JP2002005831A - Absorptiometric analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nondispersive absorptiometeric analyzer, whose constitution is simple and with which a high accuracy computed result is obtained, with respect to a desired gas component from among a plurality of gas components to be measured. SOLUTION: Infrared detectors 4, 5 whose number corresponds to the plurality of gas components to be measured are installed. An infrared detector 6, which receives infrared rays in a wavelength region over all of respective extinction wavelength regions of the gas components, in which the extinction wavelength regions are overlapped partly with each other, is installed. The concentration of the respective gas components is calculated. Thereby, a measured result, in which a background signal and a mutual interference degree are corrected can be obtained, using a simple constitution. When the gas components whose change range of a concentration differs largely are measured, the calculated value of the interference degree between the respective gas components is corrected, according to a weighting factor which is set so as to correspond to the respective gas components. Thereby, even with respect to a gas kind whose concentration is small, the high accuracy computed result can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absorption spectrometer, and more particularly, to a non-dispersive infrared absorption spectrometer (NDIR) configured to measure the concentrations of a plurality of measurement gas components. It is about.

[0002]

2. Description of the Related Art NDIR is frequently used when the concentration of a measurement gas component contained in a sample gas is continuously measured in real time. For example, Japanese Patent Application Laid-Open No. 10-185816 discloses an example of such a configuration of NDIR, and the publication discloses an apparatus as shown in FIG. 4 for measuring the concentration of two types of gas components, for example. . In the figure, reference numeral 31 denotes a measuring cell to which a sample gas is supplied, and an infrared light source 32 is arranged on the incident side (left side in the figure) of the measuring cell 31, while a measuring cell is There are provided a rotary chopper 33 for intermittently transmitting infrared light transmitted through 31, and, as described later, four infrared detectors 34 to 37 each configured by a pair of a band-pass filter and an infrared sensor.

[0003] The first infrared detector 34 detects the CO in the sample gas.
This is for measuring the concentration, which comprises a band-pass filter 34a for selectively transmitting infrared rays in the CO absorption wavelength band, a first measurement component infrared sensor 34b for receiving infrared rays transmitted through the filter 34a, and Is provided. The second infrared detector 35 is provided for compensating an output signal from the first infrared detector 34, and is a band-pass filter that transmits infrared light in a specific wavelength band other than the CO absorption wavelength band. 35a, and an infrared sensor 35b that receives infrared light transmitted through the filter 35a.

[0004] On the other hand, the third infrared detector 36 is for measuring the CO concentration in the sample gas, and includes a band-pass filter 36a set in the same manner as described above for the NO absorption wavelength band, A band-pass filter 37a for transmitting infrared light in a specific wavelength band other than the NO absorption wavelength band in order to compensate for an output signal from the infrared sensor 36b.
And the fourth infrared detector 3 comprising an infrared sensor 37b
7 are provided.

In such a configuration, first, the infrared sensors 34b and 35 of the first and second infrared detectors 34 and 35 are used.
b, the difference between the respective output signals from the third and fourth infrared detectors 36 and 37 is determined at the same time.
The difference between each output signal from 7b is determined. Thereby, for example, contamination of the measurement cell 31 and the cell window 31a,
The influence (hereinafter, referred to as the background signal amount) due to the fluctuation of the light amount of the infrared light source 32 is removed. Thereafter, the reference values determined in advance, that is, the reference values when CO and NO are individually flown at the unit concentration, are respectively compared, and the concentrations of CO and NO are calculated by proportional calculation according to Lambert-Beer's law. .

[0006]

In the apparatus described in the above publication, it is premised that a measurement gas component which does not overlap each absorption wavelength band is selected, and a part of each absorption wavelength band overlaps. No particular consideration is given to the measurement of gas components that interfere with each other. That is,
When measuring the concentration of such gas components, it is necessary to calculate the concentration of each gas component by further obtaining the degree of mutual interference.

For this purpose, for example, each compensation detector 35 for obtaining the amount of background signal in the above-described device.
If a detector for determining the degree of mutual interference as described above is additionally provided separately from 37, the overall number of components increases and the configuration becomes complicated.

On the other hand, an NDIR configured to measure a plurality of gas component concentrations is provided in a plasma processing apparatus such as a plasma CVD apparatus or a plasma etching apparatus in a semiconductor manufacturing process, and an exhaust gas from such a processing apparatus is provided. When trying to measure the concentration of a specific component therein, there is also a problem that the concentration of a desired gas component cannot be measured with high accuracy.

For example, in the exhaust gas from a plasma CVD apparatus in which C ₂ F ₆ or O ₂ is supplied to a reaction chamber, CF ₄ , C ₂ F ₆ , COF ₂ , and infrared rays such as CO and CO ₂ are contained. Many gas types that overlap each other are mixed. Among these gas species, for example, the A gas component is contained in the exhaust gas in the order of several thousand ppm, while the concentration of the B gas component has a large variation range of concentration such as on the order of tens of ppm. It is different.

In such a case, for the degree of mutual interference, for example, in the calculation based on the proportional calculation with the reference value as described above, the degree of interference based on the gas type having a large concentration is likely to be excessive in the calculation. For this reason, there arises a problem that it is difficult to obtain an accurate calculation result for a gas type having a small concentration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to simplify the overall configuration and to provide at least a desired gas component among a plurality of measurement gas components. On the other hand, it is an object of the present invention to provide an absorption spectrometer capable of obtaining an accurate calculation result.

[0012]

SUMMARY OF THE INVENTION Therefore, claim 1 of the present invention is provided.
In an absorption spectrometer, an infrared light source is arranged on an incident side with a measurement cell to which a sample gas is supplied interposed therebetween, and on the emission side, a number of infrared detectors corresponding to a plurality of measurement gas components in the sample gas are provided. An absorption spectrometer in which each infrared detector is provided with an infrared sensor for individual component measurement provided with a band-pass filter for selectively transmitting infrared light in a wavelength range corresponding to the absorption wavelength band of the corresponding measurement gas component. For a measurement gas component in which a part of an infrared absorption wavelength band overlaps with each other, a compensation including a compensation bandpass filter that transmits infrared light in a wavelength range over the entire absorption wavelength band of the measurement gas component. In addition to the above, an infrared sensor is further provided, and from each output of the infrared sensor for compensation and the infrared sensor for measuring each individual component, a concentration calculation formula stored in advance is used. It is characterized in that there is provided a calculating means for calculating the concentration of each measured gas component.

Regarding the operation in this configuration, for example,
The case where the concentrations of various gas components (X gas component and Y gas component) are measured will be described as an example. Two individual component measuring infrared sensors provided corresponding to each gas component are provided. For each of the absorbance signals S _X , S _Y, and S _T obtained from output signals from a total of three infrared sensors with the infrared sensor for use, the concentration of the X gas component, the concentration of the Y gas component,
And a relational expression (equation) in which three of the background signals are unknown. Therefore, the concentration of each of the gas components X and Y can be obtained by performing an operation according to a concentration calculation equation that solves this simultaneous equation. On the other hand, even when three or more gas components are mixed, the concentration of each gas component can be obtained in the same manner as described above.

Therefore, in this case, in addition to the number of infrared detectors corresponding to each measurement gas component, only one pair of a compensating bandpass filter and a pair of infrared sensors is provided. Since a measurement result in which the ground signal and the degree of mutual interference are corrected together can be obtained, the overall configuration is simplified.

According to a second aspect of the present invention, there is provided an absorption spectrometer according to the first aspect, further comprising weight coefficient setting means for setting a weight coefficient corresponding to each of the measured gas components, wherein the arithmetic means comprises the concentration calculation formula. It is characterized in that the concentration of each measurement gas component is calculated by performing a correction based on the magnitude of the weighting coefficient in the calculation formula of the degree of interference between the measurement gas components therein.

According to this configuration, for example, when measuring the measurement gas components whose concentration change ranges are largely different as described above, the degree of interference based on the gas type having the large concentration is suppressed in accordance with the weight coefficient. You can do so. Therefore, by setting the weight coefficient as described above,
A highly accurate calculation result can be obtained even for a gas type having a small concentration.

[0017]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. First, the configuration of the apparatus will be described using an example in which the concentrations of two types of gas components, an X gas component and a Y gas component, in which a part of the infrared absorption wavelength band overlaps each other, are measured.

As shown in FIG. 1, in the absorption spectrometer in this case, the white infrared light source 2 and the light emitted from the light source 2 are intermittently arranged on the incident side of the measurement cell 1 through which the sample gas is supplied and circulated. A rotary chopper 3 is provided, and three infrared detectors 4, 5, and 6 are arranged on the emission side of the measurement cell 1. Each of the detectors 4, 5, 6 is provided with an infrared sensor 4b, 5b, 6 provided with a band-pass filter 4a, 5a, 6a, which will be described later, on the infrared incident surface side.
b. These infrared sensors 4b
Solid-state sensors such as a pyroelectric sensor and a semiconductor sensor are used for 5b and 6b.

With such a configuration, the infrared light emitted from the light source 2 is incident on the measuring cell 1 as a light beam intermittently transmitted by the chopper 3 at a constant period, and is transmitted through the measuring cell 1 so that the infrared rays are emitted from the sample gas. The infrared rays in a specific wavelength range are absorbed by the measurement gas contained in the sample according to the component concentration. Then, the luminous flux transmitted through the measuring cell 1 is transmitted through the band-pass filters 4a, 5a, and 6a, and the respective infrared sensors 4b
5b and 6b, and these infrared sensors 4b and 5
An electric signal corresponding to the amount of incident light at b · 6b is input to a computing unit (computing means) 7 described later. The calculator 7 converts the electric signal into an absorbance signal, calculates the concentration of each measurement gas component, and outputs the obtained concentration signals C _X and C _Y to the outside.

FIG. 2A is a schematic diagram of the absorption spectrum of two types of measurement gas components X and Y to be measured by the above-mentioned apparatus. As shown in the figure, when a part of each absorption wavelength band of infrared rays in each measurement component X and Y overlaps, the band-pass filter 4a in the first detector 4 among the three detectors 4 to 6 described above. Indicates that the transmission wavelength band has a wavelength region (λ ₁₎ slightly lower than the peak region of the absorption wavelength band in the measurement component X, as shown by the solid line F _A in FIG.
To [lambda] _2: hereinafter, it is configured to transmit infrared A that region).

Thus, from the output of the infrared sensor 4b of the first detector 4, the area of the portion indicated by the broken line in FIG. 3C, that is, the measurement component in the A region (λ _{1 to} λ ₂ ) An absorbance signal corresponding to a value obtained by adding the integral S _{A (X)} of the absorption spectrum of _X to the integration value S _{A (Y)} of the absorption spectrum of the measurement component Y (hereinafter, the A region absorbance signal S
_A ) is obtained.

On the other hand, the band-pass filter 5a in the second detector 5, the transmission wavelength band, as indicated by the broken line F _B in FIG. (B), including the peak area in the absorption wavelength band of the measurement component Y Wavelength region (λ _{3 to} λ ₄ : below,
It is set so as to transmit infrared rays (referred to as area B). As a result, the output of the infrared sensor 5b of the second detector 5 is mainly used as an integral value SB _(Y) of the absorption spectrum of the measurement component Y in the B region as shown in FIG. And the integral S of the absorption spectrum of the measurement component X
Absorbance signals corresponding to a value obtained by adding _B to _(X) (hereinafter referred to as B region absorbance signal S _B) is obtained.

[0023] Then, a band-pass filter 6a in the third detector 6, the transmission wavelength band, in FIG. (B) as indicated by a chain line F _T, the absorption wavelength band of the measurement component X · Y It is set so as to transmit infrared rays in the entire wavelength region (λ _{1 to} λ ₅ : hereinafter, referred to as T region).
Therefore, the infrared sensor 6 in the third detector 6
From the output of b, the measurement components X and Y shown in FIG.
Corresponding absorbance signal to a value that the integration value is added to each other in each absorption spectrum (hereinafter, referred to as T region absorbance signal S _T) is obtained.

In the above description, the infrared sensors 4b and 5b of the first and second detectors 4 and 5 are provided as infrared sensors for measuring individual components, and the band-pass filter 6a and the infrared sensor 6b of the third detector 6 Are provided as a compensation bandpass filter and a compensation infrared sensor, respectively.

In the arithmetic unit 7, first, the output of each of the infrared sensors 4b, 5b, and 6b is converted into each of the A region and B
Three absorbance signal S _A for each area · T region, S _B, the process of converting the S _T is performed.

On the other hand, when the measurement component X alone flows into the measurement cell 1 in a unit concentration, the A ·
Reference absorbance α _{A (X)}・ α _{B (X)}・ α _{T (X)} for each area of BT
Is obtained and stored in advance. In addition, as for the measurement component Y, the reference absorbance α _{A (Y)} · α _{B (Y)} · α _{T (Y)} for each region when the measurement component Y alone flows in the unit concentration is stored. . Therefore, each measurement component X ·
If the concentration of Y and C _X · C _Y, and these, the absorbance signals described above S _A, S _B, between S _T, equation as follows holds.

Here, the third term on the right side of each of the above equations is a noise component (the above-described background signal). The intensity of this noise component is substantially constant in the entire wavelength region, and ε is a noise component corresponding to a unit wavelength width. _A , Δλ _A , Δλ _B , Δλ _T
The respective wavelength widths of the region, the B region, and the T region are set.

The above three relational expressions (1), (2) and (3) are
This is a simultaneous equation in which _X , C _Y, and ε are unknown. By solving these equations, the concentration C _{X of} the measurement component _X and the concentration C _Y of the measurement component Y can be obtained. That is, when the above relational expression is rewritten using a matrix,

(Equation 1) From now on, for C _X , C _Y , and ε,

(Equation 2) Becomes Such a density calculation formula is stored in the computing unit 7 in advance, and a calculation according to the calculation formula is performed, and the calculated density C _X · C _Y is output to the outside.

As described above, in the above-described apparatus, even when the concentrations of two types of gas components, the measurement component X and the measurement component Y, in which a part of the infrared absorption wavelength band overlaps each other, each measurement component X is measured. Two detectors 4 each corresponding to Y
5, it is possible to obtain a measurement result in which the background signal and the degree of mutual interference are corrected together by adding only one detector 6 for detecting the total absorbance of both measurement components X and Y. Therefore, the overall configuration is simple.

In the above description, an example of an apparatus configuration in which two components are to be measured has been taken as an example. However, in an apparatus for measuring more gas components of three or more components, the detector corresponding to each gas component is also provided with a whole. The concentration of each gas component can be calculated in the same manner as described above simply by additionally providing a detector for detecting the absorbance over the range.

By the way, for example, when two types of gas components are to be measured as described above, the concentration of one measurement component X is on the order of several thousand ppm, and the concentration of the other measurement component Y is several tens of ppm.
As in the case of pm, simultaneous measurement in a state where the change ranges of the concentrations of both measurement components X and Y are greatly different may be premised.

FIG. 3 schematically shows the absorption spectrum of each measurement component XY at this time. In this case, even if it is an operation of the using the second derived from the detector 5 B regions absorbance signal S _B corresponding to the measured component Y, accurate results for the concentration C _Y measurement component Y Is difficult to obtain. That is, the relationship between the first term in _{(2) C X · α B} (X) The second term of the S _B C _Y · α
_{B (Y)} means that even if there is a relatively large difference between α _{B (X)} and α _{B (Y)} , a further difference (C _X ≫C _Y ) between C _X and C _Y if there is, Will be. Therefore, the measured concentration change of component Y is hardly reflected, only performed calculation as deemed to have occurred by the change in concentration C _X change in S _B also in the measurement component X.

However, the measurement component X in the B region
The change in the intensity of the absorption spectrum, that is, the spectrum intensity at the foot portion away from the peak region of the infrared absorption band, sufficiently maintains the linearity with respect to the change in concentration as the concentration of the measurement component X increases. Instead, it is actually kept rather constant. Therefore,
The degree of interference of the measurement component X with the B region is calculated by the above C _X · α
_{If B (X)} is used as it is, a large error component will be mixed into it. Accordingly, the density C _{Y of the} measurement component Y may be calculated by a calculation that directly follows the density calculation formula described above.
Is not calculated with high accuracy, and the accuracy is rather deteriorated.

Therefore, when it is assumed that two types of gas components having significantly different concentrations are to be measured as described above, FIG.
As shown in (1), a weight coefficient is set for each measurement gas component via a coefficient input device (weight coefficient setting means) 10 connected to the arithmetic unit 7, and stored in the arithmetic unit 7. The weighting factor may be set based on, for example, the degree of toxicity, based on the global warming potential, or based on the priority of operation of the apparatus.

For example, in the above case, when the measurement component Y that changes in a trace concentration range is more noticeable than the measurement component X, and therefore, when a more accurate measurement result is desired for the measurement component Y, The weighting coefficient of the measurement component X is set to 1, and a larger value, for example, 100 is set for the measurement component Y.

When such a weight coefficient is set,
The arithmetic unit 7, for example, the relationship for the absorbance signal S _B in the B region corresponding to the measurement component Y (2), And the concentrations of the measurement components X and Y are calculated in the same manner as described above from the equation (2 ′) and the equations (1) and (3).

The above equation (2 ') shows that, assuming that a detection value 100 times larger than the actual detection value S _B is obtained, this change is caused by the change of the measurement component X to the B region. A relational expression that the degree of interference (C _X · α _{B (X)} ) hardly changes and is considered to be mainly caused by the change (100C _Y · α _{B (Y)} ) of the measurement component Y, ie, the measurement component X Is corrected so that the degree of interference becomes smaller in accordance with the actual situation. Also, the calculated value of the second term on the right side of the above equation (2 ′) is
The order is almost equivalent to the calculated value of the term, and the calculation in which the density change of the measurement component Y is sufficiently reflected is performed.

In this case, the accuracy of the density calculation result for the measurement component X for which the weighting coefficient is set to a small value may be impaired, but at least the measurement component Y having a high degree of attention is attained.
For, a highly accurate calculation result can be obtained.

When there are three types of measurement components, for example, in an apparatus configuration for measuring the component Z in addition to the measurement components X and Y, for example, the weight coefficient for the measurement component X is 1, and the measurement component Y Is 100,
When the weighting coefficient for the measurement component Z is set to 30, an absorbance signal S _B corresponding to the measurement component Y and an infrared ray in the wavelength region C corresponding to the measurement component Z are provided. The relational expression for the absorbance signal S _C obtained from the detector is To the respective concentrations C _X , C _Y, and C _{Z of} the respective components X, Y, and _Z.
Is calculated. As a result, a more accurate calculation result is obtained for at least a component having a larger weighting coefficient. Furthermore, even when the number of measurement components becomes four or more, by setting the weighting factors as described above, it is possible to obtain a highly accurate calculation result at least for specific components whose weighting factors are set to large values. Can be

As described above, it is assumed that multi-component measurement in which a part of the infrared absorption wavelength band overlaps each other, and even if there is a large difference in the concentration change range of each measurement component, it is specified by setting the weighting coefficient. An analyzer that can accurately determine the concentration of a component can be suitably used, for example, for analyzing exhaust gas from a plasma processing apparatus in a semiconductor manufacturing process.
In the semiconductor manufacturing process, a plasma CVD apparatus for forming a film on a semiconductor substrate such as silicon by converting a processing gas into plasma and a plasma etching apparatus for performing dry etching are frequently used, and from such a plasma processing apparatus,
A large number of gas species having similar compositions and thus having a large overlap of infrared absorption wavelength bands are exhausted in a mixed manner. Examples of combinations of the exhaust gas types are shown in Tables 1 and 2 by adding the order of the concentration range for each gas type.

[0041]

[Table 1]

[0042]

[Table 2]

Among these gas species, there are toxic substances and substances that affect the global environment such as global warming. Therefore, for example, regarding the abatement device (exhaust gas treatment device) provided at the subsequent stage of the plasma treatment device,
It is necessary to accurately measure the concentration range by paying attention to the special substances as described above, and to design them so that they can be completely eliminated.

However, conventionally, in an analysis in a state where many types of gases are mixed and interfere with each other as described above,
For example, a gas type having a low concentration cannot be accurately measured, and therefore, the above-described exclusion device has to be designed with an excessive performance specification.

Therefore, in the analysis of such an exhaust gas treatment,
By using the above-mentioned absorption spectrometer and setting the weight coefficient for each gas type in accordance with the degree of attention, it is possible to perform a quantitative analysis of a desired gas type with high accuracy. For example, from the viewpoint of toxicity, weights such as CO ₂ and CF ₄ are low, weights such as CO and HF are high, and the weight coefficient is set small for the former and large for the latter. As a result, it is possible to more completely perform the processing of the predetermined gas type with the exclusion device, and furthermore, it is possible to design and manufacture the exclusion device with the minimum required performance specifications, thereby reducing the overall cost. Becomes possible.

Although the specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various changes can be made within the scope of the present invention.
For example, in the above description, an example has been given in which the weighting factor is set corresponding to each measurement component. However, a configuration in which the weighting factor is set corresponding to a combination of components that interfere with each other, for example, a combination of the A component and the B component In addition, a configuration may be adopted in which the weighting factor is set in accordance with the combination of the A component and the C component. Furthermore, it is also possible to configure so that the weighting factor can be set so as to correspond to the degree of interference of the B component with the A component and the degree of interference of the A component with the B component.

[0047]

As described above, in the absorption spectrometer according to the first aspect of the present invention, in addition to the number of infrared detectors corresponding to each measurement gas component, one bandpass filter for compensation is provided. By simply providing a pair of a sensor and an infrared sensor, a measurement result in which the background signal and the degree of mutual interference are corrected together can be obtained, so that the entire configuration is simplified.

In the absorption spectrometer according to the second aspect, even when, for example, measurement of a measurement gas component having a greatly different range of change in concentration is performed, the degree of interference based on the type of gas having high concentration is suppressed in accordance with the weighting coefficient. Is performed, a highly accurate calculation result can be obtained even for a gas type having a small concentration.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an absorption spectrometer according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining absorbance signals obtained by outputs from a plurality of infrared detectors in the above-mentioned absorption spectrometer. FIG. 2 (a) is a graph showing absorption spectra of two kinds of measurement gas components, and FIG. b) is a graph showing the transmission characteristics of each band-pass filter provided in the infrared detector, and (c) is an explanatory diagram of the absorbance signal obtained by the output from the first infrared detector, and (d) () Is an explanatory diagram of an absorbance signal obtained by an output from the second infrared detector.

FIG. 3 is a graph showing the absorption spectra of two types of measurement gas components whose concentration change ranges are largely different.

FIG. 4 is a schematic diagram of a configuration of a conventional absorption spectrometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Measurement cell 2 Infrared light source 3 Rotary chopper 4.5.6 Infrared detector 4a / 5a Bandpass filter 4b / 5b Infrared sensor (infrared sensor for individual component measurement) 6a Bandpass filter (bandpass filter for compensation) 6b Infrared Sensor (compensation infrared sensor) 7 Computing unit (computing means) 10 Coefficient input device (weight coefficient setting means)

Claims (2)

[Claims] 1. An infrared light source is arranged on an incident side with a measurement cell to which a sample gas is supplied interposed therebetween, and on the emission side, a number of infrared detectors corresponding to a plurality of measurement gas components in the sample gas are provided. Each infrared detector is an absorption spectrometer that is formed by providing an infrared sensor for individual component measurement provided with a bandpass filter that selectively transmits infrared in a wavelength range corresponding to the absorption wavelength band of the corresponding measurement gas component. For a measurement gas component in which a part of the infrared absorption wavelength band overlaps with each other, a compensation band pass filter for transmitting infrared light in a wavelength range over the entire absorption wavelength band of the measurement gas component is provided. In addition to installing an infrared sensor, each output from the infrared sensor for compensation and the infrared sensor for individual component measurement is calculated according to a concentration calculation formula stored in advance. Absorption spectrometer, characterized in that there is provided a calculating means for calculating the concentration of the constant gas component. 2. A weighting factor setting means for setting a weighting factor corresponding to each measurement gas component, wherein said calculating means calculates a degree of interference between each measurement gas component in said concentration calculation expression. 2. The absorption spectrometer according to claim 1, wherein a correction based on the magnitude of the weight coefficient is performed to calculate the concentration of each measurement gas component.