JP2001174213A - Optical phase controller for phase shift interferometer for plane measurement and optical phase control method for the same, and storage medium with optical phase control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical phase controller and method of a phase shift interferometer for plane measurement for operating highly accurate phase shift, without using special devices and a storage medium storing an optical phase control program. SOLUTION: A phase for minimizing a difference value between the maximum value and a minimum value for the brightness intensity of the mutual pixels of an interference fringe picture (image I) at a phase 0 deg. and an interference fringe image (second image IIA), obtained by shifting the phase of the first picture is obtained. Thus, interference fringe images can be obtained at the phase 0 deg. and a phase 180 deg., and to obtain an interference fringe image at a phase 90 deg. by calculating the intermediate position of the center of gravity position of the interference fringes of the interference fringe images, and to obtain the phase shape of an object 1 to be measured by operating plane analysis based on the three interference fringe image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical phase control device, an optical phase control method, and a storage medium storing an optical phase control program for a phase shift interferometer for plane measurement.

[0002]

2. Description of the Related Art Conventionally, there is a phase shift method using a phase shift interferometer as one of the techniques for measuring the planar shape of an object to be measured such as an optical part or a mirror-finished metal part. In this phase shift method, at least three times of the surface of the object to be measured is
This is to acquire two interference fringe images and process them to measure the planar shape of the object to be measured. Specifically, the optical path length variable method that physically changes the optical path length by a small amount, and the optical path length There is a wavelength variable method in which the wavelength of the light source is changed by a minute amount while the light source is fixed.

For example, in a phase shift method of an interference fringe image by a variable optical path length method, a phase shift interferometer shown in FIG. 1 is used. FIG. 1 is a configuration diagram of an optical system portion of a conventional phase shift Fizeau interferometer.

In FIG. 1, the interferometer mainly includes
A light source 1 made of a red semiconductor laser, a lens 2 for expanding the laser light from the light source 1, a half mirror 3 for transmitting the laser light from the lens 2, and a collimating lens 4 for making the transmitted light of the half mirror 3 parallel. A reference plate 5 that emits the measurement wavefront to the DUT 6 and whose emission side surface forms a reference wavefront; and a parallel light reflected by the test surface (measurement surface) of the DUT 6 and the reference plate 5. CCD for acquiring an interference fringe image formed by overlapping the parallel light reflected on the emission side surface through the half mirror 3 and the imaging lens 7
And a camera 8. The shape of the test surface of the DUT 6 is calculated based on the brightness information of the previously obtained interference fringe image. The reference plate 5 is supported by the fringe scan electrostrictive element 9, and the displacement of the fringe scan electrostrictive element 9 is controlled by a displacement control device 10.

When measuring the planar shape of the DUT 6 using this interferometer, the reference plate 5 is moved relative to the DUT 6 using the electrostrictive element 9 supporting the reference plate 5. Meanwhile, the CCD camera 8 acquires three interference fringe images as shown in FIG. At this time, assuming that the wavelength of the laser beam is λ, three interference fringe images are acquired by changing the optical path length between the reference plate 5 and the DUT 6 by λ / 4 by moving the reference plate 5. . FIG. 3 is an enlarged view of the interference fringe image shown in FIG.

For the above three interference fringe images, if the brightness intensity of the pixel of each image is In (x, y) [n: image number, x, y: x and y coordinates of pixel] The phase information φ (x, y) of the planar shape of the DUT 6 [x, y: coordinates in units of pixels on the DUT 6 associated with the interference fringe image]

[0007]

(Equation 1)

[0008]

Further, based on the phase information φ (x, y), a phase connection process and a conversion process for converting the phase value in units of the wavelength λ of the laser beam into the dimension value of the surface to be measured of the DUT 6 are performed. Thereby, data of the planar shape of the device under test 6 can be obtained.

The amount of change in the optical path length by which the phase of the planar shape of the DUT 6 is changed by the electrostrictive element 9 is a fraction of the wavelength λ of the laser light. If the amount of phase change with respect to is not accurate, a shape calculation error due to a phase change error of each interference fringe image will occur as shown in FIG.

Therefore, it is necessary to accurately control the amount of phase shift so that the phase information φ (x, y) becomes an accurate value. The fact that the amount of phase shift needs to be accurately controlled is the same as in the phase shift method of the interference fringe image by the wavelength variable method described above. However, in this case, a wavelength control device that changes the wavelength λ of the laser light of the light source 1 is connected to the light source 1 instead of the displacement control device 10.

[0012]

However, in the phase shift method of the interference fringe image by the above-mentioned variable optical path length method,
Since the electrostrictive element 9 is used as a means for performing a phase shift, the displacement amount of the reference plane 5 can be adjusted by reducing the phase shift error by additionally providing the displacement control device 10 in the part of the electrostrictive element 9. However, the high-precision displacement control device 10 is generally expensive. In addition, when the method is used on a manufacturing or inspection line, accurate planar analysis cannot be performed due to drift of the electrostrictive element 9 due to repeated measurements a plurality of times.

On the other hand, the phase shift method of the interference fringe image by the wavelength variable method has an advantage that it can be easily realized by a laser light source and does not need to physically change an optical path length. In order to control, it is necessary to control the temperature of the laser light source with extremely high accuracy,
Equipment becomes expensive. In addition, when the method is used in a manufacturing or inspection line, there is a problem that an accurate plane analysis cannot be performed due to a change in an installation environment (for example, a change in temperature).

The present invention has been made in view of the above points, and has an optical phase control apparatus for a plane-measuring phase shift interferometer capable of performing a high-accuracy phase shift without using a special apparatus. An object of the present invention is to provide a storage medium storing an optical phase control method and an optical phase control program.

[0015]

According to a first aspect of the present invention, there is provided an optical phase control apparatus for a phase shift interferometer for plane measurement, comprising: an interferometer for forming an interference fringe; A phase shift interferometer for plane measurement, comprising: an imaging storage unit for storing; an image processing unit for performing image processing of the interference fringes stored by the imaging storage unit; and a phase shift unit for shifting the phase of the interference fringes. In the optical phase control device, the image arithmetic processing means detects an optical phase shift amount from the position change information of the interference fringes, and sets the phase so that the optical phase shift amount becomes a predetermined optical phase shift amount. It is characterized in that the shift means is controlled.

According to a second aspect of the present invention, there is provided an optical phase control device for a plane measurement phase shift interferometer according to the first aspect, wherein the image arithmetic processing means comprises: The optical phase shift amount is detected from information of only a predetermined portion of the interference fringe.

According to a third aspect of the present invention, there is provided an optical phase control apparatus for a plane measurement phase shift interferometer according to the first or second aspect.
The image calculation processing means, the difference between the maximum value and the minimum value of the sum or difference of the brightness intensities of the first image of the interference fringes and the second image obtained by shifting the phase of the interference fringes of the first image, It is characterized in that the control of the phase shift means is continued until it falls within a predetermined allowable range.

According to a fourth aspect of the present invention, there is provided an optical phase control apparatus for a plane measurement phase shift interferometer according to any one of the first to third aspects. The image processing unit calculates a control amount of the phase shift unit when the phase of the interference fringe is 90 ° based on a control amount of the phase shift unit when the phase of the interference fringe is 0 ° and 180 °. It is characterized by doing.

According to a fifth aspect of the present invention, there is provided an optical phase control apparatus for a plane measurement phase shift interferometer according to any one of the first to third aspects. The image arithmetic processing unit is configured to control the phase shift unit so that the phase of the interference fringe becomes 90 ° based on the average value of the control amount of the phase shift unit when the phase of the interference fringe is 0 ° and 180 °. It is characterized by performing control.

The optical phase control device of the phase shift interferometer for plane measurement according to claim 6 is an interference fringe image obtaining means for obtaining an interference fringe formed by the phase shift interferometer for plane measurement as an interference fringe image; Image processing means for performing image processing of the interference fringe image obtained by the interference fringe image obtaining means,
Phase shifting means for shifting the phase of the interference fringe from a reference phase, wherein the interference fringe image obtaining means forms at least three interference fringe images corresponding to the phase of the interference fringe shifted by the phase shifting means. In the optical phase control device of the plane measurement phase shift interferometer to be obtained, the image processing means sets a phase shift amount for a final acquisition purpose based on the number of interference fringe images acquired by the interference fringe image acquisition means. Calculating and detecting a phase shift amount of the interference fringe shifted by the phase shift unit, and further controlling the phase shift unit so that the detected phase shift amount becomes the phase shift amount of the final acquisition purpose. It is characterized by.

According to a seventh aspect of the present invention, there is provided an optical phase control apparatus for a plane measurement phase shift interferometer according to the sixth aspect, wherein the image processing means comprises: The brightness of the first interference fringe image acquired by the interference fringe image acquiring unit at the reference phase and the second interference fringe image acquired by the interference fringe image acquiring unit after the phase shift unit shifts from the reference phase. The control of the phase shift means is continued until the difference between the maximum value and the minimum value of the sum or difference of the magnitudes falls within a predetermined allowable range.

An optical phase control method of a phase shift interferometer for plane measurement according to claim 8, wherein the interference fringe image obtaining step of obtaining an interference fringe formed by the phase shift interferometer for plane measurement as an interference fringe image; An image processing step of performing image processing of the interference fringe image obtained in the interference fringe image obtaining step, and a phase shift step of shifting a phase of the interference fringe from a reference phase, and in the interference fringe image obtaining step, In the optical phase control method of the plane-measuring phase shift interferometer for acquiring at least three interference fringe images corresponding to the phases of the interference fringes shifted by the phase shifting step, A phase shift amount for a final acquisition purpose is calculated based on the number of interference fringe images acquired in the image acquisition step, and a phase shift of the interference fringe shifted in the phase shift step is performed. Detecting the amount, further said detected phase shift amount and controls the phase shift process so that the phase shift amount of the last acquisition purposes.

A storage medium according to a ninth aspect of the present invention is a storage medium storing an optical phase control program of a phase shift interferometer for plane measurement, wherein the program is an interference fringe formed by the phase shift interferometer for plane measurement. An interference fringe image acquisition module that acquires the image as an interference fringe image, an image processing module that performs image processing on the interference fringe image acquired by the interference fringe image acquisition module, and a phase that shifts the phase of the interference fringe from a reference phase. With a shift module,
The interference fringe image obtaining module obtains at least three interference fringe images corresponding to the phase of the interference fringes shifted by the phase shift module, and the image processing module is obtained by the interference fringe image obtaining module. A phase shift amount for a final acquisition purpose is calculated based on the number of interference fringe images, a phase shift amount of the interference fringes shifted by the phase shift module is detected, and the detected phase shift amount is calculated for the final acquisition purpose. The phase shift module is controlled so that the amount of phase shift becomes the following.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 is a configuration diagram of an optical part of the phase shift interferometer according to the embodiment of the present invention.

In FIG. 5, the interferometer is a Fizeau interferometer, which mainly includes a light source 11 composed of a red semiconductor laser, a lens 12 for expanding the laser light from the light source 11, and a laser light from the lens 12. , A collimating lens 14 for making the transmitted light of the half mirror 13 parallel, a reference plate 15 for emitting a measurement wavefront to the DUT 16 and an emission side surface forming a reference wavefront, and a reference plate. An interference light formed by overlapping the parallel light reflected on the test surface of the DUT 16 with the parallel light reflected on the emission side surface of the reference plate 15, and the fringe scan electrostrictive element 19 supporting the reference 15. Camera 18 which obtains the transmitted light through the half mirror 13 and the imaging lens 17
And an image processing apparatus 20 that acquires the interference light acquired by the CCD camera 18 as an interference fringe image, finally determines the phase shift amount of the interference fringe, and obtains the data of the planar shape of the surface to be measured of the DUT 16. And an electrostrictive element driver 21 for driving the electrostrictive element 19 based on the phase shift amount determined by the image processing apparatus 20.

The image processing apparatus 20 includes memories 30 to
37. The memories 30 to 37 do not need to be configured as separate hardware. For example, a file that plays the role of the memories 30 to 37 may be provided in one hard disk. In the phase shift interferometer of FIG. 5, the displacement control device 10 shown in FIG. 1 is not used as a conventional technique.

In the case of the phase shift method of the interference fringe image by the wavelength variable method, a light source driver for changing the wavelength λ of the laser light of the light source 1 is replaced by the light source 11 and the image processing device 20 instead of the electrostrictive element driver 21. Connected between

Hereinafter, a method of calculating the planar shape of an object to be measured using the optical phase control method of the phase shift interferometer for planar measurement according to the embodiment of the present invention will be described with reference to FIGS. .

The calculation method obtains interference fringe images each having a phase shifted by λ / 4, for example, an interference fringe image having three phases of 90 ° and 180 ° with the first image having a phase of 0 °. Is subjected to known phase connection processing and conversion processing to calculate the planar shape. In the present embodiment, interference fringe images are acquired in the order of 0 °, 180 °, and 90 °.

FIG. 12 and FIG. 13 are flowcharts of an interference fringe image acquisition process in the phase shift interferometry.
This processing is executed by the image processing device 20.

In FIG. 12, first, one interference fringe image (hereinafter, referred to as "I-th image") is acquired at a phase of 0 ° and stored in the memory 30 (step S1). This I-th image is shown in FIG.

Next, with respect to the bright interference fringes in the I-th image shown in FIG. 6, the position of the center of gravity A is calculated, and the coordinates of the pixel on the screen at the position of the center of gravity A are stored in the memory 31 (step S2).

Hereinafter, a method of calculating the position A of the center of gravity of the bright interference fringes of the I-th image will be specifically described.

The center of gravity A of the bright interference fringes is determined by appropriately performing a mask process and a threshold process on an area where the interference fringes appear in the interference fringe image shown in FIG. Can be detected.

In the example shown in FIG. 7, four barycentric positions A, B, C, and D are detected in the observation area for observing interference fringes. After grasping the order in the screen from the information, the information is temporarily stored in the memory. At this time, in the peripheral part of the observation area, the interference fringes generally appear as incomplete fringes of only a part, and thus the barycentric position obtained in this part is excluded.

Then, from the coordinates of each position of the center of gravity, the distance between adjacent centers of gravity is obtained, and the maximum value is obtained. Then, when a circle having the radius of the maximum value of the distance between the interference fringes from the center of the image is drawn using this maximum value, the centroid positions C and D that do not fall within this area are excluded as invalid. , Extract only the effective barycentric positions A and B that fall within this area.

Since the position of the center of gravity of the interference fringes required in the subsequent phase control process is one, any one of the positions of the centers of gravity A and B in the effective range circle (here, the center of gravity) Only for the barycenter position A), the coordinate values of the pixels on the image are left in the memory 31 and the others are deleted.

Returning to FIG. 12, in step S3, the phase is slightly shifted by about 1/20 of the fringe interval. Specifically, a command value to the electrostrictive element driver 21 necessary for approximately changing the phase shift amount from about 0 ° to about 180 ° to the electrostrictive element driver 21 is obtained in advance, and an appropriate coefficient (10 This value is input to the electrostrictive element driver 21 as an actual command value.

Next, an interference fringe image whose phase is slightly shifted from that of the I-th image (hereinafter referred to as “IIA image”) is obtained, and this IIA image is stored in a memory 32 different from the above-mentioned I-th image. Then, the center of gravity B of the bright interference fringe in the IIA image is calculated, and the coordinates of the pixel on the screen at the center of gravity B are stored in the memory 33 (step S4).
5).

Hereinafter, a method of calculating the position B of the center of the bright interference fringes in the IIA image will be specifically described.

FIG. 8 schematically shows the positional relationship between interference fringes in the IIA image and the Ith image. One of these interference fringes
In this embodiment, the amount of movement of each time is as small as about 1/20 of the fringe interval.
On the other hand, by selecting the center of gravity B of the closest interference fringe in the IIA image, it is possible to supplement the movement of the center of gravity of the focused interference fringe. The coordinates of the new center-of-gravity position B are required to supplement the next movement of the focused interference fringe.

Referring again to FIG. 12, the sum of the brightness intensities of the corresponding pixels in the entire image of the I-th image and the II-th image is obtained, and the difference between the maximum value and the minimum value of these values is obtained. The difference value Xn is stored in the memory 34 (Step S6).

Next, the image processing apparatus 20 again inputs the command value to the electrostrictive element driver 21 and slightly shifts the phase (step S7), and the interference fringe image (FIG. 2B) is slightly shifted from the IIA image. Hereinafter, the “IIIA image” is acquired, and this IIIA image is overwritten on the memory 32 (step S8). Then, the center of gravity C of one interference fringe in the IIIA image closest to the center of gravity B is calculated, and the coordinates of the center of gravity C are overwritten in the memory 33 (step S9).

Next, in the entire image of the I-th image and the III-A image, the sum of the brightness intensities of the corresponding pixels is calculated, the difference between the maximum value and the minimum value of these values is obtained, and this difference value Xn + 1 is calculated. A memory 35 different from the difference value Xn
(Step S10).

In the following step S11, the difference value Xn + 1
Is smaller than a predetermined convergence value Z.
If the result of the determination in step S11 is that the difference value Xn + 1 is larger than the predetermined convergence value Z, it is determined whether or not the difference value Xn + 1 is smaller than the difference value Xn stored in the memory 34 in step S6 (step S6). S12).

As a result of the determination in step S12, the difference value Xn
If +1 is smaller than the difference value Xn, the difference value Xn + 1
Is overwritten as the difference value Xn in the memory 34 (step S
13) While repeating the processing of steps S7 to S12, when the difference value Xn + 1 is larger than the difference value Xn, the moving amount of the electrostrictive element 19 is reduced (that is, the phase shift amount is reduced), and the moving direction is further reduced. Is reversed (step S14), and the processing of steps S7 to S12 is repeated.

If the difference value Xn + 1 is smaller than the predetermined convergence value Z as a result of the determination in step S11,
The phase of the image currently stored in the memory 32 is set to 180 °
The image is stored in the memory 36 as an interference fringe image (hereinafter, referred to as a “third image”) when the image is shifted (step S15).

As described above, the position at the time when the phase is shifted by 180 ° can be obtained easily and with high accuracy by the processing of steps S1 to S14.

The reason will be specifically described below.

When the interference fringes appear in the vertical direction as shown in FIG. 8, for example, a horizontal pixel row at a middle position in the vertical direction of the interference fringe image (a line drawn horizontally at the center in FIG. 8) Focusing on the brightness intensity distribution in
The brightness intensities of the I-th image, the II-A image, and the sum of these are as shown in FIG. FIGS. 10A to 10E show the brightness intensities shifted from 0 ° to 180 ° by 45 ° from each other.

As shown in FIGS. 10A to 10E, the I-th
For the image and the IIA image, the sum of the values of the brightness intensities of the pixels on the corresponding images is calculated, and a position where the difference between the maximum value and the minimum value of the obtained value in the entire screen is minimized is searched. Actually, it is effective to find a position where the difference between the maximum value and the minimum value is minimized because of the influence of image noise and the like. At this time, it is necessary to remove isolated point noise and the like by filtering.

For the I-th image and the IIA-th image, the difference between the brightness intensities of the pixels on the corresponding images is calculated, and the difference between the maximum value and the minimum value of the obtained value in the entire screen is calculated. The position when the phase is shifted by 180 ° can also be obtained by searching for the position where the phase becomes maximum.

Returning to FIG. 12, the intermediate position of the center of gravity of the interference fringes of the I-th image obtained in step S1 and the III-th image obtained in step S15 is obtained (step S1).
16).

Hereinafter, a method of obtaining the intermediate position will be described with reference to FIG. FIG. 11 shows the images I and II.
4 schematically shows the relationship between interference fringes and the center of gravity of the interference fringes for an I image.

As shown in FIG. 11, since the center of gravity of each interference fringe is obtained from the I-th image having a phase of 0 ° and the III-th image having a phase of 180 °, the first image having a phase of 90 ° to be obtained is obtained.
The position of the center of gravity of the interference fringes in the II image is exactly the middle position between the two positions of the center of gravity described above. That is, this intermediate position is obtained by calculating the average value of the output of the electrostrictive element driver 21 at the phase of 0 ° and the output of the electrostrictive element driver 21 at the phase of 180 °. The output can be easily obtained.

Here, since the image corresponding to the obtained intermediate position is an interference fringe image having a 90 ° phase, this interference fringe image is stored in the memory 37 as the II image (step S1).
7) The test is performed by performing a plane analysis on the three interference fringe images obtained in the above processing, each having a phase difference of 90 °, based on a plane shape analysis method using a general interferometer. The data of the plane shape of the surface is acquired (Step S1)
8).

As described above, according to the present embodiment,
The difference value between the maximum value and the minimum value of the sum of the brightness intensities of the pixels of the interference fringe image (I-th image) and the interference fringe image (IIA image) in which the phase of the I-th image is shifted at the phase of 0 ° is minimized. By obtaining an interference fringe image at a phase of 0 ° and 180 °, and obtaining an intermediate position of the center of gravity of the interference fringes of these interference fringe images, a phase of 90 ° is obtained.
, And a plane analysis is performed on the basis of these three interference fringe images to obtain a planar shape of the measured object 16. , It is possible to perform a highly accurate phase shift.

Further, since the phase shift amount is always detected from the state of the interference fringes, even if the measurement is continuously performed for a long time, only the wavelength of the laser light source 11 is stabilized, so that the electrostrictive element 19 and the A highly accurate phase shift can be performed without being affected by the drift of the displacement meter for detecting the shift amount.

Further, since the position of the center of gravity of the interference fringes is used for moving the interference fringes and counting the number of the interference fringes, it is very advantageous for automation of inspection lines and the like.

In the above step S12, when the difference value Xn + 1 is smaller than the predetermined convergence value Z, the image currently stored in the memory 32 is stored in the memory 36 as the third image. The image stored in the memory 32 when the determination in step S11 has been performed a predetermined number of times may be stored in the memory 36 as the third image.

Further, in the present embodiment, in order to obtain a 180 ° phase difference, the sum or difference of two images is calculated for all pixels. Since the calculation time is proportional to the number of pixels, the calculation speed can be easily improved by reducing the number of pixels. For example, by selecting pixels involved in the calculation in a diagonal, radial, or grid shape, the calculation speed can be increased independently of the direction of the interference fringes.

Further, in the present embodiment, the phase 0 °, 90 °
Although three images of 180 ° and 180 ° are used, the number of images is not limited to three, and three or more images may be used.

Further, in the above-described series of processing, detection of the center of gravity of interference fringes is a function built into hardware in recent hardware for image input. In addition, the calculation speed can be detected almost in real time. Also, since the position of the center of gravity of the interference fringes can be detected, by counting the number, the approximate number of interference fringes can be ascertained. It is easy to control the distortion element 19 and control the attitude of the reference plate 5 so that the number of interference fringes suitable for measurement is obtained.

Further, since the movement of the interference fringes is detected not from the shape of the interference fringes but from the brightness intensity of each pixel in the entire image, even if the interference fringes have a directionality or a slight curvature, the interference fringes are detected. Can be accurately detected. However, when the test surface is a spherical surface of high intensity and the interference fringes draw concentric circles, the electrostrictive element 19 is controlled in advance, and the posture of the reference plate 15 is adjusted so that the center of gravity of the interference fringes is arranged substantially linearly. By changing it, the present invention can be applied.

In the present embodiment, the process of acquiring an interference fringe image in the phase shift interferometry has been described.
Even if this process is written as a program in a storage medium, and the program is read from the storage medium and executed by a known device, the above-described process can be executed. The storage medium is a floppy disk, hard disk, CD-RO
Although various types such as M and MO are conceivable, it is not necessary to limit to a specific type, and any type can be used as long as the program can be stored.

The present invention can be applied to a phase shift method of an interference fringe image by a wavelength variable method.

[0068]

As described above in detail, according to the optical phase control device of the phase shift interferometer for plane measurement according to the first aspect, the image arithmetic processing means uses the optical phase shift information based on the position change information of the interference fringes. The amount of the phase shift is detected and the phase shift means is controlled so that the amount of the optical phase shift becomes a predetermined amount of the optical phase shift. An accurate phase shift can be performed.

According to the optical phase control device of the phase shift interferometer for plane measurement according to the second aspect, the image arithmetic processing means detects the optical phase shift amount from information of only a predetermined portion of the interference fringe. The phase shift amount of the interference fringes can be accurately detected even if the direction of the interference fringes and some curvature are present.

According to the optical phase control apparatus of the phase shift interferometer for plane measurement of the third aspect, the image arithmetic processing means is configured to shift the phase of the first image of the interference fringes and the phase of the interference fringes of the first image. Since the control of the phase shift means is continued until the difference between the maximum value and the minimum value of the sum or difference of the brightness intensities of the two images falls within a predetermined allowable range, the phase of the interference fringes of the first image can be accurately determined. An image of interference fringes shifted by 180 ° can be obtained.

According to the optical phase control system of the fourth aspect,
The image calculation processing means may determine that the phase of the interference fringes is
Since the control amount of the phase shift means when the phase of the interference fringe is 90 ° is calculated based on the control amount of the phase shift means at the time of, the control of the phase shift means when the phase of the interference fringe is 90 ° is easily performed. The amount can be calculated.

An optical phase control apparatus for a phase shift interferometer for plane measurement according to claim 6, an optical phase control method for a phase shift interferometer for plane measurement according to claim 8, and a phase shift interference for plane measurement according to claim 9. According to the storage medium storing the optical phase control program of the meter, the phase shift amount of the final acquisition purpose is calculated based on the number of acquired interference fringe images, and the phase shift amount of the shifted interference fringe is detected. Further, since the detected phase shift amount is controlled to be the phase shift amount intended for the final acquisition, highly accurate phase shift can be performed without using a special device.

According to the optical phase control device of the phase shift interferometer for plane measurement according to claim 7, the image processing means comprises: a first interference fringe image acquired by the interference fringe image acquiring means at the reference phase; The difference between the maximum value and the minimum value of the sum or difference of the brightness intensities with the second interference fringe image acquired by the interference fringe image acquiring means after the means shifts from the reference phase falls within a predetermined allowable range. Since the control of the phase shift means is continued until the phase of the interference fringes of the first interference fringe image
An interference fringe image shifted by 0 ° can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical system portion of a conventional phase shift Fizeau interferometer.

FIG. 2 is a diagram of three interference fringe images with changed phases.

FIG. 3 is an enlarged view of a part of the interference fringe image of FIG. 2;

FIG. 4 is a diagram showing a shape calculation error caused by a phase change error in each interference fringe.

FIG. 5 is a configuration diagram of an optical system portion of the phase shift Fizeau interferometer according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of an interference fringe image.

FIG. 7 is a diagram illustrating an example of an interference fringe image obtained by performing a mask process and a threshold process to determine a barycentric position of the interference fringes.

FIG. 8 is a diagram schematically showing a positional relationship between interference fringes in an I-th image and a II-A image.

FIG. 9 is a diagram illustrating an I-th image, a IIA image, and the brightness intensity of each of the sum thereof.

FIG. 10 further increases the brightness intensity shown in FIG.
It is a figure calculated every 45 degrees up to 0 degree.

FIG. 11 is a diagram schematically showing a relationship between interference fringes in the I-th image and the III-th image and the position of the center of gravity of the interference fringes.

FIG. 12 is a flowchart illustrating a program for detecting a planar shape of a test surface.

FIG. 13 is a flowchart showing a program for detecting a planar shape of a surface to be measured.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 laser light source 12 lens 13 half mirror 14 collimating lens 15 reference plate 16 DUT 17 imaging lens 18 CCD camera 19 fringe scan electrostrictive element 20 image processing device 21 electrostrictive element driver

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Claims (9)

[Claims] 1. An interferometer for forming an interference fringe, an imaging storage unit for storing the interference fringe as an image, an image processing unit for performing image processing of the interference fringe stored by the imaging storage unit, An optical phase control device for a plane measurement phase shift interferometer having a phase shift means for shifting the phase of the fringes, wherein the image arithmetic processing means detects an optical phase shift amount from position change information of the interference fringes, An optical phase control apparatus for a plane-measuring phase shift interferometer, wherein the phase shift means is controlled so that the optical phase shift amount becomes a predetermined optical phase shift amount. 2. The phase shift interferometer for plane measurement according to claim 1, wherein said image calculation processing means detects said optical phase shift amount from information of only a predetermined portion of said interference fringes. Optical phase controller. 3. The image processing unit according to claim 1, wherein the first image of the interference fringes and the sum or difference of the brightness intensities of the second images obtained by shifting the phase of the interference fringes of the first image are minimum and maximum values. 3. The optical phase control device for a phase shift interferometer for plane measurement according to claim 1, wherein the control of the phase shift means is continued until the difference between the phase shift and the difference falls within a predetermined allowable range. 4. The image processing unit according to claim 1, wherein the phase shift when the phase of the interference fringe is 90 ° is based on the control amount of the phase shift unit when the phase of the interference fringe is 0 ° and 180 °. 4. The optical phase control device for a phase shift interferometer for planar measurement according to claim 1, wherein a control amount of the means is calculated. 5. The image processing unit according to claim 1, wherein the phase of the interference fringe is 90 ° based on the average value of the control amount of the phase shift unit when the phase of the interference fringe is 0 ° and 180 °. 4. The optical phase control device of a phase shift interferometer for plane measurement according to claim 1, wherein the phase shift means is controlled. 6. An interference fringe image acquiring means for acquiring an interference fringe formed by a plane measurement phase shift interferometer as an interference fringe image, and performing image processing of the interference fringe image acquired by the interference fringe image acquiring means. Image processing means; and phase shifting means for shifting the phase of the interference fringes from a reference phase, wherein the interference fringe image acquiring means has at least three phases corresponding to the phase of the interference fringes shifted by the phase shifting means. In the optical phase control device of the plane shift phase shift interferometer for acquiring two interference fringe images, the image processing unit may be configured to obtain a final acquisition object based on the number of interference fringe images acquired by the interference fringe image acquisition unit. And the phase shift amount of the interference fringes shifted by the phase shift means is detected, and the detected phase shift amount is calculated by the phase shift amount. Optical phase control unit for a planar measuring phase shift interferometry, characterized in that for controlling the phase shift unit so that the phase shift amount acquisition purposes. 7. The image processing unit includes: a first interference fringe image acquired by the interference fringe image acquiring unit at the reference phase;
The difference between the maximum value and the minimum value of the sum or difference of the brightness intensities with the second interference fringe image obtained by the interference fringe image obtaining unit after the phase shift unit has shifted from the reference phase,
7. The optical phase control device for a phase shift interferometer for planar measurement according to claim 6, wherein the control of the phase shift means is continued until the control value falls within a predetermined allowable range. 8. An interference fringe image acquiring step of acquiring an interference fringe formed by the plane measurement phase shift interferometer as an interference fringe image, and performing image processing of the interference fringe image acquired in the interference fringe image acquiring step. An image processing step, including a phase shift step of shifting the phase of the interference fringes from a reference phase, in the interference fringe image obtaining step, at least corresponding to the phase of the interference fringes shifted by the phase shift step In the optical phase control method for a plane-shifting phase shift interferometer for acquiring three interference fringe images, the image processing step includes: obtaining a final image based on the number of interference fringe images acquired in the interference fringe image acquiring step. Calculating a target phase shift amount and detecting a phase shift amount of the interference fringes shifted in the phase shifting step, and further detecting the detected phase shift amount in the final acquisition Optical phase control method of a flat measuring phase shift interferometry, characterized in that for controlling the phase shift process so that the phase shift amount of the target. 9. A storage medium storing an optical phase control program for a plane measurement phase shift interferometer, wherein the program acquires an interference fringe formed by the plane measurement phase shift interferometer as an interference fringe image. Interference fringe image acquisition module, an image processing module that performs image processing of the interference fringe image acquired by the interference fringe image acquisition module, and a phase shift module that shifts the phase of the interference fringe from a reference phase, The interference fringe image obtaining module obtains at least three interference fringe images corresponding to the phase of the interference fringes shifted by the phase shift module, and the image processing module is obtained by the interference fringe image obtaining module. Based on the number of interference fringe images, the phase shift amount for the final acquisition purpose is calculated and the phase shift mode is calculated. A storage medium for detecting a phase shift amount of the interference fringes shifted by a module, and further controlling the phase shift module so that the detected phase shift amount becomes the phase shift amount of the final acquisition purpose. .