JP2019196947A - Optical device and shape measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a shape measurement error. An optical device (1) includes an acquisition unit (151) that acquires a first interference light group of a plurality of interference lights each having a different phase and a second interference light group in which the phase of the first interference light group is offset. The first interference light group is analyzed by the phase shift method to determine the first phase, which is the phase at each of a plurality of positions of the measurement target, and the second interference light group is analyzed by the phase shift method to measure the plurality of measurement target objects. For the phase determination unit 152 that determines the second phase that is the phase at each position, and for each of the plurality of positions of the measurement target, when the phase is within a predetermined section, the weight is set to be larger than when the phase is outside the section. And a combining unit 153 that combines the first phase and the second phase. [Selection diagram] Fig. 6

Description

  The present invention relates to an optical device and a shape measuring method.

  Multiple interference fringe images of the sample light reflected by the test surface and the reference light reflected by the reference surface due to light irradiation are captured in different optical phases, and the multiple interference fringe images are analyzed and examined. A phase shift interferometer that measures the shape of a surface is known (see, for example, Patent Document 1).

JP 2001-108417 A

  In the conventional interferometer, on the measurement principle of calculating the phase corresponding to the shape component of the object to be measured by the arc tangent of the four arithmetic operations of the interference intensity, the value of the tangent function with the phase of the interference light as a variable is in the divergence part. There is a tendency for the repeatability of the measured value to deteriorate. In addition, a fixed error having a deviation according to the phase may occur due to an error factor caused by the measurement system. For these reasons, the error in measuring the shape of the test surface may increase.

  Therefore, the present invention has been made in view of these points, and an object thereof is to provide a technique for reducing a shape measurement error.

  In the first aspect of the present invention, a first interference light group of a plurality of interference lights having different phases, which are a reflection of the reflected light reflected from the reference surface and the measurement light reflected from the measurement object, and the first An acquisition unit that acquires a second interference light group obtained by offsetting the phase of the interference light group, and a first phase that is a phase at each of a plurality of positions of the measurement object by analyzing the first interference light group by a phase shift method. A phase determining unit that determines a phase, determines a second phase that is a phase at each of a plurality of positions of the measurement object by analyzing the second interference light group by the phase shift method, and a plurality of the measurement objects For each of the positions, when the phase determined by the phase determination unit is within a predetermined interval, the first phase and the second phase are combined with a greater weight than when the phase is outside the interval. And the synthesis part Provides an optical device comprising a.

  The synthesizing unit, when one phase of the first phase and the second phase is within a predetermined interval and the other phase is outside the predetermined interval, weight of the phase within the interval May be set to 1 and the phase weight outside the interval may be set to 0.

  For example, the synthesizing unit may calculate a value of a tangent function having the phase as a variable among the first phase and the second phase determined by the phase determining unit for each of a plurality of positions of the measurement object. The weight having the larger absolute value is made smaller than the weight having the smaller absolute value of the value of the tangent function having the phase as a variable, and the first phase and the second phase are combined.

  The combining unit may combine the first phase and the second phase with equal weights.

  The optical device includes the first interference light group and the second interference so that a phase analysis error periodically generated in each of the first phase and the second phase determined by the phase determination unit is inverted. You may further provide the phase adjustment part which adjusts the phase difference with an optical group.

  The combining unit corrects the weights of the first phase and the second phase by using correction values set in advance for the first phase and the second phase, respectively. The second phase may be combined.

  The optical device includes: a light source that irradiates light to the reference surface and the measurement object; and a wavelength changing unit that changes a wavelength of light emitted by the light source so that phases of the plurality of interference lights are different from each other. Furthermore, you may provide.

  In the second aspect of the present invention, a first interference light group of a plurality of interference lights having different phases, which are reflected by the computer and reflected by the reference surface and the measurement light reflected by the measurement object, are executed by the computer. Obtaining a second interference light group obtained by offsetting the phase of the first interference light group, and analyzing the first interference light group by a phase shift method to determine the phase at each of a plurality of positions of the measurement object. Determining the first phase, and analyzing the second interference light group by the phase shift method to determine a second phase that is a phase at each of a plurality of positions of the measurement object; and the measurement object For each of the plurality of positions, when the phase determined by the phase determination unit is within a predetermined interval, the first phase and the first phase are increased with a weight greater than when the phase is outside the interval. It provides a shape measuring method comprising the steps of combining the phase and.

  According to the present invention, it is possible to reduce the shape measurement error.

It is a figure which shows the structure of the conventional optical apparatus. It is a figure for demonstrating that an error will increase, when the absolute value of a tangent function becomes large. It is a figure for demonstrating offsetting a phase. It is a figure for demonstrating the structure of an optical apparatus. It is a figure which shows the function structure of an optical apparatus. It is a figure for demonstrating the process which the control part of an optical apparatus performs. It is a flowchart of the process which an optical apparatus performs. It is a figure for demonstrating determining the weight of a phase based on an area. It is a figure for demonstrating a phase analysis error. 10 is a flowchart of processing executed by a control unit of an optical device according to Modification Example 2. It is a figure for demonstrating correcting a weight using the set correction value.

(Outline of the conventional optical device 5)
First, an outline of the conventional optical device 5 and problems of the conventional phase shift method will be described. FIG. 1 is a diagram showing a configuration of a conventional optical device 5. The optical device 5 includes a light source 11, an optical system 12, a camera 13, a storage unit 14, a control unit 15, a reference surface 3, and a measurement object 4.

  The light source 11 irradiates the reference surface 3 and the measurement object 4 with light. The light source 11 is, for example, a semiconductor laser, and the wavelength of light to be output can be changed by changing the injection current input to the light source 11.

  The optical system 12 includes a pinhole 120, a plurality of lenses 121 (121 a and 121 b), a beam splitter 122, and light emitted from the light source 11 is an enlarged optical system (pinhole 120, lens 121 a, pinhole 120, beam splitter 122 , And the lens 121b) to irradiate the reference surface 3 and the measurement object 4.

  The measurement light reflected from the measurement object 4 and the reference light reflected from the reference surface 3 enter the beam splitter 122 again. The measurement light and the reference light incident on the beam splitter 122 are reflected by the beam splitter 122 and enter the camera 13. The camera 13a detects the intensity of the irradiated interference light. The camera 13 transmits the detected intensity of the interference light to the control unit 15 as an interference light image (hereinafter also referred to as interference fringe).

  The control unit 15 acquires the interference light intensity detected by the camera 13 as an interference light image. And the control part 15 analyzes the intensity | strength of interference light by a phase shift method, and determines the phase in each of several position of the measuring object 4. FIG.

(Phase shift method by changing the wavelength of light)
Here, the phase shift method by changing the wavelength of the light irradiated to the reference surface and the measurement object will be described. The interference light obtained by causing the reference light reflected from the reference surface 3 and the measurement light reflected from the measurement object 4 to interfere with each other with an optical path length difference Δl (x, y) is expressed by Expression (1).

The interference light when the wavelength of the irradiated light is moved by the wavelength change amount Δλ is expressed by Expression (2).

When the wavelength change amount Δλ with respect to the wavelength λ is small, Equation (2) can be approximated to Equation (3).
In Expression (3), the second term in the cosine function corresponds to the phase shift amount Δφ (x, y) when the wavelength of the irradiated light is changed. The phase shift amount Δφ (x, y) is a function of the optical path length difference Δl (x, y).

When the distance between the reference surface 3 and the measurement object 4 is sufficiently large with respect to the undulation of the shape of the measurement object 4 included in the optical path length difference Δl (x, y), the phase shift amount Δφ (x, y) is It can be regarded as a uniform amount in the plane. When the phase shift amount Δφ (x, y) can be regarded as an in-plane uniform amount, the phase shift amount Δφ is expressed by the following equation (4).

  Assuming that the wavelength λ of the irradiated light is 1000 nm and the optical path length difference Δl is 10 mm, interference light whose phase is shifted by 90 degrees (= π / 2) can be acquired by changing the wavelength of the irradiated light by 25 pm.

When acquiring the interference light image of i sheets which changed the wavelength of the light irradiated to the reference surface 3 and the measuring object 4, and shifted the phase, Formula (3) is Formula (5) using Formula (4). ).

For example, in the case of the 4-step phase shift method in which one period of the interference light is divided into four and the phase is shifted by 90 degrees (π / 2), the intensity I _i (x, y) of the plurality of interference lights is expressed by the equation (6). By substituting into, the phase φ (x, y) at each of the plurality of positions of the measurement object 4 can be obtained.

(Problems of the conventional phase shift method)
Here, it will be described that the error increases when the absolute value of the tangent function having the phase as a variable increases. FIG. 2 is a diagram for explaining that the error increases as the absolute value of the tangent function increases. FIG. 2A is a schematic diagram of a graph of (I ₂ −I ₄ / I ₁ −I ₃ ) = tan φ. Note that W = (I ₂ −I ₄ / I ₁ −I ₃ ). As shown in FIG. 2A, | tan φ | increases as φ approaches π / 2.

Thus, when | tan φ | becomes large, φ (x, y) is difficult to change even if the value of I ₁ -I ₃ changes. FIG. 2B is a schematic diagram of a graph of φ (x, y) = tan ⁻¹ (W). For ^example, in the region having a large absolute value of ^tan -1 (W), W is the case where changes in W1' from W1, the amount of change from phi ₁ to phi ₁ 'is reduced. Thus, when the amount of change from φ ₁ to φ ₁ ′ becomes small, there is a concern that although there is a difference in the shape of the actual measurement object 4, it is considered that there is no difference.

When I ₁ and I ₃ are substantially equal, the calculation result of I ₁ -I ₃ is close to zero. In floating point arithmetic, a floating point number is treated as a fixed number of significant digits. Therefore, when addition / subtraction is performed so that the calculation result is close to 0, the number of missing significant digits is automatically supplemented with 0. For example, if a calculation such as “1.2345789 × 10 ² −1.234556780 × 10 ² ” is performed, the calculation result is “9 × 10 ⁻⁶ ”, and the number of significant digits is reduced. In this case, the number of significant digits is reduced from 9 digits to 1 digit. As described above, when addition / subtraction is performed so that the calculation result is close to 0 in the floating-point operation, an error occurs between the calculation result and the true value. When a calculation such as multiplying a value including such an error by a large number is performed, the error increases because the digit including the error rises to the upper digit.

  Therefore, the optical device according to the embodiment divides the interference light in which the reference light and the measurement light interfere into two, and optically offsets the phase of the divided interference light in accordance with the number of divisions. To do. Next, the optical device acquires a first interference light group of a plurality of interference lights each having a different phase, and acquires a second interference light group whose phase is offset with respect to the phase of the first interference light group. Subsequently, the optical device analyzes the first interference light group by the phase shift method and determines a first phase that is a phase at each of a plurality of positions of the measurement object 4. Further, the optical device analyzes the second interference light group by the phase shift method and determines a second phase that is a phase at each of a plurality of positions of the measurement object 4.

FIG. 3 is a diagram for explaining that the phase is offset. 3, a graph g1 indicated by the solid line is a graph g1 of tangent function with a first phase phi ₁ variable phi (phi). A graph g2 indicated by a broken line is a tangent function graph g2 (φ + φ _offset ) in which the second phase φ ₂ is expressed using the variable φ. As shown in FIG. 3, a first phase phi ₁ of the first interference light group was the source of the graph g1, graph g2 (φ + φ _offset) second interference light group in the second phase which was the source of phi ₂ is different, the value of the graph g1 is different from the value of the graph g2. In other words, the sections in which the error increases as the value of the tangent function increases in the graph g1 and the graph g2.

As described above, in the two phases, when the sections in which the error increases are different from each other, the phase weight in the section in which the error is small is increased, and the phase weight in the section in which the error is increased is decreased. , The contribution ratio of the phase with a large error can be reduced. Therefore, for each of the plurality of positions of the measuring object 4, the optical device increases the weight when the phase is within a predetermined interval, compared with the case where the phase is outside the interval, and calculates the first phase and the second phase. Synthesize. The predetermined section is a section in which the value when the phase is substituted into the tangent function is smaller than the predetermined value. The predetermined values are a function that takes the absolute value of the first tangent function g (φ _t ) with the first phase φ ₁ = φ as a variable, and a second tangent function g with the second phase φ ₂ = φ + φ _offset as a variable. It is the value of the phase at the intersection with the function taking the absolute value of (φ + φ _offset ). By doing in this way, the optical apparatus can make the contribution rate with the larger error included in the phase small when creating the shape of the measuring object 4 based on the phase. Therefore, the optical device can reduce the measurement error of the shape of the measurement object 4 based on the phase.

[Configuration and Function of Optical Device 1]
The configuration and function of the optical device 1 will be described with reference to FIGS. FIG. 4 is a diagram for explaining the configuration of the optical device 1. FIG. 5 is a diagram illustrating a functional configuration of the optical device 1. The optical device 1 includes a light source 11, an optical system 12, a camera 13 a, a camera 13 b, a storage unit 14, a control unit 15, a display unit 16, a reference surface 3, and a measurement object 4.

  The light source 11 irradiates the reference surface 3 and the measurement object 4 with light. The light source 11 is, for example, a semiconductor laser, and the wavelength of light to be output can be changed by changing the injection current input to the light source 11.

  The optical system 12 includes a plurality of lenses 121 (121a and 121b), a plurality of beam splitters 122 (122a and 122b), a plurality of λ / 4 plates 123 (123a and 123b), and a plurality of polarizing plates 124 (124a and 124b). Have The light emitted from the light source 11 is magnified by the magnifying optical system (the lens 121a, the pinhole 120, the beam splitter 122a, and the lens 121b), and is irradiated to the reference surface 3 and the measurement object 4.

  The measurement light reflected from the measurement object 4 is converted by the λ / 4 plate 123a disposed between the reference surface 3 and the measurement object 4 so that the reference light reflected from the reference surface 3 and the polarization plane are orthogonal to each other. Is done. Then, the reference light and the measurement light are incident on the beam splitter 122a in a state of being superimposed as non-interference light.

  When the non-interfering light reflected by the beam splitter 122a is incident on the λ / 4 plate 123b, the reference light and the measurement light are converted into circularly polarized light in the opposite directions. The light converted into the circularly polarized light in the reverse direction is incident on the beam splitter 122b and divided into two.

  When one of the divided lights passes through the polarizing plate 124a disposed between the beam splitter 122b and the camera 13a, the reference light and the measurement light are converted so as to interfere with each other, and enter the camera 13a. . Further, when the other part of the light divided into two passes through the polarizing plate 124b disposed between the beam splitter 122b and the camera 13b, the reference light and the measurement light are converted so as to interfere with each other, and the camera 13b. Is incident on.

  At this time, the transmission axis of the polarizing plate 124a and the transmission axis of the polarizing plate 124b are set at different angles in a plane perpendicular to the optical axis. In this way, the reference light and measurement light that have passed through the polarizing plate 124a interfere with the reference light and measurement light that have passed through the polarizing plate 124b at different phases. For example, when the transmission axis of the polarizing plate 124b is rotated by 45 degrees in a plane perpendicular to the optical axis with respect to the polarizing plate 124a, the interference occurs with the phase being offset by 90 degrees.

  Each of the camera 13a and the camera 13b detects the intensity of incident interference light. Each of the camera 13a and the camera 13b transmits the detected intensity of the interference light to the control unit 15 as an interference light image (hereinafter also referred to as interference fringe).

  The storage unit 14 is a storage medium including a ROM (Read Only Memory) and a RAM (Random Access Memory). The storage unit 14 stores a program executed by the control unit 15.

  The control unit 15 is a calculation resource including a processor such as a CPU (Central Processing Unit). The control unit 15 implements functions as the wavelength changing unit 150, the acquiring unit 151, the phase determining unit 152, the combining unit 153, and the shape creating unit 154 by executing the program stored in the storage unit 14.

(Outline of processing executed by the control unit)
Hereinafter, the processing executed by the control unit 15 of the optical apparatus 1 will be described with reference to FIGS. 5 and 6. FIG. 6 is a diagram for explaining processing executed by the control unit 15 of the optical device 1. In the following description, x represents the x coordinate of the pixel of the camera 13, and y represents the y coordinate of the pixel of the camera 13.

  The wavelength changing unit 150 changes the wavelength of the light emitted from the light source 11 so that the phases of the plurality of interference lights are different from each other. For example, in the case of the above four-step phase shift method, the wavelength changing unit 150 changes the wavelength of the light source 11 so that the phase is shifted by 90 degrees (π / 2).

Next, the acquisition unit 151 includes a first interference light group I _1j (x, x, a plurality of interference lights having different phases from each other, in which the reflected light reflected from the reference surface 3 and the measurement light reflected from the measurement object 4 interfere with each other. y) is acquired from the camera 13a ((A) of FIG. 6). Further, the acquisition unit 151 acquires the second interference light group in which the reflected light and the measurement light offset the phase of the first interference light group I _1j (x, y) from the camera 13b ((B) in FIG. 6). ). Specifically, the acquisition unit 151 causes the reflected light and the measurement light to interfere with each other in a state where the phase is offset by 90 degrees relative to the phase of the first interference light group I _1j (x, y). A second interference light group I _2j (x, y) of a plurality of interference lights having different values is acquired. Each time the wavelength changing unit 150 changes the wavelength of light emitted from the light source 11, the acquiring unit 151 receives the first interference light group I _1j (x, y) and the second interference light from the camera 13a and the camera 13b, respectively. Get the group I _2j (x, y).

The phase determination unit 152 analyzes the first interference light group I _1j (x, y) acquired by the acquisition unit 151 by the phase shift method, and a first phase φ ₁ that is a phase at each of a plurality of positions of the measurement object 4. (X, y) is determined ((C) of FIG. 6). Further, the phase determination unit 152 analyzes the second interference light group I _2j (x, y) acquired by the acquisition unit 151 by the phase shift method, and is a second phase that is a phase at each of a plurality of positions of the measurement object 4. φ ₂ (x, y) is determined ((D) of FIG. 6).

The synthesizer 153 determines whether the phases φ ₁ (x, y) (= φ (x, y)) and φ ₂ (x, y) = (φ (x, y) + φ _offset ) are within a predetermined interval. Is determined ((E) of FIG. 6). Then, the combining unit 153 increases the weight when the phase is within the predetermined interval as compared to when the phase is outside the interval, and the first phase φ ₁ (x, y) and the second phase φ ₂ (x, y) is synthesized ((F) of FIG. 6).

The synthesizer 153 synthesizes the coefficient k applied when the phase is within the section larger than the coefficient k applied when the phase is outside the section. The coefficient k is a function of the phase φ (x, y), the first phase φ ₁ (x, y) is multiplied by the coefficient k ₁ (φ ₁ (x, y)), and the second phase φ ₂ (x , Y) is multiplied by a coefficient k ₂ (φ ₂ (x, y)). More specifically, the synthesizing unit 153 synthesizes the first phase φ ₁ (x, y) and the second phase φ ₂ (x, y) using Expression (7).
φ _synth = k ₁ (φ ₁ (x, y)) · φ ₁ (x, y) + k ₂ (φ ₂ (x, y)) · φ ₂ (x, y) Equation (7)
Then, the combining unit 153 transmits a combined phase φ _synth (x, y) obtained by combining the first phase φ ₁ (x, y) and the second phase φ ₂ (x, y) to the shape creating unit 154.

The shape creation unit 154 creates the shape of the measurement object 4 based on the synthesized phase φ _synth (x, y) synthesized by the synthesis unit 153 ((G) in FIG. 6). The shape creation unit 154 displays the created shape of the measurement object 4 on the display unit 16 that displays various types of information. The display unit 16 is, for example, a liquid crystal display, but is not limited thereto. In addition, the shape creation unit 154 may store the created shape of the measurement object 4 in the storage unit 14 or may transmit it to another device via a communication unit (not shown).

  FIG. 7 is a flowchart of processing executed by the optical apparatus. First, the acquisition unit 151 acquires a first interference light group and a second interference light group (step S1). Next, the phase determination unit 152 determines the first phase of the first interference light group and the second phase of the second interference light group (step S2).

The synthesizer 153 determines whether φ (x, y) is within a predetermined section (step S3). The synthesizing unit 153 increases the weight when the phase is within the predetermined interval as compared with when the phase is outside the interval, and the first phase φ ₁ (x, y) and the second phase φ ₂ (x, y) _Are synthesized (step S4), and the synthesized phase φ _synth (x, y) is transmitted to the shape creation unit 154. Then, the shape creation unit 154 creates the shape of the measurement object 4 based on the synthesized phase φ _synth (x, y) synthesized by the synthesis unit 153 (step S5), and the shape of the created measurement object 4 Is output (step S6).

  As described above, the optical device 1 determines two phases based on the two interference light groups offset in phase, and when the determined phase is within a predetermined section, the optical device 1 is weighted more than when it is outside the predetermined section. Heavily synthesize. Then, the optical device 1 creates the shape of the measurement object 4 using the synthesized phase. By doing in this way, the optical apparatus 1 can reduce the calculation error even when the value of the tangent function having the phase of the interference light as a variable becomes large due to the measurement principle. Therefore, the optical device 1 can reduce the measurement error of the shape of the measurement object 4.

  The combining unit 153 may set one weight to 1 and set the other weight to 0 as the best case of increasing one weight and reducing the other weight. For example, if one of the first phase and the second phase is within a predetermined interval and the other phase is outside the predetermined interval, the combining unit 153 calculates the weight of the phase within the interval. 1 and the weight of the phase outside the interval is set to 0. In other words, the synthesizing unit 153 selects the phase that is within the section, and combines the first phase and the second phase without selecting the phase that is outside the section.

Hereinafter, processing executed by the control unit 15 of the optical device 1 will be described. FIG. 8 is a diagram for explaining the determination of the phase weight based on the section. First, the phase determination unit 152 determines the first phase φ ₁ and the second phase φ ₂ . Subsequently, the synthesizing unit 153 calculates the average phase of each of the first phase φ ₁ and the second phase φ ₂ . Specifically, the combining unit 153, an average phase A1 with respect to the first phase phi _1, respectively calculates the average phase A2 for the second phase phi _2. Then, the synthesis unit 153 calculates φ _offset that is the difference between the average phase A1 and the average phase A2. FIG. 8A shows the first phase φ ₁ and the second phase φ ₂ determined by the phase determination unit 152, and the average phase A 1, average phase A 2, and φ _offset calculated by the synthesis unit 153.

Next, the synthesizing unit 153 adds φ _offset to the phase having the smaller absolute value among the absolute value of the first phase φ _{1 and} the absolute value of the second phase φ ₂ . Here, although it is assumed that the synthesis unit 153 adds φ _offset to the phase φ ₂ (FIG. 8B), φ _offset may be added to the phase φ ₁ .

The synthesizing unit 153 sets the weight of the phase within the predetermined interval to 1 as the value of the phase φ. Specifically, the synthesizing unit 153 synthesizes the first phase φ ₁ and the second phase φ ₂ using the following formula (9) and the above formula (7).
α ≦ φ ₁ <β ⇒ k (φ ₁ ) = 1, k (φ ₂ ) = 0
φ ₁ <α, β ≦ φ ₁ ⇒ k (φ ₁ ) = 0, k (φ ₂ ) = 0 Formula (8)
FIG. 8C is a graph in which the combined function φ _synth is plotted with the phase φ value set to 1 for the phase weight in a predetermined interval and 0 for the phase outside the interval.

  The above-mentioned α and β may be set as appropriate by the business operator who manufactures the optical device 1. For example, when α = π / 2 and β = 3π / 2 are set, they are generated at a half cycle. Phase analysis error can be reduced. A plurality of α and β may be set. For example, when the interval between α and β is set to π / 4, the synthesis unit 153 sets the weight of the tangent function with the phase as a variable to diverge to infinity, and does not diverge to infinity. The weight of one is set to 1. By doing in this way, since the optical apparatus 1 can measure the shape of the measuring object 4 without using the phase in which the error increases, the error can be reduced.

  In the present embodiment, the case where the optical system 12 divides the interference light into two has been described. However, the number of the interference light is not limited to this, and may be three or more. In the present embodiment, the case where the angle at which the polarizing plate 124 is rotated is 45 degrees, but the angle at which the polarizing plate 124 is rotated is not limited to this. If the polarizing plate 124a and the polarizing plate 124b are not at the same angle, the phase at which the absolute value of the tangent function increases can be made different.

(Modification 1)
The optical device 1 synthesizes the first phase and the second phase with the weight determined based on the value of the tangent function with the phase as a variable when both the first phase and the second phase are within a predetermined interval. To do. Hereinafter, the combining unit 153 of the optical device 1 according to Modification 1 will be described.

The synthesizer 153 has a tangent function with the phase having a variable as the weight of the first phase and the second phase determined by the phase determining unit 152, which has the larger absolute value of the value of the tangent function having the phase as a variable. The first phase and the second phase are synthesized by making the absolute value of the first value smaller than the smaller weight. Specifically, the synthesizing unit 153 compares | tan (φ ₁ (x, y)) | with | tan (φ ₂ (x, y)) | ((E) in FIG. 6) to determine the phase. Of the first phase φ ₁ (x, y) and the second phase φ ₂ (x, y) determined by the determination unit 152, the one having the larger absolute value of the value of the tangent function with the phase as a variable is determined. . The synthesizing unit 153 sets the weight of the tangent function having the phase as a variable having a larger absolute value to be smaller than the weight having the smaller absolute value of the value of the tangent function having the phase as a variable. The phase φ ₁ (x, y) and the second phase φ ₂ (x, y) are combined.

The combining unit 153 combines the coefficient k applied to the larger absolute value of the value of the tangent function with the phase as a variable smaller than the coefficient k applied to the smaller absolute value of the value of the tangent function having the phase as the variable. To do. The coefficient k is a function of the phase φ (x, y), the first phase φ ₁ (x, y) is multiplied by the coefficient k ₁ (φ ₁ (x, y)), and the second phase φ ₂ (x , Y) is multiplied by a coefficient k ₂ (φ ₂ (x, y)). More specifically, the synthesizing unit 153 synthesizes the first phase φ ₁ (x, y) and the second phase φ ₂ (x, y) using Expression (7). Then, the combining unit 153 transmits a combined phase φ _synth (x, y) obtained by combining the first phase φ ₁ (x, y) and the second phase φ ₂ (x, y) to the shape creating unit 154.

  As described above, the optical device 1 determines two phases based on the two interference light groups offset in phase, and selects the weight of the two phases having the larger absolute value of the tangent function having the phase as a variable. The absolute value of the tangent function with the phase as a variable is made smaller than the smaller weight and is synthesized. Then, the optical device 1 creates the shape of the measurement object 4 using the synthesized phase. By doing in this way, the optical apparatus 1 can reduce the calculation error even when the value of the tangent function having the phase of the interference light as a variable becomes large due to the measurement principle. Therefore, the optical device 1 can reduce the measurement error of the shape of the measurement object 4.

  Note that the combining unit 153 may determine in advance a phase to increase the weight when both the first phase and the second phase are within a predetermined section. The operator that manufactures the optical device 1 may determine the phase for increasing the weight as appropriate, but may be determined by the optical device 1. For example, the optical apparatus 1 measures the shape of the measurement object 4 a plurality of times, and includes a variation σ1 determined based on a plurality of first phases obtained by the plurality of measurements and a variation σ2 determined based on the plurality of second phases. Among them, the weight of the phase with small variation is increased. Specifically, the optical device 1 determines the weight of the first phase and the weight of the second phase based on the ratio of the variation σ1 and the variation σ2. By doing so, the optical device 1 combines the first phase and the second phase by increasing the weight of the smaller phase variation, so that the measurement error of the shape of the measurement object 4 can be reduced. .

  The combining unit 153 may equalize the weight of the first phase and the weight of the second phase when both the first phase and the second phase are within a predetermined interval. For example, when the first phase and the second phase are both within a predetermined section and the difference between the variation σ1 and the variation σ2 is equal to or less than the predetermined difference, the synthesis unit 153 The two phase weights are made equal. For example, the synthesis unit 153 determines a predetermined difference based on the measurement accuracy required by the size of the unevenness of the measurement object 4.

(Modification 2)
When the wavelength of light emitted from the light source 11 is changed, the actually changed wavelength change amount may be different from the set wavelength change amount Δλ. In this case, the light intensity I detected by the camera 13 includes an error proportional to the difference between the set wavelength change amount Δλ and the actually changed wavelength change amount. The interference light in the case of including the error Er is expressed by Expression (8).

  The error Er in Expression (8) appears in the calculation result as a three-phase analysis error that periodically occurs in the phase determined by the phase determination unit 152. The phase analysis error is generated by increasing / decreasing at a half cycle (double frequency) with respect to the cycle of the trigonometric function determined by the intensities of a plurality of interference lights having different phases. Hereinafter, a phase analysis error that occurs in a half cycle will be described.

  FIG. 9 is a diagram for explaining the phase analysis error. FIG. 9A schematically shows the measurement object 4 tilted so that one period of a trigonometric function determined by the intensities of a plurality of interference lights having different phases in a predetermined length in the x-axis direction is accommodated. It is. Here, it is assumed that the measurement object 4 is an ideal plane with a smooth surface.

  FIG. 9B plots the intensity of the interference light in which the measurement light reflected from the ideal plane shown in FIG. 9A interferes with the reference light, where the horizontal axis is the x coordinate and the vertical axis is the intensity of the interference light. It is a graph. FIG. 9C is a graph in which the phase analysis error generated by analyzing the interference light in FIG. 9B is plotted with the horizontal axis representing the x coordinate and the vertical axis representing the magnitude of the error.

  FIG. 9D is a graph plotting the intensity of the interference light obtained by offsetting the phase of the interference light of FIG. 9B by 90 degrees. FIG. 9E is a graph plotting phase analysis errors caused by analyzing the interference light of FIG. 9D.

  The phase analysis error shown in FIG. 9C and the phase analysis error shown in FIG. 9E are states in which the phases are inverted. By combining the two phases with the phase analysis error inverted, the phase analysis error can be canceled. FIG. 9F is a graph plotting the phase analysis error canceled by combining the two phases with the phase analysis error inverted.

  As described above, the optical apparatus 1 uses the fact that the phase analysis error is generated at a cycle of 1 / integer with respect to the cycle of the trigonometric function determined by the intensities of the plurality of interference lights having different phases. Synthesizes two phases in the inverted state. By doing so, the optical device 1 can cancel the phase analysis error. Therefore, the optical device 1 can measure the shape of the measurement object 4 in a state where the influence of the phase analysis error is reduced. Hereinafter, the functional configuration of the optical device 1 according to Modification 1 will be described. The control unit 15 of the optical device 1 according to Modification 1 implements a function as the phase adjustment unit 156 by executing a program stored in the storage unit 14.

The phase adjustment unit 156 includes the first interference light group I _1j (so that the phase analysis error periodically generated in each of the first phase φ ₁ and the second phase φ ₂ determined by the phase determination unit 152 is inverted. The phase difference between x, y) and the second interference light group I _2j (x, y) is adjusted. For example, the phase adjustment unit 156 rotates the polarizing plate 124b of the optical system 12 to rotate the phase difference between the first interference light group I _1j (x, y) and the second interference light group I _2j (x, y). Adjust. More specifically, the phase adjusting unit 156 rotates the transmission axis of the polarizing plate 124b with respect to the polarizing plate 124a by 45 degrees in a plane perpendicular to the optical axis. In this way, the phase adjustment unit 156 can set the phase difference between the first interference light group I _1j (x, y) and the second interference light group I _2j (x, y) to 90 degrees.

Next, in a state where the phase difference between the first interference light group I _1j (x, y) and the second interference light group I _2j (x, y) is 90 degrees, the phase determination unit 152 A second phase is determined. Subsequently, the combining unit 153 includes the first phase weight in a state where the phase difference between the first interference light group I _1j (x, y) and the second interference light group I _2j (x, y) is 90 degrees. The first phase and the second phase are synthesized by making the weight of the second phase equal. Then, the shape creation unit 154 creates the shape of the measurement object 4 based on the combined phase obtained by combining the first phase and the second phase in a state where the phase difference is 90 degrees. By doing so, the optical device 1 can cancel the phase analysis error.

  The optical device 1 may execute the above-described processing when receiving an instruction to cancel the phase analysis error from another device. In this case, the control unit 15 of the optical device 1 realizes a function as the instruction receiving unit 155 by executing a program stored in the storage unit 14.

The instruction receiving unit 155 receives an instruction to execute processing for canceling the phase analysis error from another device via a communication unit (not shown). Specifically, the instruction receiving unit 155 receives an instruction to cancel the phase analysis error. For example, the instruction receiving unit 155 receives information indicating a dominant integer as a phase analysis error by the phase shift method among a plurality of phase analysis errors as a predetermined integer. Specifically, the instruction receiving unit 155 may receive an integer in which the magnitude of the phase analysis error is larger than the magnitude of other phase analysis errors as an integer dominant as the phase analysis error. Further, the instruction receiving unit 155 may receive a phase difference that inverts a phase analysis error periodically generated in each of the first phase φ ₁ and the second phase φ ₂ . Then, the combining unit 153 combines the weights of the first phase and the second phase with the same weight on condition that the instruction receiving unit 155 has received the instruction.

  Hereinafter, the processing executed by the control unit 15 of the optical device 1 according to Modification 1 will be described with reference to FIG. FIG. 10 is a flowchart of processing executed by the control unit 15 of the optical device 1 according to the first modification. First, the instruction receiving unit 155 receives an instruction to execute processing for canceling the phase analysis error from another device (step S11).

Next, the phase adjustment unit 156 adjusts the phase difference between the first interference light group and the second interference light group on the condition that the instruction reception unit 155 has received the instruction (step S12). For example, the phase adjustment unit 156 is configured so that the phase difference between the first interference light group I _1j (x, y) and the second interference light group I _2j (x, y) is 90 degrees with respect to the polarizing plate 124a. Thus, the transmission axis of the polarizing plate 124b is rotated by 45 degrees in a plane perpendicular to the optical axis.

  The acquisition unit 151 uses the difference between the first initial phase determined by the first interference light group and the second initial phase determined by the second interference light group as the phase difference between the first interference light group and the second interference light group. Obtain (step S13).

  The synthesizing unit 153 determines whether or not the phase difference indicated by the instruction corresponds to the phase difference acquired by the acquiring unit 151 (step S14). For example, the synthesis unit 153 determines that the difference between the phase difference indicated in the instruction and the phase difference acquired by the acquisition unit 151 is equal to or smaller than a predetermined value, and does not correspond to the case where the difference is larger than the predetermined value. Is determined. The predetermined value is, for example, larger than the phase difference error acquired by the acquisition unit 151.

  When the synthesis unit 153 determines that the phase difference indicated by the instruction does not correspond to the phase difference acquired by the acquisition unit 151 (No in step S14), the synthesis unit 153 proceeds to step S12, and the phase difference indicated by the instruction and the acquisition unit Steps S12 to S14 are repeated until it is determined that the phase difference acquired by the above corresponds. If the combining unit 153 determines that the phase difference indicated by the instruction corresponds to the phase difference acquired by the acquiring unit (Yes in step S14), the combining unit 153 combines the weights of the first phase and the second phase equal to each other (step S14). Step S15).

  As described above, the optical device 1 according to the modified example 1 adjusts the phase difference between the first interference light group and the second interference light group so that the phase analysis error is reversed, and the first phase and the second phase are adjusted. Combining with equal weight. By doing in this way, the optical apparatus 1 which concerns on the modification 1 can cancel a phase analysis error.

(Modification 3)
Since the camera that acquires the first interference light and the camera that acquires the second interference light are different from each other, the variation in the intensity of the interference light detected by the camera may be different. For example, when the variation in the intensity of the second interference light acquired by the camera 13b is smaller than the variation in the intensity of the first interference light acquired by the camera 13a, the intensity of the second interference light is greater than the intensity value. It can be said that the reliability is high. As described above, when the reliability of the intensity value is different, the measurement error of the shape of the measurement object 4 can be reduced by correcting the phase weight based on the reliability.

  Therefore, the synthesis unit 153 corrects the weight using a preset correction value. For example, the synthesis unit 153 corrects the weights of the first phase and the second phase by using the correction values set in advance for the first phase and the second phase, respectively. Synthesize the phase. The company that manufactures the optical device 1 may set the correction value as appropriate, but may be determined by the control unit 15 of the optical device 1 executing a process for determining the correction value.

(Process to determine the correction value)
First, the acquisition unit 151 acquires a first interference light group and a second interference light group. Subsequently, the phase determination unit 152 determines the first phase of the first interference light group and the second phase of the second interference light group.

  Next, the acquisition unit 151 acquires again the first interference light group and the second interference light group in the same measurement object 4 as the first interference light group and the second interference light group acquired previously. Subsequently, the phase determination unit 152 determines the first phase of the first interference light group acquired again and the second phase of the second interference light group acquired again. In this way, the phase determination unit 152 determines a plurality of first phases and a plurality of second phases for the same measurement object 4.

The synthesizing unit 153 statistically analyzes the plurality of first phases and calculates the first variation σ ₁ of the first phase. Similarly, the synthesis unit 153 statistically analyzes the plurality of second phases and calculates the second variation σ ₂ of the second phase. Then, the combining unit 153 sets the correction values for the first phase and the second phase so that the weight with the larger variation σ is smaller than the weight with the smaller variation σ.

FIG. 11 is a diagram for explaining that the weight is corrected using the set correction value. In FIG. 11, description will be made assuming that the first variation σ ₁ is larger than the second variation σ ₂ and σ ₁ = M · σ ₂ . In this case, the combining unit 153 sets the correction value _{C 1} of the weight of the first phase 1 / (1 + M) and to set the correction value _{C 2} of the weight of the second phase M / (1 + M) and.

First, the phase determination unit 152 determines the first phase φ ₁ and the second phase φ ₂ . FIG. 11A is a graph in which the first phase φ ₁ and the second phase φ ₂ determined by the phase determination unit 152 are plotted.

Next, the combining unit 153, the correction value C ₁ of the weight of the first phase by multiplying the first phase phi _1, multiplies the correction value C ₂ of the weight of the second phase to the second phase phi _2. FIG. 11 (B) first and corrected phase _{C 1} phi ₁ that has been multiplied by the correction value _{C 1} of the weight of the first phase to the first phase phi _1, the correction value _{C 2} of the weight of the second phase second is a graph plotting the second and corrected phase C ₂ phi ₂ that is multiplied by the phase phi _2.

Subsequently, the synthesizing unit 153 adds φ _offset which is a difference between the first phase φ ₁ and the second phase φ ₂ to the second corrected phase C ₂ φ ₂ (FIG. 11C). Then, the combining unit 153 combines the first corrected phase C ₁ φ ₁ and the second corrected phase C ₂ φ _{2 obtained} by adding φ _offset . FIG. 11D is a graph plotting the composite phase.

By doing in this way, since the optical apparatus 1 can take the weighted average according to dispersion | variation, it can improve the reliability of synthetic _{| combination} phase (phi) _synth . In the above description, the combining unit 153 calculates the variation in the intensity of the interference light. However, the present invention is not limited to this, and depending on the amount of error generated due to the characteristics inherent in the observation system between the camera 13a and the camera 13b, You may set the correction value C of a weighting coefficient. For example, the synthesizing unit 153 may set the correction value of the weighting coefficient according to the section or the value using the correction value of the weighting coefficient as a function of the first phase φ ₁ or the second phase φ ₂ .

  As described above, it has been described that the combining unit 153 determines the correction value for correcting the weight. However, the present invention is not limited to this, and the combining unit 153 may determine the weight based on the reliability of the acquired interference light intensity value. Good. In this case, the synthesizing unit 153 analyzes the weight of the phase obtained by analyzing the interference light group having the high reliability of the intensity value of the interference light among the reliability of the first interference light group and the reliability of the second interference light group. Is made heavier than the weight of the phase obtained by analyzing the interference light group with low reliability of the intensity value of the interference light. Further, the combining unit 153 may set the phase weight obtained by analyzing the interference light group with high reliability to 1 and set the phase weight obtained by analyzing the interference light group with low reliability to 0.

[Effect of Optical Device 1 According to Embodiment]
As described above, the optical device 1 determines a plurality of phases based on a plurality of interference light groups offset in phase, and of the plurality of phases, the absolute value of the tangent function having the phase as a variable is larger. The weight is synthesized by making it smaller than the weight having the smaller absolute value of the tangent function having the phase as a variable. Then, the optical device 1 creates the shape of the measurement object 4 using the synthesized phase. By doing in this way, the optical apparatus 1 can reduce the calculation error even when the value of the tangent function having the phase of the interference light as a variable becomes large due to the measurement principle. Therefore, the optical device 1 can reduce the measurement error of the shape of the measurement object 4.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment, A various deformation | transformation and change are possible within the range of the summary. is there. In addition, the specific embodiments of device distribution / integration are not limited to the above-described embodiments, and all or part of the devices may be configured to be functionally or physically distributed / integrated in arbitrary units. Can do. In addition, new embodiments generated by any combination of a plurality of embodiments are also included in the embodiments of the present invention. The effect of the new embodiment produced by the combination has the effect of the original embodiment.

  In the above embodiment, as an optical system for imparting a phase difference to the interference light obtained by each camera, the non-interference light composed of orthogonally polarized reference light and measurement light is rotated counterclockwise by a λ / 4 plate. A method of giving a phase difference depending on the installation angle of the transmission axis of the polarizing plate after being divided into circularly polarized light was shown. However, the present invention is not limited to this, and a method may be used in which light in a non-interference state is divided as linearly polarized light and a common polarization component of reference light and measurement light is extracted by a polarizing plate and interfered. In this case, a wavelength plate may be disposed on the divided optical path to give a phase difference between the reference light and the measurement light, thereby obtaining interference light that interferes with a predetermined phase difference. Further, the beam splitter and the polarizing plate may be replaced with a polarizing beam splitter having both functions. In addition to these methods, any method may be used as long as it is a general method for obtaining an interference signal from a non-interfering test light beam. Furthermore, in the above description, the phase shift method by changing the wavelength of light is used, but the method of shifting the phase is not limited to this. For example, the optical path length difference may be changed by moving the reference surface or the measurement object in the optical axis direction, and the phase of the interference light may be shifted, or the phase of the interference light may be shifted by another method. .

  Further, the optical device 1 according to the embodiment determines the phase weight based on whether or not each of the plurality of positions of the measurement object 4 is within a predetermined section. Not only this but the optical apparatus 1 makes a phase a variable among the 1st phase and the 2nd phase about each of several position of the measuring object 4 irrespective of whether it is in a predetermined area. The first phase and the second phase may be synthesized by making the weight having the larger absolute value of the tangent function smaller than the weight having the smaller absolute value of the tangent function having the phase as a variable.

DESCRIPTION OF SYMBOLS 1 Optical apparatus 3 Reference surface 4 Measurement object 5 Optical apparatus 11 Light source 12 Optical system 13 Camera 14 Storage part 15 Control part 16 Display part 120 Pinhole 121 Lens 122 Beam splitter 123 λ / 4 plate 124 Polarizing plate 150 Wavelength changing part 151 Acquisition unit 152 Phase determination unit 153 Combining unit 154 Shape creation unit 155 Instruction reception unit 156 Phase adjustment unit

Claims (8)

A first interference light group of a plurality of interference lights having different phases, each of which is a reflection of the reflected light reflected from the reference surface and the measurement light reflected from the measurement object, and a second offset of the phase of the first interference light group An acquisition unit for acquiring the interference light group;
The first interference light group is analyzed by a phase shift method to determine a first phase that is a phase at each of a plurality of positions of the measurement object, and the second interference light group is analyzed by the phase shift method to determine the first phase. A phase determining unit that determines a second phase that is a phase at each of a plurality of positions of the measurement object;
For each of a plurality of positions of the measurement object, when the phase determined by the phase determination unit is within a predetermined section, the first phase and the phase are set with a weight greater than that when the phase is outside the section. A combining unit that combines the second phase;
An optical device comprising: The synthesizing unit, when one phase of the first phase and the second phase is within a predetermined interval and the other phase is outside the predetermined interval, weight of the phase within the interval And 1 for the phase weight outside the interval,
The optical device according to claim 1. The synthesizing unit, for each of a plurality of positions of the measurement object, out of the first phase and the second phase determined by the phase determining unit, an absolute value of a value of a tangent function having the phase as a variable A weight having a larger value is made smaller than a weight having a smaller absolute value of a value of a tangent function having the phase as a variable, and the first phase and the second phase are combined.
The optical device according to claim 1. The combining unit combines the first phase and the second phase with equal weights;
The optical device according to claim 1. The order of the first interference light group and the second interference light group is such that a phase analysis error periodically generated in each of the first phase and the second phase determined by the phase determination unit is inverted. A phase adjustment unit for adjusting the phase difference;
The optical device according to claim 4. The combining unit corrects the weights of the first phase and the second phase by using correction values set in advance for the first phase and the second phase, respectively. Combining with the second phase;
The optical device according to any one of claims 1 to 5. A light source for irradiating light to the reference surface and the measurement object;
The optical apparatus according to claim 1, further comprising: a wavelength changing unit that changes a wavelength of light emitted from the light source so that phases of the plurality of interference lights are different from each other. The computer runs,
A first interference light group of a plurality of interference lights having different phases, each of which is a reflection of the reflected light reflected from the reference surface and the measurement light reflected from the measurement object, and a second offset of the phase of the first interference light group Obtaining an interference light group;
The first interference light group is analyzed by a phase shift method to determine a first phase that is a phase at each of a plurality of positions of the measurement object, and the second interference light group is analyzed by the phase shift method to determine the first phase. Determining a second phase that is a phase at each of a plurality of positions of the measurement object;
For each of the plurality of positions of the measurement object, when the phase determined by the phase determination unit is within a predetermined section, the weight is set larger than when the phase is outside the section, and the first phase and Combining the second phase;
A shape measuring method comprising: