Pressure type flow control device

Abstract

To provide a pressure-type flow rate control device capable of correcting a flow rate on the basis of self-diagnosis results.SOLUTION: A pressure-type flow rate control device 10 comprises: a diaphragm unit 2; an upstream control valve 6; an upstream pressure sensor 3 detecting an upstream pressure P1; a downstream pressure sensor 4 detecting a downstream pressure P2; and a control mechanism having a self-diagnosis function which makes a diagnosis using pressure drop data and reference pressure drop data of the upstream pressure. The control mechanism is configured so as to perform the steps of: diagnosing presence / absence of the occurrence of an opening change of the diaphragm unit using pressure drop data acquired during a period during which a critical expansion condition is satisfied; and determining a correction formula for correcting a flow rate setting signal from outside on the basis of diagnosis results of presence / absence of the occurrence of the opening change. When performing flow rate control after self-diagnosis, the control mechanism controls the control valve 6 using an internal flow rate control signal generated according to the correction formula.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pressure-type flow control device used in semiconductor manufacturing equipment, chemical plants, etc., and particularly to a pressure-type flow control device having a self-diagnosis function.

Background Art

[0002] In semiconductor manufacturing equipment and chemical plants, various flow meters and flow control devices are used to control the flow rate of material gases, etching gases, etc. Among these, the pressure-type flow control device is widely used because it can control the mass flow rate of various fluids with high precision by a relatively simple mechanism combining a control valve and a throttle section (e.g., an orifice plate or a critical nozzle). Different from a thermal flow control device, the pressure-type flow control device has excellent flow control characteristics in that stable flow control can be performed even when the primary supply pressure (the pressure upstream of the control valve) fluctuates greatly.

[0003] Some pressure-type flow control devices adjust the flow rate by controlling the fluid pressure upstream of the throttle section (hereinafter sometimes referred to as the upstream pressure P1). The upstream pressure P1 is usually controlled by adjusting the opening degree of a control valve provided upstream of the throttle section. When the critical expansion condition (upstream pressure P1 / downstream pressure P2 ≥ about 2: in the case of argon gas) is satisfied, the velocity of the gas flowing through the throttle section is fixed at the speed of sound, and it is known that the mass flow rate of the gas flowing downstream of the throttle section is proportional to the upstream pressure P1 regardless of the magnitude of the downstream pressure P2 on the downstream side of the throttle section, and the flow rate can be controlled by controlling the upstream pressure P1.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, due to long-term use or the like, especially depending on the type of gas used, corrosion, clogging, etc. may occur in the throttle portion of the pressure type flow control device. In this case, the opening area of the throttle portion changes, and the flow rate calculated from the upstream pressure P1 deviates from the actual flow rate that was initially compatible. Further, since the pressure type flow control device typically does not have a flow meter such as a thermal sensor, it is not possible to directly measure the actual flow rate of the gas flowing through the flow path after the opening of the throttle portion has fluctuated. For this reason, a pressure type flow control device having a self-diagnosis function for determining whether or not an abnormality has occurred in the throttle portion by utilizing the configuration of the pressure type flow control device has been proposed.

[0006] In the pressure type flow control device described in Patent Document 1, during the period when the critical expansion condition is satisfied, the drop in the upstream pressure after closing the control valve is measured, and self-diagnosis is performed by comparing this with a reference value. Further, it has been found that the relationship ln(P1(t) / P1i)=-α·t (where P1(t) is a function of the upstream pressure P1 with respect to time t and P1i is the initial upstream pressure) holds during the pressure drop period, and it is disclosed that it is possible to determine whether or not an abnormality has occurred in the throttle portion by comparing the slope α obtained from the pressure measurement result with a reference slope α0. The self-diagnosis method described in Patent Document 1 has the advantage that self-diagnosis can be started from an arbitrary flow rate or an arbitrary initial upstream pressure regardless of the flow rate at that time, for example, at the end of a semiconductor manufacturing process.

[0007] However, even if it is determined as a result of self-diagnosis that clogging or opening expansion has occurred in the throttle portion, it is possible to give a warning to the user, but it is difficult to continue using the device as it is. For this reason, conventionally, when an abnormality in the throttle portion was detected, replacement of the throttle portion was required, but replacement of only the throttle portion was not easy. Therefore, as a practical measure, the entire pressure type flow control device was often replaced with a new one.

[0008] If the pressure-type flow control device is replaced each time, the cost will increase significantly and the convenience will also decrease. In particular, in an operating environment where the aperture of the throttle portion is likely to change, such as when the corrosiveness of the gas used is high, the frequency of replacing the pressure-type flow control device becomes high, which is a major problem. Therefore, there has been a demand for a pressure-type flow control device that can be used stably for a longer period even when the aperture of the throttle portion is likely to change.

[0009] The present invention has been made in view of the above problems, and the main object thereof is to provide a pressure-type flow control device that can be used more stably and continuously.

Means for Solving the Problems

[0010] A pressure-type flow control device according to an embodiment of the present invention includes a throttle portion, a control valve provided upstream of the throttle portion, an upstream pressure sensor that detects an upstream pressure that is the pressure of a flow path between the throttle portion and the control valve, a downstream pressure sensor that detects a downstream pressure that is the pressure of a downstream flow path of the throttle portion, and a control mechanism having a self-diagnosis function for diagnosing using pressure drop data of the upstream pressure measured by the upstream pressure sensor and reference pressure drop data. The pressure-type flow control device is configured such that the control mechanism diagnoses the presence or absence of an aperture change of the throttle portion using the pressure drop data acquired during a period in which a critical expansion condition indicating that a pressure ratio of the upstream pressure to the downstream pressure after closing the control valve is equal to or greater than a specified value is satisfied, and determines a correction formula for correcting a flow rate setting signal from the outside based on the diagnosis result of the presence or absence of the aperture change. When performing flow rate control after self-diagnosis, the control valve can be controlled using an internal flow rate control signal obtained by correcting the flow rate setting signal by the correction formula.

[0011] In one embodiment, the step of diagnosing the presence or absence of the opening change further includes a step of calculating a flow rate error with respect to a reference flow rate caused by the opening change, and the correction formula is determined based on the calculated flow rate error.

[0012] In one embodiment, when the flow rate specified by the flow rate setting signal is N and the calculated flow rate error is x%, the correction formula is given by N - N·x%.

[0013] In one embodiment, the control mechanism is configured to generate a flow rate output signal for external output by performing an inverse conversion of the correction formula on the internal flow rate control signal.

[0014] In one embodiment, as the pressure drop data and the reference pressure drop data, the slope α of a straight line defined by ln(P1(t) / P1i) = -αt is used, where P1(t) is a function of the upstream pressure with respect to time, P1i is the initial upstream pressure at the start of the pressure drop, and t is time.

[0015] In one embodiment, the control mechanism has a reference slope α0 corresponding to the slope α of the straight line defined by ln(P1(t) / P1i) = -αt, associated with the initial upstream pressure P1i.

Advantages of the Invention

[0016] According to the pressure type flow rate control device of the embodiment of the present invention, self-diagnosis can be accurately performed using the pressure drop data under critical expansion conditions, and flow rate control correction can be performed based on the result of the flow rate self-diagnosis. Therefore, it is possible to perform flow rate control more continuously and accurately.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the embodiments described below.

[0019] FIG. 1 shows a pressure type flow rate control device 10 according to the present embodiment. The pressure type flow rate control device 10 includes a throttle portion 2 provided in a flow path 1, a control valve 6 provided upstream of the throttle portion 2, an upstream pressure sensor 3 for detecting the upstream pressure P1 between the throttle portion 2 and the control valve 6, a downstream pressure sensor 4 for detecting the downstream pressure P2 on the downstream side of the throttle portion 2, and a temperature sensor 5 for detecting the temperature between the throttle portion 2 and the control valve 6.

[0020] As the upstream pressure sensor 3 and the downstream pressure sensor 4, for example, a semiconductor piezoresistive diffused pressure sensor or a capacitance manometer is used. As the temperature sensor 5, for example, a resistance thermometer or a thermistor is used. As the control valve 6, for example, a piezo element-driven valve (hereinafter sometimes referred to as a piezo valve) that opens and closes a metal diaphragm valve body by a piezo actuator is used. The piezo valve is a valve (proportional valve) that can be opened to an arbitrary opening degree by adjusting the drive voltage applied to the piezo element. Further, as the throttle portion 2, for example, an orifice plate or a critical nozzle is used, and the opening diameter of the throttle portion 2 is set to, for example, 10 to 2000 μm.

[0021] The pressure type flow control device 10 also includes a control mechanism (or control circuit) 7 connected to each of the sensors 3, 4, 5 and the control valve 6. The control mechanism 7 is configured to be able to execute a self-diagnosis function at the end of the process of the semiconductor manufacturing apparatus (when the gas supply to the process chamber is stopped). The control mechanism 7 of the present embodiment incorporates a CPU, a memory, an A / D converter, etc. provided on a circuit board, and includes a computer program for executing the operations described later, and is realized by a combination of hardware and software. Some or all of the components of the control mechanism 7 may be provided outside the pressure type flow control device 10.

[0022] The upstream side of the pressure type flow control device 10 is connected to a gas supply source (not shown), and the downstream side is connected to a process chamber 12 of a semiconductor manufacturing apparatus via a shut-off valve 11 (typically an on-off valve). A vacuum pump 13 is connected to the process chamber 12, and the inside of the process chamber 12 can be evacuated when the gas G is supplied. In the embodiment shown in FIG. 1, the shut-off valve 11 is arranged outside the pressure type flow control device 10, but the shut-off valve 11 may be incorporated in the pressure type flow control device 10. As the shut-off valve 11, for example, an AOV (air-driven valve) or an electromagnetic valve is used.

[0023] In a semiconductor manufacturing process, when supplying gas to the process chamber 12, the control mechanism 7 uses the outputs of the upstream pressure sensor 3 (and the downstream pressure sensor 4 and temperature sensor 5) to calculate the flow rate by computation, and controls the control valve 6 so that the flow rate passing through the throttle portion 2 becomes the set flow rate. The flow rate obtained by the computation may be displayed as a flow rate output value on the display unit of the external control device.

[0024] More specifically, when the critical expansion condition (P1 / P2 ≧ about 2: in the case of argon gas) is satisfied, the calculated flow rate is obtained from the output of the upstream pressure sensor 3 according to the relationship of the flow rate Q = K1P1 (K1 is a proportional coefficient depending on the fluid type and fluid temperature), and the control valve 6 is feedback-controlled so that the calculated flow rate becomes the same as the set flow rate. Also, under non-critical expansion conditions, the flow rate Q = K2P2 m (P1 - P2) n (K2 is a proportional coefficient depending on the fluid type and fluid temperature, and the exponents m and n are values derived from the actual flow rate), and the control valve 6 is feedback-controlled so that the calculated flow rate becomes the same as the set flow rate.

[0025] In addition, the pressure-type flow rate control device 10 of the present embodiment is configured to perform self-diagnosis at the end of the process when the control valve 6 shifts to the closed state and stops the gas supply. At the end of the process, in addition to the control valve 6, the shut-off valve 11 can also be closed to perform self-diagnosis. In this case, in an arbitrary gas supply line, the self-diagnosis process can be executed without affecting semiconductor manufacturing using other gas supply lines.

[0026] The graph shown by the solid line in FIG. 2 is a graph showing the changes in the upstream pressure P1 and the downstream pressure P2 when the control valve 6 is closed. As shown in FIG. 2, when the control valve 6 receives a closing command at time t1 and remains in the closed state thereafter, the upstream pressure P1 drops from the initial upstream pressure P1i during gas flow, and the downstream pressure P2 also drops from the initial downstream pressure P2i.

[0027] And in this embodiment, self-diagnosis is performed based on P1(t) measured during the critical expansion period Δt between times t1 and t2 that satisfy the critical expansion conditions, that is, within the period when P1 / P2 ≥ approximately 2 (in the case of argon gas). In this way, by performing self-diagnosis while confirming whether it is actually under the critical expansion conditions, it is possible to ensure the maximum pressure drop data acquisition period effective for diagnosis regardless of the design of the fluid supply control system or the content of the semiconductor manufacturing process. Also, in recent years, although the downstream pressure P2 at the time of gas supply (i.e., the initial downstream pressure P2i in FIG. 2) may sometimes be relatively high, since self-diagnosis is performed after determining whether it is actually under the critical expansion conditions, the diagnostic accuracy can be improved. Moreover, by closing only the control valve 6, the period during which the critical expansion conditions can be maintained becomes longer, so self-diagnosis can be performed more easily.

[0028] On the other hand, the graph shown by the dashed line in FIG. 2 is a graph showing the changes in the upstream pressure P1 and the downstream pressure P2 when the shut-off valve 11 is closed simultaneously with the control valve 6. The upstream pressure P1 drops from the initial upstream pressure P1i during gas flow, and the downstream pressure P2 rises from the initial downstream pressure P2i during gas flow. That is, pressure fluctuations occur so that the differential pressure is eliminated between the upstream side and the downstream side of the throttle portion 2, and the upstream pressure P1 and the downstream pressure P2 converge to substantially the same equilibrium pressure value P’’ over time. Although the critical expansion period Δt’ between times t1 and t2’ that satisfy the critical expansion conditions is shorter than in the case of the solid line, since the shut-off valve 11 is closed, the self-diagnosis process can be executed without affecting semiconductor manufacturing using other gas supply lines.

[0029] The pressure ratio P1 / P2 indicating the lower limit of the critical expansion conditions varies depending on the gas species. For example, in the case of argon gas, it is 2.05, but for hydrogen it is 1.90, and for nitrogen it is 1.89, and there are determined values for each gas species. Also, the critical expansion conditions change depending on the upstream gas temperature. Therefore, the control mechanism 7 may be configured to determine the determination formula for the critical expansion conditions at the time of self-diagnosis based on at least one of the gas type and the gas temperature.

[0030] The following is a specific example of self-diagnosis. After closing the control valve 6, the control mechanism 7 checks whether it is under critical expansion conditions from the measured upstream pressure P1 and downstream pressure P2, and compares the pressure drop data P1(t) of the upstream pressure P1 measured during the critical expansion period Δt with the reference pressure drop data Y(t) stored in advance. The reference pressure drop data Y(t) is generally measured in advance before factory shipment and stored in the memory of the control mechanism 7. Here, the reference pressure drop data Y(t) is the normal pressure drop data measured in advance before factory shipment, but it may also be measurement data in an abnormal state, previous measurement data, or setting data not based on measurement, etc.

[0031] Figure 3 shows the pressure drop curve A1 of the normal upstream pressure P1, the pressure drop curve A2 when the throttle part is clogged, and the pressure drop curve A3 when the aperture of the throttle part is enlarged due to corrosion, etc., after closing the control valve 6.

[0032] As can be seen from Figure 3, when the throttle part 2 is clogged, since the gas is more difficult to flow, the pressure drop curve A2 shifts upward with respect to the normal pressure drop curve A1. At this time, the time required for the upstream pressure P1 to drop to a predetermined value becomes longer. Also, the upstream pressure P1 after a predetermined time has elapsed after closing the control valve 6 becomes higher than normal.

[0033] On the other hand, when the aperture of the throttle part 2 is enlarged, since the gas is easier to flow, the pressure drop curve A3 shifts downward with respect to the normal pressure drop curve A1. At this time, the time required for the upstream pressure P1 to drop to a predetermined value becomes shorter. Also, the upstream pressure P1 after a predetermined time has elapsed after closing the control valve 6 becomes lower than normal.

[0034] Therefore, by comparing the measured pressure drop curve with the normal pressure drop curve stored in memory, it is possible to determine whether there are abnormalities such as clogging or opening enlargement in the throttle portion. In particular, in this embodiment, since self-diagnosis is performed only during the period when the critical expansion condition is satisfied even after the control valve 6 is closed, this can be carried out with improved diagnostic accuracy at the end of the semiconductor manufacturing process or the like.

[0035] The comparison between the pressure drop data P1(t) of the upstream pressure P1 and the reference pressure drop data Y(t) can be performed by obtaining the cumulative difference generated for each sampling point, but it is also possible to perform it by other methods.

[0036] FIG. 4(a) shows an example of the reference pressure drop data Y(t). The upstream pressure indicated by the reference pressure drop data Y(t) generally decays exponentially. And the reference pressure drop data Y(t) can also be expressed as the reference pressure drop data Z(t) shown by the following formula (1), as shown in FIG. 4(b). Z(t)=ln(P1(t) / P1i)=-(SC(RT) 1 / 2 / V)t ···(1)

[0037] In the above formula (1), P1i is the initial upstream pressure at the time of closing of the control valve 6, P1(t) is the upstream pressure after the lapse of time t, S is the opening cross-sectional area of the throttle portion 2, C is the gas specific heat ratio, R is the gas constant, T is the gas temperature, V is the internal volume of the flow path between the control valve 6 and the throttle portion 2, and t is the time.

[0038] As can be seen from formula (1), the logarithm of the time function P1(t) of the upstream pressure P1 divided by the initial upstream pressure P1i has a slope α(=SC(RT) 1 / 2It can be expressed as -α·t using ( / V). This slope α (more precisely, it is a negative slope -α, but hereinafter, the positive α as an absolute value will be described as the slope) includes the opening cross-sectional area S as an element. Therefore, by memorizing the reference slope α0 measured during normal operation and comparing it with the slope α of the approximate straight line obtained from the measurement of the upstream pressure P1 during self-diagnosis, the change in the opening cross-sectional area S can also be detected.

[0039] More specifically, when the slope α obtained by measurement is smaller than the threshold with respect to the reference slope α0 (that is, the slope of the linear graph is gentler), it can be determined that the opening cross-sectional area S is smaller than the reference, and there is an opening reduction such as clogging in the throttle portion 2. Also, when the slope α obtained by measurement is larger than the threshold with respect to the reference slope α0 (that is, the slope of the linear graph is steeper), it can be determined that the opening cross-sectional area S is larger than the reference, and there is an opening enlargement due to corrosion or the like in the throttle portion 2.

[0040] Also, the above-mentioned logarithmically transformed reference pressure drop data Z(t) = ln(P1(t) / P1i) shows almost the same straight line regardless of the initial upstream pressure P1i and the initial flow rate, that is, the starting upstream pressure P1i or the magnitude of the starting flow rate immediately before the control valve is closed, as confirmed by the experiments of the present inventors. Therefore, as the reference slope α0, one value can be used regardless of the magnitude of the initial flow rate.

[0041] However, in other embodiments, self-diagnosis can also be performed using reference pressure drop data (reference slope α0) associated with the initial flow rate. FIG. 5 is a graph showing the reference slope αx set in association with the initial flow rate. As can be seen with reference to FIG. 5, the relationship between the initial flow rate and the reference slope αx is such that data of a plurality of discrete fixed points D1 to D6 (combinations of the initial flow rate and the reference slope) are stored as a correction table in the memory of the control mechanism 7, and when the initial flow rate is between the fixed points D1 to D6, the reference slope can be obtained by calculation with reference to the correction table. Specifically, as shown in FIG. 5, for example, when the initial flow rate is at X% of the flow rate between two fixed points D3 and D4, the reference slope αx can be obtained by calculation with reference to the equation of the straight line connecting these two fixed points D3 and D4 from the initial flow rate X%.

[0042] In this way, when the control mechanism 7 has the reference slope αx as a function of the initial flow rate X% or the initial upstream pressure P1i, it may be possible to use a more appropriate reference slope αx for any initial flow rate X% or initial upstream pressure P1i. Thereby, the accuracy of self-diagnosis can be further improved.

[0043] Note that the above reference slope and the measured slope during self-diagnosis can also be obtained using only a part of the pressure drop data (for example, the period from 100% flow rate to the decrease to 70% flow rate). By selectively using the data in the initial stage to obtain the slope of ln(P1(t) / P1i), the number of samples can be reduced, so that the speed of data sampling can be realized. As a result, self-diagnosis is possible even in a short time such as between a plurality of steps constituting one process of semiconductor manufacturing, and it is also possible to detect abnormalities more frequently.

[0044] Also, as described above, the slope α (=SC(RT) 1 / 2 / V) can also change depending on the gas temperature T. Therefore, by correcting the slope α or the reference slope α0 based on the temperature T, the change in the throttle opening cross-sectional area S can be estimated more accurately.

[0045] As described above, it is possible to measure the change in the opening area of the throttle portion by measuring the upstream pressure after the control valve is closed at the end of the process or the like. However, when a significant change in the opening area is detected, the pressure-type flow control device of the present embodiment further determines the degree of flow rate error generated from that degree. Then, based on the obtained flow rate error, a correction formula for correcting the flow rate setting signal given from the outside is determined. Then, an internal flow control signal is generated according to the correction formula, and using this, subsequent flow control is performed so as to conform to the current throttle portion opening area. As a result, even after the opening area of the throttle portion changes, the pressure-type flow control device can be continuously used without the need to replace the throttle portion or the pressure-type flow control device. For this reason, even when controlling the flow rate of a gas with relatively high corrosiveness such as HF (hydrogen fluoride), it is possible to continuously and stably control the flow rate over a longer period regardless of the occurrence of a change in the opening area of the throttle portion.

[0046] Note that Patent Document 2 (International Publication No. 2021 / 111979) by the applicant of the present application describes performing self-diagnosis using the pressure (supply pressure P0) on the upstream side of the flow control device and calibrating the flow control device based on the result. However, it should be noted that Patent Document 2 is not related to the technique of performing self-diagnosis at the end of the process or the like using the upstream pressure P1 with the control valve closed, and does not disclose the specific calibration method of the flow control device.

[0047] Hereinafter, a specific example of flow control in the present embodiment will be described. FIG. 6 is a flowchart showing a process of determining a correction formula for generating an internal flow control signal based on the result of self-diagnosis performed by the pressure-type flow control device 10. FIG. 7 is a diagram for explaining a mode of performing flow control using the internal flow control signal generated based on the measured flow rate error in the pressure-type flow control device 10.

[0048] As shown in FIG. 6, in the pressure type flow control device 10, self-diagnosis for determining the state of the throttle portion is performed. First, as shown in step S1, with the gas flowing at a set flow rate, for example, 60% of the set flow rate, the control mechanism 7 receives a command to stop the gas supply and issues a close command (for example, a flow rate 0% command) to the control valve 6.

[0049] Next, as shown in step S2, while determining whether or not the critical expansion condition is satisfied based on the outputs of the upstream pressure sensor 3 and the downstream pressure sensor 4, the output of the upstream pressure sensor 3 is sampled to obtain pressure drop data P1(t).

[0050] Next, as shown in step S3, according to the relationship of ln(P1(t) / P1i)=-αt, the slope α of the approximate straight line is obtained by the least squares method or the like and compared with the reference slope α0 previously stored in the memory. Next, as shown in step S4, when this comparison result is within the allowable range, for example, when the absolute value of the difference (α-α0) is equal to or less than the threshold value, as shown in step S7, it is determined that there is no abnormality in the throttle portion and no correction of the flow control signal is required, and the diagnosis process is terminated.

[0051] On the other hand, in step S4, when it is determined that the error is not within the allowable range, as shown in step S5, in the current state, the amount of flow error occurring is obtained by calculation. In this process, for example, based on Equation (1), the difference (α-α0) is converted into the change amount ΔS of the opening cross-sectional area of the throttle portion 2 and substituted into the flow rate calculation formula Q = K1P1 to obtain it. Here, in the flow rate calculation formula Q = K1P1, the coefficient K1 is given by, for example, K1 = S·FF / T 1 / 2 Here, in this formula, S is the above-mentioned opening cross-sectional area, FF is a constant determined by the gas physical properties (sometimes called a flow factor), and T is the gas temperature. Therefore, if the change amount ΔS of the opening cross-sectional area can be detected, it is possible to obtain by calculation how much the calculated flow rate obtained from the current Q = K1P1 deviates from the actual flow rate.

[0052] In this way, the flow rate error Qe is obtained from the result of the self-diagnosis process. The flow rate error Qe is typically obtained as an error rate with respect to the flow rate. For example, when the reference flow rate, which is a target value given from the outside, is 10 sccm, and it is found that the flow rate error obtained from the change amount ΔS of the above-mentioned opening cross-sectional area is +1.5%, even though the displayed flow rate is 10 sccm, it can be considered that the actually flowing gas is 10.15 sccm.

[0053] Therefore, based on the obtained flow rate error, a correction formula for generating an internal flow rate control signal to be used in subsequent flow rate control is determined. The correction formula is given by, for example, N - N·x% when the flow rate error is x% and the set flow rate is N. If the correction formula is determined in this way, then afterwards, by correcting the external flow rate setting signal using the correction formula to generate an internal flow rate control signal and controlling the control valve according to the internal flow rate control signal, it becomes possible to perform flow rate control as set even in a state where a change in the opening area has occurred.

[0054] FIG. 7 shows the control operation when performing flow rate control using a correction formula determined based on the determined error x% when it is desired to flow gas at 10 sccm in a pressure-type flow rate control device with a full-scale (rated) flow rate of 100 sccm.

[0055] As shown in FIG. 7, an external control mechanism 20 is connected to the pressure-type flow rate control device 10. The external control mechanism 20 is provided between the external device operated by the user and the control mechanism 7 of the pressure-type flow rate control device 10, but it may be incorporated in the external device or may be incorporated as a part for controlling input / output signals in the pressure-type flow rate control device 10.

[0056] First, when a command to flow gas at 10 sccm is input from an external device, the external control mechanism 20 converts it into a command to flow gas at 10% of the rated (100 sccm) flow rate via a flow rate value conversion circuit. This 10% flow rate setting signal is input to the control mechanism of the pressure type flow rate control device 10, and the pressure type flow rate control device 10 generates an internal flow rate control signal based on the above-mentioned flow rate error x% obtained in a self-diagnosis process performed in advance. Here, for the 10% flow rate setting, it corrects to a signal of 10% - 10%×x%. For example, when the flow rate error caused by the influence such as an opening enlargement is 1.5% as above, the internal flow rate control signal sets the target flow rate to 10% - 10%×x% = 9.85% flow rate. Also, for example, when the flow rate error caused by the influence such as an opening clogging is -1.5%, the target flow rate is set to 10% - 10%×x% = 10.15% flow rate.

[0057] Then, by controlling the control valve 6 with the internally flow rate control signal corrected in this way, it becomes possible to control the gas flow rate according to the input flow rate setting signal while the opening area of the throttle part is in a changed state.

[0058] However, although the internal flow rate control signal is corrected, the signal to be output to the outside such as the flow rate display signal is different from the internal flow rate control signal. Therefore, in this embodiment, the flow rate output signal obtained as a result of flow rate control according to the internal flow rate control signal is now subjected to the inverse conversion of the applied correction formula to generate a flow rate output signal in the restored state. As a result, as the flow rate output signal for output to the outside, an output corresponding to 10% flow rate is given to the external control mechanism 20, and the flow rate corresponding to 10% flow rate (10 sccm) is also displayed as the signal displayed to the user.

[0059] As described above, the embodiments of the present invention have been explained, but various modifications are possible. For example, in the above, the case where the correction formula is set to N - N·x% with the flow rate being N and the identified flow rate error being x% has been explained, but it is not limited to this. For example, the correction formula may be set to N×(100 / (100 + x)) in order to set the value obtained by dividing by the flow rate change rate including the error x% as the target flow rate. Further, in the above, the mode of determining the correction formula based on the flow rate error x% obtained from the self-diagnosis process at the end of the process and generating the internal flow rate control signal from the next time onward has been explained, but the self-diagnosis process may be performed for each start flow rate, the flow rate error x may be measured respectively, and the internal flow rate control signal from the next time onward may be generated using the flow rate error x corresponding to each set flow rate. Further, control may be performed using different correction formulas when the controlled flow rate is in the large flow rate range and when it is in the small flow rate range.

Industrial Applicability

[0060] The pressure type flow rate control device according to the embodiment of the present invention is suitably used for accurately controlling the flow rate of the gas supplied in semiconductor manufacturing equipment and the like over a long period of time.

Explanation of Signs

[0061] 1 Flow path 2 Throttle part 3 Upstream pressure sensor 4 Downstream pressure sensor 5 Temperature sensor 6 Control valve 7 Control mechanism 10 Pressure type flow rate control device 11 Shut-off valve 12 Process chamber 13 Vacuum pump

Claims

1. A throttle portion, a control valve provided upstream of the throttle portion, an upstream pressure sensor that detects an upstream pressure which is the pressure of a flow path between the throttle portion and the control valve, a downstream pressure sensor that detects a downstream pressure which is the pressure of a downstream flow path of the throttle portion, and a control mechanism having a self-diagnosis function for diagnosing using pressure drop data of the upstream pressure measured by the upstream pressure sensor and reference pressure drop data. A pressure-type flow control device comprising: The control mechanism, using the pressure drop data acquired during a period in which a critical expansion condition indicating that a pressure ratio of the upstream pressure to the downstream pressure after closing the control valve is equal to or greater than a specified value is satisfied, diagnosing the presence or absence of an opening change of the throttle portion, and calculating a flow rate error with respect to a reference flow rate caused by the opening change of the throttle portion; Based on the diagnosis result of the presence or absence of the opening change, determining a correction formula for correcting a flow rate setting signal from the outside based on the calculated flow rate error, wherein the flow rate specified by the flow rate setting signal is N, and when the calculated flow rate error is x%, the correction formula is given by N - N·x%; is configured to execute, When performing flow rate control after self-diagnosis, it is configured to be able to control the control valve using an internal flow rate control signal obtained by correcting the flow rate setting signal with the correction formula, A pressure-type flow control device configured to generate a flow rate output signal for external display by performing an inverse conversion of the correction formula on the flow rate output signal obtained as a result of flow rate control according to the internal flow rate control signal.

2. As the pressure drop data and the reference pressure drop data, the slope α of a straight line defined by ln(P1(t) / P1i) = -αt is used, where P1(t) is a function of the upstream pressure with respect to time, P1i is the initial upstream pressure at the start of the pressure drop, and t is time. The pressure-type flow control device according to Claim 1.

3. The control mechanism has a reference slope α0 corresponding to the slope α of the straight line defined by ln(P1(t) / P1i) = -αt associated with the initial upstream pressure P1i. The pressure-type flow control device according to Claim 2.

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