Gas concentration sensor and method of using same

Abstract

The optical gas concentration sensor includes a sample cell having an inlet port and an outlet port through which gas can pass, a light source configured to emit light into the interior of the sample cell, a photodetector disposed outside the sample cell, and an optical waveguide assembly optically coupling the interior of the sample cell to the detector. The optical waveguide assembly includes a first optical waveguide coupled to the sample cell, a second optical waveguide coupled to the detector, and an optical coupler optically coupling the first optical waveguide to the second optical waveguide. The first optical waveguide has optical transmission characteristics different from those of the second optical waveguide at wavelengths within the wavelength range of 1.5 μm to 18 μm.

Description

[Technical Field]

[0001] background I.Technical field FIELD OF THE INVENTION Embodiments of the present invention relate generally to measuring gas concentrations, and more particularly to measuring the concentration of precursors in a carrier gas. [Background technology]

[0002] II. Background In semiconductor manufacturing processes, various liquid or solid materials are gasified by heating to form material gases. These material gases are then introduced into a vacuum chamber, for example, during chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes. Some of these chemical processes utilize optical gas concentration measurement sensors, such as non-dispersive infrared (NDIR) gas concentration sensors, to monitor gas concentrations.

[0003] A typical NDIR gas concentration sensor includes a gas sample cell, an infrared (IR) light source, an IR detector, and an electronic assembly that receives information from the IR detector. The IR light source emits light that passes through the gas sample cell to the IR detector, and variations in the light transmitted from the IR light source to the IR detector due to absorption by the sample gas can be used to estimate the concentration of the gas in the gas sample cell.

[0004] However, high temperature environments, such as those found in many CVD and ALD processes, can significantly limit the lifetime of such NDIR gas concentration sensors, as well as many other types of gas sensors, because many of the electronic components experience a rapid decrease in lifetime when exposed to temperatures above 100° C. (e.g., at or near 200° C.). Additionally, the performance stability of conventional IR detectors typically deteriorates with increasing temperature, especially above 100° C. Furthermore, electronic components capable of operating at temperatures above 100° C. can be undesirably expensive.

[0005] Furthermore, conventional NDIR gas concentration sensors (and other conventional binary gas sensors, such as ultrasonic sensors) are susceptible to environmental fluctuations and long-term drift factors (e.g., window contamination over time). Also, some precursor gases degrade over time, making it impossible to distinguish between degradation by-products using such conventional NDIR or binary gas sensors.

[0006] Therefore, there is a need in the art for a new optical gas concentration sensor that solves some of the current problems, particularly for use in measuring precursor gas concentrations in high temperature environments. Summary of the Invention [Problem to be solved by the invention]

[0007] overview One embodiment of the present invention can be broadly characterized as an optical gas concentration sensor including a sample cell having an inlet port and an outlet port through which gas can pass, a light source configured to emit light into the interior of the sample cell, a photodetector disposed external to the sample cell, and an optical waveguide assembly optically coupling the interior of the sample cell to the detector. The optical waveguide assembly includes a first optical waveguide coupled to the sample cell, a second optical waveguide coupled to the detector, and an optical coupler optically coupling the first optical waveguide to the second optical waveguide. The first optical waveguide has optical transmission characteristics different from those of the second optical waveguide at wavelengths within a wavelength range of 1.5 μm to 18 μm. [Brief explanation of the drawings]

[0008] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 shows a schematic diagram of an optical gas concentration sensor according to one embodiment of the present invention.

[0009] [Figure 2] FIG. 2 shows a schematic diagram of the light source shown in FIG. 1, according to one embodiment of the present invention.

[0010] [Figure 3] 3 and 10 show schematic diagrams of the detector shown in FIG. 1 according to an embodiment of the present invention.

[0011] [Figure 4] FIG. 4 shows a schematic diagram of the filter assembly shown in FIG. 3, according to one embodiment of the present invention.

[0012] [Figure 5] FIG. 5 shows a graph of the radiance detectable by the detector shown in FIG. 3 versus wavelength.

[0013] [Figure 6] FIG. 6 shows a graph of the absorption spectra of different materials at different wavelengths.

[0014] [Figure 7] FIG. 7 shows a graph of the output of a conventional NDIR gas concentration sensor as a function of time.

[0015] [Figure 8] FIG. 8 shows a graph of the output of the gas concentration sensor shown in FIG. 1 as a function of time.

[0016] [Figure 9] FIG. 9 shows a schematic diagram of a system into which the housing shown in FIG. 1 may be incorporated, according to one embodiment of the present invention. [Figure 10] 3 and 10 show schematic diagrams of the detector shown in FIG. 1 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Detailed Description Examples of embodiments will now be described with reference to the accompanying drawings, in which, unless explicitly stated, the sizes, positions, etc. of components, features, elements, etc., as well as distances between them, are not necessarily drawn to scale and are exaggerated for clarity.

[0018] The terms used in the specification are for the purpose of describing particular exemplary embodiments only and are not intended to be limiting. As used herein, the singular is intended to include the plural unless the content clearly dictates otherwise. Furthermore, it should be understood that the terms "comprises" and / or "comprising," when used herein, identify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise specified, when a range of values ​​is described, the range includes both the upper and lower limits of the range, as well as any subranges therebetween. Unless otherwise indicated, terms such as "first" and "second" are used merely to distinguish elements from one another. For example, one node may be referred to as a "first node," and similarly, another node may be referred to as a "second node," or vice versa. Section headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described.

[0019] Unless otherwise indicated, terms such as "about," "approximately," and the like mean that the amount, size, composition, parameter, and other quantities and characteristics do not and need not correspond to exact values, but may be approximated and / or may be larger or smaller, as appropriate, to reflect tolerances, conversion factors, rounding, measurement error, and the like, and other factors known to those of ordinary skill in the art.

[0020] Unless otherwise indicated, spatially relative terms such as "below," "down," "lower," "upper," and "above" may be used herein for ease of description when describing the relationship of an element or feature to other elements or features, as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations in addition to those depicted in the figures. For example, an element described as being "below" or "below" another element or feature would be oriented "above" the other element or feature if the object in the figure were inverted. Thus, the exemplary term "below" can encompass both an orientation of above and below. When an object is oriented in another way (e.g., rotated 90 degrees or at another orientation), the spatially relative descriptors used herein can be interpreted accordingly.

[0021] Like numbers refer to like elements throughout the drawings, and thus, the same or similar numbers may be described with reference to other drawings even if they are not mentioned or described in the corresponding drawing, and elements without a reference number may be described with reference to other drawings.

[0022] It will be understood that many different forms and embodiments are possible without departing from the spirit and teachings of this disclosure, and that this disclosure should not be construed as limited to the example embodiments set forth herein. Rather, these examples and embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0023] FIG. 1 shows a schematic diagram of an optical gas concentration sensor according to one embodiment of the present invention.

[0024] 1, an optical gas concentration sensor, such as sensor 100, may be provided within an insulated housing 102. Sensor 100 may include a gas sample cell 104 located within insulated housing 102 and may have one or more optical couplers (e.g., first optical coupler 106 and second optical coupler 108) and one or more gas flow ports (e.g., inlet gas flow port 110 and outlet gas flow port 112).

[0025] As configured as described above, the gas sample cell 104 may be configured to receive a gas, such as a high-temperature process gas (e.g., referred to herein simply as “gas,” which may be a gas mixture including a carrier gas and one or more precursor gases), through the inlet gas flow port 110 and exhaust the gas through the outlet gas flow port 112. When the gas is flowing through the sample cell 104, the temperature within the housing 102 typically exceeds 100° C. (e.g., above about 120° C., 150° C., 200° C., 220° C., etc., or any temperature between these values). Although not shown, a temperature control element (e.g., a heater) may be provided (e.g., within the housing) to heat the interior of the housing 102. Operation of the temperature control element may be controlled by a thermostat (also not shown) to maintain the interior of the housing at a constant or substantially constant temperature. Maintaining at least a substantially constant temperature within the housing 102 facilitates consistent operation of the sensor 100.

[0026] The enclosure 102 itself can be mounted at any suitable or desired location along a line for transporting precursor gases to a chamber where CVD or ALD is to be performed. For example, FIG. 9 schematically illustrates that the enclosure 102 can be mounted within a gas cabinet 900, within which a precursor ampoule 902 is located. The precursor ampoule 902 can be mounted in any suitable manner known in the art (e.g., the precursor ampoule 902 can be coupled to a carrier gas input line 904 and a precursor gas outlet line 906). In this case, the enclosure 102 can be positioned such that the gas sample cell 104 is in fluid communication with the precursor gas overview line 906 via the inlet gas flow port 110 and outlet gas flow port 112 described above.

[0027] Additionally or alternatively, the housing 102 may be located outside the gas cabinet 900 at a location upstream of the precursor gas supply switch 908 (e.g., in fluid communication with the precursor gas outlet 906). In this case, the housing 102 may be positioned such that the gas sample cell 104 is in fluid communication with the precursor gas summary line 906 via the inlet gas flow port 110 and outlet gas flow port 112 described above.

[0028] Additionally or alternatively, the housing 102 may be positioned outside the gas cabinet 900 at a location downstream of the precursor gas supply switch 908. For example, the housing 102 may be positioned such that the gas sample cell 104 is in fluid communication with the precursor gas supply line 912 via the inlet gas flow port 110 and outlet gas flow port 112 described above.

[0029] 1, the sensor 100 may also include a light source 114, a light detector 116, an analyzer 118, and a controller 120. The housing 102 is constructed from one or more insulating materials to prevent heat transfer from the interior of the housing 102 (e.g., where the light detector 116, the analyzer 118, and the controller 120 are located) to areas outside the housing 102.

[0030] Light source 114 may be located within sample cell 104 (e.g., after second optical coupler 108) and may be capable of emitting light into gas sample cell 104 via second optical coupler 108 (in response to one or more power or command signals output by controller 120 via link 115). Link 115 may enter the interior of housing 102 through an insulated access port (not shown) formed in the wall of housing 102 by any known or suitable means. In one embodiment, controller 120 is configured to operate light source 114 in a pulsed mode (e.g., light source 114 is strobed or intermittently flashed), a continuous mode, the like, or any combination thereof.

[0031] Generally, the second optical coupler 108 is configured to direct light emitted by the light source 114 toward the sample cell 104. The second optical coupler 108 is sealingly coupled within the sample cell 104 to prevent gas introduced into the sample cell 104 (e.g., via the inlet gas flow port 110) from reaching the light source 114. In one embodiment, the second optical coupler 108 includes a window (e.g., that is at least substantially transparent to the light to be measured) sealingly coupled to the sample cell 104, and a concavely curved mirror or lens (e.g., configured to focus or collimate light emitted by the light source 114 and passing through the window into the sample cell 104) positioned between the window and the light source 114. In other embodiments, the second optical coupler 108 may include a lens (e.g., at least substantially transparent to the light emitted by the light source 114) that is hermetically coupled to the sample cell 104 and that is also configured to focus or collimate the light emitted by the light source 114 and entering the sample cell 104 (thus eliminating the need for the window described above).

[0032] The light emitted by light source 114 (also referred to herein as "measurement light") has one or more wavelengths ranging from 1.5 μm (or thereabouts) to 18 μm (or thereabouts). This wavelength range can be understood to occupy the mid-infrared (IR) region of the electromagnetic spectrum. Light source 114 is provided as a high-intensity mid-IR source to limit light attenuation through the mid-IR light guide and provide a high flux at the detector, thereby enabling highly sensitive concentration measurements. For typical blackbody radiators (also known as thermal sources), such as a globar (also known in the art as a "globar"), the temperature of the radiator must be greater than 1500°C.

[0033] In one embodiment, light source 114 is provided as a thermal light source (e.g., a blackbody radiator) capable of emitting measurement light at temperatures exceeding 1500°C (e.g., 1600°C, 1700°C, 1800°C, etc., or any value between these values). To this end, the thermal light source may include one or more radiating elements formed from materials such as silicon, silicon carbide, chromium-nickel alloy, tungsten, ceramic, etc., or any combination thereof. However, to ensure a meaningful operational lifetime of the thermal light source, the radiating element(s) are hermetically sealed (e.g., to prevent or minimize corrosion or oxidation of the radiating element(s)).

[0034] In another embodiment, light source 114 is implemented as one or more mid-IR light-emitting diodes (LEDs). Generally, when LEDs are operated in a continuous wave mode, the light emitted by a mid-IR LED is not as bright as the light emitted by a thermal light source, as described above. However, when operated in a pulsed mode, there are several advantages to using an LED light source. When operated in a pulsed mode, LEDs can emit light at very high powers, and when placed on a thermoelectric cooler, the output light level can be more stable than a conventional blackbody radiator. In addition, LEDs consume less power and are more compact than conventional blackbody radiators, making them suitable for more compact designs. In this embodiment, light source 114 is implemented as one or more mid-IR LEDs having an emission spectrum covering the 1-8 μm wavelength range of the electromagnetic spectrum. Alternatively, light source 114 may be implemented as multiple mid-IR LEDs having different emission spectra that partially overlap within the mid-IR wavelength range of the electromagnetic spectrum. For example, light source 114 may be implemented as light source 200 shown in FIG. 2. The light source 200 includes a first LED 202 (e.g., emitting light in a first mid-IR wavelength range), a second LED 204 (e.g., emitting light in a second mid-IR wavelength range that partially overlaps with the first mid-IR wavelength range), and a beam splitter 206 (e.g., a dichroic beam splitter, a 50 / 50 beam splitter, etc.) configured to combine the optical radiation output by the first LED 202 and the second LED 204.

[0035] In another example, the light source 114 may be provided as one or more LEDs (e.g., the first LED 202 and the second LED 204 described above) mounted on a common substrate (e.g., a PCB) and positioned closely together to emit light into a common delivery fiber (e.g., a multimode, large-core, high-NA optical fiber) so that the light emitted by the LEDs is injected into the core of the delivery fiber. If desired, one or more lenses or curved mirrors may be positioned between the LEDs and the delivery fiber to focus the light emitted by the LEDs into the core of the delivery fiber. In either case, the precise location of the cores can be aligned to obtain equal amounts of power from the LEDs, or to obtain more light from one LED than another, depending on the spectral requirements of the sensor 100. The core size of the delivery fiber limits the amount of light that can be coupled, so the LEDs should be as close as possible. Therefore, it may be desirable to use LEDs that can emit light to the edge of their respective output faces.

[0036] 1 , the photodetector 116 is optically coupled to the sample cell 104 via an optical waveguide assembly 122 and is in optical communication with the interior of the sample cell 104 (e.g., after the first optical coupler 106). Generally, the first optical coupler 106 is configured to guide measurement light emitted by the light source 114 and transmitted through the second optical coupler 108 and the gas within the sample cell 104 into the optical waveguide assembly 122. The first optical coupler 106 is hermetically coupled to the sample cell 104 to prevent gas introduced into the sample cell 104 (e.g., via the inlet gas flow port 110) from reaching the optical waveguide assembly 122. In one embodiment, first optical coupler 106 may include a window (e.g., at least substantially transparent to the measurement light) hermetically coupled to sample cell 104 and a concavely curved mirror or lens (e.g., configured to focus measurement light transmitted through the window onto a first end of optical waveguide assembly 122) disposed between the window and optical waveguide assembly 122. In other embodiments, first optical coupler 106 may include a lens (e.g., at least substantially transparent to the measurement light) hermetically coupled to sample cell 104 and also configured to focus measurement light transmitted through sample cell 104 onto a first end of optical waveguide assembly 122 (thus eliminating the need for a window as described above).

[0037] The optical waveguide assembly 122 may include a first optical waveguide 124 and a second optical waveguide 126, each configured to transmit measurement light. The first optical waveguide 124 is optically coupled to the second optical waveguide 126 (e.g., by an optical connector 128). Thus, a first end of the first optical waveguide 124 (i.e., the first end of the optical waveguide assembly 122 described above) may be connected to the sample cell 104 (e.g., at a position after the first optical coupler 106), and a first end of the second optical waveguide 126 may be connected to the detector 116. A second end of each of the first optical waveguide 124 and the second optical waveguide 126 may be connected to the optical connector 128 such that the first optical waveguide 124 and the second optical waveguide 126 are in optical communication with each other. In general, optical connector 128 may be provided as any known or suitable connector configured to place first optical waveguide 124 and second optical waveguide 126 in optical communication with each other when the two waveguides are connected. Additionally, optical connector 128 is attached to housing 102 at an opening (not shown) therein.

[0038] The first optical waveguide 124 is disposed within the housing 102 and is configured to maintain suitable optical properties (e.g., to maintain an acceptably high transmittance of the measurement light) and mechanical properties (e.g., to have a suitably high glass transition temperature) at the elevated temperatures within the housing 102. Examples of waveguides that can be used as the first optical waveguide 124 include optical waveguides (e.g., optical fibers, optical fiber bundles, etc.) such as ZrF4 fibers (e.g., ZBLAN), indium fluoride (e.g., InF3) fibers, chalcogenide infrared (CIR) fibers (e.g., As2S3 core / AsS cladding), polycrystalline infrared (PIR) fibers (e.g., silver halide PIR fibers), hollow core fibers, etc., or any combination thereof.

[0039] The second optical waveguide 126 may be provided as any optical waveguide (e.g., an optical fiber, an optical fiber bundle, etc.) capable of suitably transmitting measurement light at lower temperatures (e.g., at the temperature of the ambient environment in the vicinity outside the housing 102). In one embodiment, the second optical waveguide 126 has a higher optical transmittance of measurement light than the first optical waveguide 124, but the length of the first optical waveguide 124 is shorter than the length of the second optical waveguide 126. Thus, the difference in optical transmission loss between the first optical waveguide 124 and the second optical waveguide 126 can be minimized or reduced. Generally, the first optical waveguide 124 is only as long as necessary to connect the sample cell 104 and the housing 102. Typically, the first light guide 124 has a length that is 60 cm or less (e.g., 55 cm, 40 cm, 30 cm, 20 cm, 10 cm, 5 cm or less, etc., or any value between these values). The second light guide 126 may have a length that is greater than any of the above-mentioned lengths of the first light guide 124 (e.g., may have a length that is over 1 meter or more).

[0040] Although the optical waveguide assembly 122 is described above as including two optical waveguides, it will be appreciated that the optical waveguide assembly 122 may include more than two optical waveguides optically connected to one another, or may have a single optical waveguide (e.g., provided as described above with respect to the first optical waveguide 124).

[0041] Generally, detector 116 is adapted to generate and output a detection signal to analyzer 118 when measurement light transmitted through optical waveguide assembly 122 is incident on it (on its active area), the detection signal being indicative of the amount of light detected by detector 116. In embodiments in which light source 114 is operated in a pulsed mode (e.g., as described above), detector 116 may be provided as an InAsSb or MCT type detector. Furthermore, in embodiments in which light source 114 is operated in a pulsed mode (e.g., as described above), detector 116 may be operated (e.g., in response to one or more control signals output by controller 120) in synchronization with the pulsed mode operation of light source 114 to optimize the SNR of the detected signal.

[0042] As exemplarily shown in FIG. 3 , the detector 116 may include a photodetector 300 and a filter assembly 302. The photodetector 300 is sensitive to mid-IR light as described above and is capable of generating and outputting a detection signal. The filter assembly 302 includes multiple optical filters, each configured to transmit a different wavelength band, positioned in front of the active area of ​​the photodetector 300 (i.e., the area of ​​the photodetector 300 that converts photons into electrical current). Thus, measurement light transmitted through the optical waveguide assembly 122 passes through the optical filters of the filter assembly 302 before propagating to the photodetector 300. In one embodiment, the filter assembly 302 may be provided as a filter assembly that is movable (e.g., rotatable, as indicated by arrow 304) relative to the photodetector 300 to selectively position a single filter in front of the active area of ​​the photodetector 300. It should therefore be understood that, as is known in the art, detector 116 may include a motor and appropriate mechanical linkages for achieving movement of filter assembly 306. Although not shown, a focusing lens may be disposed between optical waveguide assembly 122 and filter assembly 302 to focus the measurement light exiting optical waveguide assembly 122 (e.g., at or near the active area of ​​filter assembly 302 or photodetector 300).

[0043] FIG. 4 illustrates an example embodiment of a filter assembly 302. Referring to FIG. 4, the filter assembly 302 may be provided as a filter wheel 400 having a wheel body 402 (which may include, for example, an axial hole 401) and a plurality of windows defined therein. Each window is fitted with an optical filter configured to transmit a particular wavelength band. For example, the wheel body 402 is shown as including a first optical filter 404, a second optical filter 406, and a third optical filter 408 fitted to respective windows formed in the wheel body 402. The first optical filter 404 may be configured to transmit a first wavelength band. The second optical filter 406 may be configured to transmit a second wavelength band. The third optical filter 408 may be configured to transmit a third wavelength band. The dotted circle 410 represents measurement light transmitted through the optical waveguide assembly 122 and incident on the filter assembly 302 along an axis perpendicular to the optical filter (e.g., with an optical filter such as the first optical filter 404 as exemplarily shown in FIG. 4).

[0044] Generally, the center wavelength of the first wavelength band is between the center wavelengths of the second wavelength band and the third wavelength band. Furthermore, the first wavelength band does not overlap or adjoin the second wavelength band or the third wavelength band. See, for example, graph 500 of radiance detectable by detector 300 versus wavelength in FIG. 5. In FIG. 5, a first wavelength band (also referred to herein as the "signal band") is identified at 502, a second wavelength band (also referred to herein as the "first reference band") is identified at 504, and a third wavelength band (also referred to herein as the "second reference band") is identified at 506. However, in other embodiments, first wavelength band 502 may adjoin second wavelength band 504 and / or third wavelength band 506.

[0045] As exemplarily shown in FIG. 5, a first wavelength band 502 may cover a wavelength range from 3.42 μm (or thereabouts) to 3.65 μm (or thereabouts), a second wavelength band 504 may cover a wavelength range from 3.8 μm (or thereabouts) to 4.00 μm (or thereabouts), and a third wavelength band 506 may cover a wavelength range from 3.2 μm (or thereabouts) to 3.3 μm (or thereabouts). However, it will be understood that the ranges of the first, second, and third wavelength bands may be selected based on the precursor gas(es) being monitored, degradation by-products of the precursor gas(es) that may be present in the sample cell 104, contaminants that may accumulate on the first optical coupler 106 or the second optical coupler 108, variations in the emission spectrum of the light source 114 that may be expected to occur, variations in the transmission spectrum of the optical waveguide assembly 122 that may be expected to occur, variations in the detection spectrum of the detector 116 that may be expected to occur, or any combination thereof.

[0046] The emission spectrum of the light source 114 may change due to one or more factors, such as the temperature of the light source 114 (e.g., if the light source 114 is implemented as a thermal light source), the age of the light source 114 (e.g., if the light source 114 is implemented as an LED), etc., or any combination thereof. The transmission spectrum of the light guide assembly 122 may change due to one or more factors, such as a temperature change in one or more components of the light guide assembly 122 (e.g., of the first light guide 124 and / or the second light guide 126), movement of one or more components of the light guide assembly 122 (e.g., bending of the first light guide 124 and / or the second light guide 126), the presence of contaminants that may accumulate on the optical surfaces of the light guide assembly 122, etc., or any combination thereof. The detection spectrum of the detector 116 may change due to one or more factors, such as temperature changes in the detector 116, the presence of contaminants that may accumulate on the active area of ​​the detector 116, the age of the detector 116, etc., or any combination thereof.

[0047] Generally, however, the range of the first, second, and third wavelength bands should be in the mid-IR region of the electromagnetic spectrum, since many of the precursors used in the semiconductor industry have strong absorption between 2 and 7 μm. The variations in the emission spectrum of the light source 114, the variations in the transmission spectrum of the optical waveguide assembly 122, and the variations in the detection spectrum of the detector 116 may be collectively and / or collectively referred to as "baseline variations."

[0048] For example, Figure 6 shows a graph 600 of absorption spectra of various materials at different wavelengths. In particular, line 602 represents the absorption spectrum of an exemplary precursor gas that can be measured by optical gas concentration sensor 100, and line 604 represents the absorption spectrum of degradation by-products and / or contaminants on the optical coupler of sample cell 104. In this example, signal band 502 is selected to cover a wavelength band in which the exemplary precursor gas exhibits strong absorption. Second reference band 506 is selected to cover a wavelength band in which expected degradation by-products or contaminants exhibit strong absorption. First reference band 504 is selected to cover a wavelength band in which baseline variations can be detected (e.g., in a region of the wavelength spectrum in which the exemplary precursor gas and expected degradation by-products and contaminants do not exhibit strong wavelength absorption).

[0049] When the first optical filter 404 (i.e., an optical filter configured to transmit a signal band) is positioned in front of the active area of ​​the photodetector 300, the detection signal generated by the detector 116 can be referred to as the "signal detection signal." Similarly, when the second optical filter 406 (i.e., an optical filter configured to transmit a first reference band) is positioned in front of the active area of ​​the photodetector 300, the detection signal generated by the detector 116 can be referred to as the "first reference detection signal," and when the third optical filter 408 (i.e., an optical filter configured to transmit a second reference band) is positioned in front of the active area of ​​the photodetector 300, the detection signal generated by the detector 116 can be referred to as the "second reference detection signal." Thus, the filter wheel 400 of the detector 116 may rotate once (e.g., as described above) to generate and output the signal detection signal, the first reference detection signal, and the second reference detection signal. It will be appreciated that the filter wheel 400 may rotate multiple times to repeatedly generate and output the above signals.

[0050] 3 and 4, detector 116 may be provided as exemplarily shown in FIG. 10, including a plurality of photodetectors (e.g., a first photodetector 1000a, a second photodetector 1000b, and a third photodetector 1000c, each collectively referred to as photodetectors 1000) and a corresponding one of a plurality of filters disposed in front of the active area of ​​each photodetector 1000. For example, the above-described first optical filter 404, second optical filter 406, and third optical filter 408 may be disposed in front of the active areas of first photodetector 1000a, second photodetector 1000b, and third photodetector 1000c, respectively. Although not shown, a focusing lens may be disposed between the optical waveguide assembly 122 and the detector 116 and configured to focus the measurement light exiting the optical waveguide assembly 122 (e.g., onto the active area of ​​the filter assembly 302 or the photodetector 300 or a location nearby) so that the first optical filter 404, the second optical filter 406, and the third optical filter 408 are simultaneously illuminated with the measurement light. The detector 116 shown in FIG. 10 is configured as described above and is therefore capable of simultaneously generating the signal detection signal, the first reference detection signal, and the second reference detection signal, and may output such signals to the analyzer 118.

[0051] The analyzer 118 is communicatively coupled to the output of the detector 116 (e.g., to receive the detection signal output from the detector 116). Generally, the analyzer 118 is configured to determine or estimate the concentration of the precursor gas received in the gas sample cell 104 based on the detection signal output by the detector 116. In one embodiment, the concentration of the precursor gas can be determined or estimated by calculating the relative difference between the value encoded by the signal detection signal (i.e., the "signal band value") and the values ​​encoded by the first and second reference detection signals (i.e., the "first reference band value" and the "second reference band value"). For example, the detection signal output from the detector 116 can be considered as a vector, where different absorption spectra from different molecules in the precursor gas correspond to different absorption vectors. Spectroscopic tools such as classical least squares (CLS), partial least squares (PLS), deep learning, etc. can be used to distinguish and quantify the composition of the precursor gas. In another example, the concentration C of the precursor gas in the sample cell 104 can be calculated by calculating the relative difference between the value encoded by the signal detection signal (i.e., the "signal band value") and the values ​​encoded by the first and second reference detection signals (i.e., the "first reference band value" and the "second reference band value"). P can be determined by the following equation (1): C P =-a1*log(signal band value)+(a2*log(first reference band value)+a3*log(second reference band value)) where a1, a2 and a3 are calibration parameters.

[0052] The advantage of using three optical filters, each with three different wavelength bands, over the prior art, which uses only two optical filters providing only two wavelength bands (i.e., a signal band and a single reference band), can be understood by reference to FIG. 7 (showing an example of the sensor drift that exists when using only a signal band and a single reference band) and FIG. 8 (showing an example of the sensor drift that exists when using a signal band and two reference bands). FIGS. 7 and 8 show the variation over time of the concentration of the precursor gas PDMAT in a gas mixture (the Y-axis of these graphs indicates partial pressure, but those skilled in the art will understand that the partial pressure of a particular gas in a gas mixture is proportional to the concentration of that particular gas in the mixture). In FIG. 7, the output of a conventional NDIR gas concentration sensor using only two wavelength bands (i.e., a signal band and a single reference band) varies over time, since the signal band and a single reference band cannot accurately detect the signs of the baseline drift described above over time. However, by using a sensor 100 with two reference bands in accordance with the principles of the present invention, baseline drift can be detected (e.g., by analyzer 118) and compensated to eliminate or reduce drift in sensor 100 readings over time (i.e., due to baseline drift), as shown, for example, in FIG. 8.

[0053] Generally, analyzer 118 can detect baseline drift by 1) processing the reference detection signals output by detector 116 to determine a measurement relationship between the reference band values ​​encoded by the output reference detection signals, and 2) comparing the measurement relationship to a predetermined calibration relationship to determine a difference. If a difference exists (or if the difference is greater than some predetermined threshold), baseline drift can be considered detected, and analyzer 118 can compensate (e.g., eliminate or reduce) the baseline drift. In one embodiment, analyzer 118 minimizes or reduces the difference between the measurement relationship and the calibration relationship, and then compensates for the baseline drift by scaling the first and second reference band values ​​(e.g., by adjusting / changing the above-mentioned calibration parameters a2 and a3, respectively) to adjust the above-mentioned calibration parameter a1 using techniques suitable or known in the art.

[0054] For example, in the embodiment described above, sensor 100 is calibrated to generate reference detection signals for two separate reference bands. Thus, analyzer 118 may process the first and second reference detection signals output by detector 116 (e.g., by performing a linear regression on the first and second reference band values ​​using any suitable technique known in the art) and compensate for baseline drift (e.g., by adjusting / changing the above-mentioned calibration parameters a2 and a3, respectively) to minimize or reduce the difference between the measurement relationship and the calibration relationship. Analyzer 118 may then adjust the above-mentioned calibration parameter a1 using any suitable or known technique in the art.

[0055] While the above describes an embodiment in which three optical filters are used to determine the concentration of precursor gas in sample cell 104, it will be appreciated that more than three filters (and thus more than three wavelength bands) can be used to generate more measurements, thereby improving the robustness and accuracy with which the precursor gas concentration can be determined. For example, using two reference bands as described above can be beneficial in eliminating or reducing baseline fluctuations that are linear in nature (e.g., baseline fluctuations resulting from changes in emitter temperature). However, if the baseline fluctuations are not linear (i.e., if higher-order factors are present), more than two reference bands can be used (thus, for example, higher-order polynomial regression can be used to eliminate / reduce higher-order baseline fluctuations). Additionally, if the gas stream in sample cell 104 contains multiple chemicals (e.g., precursor gases and degradation byproducts of precursor gases) and the absorption characteristics of these chemicals overlap, more signal bands can be provided to separate the readings of each chemical.

[0056] Generally, the controller 120 includes one or more processors capable of generating control signals (e.g., upon executing instructions or otherwise). The processor may be implemented as one or more general-purpose computer processors, microprocessors, digital signal processors, programmable logic devices (PLDs), field programmable gate arrays (FPGAs), field programmable object arrays (FPOAs), application-specific integrated circuits (ASICs) including digital, analog, and mixed analog / digital circuitry, or other suitable forms of circuitry capable of executing instructions or generating control signals, or any combination thereof. Execution of instructions may occur on a single processor, may be distributed across multiple processors, may occur in parallel across multiple processors within a device or across a network of devices, or the like. The controllers described herein may include tangible media, such as computer memory, accessible by the processor (e.g., via one or more wired or wireless communication links). As used herein, computer memory (or more simply, "memory") includes magnetic media (e.g., magnetic tape, hard disk drives, etc.), optical disks, volatile or non-volatile semiconductor memory (e.g., RAM, ROM, NAND flash memory, NOR flash memory, SONOS memory, etc.), and the like, and may be locally accessible, remotely accessible (e.g., over a network), or a combination thereof. Generally, the instructions described above may be stored as computer software (e.g., executable code, files, instructions, etc., library files, etc.). Such computer software may be written in, for example, C, C++, Visual Basic, Java, Python, Tel, Perl, Scheme, Ruby, assembly language, hardware description languages ​​(e.g., VHDL, VERILOG, etc.), etc., and may be readily produced by one of ordinary skill in the art from the description set forth herein. Computer software is typically stored in one or more data structures carried by computer memory.

[0057] As described above, embodiments of the present invention provide many advantages over conventional gas concentration sensors. For example, the optical waveguide assembly 122 allows the sample cell 104 to be mechanically detached from the rest of the sensor 100 (e.g., the detector 116, the analyzer 118, and the controller 120). As a result, the detector 116, the analyzer 118, and the controller 120 can be safely located outside the housing 102 (e.g., at room temperature), while the sample cell 104 can be compact and easily fit within the housing 102. The use of an enclosed, high-temperature blackbody radiator or other high-intensity light source 114 and a high-speed detector 116 can optimize the SNR performance of the sensor 100. Spectroscopy is used to improve the stability of the sensor 100. Without such spectroscopy, variations in the transmission spectrum through the optical fiber would reduce the accuracy and stability of the gas concentration measurement.

[0058] The foregoing is a description of embodiments and examples of the present invention and is not to be construed as limiting thereof. While several specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily recognize that many modifications to the disclosed embodiments and examples, as well as other embodiments, are possible without significantly departing from the novel teachings and advantages of the present invention. For example, while sensor 100 has been described above as having a single-pass sample cell configuration (i.e., measurement light traverses the entire length of the sample cell in one pass), it will be understood that sensor 100 may also have a multi-pass sample cell configuration (i.e., one or more mirrors are positioned within sample cell 104 to increase the optical path length of measurement light within the sample cell, as known in the art). In another example, the optical filter of detector 116 may be implemented as a MEMS-based Fabry-Perot filter. In yet another example, detector 116 may include a photodetector disposed at the optical output of optical waveguide assembly 122 (e.g., as described above), or an angle-adjustable optical filter may be disposed within sample cell 104 to filter the light emitted by light source 114 (e.g., as described in U.S. Pat. No. 9,651,422, incorporated herein by reference in its entirety). In another example, while detector 116 is shown as being optically coupled to the interior of sample cell 104 via optical waveguide assembly 122, optical waveguide assembly 122 can be omitted, and detector 116 can be mounted directly to sample cell 104 so as to be in optical communication with the interior of sample cell 104. Accordingly, all such modifications are intended to be included within the scope of the present invention, as defined in the claims. For example, those skilled in the art will understand that the subject matter of any sentence, paragraph, example, or embodiment can be combined with some or all of the subject matter of any other sentence, paragraph, example, or embodiment, except where such combinations would be mutually exclusive. Therefore, the scope of the invention should be determined by the following claims and any equivalents to those claims that are to be included therein.

Claims

1. a sample cell having an inlet port and an outlet port through which a gas can pass; a light source configured to emit light into the sample cell; a photodetector disposed external to the sample cell; an optical waveguide assembly optically coupling the interior of the sample cell to the detector, a first optical waveguide coupled to the sample cell; a second optical waveguide coupled to the detector; an optical coupler that optically couples the first optical waveguide to the second optical waveguide; an optical waveguide assembly including: Equipped with the first optical waveguide has optical transmission characteristics different from those of the second optical waveguide at wavelengths in a wavelength range of 1.5 μm to 18 μm; Optical gas concentration sensor.

2. The optical gas concentration sensor of claim 1 , further comprising an insulated housing, the sample cell being disposed within the insulated housing.

3. The optical gas concentration sensor of claim 2 , wherein the optical coupler is connected to the thermally insulated housing.

4. 2. The optical gas concentration sensor of claim 1, wherein the length of the first optical waveguide is shorter than the length of the second optical waveguide.

5. The optical gas concentration sensor of claim 1 , wherein the first optical waveguide comprises at least one optical fiber.

6. The first optical waveguide is made of ZrF 4 , InF 3 10. The optical gas concentration sensor of claim 1, comprising a material selected from the group consisting of a silver halide material, a chalcogenide material, and a silver halide material.

7. The photodetector at least one photodetector; a plurality of optical filters arranged and configured to transmit different wavelength bands in the mid-IR region of the electromagnetic spectrum to the at least one photodetector; 10. The optical gas concentration sensor of claim 1, comprising:

8. The optical gas concentration sensor of claim 7 , wherein the at least one photodetector comprises a single photodetector.

9. The optical gas concentration sensor of claim 7 , wherein the at least one photodetector comprises a plurality of photodetectors.

10. 10. The optical gas concentration sensor of claim 9, wherein different optical filters of the plurality of optical filters are disposed on different photodetectors of the plurality of photodetectors.

11. The plurality of optical filters include: a first optical filter configured to transmit a first band of wavelengths in the wavelength range of the electromagnetic spectrum; a second optical filter configured to transmit a second wavelength band in the wavelength range of the electromagnetic spectrum; a third optical filter configured to transmit a third wavelength band in the wavelength range of the electromagnetic spectrum; and Including, the first wavelength band does not overlap with the third wavelength band; 8. The optical gas concentration sensor of claim 7.

12. 12. The optical gas concentration sensor of claim 11, wherein the second wavelength band does not overlap with the first or third wavelength bands.

13. 12. The optical gas concentration sensor of claim 11, wherein the second wavelength band is between the first wavelength band and the third wavelength band.

14. 12. The optical gas concentration sensor of claim 11, wherein wavelengths within the second wavelength band tend to be more strongly absorbed by the gas than wavelengths within the first or third wavelength bands.

15. 15. The optical gas concentration sensor of claim 14, wherein wavelengths within the first wavelength band are more likely to be absorbed by by-products of the gas or contaminants within the sample cell than wavelengths within the second or third wavelength bands.

16. 16. The optical gas concentration sensor of claim 15, wherein wavelengths within the third wavelength band are less likely to be absorbed by the gas, by-products of the gas, or contaminants within the sample cell than wavelengths within the first or second wavelength bands.

17. 12. The optical gas concentration sensor of claim 11, further comprising an analyzer coupled to an output of the detector and configured to determine the concentration of the gas in the sample cell based on a detection signal output by the at least one photodetector in response to receiving light transmitted through the first, second, and third optical filters.

18. The optical gas concentration sensor of claim 1 , further comprising an analyzer coupled to an output of the detector and configured to determine the concentration of the gas in the sample cell.

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