JP2006337346A - Absolute flow rate calibration system in flow rate control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to perform an absolute flow rate calibration with high accuracy by a process gas in a flow rate control device. <P>SOLUTION: The system comprises a gas flow path 30 between a first shutoff valve 21 and a second shutoff valve 22, an evacuation flow path 31 connecting an inlet of a vacuum pump 14, a third shutoff valve 23 mounted on the evacuation flow path 31, a pressure sensor 11, a temperature sensor 12 and a fourth shutoff valve 24, and connecting the above, and a calibration control device which memorizes a volume value of a predetermined space comprising of an outlet of a mass controller 10 of compression factor data of the gas species, the second shutoff valve 22 and the third shutoff valve 23. At the first measurement and the second measurement, a mass G<SB>1</SB>is obtained from a pressure P<SB>1</SB>, a temperature T<SB>1</SB>, the first compression factor Z<SB>1</SB>corresponding to these, and a volume V, and the mass G<SB>2</SB>is obtained from the pressure P<SB>1</SB>, the temperature T<SB>2</SB>, the second compression factor Z<SB>2</SB>corresponding to these, and the volume V at the second measurement, the absolute flow rate of the mass flow controller 10 is calibrated from the difference of the mass G<SB>1</SB>and the mass G<SB>2</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for verifying an absolute flow rate of a flow control device used in a gas system in a semiconductor manufacturing process.

In a film forming apparatus or a dry etching apparatus in a semiconductor manufacturing process, for example, a special gas such as silane or phosphine, a corrosive gas such as chlorine gas, and a combustible gas such as hydrogen gas are used.
The flow rate of these gases must be strictly controlled.
The reason is that the gas flow rate directly affects the quality of the process. That is, the film quality in the film forming process and the quality of circuit processing in the etching process are greatly affected by the accuracy of the gas flow rate, and the yield of the semiconductor product is thereby determined.

Another reason is that many of these types of gases are harmful to the human body and the environment, or explosive. For this reason, these gases after use are not allowed to be discarded directly into the atmosphere, and must be equipped with a detoxifying means corresponding to the gas type. However, such an abatement means usually has a limited processing capacity, and if a flow rate exceeding an allowable value flows, it may not be able to be treated and may lead to outflow of harmful gas to the environment or damage to the abatement means.
In addition, these gases, particularly those having a high purity and no dust that can be used in the semiconductor manufacturing process, are expensive, and depending on the type of gas, there are restrictions on use due to natural degradation, so that they cannot be stored in large quantities.

On the other hand, the flow rate of these gases required by equipment in the semiconductor manufacturing process is about 2 to 2000 sccm, and it is required to flow a constant flow rate with high accuracy in a considerably wide range.
Therefore, conventionally, a known mass flow controller, which is a flow rate control device, is arranged in the semiconductor manufacturing process circuit so as to flow an optimum flow rate for each gas type. And this mass flow controller can respond to a change of a process recipe by changing a setting flow rate by changing an applied voltage.

However, among these gases used in the semiconductor manufacturing process, so-called process gases, in particular, a film forming material gas may cause solids to be deposited in the gas line due to its characteristics, and may change the flow volume. The mass flow controller uses a thin tube inside to supply a constant flow rate with high accuracy. If a small amount of solid matter is deposited in such a portion, the flow rate accuracy to be supplied deteriorates. In addition, since highly corrosive gas used for etching processes is flowed, even if a highly corrosion-resistant material such as stainless steel is used in the mass flow controller, corrosion is inevitable and aging may occur. Yes, this also deteriorates the flow rate accuracy.
In this way, since the relationship between the applied voltage and the actual flow rate changes and the actual flow rate may change, the flow rate of the mass flow controller needs to be periodically calibrated and calibrated.

The flow rate verification of this mass flow controller is basically performed using a membrane flow meter, but this measurement is performed with a part of the pipe removed, and after the measurement, the pipe is reassembled and checked for leaks. Have to do. For this reason, work is very troublesome.
Therefore, it is ideal that the flow rate verification can be performed without removing from the piping.
As a method of performing the flow rate verification with the pipes assembled, it may be possible to use a vacuum system provided in the process chamber, but this method is insufficient in terms of required time and accuracy.

For example, as a system for measuring a flow rate by measuring a pressure drop in a space of a certain volume and verifying a flow rate of a mass flow controller by a build-down method, a method such as Patent Literature 1 filed and patented by the present applicant is disclosed. is there.
Patent Document 1 discloses a mass flow controller absolute flow rate verification system. FIG. 14 shows the piping diagram.
This system uses an inert gas such as nitrogen gas as a measurement gas, and measures the pressure drop rate through the mass flow controller 10 from a state where the gas line is filled with a predetermined measurement gas. For this purpose, a pressure sensor 11 and a measurement gas tank 102 for storing measurement gas via a measurement on-off valve 101 are provided on a pipe 110 between the inlet of the mass flow controller 10 and the first on-off valve 100, and the mass flow is provided. After the process gas supply to the controller 10 is shut off by the first on-off valve 100, the measurement on-off valve 101 is opened, and the time T required for a predetermined pressure drop is measured by the pressure sensor 11, whereby the absolute flow rate of the mass flow controller 10 is measured. Can be easily and conveniently assayed.

However, in the method of Patent Document 1, it is necessary to use an inert gas such as nitrogen gas as the measurement gas. In measuring the flow rate, the temperature is kept constant, the volume in the circuit is calculated using the ideal gas state equation based on the change in pressure, and the flow rate is calculated based on the elapsed time T and the volume. Because it is.
However, the process gas that actually flows through the line is a compressed fluid, and the flow rate when the process gas is actually used is the same as when the calibration is performed with an inert gas such as nitrogen gas that is close to the ideal gas. There is no guarantee.
In addition, the system cannot be used during such measurement, and it takes time for the process gas purity in the line to recover when the system is restarted after measurement is completed. There was a problem that the operating rate of the system was lowered.
Further, in the method of Patent Document 1, even if it is found as a result of the measurement that the flow characteristic of the mass flow controller 10 is deviated from the initial state, the calibration has to be performed separately by the system user.
Therefore, the present applicant also discloses a method as described in Patent Document 2.
Patent Document 2 discloses a gas piping system verification system. FIG. 15 shows a schematic diagram of the piping.

In the invention according to Patent Document 2, a process gas is supplied from a process gas source to a process chamber 121 via a gas line including a first cutoff valve 100, a mass flow controller 10 downstream thereof, and a final cutoff valve 120 downstream thereof. The gas piping system that supplies the gas has a pressure sensor 11 that measures the pressure on the inlet side of the final cutoff valve 120, opens the first cutoff valve 100, and closes the final cutoff valve 120. This is a system for measuring the flow rate of the mass flow controller 10 by measuring the pressure rise when the process gas is introduced to the upstream side of the final shutoff valve 120 through the mass flow controller 10 by the pressure sensor 11.
In this system, when the flow rate of the mass flow controller 10 is verified, both the first cutoff valve 100 and the final cutoff valve 120 are first opened. At this time, while the process gas is supplied from the process gas source, the portion downstream of the mass flow controller 10 communicates with an exhaust pump downstream of the process chamber 121.
In this type of gas piping system, an exhaust pump is usually provided further downstream of the process chamber 121, and in this case, the pressure in that part drops to near vacuum. Moreover, when the exhaust pump is not provided, it falls to the vicinity of atmospheric pressure. The pressure is measured by the pressure sensor 11.

Next, the final stage shutoff valve 120 is closed to shut off the exhaust to the process chamber 121 side. Then, since the gas flow rate is regulated by the mass flow controller 10, the pressure gradually increases in the portion between the mass flow controller 10 and the final shutoff valve 120 by the process gas. For this reason, since the measured value of the pressure sensor 11 gradually increases, the flow rate of the mass flow controller 10 is verified by this increase.
Specifically, the test is performed by calculating the slope of the change over time in the pressure increase by the least square method and comparing it with the initial slope.
As a result, the flow rate of the mass flow controller 10 can be verified by the process gas.
If the flow rate of the mass flow controller 10 deviates from the initial value as a result of the flow rate verification, the flow rate is automatically corrected by a command from a main body controller (not shown). Gas can be supplied.

As another method, there is a method of measuring the absolute flow rate of the flow rate control device by a method as in Patent Document 3.
Patent Literature 3 discloses a gas mass flow measurement system, and FIG. 16 shows a conceptual diagram.
In FIG. 16, the input terminal 134 connected to the pressure transducer 130 and the temperature sensitive resistor element 138 electrically connected between the input terminal 134 and the output terminal 142 are connected and fixed. The temperature sensitive resistance element 140 is electrically connected between the output terminal 142 and the ground 136.
The pressure transducer 130 is any relatively high precision pressure gauge, for example, a capacitance manometer using a movable metal diaphragm that is responsive to the gas pressure being measured.

By means of a circuit electrically connected to the pressure transducer 130, the resistance value of this resistive element varies directly (in direct proportion) with temperature, increases with increasing temperature and decreases with decreasing temperature. As the temperature of the gas in contact with the resistance element 138 increases, its resistance value increases. The magnitude of the output voltage V appearing across the fixed sensitive resistor element 140 will therefore decrease, but a larger portion of the overall signal voltage will drop across the temperature sensitive resistor element 138. Because it does.
Therefore, by connecting this pressure transducer 130 to a chamber having a known volume provided downstream of the mass flow controller 10 connected to a gas source (not shown), the average gas flow rate of the mass flow controller 10 is determined. A relatively simple device to calibrate will be provided.
According to the method of Patent Document 3, the flow rate of the mass flow controller can be obtained in proportion to the number of moles of gas inside the chamber, and the process gas itself can also be measured by the fluid to be measured. In this case, mathematical calculation is not required, and it is not necessary to separately measure pressure and temperature.
Japanese Patent No. 2635929 Japanese Patent No. 3367811 Japanese Patent No. 3022931

  However, there is a strong demand from users who want to perform verification based on the actual flow rate of the mass flow controller, and in Patent Document 1, since an absolute flow rate verification is performed using the measurement gas, an appropriate flow rate flows when the process gas is used. According to Patent Document 2, the mass flow controller can be verified by the actual process gas used. However, the mass flow controller is verified by comparing it with the initial data of the rate of increase in pressure. Since it is a flow rate verification, an absolute flow rate verification cannot be performed.

According to the method of Patent Document 3, the absolute flow rate verification of the mass flow controller using process gas is possible. However, in actuality, the absolute flow rate using a highly accurate pressure gauge and a temperature sensitive resistance element is used. In terms of whether or not high-accuracy flow rate can be verified, correction by pressure and correction by the temperature of the fluid in the flow path are performed, but it is corrected by a coefficient specific to the gas type. In addition, it is unclear whether the value of the absolute flow rate of the process gas can be obtained with high accuracy, and there is no detailed description thereof.
In other words, with the methods of Patent Documents 1 to 3, it is considered difficult to perform a highly accurate absolute flow rate verification.

Furthermore, in the method of Patent Document 2, it is an absolute condition that the volume is constant.
In Patent Document 2, the volume of the space between the final shutoff valve of the flow path connected to the process chamber and the mass flow controller needs to be constant. If the volume of this space changes, it should be a reference. The data is lost and the mass flow controller cannot be calibrated after the modification.
The same can be said in Patent Document 3. In order to obtain the flow rate, it is described that an increase in pressure in a chamber having a known constant volume is measured using an electric circuit triggered by a pressure sensor. Therefore, if the volume of the space to be measured is changed by remodeling, the flow rate cannot be accurately verified. In addition, the chamber here refers to a container for measuring the pressure connected to a pipe having a known constant volume, and the volume of the chamber is sufficient so that it is hardly affected by the flow path change. Although a large system can be considered, it is not feasible in a semiconductor manufacturing apparatus with severe spatial constraints.
However, remodeling of the gas integrated unit can frequently occur due to a manufacturing plan, a design change or the like, and realization of the absolute flow path measuring means corresponding to the remodeling is very demanded by the user.

  Therefore, the present invention has been made to solve such a problem. (1) It is possible to perform a high-accuracy absolute flow rate verification of a flow rate control device represented by a mass flow controller with a process gas. ) Providing an absolute flow rate verification system that can realize the verification of the absolute flow rate of the flow control device by obtaining the volume even if the volume of the flow path has changed due to modification, etc. With the goal.

In order to achieve the above object, the flow control device absolute flow verification system of the present invention has the following characteristics.
(1) The absolute flow rate of the flow rate control device is verified in a flow rate control unit having a first shut-off valve and a second shut-off valve provided in a gas flow path that communicates the outlet of the flow rate control device and the inlet of the process chamber. In the flow rate control device absolute flow rate verification system, an exhaust passage that communicates the gas passage between the first shut-off valve and the second shut-off valve and an inlet of a vacuum pump, and the exhaust passage is provided. A pressure sensor, a temperature sensor, the pressure sensor, and the temperature sensor provided in the exhaust passage between the third cutoff valve, the fourth cutoff valve, the third cutoff valve, and the fourth cutoff valve. And control for storing the volume value of the predetermined space formed by the compression factor data specific to the gas type, the outlet of the flow rate control device, the second shut-off valve, and the fourth shut-off valve And at the time of the first measurement A first compression factor value corresponding to the first pressure value by the pressure sensor and the first temperature value by the temperature sensor is read from the compression factor data of the test control device, and the first pressure value, A first mass is obtained from the first temperature value, the volume value, and the first compression factor value, and a second pressure value by the pressure sensor and a second temperature value by the temperature sensor at the time of the second measurement are obtained. A corresponding second compression factor value is read from the compression factor data of the test control device, and a second mass is calculated from the second pressure value, the second temperature value, the volume value, and the second compression factor value. The absolute flow rate of the flow control device is verified based on the difference between the first mass and the second mass.

Note that the fluid control device referred to here refers to a device that controls the flow rate of fluid, represented by a mass flow controller or the like.
The compression factor referred to here is a variable represented by the equation Z = PV / RT, where V is the volume of 1 mol of gas at pressure P and absolute temperature T, and R is the gas constant. This represents the deviation of the actual gas from the ideal gas, and shows a different value depending on the gas type. In the ideal gas, Z = 1. Z is also called a compression coefficient.

This compression factor is a function of temperature and pressure, as expressed in the equation, and tends to change little at high temperatures and low pressures, but is often used at room temperature when applied to semiconductor manufacturing process gases. Therefore, the value of Z changes with temperature and pressure. However, a variable with less error such as a correction factor specific to the gas type instead of the compression factor may be used.
The compression factor data referred to here is data obtained by converting the numerical value of the compression factor corresponding to the temperature and pressure measured in advance, and has different data depending on the gas type. However, in the case of using only limited gas types, it is also possible to calculate by a calculation formula without having data.
The process chamber here refers to a chamber in which a semiconductor manufacturing process is performed using a process gas.

(2) In the flow rate control device absolute flow rate verification system described in (1), the flow rate control device is configured to flow a predetermined flow rate given in advance, and the first measurement time and the second measurement time have elapsed. A first method that is determined based on time, and a second method that is determined based on a predetermined pressure when the first measurement and the second measurement are performed. Switching is performed according to the constant flow rate.
The elapsed time here changes depending on the flow rate in order to reduce the error in the flow rate verification of the flow rate control device, and it has been confirmed by experiments that a longer time is required as the flow rate is lower.
The predetermined pressure here is a pressure value used to verify the flow rate of the flow control device instead of the elapsed time, and when the flow rate of the process gas used for verification is large, the pressure increases instantaneously. Therefore, it is possible to measure with higher accuracy by performing the measurement based on the pressure, and it has been confirmed by experiments.

(3) The absolute flow rate of the flow rate control device is verified in a flow rate control unit having a first shut-off valve and a second shut-off valve provided in a gas flow path communicating with the outlet of the flow rate control device and the inlet of the process chamber. In the flow rate control device absolute flow rate verification system, an exhaust passage that communicates the gas passage between the first shut-off valve and the second shut-off valve and an inlet of a vacuum pump, and the exhaust passage is provided. A pressure sensor, a temperature sensor, the pressure sensor, and the temperature sensor provided in the exhaust passage between the third cutoff valve, the fourth cutoff valve, the third cutoff valve, and the fourth cutoff valve. A first control space formed by closing the first shut-off valve, the second shut-off valve, and the third shut-off valve, and the third shut-off And the fourth shut-off valve is closed Is formed by the, spaced from the first sealed space in the third shut-off valve, if there is a second sealed space volume V ₂ is known, the gas to the first closed space and the second closed space The pressure P ₁ and the temperature T ₁ are satisfied, the first sealed space or the second sealed space is evacuated, the pressure P ₂ and the temperature T ₂ after evacuation are measured, and the third cutoff is measured The valve is opened, the first sealed space and the second sealed space are communicated, and the pressure P ₃ and the temperature T ₃ are measured after time, and the pressure P ₁ , the temperature T ₁ , the pressure P ₂ , the temperature are measured. The volume V ₁ of the first sealed space is obtained based on T ₂ , the pressure P ₃ , the temperature T ₃ , and the volume V ₂ .

The following operations and effects can be obtained by the flow control device absolute flow verification system of the present invention having such characteristics.
(1) The absolute flow rate of the flow rate control device is verified in a flow rate control unit having a first shut-off valve and a second shut-off valve provided in a gas flow path that communicates the outlet of the flow rate control device and the inlet of the process chamber. In the flow rate control device absolute flow rate verification system, an exhaust passage that communicates the gas passage between the first shut-off valve and the second shut-off valve and an inlet of a vacuum pump, and the exhaust passage is provided. A pressure sensor, a temperature sensor, the pressure sensor, and the temperature sensor provided in the exhaust passage between the third cutoff valve, the fourth cutoff valve, the third cutoff valve, and the fourth cutoff valve. And control for storing the volume value of the predetermined space formed by the compression factor data specific to the gas type, the outlet of the flow rate control device, the second shut-off valve, and the fourth shut-off valve And at the time of the first measurement A first compression factor value corresponding to the first pressure value by the pressure sensor and the first temperature value by the temperature sensor is read from the compression factor data of the test control device, and the first pressure value, A first mass is obtained from the first temperature value, the volume value, and the first compression factor value, and a second pressure value by the pressure sensor and a second temperature value by the temperature sensor at the time of the second measurement are obtained. A corresponding second compression factor value is read from the compression factor data of the test control device, and a second mass is calculated from the second pressure value, the second temperature value, the volume value, and the second compression factor value. Since it is characterized in that the absolute flow rate of the flow control device is verified by the difference between the first mass and the second mass, a measurement gas such as nitrogen gas close to an ideal gas is not used. Mass flow control It is possible to verify the absolute flow rate of the flow control device using the process gas flowing through the roller, and the ideal gas equation of state is corrected by the compression factor corresponding to each pressure value and temperature value at each time point. Since the calculation is performed, an absolute flow rate with high accuracy can be obtained, thereby achieving an excellent effect that the absolute flow rate of the flow control device can be verified.

When the absolute flow rate is calculated using the equation of state of the ideal gas, there is a deviation from the absolute flow rate of the real gas. Therefore, in order to correct the non-ideal behavior of the real gas, a simple correction factor as shown in Patent Document 3 is used. The correction using was performed. However, since the compression factor that exhibits non-ideal behavior is a function of pressure and temperature, the value of the compression factor varies depending on the pressure and temperature at the time of measurement. Therefore, by using the first compression factor and the second compression factor responsive to the respective pressures and temperatures during the first measurement and the second measurement, it is possible to calculate an appropriate absolute flow rate at each measurement.
And since it becomes possible to obtain an accurate absolute flow rate using real gas in this way, there is no difference from the actual use state, as in the case of calibration using measurement gas, Since the verification is possible by the absolute flow rate and the calibration is performed by the verification, the absolute flow rate of the gas supplied to the semiconductor device can be grasped.

(2) In the flow rate control device absolute flow rate verification system described in (1), the flow rate control device is configured to flow a predetermined flow rate given in advance, and the first measurement time and the second measurement time have elapsed. A first method that is determined based on time, and a second method that is determined based on a predetermined pressure when the first measurement and the second measurement are performed. Since switching is performed according to the constant flow rate, there is an excellent effect that it is possible to perform an accurate test that matches the flow rate of the gas passing through the flow rate control device.
The flow rate of the process gas that flows through the mass flow controller, which is a flow control device of the gas integrated unit, for example, is generally 2 sccm to 2000 sccm in flow rate that passes through the mass flow controller, and the absolute flow rate verification of the mass flow controller is performed In addition, it is necessary to verify at the same flow rate as the usage state.

However, pressure and time are in a proportional relationship, and when the flow rate is small, it is difficult to increase the pressure.Therefore, it is necessary to observe the change over time. Will change. In this case, if the pressure increases in a short time due to the responsiveness of the device, the accuracy may be deteriorated if the pressure is measured based on the elapsed time. Further, since the measurement is performed at a portion close to the maximum range, the range of the pressure sensor may be shaken depending on the response accuracy. Although it seems to be sufficient to provide each with a pressure sensor, a pressure sensor with high accuracy is expensive, and it becomes a problem in a gas integrated unit that requires further integration in terms of space efficiency.
Therefore, by adopting a system that performs the measurement based on the elapsed time when the flow rate is low, and based on the predetermined pressure when the flow rate is high, and verifies the absolute flow rate, it is low cost and space efficient. Excellent and accurate flow rate verification can be realized.

(3) The absolute flow rate of the flow rate control device is verified in a flow rate control unit having a first shut-off valve and a second shut-off valve provided in a gas flow path communicating with the outlet of the flow rate control device and the inlet of the process chamber. In the flow rate control device absolute flow rate verification system, an exhaust passage that communicates the gas passage between the first shut-off valve and the second shut-off valve and an inlet of a vacuum pump, and the exhaust passage is provided. A pressure sensor, a temperature sensor, the pressure sensor, and the temperature sensor provided in the exhaust passage between the third cutoff valve, the fourth cutoff valve, the third cutoff valve, and the fourth cutoff valve. A first control space formed by closing the first shut-off valve, the second shut-off valve, and the third shut-off valve, and the third shut-off And the fourth shut-off valve is closed Is formed by the, spaced from the first sealed space in the third shut-off valve, if there is a second sealed space volume V ₂ is known, the gas to the first closed space and the second closed space The pressure P ₁ and the temperature T ₁ are satisfied, the first sealed space or the second sealed space is evacuated, the pressure P ₂ and the temperature T ₂ after evacuation are measured, and the third cutoff is measured The valve is opened, the first sealed space and the second sealed space are communicated, and the pressure P ₃ and the temperature T ₃ are measured after time, and the pressure P ₁ , the temperature T ₁ , the pressure P ₂ , the temperature are measured. Since the volume V ₁ of the first sealed space is obtained based on T ₂ , the pressure P ₃ , the temperature T ₃ , and the volume V ₂ , without using a special measuring instrument, Without using a measuring tank that reduces the space efficiency of the gas integrated circuit, Open and close the shut-off valve provided in the above, measure the pressure and temperature as if the space in the flow path is a tank, and determine the unknown volume. If the flow volume changes due to modifications, etc. Even so, there is an excellent effect that the absolute flow rate of the flow rate control device can be verified.

  In order to verify the absolute flow rate of the flow control device, it is necessary to accurately grasp the internal volume of the device and piping. This is because the flow rate flowing through the flow rate control device is calculated using the ideal gas equation corrected by the compression factor, and therefore cannot be calculated unless the volume is accurately known. Therefore, if there is a method for obtaining the volume in this way, it is possible to specify the volume in the assembled state even if it is modified, which contributes to shortening the time, and also causes an error in the volume that occurs when disassembled and assembled. An excellent effect is also born that does not have to be a problem.

Embodiments of the present invention will be described below with reference to the drawings. First, the configuration of the first embodiment will be described.
(First embodiment)
FIG. 1 shows a flow path configuration diagram of a minimum configuration necessary for verifying an absolute flow rate of a flow rate control device used in a semiconductor manufacturing process.
The mass flow controller 10 that is a fluid control device is connected to a gas flow path 30 that is connected to an inlet of a process chamber 13 in which a semiconductor manufacturing process using a process gas is performed. The first shut-off valve 21 and the second shut-off valve 22 are provided on the gas flow path 30 that communicates the outlet of the mass flow controller 10 and the inlet of the process chamber 13.
Further, an exhaust passage 31 connected to the vacuum pump 14 is connected between the first cutoff valve 21 and the second cutoff valve 22. Further, the exhaust flow path 31 is provided with a third shut-off valve 23 and a fourth shut-off valve 24. Between the third shut-off valve 23 and the fourth shut-off valve 24, a pressure sensor 11 and a temperature sensor 12 are provided. Is provided. The portion where the third shut-off valve 23, the pressure sensor 11, the temperature sensor 12, and the fourth shut-off valve 24 are provided in the exhaust passage 31 is referred to as a test unit 20 for convenience of explanation.
The first shutoff valve 21, the second shutoff valve 22, the third shutoff valve 23, and the fourth shutoff valve 24 are air operated diaphragm valves connected to a fluid connection unit (not shown). This shut-off valve does not necessarily need to be air operated, but in the semiconductor manufacturing process, there are cases where flammable gas is used as described above. Things are often used.

The verification unit 20 is actually attached to a circuit as shown in FIG.
FIG. 2 is a piping diagram showing a part of an actual line.
That is, a plurality of gas lines, that is, three flow paths of the first gas supply path 33, the second gas supply path 34, and the third gas supply path 35 in FIG. 2 are connected to the gas flow path 30 via the mass flow controller 10. The exhaust passage 31 is connected to the gas passage 30 between the first cutoff valve 21 and the second cutoff valve 22.
The first gas supply path 33, the second gas supply path 34, and the third gas supply path 35 are provided with a pressure gauge 15 and a fifth shut-off valve 28, and the first purge valve 25 and the second purge valve 26 are provided. The purge line 32 connected via the N2 is connected, and is used when N ₂ purge is performed. The purge line 32 includes the pressure gauge 15 and the regulator 16, and joins the gas flow path 30 via the third purge valve 27.
The exhaust passage 31 is provided with a third shut-off valve 23, a fourth shut-off valve 24, a pressure sensor 11 and a temperature sensor 12, which are the verification unit 20, and is connected to the vacuum pump 14, and the gas passage 30 is connected to the process chamber 13.

Next, as an example of these actual uses, FIG. 3 shows a configuration diagram of a gas integrated unit as an example of a real line, and FIG. 4 shows a side view thereof.
As shown in FIG. 3, the verification unit 20 is provided at one end of the gas accumulation unit, and the mass flow controller 10 provided in each block can be verified. Note that FIG. 3 shows only three gas supply paths corresponding to FIG. 2, but it is possible to connect more gas supply paths to an actual gas integrated unit. And these are stored in gas box as one unit.

The present invention enables the mass flow controller 10 to perform an absolute flow rate verification by connecting and controlling the verification unit 20 provided in the gas accumulation unit configured as described above to the verification control device.
Next, the procedure will be described.
First, a calculation procedure for obtaining the flow rate Q will be described.
Flow rate Q can be determined in relation to time and the inflow mass dG dt, calculated as an absolute flow rate Q _o at temperature 0 ℃ to test the mass flow controller 10.
Therefore, it can be expressed by the equation dG = r ₀ Q ₀ dt. Here, the specific weight r ₀ is a characteristic _value of the substance.
dG can be obtained by the equation of state of the ideal gas from the pressure and temperature measured at each time point during the first measurement and the second measurement.
That is, PV = nRT, the gas constant R at this time is determined by the gas type, the pressure P is measured by the pressure sensor 11, the temperature T is measured by the temperature sensor 12, and the volume V is known. If the mass equation is used instead of the number of moles n in the state equation, it can be expressed as PV = GRT.

Therefore, it is possible to establish two equations using the pressure P ₁ and temperature T ₁ measured during the first measurement and the pressure P ₂ and temperature T ₂ measured during the second measurement, and the mass G at that time mass G ₁ during the first _measurement, the time of the second measurement can be expressed by mass G _2, the difference dG formula.
That is, dG = G ₂ −G ₁ = (P ₁ / T ₁ −P ₂ / T ₂ ) (V / R).
Based on this formula, it is expressed as Q ₀ = (P ₁ / T ₁ −P ₂ / T ₂ ) (V / R) / (r ₀ t) by substituting into the formula of the absolute flow rate Q ₀ described above. The
However, the ideal gas equation of state applies only to the ideal gas, and in an actual gas, it differs for each gas molecule, such as intermolecular attractive force, molecular size, and aggregation state, and the ideal gas state The equation needs to be corrected and used.
What is used for this correction is a compression factor Z, which is a dimensionless quantity indicating the non-ideal behavior of a real gas.
The compression factor Z is expressed by the equation Z = PV / RT, and is also expressed as Z = Z (P, T). That is, it can be said that the compression factor Z is a function of the pressure P and the temperature T.

Since the compression factor Z is a variable unique to the gas, it shows a different value depending on the gas as shown in FIG. Further, since the compression factor Z is a function of the pressure P and the temperature T, it also changes depending on the pressure P and the temperature T. These are shown in FIG. 6 and FIG.
FIG. 5 is a table showing the values of compression factors Z of typical process gases under the conditions of a pressure of 300 kPa and a temperature of 300K. The compression factor Z has a large influence under high pressure and low temperature. In fact, as shown in FIG. 5, it can be seen that the higher the molecular weight, the more deviated from the ideal gas condition of Z = 1.

H ₂ and H _e, for those small molecular weight, such as N ₂ is close to Z = 1, the nitrogen gas may be said to be approximately the same as the ideal gas is particularly inert gases. However, in NH ₃ and SF ₆ , the influence becomes so large that it cannot be ignored. In SF ₆ , the compression factor Z is 0.961, which is shifted by nearly 0.04.
6 and 7 are diagrams showing how the compression factor Z actually changes due to the change in temperature and pressure due to gas, and FIG. 6 shows the change of the compression factor Z of SF ₆ with temperature. FIG. 7 is a graph showing changes in the compression factor Z of H ₂ with temperature.
In each graph, the vertical axis indicates the compression factor Z, the horizontal axis indicates the temperature [° C.], and the curves at 20 kPa, 50 kPa, 75 kPa, and 101.3 kPa are respectively shown.

Similarly, in the SF ₆ curve shown in FIG. 6 and the H ₂ curve shown in FIG. 7, the value of the compression factor Z approaches 1 depending on the temperature, and the value of the compression factor Z increases from 1 as the pressure increases. It can be seen that the rate of change with temperature is getting stronger. In particular, it can be seen that the compression factor Z of SF ₆ is greatly affected by temperature and pressure.
Therefore, in order to use the above-described ideal gas equation of state, it is necessary to correct by the compression factor Z such that PV = ZnRT, and thereby a correct value can be calculated.
Accordingly, the absolute flow rate Q ₀ is expressed as Q ₀ = (P ₁ / (Z ₁ T ₁ ) −P ₂ / (Z ₂ T ₂ )) (V / R) / (r ₀ t).

In this way, the flow rate of the mass flow controller 10 can be calculated. Since the correction is made by the compression factor Z responding to them at each measurement time point, that is, at the time of the first measurement, the first compression factor Z ₁ and the second measurement in response to the measured pressure P ₁ and temperature T _1. in time, measured pressure P _2, and so the second compression factor Z ₂ in response to the temperature T _2, for performing appropriate correction, it is possible to obtain a value close to the true flow rate, i.e. the mass flow controller 10 It is possible to perform an absolute flow rate verification.

  FIG. 8 shows the accuracy of the flow rate verification when the compression factor Z is used for the absolute flow rate verification of the mass flow controller 10 and when the compression factor Z is not used. The accuracy of this flow rate verification indicates the error rate from the true value of the flow rate, and the vertical axis indicates the verification accuracy [%] and the horizontal axis indicates the flow rate [sccm]. Thus, compared with the case where the compression factor Z is not used for the absolute flow rate verification of the mass flow controller 10, when the absolute flow rate is verified using the compression factor Z, the accuracy is clearly different. Recognize. When the absolute flow rate is verified using the compression factor Z, it can be seen that the accuracy is close to the target accuracy.

By the way, the flow range of the mass flow controller 10 provided in the actual gas integrated unit is as wide as 2 sccm to 2000 sccm. This is because the amount of gas required varies depending on the type of gas used. However, as shown in FIG. 2, it is necessary to perform the verification of the absolute flow rate of a plurality of mass flow controllers 10 with one verification unit 20, so it is not convenient that the flow rate range is wide.
This is because it is necessary to measure with the same pressure sensor 11, and the reference volume is the same regardless of which mass flow controller 10 is measured, and the flow path is used as a measurement space. The volume is about 100cc. Therefore, when supplying a gas at a flow rate of 2 sccm, it takes time to measure a pressure change as much as necessary. However, when supplying a gas at a flow rate of 2000 sccm, the gauge of the pressure sensor 11 is instantaneously supplied. The pressure changes with such a momentum that it is shaken off. On the other hand, if the pressure sensor 11 that can accurately detect the pressure when the flow rate is 2 sccm is selected, the range is inevitably determined. Therefore, when the flow rate is 2000 sccm, the limit range of the pressure sensor is reached instantaneously. It becomes.

This is shown in the graph of FIG. 9 and the table of FIG.
FIG. 9 shows a graph showing the relationship between pressure and measurement time. FIG. 10 is a table showing the relationship between pressure and measurement time in the case of a certain volume when the fluid is nitrogen.
The vertical axis in FIG. 9 is pressure [kPa] and the horizontal axis is measurement time [sec]. As shown here, the pressure and measurement time are directly proportional, and the measurement flow rate is 20 sccm, 50 sccm, and 100 sccm. The change at the time is different, and it can be seen that the slope becomes stronger as the flow rate increases.
From the table shown in FIG. 10, it can be seen that the required pressure is reached in 0.7 seconds when the measured flow rate is 2000 sccm.
Therefore, in order to cope with this, it is necessary to switch the reference depending on the set supply flow rate. That is, for example, when the set flow rate is 2 sccm to less than 1000 sccm, the pressure and temperature are measured based on the elapsed time dt, and when the set flow rate is 1000 sccm to 2000 sccm, the temperature and time are measured based on the pressure. . By taking such a method, it is possible to maintain the measurement accuracy,
In the table of FIG. 10, the numbers written in bold are set values. For example, when the gas flow rate is 10 sccm, dt = 10 is set, and when measured, the result is dP = 3 kPa. When the gas flow rate is 1000 sccm, dP = 23 kPa is set, and the time taken until the pressure from the pressure P ₁ to the pressure P ₂ becomes 23 kPa is 1.3 sec.

Next, an actual measurement procedure based on these procedures will be described using the flow shown in FIG.
FIG. 11 is a flow chart showing an absolute flow rate verification procedure by the circuit shown in FIG. 1, and the absolute flow rate verification is performed on the actual line by the same procedure.
When the flow rate measurement mode is selected, the state of each shut-off valve is set in S1. The first shut-off valve 21, the third shut-off valve 23, and the fourth shut-off valve 24 shown in FIG. 1 are all opened, and the second shut-off valve 22 is closed so that the gas flows to the exhaust passage 31 side. . At this time, the first cutoff valve 21 other than the mass flow controller 10 for verifying the absolute flow rate needs to be closed. That is, in FIG. 2 in which a plurality of lines are connected, for example, when performing an absolute flow rate verification of the mass flow controller 10 provided in the first gas supply path 33, the second gas supply path 34 and the third gas supply path 35 are connected. The provided first shutoff valve 21 needs to be closed. This is because only the absolute flow rate verification of one mass flow controller 10 can be performed at a time, and otherwise the absolute flow rate verification of the mass flow controller 10 provided in the first gas supply path 33 cannot be performed. The same applies to the absolute flow rate verification of other mass flow controllers 10.

Next, in S2, a process gas is caused to flow in a set flow rate state to the mass flow controller 10 that measures the absolute flow rate. Then, after the process gas is flowed until the flow rate of the mass flow controller 10 is stabilized, the fourth shutoff valve 24 is closed, and the pressure in the flow channel regarded as a tank increases. Thus, the space formed by the fourth shut-off valve 24, the second shut-off valve 22, and the outlet of the mass flow controller 10 becomes a bag path having a volume V. On the other hand, a constant flow rate of gas flows from the mass flow controller 10; The volume inside the space gradually increases.
In S4, the pressure of the pressure sensor 11 set by the, the temperatures T ₁ measured by the temperature sensor 12 to have reached the pressure P _1, starts measuring.

In S5, to check whether the pressure in the pressure sensor 11 reaches the set pressure, when it reaches the set pressure (S5: Yes), the elapsed time when the pressure reached the pressure P ₂ is the set pressure in S8 Measure. On the other hand, it does not reach the set pressure (S5: No), when it reaches the set time to check in S6 (S6: Yes), the pressure _{P 2} at that time in S7, the measured temperature _{T 2.} If the set time has not been reached in S6 (S6: No), it is checked in S5 whether the set pressure has been reached again.
That is, here, the measurement standard is different when the set pressure or set time is reached first. Therefore, in FIG. 10, when the sum of 23 kPa, which is the set pressure range dP that is the set pressure _first , and the pressure P ₁ is reached _first , the time is the second measurement time, the elapsed time, the temperature T ₂ is measured. The pressure P ₂ at this time is equal to the set pressure.
If the measurement time dt first reaches 10 sec, the time is set as the second measurement time, and the pressure P ₂ and the temperature T ₂ are measured. For example, in setting the flow rate of the mass flow controller 10 is 50 sccm, the fluid being used was nitrogen, since the measurement time dt According to the table shown in FIG. 10 is 10 sec, after the pressure _{P 1} measured after standing 10 seconds measuring a pressure _{P 2} and temperature _{T 2.} Since the set pressure range dP at this time is 10 kPa, the pressure P ₂ is equal to the value of the pressure P ₁ + dP. For example, assuming that the set flow rate of the mass flow controller 10 is 2000 sccm and the fluid used is nitrogen, the set pressure range dP is 23 kPa according to the table shown in FIG. It can be seen that it takes 7 seconds.
In addition, according to the set flow rate set in the mass flow controller 10, it may be determined whether the determination is based on the pressure or the elapsed time. In FIG. 10, when the set flow rate is less than 2 sccm to less than 1000 sccm, the pressure and temperature are measured based on the elapsed time dt. When the set flow rate is 1000 sccm to 2000 sccm, the temperature and time are measured based on the pressure. Is measured.

Then, S9 in the pressure P ₁ during the first _measurement, the temperature T _1, the first compression factor Z _1, read from the compressed factor data stored in the verification control device, the pressure P ₂ during the second measurement Then, the second compression factor Z ₂ is read from the compressed data stored in the test control device from the temperature T ₂ . In S10, the absolute flow rate _Qo is calculated by the procedure as described above based on the gas state equation.
By the above procedure, the absolute flow rate verification of the mass flow controller 10 becomes possible, and the mass flow controller 10 can be calibrated with this value. However, the calibration of the mass flow controller 10 is performed by changing the applied voltage, and an appropriate flow rate can be obtained after the calibration. It will shift. Experience shows that if used, the gas concentration in the chamber will deviate from the design value, resulting in a worsening of process yield, so that an alarm should be issued when the deviation limit is exceeded. It is preferable.

Next, a second embodiment of the present invention will be described.
(Second embodiment)
It is not uncommon for gas integrated units used in semiconductor manufacturing processes to be modified due to changes in production plans or products. However, even in the first embodiment in which the equation of state of the ideal gas so far is corrected with the compression factor Z and the absolute flow rate is calculated, the flow path configuration changes due to modification, and the volume V used for the calculation changes. The flow rate cannot be calculated. Therefore, focusing on this problem, a method for obtaining the volume V that has changed due to the modification in the flow path configuration of the first embodiment will be disclosed as a second embodiment.
Since the configuration of the second embodiment is as described above and is the same as that of the first embodiment, description of the configuration is omitted.

Here, for the sake of brevity, the description will be made with reference to FIG.
Volume V ₁ of the first sealed space formed by a part of the gas flow path 30 and the exhaust flow path 31 by closing the first shut-off valve 21, the second shut-off valve 22, and the third shut-off valve 23 in FIG. With the volume V ₂ of the second sealed space formed by a part of the exhaust passage 31 by closing the third shut-off valve 23 and the fourth shut-off valve 24, the ideal gas state equation of the first embodiment was used. The value of volume V is obtained. That is, V = V ₁ + V ₂ .
However, strictly speaking, since there is a volume V ₃ of the flow path from the outlet of the mass flow controller 10 to the first shut-off valve 21, V = V ₁ + V ₂ + V ₃ , but the mass flow controller 10 and the first Since the shut-off valve 21 is provided in the immediate vicinity, the volume V ₃ is very small compared to the volumes V ₁ and V ₂ , and there are almost no cases where this part is remodeled. I do.

If the flow path is changed due to expansion of the line or addition of equipment, the volume V ₁ may change. However, the portion constituting the volume V ₁ was, are assembled to the components of the gas accumulation unit body, it is extremely difficult to measure the volume removed from the gas integrated unit. On the other hand, the possibility that the volume V ₂ is modified is very low, the volume V ₂ before assembling the gas integrated unit, for example, be assayed using a measuring instrument such as a membrane flowmeter, it is then assembled to the gas integrated unit body It should be. That volume V ₂ is always it can be treated as known values.

Therefore, it is desirable to be able to measure the volume V ₁ in a state assembled.
12 and 13, in the configuration of FIG. 1, is shown as a flow chart the means for measuring the volume V ₁ is unknown. Note that FIG. 12 and FIG. 13 perform calculations based on substantially the same method.
First, a description will be given from FIG.
When the volume measurement mode is selected, the state of each shut-off valve is set in S11. The first shut-off valve 21, the third shut-off valve 23, and the fourth shut-off valve 24 shown in FIG. 1 are all opened, and the second shut-off valve 22 is closed so that the gas flows to the exhaust passage 31 side. . At this time, the first shut-off valve 21 other than the mass flow controller 10 to be subjected to volume measurement needs to be closed. That is, in FIG. 2 in which a plurality of lines are connected, for example, when volume measurement is performed using the mass flow controller 10 provided in the first gas supply path 33, the second gas supply path 34 and the third gas supply path. The first shut-off valve 21 provided in 35 needs to be closed. This is because volume measurement cannot be performed using two or more mass flow controllers 10 at the same time, and volume measurement using the mass flow controller 10 provided in the first gas supply path 33 cannot be performed unless this is done. The same can be said when volume measurement is performed with other mass flow controllers 10. However, once the volume measurement is performed, the volume can be obtained with high accuracy. Therefore, the volume measurement using the other mass flow controller 10 is only a confirming meaning, but the more reliable volume can be obtained. Measurement may be possible.

Next, in S12, nitrogen gas is allowed to flow with the mass flow controller 10 at the set flow rate state. In this case, unlike the first embodiment, since the volume V ₁ of the flow path is not known, because it is necessary to make measurements using the gas close to the ideal gas.
When the supply flow rate of nitrogen gas passing through the mass flow controller 10 is stabilized, the fourth shutoff valve 24 is closed in S13. By doing so, the flow path is closed by the second shutoff valve 22 and the fourth shutoff valve 24 to form a bag path, so that the outlet of the mass flow controller 10, the second shutoff valve 22, and the fourth shutoff valve 24 are formed. The space pressure starts to rise. When the pressure in the flow path reaches the pressure P ₁ , the first shut-off valve 21 is closed in S 14, thereby creating a sealed space of volume V ₁ + volume V ₂ . Next, the pressure P ₁ and the temperature T ₁ are measured in S15.

When the measurement is finished, the third cutoff valve 23 is closed and the fourth cutoff valve 24 is opened in S16. Thereby, the first sealed space volume V ₁ was a raw pressure conditions, a second closed space volume V ₂ is opened. Thereafter, in S17, the vacuum pump 14 is evacuated and the fourth shut-off valve 24 is closed again. Since the vacuum pump 14 used in the semiconductor manufacturing process is often equipped with a high vacuum generating device such as a turbo molecular pump or a dry pump, it is possible to create a substantially vacuum state. in that close the fourth shut-off valve 24, a second sealed space volume V ₂ is capable of holding a high vacuum state. In S18, the measured pressure _{P 2} and the temperature _{T 2} in this state.

Then, by opening the third shut-off valve 23 at S19, a first closed space and communicates a second enclosed space, the pressure _{P 3,} for measuring the temperature _{T 3.}
In this way, the pressure in the first sealed space with the unknown volume V ₁ is the pressure P ₁ , the temperature is the temperature T ₁ , and the pressure in the second sealed space with the known volume V ₂ is the pressure P 1. _2. The volume of the space in the state where the temperature is the temperature T ₂ and the state where the first sealed space and the second sealed space are communicated is the volume V ₁ + volume V ₂ , the pressure is the pressure P ₃ , and the temperature is A state at temperature T ₃ is obtained.
In S20, the ideal gas equation based on these, determine the volume _{V 1} is unknown. In this way, it is possible to know the volume V ₁ of the first closed space after remodeling.

The calculation procedure using the ideal gas equation of state is as follows.
When the above-described state is expressed by equations, three equations are obtained: P ₁ V ₁ = n ₁ RT ₁ , P ₂ V ₂ = n ₂ RT ₂ , P ₃ (V ₁ + V ₂ ) = n ₃ RT ₃ .
Here, R is a gas constant, and _nx is the number of moles. Incidentally, the higher the degree of sealing space, the number of moles is should be stored, said to be _{n 1 + n 2 = n 3} .
Therefore, when the above equation is arranged for the gas constant R and expressed by the relationship of the number of moles, V ₁ = (T ₁ (P ₂ T ₃ −P ₃ T ₃ )) / (T ₂ (P ₃ T ₁ −P ₁₎ T ₃ )) V ₂ .
Since all the right terms of the above equation are known, the volume V ₁ can be obtained by calculation.

Next, FIG. 13 will be described.
When the volume measurement mode is selected, the state of each shut-off valve is set in S21. The first shut-off valve 21, the third shut-off valve 23, and the fourth shut-off valve 24 shown in FIG. 1 are all opened, and the second shut-off valve 22 is closed so that the gas flows to the exhaust passage 31 side. . At this time, the first shut-off valve 21 other than the mass flow controller 10 to be subjected to volume measurement needs to be closed. The reason is the same as in the case of FIG.

Next, in S22, nitrogen gas is allowed to flow with the mass flow controller 10 at the set flow rate state. In this case, unlike the first embodiment, since the volume V ₁ of the flow path is not known, because it is necessary to make measurements using the gas close to the ideal gas.
When the supply flow rate of nitrogen gas passing through the mass flow controller 10 is stabilized, the fourth shutoff valve 24 is closed in S23. By doing so, the flow path is closed by the second shutoff valve 22 and the fourth shutoff valve 24 to form a bag path, so that the outlet of the mass flow controller 10, the second shutoff valve 22, and the fourth shutoff valve 24 are formed. The space pressure starts to rise. When the pressure in the flow path reaches the pressure P _1, in S24, it closes the third shut-off valve 23, thereby, be ready second sealed space volume V _2. Next, the pressure P ₁ and the temperature T ₁ are measured in S15.

When the measurement is completed, the first cutoff valve 21 is closed and the second cutoff valve 22 is opened in S26. As a result, the second sealed space with the volume V ₂ is maintained in the same pressure state. Thereafter, the process chamber 13 is evacuated in S27, and the second shut-off valve 22 is closed again. In many cases, the process chamber 13 provided for the semiconductor manufacturing process is provided with a vacuum pump or the like for generating a high vacuum, and it is possible to create a substantially vacuum state as in FIG. by closing the shut-off valve 22, the first closed space volume V ₁ was capable of holding a high vacuum state.

Then, by opening the third shut-off valve 23 at S28, a first closed space and communicates a second enclosed space, the pressure _{P 2,} to measure the temperature _{T 2.}
In this way, in the second sealed space of the known volume V ₂ , the pressure is the pressure P ₁ , the temperature is the temperature T ₁ , the unknown _first volume of the sealed space V ₁ and the volume V ₂ A state in which the pressure in the state where the second sealed space is communicated is the pressure P ₂ and the temperature is the temperature T ₂ is obtained.
In S20, the ideal gas equation based on these, determine the volume _{V 1} is unknown. In this way, it is possible to know the volume V ₁ of the first closed space after remodeling.

The calculation procedure using the ideal gas equation of state is as follows.
When the above-described state is expressed by equations, _two equations of P ₁ V ₂ = n ₁ RT ₁ and P ₂ (V ₁ + V ₂ ) = n ₂ RT ₂ are obtained.
Here, R is a gas constant, and _nx is the number of moles. Note that if the degree of sealing of the space is high, the number of moles should be preserved and the vacuum state is realized at a high level, so it can be said that n ₁ = n ₂ .
Therefore, when the above formula is arranged for the gas constant R and expressed by the relationship of the number of moles, it is expressed as V ₁ = (P ₁ T ₁ −P ₂ T ₂ ) / (P ₂ T ₂ ) V ₂ .
Since all the right terms of the above equation are known, the volume V ₁ can be obtained by calculation.

The two procedures shown in FIG. 12 and FIG. 13 are methods based on substantially the same idea. The first sealed space and the second sealed space are filled with nitrogen gas, and the pressure P ₁ , The temperature T ₁ is measured, the first sealed space or the second sealed space is evacuated, the pressure P ₂ and the temperature T ₂ after evacuation are measured, the third shut-off valve is opened, and the first sealed space and The second sealed space is communicated, and after time, the pressure P ₃ and the temperature T ₃ are measured, the pressure P ₁ , the temperature T ₁ , the pressure P ₂ , the temperature T ₂ , the pressure P ₃ , the temperature T ₃ , and the volume V ₂ , by a specific means for calculating the volume V _1.
However, depending on the user's device, the capability of the vacuum generator provided in the process chamber 13 provided in the gas flow path 30 is not high, and a high vacuum cannot be generated, or a high vacuum is applied to the exhaust flow path 31. The above two methods have been proposed because there is a possibility that the vacuum pump 14 having the ability to generate the pressure is not connected.

According to this method, if it is possible to create a vacuum by one of the process chamber 13 or vacuum pump 14, to the volume V ₁ was capable of calculating, when the degree of vacuum in the vacuum pump 14 side is not high, the method of FIG. 12 if, an excellent effect of being able to calculate the small volume V ₁ of the error.
In addition, by providing a method for obtaining the unknown volume that is produced after the gas integrated unit is modified in the semiconductor manufacturing process, the mass flow controller 10 according to the method of the first embodiment can be used even after the gas integrated unit is modified. Absolute flow rate verification can be performed.

According to the mass flow controller absolute flow rate verification system of the present invention described above, the following excellent actions and effects can be obtained.
(1) Mass flow in a flow control unit having a first shut-off valve 21 and a second shut-off valve 22 provided in a gas flow path 30 that communicates an outlet of the mass flow controller 10 that is a flow control device and an inlet of the process chamber 13. In the mass flow controller 10 absolute flow verification system that verifies the absolute flow rate of the controller 10, an exhaust flow path 31 that communicates the gas flow path 30 between the first cutoff valve 21 and the second cutoff valve 22 and the inlet of the vacuum pump 14. A pressure sensor provided in the exhaust passage 31 between the third shut-off valve 23 and the fourth shut-off valve 24 provided in the exhaust passage 31, and the third shut-off valve 23 and the fourth shut-off valve 24. 11 and the temperature sensor 12, the pressure sensor 11 and the temperature sensor 12, and the compression factor data specific to the gas type, the outlet of the mass flow controller 10, and the second shielding. A valve 22, a test control unit for storing the volume value of a predetermined space formed by the fourth shutoff valve 24 has a, in the first time of measurement, the pressure P ₁ by the pressure sensor 11, temperature sensor 12 is read out from the compression factor data verification control device a first compression factor _{Z 1} corresponding to the temperatures _{T 1} by the pressure _{P 1,} temperatures _{T 1,} volume V, and the mass _{G 1} from the first compression factor _{Z 1} The second compression factor Z ₂ corresponding to the pressure P ₁ by the pressure sensor 11 and the temperature T ₂ by the temperature sensor 12 at the time of the second measurement is read from the compression factor data of the test control device, and the pressure P _{2 is obtained.} The mass G ₂ is obtained from the temperature T ₂ , the volume V, and the second compression factor Z ₂ , and the absolute flow rate of the mass flow controller 10 can be verified by the difference between the mass G ₁ and the mass G ₂ .

  This makes it possible to verify the absolute flow rate of the mass flow controller 10 using a process gas of a gas type that actually flows to the mass flow controller 10 instead of a measurement gas such as nitrogen gas close to the ideal gas. Since the equation of state of the gas is corrected and calculated by the compression factor Z corresponding to each of the pressure value and the temperature value at each time point, an absolute flow rate with high accuracy is obtained, and thereby the absolute flow rate test of the mass flow controller 10 is performed. There is an excellent effect that it becomes possible.

If the absolute flow rate is calculated using the equation of state of the ideal gas, it will deviate from the absolute flow rate of the real gas, so a correction factor is added to correct the non-ideal behavior of the real gas. Since the compression factor that exhibits ideal behavior is a function of pressure and temperature, the value varies depending on the pressure and temperature at the time of measurement. Therefore, if a correction coefficient is simply added, when calculating the absolute flow rate by the pressure drop in the sealed space or the pressure rise, the compression factor Z to be corrected when the pressure is low and when the pressure is high. Although the values are different and the calculated absolute flow rate is deviated, the first compression factor Z ₁ and the second compression factor Z ₂ responding to the respective pressures and temperatures at the first measurement time and the second measurement time. By using, it is possible to calculate an appropriate absolute flow rate at each measurement.
And since it becomes possible to obtain an accurate absolute flow rate using real gas in this way, there is no difference from the actual use state, as in the case of calibration using measurement gas, Since the verification is possible by the absolute flow rate and the calibration is performed by the verification, the absolute flow rate of the gas supplied to the semiconductor device can be grasped.

(2) In the absolute flow rate verification system for the flow rate control device described in (1), the mass flow controller 10 flows a constant flow rate given in advance, and the elapsed time is based on the first measurement time and the second measurement time. Switching between the first method to be determined and the second method to determine the first measurement time and the second measurement time based on a predetermined pressure according to a constant flow rate of the fluid passing through the mass flow controller 10 at the time of measurement. Therefore, it is possible to perform an accurate test that matches the flow rate of the gas passing through the mass flow controller 10.
For example, the flow rate of the process gas flowing through the mass flow controller 10 which is a flow rate control device of the gas integrated unit has a width of 2 cc to 2000 cc in the flow rate passing through the mass flow controller 10, and the absolute flow rate verification of the mass flow controller 10 is performed. It is also necessary to verify the flow rate with the same setting as the usage state.

However, there is a proportional relationship between pressure and time.When the flow rate is small, the pressure does not increase easily, so it is necessary to observe the change over time. Will change. In this case, if the pressure increases in a short time due to the responsiveness of the device, the accuracy may be deteriorated if the pressure is measured based on the elapsed time. Moreover, since the measurement is performed at a portion close to the maximum range, there is a possibility that the range of the pressure sensor 11 may be shaken depending on the response accuracy.
Therefore, when the flow rate is small, measurement is performed based on the elapsed time, and when the flow rate is large, measurement is performed based on a predetermined pressure, and the absolute flow rate is verified, so that accurate flow rate verification can be realized.

(3) Mass flow in a flow control unit having a first shut-off valve 21 and a second shut-off valve 22 provided in a gas flow path 30 that communicates the outlet of the mass flow controller 10 that is a flow control device and the inlet of the process chamber 13. In the flow rate control device absolute flow rate verification system for verifying the absolute flow rate of the controller 10, an exhaust flow path 31 that communicates the gas flow path 30 between the first cutoff valve 21 and the second cutoff valve 22 and the inlet of the vacuum pump 14. A pressure sensor provided in the exhaust passage 31 between the third shut-off valve 23 and the fourth shut-off valve 24 provided in the exhaust passage 31, and the third shut-off valve 23 and the fourth shut-off valve 24. 11, the temperature sensor 12, and the test control device that connects the pressure sensor 11 and the temperature sensor 12, and the first cutoff valve 21, the second cutoff valve 22, and the third cutoff valve 23 are closed. A first closed space formed by the third shut-off valve 23, and the fourth shut-off valve 24 is formed by being closed and separated from the first closed space by the third shut-off valve 23, the volume V ₂ There is a known second sealed space, the first sealed space and the second sealed space are filled with gas, the pressure P ₁ and the temperature T ₁ are measured, and the first sealed space or the second sealed space is evacuated. The pressure P ₂ and the temperature T ₂ after evacuation are measured, the third shut-off valve 23 is opened, the first sealed space and the second sealed space are communicated, and the pressure P ₃ and the temperature T ₃ are measured after time. The volume V ₁ of the first sealed space is obtained based on the pressure P ₁ , the temperature T ₁ , the pressure P ₂ , the temperature T ₂ , the pressure P ₃ , the temperature T ₃ , and the volume V ₂ . Measurements that do not use special measurement equipment and reduce the space efficiency of gas integrated circuits By opening and closing the shut-off valve provided in the flow path without using a tank, etc., it is possible to determine the unknown volume by measuring the pressure and temperature, assuming the space in the flow path as a tank, remodeling, etc. Even if the volume of the flow path is changed by the above, there is an excellent effect that the absolute flow rate of the flow rate control device can be verified.

  In order to verify the absolute flow rate of the mass flow controller 10, it is necessary to accurately grasp the internal volume of the equipment and piping. This is because the flow rate that flows to the mass flow controller 10 is calculated using the ideal gas equation of state, and cannot be calculated unless the volume is accurately known. Therefore, if there is a method for obtaining the volume in this way, it is possible to specify the volume in the assembled state even if the modification is performed, which contributes to shortening the time and also causes an error in the volume that occurs when disassembling and assembling. There is also an excellent effect that it is not necessary to make it a problem.

The flow-path block diagram of the minimum structure required in order to test | inspect the absolute flow volume of the flow control apparatus of 1st Example is shown. It is a partial piping figure at the time of applying to an actual line of the 1st example. It is an example of the block diagram of the gas integration unit of 1st Example. FIG. 4 is a side view of the gas integrated unit shown in FIG. 3 according to the first embodiment. It is the table | surface which showed the value of the compression factor Z for every substance in a 300 kPa and 300K environment. Of the first embodiment, is a graph showing the effect of temperature and pressure of the compressed factor Z of SF ₆ is one example of a process gas flowing through the gas integrated unit. Of the first embodiment, it is a graph showing the effect of temperature and pressure of the compressed factor Z of the N ₂ is the gas for purging through the gas integrated unit. It is the graph which showed an example of the precision at the time of carrying out the absolute flow test using the compression factor Z of 1st Example, and when carrying out the absolute flow test without using the compression factor Z. It is the graph which showed the relationship between a pressure and measurement time of 1st Example. The relationship between pressure and measurement time in the case of a certain volume when the fluid is nitrogen in the first embodiment is shown in a table. It is the flowchart which showed the verification procedure of the absolute flow by the circuit shown in FIG. 1 of 1st Example. In the configuration of FIG. 1 of the second embodiment, one means for measuring an unknown volume V ₁ is shown as a flowchart. In the configuration of FIG. 1 of the second embodiment, another means for measuring the unknown volume V ₁ is shown as a flowchart. The piping diagram of the mass flow controller absolute flow volume verification system of patent document 1 is shown. The schematic diagram of piping of the inspection system of the gas piping system of patent document 2 is shown. The conceptual diagram about the gas mass flow measurement system of patent document 3 is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Mass flow controller 11 Pressure sensor 12 Temperature sensor 13 Process chamber 14 Vacuum pump 15 Pressure gauge 16 Regulator 20 Verification unit 21 1st cutoff valve 22 2nd cutoff valve 23 3rd cutoff valve 24 4th cutoff valves 25, 26, 27 Purge valve 28 Fifth shut-off valve 30 Gas flow path 31 Exhaust flow path 32 Purge line 33 First gas supply path 34 Second gas supply path 35 Third gas supply path dG Inflow mass G ₁ , G ₂ mass dP Set pressure range P ₁ , P ₂ , P ₃ pressure Q ₀ absolute flow rate T ₁ , T ₂ , T ₃ temperature V ₁ , V ₂ , V ₃ volume Z ₁ first compression factor Z ₂ second compression factor r ₀ specific weight dt elapsed time

Claims (3)

A flow control device for verifying an absolute flow rate of the flow control device in a flow control unit having a first shut-off valve and a second shut-off valve provided in a gas flow path communicating with an outlet of the flow control device and an inlet of the process chamber In the absolute flow verification system,
An exhaust passage communicating the gas passage between the first shut-off valve and the second shut-off valve and an inlet of a vacuum pump;
A third cutoff valve and a fourth cutoff valve provided in the exhaust flow path;
A pressure sensor and a temperature sensor provided in the exhaust flow path between the third cutoff valve and the fourth cutoff valve;
A volume of a predetermined space formed by connecting the pressure sensor and the temperature sensor, the compression factor data specific to the gas type, the outlet of the flow rate control device, the second shut-off valve, and the fourth shut-off valve A test controller for storing values,
The first compression factor value corresponding to the first pressure value by the pressure sensor and the first temperature value by the temperature sensor at the time of the first measurement is read from the compression factor data of the test control device, and the first The first mass is determined from one pressure value, the first temperature value, the volume value, and the first compression factor value,
A second compression factor value corresponding to the second pressure value by the pressure sensor and the second temperature value by the temperature sensor at the time of the second measurement is read from the compression factor data of the test control device, and the second The second mass is determined from the two pressure values, the second temperature value, the volume value, and the second compression factor value,
The flow rate control device absolute flow rate verification system, wherein the absolute flow rate of the flow rate control device is verified based on a difference between the first mass and the second mass. In the flow control device absolute flow verification system according to claim 1,
The flow rate control device flows a constant flow rate given in advance,
A first method for determining the first measurement time and the second measurement time based on an elapsed time;
A second method for determining the first measurement time and the second measurement time based on a predetermined pressure;
A flow rate control device absolute flow rate verification system that switches according to the constant flow rate of the fluid that passes through the flow rate control device during measurement. A flow control device for verifying an absolute flow rate of the flow control device in a flow control unit having a first shut-off valve and a second shut-off valve provided in a gas flow path communicating with an outlet of the flow control device and an inlet of the process chamber In the absolute flow verification system,
An exhaust passage communicating the gas passage between the first shut-off valve and the second shut-off valve and an inlet of a vacuum pump;
A third cutoff valve and a fourth cutoff valve provided in the exhaust flow path;
A pressure sensor and a temperature sensor provided in the exhaust flow path between the third cutoff valve and the fourth cutoff valve;
A controller for verification connecting the pressure sensor and the temperature sensor,
A first sealed space formed by closing the first cutoff valve, the second cutoff valve, and the third cutoff valve;
The third shut-off valve, and the fourth shut-off valve is formed by being closed, the spaced between said first closed space by the third shut-off valve, if there is a second sealed space volume V ₂ is known ,
Filling the first sealed space and the second sealed space with gas, and measuring the pressure P ₁ and the temperature T ₁ ,
The first sealed space or the second sealed space is evacuated, and the pressure P ₂ and the temperature T ₂ after evacuation are measured,
Opening the third shut-off valve, communicating the first sealed space and the second sealed space, and measuring the pressure P ₃ and the temperature T ₃ after time;
Based on the pressure P ₁ , the temperature T ₁ , the pressure P ₂ , the temperature T ₂ , the pressure P ₃ , the temperature T ₃ , and the volume V ₂ , the volume V ₁ of the first sealed space is obtained. A flow control device absolute flow verification system characterized by that.

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