Laminar flow restrictor

Abstract

Devices for controlling gas flow are important components for delivering process gases used in semiconductor manufacturing. These devices for controlling gas flow often rely on flow restrictors that can provide a known flow impedance for the process gas. In one embodiment, a flow restrictor is disclosed that is composed of multiple layers, where one or more of the layers have a flow channel extending from a first hole at a first end of the flow restrictor to a second hole located at a second end of the flow restrictor.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 882,794, filed on August 5, 2019, the entire content of which is incorporated herein by reference. Background Art

[0003] Mass flow control has been one of the key technologies in semiconductor chip manufacturing. Devices for controlling mass flow are important for providing known flow rates of process gases for semiconductor manufacturing and other industrial processes. Such devices are used to measure and accurately control fluid flow for various applications. This control can be achieved by using precisely calibrated laminar flow restrictors.

[0004] As chip manufacturing technology has advanced, the demand for flow control devices has also increased. Semiconductor manufacturing processes increasingly require improved performance, including more accurate measurements, lower equipment costs, improved transient response times, and better consistency in gas delivery times. To improve the consistency of gas delivery, improvements to the flow restrictor are needed. Summary of the Invention

[0005] The technology relates to a laminar flow restrictor for a mass flow controller or other gas delivery device. One or more of these gas delivery devices can be used in a wide range of processes, such as semiconductor chip manufacturing, solar panel manufacturing, etc.

[0006] In one embodiment, the present invention is a flow restrictor for restricting gas flow. The flow restrictor has a first end, a second end, and a longitudinal axis extending from the first end to the second end. A plurality of first layers extend from the first end to the second end along the longitudinal axis. A plurality of second layers extend from the first end to the second end along the longitudinal axis. A first hole at the first end is defined by the plurality of first layers and the plurality of second layers. A second hole at the second end is defined by the plurality of first layers and the plurality of second layers. A flow channel is defined by the plurality of first layers and the plurality of second layers, and the flow channel extends from the first hole to the second hole.

[0007] In another embodiment, the present invention is a mass flow control device for delivering a fluid. The mass flow control device has a valve that includes an inlet channel, an outlet channel, a valve seat, and a closing member. The mass flow control device also has a flow restrictor located in one of the inlet channel or the outlet channel. The flow restrictor has a first end, a second end, and a longitudinal axis extending from the first end to the second end. A plurality of layers extend substantially parallel to the longitudinal axis. A first hole is located at the first end and a second hole is located at the second end. A flow channel is defined by the plurality of layers, and the flow channel is fluidly coupled to the first hole and the second hole.

[0008] In yet another embodiment, the present invention is a method of manufacturing a flow limiter. First, a plurality of layer blanks are provided, the layer blanks having a first edge, a second edge opposite the first edge, a third edge, a fourth edge opposite the third edge, a front face, and a back face opposite the front face. A first cavity is formed in the front face of the first layer blank of the plurality of layer blanks. The plurality of layer blanks are stacked. Subsequently, the plurality of layer blanks are joined to form a resistor stack having a first untrimmed end and an opposite second untrimmed end. The first untrimmed end of the resistor stack is formed by the first edge of the plurality of layer blanks, and the second untrimmed end of the resistor stack is formed by the second edge of the plurality of layer blanks. Finally, material is removed from the first untrimmed end of the layer blanks to expose the first cavity and form a first hole.

[0009] Other applications of the present technology will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments, are intended for purposes of illustration only and are not intended to limit the scope of the present technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention of the present disclosure will be more fully understood from the detailed description and the drawings, in which:

[0011] Figure 1 is a schematic diagram of a process using one or more laminar flow limiters.

[0012] Figure 2 is a schematic diagram of a mass flow controller that can be used in the Figure 1 process.

[0013] Figure 3 is a perspective view of a first embodiment of a laminar flow limiter of a mass flow controller that can be used for Figure 2

[0014] Figure 4 is an illustration of a perspective view of a part of a layer forming the Figure 3 flow limiter.

[0015] Figure 5A is Figure 4 an end view of a part of the flow limiter.

[0016] Figure 5B is Figure 5A a detailed view of region VB of

[0017] Figure 6 is Figure 4 an exploded perspective view of a part of the flow limiter.

[0018] Figure 7 is Figure 4 ​Cross-sectional view of a part of the flow limiter taken along VII-VII of the line.

[0019] Figure 8 is Figure 3 Top view of the first layer of the flow limiter.

[0020] Figure 9 is Figure 3 Top view of the second layer of the flow limiter.

[0021] Figure 10 Isometric view of the second embodiment of the laminar flow limiter.

[0022] Figure 11 is to illustrate the formation of Figure 10 Isometric view of a part of the layer of the flow limiter.

[0023] Figure 12A is Figure 11 End view of a part of the flow limiter.

[0024] Figure 12B is Figure 12A Detailed view of area XIIB.

[0025] Figure 13 is Figure 11 Exploded isometric view of a part of the flow limiter.

[0026] Figure 14 is Figure 11 Cross-sectional view of a part of the flow limiter taken along XIV-XIV of the line.

[0027] Figure 15 is Figure 10 Top view of the first layer of the flow limiter.

[0028] Figure 16 is Figure 10 Top view of the second layer of the flow limiter.

[0029] Figure 17 Isometric view of a part of the third embodiment of the laminar flow limiter.

[0030] Figure 18 is Figure 17 End view of a part of the flow limiter.

[0031] Figure 19 is Figure 17 Exploded isometric view of a part of the flow limiter.

[0032] Figure 20 is Figure 17 Cross-sectional view of a part of the flow limiter taken along XX-XX of the line.

[0033] Figure 21 is Figure 17 The top view of the first layer of the flow limiter of

[0034] Figure 22 is Figure 17 The top view of the second layer of the flow limiter of

[0035] Figure 23 The perspective view of a part of the fourth embodiment of the laminar flow limiter.

[0036] Figure 24 is Figure 23 The end view of a part of the flow limiter of

[0037] Figure 25 is Figure 23 The exploded perspective view of a part of the flow limiter of

[0038] Figure 26 is Figure 23 The cross-sectional view of a part of the flow limiter taken along line XXVI-XXVI of

[0039] Figure 27 is Figure 23 The top view of the first layer of the flow limiter of

[0040] Figure 28 is Figure 23 The top view of the second layer of the flow limiter of

[0041] Figure 29 is Figure 23 The top view of the third layer of the flow limiter of

[0042] Figure 30 The perspective view of the fifth embodiment of the laminar flow limiter.

[0043] Figure 31 is to illustrate the formation of Figure 30 The perspective view of a part of the layer of the flow limiter of

[0044] Figure 32 is Figure 31 The end view of a part of the flow limiter of

[0045] Figure 33 is Figure 31 The exploded perspective view of a part of the flow limiter of

[0046] Figure 34 is Figure 31 The cross-sectional view of a part of the flow limiter taken along line XXXIV-XXXIV of

[0047] Figure 35 isFigure 31 Top view of the first layer of the flow limiter.

[0048] Figure 36 Is Figure 31 Top view of the second layer of the flow limiter.

[0049] Figure 37 Exploded perspective view of multiple layer blanks, showing the method of manufacturing the disclosed flow limiter.

[0050] Figure 38 Is Figure 37 Top view of the first layer of the present invention.

[0051] Figure 39 Is Figure 37 Top view of the second layer of the present invention.

[0052] Figure 40 Is according to Figure 37 Perspective view of the impedance stack of the present invention before trimming.

[0053] Figure 41 Is according to Figure 37 Perspective view of the impedance stack of the present invention after trimming. Detailed Description

[0054] The description of illustrative embodiments in accordance with the principles of the present invention is intended to be read in conjunction with the accompanying drawings, which are considered to be a part of the entire written description. In the description of the embodiments of the present invention disclosed herein, any reference to direction or orientation is for convenience of description only and is not intended to limit the scope of the present invention in any way. Relative terms, such as "lower", "upper", "horizontal", "vertical", "above", "below", "upward", "downward", "left", "right", "top" and "bottom" and their derivatives (e.g., "horizontally", "downwardly", "upwardly", etc.) should be interpreted to refer to the orientation as subsequently described or as shown in the drawings under discussion. These relative terms are for convenience of description only and do not require the device to be constructed or operated in a particular orientation unless explicitly stated. Terms such as "attached", "fixed", "connected", "coupled", "interconnected" and similar terms refer to a relationship in which structures are directly or indirectly fixed or attached to each other through intervening structures, and both movable or rigid attachments or relationships, unless otherwise explicitly stated. In addition, the features and advantages of the present invention are illustrated by reference to the preferred embodiments. Therefore, the present invention is expressly not limited to such preferred embodiments, which illustrate some possible non-limiting combinations of features that may exist alone or in other combinations of features; the scope of the present invention is defined by the appended claims.

[0055] The present invention relates to a laminar flow restrictor in a device for controlling gas flow. In some embodiments, the device can be used as a mass flow controller to deliver a gas of known mass flow rate to a semiconductor or similar process. Semiconductor manufacturing is an industry that requires high-performance control of gas flow. With the advancement of semiconductor manufacturing technology, customers have recognized the need for flow control devices with higher accuracy and repeatability in the quality of the delivered gas flow. Modern semiconductor processes require strict control of the quality of the gas flow, minimization of response time, and highly accurate gas flow. The present invention improves the accuracy and repeatability of the delivered flow rate.

[0056] Figure 1 FIG. shows a schematic diagram of an exemplary processing system 1000 that uses one or more laminar flow restrictors. The processing system 1000 can utilize a plurality of flow control devices 100 that are fluidly coupled to a processing chamber 1300. The plurality of flow control devices 100 are used to supply one or more different process gases to the processing chamber 1300. Articles such as semiconductors can be processed within the processing chamber 1300. A valve 1100 isolates each flow control device 100 from the processing chamber 1300 such that each flow control device 100 can be selectively connected to or isolated from the processing chamber 1300, thereby facilitating various different processing steps. The processing chamber 1300 can include an applicator to apply the process gas delivered by the plurality of flow control devices 100, thereby enabling selective or diffusive distribution of the gas supplied by the plurality of flow control devices 100. Additionally, the processing system 1000 can also include a vacuum source 1200 that is isolated from the processing chamber 1300 by the valve 1100 to effect evacuation of the process gas or to facilitate purging of one or more of the flow control devices 100 to effect switching between process gases within the same flow control device 100. Optionally, the flow control device 100 can be a mass flow controller, a diverter, or any other device that controls the flow of process gas in a processing system. Additionally, if desired, the valve 1100 can be integrated into the flow control device 100.

[0057] Processes that can be performed in the processing system 100 can include wet cleaning, lithography, ion implantation, dry etching, atomic layer etching, wet etching, plasma ashing, rapid thermal annealing, furnace annealing, thermal oxidation, chemical vapor deposition, atomic layer deposition, physical vapor deposition, molecular beam epitaxy, laser lift-off, electrochemical deposition, chemical mechanical polishing, wafer testing, or any other process that uses a controlled volume of process gas.

[0058] Figure 2FIG. 0 shows a schematic diagram of an exemplary mass flow controller 101, which is a device 100 for controlling flow rates that can be used in a processing system 1000. The mass flow controller 101 has a gas supply of process gas fluidly coupled to an inlet 104. The inlet is fluidly coupled to a proportional valve 120 that can vary the volume of process gas flowing through the proportional valve 120. The proportional valve 120 meters the mass flow rate of the process gas through a P1 volume 106. The proportional valve 120 can provide proportional control of the process gas such that it does not need to be fully open or closed, but can have intermediate states to allow control of the mass flow rate of the process gas.

[0059] The P1 volume 106 is fluidly coupled to the proportional valve 120 and is the sum of all volumes within the mass flow controller 101 between the proportional valve 120 and a flow limiter 160. A pressure transducer 130 is fluidly coupled to the P1 volume 106 to be able to measure the pressure within the P1 volume 106. An on / off valve 150 is located between the flow limiter 160 and the proportional valve 120 and can be used to completely stop the process gas from flowing out of the P1 volume 106. Optionally, the flow limiter 160 can be located between the on / off valve 150 and the proportional valve 120 in an alternative configuration. Finally, the flow limiter 160 is fluidly coupled to an outlet 110 of the mass flow controller 101. In a processing system, the outlet 110 is fluidly coupled to a valve 1100 or directly to a processing chamber 1300.

[0060] Inside the first on / off valve 150 are a valve seat and a closing member. When the device 100 is delivering process gas, the first on / off valve 150 is in an open state such that the valve seat and the closing member are not in contact. This allows the process gas to flow and provides a negligible restriction to fluid flow. When the first on / off valve 150 is in a closed state, the closing member and the valve seat are spring-biased into contact, thereby preventing the process gas from flowing through the first on / off valve 150.

[0061] The flow limiter 160 is used in combination with the proportional valve 120 to meter the flow rate of the process gas. In most embodiments, the flow limiter 160 provides a known restriction to fluid flow. The first characterized flow limiter 160 can be selected to have a specific flow impedance to deliver a desired range of mass flow rates of a given process gas. The flow limiter 160 has a greater flow impedance than the channels upstream and downstream of the flow limiter 160.

[0062] Optionally, the mass flow controller 101 includes one or more P2 pressure transducers downstream of the flow restrictor 160 and the on / off valve 150. The P2 pressure transducer is used to measure the pressure difference across the flow restrictor 160. In some embodiments, the P2 pressure downstream of the flow restrictor 160 can be obtained from another device 100 connected to the processing chamber, and the readings are transmitted to the mass flow controller 101.

[0063] Optionally, temperature sensors can be employed to further improve the accuracy of the mass flow controller 101. They can be mounted in the base of the mass flow controller 101 near the P1 volume 106. Additional temperature sensors can be used at various locations, including the proportional valve 120, the pressure transducer 130, and the on / off valve 150.

[0064] Turning reference Figures 3 - 9 , a first embodiment of the flow restrictor 160 is shown in more detail. The flow restrictor 160 is configured to form multiple layers of a restrictor stack 170. The restrictor stack 170 can take the form of an elongated rectangular shape as Figure 3 shown. The flow restrictor 160 extends along the longitudinal axis A-A from a first end 161 to a second end 162. Multiple layers 210 including flow channels are sandwiched between multiple outer layers 220 that do not include flow channels. The flow restrictor 160 has a first side 163 and an opposite second side 164 formed by the multiple layers 210, 220. The flow restrictor 160 also includes a front face 165 and an opposite back face 166. The outer layers 220 enclose the flow channels on opposite sides of the layers 210 that include flow channels. The thickness of the outer layers 220 can be the same as or different from the thickness of the layers 210 that include flow channels. Figure 4 The selection of the layers 210 is shown, which illustrates the portions of the flow channels and the configuration of the layers 210. Each layer 210 extends from a first end 213 to a second end 214. Multiple portions of the flow channels can be seen in Figure 4 . The details of the flow channels will be discussed in more detail below.

[0065] Turning Figure 5A and 5B, layer 210 includes a plurality of holes 212 formed at opposite ends 213, 214 of layer 210. This enables gas to flow longitudinally along layer 210 along longitudinal axis A-A from the first end 213 to the second end 214. In an alternative embodiment, the holes 212 need not be on opposite ends, but may be formed on adjacent sides or may be specifically formed on one end. The holes 212 may also be formed such that gas flows perpendicular to the shorter direction of the rectangular layer 210 along longitudinal axis A-A. Layer 210 need not be rectangular and may be square or any other desired shape. It is further contemplated that holes may be formed in the plane of layer 210, allowing gas to flow perpendicular to the plane of layer 210 and then turn and flow in the plane of layer 210. The specific arrangement of the holes 212, the shape of layer 210, and the shape of the resulting flow restrictor 160 may be adjusted as needed according to the shape of the flow channel that houses the resulting flow restrictor 160. It is even contemplated that the flow restrictor 160 may have an annular configuration, where the holes 212 are formed in the circumference of the flow restrictor 160 and / or the holes 212 are formed such that gas flows perpendicular to some or all of the planes of layer 210.

[0066] Figure 6 An exploded view of layer 210 is shown. Layer 210 includes two first layers 230 and two second layers 260. As Figure 8 and 9 best shown, the first layer 230 has a first side 231, a second side 232, a third side 233, a fourth side 234, a front face 235, and an opposite back face 236. The second layer 260 has a first side 261, a second side 262, a third side 263, a fourth side 264, a front face 265, and an opposite back face 266. The first layer 230 has a series of flow channels, including an inlet channel 237, a U-shaped channel 238, and a longitudinal channel 239. The inlet channel and the U-shaped channel are each formed only in a portion of the thickness of the first layer 230, while the longitudinal channel 239 extends through the entire thickness of the first layer 230. The second layer 260 also has an inlet channel 267 and a U-shaped channel 268 formed in the front face 265, which correspond to the inlet channel 237 and the U-shaped channel 238 of the first layer 240. When the first layer 230 and the second layer 260 are stacked face-to-face with the front faces 235, 265, the inlet channels 237, 267 form holes 212 on the first sides 231, 261 and the second sides 232, 262 of the layers 230, 260. As Figure 7 best shown, in combination with additional first layers 230 and second layers 260, a plurality of flow channels 270 are formed, which extend from the holes 212 at one end 213 of the plurality of layers 210 to the opposite second end 214 of the plurality of layers 210.

[0067] Return Figure 5A, the hole 212 has a first edge 215, a second edge 216, a third edge 217, and a fourth edge 218. The first edge 215 is formed by the first layer 230, the second edge 216 is formed by the second layer 260, and the third edge 217 and the fourth edge 218 are each formed by a portion of the first layer 230 and a portion of the second layer 260.

[0068] The flow channel 270 can vary in any desired manner to achieve a desired flow impedance. For example, the number of flow channels 270 can be increased or decreased by reducing or increasing the number of the plurality of layers 210. Additionally, the length of the flow channel 270 can be increased or decreased by changing the number of times the flow channel 270 doubles back on itself, thereby changing the final number of the U-shaped channels 238, 268, and the longitudinal channels 239. A greater or lesser number of flow channels 270 can be formed in pairs of the first layer 230 and the second layer 260. The width of the flow channel 270 can also be increased or decreased, and the thicknesses of the first layer 230 and the second layer 260 can be changed. In fact, the same thickness need not be used for each pair of the first layer 230 and the second layer 260. Each layer in the plurality of layers 210 can be varied individually to change the final flow impedance of the flow limiter 160.

[0069] The flow limiter 160 is manufactured by first etching each layer 210 individually or in an array. The layers 210 can all be formed of the same material or can be formed of different materials. The etching can be performed in a single step or a series of steps to obtain the desired plurality of depths. Alternative processes such as laser ablation, micromachining, or other known processes can also be used. Once the plurality of layers 210 have been formed, they are assembled with the unetched outer layer 220 and joined by diffusion bonding. Similarly, as is known in the art, alternative techniques such as conventional bonding using adhesives, welding, or similar processes can also be used. The resulting stack of the layers 210, 220 is joined, sealing the flow channel 270 and forming the flow limiter 160. Subsequent finishing steps can be performed to change the overall shape or dimensions of the flow limiter 160 to fit the dimensions of the flow channel in which the flow limiter 160 is to be installed. These processes can include grinding, machining, laser cutting, water jetting, or other known techniques. In fact, the flow limiter 160 need not remain rectangular and can be formed into a cylindrical shape, as will be discussed further below.

[0070] Turning Figures 10 - 16 , at Figure 10Best shows the second embodiment of the flow limiter 300. Unless otherwise specified, the reference numerals are the same as those of the first embodiment of the flow limiter 160. The second embodiment of the flow limiter 300 extends along the longitudinal axis A-A from the first end 302 to the second end 303 and is also formed by a plurality of layers 310 having flow channels and a plurality of outer layers 320 without flow channels. After bonding, the layers 310, 320 are post-processed into a cylindrical shape, which helps to insert into a cylindrical hole, enabling the flow limiter 300 to be easily installed into a valve or other flow device.

[0071] As Figure 11 shown, the selection of the layer 310 is shown in a perspective view. The layer 310 extends from the first end 313 to the second end 314 opposite the first end 313. Figure 12A and 12B Best illustrates the hole 312 formed in the first end 313 of the layer 310. It can also be seen that the layer 310 includes two first layers 330 and two second layers 360. As Figure 12B best shown, the hole 312 has a first edge 315, a second edge 316 opposite the first edge 315, a third edge 317, and a fourth edge 318 opposite the third edge 317. The first edge 315 and the second edge 316 are formed by the first layer 330. The third edge 317 and the fourth edge 318 are both formed by the second layer 360.

[0072] Figure 13 Shows an exploded view of the layer 310, better illustrating the flow channel of the flow limiter 300. Figure 15 and 16 Show the first layer 330 and the second layer 360 respectively. The first layer 330 has a first side 331, a second side 332, a third side 333, a fourth side 334, a front side 335, and an opposite back side 336. The second layer 360 has a first side 361, a second side 362, a third side 363, a fourth side 364, a front side 365, and an opposite back side 366. The first layer 330 has a series of longitudinal channels 339 terminating at the layer transition hole 340. The longitudinal channels 339 and the layer transition hole 340 extend through the entire first layer 330. The second layer 360 has notches 369 extending from the first and second sides 361, 362. The notches 369 also extend through the entire second layer 360. As best shown in Figure 14 When the layers 330, 360 are alternately stacked as shown, the hole 312 is formed by the open ends of the notches 369. As shown, the flow channel 370 is formed by the stacking of the layers 330, 360. In an alternative embodiment, the layer transition hole can be formed in a variety of shapes and can be formed with or without a flow channel profile at the end of the channel, or with a profile of a different shape.

[0073] Once again, multiple layers 330, 360 are stacked and assembled with the outer layer 320. These layers are then joined by diffusion bonding or a similar technique. The resulting impedance stack is then ground or machined into a cylindrical shape as shown in Figure 10 . The cylindrical shape also incorporates an annular groove to facilitate the installation of a seal that seals the flow restrictor 300 to the aperture of the device to ensure that the only gas passing through the flow restrictor 300 must pass through the channel 370. In other embodiments, the final component can be machined into a different shape or alternatively retain its original shape formed by the joined impedance stack.

[0074] A third embodiment of the flow restrictor 400 is shown in Figures 17 - 22 . Figure 17 A selection of the multiple layers 410 that form the flow channels of the flow restrictor 400 is shown. The outer layers are not shown in this embodiment as they are substantially the same as the outer layers of the other embodiments. The multiple layers 410 extend from a first end 413 to a second end 414 opposite the first end 413. As best shown in Figure 18 , apertures 412 are formed in the first end 413 and the second end 414 to allow gas to enter and exit the flow restrictor 400. Figure 19 An exploded view of the multiple layers 410 is shown to better illustrate the flow channels. It can be seen that the multiple layers 410 include two first layers 430 and two second layers 460.

[0075] Figure 21 and 22The first layer 430 and the second layer 460 are shown respectively. The first layer 430 has a first side 431, a second side 432, a third side 433, a fourth side 434, a front side 435, and an opposite back side 436. The second layer 460 has a first side 461, a second side 462, a third side 463, a fourth side 464, a front side 465, and an opposite back side 466. The first layer 430 has a series of longitudinal channels 439, which have an elongated configuration with straight sides and rounded corners at each end. The second layer 460 has a notch 469 that transitions from a U-shape with parallel sides to slanted sides, the width of the slanted sides increasing as they approach the first side 461 or the second side 462 of the second layer 460. When the first and second layers are aligned, the notch 469 overlaps with the longitudinal channels 439. The second layer 460 also has a D-shaped hole 468 that allows the connection of two adjacent longitudinal channels 439 to increase the effective length of the flow channel from one hole 412 to another. There is no limit to the number of D-shaped holes 468 that can be employed. Additionally, the holes 468 do not need to be limited to D-shaped; they can be of any desired shape to facilitate the connection between adjacent longitudinal channels 439. In an alternative embodiment, the shape of the notch 469 can be different. For example, shapes such as rectangular, wedge-shaped, or other shapes can be used. Furthermore, the longitudinal channels 439 can have a profile therein to improve the flow characteristics. Thus, the longitudinal channels 439 do not need to be formed with a constant width and can have a varying width at either end or anywhere along their length. In a further embodiment, a third layer (or multiple layers) can be interleaved between the first layer 430 and the second layer 460 such that each first layer 430 only contacts one second layer 460, and the holes 468 between subsequent sheets do not allow flow transition except between adjacent first layer 430 and second layer 460.

[0076] As can be best seen in Figure 20 when the layers 430, 460 are alternately stacked as shown, the holes 412 are formed by the open ends of the notches 469. As shown, the flow channel 470 is formed by the stacking of the layers 430, 460. In this embodiment, the layers 430, 460 have the same thickness, but can have different thicknesses if desired.

[0077] A fourth embodiment of the flow restrictor 500 is shown in Figures 23 - 29 which is shown. Figure 23 A selection of multiple layers 510 that form the flow channel of the flow restrictor 500 is shown. The outer layers are not shown in this embodiment as they are substantially the same as the outer layers of other embodiments. The multiple layers 510 extend from a first end 513 to a second end 514 opposite the first end 513. As Figure 24 best shown, holes 512 are formed in the first end 513 and the second end 514 to allow gas to enter and exit the flow restrictor 500.Figure 25 Shows an exploded view of multiple layers 510 to better illustrate the flow channels. It can be seen that the multiple layers 510 include a first layer 530, a second layer 560, and a third layer 580.

[0078] Figures 27 - 29 The first layer 530, the second layer 560, and the third layer 580 are shown respectively. The first layer 530 has a first side 531, a second side 532, a third side 533, a fourth side 534, a front side 535, and an opposite back side 536. The second layer 560 has a first side 561, a second side 562, a third side 563, a fourth side 564, a front side 565, and an opposite back side 566. The first layer 530 has a series of longitudinal channels 539, which have an elongated configuration with straight sides and rounded corners at each end. The second layer 560 has notches 569 that transition from a U-shape with parallel sides to sloping sides, and the width of the sloping sides increases as they approach the first side 561 or the second side 562 of the second layer 560. When the first and second layers are aligned, the notches 569 overlap with the longitudinal channels 539. The third layer 580 has a first side 581, a second side 582, a third side 583, a fourth side 584, a front side 585, and an opposite back side 586. As can be best seen in Figure 26 When the layers 530, 560 are alternately stacked as shown, the holes 512 are formed by the open ends of the notches 569. As shown, the flow channels 570 are formed by the stacking of the layers 530, 560. In this embodiment, the layers 530, 560 have the same thickness, but can have different thicknesses if desired. The third layer can be used to reduce the density of the flow channels, ensuring that the flow is more evenly distributed across the cross-section of the flow restrictor 500. This is particularly useful for producing flow restrictors with very high flow impedance.

[0079] A fifth embodiment of the flow restrictor 600 is shown in Figures 30 - 36 . Figure 30 The flow restrictor 600 is shown in a perspective view. The flow restrictor 600 extends from a first end 602 to a second end 603 and has an outer layer 620 that encloses a layer 610 with flow channels therein. The selection of the layer 610 is shown in a perspective view in Figure 31 These layers 610 extend from a first end 613 to a second end 614 and have holes 612 at the first end 613 and the second end 614. Figure 33 An exploded view of the layer 610 is shown, illustrating two first layers 630 and two second layers 660.

[0080] The first layer 630 and the second layer 660 are in Figure 35 and 36Shown in. The first layer 630 has a first side 631, a second side 632, a third side 633, a fourth side 634, a front face 635, and an opposite back face 636. The second layer 660 has a first side 661, a second side 662, a third side 663, a fourth side 664, a front side 665, and an opposite back side 666. The first layer 630 has a series of longitudinal channels 639, which have an elongated configuration and converge with the U-shaped portion 640 or the opening 641. The second layer 660 does not have any flow channels or other features. It can be seen that in the flow restrictor 600, the gas remains only on a single layer 630 and does not transition between the first layer 630 and the second layer 660. Instead, it enters through the opening 641 at the first side 631, travels downward along the longitudinal channel 639, returns along the U-shaped portion 640 at least twice, and then exits through the opening 641 on the second side 632. The exact flow path can be changed to a zigzag, utilize more than two U-shaped portions 640, have no U-shaped portion 640, or adopt any other path on the layer 630. However, in this embodiment, it never flows through the second layer 660. The longitudinal channel 369, the U-shaped portion 640, and the opening 641 all extend through the entire thickness of the first layer 630. In an alternative configuration, single-sheet flow can be obtained by forming a flow channel depth that only partially penetrates the sheet, such that the sheet size remains intact during the assembly process prior to bonding.

[0081] As Figure 34 Best shown in, the flow channel 670 is formed by the stacking of the shown layers 630, 660. In this embodiment, the layers 630, 660 have the same thickness, but can have different thicknesses if desired. The layers 630, 660 are separately formed from different materials that have different reactivities when exposed to etching chemicals. The material of the first layer 630 can be more reactive than the material of the second layer 660, thereby facilitating the effective etching of the first layer 630 without significantly etching the second layer 660. A layer pair is formed by assembling one first layer 630 with one second layer 660. Then the layer pair is diffusion bonded so that they are not easily separated. As described above, other bonding techniques can be used. Then, the layer pair is etched such that the flow channel 670 is formed into the first layer 630 without etching the second layer 660. Then the layer pairs are assembled into a plurality of layers 610 having the flow channel 670. The outer layer 620 is also assembled with the plurality of layers 610 having the flow channel 670. Finally, the layers 610, 620 are diffusion bonded together. Optionally, post-processing such as grinding can be used to form the flow restrictor 600 and make it suitable for installation into the flow channel of the device.

[0082] Note that the flow channels need not extend straight from one end of the flow restrictor to the other end of the flow restrictor, nor need they turn back in parallel rows. Instead, it is contemplated that the flow channels can be zigzag, arcuate, or take any other path required to achieve the desired flow impedance in the completed flow restrictor. Multilayer transitions can also be made, enabling the use of bifurcated and rejoined flow channels, with the transition spanning more than two or three layers, etc. Further contemplated is that the flow restrictor can incorporate the features of a particular embodiment, enabling the construction of hybrids of the disclosed embodiments. The flow restrictor designs disclosed above can be used to achieve highly laminar flow and higher part-to-part reproducibility. When manufacturing a flow control device using one or more laminar elements, this high reproducibility reduces calibration requirements.

[0083] Details of a method of forming a flow restrictor in accordance with the present invention are shown in Figures 37 - 41 as follows. Figure 37 A plurality of layer blanks 710 are shown in exploded view. Each layer blank has a first edge 711, a second edge 712 opposite the first edge, a third edge 713, and a fourth edge 714 opposite the third edge. The layer blank 710 further includes a front face 715 and a back face 716 opposite the front face 715. The layer blank 710 is formed into a first layer 730 and a second layer 760, as further shown in Figure 38 and 39 as follows. The first layer 730 is modified from the layer blank 710 by forming a second cavity 732 in the first layer 730. The second layer 760 is modified from the layer blank 710 by forming a first cavity 761 and a third cavity 763 in the second layer 760. The first cavity 761, the second cavity 732, and the third cavity 763 are formed in the front face 715 of their respective first layer 730 and second layer 760. Preferably, the cavities 761, 732, 763 are formed through the thickness of the layers 730, 760. In some embodiments, some or all of the cavities 761, 732, 763 may be formed only partially through the thickness of the layers 730, 760. In the method shown, the cavities 761, 732, 763 are formed from the front face 715 to the back face 716. The cavities 761, 732, 763 are spaced apart from the first edge 711, the second edge 712, the third edge 713, and the fourth edge 714 of the layer blank 710.

[0084] The cavities 761, 732, 763 are formed by etching the layer blank 710. Alternative processes are available, such as micromachining, laser ablation, or other known techniques. As shown in Figure 40As shown, the impedance stack 770 is formed by a plurality of layers 730, 760. After forming the cavities 761, 732, 763, the layers 730, 760 are stacked in alternating layers, ensuring that the layers 730, 760 remain aligned such that the second cavity 762 overlaps with the first cavity 761 and the third cavity 763. The layers 730, 760 are then joined to form the impedance stack 770 as a single component. The layers 730, 760 can be joined by diffusion bonding, welding, gluing, or any other known technique.

[0085] The impedance stack 770 includes a first untrimmed end 771 formed by the first edge 711 of the first layer 730 and the second layer 760. The opposite second untrimmed end 772 is formed by the second edge 712 of the first layer 730 and the second layer 760 of the impedance stack 770. It can be seen that there are no exposed cavities on the untrimmed ends 771, 772. In an alternative embodiment, only one of the layers 730, 760 needs to have a cavity, while the other layers 730, 760 do not have cavities. This allows for the formation of an impedance, such as Figures 30 - 36 the impedance shown in. In yet other embodiments, three or more different types of layers can be used, such as Figures 23 - 27 shown in. These layers do not need to be stacked alternately, but can simply be separated from each other. Thus, if desired, the unmodified layer blank 710 can be interleaved with the first and second layers. Any combination of layers can be made as long as at least one flow channel is formed in the trimmed flow impedance.

[0086] Figure 41 The impedance stack 770 is shown after the trimming operation has been completed. These trimming operations can take one of two alternative forms. In the first process, the untrimmed ends 771, 772 are disconnected from the impedance stack 770 to expose the first cavity 761 and the third cavity 763. The exposed first cavity 761 and third cavity 763 form holes 712 at the first trimmed end 773 and the second trimmed end 774. This results in a flow channel extending from the hole 712 at the first trimmed end 773 to the hole 712 at the second trimmed end. Optionally, additional material removal operations can be performed on the impedance stack 770 before removing the untrimmed ends 771, 772. The advantage of doing this is that the amount of debris entering the flow channel can be minimized, ensuring that the resulting flow restriction closely matches the theoretical flow restriction provided by the flow restrictor. In addition, by ensuring that debris does not enter the flow channel, the manufacturing repeatability is greatly improved.

[0087] In an alternative second process, the untrimmed ends 771, 772 of the impedance stack 770 are removed by conventional material removal processes such as machining, milling, turning, sawing, grinding, electrical discharge machining, or etching. Once the untrimmed ends 771, 772 are removed to form trimmed ends 773, 774, the impedance stack 770 is rinsed with deionized water. An electropolishing process is used to dissolve any residual metal particles and produce a surface with very low roughness. Next, deionized water is pumped through the flow channels to rinse the electropolishing solution. The impedance stack 770 is then dried, and any remaining free iron, phosphates, and sulfates are removed using a nitric acid solution. This results in a very clean surface free of contaminants.

[0088] While the invention has been described with respect to specific examples, including the presently preferred modes of practicing the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above systems and techniques. It should be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the invention. Accordingly, the spirit and scope of the invention should be broadly construed as set forth in the appended claims.

Claims

1. A flow restrictor for restricting gas flow, the flow restrictor comprises: a first end; a second end, a longitudinal axis extending from the first end to the second end; a plurality of first layers extending along the longitudinal axis from the first end to the second end; a plurality of second layers extending along the longitudinal axis from the first end to the second end; a first hole at the first end defined by the plurality of first layers and the plurality of second layers; a second hole at the second end defined by the plurality of first layers and the plurality of second layers; wherein a flow channel is defined by the plurality of first layers and the plurality of second layers, the flow channel extending from the first hole to the second hole; and wherein each of the plurality of first layers includes a first side, a second side opposite the first side, a third side, a fourth side opposite the third side, a front face, and an opposite back face, the flow channel including a longitudinal channel formed in the front face of each of the first layers; the longitudinal channel of each of the first layers extends from the front face through the first layer and to its opposite back face.

2. The flow restrictor according to claim 1, further comprising a plurality of first holes, a plurality of second holes, and a plurality of flow channels, each of the plurality of flow channels extending from a single hole among the first holes to a single hole among the second holes.

3. The flow restrictor according to claim 1, wherein, the plurality of first layers and the plurality of second layers are arranged in an impedance stack including alternating layers of the plurality of first layers and the plurality of second layers.

4. The flow restrictor according to claim 1, wherein, each of the plurality of first layers is spaced apart and isolated from each other layer among the plurality of first layers.

5. A mass flow control device for delivering a fluid, the mass flow control device comprises: a valve including an inlet channel, an outlet channel, a valve seat, and a closing member; a flow restrictor located in one of the inlet channel or the outlet channel, the flow restrictor comprising: a first end; a second end, a longitudinal axis extending from the first end to the second end; a plurality of first layers extending along the longitudinal axis from the first end to the second end; a plurality of second layers extending along the longitudinal axis from the first end to the second end; a first hole at the first end defined by the plurality of first layers and the plurality of second layers; a second hole at the second end defined by the plurality of first layers and the plurality of second layers; and a flow channel defined by the plurality of first layers and the plurality of second layers, the flow channel extending from the first hole to the second hole; wherein each of the plurality of first layers includes a first side, a second side opposite the first side, a third side, a fourth side opposite the third side, a front face, and an opposite back face, the flow channel including a longitudinal channel formed in the front face of each of the first layers; the longitudinal channel of each of the first layers extends from the front face through the first layer and to its opposite back face.

6. The mass flow control device according to claim 5, wherein, the flow restrictor is configured to form a plurality of layers of a restrictor stack, the restrictor stack including the plurality of first layers and the plurality of second layers.

7. The mass flow control device according to claim 6, wherein, each layer of the plurality of first layers is spaced apart from and isolated from each other layer of the plurality of first layers.

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