JP3466713B2 - Measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for measuring the three-dimensional shape of an object by utilizing the interference of light.

[0002]

2. Description of the Related Art Conventionally, for example, Applied Optics Vol. 19 No. 1 (1) has been used as a measuring device that relatively accurately measures the shapes of optical members such as lenses and mirrors by utilizing the interference of light.
980) Optical heterodyne interferometers such as those introduced in P154 to P160 are known.

This optical heterodyne interferometer irradiates two light waves whose frequencies are slightly different from each other to an object to be measured and a reference plane mirror, respectively. Then, the reflected light from the object to be measured and the reflected light from the reference plane mirror interfere with each other, and in the scanning type light detection means such as an image dissector camera, the interference light is received by the image sensor, and the image sensor is two-dimensionally The beat signal is detected at each measurement point by scanning the object, and the phase of the beat signal is analyzed to obtain the shape of the object.

However, in many cases, it takes several seconds to several tens of seconds until the beat signal is detected from all the measurement points. If the object to be measured or the reference plane mirror is displaced during this time, the beat signal Since it is detected as a phase shift,
The measurement accuracy will decrease.

An optical heterodyne interferometer which eliminates such measurement error and enables highly accurate measurement is disclosed in Japanese Patent Laid-Open No. 5-5.
No. 610 is disclosed. FIG. 5 is a block diagram of this conventional optical heterodyne interferometer.
The light wave emitted from is reflected by the mirror 2 and split into two by the beam splitter 3. Of these, the transmitted light (hereinafter referred to as the test light wave) is shifted by the frequency f1 in the black cell 5 driven by the black cell driver 4, is reflected by the mirror 6, and is polarized by the (λ / 2) plate 7 to have a polarization plane of 90 °. The light beam is rotated by a degree and enters the polarized beam splitter 8. on the other hand,
A light beam reflected by the beam splitter 3 (hereinafter referred to as a reference light wave) is shifted by a frequency f2 by a black cell 9 driven by a black cell driver 4, reflected by a mirror 10 and incident on a polarization beam splitter 8. In the polarization beam splitter 8, the test light wave and the reference light wave are combined, and the beam expander 11 expands the beam diameter,
The polarization beam splitter 12 separates the test light wave and the reference light wave again.

The test light wave is circularly polarized by the (λ / 4) plate 13, passes through the collimator lens 14, and is irradiated onto the object B to be measured. The test light wave reflected by the device under test B is circularly polarized in the opposite direction to that at the time of incidence, and the plane of polarization of the (λ / 4) plate 13 is rotated by 90 ° from that at the time of incidence. Due to this polarization state, the test light wave is reflected upward by the polarization beam splitter 12. On the other hand, the reference light wave is reflected by the polarization beam splitter 12 to be circularly polarized by the (λ / 4) plate 15, is reflected by the reference plane mirror 16 and is circularly polarized in the opposite direction to the incident light, and (λ / 4) The plate 15 converts the plane of polarization into a linearly polarized light which is rotated by 90 °. As a result, since the light beam passes through the polarization beam splitter 12, it is combined with the test light wave reflected upward here, so that the wavefronts of the test light wave and the reference light wave are matched by the polarizing plate 17 and interfere with each other. And is split into two by the beam splitter 18.

The luminous flux transmitted through the beam splitter 18 is
An image dissector camera (hereinafter, I
The light is received by the image pickup device 19a of the D camera 19),
Converted to beat signal. On the other hand, the beam splitter 18
The light flux reflected by the light passes through the pinholes 20a to 20c of the pinball plate 20 shown in FIG. 6 and the three reference point images Ra to Rc.
As a result, the light is received by each of the photodetectors 21a to 21c and converted into a beat signal. The output of the photodetector 21a is input to each of the phase meters 22a to 22c, and the photodetector 21a
The outputs of b and 21c are input to the phase meters 22b and 22c, respectively.

FIG. 7 is a front view of the image pickup device 19a of the ID camera 19 at the time of measurement. The image pickup device 19a has Nx pixels designated by an address (X, Y) in the X direction and Ny pixels in the Y direction. Are arranged one by one, and the phase of each address (X, Y) of the interference fringe image P received here is the object to be measured B.
Represents the shape of.

Also, in the figure, reference point images Ra, Rb, respectively received by the photodetectors 21a to 21c together with the interference fringe image P are shown.
Rc is also shown, and these reference point images Ra, Rb, and Rc are pinholes 20a to 20c of the pinhole plate 20 shown in FIG.
Corresponding to the image extracted from the interference fringe image P, and is received by the photodetectors 22a to 22c, respectively. In this conventional example, the reference point image Ra is used by using the principle of the heterodyne interferometry.
As the reference point, the phase of the interference fringe image P is determined by obtaining the phase difference between this reference point and the address (X, Y) of the interference fringe image P, and the beat signal obtained by the photodetector 21a is used as the reference signal. Let R be the beat signal obtained by the ID camera 19 be the measurement signal S, and the phase meter 22a detects the phase difference φa between the reference signal R and the measurement signal S.

The computer 23 detects the measurement signal R for each pixel from the ID camera 19 by designating the address (X, Y) and inputs it to the phase meter 22a. Phase meter 2
2a is a phase difference φa between the address (X, Y) and the reference point image Ra based on the output of the ID camera 19 and the photodetector 21a.
(X, Y) is calculated and stored in the buffer memory 24.
Here, in a state where there is no error factor in other optical elements such as making the reference plane mirror 16 an ideal plane and the measured object B has no shape error, the phase difference φa between the measurement signal S and the reference signal R is
(X, Y) becomes 0 for all addresses (X, Y). That is, the phase difference φa (X, Y) is calculated by the collimator lens 14
And the deviation from the spherical wave, and directly represents the shape error of the object to be measured B.

When the phase difference φa (X, Y) is stored in the buffer memory 24 for all addresses (X, Y),
The computer 23 analyzes the two-dimensional distribution of this phase difference φa (X, Y) and obtains the shape of the object B to be measured as a wavefront aberration.

However, while the image pickup device 19a is two-dimensionally scanned in the ID camera 19 to detect the measurement signal R pixel by pixel, the object to be measured B and the reference plane mirror 1 are detected.
If 6 or the like vibrates or tilts, the phase of the beat signal shifts and a measurement error occurs. Therefore, the phase difference between the reference point image Ra and the reference point images Rb and Rc is detected, and the phase shift is corrected. The phase difference between the reference point images Ra and Rb is detected by the phase meter 22b as the phase difference φab between the beat signals of the photodetectors 21a and 21b, and the phase difference between the reference point images Ra and Rc is detected by the photodetector 22a. The phase difference 22ac of the beat signal of the detector 21c is detected by the phase meter 22c. These phase differences φab and φac are stored in the buffer memory 24, and the phase correction amount C (X, Y) is stored in the computer 23.
Is required.

As shown in FIG. 7, since the reference point images Ra to Rc on the image pickup device 19a form a right triangle, φ
ab represents a phase difference corresponding to the relative displacement between the measured object B and the reference mirror 6 in the Y direction, and φac represents the relative displacement between the measured object B and the reference mirror 6 in the X direction. It represents the corresponding phase difference. At the time of detecting φa (X, Y), the phase difference detected by the phase meters 22b and 22c is calculated as φab
(X, Y) and φac (X, Y), the ID camera 19
The phase correction amount C (X, Y) at the address (X, Y) of the image pickup device 19a can be expressed by the following equation. C (X, Y) = φab (X, Y) Y · dw / Ly −φac (X, Y) X · dw / Lx (1)

The constant dw is the distance between the pixels of the image sensor of the ID camera 19 in the X and Y directions, and the constant Ly is the reference point image.
A constant Lx, which is the distance between Ra and Rb, represents the distance between the reference point images Ra and Rc. Using this equation (1), the true wavefront aberration φ (X, Y) can be obtained from the following equation. φ (X, Y) = φa (X, Y) -C (X, Y) (2)

Therefore, since the phase correction amount C (X, Y) is calculated while detecting the phase difference φa (X, Y), the measurement error caused by the physical displacement of the object B to be measured is caused. Can be removed.

[0016]

However, in the optical heterodyne interferometer shown in FIG. 5, when the object B to be measured is, for example, a spherical lens, the spherical lens moves parallel to the optical axis during two-dimensional scanning of the measuring surface. Then, defocus fluctuations occur in the phase of the beat signal, and when the object to be measured B is a cylindrical lens, when the cylindrical lens rotates around the optical axis, rotational fluctuations occur in the phase of the beat signal, and these fluctuations occur. Although it is a cause of measurement error, correction for these fluctuations has not been implemented.

An object of the present invention is to solve the above problems,
A measuring device that can accurately measure the shape of an object to be measured by correcting not only tilt fluctuations due to physical displacement that occurs in interference information but also defocus fluctuations and rotation fluctuations around the optical axis. To provide.

[0018]

Means for Solving the Problems A measuring device according to the present invention for achieving the above object comprises an irradiating means for irradiating a measurement area of an object to be measured with a coherent light wave to be measured, and An interference unit that interferes with the reference light used as a reference when obtaining interference information and a reflected test light wave, and an interference information detection unit that detects interference information between the test light wave and the reference light wave,
In a measuring device for measuring the shape of the object to be measured based on a signal of the interference information detecting means, an inclination variation information detecting means for detecting inclination variation information of the object to be measured while detecting the interference information, Defocus variation information detecting means for detecting defocus variation information of the object to be measured, rotation variation information detecting means for detecting rotation variation information about the optical axis of the object to be measured, tilt variation information, defocus variation A correction unit that corrects the interference information based on the information and the rotation variation information.

[0019]

The measuring device having the above-mentioned structure is provided with the object to be measured and the tilt variation information, the defocus variation information, which are generated in the interference information,
The rotation variation information about the optical axis is detected, and the interference information is corrected based on the variation information.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a configuration diagram of the first embodiment, in which a mirror 32 is arranged on the emission optical path of a laser light source 31 that emits a coherent light beam, and a beam splitter is provided on the optical path in the reflection direction of the mirror 32. 33, a black cell 34, and a mirror 35 are arranged, and a (λ / 2) plate 36 and a polarization beam splitter 37 are arranged on the optical path in the reflection direction of the mirror 35. The black cell 38 and the mirror 39 are provided on the optical path in the reflection direction of the beam splitter 33.
Are sequentially arranged and reflected by the mirror 39 so that the light beam enters the polarization beam splitter 37. The black cells 34 and 36 are driven by the black cell driver 40, and the frequency of incident light is shifted to a predetermined value by the acousto-optic effect.

Further, on the optical path behind the polarization beam splitter 40, a beam expander 41, a polarization beam splitter 42, a (λ / 4) plate 43, and a collimator lens 4 are provided.
4. The device under test B is sequentially arranged. On the optical path in the reflection direction below the polarization beam splitter 42, (λ /
4) A plate 45 and a reference plane mirror 46 are sequentially arranged, and a polarizing plate 47, a beam splitter 49, an ID camera 5 are provided on the optical path in the reflection direction above the polarization beam splitter 42.
0s are sequentially arranged. Also, the beam splitter 4
In the reflection direction of 9, a pinhole plate 51 having three pinholes 51b to 51d arranged at equal angles around the pinhole 51a is arranged.
The four light beams emitted from the
The light is received at 52d.

The output of the photodetector 52a is the phase meters 53a-5.
3d, and the outputs of the photodetectors 52b to 52d are connected to the phase meters 53b to 53d, respectively. The output of the ID camera 50 is also connected to the phase meter 53a. The outputs of the phase meters 53a to 53d are connected to the computer 55 via the buffer memory 54, and the output of the computer 55 is connected to the ID camera 50. A random access camera may be used instead of the ID camera 50.

The light wave emitted from the laser light source 31 is reflected by the mirror 32 and split into two by the beam splitter 33. Of these, the frequency of the transmitted light is shifted by f1 by the black cell 34 as the test light wave, and the (λ / 2) plate 36
The plane of polarization is rotated by 90 ° by the beam splitter 37
Incident on. On the other hand, the reflected light beam from the beam splitter 33 has its frequency shifted by f2 by the black cell 38 as a reference light wave, is reflected by the mirror 37, and enters the polarization beam splitter 37. In the polarization beam splitter 37, the test light wave and the reference light wave are combined, the beam diameter is expanded by the beam expander 41, and the light beam enters the polarization beam splitter 42.

The test light wave and the reference light wave are light waves which become the heterodyne signals f1-f2 with a very slight frequency difference, and the polarization planes are orthogonal to each other, so the polarization beam splitter 42
Will be separated again. The test light wave is the polarization beam splitter 4
After passing through 2, the (λ / 4) plate 43 converts the light into circularly polarized light, passes through the collimator lens 44, and illuminates the object to be measured B. The test light wave reflected by the device under test B returns to the same optical path as circularly polarized light having a reverse rotation to that at the time of incidence, and the polarization plane is rotated by 90 degrees from that at the time of incidence by the (λ / 4) plate 43. It is polarized. Due to this polarization state, it is reflected upward by the polarization beam splitter 42.

On the other hand, the reference light wave is the polarization beam splitter 4
The light is reflected downward by 2 and is circularly polarized by the (λ / 4) plate 45, is reflected by the reference plane mirror 46, and returns on the same optical path.
In this state, the reference light wave is circularly polarized in the opposite direction to the incident light wave, so that the (λ / 4) plate 45 is made into linearly polarized light whose polarization plane is rotated by 90 °, and is transmitted through the polarization beam splitter 42. . As a result, the test light wave and the reference light wave are combined again in the polarized beam splitter 42,
After passing through the polarizing plate 47, the wavefronts of the test light wave and the reference light wave coincide with each other and interfere with each other, and are split into two by the beam splitter 49.

The luminous flux transmitted through the beam splitter 49 is
The interference fringe image P is received by the image pickup device 50a of the ID camera 50 and converted into a beat signal. On the other hand, the light beam reflected by the beam splitter 49 passes through the pinholes 51a to 51d of the pinball plate 51 and is separated into four light beams.
Photodetectors 52a to 52d as reference point images Ra to Rd, respectively.
The light is received by and is detected as a beat signal.

FIG. 2 is a front view of the image pickup device 50a of the ID camera 50 at the time of measurement. The image pickup device 50a has Nx pixels arranged in the X direction and Ny pixels arranged in the Y direction. The interference fringe image P received here represents the phase of the spherical wave formed by the collimator lens 44, and this phase directly represents the shape of the measured object B. Further, in the figure, the image sensor 50
Photodetectors 51a-5a together with the interference fringe image P received by a
The reference point images Ra to Rd received at 1d are also shown. These reference point images Ra to Rd are the pinholes 5 of the pinhole plate 51.
It is extracted from the interference fringe image P by 1a to 51d.

At the time of actual measurement, the examiner uses the photodetector 52a.
And the optical axis of the incident light are matched with each other, and the diameter of the incident light is adjusted so that the light receiving levels of the photodetectors 52b to 52d become the levels at which the beat signal can be obtained. From the geometrical position on the imaging element 50a, the photodetectors 52a to 52d are detected.
Are addresses (0, 0), (N, 0), (√3N / 2, -N / 2) of the image sensor 50a of the ID camera 50,
A beat signal equal to the pixel at (−√3N / 2, −N / 2) is detected.

ID camera 50 and photodetectors 52a to 52
The beat signal obtained in d is the test light wave that is the light reflected by the object to be measured B and the reference plane mirror 4 having an ideal plane.
It is a beat signal of frequency | f1-f2 | generated by the interference with the reference light reflected at 6. The output of the ID camera 50 is input as the measurement signal S and the beat signal of the photodetector 52a is input as the reference signal R to the phase meter 53a, and the phase difference φ between the measurement signal S and the reference signal R is input.
a is detected, and the shape of the object B to be measured is obtained based on this phase difference φa. The phase detector 53b has a photodetector 5
The beat signals of 2a and 52b are input, the beat signals of the photodetectors 52a and 52c are input to the phase meter 53c, and the phase differences φab to φad between the beat signals input in the phase difference meters 53b to 53d. Is detected, and the measurement result is corrected based on these phase differences.

By specifying the address (X, Y), the computer 55 two-dimensionally scans the image pickup device 50a in the ID camera 50 to detect the measurement signal S for each pixel and input it to the phase meter 53a. . The phase meter 53a detects the phase difference φa between the measurement signal S at the address (X, Y) and the reference signal R at the address (0, 0) obtained by the photodetector 52a.
(X, Y) is calculated and stored in the buffer memory 54.

In the present embodiment, it is assumed that there is no error component of other optical elements such as the reference plane mirror 46 being an ideal plane, and the object to be measured B has no shape error and is detected by the ID camera 50. The phase difference φa between the measurement signal S and the reference signal R becomes 0 for all addresses (X, Y). That is, this phase difference φa represents the deviation from the spherical wave formed by the collimator lens 44, and directly represents the shape error of the object B to be measured. The computer 55 uses the phase difference φa (X, Y) stored in the buffer memory 54 to obtain the shape of the object to be measured B as spherical aberration using the principle of the heterodyne interferometry as described in the conventional example.

Further, the computer 55 uses the phase difference φa (X,
Y) while detecting the phase difference φa (X, Y), or at a cycle sufficiently shorter than the cycle of mechanical vibration, the phase meters 53b to 53d are arranged between the beat signals. Of the phase difference φab to φad of the buffer memory 5
4 and the phase difference φa generated when the measured object B is displaced based on the stored phase differences φab to φad.
The phase correction amount C (X, Y) of (X, Y) is obtained.

This phase correction amount C (X, Y) is the expression of the conventional example.
A correction term for the sphere is added to (2), and it can be expressed as the following equation. C (X, Y) = a1 · X · dw / N + a2 · Y · dw / N + a3 · (X 2 + Y 2) dw 2 / N 2 ... (3)

Here, the constant dw represents the pixel interval of the image sensor 50a, and N represents the radius of the circle M in FIG.
The first and second terms on the right side of the equation (3) are terms for correcting relative displacement between the object to be measured B and the reference plane mirror 46, and the third term
The term is a term for correcting the defocus fluctuation of the interference light. Further, the variable a1 is the phase difference corresponding to the relative displacement amount between the object to be measured B and the reference plane mirror 46 in the X direction, and the variable a2 is the relative difference between the object to be measured B and the reference plane mirror 46 in the Y direction. The variable a3 is the phase difference corresponding to the shift amount, and the variable a3 is the phase difference corresponding to the shift amount in the normal direction of the circumference of the circle M.

On the other hand, φab is the address (0,0) and (N,
0), φac is the phase difference between addresses (0,0) and (√3N / 2, −N / 2), and φad is the address (0,0) and (−√3N /). 2, −N / 2). Each phase meter 5 when φa (X, Y) is detected
The phase difference detected at 3b to 53d is φab
(X, Y) to φad (X, Y). Phase difference φab (X,
Y) to φad (X, Y) can be expressed by a linear combination of variables a1 to a3, and can be expressed by the following equation. Ax = Z (4)

Here, x is 1 × whose components are variables a1 to a3.
3 is a vertical matrix, and Z is the phase difference φab (X, Y), φac
It is a 1 × 3 vertical matrix having (X, Y) and φad (X, Y) as components, and the components of the matrix A have phase differences φab (X, Y) and φ.
These are the coefficients of ac (X, Y) and φad (X, Y). By solving the equation (4) for the matrix x, the following equation is obtained. x = (A ^T A) ^-1 A ^T Z (5)

Since the reference point images Ra to Rd shown in FIG. 2 are received by the photodetectors 52a to 52d, respectively, the matrix A is a three-dimensional square matrix, and therefore the equation (4) is expressed by the following equation. Can be simplified to x = A ^-1 Z (6)

If N = 1 with a circle M having a radius N as a unit circle, the components of the matrix A are determined, and equation (4) can be expressed as shown in equation (7).

[0039]

[Formula 7]

Equation (5) is defined as √3 = 1.732,
It can be expressed as shown in (8).

[0041]

[Formula 8]

Therefore, the phase difference φab (X, Y), φac
The variables a1 to a3 can be obtained by measuring (X, Y) and φad (X, Y). Using equation (8), equation (3)
When is modified, the phase correction amount C (X, Y) is given by the following equation. C (X, Y) = ( φac-φad) X · dw / (3N) + √3 (2φab-φac-φad) Y · dw / (3N) + (φab + φac + φad) · (X 2 + Y 2) dw 2 / (3N ² ) (9)

In the right side of the equation (9), the address (X, Y) given to the phase difference is omitted, and the matrix A element √
3 is an irrational number. From the equation (9), the true wavefront aberration φ (X, Y) based on the shape of the object B to be measured becomes as shown in the following equation. φ (X, Y) = φa (X, Y) -C (X, Y) (10)

The computer 55 calculates the true wavefront aberration φ (X, Y) for each address (X, Y) according to the equations (9) and (10).
Is calculated and the three-dimensional shape of the measured object B is obtained. In addition, the phase difference φa when there is no error in the shape of the measured object B
(X, Y) is previously stored in the computer 55 as a system error, and after the system error φa (X, Y) is subtracted from the measured value of φa (X, Y), the equation (10) is obtained.
Is assigned to.

FIG. 3 is a block diagram of the second embodiment, in which tilt variation information of the object to be measured and the reference plane mirror, defocus variation information of the object to be measured, and rotation fluctuation information about the optical axis of the object to be measured. Etc. can be detected, and the same reference numerals as those in the first embodiment represent the same members. The device under test B is a cylindrical lens, and instead of the collimator lens 44, a cylindrical collimator lens 61 that generates a cylindrical wavefront is arranged.

Further, on the optical path in the direction of reflection of the beam splitter 49, the pinhole plate 6 having four pinholes 64b to 62e at an equal angle around the pinhole 62a at the center.
2 are arranged, and the light fluxes emitted from the pinholes 62a to 62e are received by the five photodetectors 63a to 63e, respectively. The outputs of the photodetectors 63a to 63e are connected to the phase meters 64a to 64e, respectively, and the outputs of the photodetector 63a are also connected to the phase meters 64b to 64e, respectively. Further, the output of the ID camera 50 is connected to the phase meter 64a. The outputs of the phase meters 64a to 64e are sent to the computer 55 via the buffer memory 54.
To the object to be measured B based on the output of the phase meter 64a.
Is obtained, and the measurement result is corrected based on the outputs of the phase meters 64b to 64e.

FIG. 4 is a front view of the image pickup device 50a of the ID camera 50 at the time of measurement. The interference fringe image P received here represents the phase of the cylindrical wavefront formed by the cylindrical collimator lens 61. Indicates the shape error of the object B to be measured directly. Further, in the figure, the reference fringe images Ra to Re received by the photodetectors 63a to 63e are also shown together with the interference fringe image P received by the image sensor 50a. These reference point images Ra to Re are pinhole plates 6
The two pinholes 62a to 62e extract the interference fringe image P.

When the center of the image sensor 50a is aligned with the optical axis by performing alignment, the photodetectors 63a to 63e are assigned addresses (0, 0) and (N / √) due to the geometrical conditions on the image sensor 50a. 2, N / √2), (N / √2,-
N / √2), (-N / √2, -N / √2), (-N / √2
2, the beat signal obtained from N / √2) will be detected.

The computer 55 two-dimensionally scans the image sensor 50a in the ID camera 50 by designating the address (X, Y), detects the measurement signal S for each pixel, and inputs it to the phase meter 64a. To do. In the phase meter 64a, the measurement signal of the address (X, Y) and the address (0,
0) and the phase difference φa (X, Y) with the reference signal R,
It is stored in the buffer memory 54. Furthermore, the computer 5
5 is the phase difference φa (X,
From Y), the shape of the measured object B is obtained as the wavefront aberration.

In the present embodiment, the measurement signal detected by the ID camera 50 when there is no error component of other optical elements such as the reference plane mirror 46 being an ideal plane and the object B to be measured has no shape error. The phase difference φa between S and the reference signal R becomes 0 for all addresses (X, Y). Therefore, the phase difference φa represents a deviation from the cylindrical wavefront formed by the cylindrical collimator lens 61, and directly represents an error in the shape of the object B to be measured.

Further, the phase meters 63b to 63e have a phase difference φa.
Simultaneously with the detection of (X, Y), or at a cycle sufficiently shorter than the cycle of mechanical fluctuation, the reference signal R obtained by the photodetector 62a and the beats obtained by the photodetectors 63b to 63e. The phase differences φab, φac, φad, and φae with the signal are detected, stored in the buffer memory 54, and stored in the computer 55.
At C, the phase correction amount C (X, Y) of the phase difference φa (X, Y)
Is being detected. This phase correction amount C (X, Y) is expressed by the following equation when the object to be measured B is a cylindrical lens and a term regarding the rotational fluctuation around the optical axis is added to the right side of equation (9). it can. C (X, Y) = a1 · X · dw / N + a2 · Y · dw / N + a3 · (X 2 + Y 2) dw 2 / N 2 + a4 · X · Y · dw 2 / N 2 ... (11)

Here, the first and second terms on the right side of the equation (11) are terms for correcting the relative displacement between the object to be measured B and the reference plane mirror 46, and the third term is the defocus fluctuation. The fourth term is a term for correcting fluctuations around the optical axis. The variable a1 is the object to be measured B and the reference plane mirror 46.
Is a phase difference corresponding to the amount of relative deviation in the X direction, and variable a2 is a phase difference corresponding to the amount of relative deviation between the object to be measured B and the reference plane mirror 46 in the Y direction, and variable a3 is a circle. A phase difference corresponding to the amount of deviation of the circumference of M in the normal direction,
a4 represents the phase difference in the radius direction of the circle M corresponding to the rotation around the optical axis.

On the other hand, φab is the address (0,0) and (N /
2 ^1/2 , N / 2 ^1/2 ) and φac is the phase difference between address (0, 0) and (N / 2 ^1/2 , -N / 2 ^1/2 ). , Φad are addresses (0, 0) and (-N / 2
^1/2 , -N / ^21/2 ), and φae is the phase difference between address (0,0) and (-N / ^21/2 , N / ^21/2 ). .

Therefore, when the phase difference φa (X, Y) is detected, these phase differences are calculated from φac (X, Y) to φae (X,
Y), the phase difference φab (X, Y) to φae (X, Y)
Can be expressed by a linear expression of variables a1 to a4 as in Expression (2),
When the variables a1 to a4 are represented by the phase differences φab to φac as in (8),
The phase correction amount C (X, Y) can be obtained from the following equation. C (X, Y) = √2 (φab + φac-φad-φae) X · dw / (4N) + √2 (φab-φac-φad + φae) Y · dw / (4N) + (φab + φac + φad + φae) · (X 2 + Y 2 ) Dw ² / (4N ² ) + (φab−φac + φad−φae) X · Y · dw ² / (2N ² ) ... (12)

Therefore, the true wavefront aberration φ (X, Y) based on the object to be measured B is given by the following equation. φ (X, Y) = φa (X, Y) -C (X, Y) (13)

The computer 55 calculates the wavefront aberration φ (X, Y) for each address (X, Y) according to the equations (12) and (13), and obtains the three-dimensional shape of the object B to be measured. . In addition,
Phase difference φa (X,
Y) is stored in the computer 55 in advance as a system error, and is substituted into the equation (13) after the system error φa (X, Y) is subtracted from the measured value of φa (X, Y).

[0057]

As described above, according to the present invention, even when the object to be measured is a spherical lens or a cylindrical lens, the inclination variation corresponding to the relative displacement amount caused by the displacement of the object to be measured, the reference plane mirror, or the like. In addition to the information, the defocus fluctuation information and the rotation fluctuation information about the optical axis are detected to correct the interference information, so that highly accurate measurement can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment.

FIG. 2 is a front view of an image pickup element of an ID camera.

FIG. 3 is a configuration diagram of a second embodiment.

FIG. 4 is a front view of an image pickup element of an ID camera.

FIG. 5 is a configuration diagram of a conventional example.

FIG. 6 is a front view of a pinhole plate.

FIG. 7 is a front view of an image pickup element of an ID camera.

[Explanation of symbols]

31 laser light source 33,49 Beam splitter 37, 42 Polarizing beam splitter 36 (λ / 2) plate 43, 45 (λ / 4) plate 46 reference plane mirror 47 Polarizer 51,62 Pinhole plate 52a-52d, 63a-63e Photodetector 53a-53d, 64a-64e Phase meter 54 buffer memory 55 Computer 61 Cylindrical lens

─────────────────────────────────────────────────── ─── Continued Front Page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01B 9/00-11/30 G01M 11/00-11/08

Claims (4)

(57) [Claims] 1. An irradiation unit for irradiating a measurement area of a measurement object with a coherent test light wave, and a reference light used as a reference when obtaining interference information with the test light wave reflected by the measurement area. A measuring device having interference means for interfering with each other and interference information detecting means for detecting interference information between the test light wave and the reference light wave, and measuring the shape of the object to be measured based on a signal from the interference information detecting means. In, while detecting the interference information, tilt variation information detection means for detecting the tilt variation information of the measured object, defocus variation information detection means for detecting the defocus variation information of the measured object, A rotation fluctuation information detecting unit that detects rotation fluctuation information about the optical axis of the object to be measured, and a correction unit that corrects the interference information based on the tilt fluctuation information, the defocus fluctuation information, and the rotation fluctuation information. Featuring Measuring device. 2. The test light wave and the reference light wave have different frequencies from each other, and the interference information detecting means includes first detecting means for detecting a beat signal and second detecting means, and the first detecting means. Detects the beat signals from all the measurement points in the measurement area, and the second detection means continuously detects the beat signals at a plurality of points not less than the same line in the measurement area. The interference information means is the first
The measuring device according to claim 1, wherein the change in the phase of the interference light is detected based on the mutual relationship between the beat signal obtained by the detecting means and the plurality of beat signals obtained by the second detecting means. . 3. When the object to be measured is a spherical lens, the second detecting means beats at least four or more points in the measuring area while the first detecting means detects the beat signal. The measuring device according to claim 2, wherein a signal is detected and recorded in a recording means, and the beat signal obtained by the first detecting means is corrected by the signal recorded in the recording means. 4. When the object to be measured is a cylindrical lens, the second detecting means beats at least five points or more in the measuring area while the first detecting means detects the beat signal. The measuring device according to claim 2, wherein the signal is detected and recorded in the recording means, and the beat signal obtained by the first detecting means is corrected based on the signal recorded in the recording means.