Method and apparatus for pressure-based mass flow control - Patents.com

Abstract

A mass flow controller is provided that can improve bleed times and can be manufactured with reduced complexity and cost. The mass flow controller includes a body having a valve outlet lumen defining a flow path, and an adjustable valve configured to control a flow of gas through the flow path. A valve element includes an adjustable valve outlet orifice and is disposed within the lumen. The mass flow controller further includes a pressure drop element disposed within the lumen and coaxially with the valve element. An upstream pressure sensor is configured to detect a pressure at a location within the flow path between the adjustable valve and the pressure drop element, and a controller is configured to determine a flow rate through the flow path based on the pressure detected by the upstream pressure sensor.

Description

Related Applications

[0001] This application is a continuation of U.S. Application No. 17 / 651,751, filed February 18, 2022, the entire teachings of which are incorporated herein by reference. [Background technology]

[0002] Semiconductor manufacturing processes can involve the delivery of multiple different gases and gas mixtures in varying amounts throughout several processing steps. Typically, 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 a processing tool (e.g., chemical vapor deposition reactor, vacuum sputtering machine, plasma etcher, etc.). Other components (e.g., valves, pressure regulators, mass flow controllers (MFCs), mass flow ratio controllers (FRCs), mass flow meters (MFMs), mass flow verifiers (MFVs), etc.) can 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 accurate delivery of process gases.

[0003] A conventional pressure-based mass flow controller (PBMFC) includes a flow control valve and a pressure drop element, such as a flow nozzle, laminar flow element, or a porous media flow restrictor. The MFC can measure the flow rate using one pressure sensor if a flow nozzle is used and the flow is under critical flow conditions, or two pressure sensors under non-critical flow conditions. If a laminar flow element or a porous media flow restrictor is used as the pressure drop element, two pressure sensors are used to measure the flow rate. Summary of the Invention

[0004] An improvement to pressure-based mass flow controllers is provided. The improved mass flow controller can reduce dead volume in the device, shorten bleeding time when valves are closed, and can be manufactured with reduced complexity and cost.

[0005] The mass flow controller includes a body having a valve outlet lumen defining a flow path and an adjustable valve configured to control a flow of gas through the flow path. A valve element includes an adjustable valve outlet orifice and is disposed within the lumen. The mass flow controller further includes a pressure drop element disposed coaxially with the valve element within the lumen. An upstream pressure sensor is configured to detect a pressure at a location within the flow path between the adjustable valve and the pressure drop element, and a controller is configured to determine a flow rate through the flow path based on the pressure detected by the upstream pressure sensor.

[0006] The pressure drop element may be adjacent to the exit orifice within the lumen, may be a minimal distance within the lumen relative to the exit orifice, or a combination thereof. For example, the volume between the pressure drop element and the exit orifice within the lumen may be less than about 0.05 cm. 3 The lumen can be substantially perpendicular to a surface of the body to which the adjustable valve is attached. The pressure drop element can be or include a flow nozzle, a laminar flow element, a porous media flow restrictor, or a combination thereof.

[0007] The body can further define a pressure measurement conduit extending from a location in the flow path between the adjustable valve and the pressure drop element to a surface of the body. For example, the pressure measurement conduit can extend laterally from the lumen to a surface of the body where the upstream pressure sensor is mounted.

[0008] The mass flow controller can further include a downstream pressure sensor configured to detect a pressure downstream of the pressure drop element, and the controller can be further configured to determine the flow rate based on the pressure detected by the downstream pressure sensor.

[0009] The body can further include a controller inlet lumen and a controller outlet lumen, the valve outlet lumen being disposed generally transverse to at least one of the controller inlet lumen and the controller outlet lumen. A valve actuator of the adjustable valve can actuate a valve member (e.g., a valve plug or armature) in a direction coaxial with the valve outlet lumen.

[0010] The mass flow controller can include a body defining a flow path and an adjustable valve configured to control a flow of gas through the flow path. The adjustable valve includes a pressure drop element disposed within an outlet orifice of the valve. The mass flow controller further includes an upstream pressure sensor configured to sense a pressure at a location within the flow path between an armature of the adjustable valve and the pressure drop element. A controller of the apparatus is configured to determine a flow rate through the flow path based on the pressure sensed by the upstream pressure sensor.

[0011] The outlet orifice valve can include a body defining a pressure measurement conduit disposed upstream of the pressure drop element. The pressure measurement conduit of the mass flow controller body can be in fluid communication with the pressure measurement conduit of the outlet orifice.

[0012] The mass flow controller can further include a downstream pressure sensor configured to detect a pressure downstream of the pressure drop element, and the controller can be further configured to determine the flow rate based on the pressure detected by the downstream pressure sensor.

[0013] The pressure drop element can be or include a flow nozzle, a laminar flow element, a porous media flow restrictor, or a combination thereof. A retainer can be disposed within the exit orifice and configured to retain the pressure drop element. For example, the retainer can be configured to retain the porous media of the porous media flow restrictor.

[0014] The body defining the flow passage can include a valve outlet lumen in which a valve element including an outlet orifice of the adjustable valve can be disposed. The body can further include a controller inlet lumen and a controller outlet lumen, the valve outlet lumen being disposed generally transverse to at least one of the controller inlet lumen and the controller outlet lumen. A linear valve actuator of the adjustable valve can actuate the valve member in a direction coaxial with the valve outlet lumen.

[0015] A method of assembling a mass flow controller includes disposing a pressure drop element and a valve element including an outlet orifice of an adjustable valve substantially coaxially within a body defining a flow path. The adjustable valve is configured to control a flow of gas through the flow path. The method further includes disposing an upstream pressure sensor in a pressure measurement conduit extending from the flow path to a surface of the body.

[0016] The pressure reduction element can be located within the bore adjacent to the exit orifice, a minimum distance within the bore relative to the exit orifice, or a combination thereof. The pressure reduction element and the exit orifice of the adjustable valve can be integral. [Brief description of the drawings]

[0017] The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views, and in which the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the embodiments. [Figure 1]FIG. 1 is a schematic diagram of a prior art pressure-based mass flow controller. [Diagram 2] 2 is a graph showing an example of a response of the mass flow controller shown in FIG. 1. [Diagram 3] FIG. 1 is a schematic diagram of an example of a pressure-based mass flow controller. [Figure 4] FIG. 2 is a schematic diagram of another example of a pressure-based mass flow controller. [Figure 5A] 5 is a cross-sectional perspective view of an example pressure reduction element for inclusion in the device of FIG. 4. [Figure 5B] 5 is a cross-sectional view of an example of a flow nozzle for inclusion as a pressure drop element in the device of FIG. 4. [Figure 5C] 5 is a cross-sectional view of another example of a flow nozzle for inclusion as a pressure drop element in the device of FIG. 4. [Figure 6A] 5A-5C are cross-sectional views of example porous media elements for inclusion as pressure drop elements in the device of FIG. [Figure 6B] 5 is a cross-sectional view of another example of a porous media element for inclusion as a pressure drop element in the device of FIG. 4. [Figure 7A] 5A-5C are cross-sectional views of example laminar flow elements for inclusion as pressure drop elements in the device of FIG. 4. [Figure 7B] 5 is a cross-sectional view of another example of a laminar flow element for inclusion as a pressure drop element in the device of FIG. 4. [Figure 8] 5 is a graph showing an example of a response of a mass flow controller having the configuration shown in FIG. 3 or FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Example embodiments are described below.

[0019] In pressure-based mass flow control, the mass flow rate can be measured by a pressure sensor and a temperature sensor with a critical flow nozzle under critical flow conditions, or by two pressure sensors and a temperature sensor under non-critical flow conditions. Using either approach, the pressure upstream of the flow nozzle is typically obtained and used in the flow calculation. Flow calculations for pressure-based mass flow control are generally known in the art.

[0020] A prior art pressure-based mass flow controller (PBMFC) is shown in FIG. The PBMFC 100 includes a body 110 to which a control valve 120 is attached. The control valve includes a valve actuator 122 and a valve member 124 (e.g., a valve plug or armature). As illustrated, a valve element 126 including an outlet orifice 128 of the control valve is disposed within a bore 146 of the flow body 110. However, the valve element 126 may alternatively be sealed to the flow body 110. The PBMFC further includes a pressure drop element, such as a flow nozzle 150, with an upstream pressure sensor 160 and a downstream pressure sensor 162 disposed upstream and downstream of the flow nozzle 150, respectively. A control processor 170 may be configured to operate the control valve 120 to adjustably control the flow of fluid through the device, obtain pressure measurements from the pressure sensors 160 and 162, and obtain temperature measurements from a temperature sensor (not shown in FIG. 1). The flow body includes several lumens 132, 134, 136, 146, 144, and 142 through which fluid may flow.

[0021] Residual gas in the dead volume (Vd) between the exit orifice 126 of the control valve 120 and the flow nozzle 150 (i.e., the bores 146 and 144) can escape when the control valve 120 is closed. bleeding ) can be calculated by: where Cr is the conductance of the flow nozzle.

[0022] t bleeding=4*(Vd / Cr) (1)

[0023] For low flow applications (e.g., full-scale flow rates <100 sccm), the conductance (Cr) of the flow nozzle is also typically small, which can result in long bleeding times when the valve is closed. As shown in the example response illustrated in Figure 2, with a dead volume of about 10 cc, the bleeding time can be about 120 seconds from valve closure, which can result in a significant amount of fluid flow into the process chamber after the zero set point is provided.

[0024] During manufacture of the device shown in FIG. 1, the flow body 110 is first machined to include lumens 132, 134, 136, 146, 144, and 142. The flow nozzle 150 is then inserted through the opening 140 at the end of the flow body and installed within the lumen 144. After placement of the flow nozzle, the flow body returns to the machining process and a metal plug is inserted into the lumen 144 at the opening 140 to cap the open end of the body, as shown in dashed lines. The metal plug can then be welded to the flow body surface and polished. The device then returns to the assembly line for further assembly, such as attaching pressure sensors and constructing control valves. The manufacturing costs of the PBMFC shown in FIG. 1 are high due to the repeated machining and assembly process and to ensure that the flow nozzle is not adversely affected during the plugging process. Because the flow nozzle provides a precise, small sized opening, exposure to dust and other particles during machining can have significant adverse effects by blocking or partially blocking the nozzle orifice. Typically, the assembly steps of MFCs are performed in a clean room, ensuring that the assembly is in a particle-free environment.

[0025] To overcome the problems associated with bleeding time and manufacturing process, an improved PBMFC is provided in which a pressure drop element (e.g., a flow nozzle) is located within the same bore as the outlet orifice of the flow control valve.

[0026] An example mass flow controller is shown in FIG. 3. The MFC 200 includes a body 210 having a valve outlet bore 246. An adjustable control valve 220 is configured to control the flow of a fluid (e.g., gas) through a flow path defined at least in part by the bore 246. A valve element 226 including an outlet orifice 228 is disposed within the bore 246. A pressure drop element 250 (shown as a flow nozzle) is disposed coaxially with the valve element 226 within the bore 246. The MFC further includes at least one pressure sensor, specifically an upstream pressure sensor 260, configured to detect a pressure at a location in the flow path between the adjustable valve 220 and the pressure drop element 250. Optionally, a downstream pressure sensor 262 is included and configured to detect a pressure at a location downstream of the pressure drop element 250. A control processor 270 can be configured to determine a flow rate through the flow path based on the pressure detected by the upstream pressure sensor 260 (and optionally the downstream pressure sensor 262). The control processor 270 may be further configured to control the opening and closing of the adjustable valve 220 .

[0027] The control processor 270, adjustable control valve 220, and pressure sensors 260, 262 may be disposed within a housing 290 that is attached to the body 210. A temperature sensor 280 may be included within the housing or body and may be configured to detect the temperature of the fluid traveling through the flow path.

[0028] 3, the pressure drop element 250 can be positioned within the lumen 246 adjacent to the exit orifice 228. The pressure drop element can be positioned within the lumen a minimal distance (e.g., about 0.05 cm) to the exit orifice. 3The minimum distance may be, for example, a distance that allows for coupling of the pressure sensor to the volume between the exit orifice and the pressure drop element. The body 210 may define pressure measurement conduit(s) 238, 248 to fluidly couple the pressure sensor(s) 260, 262 to respective measurement points within the lumen 246.

[0029] The lumen 246 may be substantially perpendicular to the surface 212 of the body 210 to which the adjustable valve 220 is mounted. The pressure measurement conduit(s) 238, 248 may extend laterally from the lumen 246 to the surface 212, where the pressure sensor(s) 260, 262 may be mounted.

[0030] The body 210 may further include a controller inlet lumen 234 and a controller outlet lumen 244, with a valve outlet lumen 246 disposed generally transverse to the controller inlet and controller outlet lumen. Optionally, additional lumens 232, 242 may be included to provide device inlets and outlets at the surface 214 opposite the body surface 212, and a lumen 236 may be included to connect the controller inlet lumen 234 to the control valve 220.

[0031] The adjustable control valve 220 may include a valve actuator 222 that actuates a valve member 224 (eg, a valve plug or armature) in a direction coaxial with the valve outlet bore 246 .

[0032] As used herein, the term "adjustable control valve" refers to a valve that can provide a controllable range of openings and excludes on / off type valves. The openness of an adjustable control valve can be controlled in response to a control signal, thereby controlling the flow rate through the valve. An adjustable control valve can alternatively be referred to as a proportional control valve.

[0033] Examples of control valves suitable for use as adjustable control valves in the provided devices include solenoid valves, piezoelectric valves, and step motor valves.

[0034] As previously described with respect to FIG. 1, a mass flow controller typically includes one adjustable control valve for controlling the flow of fluid through the system. Typically, the adjustable control valve and pressure sensor are mounted on one surface of a body that defines a flow path through the system. Optionally, additional valves (e.g., on / off valves) can be included in the system to isolate a portion of the flow path through the system. Such additional valves increase the size and cost of the device. In addition to having an on / off valve as an additional element of the device, such devices typically require the body to define a more circuitous or complex flow path than that shown in FIG. 3. An advantage of the configuration shown in FIG. 3 is that a reduction in dead volume (occurring in the portion of the flow path following the position of the adjustable control valve) can be achieved without including additional valves (e.g., on / off valves) and without having to define a more complex flow path within the body of the device.

[0035] By mounting the adjustable control valve to the surface of the body such that the valve member can be actuated in a direction coaxial with the valve outlet bore, and by including a coaxially disposed pressure drop element within the same bore, a flow path can be achieved that is significantly shorter and easier to manufacture than prior art devices.

[0036] Another example mass flow controller is shown in FIG. 4. FIG. 4 includes several elements similar to those shown in FIG. 3 and labeled with similar numbering. The MFC 300 includes a body 310 defining a flow path (e.g., including a valve outlet lumen 246) and an adjustable valve 220 configured to control a flow of gas through the flow path. The adjustable valve 220 includes a pressure drop element 350 disposed within an outlet orifice 328 of the valve. An upstream pressure sensor 260 is configured to detect a pressure at a location within the flow path between a valve member 224 (e.g., a valve plug or armature) of the adjustable valve and the pressure drop element 350. A controller 270 can be configured to determine a flow rate through the flow path based on the pressure detected by the upstream pressure sensor 260 (and optionally, the downstream pressure sensor 262).

[0037] The exit orifice 328 may include a body 352 that defines a pressure measurement conduit 354 disposed upstream of the pressure drop element 350 or a portion 356 of the pressure drop element that provides the pressure drop (e.g., a narrow nozzle portion). The body 310 may define a pressure measurement conduit 338 in fluid communication with the exit orifice pressure measurement conduit 354. As illustrated, the pressure measurement conduit may extend laterally from the exit orifice 328 to the surface 212 to which the pressure sensor 260 is mounted.

[0038] The pressure drop element 250, 350 can be or include a flow nozzle, a laminar flow element, and a porous media flow restrictor. When included within the outlet orifice of the adjustable valve, a retainer (e.g., sleeve 455, FIG. 6B) can be disposed within the outlet orifice and configured to retain the porous media.

[0039] Examples of suitable flow nozzles include conical flow nozzles, tapered flow nozzles, and plates with orifice(s). Examples of suitable laminar flow elements include annular elements, corrugated elements, single tubes, and bundled tubes. Examples of suitable porous media flow restrictors include porous sintered metal filters and porous ceramic filters.

[0040] Example configurations of pressure drop elements for inclusion within an outlet orifice of an adjustable valve are shown in Figures 5A-7B. As shown in Figure 5A, pressure drop element 350 can be or include a flow nozzle, with body 352 defining both a nozzle 356 and a pressure measurement conduit that allows fluid communication with a pressure sensor to a location upstream of nozzle 356. Further example configurations of flow nozzle type pressure drop elements are shown in Figures 5B and 5C. In Figures 5B and 5C, pressure measurement conduit 354 is defined in the tapered wall 358 of the nozzle (Figure 5B) or in the transition between straight portion 357 and tapered portion 359 of the nozzle wall (Figure 5C).

[0041] Example configurations of porous media type pressure drop elements are shown in Figures 6A and 6B. Body 452 can define a pressure measurement conduit in a straight section 457 (Figure 6A) of a receptacle configured to hold porous media 456, or in a tapered section 459 (Figure 6B) disposed upstream of porous media 456. A retaining portion 455 (e.g., a sleeve) can be configured to hold the porous media within the element.

[0042] Example configurations of laminar flow type pressure drop elements are shown in Figures 7A and 7B. Body 552 can define a pressure measurement conduit 554 in a straight section 557 (Figure 7A) of the wall of laminar flow element 556, or in a tapered section 559 (Figure 7B) of the wall of laminar flow element 556. The annular portion between body 552 and plug 558 forms the laminar flow path.

[0043] An example bleed time response for the MFC discussed above and shown in Figures 3 and 4 is shown in Figure 8. For example, if the dead volume is about 0.25 cc, the bleed time can be about 5 seconds from valve closure, and if the dead volume is about 0.52 cc, the bleed time can be about 15 seconds from valve closure. The estimated bleed times are a significant improvement over the bleed times associated with the prior art MFC shown in Figure 1.

[0044] Additionally, the provided MFC configuration significantly reduces manufacturing complexity and cost: the pressure drop elements of the MFC can be placed within the body of the device without the need for additional machining steps.

[0045] A method of assembling an MFC includes disposing a pressure drop element and a valve element including an outlet orifice of an adjustable valve substantially coaxially within a body defining a flow path. For example, the pressure drop element can be disposed adjacent to the outlet orifice within the bore, or the pressure drop element and the outlet orifice of the adjustable valve can be integral. The method further includes disposing an upstream pressure sensor in a pressure measurement conduit extending from the flow path to a surface of the body.

[0046] The MFC's control processor 270 can be configured to control the flow of gas through the flow passage based on the flow rate determined from pressure and temperature readings. Methods for determining flow rate using an upstream pressure sensor (e.g., sensor 260) under critical flow conditions and using both upstream and downstream pressure sensors (e.g., sensors 260, 262) under non-critical flow conditions are generally known in the art. An example method for determining mass flow rate under choked and non-choked flow conditions is described in U.S. Patent No. 10,514,712, the teachings of which are incorporated herein in their entirety.

[0047] The teachings of all patents, published applications, and references cited herein are incorporated by reference in their entirety.

[0048] While exemplary embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the embodiments encompassed by the appended claims.

Claims

1. A mass flow controller, a body having a valve outlet lumen defining a flow path; an adjustable valve configured to control a flow of gas through the flow passage; and a valve element including an outlet orifice of the adjustable valve, the valve element being disposed within the lumen; a pressure reduction element disposed within the bore and coaxially with the valve element; an upstream pressure sensor configured to sense a pressure at a location in the flow path between the adjustable valve and the pressure drop element; a controller configured to determine a flow rate through the flow path based on the pressure detected by the upstream pressure sensor.

2. 2. The mass flow controller of claim 1, wherein the pressure drop element is within the bore adjacent the exit orifice.

3. 2. The mass flow controller of claim 1, wherein the pressure drop element is positioned a minimal distance within the bore relative to the exit orifice.

4. The volume within the bore between the pressure drop element and the exit orifice is about 0.05 cm ３ 2. The mass flow controller of claim 1 , wherein

5. The mass flow controller of claim 1 , wherein the bore is substantially perpendicular to a surface of the body to which the adjustable valve is mounted.

6. The mass flow controller of claim 1 , wherein the body further defines a pressure measurement conduit extending from the location in the flow path between the adjustable valve and the pressure drop element to a surface of the body.

7. 7. The mass flow controller of claim 6, wherein the pressure measurement conduit extends laterally from the bore to a surface of the body on which the upstream pressure sensor is mounted.

8. 2. The mass flow controller of claim 1, further comprising a downstream pressure sensor configured to detect a pressure downstream of the pressure drop element, the controller further configured to determine the flow rate based on the pressure detected by the downstream pressure sensor.

9. 2. The mass flow controller of claim 1, wherein the pressure drop element is a flow nozzle.

10. 2. The mass flow controller of claim 1, wherein the pressure drop element is a laminar flow element.

11. 2. The mass flow controller of claim 1, wherein the pressure drop element is a porous media flow restrictor.

12. 2. The mass flow controller of claim 1, wherein the body further comprises a controller inlet lumen and a controller outlet lumen, the valve outlet lumen being disposed generally transverse to at least one of the controller inlet lumen and the controller outlet lumen.

13. 2. The mass flow controller of claim 1, wherein a valve actuator of the adjustable valve drives a valve member in a direction coaxial with the valve outlet bore.

14. A mass flow controller, a body defining a flow path; an adjustable valve configured to control a flow of gas through the flow passage, the adjustable valve including a pressure drop element disposed within an exit orifice of the valve; an upstream pressure sensor configured to sense a pressure at a location in the flow path between the armature of the adjustable valve and the pressure drop element; a controller configured to determine a flow rate through the flow path based on the pressure detected by the upstream pressure sensor.

15. The mass flow controller of claim 14 , wherein the outlet orifice of the valve includes a body defining a pressure measurement conduit disposed upstream of the pressure drop element.

16. 16. The mass flow controller of claim 15, wherein the body defining the flow passage further defines a pressure measurement conduit in fluid communication with the pressure measurement conduit of the exit orifice.

17. 15. The mass flow controller of claim 14, further comprising a downstream pressure sensor configured to sense a pressure downstream of the pressure drop element, the controller further configured to determine the flow rate based on the pressure sensed by the downstream pressure sensor.

18. 15. The mass flow controller of claim 14, wherein the pressure drop element is a flow nozzle.

19. 15. The mass flow controller of claim 14, wherein the pressure drop element is a laminar flow element.

20. 15. The mass flow controller of claim 14, wherein the pressure drop element is a porous media flow restrictor.

21. The mass flow controller of claim 14 , further comprising a retainer disposed within the exit orifice and configured to retain the pressure drop element.

22. 15. The mass flow controller of claim 14, wherein the body defining the flow passage includes a valve outlet bore, and a valve element includes the outlet orifice of the adjustable valve disposed within the valve outlet bore.

23. 15. The mass flow controller of claim 14, wherein the body further comprises a controller inlet lumen and a controller outlet lumen, the valve outlet lumen being disposed generally transversely to at least one of the controller inlet lumen and the controller outlet lumen.

24. 15. The mass flow controller of claim 14, wherein the linear valve actuator of the adjustable valve drives a valve member in a direction coaxial with the valve outlet bore.

25. 1. A method for assembling a mass flow controller, comprising: disposing substantially coaxially within a body defining a flow passage a pressure drop element and a valve element including an adjustable valve outlet orifice configured to control flow of gas through said flow passage; and disposing an upstream pressure sensor in a pressure measurement conduit extending from the flow passage to a surface of the body.

26. 26. The method of claim 25, wherein the pressure drop element is disposed within the bore adjacent the exit orifice.

27. 26. The method of claim 25, wherein the pressure drop element is positioned a minimal distance within the bore relative to the exit orifice.

28. 26. The method of claim 25, wherein the pressure drop element and the outlet orifice of the adjustable valve are integral.

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