JP4058005B2 - Infrared gas analyzer calibration method - Google Patents

Description

  The present invention relates to a calibration method for an infrared gas analyzer used in a semiconductor manufacturing system (semiconductor manufacturing process).

  As a gas analyzer used in a semiconductor manufacturing system, there is an infrared gas analyzer that measures a gas component by an NDIR method (non-dispersive infrared gas analysis method) which is a kind of infrared absorption method. The sensitivity of this infrared gas analyzer Calibration is generally performed by sending a calibration gas of known concentration to the gas analyzer.

  By the way, the gas used in the semiconductor manufacturing system is a gas in a standard state, for example, supplied directly from a gas cylinder or the like, and its concentration is kept at a predetermined value, and a gas or the like that is a solid or liquid in a standard state. For example, it may be necessary to form the material from a solid or liquid raw material in the supply line, or the concentration may fluctuate over time due to unstable properties. is there. And, the sensitivity calibration of the infrared gas analyzer for measuring the former gas can be performed without any problem because a gas of a predetermined known concentration used for the calibration can be obtained relatively easily from a gas cylinder or the like. In the infrared gas analyzer for measuring the latter gas, it is extremely difficult to obtain a gas having a predetermined known concentration used for sensitivity calibration, and there is a disadvantage that sensitivity calibration cannot be performed easily and accurately. It was.

  The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to use an infrared gas analyzer that is used in a semiconductor manufacturing system and uses a gas that is impossible or difficult to achieve a predetermined concentration as a measurement target gas. It is intended to provide a method for calibrating an infrared gas analyzer capable of easily and accurately performing sensitivity calibration.

  To achieve the above object, a calibration method for an infrared gas analyzer according to the present invention uses a gas having an infrared absorption wavelength that flows through a gas line of a semiconductor manufacturing system as a measurement target gas, and detects the measurement target gas. A method for calibrating an infrared gas analyzer equipped with a wavelength detector, wherein a gas having a predetermined concentration having an infrared absorption wavelength flows outside the detection region of the measurement wavelength detector in another gas line of the semiconductor manufacturing system. In addition, a branch line for introducing the predetermined concentration gas into the infrared gas analyzer as a calibration gas is provided, and a calibration wavelength detector for detecting the calibration gas is provided in the infrared gas analyzer, thereby detecting the calibration wavelength. The detection signal of the wavelength detector for measurement is corrected based on the detection signal of the calibration gas by the detector (claim 1).

  Further, a comparison wavelength detector having a detection region outside the detection region of the measurement wavelength detector and the calibration wavelength detector, and infrared absorption within the detection region of the measurement wavelength detector and the calibration wavelength detector. A line for introducing a reference gas having no wavelength may be provided in the infrared gas analyzer (claim 2).

  In any of the above infrared gas analyzer calibration methods, the infrared gas analyzer may be provided with two reference wavelength detectors for detecting infrared rays having wavelengths shorter and longer than the infrared absorption wavelength of the measurement target gas. (Claim 3)

  According to the first aspect of the present invention, even if the measurement target gas of the infrared gas analyzer is a gas that is impossible or difficult to achieve a predetermined concentration, the gas having the predetermined concentration is used as a calibration gas. The sensitivity of the measurement components of the infrared gas analyzer can be confirmed easily and accurately.

  Moreover, since the calibration gas is a gas used in a semiconductor manufacturing system, the calibration method of the infrared gas analyzer according to the present invention is simple and low, for example, by improving only a part of an existing semiconductor manufacturing system. It can be carried out at a low cost, and the maintenance of the infrared gas analyzer can be easily performed.

  According to the second aspect of the invention, since the comparative wavelength detector and the reference gas are used, in addition to the above effect, an effect that a better sensitivity calibration can be performed is obtained.

  According to the invention which concerns on Claim 3, the measurement stability of an infrared gas analyzer improves. That is, in the conventional infrared gas analyzer, the detection obtained by the reference wavelength detector that detects infrared light having a shorter wavelength than the measurement wavelength of the measurement target gas (the wavelength that is the detection range of the measurement wavelength detector). The concentration of the gas to be measured is derived from the difference between the signal and the detection signal of the measurement wavelength detector.

  Therefore, for example, impurities such as powder adhere to the inner wall of the cell constituting the optical system, and contamination having wavelength dependency increases with time in the optical system. At this time, the conventional infrared gas analyzer described above is used. However, there is a problem that the intensity distribution of the infrared light incident on each detector through the optical system changes, and the error amount included in the concentration information of the measurement component increases only by the signal difference.

  However, in the invention according to claim 3, since the wavelength for obtaining the reference gas detection signal is obtained from at least two positions on the short wavelength side and the long wavelength side of the measurement wavelength, an optical system having wavelength dependency is obtained. The influence of dirt on the measurement of the infrared gas analyzer can be suppressed as much as possible, and the measurement stability can be greatly improved.

FIG. 1 shows an example of the configuration of a semiconductor manufacturing system equipped with an infrared gas analyzer to which the infrared gas analyzer calibration method according to the first embodiment of the present invention is applied. A CVD chamber used for manufacturing (a plasma CVD chamber in this embodiment), and on the upstream side thereof, a first supply line 2 for supplying Pb (DPM) ₂ gas as a source gas used for semiconductor manufacturing, and CVD A second supply line 3 for supplying NF ₃ gas used for cleaning the chamber 1 is connected. A discharge line 4 is connected to the downstream side of the CVD chamber 1.

Specifically, the first supply line 2 includes a container 5 heated by, for example, a heater (not shown), and sublimates powdery Pb (DPM) ₂ accommodated in the container 5 to obtain Pb (DPM ) It is configured to obtain ₂ gas. This Pb (DPM) ₂ gas is sent to the infrared gas analyzer 6 (details will be described later) through the first supply line 2 by the carrier gas (Ar in this embodiment) CG, and its concentration is After being measured, it is supplied to the CVD chamber 1.

Further, based on the detected value of Pb (DPM) ₂ gas obtained by the infrared gas analyzer 6, a flow rate adjusting mechanism (not shown) of the carrier gas CG and a heater for heating the container 5 are feedback-controlled. Accordingly, the flow rate of the carrier gas CG and the temperature of the container 5 are appropriately adjusted so that the flow rate and concentration of the Pb (DPM) ₂ gas supplied from the first supply line 2 to the CVD chamber 1 have appropriate values. The

  A branch line 8 to be described later is connected between the container 5 of the first supply line 2 and the infrared gas analyzer 6 via a three-way switching valve (for example, a three-way electromagnetic valve) 7.

On the other hand, the second supply line 3, the gas cylinder a predetermined concentration of NF ₃ gas from (not shown) is configured to supply to the CVD chamber 1, on its way, infrared gas the NF ₃ gas A branch line 8 for introducing the gas into the analyzer 6 as a calibration gas is connected via a three-way switching valve (for example, a three-way electromagnetic valve) 9.

The infrared gas analyzer 6 measures Pb (DPM) ₂ gas and measures a gas component by the NDIR method. The infrared light from the light source 10 passes through the cell 11 and enters the detection unit 12. It is configured as follows. Here, 13 and 14 are gas inlets and gas outlets formed in the cell 11, 15 and 16 are infrared transmissive cell windows provided at both ends of the cell 11, and 17 is a cell 11 and a detector 12. The chopper for modulation disposed between the two is configured to rotate at a constant period by a driving mechanism (not shown). The chopper 17 may be provided between the light source 10 and the cell 11.

18 is a band-pass filter provided in the measuring wavelength detector 19 for detecting the Pb (DPM) ₂ gas, Pb (DPM) of infrared absorption _{wavelength 2} gas absorbs, measurement using the detection An infrared ray having a wavelength for use (in this embodiment, a wavelength of 1350 cm ^{-1 to} 1400 cm ^-1 ) is transmitted.

Reference numeral 20 denotes a band-pass filter provided in the calibration wavelength detector 21 for detecting NF ₃ gas as a calibration gas, which is not absorbed by Pb (DPM) ₂ gas or can be ignored. The calibration wavelength is as close as possible to the measurement wavelength (in this example, the infrared absorption wavelength of the NF ₃ gas, which is a wavelength of 880 cm ^{−1 to} 920 cm ⁻¹ ), as long as it absorbs only to a certain extent. It is configured. That is, the NF ₃ gas has an infrared absorption wavelength outside the detection region of the measurement wavelength detector 19.

  Then, detection signals proportional to the energy of the infrared rays that have passed through the cell 11 and the bandpass filters 18 and 20 are output from the detectors 19 and 21 constituting the detection unit 12 to the calculation unit 22.

Next, a method for calibrating the infrared gas analyzer 6 will be described.
First, the three-way switching valve 7 is operated to switch from the state in which the port 7a and the port 7b communicate to the state in which the port 7a and the port 7c communicate, and the three-way switching valve 9 is operated to connect the port 9a and the port 9b. The port 9a and the port 9c are switched to the state where the port 9a and the port 9c are communicated. In this state, NF ₃ gas having a predetermined concentration flowing through the second supply line 3 is introduced into the infrared gas analyzer 6 through the branch line 8.

With the above operation, in the infrared gas analyzer 6, the calibration gas detection signal from the calibration wavelength detector 21 is output to the calculation unit 22. The computing unit 22 then measures the wavelength detector 19 for measurement based on the difference between the NF ₃ gas concentration indicated by the calibration gas detection signal and the actual NF ₃ gas concentration (predetermined concentration) set in advance. A correction value for calibrating the sensitivity is derived. For example, when the deviation is 10%, the correction value is set to 10%, and the measurement gas detection signal output from the measurement wavelength detector 19 to the calculation unit 22 is corrected by 10%. The sensitivity ratio between the two detectors 19 and 21 is obtained in advance.

FIG. 2 shows an example of the configuration of a semiconductor manufacturing system including an infrared gas analyzer to which the infrared gas analyzer calibration method according to the second embodiment of the present invention is applied. In addition, the same code | symbol is attached | subjected about the member of the same structure as what was shown in FIG. 1, and the description is abbreviate | omitted.
In FIG. 2, reference numeral 23 is a comparative gas line that is connected to the branch line 8 via the on-off valve 24 and supplies a comparative gas. As the comparative gas, a gas having no infrared absorption wavelength within the range of the measurement wavelength and the calibration wavelength (1350 cm ^{−1 to} 1400 cm ⁻¹ and 880 cm ^{−1 to} 920 cm ⁻¹ ) is used. A gas composed of monoatomic molecules such as N ₂ without external absorption (N ₂ gas in this embodiment) or an inert gas such as Ar is used.

Reference numeral 25 denotes a comparison filter provided with a band-pass filter 26 that transmits infrared rays having wavelengths different from the measurement wavelength and the calibration wavelength (1350 cm ^{−1 to} 1400 cm ⁻¹ and 880 cm ^{−1 to} 920 cm ⁻¹ ). It is a wavelength detector. That is, the comparison wavelength detector 25 has a detection region outside the detection region of the measurement wavelength detector 19 and the calibration wavelength detector 21, and the detection of the measurement wavelength detector 19 and the calibration wavelength detector 21. This detector is for detecting a comparative gas having no infrared absorption wavelength in the region, and a detection signal proportional to the energy of infrared rays that have passed through the cell 11 and the band-pass filter 26 and entered from the detector 25. It is output to the calculation unit 22.

  Here, the measurement wavelength detector 19, the calibration wavelength detector 21 and the comparison wavelength detector 25 are, for example, on a plane perpendicular to the traveling direction of infrared rays from the light source 10, as shown in FIG. The chopper 17 is located on the same circumference around the rotation shaft 17a.

In the semiconductor manufacturing system having the above-described configuration, calibration and measurement of the infrared gas analyzer 6 are performed as follows.
First, a comparison gas detection signal is obtained in advance. That is, the ports 7a and 7c of the three-way switching valve 7 are made to communicate with each other and the on-off valve 24 is opened. At this time, the NF ₃ gas flowing through the second supply line 3 passes through the branch line 8 and the infrared gas analyzer. 6, the ports 9 a and 9 b of the three-way switching valve 9 are communicated, and if necessary, an on-off valve (not shown) provided in the second supply line 3 is closed. Then, by introducing N ₂ gas as a reference gas having a predetermined concentration flowing through the comparison gas line 23 into the infrared gas analyzer 6 through the branch line 8, the infrared gas analyzer 6 uses the comparison wavelength detector 25. The comparison gas detection signal from is output to the calculation unit 22.

Specifically, the relationship between the wavelength of the infrared ray transmitted through the cell 11 and the light intensity when N ₂ gas is introduced into the cell 11 is represented by a graph indicated by a symbol R in FIG. Then, only a suitable range of infrared rays indicated by symbol h in FIG. 4 selected by the band-pass filter 26 is incident on the comparison wavelength detector 25, and a comparative gas detection signal corresponding to the incident infrared energy is calculated. Input to the unit 22. Thereby, a comparative gas detection signal is obtained.

In the calibration of the infrared gas analyzer 6, the ports 7a and 7c of the three-way switching valve 7 are communicated, the ports 9a and 9c of the three-way switching valve 9 are communicated, and the on-off valve 24 is closed. Then, the NF ₃ gas having a predetermined concentration flowing through the second supply line 3 is introduced into the infrared gas analyzer 6 through the branch line 8. With this operation, in the infrared gas analyzer 6, the calibration gas detection signal from the calibration wavelength detector 21 is output to the calculation unit 22.

Specifically, the relationship between the wavelength of the infrared rays that pass through the cell 11 and the light intensity when the NF ₃ gas is introduced into the cell 11 is represented by a graph indicated by a symbol Q in FIG. Then, the calibration wavelength detector 21 receives only an infrared ray in an appropriate range indicated by the symbol b in FIG. 4 selected by the bandpass filter 20, and a calibration gas detection signal corresponding to the incident infrared energy. Input to the calculation unit 22.

Thereafter, the calculation unit 22 derives the NF ₃ gas concentration by subtracting the calibration gas detection signal from the comparison gas detection signal obtained in advance, and the derived NF ₃ gas concentration is set to the actual value set in advance. Based on the deviation from the NF ₃ gas concentration (predetermined concentration), a correction value for calibrating the sensitivity of the measurement wavelength detector 19 is derived. For example, when the deviation is 10%, the correction value is set to 10%, and the sensitivity of the measurement wavelength detector 19 is calibrated. Note that the sensitivity ratio of the three detectors 19, 21, and 25 is obtained in advance.

The measurement by the infrared gas analyzer 6 is performed in a state where the port 7a and the port 7b of the three-way switching valve 7 communicate with each other and the port 9a and the port 9b of the three-way switching valve 9 communicate with each other. That is, at this time, Pb (DPM) ₂ gas flowing through the first supply line 2 is supplied to the infrared gas analyzer 6, and a measurement gas detection signal from the measurement wavelength detector 19 is output to the calculation unit 22.

Specifically, the relationship between the wavelength of the infrared ray transmitted through the cell 11 and the light intensity when Pb (DPM) ₂ gas is introduced into the cell 11 is represented by a graph indicated by a symbol P in FIG. Then, the measurement wavelength detector 19 receives only an infrared ray in an appropriate range indicated by the symbol a in FIG. 4 selected by the band pass filter 18 and a measurement gas detection signal corresponding to the incident infrared energy. Input to the calculation unit 22. Thereafter, the concentration of Pb (DPM) ₂ gas is obtained by correcting the value obtained by subtracting the measurement gas detection signal from the comparison gas detection signal obtained in advance using the correction value described above.

  FIG. 5 shows an example of the configuration of a semiconductor manufacturing system including an infrared gas analyzer to which the infrared gas analyzer calibration method according to the third embodiment of the present invention is applied. In addition, the same code | symbol is attached | subjected about the member of the same structure as what was shown in FIG. 1, and the description is abbreviate | omitted.

Reference numeral 27 denotes a first reference wavelength detector provided with a band-pass filter 28 that transmits infrared rays having wavelengths shorter than the measurement wavelength and calibration wavelength (1350 cm ^{−1 to} 1400 cm ⁻¹ and 880 cm ^{−1 to} 920 cm ⁻¹ ). It is a vessel. Reference numeral 29 denotes a second reference filter provided with a band-pass filter 30 that transmits infrared rays having wavelengths longer than the measurement wavelength and the calibration wavelength (1350 cm ^{−1 to} 1400 cm ⁻¹ and 880 cm ^{−1 to} 920 cm ⁻¹ ). It is a wavelength detector. Then, from each detector 27, 29, a detection signal that is transmitted through the cell 11 and the bandpass filters 28, 30 and is incident on each detector is output to the calculation unit 22.

  In this embodiment, the measurement wavelength detector 19, the calibration wavelength detector 21, and the two reference wavelength detectors 27 and 29 are perpendicular to the traveling direction of infrared rays from the light source 10, as shown in FIG. On the surface, the chopper 17 is positioned at substantially equal intervals in the circumferential direction on the same circumference around the rotation shaft 17a.

  Here, when there is no substance having an infrared absorption wavelength in the cell 11, the relationship between the wavelength of the infrared light from the light source 10 that transmits the cell 11 and the light intensity is indicated by a symbol G in FIG. Represented by a graph. Then, only the infrared ray in an appropriate range indicated by the symbol z in FIG. 7A selected by the bandpass filter 20 is incident on the measurement wavelength detector 19, and the calibration gas corresponding to the incident infrared energy. A detection signal is input to the calculation unit 22. That is, the calibration gas detection signal at this time is represented by the area of the area Z formed on the lower side of the graph G in the range z.

  Similarly, only the infrared ray in an appropriate range indicated by the symbol x in FIG. 7A selected by the band pass filter 28 is incident on the first reference wavelength detector 27 and corresponds to the incident infrared energy. The first reference gas detection signal is input to the calculation unit 22. Further, only the infrared ray in an appropriate range indicated by the symbol y in FIG. 7A selected by the band pass filter 30 is incident on the second reference wavelength detector 29, and the second reference wavelength detector 29 corresponds to the incident infrared energy. One reference gas detection signal is input to the calculation unit 22. That is, the first and second reference gas detection signals are represented by areas X and Y formed on the lower side of the graph G in the ranges x and y, respectively.

  The ranges x and y are set so that the total area of the areas X and Y matches the area of the area Z. In this embodiment, the areas of the areas X and Y are respectively the areas of the area Z. It is set to be 1/2.

  In addition, the calculation unit 22 is provided with a calculation circuit that subtracts the measurement gas detection signal from the total of the first and second reference gas detection signals.

In the semiconductor manufacturing system configured as described above, the calibration method of the infrared gas analyzer 6 is exactly the same as the method shown in the first embodiment, but the measurement in the infrared gas analyzer 6 is performed as follows. Is different.
First, the ports 7a and 7b of the three-way switching valve 7 are in communication with each other, and the ports 9a and 9b of the three-way switching valve 9 are in communication. As a result, the Pb (DPM) ₂ gas flowing through the first supply line 2 is supplied to the infrared gas analyzer 6, and the measurement gas detection signal from the measurement wavelength detector 19 and the first and second reference gas detections are detected. The signal is output to the calculation unit 22.

At this time, when the Pb (DPM) ₂ gas is introduced into the cell 11, the relationship between the wavelength of the infrared ray transmitted through the cell 11 and the light intensity is represented by a graph indicated by reference numeral G ′ in FIG. The Then, the arithmetic circuit provided in the arithmetic unit 22 performs an operation of subtracting the area A ′ of the area formed below the graph G ′ in the range z from the total area of the areas X and Y. Thus, the concentration of Pb (DPM) ₂ gas is obtained. Finally, the value of the concentration of the thus been obtained was Pb (DPM) ₂ gas, as shown in the first embodiment, it is corrected using the correction value.

Here, the infrared gas analyzer 6 that measures gas components by the NDIR method has the following problems.
(1) The light source 10 to be used emits light at an arbitrary temperature of 800 to 1300 ° C., but has an intensity distribution characteristic depending on the wavelength according to Planck's radiation type. Moreover, the intensity | strength of a short wavelength is high.
(2) In the cell 11, adhesion of impurities (in this embodiment, the sublimated Pb (DPM) ₂ gas is considered to be solidified to become powder, which becomes impurities) occurs, and the time As the process progresses, the amount of adhesion increases. For example, a reflecting mirror (not shown) is disposed in the cell 11 and the reflecting mirror is coated with gold to increase the reflectance. However, the reflectance decreases due to adhesion of impurities. Further, the decrease in reflectance has wavelength characteristics, and the decrease in wavelength becomes more severe as the wavelength becomes shorter due to scattering by powder.

  However, in the semiconductor manufacturing system having the above-described configuration, since infrared light having a shorter wavelength and longer wavelength than the wavelength of the infrared light for detecting the measurement target gas is used for reference, contamination having wavelength dependency is caused by contamination of the measurement target gas. The influence on measurement (change in light intensity distribution due to contamination of the optical system) can be reduced, and the measurement accuracy and stability of the infrared gas analyzer are greatly improved.

The present invention is not limited to the above-described embodiment, and can be implemented with various modifications. For example, in each embodiment, the gas to be measured by the infrared gas analyzer 6 is not limited to Pb (DPM) ₂ but is a gas that is used in a semiconductor manufacturing system (process) and is not easily supplied from a gas cylinder or the like. I just need it.

The calibration gas is not limited to NF ₃ gas, but is used in a semiconductor manufacturing system (process) and easily supplied as a gas having a predetermined concentration from a gas cylinder or the like. The gas may be any gas that is as close as possible to the infrared absorption wavelength of the gas to be measured and that has no absorption due to the above or can be ignored. NF ₃ used in this embodiment is a cleaning gas for the CVD chamber in the semiconductor manufacturing system. In addition, various cleaning gases and etching gases such as CF ₄ and C ₂ F ₆ can be used.

It is explanatory drawing which shows roughly the structure of the semiconductor manufacturing system provided with the infrared gas analyzer to which the calibration method of the infrared gas analyzer which concerns on 1st Example of this invention is applied. It is explanatory drawing which shows roughly the structure of the semiconductor manufacturing system provided with the infrared gas analyzer to which the calibration method of the infrared gas analyzer which concerns on 2nd Example of this invention is applied. It is a front view which shows roughly the structure of each detector in the said Example. It is a graph which shows roughly the relationship between the frequency of the infrared rays from the light source which permeate | transmitted measurement object gas, calibration gas, and comparative gas, respectively, and light intensity. It is explanatory drawing which shows roughly the structure of the semiconductor manufacturing system provided with the infrared gas analyzer to which the calibration method of the infrared gas analyzer which concerns on 3rd Example of this invention is applied. It is a front view which shows roughly the structure of each detector in the said Example. (A) is a graph schematically showing the relationship between the infrared wavelength from the light source and the light intensity, and (B) is a schematic relationship between the infrared wavelength from the light source that has passed through the measurement target gas and the light intensity. It is a graph shown in.

Explanation of symbols

2 First supply line 3 Second supply line 6 Infrared gas analyzer 8 Branch line 19 Wavelength detector for measurement 21 Wavelength detector for calibration

Claims (3)

  A method for calibrating an infrared gas analyzer comprising a measurement wavelength detector for detecting a gas to be measured by using a gas having an infrared absorption wavelength flowing through a gas line of a semiconductor manufacturing system as a measurement target gas. Introducing the predetermined concentration gas into the infrared gas analyzer as a calibration gas into another gas line of the semiconductor manufacturing system in which a predetermined concentration gas having an infrared absorption wavelength flows outside the detection region of the wavelength detector In addition to providing a branch line, a calibration wavelength detector for detecting the calibration gas is provided in the infrared gas analyzer, and the measurement wavelength detector is detected based on the detection signal of the calibration gas by the calibration wavelength detector. A method of calibrating an infrared gas analyzer, comprising correcting a signal.   A comparison wavelength detector having a detection region outside the detection region of the measurement wavelength detector and the calibration wavelength detector, and an infrared absorption wavelength within the detection region of the measurement wavelength detector and the calibration wavelength detector. The infrared gas analyzer calibration method according to claim 1, wherein the infrared gas analyzer is provided with a line for introducing a reference gas that is not included.   The infrared gas analyzer calibration method according to claim 1, wherein two reference wavelength detectors for detecting an infrared ray having a shorter wavelength and a longer infrared ray than an infrared absorption wavelength of the measurement target gas are provided in the infrared gas analyzer.

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