Concentration measuring device and method

Abstract

To measure concentration by using the absorbance of pure water that is measured even if the liquid temperature is unknown.SOLUTION: An estimation circuit 103 estimates an estimation value of a liquid temperature from the absorbance of pure water measured by an absorbance meter 102 by using a liquid temperature estimation regression formula expressing a correlation between the absorbance of pure water at a predetermined measurement wavelength and the liquid temperature of pure water when measuring the absorbance of pure water. A concentration calculation circuit 104 obtains the concentration of a constituent in solution from the absorbance of the solution measured by the absorbance meter 102 by using a concentration regression formula corrected by an estimation value estimated by the estimation circuit 103. A concentration calculation circuit 104 corrects a constant term of a concentration regression formula by an estimation value estimated by the estimation circuit 103 and obtains a constituent concentration by using a concentration regression formula in which a constant term is corrected.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a concentration measurement device and method. [Background technology]

[0002] There is known a technique for measuring the concentration of a chemical solution such as a semiconductor cleaning solution by utilizing light absorption (Patent Document 1). This measurement technique uses the transmitted light intensity (spectrum) of pure water near room temperature as a reference and measures the concentration of the chemical solution by the amount of change in light intensity (absorbance) from the reference spectrum of the chemical solution to be measured. At the production site, it is not easy to always measure the transmitted light intensity of pure water. Concentration measurements at the production site are performed using a concentration measuring device attached to a container containing the chemical solution. For this reason, the transmitted light intensity of the pure water (reference spectrum) that serves as the reference is measured by discharging the chemical solution contained in the container, cleaning the inside of the container, and then filling the container with pure water. Thus, in order to obtain the reference spectrum, cumbersome operations such as stopping production are required.

[0003] On the other hand, if the same reference spectrum is always used in measuring absorbance, accurate measurements cannot be performed due to changes over time in the light source of the concentration measuring device, deviations in the mounting position of the concentration measuring device, etc. Therefore, in general, the reference spectrum is reacquired periodically (e.g., once every 2 or 3 years), and the chemical concentration during production is measured by measuring absorbance using a reference spectrum that is periodically measured and updated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-331386 A Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, in the concentration measurement using the above-mentioned light absorption (absorbance), the liquid temperature at the time of acquiring the reference spectrum is necessary, but in many cases, the liquid temperature is not measured or controlled in the liquid container in which the concentration measurement device is installed. Therefore, there is a demand for a method that can perform concentration measurement by measuring absorbance using the transmitted light intensity of the pure water being measured, even if the liquid temperature is unknown.

[0006] The present invention has been made to solve the above problems, and has an object to make it possible to estimate the liquid temperature from the absorbance of the measured pure water even when the liquid temperature is unknown, and to measure the concentration by correcting the concentration regression equation. [Means for solving the problem]

[0007] The concentration measurement device according to the present invention includes a memory circuit configured to store a concentration regression equation for determining the concentration of a component in a solution from the absorbance of the solution whose concentration is to be measured, and a liquid temperature estimation regression equation that expresses the correlation between the absorbance of pure water and the temperature of the pure water at the time the absorbance of the pure water is measured; an absorbance meter that measures the absorbance of each of the solution and the pure water; an estimation circuit configured to estimate an estimate of the liquid temperature from the absorbance of the pure water measured by the absorbance meter using the liquid temperature estimation regression equation; and a concentration calculation circuit configured to determine the concentration of a component in the solution from the absorbance of the solution measured by the absorbance meter, using the concentration regression equation corrected with the estimated value.

[0008] In one configuration example of the concentration measuring device, the concentration calculation circuit corrects the constant term of the concentration regression equation with the estimated value.

[0009] The concentration measurement method of the present invention includes a first step of measuring the absorbance of pure water, a second step of estimating an estimate of the liquid temperature from the absorbance measured in the first step using a liquid temperature estimation regression equation that expresses the correlation between the measured absorbance of pure water and the liquid temperature of the pure water at the time of measuring the absorbance of pure water, a third step of measuring the absorbance of a solution whose concentration is to be measured, and a fourth step of correcting the concentration regression equation, which determines the concentration of a component in the solution from the measured absorbance of the solution, with the estimated value, and determining the concentration of the component in the solution from the absorbance measured in the third step using the corrected concentration regression equation.

[0010] In one configuration example of the above concentration measurement method, in the fourth step, the constant term of the concentration regression equation is corrected with the estimated value. Effect of the Invention

[0011] As described above, according to the present invention, even if the liquid temperature is unknown, the liquid temperature can be estimated from the absorbance of the pure water being measured, and the concentration can be measured using the estimated liquid temperature. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of a concentration measuring device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a partial configuration of the concentration measuring device according to the embodiment of the present invention. [Diagram 3] FIG. 3 is a flowchart illustrating a concentration measuring method according to an embodiment of the present invention. [Figure 4] FIG. 4 is a characteristic diagram showing the correlation between the absorbance and liquid temperature of pure water. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A concentration measurement device according to an embodiment of the present invention will now be described with reference to Fig. 1. This concentration measurement device includes a memory circuit 101, an absorption spectrometer 102, an estimation circuit 103, and a concentration calculation circuit 104.

[0014] The memory circuit 101 stores a concentration regression equation for determining the concentration of a component in a solution from the absorbance of the solution to be measured, and a liquid temperature estimation regression equation that shows the correlation between the absorbance of pure water and the temperature of the pure water at the time of measuring the absorbance of the pure water. The measurement wavelength in measuring the absorbance can be set appropriately.

[0015] The absorbance meter 102 measures the absorbance of each of the solution and pure water. The absorbance meter 102 includes a light source 121, a spectroscope 122, a light source control circuit 123, a spectrometry control circuit 124, a light receiving control circuit 125, and a controller 126, as shown in FIG.

[0016] The light source 121 emits light including a measurement wavelength corresponding to a component (solute) of a solution whose concentration is to be measured. The spectroscope 122 separates the received light. The spectroscope 122 may be, for example, a grating type or a Fabry-Perot type. The light emitted from the light source 121 passes through the solution whose component concentration is to be measured and is received by the spectroscope 122.

[0017] The light source control circuit 123 controls the lighting of the light source 121 under control of the controller 126. For example, the light source control circuit 123 controls the light source 121 to emit light in a predetermined wavelength band with a predetermined intensity.

[0018] The spectroscopic control circuit 124 controls the spectrometer 122 under control of the controller 126. For example, the spectroscopic control circuit 124 controls a voltage applied between two mirrors of the Fabry-Perot type spectrometer 122, thereby appropriately controlling the wavelength of light received by the light receiving element.

[0019] The light-receiving control circuit 125 measures the intensity of the dispersed light (transmitted light intensity) under the control of the controller 126. For example, when the light-receiving control circuit 125 receives an electrical signal indicating the intensity of the light measured by the spectroscope 122, the light-receiving control circuit 125 converts the received electrical signal into a numerical value indicating the intensity of the light, and outputs the converted numerical value.

[0020] The controller 126 controls the light source 121 and the spectroscope 122, acquires the intensity of transmitted light at a measurement wavelength that is separated by the spectroscope 122 through the solution to be measured, and calculates the absorbance.

[0021] For example, the controller 126 obtains the transmitted light intensity of the measurement wavelength corresponding to the measurement target component from the light passing through the solution to be measured. For example, when the measurement target components are ammonia and hydrogen peroxide, the controller 126 selects a measurement wavelength corresponding to ammonia and a measurement wavelength corresponding to hydrogen peroxide, and controls the light source control circuit 123 to turn on the light source 121, thereby emitting light in a wavelength band including the measurement wavelength.

[0022] The controller 126 also controls the spectroscopic control circuit 124 to separate light of a measurement wavelength from light received by the spectrometer 122 through the solution to be measured. The controller 126 also acquires the intensity of light (transmitted light intensity) of the measurement wavelength measured by the spectrometer 122 via the light receiving control circuit 125. For example, the controller 126 causes the spectrometer 122 to measure the light intensity of a measurement wavelength corresponding to ammonia, and then causes the spectrometer 122 to measure the transmitted light intensity of a measurement wavelength corresponding to hydrogen peroxide. The controller 126 also acquires the transmitted light intensity of each measured measurement wavelength to determine absorbance.

[0023] The controller 126 is a computer device equipped with a CPU (Central Processing Unit), a main storage device, an external storage device, etc. The CPU operates (executes) a program deployed in the main storage device, thereby realizing each of the above-mentioned functions. The above-mentioned programs are programs for causing a computer to execute each of the above-mentioned control functions. The controller 126 can also be configured with a programmable logic device (PLD) such as an FPGA (field-programmable gate array).

[0024] The estimation circuit 103 estimates an estimated value of the liquid temperature from the absorbance of pure water measured by the absorbance meter 102, using a liquid temperature estimation regression equation that expresses the correlation between the absorbance of pure water at a predetermined measurement wavelength and the liquid temperature of pure water at the time of measuring the absorbance of pure water. The concentration calculation circuit 104 obtains the concentration of a component in the solution from the absorbance of the solution measured by the absorbance meter 102, using the concentration regression equation corrected with the estimated value estimated by the estimation circuit 103. The concentration calculation circuit 104 corrects the constant term of the concentration regression equation with the estimated value estimated by the estimation circuit 103, and obtains the component concentration using the concentration regression equation with the corrected constant term.

[0025] The estimation circuit 103 and the concentration calculation circuit 104 can be computer devices equipped with a CPU, a main storage device, an external storage device, etc. The CPU operates (executes) a program loaded in the main storage device, thereby realizing each of the above-mentioned functions. The above-mentioned programs are programs for causing a computer to execute each of the above-mentioned control functions. The estimation circuit 103 and the concentration calculation circuit 104 can also be configured with a programmable logic device (PLD) such as an FPGA (field-programmable gate array).

[0026] Next, a concentration measuring method according to an embodiment of the present invention will be described with reference to FIG.

[0027] First, in a first step S101, the absorbance of pure water is measured by the absorbance meter 102. The measurement wavelength in measuring the absorbance of pure water can be set appropriately.

[0028] Next, in a second step S102, the estimation circuit 103 estimates an estimate of the liquid temperature (liquid temperature estimate value) from the absorbance measured in the first step S101 using a liquid temperature estimation regression equation that represents the correlation between the measured absorbance of pure water and the liquid temperature of the pure water at the time the absorbance of pure water was measured.

[0029] Next, in a third step S103, the absorbance meter 102 measures the absorbance of the solution to be measured. The measurement wavelength for measuring the absorbance of the solution can be set appropriately. Next, in a fourth step S104, the concentration calculation circuit 104 corrects the concentration regression equation for determining the concentration of a component in the solution from the measured absorbance of the solution with the estimated liquid temperature value determined in the second step S102, and determines the concentration of the component in the solution from the absorbance measured in the third step using the corrected concentration regression equation. In the fourth step S104, the constant term of the concentration regression equation is corrected with the estimated liquid temperature value estimated by the estimation circuit 103, and the component concentration is determined using the concentration regression equation with the corrected constant term.

[0030] As described above, according to the embodiment, the liquid temperature is estimated from the measured absorbance of the pure water. Therefore, even if the liquid temperature is unknown, the liquid temperature can be estimated from the measured absorbance of the pure water and the concentration regression equation can be corrected to measure the concentration.

[0031] A more detailed description will be given below. In the following, an example will be described in which the concentration (component concentration) of ammonia and hydrogen peroxide in a solution in which ammonia (NH3) and hydrogen peroxide (H2O2) are dissolved is measured as a cleaning solution used in the manufacturing process of a semiconductor device. In the measurement, for example, transmitted light intensity is measured using wavelength 1, wavelength 2, and wavelength 3, each of which has a different wavelength. In the following, for simplicity of explanation, the wavelengths will be explained as wavelength 1, wavelength 2, and wavelength 3, but the measurement wavelengths in the present invention are not limited to three wavelengths.

[0032] Using the absorbance A1 from the measurement using wavelength 1, the absorbance A2 from the measurement using wavelength 2, and the absorbance A3 from the measurement using wavelength 3, and the regression coefficients b0, b1, b2, and b3, the concentration regression equation for calculating each concentration C can be expressed as C=b1A1+b2A2+b3A3+b0. Here, each absorbance is the common logarithm of the value obtained by dividing the transmitted light intensity I of the solution to be measured by the transmitted light intensity I0 of pure water, multiplied by -1, and the concentration regression equation for calculating the concentration C can be expressed by the following formula (1) using the transmitted light intensity I of the solution and the transmitted light intensity I0 of pure water.

[0033]

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[0034] However, even if the same concentration measuring device is used, the transmitted light intensity I0 of the pure water measured changes due to changes over time in the light source used to measure the transmitted light intensity, or due to misalignment of the light source or spectrometer installation position. For this reason, problems occur such as measurement results differing depending on the time of measurement, even if the component concentration in the solution to be measured is constant. To solve such problems, it is necessary to periodically measure the transmitted light intensity I0 of the pure water. The transmitted light intensity I0 of the pure water changes depending on the temperature T0 (℃) at the time of measurement, and the concentration C can be expressed as a function of temperature T0℃ as shown in equation (2).

[0035]

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[0036] As described above, in the concentration regression equation for calculating the concentration, the pure water transmitted light intensity I0 changes depending on the temperature T0 (°C) at the time of measurement. For this reason, if the liquid temperature in the measurement of the transmitted light intensity of pure water is different between the initial measurement and the remeasurement, it is not sufficient to simply remeasure the pure water transmitted light intensity I0 and update it to transmitted light intensity I'0. In order to calculate the concentration C' using the remeasured pure water transmitted light intensity I'0, a concentration regression equation is created by adding a constant term β(T) that changes with temperature, as shown in equation (3).

[0037]

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[0038] However, in many cases, the liquid temperature is not measured or controlled in the liquid container where the concentration measuring device is installed, so it may not be possible to define the constant term β(T) that changes with temperature.

[0039] On the other hand, there is a correlation between the absorbance and liquid temperature of pure water, as shown in Figure 4. The numerical values ​​shown in the graph of Figure 4 are the measurement wavelengths, and are indicated by λ1, λ2, and λ3. From the correlation between the absorbance of pure water at the measurement wavelength and the liquid temperature T of pure water at the time of measuring the absorbance of pure water, a liquid temperature estimation regression equation can be created by using the regression coefficients B0, B1, B2, and B3, as shown in the following equation (4).

[0040]

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[0041] Using absorbance A1, absorbance A2, and absorbance A3, equation (4) can be expressed as "T = B1A1 + B2A2 + B3A3 + B0 (5)." By substituting the absorbance A1, absorbance A2, and absorbance A3 of the pure water measured during the actual concentration measurement into equation (5), the liquid temperature of the pure water during the actual measurement, T = T0'℃, can be calculated. By using the liquid temperature calculated in this way and using the concentration regression equation in which the constant term β(T) is corrected to the constant term β(T0'), an accurate concentration C' can be calculated.

[0042] As described above, according to the present invention, it is possible to estimate an estimated value of the liquid temperature from the measured absorbance of pure water using a liquid temperature estimation regression equation that expresses the correlation between the absorbance of pure water and the temperature of the pure water at the time of measuring the absorbance of pure water, and it is possible to measure the concentration using the measured absorbance of pure water even if the liquid temperature is unknown.

[0043] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0044] 101...memory circuit, 102...absorbance meter, 103...estimation circuit, 104...concentration calculation circuit.

Claims

1. a memory circuit configured to store a concentration regression equation for determining a concentration of a component in a solution based on the absorbance of the solution to be measured, and a liquid temperature estimation regression equation that represents a correlation between the absorbance of pure water and the temperature of the pure water at the time of measuring the absorbance of the pure water; an absorbance meter for measuring the absorbance of each of the solution and pure water; an estimation circuit configured to estimate an estimated value of a liquid temperature from the absorbance of pure water measured by the absorption spectrometer using the liquid temperature estimation regression equation; a concentration calculation circuit configured to calculate the concentration of the component in the solution from the absorbance of the solution measured by the absorbance meter, using the concentration regression equation corrected by the estimated value; A concentration measuring device comprising:

2. 2. The concentration measuring device according to claim 1, The concentration calculation circuit is a concentration measurement device that corrects a constant term of the concentration regression equation with the estimated value.

3. A first step of measuring the absorbance of pure water; a second step of estimating an estimated value of the liquid temperature from the absorbance measured in the first step by using a liquid temperature estimation regression equation that represents a correlation between the measured absorbance of the pure water and the liquid temperature of the pure water at the time of measuring the absorbance of the pure water; a third step of measuring the absorbance of the solution whose concentration is to be measured; a fourth step of correcting a concentration regression equation for determining a concentration of the component in the solution from the measured absorbance of the solution with the estimated value, and determining a concentration of the component in the solution from the absorbance measured in the third step using the corrected concentration regression equation; A concentration measurement method comprising:

4. 4. The method for measuring concentration according to claim 3, In the fourth step, a constant term of the concentration regression equation is corrected with the estimated value.

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