Method and apparatus for controlling the division of a fluid flow
The system uses pressure sensors and controllable valves with a controller to rapidly adjust flow rate ratios in semiconductor applications, overcoming the limitations of existing controllers by achieving precise and fast transitions in flow rate adjustments.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- PIVOTAL SYSTEMS CORP
- Filing Date
- 2024-05-17
- Publication Date
- 2026-05-25
AI Technical Summary
Current flow rate ratio controllers in the semiconductor industry struggle with achieving rapid and precise adjustments in flow ratios, often taking several seconds due to their reliance on mass flow controllers designed for standalone flow rate control, which are not ideal for split flow applications.
A system utilizing pressure sensors and controllable valves with a controller that determines and adjusts valve positions based on lookup tables or mathematical formulas to achieve precise flow rate ratios within one second, independent of the total flow rate, by measuring inlet and downstream pressures to quickly establish the required valve positions.
Enables rapid transition times of one second or less for achieving precise flow rate ratios in multiple channels, reducing setup time and maintaining accuracy even at varying flow rates, without the need for temperature measurements.
Smart Images
Figure 2026516531000001_ABST
Abstract
Description
Technical Field
[0001] 〔Related Application〕 This application claims priority from U.S. Patent Application No. 18 / 666,747, filed on May 16, 2024, which claims the benefit of priority from U.S. Provisional Patent Application No. 63 / 467,863, filed on May 19, 2023, the entire disclosure of which is incorporated herein by reference.
Background Art
[0002] Controlling the mass flow rate of a fluid is important for many industrial processes. In the semiconductor industry, the mass flow rate must be particularly accurate because a deviation of just a few percent can lead to process failures. With the mass flow rate of a fluid typically established by a mass flow controller (MFC), in many cases it is desirable to split the flow of one or more MFCs into multiple flows where all flow components are the same but the flow rates of the multiple flows are controlled to a desired ratio. In the semiconductor industry, these ratios must be extremely accurate and any desired change in the flow rate ratio must be achieved very quickly.
[0003] An industry-standard flow splitter device is a flow rate ratio controller (FRC) that contains one inlet for the incoming fluid and multiple outlets for multiple controlled flows. Each of the outlets is called a channel and, depending on the number of outlets, is commonly referred to as, for example, a 2-channel or 3-channel FRC. At present, typical FRCs used in the semiconductor industry are used to control gas flows and contain 2, 3, or 4 channels.
[0004] Currently available FRCs typically use MFCs to control the flow in each channel, i.e., they are sometimes called mass flow ratio controllers. While MFCs are used to control gas flow, their use in FRCs is not ideal. In standalone situations, an MFC is commanded to flow at a specific flow rate. This is the purpose for which MFCs are designed. In an FRC, the inlet flow rate is initially unknown, and the command sent to the FRC is for a specific ratio of the outlet flow rates, while the total flow rate is not part of the command and can be changed while the FRC is operating. Adjusting between MFCs to obtain the desired outlet flow ratio is not a simple task and can take several seconds to accomplish. [Overview of the project] [Problems that the invention aims to solve]
[0005] As the semiconductor industry moves towards shorter and more precise processes, even small transition times can impact process quality. The industry needs flow splitting techniques that can perform transitions in less than a second. [Means for solving the problem]
[0006] The following summary of the disclosure of the present invention is included to provide a basic understanding of some aspects and features of the present invention. This summary is not a comprehensive overview of the present invention and is therefore not intended to specifically identify any major or important elements of the present invention or to define its scope. Its sole purpose is to present some concepts of the present invention in a simplified form as an introduction to the more detailed explanation presented below.
[0007] Embodiments of the present invention relate to dividing a fluid flow into two or more channels according to a directive specifying a ratio of flow rates in each channel, typically described as a percentage of the flow rate in each channel, with the entire channel equaling 100%. Embodiments of the present invention provide a transition time of one second or less to change the ratio after a change in the overall fluid flow rate at the inlet or to achieve a precise flow rate. In these embodiments, the flow rate in each channel is controlled by a valve that can be opened to a specific position specified by a lookup table, graph, formula, etc. Each channel has a pressure sensor downstream of the valve that measures and reports the downstream pressure, and the upstream pressure is provided by a pressure sensor on the inlet that is common to all channels. The ratio of flow rates through different channels is established by (1) determining the required position of each valve for the desired flow rate ratio, and (2) moving the valves to those positions.
[0008] The disclosed embodiments provide a system for dividing an inlet fluid flow into a plurality of outlet flows, comprising: an inlet for receiving an inlet fluid flow; an inlet pressure sensor positioned at the inlet and coupled to the fluid flow, measuring the inlet pressure and generating an inlet pressure signal; two or more flow lines connected to the inlet; a plurality of controllable valves, each positioned in one of the flow lines and each independently controllable to a desired position; a plurality of outlet pressure sensors, each positioned downstream of each of the controllable valves, measuring the downstream pressure and generating an outlet pressure signal; and a controller that receives a ratio signal, an inlet pressure signal, and an outlet pressure signal, and therefrom determines the required valve position for each of the controllable valves for various combinations of fluid flow and inlet pressure, and transmits a control signal to each of the controllable valves to assume the required valve position.
[0009] In the manner disclosed, a system is provided for dividing an inlet fluid flow into a plurality of outlet flows, comprising: an inlet for receiving an inlet fluid flow; an inlet pressure sensor positioned at the inlet, coupled to the fluid flow, measuring the inlet pressure and generating an inlet pressure signal; two or more flow lines connected to the inlet; a plurality of controllable valves, each positioned at one of the flow lines and capable of being independently controlled to a desired position; and a controller that receives a ratio signal and an inlet pressure signal, from which determines the required valve position for each of the controllable valves for various combinations of fluid flow and inlet pressure, and transmits a control signal to each of the controllable valves to assume the required valve position.
[0010] Various additional purposes, features, and advantages of embodiments of the present invention can be more fully recognized by referring to the following detailed description and accompanying drawings.
[0011] The accompanying drawings, incorporated into and constituting part of this specification, illustrate embodiments of the present invention and contribute to illustrating and explaining the principles of the invention, along with their descriptions. The drawings are intended to illustrate the main features of the exemplary embodiments in a schematic manner. The drawings are not intended to depict all features or relative dimensions of the elements depicted in the actual embodiments, and are not drawn to scale. [Brief explanation of the drawing]
[0012] [Figure 1] This diagram shows a conventional 3-channel flow divider. [Figure 2] This is a simplified diagram of a device according to an embodiment of the present invention. [Figure 2A] This figure shows an apparatus according to another embodiment. [Figure 2B] This is a flowchart of the process according to the embodiment. [Figure 3] This is a graphical representation of key parameters recorded during operation of the device according to an embodiment of the present invention. [Figure 3A] This is a flowchart of the process according to the embodiment. [Modes for carrying out the invention]
[0013] Embodiments of controllers and methods that divide the flow of the present invention are described here with reference to the drawings. Different embodiments or combinations thereof can be used for different applications or to achieve different benefits. Depending on the outcomes to be achieved, the different features disclosed herein can be used individually, in combination with other features, in part or in whole, while balancing the advantages with the requirements and constraints. Thus, certain benefits will be emphasized with reference to different embodiments, but are not limited to the embodiments disclosed herein. That is, the features disclosed herein are not limited to the embodiments described herein, but rather may be “mixed and adapted” with other features and incorporated into other embodiments even if they are not expressly described herein.
[0014] Figure 1 is a simplified diagram of the prior art. Each channel of the flow divider 100 contains MFCs 101, 102, and 103 that control the flow in that channel. In a typical application in the semiconductor industry, the flow divider is installed on a process tool such as a plasma etching apparatus or chemical vapor deposition (CVD) tool, immediately downstream of a group of flow controllers that control the flow of individual gases. The gas mixture flowing from the group of individual flow controllers enters the flow divider at inlet 104. The process tool sends setpoint commands to the flow divider controller 108 that specify the required flow ratio or percentage in channels 105, 106, and 107. The flow divider controller does not have information about the total flow rate flowing into inlet 104. The difficulty of the prior art is that the MFCs are designed to receive setpoint commands for desired flow rates rather than ratios. As a result, the flow divider controller must adjust the flow rate setpoint commands to each MFC so that the total flow rate is divided into the required ratios. Since the required flow rate is not initially known, and this is an iterative process, and because the MFC typically requires at least 0.5 seconds for those flow sensors to obtain accurate readings, the entire process to achieve a stable flow at the correct ratio may take several seconds.
[0015] Figure 2 is a simplified diagram of an embodiment of the apparatus according to the present invention. This is an example of a three-channel flow divider. The flow divider controller 212 continuously reads pressure signals from pressure sensors 208, 209, 210, and 211. The controller also commands the required positions for valves 201, 202, and 203. As illustrated by the solid lines drawn in Figure 2, each valve has its own position reference, e.g., a lookup table, which is contained in the controller's memory and specifies the required valve position for a given combination of upstream pressure, downstream pressure, and required flow rate. Since the total flow rate is not known when the ratio or percentage setpoint command is first transmitted by the process tool, determining the required valve position for the commanded ratio may require an iterative process. However, compared to the prior art situation, in this case both the valve position and pressure readings are established within milliseconds, providing information on the actual flow rate much faster than with prior art devices, and allowing the entire stabilization to the new total flow rate to occur in one second or less. If the overall flow rate remains constant and the commanded ratio changes, this change can be made by simply moving the valves according to readings from the position reference for each valve. Since the overall flow rate is known by adding the flow rate values from the position reference after the iterative process described above, the flow rate required for each channel at the new ratio or percentage can be quickly calculated, and each valve can be quickly moved to its required position using its respective lookup table.
[0016] For a typical flow divider used in semiconductor wafer processing, the operating ranges for inlet and downstream pressures are specified. The configuration of a lookup table for each individual valve then involves measuring the flow rate for various inlet and downstream pressures within the operating range while moving the valve to different positions within that range. The number of points measured for each of these variables will depend on the desired accuracy.
[0017] Instead of a look-up table, as illustrated by the dashed box in FIG. 2, a mathematical formula or a multi-dimensional graph can be used to determine the required valve position. Presumably, this mathematical formula or graph will be determined empirically from data collected in a manner similar to that described above for the look-up table.
[0018] In some applications, the downstream pressure may be known in advance. A typical example is thought to be the case where the downstream pressure is determined by a processing chamber in which the pressure in the processing chamber is very close to a vacuum in this case, by measuring only the upstream inlet pressure, the required position of the valve can be determined.
[0019] Only in applications where the downstream pressure is known in advance and it is known in advance that a flow splitter is used, the cost can be saved by removing the downstream pressure sensor, and a flow splitter as shown in FIG. 2A can be obtained. In such a case, the value for the pressure at the outlet (i.e., the channel) is set as the processing chamber pressure.
[0020] The disclosed embodiment provides a system for splitting a fluid flow into a plurality of flows, including an inlet for receiving the fluid flow, a pressure sensor at the inlet coupled to the fluid flow for measuring the inlet pressure, two or more flow lines connected to the inlet, a valve at each of the flow lines controllable to a desired position, and means for determining the required valve position for various combinations of the fluid flow and the inlet pressure for each of the valves. The position of each valve can be adjusted to match a setpoint command sent to a system that defines the flow rate at each of the flow lines to a desired ratio or percentage with respect to the flow rate.
[0021] It should be noted that the arrangements shown in FIGS. 2 and 2A do not require temperature measurement. Conversely, the MFC relies on a high temperature coefficient resistance wire as a sensor that uses the principles of thermodynamics to derive the mass flow rate and measures the temperature difference (ΔT = T2 - T1) across the heater mounted on the side stream. Therefore, the MFC requires a steady flow of gas through the side stream, which increases the time it takes to set the MFC to the desired flow rate. Conversely, the systems of FIGS. 2 and 2A do not require temperature measurement and instead rely on position references, so the setup time is much shorter than when using an MFC. Furthermore, the initial position of each valve can be determined by referring to the position reference without knowing the total inlet flow rate.
[0022] In one embodiment of the present invention, the adjustment of the valve position is performed in the following steps in accordance with FIG. 2B: 1. The process tool establishes a gas flow into the inlet of the flow splitter and simultaneously commands the flow splitter with the setpoint of the required ratio of the channels in step 200. 2. In step 215, the flow splitter controller commands all valves, which are typically normally open (NO) valves, to close to a specific preset position, which is typically in the range of about 80-95% of the maximum open position, but may be outside this range. The purpose of this step is to leave some margin for upward movement (i.e., opening) with respect to the valve position if necessary. (If the valve is a normally closed valve, this command is to open, and the process is the mirror image of the process described for normally open valves). 3. At 220, while the valve with the maximum required opening (highest flow rate) determined from the required ratio reaches its preset position and remains at an initial preset position of about 80-95% of its maximum open position, all other valves continue to close beyond their initial preset positions upon receiving a command from the controller. Here, the flow rate passing through this first valve can be determined using its position reference such as a look-up table. 4. As the valves remain closed, the flow rate passing through the second maximum flow valve is determined using a positional reference, and the ratio of that flow rate to the maximum flow valve is continuously calculated until the desired ratio is reached. In step 225, the second maximum flow valve reaches its correct opening value, the ratio between the second maximum flow valve and the maximum flow valve is achieved, and the movement of the second maximum flow valve stops. With the valves at the maximum required opening and the valves at the second largest required opening at the correct flow ratio, these valves remain in their respective positions, while one or more other valves (depending on the number of channels) remain closed, and each of the N valves stops when it reaches a position in 230 where the flow ratio between its flow rate and the flow rate of the maximum flow valve is achieved. While the N valves are closed, the ratio between the first two valves may change slightly, so the valve with the second largest opening needs to be adjusted, but this adjustment will be very small. This pattern can be repeated until all valves are adjusted to their required flow ratios. At this point, the total flow rate can be calculated by adding all the valve flow rates, for example, those shown by a lookup table, to the values of all valves, referencing the positional reference, and then multiplying by 235. In 5.240, the flow ratio is checked to see if it is correct. If it is correct, the process proceeds to monitor the flow rate for any changes in 245. Conversely, if the flow ratio is not correct, the ratio can be adjusted using iterative processes in 250.
[0023] If the overall flow rate changes at 245, it may be necessary to adjust the valve position, but the adjustment will be small.
[0024] When the required ratio changes, the valve needs to be moved accordingly, but this change can be done very quickly because the total flow rate is already known and the required position can be determined directly from a lookup table.
[0025] In other words, the present invention provides a method for dividing fluid flow in a flow divider, comprising the steps of: establishing a position reference for each valve in the flow divider by measuring the inlet pressure and the fluid flow passing through the valves at multiple valve positions and storing the position reference in the controller; receiving a signal in the controller representing a desired flow rate ratio of fluid flow in multiple channels of the flow divider; measuring the pressure at the inlet of the flow divider; and transmitting a signal from the controller to drive each valve to a position corresponding to a desired flow rate ratio using the inlet pressure and the position reference for each valve.
[0026] One of the major advantages of the present invention is that the required valve position is not affected by the overall flow rate. Similarly, since the inlet pressure changes with the overall flow rate, the present invention also ensures that the valve position is not affected by the inlet pressure. Figure 3 shows three graphs illustrating the operation of an embodiment of the present invention. The upper graph 301 shows the command setpoints for each of the three channels, the middle graph 302 shows the valve positions for each of the three channels, and the lower graph 303 shows the overall flow rate of gas entering the inlet of the three-channel flow divider, according to an arbitrary example.
[0027] In this embodiment, when the overall inlet flow rate changes, the valve with the maximum flow rate remains at a constant position 306, 307, while the other valves are adjusted to maintain their commanded set values. As can be seen, when the flow rate changes from 1000 sccm (standard cubic centimeters / min) 304 to 200 sccm 305, the positions of the other valves hardly change. Valve 3 shows the largest change, but this change is no more than about 1% when the flow rate changes from 1000 sccm 308 to 200 sccm 309.
[0028] This insensitivity to the overall inlet flow rate can be advantageously used in selecting the starting position for the flow divider. When the process tool commands a setpoint for each channel, the flow from the upstream flow controller has probably just begun. As a result, the flow divider receives the setpoint command before the flow reaches the divider. Such conditions are unsustainable for MFC-based flow dividers because an MFC cannot determine the flow rate and set the position without the gas flowing and creating a temperature difference. Fortunately, with respect to the present invention, this uncertainty is not an issue when using the embodiments described. Until the flow rate increases sufficiently to be measurable and controllable, the flow divider can assume a certain predetermined overall inlet flow rate, and the flow division will be very close to an exact percentage. Typical overall flow rates that can be assumed are the maximum specified flow rate, or 50% of the maximum specified flow rate, or any other value determined to be reasonable by those skilled in the art. For example, if a 3-channel flow divider has a maximum flow rate of 1000 sccm for each channel, a typical assumed initial total flow rate would be 3000 sccm or 1500 sccm.
[0029] Using this method of assuming an initial flow rate, embodiments of the present invention can perform the following steps: 1. The process tool initiates the gas flow into the inlet of the flow divider and simultaneously commands the flow divider to set a required ratio or percentage value. 2. The flow divider assumes a total flow rate equal to a predetermined value until the flow rate into the flow divider becomes large enough to allow accurate measurement of the flow rate in each channel and therefore the total flow rate.315 3. A valve with maximum flow rate typically moves to a position within approximately 80-95% of its maximum open position, although it may also move outside this range.320 The purpose of this stage is to leave some margin for upward movement of the valve position as needed. 4. Since the total flow rate is a preset value (though not necessarily the actual value), the percentage for each channel is known, and the valve position of the channel with the maximum flow rate is known, the position of each of the remaining valves can be quickly determined. The valves then move to their required positions. 5. With the flow rate into the flow divider increased to a level sufficient to allow accurate measurement of the flow rate in each channel, the determination of the required valve position is performed at 340 using the actual flow rate. If the ratio is correct, the controller continues to monitor the flow rate at 245; otherwise, it adjusts the valves using an iterative process until the correct ratio is reached.
[0030] When the total inlet flow rate is very low, the pressure signal P in The signal-to-noise ratio (SNR) becomes too low to perform accurate measurements. During this time, the system of the present invention uses assumed, predetermined, or pre-set overall flow rate values. When the flow rate rises to a level sufficient for the pressure signal to provide a good SNR, for example, exceeding a pre-set threshold, the flow divider can determine the flow rate in each channel and establish the correct flow rate percentage through an iterative correction process.
[0031] Another feature made possible by its insensitivity to the total flow rate is its ability to maintain an accurate flow rate even when the total flow rate falls below a value for which accurate total flow rate measurement is possible. The reason why such very low flow rates cannot be accurately measured is that the pressure signal is very low, i.e., the signal-to-noise level is very low. For example, if the minimum total flow rate for which good measurement is possible is 20 sccm, and the total flow rate falls below 20 sccm, the flow divider can assume the total flow rate is 20 sccm and control the valve accordingly, changing the valve position if the set value changes or, for example, if the downstream pressure changes. Normal operation will resume when the total flow rate exceeds 20 sccm.
[0032] Another feature of this invention is the ability to fix the valve position when the percentage does not change. This allows for the generation of a more stable flow and remains accurate even when the overall inlet flow rate changes.
[0033] Using the disclosed embodiments, a method for configuring a flow divider is provided, comprising the steps of: manufacturing an inlet configured to receive a fluid flow; attaching a pressure sensor to the inlet; manufacturing a plurality of flow channels, each communicating with the inlet; inserting electrically controlled valves into each of the plurality of flow channels; electrically connecting the pressure sensor and each electrically controlled valve to a controller; and configuring a position reference within the controller for each electrically controlled valve, wherein the position reference indicates a relationship between the valve position, the upstream pressure, and the fluid flow through the electrically controlled valve. [Explanation of symbols]
[0034] 201 Valve 1 204 Entrance 205 channels 208 Pressure Sensor 212 Controllers
Claims
1. A system for dividing an inlet fluid flow into multiple outlet flows, The inlet for receiving the aforementioned inlet fluid flow, An inlet pressure sensor positioned at the inlet, coupled to the fluid flow, measures the inlet pressure and generates an inlet pressure signal, Two or more flow lines connected to the aforementioned inlet, A plurality of controllable valves, each positioned in one of the aforementioned flow lines and capable of independently controlling each of them to a desired position, A controller that receives the ratio signal and the inlet pressure signal, determines the required valve position for each of the controllable valves for various combinations of fluid flow and inlet pressure, and transmits a control signal to each of the controllable valves to take the required valve position. A system that includes this.
2. The system according to claim 1, further comprising a plurality of outlet pressure sensors, each positioned downstream of each of the controllable valves, which measure the downstream pressure and generate an outlet pressure signal.
3. The system according to claim 1, wherein the controllable valve is a normally open valve.
4. The system according to claim 1, wherein the controllable valve is a normally closed valve.
5. The system according to claim 1, wherein the controller includes a position reference for each controllable valve, the position reference relating the valve position, the inlet pressure, and the flow rate through the valve.
6. The system according to claim 1, wherein the position reference is one of a lookup table, a formula, or a multidimensional graph.
7. The system according to claim 1, wherein the fluid is a gas.
8. The system according to claim 1, wherein the fluid is a liquid.
9. The system according to claim 1, wherein the position of each valve can be adjusted so that the flow rate in each of the flow lines matches a set value command sent to a system that determines a desired ratio or percentage of the flow rate.
10. The system according to claim 1, wherein the position of the controllable valve that controls the maximum flow rate among the plurality of controllable valves is set to a predetermined value.
11. The system according to claim 10, wherein the predetermined value is between 80% and 95% of the maximum valve position.
12. The system according to claim 10, wherein the predetermined value is 50% or greater than the maximum valve position.
13. A system for dividing a fluid flow into multiple flows, An inlet for receiving the aforementioned fluid flow, An inlet pressure sensor at the inlet, which is coupled to the fluid flow and measures the inlet pressure, Two or more flow lines connected to the aforementioned inlet, A valve in each of the flow lines that can be controlled to a desired position, A means for determining the required valve position for each valve for various combinations of fluid flow rate and inlet pressure, A system that includes this.
14. The system according to claim 13, wherein the position of each valve can be adjusted so that the flow rate in each of the flow lines matches a set value command sent to a system that determines a desired ratio or percentage of the flow rate.
15. A method for dividing a fluid flow into multiple fluid flows in a flow divider having an inlet and a plurality of flow channels, each of which has a valve, A step of reading the pressure upstream and downstream of the valve in each of the flow channels, A step of reading a set value command that specifies the ratio or percentage flow rate for each of the flow channels, The steps include establishing the necessary valve positions in each flow channel in order to establish the flow ratio or percentage specified by the set value, Methods that include...
16. The method according to claim 15, wherein the required valve positions in each flow channel are determined from a look-up table.
17. The method according to claim 16, wherein the lookup table is established by measuring the flow rate in each channel as a function of valve position, upstream pressure, and downstream pressure.
18. The method according to claim 15, wherein the required valve positions in each flow channel are determined from a mathematical formula or a multidimensional graph.
19. The method according to claim 15, wherein the step of establishing the required valve positions in each flow channel begins by setting the valve having the maximum flow rate to a predetermined position.
20. The method according to claim 19, wherein the step of establishing the required valve positions relative to other valves is performed by assuming a certain overall inlet flow rate.
21. The method according to claim 15, wherein, after the required valve positions in each flow channel have been established, the valves are held in a fixed position for a period of time.
22. The method according to claim 21, wherein the period is until the set value changes.
23. A method for dividing a fluid flow into multiple fluid flows in a flow divider having an inlet and a plurality of flow channels, each of which has a valve, The steps include reading the pressure upstream of the aforementioned valve, A step of reading a set value command that specifies a ratio or flow rate percentage for each of the flow channels, The steps include establishing the necessary valve positions in each flow channel in order to establish the flow rate percentage specified by the set value, Methods that include...