has irregularities, the interference fringes shift at the place where the irregularities exist (interference fringes that occur when the sample surface 20S is completely flat). Let Pt be the position of the bright region (or dark region) of the interference fringe, and Pr be the position of the bright region (or dark region) of the interference fringes in the place where the unevenness exists, which corresponds to the bright region (or dark region). , Pt ≠ Pr, and the position of the bright region (or dark region) changes). By calculating the phase of the interference fringes representing the deviation of the interference fringes, the unevenness of the sample surface 20S, that is, the flatness can be measured.

In the present embodiment, the spatial resolution of the sample surface 20S in the flatness measurement is set to about 4 mm. Therefore, the inclination angle θ of the mounting surface 15U of the inclination member 15 is set so that the interval between the bright regions (or dark regions) of the interference fringes is about 4 mm. Since the diameter of the measurement sample 20 is 120 mm, the number of bright regions (or dark regions) of the interference fringes is about 30 on the entire surface of the sample surface 20S.

Expressed in one dimension for simplicity, the light intensity I (X) of the interference fringes is generally,
I (X)
= B (X) + Acos (KX + φ (X))
= B (X) + (A / 2) e ^{j (KX + φ (X))} + (A / 2) e ^{−j (KX + φ (X))} (Equation 1)
It is represented by. In the above (Equation 1), the coefficients A and B depend on the transmittance of the first, second and third optical systems L1, L2 and L3, the reflectance of the sample surface 20S and the like. The phase φ represents the flatness of the sample surface 20S. The coefficient K is the wave number of the interference fringes. The coefficient K can be increased by making the interference fringes denser (that is, improving the spatial resolution of the interference fringes).

Returning to FIG. 7, in step S1010, the Fourier transform calculation unit 161 Fourier transforms the entire interference fringe image 30 based on the pixel values for each coordinate (X, Y) of the interference fringe image 30. By Fourier transform, the three terms on the right side of the above (Equation 1) can be separated. FIG. 4 schematically shows the result of the Fourier transform when expressed in one dimension for the sake of simplicity. In FIG. 4, the horizontal axis represents the spatial frequency and the vertical axis represents the power spectrum. FIG. 5 schematically shows the result of the Fourier transform when expressed in two dimensions. In FIGS. 4 and 5, the peak value P1 corresponds to the first term on the right side of the above (Equation 1) and is a DC component. Further, the peak values P2 and P3 at both ends of the peak value P1 correspond to the second and third terms on the right side of the above (Equation 1), respectively, and include the frequency component and the phase component of the interference fringes. As can be seen from the above (Equation 1), since the peak values P2 and P3 including the phase φ are conjugated, only one of the data needs to be used.

Returning to FIG. 7, in step S1015, the inverse Fourier transform calculation unit 162 extracts a spectrum in a predetermined frequency range including the peak value at one end. In the example of FIG. 4, the inverse Fourier transform calculation unit 162 extracts the spectrum of the frequency range D3 including the peak value P3 at the right end, which is three times the half width D. The frequency range D3 in FIG. 4 corresponds to the frequency range RD3 in FIG.

Returning to FIG. 7, in step S1020, the inverse Fourier transform calculation unit 162 performs inverse Fourier transform on the spectrum extracted in step S1015 with the frequency shifted by K. by this,
Ift (X) = (A / 2) e ^{jφ (X)} (Equation 2)
^{Is obtained, and the phase φ = tan -1} (I / R) can be obtained from the real part (R) and the imaginary part (I).

In step S1025, the flatness calculation unit 152 eliminates the term (KX) from the above (Equation 2) to obtain the phase φ. In the above (Equation 1) and (Equation 2), as described above, they are expressed in one dimension for simplicity, but in reality, the flatness calculation unit 152 is as shown in FIG. , The phase φ is obtained for each coordinate (X, Y). In FIG. 6, the phase change is shown in grayscale from white to black.

Returning to FIG. 7, in step S1030, the flatness calculation unit 152 refers to each coordinate (X, Y) using the phase φ calculated in step S1025, the inclination angle θ, and the wavelength λ of the light source unit 105. The height ΔZ of the sample surface 20S from the plane 20P,
ΔZ = (λ / cosθ) φ / 4π (Equation 3)
Calculated by. Since the phase φ calculated in step S1025 is in the range of 0 ≦ φ ≦ 2π, if a 2π jump occurs in the phase φ, the phase connection can be made by correcting + 2π or -2π. Will be done.

The flatness calculation unit 152 further obtains the maximum value ΔZmax and the minimum value ΔZmin of the height ΔZ, and sets the difference ΔZdif between them as ΔZdim = ΔZmax−ΔZmin.
This difference ΔZdif is calculated as the flatness of the sample surface 20S. After that, the operation of FIG. 7 ends.

The flatness calculation unit 152 may display the difference ΔZdiv as the flatness of the sample surface 20S on the display 115. Further, the flatness calculation unit 152 may obtain an index other than the difference ΔZdif obtained from the height ΔZ as the flatness of the sample surface 20S. In this embodiment, steps S101 to S1030 correspond to an example of a flatness calculation step.

As described above, in the present embodiment, the entire interference fringe image 30 obtained by imaging the sample surface 20S is Fourier transformed to calculate the phase φ of the interference fringes, and the flatness of the sample surface 20S is obtained. ing. Therefore, according to the present embodiment, the measurement time can be shortened as compared with the conventional method of moving the optical member P. According to this embodiment, the measurement time can be shortened to about 100 msec. Therefore, in the factory where the measurement sample 20 is produced, each measurement is performed without retaining the measurement sample 20 continuously transported in the inspection process for a long time. The flatness of the sample 20 can be measured.

Generally, the analysis of the interference fringes can be performed by calculating the phase of the interference fringes in the local region, but in this case, if a foreign substance or the like exists in the local region, the phase cannot be calculated in the local region. appear. Further, since the calculated phase φ is in the range of 0 ≦ φ ≦ 2π, when there is a jump of 2π between adjacent local regions, it is necessary to connect the phases while correcting + 2π or -2π. However, when a local region in which the phase cannot be calculated occurs, the phase cannot be connected between adjacent local regions, so that the local region becomes the starting point and adversely affects the entire measurement region.

On the other hand, in the present embodiment, the entire interference fringe image 30 is Fourier transformed and expanded into a spatial frequency spectrum, and a desired spatial frequency spectrum region is extracted. Therefore, it is possible to remove the high frequency component caused by the foreign matter in the local region as described above. Furthermore, the extracted spatial frequency spectral region is inverse Fourier transformed. Therefore, the phase of the interference fringes can be calculated without the adverse effect of foreign matter.

Further, in the present embodiment, the sample surface 20S of the measurement sample 20 is arranged so as to be inclined in one direction with respect to the reference plane 20P of the optical member P. Therefore, according to the present embodiment, it is possible to generate interference fringes in which light and dark patterns are arranged in one direction.

Further, in the present embodiment, the interfering light is obliquely incident on the sample surface 20S by using the oblique interferometer 10. The measurement accuracy of the flatness depends on the S / N of the interference fringe image 30 obtained by the imaging unit 110, but when the coherent light is obliquely incident on the sample surface 20S, the sample surface 20S becomes a rough surface. Even if there is, the intensity of the specular reflection component of the reflected light is generally improved. Therefore, since the S / N of the interference fringe image 30 can be increased, the flatness can be measured with higher accuracy.

Further, in the present embodiment, the mounting surface 15U of the inclined member 15 is provided so that the distance between the bright region 30a or the dark region 30b of the interference fringes corresponds to the spatial resolution of the sample surface 20S required for the flatness measurement. The tilt angle is fixed. Therefore, various spatial resolutions can be supported by replacing the tilting member 15 with a mounting surface 15U having a different tilt angle. Further, in the present embodiment, it is preferable to set the interval of the interference fringes according to the required spatial resolution while considering the sharpness of the interference fringes and the resolution of the imaging unit 110.

(others)
(1) In the above embodiment, when the inclined member 15 is arranged so that the lower surface 15D of the inclined member 15 is a horizontal plane parallel to the horizontal direction, the mounting surface 15U has an inclination angle in one direction with respect to the lower surface 15D. Although it is formed so as to be inclined at θ, the structure of the inclined member 15 is not limited to this. For example, a flat plate-shaped mounting plate on which the measurement sample 20 is placed may be supported by at least two piezo elements on the support base so that the inclination angle θ of the mounting plate can be changed. Alternatively, a flat plate-shaped mounting plate is rotatably supported around one end thereof, and the other end is rotatably supported by a cylinder, a bolt, or the like so that the inclination angle θ of the mounting plate can be changed. You may.

(2) In the above embodiment, the Fourier transform calculation unit 161 Fourier transforms the entire interference fringe image 30 based on the pixel values for each coordinate (X, Y) of the interference fringe image 30, but calculates the Fourier transform. The method is not limited to this. For example, the Fourier transform calculation unit 161 first calculates in the line of the coordinate Y1 with the one-dimensional X coordinate, and then in the line of the coordinate Y2, calculates with the one-dimensional X coordinate, and so on. It may be calculated with the X coordinate of, and the calculation result may be integrated in the Y-axis direction.

Alternatively, depending on the specifications of the measurement sample 20, if the flatness needs to be evaluated only for one line in the radial direction at the predetermined Y coordinate, or if the flatness needs to be evaluated only in the predetermined 45 degree direction, the flatness needs to be evaluated in advance. When the flatness needs to be evaluated only in the determined two directions, the Fourier transform calculation unit 161 may perform the Fourier transform with the one-dimensional X coordinate.

(3) In the above embodiment, the optical member P is arranged so that the reference plane 20P is parallel to the horizontal plane orthogonal to the vertical direction, and the mounting surface 15U of the inclined member 15 is arranged with respect to the horizontal plane orthogonal to the vertical direction. It is formed so as to be inclined, but it is not limited to this. For example, the upper surface of the inclined member 15 may be formed so as to be parallel to the horizontal plane orthogonal to the vertical direction, and the optical member P may be arranged so that the reference plane 20P is inclined to the horizontal plane orthogonal to the vertical direction. .. That is, the sample surface 20S of the measurement sample 20 and the reference plane 20P of the optical member P may be arranged so as to be inclined in one direction with each other.

(4) In the above embodiment, the flatness calculation unit 152 extracts the power spectrum of the frequency range D3 including the peak value P3 at the right end, which is three times the half width D, but is not limited to this. The flatness calculation unit 152 may extract, for example, a frequency range of about twice the full width at half maximum D, including the peak value P3 at the right end. The flatness calculation unit 152 may, for example, extract a predetermined frequency range including the peak value P2 at the left end. In short, the flatness calculation unit 152 may extract a frequency range that includes the peak value P2 at the left end or the peak value P3 at the right end and does not overlap with the peak value P1 at the center.

15 Inclined member 15U Mounting surface 20 Measurement sample 20S Sample surface 20P Reference plane 30 Interference fringe image 10 Oblique interferometer 100 Flatness measuring device 105 Light source unit 151 Measurement control unit 152 Flatness calculation unit 161 Fourier transform calculation unit 162 Inverse Fourier Conversion calculation unit P Optical member

Claims (6)

An optical member having a reference plane and forming an optical coherometer between the reference plane and the sample surface of the measurement sample, and an oblique incident interferometer provided with a light source unit that obliquely irradiates the reference plane with coherent light.
An inclined member that inclines the sample surface in one direction with respect to the reference plane,
A flatness calculation unit for obtaining the flatness of the sample surface based on the interference fringes formed by the oblique incident interferometer is provided.
Flatness measuring device. The tilting member tilts the sample surface in one direction with respect to the reference plane so as to meet the spatial resolution required for the flatness.
The flatness measuring device according to claim 1. The flatness calculation unit obtains a spatial frequency spectrum from the interference fringes formed by the oblique incident interferometer, and obtains the phase of the interference fringes from a predetermined frequency range including the frequency component of the interference fringes in the spatial frequency spectrum. The flatness is obtained from the phase of the obtained interference fringes.
The flatness measuring device according to claim 1 or 2. Using an optical member having a reference plane and forming an optical coherometer between the reference plane and the sample surface of the measurement sample, and an oblique incident interferometer provided with a light source unit that obliquely irradiates the reference plane with coherent light. A flatness measuring method for determining the flatness of the sample surface.
A tilting step that tilts the sample surface in one direction with respect to the reference plane.
A flatness calculation step for obtaining the flatness of the sample surface based on the interference fringes formed by the oblique incident interferometer is provided.
Flatness measurement method. The tilting step tilts the sample surface in one direction with respect to the reference plane so as to meet the spatial resolution required for the flatness.
The flatness measuring method according to claim 4. In the flatness calculation step, the spatial frequency spectrum is obtained from the interference fringes formed by the oblique incident interferometer, and the phase of the interference fringes is obtained from a predetermined frequency range including the frequency component of the interference fringes in the spatial frequency spectrum. The flatness is obtained from the phase of the obtained interference fringes.
The flatness measuring method according to claim 4 or 5.

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