JP5480479B2 - Shape measuring device and calibration method of shape measuring device - Google Patents

Description

  The present invention relates to a shape measuring apparatus and a calibration method for the shape measuring apparatus.

Conventionally, by irradiating light to a measurement object in a right angle direction, sample light that is reflected light from the measurement object interferes with reference light that is reflected light from a reference surface, and generated interference fringes. A shape measuring device that measures the surface shape of an object to be measured by analysis is known (see, for example, Patent Document 1).
In addition, by irradiating the measurement object with light in an oblique direction, the measurement range can be expanded as compared with the case where light is irradiated in a right angle direction, and the flatness of a surface with a large swell or rough surface can be measured. A shape measuring apparatus is also known (see, for example, Patent Document 2). This measuring apparatus is also called a grazing incidence interferometer.
As a method for analyzing these interference fringes, a phase shift method in which the surface shape is measured from a plurality of acquired interference fringes by shifting the phase of the interference fringes by a method such as displacing the reference surface is generally used. Used for.
However, such a phase shift method has a problem that the measurement time becomes long because there is an operation such as displacing the reference surface while acquiring a plurality of interference fringes.

On the other hand, the inventors, in the shape measuring apparatus described in Patent Documents 1 and 2, divide the measurement light obtained by superimposing the sample light and the reference light into three by a prism, and set the phase of each divided light to a polarizing plate And three interference fringes with optically different phase differences were generated simultaneously. Then, three interference fringes can be photographed simultaneously using three image sensors.
According to this method, it is possible to speed up the shape measurement by instantaneously capturing a plurality of interference fringes necessary for the arithmetic processing by the phase shift method.

Japanese Patent No. 3766319 JP 2008-32690 A

In the shape measuring apparatus described in Patent Documents 1 and 2, the measurement light is divided into three by the prism through a quarter-wave plate arranged on the light source side of the prism, and each divided light is divided. And pass through three polarizing plates having different transmission axis directions. At this time, measurement of the shape of the measurement object is performed on condition that each corresponding point of the interference fringes generated in each divided light has the same intensity and has a phase shift amount given according to the design value. Done.
However, in reality, the biases and the amplitudes of the three interference fringes differ from each other due to the split intensity error of the prism, the installation error of the fast axis and the slow axis of the quarter-wave plate, and the like. In addition, due to an error in the installation angle of the transmission axis of the polarizing plate, the optically applied phase shift amount is not as designed.
Therefore, the obtained three interference fringes are not interference fringes that are phase-shifted as designed according to the principle, but interference fringes with different parameters such as bias, amplitude, and phase shift amount. When the interference fringes are used as they are, there is a first problem that the measurement accuracy is lowered.

  On the other hand, in order to reduce the parameter error, a method of manufacturing a measuring device according to the design value by using highly accurate optical components and performing advanced adjustment is also conceivable. There is a second problem of becoming an expensive device.

  On the other hand, the intensity and distribution of interference fringes are unique to the configured optical system.For example, if the optical axis is slightly shifted during repeated measurement, the intensity and distribution of interference fringes change. End up. In addition, the intensity and distribution state of interference fringes also change due to changes in geometric dimensions due to changes over time of the housing of the measuring device and changes in the performance of optical components due to changes in temperature. Moreover, when measuring a measurement object having different surface properties (materials, etc.), the intensity and distribution state of interference fringes change. On the other hand, if the initial parameters set at the time of manufacturing the measuring apparatus are continuously used, the measurement accuracy is deteriorated due to changes in the interference fringe intensity and distribution state. Therefore, it is necessary to calibrate the interference fringe parameters periodically or immediately before the measurement. At that time, it is desired that the user can easily calibrate in the use environment and maintain the measurement accuracy (third problem).

  An object of the present invention is a shape measuring apparatus that can solve the first to third problems described above, and can calibrate information on bias, amplitude, and phase of interference fringes without using an expensive apparatus. Another object of the present invention is to provide a shape measuring device and a method for calibrating the shape measuring device, which can be easily calibrated by the user in the use environment and can improve the measurement accuracy.

The shape measuring apparatus of the present invention emits light that irradiates a measurement object, and a sample that is reflected from the measurement object and a light source that becomes a reference light without irradiating a part of the light to the measurement object A combining unit that superimposes the light and the reference light to obtain measurement light, a measurement light dividing unit that divides the measurement light into a plurality of divided measurement lights, and an optical axis of the divided measurement light, respectively. Based on the polarization unit that generates an interference fringe by giving a different phase difference to the divided measurement light, a plurality of imaging units that capture the interference fringe for each of the divided measurement light, and the plurality of captured interference fringes, A measurement control unit that measures the shape of the object to be measured using information on bias, amplitude, and phase of interference fringes calibrated in advance for each imaging unit, and the light source includes: , Wavelength that can change the wavelength of emitted light A variable light source, the measurement control unit, for each of the imaging unit, and a light source control unit that changes the wavelength of the light from the light source, and when calibrating each information of bias, amplitude and phase of the interference fringes in advance Based on a plurality of interference fringes obtained by changing the wavelength of the light source, a calibration control unit that calibrates each information of the bias, amplitude, and phase, and the imaging when measuring the shape of the measurement object An analysis unit that analyzes shape information of the measurement object based on a plurality of interference fringes simultaneously acquired by the unit and given different phase differences, and each information of the bias, amplitude, and phase calibrated in advance, The shape measuring apparatus includes an optical path difference adjustment mechanism capable of adjusting an optical path difference (Δl) between the optical path length of the reference light and the optical path length of the sample light, and the optical path difference (Δl ) Change the wavelength (λ) of the light source Phase shift of the interference fringes when only varied ^{(Δλ) (2π / λ 2} × ΔlΔλ) is such that the above 2 [pi, characterized in that it is set.

  Here, the present invention relates to a simultaneous imaging type shape measuring apparatus that simultaneously captures interference fringes with different phase differences with a plurality of imaging units. Or a so-called oblique incidence interferometer that irradiates light at a predetermined incident angle from an oblique direction to the measurement object.

  According to this configuration, information on bias, amplitude, and phase in a plurality of interference fringes with different phase differences can be easily obtained as calibration parameters, and interference fringes with different phase differences are given. It is possible to reduce errors caused by deviations in the bias and amplitude between them and the deviation of the phase shift amount between the interference fringes from the design value, thereby improving the measurement accuracy and solving the first problem.

  Specifically, since interference fringes acquired by a plurality of imaging units have different bias, amplitude, and phase characteristics, a plurality of interference fringes by light of different wavelengths are acquired for each imaging unit. Thus, each information of bias, amplitude and phase of the interference fringes can be calculated individually. At this time, since the variable wavelength light source capable of changing the wavelength of light is used, the user can easily calibrate the bias, amplitude and phase parameters only by appropriately setting the change amount of the wavelength. Since the bias, amplitude variation, and phase shift deviation are not reduced, an interference optical system need not be configured using a high-precision optical element, and an expensive apparatus is not required. In addition, since the advanced adjustment is not required, the second problem can be solved. Therefore, the user can perform the periodic readjustment work necessary for the high-precision measuring apparatus, and the time and cost required for the readjustment work can be reduced.

  In addition, when the shape measuring device changes over time or temperature, or when measuring objects with different surface properties (materials, etc.), new variations in bias and amplitude between interference fringes and interference Even if an error due to the deviation of the phase shift amount between the fringes occurs, the user can easily calibrate the parameters periodically or immediately before the measurement in the usage environment, so that the measurement accuracy is maintained. And the third problem can be solved.

  In the shape measuring apparatus of the present invention, it is preferable to include an incident angle variable mechanism that can change an incident angle of light emitted from the light source to the measurement object.

  According to this configuration, the incident angle of the light irradiated to the measurement object can be changed by the variable incident angle mechanism, so that the height (fringe sensitivity) represented by the adjacent fringes in the imaged interference fringes can be changed. Measurement according to the shape of the measurement object can be performed. When changing the incident angle, the measurement surface of the measurement object may be tilted by a predetermined angle with respect to the light from the light source, or an interference optical system such as a light source and an imaging unit may be provided with the measurement object as it is. It may be moved. At this time, the intensity of the sample light from the object to be measured changes according to the incident angle, and there is a possibility that errors due to variations in bias and amplitude and deviations in the phase shift amount between interference fringes may occur. Even in such a case, since the parameters can be easily calibrated, highly accurate measurement can be maintained.

In the shape measuring apparatus of the present invention, the optical path difference (Δl) between the optical path length of the reference light and the optical path length of the sample light is obtained by changing the wavelength (λ) of the light source by a change amount (Δλ). It is preferable that the phase shift amount (2π / λ ² × ΔlΔλ) of the interference fringes is set to be 2π or more.

Here, if the range of the phase shift amount of the interference fringes obtained by changing the wavelength is 2π or more, the phase of the interference fringes at the time of calibration can be changed by one period or more, and the phase of one period can be obtained. In this range, a plurality of interference fringes having different phase differences can be acquired, and calibration parameters can be calculated with high accuracy by the least square method.
According to this configuration, for example, a relatively inexpensive semiconductor laser can be employed as the wavelength variable light source by setting the optical path difference (Δl) so that the phase shift amount of the interference fringes is 2π or more. . When adopting a semiconductor laser, it is necessary to pay attention to the fact that the wavelength variable range must be relatively narrow in order to suppress the change in emission intensity due to the change in wavelength within a predetermined range. However, even when the change amount (Δλ) of the usable wavelength (λ) is limited in this way, the phase shift amount of the interference fringes can be set by appropriately setting the optical path difference (Δl) of the interference optical system. (2π / λ ² × ΔlΔλ) can be set to 2π or more, and the measurement apparatus can be calibrated. Therefore, a relatively inexpensive semiconductor laser can be employed without being affected by the change in emission intensity due to the change in wavelength.

The shape measuring apparatus of the present invention preferably includes an optical path difference adjusting mechanism capable of adjusting the optical path difference.
Here, as the optical path difference adjusting mechanism, a mechanism that makes the optical path length of the reference light or sample light variable may be used, or a medium that changes the speed of light is installed on the optical path of the reference light or sample light. Thus, a mechanism for adjusting the optical path difference may be used.

According to this configuration, the optical path difference can be adjusted to an arbitrary length by the optical path difference adjustment mechanism. When the optical path difference is constant, usable wavelength tunable light sources may be limited, or there may be restrictions on the design of the interference optical system configured for the light source to be used. Accordingly, by adjusting the optical path difference according to the change amount of the wavelength of the light source to be used, the necessary phase shift amount (2π / λ ² × ΔlΔλ) of the interference fringes can be obtained, so that the wavelength variable light source can be freely selected. The degree can be increased.

  In the shape measuring apparatus according to the aspect of the invention, it is preferable that the calibration control unit calibrates the bias, amplitude, and phase information in advance based on interference fringes acquired using the measurement object.

  According to this configuration, since the parameter is calibrated using the measurement object, when measuring a plurality of measurement objects having the same shape continuously, the shape value and the calibration value are measured during the first shape measurement. If these parameters are acquired simultaneously, the subsequent shape measurement can use the acquired parameters as they are and perform shape measurement by one simultaneous imaging.

  In the shape measuring apparatus of the present invention, the calibration control unit calibrates the bias, amplitude, and phase information in advance based on interference fringes acquired using a calibration substrate made of the same material as the measurement object. It is preferable to do.

  According to this configuration, since the parameters are calibrated using the calibration substrate made of the same material as that of the measurement object, more accurate calibration can be performed.

In the calibration method for a shape measuring apparatus according to the present invention, a light source that emits light for irradiating the measurement object and a reference light without irradiating a part of the light to the measurement object, and an optical path length of the reference light And an optical path difference adjustment mechanism capable of adjusting the optical path difference (Δl) between the sample light and the optical path length of the sample light, and a combining unit that superimposes the sample light reflected from the measurement object and the reference light to obtain measurement light, A measuring light splitting unit that splits the measuring light into a plurality of split measuring lights and an optical axis of the split measuring light, respectively, and gives different phase differences to the split measuring light to generate interference fringes. A polarization unit, a plurality of imaging units that capture the interference fringes for each of the divided measurement lights, and a bias, amplitude, and phase of interference fringes that are calibrated in advance for each imaging unit based on the plurality of captured interference fringes Using the information of, the shape of the measurement object Said bias, a method of calibrating the amplitude and phase each information in the shape measuring apparatus and a measurement control section for measuring, the light source is a wavelength-tunable light source for changing the wavelength of light emitted, the optical path difference (Δl) is set so that the phase shift amount (2π / λ ² × ΔlΔλ) of the interference fringes when the wavelength (λ) of the light source is changed by the change amount (Δλ ) is 2π or more. A setting step for setting the amount of change in the wavelength of light from the light source , an irradiation step for irradiating the measurement object with the set amount of change, and interference fringes generated for each amount of change in the wavelength, An imaging process for imaging each of the plurality of imaging units, and a calculation process for calculating each information of the bias, amplitude, and phase based on the captured interference fringes are configured. .

  According to this configuration, as described above, it is possible to calibrate the interference fringe bias, amplitude and phase information without using an expensive device, and the user can easily calibrate and measure in the usage environment. Accuracy can be improved.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings.
In the second and later embodiments described later, the same reference numerals are given to the same components and the same members as the components in the first embodiment described below, and the description will be simplified or omitted. .

[First Embodiment]
FIG. 1 is an overall configuration diagram of a shape measuring apparatus 1 of the present embodiment.
As shown in FIG. 1, the shape measuring apparatus 1 is a so-called grazing incidence interferometer that mainly includes an irradiation unit 10, a detection unit 30, and a measurement control unit 40.

[Overall configuration of interference optical system]
The irradiation unit 10 includes a light source 11, lenses 12 and 13, a light beam splitting element 14, a half-wave plate 15 that is an optical element that rotates a polarization plane, and a light beam combining element (synthesizing unit) 16. Here, a part of the light from the light source 11 is arranged so as to be irradiated at a predetermined angle in the normal direction of the measurement surface of the measurement object 20 via the lenses 12 and 13 and the light beam splitter 14. ing. In the first embodiment, a part of the light B emitted from the light source 11 is transmitted through the light beam splitting element 14 while changing its path, and is irradiated onto the half-wave plate 15. Thus, the light which is not irradiated to the measuring object 20 is called reference light B1. On the other hand, a part of the light B from the light source is transmitted through the light beam splitting element 14 without changing the course, and is irradiated onto the measurement object 20. The reflected light from the measurement object 20 is referred to as sample light B2.

  The detection unit 30 includes a quarter wavelength plate 31, a lens 32, a three-divided prism (measurement light division unit) 33, a plurality of polarizing plates (polarization units) 34A to 34C, and a plurality of imaging units 35A to 35C. Is provided.

The light B emitted from the light source 11 enters the light beam splitting element 14 as a parallel light beam through the lenses 12 and 13 and is split into two light beams. One of the divided light beams is irradiated on the measurement surface of the measurement object 20 from an oblique direction. On the other hand, the other (reference light B1) of the light beam split by the light beam splitting element 14 is converted by the half-wave plate 15 into a polarization component orthogonal to the polarization component before passing. Then, the sample light B 2 reflected from the measurement object 20 and the reference light B 1 split by the light beam splitting element 14 are overlapped by the light beam combining element 16. The combined light beam is referred to as measurement light B3. The measurement light B3 is converted into clockwise and counterclockwise circularly polarized light by the quarter wavelength plate 31. The measurement light B <b> 3 that has become circularly polarized light is divided in three directions by the three-divided prism 33. Here, the light beam divided in three directions is referred to as divided measurement light. The divided measurement light passes through the polarizing plates 34A to 34C arranged on the optical axes of the divided measurement light with the transmission axes being different from each other, and is given different phase differences. Due to the polarizing plates 34A to 34C, each split measurement light generates interference fringes with different phase differences (phase shifts). The phase-shifted interference fringes are picked up by the image pickup sections 35A to 35C as interference fringe images.
And a measurement control part measures the surface shape of the measuring object 20 based on the interference fringe image acquired by the imaging parts 35A-35C.

  In the configuration of the interference optical system as described above, the light source 11 employs a wavelength variable light source that emits light of different wavelengths.

[Overall configuration of control system]
FIG. 2 is a block diagram showing the overall configuration of the control system of the shape measuring apparatus 1.
As shown in FIG. 2, the measurement control unit 40 mainly includes a light source control unit 41, a calibration control unit 42, a parameter storage unit 43, an interference fringe analysis unit (analysis unit) 44, and an analyzed measurement value. A measurement data display unit 45 to be displayed is provided.

The light source control unit 41 changes the wavelength of the light emitted from the light source 11 by the change amount Δλ.
The calibration control unit 42 uses the predetermined calibration substrate 20 </ b> A as the measurement target 20 to calibrate the interference fringe bias, amplitude, and phase information in advance, and thus the interference acquired by the imaging units 35 </ b> A to 35 </ b> C. Based on the fringe intensity information, the interference fringe bias, amplitude, and phase information are calculated for each pixel of each of the imaging units 35A to 35C and output to the parameter storage unit 43 as calibration parameters. The calibration substrate 20A is made of the same material as that of the measurement object 20. The calibration control unit 42 changes the wavelength of the light source 11 N times, and acquires interference fringe intensity information for each predetermined change amount Δλ.
The parameter storage unit 43 creates a correction table for the calculated parameter and stores it for each pixel of each of the imaging units 35A to 35C.
The interference fringe analysis unit 44 refers to the parameters in the parameter storage unit 43 based on the interference fringe intensity information acquired by the imaging units 35A to 35C at the time of shape measurement, and performs arithmetic processing according to the phase shift method. It carries out and analyzes the surface shape information of the measuring object 20. Then, the analyzed measurement data is output to the measurement data display unit 45.

  The interference fringe imaging in the control system as described above can be automatically operated by executing a program for operating the light source 11 and the imaging units 35A to 35C using the electronic computer 40A and the control device 40B shown in FIG. It is like that.

[Parameter calculation method]
A method of calculating the parameters (bias, amplitude, phase shift amount) of the shape measuring apparatus 1 based on the interference fringe intensity information acquired by the imaging units 35A to 35C will be described.
The obtained interference fringe intensity Ii (x, y, λ) is expressed by equation (1). The display of (x, y) in the formula is a display of points corresponding to the pixels of the imaging units 35A to 35C in XY coordinates, and the variable to which (x, y) is attached is a pixel. Each numerical value shall be indicated. Further, λ represents the wavelength of light from the light source 11, and i represents a number for distinguishing the plurality of imaging units 35A to 35C. In the present embodiment, the three imaging units 35A to 35C are represented by i = 1, 2, 3.

Here, Bi (x, y) represents the bias of each pixel, and Ai (x, y) represents the amplitude of each pixel. Δl (x, y) will be described with reference to FIG.
FIG. 3 is a partially enlarged view of FIG. In the above equation (1), Δl (x, y) indicates an optical path difference, and the optical path length l of the reference light B1 from the splitting by the light beam splitting element 14 in FIG. _{The difference} between ₁ and the optical path length l ₂ of the sample light B ₂ (where l ₂ = l ₂₁ + l ₂₂ ) is shown. δφi (x, y) is an optically applied phase shift amount of interference fringes. In this embodiment, δφi (x, y) is provided by polarizing plates 34A to 34C disposed between the three-divided prism 33 and the imaging units 35A to 35C. Represents the amount of phase shift.

  The interference fringe intensity Iij (x, y, Δλj) when the wavelength λ is slightly changed by the change amount Δλj is expressed by the equation (2).

Here, j indicates the number of times to change the wavelength λ. In this embodiment, N interference fringes are acquired by changing the wavelength λ N times. These N changes are indicated by j = 1, 2,.
Equation (2) is obtained by using the phase Fi (x, y) of the measurement light B3 and the phase change rate G (x, y) when the wavelength λ is changed by a predetermined unit amount. Can be shown as: The phase Fi (x, y) of the measurement light B3 is obtained by adding the phase shift amount δφi (x, y) to the phase based on the optical path difference Δl (x, y). The amount of phase shift based on the change in wavelength λ is represented by G (x, y) Δλj.

  In Expression (3), when the wavelength λ is changed by the change amount Δλj, the phase of the interference fringes is shifted by G (x, y) Δλj. ), The phase Fi (x, y) can be calculated. Such a method is called a phase shift method. That is, if a plurality of phase-shifted interference fringes are acquired for each of the imaging units 35A to 35C, the phase Fi (x, y), the bias Bi (x, y) in the measurement light B3 for each of the imaging units 35A to 35C, and The amplitude Ai (x, y) can be obtained independently. Further, if the relative phase shift amount of the phase Fi (x, y) is calculated in advance, the individual phase shift amounts δφi (x, y) can be easily calculated.

Next, a specific method for calculating the interference fringe bias Bi (x, y), amplitude Ai (x, y), and phase Fi (x, y) will be described.
In the present invention, it is only necessary to obtain three or more phase-shifted interference fringes for each of the imaging units 35A to 35C by changing the wavelength λ. In the present embodiment, as an example, as shown in Expression (4) Next, the case where the phase shift amount G (x, y) Δλj based on the change of the wavelength λ is set to be the value of each of N points obtained by equally dividing one phase (2π) of the interference fringes will be described. To do.

  The bias Bi (x, y), amplitude Ai (x, y), and phase Fi (x, y) are calculated by performing the following calculation under the condition of the equation (4). The following formula is based on the least square method for the purpose of suppressing the influence of errors and increasing the measurement accuracy.

Here, the phase F ₁ (x, y) of the interference fringes acquired by the imaging unit 35A with i = 1 is set as a reference phase for calculating the shape of the measurement object 20. Then, instead of the phase shift amounts δφ ₂ (x, y) and δφ ₃ (x, y) optically applied in the shape measuring apparatus 1, the phase F ₂ (x, y) and the phase F ₁ (x , y) and the difference between the phase F ₃ (x, y) and the phase F ₁ (x, y) are calculated, and the imaging unit 35B with i = 2, 3 with respect to the imaging unit 35A with i = 1. , 35C relative phase shift amounts α (x, y) and β (x, y).

Here, when relative phase shift amounts α (x, y) and β (x, y) are used instead of the phase shift amounts δφ ₂ (x, y) and δφ ₃ (x, y), And is only added to the phase F ₁ (x, y) calculated by the phase shift method. For example, when measuring the relative shape of the measuring object 20 with respect to the reference surface, no problem arises due to its nature.

  As described above, the parameters (bias Bi (x, y), amplitude Ai (x, y), and relative phase shift amounts α (x, y), β (x, y)) of the measurement apparatus are calculated. The Calculation of such parameters is called calibration, and a specific calibration method for the shape measuring apparatus 1 will be described below.

[Calibration method of shape measuring apparatus 1]
For example, when it is necessary to re-measure parameters in the shape measuring apparatus 1 or when calibration is performed periodically, the parameters are calibrated as follows. Here, a case where the calibration substrate 20A (FIG. 1) is used as a measurement object will be described.
FIG. 4 is a flowchart showing a calibration procedure.
First, the change amount Δλj of the wavelength λ is set by the calibration control unit 42 (step of setting Δλj, step 11, hereinafter “step” is abbreviated as “S”). Then, the light source control unit controls the light source 11 according to the change amount Δλj, and irradiates the calibration substrate 20A with light of the change amount Δλj (irradiation step S12).
Next, the imaging units 35 </ b> A to 35 </ b> C image the three interference fringes to which the different phase differences are generated (imaging process S <b> 13). Then, the interference fringe intensity is detected and output to the calibration control unit 42 (intensity information detection step S14). The calibration control unit 42 determines whether or not there is the next change amount Δλj (S15), and repeatedly executes Δλj setting step S11 to intensity information detection step S14 for all the set change amounts Δλj. To do. In this way, N interference fringes are obtained for each change amount Δλj of the predetermined wavelength λ.
Next, parameters are calculated from a plurality of interference fringe intensity information acquired by the calibration control unit 42 (parameter calculation step S16), and stored in the parameter storage unit 43 (parameter storage step S17).
This completes parameter calibration.

[Method for measuring the shape of the measurement object]
The measurement object 20 is installed instead of the calibration substrate 20A, and interference fringes are measured according to the following procedure.
FIG. 5 is a flowchart showing the procedure of shape measurement.
First, the measurement object 20 is irradiated with light having a predetermined wavelength λ (irradiation step S21).
Next, the imaging units 35A to 35C image the three interference fringes to which the different phase differences are generated (imaging step S22). Then, the interference fringe intensity is detected and output to the interference fringe analysis unit 44 (intensity information detection step S23).
Next, the three pieces of interference fringe intensity information acquired by the interference fringe analysis unit 44 are analyzed with reference to parameters stored in advance (parameter reference step S24), and the shape information of the measurement object 20 and An optical path difference Δl (x, y) is calculated (shape calculation step S25).
Thereby, shape measurement of the measuring object 20 is completed.

  In addition, about the specific calculation method of a shape, the method described in the patent 3766319 is employable.

  In addition, the shape measuring apparatus 1 according to the present embodiment includes an incident angle variable mechanism (not shown) that can change the incident angle of the light emitted from the light source 11 to the measurement object 20. The incident angle variable mechanism can change the incident angle of the light applied to the measurement object 20, so that the height (fringe sensitivity) represented by adjacent fringes in the imaged interference fringe can be changed. Measurements according to 20 shapes can be performed. In addition, when changing an incident angle, what is necessary is just to move interference optical systems, such as the light source 11 and the imaging parts 35A-35C, leaving the measuring object 20 as it is. At this time, the intensity of the sample light B2 from the measurement object 20 changes according to the incident angle, and there may be an error due to variations in bias and amplitude, or deviations in the amount of phase shift between interference fringes. Even in such a case, since the parameters can be easily calibrated, highly accurate measurement can be maintained.

[Selection of optical path difference in light source and interference optical system]
Next, a variable wavelength light source (light source 11) and a method for selecting the optical path difference Δl applicable to the present embodiment will be described.
There are various light sources 11 in terms of performance conditions of an oscillation wavelength region of wavelength λ and a wavelength variable range that is a variable range of minute change Δλ of wavelength λ.
In this embodiment, the light source 11 having a predetermined specification is used in the optical system having the predetermined optical path difference Δl (x, y) shown in FIG. That is, by adjusting the wavelength λ and the change amount Δλ, the light source 11 is selected that can set the phase shift amount G (x, y) Δλ to one period or more (2π or more) of the interference fringes. Specifically, the phase shift amount G (x, y) Δλ (= −2π / λ × Δl (x, y) Δλ, which is a phase term in the sine and cosine functions in the equations (6) and (7). ) Is selected according to the optical path difference Δl (x, y), with the light source 11 having the performance of the oscillation wavelength region and the wavelength variable range where the phase of the interference fringes is one cycle or more (2π or more). .

  On the other hand, the interference optical system may be designed according to the performance of the light source 11 to be used. For example, an optical path difference Δl corresponding to the performance of the light source 11 may be set to form an interference optical system having the optical path difference Δl. If it does in this way, the shape measuring apparatus 1 of this embodiment can be comprised using the existing light source 11. FIG.

A specific selection method for the applicable characteristics of the light source 11 and the set value of the applicable optical path difference Δl will be described with reference to FIGS.
6 to 8 show the interference fringe phase (phase shift amount G () with respect to the change amount Δλ of the wavelength λ for each optical path difference Δl (x, y) when the wavelength λ of the light source 11 is 450, 650, 780 nm. It is a graph which shows the relationship of x, y) (DELTA) (lambda).
In these drawings, if a light source 11 or an interference optical system having an optical path difference Δl such that the phase shift amount G (x, y) Δλ changes by 2π or more is selected, the phase shift amount G satisfying the equation (4) is satisfied. (x, y) Δλj can be set, and calibration by the method of this embodiment can be performed.

  For example, in FIG. 6, when an interference optical system having an optical path difference Δl of 5 mm is used, a light source having a wavelength change amount Δλ of approximately 0.042 nm or more may be selected. On the other hand, if the interference optical system has an optical path difference Δl of 20 mm, a light source having a change amount Δλ of wavelength λ of approximately 0.01 nm or more may be selected. 6 to 8, as the wavelength λ of the light source is larger, the amount of change Δλ of the wavelength λ of the light source required when the same optical path difference Δl is used becomes larger, and the variable range of the amount of change Δλ is larger. A light source is required.

  In the present embodiment, a semiconductor laser that is available at a relatively low cost is used as the light source 11. The semiconductor laser has a simple device configuration in which the oscillation wavelength can be changed simply by changing the load current. However, in the semiconductor laser, the variable range of the wavelength λ that does not greatly change the emission intensity is relatively narrow, for example, about 0.005 nm to 0.01 nm when the wavelength λ is 686 nm. When the change amount Δλ of the wavelength λ of the light source 11 is about 0.005 nm to 0.01 nm, the optical path difference Δl satisfying the equation (4) is about 47 mm to 94 mm. Accordingly, if the interference optical system is set so that the optical path difference Δl is 47 mm to 94 mm or more, the necessary phase shift amount G (x, y) Δλj can be obtained only by appropriately changing the load current of the semiconductor laser. The shape measuring apparatus 1 can be easily calibrated by the above-described phase shift method.

Further, the semiconductor laser has a temperature-dependent characteristic of the oscillation wavelength, and the amount of change Δλ of the wavelength λ with respect to the temperature change is about, for example, in the case of the semiconductor diode DL-6148-030 (manufactured by Tottori Sanyo Electric Co., Ltd.). It is 0.15 nm / ° C. Even when the wavelength λ changes due to a temperature change, the emission intensity can be suppressed within a predetermined amount of change, so the method of changing the wavelength λ by changing the temperature of the semiconductor laser is applied to the calibration method of this embodiment. Can be made.
Specifically, when using a semiconductor laser having a wavelength λ of 638 nm, if the temperature of the semiconductor laser is changed by 0.5 ° C., the wavelength λ changes by 0.075 nm. When the change amount Δλ of the wavelength λ is 0.075 nm, the optical path difference Δl needs to be set to 5.4 mm in order to make the phase shift amount G (x, y) Δλ 2π or more. Therefore, by adjusting the optical path length l ₁ of the reference light B ₁ and the optical path length l ₂ of the sample light B 2 shown in FIG. 3, an interference optical system in which the optical path difference Δl is 5.4 mm is formed, so that the wavelength varies depending on the temperature change. A method of changing λ can be implemented.

  The light source 11 is not limited to a semiconductor laser, and an external resonator type wavelength variable laser or the like may be employed. In the external resonator type tunable laser, for example, the TLB-6300 series (manufactured by New Focus) can be adopted, and the wavelength λ of the laser light is 638 nm, and the wavelength variation Δλ is 0.1 nm. In order to set the phase shift amount G (x, y) Δλ to 2π or more, it is necessary to set the optical path difference Δl to 4.2 mm.

[Effects of this embodiment]
According to this embodiment, the following effects can be achieved.
(1) Information on bias, amplitude, and phase in a plurality of interference fringes to which different phase differences (phase shift amounts δφ) are given can be easily obtained as calibration parameters. Measurement accuracy can be improved by reducing errors caused by variations in amplitude and a deviation of the phase shift amount between interference fringes from the design value. Specifically, by acquiring a plurality of interference fringes with light of different wavelengths λ for each of the imaging units 35A to 35C, each information on the bias, amplitude, and phase of the interference fringes can be individually calculated. At this time, since the wavelength tunable light source capable of changing the wavelength λ of light is used, the bias, amplitude and phase parameters can be easily calibrated. Therefore, it is not necessary to construct an interference optical system using a high-precision optical element, and an expensive apparatus is not required, and advanced adjustment is not required. Therefore, it becomes possible for the user himself to carry out periodic readjustment work necessary for a high-precision measuring device, and it is not necessary to prepare a device necessary only for readjustment (calibration). Time and cost for adjustment work can be reduced.

(2) When a change with time of the shape measuring apparatus 1 or a change in temperature of the measurement environment occurs, or when measuring a measurement object 20 having a different surface property (such as a material), a new bias between interference fringes and Even if there is an error due to variations in amplitude or deviations in the amount of phase shift between interference fringes, the user can easily calibrate parameters in the usage environment regularly or immediately before measurement. Measurement accuracy can be maintained.

(3) Even when the change amount Δλ of the usable wavelength λ is limited, the phase shift amount (2π / λ ² × ΔlΔλ) of the interference fringes can be set by appropriately setting the optical path difference Δl of the interference optical system. Can be made 2π or more, and the shape measuring apparatus 1 can be calibrated. Therefore, a relatively inexpensive semiconductor laser can be employed without being affected by the change in emission intensity due to the change in wavelength λ.

(4) Since the parameters are calibrated using the calibration substrate 20A made of the same material as the measurement object 20, more accurate calibration can be performed.

[Second Embodiment]
Next, a shape measuring apparatus 1A according to a second embodiment of the present invention will be described with reference to the drawings. In the shape measuring apparatus 1 of the first embodiment described above, the wavelength tunable light source 11 that can be used for the configured interference optical system (such as the optical path difference Δl) is limited or configured for the light source 11 to be used. In some cases, there are restrictions on the design of the interference optical system. On the other hand, in the shape measuring apparatus 1A of the present embodiment, the optical path difference Δl is configured to be adjustable according to the change amount Δλ of the wavelength λ of the light source 11 to be used, and the usable wavelength variable light source 11 is selected. The degree of freedom can be increased.

FIG. 9 is an overall configuration diagram showing the shape measuring apparatus 1A.
As shown in FIG. 9, an optical path length variable unit 50 as an optical path difference adjusting mechanism is provided on the optical axis of the reference light B1. The optical path length variable unit 50 includes a pair of mirrors 51 and 52 and a movable right-angle mirror 53. The movable right-angle mirror 53 has two reflecting surfaces orthogonal to each other, and forms reflected light parallel to incident light. The reference light B 1 from the light beam splitting element 14 on the light source side is reflected by the one mirror 51 to the movable right-angle mirror 53, and further reflected by the movable right-angle mirror 53 toward the other mirror 52. Then, the reference light B 1 reflected by the other mirror 52 enters the light beam combining element 16. Thus, the optical path length variable unit 50 forms the delayed optical path of the reference light B1, and the optical path length of the delayed optical path can be made variable. That is, the optical path difference Δl can be adjusted to an arbitrary length by moving the movable right-angle mirror 53 to an arbitrary position.
The same effect can be obtained even if the optical path length variable unit 50 is arranged on the optical path of the sample light B2.

According to this embodiment, in addition to the effects substantially the same as the effects (1) to (4), the following effects can be achieved.
(5) When the shape measuring apparatus 1A includes the optical path length variable unit 50, the optical path difference Δl can be adjusted to an arbitrary length, and the change amount Δλ of the wavelength λ usable in the light source 11 is limited. Even so, by appropriately changing the optical path difference Δl of the interference optical system, the phase shift amount (2π / λ ² × ΔlΔλ) of the interference fringes can be made 2π or more, and the shape measuring apparatus 1A is calibrated. it can. For example, the freedom degree of selection of the wavelength variable light source 11 which can be used with respect to the once constructed interference optical system can be increased.

[Modification of the present invention]
It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in each of the above-described embodiments, the method of using the calibration substrate instead of the measurement object when calculating the parameter (bias, amplitude, phase shift amount) information in advance has been described. You may use it to calculate the parameters.

  Also, when measuring the same measurement object multiple times, or when measuring multiple measurement objects of the same shape continuously, the shape value and calibration parameters are acquired simultaneously during the first shape measurement. Then, in the subsequent shape measurement, the acquired parameters can be used as they are, and the shape measurement by one simultaneous imaging can be performed.

  In each of the above embodiments, a semiconductor laser, an external resonator type wavelength tunable laser, or the like has been described as the wavelength tunable light source. However, the phase shift amount G (x, y) is set by setting the wavelength variation Δλ and the optical path difference Δl. The light source can be adjusted so that Δλ can be adjusted to 2π or more, and is not limited to the principle and method of oscillation and wavelength tuning.

  Further, in each of the above embodiments, as shown in Expression (4), the phase shift amount based on the wavelength change is set to be the value of each of N points obtained by equally dividing one phase of the interference fringe. However, if at least three points are set and at least three phase-shifted interference fringes are acquired, the parameters can be calculated. Further, the phase shift amount based on the change in wavelength is not limited to the case of equally dividing one phase of the interference fringe, and any three points in at least one phase cycle may be set.

The shape measuring apparatus of the present invention is not limited to an oblique incidence interferometer, and may be an interferometer that irradiates light in a direction perpendicular to a measurement object.
In each of the above embodiments, the shape measuring device provided with the incident angle varying mechanism has been described. However, the shape measuring device of the present invention does not necessarily require the incident angle varying mechanism.

In addition, the best configuration, method and the like for carrying out the present invention have been disclosed above, but the present invention is not limited to this. That is, the invention has been illustrated and described with particular reference to certain specific embodiments, but without departing from the spirit and scope of the invention, Various modifications can be made by those skilled in the art in terms of material, quantity, and other detailed configurations.
Therefore, the description limited to the shape, material, etc. disclosed above is an example for easy understanding of the present invention, and does not limit the present invention. The description by the name of the member which remove | excluded the limitation of one part or all of such is included in this invention.

  The present invention can be used for a shape measuring apparatus using a simultaneous imaging interferometer.

The whole block diagram which shows the shape measuring apparatus which concerns on 1st Embodiment of this invention. The block diagram which shows the whole structure of the control system of the said shape measuring apparatus. The elements on larger scale of the said shape measuring apparatus in FIG. The flowchart which shows the procedure of calibration of the said shape measuring apparatus. The flowchart which shows the procedure of the shape measurement of the said shape measuring apparatus. The graph which shows the relationship of the phase shift amount of an interference fringe with respect to the variation | change_quantity of a wavelength when the wavelength of the light source of the said shape measuring apparatus is 450 nm. 7 is a graph when the wavelength of the light source is 650 nm in FIG. 8 is a graph when the wavelength of the light source is 780 nm in FIG. The whole block diagram which shows the shape measuring apparatus which concerns on 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A ... Shape measuring apparatus 11 ... Light source (wavelength variable light source)
16 ... Light beam synthesis element (synthesis unit)
20 ... Measurement object 20A ... Calibration substrate 33 ... Three-divided prism (measurement beam splitting section)
34A to 34C: Polarizing plate (polarizing part)
35A to 35C ... Imaging unit 40 ... Measurement control unit 41 ... Light source control unit 42 ... Calibration control unit 44 ... Interference fringe analysis unit (analysis unit)
50: Optical path length variable section (optical path difference adjusting mechanism).

Claims (5)

A light source that emits light that irradiates the measurement object, and a part of the light that becomes the reference light without being irradiated to the measurement object;
A combining unit that superimposes the sample light reflected from the measurement object and the reference light to form measurement light;
A measurement light dividing unit that divides the measurement light into a plurality of divided measurement lights; and
A polarization unit that is provided on each of the optical axes of the divided measurement lights and generates interference fringes by giving different phase differences to the divided measurement lights;
A plurality of imaging units for imaging the interference fringes for each of the divided measurement lights;
A measurement control unit that measures the shape of the measurement object using each information of bias, amplitude, and phase of the interference fringe calibrated in advance for each imaging unit based on the plurality of captured interference fringes; A shape measuring device comprising:
The light source is a wavelength tunable light source capable of changing the wavelength of emitted light,
The measurement control unit
A light source controller that changes the wavelength of light from the light source;
When each information of bias, amplitude, and phase of the interference fringe is calibrated in advance, each of the bias, amplitude, and phase is based on a plurality of interference fringes obtained by changing the wavelength of the light source for each imaging unit. A calibration control unit for calibrating information;
When measuring the shape of the measurement object, based on a plurality of interference fringes simultaneously acquired by the imaging unit and given different phase differences, and each information of the bias, amplitude and phase calibrated in advance, An analysis unit for analyzing shape information of the measurement object ,
The shape measuring apparatus includes an optical path difference adjustment mechanism capable of adjusting an optical path difference (Δl) between the optical path length of the reference light and the optical path length of the sample light,
The optical path difference (Δl) is such that the phase shift amount (2π / λ ² × ΔlΔλ) of the interference fringes when the wavelength (λ) of the light source is changed by a change amount (Δλ ) is 2π or more. A shape measuring device characterized by being set . In the shape measuring apparatus according to claim 1,
A shape measuring apparatus comprising an incident angle variable mechanism capable of changing an incident angle of light emitted from the light source to the measurement object. In the shape measuring device according to claim 1 or 2 ,
The shape measuring apparatus, wherein the calibration control unit calibrates the bias, amplitude, and phase information in advance based on interference fringes acquired using the measurement object. In the shape measuring device according to any one of claims 1 to 3 ,
The calibration control unit calibrates the bias, amplitude, and phase information in advance based on interference fringes acquired using a calibration substrate made of the same material as the measurement object. apparatus. A light source that emits light that irradiates the measurement object, and a part of the light that becomes the reference light without being irradiated to the measurement object;
An optical path difference adjustment mechanism capable of adjusting an optical path difference (Δl) between the optical path length of the reference light and the optical path length of the sample light;
A combining unit that superimposes the sample light reflected from the measurement object and the reference light to form measurement light;
A measurement light dividing unit that divides the measurement light into a plurality of divided measurement lights; and
A polarization unit that is provided on each of the optical axes of the divided measurement lights and generates interference fringes by giving different phase differences to the divided measurement lights;
A plurality of imaging units for imaging the interference fringes for each of the divided measurement lights;
A measurement control unit that measures the shape of the measurement object using each information of bias, amplitude, and phase of the interference fringe calibrated in advance for each imaging unit based on the plurality of captured interference fringes; A calibration method for each information of the bias, amplitude and phase in a shape measuring apparatus comprising:
The light source is a wavelength tunable light source capable of changing the wavelength of emitted light,
The optical path difference (Δl) is such that the phase shift amount (2π / λ ² × ΔlΔλ) of the interference fringes when the wavelength (λ) of the light source is changed by a change amount (Δλ ) is 2π or more. Is set,
A setting step for setting the amount of change in the wavelength of light from the light source;
An irradiation step of irradiating the measurement object with the set amount of change;
An imaging step of imaging the interference fringes generated for each change amount of the wavelength with the plurality of imaging units,
A calibration step for calculating the bias, amplitude and phase information based on the captured interference fringes.

Images