Patent Publication Number: US-2022228896-A1

Title: Pressure control system, pressure control method, and pressure control program

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pressure control system, a pressure control method, and a pressure control program. 
     2. Description of the Related Art 
     As described in Japanese Patent Application Laid-open No. 2004-280688, there has conventionally been thought of a fluid control apparatus having a configuration including an upstream valve provided on the upstream of fluid resistance provided in a channel through which a fluid flows and a downstream valve provided on the downstream of the fluid resistance, the fluid control apparatus controlling a flow rate of the fluid flowing through the channel by controlling the upstream valve and the downstream valve. 
     To shut off the channel, the fluid control apparatus fully closes both the upstream valve and the downstream valve. If the pressure between the upstream valve and the downstream valve (closed space including the fluid resistance) fluctuates every time flow rate control starts thereafter, the fluid control apparatus fails to stably start the flow rate control. To stably start flow rate control, the pressure between the upstream valve and the downstream valve (closed space including the fluid resistance) is preferably set to a predetermined convergent pressure. 
     Conventionally, therefore, both the upstream valve and the downstream valve are fully closed and then the upstream valve is opened to cause the fluid to flow into the channel. The upstream valve is closed when an upstream pressure on the fluid resistance reaches a predetermined target pressure. 
     In the configuration that closes the upstream valve when the upstream pressure on the fluid resistance reaches the predetermined target pressure, however, the channel through which the fluid flows is blocked on the downstream of the fluid resistance. As a result, the pressure in the closed space including the fluid resistance exceeds the predetermined convergent pressure (refer to  FIG. 4( a ) ). If flow rate control is started in a state where the pressure exceeds the predetermined convergent pressure, the accuracy of flow rate measurement deteriorates, resulting in reduced controllability in flow rate control. To prevent the upstream pressure from exceeding the predetermined convergent pressure, it is possible to perform on-off control on the upstream valve; however, such a configuration increases the time until the upstream pressure converges to the convergent pressure (refer to  FIG. 4( b ) ). 
     SUMMARY OF THE INVENTION 
     To address the disadvantages described above, an object to of the present invention is to control convergent pressure of a closed space provided with a fluid resistance at high speed while an upstream valve provided on the upstream of the fluid resistance prevents overshooting. 
     A pressure control system according to the present invention is a pressure control system that is provided with a fluid resistance in a channel forming a closed space and is configured to control pressure of the closed space by controlling an upstream valve provided on the upstream of the fluid resistance. The pressure control system includes: a convergent pressure arithmetic unit configured to calculate convergent pressure of the closed space when the upstream valve is fully closed using at least one of upstream pressure and downstream pressure on the fluid resistance in the channel; and a valve controller configured to compare the calculated convergent pressure with a predetermined target convergent pressure and fully close the upstream valve based on a result of the comparison. 
     The pressure control system calculates the convergent pressure of the closed space when the upstream valve is fully closed using at least one of the upstream pressure and the downstream pressure on the fluid resistance. The pressure control system compares the calculated convergent pressure with the predetermined target convergent pressure and fully closes the upstream valve based on the result of the comparison. Consequently, the pressure control system can control the convergent pressure of the closed space at high speed while preventing overshooting. The predetermined target convergent pressure is set based on such a pressure that enables a fluid of a full-scale (100%) set flow rate to flow just after the valve is opened to start flow rate control. 
     The valve controller preferably fully closes the upstream valve when the calculated convergent pressure is equal to or higher than the predetermined target convergent pressure. 
     The pressure control system according to the present invention may further include a downstream valve provided on the downstream of the fluid resistance in the channel, fully closing the downstream valve forming a closed space on the downstream of the fluid resistance. 
     In this configuration, the convergent pressure arithmetic unit preferably calculates the convergent pressure using the upstream pressure on the fluid resistance, the downstream pressure on the fluid resistance, a channel volume between the fluid resistance and the upstream valve, and a channel volume between the fluid resistance and the downstream valve. 
     The convergent pressure arithmetic unit preferably calculates the convergent pressure using the following expression. 
     
       
         
           
             
               
                 
                   
                     P 
                     CONV 
                   
                   = 
                   
                     
                       
                         
                           P 
                           1 
                         
                         ⁢ 
                         
                           V 
                           1 
                         
                       
                       + 
                       
                         
                           P 
                           2 
                         
                         ⁢ 
                         
                           V 
                           2 
                         
                       
                     
                     
                       
                         V 
                         1 
                       
                       + 
                       
                         V 
                         2 
                       
                     
                   
                 
               
               
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     where P CONV  is the convergent pressure, P 1  is the upstream pressure on the fluid resistance, P 2  is the downstream pressure on the fluid resistance, V 1  is the channel volume between the fluid resistance and the upstream valve, and V 2  is the channel volume between the fluid resistance and the downstream valve. 
     In the pressure control system according to the present invention, the closed space may be formed on the downstream of the fluid resistance by a closed container being coupled to the downstream of the fluid resistance in the channel. The convergent pressure arithmetic unit may calculate the convergent pressure using the upstream pressure on the fluid resistance, the downstream pressure on the fluid resistance, the channel volume between the fluid resistance and the upstream valve, and the volume of the channel on the downstream of the fluid resistance and the volume of the closed container. 
     The convergent pressure arithmetic unit preferably calculates the convergent pressure in real time using at least one of the upstream pressure and the downstream pressure on the fluid resistance in the channel. 
     The convergent pressure arithmetic unit preferably calculates the convergent pressure by correcting a change over time in the volume of the closed space or the channel. 
     The upstream valve is preferably provided with a position sensor configured to detect the position of a disc with respect to a seat. If the pressure control system includes the downstream valve, the downstream valve is preferably provided with a position sensor configured to detect the position of a disc with respect to a seat. 
     A pressure control method according to the present invention is a pressure control method performed by a pressure control system that is provided with a fluid resistance in a channel forming a closed space and is configured to control pressure of the closed space by controlling an upstream valve provided on the upstream of the fluid resistance. The pressure control method includes: calculating convergent pressure of the closed space when the upstream valve is fully closed using at least one of upstream pressure and downstream pressure on the fluid resistance in the channel; and comparing the calculated convergent pressure with a predetermined target convergent pressure and fully closing the upstream valve based on a result of the comparison. 
     A pressure control program according to the present invention is a pressure control program for use in a pressure control system that is provided with a fluid resistance in a channel forming a closed space and is configured to control pressure of the closed space by controlling an upstream valve provided on the upstream of the fluid resistance. The pressure control program causes a computer to function as: a convergent pressure arithmetic unit configured to calculate convergent pressure of the closed space when the upstream valve is fully closed using at least one of upstream pressure and downstream pressure on the fluid resistance in the channel; and a valve controller configured to compare the calculated convergent pressure with a predetermined target convergent pressure and fully close the upstream valve based on a result of the comparison. 
     According to the present invention, the convergent pressure of the closed space provided with the fluid resistance can be controlled at high speed while the upstream valve provided on the upstream of the fluid resistance prevents overshooting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a fluid control apparatus (pressure control system) according to an embodiment of the present invention; 
         FIG. 2  is a graph indicating a method for controlling convergent pressure according to the embodiment: 
         FIG. 3  is a schematic of the fluid control apparatus (pressure control system) according to a modification of the embodiment; and 
         FIGS. 4( a ) and 4( b )  are graphs indicating methods for controlling convergent pressure according to the conventional technology. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments of a fluid control apparatus including a pressure control system according to the present invention are described below with reference to the accompanying drawings. 
     Apparatus Configuration 
     A fluid control apparatus  100  according to the present embodiment is used to supply gas serving as fluid to a chamber  300  at a set flow rate in a semiconductor manufacturing process, for example. The set flow rate is a step signal that rises or falls stepwise from a certain flow rate value to another flow rate value. The flow rate achieved by the fluid control apparatus  100  reaches the set flow rate in a predetermined period of time, and the magnitude of noise in a steady state falls within an allowable range. 
     Specifically, as illustrated in  FIG. 1 , the fluid control apparatus  100  includes fluid devices  10   a  to  10   f  and a control mechanism COM. The fluid devices  10   a  to  10   f  are sensors and valves, for example, provided to a channel  200  through which gas flows. The control mechanism COM controls the fluid devices  10   a  to  10   f.    
     The fluid devices  10   a  to  10   f  according to the present embodiment are a supply pressure sensor  10   a , an upstream valve  10   b , an upstream pressure sensor  10   c , a fluid resistance  10   d , a downstream pressure sensor  10   e , and a downstream valve  10   f . The fluid devices  10   a  to  10   f  are provided to the channel  200  in order from the upstream. The fluid resistance  10   d  is a laminar flow element, for example, and generates differential pressure corresponding to the flow rate of gas flowing in front of and behind the fluid resistance  10   d.    
     The supply pressure sensor  10   a  monitors the pressure of gas supplied from the upstream. The supply pressure sensor  10   a  is not necessarily provided if stable supply pressure is ensured, for example. 
     The upstream pressure sensor  10   c  measures upstream pressure P 1  on the fluid resistance  10   d  in the channel  200 . Specifically, the upstream pressure sensor  10   c  measures the upstream pressure P 1  corresponding to the pressure of gas charged in an upstream volume V 1 , which is the volume between the upstream valve  10   b  and the fluid resistance  10   d  in the channel  200 . 
     The downstream pressure sensor  10   e  measures downstream pressure P 2  on the fluid resistance  10   d  in the channel  200 . Specifically, the downstream pressure sensor  10   e  measures the downstream pressure P 2  corresponding to the pressure of gas charged in a downstream volume V 2 , which is the volume between the fluid resistance  10   d  and the downstream valve  10   f  in the channel  200 . 
     The upstream valve  10   b  and the downstream valve  10   f  according to the present embodiment are of the same type. The upstream valve  10   b  and the downstream valve  10   f  are piezo valves in which a disc is driven by an actuator, such as a piezoelectric element, in a manner attachable to and detachable from a seat. The valve opening of the upstream valve  10   b  and the downstream valve  10   f  is changed depending on a voltage applied as an operating amount. The upstream valve  10   b  and the downstream valve  10   f  are each provided with a position sensor  101  that detects the position of the disc with respect to the seat. By using the position detected by the position sensor  101 , the fluid control apparatus  100  can accurately perform flow rate control with the upstream valve  10   b  or the downstream valve  10   f.    
     The control mechanism COM is what is called a computer including a CPU, a memory, an A/D converter, a D/A converter, and an input-output unit, for example. The control mechanism COM implements the functions of at least a flow rate calculator  20  and a valve controller  30  by executing a flow rate control program stored in the memory and causing various devices to cooperate. 
     The flow rate calculator  20  calculates a flow rate value based on the upstream pressure P 1  and the downstream pressure P 2 . The flow rate calculator  20  calculates a resistance flow rate corresponding to the flow rate of gas flowing through the fluid resistance  10   d  based on the upstream pressure P 1  and the downstream pressure P 2  using an existing expression. The flow rate calculator  20  may calculate an upstream valve flow rate corresponding to the flow rate of gas flowing through the upstream valve  10   b  based on the resistance flow rate and the upstream pressure P 1 . The flow rate calculator  20  may calculate a downstream valve flow rate corresponding to the flow rate of gas flowing through the downstream valve  10   f  based on the resistance flow rate and the downstream pressure P 2 . 
     The valve controller  30  performs feedback control on at least one of the upstream valve  10   b  and the downstream valve  10   f  such that the flow rate calculated by the flow rate calculator  20  approaches a predetermined flow rate target value. The valve controller  30  may perform feedback control on the upstream valve  10   b  such that the upstream pressure P 1  obtained by the upstream pressure sensor  10   c  approaches a predetermined pressure target value without performing flow rate control on the upstream valve  10   b . The valve controller  30  may perform feedback control on the downstream valve  10   f  such that the downstream pressure P 2  obtained by the downstream pressure sensor  10   e  approaches a predetermined pressure target value without performing flow rate control on the downstream valve  10   f.    
     Convergent Pressure Control on a Closed Space 
     The control mechanism COM of the fluid control apparatus  100  according to the present embodiment has a function to control convergent pressure of a closed space formed when the upstream valve  10   b  and the downstream valve  10   f  are fully closed. The convergent pressure of the closed space is pressure stabilized after a predetermined period of time has elapsed since closing the upstream valve  10   b  and the downstream valve  10   f.    
     Specifically, the control mechanism COM further includes a convergent pressure arithmetic unit  40  that calculates convergent pressure P CONV  of the closed space when the upstream valve  10   b  is fully closed using at least one of the upstream pressure P 1  and the downstream pressure P 2  on the fluid resistance  10   d  in the channel  200 . The valve controller  30  compares the calculated convergent pressure P CONV  with a predetermined target convergent pressure P T_CONV  and fully closes the upstream valve  10   b  based on the result of the comparison. 
     The convergent pressure arithmetic unit  40  calculates the convergent pressure P CONV  sequentially (in real time) during process control using at least one of the upstream pressure P 1  and the downstream pressure P 2  on the fluid resistance  10   d  in the channel  200 . Specifically, the convergent pressure arithmetic unit  40  calculates the convergent pressure P CONV  using the upstream pressure P 1  on the fluid resistance  10   d , the downstream pressure P 2  on the fluid resistance  10   d , the channel volume (upstream volume) V 1  between the fluid resistance  10   d  and the upstream valve  10   b , and the channel volume (downstream volume) V 2  between the fluid resistance  10   d  and the downstream valve  10   f.    
     The convergent pressure arithmetic unit  40  according to the present embodiment calculates the convergent pressure P CONV  of the closed space formed between the upstream valve  10   b  and the downstream valve  10   f  using the following expression. The convergent pressure arithmetic unit  40  does not necessarily calculate the convergent pressure P CONV  using the following expression and may calculate it using a lookup table. In this case, a lookup table may be used that has three parameters of the upstream pressure P 1 , the downstream pressure P 2 , and the convergent pressure P CONV  of the closed space on the respective axes. 
     
       
         
           
             
               
                 
                   
                     P 
                     CONV 
                   
                   = 
                   
                     
                       
                         
                           P 
                           1 
                         
                         ⁢ 
                         
                           V 
                           1 
                         
                       
                       + 
                       
                         
                           P 
                           2 
                         
                         ⁢ 
                         
                           V 
                           2 
                         
                       
                     
                     
                       
                         V 
                         1 
                       
                       + 
                       
                         V 
                         2 
                       
                     
                   
                 
               
               
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     where P CONV  is the convergent pressure of the closed space, P 1  is the upstream pressure on the fluid resistance  10   d , P 2  is the downstream pressure on the fluid resistance  10   d , V 1  is the channel volume between the fluid resistance  10   d  and the upstream valve  10   b , and V 2  is the channel volume between the fluid resistance  10   d  and the downstream valve  10   f.    
     As illustrated in  FIG. 2 , when the calculated convergent pressure P CONV  is equal to or higher than the predetermined target convergent pressure P T_CONV , the valve controller  30  fully closes the upstream valve  10   b . The predetermined target convergent pressure P T_CONV  is set based on such a pressure that enables gas of a full-scale (100%) set flow rate to flow just after the upstream valve  10   b  and the downstream valve  10   f  are opened. 
     The following describes a series of operations for adjusting the convergent pressure of the closed space between the upstream valve  10   b  and the downstream valve  10   f  to the target convergent pressure P T_CONV . 
     First, the valve controller  30  fully closes the upstream valve  10   b  and the downstream valve  10   f  in a normal gas supply state in which gas is flowing through the channel  200 , thereby shutting off the flow of gas. The valve controller  30  fully closes the upstream valve  10   b  first and then fully closes the downstream valve  10   f.    
     After fully closing the upstream valve  10   b  and the downstream valve  10   f  to shut off the channel  200 , the valve controller  30  opens the upstream valve  10   b  and causes gas to flow into the space between the upstream valve  10   b  and the downstream valve  10   f . The upstream pressure sensor  10   c  detects the upstream pressure P 1 , and the downstream pressure sensor  10   e  detects the downstream pressure P 2 . 
     The convergent pressure arithmetic unit  40  that has acquired the upstream pressure P 1  and the downstream pressure P 2  calculates the convergent pressure P CONV  in real time while the gas is flowing into the space between the upstream valve  10   b  and the downstream valve  10   f . The valve controller  30  sequentially acquires the convergent pressure P CONV  calculated by the convergent pressure arithmetic unit  40  and compares it with the predetermined target convergent pressure P T_CONV . When the calculated convergent pressure P CONV  reaches the predetermined target convergent pressure P T_CONV , the valve controller  30  fully closes the upstream valve  10   b  (refer to  FIG. 2 ). As a result, the pressure of the closed space between the upstream valve  10   b  and the downstream valve  10   f  converges to the predetermined target convergent pressure P T_CONV  after a predetermined period of time has elapsed. To start supplying gas to the chamber thereafter, the valve controller  30  starts to control the upstream valve  10   b  and the downstream valve  10   f  based on a predetermined set flow rate. 
     Advantageous Effects of the Present Embodiment 
     The fluid control apparatus  100  according to the present embodiment having the configuration described above calculates the convergent pressure P CONV  of the closed space when the upstream valve  10   b  is fully closed using at least one of the upstream pressure P 1  and the downstream pressure P 2  on the fluid resistance  10   d . The fluid control apparatus  100  compares the calculated convergent pressure P CONV  with the predetermined target convergent pressure P T_CONV  and fully closes the upstream valve  10   b  based on the result of the comparison. Consequently, the fluid control apparatus  100  can control the convergent pressure P CONV  of the closed space at high speed while preventing overshooting. 
     Other Embodiments 
     While the embodiment described above, for example, calculates the convergent pressure P CONV  using the upstream pressure P 1  on the fluid resistance  10   d , the downstream pressure P 2  on the fluid resistance  10   d , the channel volume V 1  between the fluid resistance  10   d  and the upstream valve  10   b , and the channel volume V 2  between the fluid resistance  10   d  and the downstream valve  10   f , the embodiment is not limited thereto. The embodiment may calculate the convergent pressure P CONV  using only one of the upstream pressure P 1  on the fluid resistance  10   d  and the downstream pressure P 2  on the fluid resistance  10   d . In this case, the embodiment calculates in advance the relation between the convergent pressure P CONV  and one of the upstream pressure P 1  on the fluid resistance  10   d  and the downstream pressure P 2  on the fluid resistance  10   d . Based on the relation, the embodiment calculates the convergent pressure P CONV . 
     While the embodiment described above fully closes the upstream valve  10   b  to control the convergent pressure if the calculated convergent pressure P CONV  is equal to the predetermined target convergent pressure P T_CONV , the embodiment is not limited thereto. The embodiment may assume a case where the calculated convergent pressure P CONV  exceeds the target convergent pressure P T_CONV  and set a determination range with respect to the predetermined target convergent pressure P T_CONV . If the calculated convergent pressure P CONV  falls within the determination range, the embodiment may fully close the upstream valve  10   b.    
     While the embodiment described above forms the closed space on the downstream of the upstream valve  10   b  by fully closing the downstream valve  10   f , the embodiment is not limited thereto. The embodiment may form the closed space on the downstream of the upstream valve  10   b  without fully closing the downstream valve  10   f . As illustrated in  FIG. 3 , for example, the embodiment may have a configuration that includes a closed container  400  coupled to the channel  200  provided with the fluid resistance  10   d , thereby forming a closed space on the downstream of the fluid resistance  10   d . In this configuration, the convergent pressure arithmetic unit  40  may calculate the convergent pressure P CONV  using the upstream pressure on the fluid resistance  10   d , the downstream pressure on the fluid resistance  10   d , the channel volume between the fluid resistance  10   d  and the upstream valve  10   b , and the volume of the channel on the downstream of the fluid resistance  10   d  and the volume of the closed container  400 . 
     The convergent pressure arithmetic unit  40  according to the embodiment described above may calculate the convergent pressure P CONV  by correcting a change over time in the volume of the closed space or the channel  200 . The convergent pressure arithmetic unit  40  may change the target convergent pressure by considering a change over time in the volume of the closed space or the channel  200 . The convergent pressure arithmetic unit  40  may include an alarm output unit that outputs alarm signals when the convergent pressure of the closed space has a difference of equal to or larger than a predetermined value with respect to the target convergent pressure as a result of controlling the convergent pressure based on the calculated convergent pressure. 
     The upstream volume V 1  and the downstream volume V 2  may possibly fluctuate due to variation in the position accuracy of the ends of the fluid resistance depending on the accuracy of processing the fluid resistance (laminar flow element). In this case, the convergent pressure arithmetic unit  40  may correct a change in volume in front of and behind the fluid resistance depending on the accuracy of processing the fluid resistance (laminar flow element). 
     While the embodiment described above is a twin-valve fluid control apparatus including the upstream valve  10   b  and the downstream valve  10   f , it may be a single-valve fluid control apparatus including the upstream valve  10   b  alone. 
     While the embodiment described above is a fluid control apparatus that incorporates a pressure control system, it may be a pressure control system alone not incorporated in a fluid control apparatus. 
     The fluid resistance  10   d  according to the embodiment described above is a laminar flow element, it simply needs to be a resistor that generates pressure difference in the channel and may be an orifice, for example. 
     Various changes and combinations of the embodiments may be made without departing from the spirit of the present invention.