Concentration measuring device

Abstract

The concentration measuring device (100) includes: a measuring space (10A) connected to an entrance window (18a) and an exit window (18b) and having fluid flowing into it; a light source (20) that emits measuring light (L) that passes through the entrance window and enters the measuring space; a photodetector (24) that receives measuring light that passes through the measuring space and exits through the exit window; and a processing circuit (28) configured to calculate the concentration of the fluid. The photodetector has a sensor unit composed of multiple light-receiving elements. The optical path length of the light reaching the first light-receiving element (p1) is different from the optical path length of the light reaching the second light-receiving element (p2). When the concentration of the fluid is calculated based on the output of the first light-receiving element, the corresponding first optical path length is used for concentration calculation, and when the concentration of the fluid is calculated based on the output of the second light-receiving element, the corresponding second optical path length is used for concentration calculation.

Description

Technical Field

[0001] This invention relates to a concentration measuring device, and more particularly to a concentration measuring device configured to measure the concentration of a fluid based on the absorbance of light passing through the fluid. Prior Technology

[0002] Previously, an optical concentration measuring device was known that determined the concentration of organometallic (MO) feedstock gas used in semiconductor manufacturing based on absorbance. This type of concentration measuring device includes a measuring unit that directs light of a specified wavelength from a light source through an entrance window to the fluid flow, and a light-receiving element that receives the transmitted light passing through the measuring unit to measure the absorbance. From the measured absorbance, the fluid concentration can be calculated according to the Lambert-Beer law (e.g., Patent Document 1).

[0003] Furthermore, a concentration measuring device is known, which is configured to have an entrance window and an exit window facing each other on the side wall of a process chamber in a plasma CVD apparatus or the like, and to measure the concentration of a gas in the chamber by the absorbance of the measuring light passing through the chamber. Patent Document 2 of the applicant in this case discloses a concentration measuring device configured to use the interior of a chamber as the measuring space, and to measure the concentration of introduced TiCl4 gas or NO2 gas based on absorbance. [Previous Technical Documents] [Patent Literature]

[0004] [Patent Document 1] International Publication No. 2018 / 021311 [Patent Document 2] International Publication No. 2020 / 085236 [Patent Document 3] Japanese Patent Application Publication No. 2004-138425 Summary of the Invention

[0005] [The problem that the invention aims to solve] However, in conventional concentration measuring devices, the intensity of light passing through the fluid is measured using a light-receiving element (such as a photodiode). While this allows for the measurement of the overall fluid concentration in the measurement space, it presents challenges in determining the detailed concentration distribution when there are regional concentration inhomogeneities due to fluid movement.

[0006] The present invention was made in view of the above-mentioned problems, and its main objective is to provide a concentration measuring device that can measure the concentration of fluid in the measuring space in a more detailed and accurate manner. [Methods used to solve problems]

[0007] The concentration measuring device according to an embodiment of the present invention includes: a measuring space connected to an entrance window and an exit window, wherein a fluid flows into the space; a light source emitting measuring light that passes through the entrance window and enters the measuring space; a photodetector receiving the measuring light that passes through the measuring space and exits through the exit window; and a processing circuit configured to calculate the concentration of the fluid in the measuring space based on the output of the photodetector. The photodetector has a sensor section composed of a plurality of light-receiving elements, wherein the plurality of light-receiving elements includes a first light-receiving element and a second light-receiving element. The light receiving element has two light path lengths. The light path length of the light reaching the first light receiving element in the measurement space is the first light path length. This is different from the light path length of the light reaching the second light receiving element in the measurement space, which is the second light path length. The processing circuit is configured such that when the concentration of the fluid is determined based on the output of the first light receiving element, the concentration is calculated using the corresponding first light path length. When the concentration of the fluid is determined based on the output of the second light receiving element, the concentration is calculated using the corresponding second light path length.

[0008] In one embodiment, the aforementioned concentration measuring device further comprises: a parallel light lens, which is disposed between the aforementioned light source and the aforementioned entrance window or between the aforementioned exit window and the aforementioned photodetector at least one of them.

[0009] In one embodiment, the aforementioned concentration measuring device further comprises: a telecentric lens, which is disposed between the aforementioned light source and the aforementioned entrance window or between the aforementioned exit window and the aforementioned photodetector.

[0010] In one embodiment, the aforementioned entrance window and the aforementioned exit window are configured in a non-parallel manner.

[0011] In one embodiment, in the aforementioned sensor section of the aforementioned photodetector, the aforementioned plurality of light-receiving elements are arranged linearly or in a matrix as pixels.

[0012] In one embodiment, the light path length of the light reaching the light-receiving element contained in the column or row of the first pixel in the aforementioned measurement space is the same for each pixel; the light path length of the light reaching the light-receiving element contained in the column or row of the second pixel in the aforementioned measurement space is the same for each pixel; and the light path length of the light reaching the light-receiving element contained in the column or row of the first pixel in the aforementioned measurement space is different from the light path length of the light reaching the light-receiving element contained in the column or row of the second pixel in the aforementioned measurement space.

[0013] In one embodiment, the aforementioned sensor unit is configured to determine the concentration by selectively using the output of a portion of the pixel region.

[0014] In one embodiment, the aforementioned concentration measuring device further includes a lens that focuses the light emitted through the aforementioned emission window, and the aforementioned sensor unit is configured to determine the concentration by selectively using the output of a pixel area that irradiates a portion of the focused light.

[0015] In one embodiment, the aforementioned sensor unit is configured to calculate the concentration by summing the output of a portion of the pixel area.

[0016] In one embodiment, the aforementioned sensor unit is configured such that multiple segments, each containing a plurality of pixels, are defined, and the density is determined by using the average output of the pixels contained in the segment as the output of that segment. [The effects of the invention]

[0017] The concentration measuring device according to the embodiment of the present invention can perform more detailed concentration measurements with improved accuracy. Simple Explanation of the Diagram

[0018] [Figure 1] is a schematic diagram showing the structure of the concentration measuring device according to an embodiment of the present invention. [Figure 2] An example of a photographic image of the image sensor of the photodetector included in an embodiment of the present invention for a concentration measuring device. [Figure 3] A view from above of the chamber containing the concentration measuring device of the embodiment of the present invention. [Figure 4](a) shows the pixels at different positions in the horizontal direction, and (b) is a graph showing the relationship between the measured gas concentration and absorbance of each pixel. [Figure 5] A graph showing the relationship between gas concentration and absorbance / d after adjusting the optical path length of the data in the graph shown in Figure 4(b). [Figure 6] is a diagram illustrating a method for achieving a high S / N ratio when using an image sensor as a photodetector to perform concentration measurement. [Figure 7] is a diagram illustrating other methods for achieving a high S / N ratio when using an image sensor as a photodetector for concentration measurement. [Figure 8] is a diagram illustrating another method for achieving a high S / N ratio when using an image sensor as a photodetector for concentration measurement. [Figure 9] is a diagram illustrating another method for achieving a high S / N ratio when using an image sensor as a photodetector for concentration measurement. Implementation

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited to the following embodiments. Furthermore, the following description refers to a concentration measuring device when the measured object is a gas supplied to the process chamber; however, in other embodiments, the measured object may be a fluid other than a gas, such as a liquid.

[0020] Figure 1 is a diagram showing a structural example of the concentration measuring device 100 of this embodiment. The concentration measuring device 100 is configured to measure the concentration of gas supplied to the chamber 10 (measuring space 10A) of the semiconductor manufacturing apparatus through the gas supply line 2.

[0021] Inside chamber 10, a carrier disk 12 for holding semiconductor devices (not shown) is provided, and a spray plate 14 is disposed above the carrier disk 12. The spray plate 14 is arranged parallel to the carrier disk 12 with a predetermined gap. Furthermore, a number of holes are formed on the spray plate 14 to allow supplied gas to pass through.

[0022] The gas introduced into chamber 10 is diffused by spray plate 14 and supplied to the wafer in a substantially uniform manner. Furthermore, below the carrier disk 12, chamber 10 is connected to exhaust line 4, on which vacuum pump 16 is installed, to expel excess gas from chamber 10. Vacuum pump 16 is also used to evacuate chamber 10.

[0023] Furthermore, a pressure sensor and a temperature sensor (not shown) are installed on chamber 10 to measure the pressure and temperature of the gas inside chamber 10. For example, a silicon single-crystal pressure sensor or a capacitive pressure gauge with a pressure-sensing diaphragm equipped with a strain gauge can be used as the pressure sensor. For example, a thermocouple, a thermistor, or a platinum resistance thermometer can be used as the temperature sensor.

[0024] A mixed gas G of the desired concentration, with flow rate controlled, is supplied from gas supply line 2 via a flow control device (not shown). The mixed gas G is generated, for example, by mixing a carrier gas such as N2 with a feed gas such as NO2 at any mixing ratio (or flow rate ratio), and the concentration can be adjusted arbitrarily. As the flow control device, a known pressure-type flow control device described in Patent Document 3 can be used, for example. The pressure-type flow control device has a throttling section and a device valve, configured to adjust the opening of the control valve based on the upstream pressure of the throttling section, thereby controlling the flow rate. A thermal mass flow control device (MFC) can also be used as the flow control device.

[0025] The concentration measuring device 100 is configured to measure the concentration of a measuring gas (e.g., NO2 gas) in the measuring space 10A of the mixed gas G flowing into the chamber 10 based on the absorbance of the measuring light L passing through the mixed gas G. For this purpose, the concentration measuring device 100 includes a light source 20 that emits light through an entrance window 18a provided on one side of the chamber 10 and enters the chamber 10, and a photodetector 24 that receives light emitted through an exit window 18b provided on the other side of the chamber 10.

[0026] The measuring light L emitted from the light source 20 can either pass through the measuring space 10A as shown in the diagram and directly strike the photodetector 24, or it can be reflected once or multiple times using a reflective member such as a mirror before striking the photodetector 24. When using a reflective member, the entrance window 18a and the exit window 18b may not be arranged opposite each other. The entrance window 18a and the exit window 18b only need to be connected to the measuring space 10A and can be set in any position.

[0027] The light source 20 can emit light with a wavelength that the gas being measured can absorb, serving as the measuring light L. When measuring the concentration of NO2 gas in N2 gas, light with a wavelength of 350-550 nm can be used as the light source, particularly light with a wavelength around 405 nm, which has high absorbency. Furthermore, when measuring the concentration of organometallic materials such as TEOS (tetraethoxysilane), TMGa (trimethylgallium), and TMAl (trimethylaluminum), ultraviolet light with a wavelength of 200-400 nm can be used as the measuring light. It goes without saying that the wavelength of the measuring light L can be arbitrarily selected based on the absorption characteristics of the gas being measured, such as the infrared region with wavelengths above 1 μm. Moreover, it is known that common carrier gases, such as nitrogen and argon, do not absorb light with wavelengths above approximately 100 nm.

[0028] As the light-emitting element emitting light of the aforementioned wavelengths, an LED or a laser diode can be used. The light source 20 can be configured to switch between light of different wavelengths emitted by multiple light-emitting elements, or to synthesize light of different wavelengths and emit it. When switching between different wavelengths and emitting light, one wavelength can be used as light in the absorption wavelength band for concentration measurement, and the other wavelength can be used as light in the non-absorption wavelength band for detecting abnormalities in the optical system.

[0029] Furthermore, the light source 20 can be configured to continuously emit the measurement light L, or it can be configured to emit the measurement light L in a pulsed manner. The light source 20 can be configured to emit light of the same wavelength continuously or in a pulsed manner, or it can be configured to change the emission wavelength according to time. As long as the appropriate measurement light L is emitted, the emission pattern of the light source 20 is not particularly limited. Furthermore, it is possible to provide one photodetector 24 for multiple light sources 20, or to provide multiple photodetectors 24 for one light source 20.

[0030] The entrance window 18a and exit window 18b are transparent to light emitted from the light source 20 and are disposed on the side of the chamber 10, located between the spray plate 14 and the carrier disk 12. In this structure, the concentration of the mixed gas G supplied to the wafer placed on the carrier disk 12 can be directly measured by the measuring light L. When ultraviolet light is used as the measuring light, the entrance window 18a and exit window 18b are preferably made of materials with high ultraviolet transmittance, such as sapphire glass, calcium fluoride, or magnesium fluoride.

[0031] In this specification, light refers not only to visible light, but also includes at least infrared and ultraviolet light, and may include electromagnetic waves of any wavelength. Furthermore, transmittance refers to the internal transmittance of the measurement light L incident on the measurement space 10 Å being high enough to allow for concentration measurement.

[0032] The light source 20 and the photodetector 24 are connected to the processing circuit 28. The processing circuit 28 controls the light source 20 and can determine the concentration of the mixed gas G based on the detection signal from the photodetector 24. The processing circuit 28 is composed of, for example, a processor and memory mounted on a circuit board, and includes a computer program that performs prescribed calculations based on input signals, implemented through a combination of hardware and software.

[0033] The concentration calculation unit of the processing circuit 28 can calculate the absorbance Aλ (=-log10(I / I0)) of wavelength λ based on the detection signal of the photodetector 24. Specifically, the gas concentration C can be calculated based on the Lambert-Beer law shown in the following equation (1). Aλ=-log10(I / I0)=αdC …(1)

[0034] In equation (1) above, I0 is the intensity of the incident light incident into the measurement space, I is the intensity of the light passing through the measurement space, α is the molar absorptivity (m² / mol), d is the light path length (m) within the measurement space, and C is the concentration (mol / m³). The molar absorptivity α is a coefficient that depends on the light-absorbing substance, and its value relative to the measurement wavelength is known in advance. Furthermore, the incident light intensity I0 in the above equation can also be the intensity of the light detected by the photodetector 24 when there is no light-absorbing gas in the measurement space 10A (for example, when it is filled with a non-light-absorbing cleaning gas, or when it is evacuated).

[0035] Furthermore, as mentioned above, the concentration of the gas to be measured in the mixed gas (or the flow ratio of the carrier gas to the gas to be measured) can be determined by taking into account the temperature T and total pressure Pt of the gas in the process chamber. More specifically, for example, as disclosed in Patent Document 2, the concentration measuring device 100 can also determine the gas concentration based on the following equation (2) derived from the Lambert-Beer law, with reference to the outputs of the pressure sensor and the temperature sensor. Cv=(RT / α'dPt)·ln(I0 / I) …(2)

[0036] In the above formula, Cv is the concentration (volume %) of the gas to be measured (representing the absorbent gas) in the gas mixture, α' is the absorptivity of the gas to be measured, Pt is the total gas pressure measurable by a pressure sensor, T is the gas temperature measurable by a temperature sensor, and R is the gas constant. Also, similar to the Lambert-Beer law, d is the light path length in the measurement space, I0 is the incident light intensity, and I is the transmitted light intensity. The absorptivity α' can be determined by pre-measuring the absorbance of a known concentration of absorbent gas flowing through it.

[0037] As described above, light of the wavelength band that the gas can absorb is emitted from the light source 20, and the processing device 28 calculates the absorbance Aλ based on the output of the photodetector 24, thereby obtaining the gas concentration C. In addition to the output of the photodetector 24, the processing device 28 can also calculate the concentration or volume fraction Cv of the gas in the mixed gas based on the measured gas temperature T and the total gas pressure Pt.

[0038] Furthermore, the light path length d within the aforementioned measurement space, in this embodiment, corresponds to the distance between the inner surfaces of the incident window 18a and the exit window 18b in the direction of light propagation, and has been determined through prior measurement or other methods. The light path length d is, for example, set to 200mm to 400mm. However, when the incident window 18a and the exit window 18b are not arranged parallel to each other, the distance between them may vary depending on the position of the light passing through the windows. This will be described in detail later.

[0039] Furthermore, in the concentration measuring apparatus 100 of this embodiment, an incident-side telecentric lens 22 is disposed between the light source 20 and the incident window 18a, and similarly, an exit-side telecentric lens 26 is disposed between the exit window 18b and the photodetector 24. In this dual-telecentric lens system constructed using these telecentric lenses 22 and 26, the imaging magnification does not change with the position of the object (distance from the photodetector 24) in the direction of light travel. As shown in the figure, the measuring light L from the light source 20, as the principal ray, is a surface beam with substantially the same optical path length at each position of the lens, incident on the photodetector 24.

[0040] Furthermore, although this embodiment uses bilateral telecentric lenses as optical elements to form an optical system that achieves a viewing angle of 0° that is independent of the object's position and has a constant magnification, it is not limited to this. As long as the measuring light L can be parallel or substantially non-intersecting, the optical system can be constructed using any optical element (e.g., a parallel light lens, or a lens that converts non-parallel light into near-parallel light). For example, the telecentric lenses 22 and 26 in this embodiment can be the VS-TCM01-180 manufactured by VS Technology Co., Ltd. of Japan.

[0041] Here, the photodetector 24 has a plurality of light-receiving elements (pixels) arranged in a matrix. The plurality of light-receiving elements are, for example, composed of photodiodes, and the photodetector 24 is, for example, composed of a CMOS image sensor or a CCD image sensor. The number of pixels is, for example, 50×50 pixels to 200×200 pixels.

[0042] Using this photodetector 24, the in-plane intensity distribution of the measurement light L received from the light source 20 can be output as a 2D image, for example. Furthermore, since a telecentric lens is used, regardless of the position in the measurement space (distance from the light source 20 or the photodetector 24), the light absorption characteristics within the measurement area with a constant actual field of view can be regarded as a spatially equivalent measurement object for 2D measurement.

[0043] However, the plurality of light-receiving elements constituting the photodetector 24 do not necessarily have to be arranged in a matrix. For example, the pixels can be arranged in a straight line to form a linear sensor. The plurality of light-receiving elements constituting the photodetector 24 can be arranged in any pattern as long as they are placed at different positions on the plane orthogonal to the direction of travel of the measurement light L.

[0044] Furthermore, in Figure 1, for simplicity, the measurement light L is depicted as traveling as parallel light when the telecentric lens magnification is 1x. However, in reality, the measurement light can be either focused or diffused depending on the telecentric lens magnification. For example, when the telecentric lens magnification is 1 / 10, the pixel array size in the photodetector 24 is 3.2mm × 3.2mm. In contrast, regardless of its position in space, the actual field of view is 32mm × 32mm. Therefore, the telecentric lens 22 on the light source side may need to be prepared to be sufficiently larger than the actual field of view size.

[0045] Figure 2 illustrates an example of a captured image of an image sensor constituting the photodetector 24. In this example, the photodetector 24 is configured to detect light passing through the space between the lower surface 14B of the spray plate 14 and the upper surface 12U of the carrier disk 12. Furthermore, the edge line EL corresponds to the position of the side end face of the wafer placed on the carrier disk 12. In this example, the photodetector 24 is configured to measure the gas concentration in the outer peripheral region of the wafer.

[0046] Furthermore, Figure 2 shows the triangular markers M1 and M2 used for position adjustment. Marker M1 is a pair of light-shielding members located on the front side (window side) of the telecentric lens 22 on the light source side, and on the other hand, marker M2 is a pair of light-shielding members located on the rear side (window side) of the telecentric lens 26 on the photodetector side. These markers are the same size. As can be seen from Figure 2, because the imaging magnification is equal by using telecentric lenses, the image sensor can capture images with markers of the same size regardless of the positions of markers M1 and M2.

[0047] Using these marks M1 and M2, the position of the optical system can be appropriately adjusted, and the area clamped by the two side lines SL is set as the concentration measurement range. Furthermore, after the position adjustment of the optical system is completed, the marks M1 and M2 can be removed from the device when the actual concentration measurement is performed.

[0048] Figure 3 is a schematic diagram of the chamber 10 viewed from above, showing the configuration of the concentration measurement lines of the wafer 19 and 2 system placed on the carrier disk 14 as shown in Figure 1. As shown in Figure 3, in this embodiment, as concentration measurement lines, a first measurement line (the actual field of view) R1 is provided, which is formed in such a way that the measurement light L1 passes through the central region of the wafer 19, and a second measurement line R2 is formed in such a way that the measurement light L2 passes through the peripheral region of the wafer 19.

[0049] In the first measurement line R1 and the second measurement line R2, the measurement light L1 and L2 are arranged to pass through the chamber via an entrance window 18a and an exit window 18b, which are sealed and fixed to the opening of the outer wall 11 of the chamber 10. For each measurement line R1 and R2, a light source 20 that emits measurement light incident through the entrance window 18a and a photodetector 24 that receives measurement light emitted through the exit window 18b are provided, thus providing an independent concentration measurement device for each measurement line. Furthermore, the processing circuit 28 (see Figure 1) of each concentration measurement device may be common.

[0050] Furthermore, although omitted in Figure 3, similar to the concentration measuring device 100 shown in Figure 1, each concentration measuring device is equipped with a telecentric lens, and a bilateral telecentric lens system is formed in each measuring line. Also, similar to the concentration measuring device 100 shown in Figure 1, the photodetector 24 is constructed using an image sensor with a pixel array, capable of measuring the concentration distribution in the cross-section of the measuring line. Moreover, for simplicity, each measuring beam L1 and L2 is shown as a thicker dashed line in Figure 3, but in reality, measuring beams L1 and L2 correspond to beams with both horizontal and vertical widths.

[0051] In this structure, in the first measurement line R1, the gas concentration in the central region of the wafer can be measured in two dimensions primarily by means of a measurement beam L1 with widths in both the horizontal and vertical directions. The concentration measurement device of the first measurement line R1 can output, for example, an image, the concentration distribution within a sectional plane (actual field of view) with a specified width in the horizontal and vertical directions of the chamber, based on the output of a photodetector 24 with multiple pixels.

[0052] Furthermore, in the second measurement line R2, the gas concentration in the periphery of the wafer can be measured in two dimensions primarily by means of a measurement beam L2 with widths in both the horizontal and vertical directions. The concentration measurement device of the second measurement line R2 can output, for example, an image, the concentration distribution of a partitioned area with a specified width in the horizontal and vertical directions of the chamber based on the output of the photodetector 24.

[0053] Thus, by performing two-dimensional measurements of the gas concentration in different regions of the wafer within the process chamber, compared to the previous method of using a single light-receiving element to perform one-dimensional concentration measurements through a system of measurement lines, a more detailed understanding of the gas concentration or gas concentration distribution within the chamber can be obtained. This allows for more accurate determination of the supply quantity and easier implementation of appropriate gas supply in applications such as ALD processes, where a specified amount of gas must be supplied within a short period, thereby improving the quality of the manufactured semiconductor devices.

[0054] However, in the second measurement line R2 used for the concentration measurement of the outer periphery of the wafer in the aforementioned two-dimensional measurement, as shown in Figure 3, the optical path length of the measurement light L2, which has a width in the horizontal direction of the chamber, varies depending on its position. This is because the entrance window 18a and the exit window 18b are configured in a non-parallel manner (at an angle of approximately 60°).

[0055] In this situation, the light path length d1 of light passing through the closer window segments (lower line A in the example shown in Figure 3) is relatively small, while the light path length d2 of light passing through the closer window segments (upper line B in the example shown in Figure 3) is relatively large. Furthermore, even at the same gas concentration, the absorbance of light path length d1 is lower, while the absorbance of light path length d2 is higher. This means in the image shown in Figure 2 that the light detected by the left pixel (left line A) has a relatively low output, while the light detected by the right pixel (right line B) has a relatively high output.

[0056] Therefore, in this embodiment, the optical path length d is not set to a constant regardless of the pixel position for density detection. Instead, the optical path length d in the above-mentioned formula (1) or (2) used to calculate the density is changed according to the pixel position. Furthermore, since the window distance does not change in the vertical direction of the chamber, the optical path length in the longitudinal direction (column direction) can be considered constant regardless of the pixel position. Therefore, in this embodiment, the optical path length used for density calculation is changed only according to the pixel's horizontal (row) position.

[0057] For example, in the configuration shown in Figure 3, for pixels in the left column of the effective pixel area, the density is calculated using the shortest optical path length d1 corresponding to their position. Similarly, for pixels in the right column of the effective pixel area, the density is calculated using the longest optical path length d2 corresponding to their position. Furthermore, for pixel columns located between these columns, the density is calculated using the corresponding optical path length d(x) = d1 + (d2 - d1) × (x - 1) / (xm - 1) (where x is the column number and xm is the total number of columns). Thus, by correcting the optical path length according to the left and right positions of the pixel columns, the density can be calculated more accurately in two dimensions.

[0058] Furthermore, this explanation addresses pixel columns with different light path lengths in the left and right positions. However, it's also possible that the different light path lengths occur in the top and bottom positions, not the left and right. In this case, the light path lengths set for each pixel row can be used. For example, the light path lengths corresponding to the top and bottom positions (row numbers) can be used to calculate the density. Alternatively, the density can be calculated using the light path lengths corresponding to the individual positions of specific pixels (e.g., values ​​determined by both row and column numbers). In cases where pixels are not arranged in a matrix, the light path lengths associated with each pixel can also be used.

[0059] Figure 4(a) shows five pixels p1, p2, p3, p4, and p5 at different horizontal positions in the image captured by the image sensor set on the second measurement line R2 shown in Figure 3. Furthermore, the left boundary line A of the effective pixel area shown in Figure 4(a) corresponds to the boundary A on the short light path side of the second measurement line R2 shown in Figure 3, and the right boundary line B of the effective pixel area corresponds to the boundary B on the long light path side of the second measurement line R2 shown in Figure 3.

[0060] Figure 4(b) is a graph showing the relationship between the absorbance (-log10(I / I0)) measured for each of the pixels p1, p2, p3, p4, and p5 shown in Figure 4(a) and the concentration of the gas being measured. Furthermore, the actual optical path length d of the light incident on pixels p1, p2, p3, p4, and p5 within the measurement space is different, being 331.05 mm, 338.42 mm, 346.05 mm, 353.68 mm, and 361.05 mm, respectively.

[0061] As shown in Figure 4(b), the relationship between the measured gas concentration and absorbance is approximately linear in all pixels p1, p2, p3, p4, and p5, consistent with equations (1) and (2) above. However, some deviations can be observed in the relationship between the measured gas concentration and absorbance at different positions in the horizontal direction for pixels p1, p2, p3, p4, and p5. This is because pixels receiving light with a longer actual optical path length within the cavity (e.g., pixel p5) absorb more light, while pixels receiving light with a shorter optical path length within the cavity (e.g., pixel p1) absorb less light. Therefore, even at the same measured gas concentration, different absorbance values ​​will be displayed for each pixel.

[0062] In contrast, as shown in Figure 5, regarding the data in Figure 4(b), if the absorbance is divided by the optical path length d of each pixel, then pixels p1, p2, p3, p4, and p5 will all exhibit the same relationship. In other words, the deviation in the relationship between the pixels shown in Figure 4(a) can be presumed to be based on the difference in optical path length d.

[0063] The results above show that when calculating the concentration based on the light intensity I0 detected by each pixel p1, p2, p3, p4, and p5, if the corresponding light path length d is used for concentration calculation at each pixel, the influence caused by the pixel position can be eliminated, and the concentration can be calculated more accurately at any pixel.

[0064] Thus, by applying optical path length-related corrections to the arranged pixels, the 2D concentration distribution can be measured more accurately. In particular, in the scenario shown in Figure 3(a), the 2D concentration distribution measurement of the wafer periphery of the second measurement line R2 can be performed more accurately. Furthermore, in the first measurement line R1, since the incident window 18a and the exit window 18b are arranged in parallel, the optical path length does not change with the pixel position and therefore optical path length correction is not required.

[0065] Figure 6 illustrates a method for obtaining a higher signal-to-noise ratio (S / N ratio) when using an image sensor to construct a photodetector in a concentration measurement device as described above. In the method shown in Figure 6, pixels with high light intensity of light L are selected from the output of the image sensor (e.g., 140×140 pixels), while pixels with low light intensity are excluded. In this method, the pixels used for concentration measurement are selected within a selection range Rs of a portion of the sensor surface (or sensor section) Im, thus achieving a high S / N ratio. Therefore, even when the light source output tends to be low, such as when ultraviolet light is used as the measurement light, a signal with a high S / N ratio can be obtained.

[0066] Figures 7(a) and (b) illustrate other methods for obtaining a high S / N ratio. In this example, as shown in Figure 7(a), the measurement light L is focused in front of the image sensor using a lens or the like. As shown in Figure 7(b), the focused high-intensity light Lf is irradiated onto a portion of the sensor surface Im. Then, by selectively using the output of pixels within a selected range Rs of this region for concentration measurement, a high S / N ratio is achieved.

[0067] Figure 8 illustrates another method for obtaining a high S / N ratio. In this example, as shown in Figure 6, pixels with high light intensity in the image sensor are selected, and the light intensity is obtained by summing the outputs of pixels within a selected range R of the sensor surface Im. Furthermore, in this case, the incident light intensity is also calculated using the summed value of the corresponding selected pixels. This reduces the output variation of each pixel, achieving a high S / N ratio.

[0068] Figure 9 illustrates another method for achieving a high signal-to-noise ratio (S / N ratio). In this example, the effective area of ​​the sensor surface Im of the image sensor is divided into multiple segments Rd (here, 16 segments), each containing the same number of pixels (e.g., 32×32 pixels), and the average intensity of the pixels in each segment is set to the light intensity of that segment. In this way, a high S / N ratio can be achieved while simultaneously measuring the concentration distribution within the segments.

[0069] The concentration measuring apparatus of the present invention has been described above according to an embodiment, but various modifications are possible. For example, the situation where the difference in light path length occurs due to the non-parallel arrangement of the entrance and exit windows has been explained above, but there are other situations, such as the light source or photodetector being arranged at different heights in the vertical direction, which may also cause changes in the light path length within the measuring space due to other factors. Furthermore, even if the entrance and exit windows are parallel to each other, the light path length may vary depending on the thickness of the entrance or exit windows or the arrangement structure of the chamber. The present invention can be used in any embodiment of a concentration measuring apparatus that uses a photodetector with multiple light-receiving elements, where the light path length varies depending on the light-receiving position, as described above. [Potential for industrial application]

[0070] The concentration measuring device resulting from the embodiments of the present invention is ideally applicable to the determination of the concentration of raw material gases used in semiconductor manufacturing, as well as for the determination of the concentration of various other gases and liquids.

[0071] 2: Gas supply line 4: Exhaust wire 10: Chamber 10A: Measurement Space 12: Carrier disk 14: Sprayer Panel 16: Vacuum pump 18a: Entrance window 18b: Exit Window 19: Wafer 20: Light source 22: Telecentric lens on the incident side 24: Photodetector 26: Telecentric lens on the exit side 28: Processing Circuit 100: Concentration measuring device G: Mixed gas Im: Sensor surface L: Measurement of light L1: Measurement of light L2: Measurement of light Lf: High Intensity Light p1: pixel p2: pixel p3: pixels p4: pixels p5: pixels R1: Measurement Line 1 R2: Second measuring line Rd: Section Rs: Select range

Claims

1. A concentration measuring device comprising: a measuring space connected to a first entrance window and a first exit window, wherein a fluid flows into the space; a first light source emitting measuring light that passes through the first entrance window and enters the measuring space; a first photodetector receiving measuring light that passes through the measuring space and exits through the first exit window; a second entrance window and a second exit window connected to the measuring space; a second light source emitting measuring light that passes through the second entrance window and enters the measuring space; a second photodetector receiving measuring light that passes through the measuring space and exits through the second exit window; and a processing circuit configured to calculate the concentration distribution of the fluid in the measuring space based on the outputs of the first and second photodetectors. The first entrance window and the first exit window are arranged non-parallel, while the second entrance window and the second exit window are arranged parallel. Light emitted from the first light source passes through a region at a relatively edge of the measurement space, and light emitted from the second light source passes through a region at a relatively central area of ​​the measurement space. Both the first and second photodetectors have a sensor section composed of a plurality of light-receiving elements, including at least a first light-receiving element and a second light-receiving element. The optical path length of light reaching the first light-receiving element through the first exit window within the measurement space is the first optical path length, which differs from the optical path length of light reaching the second light-receiving element within the measurement space. The aforementioned processing circuit is configured such that, when calculating the concentration of the fluid based on the output of the aforementioned first light-receiving element, the concentration is calculated using the corresponding first light path length, and when calculating the concentration of the fluid based on the output of the aforementioned second light-receiving element, the concentration is calculated using the corresponding second light path length.

2. The concentration measuring device as described in claim 1, wherein, It also features: a parallel light lens, which is disposed at least between the first light source and the first entrance window or between the first exit window and the first photodetector.

3. The concentration measuring device as described in claim 1, wherein, It also features: a telecentric lens, which is disposed at least between the first light source and the first entrance window or between the first exit window and the first photodetector.

4. The concentration measuring device as described in any of claims 1 to 3, wherein, In the aforementioned sensor section of the first photodetector, the aforementioned plurality of light-receiving elements are arranged in a linear or matrix manner as pixels.

5. The concentration measuring device as described in claim 4, wherein, In the aforementioned sensor section of the first photodetector, the aforementioned plurality of light-receiving elements are arranged in a matrix as pixels. The light path length of the light reaching the light-receiving elements in the column or row of the first pixel within the aforementioned measurement space is the same for each pixel. The light path length of the light reaching the light-receiving elements in the column or row of the second pixel within the aforementioned measurement space is the same for each pixel. However, the light path length of the light reaching the light-receiving elements in the column or row of the first pixel within the aforementioned measurement space is different from the light path length of the light reaching the light-receiving elements in the column or row of the second pixel within the aforementioned measurement space.

6. The concentration measuring apparatus as described in claim 4, wherein, The aforementioned sensor unit is configured to determine the concentration by selectively using the output of a portion of the pixel region.

7. The concentration measuring apparatus as described in claim 4, wherein, It also has a lens that focuses the light emitted through the aforementioned first emission window, and the aforementioned sensor unit is configured to determine the concentration by selectively using the output of a pixel area that irradiates a portion of the focused light.

8. The concentration measuring apparatus as described in claim 4, wherein, The aforementioned sensor unit is configured to calculate the concentration by summing the output of a portion of the pixel area.

9. The concentration measuring apparatus as described in claim 4, wherein, In the aforementioned sensor unit, multiple segments containing multiple pixels are defined, and the density is determined by using the average output of the pixels contained in the segment as the output of the segment.

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