Flow rate measurement device and fluid control device

Abstract

A flow rate measurement device 10 provided on the upstream side of a flow rate control device 20 comprises: a first upstream on-off valve V1; a second upstream on-off valve V2 provided on the downstream side of the first upstream on-off valve; a supply pressure sensor 12 that measures the fluid pressure on the downstream side of the second upstream on-off valve; and a processing circuit 16 connected to the first upstream on-off valve, the second upstream on-off valve, and the supply pressure sensor, and the flow rate measurement device is configured so as to measure a flow rate Q using a first pressure drop rate S measured on the basis of the output of the supply pressure sensor after the first upstream on-off valve is closed in a state in which the second upstream on-off valve has been opened, a second pressure drop rate S' measured on the basis of the output of the supply pressure sensor after the second upstream on-off valve is closed, a known volume Va between the first upstream on-off valve and the second upstream on-off valve, and a gas pressure coefficient z associated with the type, pressure, and temperature of the fluid.

Description

Flow rate measuring device and fluid control device

[0001] The present invention relates to a flow rate measurement device and a fluid control device, and more particularly to a flow rate measurement device configured to utilize a build-down method and a fluid control device including the same.

[0002] In gas supply systems for semiconductor manufacturing equipment and chemical plants, multiple types of gases are often supplied to a process chamber by switching between them. The gases supplied to the process chamber include source gases, etching gases, purge gases, etc. The flow rates of the supplied gases are controlled by flow rate control devices installed on the supply lines corresponding to each gas.

[0003] Known flow rate control devices installed in gas supply lines include mass flow controllers (thermal mass flow controllers) and pressure-type flow rate control devices. Of these, pressure-type flow rate control devices are widely used because they can control the mass flow rate of various fluids with high precision using a relatively simple mechanism that combines a control valve and a throttle unit (e.g., an orifice plate or a critical flow nozzle).

[0004] A pressure-type flow rate control device is configured to control the fluid pressure upstream of a throttle section (hereinafter sometimes referred to as upstream pressure P1 or control pressure P1) by adjusting the opening of a control valve, and to cause fluid to flow downstream of the throttle section at a flow rate corresponding to the upstream pressure P1, or the upstream pressure P1 and downstream pressure P2 (fluid pressure downstream of the throttle section). Pressure-type flow rate control devices have excellent flow rate control characteristics, allowing stable flow rate control even in situations where the primary supply pressure, i.e., the fluid pressure upstream of the control valve, fluctuates greatly.

[0005] Furthermore, when operating a flow control device, it is desirable to check the flow rate accuracy and calibrate the device from time to time. In particular, the pressure-type flow control device described above only references pressure and does not have a direct flow rate measurement means, so it becomes difficult to grasp the correct flow rate when the diameter of the throttle section changes due to aging or other reasons. Therefore, it would be advantageous if the pressure-type flow control device could measure the flow rate. It is known that the diameter of the throttle section can change over time due to clogging caused by gas accumulation in the opening or corrosion caused by gas.

[0006] Known flow rate measurement methods applicable to pressure-type flow control devices include the build-up method and the build-down method. The build-up method measures the flow rate of a gas downstream of a flow control device based on the rate of pressure increase (i.e., pressure increase ΔP / time required Δt) after a valve downstream of a build-up volume is closed. The build-down method measures the flow rate of a gas upstream of a flow control device based on the rate of pressure decrease (i.e., pressure decrease ΔP / time required Δt) after a valve upstream of a build-down volume is closed.

[0007] The build-down method is disclosed, for example, in Patent Document 1. In the build-down method, gas present in a build-down volume upstream of a flow control device is allowed to flow out through the flow control device even after the upstream on-off valve is closed. Then, by measuring the pressure drop rate (ΔP / Δt) and temperature (T) in the build-down volume at that time, the flow rate Q can be calculated, for example, from Q = K × (ΔP / Δt) × V / RT (K: constant, R: gas constant, V: volume of the build-down volume). The flow rate calculated by the build-down method is compared with the flow rate indicated by the flow control device and can be used to calibrate the flow control device.

[0008] International Publication No. 2013 / 179550 Patent No. 2635929 Patent No. 4648098 Japanese Patent Application Laid-Open No. 2021-163410

[0009] When measuring a flow rate by the build-down method, a build-down chamber (tank) or the like connected to a flow path may be used as the build-down volume (see, for example, Patent Document 2). However, when measuring a small flow rate, the larger the volume, the smaller the pressure drop rate, which results in a problem that it takes a long time to measure the flow rate. Furthermore, when a build-down chamber or the like is provided, there is a problem that it is difficult to clean when using a gas that is prone to adhesion (e.g., HF gas).

[0010] For this reason, there are cases where the flow path between the upstream on-off valve and the control valve of the pressure-type flow control device is used as the build-down volume, without connecting a separate build-down chamber, and the flow rate is determined by measuring the rate of drop in the supply pressure P0 in this flow path. In this case, even small flow rates (e.g., 30 sccm or less) can be measured accurately in a relatively short time, and since a separate chamber is not connected, there are advantages in that the gas supply system can be provided in a compact form.

[0011] However, to measure small flow rates, the volume of the flow path used as the build-down volume must also be small. When measuring absolute flow rates, even if the volume is small, the accuracy of the flow measurement is significantly reduced if the value cannot be accurately determined. For relative flow rates, even if the build-down volume is not accurately determined, as long as the volume does not change, the device can be calibrated against an accurate flow rate and the flow rate can be measured accurately based on this flow rate. However, it is difficult to accurately measure absolute flow rates.

[0012] In particular, the flow path capacity changes when the flow control device is replaced or when the flow path is improved, etc. For this reason, with the conventional build-down method, it is necessary to calculate the changed capacity every time the configuration is changed.

[0013] The present invention has been made to solve the above-mentioned problems, and its main object is to provide a flow measurement device that can accurately measure absolute flow rates using the build-down method in a relatively compact manner, regardless of changes in the volume of the flow path due to replacement of the flow control device, etc., and a fluid control device equipped with the same.

[0014] A flow measurement device according to an embodiment of the present invention is connected to the upstream side of a flow control device and comprises a first upstream on-off valve, a second upstream on-off valve provided downstream of the first upstream on-off valve, a supply pressure sensor that measures the fluid pressure downstream of the second upstream on-off valve, and a processing circuit connected to the first upstream on-off valve, the second upstream on-off valve, and the supply pressure sensor, wherein the processing circuit is configured to measure a flow rate using, with the second upstream on-off valve open, a first pressure drop rate measured based on the output of the supply pressure sensor after the first upstream on-off valve is closed, a second pressure drop rate measured based on the output of the supply pressure sensor after the second upstream on-off valve is closed, a known volume value between the first upstream on-off valve and the second upstream on-off valve, and a gas pressure coefficient associated with the type, pressure, and temperature of the fluid.

[0015] In one embodiment, the flow measurement device further includes a temperature sensor that measures the temperature of the fluid downstream of the first upstream on-off valve, and is configured to measure the flow rate using a first fluid temperature measured by the temperature sensor during a period in which a first pressure drop rate is measured, and a second fluid temperature measured by the temperature sensor during a period in which a second pressure drop rate is measured.

[0016] In one embodiment, the flow measurement device is configured to measure the flow rate according to the calculation formula Q = 273.15 × αzSS'Va / (S'T-ST'), where Q is the calculated flow rate, α is a coefficient, z is a gas compression coefficient, Va is a known volume value between the first upstream on-off valve V1 and the second upstream on-off valve V2, S is the first pressure drop rate, S' is the second pressure drop rate, T is the first fluid temperature, and T' is the second fluid temperature.

[0017] In one embodiment, an unknown volume from the second upstream on-off valve to the flow rate control device is connected downstream of the known volume from the first upstream on-off valve to the second upstream on-off valve.

[0018] In one embodiment, the first pressure drop rate and the second pressure drop rate are measured within a predetermined pressure range.

[0019] A fluid control device according to an embodiment of the present invention includes any one of the flow rate measurement devices described above and a flow rate control device provided downstream of the flow rate measurement device.

[0020] In one embodiment, the flow control device is a pressure-type flow control device that includes a control valve, a throttle section provided downstream of the control valve, and an upstream pressure sensor that measures the fluid pressure between the control valve and the throttle section, and is configured to control the flow rate by feedback-controlling the control valve based on the output of the upstream pressure sensor.

[0021] In one embodiment, the fluid control device is configured to correct the control flow rate of the flow rate control device provided downstream based on the measured flow rate verified using the flow rate measurement device.

[0022] According to the fluid control device of the embodiment of the present invention, the absolute flow rate can be measured with higher accuracy using the build-down method.

[0023] 1 is a schematic diagram showing the configuration of a fluid supply system including a fluid control device and a flow measurement device according to an embodiment of the present invention; 2 is a diagram showing an example of a flow control device provided in a fluid control device according to an embodiment of the present invention; 3 is a diagram for explaining the procedure of flow rate measurement using a flow measurement device according to an embodiment of the present invention, where (a) shows a first pressure drop measurement and (b) shows a second pressure drop measurement; 4 is a diagram showing the procedure of flow rate measurement using a flow measurement device according to an embodiment of the present invention, showing the set flow rate of the flow control device, the opening and closing operation of a first upstream opening and closing valve, the opening and closing operation of a second upstream opening and closing valve, and the corresponding change in supply pressure over time, respectively;

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the embodiments described below.

[0025] 1 shows a gas supply system 100 including a fluid control device 50 according to an embodiment of the present invention. The fluid control device 50 is configured to include a flow measurement device 10 according to an embodiment of the present invention and a flow control device 20 of any type provided downstream of the flow measurement device 10. The gas supply system 100 is configured to supply gas G, which is supplied via a flow path 4 from a gas supply source 2, to a process chamber 8 of a semiconductor manufacturing apparatus via the fluid control device 50 (i.e., the flow measurement device 10 and the flow control device 20).

[0026] A vacuum pump 9 is connected to the process chamber 8, and the chamber and the upstream flow path can be evacuated. A stop valve 6 is provided between the flow rate control device 20 and the process chamber 8, and the supply of gas to the process chamber 8 can be stopped using the stop valve 6.

[0027] In the gas supply system 100, various gases used in semiconductor manufacturing processes, such as source gas, etching gas, or purge gas, can be supplied from the gas supply source 2. The gas supply source 2 may also supply HF gas as a gas for cleaning or dry etching.

[0028] Although a single-system embodiment consisting of one gas supply line will be described here, multiple gas supply lines may be commonly connected to process chamber 8. In this case, each gas supply line is provided with a flow rate measuring device 10, a flow rate control device 20, and a stop valve 6. In a multi-system embodiment, stop valve 6 can be used to switch the gas supplied to process chamber 8, and the flow rate can be controlled and measured for each gas.

[0029] In this embodiment, the flow measurement device 10 includes a first upstream on-off valve V1, a second upstream on-off valve V2 provided downstream thereof, a supply pressure sensor 12 that measures the pressure (supply pressure P0) of the fluid between the second upstream on-off valve V2 and the flow control device 20, and a temperature sensor 14 that measures the temperature of the fluid. In the example shown in the figure, the temperature sensor 14 and the supply pressure sensor 12 are provided separately upstream of the flow control device 20, but if the temperature sensor and pressure sensor built into the flow control device 20 can be used instead, there is no need to provide the temperature sensor 14 and the supply pressure sensor 12 separately.

[0030] The first upstream on-off valve V1 and the second upstream on-off valve V2 may be, for example, air-operated valves (AOVs), but are not limited thereto and may alternatively be piezo valves (piezo element-driven valves) or solenoid valves. The supply pressure sensor 12 is preferably a silicon single crystal pressure sensor having a pressure-sensitive diaphragm with a strain gauge or a capacitance manometer. The temperature sensor 14 is preferably a thermistor or a platinum resistance thermometer.

[0031] The flow measurement device 10 is disposed upstream of the flow control device 20. In this embodiment, the flow measurement device 10 is configured to measure the absolute flow rate of the flowing gas using a processing circuit 16 connected to the first upstream on-off valve V1, the second upstream on-off valve V2, the supply pressure sensor 12, and the temperature sensor 14 while causing the gas G to flow downstream at a flow rate controlled by the flow control device 20. The processing circuit 16 may incorporate a CPU, memory, an A / D converter, etc., and may include a computer program configured to execute the control operations or arithmetic processing operations described below, and may be realized by a combination of hardware and software. Specific procedures for flow measurement using the flow measurement device 10 will be described later.

[0032] 2 shows an exemplary configuration of the flow control device 20. The flow control device 20 used in this embodiment is a pressure-type flow control device, and includes a control valve 22, a throttle section 24 downstream of the control valve 22, and an upstream pressure sensor 26 that measures the pressure between the control valve 22 and the throttle section 24 (upstream pressure P1).

[0033] The flow control device 20 may include a downstream pressure sensor 28 that measures the pressure (downstream pressure P2) downstream of the throttle unit 24. The flow control device 20 may also include a temperature sensor (not shown) that measures the fluid temperature between the control valve 22 and the throttle unit 24. Furthermore, the flow control device 20 may include the supply pressure sensor 12 shown in FIG. 1 built in upstream of the control valve 22.

[0034] The flow rate control device 20 is configured to control the flow rate of gas flowing downstream of the throttle unit 24 by adjusting the aperture of the control valve 22 based on the output of the upstream pressure sensor 26, etc. The throttle unit 24 may be an orifice plate, a critical flow nozzle, a sonic nozzle, or the like. The diameter of the orifice or nozzle is set to, for example, 10 μm to 2000 μm. The control valve 22 may be, for example, a piezoelectric element-driven valve. A piezoelectric element-driven valve can adjust the amount of movement of the diaphragm valve element by controlling the voltage applied to the piezoelectric element, and the aperture can be adjusted as desired.

[0035] The flow control device 20 can control the flow rate by utilizing the principle that, when the critical expansion condition P1 / P2 is greater than or equal to approximately 2 (where P1 is the upstream pressure, P2 is the downstream pressure, and approximately 2 is the case for nitrogen gas), the flow rate Q is determined by the upstream pressure P1, regardless of the downstream pressure P2. When the critical expansion condition is satisfied, the flow rate Q is calculated from Q = K1 × P1 (K1 is a constant that depends on the type of fluid and the fluid temperature). Furthermore, when the downstream pressure sensor 28 is provided, even when the critical expansion condition is not satisfied, the flow rate Q can be calculated from Q = K2 × P2^m × (P1 - P2)^n (where K2 is a constant that depends on the type of fluid and the fluid temperature, and m and n are exponents derived from the actual flow rate).

[0036] When the set flow rate Qs is input to the control circuit, the flow rate control device 20 calculates the calculated flow rate Qc according to the above formula and performs feedback control on the control valve 22 so that the calculated flow rate Qc approaches the input set flow rate Qs. The calculated flow rate Qc may be displayed on an external monitor as a flow rate output value.

[0037] However, the flow rate control device 20 is not limited to a pressure type flow rate control device, and may be a flow rate control device of another type such as a thermal type mass flow device. Regardless of the type of flow rate control device 20 used, the flow rate measurement device 10 connected to the upstream side thereof is configured to measure the actual absolute flow rate while the gas is flowing downstream at a flow rate controlled by the flow rate control device 20.

[0038] A flow rate measurement method using the flow rate measurement device 10 will be described below with reference to FIGS.

[0039] 3(a) and (b) show two separate pressure drop measurements (first measurement and second measurement) performed using the flow measurement device 10. In Fig. 3(a) and (b), the first upstream on-off valve V1 and the second upstream on-off valve V2 constituting the flow measurement device 10 are shown in black when closed and in white when open.

[0040] As shown in FIG. 3( a), in the first measurement, the flow measurement device 10 starts from a state in which gas is flowing stably at a flow rate controlled by the flow control device 20, closes the first upstream on-off valve V1, keeps the second upstream on-off valve V2 open, and measures the subsequent drop in supply pressure P0 using the supply pressure sensor 12.

[0041] 3(b), in the second measurement, the flow measurement device 10 closes only the second upstream on-off valve V2 from a state in which gas is flowing stably at a flow rate controlled by the flow control device 20, and measures the subsequent drop in supply pressure P0 using the supply pressure sensor 12. Note that in the second measurement, although Fig. 3(b) shows a state in which the first upstream on-off valve V1 is open, the first upstream on-off valve V1 may be open or closed after the second upstream on-off valve V2 is closed.

[0042] 3(a), after the first upstream on-off valve V1 is closed, gas in the flow path from the first upstream on-off valve V1 to the flow control device 20 (more specifically, to the control valve 22 of the flow control device 20) flows downstream through the flow control device 20. At this time, the flow rate can be calculated by measuring the pressure drop rate based on the build-down method.

[0043] The build-down volume in the first measurement corresponds to the sum of the illustrated volume Va (i.e., the volume of the flow path between the first upstream on-off valve V1 and the second upstream on-off valve V2) and volume Vb (i.e., the volume of the flow path between the second upstream on-off valve V2 and the flow control device 20). Therefore, the calculated flow rate Q using the build-down method is given by, for example, the following formula: Q = αzS(Va + Vb) × (273.15 / T) (1)

[0044] The build-down volume in the second measurement corresponds to the volume Vb shown in the figure. Therefore, the calculated flow rate Q using the build-down method is given by, for example, the following formula: Q=αzS′Vb×(273.15 / T′) (2)

[0045] In the above formula (1), α is a unit conversion coefficient [atm·s / kPa·min], z is a gas compression coefficient (dimensionless quantity), Va is a volume [cc] of the flow path between the first upstream on-off valve V1 and the second upstream on-off valve V2, Vb is a volume [cc] of the flow path (including the volume of the connection part of the supply pressure sensor 12) between the second upstream on-off valve V2 and the flow control device 20, S and S′ are pressure drop rates ΔP / Δt [kPa / s] measured using the supply pressure sensor 12, and T and T′ are temperatures [K] measured using the temperature sensor 14.

[0046] Here, the volume Va is a known volume that can be measured with high accuracy in advance before incorporating the flow measurement device 10 into the gas supply system 100. The accurate volume Va can be measured in various ways, for example, by connecting a reference flow meter to a system that can flow gas at an accurate absolute flow rate and applying the build-up method or the build-down method, or by connecting to the capacity of another known volume and using Boyle's law. The volume Va is set to, for example, about 0.1 to 10 cc. The measured value of the volume Va is stored in the memory of the flow measurement device 10.

[0047] On the other hand, the volume Vb may vary in size depending on the system in which the flow measurement device 10 is incorporated, and it may be difficult to measure accurately after the flow measurement device 10 is incorporated into the system. Furthermore, in the build-down method, the internal flow path on the inlet side of the flow control device 20 may also need to be included in the build-up volume, and the volume Vb may vary depending on the type of flow control device 20 used, resulting in an unknown volume. That is, in this embodiment, the unknown volume Vb is connected downstream of the known volume Va.

[0048] Therefore, in this embodiment, two pressure drop measurements (measurements of the first pressure drop rate S and the second pressure drop rate S') are performed as described above, and the flow rate Q is calculated based on a flow rate calculation formula that does not include the volume Vb.

[0049] More specifically, the flow rate measurement device of this embodiment performs the above-mentioned two (two types of) pressure drop measurements, and calculates the flow rate based on the following equation (3) derived by combining the above equations (1) and (2) and eliminating the volume Vb from them: Q=273.15×αzSS′Va / (S′T−ST′) (3)

[0050] As described above, according to the formula (3), an accurate flow rate can be measured by the build-down method without using the unknown volume Vb from the second upstream on-off valve V2 to the flow control device 20.

[0051] Furthermore, in this embodiment, the flow rate is calculated after correction using the gas compressibility coefficient z, as shown in equation (3). Here, the gas compressibility coefficient z (or compressibility factor z) is the difference between an ideal gas that satisfies PV = nRT (P is pressure, V is volume, n is amount of substance, and T is temperature) and a real gas, and is caused by the influence of intermolecular forces and the volume of the molecules themselves, which cannot be ignored in real gases. For ideal gases, z = PV / nRT = 1, but for real gases, z can take on values ​​other than 1 depending on the gas type, pressure, and temperature.

[0052] The compression factor z is determined based on the type, pressure, and temperature of the gas. Therefore, by storing the compression factor z in association with the pressure and temperature for each gas type and reading out the corresponding compression factor z during actual measurement to calculate the flow rate, it is possible to more accurately determine the absolute flow rate of gas in various states. Note that the technology for measuring gas flow rates taking the compressibility factor into account is disclosed in, for example, Patent Document 3 (Japanese Patent No. 4648098).

[0053] In particular, when the build-down method is applied to measure the flow rate upstream of the flow control device, as in this embodiment, the measured pressure (supply pressure P0) is significantly greater than the measured pressure when, for example, the flow rate is measured downstream using the build-up method. In this case, although it depends on the gas type, it may be difficult to accurately determine the absolute flow rate unless correction is made using the compression coefficient z. Therefore, in this embodiment, correction using the compression coefficient z is introduced, which is particularly effective when the build-down method is applied upstream to determine the absolute flow rate.

[0054] 4 shows a specific flow rate measurement procedure using the flow measurement device 10. First, at time t0, flow rate measurement is started in accordance with a command received from an external device. At this time, the first upstream on-off valve V1 and the second upstream on-off valve V2 are open, the set flow rate Qs of the flow control device 20 is maintained at a predetermined value, and gas flows downstream at a flow rate corresponding to the set flow rate Qs.

[0055] Then, after a waiting time W to further ensure that the gas flow is stable, only the first upstream on-off valve V1 is closed at time t1. At this time, the second upstream on-off valve V2 is maintained open, so gas contained in the build-down volume (volume Va+volume Vb) between the first upstream on-off valve V1 and the flow control device 20 flows out downstream via the flow control device 20. As this gas flows out, the supply pressure P0 decreases.

[0056] Here, the first pressure drop measurement is performed. Here, a measurement start pressure Pa and a measurement end pressure Pb are set in advance, and a pressure drop rate S (=ΔP / Δt) of the pressure drop from the measurement start pressure Pa to the measurement end pressure Pb is measured. More specifically, in this embodiment, the output of supply pressure sensor 12 is monitored, and the time Δt required from time t1a when supply pressure P0 reaches measurement start pressure Pa to time t1b when it reaches measurement end pressure Pb is measured. The preset ΔP is divided by the measured required time Δt to determine the first pressure drop rate S (=ΔP / Δt).

[0057] In this way, by measuring the pressure drop rate limited to the range from the measurement start pressure Pa to the measurement end pressure Pb, even for gases such as HF gas that tend to cluster due to pressure, it is possible to perform measurement limited to a pressure range in which it has been confirmed that clustering does not occur (for example, Patent Document 4). Therefore, for specific gases, it is possible to perform more accurate flow rate measurement.

[0058] However, the measurement of the pressure drop rate ΔP / Δt is not limited to this, and can be performed in various ways. For example, the supply pressure P0 can be sampled at a predetermined interval over the period from when the measurement start pressure Pa is reached until the measurement end pressure Pb is reached, and the slope of the line of the pressure drop versus time t can be calculated from the sampled data using a least-squares method or the like, and this can be used as the pressure drop rate ΔP / Δt. Furthermore, although the above describes a mode in which the measurement start pressure Pa and the measurement end pressure Pb are set in advance and the required time Δt is measured, the time Δt can also be set in advance, and ΔP can be measured based on the output of the pressure sensor at the time Δt has elapsed after the measurement start pressure Pa is reached, thereby obtaining the pressure drop rate. Any measurement method can be used as long as it is possible to measure the pressure drop rate during the period in which the pressure drop occurs.

[0059] During the first pressure drop measurement, the gas temperature T is also measured. The gas temperature T may be, for example, an average temperature during the measurement period. The first pressure drop rate S (=ΔP / Δt) and the gas temperature T measured in this manner are temporarily stored in memory.

[0060] Next, at time t1b, when the first pressure drop measurement is completed, the first upstream on-off valve V1 is opened to allow gas to continue flowing downstream at the set flow rate Qs in order to perform the second measurement. As with the first measurement, a waiting time W is set to further ensure that the gas flow is stable.

[0061] Next, at time t2, the second upstream on-off valve V2 is closed to perform a second pressure drop measurement. At this time, gas contained in the build-down volume (volume Vb) between the second upstream on-off valve V2 and the flow control device 20 flows out downstream via the flow control device 20. As this gas flows out, the supply pressure P0 decreases. Note that although the first upstream on-off valve V1 is open in the illustrated example, the first upstream on-off valve V1 may also be closed to more reliably prevent gas from flowing in from the upstream side due to valve leakage.

[0062] Then, similarly to the first pressure drop measurement, the time Δt' required from time t2a when the supply pressure P0 reaches the measurement start pressure Pa to time t2b when the supply pressure P0 reaches the measurement end pressure Pb is measured, and the second pressure drop rate S' (= ΔP / Δt') is calculated by dividing the predetermined ΔP by the measured time Δt'. As with the measurement of the first pressure drop rate S, the measurement of the second pressure drop rate S' can be performed in various ways as described above.

[0063] During the second pressure drop measurement, the gas temperature T' is also measured. The gas temperature T' may be, for example, the average temperature during the measurement period. The pressure drop rate S' (= ΔP / Δt') and the gas temperature T' thus measured are temporarily stored in memory.

[0064] Thereafter, during the flow rate calculation period C, the flow rate Q is calculated using the obtained measured values, the pressure drop rates S and S', and the gas temperatures T and T', according to the above equation (3), i.e., Q = 273.15 × αzSS'Va / (S'T-ST'). At this time, the gas compression coefficient z is a value determined based on the gas type, pressure, and temperature, and is read from memory. The volume Va is also a fixed value that has been stored in advance in memory. At time t3 when the flow rate calculation is completed, the flow rate measurement ends.

[0065] In this way, by performing two pressure drop rate measurements (and temperature measurements) with different build-down volumes, it is possible to measure the actual absolute flow rate of the gas whose flow rate is controlled at the set flow rate Qs by the flow rate controller 20, even if the volume Vb of the build-down volume between the second upstream on-off valve V2 and the flow rate controller 20 is unknown. The measured absolute flow rate may be used to calibrate the flow rate controller 20.

[0066] If the flow control device 20 is a pressure-type flow control device, its calibration can be easily performed by updating the flow calculation formula of the flow control device 20 (e.g., the value of K1 in Q = K1 x P1) based on, for example, the ratio between the absolute flow rate measured by the flow measurement device 10 and the flow rate indicated by the flow control device 20.

[0067] The flow measurement device 10 has a relatively simple configuration and can be relatively easily added and installed upstream of the flow control device 20 in an existing gas supply system, and has the advantage of being able to measure absolute flow rates, which have not been easy to measure in the past. Even when multiple gas types are supplied, it is relatively easy to install a flow measurement device individually on each gas supply line, and by measuring the flow rate using a gas pressure coefficient corresponding to the gas type, pressure, and temperature, the absolute flow rate of each of the desired gases can be measured with high accuracy.

[0068] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the flow control device 20 is not limited to the pressure-type flow control device described above, and other types of flow control devices (e.g., thermal mass flow controllers) can be used. However, the fluid control device 50 of this embodiment is particularly useful in an embodiment equipped with a pressure-type flow control device that does not have a direct flow rate measurement means. Furthermore, the first pressure drop rate measurement (measurement of the first pressure drop rate S) and the second pressure drop rate measurement (measurement of the second pressure drop rate S') may be performed in the reverse order; that is, the measurement of the second pressure drop rate S' may be performed before the measurement of the first pressure drop rate S.

[0069] The flow measurement device and fluid control device according to the embodiments of the present invention are suitably used to measure the absolute flow rates of various gases using the build-down method.

[0070] 2 Gas supply source 4 Flow path 6 Stop valve 8 Process chamber 9 Vacuum pump 10 Flow rate measuring device 12 Supply pressure sensor 14 Temperature sensor 16 Processing circuit 20 Flow rate control device 22 Control valve 24 Throttle section 26 Upstream pressure sensor 28 Downstream pressure sensor 50 Fluid control device 100 Gas supply system P0 Supply pressure P1 Upstream pressure P2 Downstream pressure V1 First upstream on-off valve V2 Second upstream on-off valve

Claims

1. A flow measuring device connected to the upstream side of a flow control device, First upstream on / off valve, A second upstream on-off valve is provided downstream of the first upstream on-off valve, A supply pressure sensor for measuring the fluid pressure downstream of the second upstream on-off valve, The processing circuit connected to the first upstream on-off valve, the second upstream on-off valve, and the supply pressure sensor, The processing circuit is equipped with, With the second upstream on-off valve open, the first pressure drop rate measured based on the output of the supply pressure sensor after closing the first upstream on-off valve, The second pressure drop rate measured based on the output of the supply pressure sensor after closing the second upstream on / off valve, The known volume value between the first upstream on-off valve and the second upstream on-off valve, The gas compressibility coefficient associated with the type of fluid, pressure, and temperature. A flow rate measuring device configured to measure flow rate using [a specific method / tool].

2. The system further includes a temperature sensor for measuring the temperature of the fluid downstream of the first upstream on-off valve, The flow rate measuring device according to claim 1, further configured to measure the flow rate using a first fluid temperature measured by the temperature sensor during a period for measuring a first pressure drop rate, and a second fluid temperature measured by the temperature sensor during a period for measuring a second pressure drop rate.

3. The flow rate measuring device according to claim 2, configured to measure the flow rate according to the calculation formula Q = 273.15 × αzSS'Va / (S'T - ST'), where Q is the calculated flow rate, α is a coefficient, z is the gas compression coefficient, Va is the value of a known volume between the first upstream on-off valve V1 and the second upstream on-off valve V2, S is the first pressure drop rate, S' is the second pressure drop rate, T is the first fluid temperature, and T' is the second fluid temperature.

4. A flow rate measuring device according to any one of claims 1 to 3, wherein an unknown volume from the second upstream on-off valve to the flow rate control device is connected downstream of a known volume from the first upstream on-off valve to the second upstream on-off valve.

5. The flow rate measuring device according to any one of claims 1 to 3, wherein the measurement of the first pressure drop rate and the second pressure drop rate is performed within a predetermined pressure range.

6. A flow rate measuring device according to any one of claims 1 to 3, The flow control device provided downstream of the flow measuring device and A fluid control device equipped with the following features.

7. The fluid control device according to claim 6, wherein the flow rate control device comprises a control valve, a throttling section provided downstream of the control valve, and an upstream pressure sensor for measuring the fluid pressure between the control valve and the throttling section, and is configured to control the flow rate by feedback control of the control valve based on the output of the upstream pressure sensor.

8. The fluid control device according to claim 6, configured to correct the control flow rate of the flow control device provided downstream based on the measured flow rate verified using the flow rate measuring device.