Flow measuring device

Abstract

To provide a flow measuring device with which it is possible to measure the flow of a gas accurately by a buildup method that is controlled by a flow control device.SOLUTION: A flow measuring device 20 is connected to a flow path between a downstream valve V1 and a gas use device in a gas supply system 100 having a flow control device 10 and the downstream valve V1, and is constituted so as to measure the flow of a gas that is controlled by the flow control device 10. The flow measuring device comprises: a flow path L2 for exhaust that is provided with an exhaust-side on / off valve V2; a flow path L3 for measurement that branches from the flow path for exhaust on the upstream side of the exhaust-side on / off valve V2 and is provided with a pressure sensor 22 and a temperature sensor 24; and a built-in flow control device 30 which is connected to the flow path L3 for measurement, and which controls the flow of a gas from the outside and flows the gas into the flow path L3 for measurement.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a flow rate measuring device for measuring the flow rate of a gas controlled by a flow rate control device used in semiconductor manufacturing equipment, pharmaceutical manufacturing equipment, chemical plants, etc.

Background Art

[0002] In semiconductor manufacturing equipment or chemical plants, etc., it is required to supply gas to a gas-using device such as a process chamber at an appropriate flow rate. As a gas flow rate control device, a mass flow controller (thermal mass flow control device) or a pressure type flow rate control device is known.

[0003] In a flow rate control device, the flow rate needs to be managed with high precision, and it is preferable to confirm the flow rate accuracy and calibrate the flow rate control device at any time. As a flow rate measuring method for measuring the flow rate of a gas controlled by a flow rate control device, for example, the build-up method is known. The build-up method is a method of measuring the flow rate by detecting a change in the pressure of a gas flowing into an internal known volume (build-up volume).

[0004] More specifically, the build-up method is a method of obtaining the flow rate by flowing gas into a pipe or a tank with a known volume (V) provided downstream of the flow rate control device and measuring the gas pressure increase rate (ΔP / Δt) and the gas temperature (T) at that time. In the build-up method, when the gas constant is R, for example, the flow rate Q can be obtained according to Q = 22.4×(ΔP / Δt)×V / RT.

[0005] Patent Document 1 discloses a method of connecting a flow measurement device as a flow reference device to the downstream side of a flow control device incorporated in a gas supply system and performing flow measurement by the buildup method using this device. In this method, gas from the flow control device is allowed to flow into a tank of the flow measurement device, and the flow rate is measured by measuring the rate of pressure rise in the tank. By performing flow measurement in this way, the flow accuracy of the flow control device can be confirmed at any time. Therefore, when the accuracy has decreased, the flow control device can be calibrated to provide a highly reliable flow control device over a long period of time.

[0006] Further, Patent Document 2 discloses a gas flow rate verification unit that is provided with two valves and a pressure sensor that measures the pressure between them as a flow rate measurement device by the buildup method and is connected to the downstream side of the flow control device. In the gas flow rate verification unit described in Patent Document 2, the combined flow path on the downstream side of the flow control device and the flow path between the two valves is used as the buildup volume.

[0007] When measuring the flow rate by the buildup method in this way, it is necessary to flow gas into a volume of known capacity. And when using the flow path on the downstream side of the flow control device as the buildup volume as in the fluid system described in Patent Document 2, not only the volume of the flow path in the gas flow rate verification unit but also the volume of the flow path between the flow control device and the gas flow rate verification unit must be known in advance. This flow path volume may be known in some cases, but since the gas flow rate verification unit is connected to various fluid systems, it is often unknown at the time of connection. Therefore, for each fluid system to which the gas flow rate verification unit is connected, the volume of the buildup volume may be determined by measurement.

[0008] In Patent Document 2, the gas flow rate measurement unit is connected to a common flow path on the downstream side of a flow rate control device provided in each of a plurality of gas supply lines. After connecting the gas flow rate measurement unit, the build-up volume is determined by measurement. Specifically, a high-precision flow meter is connected to the upstream side of the flow rate control device of one gas supply line, and gas is flowed at an accurate known flow rate that can be determined thereby, and the actual volume V of the build-up volume is determined by measuring the rate of pressure increase in the build-up volume at that time. Also, a method of determining the flow path volume on the system side and the actual volume V of the build-up volume using Boyle's law is also disclosed.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, in the measurement method described in Patent Document 2, while the flow path volume on the system side is determined by measurement, the volume between the two shut-off valves constituting the gas flow rate measurement unit needs to be stored in advance in the storage means as a known volume. And at the time of flow rate measurement, after reading out the known volume between the two shut-off valves from the storage means as a specified value, the flow path volume on the system side is determined by measurement and calculation.

[0011] For this reason, when the volume inside the gas flow rate measurement unit changes, in the method described in Patent Document 2, there is a possibility that the measurement accuracy may decrease. Note that the volume inside the gas flow rate measurement unit may change, for example, due to the deposition of gas on the inner wall of the unintended flow path or the corrosion of the inner wall of the flow path.

[0012] The present invention has been made in view of the above problems, and is an apparatus for measuring flow rate using the build-up method, and its main object is to provide a flow rate measuring apparatus capable of measuring the build-up volume in detail in a relatively short time at an arbitrary timing.

Means for Solving the Problems

[0013] The flow rate measuring apparatus according to an embodiment of the present invention is a gas supply system having a flow rate control device, a downstream valve provided on the downstream side of the flow rate control device, and a gas using device connected to a flow path on the downstream side of the downstream valve. A flow rate measuring device configured to measure the flow rate of the gas controlled by the flow rate control device, which is connected to a flow path between the downstream valve and the gas using device, and includes an exhaust system flow path provided with an exhaust side on-off valve, a measurement flow path branched from the exhaust system flow path upstream of the exhaust side on-off valve and provided with a pressure sensor and a temperature sensor, and a built-in flow rate control device connected to the measurement flow path for controlling the flow rate of gas from the outside and flowing it into the measurement flow path.

[0014] In a certain embodiment, the flow rate measuring device is configured to calculate the volume of the build-up capacity constituted by the measurement flow path by monitoring the output of the pressure sensor when gas from the outside is flowed into the closed measurement flow path at the flow rate controlled by the built-in flow rate control device.

[0015] In a certain embodiment, the flow rate measuring device is configured to calculate the volume of the flow path from the downstream valve to the flow rate measuring device by monitoring the output of the pressure sensor when gas from the outside is flowed into the measurement flow path and the flow path from the downstream valve to the flow rate measuring device with the downstream valve closed at the flow rate controlled by the built-in flow rate control device.

Effects of the Invention

[0016] By using the flow rate measuring device according to the embodiment of the present invention, it is possible to accurately measure the flow rate of the gas controlled by the flow rate control device in a relatively short time.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

[0019] FIG. 1 shows a gas supply system 100 to which a flow rate measuring device 20 according to an embodiment of the present invention is connected. The gas supply system 100 is configured to supply gas from a plurality of gas supply lines to a process chamber (gas using device) 6 of a semiconductor manufacturing apparatus via an on-off valve 4 provided in a common line. A vacuum pump 8 is connected to the process chamber 6, and the inside of the chamber and the flow path connected thereto can be evacuated. The flow rate measuring device 20 may be detachably connected to the gas supply system 100.

[0020] Each gas supply line is provided with a gas supply source 2, a flow rate control device 10, and a downstream valve V1. The gas from the gas supply source 2 is flow rate controlled by the flow rate control device 10 and then supplied to the process chamber 6. The gas supply source 2 stores various arbitrary gases such as a material gas, an etching gas, and a purge gas. The downstream valve V1 is used to switch the line for gas supply, and by controlling the opening and closing of the downstream valve V1 of each line, any gas type can be supplied to the process chamber 6.

[0021] The type of the flow rate control device 10 is not particularly limited, but in this embodiment, a known pressure type flow rate control device is used. The flow rate control device 10 includes, for example, a throttle portion having a fine opening, a control valve provided upstream of the throttle portion, and a pressure sensor that measures the pressure (hereinafter sometimes referred to as the upstream pressure) between the throttle portion and the control valve. The flow rate control device 10 performs feedback control on the opening degree of the control valve based on the output of the pressure sensor, and controls the upstream side of the throttle portion to a pressure corresponding to the set flow rate, so that gas can flow at the set flow rate on the downstream side of the throttle portion.

[0022] However, in the pressure type flow rate control device 10, due to clogging in the throttle portion or enlargement of the opening due to corrosion during use, the relationship between the upstream pressure and the flow rate may change. However, since the pressure type flow rate control device usually does not have a mechanism that can directly measure the flow rate, it is difficult to immediately detect such a change in the relationship, especially even if an abnormality has occurred in the throttle portion.

[0023] In contrast, in this embodiment, as will be described later, the actual flow rate can be measured using the flow rate measuring device 20 by the build-up method, and based on this measurement result, the flow rate control device 10 can be calibrated. Therefore, accurate flow rate control can be continuously performed over a long period while the flow rate control device 10 is incorporated in the gas supply system 100. In the gas supply system 100, the main flow path portions constituting the build-up volume for flowing gas through the flow rate control device 10 during flow rate measurement by the build-up method are shown in thick lines in FIG. 1.

[0024] As shown in FIG. 1, the flow rate measuring device 20 is connected via an on-off valve 5 in a common flow path L1 on the downstream side of the flow rate control device 10 and the downstream valve V1, and can perform flow rate measurement by the build-up method. In this configuration, gas flow-controlled by the flow rate control device 10 can be made to flow into the flow rate measuring device 20 from an arbitrary line, whereby the flow rate of the gas flowing through an arbitrary gas line can be measured.

[0025] The flow rate measuring device 20 has an exhaust flow path L2 provided with an exhaust side on-off valve V2, and a measurement flow path L3 that branches from the exhaust flow path L2 upstream of the exhaust side on-off valve V2 and is provided with a pressure sensor 22 and a temperature sensor 24. Further, the flow rate measuring device 20 is provided with a controller 26 for controlling the operation of each valve and the like in order to perform build-up flow rate measurement described later and to measure the volume of the flow path constituting the build-up volume inside the flow rate measuring device 20.

[0026] In the flow rate measuring device 20, the downstream side of the exhaust flow path L2 is connected to a vacuum pump 28 via an exhaust valve V4. In the embodiment shown in FIG. 1, a separate vacuum pump 28 is provided from the vacuum pump 8 connected to the process chamber 6, but it is not limited to this. Without preparing the vacuum pump 28, the downstream side of the flow rate measuring device 20 may be connected to the vacuum pump 8 connected to the process chamber 6. However, in this case, on-off valves are provided in each exhaust line so that the exhaust from the process chamber 6 and the exhaust from the flow rate measuring device 20 can be switched.

[0027] Also, in the measurement flow path L3 of the flow rate measuring device 20, a first on-off valve V3 and a second on-off valve V5 are provided so as to sandwich a pressure sensor 22 and a temperature sensor 24. The flow path between the first on-off valve V3 and the second on-off valve V5 is used as part of the build-up volume during build-up flow rate measurement. And a supply line of an inert gas such as nitrogen gas is connected to the second on-off valve V5 via a highly accurate built-in flow rate control device 30 and a supply valve V6. The measurement flow path L3 is configured to be able to flow the gas from the flow rate control device 10 and also to be able to flow an inert gas for volume measurement from the outside.

[0028] FIG. 2 shows a more specific configuration example of the flow rate measuring device 20. As shown in FIG. 2, the flow rate measuring device 20 may have, for example, a pair of pressure sensors 22a and 22b between the first on-off valve V3 and the second on-off valve V5. One of the pair of pressure sensors 22a and 22b may function as a high-pressure one and the other as a low-pressure one, or they may be pressure gauges of the same range and can be used for double-checking in this case. Also, if it is a pressure sensor capable of measuring a wide range, only one pressure sensor may be used.

[0029] Also, as the built-in flow rate control device 30 for controlling the flow rate of the inert gas from the outside, for example, a pressure-type flow rate control device including a throttle portion 32, a control valve 34 on the upstream side of the throttle portion 32, and a pressure sensor 36 for measuring the pressure between the throttle portion 32 and the control valve 34 can be used.

[0030] As the throttle section 32, an orifice plate, a critical nozzle, a sonic nozzle, or the like is used. The diameter of the orifice or nozzle is set, for example, to 10 μm to 2000 μm. As the control valve 34, for example, a piezo element-driven valve is used. The piezo element-driven valve can adjust the movement amount of the diaphragm valve body by controlling the voltage applied to the piezo element, and its opening degree can be arbitrarily adjusted with good responsiveness. Further, as the pressure sensor 36, for example, a silicon single crystal pressure sensor having a pressure-sensitive diaphragm provided with a strain gauge, or a capacitance manometer is used. Note that the same type can also be used as the pair of pressure sensors 22a and 22b.

[0031] The built-in flow rate control device 30 performs flow rate control by utilizing the principle that when the critical expansion condition: PU / PD ≥ about 2 is satisfied, the flow rate Q is determined by the upstream pressure PU regardless of the downstream pressure PD. Here, PU is the gas pressure (upstream pressure) on the upstream side of the throttle section, PD is the gas pressure (downstream pressure) on the downstream side of the throttle section, and about 2 is the case of nitrogen gas. When the critical expansion condition is satisfied, the flow rate Q on the downstream side of the throttle section is given by Q = K1·PU (K1 is a constant depending on the type of fluid and the fluid temperature). To perform flow rate control, a set flow rate is input to the control circuit, and the control circuit calculates the flow rate Q according to the above formula based on the output of the pressure sensor 36 or the like, and feedback-controls the control valve 34 so that this flow rate approaches the input set flow rate.

[0032] Note that the configuration of the built-in high-precision flow control device 30 itself may be the same as that of the flow control device 10 provided in each gas supply line of the gas supply system 100. However, the built-in flow control device 30 is only used when measuring the volume of the build-up capacity, and at this time, unlike the flow control device 10, actual gas does not flow, but an inert gas such as nitrogen gas flows. For this reason, the possibility of deposits or corrosion occurring at the opening of the throttle portion 32 is low, and since the opening area of the throttle portion 32 is maintained constant, high flow control accuracy is maintained over a long period. Therefore, compared with the flow control device 10, high-precision flow control is possible. In addition, since the built-in flow control device 30 is used as a flow reference device, the required time may increase significantly, but it may be calibrated sufficiently in advance at a level stricter than the calibration level of each flow control device 10.

[0033] Referring to FIG. 1 again, in the gas supply system 100, the build-up flow measurement can be performed, for example, as follows. First, with the downstream valve V1 of the flow control device 10 in each gas line and the on-off valve 4 on the process chamber side closed, and the on-off valve 5 on the flow measurement device side open, in the flow measurement device 20, the first on-off valve V3 of the measurement flow path L3 is open, the second on-off valve V5 is closed, and the exhaust side on-off valve V2 and the exhaust valve V4 of the exhaust flow path L2 are opened, and the inside of the build-up capacity is evacuated using the vacuum pump 28.

[0034] Next, with the exhaust side on-off valve V2 in the flow measurement device 20 closed, and while maintaining the state where the first on-off valve V3 is open and the second on-off valve V5 is closed, gas is introduced into the build-up capacity at the set flow rate from the flow control device 10 to be measured. At this time, using the pressure sensor 22 and the temperature sensor 24 provided in the flow measurement device 20, the pressure rise rate (ΔP / Δt) and the gas temperature Tb in the build-up capacity can be measured.

[0035] If the volume value V of the build-up volume is known, the flow rate by the build-up method can be determined based on Q = 22.4×(ΔP / Δt)×V / RT as in the prior art. Here, (ΔP / Δt) is the pressure rise rate, T is the gas temperature, and R is the gas constant. However, the volume value V of the build-up volume varies depending on each gas supply system 100 to be incorporated and is often unknown. Therefore, it is advantageous if the volume value of the build-up volume can be determined in advance using the flow rate measuring device 20.

[0036] In addition to determining the volume value of the build-up volume, when the flow path constituting the build-up volume is complicated and long, for example, as described in Patent Document 3, the gas temperature Tb that can be measured in the flow rate measuring device may be different from the gas temperature Ta in the flow path L1, for example. It is advantageous if the build-up flow rate can be determined using a flow rate calculation formula with reduced temperature influence.

[0037] FIG. 3 shows the volume values Vst, Va, Vb and the temperature values Tst, Ta, Tb at each modeled location on the downstream side of the flow rate control device 10. Here, Vst and Tst refer to the volume value and the gas temperature from the flow rate control device 10 to the downstream valve V1, Va and Ta refer to the volume value and the gas temperature in the flow path L1 from the downstream valve V1 to the flow rate measuring device 20, and Vb and Tb refer to the volume value and the gas temperature inside the flow rate measuring device 20. Note that since the volume Vst is typically a very small value compared to the total volume of the build-up volume, typically, there is no problem using a specified value derived from the device design, and the temperature Tst can be substituted with the output of a temperature sensor built into the flow rate control device 10, for example.

[0038] In a system having such a configuration, the flow rate Q is given by, for example, the following formula.

Equation

[0039] Here, in the above formula, P2 is the gas pressure after buildup when the front and back of the buildup volume are sealed after the buildup time of Δt has elapsed, and P1 is the pressure at the time of simultaneous sealing when the front and back of the buildup volume are sealed simultaneously. By performing pressure correction using the simultaneous sealing pressure in this way, line dependency can be reduced, and the buildup volume can be obtained more accurately. A method for correcting the buildup flow rate by measuring the simultaneous sealing pressure P1 as described above is disclosed in, for example, Patent Document 3. (P2 - P1) corresponds to the increase in the buildup pressure after correcting for line dependency, and (P2 - P1) / Δt corresponds to a similar buildup pressure increase rate.

[0040] Therefore, by using the flow rate measuring device 20 to measure Vb and Tb, and further measuring Va and Ta and storing them in the memory, they can be used when measuring the build-down flow rate.

[0041] Hereinafter, a method for measuring the volume value of the buildup volume using the flow rate measuring device 20 will be described with reference to FIGS. 4(a) and (b), and a method for measuring the buildup flow rate using the flow rate measuring device 20 will be described with reference to FIG. 5. In each figure, the black-painted valve means an open state, and the white-painted valve means a closed state. Also, for the sake of simplicity of explanation, hereinafter, the downstream valve V1, the exhaust side on-off valve V2, the first on-off valve V3, the exhaust valve V4, the second on-off valve V5, and the supply valve V6 may be simply referred to as valves V1, V2, V3, V4, V5, and V6, respectively.

[0042] First, close valve V1 and valve V5, and open the other valves V2 and V3 to evacuate the piping (common flow path L1) and the measurement flow path L3 in the flow rate measurement device 20. Then, as shown in Fig. 4(a), close valve V3, open valve V5 and valve V6, and flow an inert gas into the measurement flow path L3 at the set flow rate indicated by the built-in flow rate control device 30 to perform a build-up. At this time, use the pressure sensor 22 to measure the pressure P2 after the build-up, and also measure the simultaneous sealing pressure P1 when valves V3 and V5 are simultaneously sealed, and obtain the corrected build-up pressure increase rate (P2 - P1) / Δt. Also, measure the gas temperature Tb. Thus, (Vb / Tb) can be calculated based on the following formula.

Equation

[0043] Next, after evacuating the piping etc. in the same manner as above, as shown in Fig. 4(b), close valves V1 and V2, open valves V3, V5 and V6, and flow an inert gas into the combined volume of the piping (common flow path L1) and the measurement flow path L3 in the flow rate measurement device 20 at the flow rate Q indicated by the built-in flow rate control device 30 as the build-up volume to perform a build-up. At this time, use the pressure sensor 22 to measure the pressure P2 after the build-up, and also measure the simultaneous sealing pressure P1 when valves V2 and V5 are simultaneously sealed, thereby obtaining the corrected build-up pressure increase rate (P2 - P1) / Δt. Also, measure the gas temperature Tb. Also, using (Vb / Tb) measured in Fig. 4(a), (Va / Ta) can be calculated based on the following formula.

Equation

[0044] According to this method, by using the pressure sensor 22 and the temperature sensor 24 provided in the flow rate measuring device 20, it is possible to calculate the value (Va / Ta) obtained by dividing the volume Va on the common flow path side, which is difficult to measure, by the gas temperature Ta on the common flow path side, which is difficult to measure.

[0045] As described above, if (Vb / Tb) and (Va / Ta) are obtained, the actual flow rate of the real gas flowing under flow rate control by the flow rate control device 10 can be obtained by the build-up method. Specifically, after evacuating the inside of the pipe, the measurement flow path, etc., and closing the valve V2 and the valve V5, as shown in FIG. 5, the valve V1 is opened (and the valve V3 is kept open), and gas is flowed into the build-up volume composed of the common flow path L1 and the measurement flow path L3 to perform build-up.

[0046] Then, the pressure sensor 22 measures the pressure P1 at the time of simultaneous sealing and the pressure P2 after build-up, and the actual flow rate Q can be measured based on the following formula.

Equation

[0047] Note that, as described above, since Vst / Tst can be considered known, if Va / Ta and Vb / Tb are measured using the flow rate control device 30 built in the flow rate measuring device 20 as described above, the actual flow rate of the gas controlled by the flow rate control device 10 can be measured. In this way, by using the highly accurate built-in flow rate control device 30, Va / Ta and Vb / Tb can be measured with high accuracy at any timing without using real gas. Therefore, for example, even when deposits are generated in the measurement flow path L3 and the volume fluctuates, the build-up flow rate measurement of real gas can be accurately performed over a long period using the build-up volume in which the volume value is corrected by re-measuring the volume.

[0048] As described above, as a result of measuring the gas flow rate from the flow control device 10 using the flow measurement device 20, if there is a large difference between the output flow rate of the flow control device 10 and the measured flow rate measured by the flow measurement device 20, it is considered that a flow control failure has occurred in the flow control device 10. Therefore, it is preferable to calibrate the flow control device 10 when comparing the output flow rate and the measured flow rate of the flow control device 10 and the difference exceeds the threshold value.

[0049] For example, when the flow control device 10 is a pressure type flow control device, when the measured flow rate by the flow measurement device 20 is sufficiently small with respect to the output flow rate of the flow control device 10, it can be determined that the throttle portion 12 of the flow control device 10 is clogged and the gas cannot flow at an accurate flow rate only by referring to the upstream pressure PU. In this case, the flow control device 10 can be calibrated so that the gas can flow at an accurate control flow rate by updating the constant K1 of the above Q = K1·PU, which is the flow rate formula of the flow control device 10, to a smaller value corresponding to the actual flow rate.

Industrial Applicability

[0050] The flow measurement device according to the embodiment of the present invention is suitably used for measuring the actual flow rate of the gas flowing at the flow rate controlled by the flow control device by the build-up method.

Explanation of Signs

[0051] 2 Gas supply source 4 On-off valve 5 On-off valve 6 Process chamber (gas using device) 8 Vacuum pump 10 Flow control device 20 Flow measurement device 22 Pressure sensor 24 Temperature sensor 26 Control circuit 28 Vacuum pump 30 High-precision flow control device 100 Gas supply system V1 Downstream valve V2 Exhaust side on-off valve V3 First on-off valve V4 Exhaust valve V5 Second on-off valve V6 Supply valve

Claims

1. In a gas supply system having a flow rate control device, a downstream valve provided on the downstream side of the flow rate control device, and a gas using device connected to a flow path on the downstream side of the downstream valve, a flow rate measuring device connected to a flow path between the downstream valve and the gas using device and configured to measure the flow rate of the gas controlled by the flow rate control device, an exhaust flow path provided with an exhaust side on-off valve, a measurement flow path branched from the exhaust flow path upstream of the exhaust side on-off valve and provided with a pressure sensor and a temperature sensor, and a built-in flow rate control device connected to the measurement flow path and configured to control the flow rate of external gas and flow it into the measurement flow path The flow rate measuring device comprising.

2. The flow rate measuring device according to claim 1, wherein the volume of the build-up capacity constituted by the measurement flow path can be calculated by monitoring the output of the pressure sensor when external gas is flowed into the closed measurement flow path at the flow rate controlled by the built-in flow rate control device.

3. The flow rate measuring device according to claim 1 or 2, wherein the volume of the flow path from the downstream valve to the flow rate measuring device can be calculated by monitoring the output of the pressure sensor when external gas is flowed into the measurement flow path and the flow path from the downstream valve to the flow rate measuring device with the downstream valve closed at the flow rate controlled by the built-in flow rate control device.

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