Method and apparatus for mass flow control

Abstract

A self-validated mass flow control (MFC) apparatus and a method of providing self-validated mass flow control are provided. The MFC includes a chamber configured to receive a fluid, an upstream valve disposed upstream of the chamber, and a downstream control valve disposed downstream of the chamber. The MFC further includes a pressure drop assembly disposed downstream of the downstream control valve, and first and second pressure sensors. A controller of the MFC is configured to control actuation of the downstream control valve by switching between a flow-based feedback control and a pressure-based feedback control. In the flow-based feedback control, the flow is monitored based on a rate of pressure decay in the chamber detected by the first pressure sensor when the upstream control valve is closed. In pressure-based feedback control, the pressure upstream of the pressure drop assembly detected by the second pressure sensor is monitored.

Description

[0001] Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 433,310, filed Dec. 16, 2022. The entire teachings of the above application are incorporated herein by reference. Background of the Invention

[0003] Semiconductor manufacturing processes may involve delivering various amounts of several different gases and gas mixtures in a number of processing steps. Generally, gases are stored in tanks at a processing facility, and a gas metering system is used to deliver metered amounts of gas from the tanks to processing tools such as chemical vapor deposition reactors, vacuum sputtering machines, plasma etching machines, etc. Other components such as valves, pressure regulators, mass flow controllers (MFCs), mass flow ratio controllers (FRCs), mass flow meters (MFMs), mass flow verifiers (MFVs), etc. may be included in the gas metering system or in the flow path from the gas metering system to the processing tool. Components such as MFCs, FRCs, MFMs, and MFVs are provided to ensure precise delivery of process gases.

[0004] Generally, a mass flow controller (MFC) controls and monitors in real time the fluid flow rate (e.g., of a gas or vapor) such that the flow rate of the gas mass passing through the device can be metered and controlled. Conventional pressure-based MFCs include a flow control valve and a pressure drop component (such as a flow nozzle). The MFC may use one or more pressure sensors to measure the flow rate. The MFC controls the flow rate based on a given setpoint typically predefined by a user or an external device (such as a semiconductor tool). The setpoint may change with each step of the process. Summary of the Invention

[0005] A mass flow control device capable of self-verification and a method of providing self-verifying mass flow control are provided.

[0006] A mass flow controller (MFC) includes a chamber configured to receive a fluid, an upstream valve disposed upstream of the chamber, and a downstream control valve disposed downstream of the chamber. The MFC further includes a pressure drop component disposed downstream of the downstream control valve, and a first pressure sensor and a second pressure sensor. The first pressure sensor detects the fluid pressure in the chamber, while the second pressure sensor detects the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component. The MFC further includes a controller configured to control the actuation of the downstream control valve. The controller is configured to switch between flow-based feedback control and pressure-based feedback control in order to operate the control valve. In flow-based feedback control, the flow rate is monitored based on the rate of pressure decay in the chamber detected by the first pressure sensor when the upstream control valve is closed. In pressure-based feedback control, the pressure upstream of the pressure drop component detected by the second pressure sensor is monitored.

[0007] The controller of the MFC can be further configured to: during flow-based feedback control, record the pressure detected by the second pressure sensor for use during pressure-based feedback control. A pressure setpoint for pressure-based feedback control can be established based on the recorded pressure. Alternatively or additionally, a coefficient for calculating the flow rate during pressure-based feedback control can be determined. The coefficient can be determined based on the recorded pressure.

[0008] During flow-based feedback control, the controller of the MFC can be configured to measure the flow rate Q of the fluid and compare the measured flow rate with the flow rate setpoint Q sp For example, the measured flow rate Q can be determined according to the following formula:

[0009]

[0010] where V is the volume of the chamber, Tstp is the standard temperature, Pstp is the standard pressure, P1 is the fluid pressure in the chamber detected by the first pressure sensor, and T is the detected fluid temperature.

[0011] During pressure-based feedback control, the controller of the MFC can be configured to determine the flow rate Q of the fluid cf and compare the determined flow rate with the flow rate setpoint Q sp For example, the determined flow rate Q cf can be calculated according to the following formula:

[0012] Q cf = K cf· P2 (2)

[0013] where K cf is a coefficient, and P2 is the pressure detected by the second pressure sensor. The coefficient K cf can be determined according to the following formula:

[0014] K cf = Q / P cf (3)

[0015] where Q is the stable flow rate determined during flow-based feedback control, and P cf is the pressure detected by the second pressure sensor during the stable flow period at the stable flow rate Q. Alternatively, the controller can be configured to determine the flow rate Q of the fluid based on a look-up table cf .

[0016] The controller of the MFC may include a flow controller and a pressure controller. The flow controller may be configured to monitor the flow rate based on the decay rate and compare the monitored flow rate with a flow rate setpoint. The pressure controller may be configured to monitor the pressure detected by the second pressure sensor and compare the monitored pressure with a pressure setpoint. Optionally, the upstream valve may be a control valve.

[0017] A method of controlling a flow rate includes switching between flow-based feedback control and pressure-based feedback control of the actuation of a downstream control valve of a mass flow controller. The flow-based feedback control includes monitoring the flow rate based on the pressure decay rate of the fluid in the chamber of the mass flow controller. The pressure decay rate is based on the pressure detected by a first pressure sensor when a valve upstream of the chamber is closed, and the first pressure sensor detects the fluid pressure in the chamber. The pressure-based feedback control includes monitoring the pressure upstream of a pressure drop component based on the pressure detected by a second pressure sensor. The pressure drop component is disposed downstream of the downstream control valve, and the second pressure sensor detects the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component.

[0018] The method may further include: during the flow-based feedback control, recording the pressure detected by the second pressure sensor for use during the pressure-based feedback control. The pressure setpoint for the pressure-based feedback control may be established based on the recorded pressure. Alternatively or additionally, a coefficient for calculating the flow rate during the pressure-based feedback control may be determined. The coefficient may be determined based on the recorded pressure.

[0019] During the flow-based feedback control, the method may include measuring the flow rate Q of the fluid and comparing the measured flow rate with a flow rate setpoint Qsp. The measured flow rate may be calculated according to Equation 1 above.

[0020] During the pressure-based feedback control, the method may include determining the flow rate Q of the fluid cf and comparing the determined flow rate with a flow rate setpoint Q sp The determined flow rate Q cf may be determined according to Equation 2 above, and the coefficient used in Equation 2 may be determined according to Equation 3 above.

[0021] A mass flow controller (MFC) includes a chamber configured to receive a fluid, an upstream valve disposed upstream of the chamber, and a downstream control valve disposed downstream of the chamber. The MFC further includes a pressure drop component disposed downstream of the downstream control valve, and a first pressure sensor and a second pressure sensor. The first pressure sensor detects the fluid pressure in the chamber, while the second pressure sensor detects the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component. The MFC further includes a controller configured to control the actuation of the downstream control valve. The controller is configured to: monitor the pressure upstream of the pressure drop component detected by the second pressure sensor; determine a flow rate based on the monitored pressure and a coefficient; control the actuation of the downstream control valve based on adjusting the determined flow rate to a flow setpoint; determine a verification flow rate based on the pressure decay rate in the chamber detected by the first pressure sensor when the upstream control valve is closed; and update the coefficient based on the verification flow rate.

[0022] A mass flow controller (MFC) includes a chamber configured to receive a fluid, an upstream valve disposed upstream of the chamber, and a downstream control valve disposed downstream of the chamber. The MFC further includes a pressure drop component disposed downstream of the downstream control valve, and a first pressure sensor and a second pressure sensor. The first pressure sensor detects the fluid pressure in the chamber, while the second pressure sensor detects the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component. The MFC further includes a controller configured to control the actuation of the downstream control valve, and the controller maintains a controlled flow rate based on the pressure detected by at least one of the first pressure sensor and the second pressure sensor and recalibrates the pressure-based flow control during the controlled flow rate based on the pressure detected by the second pressure sensor and the pressure decay rate detected by the first pressure sensor.

[0023] A method of controlling a flow rate includes maintaining a controlled flow rate by controlling the actuation of a downstream control valve based on the pressure detected by at least one of a first pressure sensor and a second pressure sensor. The first pressure sensor detects the fluid pressure in a chamber configured to receive the fluid. The second pressure sensor detects the fluid pressure downstream of the downstream control valve and upstream of a pressure drop component disposed downstream of the downstream control valve. The method further includes recalibrating the pressure-based flow control during the controlled flow rate based on the pressure detected by the second pressure sensor and the pressure decay rate detected by the first pressure sensor.

[0024] A mass flow controller (MFC) includes a chamber configured to receive a fluid, an upstream valve disposed upstream of the chamber, and a downstream control valve disposed downstream of the chamber. The MFC further includes a pressure drop component disposed downstream of the downstream control valve, and a first pressure sensor and a second pressure sensor. The first pressure sensor detects the fluid pressure in the chamber, while the second pressure sensor detects the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component. The MFC further includes a controller configured to control the actuation of the downstream control valve. The controller is configured to: provide pressure-based flow control based on monitoring of the pressure upstream of the pressure drop component detected by the second pressure sensor. The controller is further configured to: determine a verification flow rate based on the rate of pressure decay in the chamber detected by the first pressure sensor when the upstream control valve is closed, while maintaining pressure-based flow control or flow control based on the rate of pressure decay in the chamber; and recalibrate the pressure-based flow control based on the verification flow rate.

[0025] The MFC may further be configured to switch between providing pressure-based flow control and providing flow control based on flow rate monitoring, the flow rate monitoring being based on the rate of pressure decay in the chamber detected by the first pressure sensor. Alternatively, the MFC may further be configured to maintain a controlled flow rate based on pressure-based flow control during determination of the verification flow rate.

[0026] A method of controlling a flow rate includes: providing pressure-based flow control of the actuation of a downstream control valve of a mass flow controller; and determining a verification flow rate based on the rate of pressure decay in the chamber of the mass flow controller, while maintaining pressure-based flow control or flow control based on the rate of pressure decay in the chamber. The method further includes recalibrating the pressure-based flow control based on the verification flow rate. The rate of pressure decay is based on the pressure detected by the first pressure sensor when the upstream control valve is closed, and the first pressure sensor detects the fluid pressure in the chamber. The pressure-based flow control is based on monitoring of the pressure upstream of the pressure drop component detected by the second pressure sensor, the pressure drop component being disposed downstream of the downstream control valve, and the second pressure sensor detecting the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component.

[0027] The method may further include switching between providing pressure-based flow control and providing flow control based on flow rate monitoring, the flow rate monitoring being based on the rate of pressure decay in the chamber detected by the first pressure sensor. Alternatively, the method may further include maintaining a controlled flow rate based on pressure-based flow control during determination of the verification flow rate.

[0028] The pressure drop component may be a critical flow nozzle. Description of the Drawings

[0029] The foregoing will be clear from the following more specific description of example embodiments, as shown in the accompanying drawings, in which the same reference numerals refer to the same parts in different figures. The drawings are not necessarily to scale, but rather focus on illustrating the embodiments.

[0030] Figure 1 is a schematic diagram of an example mass flow controller.

[0031] Figure 2 is a simplified diagram showing an example of feedback control provided in a mass flow controller.

[0032] Figure 3 is shown as Figure 2 a flowchart showing an example operation of a mass flow controller having feedback control as shown.

[0033] Figure 4 is a simplified diagram showing another example of feedback control provided in a mass flow controller.

[0034] Figure 5 is shown as Figure 4 a flowchart showing an example operation of a mass flow controller having feedback control as shown.

[0035] Figure 6 is a simplified diagram showing another example of feedback control provided in a mass flow controller.

[0036] Figure 7 is shown as Figure 6 a flowchart showing an example operation of a mass flow controller having feedback control as shown. Detailed Description

[0037] A description of example embodiments is as follows.

[0038] An MFC typically includes a system controller as part of a feedback control system that provides a control signal to a control valve based on a comparison of a flow rate specified by a setpoint and a measured flow rate. Thus, the feedback control system operates the flow control valve to maintain the measured flow rate at the setpoint flow rate. In pressure-based mass flow control, under critical flow conditions, a critical flow nozzle can be used to measure the mass flow rate by a pressure sensor and a temperature sensor, or under non-critical flow conditions, the mass flow rate can be measured by two pressure sensors and a temperature sensor. Regardless of which method is used, the pressure upstream of the flow nozzle is typically obtained for flow rate calculation.

[0039] In traditional mass flow controllers (MFCs), feedback control systems assume that the MFC remains calibrated within a certain tolerance range. To test whether the MFC is within the calibration tolerance, typically an offline test of the MFC is performed, for example, using a mass flow validator (MFV). Although the offline test can be very accurate, it does not provide a solution to the problem of the MFC losing calibration during process operation. Generally, it is not until the process is complete that the loss of calibration of the MFC can be detected, which can lead to a reduction in product yield or a loss of the entire product output. The loss of output can result in significant overhead and is clearly undesirable.

[0040] Prior art methods for providing self-verification are described in U.S. 10,801,867, the entire teachings of which are incorporated herein by reference. As described therein, a flow verification check of the MFC can be performed during a transition from a non-zero setpoint to a zero setpoint. Verification of the flow rate is based on the rate of pressure decay as fluid continues to flow from a reservoir upstream of the MFC.

[0041] Other prior art methods and devices for providing self-verification in an MFC require complex hardware configurations, such as devices that require highly sensitive valve position feedback components to provide independent flow measurements, and devices that include several additional components to substantially provide a discrete mass flow validator (MFV) built into the MFC. There is a need for improved mass flow control devices and methods that can verify and / or calibrate in-situ. There is a further need to provide a self-verifying MFC in a more space-efficient configuration.

[0042] A mass flow control device capable of self-verification and a method for providing self-verifying mass flow control are provided. The device provided includes an improved control system and hardware configuration.

[0043] As Figure 1 shown, a mass flow controller 100 receives a fluid stream at an inlet 122, and the fluid flows through the body 126 of the device. The MFC 100 includes an upstream valve 102 and a downstream valve 104. As shown, both valves 102, 104 are adjustable control valves; however, the upstream valve 102 can alternatively be an on / off type valve.

[0044] As used herein, the term "control valve" refers to a valve that can provide a controllable range of open states (possibly between an open state and a closed state) and does not include an on / off type valve. The opening degree of an adjustable control valve can be controlled in response to a control signal and can control the flow rate through the valve. Adjustable control valves include proportional control valves. Examples of suitable control valves used as adjustable control valves in the device provided include solenoid valves, piezoelectric valves, and stepper motor valves.

[0045] The MFC further includes a chamber 110, a temperature sensor 106 for detecting the fluid temperature in the chamber 110, and a pressure sensor 112 for detecting the fluid pressure in the chamber 110. The chamber 110 is disposed between the upstream valve 102 and the downstream control valve 104 and is provided for pressure decay rate control measurement. The MFC further includes a critical flow nozzle 116. A second pressure sensor 114 and optionally a second temperature sensor 108 are disposed downstream of the control valve 104 and upstream of the critical flow nozzle 116. The second pressure sensor 114 is provided for pressure control measurement. The fluid flows out of the MFC at the outlet 124.

[0046] The MFC 100 further includes a controller 120 that can receive sensed temperature and pressure information from the sensors 106, 108, 112, 114 and provide control signals to operate the valves 102 and 104. The MFC 100 combines pressure decay rate flow control and pressure control for regulating the fluid flow rate through the device to a set value. For example, monitoring of the flow rate can be performed by alternating between obtaining an upstream pressure decay rate flow measurement (e.g., for comparison with a flow set value) and obtaining a downstream pressure measurement (e.g., for comparison with a pressure set value). When the flow rate through the device is regulated to the flow set value and is stable during an upstream pressure decay rate flow control period, the pressure set value for a downstream pressure control period can be determined in situ.

[0047] In an example operation of the MFC 100, an upstream pressure decay rate is obtained based on a pressure measurement obtained from the pressure sensor 112 when the upstream isolation valve 102 is closed, and this pressure decay rate is used to measure the flow rate for initial flow control. During this period, the controller 120 can compare the measured flow rate with the flow set value and generate a control signal for operating the adjustable control valve 104. When the upstream isolation valve 102 is opened to fill the volume (e.g., the volume of the chamber 110 and the fluid conduit), mass flow control is provided by controlling the downstream pressure of the device. During this period, the controller 120 can generate a flow control signal for operating the adjustable control valve 104 based on the pressure measurement obtained from the pressure sensor 114. Although this operation is described in the context of providing initial flow control based on a pressure decay rate measurement for calculating a flow rate for comparison with a flow set value, the device can alternatively be operated with an initial pressure set value for initial pressure control, and a subsequent upstream pressure decay period can be invoked to verify the pressure set value.

[0048] Traditional pressure-based MFCs typically require knowledge of gas properties to determine the flow rate measurement of gas passing through the device. Pressure decay rate measurements provide a method for determining flow rate that is independent of the gas. The pressure decay rate method may not be desirable for use in a mass flow controller because re-establishing the inlet gas flow when refilling the internal volume of the device may disrupt the flow control provided by the device.

[0049] The MFC device and method provided herein can overcome the problems of traditional pressure-based MFCs by performing flow control during an initial period and / or an intermittent period based on pressure decay rate measurements, during which the pressure downstream of chamber 110 and upstream of the critical flow nozzle 116 is also monitored. Then, the downstream pressure (P2) detected by the downstream sensor 114 during such periods can be used to establish the pressure setpoint used during the pressure control period. Thus, the MFC can self-verify accuracy periodically at any point in the process or throughout the process while providing continuous mass flow control.

[0050] The flow-based feedback control period can be relatively short such that the volume of chamber 110 is not discharged to the extent that the critical flow conditions at nozzle 116 are disrupted. For example, the upstream pressure (P1) can be monitored such that it remains above a threshold, as described further below. Optionally, valve 102 can be a proportional control valve such that the gas flow is gradually re-introduced into the volume, thereby preventing potential disruption.

[0051] In an example configuration, the controller 120 of the MFC can include two controllers: a flow controller 210 and a pressure controller 220, as Figure 2 shown. The MFC can switch between controller 210 and controller 220 to maintain a continuous controlled flow rate.

[0052] Flow-based control (Kq) is provided by flow controller 210 to generate a valve input (VI) to the control valve (valve 104) to achieve mass flow control (MFC) of the device. Flow-based control can be provided by comparing the measured flow rate (Q) with a flow setpoint (Qsp). The measured flow rate can be based on the pressure decay rate principle, which is inherently independent of the gas. In particular, the flow rate (Q) can be measured according to the following equation, where V is the volume of the chamber (e.g., chamber 110), T stp is the standard temperature, P stp is the standard pressure, P1 is the fluid pressure in the chamber detected by the first pressure sensor (e.g., by pressure sensor 112), and T is the fluid temperature detected by (e.g., temperature sensor 106):

[0053]

[0054] Pressure-based control (Kp) is provided by a pressure controller 220 to generate a valve input (VI) to a control valve (valve 104) to effect mass flow control (MFC) of the apparatus. Under critical flow conditions, the flow rate (Q) of the gas becomes independent of the downstream outlet pressure (e.g., Figure 1 P in d ) and is proportional to the pressure (e.g., Figure 1 P2 in

[0055] Q = k(mw, γ, T)·P2 (4)

[0056] Controlling the pressure (P2) upstream of the nozzle effectively controls the flow rate (Q) through the nozzle. Critical flow conditions typically occur when the pressure (P2) upstream of the nozzle is at least twice the pressure (P d ) downstream of the nozzle, as given by the following equation:

[0057] P2 ≥ 2P d (5)

[0058] Pressure-based control can be provided by comparing the measured pressure (P2) with a pressure setpoint (Psp). When the flow rate is stabilized by upstream pressure decay rate flow control, the pressure setpoint (Psp) can be determined in situ.

[0059] Figure 3 A flowchart showing an example process 300A for operating an MFC is shown in sp)(312). At this stage, the operation of the device can be switched from flow control to pressure control (316). Alternatively, flow-based control can continue until the upstream pressure (P1) is below a threshold (314). When switching to pressure-based control (316), the upstream isolation valve can be opened (which may be desirable if the upstream pressure is below the threshold), or the upstream isolation valve can be kept closed until the downstream pressure (P2) reaches stability, as shown in the flowchart. During pressure-based control, the downstream pressure (P2) is fed as an input to a pressure force feedback controller (Kp), which generates a control command (VI) to the downstream control valve 104 of the device (318). The control valve is actuated to regulate the monitored pressure (P2) to a pressure setpoint (Psp) (320). If the upstream isolation valve 102 has not been opened, then when the monitored pressure stabilizes (322), the isolation valve 102 is opened to refill the volume (324). When the upstream pressure (P1) stabilizes, the MFC can switch back to flow-based control (326). However, pressure-based control can continue for some time after the upstream pressure has stabilized.

[0060] In another example configuration, the controller 120 of the MFC can include a feedback controller 410 that can switch between flow-based control and pressure-based control, as Figure 4 shown. Flow-based control can be performed as described above with respect to Figure 2 and using Equation 1. Pressure-based control can be performed by further processing the downstream pressure measurement to compare it with the flow setpoint (Qsp).

[0061] During pressure-based feedback control, the controller 120 of the MFC can be configured to determine the flow rate Q of the fluid cf and compare the determined flow rate with the flow rate setpoint Q sp . For example, the determined flow rate Q cf can be calculated according to the following formula:

[0062] Q cf = K cf· P2 (2)

[0063] where K cf is a coefficient, and P2 is the pressure detected by the second pressure sensor. The coefficient K cf can be determined according to the following formula:

[0064] K cf = Q / P cf (3)

[0065] where Q is the stable flow rate determined during flow-based feedback control, and P cfis the pressure detected by the second pressure sensor during a stable flow period at the stable flow rate Q.

[0066] Figure 5 FIG. shows a flowchart illustrating another example process 300B for operating an MFC. Process 300B is similar to Figure 3 process 300A shown, except that the single feedback controller included in the device is capable of providing both upstream pressure decay rate feedback control and pressure-based feedback control. In particular, the feedback controller calculates a control command (308B) for controlling the downstream control valve based on the pressure decay rate measurement, and during this flow-based feedback period, determines a coefficient (K cf )(312B) for the pressure-based feedback period. During the pressure-based feedback control period, a pressure-based flow rate (Q cf )(318B) is determined, and the feedback controller calculates a control command (320B) for controlling the downstream control valve based on a comparison of this measurement with the flow rate setpoint.

[0067] Accordingly, the provided MFC 100 can alternate between periods when the upstream isolation valve is open and periods when the upstream isolation valve is closed. The device can perform mass flow control using the upstream pressure measurement (P1) during periods when the upstream isolation valve is closed, and perform mass flow control using the downstream pressure measurement (P2) during periods when the upstream isolation valve is open. The upstream pressure measurement can be used to calculate the flow rate through the device based on the principle of pressure decay rate, which is inherently gas-independent. This gas-independent measurement can inform the device of a pressure setpoint that is determined when the flow rate is stable at the determined decay rate, otherwise knowledge of gas properties and more complex calculations would be required to control the flow rate. Then, the downstream pressure measurement can be used directly (e.g., by comparison with the pressure setpoint) or indirectly (e.g., by conversion to a calculated flow rate for comparison with the flow rate setpoint, the calculated flow rate being based on a coefficient determined during flow-based feedback control) for pressure-based control.

[0068] By alternating between periods of flow-based feedback control and periods of pressure-based feedback control, the MFC can provide uninterrupted flow control while verifying the pressure-based setpoint. With a configuration such as Figure 1 shown, the downstream pressure-based control for regulating the flow rate can remain very stable even when the upstream pressure varies during volume filling. This MFC configuration can be particularly advantageous for low flow applications (such as a flow rate setpoint less than 200 sccm).

[0069] In yet another example configuration, the controller 120 of the MFC can include a feedback controller 510 that is configured to provide pressure-based feedback control, as Figure 6 shown. As shown, flow control is provided by monitoring the downstream pressure (e.g., by Equation 2), where the upstream pressure decay rate flow measurement is used to provide verification and / or recalibration. If the flow error between Qcf and Q is higher than a predetermined threshold, the coefficient of K cf can be determined or updated in-situ (e.g., K cf = Q / P2).

[0070] For example, the controller 120 can be configured to determine the flow rate Q cf based on the measured pressure P2 and the initial or provided value of the coefficient K cf . The determined flow rate Q cf can be compared with the flow setpoint Q sp to control the actuation of the control valve 104.

[0071] When the measured flow rate Q cf is controlled to the flow setpoint Q sp and stabilized, the downstream pressure (P2) can be recorded as P cf . The controller can be further configured to perform verification based on the pressure decay rate measurement. In particular, the upstream valve 102 can be closed, and the upstream pressure P1 can be monitored to obtain the flow measurement Q, e.g., by Equation 1. The upstream valve 102 can be closed for a short duration sufficient to obtain the flow measurement (e.g., less than about 5 seconds). The flow measurement Q can be used to provide verification of Q cf .

[0072] For example, if the error (ErrQcf) between Q and Q cf is higher than a predetermined threshold (e.g., ErrQcf > 0.01), the controller can update the coefficient according to Equation 3. The error (ErrQcf) can be determined as follows:

[0073]

[0074] Alternatively, the controller can periodically replace Q cf with an updated value based on the measured and verified flow rate Q. The verification can be repeated intermittently or as needed by repeating the above steps.

[0075] Figure 7 A flowchart showing an example process 600 for operating the MFC is shown in sp) is provided to the device (602), and the downstream pressure (P2) is measured and provided as an input to the flow feedback controller to determine the control valve command (604). The control valve is actuated to regulate the flow rate (Q cf ) to the flow rate setpoint (Q sp )(606). This process can continue until the downstream pressure (P2) stabilizes (608). Then the upstream isolation valve is closed (610), and a pressure decay rate flow measurement is obtained based on the upstream pressure (P1) (612). The upstream isolation valve is opened to re - establish the gas supply (614). Then the flow rate (Q cf ) based on the downstream pressure can be verified by determining the error (ErrQcf) (616). If the error is higher than the threshold (618), the coefficient(s) can be updated to provide recalibration of the device (620).

[0076] Although the flow rate measurements based on the downstream pressure described above and shown in Figure 2 、 Figure 4 and Figure 6 are represented by Equation 2 and / or Equation 4 as Q cf , the flow rate measurement based on the downstream pressure can alternatively be obtained by a look - up table (e.g., a table of pressure vs. flow rate). In the case of using the look - up table instead of Equation 2 and / or Equation 4 or as a supplement to such calculations, when the flow error between the pressure - based flow rate measurement (Q cf ) and the upstream pressure decay rate flow measurement (Q) is higher than a predetermined threshold, the MFC can update the look - up table.

[0077] Although the MFC is shown in Figure 1 as including a critical flow nozzle, the MFC can alternatively include other types of pressure drop components or flow limiters, such as laminar flow components, porous media flow limiters, orifices, or tubes.

[0078] The teachings of all patents, published applications, and references cited herein are hereby incorporated by reference in their entirety.

[0079] Although the exemplary embodiments have been specifically shown and described, those skilled in the art will understand that various changes in form and detail can be made therein without departing from the scope of the embodiments covered by the appended patent claims.

Claims

1. A mass flow controller, comprising: a chamber configured to receive a fluid; an upstream valve disposed upstream of the chamber; a downstream control valve disposed downstream of the chamber; a pressure drop component disposed downstream of the downstream control valve; a first pressure sensor configured to detect the fluid pressure in the chamber; a second pressure sensor configured to detect the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component; and a controller configured to control the actuation of the downstream control valve, the controller being configured to switch between: flow-based feedback control, the flow-based feedback control including monitoring a flow rate based on a pressure decay rate of the fluid in the chamber detected by the first pressure sensor when the upstream control valve is closed, and pressure-based feedback control, the pressure-based feedback control including monitoring the pressure upstream of the pressure drop component detected by the second pressure sensor.

2. The mass flow controller according to claim 1, wherein, The controller is further configured to: during flow-based feedback control, record the pressure detected by the second pressure sensor for use during pressure-based feedback control.

3. The mass flow controller according to claim 2, wherein The controller is further configured to establish a pressure setpoint for pressure-based feedback control based on the recorded pressure.

4. The mass flow controller according to claim 2, wherein, The controller is further configured to determine a coefficient for calculating the flow rate during pressure-based feedback control, the coefficient being determined based on the recorded pressure.

5. The mass flow controller according to claim 1, wherein During flow-based feedback control, the controller is configured to measure the flow rate Q of the fluid and compare the measured flow rate with the flow rate setpoint Q sp for comparison.

6. The mass flow controller according to claim 5, wherein, The controller is further configured to calculate the measured flow rate Q according to the following formula: where V is the volume of the chamber, T stp is the standard temperature, P stp is the standard pressure, P1 is the fluid pressure in the chamber detected by the first pressure sensor, and T is the detected fluid temperature.

7. The mass flow controller according to claim 1, wherein, During pressure-based feedback control, the controller is configured to determine a flow rate Q of the fluid cf and compare the determined flow rate with a flow rate setpoint Q sp for comparison.

8. The mass flow controller according to claim 7, wherein, The controller is further configured to calculate the determined flow rate Q according to the following formula cf :[[]]END]] Q cf = K cf. P2 where K cf is a coefficient, and P2 is the pressure detected by the second pressure sensor.

9. The mass flow controller according to claim 8, wherein, The controller is further configured to determine a coefficient K according to the following formula cf :[[]]END]] K cf = Q / P cf where Q is a stable flow rate determined during flow-based feedback control, and P cf is the pressure detected by the second pressure sensor during a stable flow period at the stable flow rate Q.

10. The mass flow controller according to claim 7, wherein, The controller is configured to determine the flow rate Q of the fluid based on a look-up table cf .

11. The mass flow controller according to claim 1, wherein, The controller includes a flow controller and a pressure controller.

12. The mass flow controller according to claim 11, wherein, The flow controller is configured to monitor the flow rate based on the decay rate and compare the monitored flow rate with a flow rate setpoint.

13. The mass flow controller according to claim 11, wherein, The pressure controller is configured to monitor the pressure detected by the second pressure sensor and compare the monitored pressure with a pressure setpoint.

14. The mass flow controller according to claim 1, wherein, The pressure drop component is a critical flow nozzle.

15. The mass flow controller according to claim 1, wherein, The upstream valve is a control valve.

16. The mass flow controller according to claim 1, further comprising a temperature sensor configured to detect the temperature of the fluid.

17. A method of controlling a flow rate, the method comprising: switching between flow-based feedback control and pressure-based feedback control of the actuation of a downstream control valve of a mass flow controller, wherein: flow-based feedback control includes monitoring a flow rate based on a pressure decay rate of the fluid in the chamber of the mass flow controller, the pressure decay rate being based on the pressure detected by a first pressure sensor when a valve disposed upstream of the chamber is closed, the first pressure sensor detecting the fluid pressure in the chamber, and pressure-based feedback control includes monitoring the pressure upstream of a pressure drop component based on the pressure detected by a second pressure sensor, the pressure drop component being disposed downstream of the downstream control valve, the second pressure sensor detecting the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component.

18. The method according to claim 17, further comprising: During flow-based feedback control, record the pressure detected by the second pressure sensor for use during pressure-based feedback control.

19. The method according to claim 18, further comprising establishing a pressure setpoint for pressure-based feedback control based on the recorded pressure.

20. The method according to claim 18, further comprising determining a coefficient for calculating a flow rate during pressure-based feedback control, the coefficient being determined based on the recorded pressure.

21. The method according to claim 17, further comprising: During flow-based feedback control, the flow rate Q of the fluid is measured and the measured flow rate is compared with a flow rate setpoint Qsp.

22. The method according to claim 21, further comprising calculating the measured flow rate Q according to the following formula: Among them, V is the volume of the chamber, T stp is the standard temperature, P stp is the standard pressure, P1 is the fluid pressure in the chamber detected by the first pressure sensor, and T is the detected fluid temperature.

23. The method according to claim 17, further comprising: During pressure-based feedback control, the flow rate Q of the fluid is determined cf and the determined flow rate is compared with a flow rate setpoint Q sp for comparison.

24. The method according to claim 23, further comprising calculating the determined flow rate Q according to the following formula cf :[[]]END]] Q cf = K cf. P2 where K cf is a coefficient, and P2 is the pressure detected by the second pressure sensor.

25. The method according to claim 24, further comprising determining a coefficient K according to the following formula cf :[[]]END]] K cf = Q / P cf where Q is the steady flow rate determined during flow-based feedback control, and P cf is the pressure detected by the second pressure sensor during the steady flow period at the steady flow rate Q.

26. The method according to claim 23, wherein Determine the flow rate Q of the fluid cf is determined based on a look-up table.

27. A mass flow controller, comprising: a chamber configured to receive a fluid; an upstream valve provided upstream of the chamber; a downstream control valve provided downstream of the chamber; a pressure drop component provided downstream of the downstream control valve; a first pressure sensor that detects the fluid pressure in the chamber; a second pressure sensor that detects the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component; and a controller configured to control the actuation of the downstream control valve, the controller maintaining a controlled flow rate based on the pressure detected by at least one of the first pressure sensor and the second pressure sensor, and recalibrating the pressure-based flow control during the controlled flow rate based on the pressure detected by the second pressure sensor and the pressure decay rate detected by the first pressure sensor.

28. A method of controlling a flow rate, the method comprising: maintaining a controlled flow rate by controlling the actuation of a downstream control valve based on the pressure detected by at least one of a first pressure sensor and a second pressure sensor, the first pressure sensor detecting the fluid pressure in a chamber configured to receive a fluid, the second pressure sensor detecting the fluid pressure downstream of the downstream control valve and upstream of a pressure drop component provided downstream of the downstream control valve; and recalibrating the pressure-based flow control during the controlled flow rate based on the pressure detected by the second pressure sensor and the pressure decay rate detected by the first pressure sensor.

29. A mass flow controller, comprising: a chamber configured to receive a fluid; an upstream valve provided upstream of the chamber; a downstream control valve provided downstream of the chamber; a pressure drop component provided downstream of the downstream control valve; a first pressure sensor that detects the fluid pressure in the chamber; a second pressure sensor that detects the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component; and a controller configured to control the actuation of the downstream control valve, the controller being configured to: provide pressure-based flow control based on monitoring of the pressure upstream of the pressure drop component detected by the second pressure sensor Determine a verification flow rate based on the rate of pressure decay in the chamber detected by the first pressure sensor when the upstream control valve is closed, while maintaining the pressure-based flow control or the flow control based on the rate of pressure decay in the chamber, and Recalibrate the pressure-based flow control based on the verification flow rate.

30. The mass flow controller according to claim 28, wherein, The controller is further configured to switch between providing the pressure-based flow control and providing a flow control based on flow rate monitoring, the flow rate monitoring being based on the rate of pressure decay in the chamber detected by the first pressure sensor.

31. The mass flow controller according to claim 28, wherein, The controller is further configured to maintain a controlled flow rate based on the pressure-based flow control during determination of the verification flow rate.

32. A method of controlling a flow rate, the method comprising: Providing a pressure-based flow control of actuation of a downstream control valve of a mass flow controller; Determining a verification flow rate based on the rate of pressure decay in the chamber of the mass flow controller, while maintaining the pressure-based flow control or the flow control based on the rate of pressure decay in the chamber; And Recalibrating the pressure-based flow control based on the verification flow rate, the rate of pressure decay being based on the pressure detected by a first pressure sensor when an upstream control valve is closed, the first pressure sensor detecting the fluid pressure in the chamber, the pressure-based flow control being based on monitoring of the pressure upstream of a pressure drop component detected by a second pressure sensor, the pressure drop component being disposed downstream of the downstream control valve, the second pressure sensor detecting the fluid pressure downstream of the downstream control valve and upstream of the pressure drop component.

33. The method of claim 32, further comprising switching between providing the pressure-based flow control and providing a flow control based on flow rate monitoring, the flow rate monitoring being based on the rate of pressure decay in the chamber detected by the first pressure sensor.

34. The method of claim 32, further comprising maintaining a controlled flow rate based on the pressure-based flow control during determination of the verification flow rate.

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