JP2002357407A - Planar shape measurement method in phase shift interference fringe simultaneous imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bias and amplitude between branch phase shift interference fringes generated by dividing an original luminous flux composed of light reflected from a reference surface and a test surface in a phase shift interference fringe simultaneous measurement apparatus. When the error in shape calculation caused by the difference is reduced by numerical calculation, the reflectance between the surface to be measured when calculating the bias and the amplitude in advance and the surface to be measured for the shape is different, and the sample light intensity is reduced. An object of the present invention is to provide a planar shape measuring method that can measure the undulating shape of a test surface with high accuracy even if different. In a simultaneous phase shift interference fringe measuring apparatus, a shape generated by a difference in bias and amplitude between branched phase shift interference fringes generated by dividing an original light beam composed of light reflected from a reference surface and a test surface. This paper proposes to calculate the shape by taking into account the error in the calculation and the intensity ratio of the sample light at the time of amplitude calculation and shape measurement, that is, the reflectance ratio, at the time of shape calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift interference fringe simultaneous measuring apparatus, that is, a source light beam in which reflected light from a test surface and a reference surface is in an optically non-interfering state into a plurality of branched original light beams. Also, the present invention relates to a phase shift interferometer that gives different fixed optical phase differences to the branched light beams and causes them to interfere with each other, simultaneously captures images with a plurality of image capturing mechanisms, and measures the shape of the surface to be measured. More specifically, the present invention provides a new method for correcting the bias and amplitude of the branched phase-shifted interference fringes obtained by the phase-shifting interferometer at each point in the observation area by correcting the bias and the amplitude to greatly improve the accuracy. Technology.

[0002]

2. Description of the Related Art For example, in a phase shift interference fringe simultaneous measuring apparatus as shown in FIG. 1 described in Japanese Patent Application No. 11-136831, a laser beam from a laser Is transmitted through the beam splitter 3 to be converted into a parallel light beam by the collimator lens 4. In this phase shift interference fringe simultaneous measurement apparatus, the reference light reflected from the parallel light beam on the reference surface 5 and the sample light transmitted through the reference surface 5 and the λ / 4 plate 6 and reflected on the test surface 7 are generated. However, the sample light again passes through the λ / 4 plate 6 so that the polarization plane is orthogonal to the reference light, and becomes the original light beam in an optically non-interference state. The reference light and the sample light included in the original light beam reflected by the beam splitter 3 pass through the λ / 4 plate 8 to be in circularly polarized states having different rotation directions from each other.
The light is split into three branched light beams by the three-division prism 9.

[0003] Further, polarizing plates 10 to 12 are arranged on the optical path of each branched light beam, the transmission axis angle of the polarizing plate is set in a plane substantially orthogonal to the optical axis, and a fixed optical phase difference is set. Is generated, and imaging is performed by the imaging mechanisms 13 to 15. Therefore,
In order to measure the shape of the surface to be inspected with high accuracy using this apparatus, it is premised that the bias and amplitude of each corresponding point in the observation region are equal between the three branched phase shift interference fringes.

[0004]

However, in an actual phase shift interference fringe simultaneous photographing apparatus, transmitted light is converted into elliptically polarized light due to a divisional intensity error in the three-division prism 9 and an installation error of the low-speed axis of the λ / 4 plate 8. For this reason, the bias and the amplitude between the three branched phase-shift interference fringes are different from each other.

As a countermeasure against this problem, conventionally, a countermeasure for calculating a representative value of bias and amplitude from a branched phase shift interference fringe image and correcting a difference between optical elements has been taken.
However, it is difficult to make the multiple optical elements intervening on the branching optical path act uniformly at the time of reflection and transmission, and the bias and amplitude values between the branching phase shift interference fringes differ for each pixel in the observation area. In reality, the method of uniformly correcting with a representative value has a drawback that a variation in bias and amplitude within one screen remains even after correction. Further, if the surface to be inspected changes and the light intensity of the sample changes, the bias and amplitude of the interference fringes change. Therefore, when a different surface to be measured is measured, a correction error occurs.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the conventional phase shift interference fringe simultaneous imaging apparatus as described above, an object of the present invention is to measure the bias and amplitude of the branch phase shift interference fringes obtained from different imaging mechanisms. Even if the surface to be measured is different from the surface to be measured at the time of shape measurement, a plane measurement method capable of measuring the surface undulation shape with high accuracy by calculating the shape in consideration of the reflectance of each surface is obtained. It is in.

[0007]

In order to achieve this object, the present invention relates to a phase shift interference fringe simultaneous measuring apparatus, which is provided by dividing an original luminous flux composed of light reflected from a reference surface and a surface to be measured. Bias between branch phase shift interference fringes, error in shape calculation due to difference in amplitude, bias, and shape calculation taking into account the ratio of sample light intensity during amplitude calculation and shape calculation, that is, reflectivity ratio newly It is intended to propose to do.

That is, in the present invention, the reference surface and the test surface are irradiated with the coherent light beam emitted from the laser light source, and the reference surface 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 that is orthogonal to each other with a polarizing optical element interposed therebetween and is in an optically incoherent state, and divides the original light beam into a plurality of branched original light beams, each of the branched original light beams. A plurality of branched phase-shift interference fringes having different fixed optical phase differences are generated through the polarizing optical element, and one position in the observation range of the surface to be measured is the same position in each branch observation coordinate system. Are obtained, image data corresponding to these interference fringes is obtained by a branch imaging mechanism provided for each branch, and the plane undulation shape of the observation range of the test surface is obtained by a phase shift method. Re-execute by numerical data In the simultaneous phase shift interference fringe imaging apparatus, when a relative optical phase difference is separately provided between the reference light and the sample light, a phase for each branch obtained by each of the branch imaging mechanisms is provided. The bias and amplitude for each branch are calculated in advance from the shift interference fringe image data, and when measuring the plane undulation shape, the bias and amplitude for each branch calculated in advance and the phase obtained when measuring the plane undulation shape are calculated. By performing shape calculation for each pixel using the shift interference fringe image data, a shape calculation error caused by a difference in bias and amplitude between branched phase shift interference fringes obtained from different branch imaging mechanisms is eliminated. In this case, the branch reference light image data obtained in the absence of the sample light is obtained in advance for each of the branch imaging mechanisms, and the bias, the sample light intensity for each pixel at the time of calculating the amplitude, and the planar relief shape meter The branch phase obtained from each of the branch imaging mechanisms is calculated by calculating the planar undulation shape by newly considering the intensity ratio of the sample light for each pixel as a reflectance ratio for each pixel as an unknown variable. Bias and amplitude between shift interference fringes are different, and even when the bias and amplitude change according to the sample light intensity, the planar shape in the phase shift interference fringe simultaneous imaging apparatus that calculates the plane undulation shape with high accuracy A measurement method is proposed.

When measuring the surface to be examined whose reflectance can be regarded as spatially uniform, instead of the reflectance ratio for each pixel, it is calculated from the reflectance of the surface to be inspected depending on the material. By giving the target surface reflectance ratio as an arithmetic setting value, the target surface undulation shape is measured from the two branched phase shift interference fringe image data obtained from the two branch imaging mechanisms. A planar shape measurement method in the phase shift interference fringe simultaneous imaging apparatus is also described.

[0010]

According to the present invention, when measuring the shape of an optical component or a mirror-finished surface to be measured, the reflectance within one observation region can be regarded as spatially uniform and depends on the material of the surface to be measured. If the reflectivity is known, instead of using the reflectivity ratio of the surface to be measured for each pixel and using it as an operational setting parameter to calculate the shape, the conventional phase shift In the phase shift interference fringe simultaneous imaging device that required three interference fringes, that is, three imaging mechanisms in the method, the shape calculation was performed using two branch phase shift interference fringes obtained from the two imaging mechanisms. This makes it possible to reduce costs by reducing the number of components.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The phase shift interference fringe simultaneous imaging apparatus used in the first embodiment of the present invention is shown in FIG.

As described above, in the phase shift interference fringe simultaneous measuring apparatus shown in FIG. 1, the beam diameter of the laser beam from the laser light source 1 is expanded by the lens 2, transmitted through the beam splitter 3, and passed through the collimator lens 4. A parallel light beam is generated, and the reference light reflected from the parallel light beam on the reference surface 5 and the sample light transmitted through the reference surface 5 and the λ / 4 plate 6 and reflected on the test surface 7 are generated. The sample light passes through the λ / 4 plate 6 again, so that the polarization plane is orthogonal to the reference light and becomes an original light beam in an optically non-interfering state, but the reference light included in the original light beam reflected by the beam splitter 3. The light and the sample light pass through the λ / 4 plate 8 to be in a state of circular polarization having different rotation directions from each other, and are split into three branched light beams by the three-piece prism 9.

Further, polarizing plates 10 to 12 are arranged on the optical path of each branched light beam, the transmission axis angle of the polarizing plate is set in a plane substantially perpendicular to the optical axis, and a fixed optical phase difference is set. Is generated, and imaging is performed by the imaging mechanisms 13 to 15.

In calculating the undulating shape of a test surface in a simultaneous phase shift interference fringe imaging apparatus, a phase shift method is generally used when calculating the shape of a test surface using interference fringes.

The interference fringe intensity information in this case is composed of a bias, an amplitude and a phase corresponding to the shape of the surface to be inspected. At least three pieces of information are required to calculate the phase from the equation of the interference fringe including these three unknowns. The above-described phase-shifted interference fringes are required. For example, three interference fringes obtained by a conventional phase shift interferometer are expressed by the following equations.

(Equation 1)

Here, I ₁ (x, y) and I ₂ (x, y
y) and I ₃ (x, y) represent the interference fringe intensity obtained from one imaging mechanism. B (x, y) and A (x, y) represent a bias and an amplitude, respectively. Α and β have a phase φ (x,
represents the amount of phase shift that is intentionally added by the interferometer to calculate y).

Here, the bias and the amplitude may have different values depending on the surface to be measured. However, it is assumed that the bias and the amplitude are the same in three interference fringes obtained by one imaging mechanism. Can be. By taking advantage of this fact, if the phase φ (x, y) is solved in consideration of three unknowns from three or more interference fringes, the shape of the surface to be inspected can be calculated without being affected by changes in bias and amplitude. it can.

In the case of the interference fringes shown in the equations (1-1) to (1-3), the phase φ (x, y) can be obtained by performing the following calculation.

(Equation 2)

On the other hand, in the phase shift interference fringe simultaneous measuring apparatus shown in FIG. 1, the branch phase shift interference fringes can be expressed by the following equation in consideration of the bias and the amplitude variation accompanying the division.

(Equation 3)

Since the bias and amplitude included in each of the branched phase-shift interference fringes are different from each other, and there are seven unknowns for three measured values in the simultaneous equations, the phase φ (x, y) remains as it is. ) Cannot be calculated. However, by utilizing the fact that the variation in bias and amplitude between the branched phase-shift interference fringes is a fixed error generated by an optical element inside the interferometer, B ₁ (x,
y), B ₂ (x, y), B ₃ (x, y), A ₁ (x, y)
By measuring y), A ₂ (x, y), and A ₃ (x, y), the phase φ (x, y) can be calculated.

Method of calculating bias and amplitude for each pixel First, B ₁ (x, y), B ₂ (x, y), B ₃
(X, y), A ₁ (x, y), A ₂ (x, y), A ₃
The procedure for calculating (x, y) will be described. In FIG. 1, an optical phase difference δ _i is separately given between the reference light and the sample light by a method such as a reference surface displacement or a wavelength change of a light source performed by a mechanism (omitted) for externally controlling the test surface 7. The phase shift interference fringes for each branch are imaged.

[0022]

(Equation 4) If δ _i is changed systematically and three or more branched phase-shift interference fringes are obtained for each branch, the bias and amplitude for each branch can be calculated. Here, as one example, δ
_{The case where i} is a value that equally divides 2π for one period of the interference fringe phase will be shown.

(Equation 5) The bias and amplitude for each branch are calculated by performing the following calculation from the interference fringes obtained for each branch under the condition of Expression (5).

(Equation 6)

(Equation 7)

The obtained B ₁ (x, y), B ₂
(X, y), B ₃ (x, y), A ₁ (x, y), A ₂
If (x, y) and A ₃ (x, y) are used as the bias and the amplitude of the branched phase-shift interference fringe obtained by the branch imaging mechanism, the unknown number φ (x, y) Since there are three measurement values, the phase φ (x, y) can be calculated.

Equation (8) shows the phase φ when the bias and the amplitude of the interference fringes are assumed not to change depending on the surface to be measured.
The calculation example of (x, y) is shown.

A method of calculating the shape of a test surface using the bias and amplitude of each pixel Hereinafter, a method described later, that is, a method of calculating the shape φ without using the reflectance ratio γ, will be described using equations (10) and (12). . After the bias is subtracted from the interference fringe intensity obtained by each of the branch imaging mechanisms obtained at the time of measuring the shape of the test surface, the amplitude is divided to convert it into interference fringes having a bias of 0 and an amplitude of 1.

(Equation 8)From equations (8-1) to (8-3), sin [φ (x,
y)], cos [φ (x, y)]
Excess number of I derived from a large number of measurements₁ ’, I _Two ’,
I_Three ′ To calculate φ (x, y) by least squares approximation
Put out.

Here, a calculation formula for obtaining φ under α and β that has been separately determined is as follows.

(Equation 9) In this case, the value φ that minimizes E is obtained from the following equation.

(Equation 10)

When the reflectance ratio γ of the surface to be inspected is not taken into consideration, the bias and amplitude obtained previously can be used as another method to obtain from the two branch imaging mechanisms. The exact solution of two unknowns sin [φ (x, y)] and cos [φ (x, y)] is calculated from only the two branched phase-shifted interference fringes to calculate the shape of the surface to be measured. Is also possible.

[Equation 11] Therefore, the phase φ (x, y) is obtained by the following equation.

(Equation 12)

When the Intensities of Reflected Light from the Surface S for Calculation of Bias and Amplitude and the Surface T for Measurement are Different Next, the case where the bias and amplitude forming the interference fringes change depending on the surface to be examined. FIG. 2 shows a model of the reference light and the sample light when the test surface S for bias and amplitude calculation is used. As shown in the figure, the reference light intensity is a (x, y) and the sample light intensity is b (x, y).
y), the reference light and the sample light intensity that reach each imaging mechanism after being divided by the three-piece prism are denoted by a ₁ (x,
y), b ₁ (x, y), a ₂ (x, y), b ₂ (x, y
y), a ₃ (x, y), and b ₃ (x, y).

B ₁ (x, y), B ₂ (x, y), B ₃ (x, y) obtained by the procedures shown in equations (4) to (7)
y), A ₁ (x, y), A ₂ (x, y), A ₃ (x, y)
The relationship between y) and the model shown in FIG. 2 is expressed by the following equation.

(Equation 13)

[Equation 14]

On the other hand, the sample light intensity at the time of measuring the measurement target surface T is b "(x, y), and the sample light intensity reaching the three branch imaging mechanisms is b ₁ " (x, y). ), B ₂ ″ (x,
y), b ₃ ″ (x, y). b ″ (x, y) and the sample light intensity b (x, y) from the surface S to be measured when calculating the bias and amplitude.
If the intensity ratio for each pixel in y) is a reflectance ratio γ (x, y), the sample light reaching the three branch imaging mechanisms also has the same ratio γ.
(X, y) is considered to be affected, so FIG.
The sample light intensity as shown in FIG.

(Equation 15)

On the other hand, the reference light intensity is a constant value independent of the surface to be inspected. In consideration of these, biases B ₁ ″ (x, y) and B ₂ ″ for each branch on the measurement target surface T are taken into consideration.
(X, y), B ₃ ″ (x, y), amplitude A ₁ ″ (x, y
y), A ₂ ″ (x, y), A ₃ ″ (x, y) and the previously obtained biases B ₁ (x, y), B ₂ (x, y), B
₃ (x, y) and amplitudes A ₁ (x, y), A ₂ (x, y),
The relation of A ₃ (x, y) is as follows.

(Equation 16)

[Equation 17] The interference fringes obtained on the measurement target surface T are expressed by the following equation.

(Equation 18)

These equations can be rewritten as follows using the reflectance ratio γ (x, y).

[Equation 19] Expressions (3-1) to (3-3) and Expressions (18-1) to (1
As can be understood from the comparison of 8-3), when the test surfaces having different reflectivities are measured with reference to the test surface S for calculating the bias and the amplitude, the bias and the amplitude included in the interference fringes are different. .

Therefore, the branch phase shift interference is calculated by the following equation (8).
, And after conversion, the phase φ
Even if (x, y) is calculated, an error occurs. here
And the error amount φ_error (Equation (25) and thereafter). Preparation
(19) to (20). Formula (18-1)
Interference obtained on the measurement target surface T expressed by the equation (18-3)
Stripe I _i "(X, y) is the bias obtained on the test surface S,
Amplitude B_i (X, y), A_i When normalized by (x, y)
Are as follows.

[0034]

(Equation 20) In equation (10), the interference fringes I _i ″ ′ (x, y); (i = 1,
Substitute 2, 3). I _i ″ ′ (x, y); (i = 1,
2, 3) are all affected by γ (x, y).

(Equation 21)

Here,

(Equation 22) Then, equation (10) ′ becomes

(Equation 23) Becomes

Here,

(Equation 24) Therefore, Expression (20) is summarized in the following expression.

(Equation 25)

Further,

(Equation 26) Toki,

[Equation 27] Formula (21) is summarized as follows.

[0038]

[Equation 28] The error φ _error is

(Equation 29) Expressed in

[Equation 30] By using the relationship, φ _error is given by the following equation.

[0039]

(Equation 31) If you further organize,

(Equation 32) Becomes

Here, V and W are respectively

[Equation 33] To show.

By the way, the phase shift amount

(Equation 34) If

(Equation 35) Becomes

Considering that γ is close to ₁ , in an interferometer in which p (γ) is small and an interference fringe with high contrast is obtained, since L ₁ = 1 and M ₁ = 0,

[Equation 36] Is obtained, and as a result, φ _error is approximately obtained as follows.

[0043]

(37)

Further, when the denominator is expanded, φ _error can be approximately expressed by the following equation.

(38) P (γ) in equation (29) is

[Equation 39] Since p (1) = 0, the error occurs only when γ = 1 (in other words, when the sample light intensity of the bias-amplitude calculation target surface S and the measurement target surface T is the same). φ _{er ror}
= 0. When γ ≠ 1, an error φ _error that fluctuates at the same frequency as the interference fringe phase φ or a higher-order frequency such as a second harmonic and a third harmonic is generated from the second term of the equation (29).

Regarding the method for calculating the exact solution of the phase from the two interference fringes shown in equation (12), equation (18-
1) ′, two interference fringes I ₁ ″ (x,
y) and I ₂ ″ (x, y) are substituted into Expression (30).

(Equation 40) However,

[Equation 41] It is. The amount of phase shift

(Equation 42) , L ₂ and M ₂ are respectively

[Equation 43] Becomes As a result, φ _error is given by equation (32).

[0046]

[Equation 44] Here, V ₂ and W ₂ each satisfy the following relationship.

[Equation 45] In the method of calculating an exact solution according to equation (12),
When γ ≠ 1 (in other words, when the sample light intensity from the bias and amplitude calculation target surface S and the measurement target surface T is different), the interference fringe phase φ is calculated according to the second and subsequent terms of Expression (32). Errors that vary at higher frequencies such as the same frequency, a second harmonic, and a third harmonic occur.

Calculation of the shape in consideration of the reflectance ratio of the surface to be inspected Therefore, unlike the methods shown in the equations (10) and (12), a new method according to the present invention, that is, a shape independent of the reflectance ratio γ The calculation method will be described below. Equation (18−
1), the reference light intensities a ₁ (x, y), a ₂ (x, y) from the interference fringe intensities expressed in the equations (18-2) and (18-3).
y) and a ₃ (x, y) are subtracted,

[Equation 46] Solve for

[0048]

[Equation 47] From equations (33-1) to (33-3)

[Equation 48] Leads to the determinant

[Equation 49] If α (x, y) and β (x, y) do not become 0,

[Equation 50] Can be solved for

This is obtained

(Equation 51) To obtain the phase φ (x, y).

(Equation 52) In the equation (36), unlike the methods of the equations (10) and (12), the influence of the reflectance ratio γ of the test surface is eliminated.

Since equation (36) holds true for the newly introduced reflectance ratio γ of the test surface, φ ′ (x, y) = φ (x , Y). That is, even when different test surfaces are measured, the shape can be calculated without being affected by the reflectance. In addition,
Γ (x, y) defined as the reflectance ratio of the test surface is obtained by the following equation.

(Equation 53)

Next, a phase shift interference fringe simultaneous measuring apparatus according to a second embodiment of the present invention will be described with reference to FIG. By the way, when measuring a mirror-finished surface such as an optical component or a mirror-finished surface, the reflectance of the surface to be measured can be regarded as uniform and its value can be specified. In such a case, the calculated shape is corrected by positively using Expression (32) to give the reflectance ratio γ of the surface to be measured as an arithmetic set value and calculating an error amount. It becomes possible.

Such a correction can be realized by subtracting equation (32) from the shape containing the error obtained from equation (30). In the simultaneous phase shift interference fringe measuring apparatus shown in FIG. 4, the laser beam from the laser light source 1 is expanded in beam diameter by the lens 2, passes through the beam splitter 3, is converted into a parallel beam by the collimating lens 4, The reference light reflected by the reference surface 5 and the sample light transmitted through the reference surface 5 and the λ / 4 plate 6 and reflected by the test surface 7 are generated as in FIG. The sample light passes through the λ / 4 plate 6 again, so that the polarization plane is orthogonal to the reference light and becomes an original light beam in an optically non-interfering state, but the reference light included in the original light beam reflected by the beam splitter 3. Light and sample light are λ /
The light passes through the four plates 8 to be in a circularly polarized state having different rotation directions, and is split by the splitting prism 16 into two branched light beams.

Polarizing plates 17 and 18 are disposed on the optical paths of the respective branched light beams to generate branched phase-shift interference fringes having a fixed optical phase difference.
Will be taken. In other words, FIG.
When configuring a phase shift interference fringe simultaneous imaging apparatus, if a specific surface to be measured is to be measured, two branch imaging mechanisms can be realized.

[0054]

As is clear from the above description, according to the first aspect of the present invention, in the phase shift interference fringe simultaneous measuring apparatus, the bias and amplitude of the interference fringe calculated in advance for each pixel and the surface to be inspected are measured. The reference surface image data that does not depend on the surface of the test object is newly taken into account by using the ratio of the sample light intensity at the time of calculating the bias and amplitude and the shape at the time of calculating the shape as a reflectance ratio using each branch imaging mechanism. By calculating the undulation shape, errors in shape calculation caused by the difference in bias and amplitude between the branched phase shift interference fringes caused by splitting the original light beam composed of the reference light and the sample light are affected. Even when the inspection surfaces are different, it can be reduced.

According to the second aspect of the present invention, as in the case of inspection of an optical component or measurement of the shape of a mirror surface, the reflectance within one observation region can be regarded as spatially uniform and the surface to be inspected can be regarded as uniform. In the case where the reflectance depending on the material is known, the shape is calculated by giving the reflectance ratio defined above as a setting parameter in the calculation, and the conventional phase shift method uses three interference fringes. That is, in a phase shift interference fringe simultaneous imaging apparatus that requires three imaging mechanisms, the shape calculation can be realized with two branched phase shift interference fringes obtained from the two imaging mechanisms. Cost reduction can be achieved by reducing the number.

[Brief description of the drawings]

FIG. 1 is a principle view of a phase shift interference fringe simultaneous imaging apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of reflected light intensity when measuring a bias and amplitude calculation target surface S in the simultaneous phase shift interference fringe imaging apparatus.

FIG. 3 is an explanatory diagram of reflected light intensity at the time of measuring a measurement target surface T in the same phase shift interference fringe simultaneous imaging apparatus.

FIG. 4 is a principle view of a phase shift interference fringe simultaneous imaging apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Lens 3 Beam splitter 4 Collimator 5 Reference surface 6 λ / 4 plate 7 Test surface 8 λ / 4 plate 9 Three-segmented prism 10, 11, 12, 17, 18 Polarizing plate 13, 14, 15, 19, 20 Imaging mechanism

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA45 FF04 FF51 GG04 HH04 JJ05 JJ19 JJ26 LL33 LL36 QQ18 QQ25 QQ26 QQ42

Claims (2)

[Claims] 1. A reference surface and a test surface are irradiated with a coherent light beam emitted from a laser light source, and polarization surfaces of the reference light and the sample light, which are reflected light from the reference surface and the test surface, are polarized by a polarizing optical element. An observation optical system that generates an original light beam in an optically non-interfering state by interposing and orthogonal to each other, and divides the original light beam into a plurality of branched original light beams, and a polarizing optical element for each of the branched original light beams. A plurality of branched phase-shift interference fringes having different fixed optical phase differences are generated through a position such that one position in the observation range of the test surface is the same position in each branch observation coordinate system. The image data corresponding to these interference fringes is acquired by the branch imaging mechanism provided for each branch, and the plane undulation shape of the observation range of the test surface is reproduced by numerical data by the phase shift method. Phase shift interference In the simultaneous fringe imaging apparatus, a phase shift interference fringe image for each branch obtained by each of the branch imaging mechanisms when a relative optical phase difference is separately provided between the reference light and the sample light. The bias and the amplitude for each branch are calculated in advance from the data, and at the time of measuring the plane undulation shape, the bias for each branch calculated in advance,
By performing a shape calculation for each pixel using the amplitude and the phase shift interference fringe image data obtained at the time of measuring the plane undulation shape, bias between the branched phase shift interference fringes obtained from different branch imaging mechanism, When resolving a shape calculation error caused by a difference in amplitude, branch reference light image data obtained in a state where there is no sample light is obtained in advance for each branch imaging mechanism, and the bias and the pixel at the time of calculating the amplitude are obtained. Each sample light intensity and the plane undulation shape are calculated by newly considering the intensity ratio of the sample light of each pixel of the sample light at the time of measurement of the plane undulation shape as an unknown variable as a reflectance ratio for each pixel. The bias and amplitude between the branched phase shift interference fringes obtained from the branched imaging mechanism are different, and the bias and the amplitude are changed according to the sample light intensity. Calculation A planar shape measuring method in a phase shift interference fringe simultaneous imaging apparatus, comprising: 2. The method according to claim 1, wherein, when measuring the test surface whose reflectance is considered to be spatially uniform, the reflectance of the test surface depends on the material instead of the reflectance ratio of each pixel. Is given as an arithmetic set value by calculating the reflectance ratio of the target surface calculated from the value of the target surface, the target surface reflectance ratio is obtained from the two branch phase shift interference fringe image data obtained from the two branch imaging mechanisms. A planar shape measuring method in a simultaneous phase shift interference fringe imaging apparatus, which performs undulating shape measurement.