JP5103711B2 - Method for measuring optical characteristics of optical member - Google Patents

Description

The present invention relates to a method for measuring optical characteristics of an optical member, and in particular , ArF (193 nm), KrF (248 nm), an excimer laser, a solid-state laser using a nonlinear optical effect, and other devices using deep ultraviolet light or vacuum ultraviolet light. The present invention relates to a method for measuring optical characteristics of an optical member used in the above.

  In recent years, VLSI has been highly integrated and highly functionalized, and a fine processing technique on a wafer is required. As a processing method thereof, a method using photolithography is performed. High imaging performance (resolution, depth of focus) is required for the projection lens of the exposure apparatus, which is the key to this photolithography technique.

The resolution and the depth of focus are determined by the wavelength of light used for exposure and the NA (numerical aperture) of the lens. When the exposure wavelength λ is the same, the angle of the diffracted light increases as the pattern becomes finer. Therefore, the diffracted light cannot be captured unless the lens NA is large. Also, the shorter the exposure wavelength λ, the smaller the angle of diffracted light in the same pattern, so the NA of the lens may be smaller.
Resolution and depth of focus are expressed by the following equations.

[Equation 1]
Resolution = k ₁ · λ / NA

[Equation 2]
Depth of focus = k ₂ · λ / (NA) ²
(Where k ₁ and k ₂ are proportional constants)
From the above equation, in order to improve the resolution, it is sufficient to increase the NA of the lens (increasing the diameter of the lens) or shorten the exposure wavelength λ, and shortening λ is advantageous in terms of depth of focus. It can be seen that it is.

Regarding the shortening of the light wavelength, at present, the exposure wavelength is gradually shortened, and an exposure apparatus using KrF excimer laser light (wavelength 248 nm) and ArF excimer laser light (wavelength 193 nm) as a light source has appeared on the market .

Since the optical lithography optical system increases the resolution to the limit, the number of lenses is large and the optical path length is long for correcting various wavefront aberrations. Therefore, if there is even a slight absorption in the optical material used in the optical system of the photolithography apparatus, the entire optical system is greatly affected by a decrease in the amount of light, and the illuminance on the wafer surface becomes insufficient. For example, with an optical path length of 1 m, even when the transmission loss amount per 1 cm is 0.5%, the light intensity finally decreases to 0.995 ¹⁰⁰ = 0.606, that is, 61%. Therefore, it is desirable for the optical member to be used to have an internal transmittance of about 99.5% or more per 1 cm, and as close as possible to 100%.

  In addition, if the optical material has absorption, a problem that the temperature rise of the optical material (lens) due to light absorption deteriorates the imaging performance.

  For these reasons, it has become very important to accurately measure the slight absorption of optical materials in order to select materials with high transmittance.

  The standard deviation σ is often used as a quantity representing the accuracy of the measured value. The standard deviation σ when N measurements are performed is given by the following equation.

[Equation 3]
σ = √ {Σ (Xi− <X>) ² / (N−1)}
Here, Xi (i = 1, 2,..., N) represents each measured value, and <X> represents an average value of the measured values.

When the variation of measured values has a normal distribution, if the true value is X, the probability that one measured value falls between X ± σ is 68%, and the probability of entering X ± 2σ is 95%. .
Here, assuming a case where it is necessary to determine whether or not the internal transmittance per 1 cm exceeds 99.5% in a sample having a thickness of 10 mm, 68 % Accuracy is insufficient, and it is necessary that the transmittance can be measured with an accuracy of 0.2% at 2σ, or preferably 0.1% or less at 2σ.

  However, the transmittance measured with a spectroscope is not limited to the absorption inside the sample to be measured, but the external influence such as the influence of absorption by substances other than the sample adhering to the sample and the scattering of light due to the surface condition of the sample itself. Factors are also included. These external factors often have no problem in the measurement requiring accuracy of about 1% to several percent, but have a great influence when accuracy of 0.1% is required. .

Thus, many attempts have been made to improve the measurement accuracy of transmittance.
For example, in Patent Document 1, a highly accurate measurement sample standard is presented in order to reduce measurement errors.

  In Patent Document 2, the transmittance of a plurality of samples having different thicknesses is measured, the transmittance when the thickness is 0 is assumed from the plurality of values, and the difference between the assumed transmittance and the theoretical transmittance is determined. A method has been proposed in which the surface loss obtained from the above is calculated in advance, and the surface loss, which is a fixed value, is added to the measured value of the transmittance to calculate the internal transmittance. FIG. 4 shows an example of a flowchart showing a transmittance measuring method in the conventional method. A surface treatment is performed on the sample to be measured, the transmittance of the sample to be measured is measured, and the transmittance of the sample to be measured is corrected using the surface loss (fixed value).

  Here, the internal transmittance of the material will be described.

What is measured by a general spectrophotometer is a transmittance (Tr) including a loss such as reflection on the surface or an absorption coefficient (α) calculated from the transmittance. Assuming that the intensity I _{0 of} light entering the detector in the absence of the measurement object, the intensity I when transmitted through the measurement object, and the thickness d [cm] of the measurement object, the following relational expression holds.

[Equation 4]
Tr (d) = I / I ₀ (1)

[Equation 5]
α = − (1 / d) log _e (Tr (d)) (2)
Moreover, the Fresnel reflectance (R) on the surface is expressed as a refractive index n.

[Equation 6]
R = (n−1) ² / (n + 1) ² (3)
If the Fresnel reflection on this surface is multiple reflection on two surfaces, the transmittance (internal transmittance) Ti (d) excluding the multiple reflection is

[Equation 7]
Tr (d) = (1-R) ² · Ti (d) / (1-R ² · Ti (d) ² ) (4)
And the transmittance (Tr). Using the above relational expression from the value of refractive index (absolute refractive index) in vacuum at 157.6 nm, 1.5593, when calculating the case of Ti (0) = 1.0, Ts = 0.909, That is, 90.9% is the value of theoretical transmittance (including Fresnel reflection) when the internal loss is 0%. In reality, however, there is a loss other than Fresnel reflection on the surface. The cause is water or hydrocarbon adsorbed on the surface.

  In other words, the transmittance (Tr) or absorption coefficient (α) measured with a spectrophotometer includes the internal loss (absorption + scattering) of the measured object in addition to the Fresnel reflection and other surface loss of the surface. It is measured. Therefore, in order to calculate the value of internal transmittance, surface loss other than Fresnel reflection must be estimated.

  Further, since the internal transmittance Ti is an amount that varies depending on the thickness of the sample, in order to compare the measured values, the thickness needs to be fixed to a certain value and compared. The following relationship holds between the internal transmittance Ti (d1) measured at the thickness d1 and the internal transmittance Ti (d2) measured at the thickness d2 for the same object.

[Equation 8]
Ti (d2) ^d1 = Ti (d1) ^d2 (5a)
Transform

[Equation 9]
Ti (d2) = Ti (d1) ^{(d2 / d1)} (5b)
When the equation (5b) is used, the internal transmittance at a certain thickness can be easily converted to the internal transmittance at another different thickness.
JP-A-8-75649 JP 2002-286913 A

However, as a result of extensive research conducted by the inventor, no matter what kind of treatment is applied to the cleaning, there are re-adhesion in the environment after the cleaning treatment, etc. I found it impossible. In particular, as the measurement wavelength becomes shorter, the amount of absorption of substances adhering to the surface increases, and even if the amount of influence is small at long wavelengths, it can be seen that there is an effect that cannot be ignored at short wavelengths. It was .

  Further, it was found that even if the surface treatment was performed under the same conditions, the surface loss varies with a certain range for each measurement batch. Furthermore, the variation of the surface loss for each measurement batch has a very adverse effect on the selection of the optical material for the optical lithography apparatus that must be determined to be 99.5% or more per 1 cm. all right.

  As a method of calculating internal transmittance, prepare multiple objects with different thicknesses, and estimate the internal transmittance per unit length, absorption coefficient, and surface loss other than Fresnel reflection from the measured transmittance values. You can also. However, there is also the problem that the complexity of preparing a plurality of objects to be measured and the assumption that they have the same internal transmittance or absorption coefficient must be made.

  Therefore, a method for correcting the transmittance was examined in consideration of the surface loss for each measurement batch. As a result, the present invention has been achieved by carrying out a method for measuring optical characteristics of optical members according to the following steps.

That is, the invention according to claim 1 is a step of preparing a sample for monitoring having a known transmittance, washing the sample to be measured and the sample for monitoring in the same batch, the washed sample to be measured, and the A step of transporting the monitor sample in the same environment, and a step of measuring optical properties of the transported sample to be measured and the monitor sample in the same batch, and using the measured value of the monitor sample calculating a loss regards surface loss and surface loss of the sample to be measured, which possess the step of correcting the transmittance or reflectance of the sample to be measured by using a surface loss, the An optical property measuring method for an optical member, wherein the wavelength of light used for measuring the optical properties is 180 nm or more and 250 nm or less .

According to a second aspect of the present invention, in the optical property measuring method of the optical member according to the first aspect , the transmittance of a plurality of samples having different thicknesses is measured, and when the thickness is zero from the plurality of values, Using the surface loss calculated from the difference between the estimated transmittance and the theoretical transmittance, the sample whose internal transmittance is calculated is used as a monitor sample whose transmittance is known. It is a method for measuring optical characteristics of an optical member.

The invention described in claim 3 is characterized in that the sample measured using the method for measuring optical properties to be measured according to claim 1 or claim 2 is used as a monitor sample having a known transmittance. It is a method for measuring optical characteristics of an optical member.

According to a fourth aspect of the present invention, there is provided the optical characteristic measuring method according to any one of the first to third aspects, wherein the transmittance is an internal transmittance at a specific thickness. This is a method for measuring optical characteristics of a member.

According to a fifth aspect of the present invention, in the optical property measurement method for an optical member according to any one of the first to fourth aspects, the cleaning used in the same batch for the sample to be measured and the sample for monitoring is wet. An optical property measurement method for an optical member, wherein the optical property is cleaning or dry cleaning.

A sixth aspect of the present invention is the method for measuring optical properties of an optical member according to the fifth aspect , wherein dry cleaning used in the same batch for the sample to be measured and the sample for monitoring is irradiation with light having a wavelength of 250 nm or less. This is a method for measuring the optical characteristics of an optical member.

A seventh aspect of the present invention is the method for measuring an optical property of an optical member according to the fifth aspect , wherein the dry cleaning used in the same batch for the sample to be measured and the sample for monitoring is to irradiate a laser. This is a method for measuring optical characteristics of an optical member.

The invention according to claim 8 is the optical property measurement method of the optical member according to claim 7 , wherein the laser used in the same batch for the sample to be measured and the sample for monitoring is an ArF excimer laser. This is a characteristic optical property measuring method for an optical member.

A ninth aspect of the present invention is the method for measuring an optical property of an optical member according to the seventh or eighth aspect , wherein the laser irradiated to the sample to be measured and the sample for monitoring has an energy density of 0.1 mJ / cm ² / An optical property measurement method for an optical member, characterized in that the intensity is any pulse of not less than 250 mJ / cm ² / pulse and the number of pulses is any number of 1000 pulses or more and 10000000 pulses or less.

A tenth aspect of the present invention is the method for measuring an optical property of an optical member according to any one of the first to ninth aspects, wherein the sample for monitoring and the sample to be measured are the same substance. It is a method for measuring optical characteristics of an optical member.

The invention according to claim 11 is the method for measuring optical properties of an optical member according to any one of claims 1 to 10 , wherein the monitor sample and the sample to be measured have the same thickness. This is a method for measuring optical characteristics of an optical member.

A twelfth aspect of the present invention is the method for measuring an optical property of an optical member according to any one of the first to tenth aspects, wherein the thickness of the monitor sample is thinner than the thickness of the sample to be measured. This is a method for measuring the optical characteristics of an optical member.

A thirteenth aspect of the present invention is the method for measuring optical characteristics of an optical member according to any one of the first to twelfth aspects, wherein the thickness of the monitor sample is 1 mm or more and 30 mm or less. It is a method for measuring optical characteristics of an optical member.

The invention according to claim 14 is characterized in that in the optical characteristics according to any one of claims 1 to 13 , a sample having an internal transmittance of 99.0% or more is used as the monitor sample. It is a method for measuring optical characteristics of an optical member.

According to a fifteenth aspect of the present invention, in the optical characteristic measurement method for an optical member according to any one of the first to fourteenth aspects, the transmittance measurement accuracy is 0.2% or less, which is twice the standard deviation. A method for measuring optical characteristics of an optical member.

The invention described in claim 16 is the optical property measurement method for an optical member according to any one of claims 1 to 15 , wherein the object to be measured is optical glass, quartz glass, or a crystal material. It is an optical property measuring method.

According to the first to sixteenth aspects, the transmittance or reflectance of the optical member used in the apparatus can be measured with high accuracy. As a result, it is possible to accurately predict the performance of the apparatus, and therefore it is possible to provide a high-quality apparatus that suppresses variations in exposure accuracy. Further, the transmittance or reflectance used in the apparatus can be reliably tested.

  Embodiments of the present invention are shown below. First, a monitoring sample that is the same substance as the sample to be measured is prepared. The sample for monitoring is not limited in thickness, but the internal transmittance must be known. If there is no sample whose internal transmittance is known, it can be prepared as follows.

For example, a plurality of samples having different thicknesses, which are considered to have the same internal transmittance value at the same thickness, such as a sample taken from a close position of the same block, are prepared. The two parallel planes of each sample are similarly optically polished. Wash to clean the surface. In this case, the cleaning is a process having an effect of cleaning the surface such as wet cleaning such as ultrasonic cleaning and IPA cleaning using IPA vapor, dry cleaning such as UV cleaning irradiating ultraviolet light, and excimer laser irradiation. However, in order to make the surface state of each sample the same, it is necessary to wash in the same batch.
Furthermore, in order to make the surface state of each sample the same, after transporting in the same environment, the transmittance at a specific wavelength to be measured is measured in the same batch. FIG. 2 is a diagram illustrating the relationship between transmittance and thickness. As shown in the figure, the value of the transmittance Tr is plotted for each thickness based on the measured value. When the approximate straight line P is obtained so as to connect these lines, the transmittance Tr (0) when the thickness of the sample is 0 mm is obtained. This Tr (0) is assumed to have a thickness of 0 mm and no internal loss, but includes Fresnel reflection and surface loss other than Fresnel reflection. FIG. 3 illustrates the relationship between Fresnel reflection, surface loss h other than Fresnel reflection, internal loss at thickness a, theoretical transmittance Ts, transmittance at 0 mm thickness, and measured transmittance at thickness a. Assuming that the surface loss h is here, there is no surface loss h other than internal loss and Fresnel reflection, but the theoretical transmittance including Fresnel reflection is the value of Ts, and Tr (0) Although it is a value including surface loss h other than Fresnel reflection and Fresnel reflection,

[Equation 10]
h = Ts−Tr (0) (6)
Is calculated. This surface loss h can be regarded as the same when the same surface is polished, washed in the same batch, and measured in the same batch. The internal transmittance Ti of the sample used for this measurement is calculated from the surface loss h not including the Fresnel reflection, the measured value of the transmittance Tr including the loss, and the theoretical transmittance Ts by the following equation.

[Equation 11]
Ti (d) = (Tr (d) + h) / Ts (7)
Therefore, from equation (7)

[Equation 12]
Ti (a) = (Tr (a) + h) / Ts
It becomes. Ti (a) is the internal transmittance of the sample of thickness a, and is a universal value that does not depend on the measurement batch.

  In this way, a sample for monitoring internal transmittance Ti (a) is obtained. Subsequently, the sample to be measured and the sample for monitoring are washed in the same batch. In this case, the cleaning is a process having an effect of cleaning the surface such as wet cleaning such as ultrasonic cleaning and IPA cleaning using IPA vapor, dry cleaning such as UV cleaning irradiating ultraviolet light, and excimer laser irradiation. However, in order to make the surface state of each sample the same, it is necessary to wash in the same batch. Moreover, in order to make the surface state the same, the transmittance | permeability in the same batch is measured after conveying both samples in the same environment. FIG. 1 is an example of a flowchart showing a transmittance measuring method in the present invention.

  Next, the surface loss hm in this measurement is calculated from the transmittance measurement value Trm of the monitor sample. Since the internal transmittance is known to be Ti (a), Ti (a) = (Trm (a) + hm) / Ts from the equation (7), that is,

[Equation 13]
hm = Ti (a) · Ts−Trm (a) (8)
Can be easily derived.

  Finally, the internal transmittance Tiv of the sample to be measured is obtained from the measured transmittance value Trv of the sample to be measured. Since the same batch is washed and measured in the same batch, the surface loss can be considered to be the same as the surface loss hm of the monitoring sample. Therefore, Tiv (d) = (Trv (d) + hm) / Ts can be calculated from the equation (7).

  In the present invention, it is not necessary to have one monitor sample and one sample to be measured, and a plurality of samples to be measured may be simultaneously measured for one monitor sample. In this case, it is necessary to wash all the samples to be measured at the same time in the same batch as the monitoring sample and measure in the same batch.

  Further, since the only requirement for the monitor sample is that the internal transmittance is known, the internal transmittance Ti (a) of the monitor sample is obtained from a plurality of samples having different thicknesses as described above. In this case, it is not necessary to measure a plurality of samples having different thicknesses thereafter. Since the internal transmittance is a universal value, this monitoring sample may be used repeatedly.

Furthermore, as a sample for monitoring, the present invention is used as a sample for monitoring, and a sample for which internal transmittance Tiv (d) has been obtained once is used as a sample for monitoring having internal transmittance Tiv (d) at the next opportunity. It is also possible to do.
In the above method, the calculation of the surface loss for each measurement is performed using the internal transmittance (Ti), but it is not always necessary to calculate the internal loss (Ti), and the surface loss is included. Even if the calculation is performed using the internal transmittance, the absorption coefficient, and the transmittance of only Fresnel reflection (Tr + h), the surface loss for each measurement can be similarly obtained.

Furthermore, in the above method, the monitor sample is the same substance as the sample to be measured. However, the monitor sample does not necessarily have to be the same substance as the sample to be measured. The invention can be applied. When the monitor sample and the sample to be measured are different, the refractive index of the two at the same wavelength is different, so the theoretical transmittance Ts is different, but the surface loss h is calculated from the theoretical transmittance Tsm corresponding to the monitor sample. The transmittance of the sample to be measured can be calculated from the surface loss h and the theoretical transmittance Tsm corresponding to the sample to be measured. However, since the surface state may vary greatly depending on the substance, it is desirable that the monitor sample and the measurement sample are the same substance.
Example 1

  First, in order to obtain a sample for monitoring, calcium fluoride crystals having different thicknesses and having the same internal transmittance value were prepared.

Four types of test specimens with a diameter of 30 mm, thicknesses of 3, 10, 20, and 40 mm were collected from adjacent parts of an ingot crystal-grown by the Bridgeman method using artificially synthesized calcium fluoride raw materials. The two parallel planes were optically polished. In order to clean the surface dirt, IPA cleaning was performed on four types of samples in the same batch. After washing, four types of samples were simultaneously set in a measurement chamber of a vacuum ultraviolet spectrophotometer CAMS manufactured by Acton Research, and the spectral transmittance from a wavelength of 140 nm to 200 nm was measured for each sample. The transmittance value at 157.6 nm is plotted against the thickness, and the transmittance Tr (0) = 90.2% at a thickness of 0 mm obtained by extrapolating this approximate line is substituted into the equation (6). Thus, h = 90.9-90.2 = 0.7 [%] was estimated as the surface loss. This surface loss may be considered to be the same when the same batch is subjected to the same cleaning process and is simultaneously measured by the same measuring device. Further, the value 90.7% obtained by adding the surface loss h = 0.7% to the measured value Tr (10) = 90.0% of the transmittance of the 10 mm-thickness sample in this measurement is 10 mm thickness. This is the transmittance (not including internal transmittance, absorption coefficient, and Fresnel reflection only) that does not include the surface loss of the sample. From the equation (7), the value 99.8% obtained by dividing the transmittance Tr (10) + h = 90.7% not including the surface loss by the theoretical transmittance Ts = 90.9% is 157.6 nm. The internal transmittance (Ti) of this 10 mm thick sample is a universal value that does not depend on the measurement batch.

Next, IPA cleaning was performed in the same batch as the sample to be measured having a diameter of 30 mm and a thickness of 10 mm, using the sample having a diameter of 30 mm and a thickness of 10 mm obtained for the internal transmittance as described above as a monitor sample. After washing, the transmittance at 157.6 nm of the sample for monitoring and the sample to be measured was measured in the same batch using a spectrophotometer.
Next, the surface loss at the time of this measurement was determined from the measured value of the monitor sample. Transmittance obtained by multiplying internal transmittance Tim (0) = 99.8% (= 0.998) of the sample for monitoring by theoretical transmittance of 90.9% (internal transmittance and absorption coefficient not including surface loss) The value of 0.8% obtained by subtracting the current measured value Trm (0) = 89.9% from 90.7% (transmittance of only Fresnel reflection) is the surface loss (hm) at the time of the current measurement. .

Next, the surface loss hm = 0.8% is added to the measured value Trv (10) = 89.7% of the sample to be measured. This value of 90.5% is the transmittance not including the surface loss of the sample to be measured having a thickness of 10 mm (only the internal transmittance, the absorption coefficient, and the Fresnel reflection). Then, a value 99.6% obtained by dividing the obtained value by Ts = 90.9 is the internal transmittance Tiv (10) of the sample to be measured at a thickness of 10 mm.
The monitoring sample and the sample to be measured were washed in the same batch, and the operation of measuring in the same batch was repeated five times. The results are shown in Table 1.

  As shown in Table 1, when the measurement accuracy of the internal transmittance of the sample to be measured was expressed by twice the standard deviation (2σ), it was 0.1%.

Needless to say, the present invention is not limited to the detailed numbers and descriptions of the following embodiments. For example, since in this embodiment shows an example of a fluoride crystal for use in apparatus using a F ₂ laser beam as a reference, the measurement wavelength is 157.6 nm, of course, the present invention is effective for other wavelengths It is. For example, in the case of a fluoride crystal used in an apparatus using ArF excimer laser light, the measurement wavelength is 193.4 nm, and the refractive index in vacuum at 193.4 nm and the equations (1) to (4) are used. Then, the transmittance when the internal loss is 0% is calculated, and thereafter, the same procedure as in the case of the wavelength of 157.6 nm may be taken. Although an example in which the present invention is carried out is shown here with respect to a calcium fluoride crystal, internal transmission is also possible in other optical materials such as optical glass such as quartz glass, other crystals such as quartz and magnesium fluoride. The technique for measuring the rate is common, and the present invention is extremely effective.
(Example 2)

  As Example 2, an example will be described in which the sample whose transmittance was obtained as the sample to be measured in Example 1 was used as a monitor sample with known transmittance. A sample having a diameter of 30 mm and a thickness of 10 mm, whose internal transmittance was determined to be 99.6% in Example 1, was used as a monitor sample, and UV cleaning was performed in the same batch as the sample to be measured having a diameter of 30 mm and a thickness of 10 mm. After UV cleaning, the sample for monitoring and the sample to be measured were simultaneously set in a spectrophotometer, and the transmittance at 157.6 nm was measured in the same batch using the spectrophotometer.

  Next, the surface loss at the time of this measurement was determined from the measured value of the monitor sample. Transmittance obtained by multiplying internal transmittance Tim (0) = 99.6% (= 0.996) of the sample for monitoring by theoretical transmittance Ts = 90.9% (internal transmittance not including surface loss) Absorption coefficient, transmittance of Fresnel reflection only) 90.5%, the current measurement value Trm (0) = 89.5%, the value obtained by 1.0% is the surface loss (hm) during this measurement. It is.

  Next, the surface loss hm = 1.0% is added to the measured value Trv (10) = 89.8% of the sample to be measured. This value of 90.8% is the transmittance not including the surface loss of the sample to be measured having a thickness of 10 mm (only the internal transmittance, the absorption coefficient, and the Fresnel reflection). Then, the value 99.9% obtained by dividing the obtained value by Ts = 90.9 is the internal transmittance (Tiv) at the thickness of 10 mm of the sample to be measured.

  The monitoring sample and the sample to be measured were washed in the same batch, and the operation of measuring in the same batch was repeated five times. The results are shown in Table 2.

As shown in Table 2, the measurement accuracy of the internal transmittance of the sample to be measured was 0.2% when expressed by twice the standard deviation (2σ).
(Example 3)

  As Example 3, an example in which the thickness of the monitor sample and the sample to be measured are different will be described below.

  First, in order to obtain the value of surface loss including Fresnel reflection, calcium fluoride crystals having different thicknesses and having the same internal transmittance value were prepared.

Three types of test pieces with a diameter of 30 mm, thicknesses of 3, 10, and 20 mm were collected from adjacent parts of an ingot crystal-grown by the Bridgman method using calcium fluoride raw materials that were artificially chemically synthesized. Two planes were optically polished. In order to clean the surface, these three types of samples were simultaneously placed in an F ₂ laser irradiation apparatus, and 1 million pulses of an F ₂ laser having an energy density of 4 mJ / cm 2 / pulse were irradiated.

  After washing, three types of samples were set simultaneously in the measurement chamber of the spectrophotometer, and the spectral transmittance at a wavelength of 157.6 nm was measured with the spectrophotometer for each sample. The transmittance value is plotted against the thickness. From the transmittance Tr (0) = 90.7% at a thickness of 0 mm obtained by extrapolating the approximate line, h = 90.9−90 as the surface loss. .7 = 0.2 [%]. This surface loss may be considered to be the same when the same batch is subjected to the same cleaning process and is simultaneously measured by the same measuring device. In addition, the value 90.8% obtained by adding the surface loss h = 0.2% to the transmittance Tr = 90.6% of the sample of 3 mm thickness in this measurement is the surface loss of the sample of 3 mm thickness. (Internal transmittance, absorption coefficient, Fresnel reflection only). A value of 99.9% obtained by dividing the transmittance of 90.8% not including the surface loss by the theoretical transmittance Ts = 90.9% is 15 mm, and the sample of 3 mm thickness at 157.6 nm is 3 mm thick. The internal transmittance Ti (3) is a universal value that does not depend on the measurement batch.

  Next, an energy density of 4 mJ / cm 2 / pulse was obtained in the same batch as the sample to be measured having a diameter of 30 mm and a thickness of 20 mm, using the sample having a diameter of 30 mm and a thickness of 3 mm as determined above for the internal transmittance. 1 million pulses of the F2 laser. After irradiation, the transmittance at 157.6 nm of the monitor sample and the sample to be measured was measured in the same batch using a spectrophotometer. Next, the surface loss at the time of this measurement was determined from the measured value of the monitor sample. Transmittance obtained by multiplying internal transmittance Tim (0) = 99.9% (= 0.999) of the monitor sample by theoretical transmittance Ts = 90.9% (internal transmittance not including surface loss, The value 0.5% obtained by subtracting the current measured value Trm (0) = 90.3% from 90.8% (absorption coefficient, transmittance of Fresnel reflection only) is the surface loss hm during the current measurement. .

  Next, the surface loss hm = 0.5% is added to the measured value Trv (20) = 89.0% of the sample to be measured. This value of 89.5% is the transmittance (including only the internal transmittance, absorption coefficient, and Fresnel reflection) of the sample to be measured having a thickness of 20 mm. Then, the value 98.5% obtained by dividing the obtained value by 90.9 is the internal transmittance Tiv (20) of the sample to be measured at a thickness of 20 mm. When the internal transmittance 98.6% at the 20 mm thickness is converted using the equation (5b), the internal transmittance Tiv (10) at the 10 mm thickness of this sample is 99.2%.

  The monitoring sample and the sample to be measured were washed in the same batch, and the operation of measuring in the same batch was repeated five times. The results are shown in Table 3.

  As shown in Table 3, the measurement accuracy of the internal transmittance of the sample to be measured was 0.1% when expressed as twice the standard deviation (2σ).

  As an example for comparison with the present invention, the transmittance of a conventional method was measured. First, in order to obtain the surface loss, calcium fluoride crystals having different thicknesses and having the same internal transmittance value were prepared.

  Four types of test specimens with a diameter of 30 mm, thicknesses of 3, 10, 20, and 40 mm were collected from adjacent parts of an ingot crystal-grown by the Bridgeman method using artificially synthesized calcium fluoride raw materials. The two parallel planes were optically polished. In order to clean the surface dirt, IPA cleaning was performed on four types of samples in the same batch. After washing, four types of samples were set simultaneously in the measurement chamber of the spectrophotometer, and the spectral transmittance from a wavelength of 140 nm to 200 nm was measured for each sample with the spectrophotometer. The transmittance value at 157.6 nm is plotted against the thickness, and the transmittance is 90.2% at a thickness of 0 mm obtained by extrapolating this approximate straight line. It was estimated that 90.2 = 0.7 [%]. This 0.7% was adopted as the surface loss when washed under the same conditions.

  Next, only a sample to be measured having a thickness of 10 mm was subjected to IPA cleaning under the same conditions, and a transmittance of 157.6 nm was measured with a spectrophotometer. The measured value Trv (10) = 89.7% plus the surface loss h = 0.7% does not include the surface loss of the sample to be measured having a thickness of 10 mm (internal transmittance, absorption coefficient). , Transmittance of Fresnel reflection only). A value 99.4% obtained by dividing the obtained value by Ts = 90.9% is the internal transmittance (Tiv) at a thickness of 10 mm of the sample to be measured.

  Only this sample to be measured was washed under the same conditions, and the measurement operation was repeated five times. The results are shown in Table 4.

  As shown in Table 4, when the measurement accuracy of the internal transmittance of the sample to be measured was expressed by twice the standard deviation (2σ), it was 0.4%.

  Examples of the optical material used in the optical measurement of the present invention include optical glass, quartz glass, and crystal material. Crystal materials include quartz and fluoride crystals. The fluoride crystal is calcium fluoride, barium fluoride, magnesium fluoride, or the like.

It is an example of the flowchart which showed the optical characteristic measuring method of the optical member in this invention. It is a figure showing the relationship between the transmittance | permeability and thickness. It is a figure showing the relationship between various loss, the transmittance | permeability, etc. FIG. It is an example of the flowchart which showed the optical characteristic measuring method of the optical member in the conventional method.

Claims (16)

Prepare a monitor sample with known transmittance,
A step of washing the sample to be measured and the sample for monitoring in the same batch, a step of carrying the washed sample to be measured and the sample for monitoring in the same environment, the sample to be measured and the sample for monitoring Measuring the optical properties of the same batch,
The surface loss is calculated using the measured value of the monitor sample, the surface loss is regarded as the surface loss of the sample to be measured, and the transmittance or reflection of the sample to be measured is used using the surface loss. and it has a step of correcting the rate,
The method for measuring an optical property of an optical member, wherein a wavelength of light used for measuring the optical property is 180 nm or more and 250 nm or less .   2. The optical property measurement method for an optical member according to claim 1, wherein the transmittance of a plurality of samples having different thicknesses is measured, the transmittance when the thickness is 0 is estimated from the plurality of values, and the estimated transmission A method for measuring optical characteristics of an optical member, wherein a sample whose internal transmittance is calculated using a surface loss obtained from a difference between the transmittance and the theoretical transmittance is used as a monitor sample whose transmittance is known.   A method of measuring an optical property of an optical member, wherein the sample measured using the method of measuring an optical property to be measured according to claim 1 or 2 is used as a monitor sample having a known transmittance.   4. The method for measuring optical characteristics of an optical member according to claim 1, wherein the transmittance is an internal transmittance at a specific thickness.   5. The optical property measurement method for an optical member according to claim 1, wherein the cleaning used in the same batch for the sample to be measured and the sample for monitoring is wet cleaning or dry cleaning. A method for measuring optical characteristics of an optical member.   6. The method for measuring optical characteristics of an optical member according to claim 5, wherein the dry cleaning used in the same batch for the sample to be measured and the sample for monitoring is to irradiate light having a wavelength of 250 nm or less. A method for measuring optical characteristics of an optical member.   6. The optical property measurement method for an optical member according to claim 5, wherein the dry cleaning used in the same batch for the sample to be measured and the sample for monitoring is to irradiate a laser. Characteristic measurement method.   8. The optical property measurement method for an optical member according to claim 7, wherein the laser used in the same batch for the sample to be measured and the sample for monitoring is an ArF excimer laser. Method. 9. The method of measuring an optical property of an optical member according to claim 7 or 8 , wherein an energy density of 0.1 mJ / cm ² / pulse or more and 250 mJ / cm ² / pulse is applied to the sample to be measured and the monitor sample. A method for measuring optical characteristics of an optical member, characterized in that the number of irradiations is any pulse number of 1000 pulses or more and 10000000 pulses or less with any one of the following intensities . 10. The method for measuring optical characteristics of an optical member according to claim 1 , wherein the monitoring sample and the sample to be measured are the same substance . 11. The optical property measuring method for an optical member according to claim 1, wherein the monitor sample and the sample to be measured have the same thickness. . An optical characteristic measuring method of the optical member according to claim 1, any one of 10, the thickness of the monitor sample optical characteristics of the optical member, wherein said thinner than the thickness of the sample to be measured Measuring method. 13. The optical property measurement method for an optical member according to claim 1, wherein the thickness of the monitor sample is 1 mm or more and 30 mm or less . 14. The method of measuring optical characteristics of an optical member according to claim 1 , wherein a sample having an internal transmittance of 99.0% or more is used as the monitor sample . An optical characteristic measuring method of the optical member according to claim 1, any one of 14, the measurement accuracy of the transmittance, the optical member characterized by at twice the standard deviation is 0.2% or less Optical property measurement method. 16. The method for measuring optical properties of an optical member according to claim 1, wherein the object to be measured is optical glass, quartz glass, or a crystal material .

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