Concentration measuring device

Abstract

A concentration measuring device 100 includes a measurement space 10A which is in contact with an entrance window 18a and an exit window 18b and into which a fluid flows, a light source 20 which emits measurement light L that is caused to enter the measurement space via the entrance window, an optical detector 24 which accepts the measurement light that has passed through the measurement space and has exited via the exit window, and a processing circuit 28 which is configured to calculate the concentration of the fluid, wherein: the optical detector has a sensor portion consisting of a plurality of light receiving elements; the optical path length of light reaching a first light receiving element p1 is different from the optical path length of light reaching a second light receiving element p2; when the concentration of the fluid is to be obtained on the basis of the output of the first light receiving element, the concentration is calculated using a corresponding first optical path length; and when the concentration of the fluid is to be obtained on the basis of the output of the second light receiving element, the concentration is calculated using a corresponding second optical path length.

Description

concentration measuring device

[0001] The present invention relates to a concentration measurement device, and more particularly to a concentration measurement device configured to measure the concentration of a fluid based on the absorbance of light that has passed through the fluid.

[0002] Conventionally, optical concentration measuring devices configured to measure the concentration of source gases such as metal organic compounds (MOs) used in semiconductor processes based on absorbance have been known. One such concentration measuring device measures absorbance by irradiating light of a predetermined wavelength from a light source through an entrance window into a measurement cell through which a fluid flows, and receiving the transmitted light with a light-receiving element. The measured absorbance can be used to determine the concentration of the fluid according to the Beer-Lambert law (see, for example, Patent Document 1).

[0003] Also, a concentration measuring device is known in which an entrance window and an exit window are arranged opposite to each other on the side wall of a process chamber of a plasma CVD device or the like, and the concentration of a gas in the chamber is measured from the absorbance of measurement light that has passed through the chamber. ４ Gas and NO ２ A concentration measurement device configured to measure the concentration of a gas based on absorbance is disclosed.

[0004] International Publication No. 2018 / 021311 International Publication No. 2020 / 085236 Japanese Patent Application Laid-Open No. 2004-138425

[0005] However, in conventional concentration measurement devices, the intensity of light passing through a fluid is measured using a single light-receiving element (such as a photodiode). In this case, although it is possible to measure the overall fluid concentration in the measurement space, there is a problem in that it is difficult to obtain a detailed concentration distribution when the concentration varies within the measurement space, for example, when concentration unevenness occurs in some places due to fluid movement.

[0006] 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 that can measure the fluid concentration in a measurement space in more detail and more accurately.

[0007] A concentration measuring device according to an embodiment of the present invention includes a measurement space that is in contact with an entrance window and an exit window and into which a fluid flows, a light source that emits measurement light that is incident on the measurement space through the entrance window, a photodetector that receives the measurement light that passes through the measurement space and exits through the exit window, and a processing circuit configured to calculate the concentration of the fluid in the measurement space based on an output of the photodetector, wherein the photodetector has a sensor unit configured by a plurality of light-receiving elements, and the plurality of light-receiving elements are a first light-receiving element and a second light-receiving element, and the first light-receiving element The device includes a first light-receiving element and a second light-receiving element, in which a first optical path length, which is the optical path length in the measurement space of light that reaches the light-receiving element, is different from a second optical path length, which is the optical path length in the measurement space of light that reaches a second light-receiving element among the plurality of light-receiving elements, and the processing circuit is configured to, when determining the concentration of a fluid based on the output of the first light-receiving element, calculate the concentration using the corresponding first optical path length, and when determining the concentration of a fluid based on the output of the second light-receiving element, calculate the concentration using the corresponding second optical path length.

[0008] In one embodiment, the concentration measuring device further includes a collimating lens disposed at least either between the light source and the entrance window or between the exit window and the photodetector.

[0009] In one embodiment, the concentration measurement device further includes a telecentric lens disposed at least either between the light source and the entrance window or between the exit window and the photodetector.

[0010] In one embodiment, the entrance window and the exit window are arranged non-parallel.

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

[0012] In one embodiment, the optical path length within the measurement space of light that reaches a light-receiving element included in a column or row of a first pixel is the same regardless of the pixel, the optical path length within the measurement space of light that reaches a light-receiving element included in a column or row of a second pixel is the same regardless of the pixel, and the optical path length within the measurement space of light that reaches a light-receiving element included in a column or row of a first pixel is different from the optical path length within the measurement space of light that reaches a light-receiving element included in a column or row of a second pixel.

[0013] In one embodiment, the sensor section is configured to obtain density by selectively using outputs from some pixel regions.

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

[0015] In one embodiment, the sensor unit is configured to calculate the density by adding up the outputs from some pixel regions.

[0016] In one embodiment, the sensor unit is configured to define a plurality of sections, each section including a plurality of pixels, and to determine the concentration by using the average output of the pixels included in a section as the output of that section.

[0017] According to the concentration measurement device of the embodiment of the present invention, more detailed concentration measurements can be performed with improved accuracy.

[0018] 4( a ) is a schematic diagram showing the configuration of a concentration measurement device according to an embodiment of the present invention; FIG. 4( b ) is an example of an image captured by an image sensor constituting a photodetector included in the concentration measurement device according to an embodiment of the present invention; FIG. 4( a ) is a diagram showing a chamber provided with the concentration measurement device according to an embodiment of the present invention as viewed from above; FIG. 4( a ) shows pixels positioned at different horizontal directions, and FIG. 4( b ) is a graph showing the relationship between the measured gas concentration and absorbance at each pixel; FIG. 4( b ) is a graph showing the relationship between the measured gas concentration and absorbance / d after optical path length correction has been performed on the data of the graph shown in FIG. 4( b ). FIG. 4( b ) is a diagram for explaining a method for achieving a high S / N ratio when performing concentration measurement using an image sensor as a photodetector; FIG. 4( b ) is a diagram for explaining another method for achieving a high S / N ratio when performing concentration measurement using an image sensor as a photodetector; FIG. 4( c ) is a diagram for explaining yet another method for achieving a high S / N ratio when performing concentration measurement using an image sensor as a photodetector; FIG. 4( c ) is a diagram for explaining yet another method for achieving a high S / N ratio when performing concentration measurement using an image sensor as a photodetector.

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments. Also, the following describes a concentration measurement device in which the measurement target is a gas supplied to a process chamber, but in other embodiments, the measurement target may be a fluid other than a gas, such as a liquid.

[0020] 1 is a diagram showing an example of the configuration of a concentration measurement apparatus 100 according to this embodiment. The concentration measurement apparatus 100 is configured to measure the concentration of a gas supplied to a chamber 10 (measurement space 10A) of a semiconductor manufacturing apparatus via a gas supply line 2.

[0021] Inside the chamber 10, there are provided a susceptor 12 for placing a semiconductor device wafer (not shown) thereon, and a shower plate 14 disposed above the susceptor 12. The shower plate 14 and the susceptor 12 are disposed parallel to each other with a predetermined gap therebetween. The shower plate 14 also has a large number of holes formed therein through which supplied gas passes.

[0022] The gas introduced into the chamber 10 is diffused by the shower plate 14 and supplied substantially uniformly onto the wafer. An exhaust line 4 equipped with a vacuum pump 16 is connected to the chamber 10 below the susceptor 12, and excess gas within the chamber 10 is exhausted. The vacuum pump 16 is also used to evacuate the chamber 10.

[0023] Furthermore, pressure and temperature sensors (not shown) are attached to the chamber 10, allowing the pressure and temperature of the gas within the chamber 10 to be measured. The pressure sensor may be, for example, a silicon single crystal pressure sensor having a pressure-sensitive diaphragm with a strain gauge, or a capacitance manometer. The temperature sensor may be, for example, a thermocouple, a thermistor, or a platinum resistance thermometer.

[0024] A mixed gas G having a desired concentration and a flow rate controlled by a flow rate control device (not shown) is supplied from the gas supply line 2. The mixed gas G may be, for example, N ２ a carrier gas such as NO ２ The gas is produced by mixing a raw material gas such as a nitrogen gas or a nitrogen gas at an arbitrary mixing ratio (or flow rate ratio), and the concentration is adjusted as desired. As the flow rate control device, for example, a known pressure-type flow rate control device described in Patent Document 3 can be used. The pressure-type flow rate control device has a throttle section and a control valve, and is configured to control the flow rate by adjusting the opening of the control valve based on the pressure upstream of the throttle section. A thermal mass flow controller (MFC) may also be used as the flow rate control device.

[0025] The concentration measuring device 100 measures a measurement gas (e.g., NO ) in a mixed gas G that has flowed into a measurement space 10A in a chamber 10. ２ The concentration measuring device 100 is configured to measure the concentration of a mixed gas (gas) based on the absorbance of measurement light L that has passed through the mixed gas G. To this end, the concentration measuring device 100 includes a light source 20 that emits light that is incident into the chamber 10 through an entrance window 18a provided on one side of the chamber 10, and a photodetector 24 that receives the light that has exited through an exit window 18b provided on the other side of the chamber 10.

[0026] The measurement light L emitted from the light source 20 may pass through the measurement space 10A as shown in the figure and head directly toward the photodetector 24, or may be reflected once or multiple times by a reflecting member such as a mirror before heading toward the photodetector 24. When a reflecting member is used, 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 may be arranged in any position as long as they are in contact with the measurement space 10A.

[0027] The light source 20 can emit light having a wavelength that can be absorbed by the measurement gas as measurement light L. ２ NO in gas ２ When measuring the concentration of a gas, light with a wavelength of, for example, 350 to 550 nm, particularly light with a wavelength around 405 nm, which has high absorbance, can be used as the light source. When measuring the concentration of organometallic gases such as TEOS (tetraethyl orthosilicate), TMGa (trimethylgallium), and TMAl (trimethylaluminum), ultraviolet light with a wavelength of, for example, 200 to 400 nm is used as the measurement light. It goes without saying that the wavelength of the measurement light L can be selected arbitrarily depending on the absorption characteristics of the gas to be measured, such as the infrared range with a wavelength of 1 μm or more. It is known that common carrier gases such as nitrogen gas and argon gas do not absorb light with a wavelength of approximately 100 nm or more.

[0028] An LED or a laser diode can be used as a light-emitting element that emits light of the above wavelengths. The light source 20 may be configured to switch between light of different wavelengths emitted from multiple light-emitting elements, or to combine and output light of different wavelengths. When switching between light of different wavelengths, one of the light beams may be used as light in an absorption wavelength band for concentration measurement, and the other may be used as light in a non-absorption wavelength band for detecting abnormalities in the optical system.

[0029] Furthermore, the light source 20 may be configured to emit the measurement light L continuously or in a pulsed manner. The light source 20 may be configured to emit light of the same wavelength continuously or in a pulsed manner, or may be configured to change the emission wavelength over time. The light emission mode of the light source 20 is not particularly limited as long as an appropriate measurement light L is emitted. Furthermore, one photodetector 24 may be provided for multiple light sources 20, or multiple photodetectors 24 may be provided for one light source 20.

[0030] The entrance window 18a and the exit window 18b are translucent to the light emitted from the light source 20 and are provided on the side of the chamber 10 at a position between the shower plate 14 and the susceptor 12. In this configuration, the concentration of the mixed gas G supplied to the wafer placed on the susceptor 12 can be directly measured by the measurement light L. When ultraviolet light is used as the measurement light, the entrance window 18a and the exit window 18b are preferably made of a material 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 to at least infrared and ultraviolet light, and may include electromagnetic waves of any wavelength. Furthermore, "translucency" means that the internal transmittance of the measurement light L incident on the measurement space 10A is sufficiently high to enable concentration measurement.

[0032] The light source 20 and the photodetector 24 are connected to a processing circuit 28, which controls the light source 20 and can measure the concentration of the mixed gas G based on the detection signal of the photodetector 24. The processing circuit 28 is configured, for example, by a processor and memory provided 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.

[0033] The concentration calculation unit of the processing circuit 28 calculates the absorbance Aλ (=−log 10 (I / I ０Specifically, the gas concentration C can be calculated based on the Beer-Lambert law shown in the following equation (1): Aλ=−log 10 (I / I0)=αdC...(1)

[0034] In the above formula (1), I0 is the intensity of the incident light incident on the measurement space, I is the intensity of the light passing through the measurement space, and α is the molar absorption coefficient (m 2 / mol), d is the optical path length in the measurement space (m), and C is the concentration (mol / m 3 ) The molar extinction coefficient α is a coefficient determined by the light-absorbing substance, and its value for the measurement light wavelength is known in advance. Note that the incident light intensity I in the above equation may be the intensity of light detected by the photodetector 24 when no light-absorbing gas is present in the measurement space 10A (for example, when the measurement space 10A is filled with a non-light-absorbing purge gas or when a vacuum is evacuated).

[0035] Furthermore, as described above, the concentration of the measurement gas in the mixed gas (or the flow rate ratio of the carrier gas to the measurement gas) can be determined by taking into consideration the temperature T and total pressure Pt of the gas in the process chamber. More specifically, as disclosed in Patent Document 2, for example, the concentration measuring device 100 can determine the gas concentration based on the following equation (2), which is an extension of the Lambert-Beer equation, by also referring to the outputs of the pressure sensor and the temperature sensor: Cv=(RT / α'dPt)·ln(I ０ / I) ...(2)

[0036] In the above formula, Cv is the concentration (volume %) of the measurement gas (gas that exhibits light absorption) in the mixed gas, α' is the absorption coefficient of the measurement gas, Pt is the total gas pressure that can be measured by the pressure sensor, T is the gas temperature that can be measured by the temperature sensor, and R is the gas constant. Also, as in the Beer-Lambert law, d is the optical path length in the measurement space, and I ０ is the incident light intensity, and I is the transmitted light intensity. The absorption coefficient α' can be obtained in advance by measuring the absorbance when a light-absorbing gas of a known concentration is flowed.

[0037] In this manner, light source 20 emits light in a wavelength band that can be absorbed by the measurement gas, and processing device 28 can determine absorbance Aλ and, therefore, gas concentration C based on the output of photodetector 24. Furthermore, processing device 28 can determine the concentration or volume fraction Cv of the measurement gas in the mixed gas based on the measured gas temperature T and gas total pressure Pt in addition to the output of photodetector 24.

[0038] In this embodiment, the optical path length d within the measurement space corresponds to the distance between the inner surfaces of the entrance window 18a and the exit window 18b in the light propagation direction, and is determined in advance by measurement or the like. The optical path length d is set to, for example, 200 mm to 400 mm. However, if the entrance window 18a and the exit window 18b are arranged non-parallel, the distance between them may vary depending on the position on the window through which the light passes. Such an embodiment will be described later.

[0039] Furthermore, in the concentration measuring device 100 of this embodiment, an entrance-side telecentric lens 22 is disposed between the light source 20 and the entrance window 18a, and similarly, an exit-side telecentric lens 26 is disposed between the exit window 18b and the photodetector 24. In a double-telecentric lens system configured using these telecentric lenses 22, 26, the imaging magnification does not change depending on the position of the object in the light traveling direction (the distance from the photodetector 24). As shown in the figure, the measurement light L from the light source 20 enters the photodetector 24 as a planar light beam whose chief ray has substantially the same optical path length regardless of the position of the lens.

[0040] In this embodiment, the optical system is formed using a double-telecentric lens as the optical element that achieves a 0° angle of view, which provides a constant imaging magnification regardless of the object position, but this is not limited to this. As long as parallel light or light whose rays do not substantially intersect is obtained as the measurement light L, the optical system can be configured using any optical element (for example, a parallel light lens or a lens that converts light that is not parallel but is close to parallel). For example, the telecentric lenses 22 and 26 in this embodiment can be a VS-TCM01-180 manufactured by VS Technology.

[0041] The photodetector 24 has a plurality of light-receiving elements (pixels) arranged in a matrix. Each of the light-receiving elements is formed, for example, by a photodiode, and the photodetector 24 is formed, for example, by a CMOS image sensor or a CCD image sensor. The number of pixels used is, for example, 50 x 50 to 200 x 200.

[0042] By using such a photodetector 24, it is possible to output the in-plane intensity distribution of the measurement light L received from the light source 20 as, for example, a two-dimensional image. Furthermore, because a telecentric lens is used, it is possible to measure the absorption characteristics in a measurement region with a constant size of the actual field of view two-dimensionally as spatially equivalent characteristics, regardless of the position in the measurement space (the distance from the light source 20 or the photodetector 24).

[0043] However, the multiple light-receiving elements constituting the photodetector 24 do not necessarily have to be arranged in a matrix, and for example, the pixels may be arranged in a linear fashion to form a line sensor. The multiple light-receiving elements constituting the photodetector 24 may be arranged in any manner as long as they are arranged at different positions on a plane perpendicular to the traveling direction of the measurement light L.

[0044] 1 shows the measurement light L as traveling as parallel light when the telecentric lens magnification is 1 for simplicity, but in reality, measurement light that is generally converged or diffused depending on the telecentric lens magnification may be used. For example, when the telecentric lens magnification is 1 / 10, the pixel array size in the photodetector 24 is 3.2 mm × 3.2 mm, while the size of the actual field of view is 32 mm × 32 mm regardless of the position in space, and it may be necessary to prepare a telecentric lens 22 on the light source side that is sufficiently larger than the actual field of view size.

[0045] 2 shows an example of an image captured by an image sensor constituting the photodetector 24. In this example, the photodetector 24 is disposed so as to detect light that has passed through the space between the lower surface 14B of the shower plate 14 and the upper surface 12U of the susceptor 12. The edge line EL corresponds to the position of the side edge of the wafer placed on the susceptor 12, and in this example, the photodetector 24 is disposed so as to be able to measure the gas concentration in the outer peripheral region of the wafer.

[0046] 2 also shows triangular marks M1 and M2 for position adjustment. Mark M1 is a pair of light-blocking members provided in front of (on the window side of) the telecentric lens 22 on the light source side, while mark M2 is a pair of light-blocking members provided on the rear of (on the window side of) the telecentric lens 26 on the photodetector side, and these marks are the same size. As can be seen from FIG. 2, because the imaging magnification is made the same using the telecentric lens, the image sensor can capture both marks of the same size regardless of the positions of marks M1 and M2.

[0047] By using these marks M1 and M2, the position of the optical system can be adjusted appropriately, and here the area between the side lines SL on both sides is set as the density measurement range. Note that after completing the position adjustment of the optical system, when actually performing density measurement, these marks M1 and M2 may be removed from the device.

[0048] Fig. 3 is a schematic diagram of the chamber 10 as viewed from above, showing the wafer 19 placed on the susceptor 14 shown in Fig. 1 and the arrangement of two concentration measurement lines. As shown in Fig. 3, in this embodiment, the concentration measurement lines include a first measurement line (observed actual field of view area) R1 formed so that measurement light L1 passes through the central area of ​​the wafer 19, and a second measurement line R2 formed so that measurement light L2 passes through the peripheral area of ​​the wafer 19.

[0049] In the first measurement line R1 and the second measurement line R2, measurement light beams L1 and L2 pass through the chamber 10 through entrance and exit windows 18a and 18b, respectively, which are arranged to seal openings in the outer wall 11 of the chamber 10. Each measurement line R1 and R2 is provided with a light source 20 that emits measurement light entering through the entrance window 18a and a photodetector 24 that receives measurement light exiting through the exit window 18b, and a separate concentration measurement device is provided for each measurement line. The processing circuit 28 (see FIG. 1) for each concentration measurement device may be shared.

[0050] Although not shown in Fig. 3, a telecentric lens is disposed in each concentration measurement device, similar to the concentration measurement device 100 shown in Fig. 1, forming a bilateral telecentric lens system in each measurement line. Similarly to the concentration measurement device 100 shown in Fig. 1, the photodetector 24 is configured using an image sensor with a pixel array, enabling measurement of the concentration distribution in the cross section of the measurement line. For simplification, each measurement light beam L1, L2 is shown by a single thick dashed line in Fig. 3, but in reality, the measurement light beams L1, L2 correspond to light beams having vertical and horizontal widths.

[0051] In this configuration, the first measurement line R1 can measure the gas concentration mainly in the central region of the wafer two-dimensionally using the measurement light L1 having a width in both the vertical and horizontal directions. The concentration measurement device of the first measurement line R1 can output, for example, as an image, the concentration distribution in a partitioned area (field of view) having a predetermined width in the horizontal and vertical directions of the chamber based on the output of the photodetector 24 having multiple pixels.

[0052] The second measurement line R2 can measure the gas concentration mainly in the wafer peripheral region two-dimensionally using the measurement light L2, which has a width in both the vertical and horizontal directions. The concentration measuring device of the second measurement line R2 can also output, for example, an image of the concentration distribution in a partitioned area having a predetermined width in the horizontal and vertical directions of the chamber based on the output of the photodetector 24.

[0053] In this way, by measuring the gas concentration in different regions of the wafer in a process chamber in two dimensions, the gas concentration or gas concentration distribution in the chamber can be known in more detail than in the conventional method of measuring the concentration in one dimension using a single light-receiving element in a single measurement line. This makes it easier to obtain an appropriate gas supply by more accurately determining the supply amount, even in applications that require a predetermined amount of gas to be supplied in a short period of time, such as an ALD process, and can improve the quality of the semiconductor devices manufactured.

[0054] However, in the second measurement line R2 for two-dimensionally measuring the concentration in the wafer peripheral region, the optical path length within the chamber of the measurement light L2, which has a width in the horizontal direction of the chamber, varies depending on the location, as shown in Figure 3. This is because the entrance window 18a and the exit window 18b are arranged non-parallel (here, at an angle of about 60°).

[0055] In this case, the optical path length d1 of light passing through the portion where the inter-window distance is closer (lower line A in the example shown in FIG. 3 ) is relatively small, and the optical path length d2 of light passing through the portion where the inter-window distance is even closer (upper line B in the example shown in FIG. 3 ) is relatively large. Even for the same gas concentration, the absorbance at optical path length d1 is low and the absorbance at optical path length d2 is high. This means that in the captured image shown in FIG. 2 , the light detected by the pixel on the left (left line A) has a relatively low output, and the light detected by the pixel on the right (right line B) has a relatively high output.

[0056] Therefore, in this embodiment, instead of detecting the concentration while assuming that the optical path length d is constant regardless of the pixel position, the optical path length d in the above calculation formula (1) or (2) for calculating the concentration is changed depending on the pixel position. Note that, since the distance between the windows does not change in the vertical direction of the chamber, the optical path length can be considered to be constant in the vertical direction (column direction) regardless of the pixel position. Therefore, in this embodiment, the optical path length used for calculating the concentration is changed only in accordance with the horizontal (row direction) position of the pixel.

[0057] For example, in the embodiment shown in Figure 3, for pixels in the leftmost column within the effective pixel area, the density is calculated using the shortest optical path length d1 corresponding to that position. For pixels in the rightmost column within the effective pixel area, the density is calculated using the longest optical path length d2 corresponding to that position. For pixel columns located between these, 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) corresponding to the left and right positions (column numbers). By correcting the optical path length in this way according to the left and right positions of the pixel columns, the density can be calculated more accurately in two dimensions.

[0058] Although the present description concerns pixel rows in which the optical path length differs between left and right positions, there are also cases in which the optical path length differs between vertical positions rather than horizontal positions of the pixels. In such cases, an optical path length set for each pixel row is used, and for example, the density may be calculated using the corresponding optical path length corresponding to the vertical position (row number). Alternatively, the density may be calculated using the corresponding optical path length at the position of each specific pixel (for example, a value determined by both the row number and the column number), or in cases in which the pixels are not arranged in a matrix, the optical path length associated with each pixel may be used.

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

[0060] FIG. 4B shows the absorbance (-log 10 (I / I ０10 is a graph showing the relationship between the measured gas concentration and the optical path length d of the light incident on pixels p1, p2, p3, p4, and p5 in the measurement space, which are actually different from each other, i.e., 331.05 mm, 338.42 mm, 346.05 mm, 353.68 mm, and 361.05 mm.

[0061] As can be seen from FIG. 4( b), the relationship between the measured gas concentration and absorbance is generally linear for all pixels p1, p2, p3, p4, and p5, and this result conforms to the above-described equations (1) and (2). However, it can be observed that the relationship between the measured gas concentration and absorbance for pixels p1, p2, p3, p4, and p5 at different horizontal positions is slightly different. This is because more absorbed light reaches a pixel that receives light with a relatively long optical path length within the chamber (e.g., pixel p5), while less absorbed light reaches a pixel that receives light with a relatively short optical path length within the chamber (e.g., pixel p1). As a result, even when the measured gas concentration is the same, each pixel exhibits a different absorbance.

[0062] In contrast, as shown in Fig. 5, when the absorbance of the data shown in Fig. 4(b) is divided by the optical path length d corresponding to each pixel, the same relationship is obtained for all of pixels p1, p2, p3, p4, and p5. In other words, it can be inferred that the deviation in the relationship between the pixels shown in Fig. 4(a) is caused by the difference in the optical path length d.

[0063] From the above results, the light intensity I detected at each pixel p1, p2, p3, p4, and p5 is ０ When calculating the density based on the above, if the density calculation is performed using the optical path length d corresponding to each pixel, it is possible to eliminate the influence of the pixel position and obtain the density of each pixel more accurately.

[0064] In this way, by correcting the optical path length for the arranged pixels, it is possible to measure the two-dimensional concentration distribution more accurately. In particular, in the embodiment shown in Figure 3(a), it is possible to more accurately measure the two-dimensional concentration distribution at the outer periphery of the wafer along the second measurement line R2. Note that in the first measurement line R1, entrance window 18a and exit window 18b are arranged in parallel, and the optical path length is considered to be constant regardless of pixel position, so optical path length correction is not necessary.

[0065] FIG. 6 is a diagram illustrating a method for achieving a higher S / N ratio (signal-to-noise ratio) when the photodetector of a concentration measuring device is configured using an image sensor as described above. In the embodiment shown in FIG. 6, pixels with a high received intensity of light L are selected from the output of an image sensor (e.g., 140 × 140 pixels), and pixels with a low received intensity are excluded. In this method, the pixels used for concentration measurement are selected from pixels within a selection range Rs, a portion of the sensor surface (or sensor unit) Im, thereby achieving a high S / N ratio. This makes it possible to obtain a signal with a high S / N ratio even when the light source output tends to be relatively low, such as when ultraviolet light is used as the measurement light.

[0066] 7A and 7B are diagrams illustrating another method for achieving a high S / N ratio. In this embodiment, as shown in FIG. 7A, measurement light L is focused using a lens or the like in front of the image sensor, and as shown in FIG. 7B, the focused high-intensity light Lf is irradiated onto a partial area of ​​the sensor surface Im. Then, a high S / N ratio is achieved by selectively using the output of pixels in a selected range Rs in this area for density measurement.

[0067] 8 is a diagram illustrating yet another method for achieving a high S / N ratio. In this embodiment, as shown in FIG. 6, pixels with high light receiving intensity are selected in the image sensor, and the light intensity is obtained by adding the outputs of pixels within a selected range R on the sensor surface Im. In this case, the incident light intensity is also calculated using the added value of the corresponding selected pixels. This reduces output variation from pixel to pixel, achieving a high S / N ratio.

[0068] 9 is a diagram illustrating yet another method for achieving a high S / N ratio. In this embodiment, the effective area of ​​the sensor surface Im of the image sensor is divided into multiple sections Rd (16 sections in this example), each of which includes the same number of pixels (e.g., 32 × 32 pixels), and the average intensity of the pixels in each section is set as the received light intensity for that section. In this way, it is possible to measure the density distribution in the section while achieving a high S / N ratio.

[0069] The concentration measurement device according to the embodiment of the present invention has been described above, but various modifications are possible. For example, while the above describes a configuration in which the difference in optical path length occurs due to the non-parallel arrangement of the entrance and exit windows, other factors may also cause the optical path length within the measurement space to change, such as when the light source and photodetector are located at different vertical heights. Furthermore, even when the entrance and exit windows are parallel to each other, the optical path length may change depending on the thickness of the entrance and exit windows and the installation structure of the window in the chamber. The present invention can be utilized in any configuration of a concentration measurement device that uses a photodetector having multiple light-receiving elements with different optical path lengths depending on the light-receiving position, as described above.

[0070] The concentration measuring device according to the embodiment of the present invention is suitably used for measuring the concentration of source gases used in semiconductor manufacturing, as well as for measuring the concentrations of various other gases and liquids.

[0071] 2 Gas supply line 4 Exhaust line 10 Chamber 10A Measurement space 12 Susceptor 14 Shower plate 16 Vacuum pump 18a Incident window 18b Exit window 19 Wafer 20 Light source 22 Incident side telecentric lens 24 Photodetector 26 Exit side telecentric lens 28 Processing circuit L, L1, L2 Measurement light R1 First measurement line R2 Second measurement line p1, p2, p3, p4, p5 Pixel 100 Concentration measurement device

Claims

1. A concentration measuring device having: a measurement space adjacent to an entrance window and an exit window, into which a fluid flows; a light source that emits measurement light that is incident into the measurement space through the entrance window; a photodetector that receives the measurement light that passes through the measurement space and exits through the exit window; and a processing circuit configured to calculate the concentration of the fluid in the measurement space based on the output of the photodetector, wherein the photodetector has a sensor unit composed of a plurality of light-receiving elements, and the plurality of light-receiving elements include at least a first light-receiving element and a second light-receiving element, and a first optical path length that is the optical path length in the measurement space of light that reaches the first light-receiving element of the plurality of light-receiving elements is different from a second optical path length that is the optical path length in the measurement space of light that reaches the second light-receiving element of the plurality of light-receiving elements, A concentration measuring device wherein the processing circuit is configured to calculate the concentration using the corresponding first optical path length when determining the concentration of a fluid based on the output of the first light receiving element, and to calculate the concentration using the corresponding second optical path length when determining the concentration of a fluid based on the output of the second light receiving element.

2. The concentration measuring device according to claim 1, further comprising a collimating lens disposed at least between said light source and said entrance window or between said exit window and said photodetector.

3. The concentration measuring device according to claim 1, further comprising a telecentric lens disposed at least between said light source and said entrance window or between said exit window and said photodetector.

4. The concentration measuring device according to any one of claims 1 to 3, wherein the entrance window and the exit window are arranged non-parallel.

5. The concentration measuring device according to any one of claims 1 to 3, wherein the plurality of light receiving elements are arranged as pixels in a line or matrix in the sensor section of the photodetector.

6. A concentration measuring device according to claim 5, wherein in the sensor section of the photodetector, the plurality of light receiving elements are arranged in a matrix as pixels, the optical path length within the measurement space of light reaching the light receiving elements included in a first pixel column or row is the same regardless of the pixel, the optical path length within the measurement space of light reaching the light receiving elements included in a second pixel column or row is the same regardless of the pixel, and the optical path length within the measurement space of light reaching the light receiving elements included in the first pixel column or row is different from the optical path length within the measurement space of light reaching the light receiving elements included in the second pixel column or row.

7. The concentration measuring device according to claim 5, wherein the sensor section is configured to obtain the concentration by selectively using the output from a portion of the pixel region.

8. A concentration measuring device as described in claim 5, further comprising a lens for focusing the light emitted through the exit window, and configured to determine the concentration by selectively using the output of a portion of the pixel area irradiated with the focused light in the sensor section.

9. The concentration measuring device according to claim 5, wherein the sensor section is configured to add up outputs from some pixel regions to determine the concentration.

10. A concentration measuring device as described in claim 5, wherein the sensor section defines a plurality of sections, each containing a plurality of pixels, and the concentration is calculated by using the average output of the pixels contained in a section as the output of that section.

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