JP7743581B2 - Flow Control Device - Google Patents

Description

The present invention relates to a flow control device that controls, for example, the flow rate of a fluid.

In semiconductor manufacturing processes, various gases are supplied into chambers while being controlled at desired flow rates. In recent years, this field has seen a demand for faster flow rate control and improved flow rate accuracy (see Patent Document 1), and to meet this demand, a flow rate control device using two control valves has been proposed.

Specifically, this flow control device has a first valve, a pressure-type flow sensor, and a second valve arranged in this order from upstream to downstream of the flow path. For example, the first valve receives feedback of the first pressure from a first pressure sensor arranged upstream of the laminar flow element that constitutes the flow sensor, and controls the first pressure so that it remains constant at a desired set pressure. Furthermore, the second valve receives feedback of the measured flow rate measured by the flow sensor, and controls the measured flow rate so that it matches the set flow rate. The set pressure is always set to a constant value regardless of the magnitude of the set flow rate.

By the way, since pressure-type flow sensors become more sensitive at lower pressures, setting the set pressure to as low a value as possible and keeping the first pressure, which is the pressure upstream of the laminar flow element, at a low pressure will improve the accuracy of flow control by the second valve.

However, if the set pressure is set too low, the first pressure will not sufficiently exceed the pressure loss in the laminar flow element and the second valve and the pressure downstream of the second valve, making it impossible to flow a large flow rate downstream of the second valve. On the other hand, if the set pressure is set to a relatively high value taking into account the set flow rate range, the sensitivity and measurement accuracy of the pressure-type flow sensor will deteriorate compared to its actual capabilities when the set flow rate is small. Specifically, as shown in the graph in Figure 6, the higher the set pressure and the larger the value of the second pressure P2, which is the pressure downstream of the fluid resistance, the lower the sensitivity of the differential pressure ΔP = _P1 - _P2 to the flow rate, and the lower the measurement accuracy will be.

JP 2015-109022 A

The present invention was made in consideration of the problems described above, and aims to provide a flow control device that can maintain high sensitivity and measurement accuracy of the flow sensor even at low flow rates, while also being able to handle large flow rates.

That is, the flow control device according to the present invention is characterized by comprising: a first valve provided in a flow path; a second valve provided in the flow path downstream of the first valve; a flow sensor that measures the flow rate of fluid in the flow path between the first valve and the second valve; a flow controller that controls a manipulated variable input to the second valve so as to reduce the deviation between the measured flow rate measured by the flow sensor and a set flow rate; and a first valve controller that uses the manipulated variable input to the second valve by the flow controller or the opening of the second valve as a controlled variable and controls the first valve so as to reduce the deviation between the controlled variable and a target variable.

The flow rate control method according to the present invention is a flow rate control method used in a flow rate control device that includes a first valve provided in a flow path, a second valve provided in the flow path downstream of the first valve, and a flow rate sensor that measures the flow rate of fluid in the flow path between the first valve and the second valve, and is characterized by comprising: a flow rate control step that controls a manipulated variable input to the second valve so as to reduce the deviation between a measured flow rate measured by the flow rate sensor and a set flow rate; and a first valve control step that uses the manipulated variable input to the second valve or the opening of the second valve as a controlled variable in the flow rate control step and controls the first valve so as to reduce the deviation between the controlled variable and a target variable.

In this case, for example, if the set flow rate changes from the initial flow rate value to a maintenance flow rate value that is smaller than the initial flow rate value, the flow controller will change the manipulated variable input to the second valve to reduce the opening of the second valve, thereby attempting to reduce the flow rate of fluid that can pass through the second valve.

When the opening of the second valve changes, the deviation between the controlled variable and the target variable in the first valve controller increases, so the first valve controller changes the opening of the first valve to return the opening of the second valve to its original value. In this example, the flow rate of the fluid flowing into the flow sensor between the first and second valves is reduced, resulting in a state where the measured flow rate is lower than the set flow rate. The flow controller then increases the opening of the second valve to increase the flow rate of the fluid passing through the second valve and reduce the deviation.

By repeating this operation of the flow rate controller and the first valve controller for each control cycle, the opening of the second valve can be returned to the same opening that was maintained at the initial flow rate value, even at the changed maintained flow rate value.

Therefore, when fluid is flowing at a small flow rate, such as the maintenance flow rate, the opening of the first valve is ultimately reduced to reduce the inflow of fluid, and the opening of the second valve can be increased so as not to provide resistance. As a result, the absolute pressure at the flow sensor is reduced, maintaining the sensitivity and measurement accuracy of the flow sensor at a high level. On the other hand, when fluid is flowing at a large flow rate, such as the initial flow rate, the opening of the first valve is increased so that the opening of the second valve is maintained at a predetermined opening, increasing the inflow of fluid. This allows a large flow rate to be achieved by exceeding the pressure loss in the flow sensor and the second valve and the pressure downstream of the second valve. In this way, the present invention can maintain high sensitivity and measurement accuracy of the flow sensor at small flow rates while also achieving the differential pressure required to flow a large flow rate.

When the flow sensor includes a fluid resistor disposed between the first valve and the second valve, a first pressure sensor disposed between the first valve and the fluid resistor, a second pressure sensor disposed between the fluid resistor and the second valve, and a flow rate calculation unit that calculates the flow rate of the fluid flowing through the fluid resistor based on the first pressure measured by the first pressure sensor and the second pressure measured by the second pressure sensor, the target amount set in the first valve controller can be a constant value that maintains the second valve at a predetermined fully open position in order to fully utilize the sensitivity and measurement accuracy of the flow sensor. In this way, the second valve remains at a large opening, making it possible to reduce the pressure at the flow sensor located upstream of the second valve, thereby improving sensitivity and measurement accuracy.

A specific control rule for the first valve controller is that when the opening of the second valve is smaller than the opening corresponding to the target amount, the first valve controller controls the opening of the first valve to decrease. When the opening of the second valve becomes smaller than the target state, the opening of the first valve decreases, reducing the flow rate supplied to the second valve. Therefore, the flow rate controller operates to increase the opening of the first valve in order to maintain the flow rate, thereby maintaining the opening of the first valve at the target opening rate.

A specific example of the configuration of the first valve and the first valve controller is one in which the first valve is a normally open type piezo valve, and the first valve controller controls the voltage applied to the first valve to increase when the control amount is smaller than the target amount.

Another example of the configuration of the first valve and the first valve controller is one in which the first valve is a normally closed type piezo valve, and the first valve controller controls the voltage applied to the first valve to decrease when the control amount is smaller than the target amount.

In order to achieve the same effects as the flow control device of the present invention by updating the program of an existing flow control device, it is sufficient to use a program for a flow control device that includes a first valve provided in a flow path, a second valve provided in the flow path downstream of the first valve, and a flow sensor that measures the flow rate of fluid in the flow path between the first and second valves, the program causing a computer to function as a flow controller that controls a manipulated variable input to the second valve so as to reduce the deviation between the measured flow rate measured by the flow sensor and a set flow rate, and a first valve controller that controls the first valve using the manipulated variable input to the second valve by the flow controller or the opening of the second valve as a controlled variable and reduces the deviation between the controlled variable and a target variable.

The program for the flow control device may be distributed electronically or may be recorded on a program recording medium such as a CD, DVD, BD, or flash memory.

A fluid control device comprising a first valve provided in a flow path, a second valve provided in the flow path downstream of the first valve, a fluid sensor that measures a physical quantity of the fluid in the flow path between the first and second valves, a fluid controller that controls a manipulated variable input to the second valve so as to minimize the deviation between the measured quantity measured by the fluid sensor and a set quantity, and a first valve controller that controls the first valve so as to minimize the deviation between the manipulated variable input to the second valve by the fluid controller or a controlled variable (the opening of the second valve) and a target quantity, can control a physical quantity of the fluid, such as flow rate, pressure, or concentration, to match the set quantity while maintaining the opening of the second valve at a desired opening and maintaining a pressure appropriate for operating the fluid sensor. Therefore, control accuracy can be improved compared to conventional methods, regardless of the type of physical quantity being controlled.

For example, in processes where gas is supplied into a chamber to form plasma, a minimum level of plasma continues to be generated even when the process is paused in the chamber. This is to keep impurities in the chamber suspended in the air and prevent them from depositing on the substrate. For this reason, a specified flow rate of gas is supplied to the chamber during the process, and when the pause period begins, the gas flow rate is reduced to the minimum maintenance flow rate required to maintain plasma.

In a flow control device equipped with a flow sensor, a control valve located downstream of the flow sensor, and a flow controller that controls the control valve based on the deviation between the flow rate measured by the flow sensor and the set flow rate, if a set flow rate is set for the flow controller that causes a large, stepped decrease in the flow rate to achieve the above-described flow rate control, and the opening of the control valve, which corresponds to the maintenance flow rate, is close to fully closed, there is a possibility that a situation may occur in which gas is not supplied to the chamber for a moment.

Specifically, because the flow sensor is located upstream of the control valve, there is a time lag relative to the actual flow rate of gas passing through the control valve. As a result, the flow controller reduces the control valve's opening to achieve the maintained flow rate. Even if the control valve is at an opening appropriate for achieving the maintained flow rate at a certain point, the flow sensor will output a measured flow rate greater than the maintained flow rate. The flow controller then further reduces the control valve's opening to eliminate the deviation between the measured flow rate and the set flow rate, which may result in the control valve being fully closed. In other words, even if the flow sensor's output is not zero, as shown in the graph in Figure 7, the control valve's opening is zero. Therefore, as shown in Figure 8, no gas actually flows downstream of the control valve, making it impossible to maintain plasma in the chamber.

To solve these problems, a flow control device can be used that includes a flow sensor equipped with a sensing mechanism that is provided in a flow path and outputs an output signal corresponding to the flow rate of the fluid flowing through the flow path; a flow rate calculation unit that calculates the flow rate based on a measurement value indicated by the output signal of the sensing mechanism and a flow rate characteristic value corresponding to the measurement value; a control valve that is provided upstream or downstream of the flow sensor; a flow rate controller that controls the control valve to minimize the deviation between the measured flow rate measured by the flow sensor and a set flow rate; and a reference governor that sets the set flow rate in the flow rate controller, which is a command flow rate with a time delay corresponding to the measurement value indicated by the output signal of the sensing mechanism.

With this configuration, the reference governor sets the set flow rate in the flow controller with a time delay corresponding to the measurement indicated by the output signal of the sensing mechanism, allowing the time delay of the flow sensor to be reflected in the set flow rate. Therefore, deviation between the measured flow rate and the set flow rate due to the time delay of the flow sensor is unlikely to occur, so even when the flow controller is attempting to achieve a flow rate equivalent to an opening close to fully closed, it is possible to prevent the control valve from being controlled to fully closed.

In addition, because the reference governor imposes a time delay on the set flow rate in response to the measurement value indicated by the output signal of the sensing mechanism, it can accurately reflect differences in the magnitude of the time delay that appears in the flow sensor due to differences in the magnitude of the flow rate, for example. Therefore, compared to when a fixed time delay is directly applied to the set flow rate, deviations caused by the time delay of the flow sensor are less likely to occur, and it is possible to prevent the control valve from fully closing and cutting off the supply of fluid at low flow rates.

A specific example of a configuration in which the reference governor accurately reflects the time delay of the flow sensor in the set flow rate is one in which the sensing mechanism includes a fluid resistance, a first pressure sensor provided upstream of the fluid resistance, and a second pressure sensor provided downstream of the fluid resistance; the flow rate calculation unit includes a coefficient determination unit that determines the flow path resistance, which is the flow characteristic value, based on the first pressure and second pressure, which are measured values indicated by the output signals of the first pressure sensor and the second pressure sensor; and an output unit that calculates the flow rate based on the first pressure, the second pressure, and the flow path resistance; and the reference governor is configured to calculate the set flow rate based on the flow path resistance determined by the coefficient determination unit and the command flow rate, and set the set flow rate in the flow rate controller.

a first valve provided in a flow path; a second valve provided in the flow path downstream of the first valve; a fluid resistor provided in the flow path between the first valve and the second valve; a first pressure sensor that measures the pressure in a first volume in the flow path that is the volume between the first valve and the fluid resistor; a second pressure sensor that measures the pressure in a second volume in the flow path that is the volume between the fluid resistor and the second valve; and a flow rate calculation unit that calculates the flow rate of the fluid flowing through the fluid resistor based on the first pressure measured by the first pressure sensor and the second pressure measured by the second pressure sensor. In a flow control device, to enable accurate identification of the size of the first volume and to further improve the accuracy of flow control by appropriately setting various parameters determined from the size of the first volume for each device even in the presence of manufacturing errors, etc., it is sufficient if the device is equipped with a diagnoser that diagnoses the volume of the first volume or the second volume, and the diagnoser calculates the size of the first volume based on the integrated value of the flow rate calculated by the flow rate calculation unit over a predetermined period of time and the amount of change in the first pressure over the predetermined period of time when the first valve is open and the second valve is closed.

To accurately identify the size of the second volume, the diagnoser needs only to calculate the size of the second volume based on the integrated value of the flow rate calculated by the flow rate calculation unit over a predetermined period of time while the second valve is open and the first valve is closed, and the amount of change in the second pressure over the predetermined period of time.

To ensure that the flow of fluid into or out of the volume whose size has been identified is stable and identification errors are less likely to occur, the specified period should be the period from when the absolute value of the difference between the first pressure and the second pressure reaches its maximum until the first pressure and the second pressure become equal.

To enable the correctness of the identified sizes of the first volume and the second volume to be verified using another method, the diagnostic device may calculate a volume ratio between the first volume and the second volume based on the difference between the first pressure at the start of the specified period and the first pressure at the end of the specified period, and the difference between the second pressure at the start of the specified period and the second pressure at the end of the specified period.

In this way, with the flow control device of the present invention, the second valve is controlled by flow rate feedback, and the first valve, which is located upstream of the second valve, is controlled so that the control amount related to the opening of the second valve matches the target amount. This allows for low pressure that demonstrates the sensitivity and measurement accuracy of the flow sensor when flowing small amounts of flow, while also allowing for a pressure difference that overcomes various pressure losses and downstream pressure when flowing large amounts of flow.

1 is a schematic diagram showing a flow rate control device according to an embodiment of the present invention; 3 is a schematic diagram showing a configuration related to flow rate control by the flow rate control device and maintaining the opening degree of a second valve in the embodiment; FIG. 5 is a schematic graph showing the operation of a first valve and a second valve of the flow rate control device in the same embodiment. 2 is a schematic diagram showing a configuration related to a reference governor of the flow rate control device in the embodiment; FIG. FIG. 10 is a schematic diagram showing an example of control of a first valve and a second valve in a conventional flow control device. 10 is a graph of flow rate vs. differential pressure showing the change in sensitivity with respect to absolute pressure in a pressure-type flow sensor. 10A and 10B are schematic diagrams showing changes in the opening degrees of a first valve and a second valve in a conventional flow control device. 10A and 10B are schematic diagrams showing examples of flow rate changes in a conventional flow rate control device. FIG. 10 is a schematic diagram showing a flow rate control device according to another embodiment of the present invention. FIG. 10 is a schematic diagram showing the deviation of the identified first volume or second volume. 10 is a flowchart showing an operation related to identification of a second volume that is performed when a process is stopped, etc. 10 is a flowchart showing an operation related to identification of the first volume that is performed when the process is stopped, etc. 10 is a flowchart showing operations related to identification of the volume ratio, the first volume, and the second volume, which are performed when the supply of gas is stopped during the process, for example.

The flow control device 100 according to the first embodiment of the present invention will be described with reference to Figures 1 to 4.

In one embodiment, the flow rate control device 100 is used to supply reactive gas at a predetermined set flow rate into a chamber where plasma is generated, for example, in a semiconductor manufacturing process. Specifically, the flow rate control device 100 supplies reactive gas at a predetermined flow rate during the process period in which dry etching is progressing in the chamber. In addition, the flow rate control device 100 supplies reactive gas at a maintenance flow rate, which is the minimum flow rate necessary to maintain plasma in the chamber, during process pauses. The maintenance flow rate is a flow rate of reactive gas that prevents, for example, Coulomb crystals from being formed by particulates (dust) in the chamber and prevents particulates from depositing on substrates in the chamber during pauses.

As shown in FIG. 1, the flow control device 100 includes a fluid device consisting of a sensor and a valve provided in a flow path, and a control and calculation mechanism COM that controls the fluid device.

The fluid equipment consists of a supply pressure sensor P0, a first valve V1, a first pressure sensor P1, a fluid resistance FR, a second pressure sensor P2, and a second valve V2, all of which are installed in the flow path. Each device is installed in this order from the upstream side.

Here, the fluid resistance FR is a laminar flow element, and the flow rate of gas flowing through the fluid resistance FR is determined by the pressure difference between its upstream and downstream sides. The first pressure sensor P1, the fluid resistance FR, the second pressure sensor P2, and the flow rate calculation unit FC (described later) constitute a flow rate sensor FS that measures the flow rate of fluid flowing through the flow path between the first valve V1 and the second valve V2. In other words, the first pressure sensor P1, the fluid resistance FR, and the second pressure sensor P2 constitute a sensing mechanism SM that outputs an output signal corresponding to the flow rate of fluid flowing through the flow path, and the flow rate calculation unit FC calculates the flow rate of fluid flowing through the flow path based on the output signal of the sensing mechanism SM. Because this flow rate sensor FS is a so-called pressure-type flow rate sensor, it has the characteristic that the lower the pressure measured by each pressure sensor, the higher the measurement accuracy of the flow rate. In this embodiment, the flow path in which the flow control device 100 is installed is connected to a vacuum chamber. Therefore, to reduce the pressure in the volume between the first valve V1 and the second valve V2 to below a predetermined value, the first valve V1 is kept at a fully closed position to reduce the amount of fluid flowing in, and the second valve V2 is kept at a predetermined position or higher to make it easier for the fluid in the volume to pass through the second valve V2.

The supply pressure sensor P0 is used to monitor the pressure of the gas supplied from the upstream side. Note that the supply pressure sensor P0 may be omitted if it is guaranteed that the supply pressure is stable.

The first pressure sensor P1 measures the pressure of the gas (hereinafter also referred to as the first pressure) charged in the first volume VL1, which is the volume in the flow path between the first valve V1 and the fluid resistance FR.

The second pressure sensor P2 measures the pressure of the gas charged in the second volume VL2, which is the volume in the flow path between the fluid resistance FR and the second valve V2 (hereinafter also referred to as the second pressure).

In this way, the first pressure sensor P1 and the second pressure sensor P2 measure the pressure in the first volume VL1 and the second volume VL2, which are the two volumes formed by the first valve V1, the fluid resistance FR, and the second valve V2. In other words, the first pressure sensor P1 and the second pressure sensor P2 measure the pressure in the volumes located before and after the fluid resistance FR.

In this embodiment, the first valve V1 and the second valve V2 are of the same type, for example, a piezo valve in which a valve element is driven relative to a valve seat by a piezo element. The second valve V2 also corresponds to the control valve in the claims. In this embodiment, the opening of the second valve V2 is controlled by flow rate feedback control using the flow rate measured by a flow sensor. Meanwhile, the opening of the first valve V1 is controlled by feedback of the voltage applied to the second valve V2 so that the voltage remains at a predetermined constant value. In other words, the opening of the first valve V1 is controlled by feedback of information about the voltage applied to a valve other than itself.

Next, the control and calculation mechanism COM will be described in detail. The control and calculation mechanism COM is a so-called computer equipped with, for example, a CPU, memory, A/D and D/A converters, input/output means, etc., and by executing a fluid control device program stored in the memory and various devices working together, it performs at least the functions of the flow rate calculation unit FC, flow rate controller 1, first valve controller 2, and reference governor 3.

The flow rate calculation unit FC calculates the flow rate based on the measurement value indicated by the output signal of the sensing mechanism SM and a flow rate characteristic value corresponding to the measurement value. Specifically, the flow rate calculation unit FC calculates the flow rate of the fluid flowing through the fluid resistance FR based on the first pressure, which is the pressure upstream of the fluid resistance FR, and the second pressure, which is the pressure downstream of the fluid resistance FR, which are the measurement values indicated by the output signal of the sensing mechanism SM. Here, the flow rate calculation unit FC calculates the flow rate not only based on the first pressure and second pressure, but also based on the flow rate characteristic value determined according to the characteristics of the fluid resistance FR.

That is, the flow rate calculation unit FC consists of a coefficient determination unit FC1 that determines the flow rate characteristic value, or flow path resistance, based on the first pressure and the second pressure, and an output unit FC2 that calculates the flow rate based on the first pressure, the second pressure, and the flow path resistance and outputs it to the flow rate controller 1.

For example, when the flow rate is Q, the flow path resistance is R, the first pressure is _P1 , and the second pressure is _P2 , the output unit FC2 calculates the flow rate based on the formula Q = ( _P1 - _P2 ) / R. Here, the flow path resistance R changes under the influence of the first pressure _P1 and the second pressure _P2 .

The coefficient determination unit FC1 determines the flow path resistance R, which is a flow rate characteristic value, from, for example, the first pressure _P1 and the differential pressure ΔP between the first pressure _P1 and the second pressure _P2 . The coefficient determination unit FC1 may be configured to calculate the flow path resistance R from a multivariate function with the first pressure _P1 and the differential pressure as parameters, or may be configured to determine the flow path resistance R by referring to a table of the flow path resistance R, the first pressure, and the differential pressure determined in advance by an experiment or the like.

The flow rate controller 1 performs flow rate feedback control of the applied voltage, which is the manipulated variable input to the second valve V2, using, for example, PID control, so as to minimize the deviation between the set flow rate set by the reference governor 3 and the measured flow rate measured by the flow rate sensor.

In this embodiment, the set flow rate is a command flow rate input by the user, for example as a step function or broken line function, which is converted by the reference governor 3 into a continuous function that reflects the time delay of the flow rate measured by the flow sensor.

The first valve controller 2 uses the applied voltage, which is the manipulated variable input to the second valve V2, as a control variable and controls the applied voltage to the first valve V1 so as to minimize the deviation between the controlled variable and a target variable. Here, the target variable is, for example, a value set by the user, and is a maintenance voltage value corresponding to the opening degree desired to be maintained at the second valve V2. In this embodiment, the opening degree corresponding to the maintenance voltage value is the fully open opening degree of the second valve V2, and by drawing a vacuum from the chamber, the volume between the first valve V1 and the second valve V2 is maintained at or below a predetermined pressure suitable for the operation of the flow sensor. Furthermore, the maintenance voltage value is a constant and is always set to a fixed value. Normally, the opening degree of the first valve V1 is controlled by feedbacking information about the first valve V1 or the physical quantity of the flow rate directly operated by the first valve V1. However, the first valve controller 2 controls the opening degree of the first valve V1 by feedbacking information about the second valve V2.

More specifically, the first valve controller 2 changes the flow rate of fluid supplied to the flow sensor and the second valve V2 according to the magnitude of the voltage applied to the second valve V2 so that the second valve V2 is maintained at a target opening. In other words, when the voltage applied to the second valve V2 is small relative to the maintenance voltage value and the opening of the second valve V2 is smaller than the target opening, the first valve controller 2 reduces the voltage applied to the first valve V1 to reduce the amount of fluid supplied to the second valve V2, thereby reducing the opening of the first valve V1. Conversely, when the opening of the second valve V2 is larger than the target opening, the first valve controller 2 increases the voltage applied to the first valve V1 to increase the amount of fluid supplied to the second valve V2, thereby increasing the opening of the first valve V1.

Now, with reference to Figures 2 and 3, we will explain how the flow rate controller 1 and first valve controller 2 configured in this manner work together. For simplicity, the influence of the reference governor 3 has been omitted in this explanation, as shown in Figure 2. Furthermore, as shown in Figure 3, the set flow rate is assumed to change in a broken line function from a predetermined flow rate during the process period to a maintenance flow rate during the pause period, and the graph shows the change over time in the voltage applied to the first valve V1 and the second valve V2.

During the process, while a stable supply is maintained at a predetermined flow rate, the voltage V1 applied to the first valve V1 and the voltage V2 applied to the second valve V2 are stabilized at approximately constant values. During this period, the value of the voltage V2 applied to the second valve V2 is approximately equal to the voltage value input to the first valve controller 2 to maintain the target amount.

Next, during the transition period between the process period and the pause period, the set flow rate input to the flow controller 1 changes significantly in a short period of time from the specified flow rate to the maintenance flow rate, so the set flow rate becomes smaller than the measured flow rate output by the flow sensor, resulting in a deviation. For this reason, the flow controller 1 reduces the applied voltage V2 so that the opening of the second valve V2 decreases and the measured flow rate decreases.

As shown in Figure 3, when the applied voltage V2 to the second valve V2 changes during the transition period, the applied voltage V2, which is the controlled variable, becomes smaller than the target maintenance voltage value, resulting in a deviation. Therefore, in order to eliminate this deviation, the first valve controller 2 reduces the applied voltage V1 to the first valve V1, reducing the opening of the first valve V1 and beginning to reduce the amount of fluid supplied to the second valve V2.

During the initial period of the pause, as the fluid supply from the first valve V1 decreases, the measured flow rate measured by the flow sensor also decreases, resulting in a deviation below the maintenance flow rate. Therefore, the flow controller 1 attempts to increase the flow rate of fluid passing through the second valve V2 by increasing the opening of the second valve V2, thereby restoring the measured flow rate to the maintenance flow rate. Furthermore, because the applied voltage V2 to the second valve V2 remains lower than the maintenance voltage, the first valve controller 2 continues to reduce the applied voltage V1 to the first valve V1, thereby reducing the amount of fluid supplied to the second valve V2. This operation is repeated every control cycle, causing the applied voltage V2 to continue to increase and the applied voltage V1 to the first valve V1 to continue to decrease. This trend continues until the applied voltage V2 to the second valve V2 eventually matches the target maintenance voltage. Ultimately, the voltage V2 applied to the second valve V2 is maintained at the maintenance voltage, and the voltage V1 applied to the first valve V1 is maintained constant at the voltage at which the voltage V2 applied to the second valve V2 matches the target maintenance voltage.

In this way, during the initial period of the pause, the opening of the second valve V2 changes to near full closure, achieving a maintenance flow rate. Thereafter, the opening of the first valve V1 is gradually decreased, and the opening of the second valve V2 is gradually increased accordingly. Therefore, even if the openings of the first valve V1 and the second valve V2 are changed, the flow rate of fluid flowing out of the second valve V2 is maintained at the maintenance flow rate. In this way, even if the set flow rate changes, the opening of the second valve V2 eventually converges to the target maintenance voltage value. Furthermore, when a small flow rate is flowing, the pressure in the volume where the flow sensor FS is installed can be reduced to the pressure that maximizes sensitivity and measurement accuracy. On the other hand, when a large flow rate is flowing, the opening of the first valve V1 is maintained at a large value, increasing the inflow of fluid. This increases the first pressure value, exceeding the pressure loss of the laminar flow element and the second valve V2 (which are fluid resistance FR), as well as the pressure downstream of the second valve V2, thereby achieving a large flow rate.

Next, the reference governor 3 will be explained with reference to Figures 1 and 4.

The reference governor 3 sets a set flow rate in the flow controller 1, which is a command flow rate input by the user with a time delay corresponding to the measurement value indicated by the output signal of the sensing mechanism SM. Specifically, as shown in Figure 1, the flow characteristic value used by the flow calculation unit FC of the flow sensor is sequentially fed back to the reference governor 3 in each control cycle. The reference governor 3 calculates the set flow rate from the command flow rate using a coefficient corresponding to the fed-back flow characteristic value, and inputs it to the flow controller 1.

Specifically, as shown in FIG. 4 , the reference governor 3 acts as a first-order lag element expressed as 1/(1 + RVs), where R is the flow resistance and V is the volume measured by the flow sensor. Here, R is not a constant but a variable with parameters of the first pressure _P1 and the differential pressure ΔP between the first and second pressures. When the reference governor 3 acts as a first-order lag element on the command flow rate, the output set flow rate reflects the time delay of the flow sensor. That is, because the flow sensor is provided upstream of the second valve V2, a predetermined time delay occurs in the measured flow rate of the flow sensor relative to the flow rate flowing through the second valve V2 by the volume, depending on the first pressure _P1 and the differential pressure ΔP. In this embodiment, the reference governor 3 also inputs a value that reflects the time delay of the flow sensor into the set flow rate. As a result, even if the set flow rate is changed from a predetermined value to a flow rate equivalent to a nearly fully closed position, such as the maintenance flow rate, it is possible to prevent excessive deviation from occurring in the flow controller 1 and prevent the second valve V2 from being momentarily fully closed. Therefore, it is possible to continuously supply the minimum flow rate necessary to continue generating plasma during the pause period.

As described above, with the flow control device 100 of this embodiment, the control of the flow controller 1 and the first valve controller 2 allows the aperture of the second valve V2 to be kept constant at the fully open aperture corresponding to the maintenance voltage, even if the set flow rate changes. Therefore, a sufficient amount of fluid can be exhausted from the downstream side of the flow control device 100, and the pressure in the sensing mechanism SM of the flow sensor can be maintained at a low pressure at which measurement accuracy is demonstrated. This allows the flow rate accuracy of the flow control device 100 to be improved compared to conventional methods. Furthermore, when a large flow rate is required, the aperture of the first valve V1 is increased, increasing the inflow of fluid and achieving the differential pressure required to achieve a large flow rate. In other words, the flow control device 100 of this embodiment can achieve a low-pressure state when a small flow rate is required and a high-pressure state when a large flow rate is required, thereby achieving both flow rate control accuracy at small flow rates and the ability to supply a large flow rate.

Furthermore, the set flow rate set by the reference governor 3 faithfully reproduces the time delay of the flow sensor, which is affected by the first and second pressures. This prevents the flow controller 1 from momentarily experiencing excessive deviations and resulting in a fully closed state, even when the set flow rate changes significantly. This prevents the second valve V2 from momentarily becoming fully closed when it is closed to maintain the flow rate during process pauses. This means that the reactive gas required to generate plasma can be continuously supplied to the chamber at all times, preventing particles and the like in the chamber from depositing on the substrate.

Flow control devices in other embodiments of the present invention will now be described.

The flow control device 100 shown in Figure 9 is equipped with a diagnoser D that identifies the size of the first volume VL1 and the second volume VL2 based on the outputs of the flow sensor FS. Note that Figure 9 omits the flow controller 1, first valve controller 2, and reference governor 3, which are related to the flow control described in the previous embodiment. The diagnoser D in this embodiment diagnoses a flow control device 100 in which a first valve V1, a first pressure sensor P1, a fluid resistance FR, a second pressure sensor P2, and a second valve V2 are provided in this order in the flow path.

The diagnostic device D shown in FIG. 9 identifies the size of the first volume VL1 and the second volume VL2, which are the internal spaces formed between the first valve V1 and the fluid resistance FR, which is part of the flow sensor FS, based on the outputs of the first pressure sensor P1, the second pressure sensor P2, the flow sensor FS, and a temperature sensor (not shown). The fluid resistance FR is a laminar flow element formed by stacking plates PL with fine grooves formed along the flow direction, as shown in FIG. 10. The sizes of the first volume VL1 and the second volume VL2 vary from the design values depending on various parameters related to the fluid resistance FR, as shown in FIG. 10. In other words, in the past, laminar flow was assumed to occur at the upstream end face of the fluid resistance FR, and the downstream end face of the fluid resistance FR was calculated based on the upstream end position of the designed fluid resistance FR. However, in reality, the position of the fluid resistance FR deviates from the design position due to differences in machining equipment, etc., and the surface LF1 where the laminar flow LF is formed also occurs a certain distance inward from the end face of the fluid resistance FR. For this reason, the inventors discovered that when the size of the first volume VL1 is calculated based on the designed end face position of the fluid resistance FR and the seal surface SL, it deviates from the actual value. Similarly, the size of the second volume VL2 also deviates from the designed size due to factors such as a misalignment of the downstream end face of the fluid resistance FR and the surface LF2 where the laminar flow LF ultimately breaks down occurring outside the fluid resistance FR.

The diagnoser D reduces the discrepancy in the magnitude of the first volume VL1 and second volume VL2, as described above, in order to improve the accuracy of the control model used in the flow control device 100, for example. Specifically, as shown in FIG. 9, the diagnoser D has the functions of at least a diagnostic operation control unit D1, a first volume calculation unit D2, a second volume calculation unit D3, a volume ratio calculation unit D4, and a calibration unit D5. The configuration and operation of each unit will be described in detail below with reference to the flowcharts in FIGS. 11, 12, and 13.

First, the procedure for identifying the size of the second volume VL2 will be explained based on the flowchart shown in Figure 11. Note that the procedure for identifying the second volume VL2 shown in Figure 11 is not performed during a process period in which the flow control device 100 supplies various gases to the chamber, but rather during a pause period in which the supply of various gases to the chamber is stopped, for example.

First, the diagnostic operation control unit D1 controls the first valve V1 to a fully closed state and the second valve V2 to a fully open state. In this way, only the downstream second valve V2 is kept fully open, and the gas in the first volume VL1 and second volume VL2 within the flow control device 100 is exhausted, for example, to an exhaust flow path (step S1).

Next, the diagnostic operation control unit D1 controls the first valve V1 to a fully open state and the second valve V2 to a fully closed state. In other words, by leaving only the upstream first valve V1 open, gas is filled into the first volume VL1 and second volume VL2 within the flow control device 100, and pressure increase begins (step S2).

Furthermore, from the point when gas filling begins, the second volume calculation unit D3 begins measuring the pressure within each volume using the first pressure sensor P1 and the second pressure sensor P2 (step S3).

The second volume calculation unit D3 determines whether the pressure difference between the pressures measured by the first pressure sensor P1 and the second pressure sensor P2 has reached a maximum (step S4). Once this pressure difference reaches a maximum, the second volume calculation unit D3 begins integrating the flow rate output by the flow sensor FS (step S5). The second volume calculation unit D3 then determines whether a sufficient amount of gas has been charged into the first volume VL1 and the second volume VL2, and the pressures measured by the first pressure sensor P1 and the second pressure sensor P2 have reached a substantially equal pressure on the high-pressure side (step S6). Once these pressures are equal, the second volume calculation unit D3 terminates the integration of the mass flow rate (step S7). Finally, the second volume calculation unit D3 divides the calculated integrated flow rate n by the change ΔP2 in the second pressure measured by the second pressure sensor P2 during the integration period to determine the size of the second volume VL2 (step S8).

The reason why the second volume VL2 can be calculated using the above procedure is as follows. The integrated value of the flow rate of gas that has passed through the fluid resistance FR and flowed into the second volume VL2 corresponds to the amount of change in the number of moles of gas that flowed in within the specified period during which the flow rate was integrated. Therefore, when the gas state equation is applied to the gas that has flowed into the second volume VL2, ΔP2·VL2 = _nRGT . Here, n is the integrated value of the flow rate, _RG is the gas constant, and T is the temperature of the gas, which is treated as a constant temperature during the specified period. Transforming this gas state equation reveals that VL2 = ( _nRGT )/ΔP2.

Next, the procedure for identifying the size of the first volume VL1 will be explained based on the flowchart shown in Figure 12. Note that the procedure for identifying the first volume VL1 shown in Figure 12 is not performed during a process period in which various gases are supplied to the chamber by the flow control device 100, but rather during a pause period in which the supply of various gases to the chamber is stopped, for example. Furthermore, while the identification of the second volume VL2 utilizes changes in gas pressure and flow rate during the pressurization process, the identification of the first volume VL1 utilizes changes in gas pressure and flow rate during the depressurization process.

First, the diagnostic operation control unit D1 controls the first valve V1 to a fully open state and the second valve V2 to a fully closed state, and waits until the pressures in the first volume VL1 and the second volume VL2 are approximately equilibrated (step ST1). Next, the diagnostic operation control unit D1 controls the first valve V1 to a fully closed state and the second valve V2 to a fully open state, evacuating gas from the first volume VL1 and the second volume VL2 and starting decompression (step ST2).

Furthermore, from the moment the second valve V2 is opened, the first volume calculation unit D2 begins measuring the pressure within each volume using the first pressure sensor P1 and the second pressure sensor P2 (step ST3).

The first volume calculation unit D2 determines whether the pressure difference between the pressures measured by the first pressure sensor P1 and the second pressure sensor P2 has reached a maximum (step ST4). When the pressure difference reaches a maximum, the first volume calculation unit D2 begins integrating the flow rate output by the flow sensor FS (step ST5).

Next, the first volume calculation unit D2 determines whether the first volume VL1 and the second volume VL2 have been sufficiently evacuated and the pressures measured by the first pressure sensor P1 and the second pressure sensor P2 are approximately equal on the low-pressure side (step ST6). When these pressures become equal, the first volume calculation unit D2 terminates the integration of the mass flow rate (step ST7). Finally, the first volume calculation unit D2 divides the calculated integrated flow rate n by the amount of change ΔP1 in the first pressure measured by the first pressure sensor P1 during the integration period to determine the size of the first volume VL1 (step ST8). Specifically, the first volume calculation unit D2, like the second volume calculation unit D3, determines the size of the first volume VL1 based on VL1 = ( _nRGT )/ΔP1, which is derived from the gas state equation. Here, n is the integrated value of the flow rate, R/ _G is the gas constant, and T is the gas temperature, which is treated as a constant temperature during the specified period.

Next, the procedure for calculating the volume ratio between the first volume VL1 and the second volume VL2 by the volume ratio calculation unit D4 will be described with reference to the flowchart in Figure 13. Note that, unlike Figures 11 and 12, the procedure shown in Figure 13 can be performed not only during a pause period, but also during a process period in which various gases are supplied into the chamber.

First, the first valve V1 and the second valve V2 are under normal flow control by the first valve controller 2 and the flow controller 1 described in the previous embodiment (step SP1). Then, the diagnostic operation control unit D1 controls the first valve V1 to a fully closed state and the second valve V2 to a fully closed state (step SP2). Note that step SP2 may not be the result of the diagnostic operation control unit D1 controlling each valve, but may occur when the set flow rate is zero during the process or when a fully closed command is input to the controller of each valve. In parallel, pressure measurements are initiated by the first pressure sensor P1 and the second pressure sensor P2 (step SP3), and the volume ratio calculation unit D4 stores the initial pressures measured by each pressure sensor (step SP4). Furthermore, the first volume calculation unit D2 and the second volume calculation unit D3 begin integrating the flow rate output by the flow sensor FS, which represents the flow rate of gas flowing through the fluid resistance FR (step SP5). Here, immediately after each valve is fully closed from the flow control state, a pressure difference exists within the flow control device 100, with the first pressure being higher than the second pressure.

The volume ratio calculation unit D4 determines whether the pressures measured by the first pressure sensor P1 and the second pressure sensor P2 are approximately equal (step SP6). When the first pressure decreases and the second pressure increases, and the pressures become approximately equal, the volume ratio calculation unit D4 stores that pressure as the equilibrium point pressure (step SP7), and the first volume calculation unit D2 and the second volume calculation unit D3 stop integrating the flow rate output by the flow sensor FR (step SP8).

The volume ratio calculation unit D4 calculates the ratio between the first volume VL1 and the second volume VL2 based on the stored initial pressures and equilibrium point pressures (step SP9). Specifically, if the initial pressure measured by the first pressure sensor P1 is P1S, the initial pressure measured by the second pressure sensor P2 is P2S, and the equilibrium point pressure is PE, the volume ratio VL1:VL2 between the first volume VL1 and the second volume VL2 can be calculated based on P1S-PE:PE-P2S=VL1:VL2.

Furthermore, the first volume calculation unit D2 divides the integrated flow rate n by P1S-PE to calculate the magnitude of the first volume VL1 (step SP10). Similarly, the second volume calculation unit D3 divides the integrated flow rate n by PE-P2S to calculate the magnitude of the second volume VL2 (step SP11). More specifically, the magnitudes of the first volume _VL1 and the second volume VL2 are calculated based on VL1=( _nRGT )/(P1S-PE) and VL2=( _nRGT )/(PE-P2S), where RGT is the gas constant and T is the gas temperature.

Furthermore, based on the magnitude and ratio of the first volume VL1 and the second volume VL2 calculated by the first volume calculation unit D2, the second volume calculation unit D3, and the volume ratio calculation unit D4, the calibration unit D5 calibrates the parameters used in the flow sensor FR to calculate the flow rate, and also calibrates various parameters used in the first valve controller 2 or the flow controller 1.

As described above, with the flow control device 100 described with reference to Figures 9 to 13, the size and ratio of the first volume VL1 and the second volume VL2 can be identified using values that reflect instrumental errors such as processing errors in the fluid resistance FR and deviations in the position of the surface where laminar flow actually occurs. Therefore, the magnitudes by which the first volume VL1 and the second volume VL2 act on the gas can be accurately obtained, making it possible to more accurately calculate the flow rate and set various parameters used in flow rate control. This makes it possible to achieve more accurate and precise flow rate control.

Note that the start and end points of the interval for calculating the integral value of the flow rate in the procedures shown in Figures 11 to 13 are not limited to those described above. For example, the integration interval may be set to the interval from a predetermined time after the differential pressure between each pressure reaches its maximum to a predetermined time before the pressures reach equilibrium. In other words, depending on the identification accuracy, the interval may be set shorter.

In the above embodiment, what was fed back to the first valve control unit was the applied voltage to the second valve, which is the manipulated variable input to the second valve. However, the second valve may be provided with a displacement sensor so that the opening of the second valve can be measured, and the measured opening measured by the displacement sensor may be fed back to the first valve controller as a controlled variable. In this case, the target quantity input to the first valve controller simply needs to be the opening value that is desired to be maintained at the second valve.

The above-described embodiments may be configured without the reference governor, as shown in the schematic diagram of Figure 2. In this case, the command flow rate set by the user and the set flow rate will be completely consistent. Conversely, as shown in the schematic diagram of Figure 4, the first valve may be omitted, and a flow control device may be configured consisting of a flow sensor, a second valve (control valve), a flow controller, and a reference governor. Furthermore, the control valve is not limited to being located downstream of the flow sensor as shown in the schematic diagram of Figure 4, and the control valve may be located upstream of the flow sensor. When the flow rate is located upstream, the reference governor may reflect in the flow controller both or either a time delay due to the characteristics of the flow sensor itself and a phase lead due to the flow sensor being located upstream by the control valve.

Furthermore, the flow rate calculation formula used in the flow rate calculation unit of the flow sensor is not limited to that described in the above embodiment. For example, if the first pressure is _P1 , the second pressure is _P2 , and the flow path resistance is R, the flow rate may be calculated based on _P12 ^- _P22 and ^the flow path resistance R. Furthermore, the coefficient determined by the coefficient determination unit is not limited to the flow path resistance R, and the value of a parameter that is necessary to calculate other types of flow rates and that changes under the influence of the first pressure or the second pressure may be determined. Furthermore, the reference governor may also sequentially feed back such parameters to reflect the time delay in the flow rate sensor in the flow rate controller.

The flow sensor is not limited to pressure-type flow sensors, and various types such as thermal and ultrasonic types may be used. If the pressure to be maintained at the second valve differs depending on the type of flow sensor, the target amount input to the first valve controller can be changed appropriately so that the second valve achieves an opening corresponding to the pressure to be maintained at the flow sensor. Furthermore, the first and second valves are not limited to normally closed types, and may be normally open types. Since the direction of voltage application is reversed depending on the valve type, the target amount input to the first valve controller can be set accordingly.

The present invention is not limited to flow control devices, but can also be applied to pressure control devices and concentration control devices, for example. That is, the first and second valves may cooperate to match the pressure of the fluid passing through the second valve to a set pressure while maintaining the opening of the second valve at a desired opening. Alternatively, the first and second valves may cooperate to match the concentration of the fluid passing through the second valve to a set concentration while maintaining the opening of the second valve at a desired opening. That is, the fluid control device of the present invention may include a first valve provided in a flow path, a second valve provided in the flow path downstream of the first valve, a fluid sensor that measures a physical quantity of the fluid in the flow path between the first and second valves, a fluid controller that controls a manipulated variable input to the second valve so as to minimize the deviation between the measured quantity measured by the fluid sensor and a set quantity, and a first valve controller that controls the first valve so as to minimize the deviation between a controlled variable, which is the manipulated variable input to the second valve or the opening of the second valve, and a target quantity. The physical quantity referred to here is a concept that includes, for example, flow rate, pressure, and concentration. Furthermore, a fluid sensor measures either the flow rate, pressure, or concentration of a fluid.

In addition, various modifications of the embodiments and combinations of parts of each embodiment may be made as long as they do not contradict the spirit of the present invention.

100... Flow control device V1... First valve V2... Second valve (control valve)
FS...flow rate sensor (fluid sensor)
SM: Sensing mechanism FC: Flow rate calculation section FC1: Coefficient determination section FC2: Output section P1: First pressure sensor P2: Second pressure sensor 1: Flow rate controller 2: First valve controller 3: Reference governor D: Diagnosis device D1: Diagnostic operation control section D2: First volume calculation section D3: Second volume calculation section D4: Volume ratio calculation section

Claims (4)

a first valve provided in the flow path;
a second valve provided downstream of the first valve in the flow path;
a fluid resistance provided in the flow path between the first valve and the second valve;
a first pressure sensor that measures a pressure in a first volume that is a volume between the first valve and the fluid resistance in the flow path;
a second pressure sensor that measures the pressure in a second volume that is a volume between the fluid resistance and the second valve in the flow path;
a flow rate calculation unit that calculates a flow rate of the fluid flowing through the fluid resistance based on a first pressure measured by the first pressure sensor and a second pressure measured by the second pressure sensor;
a diagnoser that diagnoses the volume of the first volume or the second volume,
a diagnostic device that calculates the magnitude of the first volume based on an integrated value of the flow rate calculated by the flow rate calculation unit over a predetermined period and an amount of change in the first pressure over the predetermined period while the first valve is open and the second valve is closed, and calibrates a parameter for flow rate calculation used in the flow rate calculation unit or a parameter used to control the first valve and/or the second valve based on the calculated magnitude of the first volume . 2. The flow control device according to claim 1, wherein the diagnoser calculates the magnitude of the second volume based on an integrated value of the flow rate calculated by the flow rate calculation unit over a predetermined period of time while the second valve is open and the first valve is closed, and an amount of change in the second pressure over the predetermined period of time, and calibrates a parameter for flow rate calculation used in the flow rate calculation unit or a parameter used to control the first valve and/or the second valve based on the calculated magnitude of the second volume . A flow control device according to claim 1 or 2, wherein the predetermined period is the period from when the absolute value of the difference between the first pressure and the second pressure reaches its maximum until when the first pressure and the second pressure become equal. 4. The flow control device according to claim 1, wherein the diagnoser calculates a volume ratio between the first volume and the second volume based on a difference between the first pressure at the start of the predetermined period and the first pressure at the end of the predetermined period, and a difference between the second pressure at the start of the predetermined period and the second pressure at the end of the predetermined period, and calibrates parameters for flow rate calculation used in the flow rate calculation unit or parameters used to control the first valve and/or the second valve based on the calculated volume ratio.