Mass flow controller

Abstract

In a mass flow controller that performs flow control at an action position, which is a position at which a fluid acts, at different flow rates according to a supply period, a valve opening signal is output to a flow control valve during a period from a first point in time to a second point in time. A flow rate measurement value determined on the basis of the flow rate signal is larger than a first set value that is a non-zero flow rate set value, the first set value being input to the flow rate setting means, and the second set value being input to the flow rate setting means. A valve opening signal is output to the flow rate control valve such that the flow rate measured value matches the first set value during a period from a second time point at which a second set value, which is a flow rate set value smaller than the first set value, is input to the flow rate setting means, to a third time point at which the flow rate measured value matches the first set value. A valve opening signal is output to the flow control valve such that the flow measurement value matches the second set value during a period from the third time point to the time point at which the first set value is input next time, thereby suppressing the delay and passivation of the rising edge of the flow of the fluid at the operating position.

Description

Technical Field

[0001] The present invention relates to a mass flow controller for intermittently supplying a fluid. Although not particularly limited, the present invention relates to a mass flow controller suitable for semiconductor manufacturing by atomic layer deposition. Background Art

[0002] A mass flow controller is a precision device mainly used in the manufacture of semiconductors. The mass flow controller includes: a flow sensor that outputs a flow signal corresponding to the flow rate of a fluid; a flow control valve that controls the flow rate of the fluid by adjusting the valve opening; a flow setting unit that inputs a flow setting value of the fluid; and a control unit that outputs a valve opening signal to the flow control valve. Typical uses of mass flow controllers in the manufacture of semiconductors include, for example, supplying material gas to a substrate inside a reaction chamber of a semiconductor manufacturing device via a pipe connected to the downstream side of the mass flow controller to form a film.

[0003] With the technological innovation of semiconductor manufacturing methods, mass flow controllers require new specifications. For example, in a technology called atomic layer deposition (hereinafter referred to as "ALD"), a high-precision and homogeneous thin film with controlled film thickness and composition at the atomic layer level is formed by alternately supplying a variety of material gases to the surface of a substrate in small amounts each time. In a mass flow controller used for ALD, it is required to repeat a cycle of supplying a material gas with a controlled flow rate for a short period of about 2 to 3 seconds and then cutting off the supply of the material gas in a certain cycle.

[0004] In this technical field, a mass flow controller suitable for alternately repeating the on and off of gas supply in a short cycle as described above has been proposed. For example, Patent Document 1 describes an invention of a mass flow controller that can maintain the responsiveness of flow control to the state at the time of shipment even when the flow control valve is fatigued due to repeated opening and closing. In addition, for example, Patent Document 2 describes an invention of a mass flow controller that can eliminate response delays and deviations in the timing of supplying material gas by radially arranging multiple devices near a reaction chamber.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2022-83102

[0008] Patent Document 2: Japanese Patent Application Publication No. 2021-157728 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] As described above, the material gas supply unit including the mass flow controller is usually arranged outside the main body of the semiconductor manufacturing device. Usually, the mass flow controller is separated from the reaction chamber, and a pipe for conveying the fluid is provided between the two. In addition, there is a case where a shower head is provided for the purpose of uniformly supplying the fluid to the surface of the substrate. In such a case, it takes about 0.5 seconds to 1.0 seconds for the material gas supplied from the mass flow controller to reach the position of the substrate via the pipe including the shower head. This delay time may be the reason for the reduction in the production efficiency of semiconductors produced by ALD.

[0011] In addition, the shear force caused by viscosity acts on the material gas passing through the pipe near the wall surface of the pipe, so the speed of the material gas passing through the pipe near the wall surface is slower than the speed of the material gas passing through the center of the pipe. When the speed of the material gas flowing in the pipe is distributed, the time for the material gas to reach the substrate is also distributed. As a result, the rising edge of the flow rate of the material gas at the position of the substrate is passivated. The longer the pipe, the more significant the delay and passivation of the rising edge of the material gas at the position of the substrate, which may become a cause of the quality and production efficiency of semiconductors produced by ALD.

[0012] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to improve the quality and production efficiency of semiconductors produced by ALD, for example, by shortening the time required for the rise of the flow rate of a fluid at an action position where the fluid acts.

[0013] Solutions for solving problems

[0014] The mass flow controller involved in the present disclosure comprises: a flow sensor, which outputs a flow signal corresponding to the flow rate of a fluid; a flow control valve, which controls the flow rate of the fluid by adjusting the valve opening; a flow setting unit, to which the flow setting value of the fluid is input; and a control unit, which outputs a valve opening signal to the flow control valve, wherein the mass flow controller performs flow control at an action position at different flow rates according to a supply period, and the action position is a position where the fluid acts. The control unit of the mass flow controller involved in the present disclosure is configured to perform flow control according to each of the first period, the second period, and the third period as follows.

[0015] The first period is a period from a first time point when a first setting value as a non-zero flow setting value is input to the flow setting unit to a second time point when it is determined that the fluid has reached the action position. During the first period, a valve opening signal is output to the flow control valve so that a flow measurement value determined based on the flow signal is greater than the first setting value.

[0016] The second period is a period from the second time point to a third time point, and the third time point is a time point when the second setting value as a flow setting value smaller than the first setting value is input to the flow setting unit. During the second period, a valve opening signal is output to the flow control valve so that the flow measurement value is consistent with the first setting value.

[0017] The third period is a period from the third time point to the time point when the first setting value is input next time. During the third period, a valve opening signal is output to the flow control valve so that the flow measurement value matches the second setting value.

[0018] Furthermore, the control unit is configured to repeatedly execute a control cycle consisting of the first period, the second period, and the third period once or twice or more.

[0019] If a mass flow controller having the above structure is used, the fluid flows at a flow rate greater than the first set value, which is a target flow rate setting value, during the first period, so that the fluid can be filled into the interior of the pipe in a short time. As a result, the time required for the rising edge of the flow rate of the fluid reaching the position (action position) of the substrate is shortened. In addition, when the first period ends and the second period begins, the opening of the flow control valve is controlled so that the fluid flows at a flow rate equal to the first set value as the flow rate setting value, so that the flow rate of the fluid reaching the substrate does not increase in a manner exceeding the flow rate setting value.

[0020] In a preferred embodiment of the present disclosure, the mass flow controller involved in the present disclosure further includes a display unit, which displays at least the flow measurement value. In addition, the display unit is configured to display the first information, which is different from the flow measurement value, through the display unit during the first period, and display the flow measurement value through the display unit during the second period and the third period. If a mass flow controller having the above structure is used, the excess flow temporarily flowing through the mass flow controller during the first period will not be displayed as the flow display value, so that erroneous information will not be transmitted to the operator.

[0021] In another preferred embodiment of the present disclosure, the mass flow controller involved in the present disclosure is further provided with an abnormality response unit, which is configured to perform an abnormality response action when the flow measurement value is judged to be an abnormal value. The abnormality response action is, for example, an action including at least one operation selected from the group consisting of the issuance of an alarm, the reduction of the opening of the flow control valve, and the stop of the supply of the fluid. In addition, the control unit is configured to: in the first period, even if it is judged that the flow measurement value is an abnormal value, a pseudo flow value is output as the flow measurement value to the abnormality response unit, thereby causing the abnormality response unit not to perform the abnormality response action, and the flow measurement value is output to the abnormality response unit in the second period and the third period.

[0022] When the mass flow controller having the above structure is used, the excess flow rate that temporarily flows through the mass flow controller during the first period is not output as a flow rate measurement value to the abnormality handling unit, so that unnecessary abnormality handling action is not performed.

[0023] Effects of the Invention

[0024] If the mass flow controller of the present disclosure is used, even in the case where the fluid is repeatedly flowed or stopped in a short cycle, such as in ALD, the delay and passivation of the rising edge of the flow rate of the fluid at the position of the substrate can be suppressed. As a result, the quality and production efficiency of semiconductors produced by ALD, for example, can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram illustrating the manner of using the mass flow controller according to the present invention.

[0026] Figure 2 This is a schematic block diagram showing an example of the structure of the mass flow controller according to the present invention.

[0027] Figure 3 : is a graph illustrating the change in the intensity (a) of the valve opening signal with respect to time (t) in the mass flow controller according to the present invention.

[0028] Figure 4 The graph illustrates changes in the intensity of the valve opening signal (a), the flow measurement value (b), and the flow rate (c) of the material gas at the action point in the mass flow controller according to the present invention with respect to time (t).

[0029] Figure 5 This is a graph illustrating changes in a flow rate display value (d) with respect to time (t) in a mass flow controller according to a preferred embodiment of the present invention.

[0030] Figure 6 The graph illustrates changes in the intensity (a') of the valve opening signal, the flow measurement value (b'), and the flow rate (c') of the material gas at the action position with respect to time (t) in a conventional mass flow controller. DETAILED DESCRIPTION

[0031] Please refer to the attached Figure 1 The following description and drawings illustrate examples of the embodiments of the present invention, and the embodiments of the present invention are not limited to the embodiments shown in the following description and drawings.

[0032] <use>

[0033] In a certain embodiment, the present invention controls the flow rate at the action position at different flow rates according to the supply period, and the action position is the position where the fluid acts. For example, the present invention is an invention of a mass flow controller that intermittently supplies the fluid to the action position. The fluid supplied by the mass flow controller involved in the present invention can be either a gas or a liquid. When the fluid is a gas, the effect of the present invention is more significant.

[0034] As mentioned above, the main use of mass flow controllers is in the manufacture of semiconductors. In the manufacture of semiconductors, mass flow controllers are used for the purpose of controlling the flow rate of gases used in the manufacturing process of semiconductors. In this case, the object of flow control is not only the gas called material gas that becomes the material of patterned elements, wires, or insulating layers constituting semiconductor devices, but also all gases used in the manufacturing process of semiconductors, such as gases used in the etching process of semiconductor devices.

[0035] The mass flow controller involved in the present invention supplies a fluid to an action position as a position where the fluid acts. In this specification, "action position" refers to a place where the fluid supplied by the mass flow controller achieves its original purpose of use. Below, the case where the mass flow controller involved in the present invention is used to supply material gas to a semiconductor manufacturing device and form a film on a substrate by chemical vapor deposition (CVD) is used as an example for explanation.

[0036] Figure 1This is a schematic diagram illustrating the use of the mass flow controller involved in the present invention. A substrate 6 made of silicon or other materials is pre-installed inside the reaction chamber 4 of the semiconductor manufacturing device 1. The substrate 6 is placed on the ground electrode 7 and is heated to a specified temperature by the heater 9 arranged under the ground electrode 7. The interior of the reaction chamber 4 is maintained in a vacuum state by a vacuum pump not shown connected to the exhaust pipe 10. The "vacuum state" in this specification is not limited to a strictly vacuum state such as a high vacuum, but refers to a broad concept that can also include a reduced pressure state as long as the target film formation can be carried out. The exhaust speed of the vacuum pump is controlled by a conductivity adjustment valve not shown in the figure that is arranged between the exhaust pipe 10 and the vacuum pump. By Figure 1 The vacuum system of the semiconductor manufacturing apparatus 1 is configured as shown so that the pressure inside the reaction chamber 4 is maintained at a constant value regardless of the flow rate of the material gas supplied from the mass flow controller.

[0037] The mass flow controller 2 controls the flow rate of the material gas supplied from the supply source (not shown) and supplies the material gas to the gas supply pipe 3. The material gas flows toward the right side of the figure in the gas supply pipe 3 as indicated by the arrow and reaches the reaction chamber 4 of the semiconductor manufacturing device 1 in a vacuum state. A shower head 5 is provided just above the substrate 6, and the material gas supplied from the gas supply pipe 3 is released into the reaction chamber 4 from a large number of fine holes provided on the lower surface of the shower head 5 and then reaches the surface of the substrate 6. The shower head 5 is provided for the purpose of uniformly supplying the material gas to the surface of the substrate 6.

[0038] The nozzle 5 is made of a conductor and also serves as an RF electrode. The nozzle 5 and the ground electrode 7 provided with the substrate 6 together form a pair of parallel plate electrodes. When a high-frequency power source is connected to the electrodes and energized, RF discharge is generated between the electrodes to ionize the material gas, generating a plasma 8 composed of ions and high-speed electrons. In the plasma 8, the molecules constituting the material gas are easily decomposed due to the collision of high-speed electrons. As a result, a chemical reaction with the material gas occurs on the surface of the substrate or the surface of the film deposited on the substrate, thereby forming a target film on the substrate, and the material gas achieves its original purpose of use. In other words, in Figure 1 In the illustrated embodiment, the position of the surface of the substrate and the position of the surface of the film deposited on the substrate correspond to the action position in the present invention.

[0039] exist Figure 1In the semiconductor manufacturing apparatus 1 illustrated, the RF electrode 5 and the ground electrode 7 are arranged horizontally, and the substrate 6 is set on the ground electrode 7. This electrode structure is called face down deposition, which is the most basic electrode structure. However, the use of the mass flow controller involved in the present invention is not limited to supplying material gas to a semiconductor manufacturing apparatus that adopts face down deposition as an electrode structure. In the use mode other than the above, as in the above, the place where the fluid achieves its original purpose of use can be determined as the action position.

[0040] The mass flow controller involved in the present invention controls the flow rate at the action position at different flow rates according to the supply period. In this specification, "controlling the flow rate at different flow rates according to the supply period" means that, with respect to a certain mass flow controller, the flow rate of the fluid is controlled by stably supplying the fluid at a specific flow rate during a certain supply period, and the flow rate of the fluid is controlled by stably supplying the fluid at a flow rate smaller than the specific flow rate or stopping the supply of the fluid during a supply period different from the above supply period.

[0041] More specifically, the control unit included in the mass flow controller according to the present invention is configured to perform flow rate control as follows based on each of the first period, the second period, and the third period.

[0042] The first period is a period from a first time point when a first setting value as a non-zero flow setting value is input to the flow setting unit to a second time point when it is determined that the fluid has reached the action position. During the first period, a valve opening signal is output to the flow control valve so that a flow measurement value determined based on the flow signal is greater than the first setting value.

[0043] The second period is a period from the second time point to a third time point, and the third time point is a time point when the second setting value as a flow setting value smaller than the first setting value is input to the flow setting unit. During the second period, a valve opening signal is output to the flow control valve so that the flow measurement value is consistent with the first setting value.

[0044] The third period is a period from the third time point to the time point when the first setting value is input next time. During the third period, a valve opening signal is output to the flow control valve so that the flow measurement value matches the second setting value.

[0045] Furthermore, the control unit is configured to repeatedly execute a control cycle consisting of the first period, the second period, and the third period once or twice or more.

[0046] The lengths of the first period, the second period, and the third period may all be equal, may all be different, or may only be partially equal. In addition, the first setting value newly input at the end of the third period (i.e., at the beginning of the first period included in the next control cycle) may be equal to or different from the first setting value input at the beginning of the first period included in the previous control cycle. And, the second setting value newly input at the beginning of the next third period may also be equal to or different from the second setting value input at the beginning of the third period included in the previous control cycle. Typically, the lengths of the first period, the second period, and the third period are constant throughout the entire range of all control cycles, and the first setting value and the second setting value are also constant.

[0047] In addition, the second set value, which is a flow rate set value smaller than the first set value, may also be zero. In this case, the control unit of the mass flow controller involved in the present invention outputs a valve opening signal for closing the valve to the flow control valve during the third period. That is, the mass flow controller involved in the present invention intermittently supplies the fluid to the action position. In this specification, "intermittently supplying the fluid" means that, with respect to a certain mass flow controller, a stable flow period (second period) in which the fluid is stably supplied at a constant flow rate and a stop period (third period) in which the supply of the fluid is stopped are repeated alternately in a relatively short cycle. The lengths of the stable flow period and the stop period may be equal or different. The delay and passivation of the rising edge of the flow rate of the fluid at the position of the above-mentioned substrate are phenomena that occur at the moment of switching from the stop period to the stable flow period. This phenomenon is almost not a problem when the fluid is stably supplied from the mass flow controller for a long time, but it may become a problem when the fluid is intermittently supplied. In addition, even if the second set value is not zero, the delay and passivation of the rising edge of the flow rate of the fluid at the position of the substrate may be caused at the moment when the first set value is newly input at the beginning of the first period included in the next control cycle.

[0048] 〈Hardware Structure〉

[0049] The mass flow controller involved in the present invention comprises: a flow sensor that outputs a flow signal corresponding to the flow rate of a fluid; a flow control valve that controls the flow rate of the fluid by adjusting the valve opening; a flow setting unit that sets a flow value for the input fluid; and a control unit that outputs a valve opening signal to the flow control valve. The control unit among these structural elements performs control unique to the present invention, and therefore will be described in detail later.

[0050] The flow sensor may be any flow sensor as long as it is a known flow sensor that can be used for a mass flow controller. Specifically, for example, a thermal flow sensor, a pressure flow sensor, etc. may be used. In order to quickly detect changes in the flow rate of the fluid, it is preferred to use a flow sensor with the shortest possible response time.

[0051] The flow control valve may be any flow control valve as long as it is a known flow control valve that can be used for a mass flow controller. Specifically, for example, a flow control valve composed of a valve body including a diaphragm, a valve seat, and an actuator that drives the diaphragm can be used. In order to supply as much fluid as possible during a short period of stable flow, it is preferred to use a flow control valve with as large a conductivity as possible. In addition, conductivity refers to a coefficient indicating the ease of flow of gas in the piping, and is equal to the value obtained by dividing the mass flow rate of the gas flowing in the piping by the pressure difference at both ends of the piping.

[0052] The flow setting unit may have any structure as long as it has the function of transmitting a signal corresponding to data input as a flow setting value of the fluid controlled by the mass flow controller to the control unit. As a specific example of the flow setting unit, for example, a communication unit provided for the purpose of receiving a command based on an electrical signal is equivalent, and the electrical signal is a signal from a control computer provided outside the mass flow controller.

[0053] The control unit may have any structure as long as it has the function of controlling the flow rate of the fluid by outputting a valve opening signal to the flow control valve so as to change the opening of the flow control valve. For example, the control unit is an electronic control device having a microcomputer as a main part. The microcomputer includes a CPU (processor), ROM, RAM, non-volatile memory, and an interface. The CPU is configured to implement the above functions by executing instructions (programs, routines) stored in the ROM.

[0054] Figure 2 This is a schematic block diagram showing an example of the structure of the mass flow controller according to the present invention. Figure 2 is a diagram conceptually showing the structure of the mass flow controller involved in the present invention. It should be noted that Figure 2 The figures do not specifically show the shape, structure, and combination of the mass flow controller and its structural components according to the present invention.

[0055] Figure 2The illustrated mass flow controller 2 includes a flow path 20 for fluid flow. The fluid flows into the interior of the mass flow controller 2 from the inlet 21 and flows out to the outside from the outlet 22. A flow sensor 30 and a flow control valve 40 are provided between the inlet 21 and the outlet 22 of the flow path 20. The flow sensor 30 includes a bypass 31 provided inside the flow path 20, a sensor tube 32 branched from the flow path 20, and a group of electric heating wires 33 wound on the upstream and downstream sides of the sensor tube 32. The bypass 31 has a function of keeping the ratio of the flow rate of the fluid flowing in the flow path 20 to the flow rate of the fluid branched to the sensor tube 32 constant. The bypass 31 can be composed of a laminar flow element formed by bundling a large number of pipes, for example. The sensor tube 32 branches from the flow path 20 on the upstream side of the bypass 31 and merges with the flow path 20 again on the downstream side of the bypass 31. If the set of electric heating wires 33 wound around the sensor tube 32 is energized, when the fluid flows inside the sensor tube 32, the heat generated by the energization moves from the upstream side to the downstream side, so that the temperature difference generated between the set of electric heating wires 33 causes a difference in resistance value. By detecting the difference in resistance value, the flow rate of the fluid flowing inside the sensor tube 32 can be detected, and the flow rate of the fluid flowing in the flow path 20 can be further detected. That is, Figure 2 The illustrated flow rate sensor 30 is a thermal flow rate sensor.

[0056] The flow rate of the fluid detected by the flow sensor 30 is used to control the flow rate of the fluid flowing in the flow path 20. Specifically, the control unit 50 of the mass flow controller 2 is used to control the opening of the flow control valve 40 so that the flow rate of the fluid detected by the flow sensor 30 is consistent with the flow setting value input from the control computer not shown in the figure to the flow setting unit 60. The flow control valve 40 includes a valve body 41 and its driving mechanism 42. A valve opening signal, which is a control signal output from the control unit 50, is input to the driving mechanism 42 to control the opening of the valve body 41. In the case where the driving mechanism 42 is composed of a piezoelectric element, a voltage signal can be used as the valve opening signal. As described above, Figure 2 The illustrated mass flow controller 2 includes a thermal flow sensor 30, but as described above, a pressure flow sensor or other known flow sensors may be included as the flow sensor 30. Regardless of the structure of the flow sensor 30, the mass flow controller 2 determines the flow rate of the fluid based on the flow rate signal output from the flow sensor 30, and controls the opening of the flow control valve 40 so that the flow rate matches the flow rate setting value.

[0057] As described above, the flow setting value input to the flow setting unit at the first time point is the first setting value which is a non-zero flow setting value, and the flow setting value input to the flow setting unit at the third time point is the second setting value which is a flow setting value smaller than the first setting value. In addition, when the second setting value is zero, the flow setting value input to the flow setting unit is a non-zero value (first setting value) during the stable flow period (second period), and is zero (second setting value) during the stop period (third period).

[0058] <Control unit operation>

[0059] As described above, the control unit of the mass flow controller according to the present invention is configured to perform the control operation unique to the present invention. Figures 3 to 6 , while comparing with the prior art, the operation of the control unit in the present invention is described in detail. In addition, in the following description, the following case is described as an example: the second set value as a flow rate setting value smaller than the first set value is equal to zero, the first set value is a non-zero flow rate setting value, and the period during which the flow rate setting value is the first set value and the period during which the flow rate measurement value is the second set value are alternately set, so that the fluid is intermittently supplied to the action position through the mass flow controller.

[0060] Figure 6 The graph is a graph showing the change of the valve opening signal intensity a', the flow measurement value b' and the flow rate c' of the material gas at the action position with respect to time t when the material gas is intermittently supplied using a mass flow controller according to the prior art. In the following description, the valve opening signal intensity a' is referred to as "valve opening signal a'". The time change of the signal intensity and flow rate shown here represents the use of the same Figure 1 The time change when the semiconductor manufacturing apparatus 1 is the same as the exemplified one and the mass flow controller 2 according to the present invention is replaced with a mass flow controller according to the conventional art.

[0061] The valve opening signal a' is the intensity of the signal input to the flow control valve from the control unit of the mass flow controller involved in the prior art. The relationship between the intensity of the valve opening signal, such as the current value or the voltage value, and the opening of the flow control valve can be a positive correlation or a negative correlation. That is, the flow control valve can be constructed so that the greater the intensity of the valve opening signal, the greater the opening of the flow control valve, and conversely, it can also be constructed so that the greater the intensity of the valve opening signal, the smaller the opening of the flow control valve. However, in the following, for the purpose of making the invention easy to understand, the explanation is based on the premise that the intensity of the valve opening signal and the opening of the flow control valve are in a positive correlation. That is, in the following explanation, the situation where the greater the intensity of the valve opening signal, the greater the opening of the flow control valve is described.

[0062] The flow rate measurement value b′ is determined based on a flow rate signal output by a flow rate sensor provided in a conventional mass flow controller. The flow rate c′ of the material gas at the action position is the flow rate of the material gas at the position of the surface of the substrate 6 .

[0063] like Figure 6 As shown, in the mass flow controller involved in the prior art, in the stable flow period F' from the time when a non-zero flow setting value (first setting value) is input into the flow setting unit to the time when a flow setting value (second setting value) equal to zero is input into the flow setting unit, the valve opening signal a' is fixed to a constant value. In the stop period S' from the time when a flow setting value (second setting value) equal to zero is input into the flow setting unit to the time when a non-zero flow setting value (first setting value) is next input into the flow setting unit, the valve opening signal a' is fixed to zero. In the stable flow period F', the control unit controls the opening of the flow control valve by outputting the controlled valve opening signal a' to the flow control valve so that the flow measurement value b' is consistent with the flow setting value. In the stop period S', the control unit makes the flow rate of the fluid zero by outputting the valve opening signal a' for closing the valve to the flow control valve.

[0064] By executing the above control actions, Figure 6 As shown, the change of the flow measurement value b' of the mass flow controller involved in the prior art with respect to time t is roughly consistent with the change of the valve opening signal a' with respect to time t. However, there is a certain time delay from the start of the stable flow period F' to the start of the increase of the flow measurement value b'. In addition, the rising edge of the flow rate after the flow measurement value b' starts to increase is slow, and it takes a little time to reach a stable value. These delays are caused by: the time taken from the input of the valve opening signal a' to the flow control valve to the actual start of the valve opening and / or the time taken for the movement of the material gas in the internal piping of the mass flow controller, etc.

[0065] Next, when referring to Figure 6 In the graph of the flow rate c' of the material gas at the action position shown, the time delay from the start of the stable flow period to the start of the increase in the flow rate c' and the time delay from the start of the increase in the flow rate c' to the reaching of the stable value are both greater than the time delay of the flow measurement value b'. The reason is that, as mentioned above, it takes time for the material gas supplied from the mass flow controller to reach the position of the substrate 6 through the gas supply piping 3, and the velocity distribution of the material gas is generated during the period of passing through the gas supply piping 3. The material gas that cannot reach the position of the substrate 6 during a stable flow period F' remains inside the gas supply piping 3 and the nozzle 5. The remaining material gas is discharged to the outside through the exhaust piping 10 or the purge piping not shown during the stop period S' and does not contribute to film formation.

[0066] When the general Figure 6 When the valve opening signal a' shown is compared with the change in the flow rate c' of the material gas at the action position relative to time t, it can be seen that: due to the delay in the rising edge of the flow rate c', the supply amount of the fluid in a stable flow period F' corresponding to the area of ​​the curve is greatly reduced compared to the setting. In order to compensate for the greatly reduced supply amount, it is necessary to use the valve opening signal a' to increase the opening of the flow control valve or increase the length of the stable flow period F' (extend the stable flow period F'). However, when the opening of the flow control valve is increased to increase the flow rate c' of the material gas at the action position, there is a concern that particles will be blown up inside the reaction chamber 4 due to the flow of the material gas, thereby contaminating the substrate 6. On the other hand, when the stable flow period F' is extended, there is a concern that the film formation speed in ALD will slow down and the production efficiency of the semiconductor will decrease.

[0067] Figure 3 1 is a graph illustrating the change of the intensity a of the valve opening signal relative to time t in the mass flow controller involved in the present invention. In addition, in the following description, the intensity a of the valve opening signal is simply referred to as "valve opening signal a". Figure 3 As shown, the control unit included in the mass flow controller according to the present invention performs flow rate control as follows according to each of the first period, the second period, and the third period.

[0068] During the period from the first time point to the second time point, i.e., the first period (hereinafter sometimes referred to as the "transition period T"), the control unit outputs a valve opening signal having a strength greater than the strength of the valve opening signal when the flow measurement value is consistent with the first setting value in a stable state to the flow control valve, so that the flow measurement value determined based on the flow signal is greater than the first setting value as a non-zero flow setting value. The first time point is the time point when the first setting value is input to the flow setting unit, and the second time point is the time point when it is determined that the material gas has reached the action position. Thus, during the transition period T (first period), the opening of the flow control valve is made greater than the opening of the flow control valve when the flow measurement value is consistent with the first setting value in a stable state, so that the fluid flows at a flow rate greater than the first setting value as the target. Such a control action performed by the control unit during the transition period T (first period) is a control action that does not exist in the above-mentioned prior art, and is a control action unique to the invention of the present application. Figure 3 The length of the transition period T is indicated by the symbol t T express.

[0069] During the second period from the second time point to the third time point (hereinafter sometimes referred to as the "stable flow period F"), the control unit outputs a valve opening signal to the flow control valve so that the flow measurement value is consistent with the first set value. The second time point is the time point when the material gas is judged to have reached the action position, and the third time point is the time point when the second set value, which is a flow setting value smaller than the first set value (equal to zero), is input to the flow setting unit. In this specification, the valve opening signal that is controlled so that the flow measurement value is consistent with the flow setting value is sometimes referred to as the "controlled valve opening signal". The control mentioned here specifically refers to feedback control, for example. For example, the flow measurement value is determined by performing various corrections on the flow signal output from the flow sensor. Specifically, the correction refers to correction based on a known conversion factor caused by different types of material gases. The control action performed by the control unit in the stable flow period F (second period) is basically the same as the control action in the stable flow period F' in the above-mentioned prior art.

[0070] During the third period (hereinafter sometimes referred to as "stop period S") from the third time point to the time when the first set value, which is a flow setting value larger (non-zero) than the second set value, is input to the flow setting unit, the control unit outputs a valve opening signal to the flow control valve so that the flow measurement value is consistent with the second set value. The third time point is the time point when the second set value equal to zero is input to the flow setting unit. In the example described here, since the second set value is equal to zero, the control unit outputs a valve opening signal for closing the valve to the flow control valve so that the flow measurement value is zero. The stable flow period F ends due to the start of the stop period S (third period). During the period from the start of the stop period S to the time when the first set value (which is a non-zero flow setting value larger than the second set value) is input next time, the flow control valve remains in a closed state. At the end of the stable flow period F (i.e., when the stop period S starts), control is not performed to make the fluid flow at a flow rate different from the flow setting value as in the above-mentioned transition period T.

[0071] The mass flow controller of the present invention outputs Figure 3 The valve opening signal a is used to intermittently supply the material gas to the action position. Figure 3 The control cycle shown in the example consists of a transition period T (first period), a stable flow period F (second period) and a stop period S (third period) until the original purpose of the material gas is achieved. During the period when the control cycle is repeated like this, Figure 3 The profile of the valve opening signal a shown as an example may be constant, or one or both of the intensity and time of the valve opening signal a may be changed.

[0072] Figure 4 This is a graph showing the change of the valve opening signal a, the flow measurement value b, and the flow rate c of the material gas at the action position with respect to time t in the mass flow controller according to the present invention. The time change of the signal and the flow rate shown here represents Figure 1 The time change in the semiconductor manufacturing apparatus 1 shown in the example. The valve opening signal a is a signal input to the flow control valve from the control unit of the mass flow controller involved in the present invention. The flow measurement value b is a flow measurement value determined based on the flow signal output by the flow sensor of the mass flow controller involved in the present invention. The flow rate c of the material gas at the action position is the flow rate of the material gas at the position of the surface of the substrate 6. Figure 4 The curve diagram of the valve opening signal a in the curve diagram is Figure 3 The same graph is shown again for comparison with the graph of the flow rate measurement value b and the flow rate c of the material gas at the action position. Figure 4 middle.

[0073] By executing based Figure 3 The control action of the valve opening signal a shown in FIG. Figure 4 As shown in FIG. 1 , the change of the flow measurement value b of the mass flow controller involved in the present invention relative to time t is substantially consistent with the change of the valve opening signal a relative to time t. Figure 4 The transition period T is equivalent to Figure 5 As in the case of the start of the stable flow period of the prior art shown in the figure, there is a slight time delay from the start of the transition period T to the start of the increase in the flow measurement value b. In addition, the rising edge of the flow c after the flow measurement value b starts to increase is slightly slower than the rising edge of the valve opening signal a. However, in the present invention, since an excessive valve opening signal is output to the flow control valve during the transition period T, these delays are limited compared to the case of the prior art.

[0074] Next, when referring to Figure 4 In the graph of the flow rate c of the material gas at the action position, the time delay from the start of the transition period T to the start of the flow rate c increase and the time delay from the start of the flow rate c increase to the stable value are both greater than Figure 6These time delays are small in the case of the flow rate c' of the fluid at the action position in the prior art shown. This is because, during the period from the transition period T unique to the present invention to the start of the stable flow period F, the material gas excessively supplied from the mass flow controller 2 is quickly filled into the gas supply piping 3 and the nozzle 5, so it is easy to achieve a flow rate c that is substantially equal to the flow rate setting value in the stable flow period F at the start time of the stable flow period F. In addition, in the mass flow controller involved in the present invention, the material gas that cannot reach the position of the substrate 6 during a stable flow period F is also discharged to the outside through the exhaust piping 10 or the purge piping not shown during the stop period S without contributing to film formation, but the amount of material gas that is wastefully discharged in the present invention is limited.

[0075] When the general Figure 4 When comparing the change in the valve opening signal a with the flow rate c of the material gas at the action position relative to time t, although a deviation is observed between the two in the transition period T, they are very consistent in the stable flow period F. Figure 6 The flow rate c' appears in the material gas supply amount greatly reduced compared to Figure 4 The amount of shortage in the transition period T of the flow rate c is small. Therefore, the shortage can be fully compensated by slightly increasing the flow rate setting value or slightly extending the stable flow period F. Therefore, if the mass flow controller involved in the present invention is used, the quality and production efficiency of semiconductors produced by ALD, for example, can be improved compared with the prior art.

[0076] 〈Fluid reaches the action position〉

[0077] In a preferred embodiment of the present invention, the mass flow controller of the present invention predetermines the length of the transition period T (first period), or determines the length of the transition period T during the transition period T. In order to perform the above control by the control unit of the mass flow controller of the present invention, it is necessary to know the time from the start of the supply of fluid by the mass flow controller to the arrival of the fluid at the action position under certain conditions. The length t of the transition period T is determined by this time. T. The control unit outputs an excessive valve opening signal to the flow control valve during the duration of the transition period T. If it is determined that the fluid has reached the action position, the transition period T ends and the stable flow period F (the second period) begins, and the control unit outputs a controlled valve opening signal to the flow control valve. Specifically, the control unit outputs a valve opening signal to the flow control valve so that the flow measurement value is consistent with the first set value. The transition period T starts at a first time point, which is a time point when the first set value as a non-zero flow setting value is input to the flow setting unit, but there is no input signal that triggers the end of the transition period T and the beginning of the stable flow period F. Therefore, in order for the control unit to switch the action in the transition period T to the action in the stable flow period F, the optimal length t of the transition period T under certain usage conditions must be determined in advance. T , or during the transition period T, the length t is determined T .

[0078] In order to determine the length of the transition period T T There are several methods to find the optimal value of . The first method is to detect the arrival of the fluid at the action position during the transition period T. Specifically, for example, always measure Figure 1 The pressure inside the reaction chamber 4 shown can be judged as the time point when the pressure starts to increase as the time point when the material gas reaches the action position (i.e., the second time point). As mentioned above, the pressure inside the reaction chamber 4 is maintained in a vacuum state by the vacuum pump, so the pressure inside the reaction chamber 4 rises at the moment when the material gas is released from the pores of the nozzle 5 into the reaction chamber 4. Therefore, for example, a pressure sensor that outputs a pressure signal corresponding to the pressure at the action position is also provided, and the time point when the increase in pressure after the first time point determined based on the pressure signal output from the pressure sensor becomes greater than a predetermined first threshold value can be set as the second time point.

[0079] However, when the amount of the supplied material gas is less than the volume of the reaction chamber 4, the pressure change is slight, so in such a case, it is preferable to use a pressure gauge with high sensitivity as the pressure sensor. Specifically, a known pressure gauge such as a Pirani gauge, a diaphragm gauge, an ion gauge, or a Penning gauge can be used.

[0080] Used to determine the length t of the transition period T TThe second method of finding the optimal value of is to investigate the relationship between the growth rate of the film formed by the material gas reaching the surface of the substrate and the length of the transition period T. When the length of the stable flow period F and the flow rate setting value are fixed to the minimum value that can form one atomic layer, when the length of the transition period T is gradually shortened, the film growth rate begins to decrease when the length of the transition period T becomes less than a certain value. The length of the transition period T before the film growth rate begins to decrease is t T Although the thickness of the film deposited on the substrate in one stable flow period F is only one atomic layer and is very small, the thickness of the entire atomic layer repeatedly deposited by ALD can be measured by a known method.

[0081] Used to determine the length t of the transition period T T The third method of finding the optimal value of is to estimate the length t of the transition period T based on the conductivity value obtained based on the type and temperature of the gas and the inner diameter and length of the gas supply pipe 3. T The conductivity value of commonly used gases is known. If the conductivity is known, the time required for the gas released from the mass flow controller 2 to fill the gas supply pipe 3 can be calculated, and the length t of the transition period T can be estimated based on this time. T In addition, the length t used to determine the transition period T T The method of determining the optimal value of is not limited to the method shown above.

[0082] The length t of the transition period T obtained by the method shown above is T The optimal value of can be used for the control of the control unit by inputting it into the control unit of the mass flow controller involved in the present invention in advance, or storing it in a computer provided outside the mass flow controller and inputting it into the control unit when necessary. In the case of the first method described above, the length t of the transition period T can also be determined each time by measuring the change in the pressure inside the reaction chamber 4 in situ while using the mass flow controller. T .

[0083] 〈Display unit〉

[0084] In a preferred embodiment of the present invention, the control unit of the mass flow controller involved in the present invention also has a display unit, which can at least display the flow measurement value, and the control unit is configured to display the first information as information different from the flow measurement value through the display unit during the transition period T (first period), and display the flow measurement value through the display unit during the stable flow period F (second period) and the stop period S (third period). The display unit in this preferred embodiment is typically used for the mass flow controller involved in the present invention to display and notify the operator of the current flow rate. Regarding the display of the flow rate, specifically, for example, it can be a flow rate displayed as a digital value, or it can be a flow rate displayed by an analog display such as an electromagnetic meter, or it can be a flow rate displayed by other known display methods.

[0085] The "first information" is information displayed by the display unit in place of the flow measurement value during the transition period T, and may be a predetermined constant value (e.g., zero), or may be a character string and / or image for providing certain information to the operator.

[0086] Figure 5 2 is a graph showing the change of the flow rate display value d displayed by the display unit with respect to time t in a preferred embodiment. Figure 5 The horizontal axis of the time axis is Figure 3 and Figure 4 The time axis shown is the same. Figure 5 As shown, during the transition period T, the display unit displays zero as the first information. The reason why the display unit is configured to display zero instead of the flow measurement value determined based on the flow signal during the transition period T is that when directly displaying, for example, Figure 4 When the flow measurement value b is shown as an example, a flow rate greater than the flow setting value input to the flow setting unit will be displayed, so there is a concern that erroneous information will be conveyed to the operator. Figure 4 The excessive flow rate in the illustrated transition period T is consumed mainly for filling the gas supply pipe 3 and the nozzle 5, and does not contribute at all to the film formation on the substrate 6 in the stable flow period F. By displaying zero in the transition period T, the display unit can convey to the operator information that is closer to the actual state of the flow rate of the fluid controlled by the mass flow controller, that is, information on the flow rate of the material gas at the action position.

[0087] like Figure 5As shown in FIG. 1 , during the stable flow period F and the stop period S, the display unit displays the flow measurement value. When the transition period T ends and the filling of the gas supply pipe 3 with gas is completed and the stable flow period F begins, the control unit outputs a controlled valve opening signal to the flow control valve to replace the previous excessive valve opening signal, so that the flow measurement value determined based on the flow signal is consistent with the flow setting value (first setting value). During the stable flow period F, the flow measurement value is basically as follows: Figure 4 The flow rate measurement value b shown in the example is a constant value. This flow rate is also consistent with the flow rate of the material gas at the action position. Then, when entering the stop period S, the flow rate measurement value of the material gas flowing by the mass flow controller becomes zero (the second set value). In addition, as mentioned above, during the stop period, the remaining material gas is discharged and does not contribute to film formation. Therefore, the flow rate of the material gas at the action position is substantially zero.

[0088] As described above, in a preferred embodiment, the flow display value displayed during the entire period of the stable flow period F and the stop period S is not significantly different from the actual flow rate of the material gas at the action position. In addition, when the first information, which is the information displayed on the display unit during the transition period T, is set to zero as described above, it is also possible to make the flow display value displayed by the display unit during the transition period T not significantly different from the actual flow rate of the material gas at the action position. However, as described above, the first information does not necessarily need to be a value such as zero, for example, it can also be a non-zero predetermined constant value, or it can also be an image such as a character string and / or image for providing certain information to the operator. As specific examples of such information, for example, information indicating that the flow measurement value is zero or information indicating that the flow control performed by the mass flow controller is in the transition period T can be cited, but it is not limited to them.

[0089] When the mass flow controller having the above structure is used, an excessive flow rate temporarily flowing through the mass flow controller during the transition period T (first period) is not displayed as a flow rate display value, so that erroneous information is not conveyed to the operator.

[0090] Abnormal Response Unit

[0091] In another preferred embodiment of the present invention, the mass flow controller involved in the present invention is further provided with an abnormal response unit, which is configured to perform an abnormal response action when the flow measurement value is judged to be an abnormal value. As a specific example of the condition for judging that the flow measurement value is an abnormal value, for example, the difference between the flow measurement value and the flow setting value is above a prescribed second threshold value and / or the flow measurement value is above a prescribed third threshold value. However, the condition is not limited to these and can be appropriately determined according to the required specifications of a device such as a semiconductor manufacturing device to which the mass flow controller involved in the present invention is applied.

[0092] In addition, the abnormal response action is, for example, an action including at least one operation selected from the group consisting of the issuance of an alarm, the reduction of the opening of the flow control valve, and the stop of the supply of the fluid. The alarm may be, for example, an image and / or text displayed by a display device such as the above-mentioned display unit, a sound and / or voice sounded by an acoustic device such as a buzzer and / or a speaker, or a light emitted by a warning lamp, etc.

[0093] In addition, the control unit in the preferred embodiment is configured to output a pseudo flow value as a flow measurement value to the abnormal response unit during the transition period T (first period), even if the flow measurement value is determined to be an abnormal value, and the pseudo flow value is a specified value that is not an abnormal value. Thus, it is possible to prevent the abnormal response unit from performing an abnormal response action due to such an excessive flow during the transition period T. During the transition period T, the control unit outputs a valve opening signal having a strength greater than the strength of the valve opening signal when the flow measurement value is consistent with the first set value in a stable state, so that the flow measurement value determined based on the output flow signal is greater than the first set value. On the other hand, the control unit is configured to output the flow measurement value to the abnormal response unit during the stable flow period F (second period) and the stop period S (third period).

[0094] If a mass flow controller having the above structure is used, an excessive flow rate temporarily flowing through the mass flow controller during the transition period T is not output as a flow rate measurement value to the abnormality handling unit, and therefore unnecessary abnormality handling action is not performed.

[0095] 〈Intensity of valve opening signal as a function of time〉

[0096] In a preferred embodiment of the present invention, in the mass flow controller of the present invention, the strength of the valve opening signal in the transition period T (first period) changes as a function of time. Here, "the strength of the valve opening signal changes as a function of time" means that the strength of the valve opening signal output by the flow control valve is not fixed to a constant value but changes with the passage of time. For example, when observing Figure 3In the illustrated valve opening signal a, the valve opening signal a in the transition period T (first period) changes in the following manner: it increases rapidly at the beginning of the transition period T, reaches a maximum value in a short time, and then immediately turns to decrease, and at the end of the transition period T, it is consistent with the valve opening signal in the stable flow period F (second period). The maximum value of the valve opening signal a in this case can be either a valve opening signal corresponding to the designed maximum opening of the flow control valve, or a valve opening signal with a smaller value than it. In this way, the valve opening signal is not a constant value but changes in the form of a function of time, thereby smoothly transferring from the transition period T to the stable flow period F, preventing flow overshoot at the start time of the stable flow period F.

[0097] In a preferred embodiment, the valve opening signal in the transition period T expressed as a function of time is not limited to Figure 3 and Figure 4 The time function shown in the example may be any time function. However, since the transition period T is a short time, such as less than 1 second, it is not realistic to set a complex function, and the effect is not good. Basically, as long as Figure 3 and Figure 4 A function having at least one peak as exemplified above can exert the effect of the transition period T in the present invention.

[0098] 〈Discharge of residual gas during the stop period〉

[0099] exist Figure 1 When the mass flow controller involved in the present invention is used in the illustrated manner, as described above, immediately after the valve opening signal a is set to zero and the flow control valve is closed, the material gas filled in the gas supply pipe 3 remains. Supplementary explanation is given on the treatment of the gas remaining in the gas supply pipe 3. For example, in ALD, in order to alternately switch the type of material gas during the film formation process, it is necessary to discharge the material gas remaining in the gas supply pipe 3, the nozzle 5 and the reaction chamber 4 to the outside during the stop period S (third period). For this purpose, a purge gas composed of an inert gas is usually used to discharge the material gas, or an exhaust pipe 10 is used for vacuum exhaust. In these cases, since the gas supply pipe 3 is long, there is a concern that it will take time to discharge all the material gas remaining therein.

[0100] Several solutions are considered for the above-mentioned problem. For example, a solenoid valve is provided on the upstream side and the downstream side of the gas supply pipe 3, respectively, and an inlet for purge gas is provided downstream of the solenoid valve on the upstream side, and an outlet for purge gas is provided upstream of the solenoid valve on the downstream side, thereby enabling the material gas remaining in the gas supply pipe 3 to be discharged from the outlet for purge gas in a short time without passing through the reaction chamber 4 and the showerhead 5.

[0101] In addition, for example, both the electromagnetic valve on the upstream side and the electromagnetic valve on the downstream side set as described above may be closed to maintain the state in which the material gas remains in the gas supply pipe 3, and when the material gas is used next time, the transition period T (first period) may be started from the state in which the gas supply pipe 3 is filled with the material gas. In this case, the length of the transition period T (first period) and / or the maximum value of the intensity of the valve opening signal may be set to a value different from the value when the material gas does not remain in the gas supply pipe 3 in accordance with the amount of the material gas remaining in the gas supply pipe 3. In addition, it is sufficient to prepare dedicated gas supply pipes 3 according to the type of material gas used for film formation, and independently connect the downstream ends of these multiple gas supply pipes 3 to the reaction chamber 4 or the nozzle 5.

[0102] Furthermore, even when the material gas remains in the reaction chamber 4 at the beginning of the stop period S, the film formation can be stopped quickly by, for example, temporarily cutting off the connection between the high-frequency power supply and the electrode to stop the generation of the plasma 8. By performing such an operation, incomplete film formation can be avoided during the process of exhausting the material gas to the outside.

[0103] <When the second set value is not zero>

[0104] In the above description, the following case is described as an example: by making the second set value, which is a flow rate setting value smaller than the first set value, equal to zero, and alternately setting the period during which the flow rate setting value is the first set value and the period during which the flow rate measurement value is the second set value, the first set value is a non-zero flow rate setting value, so that the fluid is intermittently supplied to the action position by the mass flow controller. Therefore, in the above description, the third period after the transition period T as the first period and the stable flow period F as the second period is referred to as the "stop period S".

[0105] However, as described above, the second set value as the flow setting value in the third period is a flow setting value smaller than the first set value as the flow setting value in the first period and the second period, and sometimes it is not necessarily zero. In the case where the second set value is non-zero as the control unit, in the mass flow controller involved in the present invention, as the action of the control unit, the period (hereinafter sometimes referred to as "small flow period L") during which a flow setting value smaller than the first set value as the flow setting value in the stable flow period F (second period) and non-zero is input to the flow input unit as the second set value becomes the third period, replacing the stop period S (third period) in which the flow measurement value is zero. In this case, the action and effect of the mass flow controller in the transition period T (first period) from the time point when the first set value is input as the flow setting value after the small flow period L (third period) to the time point when the fluid is judged to have reached the action position, that is, the second time point, is the same as the various embodiments of the present invention described above except that the initial value of the flow measurement value is non-zero.

[0106] According to this embodiment, when material gases are supplied from multiple mass flow controllers to a semiconductor manufacturing device, for example, one mass flow controller can be used to continuously supply a certain material gas during a small flow period L, while another or two or more mass flow controllers involved in any embodiment of the present invention can be used to intermittently supply other material gases.

[0107] Description of Reference Numerals

[0108] 1: semiconductor manufacturing device; 2: mass flow controller; 3: gas supply piping; 4: reaction chamber; 5: showerhead (RF electrode); 6: substrate; 7: ground electrode; 8: plasma; 9: heater; 10: exhaust piping; t: time; a: valve opening signal; b: flow measurement value; c: flow rate of material gas at the action position; d: flow display value; T: transition period (first period); t T : The length of the transition period; F: The stable flow period (the second period); S: The stop period (the third period); L: The small flow period (the third period); a': The valve opening signal (the prior art); b': The flow measurement value (the prior art); c': The flow rate of the material gas at the action position (the prior art); F': The stable flow period (the prior art); S': The stop period (the prior art).

Claims

1. A mass flow controller, comprising: A flow sensor that outputs a flow signal corresponding to the flow rate of the fluid; A flow control valve, which controls the flow of the fluid by adjusting the opening of the valve; a flow rate setting unit into which a flow rate setting value of the fluid is input; as well as a control unit, which outputs a valve opening signal to the flow control valve, The mass flow controller controls the flow rate at the action position at different flow rates according to the supply period, and the action position is the position where the fluid acts. During a first period from a first time point to a second time point, that is, a first period, the valve opening signal is output to the flow control valve so that a flow measurement value determined based on the flow signal is larger than a first set value that is a non-zero flow setting value, wherein the first time point is a time point when the first set value is input to the flow setting unit, and the second time point is a time point when it is determined that the fluid has reached the action position, During a second period from the second time point to a third time point, the valve opening signal is output to the flow control valve so that the flow measurement value is consistent with the first set value, wherein the third time point is a time point when a second set value as a flow setting value smaller than the first set value is input to the flow setting unit, During a third period from the third time point to a time point when the first setting value is input next time, the valve opening signal is output to the flow control valve so that the flow measurement value coincides with the second setting value. A control cycle consisting of the first period, the second period, and the third period is repeatedly executed once or twice or more.

2. The mass flow controller according to claim 1, wherein: The length of the first period is determined in advance, or is determined during the first period.

3. The mass flow controller according to claim 2, wherein: A pressure sensor is further provided, the pressure sensor outputting a pressure signal corresponding to the pressure at the action position, The control unit is configured to set a time point at which the increase width of the pressure determined based on the pressure signal after the first time point becomes equal to or larger than a predetermined first threshold value as the second time point.

4. The mass flow controller according to any one of claims 1 to 3, wherein: The control unit is configured to output the valve opening signal to the flow control valve so that the opening of the flow control valve during the first period begins to increase at the first time point, and turns to decrease if it reaches the specified maximum opening, and is consistent with the opening corresponding to the first set value at the second time point.

5. The mass flow controller according to claim 4, wherein: The control unit is configured to change the intensity of the valve opening signal in the first period as a function of time.

6. The mass flow controller according to any one of claims 1 to 3, wherein: further comprising a display unit capable of displaying at least the flow rate measurement value, The control unit is composed of: During the first period, first information different from the flow rate measurement value is displayed by the display unit, During the second period and the third period, the flow rate measurement value is displayed by the display unit.

7. The mass flow controller according to claim 6, wherein: The first information is information indicating that the flow rate measurement value is zero or information indicating that the flow rate control of the mass flow controller is in the first period.

8. The mass flow controller according to any one of claims 1 to 3, wherein: The device further comprises an abnormality response unit, wherein the abnormality response unit is configured to execute an abnormality response action when it is determined that the flow measurement value is an abnormal value, the abnormality response action being an action including at least one operation selected from the group consisting of issuing an alarm, reducing the opening of the flow control valve, and stopping the supply of the fluid, The control unit is composed of: During the first period, even when it is determined that the flow measurement value belongs to the abnormal value, a pseudo flow value is output as the flow measurement value to the abnormality handling unit, thereby causing the abnormality handling unit not to perform the abnormality handling action, wherein the pseudo flow value is a predetermined value that is not the abnormal value. During the second period and the third period, the flow rate measurement value is output to the abnormality handling unit.

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