Concentration measurement device

Abstract

A concentration measurement device 100 comprising: a measurement cell 10; a light source unit 20 that emits measurement light that is to enter the measurement cell; a measurement light detector 24 that receives the measurement light emitted from the measurement cell; a temperature sensor 16 that measures the element temperature of the light source unit or a temperature sensor 6 that measures the temperature of a fluid flowing in the measurement cell; and a processing circuit 28 that is connected to the measurement light detector and the temperature sensor and measures the concentration of the fluid flowing in the measurement cell, on the basis of outputs of the measurement light detector and the temperature sensor. The concentration of the fluid is obtained through calculation according to the Lambert-Beer law on the basis of the ratio of the transmitted light intensity I outputted by the measurement light detector 24 with respect to the incoming light intensity I0, and the incoming light intensity I0 is determined on the basis of the temperature measured by the temperature sensor 6, 16.

Description

concentration measuring device

[0001] The present invention relates to a concentration measuring device, and more particularly to a concentration measuring device that measures the concentration of a fluid based on the intensity of light that has passed through the fluid in a measurement cell.

[0002] Conventionally, concentration measuring devices (so-called in-line concentration measuring devices) have been known that are incorporated into gas supply lines that supply raw material gases formed from liquid materials or solid materials, such as metal organic compounds (MOs), to semiconductor manufacturing equipment, and are configured to measure the concentration of gases flowing through the gas supply lines.

[0003] In this type of concentration measuring device, light of a predetermined wavelength is emitted from a light source through a light entrance window into a measuring cell through which gas flows, and the transmitted light is received by a light receiving element to measure the absorbance. From the measured absorbance, the concentration of the gas in the measuring cell can be calculated according to the Beer-Lambert law.

[0004] In this specification, various transmitted light detection structures used to detect the concentration of a fluid are generally referred to as measurement cells, which include not only measurement cells branched off from a fluid supply line and arranged separately, but also in-line transmitted light detection structures provided midway along the fluid supply line.

[0005] Some inline concentration measuring devices are configured with a measurement cell incorporated in a fluid supply line and an electric unit located remotely from the measurement cell (see, for example, Patent Documents 1 and 2). Even when the measurement cell is heated to high temperatures (e.g., 150°C), heat damage and malfunctions can be prevented by installing optical elements and circuit elements with low high-temperature resistance in the electric unit.

[0006] Some concentration measuring devices have a configuration in which a light source device and a photodetector are directly provided in the measurement cell (for example, Patent Documents 3 and 4). When measuring the concentration of ozone gas, for example, if the measurement cell is not heated to a very high temperature, it is also possible to fix the light source, photodetector, etc. to the measurement cell.

[0007] International Publication No. 2020 / 158506 International Publication No. 2021 / 054097 International Publication No. 2023 / 013314 Japanese Patent Application Laid-Open No. 2023-105732

[0008] In the concentration measuring device for optically measuring concentration as described above, it is known to provide a temperature sensor or a pressure sensor in the measurement cell to measure the temperature and pressure of the gas in the measurement cell. The measured gas temperature and gas pressure can be used to correct the concentration measurement.

[0009] For example, Patent Document 1 discloses preventing a decrease in accuracy of concentration measurement by calculating the concentration using an extinction coefficient selected based on the gas pressure and gas temperature, and Patent Document 2 discloses correcting measurement errors corresponding to changes in the refractive index of a fluid by calculating the concentration using a correction factor associated with the gas pressure and gas temperature.

[0010] However, while simply correcting the absorption coefficient and correction factor based on the measured gas temperature as described above makes it possible to measure the concentration according to the gas state, there are cases where the correction for temperature changes in the optical system is insufficient. For this reason, there is still room for further improvement in the accuracy of optical concentration measurement devices.

[0011] The present invention has been made in view of the above-mentioned problems, and has as its main object to provide a concentration measuring device with improved measurement accuracy.

[0012] A concentration measuring device according to an embodiment of the present invention comprises a measurement cell, a light source unit that emits measurement light to be incident on the measurement cell, a measurement light detector that receives the measurement light emitted from the measurement cell, at least one of a temperature sensor that measures the element temperature of the light source unit and a temperature sensor that measures the temperature of a fluid flowing through the measurement cell, and a processing circuit connected to at least the measurement light detector and the temperature sensor and configured to measure the concentration of the fluid flowing through the measurement cell based on the outputs of the measurement light detector and the temperature sensor, wherein the concentration of the fluid is calculated in accordance with the Beer-Lambert law based on the ratio of the transmitted light intensity output by the measurement light detector to the incident light intensity, and the incident light intensity is determined based on the temperature measured by the temperature sensor.

[0013] In one embodiment, the concentration measuring device further has a reference light detector that receives a portion of the light emitted from the light source unit as reference light, and is configured to correct the concentration calculation by comparing the output of the reference light detector with a reference value, and the reference value of the reference light detector is configured to be determined based on the temperature measured by the temperature sensor.

[0014] In one embodiment, the measurement cell, the light source unit, and the measurement light detector are arranged separately, and the measurement cell, the light source unit, and the measurement light detector are connected by an optical transmission member, and both a temperature sensor that measures the element temperature of the light source unit and a temperature sensor that measures the temperature of the fluid flowing through the measurement cell are provided.

[0015] In one embodiment, the measurement cell, the light source unit, and the measurement light detector are integrally configured, and a temperature sensor is provided to measure the temperature of the fluid flowing through the measurement cell.

[0016] According to embodiments of the present invention, optical density measurements can be performed with even greater accuracy.

[0017] The present invention relates to a concentration measurement device, a method for measuring a concentration of a light source ...

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment. Also, although the following describes a concentration measurement device that measures gas, the measurement object may be a fluid other than gas, such as a liquid.

[0019] 1 shows a concentration measurement device 100 according to an embodiment of the present invention. The concentration measurement device 100 is incorporated into a gas supply line (not shown) used in a semiconductor manufacturing system or the like, and is used to measure the concentration of gas G flowing through the flow path.

[0020] The concentration measuring device 100 of this embodiment includes a fluid unit 50A that is incorporated into the gas supply line and an electric unit 50B that is disposed apart from the fluid unit 50A. The fluid unit 50A and the electric unit 50B are optically and electrically connected by optical fiber cables 12 and 14 as optical transmission members and a sensor cable (not shown).

[0021] The gas flowing through the gas supply line is, for example, HCDS (Si ２ Cl ６ ), or organometallic materials such as TEOS (tetraethyl orthosilicate), TMGa (trimethylgallium), and TMAl (trimethylaluminum). These materials are liquid at room temperature and can be vaporized by heating to, for example, about 150°C to 200°C. The generated material gas is then vaporized in a process chamber, for example, by forming a silicon nitride film (SiN ｘ film) and silicon oxide film (SiO ２ It is used to form insulating films such as silicon dioxide films.

[0022] The fluid unit 50A is provided with a measurement cell 10 having a flow path for a measurement fluid, and is capable of measuring the concentration of a gas flowing inside the measurement cell 10. In this embodiment, a light-transmitting window 2 (here, a light-transmitting plate) that contacts the flow path is provided at one end of the measurement cell 10, and a reflecting member 4 is provided at the other end of the measurement cell 10. In the fluid unit 50A through which the gas G flows, the measurement cell 10 is used as part of the flow path and also as an optical path for measurement light.

[0023] In this specification, "light" refers not only to visible light but also to at least infrared and ultraviolet light, and may include electromagnetic waves of any wavelength. "Translucent" means that the internal transmittance of the light incident on the measurement cell is sufficiently high to enable concentration measurement.

[0024] A sapphire plate is preferably used for the window 2, as it is mechanically and chemically stable and has high transmittance and resistance to the detection light (such as ultraviolet light) used in concentration measurement. However, other stable materials, such as quartz glass, can also be used. The main body (flow path forming portion) of the measurement cell 10 is made of, for example, SUS316L. The window 2 may be positioned at a slight angle (e.g., 1 to 5 degrees) from a plane perpendicular to the central axis of the measurement cell 10, which can suppress the influence of surface reflected light on the measurement, i.e., the influence of stray light on the measurement.

[0025] The reflecting member 4 is, for example, a sapphire plate having a reflective layer formed on the rear surface thereof, such as an aluminum layer or a dielectric multilayer film. The use of a dielectric multilayer film as the reflective layer makes it possible to selectively reflect light in a specific wavelength range (e.g., near-ultraviolet light). Furthermore, since the dielectric multilayer film can reflect light at any rate, a portion of the light (e.g., 10%) can be transmitted, and the light transmitted through the reflecting member 4 can be used as reference light using a photodetector installed below the reflecting member 4.

[0026] However, in other embodiments, a transmission-type measurement cell may be used instead of the reflection-type measurement cell. In a transmission-type measurement cell, light is incident from one end of the measurement cell and light that has passed through the measurement cell is emitted from the other end (without a reflecting member). In this case, the light source light and the transmitted light are transmitted by separate optical fiber cables connected to both ends of the measurement cell.

[0027] The fluid unit 50A further includes a temperature sensor 6 for measuring the temperature of the measurement gas flowing in the measurement cell 10, and a pressure sensor 8 for detecting the pressure of the measurement gas. The outputs of the temperature sensor 6 and the pressure sensor 8 are sent to the electric unit 50B via a sensor cable (not shown) and are used to measure the gas concentration.

[0028] The temperature sensor 6 may be, for example, a thermocouple, a thermistor, or a platinum resistance thermometer. The pressure sensor 8 may be, for example, a silicon single crystal pressure sensor having a pressure-sensitive diaphragm with a strain gauge, or a capacitance manometer. Although the temperature sensor 6 and the pressure sensor 8 are installed in one location here, two or more may be installed around the measurement cell 10, for example.

[0029] In addition, in the concentration measuring device 100 of this embodiment, the electrical unit 50B includes a light source unit 20 having a light source that emits light to be incident on the measuring cell 10 via the optical fiber cable 12, a measuring light detector 24 that receives the light emitted from the measuring cell 10 via the optical fiber cable 14, and a processing circuit 28 that calculates the concentration of the measured gas based on the detection signal output by the measuring light detector 24 (a detection signal corresponding to the intensity of the received light).

[0030] In this embodiment, the electric unit 50B is provided with a temperature sensor 16 for measuring the element temperature of the light source unit 20. The temperature sensor 16 may be, for example, a thermocouple, a thermistor, or a platinum resistance temperature detector. Note that although the temperature sensor 16 is installed near the light source unit 20 in this example, multiple temperature sensors 16 may be installed in other locations.

[0031] The light-receiving elements constituting the measurement light detector 24 may be, for example, photodiodes or phototransistors. The processing circuit 28 is composed of circuit elements such as a processor and memory mounted on a circuit board, includes a computer program that executes predetermined calculations based on input signals, and is realized by a combination of hardware and software. Some or all of the components of the processing circuit 28 (such as the CPU) may be provided in a device external to the electric unit 50B.

[0032] In this embodiment, the light source unit 20 is configured using two light-emitting elements 20a and 20b provided on different surfaces of a cube beam splitter 22. The light-emitting elements 20a and 20b may be LEDs or laser diodes (LDs).

[0033] The light-emitting elements 20a and 20b are configured to emit light of different wavelengths. In this configuration, frequency analysis (e.g., fast Fourier transform or wavelet transform) can be performed to measure the light intensity corresponding to each wavelength component from the detection signal detected by the measurement light detector 24. Note that instead of using multiplexed lights of different wavelengths as the light source, a single-wavelength light source can also be used, in which case the multiplexer and frequency analysis circuit can be omitted.

[0034] In this embodiment, the first light-emitting element 20a emits ultraviolet light with a wavelength of, for example, 280 nm, while the second light-emitting element 20b emits red light with a wavelength of, for example, 635 nm. As described above, the ultraviolet light from the first light-emitting element 20a is preferably used to measure the concentration of the organometallic gas in the measurement cell 10 by utilizing light absorption. On the other hand, the red light from the second light-emitting element 20b is not absorbed by the organometallic gas in the measurement cell 10 regardless of its concentration, and therefore can be used to detect abnormalities in optical elements provided on the optical path from the light source unit 20 to the measurement light detector 24.

[0035] However, the emission wavelengths of the light-emitting elements 20a and 20b are not limited to the ultraviolet and red light ranges described above, and the absorption and non-absorption bands can be appropriately selected depending on the type of gas to be measured. Furthermore, the light-emitting elements 20a and 20b may be configured to emit light of different wavelengths that can be absorbed by the gas. By absorbing light of different wavelengths and measuring the transmitted light intensity at each wavelength, the accuracy of concentration measurement can be improved.

[0036] Furthermore, in the light source unit 20, a reference light detector 26 is disposed at a position facing the first light-emitting element 20a across the cube beam splitter 22. In this configuration, a portion of the light emitted from the first light-emitting element 20a is incident on the reference light detector 26 as transmitted light, and the remainder of the light is incident on the optical fiber cable 12. The light-receiving element constituting the reference light detector 26 may be, for example, a photodiode or a phototransistor.

[0037] In the concentration measuring device 100, the optical path length of light traveling back and forth within the measurement cell 10 can be defined as twice the distance between the surface of the window 2 and the surface of the reflecting member 4. In the concentration measuring device 100, light that is incident on the measurement cell 10 and then reflected by the reflecting member 4 is absorbed by the gas present in the flow path within the measurement cell 10 at a level that depends on the concentration of the gas.

[0038] The processing circuit 28 provided in the electric unit 50B can measure the absorbance Aλ at the absorption wavelength by frequency analyzing the detection signal from the measurement light detector 24, and further calculates the gas concentration C from the absorbance Aλ based on the Lambert-Beer law shown in the following equation (1): Ｍ Aλ=−log １０ (I / I ０ ) = α'LC Ｍ ...(1)

[0039] In the above formula (1), I ０ is the intensity of light incident on the measurement cell 10, I is the intensity of light passing through the gas in the measurement cell 10, and α' is the molar absorption coefficient (m ２ / mol), L is the optical path length of the measurement cell (m), C Ｍ is the molar concentration (mol / m３ The molar absorption coefficient α' is a coefficient determined by the substance. ０ Regarding the incident light intensity I, the light intensity detected by the measurement light detector 24 when there is no light-absorbing gas in the measurement cell 10 (for example, when the measurement cell 10 is filled with a gas that does not absorb ultraviolet light or when the measurement cell is evacuated) is ０ It can be considered as such.

[0040] As described above, the optical path length L of the measurement cell 10 can be defined as twice the distance between the window and the reflecting member, thereby achieving twice the optical path length compared to a transmission-type concentration measurement device having a light entrance window and a light exit window at both ends of the measurement cell. This allows for improved measurement accuracy despite the device's compact size. Furthermore, the concentration measurement device 100 uses only one optical element on one side of the measurement cell 10 for light entrance and exit, making maintenance easier and reducing the number of parts.

[0041] The fluid unit 50A of this embodiment is also provided with a temperature sensor 6 and a pressure sensor 8, which can measure the temperature and pressure of the gas G flowing through the measurement cell 10. In this case, the concentration measurement device 100 can also refer to the outputs of the temperature sensor 6 and the pressure sensor 8 to determine the concentration of the gas flowing through the measurement cell 10, for example, from the following equation (2), as disclosed in Patent Documents 1 and 2: Cv=(RT / αLPt)·ln(I ０ / I) ...(2)

[0042] In the above formula (2), Cv is the concentration (vol %) of the measurement gas in the total gas, α is the absorption coefficient of the measurement gas, Pt is the total gas pressure that can be measured by the pressure sensor 5, T is the gas temperature that can be measured by the temperature sensor 6, and R is the gas constant. Also, similar to the Beer-Lambert law, L is the optical path length of the measurement cell, I ０ is the incident light intensity, and I is the transmitted light intensity.

[0043] In this way, when measuring a concentration based on absorbance, it has been known that the concentration is calculated taking into consideration the gas temperature T. However, the inventors of the present application have confirmed that it may be effective to perform further correction. More specifically, the inventors of the present application have confirmed that, since the intensity of the measurement light itself may vary depending on the temperature, the above-mentioned incident light intensity I ０ It has been found that by appropriately determining the concentration, it is possible to carry out concentration measurement with higher accuracy.

[0044] Figure 2 is a graph showing how the amount of light changes depending on the temperature of the optical system. For four concentration measurement devices, indicated by black circles, squares, triangles, and white circles, the output of the measurement light detector 24 is plotted while the temperature is changed with the emission intensity fixed under conditions where no light absorption occurs.

[0045] The temperature here is the output of the temperature sensor 16 for measuring the element temperature provided in the light source unit 20. However, it has been confirmed that the received light intensity of the measurement light also varies with the gas temperature measured by the temperature sensor 6 provided in the measurement cell 10, regardless of the absorbance of the gas.

[0046] As can be seen from FIG. 2, the incident light intensity I ０ can vary in various ways depending on the temperature of the optical system (at least one of the gas temperature and the element temperature of the light source) even under conditions where no light absorption occurs. Therefore, by measuring data in advance and storing it in memory before performing concentration measurement, when actually performing concentration measurement, temperature measurement is performed and the corresponding incident light intensity I read out from the memory is stored. ０ Measurements are carried out using (T).

[0047] The temperature correction of the incident light intensity is calculated by the temperature-related incident light intensity I ０ This can be done by using a table that describes the temperature (T) or by using a function that uses the temperature as a variable. Also, as described above, when measuring the concentration, the intensity of light detected by the measurement light detector 24 when there is no light-absorbing gas in the measurement cell 10 is defined as the incident light intensity I ０ When calculating the temperature-dependent correction coefficient as ０It may be possible to obtain it by applying

[0048] However, the incident light intensity I ０ (T) or its calculation formula is stored in memory, the incident light intensity I ０ The procedure for measuring the

[0049] It has been confirmed that such a change in the amount of light (temperature dependence of the intensity of received light in the light receiving element) occurs not only in the measurement light detector 24 but also in the reference light detector 26. ０ By using (T), it is possible to eliminate changes in the light intensity other than those caused by concentration. Furthermore, when determining whether an abnormality has occurred in the optical system based on the output of the reference light detector 26, the reliability of the determination can be improved.

[0050] In this way, the incident light intensity I determined based on the temperature of the optical system ０ When (T) is used, the temperature measurement may be determined based on either the output (optical element temperature) of a temperature sensor provided in the light source unit of the gas box or the output (gas temperature) of a gas sensor provided in the measurement cell, or may be determined by reference to both.

[0051] The output of the reference light detector 26 is primarily used to monitor the state of the first light-emitting element 20 a, and can also be used to correct the concentration measurement to match the current light-emitting state of the first light-emitting element 20 a.

[0052] For example, instead of the transmitted light intensity I detected by the measurement light detector 24, ｃ = I × (I ｒ０ / I ｒ ) the corrected transmitted light intensity I ｃ The concentration can be calculated using the formula I ｒ０ is the initial reference light intensity (reference value) detected by the reference light detector 26 at the time of shipment, etc., and I ｒ is the current reference light intensity measured by the reference light detector 26 at the same time that the transmitted light intensity I is measured by the measurement light detector 24 for concentration measurement.

[0053] In this embodiment, the corrected transmitted light intensity I ｃ The initial reference light intensity I required to calculate ｒ０ Also, the incident light intensity I ０ Similarly, the temperature sensor 16 for measuring the element temperature of the light source unit 20 and the temperature sensor 6 for measuring the gas temperature provided in the measuring cell 10 are used to calculate the temperature I stored in advance. ｒ０ It may be determined from the data in (T).

[0054] 3 shows the configuration of a concentration measuring device 200 according to another embodiment. In the concentration measuring device 200, a light source unit 20 and a measurement light detector 24 are directly attached to a measurement cell 10 through which gas G flows. In the concentration measuring device 200, components similar to those in the concentration measuring device 100 shown in FIG. 1 are designated by the same reference numerals, and detailed descriptions thereof may be omitted.

[0055] 1, the light source unit 20 has a configuration in which a light emitting element 20a and a reference light detector 26 are attached to different sides of a cube beam splitter 22. Note that, although the concentration measuring device 200 has only one light emitting element 20a facing the window 2, another light emitting element with a different emission wavelength may be provided facing the reference light detector 26.

[0056] 1, a transmission-type measurement cell is used in which the measurement light passes through a window 3 on the exit side and reaches the measurement light detector 24 directly without reflection. The concentration measurement device 200 is also provided with a temperature sensor 6 and a pressure sensor 8, and their outputs can be used for concentration measurement. Here, one temperature sensor 6 is installed downstream of the measurement cell 10, but multiple temperature sensors 6 may be installed near the windows 2 and 3, for example.

[0057] In this way, even in the concentration measuring device 200 of this embodiment in which the light source unit 20 and the measurement light detector 24 are integrally provided with the measurement cell 10, the incident light intensity I ０(T) is determined based on the output of the temperature sensor 6. The incident light intensity I ０ (T) is the incident light intensity I while changing the temperature before performing the concentration measurement, similar to the concentration measurement device 100. ０ is measured for each temperature, and the measurement results are stored in memory. When actually measuring the concentration, the concentration can be determined according to the information read out from the memory based on the measured temperature.

[0058] The above describes a concentration measuring device according to an embodiment of the present invention, but the present invention should not be interpreted as being limited to the above embodiment, and various modifications are possible within the scope of the spirit of the present invention.

[0059] The concentration measuring device according to the embodiment of the present invention is suitably used to measure the concentrations of various fluids flowing through flow paths in, for example, a gas supply system of a semiconductor manufacturing device.

[0060] 2 Window 4 Reflecting member 6 Temperature sensor 8 Pressure sensor 10 Measuring cell 12, 14 Optical fiber cable 20 Electric unit 20a, 20b Light-emitting element 24 Measurement light photodetector 26 Reference light detector 28 Control circuit 50A Fluid unit 50B Electric unit 100, 200 Concentration measuring device

Claims

1. A concentration measuring device comprising: a measurement cell; a light source unit that emits measurement light to be incident on the measurement cell; a measurement light detector that receives the measurement light emitted from the measurement cell; at least one of a temperature sensor that measures the element temperature of the light source unit and a temperature sensor that measures the temperature of a fluid flowing through the measurement cell; and a processing circuit connected to at least the measurement light detector and the temperature sensor and configured to measure the concentration of the fluid flowing through the measurement cell based on the outputs of the measurement light detector and the temperature sensor, wherein the concentration of the fluid is calculated in accordance with the Beer-Lambert law based on the ratio of the transmitted light intensity output by the measurement light detector to the incident light intensity, and the incident light intensity is determined based on the temperature measured by the temperature sensor.

2. The concentration measuring device according to claim 1, further comprising a reference light detector that receives a portion of the light emitted from the light source unit as reference light, and configured to correct the concentration calculation by comparing the output of the reference light detector with a reference value, the reference value of the reference light detector being configured to be determined based on the temperature measured by the temperature sensor.

3. A concentration measuring device as described in claim 1 or 2, wherein the measuring cell, the light source unit and the measuring light detector are arranged separately, the measuring cell, the light source unit and the measuring light detector are connected by an optical transmission member, and both a temperature sensor that measures the element temperature of the light source unit and a temperature sensor that measures the temperature of the fluid flowing through the measuring cell are provided.

4. A concentration measuring device as described in claim 1 or 2, wherein the measuring cell, the light source unit and the measuring light detector are integrally configured, and a temperature sensor is provided to measure the temperature of the fluid flowing through the measuring cell.

Images