JP2015081835A - Method for measuring birefringence, method for manufacturing mask blank substrate, method for manufacturing mask blank, method for manufacturing transfer mask, and method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a birefringence value of a material showing a tendency of low birefringence with high accuracy.SOLUTION: A method for measuring birefringence is provided, which includes a step of acquiring a first correspondence relation between a rotation angle of a half-wave plate and a luminous energy ratio through: steps of transmitting an inspection beam, which is emitted from a light source unit 101 and transmitted through a light-transmitting article 10, through a half-wave plate 104, then separating the inspection beam by an optical separator 108 into two linearly polarized beams orthogonal to each other, measuring luminous energy of the beams with respective two luminous energy measurement devices 106a, 106b, and calculating a luminous energy ratio by dividing one of the two measurement values by the sum of the two measurement values; and a step of repeating several times the above described steps by rotating the half-wave plate to change angles of the polarization planes. The method further includes: a step of acquiring a reference correspondence relation under the same conditions in the above step of acquiring the first correspondence relation without disposing the light-transmitting article; a step of calculating a relative luminous quantity ratio in the first correspondence relation and the reference correspondence relation at the same rotation angle of the half-wave plate; and a step of acquiring a birefringent value at the measurement position by using the relative luminous quantity ratio of the first correspondence relation, based on a preliminarily acquired correspondence relation between a relative luminous quantity ratio and a birefringent value.

Description

  The present invention relates to a method for measuring birefringence in a translucent article. The present invention also relates to a mask blank substrate manufacturing method, a mask blank manufacturing method, a transfer mask manufacturing method, and a semiconductor device manufacturing method.

  In a lithography process, which is one of semiconductor device manufacturing processes, an exposure apparatus is used to perform exposure transfer on a transfer object (for example, a resist film on a wafer). Specifically, the exposure apparatus irradiates and transmits the exposure light from the exposure light source via the illumination optical system to the transfer mask, and exposes the transfer pattern image reduced to the transfer object through the reduction optical system. The pattern is transferred.

  Further, the light source of this exposure light has been shortened in wavelength, and ArF excimer laser (wavelength 193 nm) is mainly used as exposure light in the process of manufacturing semiconductor devices in recent years. In recent semiconductor devices, as a result of the progress of pattern miniaturization, the trend of improving the resolution of a pattern image transferred to a transfer object has been stagnant.

  In order to solve this problem, a polarization illumination technique has been developed in which the polarization state of ArF excimer laser exposure light is controlled to linearly polarized light or the like by an illumination optical system and then incident on a transfer mask. However, when this polarized illumination technique is used, a desired transfer image may not be obtained depending on the transfer mask used.

  For example, since the development of polarized illumination technology, synthetic quartz glass substrates have been mainly used as substrates used for transfer masks. And in the synthetic quartz glass substrate until then, birefringence was not considered in particular. However, when polarized illumination is used for exposure light, if there is a part with a large amount of birefringence on the substrate, the polarization state of the exposure light transmitted through that part is the polarization state of the exposure light transmitted through the other normal part. There arises a problem that the focal position is not aligned when the image is formed by the reduction optical system, or the image formed is changed from the image to be transferred.

  For this reason, with regard to a transfer mask substrate that conventionally uses the polarization illumination technique, the birefringence amount of the substrate is measured by a birefringence measuring device, and a substrate having a predetermined value or less (for example, 4 nm / cm) is selected. It has been supported by use (for example, see Patent Document 1). Conventionally, as an apparatus for measuring the birefringence amount of a substrate, for example, an apparatus described in Patent Document 2 is known.

  This birefringence measuring apparatus irradiates one surface (main surface) of a measurement object (substrate) with polarized inspection light at a predetermined angle from a reference axis. Then, the inspection light emitted from the other opposing surface (opposing main surface) is separated into two by a beam splitter. Then, the two separated inspection lights are respectively incident on two analyzers that analyze lights having different polarization angles from the reference axis, and based on the results of each analysis, the birefringence amount and the birefringence at the measurement location. The angle that maximizes the amount is calculated.

  Conventionally, a transfer mask manufactured using a mask blank is inspected by using a mask inspection apparatus to check whether the formed pattern satisfies the standard. However, as a result of the miniaturization of the pattern of the transfer mask, even in the case of mask inspection, there has been a problem that improvement in resolution is stagnant and improvement in inspection accuracy is stagnant. For this reason, in recent years, application of polarized light (such as circularly polarized light) has also begun to be used for inspection light used for mask inspection (see, for example, Patent Document 3).

JP 2006-267997 A Japanese translation of PCT publication No. 2002-504673 JP 2009-003172 A

  Under the above background, the present inventor has developed an inspection method using circularly polarized light (Japanese Patent Application No. 2013-081860). Specifically, circularly polarized inspection light is irradiated onto a transparent substrate, the transmitted inspection light is separated into two linearly polarized lights whose wavefronts are orthogonal to each other, and a light quantity ratio is calculated from the two separated linearly polarized lights. To do. Based on the light quantity ratio as a reference (the light quantity ratio at which the relative transmittance when measured by a mask inspection apparatus using inspection light having a wavelength of 193 nm is 95% or more and the birefringence is equivalent to 20 nm / cm is used as a reference value). It is an invention for selecting a translucent substrate suitable as a mask blank substrate.

As a result of intensive studies, the present inventor has found the following. That is, it is difficult to select a translucent substrate having a birefringence of 5 nm / cm or less, more preferably 2 nm / cm or less, using the light amount ratio derived in the above invention, because the measurement accuracy of the light amount ratio is too low. It turned out to be.
In the above invention, the technical problem is that the light quantity of the light source of the inspection light varies from one measurement location to another or from one sheet to another, and it is possible to achieve a certain solution by introducing the concept of the light quantity ratio. Yes. However, even if the light quantity ratio is introduced, the accuracy of the two light quantity measuring devices (light receivers) and the accuracy of the quarter wavelength plate that converts the light (linearly polarized light) emitted from the inspection light source (laser light source) into circularly polarized light Since there is an error such as the accuracy of the Wollaston prism and the polarization beam splitter that separates the inspection light transmitted through the translucent substrate into two linearly polarized light, the translucent substrate is selected with a lower reference value of birefringence. It turned out to be difficult.

  In the above invention, when the inspection light transmitted through the translucent substrate is incident on the Wollaston prism or the like, the relative positions of the polarization plane of the inspection light and the Wollaston prism or the like are always in the same state. Therefore, the inspection light that has been transmitted through the light-transmitting substrate and polarized into elliptically polarized light cannot always be separated into linearly polarized light having the maximum amplitude and linearly polarized light having the minimum amplitude by a Wollaston prism or the like. In the above invention, since the maximum value and the minimum value of the light amount ratio calculated from the two linearly polarized light are not always calculated, it is difficult to calculate an accurate birefringence value.

  An object of the present invention is to measure a birefringence value of a translucent article (such as a translucent substrate) having a tendency of low birefringence with higher accuracy.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1)
A method for measuring birefringence in a translucent article having a pair of opposing surfaces,
The circularly polarized inspection light emitted from the light source unit is incident on the inside of the translucent article from the measurement point on one surface, and the inspection light emitted from the other surface is transmitted through the half-wave plate. From the two linearly polarized lights whose wavefronts are orthogonal to each other by the light separator, and the two linearly polarized lights are respectively received by the two light quantity measuring devices to measure the light quantity, and the light quantity measurement values of the two linearly polarized lights are measured. The step of calculating the light amount ratio by dividing one of the light amount measurement values by the sum of the light amount measurement values of the two linearly polarized light is to rotate the half-wave plate at the same measurement location. Is performed a plurality of times while changing the angle condition of the polarization plane of the inspection light incident on the light separator to obtain a first correspondence relationship that is a correspondence relationship between the rotation angle of the half-wave plate and the light amount ratio. Process,
The rotation angle of the half-wave plate under the same conditions as in the step of obtaining the first correspondence relationship, except that the translucent article is not disposed between the light source unit and the half-wave plate. Obtaining a standard correspondence relationship that is a correspondence relationship between the light intensity ratio and
Calculating a relative light quantity ratio of the first correspondence relationship that is a difference between the light quantity ratio of the first correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Obtaining a birefringence value at the measurement location from the correspondence between the relative light quantity ratio acquired in advance and the birefringence value using the relative light quantity ratio of the first correspondence relation. Refraction measurement method.

(Configuration 2)
A method for measuring birefringence in a translucent article having a pair of opposing surfaces,
The circularly polarized inspection light emitted from the light source unit is incident on the inside of the translucent article from the measurement point on one surface, and the inspection light emitted from the other surface is transmitted through the half-wave plate. From the two linearly polarized lights whose wavefronts are orthogonal to each other by the light separator, and the two linearly polarized lights are respectively received by the two light quantity measuring devices to measure the light quantity, and the light quantity measurement values of the two linearly polarized lights are measured. The step of calculating the light amount ratio by dividing one of the light amount measurement values by the sum of the light amount measurement values of the two linearly polarized light is to rotate the half-wave plate at the same measurement location. To obtain a first correspondence that is a correspondence between the rotation angle of the half-wave plate and the light quantity ratio, a plurality of times by changing the angle of the polarization plane of the inspection light incident on the light separator. ,
The rotation angle of the half-wave plate under the same conditions as in the step of obtaining the first correspondence relationship, except that the translucent article is not disposed between the light source unit and the half-wave plate. Obtaining a standard correspondence relationship that is a correspondence relationship between the light intensity ratio and
Calculating a relative light quantity ratio of the first correspondence relationship that is a difference between the light quantity ratio of the first correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Except for the fact that the translucent article and the inspection light are rotated by 90 degrees relative to the traveling direction of the inspection light as a rotation axis, under the same conditions as the step of obtaining the first correspondence relationship, A step of acquiring a second correspondence relationship that is a correspondence relationship between the rotation angle of the two-wavelength plate and the light amount ratio;
Calculating a relative light quantity ratio of a second correspondence relationship that is a difference between the light quantity ratio of the second correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Calculating an average value with the relative light quantity ratio of the first correspondence and the relative light quantity ratio of the second correspondence with the same rotation angle of the half-wave plate;
Calculating a corrected relative light amount ratio from a difference between the relative light amount ratio of the first correspondence relationship and the average value, or from a difference between the relative light amount ratio of the second correspondence relationship and the average value;
Using the corrected relative light amount ratio, and obtaining a birefringence value at the measurement location from a correspondence relationship between the corrected relative light amount ratio and the birefringence value acquired and set in advance. Method.

(Configuration 3)
The method further includes a step of obtaining a fitting function from the correspondence relationship between the corrected relative light amount ratio calculated from the first correspondence relative light amount ratio or the second correspondence relative light amount ratio and the rotation angle of the half-wave plate. The step of obtaining the birefringence value is a step of obtaining a birefringence value at the measurement location using a corrected relative light quantity ratio calculated from the fitting function. Measuring method.
(Configuration 4)
4. The birefringence measurement method according to Configuration 3, wherein the footing function is a function including a trigonometric function term.

(Configuration 5)
In the first correspondence relationship, the second correspondence relationship, and the reference correspondence relationship, the light quantity ratios corresponding to the same rotation angle of the half-wave plate are acquired together at three or more angles. Or the birefringence measuring method according to 4;
(Configuration 6)
6. The birefringence measurement method according to any one of configurations 3 to 5, wherein the fitting function is acquired using a least square method.

(Configuration 7)
A method for measuring birefringence in a translucent article having a pair of opposing surfaces,
The circularly polarized inspection light emitted from the light source unit is incident on the inside of the translucent article from the measurement point on one surface, and the inspection light emitted from the other surface is transmitted through the half-wave plate. From the two linearly polarized lights whose wavefronts are orthogonal to each other by the light separator, and the two linearly polarized lights are respectively received by the two light quantity measuring devices to measure the light quantity, and the light quantity measurement values of the two linearly polarized lights are measured. The step of calculating the light amount ratio by dividing one of the light amount measurement values by the sum of the light amount measurement values of the two linearly polarized light is to rotate the half-wave plate at the same measurement location. To obtain a first correspondence that is a correspondence between the rotation angle of the half-wave plate and the light quantity ratio, a plurality of times by changing the angle of the polarization plane of the inspection light incident on the light separator. ,
The rotation angle of the half-wave plate under the same conditions as in the step of obtaining the first correspondence relationship, except that the translucent article is not disposed between the light source unit and the half-wave plate. Obtaining a standard correspondence relationship that is a correspondence relationship between the light intensity ratio and
Calculating a relative light quantity ratio of the first correspondence relationship that is a difference between the light quantity ratio of the first correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Except for the fact that the translucent article and the inspection light are rotated by 90 degrees relative to the traveling direction of the inspection light as a rotation axis, under the same conditions as the step of obtaining the first correspondence relationship, A step of acquiring a second correspondence relationship that is a correspondence relationship between the rotation angle of the two-wavelength plate and the light amount ratio;
Calculating a relative light quantity ratio of a second correspondence relationship that is a difference between the light quantity ratio of the second correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Calculating an average value with the relative light quantity ratio of the first correspondence and the relative light quantity ratio of the second correspondence with the same rotation angle of the half-wave plate;
With respect to another measurement location in the translucent article or a measurement location in another translucent article, under the same conditions as the step of obtaining the first correspondence, Obtaining a third correspondence which is the correspondence of
Calculating a relative light quantity ratio of the third correspondence which is a difference between the light quantity ratio of the third correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Calculating a corrected relative light amount ratio of the third correspondence from a difference between the relative light amount ratio of the third correspondence and the average value;
Using the corrected relative light quantity ratio, from the correspondence between the corrected relative light quantity ratio and the birefringence value acquired and set in advance, another measurement location in the translucent article or measurement location in the other translucent article And a birefringence value obtaining step for obtaining a birefringence value.

(Configuration 8)
A step of obtaining a fitting function from the correspondence relationship between the corrected relative light amount ratio calculated from the relative light amount ratio of the third correspondence and the rotation angle of the half-wave plate, and obtaining the birefringence value Is a step of obtaining a birefringence value at the measurement location using a corrected relative light quantity ratio calculated from the fitting function.
(Configuration 9)
9. The birefringence measurement method according to Configuration 8, wherein the footing function is a function including a trigonometric function term.

(Configuration 10)
The first correspondence relationship, the second correspondence relationship, the third correspondence relationship, and the reference correspondence relationship indicate that the light quantity ratio corresponding to the same rotation angle of the half-wave plate is acquired at an angle of three or more directions. 10. The birefringence measurement method according to Configuration 8 or 9, which is characterized.

(Configuration 11)
The birefringence measurement method according to any one of Structures 8 to 10, wherein the fitting function is acquired using a least square method.
(Configuration 12)
The light source unit includes a laser light source and a quarter-wave plate, and the circularly polarized inspection light is obtained by transmitting linearly polarized light emitted from the laser light source through the quarter-wave plate. The birefringence measurement method according to any one of configurations 1 to 11, wherein:

(Configuration 13)
The translucent article is a translucent substrate, and the birefringence value obtained by applying the birefringence measuring method according to any one of configurations 1 to 12 to the translucent substrate is a predetermined value. The manufacturing method of the mask blank board | substrate characterized by including the process of selecting the following translucent board | substrates as a mask blank board | substrate.
(Configuration 14)
A method for producing a mask blank, comprising a step of forming a pattern forming thin film on a main surface of a mask blank substrate produced by the method for producing a mask blank substrate according to Structure 13.

(Configuration 15)
A method for producing a transfer mask, comprising a step of forming a transfer pattern on a thin film for pattern formation of a mask blank produced by the method for producing a mask blank according to Configuration 14.
(Configuration 16)
A method for manufacturing a semiconductor device, comprising a step of forming a circuit pattern on a semiconductor wafer using the transfer mask manufactured by the method for manufacturing a transfer mask according to Configuration 15.

  According to the present invention, the birefringence value of a translucent article (such as a translucent substrate) having a tendency of low birefringence can be measured with higher accuracy.

1 is a diagram illustrating an example of a configuration of a measurement apparatus 100. FIG. 3 is a diagram illustrating an example of a mask blank 20 and a transfer mask 30 that are manufactured using a translucent substrate 10. FIG. 2A shows an example of the configuration of the mask blank 20. FIG. 2B shows an example of the configuration of the transfer mask 30. It is a figure which shows each corresponding | compatible relationship between rotation angle (theta) of the half-wave plate 104, and light quantity ratio R10, R190, R1a. It is a figure which shows each correspondence of rotation angle (theta) of the half-wave plate 104, relative light quantity ratio R10s, R190s, and average value R1av. It is a figure which shows the result of having fitted with the approximate function with respect to relative light quantity ratio R10s, R190s. It is a figure which shows the result of having fitted with the approximate function with respect to correction | amendment relative light quantity ratio R10sc, R190sc. It is the figure which acquired and compared the maximum value of relative light quantity ratio R10s or correction | amendment relative light quantity ratio R10sc, and the maximum value of relative light quantity ratio R190s or correction | amendment relative light quantity ratio R190sc on various conditions. Calculated from each approximate function acquired from each correspondence relationship between the rotation angle θ of the half-wave plate 104 acquired with the number of measured rotation angles θ (the number of orientations) and the relative light quantity ratio R10s or the corrected relative light quantity ratio R10sc. It is the figure which compared the maximum value of the relative light quantity ratio R190s and correction | amendment relative light quantity ratio R190sc which were performed. It is a figure which shows the correlation with a birefringence value, a relative light quantity ratio, or a correction | amendment relative light quantity ratio.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
[measuring device]
FIG. 1 is a diagram for explaining the apparatus configuration of a measuring apparatus according to an embodiment of the present invention.
As shown in FIG. 1, a measuring apparatus 100 includes a light source unit 101 including a laser light source 102 that is a light source of inspection light and a quarter-wave plate (λ / 4 plate) 103, birefringence in the order of the inspection light route. Translucent article (translucent substrate, etc.) 10, half-wave plate (λ / 2 plate) 104, polarizing beam splitter (light separator) 108, two power meters (light quantity measuring device) ) 106a and 106b.
Detailed description is the same as [Measuring device] described later.

  The light source unit 101 has a light source that generates inspection light, and is a single wavelength that is polarized in a circularly polarized light toward a measurement location on one surface (main surface) of the light transmissive article (translucent substrate) 10. Generating light. In this example, the light source unit 101 mainly includes a laser light source 102 and a quarter wavelength plate (circular polarization converter) 103. Laser light (linearly polarized light) generated from the laser light source 102 is converted into circularly polarized light by a quarter-wave plate (circular polarization converter) 103, and is placed on a support member (substrate holder) as inspection light. The light is incident perpendicularly to the measurement location on the surface (main surface) of the article (translucent substrate) 10.

  The wavelength of the laser light emitted from the laser light source 102 is not particularly limited. Even if the translucent article which is a measurement object is a translucent substrate used for a transfer mask, it does not have to be the same as the wavelength of exposure light to which the transfer mask is applied. Further, it does not have to be the same as the wavelength of the inspection light used for pattern inspection of the transfer mask. The wavelength of the laser light source is preferably in the visible light range (wavelength 360 nm to 830 nm), and more preferably in the wavelength range 450 nm to 750 nm. When DUV light such as ArF excimer laser or KrF excimer laser is applied to the laser light source, all the equipment such as the quarter-wave plate 103, the half-wave plate 104, and the power meters 106a and 106b are made compatible with it. This is necessary, and the manufacturing cost of the measuring apparatus 100 increases. In addition, equipment for DUV light generally has a relatively short life compared to equipment for visible light.

  The light source unit 101 and the translucent article 10 can move relatively. Thereby, the incident position of the inspection light can be scanned within the surface of the translucent article 10. Accordingly, the light source unit 101 can sequentially set each position on the surface of the translucent article 10 as an inspection target position (measurement location).

  The polarizing beam splitter 108 is an example of an optical member that separates the inspection light emitted from the translucent article 10 into two linearly polarized light. The polarizing beam splitter 108 is connected to the light source unit 101 with the translucent article 10 placed on the support member interposed therebetween. The inspection light provided on the opposite side and transmitted through the translucent substrate 10 and further transmitted through the half-wave plate 104 is extracted by dividing it into two linearly polarized lights (linearly polarized beams) whose wavefronts are orthogonal to each other. The plurality of power meters 106 a and 106 b are light amount measuring devices that measure (measure) the amount of each linearly polarized light divided by the polarization beam splitter 108. The two power meters 106a and 106b are provided in the respective directions of P-polarized light and S-polarized light emitted from the polarization beam splitter 108.

  When configured in this way, there is a region in which the optical characteristics are not uniform in the translucent article 10 before the circularly polarized inspection light emitted from the light source unit 101 enters the polarization beam splitter 108. Then it will be affected. More specifically, for example, in the inspection light path, there is a region having a large birefringence in the translucent article 10, and when affected, the inspection light after passing through the translucent article 10 is It becomes elliptically polarized light. In this case, a difference occurs in the amount of light of the two linearly polarized lights divided by the polarization beam splitter 108. Further, a difference occurs in the light quantity measurement values of the power meters 106a and 106b. And the birefringence in the translucent article | item 10 can be detected appropriately based on the light quantity measurement value of the two power meters 106a and 106b.

  When the circularly polarized inspection light is not affected by birefringence in the translucent article 10, the light is theoretically incident on the polarization beam splitter 108 while remaining in a circularly polarized state. The light amounts of the two linearly polarized lights divided by the polarization beam splitter 108 are equal. Further, the light quantity measurement values of the power meters 106a and 106b are also equal. In the optical unit 101, a suitable quarter-wave plate 103 is selected so that laser light (linearly polarized light) emitted from the laser light source 102 is converted into circularly polarized light, and the incident angle of the laser light is adjusted. Yes. However, in reality, there is a tolerance in the quarter-wave plate 104 itself, and it is inevitable that a minute error occurs in the adjustment angle and the like. For this reason, the laser light transmitted through the quarter-wave plate 103 is not completely circularly polarized but slightly elliptically polarized.

  In the present invention, the influence based on the tolerance of the quarter-wave plate 103 and the adjustment error can be effectively corrected. For this reason, there is no particular limitation on the allowable range of the tolerance of the quarter wavelength plate 103 (tolerance for the function of shifting the phase of linearly polarized light by 90 [deg]), but the tolerance is within a range of ± 3 [deg]. The range is preferably ± 2 [deg].

  Even in the half-wave plate 104, there is a tolerance in itself, and it is inevitable that a minute error occurs in the adjustment angle or the like. In the present invention, the influence based on the tolerance of the half-wave plate 104 and the adjustment error can be effectively corrected. For this reason, there is no particular limitation on the allowable range of the tolerance of the half-wave plate 104 (tolerance for the function of shifting the phase of circularly polarized light by 180 [deg]), but the tolerance is within a range of ± 3 [deg]. The range is preferably ± 2 [deg].

  Even when completely circularly polarized inspection light is incident on the polarization beam splitter 108, it is difficult to make the light amounts of the two linearly polarized lights divided by the polarization beam splitter 108 completely the same. This is because there is a tolerance in the polarization beam splitter 109 itself, and it is inevitable that a minute error occurs in the adjustment angle or the like. In the present invention, the influence based on the tolerance of the polarization beam splitter 108 and the adjustment error can be effectively corrected.

  In addition, in the two power meters 106a and 106b that measure the amount of light of the two linearly polarized lights, it is inevitable that there is a tolerance between the devices. In the present invention, the light amount ratio is calculated by, for example, a computer from the step of measuring the light amount of the two linearly polarized light by the two power meters 106a and 106b and the light amount measurement values of the two linearly polarized light measured in the step. It has a process. More specifically, for example, when the light quantity measurement value of the power meter 106a is M1, and the light quantity measurement value of the power meter 106a is M2, the light quantity ratio R1 = M1 / (M1 + M2) and the light quantity ratio R2 = M2 / (M1 + M2). Perform at least one of the calculations. By applying this process of calculating the light quantity ratio, the problem of tolerance between devices in the power meters 106a and 106b can be reduced. On the other hand, the influence based on the tolerance of the quarter-wave plate 103 and the adjustment error can be effectively corrected.

  In addition, about the structure of the measuring apparatus 100, various changes are possible besides the structure demonstrated using the said FIG. In FIG. 1, a polarization beam splitter is applied as the light separator 108, but a Wollaston prism can be used instead. The half-wave plate 104 may be a stack of two quarter-wave plates with the orientation of the optical axis aligned. Thus, the half-wave plate 104 may be a birefringent element that generates a phase difference of 180 [deg] between orthogonal polarization components.

  The optical separator 108 may be configured to have an optical action equivalent to that of a polarizing beam splitter or a Wollaston prism. For example, it is possible to divide the inspection light transmitted through the translucent article 10 using a beam splitter or a half mirror while maintaining the polarization state. In this case, P-polarized light may be extracted from one of the divided lights with a quarter-wave plate or the like, and S-polarized light may be extracted from the other with a quarter-wave plate or the like. Also in this case, the light quantity ratio can be calculated by measuring the respective light quantities of P-polarized light and S-polarized light with the power meters 106a and 106b.

  The laser light at the stage of being emitted from the laser light source 102 is in the state of diffuse light although its divergence angle is small. In order to use this laser beam in the method for measuring birefringence in the translucent article of the present invention, it is desirable to perform a process for converting the laser beam into parallel light having a parallelism that can be applied as inspection light. For this reason, it is preferable to arrange a parallel light converter such as a collimator lens between the laser light source 102 and the quarter wavelength plate (circular polarization converter) 103.

  On the other hand, it is desirable that the laser light is emitted from the laser light source 102 with a stable light amount during the process of measuring the light amounts of the two linearly polarized lights by the power meters 106a and 106b. However, when the reflected light of the laser light returns to the laser light source 102, the oscillation of the laser light from the laser light source 102 tends to become unstable due to the reflected light (return light). For this reason, it is desirable to take measures to prevent the laser light reflected by any of the laser light sources 102 from returning.

  When the laser light emitted from the laser light source 102 hits the surface of the collimator lens, a part of the laser light may be reflected to be returned light. As a solution in this case, for example, it is conceivable that the laser light source 102 and the collimator lens have a positional relationship in which the center of the collimator lens is slightly shifted in parallel from the optical axis of the laser beam. In such a positional relationship, the laser light incident on the collimator lens is reflected at an angle inclined from the optical axis and does not return to the laser light source. In addition, reflected light from the circular polarization converter 103 such as a quarter-wave plate may become return light. As a solution in this case, for example, the incident surface of the quarter-wave plate 103 is disposed at a position slightly inclined from a position perpendicular to the optical axis of the laser beam incident on the surface. Can be considered.

  The reflected light of the laser light from the surface of the translucent article 10 that is the measurement object may be returned light. As a solution in this case, for example, the surface of the translucent article 10 may be arranged at a position slightly inclined from a position perpendicular to the optical axis of the laser light incident on the surface. It is done. The reflected light of the laser light from the light separator 108 such as a polarizing beam splitter or a Wollaston prism may be returned light. As a solution in this case, for example, the surface of a polarizing beam splitter, a Wollaston prism or the like is arranged at a position slightly inclined from a position perpendicular to the optical axis of the laser beam incident on the surface. It is possible.

[Measurement Method According to First Embodiment]
Next, a method for measuring birefringence according to the first embodiment of the present invention will be described.
The procedure of the birefringence measurement method (calculation method) according to the first embodiment using the measurement apparatus is as follows.
(1-1) The inspection light emitted from the laser light source 102 is polarized into circularly polarized light when passing through the quarter-wave plate 103.
(1-2) Circularly polarized inspection light is incident from a measurement point on one of the two opposing surfaces of the measurement object 10 and is emitted from the other surface.
(1-3) The inspection light emitted from the other surface is transmitted through the half-wave plate 104 and then separated into two linearly polarized lights whose wavefronts are orthogonal to each other by the polarization beam splitter 108.
(1-4) The two separated linearly polarized lights are received by the power meters 106a and 106b, respectively, and the light quantity values M10 and M20 are measured.
(1-5) The light quantity ratio R10 [%] = M10 / (M10 + M20) or the light quantity ratio R20 [%] = M20 / (M10 + M20) is calculated from the measured linearly polarized light quantity values M10 and M20.
(1-6) By rotating the half-wave plate 104 at a predetermined angle Δθ, the amount of light in a state where the polarization direction (polarization plane angle) of the inspection light emitted from the other surface is rotated by the predetermined angle Δ2θ. The ratio can be acquired. By repeating this process at one measurement location, the correspondence between the rotation angle θ of the half-wave plate 104 (polarization direction of the inspection light, the angle 2θ of the polarization plane) and the light quantity ratio R10 or R20 (first correspondence) Relationship).

(1-7) Under the same conditions except that the measurement object 10 is not disposed between the light source unit 101 (¼ wavelength plate 103) and the half wavelength plate 104, (1-1) Steps (1-6) are performed. In this case, the circularly polarized inspection light transmitted through the quarter-wave plate 103 is incident on the half-wave plate 104 while passing through only air. Thus, the reference light quantity ratio R1a [%] = M1a / (M1a + M2a), which is the ratio of the rotation angle θ of the half-wave plate 104 (the polarization direction of the inspection light, the angle 2θ of the polarization plane) and the light quantity that has passed through the air only. Alternatively, the correspondence relationship with R2a [%] = M2a / (M1a + M2a) is acquired. Theoretically, the reference light quantity ratios R1a and R2a should both be 50 [%], but in reality, they are not 50 [%] for reasons described later.

(1-8) From each correspondence, it is calculated from the inspection light transmitted through the measuring object 10 corresponding to the rotation angle θ (polarization direction of the inspection light, angle 2θ of the polarization plane) of the same half-wave plate 104. The difference between the light quantity ratio (light quantity ratio of the first correspondence relationship) R10 or R20 and the reference light quantity ratio R1a or R2a, which is the light quantity ratio calculated from the inspection light transmitted only in the air, is calculated as the relative light quantity. The ratio R10s [%] (R10s = R10-R1a, or R1a-R10) or R20s [%] (R20s = R20-R2a, or R2a-R20), and the rotation angle θ of the half-wave plate 104 (inspection light) (Corresponding to the first correspondence relationship).

(1-9) The measurement device itself of the present invention cannot directly measure the value of birefringence. Therefore, in the measurement method according to the first embodiment of the present invention, measurement is performed with a birefringence measuring apparatus (for example, HINDS Exicor ^(R) 193 DUV manufactured by HINDS) that can measure the birefringence value (birefringence amount). An operation for obtaining the relative light amount ratio R10 sb [%] or R20 sb [%] with the measuring device of the present invention is performed on a specific portion of the translucent article whose birefringence value is known, and the birefringence value and the relative light amount ratio R10 sb or The correspondence with R20sb is acquired in advance. Then, the birefringence value is acquired by fitting the relative light quantity ratio R10s or R20s acquired by the measuring apparatus of the present invention to the measurement location of the measurement object 10 to the corresponding relationship.

  Except when there is no birefringence at the measurement location, the numerical value of the relative light quantity ratio R10s or R20s is a change in the numerical value of the rotation angle θ of the half-wave plate 104 (polarization direction of the inspection light, angle 2θ of the polarization plane). It vibrates up and down in conjunction. The numerical value of the relative light amount ratio R10s or R20s applied to the correspondence relationship between the birefringence value and the relative light amount ratio R10sb or R20sb is the rotation angle θ of the acquired half-wave plate 104 (the polarization direction of the inspection light, the angle 2θ of the polarization plane) ) And the relative light quantity ratio R10s or R20s (first correspondence) is preferably the maximum value (the maximum value among the absolute values of the maximum and minimum peak values of vibration). Moreover, you may use the average value of the absolute value of each peak in the amplitude of relative light quantity ratio R10s or R20s for acquisition of a birefringence value.

(1-10) Furthermore, when applying to the manufacturing method of the substrate for mask blanks, the said measuring method is processed with respect to the translucent substrate (glass substrate) by which it processed into the shape of the substrate for mask blanks, and the surface was grind | polished. A step of selecting a translucent substrate having a birefringence value (or relative light quantity ratio R10s or R20s) acquired by application as a predetermined value or less as a mask blank substrate is included. In this case, it is preferable to arrange the translucent substrate so that the circularly polarized inspection light enters from a predetermined measurement location on one main surface of the translucent substrate and exits from the other main surface.

  The translucent article to be measured by the birefringence measuring method of the present invention is made of a material having a small birefringence (for example, 5 nm / cm or less). The translucent article to be measured is preferably made of a glass material, more preferably synthetic quartz glass. Similarly, a translucent substrate used for a transfer mask to which the polarized illumination technique is applied is also formed of a material having a small birefringence (for example, 5 nm / cm or less). The present invention is an invention for measuring the birefringence value of a translucent article or translucent substrate formed of a material having a small birefringence with higher accuracy.

  In the region of the birefringence value measured in the present invention, when the light quantity ratios R10 and R20 are obtained with the measuring device 100 for the translucent article in the birefringence value region, the translucent article There is a tendency that the influence on the light amount ratios R10 and R20 due to the tolerance of the measuring apparatus 100 itself is larger than the amount of change in the light amount ratios R10 and R20 due to the birefringence of the light. For this reason, even if the birefringence value of the translucent article is acquired using the correspondence relationship between the light quantity ratios R10 and R20 and the birefringence value in the birefringence measuring apparatus, the accuracy is lowered. The tolerance of the measuring device 100 itself includes, for example, a tolerance caused by retardation of the components of the quarter wavelength plate 103 and the half wavelength plate 104, and a tolerance caused by a rotation angle when the components are installed in the device. It is difficult to make these zero.

  FIG. 3 shows a translucent substrate having a low birefringence, in which the measurement apparatus 100 is used for a measurement location where the birefringence value of the main surface is known (1.5 nm / cm). A plot of the correspondence between the rotation angle θ [deg] of the half-wave plate 104 and the light amount ratio R10 [%] obtained by performing the steps (1-1) to (1-6) in the measurement method (FIG. (Details will be described later in [Experimental example]). FIG. 3 also shows the reference light amount ratio R1a [%], which is the light amount ratio obtained by performing the step (1-7) and the rotation angle θ [deg] of the half-wave plate 104 and the light amount that has passed only in the air. ] Is also plotted (R1a in FIG. 3).

  Since the reference light quantity ratio R1a is a light quantity ratio calculated from the inspection light that has passed only in the air, the light quantity ratio should theoretically be constant at 50% even if the half-wave plate 104 is rotated. is there. Even if there is a machine difference between the two power meters 106a and 106b, the light amount ratio should be a constant value regardless of the rotation angle θ of the half-wave plate 104. However, in actuality, as shown in the plot of R1a in FIG. 3, due to the influence of the tolerance of the device 100 itself, the device vibrates greatly due to the rotation angle θ of the half-wave plate 104.

  The plot of the light quantity ratio R10 in FIG. 3 greatly oscillates between the 54% and 47% levels depending on the rotation angle θ of the half-wave plate 104. However, this vibration is greatly influenced by the vibration of the reference light quantity ratio R1a caused by the tolerance of the measuring apparatus 100 itself. Even if a birefringence value is obtained using this light quantity ratio R10, an accurate value is obtained. It will not be. The fluctuation of the light quantity ratio R10 caused by the birefringence of the translucent substrate is obtained by removing the influence of the vibration of the reference light quantity ratio R1a and the light quantity ratio R10 and the reference light quantity ratio R1a at the same rotation angle θ of the half-wave plate 104. It becomes the difference. The difference between the light quantity ratio R10 and the reference light quantity ratio R1a is significantly smaller than the vibration amplitude of the reference light quantity ratio R1a.

  For these reasons, in the birefringence measurement method according to the first embodiment of the present invention, the light quantity ratio R10 or R20 at the measurement location of the translucent article that is the measurement object, and the inspection light transmitted only in the air. The relative light quantity ratio R10s or R20s, which is the difference from the reference light quantity ratio R1a or R2a, which is the light quantity ratio calculated from the above, is calculated, and the rotation angle θ of this and the half-wave plate 104 (the polarization direction of the inspection light, the polarization plane) Is associated with the angle 2θ). Then, the relative light quantity ratio R10sb or R20sb is calculated for the translucent article having a known birefringence value using the measuring apparatus 100, and the correspondence between the relative light quantity ratio R10sb or R20sb and the birefringence value is acquired in advance. Keep it. Further, from the correspondence between the relative light quantity ratio R10sb or R20sb and the birefringence value, the calculated maximum relative light quantity ratio R10s or R20s of the translucent article of the measurement object (vibration peak value, average value of plural peaks). Etc.) is obtained, and this is used as the birefringence value at the measurement location of the translucent article that is the measurement object.

  4 shows the correspondence between the rotation angle θ [deg] of the half-wave plate 104 shown in FIG. 3 and the light amount ratio R10 [%], and the rotation angle θ [deg] of the half-wave plate 104 and the reference. Based on the correspondence with the light quantity ratio R1a [%], the correspondence relation between the rotation angle θ [deg] of the half-wave plate 104 and the relative light quantity ratio R10 s [%] obtained by performing the step (1-8). Is plotted (R10s in the figure) (details will be described later in [Experimental example]). The plot of the relative light quantity ratio R10s in FIG. 4 oscillates between the −0.3% and + 0.3% levels depending on the rotation angle θ of the half-wave plate 104. Although there are some differences in the amplitude of vibration, most of the vibration components are caused by the birefringence of the translucent article of the measurement object. By introducing the concept of the relative light quantity ratio, the influence of the tolerance of the device 100 itself can be greatly reduced. Thereby, the birefringence value in the measurement location of the translucent article of a measuring object can be acquired with high accuracy. For example, the present invention can be applied to a production method of selecting a translucent article (translucent article) having a birefringence value of 5 nm / cm or less as an acceptable product (mask blank substrate).

  In the present invention, the relative light amount ratio is calculated by subtracting the reference light amount ratio, which is the light amount ratio calculated from the inspection light transmitted only in the air, from the light amount ratio calculated from the inspection light transmitted through the measurement object 10. Therefore, most of the influence caused by the tolerance of the measuring apparatus 100 itself can be canceled. For this reason, the birefringence of the translucent article is high even if the precision of the components (such as the quarter-wave plate 103 and the half-wave plate 104) used in the measuring apparatus 100 is not excessively high. Derived with accuracy.

  In the birefringence measuring method according to the first embodiment of the present invention described above, the steps (1-1) to (1-6) were first performed and calculated from the inspection light transmitted through the measuring object 10. After acquiring the light amount ratio, the step (1-7) is performed to acquire the reference light amount ratio that is the light amount ratio calculated from the inspection light transmitted only through the air. However, the present invention is not limited to this, and after obtaining the reference light amount ratio, which is the light amount ratio calculated from the inspection light that has passed through the air only by performing the step (1-7) first, You may make it acquire the light quantity ratio computed from the test | inspection light which permeate | transmitted the measuring object 10 by performing the process of (1-6). Further, when birefringence is measured for a plurality of translucent articles with the measuring apparatus 100, or when birefringence is measured at a plurality of locations on the surface of the translucent article, only in the air of (1-7). The step of acquiring the reference light amount ratio, which is the light amount ratio calculated from the inspection light that has passed through, may be performed only once. This is because the reference light amount ratio, which is the light amount ratio calculated from the inspection light, has a very small difference in acquired values for each measurement.

  In the birefringence measurement method according to the first embodiment, the correspondence relationship between the rotation angle θ of the half-wave plate 104 and the light quantity ratio R10 is obtained by acquiring the numerical value of the rotation angle θ in increments of a predetermined angle Δθ. The light amount ratio R10 to be acquired is also acquired. The predetermined angle Δθ for rotating the half-wave plate 104 performed in the step (1-6) is preferably 2 [deg] or less, more preferably 1 [deg] or less, and 0.5 [Deg] or less is more preferable. When the half-wave plate 104 is rotated by Δθ, the direction of the inspection light transmitted through the half-wave plate 104 is rotated by Δ2θ. Accordingly, the increment Δ2θ of the polarization direction (polarization plane angle) of the inspection light is 4 [deg] or less (when Δθ = 2 [deg] or less), 2 [deg] or less (Δθ = 1 [deg] or less, respectively) ) 1 [deg] or less (when Δθ = 0.5 [deg] or less).

  Further, in the birefringence measurement method according to the first embodiment, the correspondence between the rotation angle θ of the half-wave plate 104 and the light amount ratio R10 is obtained when the light amount ratio R10 is first acquired (initially, the light amount When the rotation angle θ of the half-wave plate 104 (when the values M10 and M20 are acquired) is 0 [deg], it is preferable to acquire until the rotation angle θ is 45 [deg] or more. ] It is more preferable to acquire until it becomes above, and it is further more preferable to acquire until it becomes above 180 [deg].

  When the range of the rotation angle θ of the half-wave plate 104 is 0 to 45 [deg], the polarization direction (polarization plane angle) 2θ of the inspection light transmitted through the half-wave plate 104 is 0 to 90 [ deg]. In the birefringence measuring method according to the first embodiment, the inspection light transmitted through the translucent article is elliptically polarized light, and the elliptically polarized light is separated into two linearly polarized lights whose wavefronts are orthogonal to each other. The light quantity values M10 and M20 of linearly polarized light are measured. When the polarization azimuth (angle of polarization plane) 2θ of the separated elliptically polarized inspection light is rotated in the range of 0 to 90 [deg] and the light quantity values M10 and M20 are measured, the maximum amplitude is obtained at each of the light quantity values M10 and M20. Either the peak or the minimum peak can be measured. The birefringence value can be obtained with high accuracy by using the relative light quantity ratio R10 or R20 that can be finally obtained from the maximum peak or the minimum peak of the light quantity values M10 and M20.

  When the range of the rotation angle θ of the half-wave plate 104 is 0 to 90 [deg], the polarization direction (polarization plane angle) 2θ of the inspection light transmitted through the half-wave plate 104 is 0 to 180 [deg]. When the polarization direction (angle of polarization plane) 2θ of the elliptically polarized inspection light is rotated in the range of 0 to 180 [deg] and the light quantity values M10 and M20 are measured, the maximum peak and minimum amplitude of each of the light quantity values M10 and M20 are measured. Both peaks can be measured. For this reason, the birefringence value can be acquired with higher accuracy.

[Measurement Method According to Second Embodiment]
Next, a birefringence measuring method according to the second embodiment of the present invention will be described.
The procedure of the birefringence measurement method (calculation method) according to the second embodiment using the measurement apparatus is as follows.
(2-1) to (2-8) Steps (1-1) to (1-8) in the birefringence measurement method according to the first embodiment are performed, and the rotation angle θ of the half-wave plate 104 is determined. Correspondence (first correspondence) between the light beam ratio R10 or R20 (polarization orientation of the inspection light, polarization plane angle 2θ), rotation angle θ of the half-wave plate 104 (polarization orientation of the inspection light, polarization plane Angle 2θ) and the reference light quantity ratio R1a or R2a, which is the light quantity ratio that has passed only in the air, the rotation angle θ of the wave plate 104 (the polarization direction of the inspection light, the angle 2θ of the polarization plane) and the relative light quantity ratio R10s. Alternatively, the correspondence relationship with R20s is acquired.

(2-9) The translucent article 10 and the inspection light (light source unit 101) are rotated by 90 degrees relative to the traveling direction of the inspection light (the traveling direction of the inspection light). (2-1) to (2-) under the same conditions except that the light source unit 101 is installed at a position rotated 90 around the rotation axis, or the light source unit 101 is rotated 90 rotations about the traveling direction of the inspection light. Step 6) is performed to obtain the correspondence (second correspondence) between the rotation angle θ of the half-wave plate 104 (polarization direction of the inspection light, the angle 2θ of the polarization plane) and the light amount ratio R190 or R290.

(2-10) Calculated from the inspection light transmitted through the measuring object 10 corresponding to the rotation angle θ of the same half-wave plate 104 (polarization azimuth of inspection light, angle 2θ of polarization plane) of each corresponding relationship. The difference between the light quantity ratio (light quantity ratio of the first correspondence relationship) R190 or R290 and the reference light quantity ratio R1a or R2a, which is the light quantity ratio calculated from the inspection light transmitted only in the air, is calculated as the relative light quantity. The ratio R190s [%] (R190s = R190-R1a or R1a-R190) or R290s [%] (R290s = R290-R2a or R2a-R290) is used, and the rotation angle θ of the half-wave plate 104 (inspection light) (Corresponding to the second correspondence relationship).

(2-11) From each correspondence relationship, the relative light quantity ratio R10s or R20s of the first correspondence relationship corresponding to the rotation angle θ of the same half-wave plate 104 (polarization direction of inspection light, angle 2θ of the polarization plane) The average value R1av (R1av = (R10s + R190s) / 2) or R2av (R2av = (R20s + R290s) / 2) is calculated between the relative light quantity ratios R190s or R290s of the first correspondence relationship.

(2-12) The corrected relative light amount ratio R10sc (R10sc = R10s−R1av) or R20sc (R20sc = R20s−R2av) is calculated from the difference between the relative light amount ratio R10s or R20s of the first correspondence relationship and the average value R1av or R2av. To do. Alternatively, the corrected relative light amount ratio R190sc (R190sc = R190s−R1av) or R290sc (R290sc = R290s−R2av) is calculated from the difference between the relative light amount ratio R190s or R290s in the second correspondence relationship and the average value R1av or R2av.

(2-13) The measurement device itself of the present invention cannot directly measure the value of birefringence. Therefore, in the measurement method according to the second embodiment of the present invention, measurement is performed with a birefringence measuring apparatus (for example, HINDS Exicor ^(R) 193 DUV manufactured by HINDS) that can measure the birefringence value (birefringence amount). An operation for obtaining the corrected relative light amount ratio R1sbc [%] or R2sbc [%] with the measuring apparatus of the present invention is performed on a specific portion of the translucent article whose birefringence value is known, and the birefringence value and the corrected relative light amount ratio are obtained. The correspondence with R1sbc or R2sbc is acquired in advance. Then, the birefringence value is obtained by applying the corrected relative light amount ratio R10sc or R20sc obtained by the measurement apparatus of the present invention to the measurement location of the measurement object 10 to the corresponding relationship. Alternatively, the correspondence relationship between the birefringence value and the corrected relative light amount ratio R190sbc or R290sbc is acquired in advance. Then, the birefringence value is acquired by applying the corrected relative light quantity ratio R190sc or R290sc acquired by the measurement apparatus of the present invention to the measurement location of the measurement object 10 to the corresponding relationship.

(2-14) Furthermore, when applying to the manufacturing method of the substrate for mask blanks, the said measuring method is processed with respect to the translucent substrate (glass substrate) by which it processed into the shape of the substrate for mask blanks, and the surface was grind | polished. A step of selecting a translucent substrate having a birefringence value (or corrected relative light quantity ratio R10sc, R20sc, R190sc, or R290sc) obtained by application as a predetermined value or less as a mask blank substrate is included. In this case, it is preferable to arrange the translucent substrate so that the circularly polarized inspection light enters from a predetermined measurement location on one main surface of the translucent substrate and exits from the other main surface.

  Plot R190 in FIG. 3 shows a second example in which the measurement apparatus 100 is used for a measurement location where the birefringence value of the main surface is known (1.5 nm / cm) in a translucent substrate having low birefringence. The correspondence relationship between the rotation angle θ [deg] of the half-wave plate 104 and the light amount ratio R190 [%] obtained by performing the steps (2-1) to (2-10) of the measurement method in the embodiment. (The details will be described later in [Experimental example]). The plot R190 oscillates greatly between the 54% and 47% levels depending on the rotation angle θ of the half-wave plate 104, as with the plot R10. The reason for this vibration is the same as in the case of plot R10.

  The plot R190S in FIG. 4 shows the correspondence between the rotation angle θ [deg] of the half-wave plate 104 and the light amount ratio R190 [%] shown in FIG. 3 and the rotation angle θ [deg] of the half-wave plate 104. ] And the reference light quantity ratio R1a [%], the rotation angle θ [deg] of the half-wave plate 104 and the relative light quantity ratio R190 s [%] obtained by performing the step (2-10) (The details will be described later in [Experimental example]). The plot of the relative light quantity ratio R190s in FIG. 4 oscillates between the −0.3% level and the + 0.3% level depending on the rotation angle θ of the half-wave plate 104. The reason for this vibration is the same as in the case of plot R10s.

  In plots R10s and R190s, the inspection light is incident on the same measurement location on the main surface of the same translucent substrate. However, the position of the translucent substrate when the plot R10s is acquired and the position of the translucent substrate when the R190s is acquired have a relationship of φ = 90 degrees rotated about the traveling direction of the inspection light as the rotation axis. Since the inspection light emitted from the other main surface of the translucent substrate passes through the half-wave plate 104, the inspection light when the plot R10s is acquired and the inspection light when the R190s are acquired are 2φ = 180. A phase difference of degrees will occur.

  As can be seen from FIG. 4, in the plots R10s and R190s, the phase of vibration between them is shifted by approximately 180 degrees. However, the plots R10s and R190s have small differences in the upper and lower peaks of each amplitude. In many cases, the plots R10s and R190s do not have a point where they intersect each other at the zero position in the relative light quantity ratio of the vertical axis of the graph. The plots R10s and R190s have a relationship in which the relative positions of the quarter-wave plate 103, the half-wave plate 104 and the measurement location of the translucent article 10 are rotated 90 times. In the light source unit 101, the laser light is converted into circularly polarized light by the quarter wavelength plate 103. However, there is a slight difference between the accuracy limit of the quarter wavelength plate 103 and the design installation position in the measuring apparatus. It is difficult to make laser light (inspection light) completely circularly polarized due to the effects of various errors. Since inspection light that is not completely circularly polarized light enters the translucent article 10, if the relative position between the half-wave plate 104 and the measurement location of the translucent article 10 is rotated 90 times, an error due to the rotation occurs. Is inevitable.

  The elliptically polarized inspection light emitted from the opposing surface of the translucent article is transmitted through the half-wave plate and the phase of the inspection light is shifted. It is difficult to shift the phase angle as designed due to the influence of a minute error between the design installation position in the measuring device. When the plot R10s is acquired and when the R190 is acquired, the relative position between the half-wave plate 104 and the measurement location of the translucent article 10 is rotated by φ = 90, but the plot R10s. And R190s are unlikely to deviate from the phase difference of 2φ = 180 degrees at all.

  From these facts, in the birefringence measurement method according to the second embodiment of the present invention, the rotation angle θ of the half-wave plate 104 (the polarization direction of the inspection light, the polarization) is performed in the same procedure as in the first embodiment. In addition to obtaining the correspondence (first correspondence) between the surface angle 2θ) and the relative light quantity ratio R10s or R20s, the translucent article 10 and the inspection light (light source unit 101), which are measurement objects, Under the same conditions except that the traveling direction of the inspection light is rotated by 90 degrees relative to the rotation axis, the inspection light is incident on the measurement location of the translucent article 10 and the rotation angle θ of the half-wave plate 104 A correspondence relationship (second correspondence relationship) between (the polarization direction of the inspection light, the angle 2θ of the polarization plane) and the relative light quantity ratio R190s or R290s is acquired. After that, the average value R1av of the relative light quantity ratios R10s and R190s (or the average value R2av of the relative light quantity ratios R20s and R290s) at the rotation angle θ of the same half-wave plate 104 is calculated. Further, correction is performed by subtracting the average value R1av from the relative light quantity ratio R10s or R190s (correction by subtracting the average value R2av from the relative light quantity ratio R20s or R290s), and the corrected relative light quantity ratio R10sc or R190sc (corrected relative light quantity ratio R20sc or R290sc). ) Is calculated. Then, the corrected relative light amount ratio R10sc or R190sc (corrected relative light amount ratio R20sc or R290sc) is applied to the correspondence relationship between the birefringence value acquired in advance and the corrected relative light amount ratio R1sbc or R2sbc. The birefringence value is acquired.

  4 shows a change in the average value R1a [%] of the relative light quantity ratios R10s [%] and R190s [%] with respect to the rotation angle θ [deg] of the half-wave plate 104 (in FIG. 4). R1a plot). FIG. 5 shows fitting of a function including a trigonometric function term to each plot of the relative light quantity ratios R10s [%] and R190s [%] corresponding to the rotation angle θ [rad] of the half-wave plate 104. The results (F10s and F190s curves in FIG. 5) are shown. FIG. 6 shows a result of fitting a function including a trigonometric function term to each plot of the corrected relative light quantity ratios R10sc and R190sc corresponding to the rotation angle θ [rad] of the half-wave plate 104 (FIG. 6). Middle curves of F10sc and F190sc).

  As can be seen from FIG. 5, it is difficult to accurately fit the relative light quantity ratios R10s and R190s that have not been corrected with the average value R1av with an approximation function including a trigonometric term (trigonometric function). It is difficult to accurately fit other approximation functions that do not contain terms.) On the other hand, it can be seen from FIG. 6 that an approximate function including a trigonometric function can be accurately fitted to the corrected relative light quantity ratios R10sc and R190sc corrected with the average value R1av. As described above, by introducing the concept of the corrected relative light quantity ratio, the influence of the tolerance of the device 100 itself can be further reduced. Thereby, the birefringence value in the measurement location of the translucent article of the measuring object can be acquired with higher accuracy. For example, the present invention can be applied to a manufacturing method of selecting a translucent article (translucent article) having a birefringence value of 2 nm / cm or less as an acceptable product (mask blank substrate).

  Other matters in the method for measuring birefringence according to the second embodiment of the present invention are the same as those in the method for measuring birefringence according to the first embodiment. Also in the birefringence measurement method according to the second embodiment of the present invention, the rotation angle θ of the half-wave plate 104 (the polarization direction of the inspection light, the angle 2θ of the polarization plane) and the light amount ratio that has passed only in the air. The step (2-7) for acquiring the correspondence relationship with the reference light quantity ratio R1a or R2a may be performed before the steps (2-1) to (2-6).

[Measurement Method According to Third Embodiment]
Next, a birefringence measuring method according to the third embodiment of the present invention will be described. The birefringence measurement method according to the second embodiment includes a correction relative light amount ratio R10sc or R20sc having a first correspondence relationship or a correction relative light amount ratio R190sc or R290sc having a second correspondence relationship and rotation of the half-wave plate 104. A step of obtaining a fitting function (approximate function) from the correspondence relationship with the angle θ (polarization direction of the inspection light, angle 2θ of the polarization plane), and corrected light quantity ratios R10scf, R20scf, R190scf calculated from the fitting function or The difference is that the method includes a step of obtaining a birefringence value at a measurement location of a translucent article using R290scf.

The procedure of the birefringence measurement method (calculation method) according to the third embodiment is as follows.
(3-1) to (3-12) The same process as (2-1) to (2-12) is performed to calculate the corrected relative light quantity ratio R10sc or R20sc of the first correspondence relationship. Alternatively, the corrected relative light quantity ratio R190sc or R290sc of the second correspondence relationship is calculated.
(3-13) The first correspondence relationship (second correspondence) in the rotation angle θ of the half-wave plate 104 (polarization direction of the inspection light, the angle 2θ of the polarization plane) and the corrected relative light quantity ratio R10sc or R20sc (R190sc or R290sc) (Relationship) is performed to fit a function to obtain a fitting function F10sc or F20sc (F190sc or F290sc). The fitting function F10sc or F20sc (F190sc or F290sc) is a two-variable function with the rotation angle θ and the correction light quantity ratio R10sc or R20sc (R190sc or R290sc) as variables.

(3-14) The maximum value of the amplitude is calculated from the fitting function F10sc or F20sc (F190sc or F290sc), and this is set as the corrected light quantity ratio R10scf or R20scf (R190scf or R290scf).
(3-15) In the same process as (2-13), the corrected relative light quantity ratio R10scf or R20scf (R190scf or R290scf) is added to the correspondence relationship between the birefringence value acquired in advance and the corrected relative light quantity ratio R1sbc or R2sbc. ) To obtain the birefringence value.

(3-16) Furthermore, when applying to the manufacturing method of the substrate for mask blanks, the said measuring method is processed with respect to the translucent substrate (glass substrate) by which it processed into the shape of the substrate for mask blanks, and the surface was grind | polished. A step of selecting a translucent substrate having a birefringence value (or corrected relative light quantity ratio R10scf, R20scf, R190scf, or R290scf) obtained by application as a predetermined value or less as a mask blank substrate is included. In this case, it is preferable to arrange the translucent substrate so that the circularly polarized inspection light enters from a predetermined measurement location on one main surface of the translucent substrate and exits from the other main surface.

  As described in the second embodiment and as shown in FIG. 6, the rotation angle θ [rad] of the half-wave plate 104 and the corrected relative light quantity ratio R10sc [%] (first correspondence) and R190sc [ %] (Second correspondence), the fitting functions (approximate functions) F10sc and F190sc can be fitted with high accuracy. The correspondence relationship between the rotation angle θ [rad] of the half-wave plate 104 shown in FIG. 6 and the corrected relative light quantity ratios R10sc [%] and R190sc [%] indicates that the increment Δθ of the rotation angle θ is 1 [deg]. ] (The step of the polarization direction of the inspection light is 2 [deg] increments). However, in the third embodiment, the step of deriving the corrected relative light quantity ratio is introduced, so that the rotation angle θ [rad] of the half-wave plate 104 and the corrected relative light quantity ratio R10sc [%] and R190sc [ %], The step Δθ of the rotation angle of the rotation angle θ [rad] of the half-wave plate 104, which is performed when acquiring the correspondence relationship with the [%]. By increasing the increment Δθ of the rotation angle, the above-described fitting of the corrected relative light quantity ratio R10sc [%] and R190sc [%] (maximum or minimum value of the amplitude in the vibration of the corrected relative light quantity ratio R10sc) is performed as described above. This is because functions can be sufficiently complemented.

  In the present invention, the fitting function (approximation function) used for fitting with the first correspondence relationship or the second correspondence relationship is a two-variable variable with the rotation angle θ of the half-wave plate 104 and the corrected relative light quantity ratio R10sc as variables. Any term can be used as long as it is a function. Examples of the function include a quadratic or higher-order function in which the variable of the rotation angle θ has a second-order or higher term, and a function including a trigonometric function having the rotation angle θ as an angle term. The fitting function is preferably a function including a term of a trigonometric function (particularly, a sine function or a cosine function). Corresponding relations (first correspondence relation and second correspondence relation) such as the rotation angle θ of the half-wave plate 104 and the corrected relative light quantity ratio R10sc are all increased as the rotation angle θ of the half-wave plate 104 increases. This is because the corrected relative light amount ratio R10sc and the like have a relationship of oscillating with a certain range of amplitude and a certain range of cycles, and a function including a trigonometric function term is most easily fitted. The fitting function is preferably obtained using the least square method.

  In order to derive the above fitting function, the rotation angle θ of the half-wave plate 104 (the polarization direction of the inspection light, the angle 2θ of the polarization plane) is an angle of 3 or more (preferably an angle of 4 or more), At least the correction light quantity ratio R10sc (in the case of the first correspondence) and R190sc (in the case of the second correspondence) are necessary. For this reason, the light quantity ratio R10 of the first correspondence relationship in which the rotation angle θ of the half-wave plate 104 (the polarization direction of the inspection light and the angle 2θ of the polarization plane) necessary for calculating the correction light quantity ratio is the same. (Or R20), a set of the second correspondence light quantity ratio R190 (or R290) and the reference light quantity ratio R1a (or R2a), and the rotation angle θ (polarization direction of the inspection light, polarization plane) of the different half-wave plates 104 At an angle 2θ) of 3 sets or more (preferably 4 sets or more).

  As described above, the correspondence between the rotation angle θ of the half-wave plate 104 (the polarization direction of the inspection light and the polarization plane angle 2θ) and the correction light quantity ratio R10sc is converted into a fitting function so that the same measurement location can be obtained. On the other hand, the influence of the tolerance of the device 100 itself can be reduced with a small number of measurements. Thereby, the birefringence value in the measurement location of the translucent article of the measuring object can be acquired with higher accuracy. For example, the present invention can be applied to a manufacturing method of selecting a translucent article (translucent article) having a birefringence value of 2 nm / cm or less as an acceptable product (mask blank substrate). Other matters in the birefringence measurement method according to the third embodiment of the present invention are the same as those in the birefringence measurement method according to the first embodiment and the second embodiment. .

[Measurement Method According to Fourth Embodiment]
Next, a birefringence measuring method according to the fourth embodiment of the present invention will be described.
In the birefringence measurement method according to the second embodiment, the average value R1av or R2av of the relative light quantity ratio is calculated. The average value R1av or R2av is calculated only at the same measurement location of the same translucent article. This is not only applicable, but can be applied to other measurement locations (not only other measurement locations of the same translucent article but also other measurement locations of translucent articles). This is because the average values R1av and R2av are correction values that occupy most of the tolerances of the measuring device, and are values that hardly change even if the measurement location or the translucent article to be measured changes.

The birefringence measurement method according to the fourth embodiment is characterized in that the average value R1av or R2av is applied as it is to other measurement locations. The method for measuring birefringence according to the fourth embodiment is as follows.
(4-1) to (4-11) Steps similar to (2-1) to (2-11) are performed, and the average value R1av or R2av is calculated.
(4-12) to (4-20) Same as (2-1) to (2-8) with respect to another measurement location of the same translucent article or a measurement location of another translucent article. The process is performed, and the correspondence (third correspondence) between the rotation angle θ of the half-wave plate 104 (polarization azimuth of the inspection light, the angle 2θ of the polarization plane) and the relative light quantity ratio R13s or R23s is obtained.

(4-21) In the same process as (2-12), the corrected relative light amount ratio R13sc (R13sc = R13s−R1av) or R23sc (R23sc = R23s) is obtained from the difference from the relative light amount ratio R13s or R23s of the third correspondence relationship. -R2av) is calculated.
(4-22) By applying the corrected relative light quantity ratio R13sc or R23sc to the correspondence relationship between the birefringence value acquired in advance and the corrected relative light quantity ratio R1sbc or R2sbc in the same process as (2-13). Get birefringence value.

(4-23) Furthermore, when applying to the manufacturing method of the substrate for mask blanks, the said measuring method is processed with respect to the translucent substrate (glass substrate) by which it processed into the shape of the substrate for mask blanks, and the surface was grind | polished. A step of selecting a translucent substrate having a birefringence value (or corrected relative light quantity ratio R13sc, R23sc) obtained by application as a predetermined value or less as a mask blank substrate is included. In this case, it is preferable to arrange the translucent substrate so that the circularly polarized inspection light enters from a predetermined measurement location on one main surface of the translucent substrate and exits from the other main surface.

  Other matters in the birefringence measurement method according to the fourth embodiment of the present invention are the same as those in the birefringence measurement method according to the first to third embodiments. .

[Manufacturing method of mask blank substrate]
A manufacturing method of a mask blank substrate according to an embodiment of the present invention includes a substrate preparation step and a substrate inspection step.

  The substrate preparation step is a step of preparing a translucent substrate having two opposing main surfaces, and prepares a translucent substrate that has been processed to become a mask blank substrate. The substrate preparation step may be a step of preparing a translucent substrate to be a mask blank substrate by the same or similar method as a known method. The translucent substrate is preferably a glass substrate, and more preferably a synthetic quartz glass substrate.

  The shape of the translucent substrate is a shape having two main surfaces facing each other in a rectangular shape and four end surfaces (side surfaces and chamfered surfaces) that are orthogonal to both main surfaces and connect each side of both main surfaces. . In this translucent substrate, it is necessary to polish at least a main surface on which inspection light is incident and a main surface that transmits through the inside of the translucent substrate to a mirror surface. It is more preferable that both the main surface, each side surface, and each chamfered surface of the translucent substrate are polished to a mirror surface. By mirror polishing, for example, the surface roughness Ra (arithmetic average roughness) of both main surfaces of the synthetic quartz glass substrate is set to about 0.5 nm or less, and the surface roughness Ra (arithmetic average roughness) of each side surface and each chamfered surface. Is about 2 nm or less. The surface roughness of the main surface is preferably 0.2 nm or less in terms of root mean square roughness (Rq). In the substrate preparation step, the main surface and the end surface may be further subjected to precision polishing or ultraprecision polishing. In addition, the dimension of the translucent board | substrate after this mirror polishing is performed is about 152.1 mm x about 152.1 mm x about 6.35 mm, for example.

A board | substrate inspection process is a process of inspecting the translucent board | substrate prepared at the board | substrate preparation process.
In this example, the substrate inspection step includes a step of measuring the birefringence of the translucent substrate that is a measurement object and a step of selecting a mask blank substrate. Regarding the step of measuring the birefringence of the translucent substrate, the same steps as those described in the respective embodiments relating to the above-described method for measuring the birefringence of the translucent article are performed. And the process of selecting the translucent board | substrate whose birefringence value obtained at the process is below the reference value of birefringence defined beforehand as a mask blank board | substrate is performed.

  In the substrate inspection process, the translucent substrate selected as the mask blank substrate has a birefringence amount equal to or less than a predetermined value in a rectangular inner region having a side of 132 mm with respect to the center of the main surface of the substrate. Is preferred. This is because, when a transfer mask is manufactured using a mask blank manufactured from the selected mask blank substrate, the region where the transfer pattern may be formed is based on the center of the main surface of the substrate. The reason is that it is a rectangular inner region having a side of 132 mm. The translucent substrate selected as the mask blank substrate is more preferably such that the birefringence amount in a rectangular inner region having a side of 142 mm with respect to the center of the main surface of the substrate is not more than a predetermined value.

  In this example, the birefringence value is a birefringence value for light having an exposure wavelength (for example, a wavelength of 193 nm) used when a transfer mask manufactured from a mask blank substrate is used. The birefringence value is determined, for example, at each point of the translucent substrate by linearly polarized light in a direction parallel to the fast axis and linearly polarized light in a direction parallel to the slow axis perpendicular to the fast axis. It can be defined as the difference in optical path length that occurs when passing through. In the following description, the birefringence value is a birefringence value (nm) per 1 cm thickness of the light-transmitting substrate. For example, when the thickness of the translucent substrate is 6.35 mm, the birefringence magnitude at the thickness of 6.35 mm is obtained at each point of the translucent substrate and converted to the thickness per 1 cm. Thus, the birefringence value per 1 cm thickness can be calculated. The reference value of the birefringence value used when selecting the mask blank substrate is preferably 5 nm / cm, more preferably 2 nm / cm, and even more preferably 1 nm / cm.

  In the mask blank substrate manufacturing method described above, in the substrate inspection step, a step of obtaining the birefringence value of the translucent substrate is performed, and a step of selecting the mask blank substrate based on the birefringence value as a selection criterion is performed. Is going. However, the substrate inspection step is not limited to this, and the step of obtaining the maximum or minimum value of the corrected relative light quantity ratio of the translucent substrate is performed, and the obtained maximum value of the corrected relative light quantity ratio of the translucent board or The step of selecting the mask blank substrate may be performed by comparing the minimum value with a predetermined reference value for the correction relative light quantity ratio. When the birefringence value of the selected mask blank substrate is required, the correspondence between the corrected relative light amount ratio and the birefringence obtained in advance from the maximum or minimum value of the corrected relative light amount ratio of the mask blank substrate. Derived from the relationship.

  The corrected relative light quantity ratio calculated as described above can also be converted into a transmittance. In this case, for example, a reference correction relative light amount ratio that is a correction relative light amount ratio when the birefringence value of the translucent material is 0 nm / cm is calculated in advance. The transmittance at the reference correction relative light amount ratio is set to 100%. Accordingly, for example, a value obtained by dividing the corrected relative light amount ratio at each measurement point by the reference corrected relative light amount ratio can be set as a transmittance (standardized transmittance) corresponding to the corrected relative light amount ratio.

  FIG. 2 shows an example of a mask blank 20 and a transfer mask 30 that are manufactured using the translucent substrate 10. FIG. 2A shows an example of the configuration of the mask blank 20. The translucent substrate 10 that has been accepted in the substrate inspection process and selected as the mask blank substrate is then used for manufacturing the mask blank 20. In the manufacturing process of the mask blank 20, the pattern forming thin film 12 is formed on the main surface of the translucent substrate 10 selected as the mask blank substrate by, for example, a known method. Thereby, the mask blank provided with the thin film for pattern formation on the low birefringence translucent board | substrate can be manufactured.

  The pattern forming thin film 12 may have any structure of a single layer structure, a multi-layer laminated structure, or a composition-graded structure. The mask blank here includes a configuration in which a hard mask film used as an etching mask when the pattern forming thin film 12 is patterned is formed on the pattern forming thin film 12. The mask blank here includes a configuration in which a resist film made of an organic material is formed on the pattern forming thin film 12 or the hard mask film. The mask blank 20 manufactured in this way is used for manufacturing the transfer mask 30.

  FIG. 2B shows an example of the configuration of the transfer mask 30. In the manufacturing process of the transfer mask 30, the pattern forming thin film 12 of the mask blank 20 is patterned by etching, for example, by a known method to form a transfer pattern. By doing in this way, the transfer mask 30 provided with the thin film which has a transfer pattern on the low birefringence translucent board | substrate can be manufactured appropriately.

  These manufactured transfer masks 30 are used for manufacturing semiconductor devices. In the manufacturing process of a semiconductor device, a circuit pattern is formed on a semiconductor wafer using a transfer mask 30 by a known method, for example. By using the transfer mask 30 including a thin film having a transfer pattern on a low birefringence light-transmitting substrate, a circuit pattern can be formed on the semiconductor wafer with high accuracy. In particular, in the case of a semiconductor device manufacturing process in which polarized illumination is applied to exposure light, when the exposure light passes through the translucent substrate of the transfer mask 30, it is difficult to affect the polarization state of the exposure light. A circuit pattern can be formed on the semiconductor wafer with higher accuracy. This also makes it possible to appropriately manufacture a high-quality semiconductor device free from malfunction defects.

  The present invention uses, for example, a mask blank substrate manufacturing method (inspection method) for producing a transfer mask to which polarized illumination is applied in exposure transfer and the influence of birefringence of the substrate is relatively large. The present invention can be suitably applied to a mask blank manufacturing method, a transfer mask manufacturing method using the mask blank, and a mask semiconductor device manufacturing method using the transfer blank. The present invention is used, for example, for mask blank substrates other than those described above (transfer masks to which unpolarized exposure light is applied, and transfer masks to which polarized illumination with a relatively small influence of birefringence of the substrate is applied. It can also be applied to a substrate).

In addition, the influence of birefringence may be a problem other than during inspection with a mask inspection apparatus. For example, even when polarized illumination is not applied, if a region having a large birefringence value is present inside the mask blank substrate, there is a possibility that transfer may be affected. Birefringence may also occur due to residual thermal stress due to thermal history, for example. In this case, a large birefringence value means that the residual thermal stress is large and is easily cracked. Therefore, it is preferable to inspect the influence of birefringence on a mask blank substrate used for a transfer mask to which polarized illumination is not applied, even if these points can be inspected by a low-cost method. I can say that.
According to the present invention, the influence of birefringence can be inspected by a simple and low-cost method.

[Experimental example]
An experimental result confirming that the influence of birefringence in the translucent substrate 10 can be detected by the birefringence measuring method according to the present invention will be described. 3 to 9 are diagrams for explaining experimental results. In this experimental example, for the convenience of measurement, a single translucent substrate 10 was used, and various measurements were performed on a plurality of locations in the translucent substrate 10. However, it can be considered that the experimental result obtained in this way is equivalent to the experimental result obtained when a plurality of translucent substrates 10 are used due to the birefringence property.

In this experimental example, the birefringence value measured with a known birefringence measuring apparatus (HINDS Exicor ^(R) 193 DUV manufactured by HINDS) is 1.5 nm / cm on a high-quality translucent substrate 10 with low birefringence. The measurement method of the third embodiment of the present invention described above was actually performed on a certain location (measurement location) using the measurement apparatus of the present invention. FIG. 3 shows the correspondence between the rotation angle θ [deg] of the half-wave plate 104 and the light quantity ratio R10 [%] and the light quantity ratio R190 [%]. This is a graph of the second correspondence relationship that is the relationship and the reference correspondence relationship that is the correspondence relationship with the light amount ratio R1a [%]. As described above, the light amount ratio R190 is a light amount ratio acquired in a state where the inspection light and the translucent substrate 10 are relatively rotated by 90 degrees with respect to the measurement conditions when the light amount ratio R10 is acquired. The ratio R1a is a light quantity ratio acquired from the inspection light that has passed only in the air.

  The reference light amount ratio should theoretically be a constant value of 50% regardless of the numerical value of the rotation angle θ of the half-wave plate 104. However, as is apparent from FIG. 3, the reference light quantity ratio R1a vibrates between the 54% and 47% levels. The light quantity ratios R10 and R190 acquired from the inspection light transmitted through the translucent substrate 10 both vibrate with the same tendency as the reference light quantity ratio R1a with respect to the numerical value of the rotation angle θ. This indicates that the light quantity ratios R10 and R190 are greatly affected by deviation from the theoretical value of the reference light quantity ratio R1a.

  FIG. 4 shows the correspondence between the rotation angle θ [deg] of the half-wave plate 104 and the relative light quantity ratio R10s [%], and the relative light quantity ratio R190s [%]. The correspondence relationship between a certain second correspondence relationship and the average value R1av [%] = (R10s [%] + R190s [%]) / 2 of the two relative light quantity ratios is graphed. The numerical values obtained by subtracting the reference light amount ratio R1a from the light amount ratios R10 and R190 corresponding to the same rotation angle θ are the relative light amount ratios R10s and R190s. As is apparent from FIG. 4, the relative light quantity ratios R10s and R190s both vibrate between + 0.3% and −0.3% with respect to the numerical value of the rotation angle θ.

  The relative light quantity ratios R10s and R190s fluctuate close to a sin curve and a cos curve, and the relative light quantity ratios R10s and R190s have a slight error between a plurality of peaks of each vibration, but 0.04% at the maximum. About relatively small. For this reason, the correlation between the relative light quantity ratio and the birefringence value of the translucent substrate is acquired in advance, and the birefringence amount at the measurement location of the translucent substrate 10 is calculated from the acquired relative light quantity ratios R10s and R190s. Is possible.

  FIG. 5 shows the result of fitting approximate curves F10s and F190s made of functions including a sin function to the real values of the relative light quantity ratios R10s and R190s. Since the real values of the relative light quantity ratios R10s and R190s have an error between a plurality of peaks of each vibration, it can be said that the approximate curves F10s and F190s of the relative light quantity ratios R10s and R190s can be fitted with high accuracy. Absent. In order to calculate the birefringence amount from the light amount ratio with higher accuracy, the approximate curves F10s and F190s need to be fitted with higher accuracy. The relative light quantity ratios R10s and R190s are acquired under the same conditions except that the positional relationship between the light transmitting substrate 10 and the inspection light in the inspection light incident on the light transmitting substrate 10 is rotated by 90 degrees. Since the inspection light emitted from the translucent substrate 10 is transmitted through the half-wave plate, the inspection light at the time of acquiring the relative light quantity ratio R10s when entering the polarizing beam splitter 108 and the inspection light at the time of acquiring R190s Is theoretically rotated by 2θ = 180 degrees. Therefore, in theory, the sign of the relative light quantity ratio (positive or negative) is opposite to the real value vibration of the relative light quantity ratio R10s with respect to the rotation angle θ of the half-wave plate 104 and the real value vibration of R190s. Should be the same except. However, as shown in FIG. 5, there is a deviation from the opposite relationship.

  FIG. 6 shows a corrected relative light quantity ratio R10sc [%] calculated by performing correction by subtracting the average value R1av [%] of two relative light quantity ratios from the relative light quantity ratio R10 s [%] at the same rotation angle θ [rad]. The correspondence relationship with the rotation angle θ [rad] of the half-wave plate 104 is graphed. In FIG. 6, the correspondence relationship between the corrected relative light amount ratio R190sc [%] calculated in the same manner and the rotation angle θ [rad] of the half-wave plate 104 is also plotted. Further, FIG. 6 also shows the result of fitting approximate curves F10sc and F190sc, which are functions including a sin function, to the real values of the corrected relative light quantity ratios R10sc and R190sc. From the results of FIG. 6, the real value vibration of the corrected relative light quantity ratio R10sc with respect to the rotation angle θ of the half-wave plate 104 and the real value vibration of the correction R190sc are signs of the relative light quantity ratio (positive or negative). It can be seen that the relationship is almost the same except that is opposite. It can also be seen that the approximate curves F10sc and F190sc of the relative light quantity ratios R10s and R190s can be fitted with very high accuracy.

  FIG. 7 shows the absolute value of the relative light quantity ratio R10s or the corrected relative light quantity ratio R10sc acquired in a state before the positional relationship between the translucent substrate 10 and the inspection light is rotated by 90 degrees (arrangement of 0 degrees in FIG. 7). The absolute value of the relative light quantity ratio R190s or the corrected relative light quantity ratio R190sc acquired in the state (90 degree arrangement in FIG. 7) after rotating the positional relationship between the maximum value of the transparent substrate 10 and the inspection light by 90 degrees. The maximum value is obtained and compared under various conditions. The plot corresponding to the “actually calculated value (in increments of 10 degrees)” on the horizontal axis of the graph is obtained by rotating the half-wave plate 104 by Δθ = 10 [deg] and calculating the relative light amount ratio R10s of each calculated rotation angle θ. From the group of R190s, the absolute value is the maximum value. The plot corresponding to the “actually calculated value (in increments of 2 degrees)” on the horizontal axis of the graph is obtained by rotating the half-wave plate 104 by Δθ = 2 [deg] and calculating the relative light quantity ratio R10s of each calculated rotation angle θ or From the group of R190s, the absolute value is the maximum value. The plot corresponding to the “actually calculated value (in 1 degree increments)” on the horizontal axis of the graph is obtained by rotating the half-wave plate 104 by Δθ = 1 [deg] and calculating the relative light quantity ratio R10s of each calculated rotation angle θ or From the group of R190s, the absolute value is the maximum value.

  The plot corresponding to the “simple approximate function calculated value (without correction)” on the horizontal axis of the graph is obtained by rotating the half-wave plate 104 by Δθ = 1 [deg] and calculating the calculated rotation angle θ and the relative light quantity ratio R10s or From the correspondence relationship with R190s, a fitting function is derived with a simple approximation function “R10s (or R190s) = bsin [4θ−d] (b and d are constants, and the unit of θ is [rad].)” It is the maximum value of the relative light quantity ratios R10sf and R190sf calculated by the fitting function. In this case, the coefficient of the fitting function of the relative light quantity ratio R10s is b = 0.316816, d = 0.99383, and the coefficient of the fitting function of the relative light quantity ratio R190s is b = −0.336485, d. = 1.14642.

  The plot corresponding to the “normal approximate function calculated value (without correction)” on the horizontal axis of the graph is obtained by rotating the half-wave plate 104 by Δθ = 1 [deg] and calculating the calculated rotation angle θ and the relative light quantity ratio R10s or From the correspondence with R190s, an approximate function of a normal sine curve “R10s (or R190s) = a + bsin [cθ−d] (a, b, c, d are constants, and the unit of θ is [rad])”. A fitting function is derived, and is the maximum value of the relative light quantity ratios R10sf and R190sf calculated by the fitting function. In this case, the coefficients of the fitting function of the relative light quantity ratio R10s are a = 0.0204372, b = 0.307949, c = 4.001438, d = 1.07544, and the fitting function of the relative light quantity ratio R190s. The coefficients of a = 0.0150264, b = 0.3437755, c = −3.99404, d = −1.07621.

  The plot corresponding to the “simple approximate function calculated value (with correction)” on the horizontal axis of the graph rotates the half-wave plate 104 by Δθ = 1 [deg], and calculates the calculated rotation angle θ and the corrected relative light quantity ratio R10sc. Alternatively, a fitting function is derived from a correspondence relationship with R190sc by a simple approximation function “R10sc (or R190sc) = bsin [4θ−d] (b and d are constants, and the unit of θ is [rad].)”. , The maximum values of the corrected relative light quantity ratios R10scf and R190scf calculated by the fitting function. In this case, the coefficient of the fitting function of the corrected relative light quantity ratio R10sc is b = 0.325701, d = 1.07243, and the coefficient of the fitting function of the corrected relative light quantity ratio R190sc is b = −0.325701. , D = 1.07243.

  The plot corresponding to “normal approximate function calculated value (with correction)” on the horizontal axis of the graph rotates the half-wave plate 104 by Δθ = 1 [deg], and calculates the calculated rotation angle θ and corrected relative light quantity ratio R10sc. Or, an approximate function of a normal sine curve “R10sc (or R190sc) = a + bsin [cθ−d] (a, b, c, d are constants, and the unit of θ is [rad])” from the corresponding relationship with R190sc. Is a maximum value of the corrected relative light quantity ratios R10scf and R190scf calculated by the fitting function. In this case, the coefficients of the fitting function of the corrected relative light quantity ratio R10sc are a = 0.264264909, b = 0.325806, c = 3.97584, d = 1.07576, and the corrected relative light quantity ratio R190sc is The coefficients of the fitting function were a = 0.264264909, b = 0.325806, c = −3.997584, d = −1.07576.

  In the case of the maximum value of the absolute values of the relative light quantity ratios R10s and R190s that are not corrected from the actual measurement values, the relative light quantity ratios R10s and R190s depend on the data acquisition interval (the half-wave plate 104 is rotated by Δθ). However, there is a slight difference (difference of 0.014 [%] to 0.016 [%]) between the case where the translucent substrate is arranged at 0 degree and the case where it is arranged at 90 degrees. Further, when the maximum relative light quantity ratios R10sf and R190sf are calculated by the fitting function derived from the relative light quantity ratios R10s and R190s that are not corrected from the actual measurement values, the translucent substrates are arranged at 0 degrees and at 90 degrees. In this case, the difference is large (difference of 0.020 [%] to 0.036 [%]).

  On the other hand, when the maximum relative light quantity ratios R10scf and R190scf are calculated by the fitting function derived from the corrected relative light quantity ratios R10sc and R190sc corrected from the actual measurement values, the translucent substrate 10 is arranged at 0 degree. There is no difference between the case of and the case of 90 degree arrangement. From these results, R1av, which is an average value of the relative light quantity ratio R10s acquired when the translucent substrate is arranged at 0 degree and the relative light quantity ratio R190s obtained when the translucent board is arranged at 90 degrees, is calculated. The corrected relative light quantity ratios R10sc and R190sc calculated by subtracting the average value R1av from the relative light quantity ratios R10s and R190s, respectively, were found to have very high accuracy.

  If the corrected relative light quantity ratios R10scf and R190scf are used, the correction relative light quantity ratio data (corrected relative light quantity ratio between the rotation angle θ of the half-wave plate 104 and the rotation angle θ + Δθ) that has not been acquired is an approximate function. It can be said that it can be complemented with high accuracy. In addition, with either a simple approximation function “R10s (or R190s) = bsin [4θ−d]” or a normal approximation function “R10s (or R190s) = a + bsin [cθ−d]”, high accuracy is achieved. It can be said that the data of the corrected relative light quantity ratio can be complemented with an approximate function with high accuracy.

  In FIG. 8, the range of the rotation angle θ of the half-wave plate 104 is 1 [deg] to 40 [deg], and the translucent substrate is arranged at 0 degrees with various numbers of measurement angles (the number of orientations). Relative light quantity ratio R10sf or corrected relative light quantity ratio calculated from each approximate function obtained by footing from the corresponding relationship between the obtained rotation angle θ of half-wave plate 104 and relative light quantity ratio R10s or corrected relative light quantity ratio R10sc. This is a comparison of the maximum value of R10scf. Similarly, it was obtained by footing from the corresponding relationship between the rotation angle θ of the half-wave plate 104 obtained with the translucent substrate disposed at 90 degrees and the relative light quantity ratio R190s or the corrected relative light quantity ratio R190sc. This is a comparison of the maximum value of the relative light quantity ratio R190sf or the corrected relative light quantity ratio R190scf calculated from each approximate function.

  In the measurement azimuth number of the light amount on the horizontal axis of the graph of FIG. 8, “40 azimuth” means that the rotation angle θ of the half-wave plate 104 is 1 [deg] to 40 [deg] and Δθ is 1 [deg]. It means that the light amount values M1 and M2 are acquired by rotating each one. “9 directions” means that the light amount values M1 and M2 were acquired with the rotation angle θ of the half-wave plate 104 being 1, 5, 10, 15, 20, 25, 30, 35, and 40 [deg], respectively. Means. “Seven azimuth” means that the light amount values M1 and M2 are acquired with the rotation angle θ of the half-wave plate 104 being 1, 10, 15, 20, 30, 35, and 40 [deg], respectively. “Five directions” means that the light amount values M1 and M2 are acquired with the rotation angle θ of the half-wave plate 104 being 1, 10, 20, 30, and 40 [deg], respectively. “Four azimuths” means that the light amount values M1 and M2 are acquired with the rotation angle θ of the half-wave plate 104 being 1, 15, 25, and 40 [deg], respectively. “Three orientations” means that the light amount values M1 and M2 are acquired with the rotation angle θ of the half-wave plate 104 being 1, 20, and 40 [deg], respectively. “Two azimuth” means that the light amount values M1 and M2 are acquired with the rotation angle θ of the half-wave plate 104 being 1,40 [deg], respectively.

  In FIG. 8, “0 degree arrangement” and “90 degree arrangement” refer to the positional relationship between the translucent substrate 10 and the inspection light, as in the case of FIG. In FIG. 8, “simple approximation function” and “normal approximation function” calculate the constants a, b, c, and d by applying functions of the same model as those applied in FIG. 7, respectively. . Then, the results of calculating the relative light quantity ratios R10sf and R190sf or the corrected light quantity ratios R10scf and R190scf with the derived approximate functions are plotted on FIG. Since the normal approximate function has four constants, the relative light quantity ratios R10s and R190s in four directions or the corrected relative light quantity ratios R10sc and R190sc are required at the minimum. For this reason, there is no result of three or less directions for the normal approximate function.

  From the results of FIG. 8, the simple approximate function and the normal approximate function derived from the relative light quantity ratios R10s and R190s are both the maximum of the relative light quantity ratios R10sf and R190sf calculated respectively between the 0 degree arrangement and the 90 degree arrangement. It is hard to say that the difference in values is large for any number of orientations and is calculated with very high accuracy. On the other hand, the normal approximation functions derived from the corrected relative light quantity ratios R10sc and R190sc are both calculated relative to the 0 degree arrangement and the 90 degree arrangement even when the number of measurement azimuths is reduced to the minimum four azimuths. The difference between the maximum values of the light intensity ratios R10scf and R190scf is very small (the plot of “normal approximation function 0 degree arrangement, with correction” and the plot of “normal approximation function 90 degree arrangement, with correction” almost overlap in FIG. It can be said that it is calculated with very high accuracy.

  Further, the simple approximation function derived from the corrected relative light quantity ratio shows that the maximum of the relative light quantity ratios R10scf and R190scf calculated respectively between the 0 degree arrangement and the 90 degree arrangement even when the number of measurement azimuths is reduced to three. The difference in values is very small (the plot of “simple approximation function 0 degree arrangement, with correction” and the plot of “simple approximation function 90 degree arrangement, with correction” almost overlap in FIG. 8) and very high. It can be said that it is calculated with accuracy. As described above, by applying the corrected relative light quantity ratios R10scf and R190scf, the maximum value of the corrected relative light quantity ratio can be calculated with high accuracy even if the number of measurement directions of the light quantity values M1 and M2 is significantly reduced. I understand that I can do it.

FIG. 9 is a diagram showing the correlation between the relative light quantity ratio [%] or the corrected relative light quantity ratio [%] and the birefringence value [nm / cm]. This is because the measuring device 100 is used to measure the birefringence value measured in advance with a known birefringence measuring device (HINDS Exicor ^(R) 193 DUV manufactured by HINDS). The absolute value of the relative light amount ratio R10s or the corrected relative light amount ratio R10sc acquired in the state before the positional relationship between the substrate 10 and the inspection light is rotated 90 degrees (0 degree arrangement), and the translucent substrate 10 The maximum values of the absolute values of the relative light quantity ratio R190s or the corrected relative light quantity ratio R190sc acquired in the state after being rotated by 90 degrees (positioned by 90 degrees) are plotted respectively. In addition, the birefringence value of the measurement location where the birefringence value is known is 2.76, 4.904, and 6.078 [nm / cm], respectively. In addition, the plot whose birefringence value is 0 [nm / cm] in FIG. 9 is the relative light quantity ratio or the corrected relative light quantity ratio acquired by measuring only air.

  When an approximate function was calculated for a plot of the correspondence relationship between the relative light quantity ratio R10s and the birefringence amount at 0 degree arrangement ("0 degree arrangement without correction" in FIG. 9), the approximate function y = 5.1307x -0.0622 was obtained. The correlation between this approximate function and the plot has a coefficient of determination R2 of 0.9987, indicating that the correlation is high. Further, when an approximate function was calculated for a plot of the correspondence relationship between the corrected relative light quantity ratio R10sc and the birefringence amount in the 0 degree arrangement (“0 degree arrangement corrected” in FIG. 9), the approximate function y = 5.1939x-0.1528 was obtained. The correlation between the approximate function and the plot has a coefficient of determination R2 of 0.999, which indicates that the correlation is very high.

In the present invention, laser light is used as inspection light, the intensity of the laser light is strong, and a technique for stabilizing the intensity has been developed (variation is small). By selecting the frequency of the analog-digital converter that measures the amount of light as 10 KHz, the measurement can be performed 10,000 times in 1 second and 1000 times in 0.1 second. For example, the measurement is performed 1000 times for one location on the substrate, and the data for 500 times in the center is used (data not having large variations at both ends is not used), so that reproducibility and measurement accuracy are good.
On the other hand, for example, in the case of a known birefringence measuring apparatus, the light source is a deuterium lamp, the light source fluctuates, the intensity of the light source is weak, and there is shot noise (photon variation). Measurement takes time, and there is a problem of light source drift (shift in the amount of light with time). The variation range of measurement data is larger than that of the device of the present invention. Therefore, it is difficult to improve accuracy.

  The measurement of the birefringence amount of the substrate by the birefringence measuring apparatus as described above calculates the accurate birefringence amount and angle, so the time required for the measurement is long. Will be reduced. The device itself is also complicated and expensive in structure. Therefore, a simpler and lower cost method is desired for a method of inspecting the influence of birefringence of a substrate for the purpose of corresponding to a mask inspection apparatus that applies polarized light to such inspection light. According to the present invention, it is possible to guarantee the amount of birefringence on the entire surface of the substrate extremely accurately by a simple and low-cost method.

  As described above, the present invention has been described using the embodiment, but the technical scope of the present invention is not limited to the scope described in the above embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  The present invention can be suitably used for, for example, a method for manufacturing a mask blank substrate.

DESCRIPTION OF SYMBOLS 10 ... Translucent article (translucent substrate), 12 ... Pattern forming thin film, 20 ... Mask blank, 30 ... Transfer mask, 100 ... Measuring apparatus, 101 ... Light source unit, 102 ... Laser light source, 103 ... 1/4 wavelength plate, 104 ... 1/2 wavelength plate, 106a, 106b ... Power meter (light quantity measuring device), 108 ... Polarized beam Splitter (light separator)

Claims (16)

A method for measuring birefringence in a translucent article having a pair of opposing surfaces,
The circularly polarized inspection light emitted from the light source unit is incident on the inside of the translucent article from the measurement point on one surface, and the inspection light emitted from the other surface is transmitted through the half-wave plate. From the two linearly polarized lights whose wavefronts are orthogonal to each other by the light separator, and the two linearly polarized lights are respectively received by the two light quantity measuring devices to measure the light quantity, and the light quantity measurement values of the two linearly polarized lights are measured. The step of calculating the light amount ratio by dividing one of the light amount measurement values by the sum of the light amount measurement values of the two linearly polarized light is to rotate the half-wave plate at the same measurement location. Is performed a plurality of times while changing the angle condition of the polarization plane of the inspection light incident on the light separator to obtain a first correspondence relationship that is a correspondence relationship between the rotation angle of the half-wave plate and the light amount ratio. Process,
The rotation angle of the half-wave plate under the same conditions as in the step of obtaining the first correspondence relationship, except that the translucent article is not disposed between the light source unit and the half-wave plate. Obtaining a standard correspondence relationship that is a correspondence relationship between the light intensity ratio and
Calculating a relative light quantity ratio of the first correspondence relationship that is a difference between the light quantity ratio of the first correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Obtaining a birefringence value at the measurement location from the correspondence between the relative light quantity ratio acquired in advance and the birefringence value using the relative light quantity ratio of the first correspondence relation. Refraction measurement method. A method for measuring birefringence in a translucent article having a pair of opposing surfaces,
The circularly polarized inspection light emitted from the light source unit is incident on the inside of the translucent article from the measurement point on one surface, and the inspection light emitted from the other surface is transmitted through the half-wave plate. From the two linearly polarized lights whose wavefronts are orthogonal to each other by the light separator, and the two linearly polarized lights are respectively received by the two light quantity measuring devices to measure the light quantity, and the light quantity measurement values of the two linearly polarized lights are measured. The step of calculating the light amount ratio by dividing one of the light amount measurement values by the sum of the light amount measurement values of the two linearly polarized light is to rotate the half-wave plate at the same measurement location. To obtain a first correspondence that is a correspondence between the rotation angle of the half-wave plate and the light quantity ratio, a plurality of times by changing the angle of the polarization plane of the inspection light incident on the light separator. ,
The rotation angle of the half-wave plate under the same conditions as in the step of obtaining the first correspondence relationship, except that the translucent article is not disposed between the light source unit and the half-wave plate. Obtaining a standard correspondence relationship that is a correspondence relationship between the light intensity ratio and
Calculating a relative light quantity ratio of the first correspondence relationship that is a difference between the light quantity ratio of the first correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Except for the fact that the translucent article and the inspection light are rotated by 90 degrees relative to the traveling direction of the inspection light as a rotation axis, under the same conditions as the step of obtaining the first correspondence relationship, A step of acquiring a second correspondence relationship that is a correspondence relationship between the rotation angle of the two-wavelength plate and the light amount ratio;
Calculating a relative light quantity ratio of a second correspondence relationship that is a difference between the light quantity ratio of the second correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Calculating an average value with the relative light quantity ratio of the first correspondence and the relative light quantity ratio of the second correspondence with the same rotation angle of the half-wave plate;
Calculating a corrected relative light amount ratio from a difference between the relative light amount ratio of the first correspondence relationship and the average value, or from a difference between the relative light amount ratio of the second correspondence relationship and the average value;
Using the corrected relative light amount ratio, and obtaining a birefringence value at the measurement location from a correspondence relationship between the corrected relative light amount ratio and the birefringence value acquired and set in advance. Method. The method further includes a step of obtaining a fitting function from the correspondence relationship between the corrected relative light amount ratio calculated from the first correspondence relative light amount ratio or the second correspondence relative light amount ratio and the rotation angle of the half-wave plate. And
The birefringence value according to claim 2, wherein the step of obtaining the birefringence value is a step of obtaining a birefringence value at the measurement location using a corrected relative light quantity ratio calculated from the fitting function. Measuring method.   4. The birefringence measuring method according to claim 3, wherein the footing function is a function including a trigonometric function term.   The first correspondence relationship, the second correspondence relationship, and the reference correspondence relationship are obtained by acquiring light amount ratios corresponding to the same rotation angle of the half-wave plate at angles of three or more directions. 3. The method for measuring birefringence according to 3 or 4.   6. The method of measuring birefringence according to claim 3, wherein the fitting function is acquired using a least square method. A method for measuring birefringence in a translucent article having a pair of opposing surfaces,
The circularly polarized inspection light emitted from the light source unit is incident on the inside of the translucent article from the measurement point on one surface, and the inspection light emitted from the other surface is transmitted through the half-wave plate. From the two linearly polarized lights whose wavefronts are orthogonal to each other by the light separator, and the two linearly polarized lights are respectively received by the two light quantity measuring devices to measure the light quantity, and the light quantity measurement values of the two linearly polarized lights are measured. The step of calculating the light amount ratio by dividing one of the light amount measurement values by the sum of the light amount measurement values of the two linearly polarized light is to rotate the half-wave plate at the same measurement location. To obtain a first correspondence that is a correspondence between the rotation angle of the half-wave plate and the light quantity ratio, a plurality of times by changing the angle of the polarization plane of the inspection light incident on the light separator. ,
The rotation angle of the half-wave plate under the same conditions as in the step of obtaining the first correspondence relationship, except that the translucent article is not disposed between the light source unit and the half-wave plate. Obtaining a standard correspondence relationship that is a correspondence relationship between the light intensity ratio and
Calculating a relative light quantity ratio of the first correspondence relationship that is a difference between the light quantity ratio of the first correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Except for the fact that the translucent article and the inspection light are rotated by 90 degrees relative to the traveling direction of the inspection light as a rotation axis, under the same conditions as the step of obtaining the first correspondence relationship, A step of acquiring a second correspondence relationship that is a correspondence relationship between the rotation angle of the two-wavelength plate and the light amount ratio;
Calculating a relative light quantity ratio of a second correspondence relationship that is a difference between the light quantity ratio of the second correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Calculating an average value with the relative light quantity ratio of the first correspondence and the relative light quantity ratio of the second correspondence with the same rotation angle of the half-wave plate;
With respect to another measurement location in the translucent article or a measurement location in another translucent article, under the same conditions as the step of obtaining the first correspondence, Obtaining a third correspondence which is the correspondence of
Calculating a relative light quantity ratio of the third correspondence which is a difference between the light quantity ratio of the third correspondence relation and the light quantity ratio of the reference correspondence relation in which the rotation angles of the half-wave plates are the same;
Calculating a corrected relative light amount ratio of the third correspondence from a difference between the relative light amount ratio of the third correspondence and the average value;
Using the corrected relative light quantity ratio, from the correspondence between the corrected relative light quantity ratio and the birefringence value acquired and set in advance, another measurement location in the translucent article or measurement location in the other translucent article And a birefringence value obtaining step for obtaining a birefringence value. A step of obtaining a fitting function from the correspondence between the corrected relative light quantity ratio calculated from the relative light quantity ratio of the third correspondence and the rotation angle of the half-wave plate;
The birefringence value according to claim 7, wherein the step of obtaining the birefringence value is a step of obtaining a birefringence value of the measurement location using a corrected relative light quantity ratio calculated from the fitting function. Measuring method.   9. The birefringence measurement method according to claim 8, wherein the footing function is a function including a trigonometric function term.   The first correspondence relationship, the second correspondence relationship, the third correspondence relationship, and the reference correspondence relationship indicate that the light quantity ratio corresponding to the same rotation angle of the half-wave plate is acquired at an angle of three or more directions. The birefringence measuring method according to claim 8 or 9, characterized in that   The method of measuring birefringence according to any one of claims 8 to 10, wherein the fitting function is acquired using a least square method.   The light source unit includes a laser light source and a quarter-wave plate, and the circularly polarized inspection light is obtained by transmitting linearly polarized light emitted from the laser light source through the quarter-wave plate. The method for measuring birefringence according to claim 1, wherein: The translucent article is a translucent substrate,
A translucent substrate having a birefringence value obtained by applying the birefringence measuring method according to any one of claims 1 to 12 to the translucent substrate is selected as a mask blank substrate. The manufacturing method of the mask blank board | substrate characterized by having the process to do.   A method for producing a mask blank, comprising a step of forming a thin film for pattern formation on a main surface of a mask blank substrate produced by the method for producing a mask blank substrate according to claim 13.   A method for producing a transfer mask, comprising a step of forming a transfer pattern on a thin film for pattern formation of a mask blank produced by the method for producing a mask blank according to claim 14.   A method for manufacturing a semiconductor device, comprising: forming a circuit pattern on a semiconductor wafer using the transfer mask manufactured by the method for manufacturing a transfer mask according to claim 15.

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