Patent Publication Number: US-8109288-B2

Title: Flow rate control system and shower plate used for partial pressure control system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 10/863,205, filed Jun. 9, 2004, now U.S. Pat. No. 7,481,240 which claims the benefit of priority to Japanese Patent Application No. 2003-163696, filed on Jun. 9, 2003. The entire contents of both of these applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a partial pressure control system, a flow rate control system, which outputs operation gas at a predetermined partial pressure ratio, and a shower plate used for the partial pressure control system. 
     DESCRIPTION OF THE RELATED ART 
     A flow rate control system which supplies operation gas to a wafer controls a flow rate of operation gas which is to be supplied to a center area and an edge area of the wafer to uniformly supply the operation gas to the wafer.  FIG. 6  is a schematic block diagram of a conventional flow rate control system  100 .  FIGS. 7 and 8  are plan views of conventional shower plates  122  ( 122 A,  122 B). 
     In a flow rate control system  100 , flow rate control devices  101 A,  101 B,  101 C and  101 D are respectively connected to gas supply sources for gas such as O 2 , Ar, C 4 F 8  or CO. The flow rate control devices  101 A to  101 D include flow rate control valves  102 A,  102 B,  102 C,  102 D and flowmeters  103 A,  103 B,  103 C,  103 D, respectively, and adjust openings of the flow rate control valves  102 A to  102 D based on flow rates detected by the flowmeters  103 A to  103 D. 
     The flow rate control devices  101 A to  101 D are connected to a partial flow control device  110  through an operation gas supply pipe  104 , and supply operation gas to an etching device  120 . In the flow rate control device  110 , flow rate control valves  111 A and  111 B are connected to the operation gas supply pipe  104  in parallel, and flowmeters  112 A and  112 B are the flow rate control valves  111 A and  111 B in series. The flow rate control valves  111 A and  111 B and the flowmeters  112 A and  112 B are connected to a controller  113 . The controller  113  controls the flow rate control valves  111 A and  111 B based on flow rates detected by the flowmeters  112 A and  112 B. The flow rate control valves  111 A and  111 B of the partial flow control device  110  are respectively connected to a center shower  125  and an edge shower  126  of the shower plate  122  incorporated in the etching device  120 . 
     The shower plate  122  is disposed above a lower electrode  121  which heats a wafer W. As shown in  FIGS. 7 and 8 , the shower plate  122  ( 122 A,  122 B) is provided with a large number of gas holes  123  in its surface opposed to the wafer W. A perfectly circular partition wall ring  124  is mounted on the shower plate  122  ( 122 A,  122 B), thereby dividing the shower plate  122  into a circular center shower  125  and an annular edge shower  126 . In the shower plate  122 A shown in  FIG. 7 , the gas holes  123 A are arranged into a square shape, and they are arranged in a form of a square from a center to a periphery of the wafer W. In the shower plate  122 B shown in  FIG. 8 , gas holes  123 B are arranged concentrically, and are arrange concentrically from a center to a periphery of the wafer W. 
     Thus, in the flow rate control system  100 , if a flow rate control valve  102 B of a flow rate control device  101 B is opened, Ar is branched into the flow rate control valves  111 A and  111 B of the partial flow control device  110  from the operation gas supply pipe  104 , and supplied onto the wafer W from the center shower  125  and the edge shower  126 . At that time, the partial flow control device  110  controls the opening and closing operation of the flow rate control valves  111 A and  111 B based on the flow rates detected by the flowmeters  112 A and  112 B, and Ar is injected at the predetermined flow rate using the center shower  125  and the edge shower  126 . Therefore, Ar can uniformly be supplied to the entire wafer W (for example, paragraphs 0032, 0037, 0039 and FIGS. 1, 5, 7 and 8 of Japanese Patent Laid-open Publication No. 10-121253). 
     According to the conventional flow rate control system  100 , however, responsivity with respect to the change of settings is inferior, and operation gas can not uniformly be supplied to the wafer W in some cases. 
     In generally, in the flow rate control system  100 , the partial flow control device  110  is provided on the side of the etching device  120 , and the gas supply source and the flow rate control devices  101 A to  101 D are provided on the side of a gas box away from the etching device  120 . Thus, the wiring volume of the operation gas supply pipe  104  is great. The partial flow control device  110  controls the flow rate control valves  111 A and  111 B based on flow rates which are output from the flowmeters  112 A and  112 B and thus, it takes time to control them. Thus, in the flow rate control system  100 , when the flow rate of operation gas is changed by the flow rate control devices  101 A to  101 D, it takes time until the flow rate of the operation gas flowing through the operation gas supply pipe  104  is stabilized, and since it takes time for the partial flow control device  110  to control, the responsivity of change of settings is inferior. On the other hand, the etching processing is carried out within a short time for preventing the chemical reaction of the operation gas. Thus, the flow rate control system  100  can not finish the control operation gas until the etching processing is completed, and can not uniformly supply the operation gas to the wafer W in some cases. 
     To enhance the responsivity, it seems better idea to control the pressure of the operation gas injected from the center shower  125  and the edge shower  126  using an absolute value instead of using the flow rate control device  110 . However, such a system for controlling the pressure of the operation gas using the absolute value, it is necessary to provide a large tank on the primary sides of the flow rate control valves  111 A and  111 B and to store the operation gas using the pressure corresponding to the absolute value, and there is a problem that operation gas is squandered. In addition, according to the system for controlling the pressure of the operation gas using the absolute value, the responsivity with respect to the change of settings is inferior. For example, when it is necessary to change the pressure ratio of operation gas which is to be output from the flow rate control valves  111 A and  111 B, the pressure of operation gas to be stored in the large tank must be changed, and it takes time to control. When it is necessary to change the kind of operation gas, since the flow rate of the operation gas to be supplied from the operation gas supply pipe  104  to the partial flow control device  110  is varied depending upon the characteristics of the operation gas, it is difficult to swiftly determine the flow rate of operation gas which is to be output from the flow rate control valves  111 A and  111 B. 
     The layout of the gas holes  123  on the shower plate  122  also one of reasons why the operation gas can not be supplied to the wafer W uniformly. That is, when the gas holes  123 A are arranged in the form of square as shown in  FIG. 7 , since distances between adjacent gas holes  123 A are constant, the discharging density of the operation gas should be constant theoretically, but the probability that the gas holes  123 A are crashed when the partition wall ring  124  is mounted is high. That is, as shown in  FIG. 9 , although the partition wall ring  124 A does not crush the gas holes  123 A, the partition wall rings  124 B,  124 C and  124 D crush one or some of the gas holes  123 A. If the gas holes  123 A are crushed, the hole areas of the gas holes  123 A are varied, and the discharging density of the operation gas can not be equalized. If the partition wall ring  124  is mounted such that the gas holes  123 A are not crushed, the shape of the partition wall ring  124  is deformed, and it becomes difficult to mount the partition wall ring  124  on the shower plate  122 A. If the gas hole  123 B are arranged concentrically as shown in  FIG. 8 , it becomes easy to mount the partition wall ring  124  such that the gas hole  123 B are not crushed. However, distances between the gas hole  123 B on the shower plate  122 B are varied, and there is a problem that the discharging density of the operation gas can not be equalized. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to provide a partial pressure control system capable of reduce wastefull consumption of operation gas, and capable of enhancing the responsivity with respect to the change of settings. It is a second object of the invention to provide a flow rate control system having excellent responsivity and capable of outputting operation gas at a precise partial pressure ratio. It is a third object of the invention to provide a shower plate used for the partial pressure control system capable of equalizing the discharging density of operation gas on a subject of supply. 
     To achieve the first object, the present invention provides a partial pressure control system comprising: a plurality of pressure control units which are branched from an operation gas supply pipe for controlling pressure of operation gas, variably; pressure detecting units which are connected the pressure control units in series for detecting the pressure of the operation gas; and a control unit which proportionally controls operation of the pressure control units based on detection result of the pressure detecting units and which relatively controls output pressures of the plurality of pressure control units. 
     The control unit may specify one of the pressure control units as a control subject, and the control unit may control only the specified pressure control unit, thereby keeping a pressure ratio. 
     The control unit may specify one of the pressure control units as the control unit based on a pressure ratio which is input to the partial pressure control system. 
     The number of the pressure control units may be two, the control unit may specify one of the two pressure control units as the control subject depending upon whether the pressure ratio which is input to the partial pressure control system is greater than 1 or not. 
     When the pressure ratio which is input to the partial pressure control system is obtained by dividing pressure in a first pressure control unit by pressure in a second pressure control unit, a target pressure of the first pressure control unit is expressed as a product of the pressure ratio and the pressure of the second pressure control unit, a target pressure of the second pressure control unit is expressed as a quotient obtained by dividing the pressure in the first pressure control unit by the pressure ratio, when the pressure ratio is smaller than 1, only the target pressure in the first pressure control unit is controlled, and when the pressure ratio is equal to or greater than 1, only the target pressure of the second pressure control unit is controlled. 
     The control unit may specify one of the pressure control units as the control subject based on the detection result of the pressure detecting unit. 
     The partial pressure control system may further comprise a zero point confirming unit, all of the pressure control units are fully opened, and when supply of the operation gas is stopped, the zero point confirming unit confirms whether pressure detected by the pressure detecting unit is within tolerance with respect to a zero point. 
     To achieve the second object, the present invention provides a flow rate control system comprising: a flow rate control device including a flow rate control valve connected to a gas supply source, and a flow rate detecting unit which detects a flow rate output by the flow rate control valve, the flow rate control device controlling the flow rate control valve based on a detection result of the flow rate detecting unit; an operation gas supply pipe connected to the flow rate control device; and a partial pressure control system including a plurality of pressure control units which are branched from the operation gas supply pipe and which control pressure of operation gas, variably, pressure detecting units which are respectively connected to the pressure control units in series and which detects pressure of the operation gas, and a control unit which proportionally controls operation of the pressure control unit based on detection result of the pressure detecting unit and which relatively controls output pressure of the pressure control units. 
     The flow rate control system may further comprise a zero point confirming unit, all of the pressure control units are fully opened, and when supply of the operation gas is stopped, the zero point confirming unit confirms whether pressure detected by the pressure detecting unit is within tolerance with respect to a zero point. 
     To achieve the third object, the present invention also provides a shower plate used for a partial pressure control system in which the shower plate is partitioned by a partition wall member and divided into a plurality of areas, the areas are connected to the partial pressure control system, and operation gas injected from each area to the supply subject is controlled. Adjacent gas holes for injecting the operation gas are arranged in a form of a regular triangle, and are arranged in a form of hexagon from a center to a periphery with respect to the supply subject. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a partial pressure control system according to a first embodiment of the present invention; 
         FIG. 2  is a schematic block diagram of a flow rate control system according to the first embodiment of the invention; 
         FIG. 3  shows one example of zero point confirmation according to the first embodiment, wherein a vertical axis shows pressure and a lateral axis shows time; 
         FIG. 4  is a plan view of a shower plate according to a second embodiment of the invention; 
         FIG. 5  shows an example of a disposition of a partition wall member according to the second embodiment of the invention; 
         FIG. 6  is a schematic block diagram of a conventional flow rate control system; 
         FIG. 7  is a plan view of a conventional shower plate; 
         FIG. 8  is a plan view of another conventional shower plate; and 
         FIG. 9  shows an example of a disposition of a partition wall member in a shower plate in which gas holes are arranged in a form of square. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The action of the embodiments will be explained. Operation gas supplied from a gas supply source is supplied to an operation gas supply pipe simultaneously when a flow rate control valve of a flow rate control device is opened. At that time, the flow rate control device detects a flow rate which is output from the flow rate control valve by means of the flow rate detecting unit, the flow rate control valve is controlled based on the detection result, thereby supplying the operation gas at the predetermined flow rate to the operation gas supply pipe. 
     The operation gas is output such that the operation gas is branched into pressure control units of the partial pressure control system from the operation gas supply pipe. The partial pressure control system detects the output pressure of the pressure control unit by means of a pressure detecting unit, and proportionally controls the pressure control unit based on the detection result of the pressure detecting unit. Since the pressure control unit of the partial pressure control system is connected to the operation gas supply pipe in a branched manner, if one of pressure control unit is proportionally controlled to vary the output pressure, output pressure of the other pressure control unit is also varied relatively. Thus, the partial pressure control system can output the operation gas from the pressure control unit at the predetermined partial pressure ratio irrespective of a flow rate of operation gas supplied from the operation gas supply pipe. 
     Even if the flow rate control system is disposed in such a manner that the flow rate control device and the partial pressure control system are separated away from each other and a piping volume of the operation gas supply pipe becomes large and the setting of the flow rate of the operation gas is changed by the flow rate control device, the partial pressure control system proportionally controls the pressure control unit based on the pressure detected by the pressure detecting unit and outputs operation gas at the predetermined partial pressure ratio irrespective of the flow rate of the operation gas supplied from the operation gas supply pipe. Therefore, the controlling time is shortened. 
     According to the flow rate control system of the present invention, the responsivity with respect to change of settings is excellent, and operation gas can be output at a precise partial pressure ratio. 
     Since the partial pressure control system controls operation gas under relative pressure based on pressure which is output from the pressure control unit, it is unnecessary to provide a large tank on the primary side of the pressure control unit to store the operation gas unlike a case where the operation gas is controlled under absolute pressure. To change the pressure ratio of operation gas which is output from each pressure control unit, it is only necessary for the partial pressure control system to control the pressure control unit. Also when the kinds of operation gas is to be changed, since the partial pressure control system controls the operation gas under the absolute pressure, it is possible to swiftly determine the pressure ratio of the operation gas which is output from each pressure control unit irrespective of kinds of operation gas. Therefore, according to the partial pressure control system, it is possible to reduce the wastefull consumption of operation gas, and to enhance the responsivity with respect to the change of settings. 
     When operation gas is to be controlled in a partial pressure manner, if one of the pressure control units having the least output pressure is specified as a subject to be controlled, the plurality of pressure control units can be controlled in a diversion manner. 
     The partial pressure control system and the flow rate control system include a zero point confirming unit, and confirm whether the control state is constant or not. 
     When the supply of operation gas is stopped in a state in which all of the pressure control units are fully opened, operation gas remaining in the operation gas supply pipe passes through the pressure control unit and flows downstream and at the same time, the pressure to be detected by each pressure detecting unit is also reduced toward the zero point. The zero point confirming unit confirms the zero point position based on the reduction of the pressure. With this, the flow rate control system and the partial pressure control system can swiftly find a trouble of the system. 
     Next, the action of the shower plate used for the partial pressure control system will be explained. 
     In the shower plate used for the partial pressure control system, areas divided by the partition wall member are connected to the partial pressure control system, and pressures of operation gases which are output the respective areas are controlled. Since the gas holes from which the operation gases are injected are arranged in the form of triangle in the shower plate, the distances between the adjacent gas holes are substantially constant. Since the gas holes are arranged in a form of hexagon from a center toward a periphery with respect to the supply subject, when the shower plate is divided by a perfectly circular partition wall member for example, the gas holes are less prone to be crushed. Therefore, the probability of crush of the gas holes by the partition wall member is lowered, and the discharging density of the operation gas can be uniform on the supply subject. 
     Next, the first embodiment of the shower plate used for the partial pressure control system, the flow rate control system and the partial pressure control system of the present invention will be explained with reference to the drawings.  FIG. 2  is a schematic block diagram of a flow rate control system  50 A. 
     The flow rate control system  50 A in  FIG. 2  is used for etching processing of a semiconductor producing apparatus. The flow rate control system  50 A has a gas supply source for gas such as O 2 , Ar, C 4 F 8  or CO, and a plurality of flow rate control devices  41 A,  41 B,  41 C and  41 D connected to the gas supply source. The flow rate control devices  41 A to  41 D includes flow rate control valves  42 A,  42 B,  42 C and  42 D and flowmeters (corresponding to “flow rate detecting unit”)  43 A,  43 B,  43 C and  43 D, and adjust the openings of the flow rate control valves  42 A to  42 D based on flow rates detected by the flowmeters  43 A to  43 D. 
     The operation gases supplied from the flow rate control devices  41 A to  41 D are injected from a shower plate  52  of a chamber  51  through an operation gas supply pipe  44  and a partial pressure control system  45 . At that time, in order to supply the operation gas to the center shower  53  and the edge shower  54  of the shower plate  52  at a predetermined partial pressure ratio, the partial pressure control system  45  controls the operation gas. 
     The partial pressure control system  45  includes a pressure control device  1 A connected to the center shower  53 , and a pressure control device  1 B connected to the edge shower  54 . The pressure control devices  1 A and  1 B includes a pressure control valve (corresponding to “pressure control units”, and if one of them is defined as a first pressure control unit, the other one can be defined as a second pressure control unit)  2 , and a pressure sensor (corresponding to “pressure detecting unit”)  3 , and they are respectively connected to controllers (corresponding to “control device” of the partial pressure control system  45 )  25  so that one of outputs is adjusted based on the detection result of the pressure sensor  3 . A central controller (including ones corresponding to “control device” of the flow rate control system  50 A)  46  for controlling the operation of the entire semiconductor producing apparatus is connected to the controller  25 . The central controller  46  always monitors the flow rate control state of the operation gas. 
       FIG. 1  is a block diagram of the partial pressure control system  45 . 
     The controller  25  of the partial pressure control system  45  are connected to valve controllers  9  incorporated in the pressure control devices  1 A and  1 B, and adjusts the openings of the normally-opened valves  8 . With this adjustment, pressures of operation gases which are output by the pressure control units comprising the valve controllers  9  and the valves  8  are controlled. A piezo-valve or the like may be used as the valve  8 . 
     The controller  25  includes a Central Processing Unit (it is called a CPU in the following description)  26 , fully opens one of the valves  8  having higher output pressure, specifies the other valve  8  having lower output pressure as a control subject, and controls the pressure ratio. The CPU  26  includes a control subject determining section  27  which determines a control subject in accordance with pressure ratio command K (here, K=target pressure P 1 /target pressure P 2 ) which is input to a device operation screen of the central controller  46 . Connected to the control subject determining section  27  in parallel are a calculating section  28  which calculates the target pressure P 2  (=P 1 /K) of the pressure control device  1 B based on the pressure ratio command K, and a calculating section  34  which calculates the target pressure P 1  (=K×P 2 ) of the pressure control device  1 A based on the pressure ratio command K. 
     A control section  30  is connected to the calculating section  28 . The control section  30  determines a control signal based on a deviation between the pressure P 2  which is fed back from the pressure sensor  3  of the pressure control device  1 B and the target pressure P 2  (=P 1 /K) of the pressure control device  1 B which is input from the calculating section  28 . The control section  30  is connected to the valve controller  9  of the pressure control device  1 B through a D/A converter  32 . The pressure sensor  3  of the pressure control device  1 B is connected to the calculating section  34  through an A/D converter  33 , and is feedback connected to an upstream of the control section  30 . 
     A control section  36  is connected to the calculating section  34 . The control section  36  determines a control signal based on a deviation between a pressure P 1  which is fed back from the pressure sensor  3  of the pressure control device  1 A and the target pressure P 1  (=KP 2 ) of the pressure control device  1 A which is input from the calculating section  34 . The control section  36  is connected to the valve controller  9  of the pressure control device  1 A through the D/A converter  38 . The pressure sensor  3  of the pressure control device  1 A is connected to the calculating section  28  through the A/D converter  39 , and is feedback connected to the upstream of the control section  36 . 
     The partial pressure control system  45  is operated as follows. 
     That is, in the flow rate control system  50 A shown in  FIG. 2 , when the flow rate control valves  42 A to  42 D of the flow rate control devices  41 A to  41 D are closed and no operation gas is supplied, a cut-signal is input to the CPU  26  of the controller  25  as shown in  FIG. 1 . The CPU  26  receives the cut-signal, and stops the operation of the valve controllers  9  of the pressure control devices  1 A and  1 B through the D/A converters  32  and  38 . Therefore, no control signal is supplied to the valves  8  of the pressure control devices  1 A and  1 B, and the valves  8  are fully (normally) opened. 
     Next, a case where Ar is supplied to the wafer W in the flow rate control system  50 A shown in  FIG. 2  will be explained. A pressure ratio command K is input to the flow rate control system  50 A from the device operation screen of the central controller  46 . When the process is transferred, the flow rate control system  50 A controls Ar in accordance with a parameter in a recipe setting screen. 
     If the flow rate control valve  42 B of the flow rate control device  41 B is opened, Ar supplied from the gas supply source is supplied to the operation gas supply pipe  44  simultaneously. At that time, the flow rate control device  41 B detects the flow rate of the Ar which is output from the flow rate control device  41 B by the flowmeter  43 B, and controls the flow rate control device  41 B based on the detection result, thereby supplying Ar to the operation gas supply pipe  44  at the predetermined flow rate. 
     The Ar is supplied to the wafer W from the shower plate  52  through the operation gas supply pipe  44  and the partial pressure control system  45 . That is, in the partial pressure control system  45 , since the valves  8  of the pressure control devices  1 A and  1 B are fully opened, pressures of the Ar passing through the pressure sensors  3  of the pressure control devices  1 A and  1 B are increased to substantially the same level, the Ar is branched from the operation gas supply pipe  44  into the valves  8  of the pressure control devices  1 A and  1 B, and is supplied to the wafer W through the center shower  53  and the edge shower  54  of the shower plate  52 . 
     At that time, the pressure sensor  3  of the pressure control device  1 A detects the pressure P 1  of the Ar which is output from the valve  8 , and outputs a detection signal to the calculating section  28  of the CPU  26  through the A/D converter  39 , and the detection signal is fed back to the control section  36 . 
     The pressure sensor  3  of the pressure control device  1 B detects the pressure P 2  of the Ar which is output from the valve  8 , outputs a detection signal to the calculating section  34  of the CPU  26  through the A/D converter  33 , and the detection signal is fed back to the control section  30 . 
     The CPU 26  receives an arbitrary pressure ratio command K (here, K=target pressure P 1 /target pressure P 2 ), and judges whether the pressure ratio command K is smaller than 1. If the pressure ratio command K is smaller than 1, i.e., the target pressure P 2  of the pressure control device  1 B is greater than the target pressure P 1  of the pressure control device  1 A, the CPU  26  judges that the valve  8  of the pressure control device  1 A is the control subject, and immediately starts controlling the valve  8  of the pressure control device  1 A. At that time, since the valve  8  of the pressure control device  1 B is fully opened, the pressure P 2  of the pressure control device  1 B is increased. The CPU  26  monitors the pressure P 2  of the pressure control device  1 B and controls the valve  8  of the pressure control device  1 A such that the pressure ratio becomes equal to the instruction value. That is, the control section  36  of the CPU  26  determines the control signal with respect to the valve  8  of the pressure control device  1 A such that the pressure P 1  of the pressure control device  1 A and the pressure P 2  of the pressure control device  1 B become equal to the partial pressure ratio based on the deviation between the target pressure P 1  (=KP 2 ) of the pressure control device  1 A and the pressure P 1  which is fed back from the pressure sensor  3  of the pressure control device  1 A. In accordance with this control, in the pressure control device  1 A, the valve controller  9  adjusts the opening of the valve  8 . Thus, the Ar is output to the wafer W at the predetermined partial pressure ratio from the center shower  53  and the edge shower  54  and is supplied to the entire wafer W uniformly. 
     If the pressure ratio command K is not smaller than 1, i.e., the pressure P 1  of the pressure control device  1 A is equal to or greater than the pressure P 2  of the pressure control device  1 B, the valve  8  of the pressure control device  1 B is controlled in the same manner as that described above so that the pressure P 2  of the pressure control device  1 B is allowed to instantaneously reach the target value. Thus, the Ar can be supplied to the center area and the edge area of the wafer W at the predetermined partial pressure ratio. In this case, a value (P 1 /K) obtained by dividing the pressure P 1  detected by the pressure sensor  3  of the pressure control device  1 A by the pressure ratio command K is used as the target pressure P 2  of the pressure control device  1 B in the calculating section  28 . 
     Next, a case in which the flow rate control system  50 A changes the flow rate of operation gas will be explained. In general, in the flow rate control system  50 A, the gas supply source and the flow rate control device  41  are provided on the side of a gas box located away from the chamber  51 , and the partial pressure control system  45  is provided on the side of the chamber  51 . Therefore, the piping volume of the operation gas supply pipe  44  becomes large in size. In such a flow rate control system  50 A, when the opening of the flow rate control valve  42 B of the flow rate control device  41 B is changed and the flow rate of operation gas to be supplied to the operation gas supply pipe  44  is changed, the partial pressure control system  45  proportionally controls the valves  8  of the pressure control devices  1 A and  1 B based on the pressures P 1  and P 2  detected by the pressure sensors  3  of the pressure control devices  1 A and  1 B irrespective of the flow rate of Ar supplied from the operation gas supply pipe  44 , and outputs the Ar at the predetermined partial pressure ratio. Therefore, the control time is shortened. Thus, the responsivity of the flow rate control system  50 A with respect to the change of settings is excellent, and it is possible to output the operation gas at a precise partial pressure ratio. 
     In the partial pressure control system  45 , since the Ar is controlled under the relative pressure based on the pressures P 1  and P 2  which are output by the valves  8  of the pressure control devices  1 A and  1 B, it is unnecessary to provide large tanks on the primary sides of the valves  8  of the pressure control devices  1 A and  1 B to store the Ar unlike a case in which the operation gas is controlled under the absolute pressure. In the partial pressure control system  45 , when the pressure ratio of Ar which is output from the valves  8  of the pressure control devices  1 A and  1 B, it is only necessary to control smaller one of the pressures P 1  and P 2  of the valves  8  of the pressure control devices  1 A and  1 B. 
     Next, a case in which the flow rate control system  50 A changes the kinds of operation gas will be explained. 
     When the flow rate control system  50 A changes the kinds of operation gas (e.g., from Ar to CO in this embodiment), the flow rate control valve  42 B of the flow rate control device  41 B is closed, and the energization to the valve controllers  9  of the pressure control devices  1 A and  1 B is stopped, and the valves  8  is fully opened. With this operation, Ar remaining downstream of the flow rate control devices  41 A to  41 D is discharged into the chamber  51  from the pressure control devices  1 A and  1 B. Then, the flow rate control valve  42 D of the flow rate control device  41 D is opened to supply CO to the partial pressure control system  45  from the operation gas supply pipe  44 , and the CO is injected from the center shower  53  and the edge shower  54  of the shower plate  52  at the predetermined partial pressure ratio. 
     In the partial pressure control system  45 , the pressure sensors  3  detect pressures P 1  and P 2  of CO which are output from the valves  8  of the pressure control devices  1 A and  1 B, and the CO is controlled under the relative pressure based on the detection results. Therefore, even if the characteristics such as compression ratio of the CO and Ar are different from each other, the partial pressure control system  45  can swiftly determines the pressure ratio of CO which is to be output from the valves  8  of the pressure control devices  1 A and  1 B. 
     Thus, according to the flow rate control system  50 A of the embodiment, the flow rate control system of this embodiment comprises the flow rate control devices  41 A to  41 D which control the flow rate control valves  42 A to  42 D based on the detection results of the flowmeters  43 A to  43 D. The flow rate control devices  41 A to  41 D include the flow rate control valves  42 A to  42 D connected to the gas supply source, and the flowmeters  43 A to  43 D which detect the flow rates which are output from the flow rate control valves  42 A to  42 D. The flow rate control system  50 A also comprises the operation gas supply pipe  44  connected to the flow rate control devices  41 A to  41 D, and the partial pressure control system  45  includes the two valves  8  which are branched from the operation gas supply pipe  44  and which variably control the operation gas, the pressure sensors  3  which are respectively connected to the valves  8  in series for detecting the pressures P 1  and P 2  of the operation gas, and the controller  25  which proportionally controls the operation of the valves  8  based on the detection result of the pressure sensors  3  to relatively control the pressures P 1  and P 2  which are output from the two valves  8 . Therefore, the responsivity with respect to the change of setting is excellent, and it is possible to output the operation gas at a precise partial pressure ratio. 
     The partial pressure control system  45  of this embodiment comprises the two valves  8  which are branched from the operation gas supply pipe  44  and which variably control the operation gas, the pressure sensors  3  which are connected to the valves  8  in series and which detect the pressures P 1  and P 2  of the operation gases, and the controller  25  which proportionally controls the operations of the valves  8  based on the detection results of the pressure sensors  3  to relatively control the pressures P 1  and P 2  of the two valves  8 . Therefore, it is possible to reduce the wastefull consumption of operation gas, and to enhance the responsivity with respect to the change of settings. 
     In the partial pressure control system  45  of this embodiment, the controller  25  specifies, as the control subject, smaller one of the pressures P 1  and P 2  of the valves  8  of the pressure control devices  1 A and  1 B, and controls the action of the control subject based on the detection result of the pressure sensor  3 . Therefore, it is possible to control the valves  8  of the pressure control devices  1 A and  1 B in a diversion manner. 
     At that time, when the partial pressure control system  45  controls the pressure P 1  to be output from the pressure control device  1 A, the partial pressure control system  45  calculates the target pressure P 1  (=K×P 2 ) of the pressure control device  1 A from the pressure P 2  detected by the pressure control device  1 B and the pressure ratio command K, and controls the opening and closing operation of the valve  8  of the pressure control device  1 A. On the other hand, when the partial pressure control system  45  controls the pressure P 2  to be output from the pressure control device  1 B, the partial pressure control system  45  calculates the target pressure P 2  (=P 1 /K) of the pressure control device  1 B from the pressure P 1  detected by the pressure control device  1 A and the pressure ratio command K, and controls the opening and closing operation of the valve  8  of the pressure control device  1 B. Thus, it is possible to shorten the control time of the valves  8 , and to enhance the processing ability of the entire system. 
     The partial pressure control system  45  and the flow rate control system  50 A, which control the partial pressure include a zero point confirming unit in the controller  25 , and confirm whether the control state is constant. When the control of the partial pressure of operation gas is to be stopped or when the kinds of operation gas are to be changed, the zero point confirming unit is allowed to operate to detect the abnormality of the partial pressure control system  45 . 
     The zero point confirming unit may be operated when the flow rate control devices  41 A to  41 D are to be closed. As shown in  FIG. 3 , the zero point confirming unit close the flow rate control devices  41 A to  41 D to stop the supply of operation gas, and when the pressures P 1  and P 2  detected by the pressure sensor  3  become equal to or smaller than predetermined threshold value D, the zero point confirming unit confirms a zero point shift based on the pressure reduction of the pressure sensor  3 . 
     More specifically, if the control of the valves  8  by the valve controllers  9  of the pressure control devices  1 A and  1 B is stopped and the flow rate control devices  41 A to  41 D are closed, operation gas remaining downstream of the flow rate control devices  41 A to  41 D is supplied into the chamber  51  from the valves  8  of the pressure control devices  1 A and  1 B. With this, the pressures P 1  and P 2  detected by the pressure sensors  3  are reduced toward the zero point. 
     When one of the pressures P 1  and P 2  of the valves  8  becomes equal to or lower than the predetermined threshold value D, pressures P 1  and P 2  of the valves  8  are detected at constant intervals (e.g., 500 ms msec intervals) by the pressure sensor  3 , and it is judged whether the detected pressures P 1  and P 2  are within tolerance. For example, the pressure difference (P 1 −P 2 ) between the pressures P 1  and P 2  is calculated, and it is judged whether the pressure difference is within tolerance C (within 0.1 kPa) with respect to the zero point, and whither each of the pressures P 1  and P 2  of the valves  8  is smaller than a predetermined threshold value B (e.g., −0.15 kPa). There, the tolerance C is a deviation amount of the zero point position which can not functionally be permitted, and the threshold value B is a value which should not be shown by the pressure sensor  3  under a normal condition. 
     If it is judged that the pressure P 1  and P 2  difference is not within tolerance C, or when it is judged that any one of the output pressures P 1  and P 2  is smaller than the predetermined threshold value B, it is judged that the output pressures P 1  and P 2  are not within tolerance C. In this case, the pressure which should be indicated under a normal condition is not indicated, abnormality is detected. If the detection of abnormality is continuously counted several times (three times in this embodiment), an alarm is given to inform an operator of the abnormality of the partial pressure control system  45 . The reason why it is necessary to count the detection of abnormality several times is to prevent an erroneous detection. With this, the flow rate control system  50 A and the partial pressure control system  45  can swiftly find a system trouble. 
     A second embodiment of the shower plate used for the partial pressure control system, the flow rate control system and the partial pressure control system will be explained.  FIG. 4  is a plan view of a shower plate  80 .  FIG. 5  shows an example of layout of a partition wall ring  83 . 
     The shower plate  80  shown in  FIG. 4  is provided in the chamber  51  like the shower plate  52  of the first embodiment, and is used for supplying operation gas to the center area and the edge area of the wafer (corresponding to “supply subject”) W at a predetermined partial pressure ratio. The shower plate  80  is of a disk-like shape, and the shower plate  80  is divided into a disk-like center shower  81  and an annular edge shower  82  by mounting a perfectly circular partition wall ring (corresponding to “partition wall member”)  83  on the shower plate  80 . A plurality of gas holes  84  injecting the operation gas are formed in a surface of the shower plate  80  opposed to the wafer W. The adjacent gas holes  84  are arranged in a form of regular triangle, and are arranged in a form of hexagon from center to periphery with respect to the wafer W. 
     The shower plate  80  supplies operation gas which is controlled by the partial pressure control system to the wafer W from the gas holes  84  of the center shower  81  and the edge shower  82 . Since the gas holes  84  of the shower plate  80  are arranged in the form of regular triangle, distances between the adjacent gas holes  84  are constant. Since the gas holes  84  are arranged in the form of hexagon from center to periphery with respect to the wafer W, the gas holes  84  are not prone to be crushed when the shower plate  80  is divided by the partition wall ring  83 . That is, when the partition wall ring  83  is mounted as shown in  FIG. 5 , although the partition wall ring  83 D crushes the gas holes  84 , the partition wall rings  83 A,  83 B and  83 C do not crush the gas holes  84 . Thus, the probability that the gas holes  84  are crushed in the case of the shower plate  80  when the perfectly circular partition wall ring  83  is mounted is remarkably low as compared with the shower plate  122 A (see  FIG. 9 ) in which the gas holes  123 A are arranged in a form of square. It is easy to mount the partition wall rings  83 . 
     The shower plate  80  used for the partial pressure control system of this embodiment is concentrically partitioned by the partition wall ring  83  and divided into a plurality of areas, and the pressure of operation gas supplied to the wafer W from each area is controlled by the partial pressure control system, the adjacent gas holes  84  injecting the operation gas are arranged in the form of regular triangle, and are arranged in the form of hexagon from the center to the periphery with respect to the wafer W. Thus, the probability that the gas holes  84  are crushed by the partition wall ring  83 , and the discharging density of operation gas can be equalized on the wafer W. 
     Although the embodiments of the present invention have been explained above, the invention is not limited to the embodiments, and various applications can be made. 
     (1) For example, in the above embodiment, the pressure of operation gas which is output from the two valves  8  is adjusted to the pressure ratio command K. Alternatively, the partial pressure of operation gas which is output from three or more valves  8  may be adjusted. 
     (2) For example, valves  8  are controlled such that the valves  8  are fully opened when the control is started, one of the valves  8  having greater output pressure is left opened and the other valve  8  having smaller output pressure is specified as the control subject in the first embodiment. Alternatively, the valves  8  may be fully closed when the control is started, and the valves  8  of the pressure control devices  1 A and  1 B may be controlled. 
     (3) For example, the partial pressure control system  45  is used for the flow rate control system  50 A which is used for a semiconductor producing apparatus in the first embodiment. However, if the purpose is to output operation gas at a predetermined partial pressure ratio, the subject to which the invention is applied is not limited to the semiconductor producing apparatus. 
     Effect of the Invention will be Explained 
     The partial pressure control system of the present invention includes a plurality of pressure control units which are branched from an operation gas supply pipe and which variably control pressure of operation gas, pressure detecting units which are respectively connected to the pressure control units in series and which detect pressure of operation gas, and a control unit which proportionally controls operation of the pressure control unit based on a detection result of the pressure detecting unit, thereby relatively controlling the pressures of the pressure control units. Therefore, it is possible to reduce wastefull consumption of the operation gas, and to enhance the responsivity with respect to change of setting and the like. 
     The flow rate control system of the present invention comprises, a flow rate control device including a flow rate control valve connected to a gas supply source, and a flow rate detecting unit which detects a flow rate output by the flow rate control valve, the flow rate control device controlling the flow rate control valve based on a detection result of the flow rate detecting unit, an operation gas supply pipe connected to the flow rate control device, and a partial pressure control system including a plurality of pressure control units which are branched from the operation gas supply pipe and which variably control pressure of operation gas, pressure detecting units which are respectively connected to the pressure control units in series and which detects pressure of the operation gas, and a control unit which proportionally controls operation of the pressure control unit based on detection result of the pressure detecting unit and which relatively controls output pressure of the pressure control units. Therefore, the responsivity with respect to the change of settings and the like is excellent, and it is possible to output operation gas at a precise partial pressure ratio. 
     In the shower plate of the present invention used for a partial pressure control system, the shower plate is partitioned by a partition wall member and divided into a plurality of areas, the areas are connected to the partial pressure control system, and operation gas injected from each area to the supply subject is controlled. Adjacent gas holes for injecting the operation gas are arranged in a form of a regular triangle, and are arranged in a form of hexagon from a center to a periphery with respect to the supply subject. Therefore, the probability that the gas holes are crushed by the partition wall member can be lower, and discharging density of the operation gas can be equalized on the supply subject.