Method, system and device for verifying mass flow based on pressure decay rate

Abstract

A mass flow verification system and apparatus verify the mass flow rate of a mass flow controller (MFC) based on the principle of pressure attenuation. Embodiments include a location for coupling a calibrated gas flow standard or MFC to be tested in a pipeline to receive a gas flow from a gas source; a control volume coupled in series to the location in the line to receive the gas flow; a current limiter coupled in series to the control volume; a pump coupled in series to the flow restrictor; and a controller adapted to allow the gas source to flow gas through the mass flow control verification system to achieve a stable pressure in the control volume, terminate gas flow from the gas source, and measure a rate of pressure decay in the control volume over time. Numerous additional aspects are disclosed.

Description

[0001] This application is a divisional application of the invention patent application with the application date of February 20, 2019, application number 201980028315.8, and invention name "Method, system and device for calibrating mass flow based on pressure decay rate".

[0002] This application claims priority to U.S. Patent Application No. 15 / 936,428, filed on March 26, 2018, entitled “METHODS, SYSTEMS, AND APPARATUS FOR MASS FLOW VERIFICATION BASED ON RATE OF PRESSURE DECAY” (Attorney Docket No. 44014915US01), which is hereby incorporated by reference in its entirety for all purposes. Technical Field

[0003] The present disclosure relates to electronic device manufacturing and, more particularly, to calibrating the mass flow rate of a mass flow controller based on a pressure decay rate. Background Art

[0004] An electronic device manufacturing system may include one or more mass flow controllers (MFCs). An MFC controls the mass flow rate of process chemicals used in the manufacture of electronic devices. The process chemicals may include various process gases (e.g., cleaning, deposition, and etchant gases) that are delivered to one or more process chambers where electronic devices may be manufactured on semiconductor wafers, glass plates, or the like. Accurate mass flow control of process gases may be used in one or more steps of the manufacturing process of the electronic device. The accurate mass flow control provided by the MFC may contribute to high yield production of electronic devices with microscopically small dimensions.

[0005] To ensure accurate delivery of process chemicals, the MFC may be periodically calibrated and calibrated. However, conventional methods of calibrating and calibrating an MFC may involve a large amount of additional bulky and expensive equipment, may be time consuming and inefficient to use, may be limited to a low mass flow rate range (e.g., only up to 3000 sccm (standard cubic centimeters per minute) nitrogen equivalent), may result in significant process downtime, and / or may not be accurate enough to ensure precise mass flow control of process chemicals. Summary of the invention

[0006] In some embodiments, a mass flow control verification system is provided. The mass flow verification system includes a location for coupling a calibrated gas flow standard or an MFC to be tested in a pipeline to receive a gas flow from a gas source; a control volume coupled in series to the location in the pipeline to receive the gas flow; a flow restrictor coupled in series to the control volume; a pump coupled in series to the flow restrictor; and a controller adapted to allow the gas source to flow gas through the mass flow control verification system to reach a stable pressure in the control volume, terminate the gas flow from the gas source, and measure the rate of pressure decay in the control volume over time.

[0007] In some other embodiments, an electronic device manufacturing system is provided. The electronic device manufacturing system includes a gas source; a mass flow controller (MFC) coupled to the gas source; a mass flow control calibration system having an inlet and an outlet, the inlet coupled to the MFC, the mass flow control calibration system including: a control volume, the control volume coupled in series to the inlet to receive a gas flow; a restrictor, the restrictor coupled in series to the control volume and the outlet; and a controller adapted to allow the gas source to flow a gas through the mass flow control calibration system to reach a stable pressure in the control volume, terminate the gas flow from the gas source, and measure the rate of pressure decay in the control volume over time; and a process chamber, the process chamber coupled to a flow path, the flow path coupled to the mass flow controller and configured to receive one or more process chemicals via the mass flow controller.

[0008] In yet other embodiments, a method for calibrating a mass flow controller is provided. The method includes the steps of causing gas to flow from a gas source through a calibrated flow standard, a control volume, and a flow restrictor at a stable pressure measured in a control volume; terminating the gas flow from the gas source; measuring a first gas pressure decay rate in the control volume; replacing the calibrated flow standard with a mass flow controller; causing gas to flow from a gas source through a mass flow controller, a control volume, and a flow restrictor at a stable pressure measured in the control volume; terminating the gas flow from the gas source; and measuring a second gas pressure decay rate in the control volume.

[0009] Further aspects, features and advantages of these and other embodiments according to the present disclosure can be readily learned from the following detailed description and accompanying drawings.Therefore, the drawings and descriptions herein are to be considered illustrative in nature, rather than restrictive. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The drawings described below are for illustration purposes only and are not necessarily drawn to scale. These drawings are not intended to limit the scope of the present disclosure in any way.

[0011] Figure 1 A first mass flow control calibration system is illustrated according to an embodiment of the present disclosure.

[0012] Figure 2 A second mass flow control calibration system is illustrated according to an embodiment of the present disclosure.

[0013] Figure 3 A third mass flow control calibration system is illustrated in accordance with an embodiment of the present disclosure.

[0014] Figure 4 A graph illustrating several pressures measured during a mass flow calibration is shown in accordance with an embodiment of the present disclosure.

[0015] Figure 5 An electronic device manufacturing system is illustrated according to an embodiment of the present disclosure.

[0016] Figure 6 A flow chart of a mass flow control calibration method is illustrated according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0017] Reference will now be made in detail to the embodiments of the present disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0018] Electronic devices having microscopically small dimensions may be produced with process gas chemistries having mass flow rate accuracy as high as + / -1%. Many mass flow controllers (MFCs) may be so specified and may meet these specifications when new, while a minority of MFCs may be so specified but may not actually meet these specifications when new or at other times. Furthermore, even initially accurate MFCs may experience a drift in the accuracy of the mass flow rate of the initially accurate MFCs over time, which may cause them to exceed the specified accuracy of the MFCs. Thus, verification and calibration of MFCs, such as those used in semiconductor manufacturing equipment, may be periodically performed to ensure accurate delivery of process gas chemistries.

[0019] Existing methods and related hardware for mass flow calibration are usually based on measuring the rate of rise (ROR) of pressure in a known volume. The ROR principle is based on the ideal gas law, which is used to associate the mass flow rate with the measured rate of rise of pressure in a known closed volume. The higher the mass flow rate, the larger the closed volume should be to ensure accuracy. The ROR principle may involve a long process (e.g., 10 hours or more in some cases) of filling a closed volume with a gas and measuring the ROR in the closed volume. The closed volume may be a process chamber of a manufacturing system or an external volume. Uncertainty about the exact volume of the process chamber or the external volume may adversely affect the accuracy of the results. The process using the ROR principle may involve the measurement of pressure, temperature, volume and time. An important problem with conventional ROR-based methods is that the known volume usually includes a reservoir and a flow path from the MFC unit under test (UUT) to the reservoir. The rate of pressure change is measured in an almost stagnant state inside the reservoir, while the dynamic pressure inside the flow path to the reservoir is not measured. The lack of a measurement of the rate of change of pressure in one of the two portions of a known volume can lead to erroneous calculations, resulting in mischaracterization of the flow out of the UUT. Compared to such conventional methods, the embodiments disclosed herein eliminate the error introduced by the volume of the flow path. The present method and apparatus operate based on measuring the rate of pressure decay in a known volume, and therefore do not include unmeasured flow paths.

[0020] More specifically, the mass flow calibration method, system and device according to one or more embodiments of the present disclosure are based on the pressure decay principle for determining the gas mass flow rate, and the unit of the gas mass flow rate may be "sccm" (standard cubic centimeters per minute) or "slm" (standard liters per minute). The mass flow calibration method, system and device based on the pressure decay principle according to one or more embodiments of the present disclosure can reduce the number of variables required to calculate the mass flow rate, can result in a smaller calibration equipment footprint, and can be more time-saving and more accurate than the conventional mass flow calibration method, system and device based on the ROR-based principle. Compared with the ROR-based method, the non-ROR pressure decay measurement can be almost instantaneous, and the calculation of the mass flow rate based on the pressure decay rate (rate of pressure decay, ROPD) principle can involve only two measurements: pressure and temperature.

[0021] The ideal gas law, also called the universal gas equation, is the equation of state for a hypothetical ideal gas. The ideal gas law is an approximation of the behavior of many gases under many conditions. The ideal gas law is usually expressed as:

[0022] (PV=nRT)

[0023] Where P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of the gas (in moles), R is the ideal or universal gas constant which is equal to the product of the Boltzmann constant and the Avogadro constant, and T is the absolute temperature of the gas.

[0024] Figure 1 Depicts an example arrangement for verifying an MFC. Figure 1 The mass flow calibration system 100 includes a gas source 102 that provides a pressurized flow of a suitable gas (e.g., nitrogen, oxygen, clean dry air (CDA), etc.) to a location 104. The flow rate of the gas can be scaled without limit by specifying the appropriate size of the monitored volume 110 and the restrictor 116. At the location 104, a reference (e.g., a calibrated flow standard) or any of the UUTs can be positioned to receive the gas. The output of the reference standard or UUT at the location 104 can be coupled to a line 106 leading to a valve 108 (e.g., an isolation valve), which is coupled to the monitored volume 110. The monitored volume 110 is monitored using a connected thermocouple 112 and a connected manometer (manometer) 114 or other suitable pressure measurement device. The output of the monitored volume 110 is coupled to the restrictor 116, which is coupled to a vacuum pump 118. In some embodiments, the restrictor 116 may be a drilled orifice restrictor or a porous media restrictor when measuring pressure and temperature downstream of the restrictor 116. The mass flow calibration system 100 operates under the control of a controller 120, which may be coupled to each operable component and each sensor component (note that for clarity of illustration, connections are not shown).

[0025] use Figure 1 , the control volume (V) (i.e., the marked volume between valve 108 and restrictor 116, including monitored volume 110) is first determined by using a calibrated flow standard in location 104. The calibrated flow standard at location 104 is given a set point, and the pressure and temperature in monitored volume 110 are allowed sufficient time to settle to a steady state. At the pressure is measured and marked as P O Time t OAt time t, the controller 120 commands the valve 108 to close. O Thereafter, the pressure inside the control volume begins to decay as the gas continues to flow through the restrictor 116. The control volume is calculated based on:

[0026] V=RT(dn / dt) / (dP / dt)

[0027] In t O Evaluating dP / dt at provides the value for the control volume where the pressure is P O , and using the set point of the calibrated flow standard at location 104 as t in the above equation O Once the volume of the control volume is determined, the calibrated flow standard at position 104 is replaced with the UUT MFC. The UUT MFC is given a set point to be calibrated. Solving the above equation for dn / dt, the accuracy of the UUT MFC can be determined by comparing the given set point to the calculated mass flow rate using the following equation:

[0028] dm / dt=(V / RT)(dP / dt)The above method assumes that the valve 108 is closed instantaneously. In reality, due to delays in communications from the controller 120 and hardware actuator responses, the actual time required for the valve 108 to fully close is somewhat smaller but exceeds to by a significant amount Δt. Due to the delay, during Δt, the calibrated gas flow still flows into the control volume while the pressure within the control volume decays at a slower rate than indicated by the above calculation. Once the valve 108 is fully closed, the calibrated gas flow no longer flows into the control volume, and the pressure inside the control volume continues to decay, but at a faster rate. Embodiments of the present disclosure provide methods and apparatus to compensate for the time Δt that the valve 108 takes to fully close. In particular, embodiments of the present disclosure provide methods for estimating dP / dt at to, even if the mass flow rate does not stabilize until after Δt has passed.

[0029] In evaluating t O In the first example method of dP / dt at Figure 1 , a mass flow calibration system 100 is shown in FIG. 1 , with a calibrated flow standard mounted at position 104 at a known set point, valve 108 is opened to establish flow through the control volume, and pressure is measured in the monitored volume 110 via pressure gauge 114. It should be noted that valve 108 is normally closed until actuated. There is sufficient time to establish a steady state, allowing a steady flow through until P can be measured. O Baseline measurement of Figure 4 400, in particular, a pressure versus time dP / dt curve 402, P O In tO Stable in the previous time. O Next, the time t is determined by locating the decay pressure inflection point 404 on the dP / dt curve 402. O +Δt. Next, using the O +Δt measured data points to determine the equation for the decay pressure. Any number of curve fitting algorithms or methods may be used to determine the equation for the curve. Then, based on the determined equation, P is converted from the measured data points to o The corrected value of dP / dt at P (i.e., point 406) is extrapolated back. Next, a calibrated flow standard is used to calibrate the flow rate at P o The corrected value of dP / dt at V is used to calculate V based on the equation as described below:

[0030] V=RT(dn / dt) / (dP / dt)

[0031] Next, the MFC UUT is mounted at position 104 set to the test set point. Valve 108 is then opened to reestablish flow through the control volume and the pressure in the monitored volume 110 is measured via pressure gauge 114. Sufficient time is allowed to establish steady state conditions, allowing steady flow through until the UUT can be P-tested. o Once P O In t O The valve 108 is closed to establish a time t for the UUT. O Next, the time t is determined by locating the decay pressure inflection point 404 on the equivalent of the dP / dt curve 402. O +Δt. Next, using the time exceeding t O The equation for the decay pressure is determined from the measured data points at +Δt. Any number of curve fitting algorithms or methods may be used to determine the equation for the curve. Next, based on the determined equation, the measured data points are extrapolated to determine the pressure drop of the UUT at P O The corrected value of dP / dt at (ie, point 406). The equation for the actual mass flow is:

[0032] dn / dt=(V / RT)(dP / dt)

[0033] Finally, using the above equation, the UUT is used to O The actual mass flow rate (dn / dT) is calculated from the corrected value of dP / dT at the test set point, which is compared to the test set point to determine any error. In some embodiments, based on the error, the UUT MFC can be calibrated to correct the error.

[0034] An alternative second example method for MFC verification can be used to further enhance the accuracy of the verification. The second method uses Figure 2 . The mass flow calibration system 200 includes a gas source 202 that provides a pressurized flow of a suitable gas (e.g., nitrogen, oxygen, clean dry air (CDA), etc.) to a location 204. The flow rate of the gas can be scaled without limit by specifying the size of the appropriate monitored volume 210 and the restrictor 216. At the location 204, a reference standard (e.g., a calibrated flow standard) or any one of the UUTs can be positioned to receive the gas. The output of the reference standard or UUT at the location 204 can be coupled to a line 206 leading to a valve 208 (e.g., an isolation valve), which is coupled to the monitored volume 210. The monitored volume 210 is monitored using a connected thermocouple 212 and a connected pressure gauge 214. The output of the monitored volume 210 is coupled to a second valve 222, which is coupled to the restrictor 216. In some embodiments, the restrictor 216 may be a borehole restrictor or a porous media restrictor when measuring pressure and temperature downstream of the restrictor 216. The output of the restrictor 216 is coupled to a vacuum pump 218. The mass flow calibration system 200 operates under the control of a controller 220, which may be coupled to each operable component and each sensor component (note that for clarity of illustration, connections are not shown).

[0035] Note that the MFC verification system 200 is structurally similar to the MFC verification system 200 except that a second valve 222 operated by the controller 220 is disposed in the pipeline between the monitored volume 210 and the restrictor 216. Figure 1 The use of the second valve 222 allows the initial pressure in the control volume to be increased above the initial stable pressure, compared to the initial pressure used in the first example method. By increasing the initial pressure before the decay period begins, it is possible to take more pressure measurements over the extended decay period and thus have more data points and thus fit a more accurate curve, from which a more accurate characteristic equation is determined. The increased initial pressure is Figure 4 The pressure dP / dt curve 408 is presented as a pressure dP / dt curve 408 over time in the graph 400. O '.

[0036] An alternative second example method for MFC calibration includes the following. Initially, both valve 208 and valve 222 are opened long enough to establish steady-state stable flow and measure pressure. Valve 222 is then closed for a period of time sufficient to produce a pressure in the control volume as high as P O 'The pressure rises. Once P is reached O', valve 222 opens while valve 208 closes. Next, the time t is determined by locating the decay pressure inflection point 410 on the dP / dt curve 408. O '+Δt'. Next, using the O The equation for the decay pressure is determined from the measured data points at '+Δt'. Any number of different curve fitting algorithms or methods may be used to determine the equation for the curve. Then, based on the determined equation, the measured data points are extrapolated at P o ' (ie, point 412). Next, using a calibrated flow standard at P o ' to calculate V based on the equation as follows:

[0037] V=RT(dn / dt) / (dP / dt)

[0038] Next, the MFC UUT is installed at position 204 in place of the reference standard, set to the test set point, and the above method is repeated to determine P o '. The equation for the actual mass flow is:

[0039] dn / dt=(V / RT)(dP / dt)

[0040] Finally, using the above equation, use the UUT at P o The actual mass flow rate (dn / dt) is calculated from the corrected value of dP / dt at ', and the actual mass flow rate is compared with the test set point to determine any error. In some embodiments, based on the error, the UUT MFC can be calibrated to correct the error.

[0041] An alternative third example method for MFC verification may be used to further improve the accuracy of the verification. The third method utilizes Figure 3. The mass flow calibration system 300 includes a gas source 302 that provides a pressurized flow of a suitable gas (e.g., nitrogen, oxygen, clean dry air (CDA), etc.) to a location 304. The flow rate of the gas can be scaled indefinitely by specifying the size of the appropriate monitored volume 310 and the restrictor 316. At location 304, a reference standard (e.g., a calibrated flow standard) or any one of the UUTs can be positioned to receive the gas. The output of the reference standard or UUT at location 304 can be coupled to a line 306 leading to a valve 308 (e.g., an isolation valve), which is coupled to the monitored volume 310. The monitored volume 310 is monitored using a connected thermocouple 312 and a connected pressure gauge 314 or other suitable pressure sensor. The output of the monitored volume 310 is coupled to the restrictor 316. In some embodiments, when measuring the pressure and temperature downstream of the restrictor 316, the restrictor 316 can be a drilled restrictor or a porous media restrictor. The output of the restrictor 316 is coupled to a vacuum pump 318. The mass flow calibration system 300 operates under the control of a controller 320, which can be coupled to each operable component and each sensor component (note that for clarity of illustration, the connections are not shown). A second valve 324 is also connected to the pipeline 306 (in parallel with the valve 308), and the second valve 324 is coupled to the second volume 326. The second volume 326 includes an output coupled to a third valve 328, and the third valve 328 has an output coupled to the monitored volume 310.

[0042] The use of the second valve 324, the second volume 326, and the third valve 328 allows the initial pressure in the control volume to be raised above the initial stable pressure, compared to the initial pressure used in the first example method. Stored pressurized gas is contained in the second volume 326 and injected into the monitored volume 310 to increase the initial pressure in the monitored volume 310 before the decay period begins. As with the second example method, this allows more pressure measurements to be made during the extended decay period (e.g., relative to the first example method), thereby having more data points and therefore fitting a more accurate curve, from which a more accurate characteristic equation is determined. As with the second example method, the increased initial pressure is Figure 4 The pressure dP / dt curve 408 is presented as a pressure dP / dt curve 408 over time in the graph 400. O '.

[0043] An alternative third example method for MFC calibration includes the following. Initially, the second valve 324 is opened to establish flow and pressurize the second volume 326. The second volume 326 may be pressurized to the pressure level of the gas source 302. In some embodiments, additional equipment (e.g., a pump) may be used to pressurize the second volume 326 to a higher level. The second valve 324 is then closed, and the first valve 308 is opened long enough to establish a steady-state stable flow and measure the pressure in the monitored volume 310. Once the baseline P is reached, O To stabilize the pressure, the first valve 308 is closed while the third valve 328 is opened. The third valve 328 is maintained open for a period of time sufficient to generate a pressure as high as P in the control volume. o 'The pressure rises. Once P is reached o ', the third valve 328 is closed. Next, the time t is determined by locating the decay pressure inflection point 410 on the dP / dt curve 408. O '+Δt'. Next, using the O The equation for the decay pressure is determined from the measured data points of '+Δt'. Any number of different curve fitting algorithms or methods may be used to determine the equation for the curve. Then, based on the determined equation, P is converted from the measured data points to o The corrected value of dP / dt at ' (ie, point 412) is extrapolated back. Next, a calibrated flow standard is used at P o ' to calculate V based on the following equation:

[0044] V = RT (dn / dt) / (dP / dt) is calculated as described above. Next, the MFC UUT is installed at position 204 in place of the reference standard, set at the test set point, and the above method is repeated to determine P o '. The equation for the actual mass flow is:

[0045] dn / dt=(V / RT)(dP / dt)

[0046] Finally, using the above equation, use the UUT at P o The actual mass flow rate (dn / dt) is calculated from the corrected value of dP / dt at ', and the actual mass flow rate is compared with the test set point to determine any error. In some embodiments, based on the error, the UUT MFC can be calibrated to correct the error.

[0047] Flow restrictors with particularly small diameter boreholes are difficult to manufacture under tight reproducibility specifications. The present example methods and apparatus remove the variability of the flow restrictor from the equation. In some embodiments, the present example methods and apparatus can be used to determine the discharge coefficient of the borehole and characterize the porous media flow restrictor by calculating the ratio of the actual mass flow rate to the theoretical calculated mass flow rate.

[0048] The use of the ideal gas equation for reduced-pressure (i.e., vacuum-based) applications described above provides sufficient accuracy for calibrating a reduced-pressure MFC. In embodiments adapted for atmospheric applications (e.g., without a vacuum pump), non-ideal gas equations (such as the following van der Waals equation) may be applied to the methods and apparatus of the present invention for mass flow calibration. The van der Waals equation is given as follows:

[0049]

[0050] And the van der Waals equation can be used instead of the ideal gas law for atmospheric applications by making gas-specific corrections to the intermolecular forces (parameter a) and finite molecular size (parameter b) of the above equation. For requirements for a wider range of mass flow calibrations, multiple volume sizes can be used. In these cases, a single optimized volume with appropriate partitions can be used. Partitions divide the volume into smaller sections and by selectively removing partitions, multiple combinations of larger volumes can be created.

[0051] Figure 5 An electronic device manufacturing system 500 is illustrated according to one or more implementations. The electronic device manufacturing system 500 may include an MFC 502, a mass flow calibration system 504, and a process chamber 506. In some implementations, the MFC 502 may represent a plurality of MFCs coupled to a common outlet via a common manifold or header, wherein the MFC 502 as described below may represent one of the plurality of MFCs to be calibrated (i.e., the only MFC of the plurality of MFCs that has gas flowing during calibration).

[0052] The process chamber 506 may be coupled to a flow path 508, which is coupled to the mass flow controller 502 via an isolation valve 510. The process chamber 506 may be configured to receive one or more process chemicals via the MFC 502, and may be configured to have a reduced pressure chemical vapor deposition process, or a reduced pressure epitaxial process, or one or more deposition, oxidation, nitration, etching, polishing, cleaning, and / or lithography processes in the process chamber.

[0053] The mass flow verification system 504 may have an inlet 512 and an outlet 514. The inlet 512 may be coupled to the MFC 502 via an isolation valve 510. The mass flow verification system 504 may be any of the mass flow verification systems 100, 200, or 300 described above.

[0054] In those embodiments where the electronic device manufacturing system 500 operates under reduced pressure application, the mass flow verification system 504 can be any of the mass flow verification systems 100, 200, or 300. The mass flow verification system 504 can be coupled to a system vacuum pump 516 of the electronic device manufacturing system 500 via an outlet 514 via an isolation valve 518. The system vacuum pump 516 can also be coupled to the process chamber 506 via the isolation valve 518.

[0055] In those embodiments where the electronic device manufacturing system 500 operates in atmospheric application, the mass flow verification system 504 may be the mass flow verification system 100 , 200 , or 300 , and the system vacuum pump 516 may be excluded from the electronic device manufacturing system 500 .

[0056] Operation of the electronic device manufacturing system 500 and / or the mass flow calibration system 504 may be controlled by a controller, such as one of the controllers 120 , 220 , or 320 .

[0057] Figure 6A flow chart of a method 600 for verifying an MFC flow rate is illustrated according to one or more embodiments. Initially, gas is supplied to a calibrated flow standard and the gas is flowed through a control volume and a flow restrictor (602) connected in series. The gas is flowed until a steady-state stable pressure is reached in the control volume. Optionally, the pressure in the control volume (604) can be increased to provide a larger range of measurable decay pressures. Next, the pressure is measured upstream of the flow restrictor in the control volume (606). Flow from the gas source is terminated, and the gas pressure decay in the control volume is measured over time (608), and this data is used together with the set point of the calibrated flow standard to calculate the actual volume of the control volume (608). The calibrated control standard is replaced with the MFC to be tested (UUT), and the gas is flowed until a steady-state stable pressure is reached in the control volume (610). Optionally, the pressure in the control volume (612) can be increased to provide a larger range of measurable decay pressures. The pressure in the control volume is measured (614), flow from the gas source is terminated, and the gas pressure decay in the control volume is measured over time based on the calculated actual control volume (616). The set point of the MFC under test is verified by comparing the set point of the MFC under test to the actual calculated mass flow rate determined by measuring the pressure decay with the installed MFC under test, wherein any difference is an error in the MFC (618). The MFC is calibrated to correct for the error determined in the MFC (620).

[0058] The above process blocks of method 600 may be executed or performed in an order and sequence not limited to those shown and described. For example, in some embodiments, one process block may be performed simultaneously with another process block or after another process block. In some embodiments, a non-transitory computer-readable medium (e.g., a removable storage disk, memory, or device) may include computer-readable instructions stored on the non-transitory computer-readable medium, which can be executed by a processor (e.g., controller 120, 220, 320) to perform process blocks 602-620 of method 600.

[0059] The above description discloses only example embodiments of the present disclosure. Modifications of the components, devices, systems, and methods disclosed above may fall within the scope of the present disclosure. Therefore, although example embodiments of the present disclosure have been disclosed, it should be understood that other embodiments may fall within the scope of the present disclosure as defined by the appended claims.

Claims

1. An electronic device manufacturing system, comprising: Gas source; a mass flow controller (MFC), the mass flow controller (MFC) coupled to the gas source; an inlet coupled to the MFC; exit; a control volume coupled in series to the inlet to receive a gas flow; a flow restrictor coupled in series and directly to the control volume and to the outlet; a controller adapted to allow the gas source to flow gas through the control volume and the restrictor to reach a steady pressure in the control volume, terminate the gas flow from the gas source, and measure a rate of pressure decay in the control volume over time; and A process chamber is coupled to a flow path, wherein the flow path includes the control volume and is coupled to the mass flow controller, the process chamber being adapted to receive one or more process chemicals via the mass flow controller.

2. The electronic device manufacturing system of claim 1, further comprising a valve coupled between the inlet and the control volume, wherein the valve is operable by the controller to terminate the flow of gas from the gas source.

3. An electronic device manufacturing system as described in claim 1, wherein the controller is used to determine the error in the MFC by comparing the set point of the MFC with an actual mass flow rate, wherein the actual mass flow rate is calculated based on the volume of the control volume, wherein the volume is determined based on the pressure decay rate in the control volume over time, and the pressure decay rate is measured by a calibrated gas flow standard. 4 . The electronic device manufacturing system of claim 1 , wherein the flow restrictor is at least one of a drilled flow restrictor or a porous medium flow restrictor.

5. The electronic device manufacturing system of claim 1, further comprising a valve coupled between the control volume and the restrictor, the valve operable by the controller to cause a pressure buildup in the control volume.

6. The electronic device manufacturing system of claim 1, further comprising a second volume coupleable to the control volume and operable by the controller to increase pressure in the control volume by supplying pressurized gas to the control volume.

7. The electronic device manufacturing system as claimed in claim 6, further comprising: a first valve for coupling the second volume to the inlet; and A second valve is provided for coupling the second volume to the control volume.

8. The electronic device manufacturing system of claim 1 , wherein the process chamber is used to perform one or more of the following items within the process chamber: a reduced pressure chemical vapor deposition process, a reduced pressure epitaxial process, or at least one of the following items: deposition, oxidation, nitration, etching, polishing, cleaning, or lithography process.

9. A method for calibrating a mass flow controller, the method comprising the following steps: flowing a gas from a gas source at a steady pressure measured in a control volume through a calibrated flow standard, the control volume, and a flow restrictor, wherein the flow restrictor is coupled in series and directly to the control volume and to an outlet; terminating the flow of the gas from the gas source; measuring a first gas pressure decay rate in the control volume; replacing the calibrated flow standard with the mass flow controller; causing the gas to flow from the gas source through the mass flow controller, the control volume, and the restrictor at a steady pressure measured in the control volume; terminating the flow of the gas from the gas source; and For purposes of calibrating the mass flow controller, a second gas pressure decay rate in the control volume is measured.

10. The method of claim 9, further comprising determining an error of the mass flow controller by: calculating a volume of the control volume based on the first gas pressure decay rate; determining an actual mass flow rate using the calculated volume based on the second gas pressure decay rate; and The actual mass flow rate is compared to a set point of the mass flow controller.

11. The method of claim 10, further comprising the steps of: Based on the determined error of the mass flow controller, the mass flow controller is calibrated.

12. The method of claim 9, further comprising the steps of: Prior to measuring the first gas pressure decay rate and the second gas pressure decay rate, the stabilized pressure in the control volume is increased.

13. A non-transitory computer-readable storage medium, wherein computer-readable instructions are stored on the non-transitory computer-readable storage medium, wherein when a processor executes the computer-readable instructions, the computer-readable instructions cause the processor to perform the method of claim 9.

14. A system comprising: an inlet, the inlet coupled to the mass flow controller, the mass flow controller coupled to a gas source; exit; a control volume coupled in series to the inlet to receive a gas flow from the gas source; a flow restrictor coupled in series and directly to the control volume and to the outlet; and a controller adapted to allow the gas source to flow gas through the control volume and the restrictor to reach a stable pressure in the control volume, terminate the gas flow from the gas source, and measure the rate of pressure decay in the control volume over time to calibrate the mass flow controller.

15. The system of claim 14, further comprising a valve coupled between the inlet and the control volume, wherein the valve is operable by the controller to terminate the flow of the gas from the gas source.

16. The system of claim 14, wherein the controller is further configured to determine an error in the mass flow controller by comparing a set point of the mass flow controller to an actual mass flow rate calculated based on a volume of the control volume, wherein the volume is determined based on a rate of pressure decay in the control volume over time, the pressure decay rate being measured by a calibrated gas flow standard.

17. The system of claim 14, wherein the flow restrictor is at least one of a drilled flow restrictor or a porous media flow restrictor.

18. The system of claim 14, further comprising a valve coupled between the control volume and the restrictor, the valve operable by the controller to cause a pressure buildup in the control volume.

19. The system of claim 14, further comprising a second volume coupleable to the control volume and operable by the controller to increase pressure in the control volume by supplying pressurized gas to the control volume.

20. The system of claim 19, further comprising: a first valve for coupling the second volume to the inlet; and A second valve is provided for coupling the second volume to the control volume.

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