JP2009270847A - Reflectance measuring device and reflectance measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflectance measuring device and a reflectance measuring method having high measurement accuracy of a reflectance of an inspection surface of an optical element. <P>SOLUTION: In this reflectance measuring device, the first photodetection intensity when measuring light is reflected by interposing the inspection surface of the optical element in an optical path through which the measuring light arrives at a photodetection means, and the second photodetection intensity when the inspection surface is not interposed, are measured, and the reflectance of the inspection surface is measured by comparison between the first photodetection intensity and the second photodetection intensity. In the device, the reflectance is corrected by measuring beforehand a measured value error of the reflectance caused by a curvature of the inspection surface, or the reflectance is corrected by measuring beforehand the measured value error of the reflectance caused by at least one of a position of the inspection surface in the optical path, an incident angle of the measuring light onto the inspection surface, and a wavelength of the measuring light. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reflectance measuring device and a reflectance measuring method for measuring the reflectance of a test surface of an optical element.

Conventionally, measurement of an optical lens is performed by measuring spectral energy distribution, spectral transmittance, spectral reflectance, and the like, and these measurements are mainly performed in the visible region.
With reference to FIG. 8, a conventional spectral reflectance measuring apparatus proposed in Japanese Patent Laid-Open No. 2000-321126 (Patent Document 1) will be described.
In this conventional example, the light beam 11 a emitted from the light source 11 enters the slit 16 via the mirrors 12 and 13, the diffraction grating 14, and the mirror 15.
The light beam 11a is made into monochromatic light by the slit 16, and this monochromatic light is divided into the reference light 18a and the measuring light 18b by the mirror 17, the sector mirror 18, etc., and the reference light 18a is passed through the integrating sphere 28 by the reflecting mirror 19. It is guided to a photomultiplier tube 27 which is a light receiving sensor.
On the other hand, the measurement light 18b is guided to the photomultiplier tube 23, which is a light receiving sensor, directly or via the integrating sphere 24 by the reflecting mirror 21 via the lens 26 to be measured, and the light beams of each light are compared by comparing them. Energy measurements are made.
The photomultiplier tube 23, the integrating sphere 24, and the sector mirror 18 are driven and controlled by the control driving unit 50.
As the light receiving sensor used in the conventional spectral reflectance measuring apparatus, silicon photodiodes, photomultiplier tubes, CCDs, and the like have been properly used depending on the application, wavelength used, required accuracy, and the like.
JP 2000-321126 A

However, in contrast to the conventional spectral reflectance measuring apparatus mainly used in the visible region, a spectral reflectance measuring device using a light beam in the ultraviolet region has been used in various directions.
In particular, light sources such as steppers used in the manufacture of semiconductors include mercury lamp g-line (λ = 4358 Å) to i-line (λ = 3650 Å), gas laser KrF (λ = 2486 、) laser, and further in the vacuum ultraviolet region. The laser has shifted to an ArF (λ = 1934Å) laser.
For this reason, it is necessary to evaluate and develop the characteristics of a lens constituting an optical system used in an exposure apparatus such as a stepper having these light sources, an antireflection film formed on the lens surface, or a mirror.
As a tool for evaluating and developing the lenses, mirrors, and the like constituting this optical system, a spectral reflectance measuring device for accurately measuring and evaluating the characteristics of the glass material and the optical film in the ultraviolet wavelength region is required.
However, the conventional spectral reflectance measuring apparatus used for measurement evaluation so far does not support measurement of lenses or mirrors having various irregularities in the ultraviolet region, and accurately measures and evaluates them. could not.

In order to perform measurement with high accuracy, the light detection intensity when the measurement light is reflected with the test surface interposed in the optical path where the measurement light reaches the light detection means, and when the test surface is not interposed Must be measured and contrasted accurately.
However, it is rare that the light receiving characteristics depending on the location of the light receiver are completely uniform.
In the case of a silicon photodiode, there is a non-uniformity in sensitivity depending on the location due to deterioration due to the manufacturing process or use time in the light receiving surface where photoelectric conversion is performed.
In the case of an integrating sphere, since there is uneven reflectance depending on the location due to coating unevenness or deterioration of the integrating sphere inner wall paint, there are cases where the test lens is not interposed and reflection is performed with the test lens interposed in the optical path. An accurate comparison cannot be made unless the light flux thus received is received by the same portion of the light receiving surface.
In particular, in the vacuum ultraviolet region, light is strongly absorbed by various substances, and the influence on the sensitivity unevenness due to contamination of the light receiving surface and the like is also remarkable.
Further, when measuring a spherical surface having various curvatures, the measurement light applied to the test lens is converged or diverged by the curvature of the test surface, and the light flux when the test surface is not interposed in the optical path. In contrast, the measurement value error was caused by the sensitivity variation of the receiver.

Here, referring to FIG. 9, when measuring a spherical surface having various curvatures of the lens, the measurement light irradiated to the test surface of the lens is converged and diverged by the curvature of the test surface, and in the optical path A state in which the light flux changes in comparison with the light beam in the case where the test surface is not interposed in will be schematically described.
With reference to FIG. 9A, a case where the test surface of the lens is not interposed in the optical path will be described.
The monochromatic measurement incident light 33 having the integrating sphere 32 and the photomultiplier tube 31 is a convergent light having a predetermined NA, and the vicinity of the opening 32a of the integrating sphere 32 is set as a focal position 33a. Incident into the sphere 32.
The light reflected by the inner wall surface 32b of the integrating sphere 32 reaches the photomultiplier tube 31 while being diffusely reflected by the inner wall surface 32b of the integrating sphere 32, and is used for measurement.

Next, FIG. 9B shows a case where a lens 34 having a negative curvature, that is, a concave surface as a test surface is interposed in the measurement optical path.
Compared to the case where the test surface of the lens is not interposed in the optical path shown in FIG. 9A, the measurement light 33 reflected by the test surface 34a of the lens 34 converges, and the focal position 33a is closer to the lens 34. Changes to.
For this reason, the light flux 33b becomes larger at the irradiation position of the inner wall surface 32b of the integrating sphere 32 than in the case where the test surface shown in FIG.

Next, FIG. 9C shows a case where a lens 35 having a positive curvature, that is, a convex surface as a test surface is interposed in the measurement optical path.
Compared with the case where the test surface of the lens is not interposed in the optical path as shown in FIG. 9A, the light reflected by the test surface 35 a of the lens 35 diverges and the focal position is opposite to the lens 35. It changes to the side.
For this reason, the light beam 33b is smaller at the irradiation position of the inner wall surface 32b of the integrating sphere 32 than in the case where the test surface shown in FIG.
As described above, when measuring a spherical surface having various curvatures, the measurement light 33 irradiated on the test surfaces 34a and 35a is converged and diverged by the curvature of the test surfaces 34a and 35a, and the test light is detected in the optical path. Unlike the light flux in the case where the surfaces 34a and 35a are not interposed, a measurement value error occurs due to sensitivity variations of the light receiver.
In addition, when the integrating sphere 32 is used as a light receiver, an opening 32a for receiving light by the detector is necessary in order to capture light due to its structure.
Depending on the size of the opening 32a, the area ratio between the inner diameter and the opening diameter of the integrating sphere 32 itself, the light receiving position of the photomultiplier tube 31 serving as a detector, and the like, the convergence and divergence of the incident measurement light 33 are affected. The way of receiving is also different.
In addition, there is a problem that the amount of error varies depending on the magnitude and positive / negative of the curvature of the test lenses 34 and 35.
In addition, the measurement light, the non-uniformity of the light receiver and the like differ depending on the measuring machine, and the amount of error also differs for each measuring machine.
Therefore, an object of the present invention is to provide a reflectance measuring apparatus and a reflectance measuring method with high accuracy in measuring the reflectance of the test surface of an optical element.

The reflectance measuring apparatus of the present invention for solving the above-described problem is the first in the case where the measurement light is reflected through the test surface of the optical element in the optical path where the measurement light reaches the light detection means. And the second photodetection intensity when the test surface is not interposed, and the reflection of the test surface is compared by comparing the first photodetection intensity and the second photodetection intensity. A reflectance measuring apparatus for measuring a reflectance, wherein the reflectance is corrected by measuring in advance a measurement value error of the reflectance due to a curvature of the test surface.
Furthermore, the reflectance measuring apparatus according to the present invention includes a first light detection intensity when the measurement light is reflected through the test surface of the optical element in the optical path where the measurement light reaches the light detection means. The second light detection intensity when the test surface is not interposed is measured, and the reflectance of the test surface is measured by comparing the first light detection intensity and the second light detection intensity. A rate measuring device,
The reflectivity is measured by measuring in advance the measurement value error of the reflectivity due to at least one of the position of the test surface in the optical path, the incident angle of the measurement light to the test surface, and the wavelength of the measurement light. It is characterized by correcting.

  According to the present invention, the measurement accuracy of the reflectance of the test surface of the optical element is high.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
First, the reflectance measuring apparatus according to the first embodiment of the present invention will be described with reference to FIG.
In the first embodiment, the measurement light 18b is reflected through the test surface 41 of the test lens 26, which is an optical element, in the optical path where the measurement light 18b reaches the photomultiplier tube 23, which is a light detection means. In this case, the first light detection intensity is measured.
Further, the second light detection intensity when the test surface 41 is not interposed is measured, the reflectance of the test surface 41 is measured by comparing the first light detection intensity and the second light detection intensity, The reflectance is corrected by measuring in advance the measurement error of the reflectance due to the curvature of the inspection surface 41.
The light source 11 includes a deuterium lamp that emits a light beam 11a having a continuous wavelength from the vacuum ultraviolet region to the visible region.
The spectroscope for performing spectroscopy is composed of a first off-axis object plane mirror 13, a reflective planar diffraction grating 14, a second off-axis object plane mirror 15, and an exit slit 16.
The spectroscope includes a so-called Zernitaner type monochromator including a reflection type plane diffraction grating 14 and two off-axis direction plane mirrors 13 and 15 as light dispersion elements.
A photomultiplier tube 27 that is a light receiving sensor receives the reference light 18 a via the integrating sphere 28.
The photomultiplier tube 23 of the light receiving sensor as the light detecting means receives the measuring light 18b via the integrating sphere 24.
The photomultiplier tube 23, the integrating sphere 24, and the sector mirror 18 are driven and controlled by the control driving unit 50.
In Example 1, the inverse dispersion, which is the wavelength difference per unit length on the exit slit 16 surface, was set to 2 nm / mm from the relationship between the light amount and the wavelength resolution.

The light beam 11 a emitted from the light source 11 is changed in direction by 90 ° by the first plane mirror 12, becomes parallel light 11 b by the first off-axis direction plane mirror 13, and enters the diffraction grating 14.
The light 11c split by the diffraction grating 14 is condensed again by the second off-axis direction plane mirror 15, forms an image on the exit slit 16 surface, and only a specific wavelength passes.
The light 11d that has passed through the exit slit 16 becomes parallel light 11e by the third off-axis direction plane mirror 17, and the sector mirror 18 that is a semicircular plane mirror is rotated to turn the reference light 18a and the measurement light 18b into time. Divided.
When the sector mirror 18 is on the optical path, the direction of 90 ° is changed, and the reference light 18a is collected by the fourth off-axis object plane mirror 19 and incident on the integrating sphere 28, and the amount of light is monitored. This is used to correct the amount of light fluctuation.
When the mirror 18 is not on the optical path, the measurement light 18b is incident on the fifth off-axis direction plane mirror 21 as it is, collected and incident on the integrating sphere 24.

The integrating sphere 24 is configured to be rotatable, rotates around the reflection point of the test surface 41 of the test lens 26 as a rotation center, and reflects from the test surface 41 when the test surface 41 is interposed in the optical path. Rotates to the position where light enters.
Therefore, in the optical path where the measurement light 18b reaches the integrating sphere 24, the first light detection intensity when the measurement light 18b is reflected through the test surface 41 and the test surface 41 is not interposed. The second light detection intensity is measured, and the reflectance of the test surface 41 is measured by comparison.
If the measurement area is visible light, barium sulfate or the like is generally applied to the inner surfaces of the integrating spheres 28 and 24. In the first embodiment, a phosphor having a characteristic of emitting light at a vacuum ultraviolet wavelength is applied. ing.
Photomultiplier tubes 27 and 23 called photomals which are detectors are attached to openings 28a and 24a of integrating spheres 28 and 24, respectively.
The vacuum ultraviolet light incident on the integrating spheres 28 and 24 illuminates the phosphor coated on the inner wall of the integrating sphere, and the emitted fluorescent light is detected while diffusely reflecting the surface of the phosphor coating on the inner surfaces of the integrating spheres 28 and 24. It reaches the photomultiplier tubes 27 and 23, which are testers, and is used for measurement.

Next, with reference to FIGS. 1 and 3, a method of correcting the reflectance measurement value in the first embodiment will be described.
In the first embodiment, first, a correction value of the reflectance measurement value at a wavelength of 193.4 nm is obtained.
First, a plurality of, for example, six types of lenses, which are optical elements having different curvatures, are prepared by polishing and cleaning a material cut out from the same material having uniform optical characteristics under the same conditions.
The reflectivity of each lens surface is cleaned to a level at which loss such as absorption is negligible. The reflectivity R% obtained by the refractive index of the material is used as the reference reflectivity Ro, or the loss due to absorption or the like of each lens surface. Is known, the value obtained by subtracting that amount is used as the reference reflectance Ro.
Alternatively, the reflectance of the flat polished surface of each lens is measured, and the value is set as the reference reflectance Ro.
Each lens has a diameter of φ30, a center thickness of 10 mm, one surface is polished to a flat surface, and the other surface is a concave surface with a radius of curvature of 28, 56, 112, and a convex spherical surface with 112, 56, 28 as well. It was.

Next, the six types of lenses having different curvatures are replaced one by one, and the lens 26 is normally measured to measure the reflectance.
In the first embodiment, only the curvature of the test surface 41 is set as a variable parameter.
However, the distance between the integrating sphere 24, which is the position of the test surface 41 in the optical path, and the test surface 41, the incident angle of the measurement light 18b on the test surface 41, the wavelength of the measurement light 18b, and the like are changed, and each parameter is changed. In some cases, the reflectance is corrected by measuring in advance the measurement value error of the reflectance.
At least one of these may be a variable parameter.
The measurement results of the reflectance of the test surface 41 of the six types of test lenses 26 having different curvatures are shown in the graph of FIG. 1, where the test surface is represented by the horizontal axis representing the wavelength of the measurement light and the vertical axis representing the reflectivity. The measured value of the reflectance varies depending on the curvature of 41.

Next, as shown in the graph of FIG. 2, the horizontal axis represents the reciprocal of the radius of curvature (1 / r), the vertical axis represents the reflectivity, and 6 measured values of 193.4 nm on the graph of FIG. 1 are plotted. Then, a polynomial approximation is performed by a least square method or the like to obtain a function of an approximate curve.
In the first embodiment, quadratic approximation is performed, and the near-order expression (1) is obtained.
Ra = a (1 / r) ^ 2 + b (1 / r) + c (1)
Ra: approximate value r: radius of curvature
a, b: coefficient c: constant (intercept)

Further, the reflectance of the test surface 41 having a radius of curvature r is measured using the same reflectance measuring apparatus of Example 1 as that for which the approximate expression (1) was obtained.
Further, the reflectance is calculated from the measured value Rm of the reflectance measured at the distance between the integrating sphere 24, which is the position of the same test surface 41, and the test surface 41, the incident angle of the same measurement light 18b, and the wavelength of the same measurement light 18b. The correction formula (2) for obtaining the correction value Rc is as follows.
Rc = Rm · Ro / Ra = Rm · Ro / (a (1 / r) ^ 2 + b (1 / r) + c) (2)
By this correction formula (2), the reflectance including the measurement value error with respect to the reference reflectance Ro due to the reflected light flux changed by the curvature of the surface 41 to be measured and the sensitivity unevenness of the light receiver in the reflectance measurement value Rm. By multiplying the reciprocal of Ra, which is the ratio, the measurement value error is corrected.
So far, the reflectance correction value of 193.4 nm has been obtained from the measurement value of 193.4 nm and the reference reflectance by the correction equation (2). However, when it is desired to obtain correction values of other wavelengths, the same method is used. Find the approximate curve function for the desired wavelength.
Thereby, the reflectance correction value of other wavelengths can be obtained.
If the sensitivity variation of the light receiver and the intensity distribution in the measurement light do not change with the wavelength or are negligible, the correction value Rc (λ) of other wavelengths may be obtained by the following equation (3).
Rc (λ) = Rm (λ) · Rc (193.4) / Rm (193.4) (3)
From this equation (3), the reflectance correction value can be obtained more easily than the method of obtaining the function of the approximate curve for each wavelength.

According to the first embodiment, the measurement value of the reflectance is corrected, the sensitivity unevenness of the light receiver, the curvature of the test surface 41, the position of the test surface 41 in the optical path, the incident angle of the measurement light 18b, the measurement light The measurement value error due to the wavelength of 18b can be corrected to reduce the measurement value error.
When the correction of Example 1 was performed, in particular, a lens having a large radius of curvature with a large error was measured with a reflectivity of 1% or more lower than the reference plane, but the difference was about 0.1%. The accuracy of absolute values has been greatly improved.
For this reason, even in the spectral reflectance measurement in the ultraviolet region, it is possible to measure a lens having various curvatures with high accuracy, and to increase the accuracy of the optical thin film such as the antireflection film and the high reflection film formed on the lens and the lens surface. Enables accurate characterization.

Hereinafter, Embodiment 2 of the present invention will be described with reference to FIGS. 4, 5, 6, and 7.
Since the main configuration of the reflectance measuring apparatus of the second embodiment is the same as that of the first embodiment, only differences will be described.
The reflectance measuring apparatus according to the second embodiment includes error amount measuring lenses 26a and 26b, which are optical elements for obtaining a reflectance correction formula, and is automatically set at the set position of the test lenses 26a and 26b in the optical path. It is configured to be able to.
Also in the second embodiment, first, a correction value at a wavelength of 193.4 nm is obtained.
The error amount measurement lenses 26a and 26b are a plurality of, for example, six types of lenses that are optical elements having different curvatures obtained by polishing and cleaning a material cut out from the same material having uniform optical characteristics under the same conditions.
The error amount measurement lenses 26a and 26b are set on the movable holder 25 so that the reflectance can be measured by sequentially interposing them in the optical path.
The reflectance of the surface of each lens 26a, 26b is cleaned to a level where loss such as absorption is negligible, and the reflectance R% obtained by the refractive index of the material is defined as the reference reflectance Ro.
Each lens 26a, 26b has a diameter of φ30, a center thickness of 10 mm, one surface is polished to a flat surface, and the other surface is a concave surface having a curvature radius of 28, 56, 112, and a curvature radius of 112, 56, 28. The convex spherical surface.

Next, a method for deriving the corrected reflectance measurement value according to the procedure of the flowchart shown in FIG. 7 will be described.
First, the “step of finding the relationship between the error amount and the changing parameter” that is the first step 101 will be described.
In the first step 101, the curvature of the test surface 41a, the distance between the integrating sphere 24, which is the position of the test surface 41a, and the test surface 41a, the incident angle of the measurement light 18b to the test surface 41a, and the measurement light This is a step of finding the relationship between at least one of the wavelengths of 18b and the measurement error of the reflectance.
In the second embodiment, the only parameter to be changed is the curvature of the lens 26a, but the distance between the integrating sphere 24, which is the position of the test surface 41a, and the test surface 41a, and the test light 41b to the test surface 41a. In some cases, the incident angle, the wavelength of the measurement light 18b, and the like. At least one of these may be a variable parameter.
In that case, the reflectance when each parameter is changed is measured, and the relationship with the error amount is obtained.
In the second embodiment, the reflectance is measured by sequentially interposing the lens 26a having different curvatures in the optical path by driving the movable holder 25.
The result is shown in the graph of FIG. 4, where the horizontal axis represents the wavelength of the measurement light 18 b and the vertical axis represents the reflectance, and the measured values differ depending on the curvature of the test surface 41 a.

Next, the “step of deriving the reflectance correction formula” that is the second step 102 will be described.
As shown in the graph of FIG. 5, the horizontal axis is the reciprocal of the radius of curvature (1 / r), and the vertical axis is the reflectivity. From the reflectivity results obtained in the first step 101, each measurement at 193.4 nm is performed. Six values are plotted, polynomial approximation is performed by the least square method or the like, and a function of the approximate curve is obtained.
In the second embodiment, quadratic approximation is performed to obtain the approximate expression (1).
Ra = a (1 / r) ^ 2 + b (1 / r) + c (1)
Ra: approximate value r: radius of curvature a, b: coefficient c: constant (intercept)

Further, the reflectance of the test surface 41a having the radius of curvature r is measured using the same reflectance measuring apparatus of Example 2 as that for which the approximate expression (1) is obtained.
Further, a correction for obtaining the correction value Rc from the measured value Rm measured at the distance between the integrating sphere 24, which is the position of the same test surface 41a, and the test surface 41, the incident angle of the same measurement light 18b, and the wavelength of the same measurement light 18b. Equation (2) is obtained.
Rc = Rm · Ro / Ra = Rm · Ro / (a (1 / r) ^ 2 + b (1 / r) + c) (2)
According to the correction formula (2), the reflectance ratio including the measurement value error with respect to the reference reflectance Ro due to the reflected light flux changed due to the curvature of the test surface 41a and the sensitivity unevenness of the light receiver in the reflectance measurement value Rm. The measured value error is corrected by multiplying by the reciprocal of Ra.

Next, the “step of measuring the surface to be measured” that is the third step 103 will be described.
The error amount measuring lens 26 a in the first step 101 is retracted from the optical path by driving the movable holder 25.
As a result, the test surface 41a having a known radius of curvature r is measured by using the same measurement light 18b as the distance between the integrating sphere 24 and the test surface 41 at the same position of the test surface 41a from which the correction formula (2) is obtained. Are set to the same incident angle and the same wavelength of the measurement light 18b.
The test surface 41a is cleaned to such a level that absorption loss due to adhesion of impurities or the like can be ignored.
The normal lens to be tested is set in a movable holder (not shown) different from the error amount measurement lens 26a, and is configured to be moved by a command from a control device such as a PC.
The reflectance is measured, and the measured value Rm is stored in the control PC.

Finally, the “step of correcting the reflectance” which is the fourth step 104 will be described.
In the fourth step 104, the measured value Rm obtained in the third step 103 is substituted into the correction formula (2) obtained in the second step 102 to obtain a correction value Rc, and the result is used as PC or the like. Is stored in the control device and displayed on a display unit or the like as necessary.
So far, the reflectance correction value of 193.4 nm has been obtained from the measurement value of 193.4 nm and the reference reflectance by the correction equation (2). However, when it is desired to obtain correction values of other wavelengths, the same method is used. By calculating the function of the approximate curve for the desired wavelength, the reflectance correction value for other wavelengths is obtained.
When the sensitivity variation of the light receiver and the intensity distribution in the measurement light 18b do not change with the wavelength or are negligible, the correction value Rc (λ) of other wavelengths may be obtained by the following equation (3). .
Rc (λ) = Rm (λ) · Rc (193.4) / Rm (193.4) (3)
By this equation (3), the reflectance correction value can be obtained more simply than the method of obtaining the function of the approximate curve for each wavelength.

According to the second embodiment, the reflectance measurement value is corrected, the sensitivity unevenness of the light receiver, the curvature of the test surface, the position of the test surface in the optical path, the incident angle, the convergence of the light flux depending on the wavelength of the measurement light, or The measurement value error due to divergence can be corrected, and the measurement value error is reduced.
When the correction of Example 2 was performed, in particular, the lens having a large curvature radius with a large error was measured to have a reflectivity of 0.2% or more lower than that of the reference plane substrate. As a result, the accuracy of the absolute value was greatly improved.
For this reason, even in the spectral reflectance measurement in the ultraviolet region, it is possible to measure a lens having various curvatures with high accuracy, and to increase the accuracy of the optical thin film such as the antireflection film and the high reflection film formed on the lens and the lens surface. Enables accurate characterization.

6 is a graph for obtaining an error amount of the reflectance measuring apparatus according to the first embodiment of the present invention. 6 is a graph for obtaining a correction value of the reflectance measuring apparatus according to the first embodiment of the present invention. It is a schematic sectional drawing of the reflectance measuring apparatus of Example 1 of this invention. It is a graph for calculating | requiring the error amount of the reflectance measuring apparatus of Example 2 of this invention. It is a graph for calculating | requiring the correction value of the reflectance measuring apparatus of Example 2 of this invention. It is a schematic sectional drawing of the reflectance measuring apparatus of Example 2 of this invention. It is a flowchart for demonstrating the process of the reflectance measuring apparatus of Example 2 of this invention. It is a schematic sectional drawing of the reflectance measuring apparatus of a prior art example. It is a schematic sectional drawing for demonstrating the subject of the reflectance measuring apparatus of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Light source 12, 13, 15, 17, 19, 21 Mirror 14 Diffraction grating 16 Slit 18 Sector mirror 23, 27 Photomultiplier tube 24, 28 Integrating sphere 25 Holder 26, 26a Test lens 41, 41a Test surface

Claims (7)

The first light detection intensity when the measurement light is reflected through the test surface of the optical element in the optical path through which the measurement light reaches the light detection means, and the first light detection intensity when the test surface is not interposed Measure the light detection intensity of 2,
A reflectance measuring device that measures the reflectance of the test surface by comparing the first light detection intensity and the second light detection intensity;
A reflectance measurement apparatus, wherein the reflectance is corrected by measuring in advance a measurement value error of the reflectance due to the curvature of the surface to be examined. A measurement value error of the reflectance due to the curvature of the test surface using a plurality of lenses which are the optical elements having different curvatures, which are obtained by polishing and cleaning a material cut out from the same material having uniform optical characteristics. The reflectance measurement apparatus according to claim 1, wherein the reflectance is corrected by measuring in advance. The first light detection intensity when the measurement light is reflected through the test surface of the optical element in the optical path through which the measurement light reaches the light detection means, and the first light detection intensity when the test surface is not interposed Measure the light detection intensity of 2,
A reflectance measuring device that measures the reflectance of the test surface by comparing the first light detection intensity and the second light detection intensity;
The reflectivity is measured by measuring in advance the measurement value error of the reflectivity due to at least one of the position of the test surface in the optical path, the incident angle of the measurement light to the test surface, and the wavelength of the measurement light. The reflectance measuring device characterized by correcting the above.   Using a plurality of lenses with different curvatures that are polished and cleaned under the same conditions, the material cut out from the same material with uniform optical properties, the position of the test lens, the incident angle of the measurement light to the test surface, The reflectance measurement apparatus according to claim 3, wherein the reflectance is corrected by measuring in advance a measurement value error of the reflectance due to at least one of wavelengths of measurement light.   5. The reflection according to claim 1, comprising a plurality of lenses which are the optical elements having different curvatures obtained by polishing and cleaning a material cut out from the same material having uniform optical characteristics under the same conditions. Rate measuring device. Finding a relationship between at least one of the curvature of the test surface, the position of the test surface, the incident angle of the measurement light to the test surface, and the wavelength of the measurement light and the measurement value error of the reflectance; ,
Deriving the reflectance correction equation;
Measuring the test surface;
The reflectivity measuring apparatus according to claim 1, wherein the reflectivity is corrected through a step of correcting the reflectivity. A reflectance measuring method using the reflectance measuring apparatus according to claim 1.

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