Patent Publication Number: US-2021180599-A1

Title: Vacuum pressure control system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2019-224247 filed on Dec. 12, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a vacuum pressure control system including a gas supply source, a vacuum chamber to be supplied with gas from the gas supply source, a vacuum control valve to adjust a pressure value in the vacuum chamber, and a vacuum pump to decompress the vacuum chamber, which are connected in series, and further including a pressure sensor to detect the pressure value in the vacuum chamber and a controller to control the vacuum control valve. The vacuum pressure control system is configured such that the controller adjusts a valve open degree of the vacuum control valve based on the pressure value detected by the pressure sensor to perform a pressure-value control of controlling the pressure value in the vacuum chamber to be a target value. 
     Related Art 
     Heretofore, as described in JPH10(1998)-252942, there is adopted a vacuum pressure control system configured to adjust a pressure value in a vacuum chamber to be a target pressure value and to retain that pressure value. This type of vacuum pressure control system is, for example, used for deposition on a wafer as a material for a semiconductor. Specifically, the pressure value of the vacuum chamber to be supplied with gas (process gas) at a flow rate required for deposition is maintained to a target value by adjusting a valve open degree of the vacuum control valve, and then deposition on the wafer that is placed in the vacuum chamber is performed. 
     SUMMARY 
     Technical Problems 
     However, the above-mentioned conventional technique has the following problem. As mentioned above, in order to maintain the pressure value in the vacuum chamber to be at the target value, the valve open degree of the vacuum control valve has to be adjusted to an optimum state. This optimum valve open degree of the vacuum control valve is, however, determined once after performing the actual pressure value control. Accordingly, as an advance preparation for the actual deposition process, there is a need to perform a process of experimentally supplying the process gas at a flow rate necessary for deposition so as to adjust the valve open degree of the vacuum control valve and to find the optimum valve open degree of the vacuum control valve at which the pressure value of the vacuum chamber agrees with the target value. For example, as shown in  FIG. 10 , an optimum valve open degree VO equal to the target value Pt is searched by gradually narrowing the valve open degree. 
     Further, the thus searched optimum valve open degree VO is used for confirming whether the actual pressure value of the vacuum chamber agrees with the target value Pt. For example, as shown in  FIG. 11 , a pressure waveform is confirmed to see whether the pressure value of the vacuum chamber is actually the target value Pt on condition that the valve open degree of the vacuum control valve is set to the optimum valve open degree VO. After completion of this confirmation operation, a deposition process is performed. 
     Further, in most cases of the deposition process, deposition is performed under plural conditions such as utilizing several types of process gas or utilizing the same type of process gas for several times but at different flow rates and at different target pressure values in each time in one unit of process. Accordingly, there is a need to perform the above-mentioned operation of searching the optimum valve open degree and the above-mentioned operation of confirming whether the actual pressure value of the vacuum chamber agrees with the target value under all the plural conditions. These advance preparations prior to the deposition process take time as types of process gas to be used increase, which may cause a bad influence on a semiconductor manufacturing efficiency. 
     The present disclosure has been made to solve the above problem and has a purpose of providing a vacuum pressure control system achieving easy calculation of an optimum valve open degree of a vacuum control valve that is necessary for making a pressure value of the vacuum chamber agree with a target value. 
     Means of Solving the Problems 
     To solve the above problem, the vacuum pressure control system of the present disclosure has the following configuration. 
     There is provided a vacuum pressure control system comprising: a gas supply source; a vacuum chamber configured to receive supply of gas from the gas supply source; a vacuum control valve configured to adjust a pressure value in the vacuum chamber; and a vacuum pump configured to decompress the vacuum chamber, which are connected in series, the vacuum pressure control system further comprising: a pressure sensor configured to detect the pressure value in the vacuum chamber; and a controller configured to control the vacuum control valve, the vacuum pressure control system configured to perform pressure value control of making the pressure value in the vacuum chamber agree with a target value by the controller adjusting a valve open degree of the vacuum control valve based on the pressure value detected by the pressure sensor while the gas is supplied at a predetermined flow rate from the gas supply source to the vacuum chamber, wherein the controller comprises a mapping program and a valve-open-degree calculation program and is configured in advance of performing the pressure value control to: approximate a relation of the pressure value in the vacuum chamber and the gas flow rate to a linear function and storing the linear function in the controller according to the mapping program; and calculate an optimum valve open degree of the vacuum control valve which is necessary for making the pressure value in the vacuum chamber agree with the target value when the gas at the predetermined flow rate is supplied based on the linear function according to the valve-open-degree calculation program, and the controller adjusts the valve open degree of the vacuum control valve based on the optimum valve open degree to make the pressure value in the vacuum chamber agree with the target value. 
     According to the above-mentioned vacuum pressure control system, the optimum valve open degree of the vacuum control valve which is necessary for making the pressure value in the vacuum chamber agree with the target value can easily be calculated. 
     The controller includes the mapping program and the valve-open-degree calculation program. According to the mapping program, the relation of the pressure value in the vacuum chamber and the gas flow rate is approximated to the linear function and the linear function is stored in the controller. Then, based on the thus stored linear function, the valve-open-degree calculation program calculates the optimum valve open degree of the vacuum control valve that is necessary for making the pressure value in the vacuum chamber agree with the target value when the gas at the predetermined flow rate is supplied, and thus the valve open degree of the vacuum control valve can be adjusted based on the calculated optimum valve open degree. 
     The relation of the pressure value in the vacuum chamber and the gas flow rate is approximated to the linear function, and thus the optimum valve open degree can be calculated from the linear function. Accordingly, in a case of performing deposition under plural conditions such as use of several types of gas, there is no need to adjust the valve open degree of the vacuum control valve by experimentally supplying the gas at a flow rate required for the deposition to the vacuum chamber on each of the plural conditions and to perform a searching operation of the optimum valve open degree which allows the pressure value of the vacuum chamber to agree with the target value. Therefore, there is less possibility of taking time for the advance preparations prior to the deposition process to cause a bad influence on the semiconductor manufacturing efficiency. 
     Herein, the predetermined flow rate represents a flow rate of the gas when the pressure control of the vacuum chamber is actually carried out, and for example, indicates a flow rate of the gas necessary for deposition on a wafer. 
     According to the vacuum pressure control system of the present disclosure, an optimum valve open degree of a vacuum control valve that is necessary for making a pressure value of a vacuum chamber agree with a target value can easily be calculated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory view showing a configuration of a vacuum pressure control system in the present embodiment; 
         FIG. 2  is a sectional view of a vacuum control valve used for the vacuum pressure control system in the present embodiment; 
         FIG. 3  is a block diagram showing a configuration of a controller used for the vacuum pressure control system in the present embodiment; 
         FIG. 4  is a table illustrating conditions for applying deposition on a wafer; 
         FIG. 5  is a flow chart showing a mapping program in the present embodiment; 
         FIG. 6  is a flow chart showing a valve-open-degree calculation program in the present embodiment; 
         FIG. 7  is a graph showing a relation between a pressure value in a vacuum chamber and a flow rate of process gas when a valve open degree of the vacuum control valve is maintained uniform; 
         FIG. 8  is a map formed according to the mapping program; 
         FIG. 9  is a graph for explaining a method of calculating an optimum valve open degree according to a valve-open-degree calculation program; 
         FIG. 10  is a graph for explaining an operation of searching the optimum valve open degree according to a conventional art; and 
         FIG. 11  is a graph used for confirming a pressure waveform when the vacuum control valve opens at the optimum valve open degree. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     An embodiment of a vacuum pressure control system according to the present disclosure is explained in detail with reference to the accompanying drawings. 
       FIG. 1  is a schematic view for explaining a configuration of a vacuum pressure control system  1 . The vacuum pressure control system  1  is for example, used for surface processing of a wafer  150  in a semiconductor manufacturing apparatus adopting a method of Atomic Layer Deposition (ALD). 
     The vacuum pressure control system  1  is, as shown in  FIG. 1 , configured such that a gas supply source  16  as a supply source of process gas (one example of gas) for surface processing of the wafer  150 , a mass flow controller  20 , a vacuum chamber  11  as a vacuum container, a vacuum control valve  30 , and a vacuum pump  15  are connected in series in this order from an upstream side. Further, on an upstream side of the mass flow controller  20 , an N 2  supply source  17  as a supply source of nitrogen gas (N 2 ) which is used for purging the process gas is connected in parallel with the gas supply source  16 . 
     The vacuum pressure control system  1  further includes a pressure sensor  12  provided between the vacuum chamber  11  and the vacuum control valve  30  via a shut-off valve  13  to detect a pressure value of the vacuum chamber  11  and includes a controller  70  which is electrically connected to the pressure sensor  12  and the vacuum control valve  30 . 
     The process gas supplied from the gas supply source  16  through a gas inflow port  11   a  or the purge gas supplied from the N 2  supply source  17  is supplied to the vacuum chamber  11  at a predetermined flow rate. Herein, the predetermined flow rate of the process gas represents a flow rate for actually performing pressure control of the vacuum chamber  11 , namely a flow rate of the process gas that is required for deposition on the wafer  150 . 
     To a gas discharge port  11   b  of the vacuum chamber  11 , a first port  41   a  of the vacuum control valve  30  is connected and to a second port  41   b  of the vacuum control valve  30 , the vacuum pump  15  is connected. Thus, the process gas or the purge gas supplied to the vacuum chamber  11  is allowed to be taken in by the vacuum pump  15 . At this time, the controller  70  obtains a pressure value inside the vacuum chamber  11  from the pressure sensor  12  and adjusts the valve open degree of the vacuum control valve  30  to perform the pressure value control of making the pressure value in the vacuum chamber  11  agree with a target value Pt. The valve open degree of the vacuum control valve  30  required for making the pressure value of the vacuum chamber  11  agree with the target value Pt is defined as an optimum valve open degree VO (see  FIGS. 10 and 11 ). 
     The vacuum pressure control system  1  having the above-mentioned configuration carries out the deposition in one process under a plurality of conditions. A plurality of the conditions are, for example, indicated as conditions 1 to 5 in a table of  FIG. 4 . A “gas type” indicated in  FIG. 4  represents a type of the process gas used for deposition. In  FIG. 4 , specific types of the gas are not indicated, but the types are simply indicated as gas A, gas B, and gas C. A “gas flow rate” represents a flow rate (a predetermined flow rate) of the process gas which is required for deposition. The gas flow rate is regulated by the mass flow controller  20  and supplied to the vacuum chamber  11  at the flow rate indicated in  FIG. 4 . A “target value” represents the target value Pt of the pressure value inside the vacuum chamber  11 . The controller  70  adjusts the valve open degree of the vacuum control valve  30  so that the pressure value agrees with this target value Pt. A “chamber temperature” represents a temperature inside the vacuum chamber  11 . Under each of the conditions, purging by N 2  gas is carried out. 
       FIG. 2  is a sectional view of the vacuum control valve  30  which is in a fully-open state. The vacuum control valve  30  is provided with an air-pressure cylinder  31  and a bellows-type poppet valve  32  assembled one on another in the figure. 
     The air-pressure cylinder  31  includes a cylinder body  33  having a hollow cylinder chamber and a piston  34  slidably assembled in the cylinder chamber in a direction parallel (in an up and down direction in the figure) to a stacking direction of the air-pressure cylinder  31  and the bellows-type poppet valve  32 . The piston  34  is urged downward by a restoring spring  35 . On an upper end of the piston  34 , a slide lever  36  extending upward is provided. 
     A potentiometer  37  as an open degree sensor is attached on an outside of the cylinder body  33 . The potentiometer  37  is embedded with a variable resistor (not shown) connected to the slide lever  36 . Integral upward and downward movement of the slide lever  36  with the piston  34  leads to changes in a variable resistance value, and the potentiometer  37  outputs this resistance value as a correlated value to a position of the piston  34  in a vertical direction to the controller  70 . 
     A bellofram  38  is provided on a lower surface of the piston  34 . The bellofram  38  is fixed to the piston  34  on its inner peripheral edge, and an outer peripheral edge of the bellofram  38  is fixed to an inner wall of the cylinder chamber. The bellofram  38  is extremely thin, and its structure is formed of strong polyester, tetoron cloth or the like covered thereon with rubber. The bellofram  38  has long deformation strokes and deep folding portions. The bellofram  38  of a cylindrical shape is a diaphragm having a uniform and unchanged effective pressure-receiving area during its deformation. The cylinder chamber includes an atmosphere chamber  33   a  and a pressurizing chamber  33   b  which are partitioned in an upper and lower direction by the piston  34  and the bellofram  38 . The atmosphere chamber  33   a  on an upper side accommodates the restoring spring  35  and is introduced with the atmosphere from a not-shown atmospheric port. The pressurizing chamber  33   b  on a lower side is introduced with compression air from a not-shown air supply source through a not-shown pressurizing port. 
     In a center portion of the piston  34 , a piston rod  39  inserted inside the bellows-type poppet valve  32  is fixed. The bellows-type poppet valve  32  is provided with the piston rod  39 , a valve element  40 , and a casing accommodating the piston rod  39  and the valve element  40 . The valve element  40  is fixed to an end portion of the piston rod  39  on a side where the piston rod  39  is inserted in the bellows-type poppet valve  32 . The casing  41  of a cylindrical shape includes the above-mentioned first port  41   a  and the second port  41   b . On an upper surface of the valve element  40 , a bellows  42  is provided. The bellows  42  is placed to enclose the piston rod  39 . 
     The valve element  40  is provided with an O ring  43  on its lower surface, and on an upper end side of the first port  41   a  of the casing  41 , a valve seat  45  to be into and out of contact with the valve element  40  is provided. When the valve element  40  is moved toward the valve seat  45  to be brought into contact with the valve seat  45 , the  0  ring  43  is under a state of being pressed by the valve element  40  and the valve seat  45 . Specifically, this state is a valve-fully-closed state of the vacuum control valve  30 , and the flow of the process gas is shut off at this time. 
     Further, upward and downward movement of the piston  34  brings upward and downward movement of the valve element  40  via the piston rod  39 . Thus, an open degree of the vacuum control valve  30  is changed. The potentiometer  37  then measures a position of the piston  34  in a vertical direction, and further a position of the valve element  40  in the vertical direction, which stands for the valve open degree of the vacuum control valve  30 , and the potentiometer  37  outputs the thus measured value to the controller  70 . 
     As shown in  FIG. 3 , the controller  70  includes a CPU  701 , an ROM  702 , an RAM  703 , and a storage unit  704 . The ROM  702  is stored with a mapping program  702   a  for forming a map used for calculating the optimum valve open degree VO and a valve-open-degree calculation program  702   b  for calculating the optimum valve open degree VO of the vacuum control valve  30  based on the formed map and then controlling the valve open degree of the vacuum control valve  30  to be the optimum valve open degree VO. The CPU  701  temporarily stores data to the RAM  703  and controls operation of the vacuum control valve  30  according to the mapping program  702   a  or the valve-open-degree calculation program  702   b . Further, the storage unit  704  stores the map formed by the mapping program  702   a.    
     &lt;Operation of Vacuum Pressure Control System&gt; 
     Operation of the above-configured vacuum pressure control system  1  is explained with the vacuum pressure control system  1  in a case that a deposition process on the wafer  150  is to be performed according to the conditions 1 to 5 indicated in the table of  FIG. 4 , for example. 
     In advance of performing an actual pressure control for the deposition process, the vacuum pressure control system  1  calculates the optimum valve open degree VO of the vacuum control valve  30  under each of the conditions 1 to 5 by the mapping program  702   a  and the valve-open-degree calculation program  702   b.    
     Firstly, the controller  70  forms a map used for calculating the optimum valve open degree VO by the mapping program  702   a.    
     When the map is to be formed, an operator operates the system to supply the process gas to the vacuum chamber  11  at a measurement flow rate Ft (see  FIG. 8 ) that is a flow rate for performing the mapping operation. The measurement flow rate Ft is a flow rate that has been predetermined by the mapping program  702   a  and is set as a value close to the actual supply amount of the process gas such as 10 L/min. 
     The mapping program  702   a  gets started while the gas at the measurement flow rate Ft is being supplied. The controller  70  adjusts the valve open degree of the vacuum control valve  30  to the predetermined valve open degree (S 11  in  FIG. 5 ). The valve-open-degree adjustment is controlled based on a resistance value which is output from the potentiometer  37 . 
     Herein, the predetermined valve open degree represents a valve open degree that has been predetermined for formation of the map, and a plurality of the valve open degrees have been set. For example, on condition that the maximum valve open degree is set at 100%, valve open degrees of 7%, 11%, 14%, 18%, 21%, 25%, 29%, 54%, 100%, and 114% are set (see  FIG. 8 ). In the present embodiment, the valve open degree is firstly adjusted as 7%. 
     After the valve open degree is adjusted to the predetermined degree, the controller  70  obtains a pressure measured value Pm 11  of the vacuum chamber  11  from the pressure sensor  12  in a state in which the process gas is supplied at the measurement flow rate Ft, and then the controller  70  stores the value Pm 11  (S 12 ). 
     Subsequently, in all the remaining predetermined valve open degrees (11%, 14%, 18%, 21%, 25%, 29%, 54%, 100%, and 114%), the process is repeated until pressure measured values Pm 12  to Pm 20  are obtained (S 13 : NO). 
     After the pressure measured values of the vacuum chamber  11  at all the valve open degrees are obtained (S 13 : YES), the controller  70  carries out the map formation (S 14 ). To be specific, at each of a plurality of the predetermined valve open degrees (7%, 11%, 14%, 18%, 21%, 25%, 29%, 54%, 100%, and 114%), the pressure measured values Pm 11  to Pm 20  are plotted to calculate the linear functions LF 11  to LF 20  with defining an intercept as zero through which the plotted pressure measured values Pm 11  to Pm 20  pass. 
     The linear functions LF 11  to LF 20  are plotted by approximating the relation between the pressure value in the vacuum chamber  11  and the flow rate of the process gas. This approximation is possible because the pressure value inside the vacuum chamber  11  increases according to an increase in the flow rate of the process gas as shown in  FIG. 7  when the flow rate of the process gas is increased in a state in which the valve open degree of the vacuum control valve  30  is fixed to 7%, for example. This applies to any valve open degree of the vacuum control valve  30  (for example, the pressure value similarly increases at the valve open degrees of 11%, 14%, 18%, 21%, 25%, 29%, 54%, 100%, and 114% as shown in  FIG. 7 ). As long as the valve open degree of the vacuum control valve  30  is constant, the pressure value of the vacuum chamber  11  increases as the flow rate of the process gas increases, and the pressure value decreases as the flow rate of the process gas decreases. In other words, the pressure value of the vacuum chamber  11  and the flow rate of the process gas is confirmed to be expressed by a proportional relation. Therefore, the relation between the pressure value of the vacuum chamber  11  and the flow rate of the process gas can be approximated to the linear functions LF 11  to LF 20  with the intercept of zero. 
     When the map formation is completed, the controller  70  stores the thus formed map in the storage unit  704  (S 15 ), and the mapping program  702   a  is ended. 
     Next, an operation of calculating the optimum valve open degree VO of the vacuum control valve  30  by the valve-open-degree calculation program  702   b  under each one of conditions 1 to 5 in  FIG. 4  is explained. 
     The optimum valve open degree VO under the condition 1 is calculated first. 
     In calculating the optimum valve open degree VO, an operator firstly operates the system to be in a condition that the process gas is supplied at a predetermined flow rate to the vacuum chamber  11 . This predetermined flow rate indicates each gas flow rate that has been defined in the respective conditions 1 to 5. In the condition 1, the predetermined flow rate is 0.5 L/min as shown in  FIG. 4 . 
     After the process gas is being supplied at the predetermined flow rate, the operator operates the valve-open-degree calculation program  702   b.    
     The controller  70  adjusts the valve open degree of the vacuum control valve  30  to any one of a plurality of predetermined valve open degrees (7%, 11%, 14%, 18%, 21%, 25%, 29%, 54%, 100%, and 114%) (see  FIG. 6 , S 21 ). The operator can thus choose any one of a plurality of the predetermined valve open degrees before operating the valve-open-degree calculation program  702   b . Herein, it is premised that a valve open degree of 11% is chosen as one example, and thus the controller  70  adjusts the valve open degree of the vacuum control valve  30  to 11%. 
     Subsequently, the controller  70  obtains a second pressure measurement value Pm 21  by the pressure sensor  12  (S 22 ). 
     After obtaining the second pressure measurement value Pm 21 , the controller  70  calculates an estimated flow rate Fe based on the map (S 23 ). For example, when the vacuum control valve  30  is set at the valve open degree of 11%, Pm 21  is substituted in the linear function LF 12 , so that the estimated flow rate Fe can be calculated. 
     The estimated flow rate Fe represents a flow rate of the process gas supplied to the vacuum chamber  11  and is equivalent to the predetermined flow rate (under the condition 1, the flow rate of 0.5 L/min). The estimated flow rate Fe equivalent to the predetermined flow rate is calculated because the vacuum control valve  30  cannot obtain information about the flow rate from the mass flow controller  20 . Further, for obtaining the information about the flow rate from the mass flow controller  20  by the vacuum control valve  30 , there is a need to configure a new circuit configuration, which could cause high costs, but as mentioned above, the controller  70  itself can calculate the flow rate as the estimated flow rate Fe, so that it becomes possible to obtain the information about the flow rate with the existing circuit configuration, which can achieve cost saving. 
     Subsequently, the controller  70  grasps the target value Pt of the pressure value in the vacuum chamber  11  (S 24 ). The target value Pt is 133 Pa under the condition 1. 
     Based on the target value Pt and the estimated flow rate Fe, the optimum valve open degree VO is then calculated (S 25 ). The relation between the pressure value and the flow rate can be approximated to the linear function, and accordingly, the target value Pt can be represented by the linear function LF 21  of the estimated flow rate Fe with the intercept as zero as shown in  FIG. 9 . By obtaining an orientation of the linear function LF 21 , it is possible to obtain the optimum valve open degree VO of the vacuum control valve  30  suitable for making the pressure value in the vacuum chamber  11  agree with the target value Pt at the estimated flow rate Fe, namely at the predetermined flow rate from the thus obtained orientation. 
     The controller  70  subsequently confirms that the pressure value in the vacuum chamber  11  actually agrees with the target value Pt by the calculated optimum valve open degree VO (S 26 ). Specifically, as shown in  FIG. 11 , the controller  70  observes a pressure waveform to confirm whether the pressure value of the vacuum chamber  11  actually agrees with the target value Pt with assuming that the valve open degree of the vacuum control valve  30  is the optimum valve open degree VO. The conventional technique requires operation of searching the optimum valve open degree VO as shown in  FIG. 10 , but the optimum valve open degree VO can be calculated as mentioned above, thus requiring no searching operation of the optimum valve open degree VO. 
     When it is confirmed that the pressure value reaches the target value Pt by the pressure waveform (S 26 : YES), the controller  70  stores the obtained optimum valve open degree VO to the storage unit  704  (S 27 ). When the pressure value disagrees with the target value Pt from the result of confirming the pressure waveform, the controller  70  gives an error notification (S 29 ), and then the valve-open-degree calculation program  702   b  is ended. 
     As mentioned above, the controller  70  repeats the process from S 21  to S 25  under all the conditions 1 to 5 (S 28 : NO) and obtains the optimum valve open degree VO under the respective conditions. After completion of the process through S 21  to S 27  under all the conditions 1 to 5 (S 28 : YES), the valve-open-degree calculation program  702   b  is ended. 
     When the actual deposition process is to be performed, the controller  70  reads out the optimum valve open degree VO from the storage unit  704  under each of the conditions, for example, reading out the optimum valve open degree VO of the condition 1 when performing deposition under the condition 1 and reading out the optimum valve open degree VO of the condition 2 when performing deposition under the condition 2 so that the valve open degree of the vacuum control valve  30  is adjusted to the optimum valve open degree VO. Thus, it is possible to control the pressure value in the vacuum chamber  11  to be the target value Pt. 
     Further, there is a case when a plurality of semiconductor manufacturing apparatuses of an identical type are installed in a plant, and in that case, only any one of a plurality of the semiconductor manufacturing apparatuses may have to be formed with a map by the mapping program  702   a , so that the optimum valve open degree VO of the vacuum control valve  30  required for making the pressure value of the vacuum chamber  11  agree with the target value Pt can be calculated. Therefore, there is less possibility of taking time for advance preparation before performing the deposition process to cause a bad influence on a semiconductor manufacturing efficiency. 
     As mentioned above, the vacuum pressure control system  1  of the present embodiment is configured such that (1) the vacuum pressure control system  1  comprises: a gas supply source  16 ; a vacuum chamber  17  configured to receive supply of process gas from the gas supply source  16 ; a vacuum control valve  30  configured to adjust a pressure value in the vacuum chamber  11 ; and a vacuum pump  15  configured to decompress the vacuum chamber  11 , which are connected in series, the vacuum pressure control system  1  further comprises: a pressure sensor  12  configured to detect the pressure value in the vacuum chamber  11 ; and a controller  70  configured to control the vacuum control valve  30 , the vacuum pressure control system  1  configured to perform pressure value control of making the pressure value in the vacuum chamber  11  agree with a target value Pt by the controller  70  adjusting a valve open degree of the vacuum control valve  30  based on the pressure value detected by the pressure sensor  12  while the gas is supplied at a predetermined flow rate from the gas supply source  16  to the vacuum chamber  11 , wherein the controller  70  comprises a mapping program  702   a  and a valve-open-degree calculation program  702   b  and is configured in advance of performing the pressure value control to: approximate a relation of the pressure value in the vacuum chamber  11  and the gas flow rate to linear functions LF 11  to LF 20  and storing the linear functions LF 11  to LF 20  in the controller  70  according to the mapping program  702   a ; and calculate an optimum valve open degree VO of the vacuum control valve  30  which is necessary for making the pressure value in the vacuum chamber  11  agree with the target value Pt when the gas at the predetermined flow rate is supplied based on the linear functions LF 11  to LF 20  according to the valve-open-degree calculation program  702   b , and thus the controller adjusts the valve open degree of the vacuum control valve  30  based on the optimum valve open degree VO to make the pressure value in the vacuum chamber  11  agree with the target value Pt. 
     According to the vacuum pressure control system  1  in the above (1), the optimum valve open degree VO of the vacuum control valve  30  necessary for making the pressure value in the vacuum chamber  11  agree with the target value Pt can be easily calculated. 
     The controller  70  includes the mapping program  702   a  and the valve-open-degree calculation program  702   b . According to the mapping program  702   a , the relation of the pressure value in the vacuum chamber  11  and the flow rate of the process gas is approximated to the linear functions LF 11  to LF 20  and the linear functions LF 11  to LF 20  are stored in the controller  70 . Then, based on the thus stored linear functions LF 11  to LF 20 , the valve-open-degree calculation program  702   b  calculates the optimum valve open degree VO necessary for making the pressure value in the vacuum chamber  11  agree with the target value Pt when the process gas at the predetermined flow rate is supplied, and thus the valve open degree of the vacuum control valve  30  can be adjusted based on the calculated optimum valve open degree VO. 
     The relation of the pressure value in the vacuum chamber  11  and the flow rate of the process gas is approximated to the linear functions LF 11  to LF 20 , and thus the optimum valve open degree VO can be calculated from the linear functions LF 11  to LF 20 . Accordingly, in a case of performing deposition under plural conditions such as use of several types of the process gas, there is no need to adjust the valve open degree of the vacuum control valve  30  by experimentally supplying the process gas at a flow rate required for the deposition to the vacuum chamber  11  under each of the plural conditions (the conditions 1 to 5) and to search the optimum valve open degree VO that allows the pressure value of the vacuum chamber  11  to agree with the target value Pt. Therefore, there is less possibility of taking time for advance preparations prior to a deposition process, which could cause a bad influence on the semiconductor manufacturing efficiency. 
     Herein, the predetermined flow rate represents a flow rate of the process gas when the pressure control of the vacuum chamber  11  is actually carried out, and for example, indicates a flow rate of the process gas necessary for deposition on the wafer  150 . 
     (2) In the vacuum pressure control system  1  described above in (1), in advance of performing the pressure value control, the mapping program  702   a  includes: obtaining a pressure measured values Pm 11  to Pm 20  of the vacuum chamber  11  at a predetermined valve open degree by the pressure sensor  12  in a state in which the process gas is supplied at a measurement flow rate determined by the mapping program  702   a  to the vacuum chamber  11  from the gas supply source  16  while the vacuum control valve  30  opens at the predetermined valve open degree, and gaining the linear functions LF 11  to LF 20 , which is formed with an intercept as zero and extending through the pressure measurement values Pm 11  to Pm 20  at the predetermined valve open degree, based on the measurement flow rate and the pressure measured values Pm 11  to Pm 20 . 
     According to the vacuum pressure control system  1  described in the above (2), the optimum valve open degree VO of the vacuum control valve  30  necessary for making the pressure value of the vacuum chamber  11  agree with the target value Pt can be easily calculated. 
     When the valve open degree of the vacuum control valve  30  is uniform, the more the flow rate of the process gas increases, the higher the pressure value in the vacuum chamber  11  becomes, and on the other hand, the lower the flow rate of the process gas is, the lower the pressure value becomes. Namely, the pressure value of the vacuum chamber  11  and the flow rate of the process gas are in a proportional relation. Accordingly, the relation of the pressure value inside the vacuum chamber  11  and the flow rate of the process gas can be approximated to the linear functions LF 11  to LF 20  (an orientation of the function depends on the predetermined valve open degree) with an intercept as zero, and thus use of these linear functions LF 11  to LF 20  achieves easy calculation of the optimum valve open degree VO of the vacuum control valve  30  necessary for making the pressure value of the vacuum chamber  11  agree with the target value Pt. 
     Further, in a plant, there may be provided a plurality of semiconductor manufacturing apparatuses of the same type. Only any one of those semiconductor manufacturing apparatuses has to obtain the above linear functions LF 11  to LF 20 , so that semiconductor manufacturing apparatuses of the same type can calculate the optimum valve open degree VO of the vacuum control valve  30 , which is necessary for making the pressure value of the vacuum chamber  11  agree with the target value Pt, by use of the common linear functions LF 11  to LF 20  in the semiconductor manufacturing apparatuses of the same type. Accordingly, there is less possibility of taking time for advance preparations prior to the deposition process and less possibility of giving a bad influence on the semiconductor manufacturing efficiency. 
     (3) In the vacuum pressure control system  1  described in the above (1) or (2), in advance of performing the pressure value control, the valve-open-degree calculation program  702   b  includes: obtaining a second pressure measured value Pm 21  in the vacuum chamber  11  by the pressure sensor  12  in a state in which the process gas at the predetermined flow rate is supplied to the vacuum chamber  11  at the predetermined valve open degree; calculating an estimated flow rate Fe of the process gas by substituting the second pressure measured value Pm 21  into the linear functions LF 11  to LF 20 ; and gaining an orientation of the linear function LF 21  with the target value Pt set as a linear function LF 21  of the estimated flow rate Fe with an intercept as zero and gaining the optimum valve open degree VO at the predetermined flow rate from the orientation. 
     According to the vacuum pressure control system  1  described in the above (3), the optimum valve open degree VO of the vacuum control valve  30 , which is necessary for making the pressure value in the vacuum chamber  11  agree with the target value Pt, can be easily calculated. 
     Each orientation of the linear functions LF 11  to LF 20  has been determined by the predetermined valve open degree, and the second pressure measured value Pm 21  under a state in which the process gas at the predetermined flow rate is being supplied to the vacuum chamber  11  is substituted into the linear functions LF 11  to LF 20 . Thus, the calculated estimated flow rate Fe is equivalent to the predetermined flow rate. 
     The relation of the pressure value inside the vacuum chamber  11  and the flow rate of the process gas has been confirmed to be approximated to the linear function with the intercept of zero, and thus the target value Pt is a function (the linear function LF 21 ) of the estimated flow rate Fe that is equivalent to the predetermined flow rate, so that the orientation of the linear function LF 21  can be calculated. This orientation represents the optimum valve open degree VO for obtaining the target value Pt at the predetermined flow rate. 
     The estimated flow rate Fe equivalent to the predetermined flow rate is calculated by the controller  70  itself, thus requiring no need to input information about the predetermined flow rate by an external device and performing calculation of the optimum valve open degree VO. Therefore, there is no need to newly configure an apparatus for inputting information about the predetermined flow rate to the vacuum control valve  30  and the controller  70 , and it is possible to calculate the optimum valve open degree VO of the vacuum control valve  30  by a conventional equipment. 
     The above embodiment is only an illustration and has no any limitation to the present disclosure. Accordingly, the present disclosure may be made with any improvements and modifications without departing from the scope of the disclosure. 
     For example, the above embodiment raises ten valve open degrees of 7%, 11%, 14%, 18%, 21%, 25%, 29%, 54%, 100%, and 114% as the predetermined valve open degree for a map formation according to the mapping program  702   a . However, the valve open degree is not limited to the above, and may be any valve open degrees and not limited to ten types. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Vacuum pressure control system 
               11  Vacuum chamber 
               12  Pressure sensor 
               15  Vacuum pump 
               16  Gas supply source 
               30  Vacuum control valve 
               70  Controller