JP2002013907A - Plane shape measuring method for phase-shift interference fringe simultaneous photographing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plane shape measuring method capable of providing a phase-shift interference fringe image that can be analyzed with high accuracy even if biases and amplitudes are different from each other at various points in observation areas of three branch phase-shift interference fringes for a phase- shift interference fringe simultaneous photographing device. SOLUTION: The biases and amplitudes of the branch phase-shift interference fringes and reference light observed for each branch are previously measured at various points in the observation areas. By using the biases and amplitudes and reference light image data acquired by the measurement, luminance conversion is given to branch phase-shift interference fringe image data acquired in succeeding measurement of tested surfaces to perform matching of the biases and amplitudes by a point-by-point basis in the observation areas, thereby sharply increasing the accuracy of a phase-shift interference fringe simultaneous measuring device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention divides an original light beam in which reflected light from a test surface and a reference surface is optically free from interference into a plurality of branched original light beams, each of which is different from a branched original light beam. The present invention relates to a phase shift interference fringe simultaneous measurement apparatus that performs simultaneous imaging with a plurality of imaging devices by giving a fixed optical phase difference and causing interference.

[0002]

2. Description of the Related Art Conventionally, a phase shift interference fringe simultaneous measuring apparatus as shown in FIG. 1 has been proposed by the present applicant in Japanese Patent Application No. 11-1368.
No. 31 has been proposed. That is, in the simultaneous phase shift interference fringe measuring apparatus, the laser beam from the laser light source 1 is expanded in beam diameter by the lens 2, passes through the beam splitter 3, and is converted into a parallel beam by the collimator lens 4. The parallel light flux transmits the reference light reflected by the reference surface 5 and the sample light transmitted through the reference surface 5 and the quarter-wave plate 6 and reflected by the test surface 7. Is orthogonal linearly polarized light and is optically free from interference.

Further, the reference light and the sample light reflected by the beam splitter 3 are turned into circularly polarized light states having different rotation directions from each other by a ８ wavelength plate 8 and are divided into three branched light beams by a trispectral prism 9. Polarizing plates 10 to 12 are arranged on the optical path of each branching light beam, the transmission axis angle of the polarizing plate is set in a plane substantially orthogonal to the optical axis, and a branch having a fixed optical phase difference is provided. Phase shift interference fringes occur, and these branched phase shift interference fringes are captured by the imaging devices 13 to 1.
5 are imaged simultaneously.

[0004]

That is, in this phase shift interference fringe simultaneous measurement apparatus, a branched phase shift interference fringe necessary for measurement is given by setting the exact angle of the transmission axis of the polarizing plates 10 to 12. However, in order to measure the undulating shape of the surface to be measured with high accuracy in this apparatus, it is premised that the bias and the amplitude between the three branched phase-shift interference fringes are equal at each point in the observation region. However, the bias and amplitude of the three branched phase-shift interference fringes due to the divisional intensity error in the three-spectrum prism 9 and the elliptically polarized transmitted light due to the error in setting the low-speed axis of the quarter-wave plate 8,
In practice, they will be different. For this reason, conventionally,
Measures have been taken to calculate a representative value of the bias and the amplitude from the branched phase-shift interference fringe image and correct the mutual difference. However, it is actually difficult to make the optical elements intervening on the branching optical path act uniformly, and in reality, the values of the bias and amplitude between the branching phase shift interference fringes are different at each point in the observation region. In addition, the method of uniformly correcting with a representative value has a problem that a variation in bias and amplitude remains in one screen after the correction.

An object of the present invention is to solve the above-described problem of the phase shift interference fringe simultaneous imaging apparatus as described above, and even if the bias and amplitude at each point in the observation region of the three branched phase shift interference fringes are different from each other. Another object of the present invention is to provide a planar shape measuring method capable of obtaining a phase shift interference fringe image which can be analyzed with high accuracy.

[0006]

In order to achieve this object, the present invention provides a method in which a bias and an amplitude value of a branched phase-shifted interference fringe and a reference light observed for each branch are previously determined at each point in an observation area. Measured, using the bias and amplitude values obtained by the measurement and the reference light image data, apply brightness conversion to the branched phase shift interference fringe image data obtained at the The present invention proposes that the simultaneous measurement of the phase shift interference fringe can be greatly improved by performing the matching for each point in the observation area. That is, in the present invention, the reference surface and the test surface are irradiated with the coherent light beam from the laser light source, and the reference light and the sample light, which are the reflected light from the reference surface and the test surface, are polarized. An observation optical system that generates an original light beam in an optically non-interfering state by intersecting the original light beam through an optical element and splitting the original light beam into a plurality of branched original light beams. Generate a plurality of branched phase-shift interference fringes, each of which has a different fixed optical phase difference via a polarizing optical element, and one position in the observation range of the surface to be measured is in each of the branch observation coordinate systems. The positions are aligned so as to be the same position, image data corresponding to these interference fringes is acquired by an imaging device provided for each branch light beam, and the plane undulation shape of the observation range of the surface to be inspected is phase-shifted. Numeric using In the simultaneous phase shift interference fringe imaging apparatus to be reproduced as data, the phase for each branch obtained by each imaging apparatus when a relative optical phase difference is separately provided between the reference light and the sample light. The bias and amplitude of each branched original light beam calculated from the shift interference fringe image data and the branch reference light image data obtained for each branched original light beam in the absence of the sample light are used to measure the planar undulation shape. Phase-shift interference fringes that perform brightness conversion of phase-shift interference fringe image data for each branch, match and adjust the bias and amplitude at each point in the observation area, and calculate the phase of each point of the interference fringe using the phase shift method. A planar shape measurement method in a simultaneous imaging device is proposed.

In the following description of a preferred embodiment of the present invention, 1) when a relative optical phase difference is separately provided between the reference light and the sample light, the wavelength of the laser light source is changed little by little. 2) a method of generating a relative optical phase difference between the reference light and the sample light by providing a relative optical phase difference between the reference light and the sample light. The method of generating the optical phase difference by slightly translating the optical axis along the optical axis, 3) When separately providing a relative optical phase difference between the reference light and the sample light, A non-reflective transmissive body having a refractive index greater than 1 in an optical path between a reference surface and the test surface,
A method of generating the optical phase difference by inserting at least one parallel plate having a different thickness from each other.4) When separately providing a relative optical phase difference between the reference light and the sample light, A non-reflective transmissive body having a refractive index greater than 1 in an optical path between the reference surface and the test surface,
A method in which an optical wedge whose two surfaces facing the reference surface and the test surface are not parallel is inserted, and the optical wedge is moved in the wedge direction in a plane substantially perpendicular to the optical axis to generate the optical phase difference; When separately providing a relative optical phase difference between the reference light and the sample light, a liquid crystal is arranged between the reference surface and the surface to be measured, and the refractive index is controlled by electric control of the liquid crystal. Variable, to generate a predetermined optical phase difference,

In the description of the embodiment of the present invention, 1) the difference between the bias obtained for each point and another point of the amplitude is determined by the bias which is arranged for each set of points within an allowable range. 2) The simple average, median or square mean value obtained from the bias and amplitude values obtained for each point is used as a representative value of the bias and amplitude at the position of each point. 3) a laser light source that can change the wavelength little by little, the reference surface or the object that can be translated little by little along the optical axis, for realizing each of the planar shape measurement methods described above. An inspection surface, a non-reflective transmissive parallel plate having a refractive index greater than 1 and located in an optical path between the reference surface and the test surface, and an optical path between the reference surface and the test surface Has a refractive index greater than 1 and moves in the wedge direction Kill optical wedge, it is also described phase shift interference fringe simultaneous imaging device incorporated a liquid crystal capable of changing the refractive index at the location to and electrically controlling the optical path between the reference surface and the test surface.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The plane shape measuring method according to the present invention uses a phase shift interference fringe simultaneous imaging device shown in FIG. The light is measured in advance at each point in the observation area, and the values of the bias and amplitude obtained by the measurement and the reference light image data are used to convert the branched phase shift interference fringe image data obtained at the time of the subsequent measurement of the test surface. On the other hand, it is characterized in that brightness conversion is performed and bias and amplitude matching is performed for each point in the observation region.

More specifically, the plane shape measuring method of the present invention will be described. When calculating the undulating shape of a test surface from three interference fringes using the phase shift method, the three interference fringes are expressed by the following equations, respectively. In general, φ (x, y) corresponding to the undulating shape of the test surface is calculated.

(Equation 1) Here, I ₁ (x, y), I ₂ (x, y), I ₃ (x, y)
y) is luminance information measured by an imaging device such as a video camera, B (x, y) and A (x, y) are bias and amplitude of each interference fringe, and α (x, y) and β ( (x, y) represents a phase shift amount intentionally added by the interferometer.

When the surface 7 to be inspected is observed by the simultaneous phase shift interference fringe measuring device shown in FIG. 1, the branched phase shift interference fringes obtained by the imaging devices 13 to 15 are also expressed by (1-1) and (1- 2
Ideally, it is expressed in the same way as (Expression) and (1-3 Expression).
However, in the phase shift interference fringe simultaneous imaging apparatus, even if the phase shift amounts α (x, y) and β (x, y) are given as planned, the 波長 wavelength plate 6 used for generating circularly polarized light is used. , 8, the bias and the amplitude between the branched phase-shift interference fringes are different from each other due to the low-speed axis setting error of 3 and the beam splitting error of the three-segment prism. Further, due to the non-uniformity of the reflectance and transmittance of the interferometer components, the bias and amplitude of the corresponding points between the three interference fringe images on arbitrary x and y coordinates are x and y. Naturally, unless measures are taken against these problems, a large error will occur at the time of shape calculation.

Therefore, in the present invention, luminance information I ₁ (x, y), I ₂ (x, y), and I ₃ (x, y) of _three interference fringes are provided.
Is subjected to luminance conversion, and the adjustment of the bias and amplitude matching between the branched phase-shift interference fringes is performed at each of the x and y points, and the phase shift amount α (x, y) given systematically, β
(X, y) is used to calculate φ (x, y). A specific method will be described below.

In consideration of the above-described problems, the interference fringes obtained by the imaging devices 13 to 15 of the phase shift interference fringe simultaneous imaging device are expressed by the following equations (2-1) to (2-3), respectively. expressed.

[0014]

(Equation 2)

When an optical phase difference δ _i is separately given between the reference light and the sample light, the obtained phase shift interference fringes for each branch are expressed by the following equations (3-1) to (3-3). Expression).

(Equation 3)

When δ _i is arbitrarily changed and three or more branch phase-shift interference fringes are obtained for each branch, the bias and amplitude for each branch can be calculated. Here, as one calculation method example, δ _i is a value δ _i = i2π / N that equally divides one period of interference fringe phase 2π; i = 1, 2, 3,.
When N is set, the bias and amplitude for each branch are calculated by the following calculation to obtain the following equations (4-1) to (4).
-3) and (5-1) to (5-3).

[0017]

(Equation 4)

The obtained B ₁ (x, y), B ₂
(X, y), B ₃ (x, y), A ₁ (x, y), A ₂
(X, y) and A ₃ (x, y) are values when measuring the bias and amplitude matching adjustment test surface S, and the reference light and the sample light are a (x, y) and b, respectively. (X, y),
The reference light and the sample light reaching the imaging devices 13 to 15 arranged for each branch are represented by a ₁ (x, y), a ₂ (x, y), a ₃
(X, y), b ₁ (x, y), b ₂ (x, y), b ₃
(X, y) (hereinafter, the dimensions of x and y are omitted and simplified). Therefore, the relationship between the bias, amplitude, reference light, and sample light for each branch is

(Equation 5) It is represented by

Next, when measuring different test surfaces T, brightness conversion is performed on the branched phase-shift interference fringe image using the previously calculated bias and amplitude values, and the bias and amplitude matching adjustment is performed. A method of calculating the undulating shape of the test surface T will be described. FIG. 2A shows a reflected light intensity model input to the imaging device when measuring the bias and amplitude matching adjustment target surface S, and FIG. 2B shows an input to the imaging device when measuring the target surface T. The respective reflected light intensity models are shown below.

In FIGS. 2A and 2B, assuming that the sample light b ′ and b at the time of measuring the surface T to be inspected have a relationship of b ′ = γb, the three imaging devices 13 to 15 The arriving sample lights are b ′ ₁ = γb ₁ , b ′ ₂ = γb ₂ , b ′ _{3, respectively.}
= Γb ₃ can be considered to be affected at a similar rate. Considering these, the biases B ₁ ′, B ₂ ′, B ₃ ′ and the amplitude A
₁ ', A _2', bias is obtained previously and A ₃ 'B
The relations between ₁ , B ₂ , B ₃ and the amplitudes A ₁ , A ₂ , A ₃ are expressed by the following equations (8-1) to (8-3) and (9-1) to (9-
3).

(Equation 6)

Therefore, the three branched phase-shift interference fringes obtained at the time of observing the test surface T are respectively

(Equation 7) Will be represented by

A in formulas (10-1) to (10-3)
₁ , a ₂ , and a ₃ are reference light intensities obtained when the sample light is shielded, and are constant values over time irrespective of the test surface. B ₁ , b ₂ , and b ₃ are B ₁ obtained from the test surface S for adjusting the bias and amplitude with a ₁ , a ₂ , and a _3.
It can be calculated from the relationships of (Equation 6-1) to (Equation 7-3) of ₁ , B ₂ and B ₃ .

The calculation of φ using the three equations (10-1) to (10-3) will be described below.
From -a ₁ ,

(Equation 8) (10-2 type) from -a _2,

(Equation 9) From (10-3 type) -a _3,

(Equation 10) Is obtained.

Then, (Equations 11-1) to (11-3)
From

[Equation 11] Is obtained.

The determinant is

(Equation 12) For example, when α = π / 2 and β = π,% 1 ≠ 0
Can be solved for φ.

Therefore, the equation (12) can be rewritten as the following equation.

(Equation 13) Becomes

Therefore, the phase φ is

[Equation 14] Which is calculated after the bias and amplitude differences between the branched phase-shifted interference fringes have been resolved at each point in the x, y plane in the observation region. It is a calculation result of the undulating shape of the test surface.

Next, a method for separately providing an optical phase difference between the reference light and the sample light in order to measure the bias and the amplitude of the branched phase shift interference fringes will be described. The interference fringe obtained from the imaging device 13 when the distance of the test surface 7 to the reference surface 5 is d (x, y) is expressed by the equation (1-1) described above.

(Equation 15) Therefore, it is expressed by the following equation.

(Equation 16) I (x, y) is the interference fringe intensity, B (x, y), A (x, y)
y) represents the bias and amplitude, respectively, and λ represents the wavelength of the laser light source 1.

Here, the interference fringe when the wavelength λ is changed by a small amount Δλ _i is

[Equation 17] here,

(Equation 18) Because

[Equation 19] It is represented by

Similarly, the interference fringes obtained by the imaging devices 14 and 15 are

(Equation 20)

## EQU1 ## That is, the amount corresponding to δ _i = C · Δλ _i and / or the wavelength of the laser light source 1 is set to Δλ
_By changing only _i , an optical phase difference can be separately added to the reference light and the sample light. Then, from a plurality of phase-shift interference fringe images obtained for each branch, (Equations 4-1) to (4-3)
By performing the operations shown in (Equation 5-1) to (Equation 5-3), the bias and amplitude of each branched phase shift interference fringe can be calculated for each of the x and y points.

Further, in providing a reference beam and a sample beam optical phase difference separately, as shown in FIGS. 3 and 4, also be [Delta] d _i translating the reference surface or the test surface in the optical axis direction, each The bias and amplitude of the branched phase-shift interference fringes can be calculated for each point of x and y. The branch phase shift interference fringe at that time is expressed by the following equation.

(Equation 21)

That is, (Equations 18-1) to (18-3)
As is clear from Equivalent when given a displacement amount [Delta] d _i which, from a plurality of phase shift interference fringe obtained for each minute EdaHara flux to (4-1
By performing the calculations shown in Expressions (4) to (4-2) and (5-1) to (5-3), the bias and amplitude of each branch phase shift interference fringe can be changed by x and y. It can be calculated for each point.

In order to separately provide an optical phase difference between the reference light and the sample light, the reference surface 5 is provided on the optical path between the reference surface 5 and the test surface 7 with a non-reflective transmissive member having a refractive index larger than 1 and having a different thickness. Even if a parallel plate is inserted, the fixed optical phase difference between the branched phase shift interference fringes can be measured.

[0035] For example, the parallel thickness of l _1, using a parallel plates 16 and 17 of l _{2, 1} a state not inserted parallel plates 16 and 17 [delta] thickness l ₁ in the refractive index n as shown in FIG. 5 When the insertion of the plate 16 is δ _{2 and} the insertion of the parallel plate 17 having a thickness l ₂ is δ ₃ , or as shown in FIG. 6, the parallel plates 18 having the same refractive index n ₁ and n ₂ and the same thickness l, 19, the state in which the parallel plates 18 and 19 are not inserted is set as δ ₁ when the parallel plate 18 with the refractive index n ₁ is inserted and δ ₂ when the parallel plate 19 with the refractive index n ₂ is inserted as δ ₃ . An optical phase difference can be separately given to the reference light and the sample light, and the bias and amplitude of the branched phase shift interference fringes can be calculated for each of x and y points.

In addition, when an optical phase difference is separately provided between the reference light and the sample light, as shown in FIG. 7, an anti-reflection having an index of refraction greater than 1 is provided in an optical path between the reference surface and the test surface. An optical wedge 7 which is a transmitting body and whose two surfaces facing the reference surface and the test surface are not parallel is inserted, and the optical wedge 7 is moved in the wedge direction in a plane substantially orthogonal to the optical axis, and each branch phase shift is performed. It is also possible to calculate the bias and amplitude of the interference fringes for each of the x and y points.

Further, as shown in FIG. 8, the liquid crystal 21 is inserted between the reference surface and the surface to be inspected, and the refractive index of the liquid crystal 21 is varied by electric control such as voltage by the control device 22 to obtain δ ₁ ,
Even if an optical phase difference corresponding to δ ₂ and δ ₃ is generated, it is possible to calculate the bias and amplitude of each of the branched phase-shift interference fringes for each of the x and y points.

Of course, the bias and amplitude B ₁ of the phase shift interference fringe of each branched original light beam obtained by the method described above.
(X, y), B ₂ (x, y), B ₃ (x, y), A ₁
(X, y), A ₂ (x, y), and A ₃ (x, y) may be used as they are for adjusting the bias and amplitude matching of the branched phase shift interference fringes by the luminance conversion.

[0039] Referring to a method of data processing more easily, 9 B ₁ (x, y) _{1-dimensional} data B ₁ (x, y ₁₎ for y ₁ with the data of which represent, The graph shows that B ₁ (x, y ₁ ) is the position x in the observation area.
Means different values for. In FIG. 9, in the present invention, a certain allowable range t is set for B ₁ (X, y ₁ ), numerical data groups within the range are collectively arranged and replaced with a representative value, and B ₁ ′ A data string as shown in (x, y ₁ ) is created. X, y
And replaces the data group in an area within a certain allowable range t with a representative value. Also, B ₂
(X, y), B ₃ (x, y), A ₁ (x, y), A ₂
The same processing is performed on (x, y) and A ₃ (x, y), and B ₂ ′ (x, y), B ₃ ′ (x, y), A ₁ ′
(X, y), A ₂ ′ (x, y), and A ₃ ′ (x, y) are created. B ₁ '(x, y), B ₂ ' (x, y), B ₃ '
(X, y), A ₁ '(x, y), A ₂ ' (x, y), A
_{By using 3} '(x, y), it is possible to save memory capacity by reducing the number of parameters held in the computer. Further, as shown in FIG. 10, B ₁ (x, y),
B ₂ (x, y), B ₃ (x, y), A ₁ (x, y), A
₂ (x, y) and A ₃ (x, y) are calculated by simple average or median B
₁ ′, B ₂ ′, B ₃ ′, A ₁ ′, A ₂ ′, A ₃ ′, or as shown in FIG. 11, B ₁ ′ (x, y) calculated from the root mean square, B ₂ '(x, y), B
_{3 '(x, y),} A 1' (x, y), A 2 '(x,
If y) and A ₃ ′ (x, y) are used, more memory capacity can be saved when calculating the undulating shape of the surface to be measured by the plane shape measuring device.

[0040]

As is apparent from the above description, according to the present invention, for each branch, the bias and amplitude of the branched phase-shifted interference fringes obtained from different distribution states are measured in advance, and the subsequent test is performed. The bias and amplitude of the branched phase shift interference fringes obtained during surface measurement are subjected to brightness conversion at each of the x and y points in the observation area to perform matching adjustment, and calculation of the undulating shape of the test significantly improves accuracy. Can be realized.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an optical system of a phase shift interference fringe simultaneous imaging apparatus according to the present invention.

FIGS. 2A and 2B are comparison models of the intensity of reflected light input to the imaging device when measuring the surfaces S and T to be measured.

FIG. 3 is a diagram illustrating a first example of the same phase shift interference fringe simultaneous imaging apparatus.
FIG. 4 is an explanatory diagram of an optical phase difference providing means.

FIG. 4 shows a second example of the same phase shift interference fringe simultaneous imaging apparatus.
FIG. 4 is an explanatory diagram of an optical phase difference providing means.

FIG. 5 is a diagram illustrating a third example of the same phase shift interference fringe simultaneous imaging apparatus.
FIG. 4 is an explanatory diagram of an optical phase difference providing means.

FIG. 6 shows a fourth example of the same phase shift interference fringe simultaneous imaging apparatus.
FIG. 4 is an explanatory diagram of an optical phase difference providing means.

FIG. 7 shows a fifth embodiment of the same phase shift interference fringe simultaneous imaging apparatus.
FIG. 4 is an explanatory diagram of an optical phase difference providing means.

FIG. 8 shows a sixth embodiment of the same phase shift interference fringe simultaneous imaging apparatus.
FIG. 4 is an explanatory diagram of an optical phase difference providing means.

FIG. 9 is an explanatory diagram of a method of calculating a bias and an amplitude of an interference fringe for each branch according to the present invention.

FIG. 10 is an explanatory diagram of a method of calculating the bias and amplitude of interference fringes for each branch by simple averaging.

FIG. 11 is an explanatory diagram of a method of calculating a bias and an amplitude of an interference fringe for each branch by a root mean square.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Lens 3 Beam splitter 4 Collimator lens 5 Reference surface 6 1/4 wavelength plate 7 Test surface 8 1/4 wavelength plate 9 3 Dispersion prism 10-12 Polarization plate 13-15 Imaging device 16-19 Parallel plate 20 Optical wedge 21 Liquid crystal 22 Controller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F064 AA09 FF01 GG13 GG22 GG32 GG38 GG44 GG52 GG53 HH03 HH08 JJ01 2F065 AA53 BB05 DD07 EE00 FF49 FF51 FF61 GG04 GG23 JJ03 JJ26 LL00 LL04 LL00 LL04 LL04 LL04 LL00

Claims (9)

[Claims] 1. A reference surface and a test surface are irradiated with a coherent light beam from a laser light source, and polarization surfaces of a reference light and a sample light, which are reflected light from the reference surface and the test surface, are polarized by a polarizing optical element. By interposing them at right angles to each other,
An observation optical system that generates an original light beam in an optically non-interfering state; and a divided stationary light beam that is divided into a plurality of branched original light beams by dividing the original light beam into a plurality of divided original light beams via a polarizing optical element. A plurality of branched phase-shifted interference fringes having an optical phase difference are generated, and the positions are aligned so that one position in the observation range of the surface to be inspected becomes the same position in each branch observation coordinate system. A phase shift interference fringe that acquires image data corresponding to these interference fringes with an imaging device provided for each branch light beam, and reproduces a plane undulation shape of the observation range of the test surface as numerical data using a phase shift method. In the simultaneous imaging device, when a relative optical phase difference is separately provided between the reference light and the sample light, the amount calculated from the phase shift interference fringe image data for each branch obtained by each of the imaging devices. Per branch The luminance of the phase shift interference fringe image data for each branch at the time of measuring the planar undulation shape using the bias, the amplitude, and the branch reference light image data obtained for each branch in the absence of the sample light, A plane shape measuring method in a phase shift interference fringe simultaneous imaging apparatus, wherein a bias and an amplitude at each point in an observation area are adjusted and adjusted, and a phase of each interference fringe point is calculated by a phase shift method. 2. The method according to claim 1, wherein when the relative optical phase difference is separately provided between the reference light and the sample light, the optical phase difference is generated by slightly changing the wavelength of the laser light source. The method for measuring a planar shape in a simultaneous phase shift interference fringe imaging apparatus according to claim 1. 3. When separately giving a relative optical phase difference between the reference light and the sample light, one of the reference surface and the test surface is slightly translated along the optical axis. 2. The method according to claim 1, wherein the optical phase difference is generated. 4. When separately providing a relative optical phase difference between the reference light and the sample light, the optical path between the reference surface and the test surface has a refractive index greater than 1 in the optical path. The planar shape in the phase shift interference fringe simultaneous imaging apparatus according to claim 1, wherein the optical phase difference is generated by inserting at least one parallel plate having a thickness different from each other in a reflection / transmission body. Measurement method. 5. When separately providing a relative optical phase difference between the reference light and the sample light, the optical path between the reference surface and the test surface has a refractive index greater than 1 in the optical path. An optical wedge, which is a reflective / transmissive body and whose two surfaces facing the reference surface and the test surface are not parallel, is inserted, and the optical wedge is moved in a wedge direction in a plane substantially orthogonal to the optical axis to thereby adjust the optical position. 2. A method according to claim 1, wherein a phase difference is generated. 6. When separately providing a relative optical phase difference between the reference light and the sample light, a liquid crystal is arranged between the reference surface and the surface to be measured, and an electrical control of the liquid crystal is performed. 2. The method according to claim 1, wherein the refractive index is varied by the step (b) to generate a predetermined optical phase difference. 7. The bias and amplitude obtained for each point, wherein the bias and amplitude are values of the bias and amplitude arranged for each set of points within an allowable range. Plane shape measurement method in the simultaneous interference fringe imaging apparatus. 8. A simple average, a median or a root mean square obtained from the bias and amplitude values obtained for each point,
8. The plane shape measuring method in the simultaneous interference fringe imaging apparatus according to claim 7, wherein the representative values of the bias and the amplitude are used for all regions regardless of the position of each point. 9. The laser light source according to claim 2, wherein the wavelength can be changed little by little, the reference surface or the test surface, the reference surface and the test object according to claim 3, wherein the laser light source can be moved in parallel little by little along the optical axis. The non-reflective transmissive parallel plate according to claim 4, having a refractive index greater than 1 and located in an optical path between the plane and the surface.
6. A wedge-shaped movable member having a refractive index greater than 1 and located in an optical path between the reference surface and the test surface.
7. The optical wedge according to claim 6, wherein the optical wedge is located in an optical path between the reference surface and the test surface, and the refractive index can be changed by electrical control.
A phase shift interference fringe simultaneous imaging apparatus comprising any one of the liquid crystals described in the above.