JPH0518857A - Fizeau interference measuring device applying phase deviation interference method - Google Patents

Abstract

PURPOSE:To measure interference with high accuracy by applying a phase deviation interference method to a Fizeau interference measuring device. CONSTITUTION:The phase shift data caused by the distance up to an optical axis of the intensity change of the interference pattern at each part in an interference region when a reference spherical surface 5 is vibrated in an optical axis direction is preliminarily calculated and, when an initial phase is calculated from intensity data becoming representation at every period when the intensity change data obtained at every part is divided into four periods, the correction factor based on the phase shift data is used to obtain an accurate initial phase.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a Fizeau interferometry method. The present invention is a highly reliable interferometric measurement capable of measuring the sphericity of each spherical surface that constitutes a recent high-performance optical system such as an ultra-high-resolution lens for printing a semiconductor integrated circuit with high accuracy of 1/100 of a wavelength. Can be applied well to

[0002]

2. Description of the Related Art Interferometers that utilize the phenomenon of light interference have been used for a long time to judge the quality of the shape of the spherical surface that constitutes an optical system. Supported by the development of electronics technology, recently it has become possible to utilize interferometers that are much more precise and reliable than ever before. A typical example is a technique called phase shift interferometry.

Interferometry before the development of phase shift interferometry is based on a static interference pattern between a surface to be measured and a reference surface which is a reference for comparison. However, it was extremely difficult to quantitatively determine the shape error of the entire surface to be measured, even though it was possible to roughly judge the quality. On the other hand, in the phase shift interferometry, when the optical path length between the measured surface and the reference surface is changed by a small amount, the change in the intensity (brightness) of the interference pattern reflects the shape error of the measured surface and causes interference. This is a technique for quantitatively obtaining the shape error of the entire surface to be measured by utilizing the fact that the timing slightly deviates at each position in the area.

FIGS. 4 and 5 show the optical arrangement of the main part of the interferometer when the phase shift interferometry is applied to the Twyman type and the Fizeau type which are commonly used as an interferometer at present. In both these figures, 3 is a beam splitter, 4 and 4'is a converging lens for converting a plane wave from a laser into a spherical wave, 5 and 5'is a reference surface which is a standard for shape measurement, 7 is a measured surface, and 8 is a measured surface. It is an image sensor surface for detecting the intensity of the interference pattern.

In the case of the Twyman interferometer shown in FIG. 4, a part of the plane wave incident from the left side of the figure is reflected by the beam splitter and further reflected by the flat reference surface 5 ', and then the beam splitter 3 is moved. It passes through and reaches the image sensor surface 8. Further, the incident plane wave that has passed through the beam splitter 3 is converted into a spherical wave by the converging lens 4 ', is further reflected by the measured spherical surface 7 arranged so as to be concentric with the spherical wave, and is again converged by the converging lens 4'. After being converted into a plane wave form by, the beam is reflected by the beam splitter 3 and reaches the image sensor surface 8. In this way, an interference pattern is formed on the image sensor due to the interference of the two wavefronts arriving on the image sensor.

On the other hand, in the case of the Fizeau interferometer shown in FIG. 5, the plane wave incident from the left side is reflected by the beam splitter 3.
After being converted into a spherical wave by the converging lens 4 after passing through, a part of it is reflected by the reference spherical surface 5 at the rear end of the converging lens which is configured so as to be concentric with the spherical wave, and the converging lens again. After being converted into a plane wave at 4, the beam is reflected by the beam splitter 3 and reaches the image sensor surface 8. Further, the spherical wave that has passed through the reference spherical surface 5 is reflected by the measured spherical surface 7 that is arranged concentrically with the spherical wave, passes through the reference spherical surface 5, and is converted into a plane wave shape by the converging lens 4. The beam is reflected by the beam splitter 3 and reaches the image sensor surface 8. In this way, a pattern is formed on the image sensor due to the interference of the two wavefronts reaching the image sensor surface.

In order to apply the phase shift interferometry to the interferometer as described above, it is necessary to change the optical path length between the reference surface and the spherical surface to be measured by about 1 wavelength, which is generally used. This is a method of slightly displacing the reference surface in the optical axis direction using a piezoelectric element or the like. When the optical path length between the reference surface and the measured spherical surface changes, the intensity I of the interference pattern at an arbitrary position on the image sensor changes sinusoidally. When the constant part in the changing value of I is a, the amplitude of the change is b, the initial phase of the change is φ, and the phase fluctuating with the displacement of the reference surface is x, the change of the value of the intensity I is generally. Can be written as

I = a + bcos (φ + x) (1) In both the Twyman interferometer and the Fizeau interferometer, on the optical axis, that is, in the central portion of the image sensor, the displacement of the reference plane is between δ and x. The following relation holds when the wavelength is λ.

[0009]

[Outside 6]

As shown in FIG. 4, in the case of the Twyman interferometer, since the reference surface is a plane, the change in the optical path length between the reference surface and the spherical surface to be measured due to the displacement δ in the optical axis direction changes in the interference region. It is the same everywhere, so the relationship (2) between δ and phase x holds not only on the optical axis but throughout the interference region. However, since the initial phase φ included in the right side of (1) differs depending on the position in the interference area due to the shape error of the measured spherical surface, the change in the intensity I of the interference pattern due to the displacement of δ changes. Depending on the position inside, the shapes are offset from each other in the δ direction. FIG. 6 shows this, and the lower part shows the relationship between δ and I at an arbitrary position outside the optical axis, for example, on the optical axis. Since (2) holds regardless of the position in the interference region, one cycle of change in I separated by two vertical lines, that is, the amount of δ change during the phase x changes by 2π is exactly the same. However, the shape of the change of I deviates from each other in the δ direction.

The basic procedure of the phase shift interferometry is that the image sensor detects a state where I changes at each position in the interference region with the shift δ of the reference surface, and from the result, the shape error of the measured spherical surface is detected. Initial phase φ at each position due to
Is a procedure for obtaining the value of. When the phase shift interferometry is applied to the Twyman interferometer, it is relatively easy to find the value of φ because the relationship of (2) is established over the entire interference region as described above, and various methods have already been used. Have been attempted, and the procedure has been publicly known (for example, Ap
plied Optics 13 No. 11 (197
4) p2693-2703, Photonics SP
ECTRA 22 No. 10 (1988) p169-
176, etc.). The following is a relatively simple method that has been used so far.

As shown in FIG. 7, a section in which I changes by one cycle due to the displacement δ of the reference surface (the displacement amount of x becomes 2π) is divided into four equal parts, and the first position 1 and three subsequent divisions are divided. detecting each position of the interference area values I ₁ ~I ₄ of I in position 2-4 by the image sensor. From these values, the value of φ at each position can be calculated as follows.

[0013]

[Outside 7]

[0014]

[Outside 8] Or

[0015]

[Outside 9] Or

[0016]

[Outside 10]

[0017]

As described above, there is no theoretically difficult problem in applying the phase-shifting interferometry to the Twyman interferometer, and the procedure for obtaining the value of the initial phase φ has already been known. There is. However, on the other hand, there is a problem in high-precision measurement, which is the original purpose of phase-shifting interferometry, for example, in an application in which the sphericity of a spherical surface is measured with an accuracy of 1/10 or less of the wavelength. As can be seen by looking at the optical arrangement of the Twyman interferometer shown in FIG. 4, an optical path in which the incident wavefront is reflected by the reference surface and reaches the image sensor surface, and an optical path in which the incident wavefront is reflected by the measured spherical surface and reaches the image sensor surface. Apart from that, the prism of the beam splitter and the converging lens are present in these separate optical paths. Therefore, the defect of such an optical element directly affects the interference pattern, and the effect is 1 / wavelength.
This is because it is extremely difficult to keep it at 10 or less.

On the other hand, in the optical arrangement of the Fizeau interferometer shown in FIG. 5, the reference surface and the measured spherical surface directly face each other without other inclusions, and the incident wavefront is reflected by the reference surface to form an image. The optical path reaching the sensor surface and the optical path reflected by the measured spherical surface and reaching the image sensor surface are common except for the space where the reference surface and the measured spherical surface directly face each other. Even if there are defects, the interference patterns are mutually canceled and have almost no effect. This means that the Fizeau interferometer is extremely advantageous for measuring the shape error of the measured spherical surface with high accuracy, and the application of the phase shift interferometry to it has already been actually carried out. And
In the case of measurement, the method of displacing the reference surface by a small amount in the optical axis direction is adopted as in the case of the Twyman interferometer. However, in the case of Fizeau interferometer,
Since the reference surface is generally a concave spherical surface except when the measured surface is a flat surface, the change in the optical path length between the reference surface and the measured spherical surface when it is displaced in the optical axis direction is not uniform over the entire surface. However, it tends to decrease with distance from the optical axis, and the degree thereof becomes more remarkable as the shape of the measured spherical surface becomes deeper, in other words, as the diameter becomes larger than the radius of curvature. Therefore, it is clear that ignoring this fact and obtaining the value of the initial phase φ in a manner similar to that performed for the Twyman interferometer will result in a systematic error in the result. If there were a feasible solution to this problem, it would have been possible to make very reliable and precise interferometric measurements, taking advantage of the Fizeau interferometer, but so far there has been no theoretical solution to this problem. No literature has been found to have been thoroughly examined, and there is no example that clarified what kind of treatment was actually performed by the Fizeau interferometer to which the phase displacement method was applied.

According to the present invention, when the phase shift interferometry is applied to the Fizeau interferometer, the amount of contribution of the shape error of the surface to be measured is determined from the change in the optical path length which is not uniform in the interference region and the accompanying change in the interference pattern. The purpose of this is to establish a procedure for accurately obtaining the interferometer, and thereby to provide a highly accurate interferometric measurement that fully utilizes the advantages of the Fizeau interferometer.

[0020]

In order to achieve the above-mentioned object, the present invention makes a light beam from a test spherical surface and a light beam from a reference spherical surface interfere with each other while vibrating at least one surface in the optical axis direction. In the Fizeau-type interference measurement method for measuring the intensity change of the interference pattern in the interference region, due to the distance from the optical axis of the intensity change at each point on the non-optical axis of the interference region when the surface vibration is performed in advance. A step of storing the phase shift information, a step of detecting the intensity change of the interference pattern on the optical axis interference pattern intensity change one cycle at each point, and a step of dividing the detected intensity change into a plurality of periods The process of detecting the intensity at the representative time point of each period or the integrated value of the intensity within each period, the intensity at the representative time point of each period or the integrated value of the intensity, and the stored phase shift information. , It is provided, comprising the steps of calculating the value of the initial phase of the intensity change of the interference pattern for each point.

The present invention also provides an interferometric measurement in a Fizeau interferometer using a phase shift interferometer of the type in which the intensity of the interference pattern in the entire interference region is changed by displacing the reference surface by a small amount in the optical axis direction. Prior to the above, the amount by which the phase of the intensity change of the interference pattern at the peripheral portion of the interference region is systematically delayed while the intensity of the interference pattern on the optical axis changes for one cycle due to the displacement of the reference surface in the direction of the optical axis, Measure or calculate the equivalent phase delay amount from the numerical value of the numerical aperture of the incident light corresponding to the peripheral edge of the interference region.When measuring the interference, the displacement in the optical axis direction of the reference surface The interval of one cycle of the intensity change of the interference pattern on the optical axis is 4
The intensity of the interference pattern at the first time point and the three subsequent time points, which are equally divided, or the integrated value of the intensity in each of the four divided intervals is used as an interference pattern provided with an image sensor for each part in the interference region. Simultaneously measured by the detection unit, the systematic delay amount of the intensity change of the interference pattern in the interference region peripheral portion, the intensity of the interference pattern at each time point obtained for each portion in the interference region or each of the intervals A calculation processing mechanism is provided for calculating the value of the initial phase of the intensity change of the interference pattern in each part of the interference region from the integrated value of the intensity.

[0022]

The principle of the first embodiment of the present invention will be described.

FIG. 1 shows the relationship between the displacement amount δ and the interference pattern intensity I when the phase shift interferometry is applied to the Fizeau interferometer and the reference spherical surface is displaced in the optical axis direction, as in FIG. The lower side of the figure shows an example of the state on the optical axis and the upper solid line in the figure at an arbitrary position outside the optical axis. As shown in this figure, when the reference surface is a spherical surface, the change in the optical path length between the reference spherical surface and the measured spherical surface with respect to the displacement amount δ is slightly reduced at the position outside the optical axis as compared with that on the optical axis. Occurs, and accordingly, the section of δ for changing one cycle of I extends by that amount. However, assuming that the change in the optical path length with δ is uniform throughout the interference region as in the case of the Twyman interferometer, and the initial state of one cycle of the change in I is the same, The relationship between I and δ at the outer position should be as shown by the upper broken line in FIG. On the other hand, the relationship of the change of I due to the displacement δ is the same as the point represented by (1) on the optical axis and the position off the optical axis, and it does not change on and off the optical axis (2). Only by the relation between δ and x of
Moreover, we want to find the initial phase φ at each position in the interference region.
Therefore, it is also possible to obtain the value of φ by a method similar to that performed by the Twyman interferometer by equally dividing a section of one cycle of the change in I due to the displacement δ into four equal parts for each position in the interference region. .

However, in this method, the point of time when the data is acquired from the image sensor is different depending on the position in the interference area, which makes the procedure extremely complicated. It is much easier to acquire the data from the image sensor at the same time for the entire interference area. Even in the case of the Fizeau interferometer, the relationship between the displacement δ and I of the reference plane on the optical axis matches that of the Twyman interferometer, so the time when data is simultaneously acquired for the entire interference region is the same as that of the Twyman interferometer on the optical axis. Let us consider a method of obtaining the values of the initial phase φ at each position in the interference region from the data thus obtained so as to match.

FIG. 2 is on the optical axis for measurement (lower side of the figure)
And the data outside the optical axis (upper side of the figure) are shown. NA is the distance from the optical axis at any position in the interference area
(Sine of the angle of inclination of the normal of the measured wavefront to the optical axis)
If the relation between the displacement δ of the reference spherical surface and the displacement x of the phase is expressed by, instead of (2),

[0026]

[Outside 11] Becomes From this, when one period of the change of I on the optical axis due to the displacement δ of the reference surface is divided into four equal parts, the amount of phase displacement within the one section is on the optical axis.

[0027]

[Outside 12] On the other hand, outside the optical axis

[0028]

[Outside 13] Can be expressed as This ε is as follows from the relationship of (5).

[0029]

[Outside 14] The value of ε can be obtained as follows.

The NA value corresponding to the periphery of the interference area is set to (N
A) When _max is set, the displacement amount δ ₁ of the reference spherical surface required to change the interference pattern intensity at the peripheral portion of the interference region by one cycle is set to x = 2π in (5).

[0031]

[Outside 15] On the other hand, since the displacement amount δ ₀ of the reference spherical surface required to change the interference pattern intensity on the optical axis for one cycle is λ / 2, the difference in the displacement amount of the reference spherical surface is

[0032]

[Outside 16] It is expressed by the relationship. From this relationship (NA) ² _max is

[0033]

[Outside 17] Can be written. Therefore, if the extension amount Δδ of the displacement amount of the reference spherical surface required to change the interference pattern intensity I for one cycle is measured on the optical axis, it corresponds to the peripheral edge of the interference region (N
A) The value of ² _max can be calculated by (7). On the other hand, when the coordinates of an arbitrary position in the interference area are represented by (x, y) with the position of the optical axis as the origin, the distance ρ from the optical axis is

[0034]

[Outside 18] Therefore, if ρ around the interference region is written as ρ _max , the value of NA corresponding to (x, y) is

[0035]

[Outside 19] Given in. This NA value may be substituted into (6) to find the value of ε at an arbitrary position within the interference region. As shown in FIG. 2, the values of I outside the optical axis at the time points 1, 2, 3, and 4 of the boundary obtained by equally dividing the interval in which I on the optical axis changes by one cycle by δ are I ₁ , respectively. If I ₂ , I ₃ , and I ₄ ,
These can be derived from (1) and are as follows. The value of _{I 1 = a + bcosφ I 2} = a + b (cosφsinε-sinφcosε) I 3 = a + b (-cosφcos2ε-sinφsin2ε) I 4 = a + b (-cosφsin3ε + sinφcos3ε) initial phase φ from these relationships are determined by the following.

[0036]

[Outside 20] Since ε = 0 on the optical axis, A ₀ = B ₀ = 2 in (10),
α ₀ = β ₀ = 0, and (10) coincides with (3) obtained for the Twyman interferometer. From this, it can be seen that (10) can be applied to the entire interference region including the optical axis of the Fizeau interferometer. This initial phase φ is set at each position (x,
By obtaining y), the optical path length information between the measured spherical surface and the reference spherical surface is calculated for the entire measured spherical surface.

Next, the principle of the second embodiment of the present invention will be described.

[0038]

[Outside 21] From these relationships, the value of the initial phase φ can be obtained using any of the following three methods.

[0039]

[Outside 22] Or

[0040]

[Outside 23] Or

[0041]

[Outside 24] Since ε = 0 on the optical axis, A ₁ = B ₁ = A ₂ = B ₂ =
2, A ₃ = B ₃ = 4; α = 1 = β ₁ = α ₂ = β ₂ = α ₃ = β ₃
= 0, and (11a), (11b), and (11c) are (4a) and (4) for the Twyman interferometer, respectively.
b) and (4c). From this (11a)
It can be seen that (11c) holds for the entire interference region including the optical axis of the Fizeau interferometer. Similar to the first embodiment,
By obtaining the initial phase φ for each position (x, y), the optical path length information between the measured spherical surface and the reference spherical surface is obtained for the entire measured spherical surface.

FIG. 3 shows the positional relationship of each part of the interferometer when the phase shift interferometry is applied to the Fizeau interferometer according to the principles of the first and second embodiments of the present invention. Is a beam expander for converting the light from the laser into a plane wave having a sufficient diameter, 3 is a beam splitter, 4 is a converging lens for converting the plane wave from the laser into a spherical wave, and 5 is the final surface of the converging lens 4 at the same time. A surface also serving as a reference spherical surface, 6 is an actuator formed of a piezoelectric element or the like for displacing the convergent lens 4 including the reference spherical surface 5 in the optical axis direction by a small amount, and 7 is arranged concentrically with the reference spherical surface 5. The measured spherical surface, 8 is an image detection unit that detects information on the interference pattern at each position in the interference region, 9 is a control unit that controls the functions of the actuator 6, the image detection unit 8, and the like. The calculation processing unit for calculating the value of the initial phase φ in the interference region in each position from the information of the interference pattern sent from the image detection unit 8, and shall have a monitor for interference patterns observed. The measurement by the phase shift interferometry shall be performed as follows.

First, after the measured spherical surface 7 is installed at a predetermined position, the actuator 6 displaces the converging lens 4 including the reference spherical surface 5 in the optical axis direction, and the intensity I of the interference pattern detected by the image detecting section 8 is detected. The displacement amount δ of the converging lens required to change by one cycle is increased from the optical axis on the optical axis at the peripheral edge of the interference region, and measured (7) to correspond to the peripheral edge of the interference region (NA). Determine the value of _max . Also,
In parallel with this, the displacement amount δ of the converging lens corresponding to the boundary that divides a period of one cycle of change of I on the optical axis into four equal parts is confirmed. Next, the converging lens is displaced by the actuator 6 by one cycle of the intensity of the interference pattern on the optical axis, and the interval of displacement is equally divided into four parts, that is, four points at the boundary, that is, marks 1 to 4 in FIG. Value of I at time I ₁
~ I ₄ or 4

[0044]

[Outside 25] Detection is performed for each position (x, y) on the surface. The calculation processing unit 10 calculates the value of (NA) for each position (x, y) in the interference region from the value of (NA) _max already obtained by (8) and (9), and further calculates it by (6 ) To obtain the value of ε. Then, in the image detection unit 8, I ₁ ~
When the value of I ₄ is to be detected, those values at each (x, y) position and the value of ε thus obtained are substituted into (10) to obtain the value of the initial phase φ. To calculate. Also,
If the displacement of the converging lens is divided into four equal parts, the integral value of I in four intervals

[0045]

[Outside 26] Is detected by the image detection unit 8, those values at each (x, y) position and the value of ε are substituted into any of (11a) to (11c). Then, the value of the initial phase φ is calculated.

Finally, the amount of change in the optical path length between the reference spherical surface and the measured spherical surface at each point on the measured spherical surface corresponding to each position (x, y) in the interference region relative to that on the optical axis. Δ
(OPD) can be easily calculated by the following equation from the amount Δφ of deviation of the value of the initial phase φ at each position (x, y) thus obtained from that on the optical axis.

[0047]

[Outside 27]

In the above embodiment, the value of (NA) _max corresponding to the peripheral portion of the interference area is set so that one cycle of the change in the interference pattern intensity due to the displacement of the reference spherical surface in the optical axis direction is on the optical axis and the peripheral portion of the interference area. The method of measuring the amount of deviation and calculating from the amount of deviation is adopted, but the following method can be considered as an alternative method. That is, a converging lens including a reference spherical surface is provided with a diaphragm used in a photographic lens, or a mechanism having an equivalent function, and is operated (the size of the diaphragm is set, that is, (NA) _max is set). As a result, the peripheral portion of the interference region can be confirmed on the monitor, and information regarding the value of (NA) _max at that time is sent to the calculation processing unit via the control unit 9.

[0049]

As described above, according to the present invention, it is possible to detect the surface shape error with the highest accuracy and reliability as far as currently conceivable, and it is possible to detect the optical system at the leading edge of the technology such as a lens for a stepper. It should help further improve performance.

[Brief description of drawings]

FIG. 1 illustrates the relationship between the displacement δ of a reference spherical surface and the interference pattern intensity I on the optical axis when a phase shift interferometer is applied to a Fizeau interferometer as a principle explanation of the first and second embodiments of the present invention. ) And an off-axis (upper) axis.

FIG. 2 illustrates a relationship of data acquisition for detecting an initial phase of an interference pattern intensity change when a phase shift interferometer is applied to a Fizeau interferometer as a principle explanation of the first and second embodiments of the present invention. It is a figure shown about an optical axis (bottom) and an optical axis off (up).

FIG. 3 is a diagram showing the overall arrangement of an interferometer based on the first and second embodiments of the present invention.

FIG. 4 is a diagram showing a main part of a Twyman interferometer to which the phase shift interferometry is applied.

FIG. 5 is a diagram showing a main part of a Fizeau interferometer to which the phase shift interferometry is applied.

FIG. 6 is a diagram showing the relationship between the displacement δ of the reference surface and the interference pattern intensity I when the phase shift interferometry is applied to the Twyman interferometer on the optical axis (bottom) and off the optical axis (top).

FIG. 7 is a diagram showing a relationship of data acquisition for detecting an initial phase of an interference pattern intensity change by applying a phase shift interferometry to a Twyman interferometer.

[Explanation of symbols]

1 laser 2 beam expander 3 beam splitter 4,4 'convergent lens 5,5 'reference plane Actuator composed of 6 piezoelectric elements 7 Measured sphere 8 Image detector or image sensor surface 9 control unit 10 Calculation unit with monitor

Claims (4)

[Claims] 1. A Fizeau type for measuring a change in intensity of an interference pattern in an interference region by causing a light beam from a test spherical surface and a light beam from a reference spherical surface to interfere with each other while vibrating at least one surface in the optical axis direction. In the interference measurement method, a step of storing phase shift information due to the distance from the optical axis of the intensity change at each point on the non-optical axis of the interference region when the surface vibration is performed in advance, and the light at each point On-axis interference pattern intensity change The process of detecting the intensity change of the interference pattern within one cycle, and the intensity at the representative time point of each period or the intensity within each period when the detected intensity change is divided into multiple periods. Of the intensity change of the interference pattern at each point based on the process of detecting the integral value of the intensity, the intensity or the intensity integral value at the representative time point for each period, and the stored phase shift information. Fizeau interferometric measuring method characterized by comprising the step of calculating the value of the phase, the. 2. The detected intensity change is divided into four periods, the representative time point is a boundary time point of each period, and the detected strength at the boundary time point of each period is I ₁ , respectively.
Let I ₂ , I ₃ , and I _4, and let ε be the phase shift within each period due to the distance from the optical axis of the intensity change at the measured point, then the initial phase φ is However, the Fizeau interference measuring method according to claim 1, wherein it is obtained from A ₀ = 1 + cos 2 ε B ₀ = cos ε + cos 3 ε α ₀ = sin 2 ε β ₀ = sin β + sin 3 ε. 3. The detected change in intensity is divided into four periods, and the integrated value of the detected intensity in each period is calculated as And the phase shift within each period due to the distance from the optical axis of the intensity change at the measured point is ε, the initial phase φ is However, A ₁ = 2 cos ε-sin 2 ε B ₁ = 2 cos 2 ε + sin ε-sin 3 ε α ₁ = −1 + cos 2 ε + 2 sin ε β ₁ = 2 sin 2 ε + cos 3 ε-cos ε or [external 4] However, A ₂ = 2cos3ε + sin2ε−sin4ε B ₂ = 1 + cos4ε−sinε + sin3ε α ₂ = 2sin3ε + cos4ε−cos2εβ ₂ = sin4ε + cosε−cos3ε or [External 5] However, the Fizeau interference measurement method according to claim 1, wherein A ₃ = 2 cos ε + 2 cos ₃ ε-sin 4 ε B ₃ = 1 + 2 cos 2 ε + cos 4 ε α ₃ = −1 + cos 4 ε + 2 sin ε + 2 sin ₃ ε β ₃ = 2 sin 2 ε + sin 4 ε. 4. A Fizeau interferometer using a phase-shifting interferometer of the type in which the intensity of an interference pattern in the entire interference region is changed by displacing a reference surface by a small amount in the optical axis direction, prior to the interference measurement. The amount by which the phase of the intensity change of the interference pattern in the peripheral area of the interference region is systematically delayed while the intensity of the interference pattern on the optical axis changes for one cycle due to the displacement of the reference surface in the optical axis direction, or Or the equivalent phase delay is calculated from the numerical value of the numerical aperture of the incident light corresponding to the peripheral part of the interference region, and during the interference measurement, on the optical axis due to the displacement of the reference plane in the optical axis direction. The interval of one cycle of the intensity change of the interference pattern is divided into four equal parts, and the intensity of the interference pattern at the first time point and three subsequent time points, or the integrated value of the intensities in each of the four divided time intervals, Within the area Simultaneously measuring each part with an interference pattern detection part equipped with an image sensor, the systematic delay amount of the intensity change of the interference pattern at the peripheral part of the interference region, and the time points obtained for each part in the interference region. 2. The Fizeau interferometer according to claim 1, further comprising a calculation processing mechanism for calculating a value of an initial phase of the intensity change of the interference pattern in each part of the interference region from the intensity of the interference pattern or the integrated value of the intensity of each section.