Flow rate control device

Abstract

To provide a pressure type flow rate control device with improved control accuracy.SOLUTION: Flow rate control devices 10, 50 each include a control valve 11, a throttle section 12 provided downstream of the control valve, a differential pressure sensor 20 that measures a differential pressure between the upstream and downstream sides of the throttle section, pressure sensors 13, 19 that measure the pressure downstream or upstream of the throttle section, and a calculation control circuit 16. The flow rate control device controls the control valve so that a calculated flow rate, which is determined based on outputs P1 and P2 of the pressure sensors and an output ΔP of a differential pressure sensor, becomes a set flow rate, and is also configured so that the differential pressure ΔP output by the differential pressure sensor is corrected based on the outputs P1 and P2 of the pressure sensors by referring to preset correction information, and the flow rate is controlled based on a corrected differential pressure ΔP'.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a flow rate control device, and more particularly to a flow rate control device provided in a gas supply line of a semiconductor manufacturing facility, a chemical manufacturing facility, or the like. [Background technology]

[0002] In semiconductor manufacturing equipment and chemical plants, various types of flow meters and flow control devices are used to control the flow rates of material gases, etching gases, etc. Among these, pressure-type flow 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 section (for example, an orifice plate or a critical flow nozzle). Unlike thermal-type flow control devices, pressure-type flow control devices have excellent flow control characteristics, allowing stable flow control even when the primary supply pressure fluctuates greatly.

[0003] Some pressure-type flow control devices adjust the flow rate by controlling the fluid pressure on the upstream side of the throttle (hereinafter referred to as the upstream pressure P1). The upstream pressure P1 is controlled by adjusting the opening of a control valve located upstream of the throttle.

[0004] When the downstream pressure P2 (fluid pressure downstream of the throttling section) is sufficiently small relative to the upstream pressure P1, the speed of the gas passing through the throttling section is fixed at the speed of sound, and the mass flow rate is determined by the upstream pressure P1, not by the downstream pressure P2. For this reason, it is possible to control the upstream pressure P1 and therefore the flow rate by feedback controlling the control valve based on the output of a pressure sensor that measures the upstream pressure P1. The pressure condition under which such behavior occurs is called the critical expansion condition, and is specified, for example, as P2 / P1≦A (or P1 / P2≧B), with the value of the critical pressure ratio A differing depending on the type of gas. Flow rate control based on the measurement of such upstream pressure P1 is sometimes called proportional control.

[0005] Patent Document 1 also describes a pressure-type flow control device in which pressure sensors are provided not only on the upstream side but also on the downstream side of the throttling section. With this pressure-type flow control device, even if the downstream pressure P2 is relatively large and does not satisfy the above-mentioned critical expansion condition, the flow rate can be calculated based on the upstream pressure P1 and the downstream pressure P2. Therefore, when a downstream pressure sensor is provided, flow control can be performed over a wider range of pressure conditions. Flow control performed based on measurements of the upstream pressure P1 and the downstream pressure P2 is sometimes called differential pressure control. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4204400 [Patent Document 2] International Publication No. 2020 / 218138 [Patent Document 3] International Publication No. 2017 / 057129 Summary of the Invention [Problem to be solved by the invention]

[0007] Recently, there are an increasing number of cases where flow control is performed under conditions where the downstream pressure P2 downstream of the throttling section is higher than in the past. In such situations, flow control under non-critical expansion conditions is often required, and it is necessary to measure the upstream pressure P1 and the downstream pressure P2. However, in conventional pressure-type flow control devices, the flow measurement error can be relatively large due to the accuracy error of the upstream pressure sensor and the downstream pressure sensor, especially the zero point deviation of the pressure sensor. The zero point deviation of the pressure sensor is an event in which the output of the pressure sensor does not indicate zero even when the actual pressure is zero, but indicates a value that is significantly different from zero.

[0008] In response to this, the applicant has proposed in Patent Document 2 a configuration in which a differential pressure sensor that directly measures the differential pressure between the upstream pressure P1 and the downstream pressure P2, and either an upstream pressure sensor or a downstream pressure sensor are provided, rather than directly measuring the upstream pressure P1 and the downstream pressure P2, respectively. The differential pressure sensor can directly measure the differential pressure ΔP=P1-P2 between the primary pressure (upstream pressure P1) and the secondary pressure (downstream pressure P2) at the throttle section, for example, by detecting the distortion of a diaphragm that deforms according to the differential pressure.

[0009] When a differential pressure sensor and an absolute pressure sensor are used in combination as described above, not only the differential pressure ΔP but also the upstream pressure P1 and downstream pressure P2 can be calculated from the output of each sensor. Therefore, it is possible to determine whether the critical expansion condition is satisfied, and it is also possible to perform both proportional control and differential pressure control in the flow control. A flow control device that combines a differential pressure sensor and an absolute pressure sensor is also described in Patent Document 3.

[0010] In such a flow control device, as disclosed in Patent Document 2, it is possible to suppress an increase in flow measurement error due to a zero point shift of the pressure sensor. The accuracy error of the differential pressure sensor can be confirmed by referring to the output of the differential pressure sensor, for example, in a situation where the valve upstream of the upstream pressure sensor and the valve downstream of the downstream pressure sensor are closed to form a sealed space, and it is also possible to perform calibration based on the result. Error correction of the differential pressure sensor performed in this way can be performed more easily than error correction of an absolute pressure sensor, which must be performed in a complete vacuum state.

[0011] However, through experiments by the present inventors, it has been found that even in a pressure-type flow control device that combines a differential pressure sensor and an absolute pressure sensor as described above, the output error (particularly the zero point deviation) of the differential pressure sensor can vary depending on the magnitude of the absolute pressure, which can reduce the accuracy of flow control.

[0012] The present invention has been made to solve the above-mentioned problems, and its main object is to provide a flow control device that can suppress the effect of pressure sensor output error on flow control and perform accurate flow control over a wide pressure range. [Means for solving the problem]

[0013] A flow control device according to an embodiment of the present invention comprises a control valve, a throttling section provided downstream of the control valve, a differential pressure sensor measuring the differential pressure between the upstream and downstream sides of the throttling section, a pressure sensor measuring the pressure downstream of the throttling section or the upstream side of the throttling section, the control valve, the differential pressure sensor, and a calculation control circuit connected to the pressure sensor, wherein the calculation control circuit is configured to control the control valve so that a calculated flow rate determined based on the output of the pressure sensor and the output of the differential pressure sensor becomes a set flow rate, and is configured to correct the differential pressure output by the differential pressure sensor based on the output of the pressure sensor by referring to preset correction information, and to control the flow rate based on the corrected differential pressure.

[0014] In one embodiment, the arithmetic and control circuit is configured to control the control valve during flow rate control so as to eliminate a difference between a set flow rate and a calculated flow rate determined based on an output of the pressure sensor and the corrected differential pressure, and the control of the control valve is performed using one of proportional control and proportional control based on a flow rate Q calculated according to Q=K1·(ΔP'+P2) or Q=K1·P1, and proportional control based on Q=K2·P2 m ΔP' n or Q = K2 · (P1 - ΔP') m ΔP' nIn the above formula, K1 and K2 are constants depending on the gas type and gas temperature, ΔP' is the corrected differential pressure, P2 is the downstream pressure output by a downstream pressure sensor provided as the pressure sensor and measuring the pressure downstream of the throttling portion, P1 is the upstream pressure output by an upstream pressure sensor provided as the pressure sensor and measuring the pressure upstream of the throttling portion, and m and n are indexes derived based on the actual flow rate.

[0015] In one embodiment, the flow control device is configured to select whether to perform the proportional control or the differential pressure control by comparing the ratio of the upstream pressure obtained by adding the corrected differential pressure and the downstream pressure output by the downstream pressure sensor to the downstream pressure output by the downstream pressure sensor, with a predetermined threshold value, or by comparing the ratio of the upstream pressure output by the upstream pressure sensor to the downstream pressure obtained by subtracting the corrected differential pressure from the upstream pressure output by the upstream pressure sensor, with a predetermined threshold value.

[0016] In one embodiment, the correction information is defined by ΔP'=ΔP+α·P2 or ΔP'=ΔP+α·P1, where in the above formula, ΔP' is the corrected differential pressure, ΔP is the differential pressure output by the differential pressure sensor, α is a preset coefficient, P2 is the downstream pressure output by a downstream pressure sensor provided as the pressure sensor and measuring the pressure downstream of the throttling portion, and P1 is the upstream pressure output by an upstream pressure sensor provided as the pressure sensor and measuring the pressure upstream of the throttling portion.

[0017] In one embodiment, the pressure sensor and the differential pressure sensor are integrally formed. Effect of the Invention

[0018] According to an embodiment of the present invention, it is possible to perform more accurate zero point adjustment of the differential pressure sensor regardless of the enclosed pressure, and a pressure-type flow control device is provided that can more appropriately control the flow rate by applying line pressure correction to the output of the differential pressure sensor. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram illustrating a gas supply system incorporating a flow rate control device according to an embodiment of the present invention; [Diagram 2] 1 is a diagram illustrating a flow rate control device according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a side view showing a specific configuration of a flow rate control device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a side view showing another specific configuration of the flow rate control device according to the embodiment of the present invention. [Diagram 5] 11 is a graph showing the relationship between downstream pressure P2 and the output of the differential pressure sensor when the differential pressure is zero. [Figure 6] 4 is a flowchart showing a flow rate control process performed by the flow rate control device according to the embodiment of the present invention. [Figure 7] FIG. 13 is a diagram showing the configuration of an integrated sensor for measuring differential pressure and downstream pressure provided in a flow control device according to another embodiment of the present invention. [Figure 8] FIG. 11 is a side view showing a specific configuration of a flow rate control device according to another embodiment of the present invention. [Figure 9] FIG. 11 is a side view showing a specific configuration of a flow rate control device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment.

[0021] 1 shows a gas supply system 100 including a flow control device 10 according to an embodiment of the present invention. The gas supply system 100 includes a gas supply source 2, a flow control device 10 provided in a flow path 4 forming a gas supply line, an upstream on-off valve 3 and a downstream on-off valve 5 provided upstream and downstream of the flow control device 10, a process chamber 6 connected downstream of the downstream on-off valve 5, and a vacuum pump 8 connected to the process chamber 6.

[0022] The flow rate control device 10 is provided to control the flow rate of gas flowing through the flow path 4. The vacuum pump 8 can evacuate the process chamber 6 and the flow path 4, and a gas whose flow rate is controlled is supplied to the process chamber 6 while the downstream side of the flow rate control device 10 is in a reduced pressure state. The gas supply source 2 may supply various gases used in the semiconductor manufacturing process, such as a source gas, an etching gas, or a carrier gas.

[0023] 1 shows only one gas supply line, a plurality of gas supply lines corresponding to each gas type may be connected to the process chamber 6 in the gas supply system 100. In this embodiment, the on-off valves (on-off valves) 3, 5 are provided on the upstream and downstream sides of the flow control device 10, but the downstream on-off valve 5 may be built into the outlet side of the flow control device 10. As the on-off valves 3, 5, valves with good blocking properties and responsiveness, such as air-operated valves (AOV), solenoid valves, and motor-operated valves, are preferably used.

[0024] Fig. 2 is a schematic diagram showing the configuration of a flow control device 10 of this embodiment. As shown in Fig. 2, the flow control device 10 includes a control valve 11 interposed in a flow path 4, a throttle section 12 provided downstream of the control valve 11, a downstream pressure sensor 13 that measures a pressure (downstream pressure) P2 downstream of the throttle section 12, a differential pressure sensor 20 that directly measures a differential pressure ΔP between the upstream side and downstream side of the throttle section 12, an inflow pressure sensor 14 that measures a pressure (supply pressure) P0 upstream of the control valve 11, a temperature sensor 15 that measures a temperature T of the fluid, and a calculation control circuit 16.

[0025] A differential pressure sensor 20, a downstream pressure sensor 13, an inflow pressure sensor 14, a temperature sensor 15, and the like are connected to the arithmetic and control circuit 16, and the arithmetic and control circuit 16 can receive the output of each sensor. The arithmetic and control circuit 16 is connected to a drive element of the control valve 11, and can adjust the opening of the control valve 11 based on the outputs of the differential pressure sensor 20, the downstream pressure sensor 13, and the temperature sensor 15 to control the flow rate of the gas flowing downstream of the throttle section 12. The inflow pressure sensor 14 can measure the pressure (supply pressure P0) of the gas supplied from the gas supply source 2 (e.g., a raw material vaporizer) shown in Fig. 1, and is used, for example, to adjust the gas supply amount or supply pressure by controlling the upstream opening / closing valve 3 based on the output of the inflow pressure sensor 14.

[0026] The pressure-type flow control device 10 configured in this manner can control the flow rate of gas flowing downstream of the throttling section 12 by adjusting the upstream pressure P1 using the control valve 11. When the critical expansion condition P1 / P2 ≧ approximately 2 (approximately 2 for nitrogen gas) is satisfied, the flow velocity of the gas passing through the throttling section 12 is fixed at the speed of sound, and flow rate control can be performed utilizing the principle that the mass flow rate is determined by the upstream pressure P1, not by the downstream pressure P2. When the critical expansion condition is satisfied, the flow rate Q is given by Q = K1 P1 (K1 is a constant that depends on the gas type and gas temperature), and flow rate control can be performed by proportional control based on the upstream pressure P1.

[0027] Even when the critical expansion condition is not satisfied, the flow control device 10 calculates Q=K2·P2 based on the upstream pressure P1 and the downstream pressure P2. m (P1-P2) n (Here, K2 is a constant that depends on the gas type and gas temperature, and m and n are exponents derived based on the actual flow rate) The flow rate Q can be calculated, and flow rate control can be performed by differential pressure control.

[0028] However, the flow control device 10 of this embodiment is equipped with a differential pressure sensor 20 and a downstream pressure sensor 13, and is configured to calculate the flow rate from the differential pressure ΔP and downstream pressure P2 output by these sensors in the same manner as described above. Specifically, the flow rate Q when the critical expansion condition is satisfied can be calculated by Q=K1·(ΔP+P2). Also, the flow rate Q when the critical expansion condition is not satisfied can be calculated by Q=K2·P2. m ΔP n The flow rate Q thus calculated is compared with the set flow rate, and the control valve 11 is feedback-controlled to eliminate the difference, thereby allowing gas to flow downstream of the throttle section 12 at the desired set flow rate.

[0029] Figures 3 and 4 are side views showing specific configurations of flow control devices 10A and 10B of other embodiments corresponding to the flow control device 10 shown in Figure 2, and diagrams showing internal flow paths (broken lines). As shown in Figures 3 and 4, the flow path 4 is formed by providing holes in the main body block 17 and the outlet block 18.

[0030] The main body block 17 and the outlet block 18 are preferably made of a material that is not reactive with the gas used, such as stainless steel (SUS316L, etc.). Although the temperature sensor 15 shown in Fig. 2 is not shown in Fig. 3 and Fig. 4, it can be used as a temperature sensor by providing a bottomed hole near the flow path 4 and placing a thermistor or the like inside it.

[0031] An orifice member serving as the throttling section 12, more specifically a gasket-type orifice member incorporating an orifice plate, is provided at the boundary between the main body block 17 and the outlet block 18. However, the throttling section 12 is not limited to an orifice plate, and may also be configured using a sonic nozzle or the like. The aperture of the orifice or nozzle is set to, for example, 10 μm to 500 μm.

[0032] An inflow pressure sensor 14, a control valve 11, a differential pressure sensor 20, and a downstream pressure sensor 13 are attached to the upper surfaces of the main body block 17 and the outlet block 18. The control valve 11 may be, for example, a piezoelectric element-driven valve composed of a metal diaphragm as a valve body and a piezoelectric element (piezo actuator) as a drive device for driving the diaphragm. The piezoelectric element-driven valve can change its opening depending on the drive voltage applied to the piezoelectric element, and can be adjusted to any opening by controlling the drive voltage.

[0033] The arithmetic and control circuit 16 is, for example, configured with a processor and memory provided on a circuit board, includes a computer program that executes a predetermined calculation based on an input signal, and can be realized by a combination of hardware and software. In the illustrated embodiment, the arithmetic and control circuit 16 is built into the flow control device 10, but some or all of its components (such as a CPU) may be provided outside the flow control device 10.

[0034] The inflow pressure sensor 14 and the downstream pressure sensor 13 may be, for example, sensors equipped with a silicon single crystal sensor chip and a diaphragm. The differential pressure sensor 20 may be a type of differential pressure sensor that has a diaphragm as a pressure-sensitive part and detects stress or strain occurring in the pressure-sensitive part with a strain sensor or the like, as disclosed in Patent Document 2. Since the upstream pressure P1 is transmitted to one surface of the diaphragm and the downstream pressure P2 is transmitted to the other surface, the differential pressure ΔP=P1-P2 can be directly measured by detecting the deformation of the diaphragm with a strain sensor or a capacitance sensor.

[0035] 3, a primary side port of the differential pressure sensor 20 is attached to the main body block 17 and communicates with the flow path upstream of the throttle unit 12. In addition, a secondary side port of the differential pressure sensor 20 is attached to the outlet block 18 and communicates with the flow path downstream of the throttle unit 12. A downstream pressure sensor 13 is also attached to the outlet block 18.

[0036] 4, both the primary side port and the secondary side port of the differential pressure sensor 20 are attached to the main body block 17. However, the secondary side port is connected to the branch flow path of the downstream pressure sensor 13 via a flow path provided in the main body block 17, and is connected to the flow path downstream of the throttle unit 12.

[0037] In any of the flow control devices 10A and 10B described above, the differential pressure sensor 20 can measure the differential pressure between the primary side and the secondary side of the throttle section. Also, the upstream pressure P1 can be calculated from the output of the differential pressure sensor 20 (differential pressure ΔP) and the output of the downstream pressure sensor 13 (downstream pressure P2) by the calculation formula: P1=ΔP+P2.

[0038] Furthermore, in the flow control devices 10A and 10B, it is possible to make the volume of the flow path (the portion shown by hatching in FIG. 3) between the control valve 11 and the throttle unit 12 relatively small. When this flow path volume is small, it is possible to reduce the amount of gas flowing out through the throttle unit 12 after the control valve 11 is closed, and therefore it is possible to improve the responsiveness of the fall when the gas flow rate is reduced.

[0039] However, the inventor has confirmed that the above-mentioned differential pressure sensor 20 may output a non-zero value depending on the magnitude of pressure, even when the pressure applied to both sides of the pressure sensing portion is the same and a differential pressure of zero should be output.

[0040] 5 is a graph showing the relationship between the absolute pressure of the downstream pressure P2 (P2 pressure) and the output (ΔP output) of the differential pressure sensor 20 when the upstream pressure P1 and the downstream pressure P2 are the same. As can be seen from Fig. 5, when the absolute pressure of the downstream pressure P2 (and the upstream pressure P1) is approximately zero, the differential pressure sensor also outputs approximately zero, and the output of the differential pressure sensor 20 is calibrated in advance so that no zero point shift occurs.

[0041] On the other hand, as the absolute pressures of the downstream pressure P2 and the upstream pressure P1 increase, the output of the differential pressure sensor, which should normally indicate zero, indicates a significant negative value. The reason for this is believed to be that in the differential pressure sensor, there is a structural asymmetry between the primary side and the secondary side in the pressure sensing part of the sensor chip, and as a result, even when the primary side pressure and the secondary side pressure are the same, stress corresponding to the line pressure is generated in the pressure sensing part.

[0042] 5, the magnitude of the zero point shift output by the differential pressure sensor has a roughly linear relationship with the magnitude of the downstream pressure P2, and the greater the downstream pressure P2, the greater the zero point shift (absolute value). Therefore, it is preferable to correct the output of the differential pressure sensor 20 according to the line pressure (the downstream pressure P2 or the upstream pressure P1 in the gas supply line undergoing flow control) and obtain a more accurate corrected differential pressure ΔP' before performing flow control.

[0043] Here, when the magnitude of the zero point shift is proportional to the magnitude of the downstream pressure P2 as shown in Fig. 5, the correction term can be defined as α·P2 using a proportionality constant α. Here, the proportionality constant α can be easily obtained by measurement by plotting the output of the differential pressure sensor 20 while changing the line pressure (here, the downstream pressure P2) under a condition where the primary side pressure and secondary side pressure of the differential pressure sensor 20 are the same (for example, a condition where the upstream on-off valve 3 and the downstream on-off valve 5 are closed to form a sealed space), and determining the slope of the straight line by the least squares method or the like.

[0044] After the proportionality constant α is calculated in this manner, the corrected differential pressure ΔP' can be calculated as ΔP'=ΔP+α·P2 based on the differential pressure ΔP output by the differential pressure sensor and the downstream pressure P2 output by the downstream pressure sensor 13. In the example shown in Fig. 5, α ≈ 0.00075, and the differential pressure ΔP can be corrected according to the correction formula ΔP'=ΔP+0.00075·P2.

[0045] However, the above correction formula is merely an example, and it goes without saying that a correction formula defined by any function may be adopted based on the relationship between the zero point shift of the differential pressure ΔP obtained by actual measurement and the downstream pressure P2. For example, the correction formula may be defined as a formula including a logarithmic function. Also, different correction formulas may be used for each predetermined pressure range depending on the magnitude of the downstream pressure P2. For example, a first correction formula may be used when the downstream pressure P2 is in the range of 0 to 30 kPa, and a second correction formula may be used when the downstream pressure P2 is in the range of 30 kPa or more.

[0046] Also, instead of using a correction formula, a table describing the relationship between the downstream pressure P2 and the correction term (ΔP'-ΔP) may be referenced to determine the corrected differential pressure ΔP' based on the output differential pressure ΔP and downstream pressure P2. In this specification, the preset correction formula or table used to determine the corrected differential pressure ΔP' based on the measured differential pressure ΔP and downstream pressure P2 as described above may be referred to as correction information. Note that the correction information also includes a correction formula or table used to determine the corrected differential pressure ΔP' based on the differential pressure ΔP and upstream pressure P1, as described later.

[0047] Using the corrected differential pressure ΔP' determined in the above manner, flow rate control can be performed in the same manner as in the past. That is, when the critical expansion condition is satisfied, the flow rate Q is calculated according to Q=K1·(ΔP'+P2) according to proportional control, and the control valve is feedback-controlled so that this calculated flow rate approaches the set flow rate, allowing gas to flow at the desired set flow rate. When the critical expansion condition is not satisfied, the flow rate Q is calculated according to Q=K2·P2 according to differential pressure control. m ΔP' n The flow rate Q is calculated by the above formula, and the control valve is feedback-controlled so that this calculated flow rate approaches the set flow rate, thereby making it possible to flow gas at the desired set flow rate.

[0048] In the above proportional control, when the downstream pressure P2 is considerably small (high vacuum state) and it is determined that the critical expansion condition is met, the differential pressure ΔP' obtained by correcting the differential pressure ΔP output by the differential pressure sensor 20 can be regarded as the upstream pressure P1. In this case, under critical expansion conditions where the downstream side is in a high vacuum state, the flow control device 10 can also perform flow control by feedback controlling the control valve so that the calculated flow rate calculated by Q=K1·ΔP' matches the set flow rate.

[0049] Furthermore, whether or not the critical expansion condition is satisfied may be determined based on the corrected differential pressure ΔP'. Specifically, in the determination formula of the critical expansion condition: P1 / P2≧B (B is a constant determined by the gas type, and is approximately 2 in the case of nitrogen gas), where P1=ΔP'+P2, whether or not the critical expansion condition is satisfied may be determined based on whether or not (ΔP'+P2) / P2≧B is satisfied. Of course, whether or not the critical expansion condition is satisfied may also be determined based on whether or not P2 / (ΔP'+P2)≦A (A is the critical pressure ratio determined by the gas type, which is the reciprocal of the above B).

[0050] 6 shows an example of a flowchart of a flow control process performed using the flow control device 10 of this embodiment. As shown in step S1, first, when a set flow rate is given and flow control is started, the downstream pressure sensor 13 and the differential pressure sensor 20 are used to measure the downstream pressure P2 and the differential pressure ΔP.

[0051] Next, as shown in step S2, a corrected differential pressure ΔP' is determined from the measured downstream pressure P2 and differential pressure ΔP. At this time, due to the influence of line pressure characteristics, when the downstream pressure P2 is higher, it is considered that both the differential pressure ΔP and the zero point shift are large, and the differential pressure ΔP is corrected according to the magnitude of the downstream pressure P2 according to the formula ΔP' = ΔP + α · P2, for example. Note that the corrected differential pressure ΔP' does not necessarily need to be determined at this stage, and may be determined each time the differential pressure ΔP and downstream pressure P2 are measured during feedback control of the control valve in the stage of proportional control or differential pressure control of the flow rate in step S4 or step S5 described later.

[0052] Next, as shown in step S3, whether or not the critical expansion condition is satisfied is determined based on whether P2 / (ΔP'+P2) is equal to or smaller than a threshold value. If the critical expansion condition is satisfied, the magnitude of the downstream pressure P2 relative to (ΔP'+P2), which corresponds to the upstream pressure P1, is sufficiently small, and the ratio of these pressures is equal to or smaller than a threshold value determined by the gas type.

[0053] If it is determined that the critical expansion condition is satisfied, proportional control is selected as shown in step S4, and feedback control of the control valve 11 is performed so that the calculated flow rate calculated by Q=K1·(ΔP'+P2) approaches the set flow rate. At this time, it is preferable that the corrected differential pressure ΔP' is calculated using preset correction information each time the differential pressure ΔP and downstream pressure P2 are measured by the differential pressure sensor 20 and the downstream pressure sensor 13, respectively, or each time the opening of the control valve 11 is adjusted.

[0054] Here, since the downstream pressure P2 is usually equal to the pressure inside the process chamber 6 and is roughly constant, the magnitude of the upstream pressure P1 or the differential pressure ΔP, ΔP' is controlled by controlling the aperture of the control valve 11. By opening the aperture of the control valve, the upstream pressure P1 or the differential pressure ΔP, ΔP' increases, and the flow rate can be increased. Also, by closing the aperture of the control valve, the upstream pressure P1 or the differential pressure ΔP, ΔP' decreases, and the flow rate can be decreased.

[0055] On the other hand, if it is confirmed in step S3 that the expansion is in a non-critical condition, the differential pressure control is selected as shown in step S5, and Q = K2 P2 m ΔP' n Feedback control of the control valve 11 is performed so that the calculated flow rate obtained by the above approaches the set flow rate. In this case, too, it is preferable that the corrected differential pressure ΔP' is calculated using preset correction information each time the differential pressure ΔP and the downstream pressure P2 are measured by the differential pressure sensor 20 and the downstream pressure sensor 13, or each time the opening of the control valve 11 is adjusted.

[0056] In this manner, in both proportional control when the critical expansion condition is satisfied and differential pressure control when the critical expansion condition is not satisfied, flow rate calculation and flow rate control are performed based on the corrected differential pressure ΔP' taking into account the line pressure characteristics, so that more accurate flow rate control can be performed regardless of the magnitude of the downstream pressure P2.

[0057] In addition, since the output of the differential pressure sensor 20 can be corrected to the line pressure based on the magnitude of the downstream pressure P2 as described above, in an isobaric state (P1=P2), such as when the upstream and downstream on-off valves 3 and 5 are closed, the zero point adjustment of the differential pressure sensor 20 can be more appropriately performed regardless of the charged pressure, even if the charged pressure is relatively high. Such zero point adjustment can be performed much more easily and accurately in a flow control device composed of only an absolute pressure sensor, compared to a case where a high vacuum state is formed by evacuation. Furthermore, compared to a flow control device having a conventional differential pressure sensor, the zero point adjustment can be performed more accurately over a wider charged pressure range. By appropriately performing the zero point adjustment of the differential pressure sensor 20 in this way and correcting and using the output of the differential pressure sensor 20 during flow control, flow control by pressure control can be performed more accurately even under a situation where the downstream pressure P2 is relatively high and the differential pressure ΔP is relatively small.

[0058] Fig. 7 shows the sensor chip configuration of an integrated pressure sensor 20A having the functions of both the differential pressure sensor 20 and the downstream pressure sensor 13 of the flow control device 10 shown in Fig. 2. Such an integrated pressure sensor combining a differential pressure sensor and an absolute pressure sensor is also disclosed in Patent Document 2.

[0059] As shown in Fig. 7, in the integrated pressure sensor 20A, two pressure-sensitive parts 24a, 24b are provided on a sensor chip 22. The two pressure-sensitive parts 24a, 24b are formed, for example, by diaphragms formed by cutting a silicon single crystal. Strain sensors 26a, 26b are provided for the pressure-sensitive parts 24a, 24b, respectively, which can sense the deformation and stress generated therein. Capacitive sensors can also be used instead of the strain sensors 26a, 26b.

[0060] A downstream pressure P2 on the downstream side of the throttling portion is transmitted to one surface (lower surface in FIG. 7) of the pressure-sensing portions 24a and 24b via a sealed liquid or the like. The opposite surface (upper surface in FIG. 7) of one pressure-sensing portion 24a is in contact with a vacuum chamber maintained at a vacuum pressure Pv. In this configuration, a pressure corresponding to the absolute pressure of the downstream pressure P2 is applied to the pressure-sensing portion 24a, so that the downstream pressure P2 can be measured by a strain sensor 26a fixed to the pressure-sensing portion 24a. Furthermore, an upstream pressure P1 on the upstream side of the throttling portion is transmitted to the opposite surface of the other pressure-sensing portion 24b via a sealed liquid or the like. In this configuration, a pressure corresponding to a differential pressure ΔP between the upstream pressure P1 and the downstream pressure P2 is applied to the pressure-sensing portion 24b, so that the differential pressure ΔP can be measured by a strain sensor 26b fixed to the pressure-sensing portion 24b.

[0061] By using the integrated pressure sensor 20A configured in this way, it is possible to measure the differential pressure ΔP and the downstream pressure P2 while saving space, and it is possible to calculate the differential pressure ΔP' corrected for the line pressure based on the correction information from these measurement results. Therefore, as described above, it is possible to suppress errors and perform flow rate measurement and flow rate control with higher accuracy.

[0062] Next, a flow control device 50 of another embodiment will be described with reference to Figures 8 and 9. Note that elements having the same configuration as the flow control devices 10, 10A, and 10B of the embodiment shown in Figures 2 to 4 are given the same reference symbols and descriptions thereof may be omitted.

[0063] 8 and 9, the flow control device 50 of this embodiment differs from the above-mentioned flow control device 10 in that it does not have a downstream pressure sensor 13 for measuring the downstream pressure P2, but instead has an upstream pressure sensor 19 for measuring the upstream pressure P1. The rest of the configuration is the same as that of the flow control device 10, and includes a control valve 11, a throttle section 12, a differential pressure sensor 20, an inflow pressure sensor 14, a temperature sensor 15, and an arithmetic control circuit 16. In this specification, the downstream pressure sensor 13 and the upstream pressure sensor 19 may be collectively referred to as a pressure sensor that measures at least one of the pressures downstream or upstream of the throttle section.

[0064] The flow control device 50 can also employ an integrated pressure sensor configuration as shown in Fig. 7. However, in the flow control device 50, the upstream pressure P1 is transmitted to the space facing the vacuum chamber across the pressure sensing unit, and the upstream pressure P1 and downstream pressure P2 are transmitted to each surface of the other pressure sensing unit.

[0065] 8 and 9, the flow control device 50 is configured to control the flow rate of gas flowing downstream of the throttling section 12, using the differential pressure ΔP output by the differential pressure sensor 20 and the upstream pressure P1 output by the upstream pressure sensor 19. Also, similar to the above-described flow control device 10, in order to remove the influence of the line pressure characteristics, the differential pressure ΔP output by the differential pressure sensor 20 is corrected based on the upstream pressure P1 measured by the upstream pressure sensor 19, to obtain a more accurate corrected differential pressure ΔP'.

[0066] Here, when the measured value of the upstream pressure P1 is used, the corrected differential pressure ΔP' can be obtained, for example, based on ΔP'=ΔP+β·P1 using a proportionality constant β. However, it is particularly important to apply the line pressure correction of the differential pressure ΔP when the differential pressure ΔP is relatively small, that is, when the difference between the upstream pressure P1 and the downstream pressure P2 is small. For this reason, in practice, the proportionality constant α (i.e., the proportionality constant derived from the graph in FIG. 5 or the like) set in the formula: ΔP'=ΔP+α·P2 including the measured value of the downstream pressure P2 may be used as is to obtain the corrected differential pressure based on ΔP'=ΔP+α·P1. Also, the downstream pressure P2 may be calculated from the measured upstream pressure P1 and differential pressure ΔP, and the corrected differential pressure ΔP' may be determined based on ΔP'=ΔP+α·(P1-ΔP).

[0067] The flow control device 50 can also perform proportional control under critical expansion conditions and differential pressure control under non-critical expansion conditions. More specifically, in proportional control under critical expansion conditions, the flow rate Q can be calculated by Q=K1·P1. In addition, in differential pressure control under non-critical expansion conditions, the flow rate Q can be calculated by Q=K2·(P1-ΔP') m ΔP' n The flow rate Q thus calculated is compared with the set flow rate, and the control valve 11 is feedback-controlled to eliminate the difference, thereby allowing gas to flow downstream of the throttle section 12 at the desired set flow rate.

[0068] In addition, whether or not the critical rod-shaped condition is satisfied can be determined, for example, by whether or not (P1-ΔP') / P1 is equal to or less than the critical pressure ratio A, or by whether or not P1 / (P1-ΔP') is equal to or greater than a threshold value B, which is the reciprocal of the critical pressure ratio A.

[0069] In the flow control device 50 described above, the output of the differential pressure sensor 20 is corrected based on the measured value of the upstream pressure P1 in accordance with preset correction information, so that flow measurement and flow control can be performed more accurately without being affected by the line pressure characteristics. [Industrial Applicability]

[0070] The flow rate control device according to the embodiment of the present invention is suitably used for precisely controlling the flow rates of various gases supplied to a process chamber in a semiconductor manufacturing device over a wide pressure range. [Explanation of symbols]

[0071] 1 Gas supply system 2 Gas supply source 3, 5 Opening and closing valve 4 Flow path (gas supply line) 6 Process Chamber 8. Vacuum Pump 10, 50 Flow control device 11 Control valve 12. Squeezing section 13 Downstream pressure sensor 14 Inlet pressure sensor 15 Temperature Sensor 16 Arithmetic and control circuit 17 Body block 18 Exit Block 19 Upstream pressure sensor 20 Differential Pressure Sensor 20A Integrated Pressure Sensor 22 Sensor chip 24a, 24b Pressure sensing part 26a, 26b Strain sensor

Claims

1. A control valve; a throttle portion provided downstream of the control valve; a differential pressure sensor for measuring a differential pressure between the upstream side and the downstream side of the throttle portion; a pressure sensor for measuring a pressure on at least one of a downstream side of the throttle portion and an upstream side of the throttle portion; the control valve, the differential pressure sensor, and a calculation control circuit connected to the pressure sensor; A flow control device comprising: the arithmetic and control circuit is configured to control the control valve so that a calculated flow rate determined based on an output of the pressure sensor and an output of the differential pressure sensor becomes a set flow rate; A flow control device configured to refer to preset correction information, correct a differential pressure output by a differential pressure sensor based on an output of the pressure sensor, and control a flow rate based on the corrected differential pressure.

2. the arithmetic and control circuit is configured to control the control valve so as to eliminate a difference between a set flow rate and a calculated flow rate determined based on an output of the pressure sensor and the corrected differential pressure during flow rate control; The control of the control valve is Q=K １ (ΔP′+P2) or Q=K １ proportional control based on the flow rate Q calculated according to P1; Q=K ２ P2 ｍ ΔP' ｎ Or Q=K ２ (P1-ΔP') ｍ ΔP′ ｎ and a differential pressure control that performs control based on the flow rate Q calculated according to In the above formula, K １ and K. ２ 2. The flow control device according to claim 1, wherein: is a constant depending on the gas type and gas temperature; ΔP' is the corrected differential pressure; P2 is the downstream pressure output by a downstream pressure sensor provided as the pressure sensor and measuring the pressure downstream of the throttling portion; P1 is the upstream pressure output by an upstream pressure sensor provided as the pressure sensor and measuring the pressure upstream of the throttling portion; and m and n are exponents derived based on an actual flow rate.

3. By comparing a ratio of an upstream pressure obtained by adding the corrected differential pressure and the downstream pressure output by the downstream pressure sensor to a predetermined threshold value, or A ratio between the upstream pressure output by the upstream pressure sensor and a downstream pressure obtained by subtracting the corrected differential pressure from the upstream pressure output by the upstream pressure sensor is compared with a predetermined threshold value. The flow control device according to claim 2 , configured to select whether to perform the proportional control or the differential pressure control.

4. A flow control device as described in any one of claims 1 to 3, wherein the correction information is defined by ΔP' = ΔP + α P2 or ΔP' = ΔP + α P1, and in the above formula, ΔP' is the corrected differential pressure, ΔP is the differential pressure output by the differential pressure sensor, α is a preset coefficient, P2 is the downstream pressure output by a downstream pressure sensor provided as the pressure sensor and measuring the pressure downstream of the throttling portion, and P1 is the upstream pressure output by an upstream pressure sensor provided as the pressure sensor and measuring the pressure upstream of the throttling portion.

5. The flow rate control device according to claim 1 , wherein the pressure sensor and the differential pressure sensor are integrally formed.

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