Flow rate control device, flow rate control method, and program for flow rate control device

Abstract

To provide a flow rate control device which can keep a pressure at the downstream side of a fluid resistance at a low pressure capable of securing flow rate accuracy independently of a magnitude of a set flow rate and continues to keep accuracy of a measured resistance flow rate high to be hardly affected by noise in a transient state.SOLUTION: The flow rate control device comprises: a resistance flow rate calculator 2 which calculates a resistance flow rate Qr being a flow rate at which a fluid flows through a fluid resistance FR, on the basis of a first measured pressure p1 and a second measured pressure p2; a flow rate controller 3 which controls a second valve V2 on the basis of a deviation between a set flow rate r_Q and the resistance flow rate Qr; a set pressure converter 4 which outputs a second set pressure r_p2 to which a target value of pressure on the downstream side of the fluid resistance FR is set and a first set pressure r_p1 being a target of a pressure on the upstream side of the fluid resistance FR on the basis of the set flow rate r_Q; and a pressure controller 6 which controls a first valve V1 on the basis of a deviation between the first set pressure r_p1 output from the set pressure converter 4 and the first measured pressure p1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a flow rate control device such as a mass flow controller used in, for example, a semiconductor manufacturing process. [Background technology]

[0002] Some flow control devices, such as mass flow controllers, are equipped with multiple control valves, and for example, the opening of each control valve is controlled by a different control law. For example, a flow control device described in Patent Document 1 has a pressure control valve, a pressure sensor, a thermal flow sensor, and a flow control valve arranged in this order from the upstream side on a flow path, and is equipped with a controller that controls the opening of the pressure control valve and the flow control valve based on the output of each sensor. The controller controls the pressure control valve so that the pressure upstream of a shunt resistor, which is part of the thermal flow sensor, is maintained at a predetermined constant pressure, and controls the flow control valve so that the deviation between the set flow rate and the measured flow rate measured by the thermal flow sensor is small.

[0003] However, the inventors of the present application have found, as a result of extensive research, that if a pressure-type flow sensor is used in place of a thermal-type flow sensor in the above-described flow control device as shown in FIG. 4 and each valve is controlled using the control law as described above, control problems may arise in applications where the set flow rate is changed appropriately from a small flow rate to a large flow rate.

[0004] That is, a pressure-type flow sensor includes a fluid resistor such as a laminar flow element, a first pressure sensor located upstream of the fluid resistor, and a second pressure sensor located downstream of the fluid resistor. The resistance flow rate, which is the flow rate of the fluid flowing through the fluid resistor, is calculated based on the difference between the squared values ​​of the measured pressures measured by each pressure sensor. The measurement accuracy of this resistance flow rate is higher when each pressure is kept low rather than high, especially for small flow rates. Specifically, as shown in the graph in Figure 5, even if the differential pressure measured by each pressure sensor and the noise amplitude superimposed on the pressure sensor are the same, the noise amplitude superimposed on the resistance flow rate increases as the second measured pressure measured by the second pressure sensor increases. Therefore, the measurement accuracy of the resistance flow rate is improved by keeping the second measured pressure as low as possible.

[0005] However, if the pressure control valve is controlled to keep the first measured pressure, which is the pressure upstream of the fluid resistance, constant at a high pressure such as the supply pressure, as in the prior art described above, when a small value is set as the set flow rate, the flow control valve will control the second measured pressure measured by the second pressure sensor to approach a high pressure equivalent to the first measured pressure in order to reduce the differential pressure of the fluid resistance. For this reason, when a small flow rate is set as the set flow rate, a large noise amplitude will appear in the resistance flow rate output from the pressure-type flow sensor, resulting in a decrease in the accuracy of flow control. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-280688 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a flow control device that can always maintain the pressure downstream of the fluid resistance at a low pressure that can ensure flow rate accuracy, regardless of the set flow rate, and that can maintain high accuracy in the measured resistance flow rate even when the set flow rate is small, thereby making it possible to maintain high flow rate control accuracy. [Means for solving the problem]

[0008] That is, the flow control device of the present invention is characterized by comprising a fluid resistor provided in a flow path, a first valve provided upstream of the fluid resistor, a second valve provided downstream of the fluid resistor, a first pressure sensor provided between the first valve and the fluid resistor, a second pressure sensor provided between the fluid resistor and the second valve, a resistance flow rate calculator that calculates a resistance flow rate, which is the flow rate of the fluid flowing through the fluid resistor, based on a first measured pressure measured by the first pressure sensor and a second measured pressure measured by the second pressure sensor, a second set pressure that is a target command for the pressure downstream of the fluid resistor and is set to a constant value, and a set pressure converter that outputs a first set pressure that is a target for the pressure upstream of the fluid resistor based on the second set pressure and the set flow rate, and a pressure controller that controls the first valve based on the deviation between the first set pressure output from the set pressure converter and the first measured pressure.

[0009] Furthermore, a flow rate control method according to the present invention is a flow rate control method using a flow rate control device including a fluid resistance provided in a flow path, a first valve provided upstream of the fluid resistance, a second valve provided downstream of the fluid resistance, a first pressure sensor provided between the first valve and the fluid resistance, and a second pressure sensor provided between the fluid resistance and the second valve, the method including a resistance flow rate calculation step of calculating a resistance flow rate, which is the flow rate of a fluid flowing through the fluid resistance, based on a first measured pressure measured by the first pressure sensor and a second measured pressure measured by the second pressure sensor; and a flow control step of controlling the second valve based on a deviation between the resistance flow rate and a controlled flow rate, which is a valve flow rate flowing out from the second valve calculated from the resistance flow rate; a set pressure conversion step of outputting a first set pressure, which is a target pressure on the upstream side of the fluid resistance, based on the set flow rate and a second set pressure, which is a target pressure on the downstream side of the fluid resistance and is set to a constant value; and a pressure control step of controlling the first valve based on a deviation between the first set pressure output in the set pressure converter step and the first measured pressure.

[0010] With such a flow control device and flow control method, various set flow rates can be achieved by the following control operation, while the pressure downstream of the fluid resistance is maintained at the desired second set pressure or a pressure close to it, thereby maintaining high measurement accuracy of the resistance flow rate from large to small flow rates and achieving high flow rate control accuracy regardless of the set flow rate.

[0011] Specifically, the pressure upstream of the fluid resistor is maintained at the first set pressure by controlling the first valve, and the controlled flow rate is maintained at the set flow rate by the second valve. Here, the first set pressure is not a fixed value but is a value that changes depending on the second set pressure, which is a target pressure upstream of the fluid resistor, and the set flow rate. Furthermore, since the second set pressure is fixed at a constant value, the first set pressure is set to a large value so that the differential pressure across the fluid resistor increases when the target value of the set flow rate is large. Conversely, when the target value of the set flow rate is small, the first set pressure is set to a small value. In other words, unlike the conventional case in which the pressure upstream of the fluid resistor is fixed and the pressure downstream of the fluid resistor is changed depending on the set flow rate, the present invention allows the target pressure downstream of the fluid resistor to be fixed and the target pressure upstream of the fluid resistor to be changed depending on the set flow rate. Therefore, the first set pressure can be set so that the pressure downstream of the fluid resistance becomes the desired low pressure depending on the various set flow rates, thereby maintaining high measurement accuracy of the resistance flow rate even when the set flow rate is small.

[0012] Since the pressure downstream of the fluid resistance can be maintained at the second set pressure while the controlled flow rate is maintained at the set flow rate of various magnitudes, for example, by setting the second set pressure to a constant low pressure, the resistance flow rate calculator can continue to calculate the resistance flow rate with high accuracy and reduced noise effects regardless of the magnitude of the set flow rate. Therefore, the flow control device of the present invention can realize a wide range of flow rates from large to small, and can improve the flow rate control accuracy compared to conventional methods even when flowing at small flow rates.

[0013] In order for the set pressure converter to output the appropriate first set pressure such that the pressure downstream of the fluid resistance becomes the second set pressure, the set pressure converter is configured to output as the first set pressure the pressure upstream of the fluid resistance required for the resistance flow rate to become the set flow rate when the pressure downstream of the fluid resistance is maintained at the second set pressure.

[0014] Here, the first set pressure is the pressure required for the resistance flow rate to reach the set flow rate when the pressure downstream of the fluid resistance is maintained at the second set pressure. Therefore, when the second valve controls the controlled flow rate to the set flow rate, the pressure downstream of the fluid resistance is maintained at or near the second set pressure. Therefore, the control operations of the first and second valves result in the pressure downstream of the fluid resistance being maintained at the desired constant second set pressure. Furthermore, because the set pressure transducer changes the first set pressure in accordance with the magnitude of the set flow rate, the pressure downstream of the fluid resistance is maintained at the second set pressure regardless of the magnitude of the set flow rate. Therefore, even when the set flow rate is small, the pressure downstream of the fluid resistance can be maintained at a low pressure, maintaining high measurement accuracy of the resistance flow rate and achieving higher flow control accuracy than conventional methods.

[0015] In order to satisfy the requirement to maintain various pressures in the process downstream of the flow control device while being able to set various second set pressures so as to maintain high accuracy of the resistance flow calculated by the resistance flow calculator, it is sufficient that the second set pressure is variable.

[0016] In order to maintain a low pressure downstream of the fluid resistance and maintain a high degree of accuracy in the calculated resistance flow rate even when a large flow rate is realized as a flow control device, the set pressure converter may be configured so that a larger value is set as the first set pressure as the set flow rate value increases.

[0017] For example, in order to measure the flow rate with high accuracy and with good responsiveness in an environment maintained at low pressure, such as a semiconductor manufacturing process, the resistance flow rate calculator needs to calculate the resistance flow rate based on the difference between the power of the first measured pressure and the power of the second measured pressure.

[0018] As a more specific configuration for calculating the resistance flow rate, the resistance flow rate calculator may calculate the resistance flow rate by multiplying the difference between the square of the first measured pressure and the square of the second measured pressure by a flow rate constant. In this case, the effect of improving the flow rate accuracy becomes more significant due to the function of keeping the pressure downstream of the fluid resistance at a low pressure regardless of the magnitude of the set flow rate according to the present invention.

[0019] For example, to prevent an inappropriate value from being set as the second set pressure, which would result in high pressure downstream of the fluid resistance, and to maintain high accuracy of the resistance flow rate, the set pressure converter may be configured to accept a constant value between 0 torr and 900 torr as the second set pressure.

[0020] For example, a specific embodiment that can reduce the number of data points required for the calibration of the resistance flow rate and provide a highly accurate resistance flow rate within a practical range is one in which the set pressure converter is configured to accept a constant value of 0 torr or more and 400 torr or less as the second set pressure.

[0021] In order to further improve the responsiveness of the flow control by controlling the valve flow rate itself flowing out from the second valve, which is the part of the flow control device closest to the supply target, the flow control device may further include a valve flow rate calculator that calculates the valve flow rate flowing out from the second valve based on the resistance flow rate and the second measured pressure, wherein the controlled flow rate is the valve flow rate, and the flow controller is configured to control the second valve based on the deviation between the set flow rate and the valve flow rate.

[0022] To reduce the memory and calculation load required for the set pressure converter to output the first set pressure based on the set flow rate and the second set pressure, thereby enabling a mass flow controller with limited calculation capabilities to quickly output the first set pressure, the set pressure converter may include a table in which the first set pressure is linked to each pair of the second set pressure and the set flow rate, and may be configured to output the first set pressure by referring to the table based on the received second set pressure and set flow rate. With this configuration, even if the set flow rate changes over time, the first set pressure can be quickly changed to the first set pressure corresponding to the target value at each instant. Therefore, even in a transient state, the set flow rate can be achieved while the pressure downstream of the fluid resistance can be maintained at the second set pressure.

[0023] For example, in order to reduce the noise superimposed on the resistance flow rate and keep it at almost zero when the second valve is fully closed and no fluid is flowing, making it less likely for a user to mistakenly believe that a flow is occurring from the second valve, while making sensor shifts or the like occurring in the resistance flow rate visible, the resistance flow rate calculator may be configured to calculate the resistance flow rate based on the first measured pressure and the second measured pressure when the second valve is open, and to calculate the resistance flow rate based on the first measured pressure and the second set pressure when the second valve is fully closed.

[0024] In order to obtain substantially the same effect as the flow control device of the present invention by updating a program in an existing flow control device, for example, a program for a flow control device used in a flow control device including a fluid resistance provided in a flow path, a first valve provided upstream of the fluid resistance, a second valve provided downstream of the fluid resistance, a first pressure sensor provided between the first valve and the fluid resistance, and a second pressure sensor provided between the fluid resistance and the second valve, the program calculating a resistance flow rate, which is the flow rate of a fluid flowing through the fluid resistance, based on a first measured pressure measured by the first pressure sensor and a second measured pressure measured by the second pressure sensor. a resistance flow rate calculator that outputs a resistance flow rate; a flow rate controller that controls the second valve based on a deviation between a set flow rate and the resistance flow rate or a controlled flow rate which is a valve flow rate flowing out of the second valve calculated from the resistance flow rate; a set pressure converter that outputs a first set pressure which is a target pressure on the upstream side of the fluid resistance based on a second set pressure which is a target pressure on the downstream side of the fluid resistance and which is set to a constant value, and the set flow rate; and a pressure controller that controls the first valve based on a deviation between the first set pressure output from the set pressure converter and the first measured pressure.

[0025] The program for the flow control device may be distributed electronically, or may be recorded on a program recording medium such as a CD, DVD, or flash memory. [Effects of the Invention]

[0026] As described above, according to the flow control device of the present invention, the first valve on the upstream side realizes the first set pressure, which is set in accordance with the second set pressure and the set flow rate, and the second valve on the downstream side realizes the controlled flow rate at the set flow rate, so that the pressure downstream of the fluid resistance can be maintained at the second set pressure or a pressure close to it. Therefore, regardless of the set flow rate, it is possible to maintain the pressure downstream of the resistance flow at a low pressure, thereby reducing noise superimposed on the calculated resistance flow rate and maintaining high accuracy. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic diagram showing a flow rate control device according to a first embodiment of the present invention. [Figure 2] 6 is a graph showing the relationship between the set flow rate, the second set pressure, and the first set pressure in the first embodiment. [Figure 3] FIG. 4 is a schematic diagram showing a flow rate control device according to a second embodiment of the present invention. [Figure 4] FIG. 1 is a schematic diagram showing a control configuration of a conventional flow rate control device. [Figure 5] 10 is a graph showing the relationship between absolute pressure and noise amplitude in a pressure-type flow sensor. DETAILED DESCRIPTION OF THE INVENTION

[0028] A flow rate control device 100 according to a first embodiment of the present invention will be described with reference to FIGS.

[0029] The flow rate control device 100 of the first embodiment is used to supply a fluid into a chamber at a predetermined set flow rate, for example, in various semiconductor manufacturing processes. The fluid may include a pure gas, a gas containing multiple types of gases, a gas-liquid mixture, a liquid, etc. The following description will be given taking the case where the fluid is a gas as an example.

[0030] As shown in FIG. 1, the flow rate control device 100 includes a fluid device including sensors and valves provided in a flow path, and a control and calculation mechanism COM that controls the fluid device.

[0031] The fluid device is provided in the flow path and includes a first valve V1, a first pressure sensor P1, a fluid resistance FR, a second pressure sensor P2, and a second valve V2. The devices are provided in this order from the upstream side.

[0032] Here, the fluid resistance FR is a laminar flow element, and the flow rate of gas flowing through the fluid resistance FR is determined according to the pressure difference between before and after the fluid resistance FR. The first pressure sensor P1, the fluid resistance FR, the second pressure sensor P2, and a resistance flow rate calculator 1 (described later) constitute a flow rate sensor FS that measures the flow rate of the fluid flowing through the flow path between the first valve V1 and the second valve V2. In the following description, the flow rate of the fluid flowing through the fluid resistance FR is also referred to as Qr.

[0033] That is, the first pressure sensor P1, the fluid resistance FR, and the second pressure sensor P2 are sensing mechanisms that output an output signal according to the flow rate of the fluid flowing through the flow path, and the resistance flow rate calculator 1 calculates the flow rate of the fluid flowing through the flow path based on the output signal of the sensing mechanisms. Because this flow sensor FS is a so-called pressure-type flow rate sensor, it has the characteristic that the lower the pressure measured by each pressure sensor, the higher the measurement accuracy of the measured flow rate. In this embodiment, the flow path in which the flow control device 100 is installed is connected to a chamber in a low vacuum state where a CVD process or the like is performed. Therefore, the environment downstream of the fluid resistance FR can also be maintained in a low vacuum state depending on the control results.

[0034] The first pressure sensor P1 measures the pressure of gas present in a first volume VL1, which is the volume between the first valve V1 and the fluid resistance FR in the flow path (hereinafter also referred to as a first measurement pressure p1).

[0035] The second pressure sensor P2 measures the pressure of the gas present in a second volume VL2, which is the volume between the fluid resistance FR and the second valve V2 in the flow path (hereinafter also referred to as a second measurement pressure p2).

[0036] In this way, the first pressure sensor P1 and the second pressure sensor P2 measure the pressures of the first volume VL1 and the second volume VL2, which are the two volumes formed by the first valve V1, the fluid resistance FR, and the second valve V2, respectively. In other words, the first pressure sensor P1 and the second pressure sensor P2 measure the pressure upstream and downstream of the fluid resistance FR, respectively.

[0037] In this embodiment, the first valve V1 and the second valve V2 are of the same type, for example, piezo valves in which a valve element is driven relative to a valve seat by a piezo element. In this embodiment, the opening of the second valve V2 is controlled by flow feedback control based on the deviation between a set flow rate r_Q set by the user and a resistance flow rate Qr measured by the flow sensor FS. Meanwhile, the opening of the first valve V1 is controlled by pressure feedback control based on the deviation between a first set pressure r_p1, which is the target pressure for the first volume VL1 converted from a second set pressure r_p2, which is the target pressure for the second volume VL2 set by the user, and a first measured pressure p1 measured by the first pressure sensor P1.

[0038] Here, pressure feedback control based on the deviation between the second set pressure r_p2 set by the user and the second measured pressure p2 measured by the second pressure sensor P2 is not performed for either valve V1 or V2. However, as will be described later, the first valve V1 is pressure controlled so that the pressure in the first volume VL1 becomes the first set pressure r_p1, and the second valve V2 is flow controlled so that the resistance flow rate Qr becomes the set flow rate r_Q, so that the pressure in the second volume VL2 is ultimately maintained at the second set pressure r_p2 or a pressure close to it.

[0039] Next, the control and calculation mechanism COM will be described in detail. The control and calculation mechanism COM is a so-called computer equipped with, for example, a CPU, memory, A / D converter, D / A converter, input / output means, etc., and performs at least the functions of a setting reception unit 1, a resistance flow rate calculator 2, a flow rate controller 3, a setting pressure converter 4, an inverse calculation result storage unit 5, and a pressure controller 6 by executing a program for a fluid control device stored in the memory and cooperating with various devices.

[0040] The setting receiving unit 2 receives a set flow rate r_Q and a second set pressure r_p2, which are control commands for the flow control device 100, from the user. The setting receiving unit 2 outputs both the set flow rate r_Q and the second set pressure r_p2 to a set pressure converter 4 (described later) and outputs only the set flow rate r_Q to the flow controller 3. The set flow rate r_Q is a parameter directly used in the feedback loop. The set flow rate r_Q is set to the flow rate the user desires to flow through the flow path or the flow rate of the fluid desired to be supplied to a subsequent chamber. The set flow rate r_Q is set as a target flow rate value as a time function, and the user can set a value between 0% and 100% for each time. For example, as shown in the graph in FIG. 2, the set flow rate is defined as a step function r_Q(t) with time t as a parameter. The set flow rate r_Q can also be defined as a ramp function or other time functions in addition to a step function. The second set pressure r_p2 is set as a constant value set by the user as the pressure in the second volume VL2 downstream of the fluid resistance FR. That is, the second set pressure cannot be set in the form of a step function or ramp function, and only a constant target pressure value is set regardless of time. More specifically, the second set flow pressure r_p2 is set to a predetermined low pressure value at which the flow sensor FS can fully demonstrate its flow accuracy.

[0041] The resistance flow rate calculator 2 calculates the flow rate based on the measured values ​​indicated by the output signals of the first pressure sensor P1 and the second pressure sensor P2 and a flow rate characteristic value corresponding to the measured values. Specifically, the resistance flow rate calculator 2 calculates the resistance flow rate Qr, which is the flow rate of the fluid flowing through the fluid resistance FR, based on the first measured pressure p1, which is the pressure upstream of the fluid resistance FR, and the second measured pressure p2, which is the pressure downstream of the fluid resistance FR. Here, the resistance flow rate calculator 2 calculates the flow rate not only based on the first measured pressure p1 and the second measured pressure p2, but also based on a flow rate constant k determined according to the characteristics of the fluid resistance FR. Specifically, the resistance flow rate calculator 2 calculates the resistance flow rate Qr by multiplying the difference between the square of the first measured pressure p1 and the square of the second measured pressure p2 by the flow rate constant k. In other words, the flow rate calculation formula used in the resistance flow rate calculator 2 is Qr = k(p1^2 - p2^2) (Formula 1).

[0042] Furthermore, the resistance flow rate calculator 2 is configured to switch the calculation method for the resistance flow rate Qr depending on whether or not a fluid is flowing through the flow path. For example, when the second valve V2 located downstream is open to an arbitrary degree, the resistance flow rate Qr is calculated by substituting the first measured pressure p1 and the second measured pressure p2 that are actually measured into the flow rate calculation formula of Equation 1. On the other hand, when the second valve V2 is fully closed, the resistance flow rate calculator 2 calculates the resistance flow rate Qr using the second set pressure r_p2 received by the setting receiving unit 1 and the differential pressure Δp between the first measured pressure p1 and the second measured pressure p2. Specifically, the resistance flow rate calculator 2 calculates the flow rate using Qr = k(Δp^2 + 2 × r_p2 × Δp) (Equation 2). Note that Equation 2 is a formula obtained by eliminating p1 from Equation 1 based on the relationship Δp = p1 - p2.

[0043] In this equation 2, Δp is a differential pressure, so the noise superimposed on the first measured pressure p1 and the second measured pressure p2 almost cancels out, and because the set second pressure r_p2 is a constant value, the calculated resistance flow rate Qr has significantly reduced noise. Therefore, when the second valve V2 is fully closed, the resistance flow rate Qr output from the resistance flow rate calculator 2 ideally will be nearly zero or will exhibit only extremely small fluctuations. Therefore, if such a resistance flow rate Qr is displayed externally when the second valve V2 is fully closed, the user can easily trust that no fluid is flowing downstream from the flow control device 100.

[0044] Furthermore, if an outflow occurs from the downstream valve V2, the resistance flow rate Qr will change by a predetermined value from zero because the differential pressure Δp is an actually measured value, and the occurrence of the outflow can be detected. In other words, if the resistance flow rate Qr is displayed as zero when the second valve V2 is fully closed, regardless of the output of the flow sensor FS, the user will not be able to detect the occurrence of the outflow. In contrast, with the flow control device 100 of the first embodiment, the resistance flow rate Qr only fluctuates slightly from zero as a reference, so the user will almost never mistakenly believe that there is an outflow when there is no outflow, and will be able to detect the occurrence of the outflow when it is actually occurring.

[0045] Furthermore, if a zero-point shift occurs in the flow sensor FS, the amount of that shift will accurately appear in the resistance flow rate Qr calculated by Equation 2. In other words, if the zero point of any of the pressure sensors is shifted due to temperature drift or other factors, the actual measured value, the differential pressure Δp, in Equation 2 will contain only the shift amount, with the noise superimposed on each measured pressure nearly canceled out. Therefore, if it is certain that there is no outflow when the second valve V2 is fully closed, the flow rate value output as the resistance flow rate Qr when the second valve V2 is fully closed will indicate the amount of shift from the zero point. In other words, if the flow sensor FS outputs zero regardless of its output when the second valve V2 is fully closed, the user will not be able to detect the zero-point shift in the resistance flow rate Qr. Furthermore, Equation 1 involves calculating the square of each measured pressure, which magnifies the noise. Therefore, even if the difference is taken, the noise is not sufficiently reduced, making it difficult to extract the amount of shift alone. Therefore, Equation 2 makes it easy to quantitatively evaluate the zero-point shift in the resistance flow rate Qr.

[0046] The flow rate controller 3 performs flow rate feedback control of the applied voltage, which is the manipulated variable mv2 input to the second valve V2, by, for example, PID control, so as to reduce the deviation between the set flow rate r_p2 received by the setting receiving unit 1 and the resistance flow rate Qr measured by the flow sensor FS. In other words, the flow rate sensor FS, the flow rate controller 3, and the second valve V2 form an independent feedback loop for controlling the flow rate. Note that, although the resistance flow rate Qr is the controlled flow rate in this embodiment, the flow rate flowing at another location in the flow path of the flow control device 100 may also be fed back as the controlled flow rate.

[0047] The set pressure converter 4 is configured to output, based on the second set pressure r_p2 and the set flow rate r_Q, the pressure upstream of the fluid resistance FR required for the resistance flow rate Qr to become the set flow rate r_ when the pressure downstream of the fluid resistance FR is maintained at the second set pressure r_p2. The relationship between the pressures before and after the fluid resistance FR and the resistance flow rate Qr is defined by the flow rate calculation formula (Equation 1) described above, so the first set pressure r_p1 can be obtained by substituting the second set pressure r_p2 into Equation 1 instead of the second measured pressure p2 and the set flow rate r_Q into Equation 1 and performing an inverse calculation for the first measured pressure p1. In this embodiment, in order to reduce the memory load on the control calculation mechanism COM, a plurality of sets of second set pressure r_p2 and set flow rate r_Q are used to calculate in advance the corresponding first set pressure r_p1 by inverse calculation of Equation 1, and a table relating to the second set pressure r_p2, set flow rate r_Q, and first set pressure r_p1 is created and stored in the inverse calculation result storage unit 5. The set pressure converter 4 refers to the table based on the second set pressure r_p2 and set flow rate r_Q set by the user, and outputs the corresponding first set pressure r_p1 to the pressure controller 6.

[0048] Here, we will qualitatively explain the relationship between the first set pressure r_p1, the second set pressure r_p2, and the set flow rate r_Q. As shown in the graph of FIG. 2, the set flow rate r_Q is defined by a step function that changes over time from a small flow rate to a large flow rate, and the second set pressure r_p2 is always set to a predetermined low, constant value. In this case, while the set flow rate r_Q is set to a small flow rate, the first set pressure r_p1 is set to a value slightly larger than the second set pressure r_p2, and a small differential pressure Δp necessary to achieve the small flow rate is set. In contrast, while the set flow rate r_Q is set to a large flow rate, the first set pressure r_p1 is set to a value significantly larger than the second set pressure r_p2. In other words, because the second set pressure r_p2 is kept constant at a low pressure, the differential pressure Δp across the fluid resistance FR required to generate the flow rate is adjusted by the magnitude of the first set pressure r_p1. Furthermore, the larger the set flow rate r_Q, the larger the value of the first set pressure r_p1 that is set, and these target values ​​have a positive correlation.

[0049] The pressure controller 6 controls the applied voltage, which is the manipulated variable mv1 input to the first valve V1, based on the deviation between the first set pressure r_p1 output from the set pressure converter 4 and the first measured pressure p1 measured by the first pressure sensor P1. In other words, the pressure controller 6, the first pressure sensor P1, and the first valve V1 form a single feedback loop. The pressure controller 6 controls the aperture of the first valve V1, so that the pressure in the first volume VL1 is kept constant at the first set pressure r_p1 output from the set pressure converter 4.

[0050] Next, a description will be given of how the pressure in the second volume VL2 downstream of the fluid resistance FR is maintained at a constant second set pressure set by the user by controlling the first valve V1 and the second valve V2.

[0051] Neither the first valve V1 nor the second valve V2 directly feedbacks and controls the second measured pressure p2, which is the pressure in the second volume VL2. That is, the first valve V1 controls the first measured pressure p1, which is the pressure in the first volume VL1, to a first set pressure r_p1, and the second valve V2 controls the resistance flow rate Qr through the fluid resistance FR to a set flow rate r_Q. Here, the first set pressure r_p1, the set flow rate r_Q, and the second set pressure r_p2 are set to satisfy Equation 1. Therefore, if the first measured pressure p1 is the first set pressure r_p1 and the resistance flow rate Qr is the set flow rate r_Q, then naturally the second measured pressure p2 will also be the second set pressure r_p2.

[0052] In this way, with the flow control device 100 of the first embodiment, the set flow rate converter 4 converts the set flow rate r_Q, which is the flow rate that is desired to flow, and the second set pressure r_p2, which is the pressure that is desired to be maintained downstream of the pressure-type flow sensor FS, into a first set pressure r_p1, which is the pressure upstream of the flow sensor FS that can simultaneously satisfy both, and the first valve V1 can be controlled so that the pressure of the first volume VL1 is maintained at this first set pressure r_p1.

[0053] Therefore, the second valve V2 can be controlled so that the set flow rate r_Q is achieved for the resistance flow rate Qr, while the first valve V1 can be controlled so that the pressure of the second volume VL2 is maintained at the second set pressure r_p2 regardless of the magnitude of the set flow rate r_Q.

[0054] As a result, while maintaining the desired flow rate, the pressure downstream of the fluid resistance FR can be maintained in a low pressure range where the pressure-type flow sensor FS can demonstrate flow rate accuracy, so the output of the flow sensor FS is not significantly affected by noise regardless of the flow rate, and flow rate control accuracy can be improved compared to conventional methods.

[0055] Next, a flow rate control device 100 according to a second embodiment of the present invention will be described with reference to Fig. 3. Note that the same components as those described in the first embodiment will be denoted by the same reference numerals.

[0056] The flow control device 100 of the second embodiment differs from the flow control device 100 of the first embodiment in that it further includes a valve flow rate calculator 7 that calculates the valve flow rate Qv, which is the flow rate flowing out from the second valve V2, based on the resistance flow rate Qr, and in that the flow rate controller 3 uses the valve flow rate Qv as the flow rate to be controlled and controls the second valve V2 based on the deviation between the valve flow rate Qv and the set flow rate r_Q.

[0057] The valve flow rate calculator 7 calculates the valve flow rate Qv by subtracting the value obtained by multiplying the time derivative of the second measured pressure p2 by a predetermined coefficient α from the resistance flow rate Qr calculated by the resistance flow rate calculator 2. That is, the valve flow rate calculator 7 calculates the valve flow rate Qv based on Qv = Qr - αd / dt(p2) (Equation 3) (d / dt is a time derivative operator). Note that, as detailed in another application by the present applicant, the fact that the valve flow rate Qv can be calculated by such an operation can be derived from applying the equation of state of gas to the second volume VL2 based on the change in mass (change in molar amount) due to the inflow and outflow of fluid into the second volume VL2, the temperature of the fluid, the second measured pressure p2, and the gas constant R. Furthermore, since this relationship can be established for any fluid to which the equation of state of gas can be applied, the fluids to which it can be applied include gases, gas-liquid mixtures, etc., and only pure liquids are excluded from the application.

[0058] In the flow control device 100 of the second embodiment configured as described above, the flow rate controller 3 can control the second valve V2 so that the valve flow rate Qv actually flowing through the second valve V2 matches the set flow rate r_Q. This enables control in which the control point and the measurement point match. This eliminates the problem of a delay in the measured flow rate during a transient state due to a misalignment between the control point and the measurement point when the resistance flow rate Qr is used, resulting in a delay in flow rate control. Furthermore, even when the controlled flow rate is set to the valve flow rate Qv in this way, the second measured pressure p2, which is the pressure downstream of the fluid resistance FR, can be maintained at a value close to the second set pressure r_p2. In other words, while eliminating control delays, the flow rate accuracy of the resistance flow rate Qr can be maintained high, as in the first embodiment, and ultimately the flow rate accuracy of the valve flow rate Qv can also be improved.

[0059] Other embodiments will be described.

[0060] For example, the setting receiving unit may be configured to only accept a constant value within the recommended operating pressure range for the flow sensor FS as the second set pressure r_p. For example, the setting receiving unit may be configured to accept a constant value between 0 torr and 900 torr as the second set pressure, or more preferably, a constant value between 0 torr and 400 torr. The acceptable pressure range may be limited as appropriate depending on the pressure required in the chamber to which the fluid is supplied and the pressure range in which the flow rate accuracy of the flow sensor can be guaranteed.

[0061] The second set pressure may be fixed so that it cannot be changed by the user. Alternatively, for example, the second set pressure that is most suitable for demonstrating the flow rate accuracy of the flow sensor may be set at the time of shipping from the factory, and thereafter only an authorized operator may be allowed to change the second set pressure.

[0062] The flow rate calculation formula used in the resistance flow rate calculator is not limited to Formula 1. For example, instead of calculating the resistance flow rate based on the difference between the squares of the pressures, the resistance flow rate may be calculated based on the difference between the power of the first measured pressure and the power of the second measured pressure. The exponent of the power is not limited to a natural number, and may be a decimal, etc.

[0063] In the past, the set pressure converter output the first set pressure by looking up a table to reduce the burden on memory, etc., but if sufficient computer resources are available, the first set pressure may be calculated by performing the inverse calculation of Equation 1 each time a set flow rate and second set pressure are received. In this case, the inverse calculation result storage unit may be omitted. Also, if there is no data in the table for a set of set flow rate, second set pressure, and first set pressure corresponding to the set, a new corresponding first set pressure may be calculated by, for example, linear interpolation of the data for the existing set.

[0064] The configuration of the set pressure converter to calculate the first set pressure based on the second set pressure and the set flow rate is not limited to a strict inverse calculation of the resistance flow rate calculation formula in Equation 1. For example, it is possible to assume that the differential pressure Δp is sufficiently small and ignore the term of the square of the differential pressure Δp in Equation 2, and calculate the first set pressure r_p1 by an approximate calculation. That is, Equation 2 may be approximated as Qr = k(2 × r_p2 × (r_p1 - r_p2)), and the first set pressure r_p2 may be calculated by r_p1 = r_p2 + Qr / (2k × r_p2). The set pressure converter may also calculate the first set pressure based on the second set pressure and the set flow rate.

[0065] The fluid resistance is not limited to a laminar flow element, but may be, for example, a flow rate restricting element such as an orifice. The first and second valves are also not limited to piezo valves, but may be control valves that are equipped with actuators based on various driving principles, such as solenoid valves, and that can achieve any opening degree.

[0066] The flow control device of each embodiment has been described as an example of a mass flow controller in which each component is packaged, but the flow control device may also be configured by combining each valve, pressure sensor, and fluid resistance individually.

[0067] In addition, various modifications of the embodiments and combinations of parts of the embodiments may be made as long as they do not go against the spirit of the present invention. [Explanation of symbols]

[0068] 100 Flow control device V1: First valve V2: Second valve FS···Flow Sensor FR...Fluid resistance P1: First pressure sensor P2: Second pressure sensor 1. Settings reception section 2...Resistance flow rate calculator 3. Flow Controller 4. Setting pressure transducer 5...Reverse calculation result storage section 6. Pressure controller

Claims

1. a fluid resistance provided in the flow path; a first valve provided upstream of the fluid resistance; a second valve provided downstream of the fluid resistance; a first pressure sensor provided between the first valve and the fluid resistance; a second pressure sensor provided between the fluid resistance and the second valve; a resistance flow rate calculator that calculates a resistance flow rate, which is a flow rate of a fluid flowing through the fluid resistance, based on a first measured pressure measured by the first pressure sensor and a second measured pressure measured by the second pressure sensor; a flow rate controller that controls the second valve based on a deviation between a set flow rate and the resistance flow rate or a control target flow rate that is a valve flow rate flowing out of the second valve calculated from the resistance flow rate; a set pressure converter that outputs a first set pressure, which is a target pressure on the upstream side of the fluid resistance, based on a second set pressure, which is a target pressure on the downstream side of the fluid resistance and is set to a constant value, and the set flow rate; a pressure controller that controls the first valve based on a deviation between the first set pressure output from the set pressure converter and the first measured pressure.

2. 2. The flow control device according to claim 1, wherein the set pressure converter is configured to output as a first set pressure the pressure upstream of the fluid resistance required for the resistance flow rate to become the set flow rate when the pressure downstream of the fluid resistance is maintained at the second set pressure.

3. The flow rate control device according to claim 1 or 2, wherein the second set pressure is variable.

4. 4. The flow control device according to claim 1, wherein the set pressure converter is configured so that the larger the value of the set flow rate, the larger the value output as the first set pressure.

5. The flow control device according to claim 1 , wherein the resistance flow rate calculator calculates the resistance flow rate based on a difference between the power of the first measured pressure and the power of the second measured pressure.

6. The flow control device according to claim 1 , wherein the resistance flow rate calculator calculates the resistance flow rate by multiplying a difference between the square of the first measured pressure and the square of the second measured pressure by a flow rate constant.

7. 7. The flow control device according to claim 1, wherein the set pressure converter is configured to accept a constant value between 0 torr and 900 torr as the second set pressure.

8. 8. The flow control device according to claim 1, wherein the set pressure converter is configured to accept a constant value between 0 torr and 400 torr as the second set pressure.

9. a table in which the first set pressure is linked to each pair of the second set pressure and the set flow rate; 9. The flow control device according to claim 1, wherein the set pressure converter is configured to output the first set pressure by referring to the table based on the received second set pressure and set flow rate.

10. a valve flow rate calculator that calculates the valve flow rate flowing out from the second valve based on the resistance flow rate and the second measured pressure, the controlled flow rate is the valve flow rate, The flow control device according to claim 1 , wherein the flow rate controller is configured to control the second valve based on a deviation between the set flow rate and the valve flow rate.

11. The resistance flow rate calculator When the second valve is open, the resistance flow rate is calculated based on the first measured pressure and the second measured pressure; 11. The flow control device according to claim 1, wherein the flow control device is configured to calculate the resistance flow rate based on the first measured pressure and the second set pressure when the second valve is fully closed.

12. A flow rate control method using a flow rate control device including a fluid resistance provided in a flow path, a first valve provided upstream of the fluid resistance, a second valve provided downstream of the fluid resistance, a first pressure sensor provided between the first valve and the fluid resistance, and a second pressure sensor provided between the fluid resistance and the second valve, a resistance flow rate calculation step of calculating a resistance flow rate, which is a flow rate of a fluid flowing through the fluid resistance, based on a first measured pressure measured by the first pressure sensor and a second measured pressure measured by the second pressure sensor; a flow rate control step of controlling the second valve based on a deviation between a set flow rate and the resistance flow rate or a control target flow rate, which is a valve flow rate flowing out of the second valve calculated from the resistance flow rate; a set pressure conversion step of outputting a first set pressure, which is a target pressure on the upstream side of the fluid resistance, based on a second set pressure, which is a target pressure on the downstream side of the fluid resistance and is set to a constant value, and the set flow rate; a pressure control step of controlling the first valve based on a deviation between the first set pressure output in the set pressure conversion step and the first measured pressure.

13. A program for a flow control device used in a flow control device including a fluid resistor provided in a flow path, a first valve provided upstream of the fluid resistor, a second valve provided downstream of the fluid resistor, a first pressure sensor provided between the first valve and the fluid resistor, and a second pressure sensor provided between the fluid resistor and the second valve, a resistance flow rate calculator that calculates a resistance flow rate, which is a flow rate of a fluid flowing through the fluid resistance, based on a first measured pressure measured by the first pressure sensor and a second measured pressure measured by the second pressure sensor; a flow rate controller that controls the second valve based on a deviation between a set flow rate and the resistance flow rate or a control target flow rate that is a valve flow rate flowing out of the second valve calculated from the resistance flow rate; a set pressure converter that outputs a first set pressure, which is a target pressure on the upstream side of the fluid resistance, based on a second set pressure, which is a target pressure on the downstream side of the fluid resistance and is set to a constant value, and the set flow rate; a pressure controller that controls the first valve based on the deviation between the first set pressure output from the set pressure converter and the first measured pressure.

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