Patent Publication Number: US-9425024-B2

Title: Load simulator

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a load simulator used in a plasma processing system or the like. 
     2. Description of Related Art 
     Recent years have seen the development of a plasma processing system in which a workpiece such as a semiconductor wafer or a liquid crystal substrate is processed using a method such as etching.  FIG. 8  is a block diagram showing the configuration of a general plasma processing system. The plasma processing system shown in  FIG. 8  includes a high frequency power source apparatus  100 , an impedance matching apparatus  200 , a high frequency measurement apparatus  300 , and a plasma processing apparatus  400 . The high frequency power source apparatus  100  outputs high frequency power, which is supplied to the plasma processing apparatus  400 . 
     The high frequency measurement apparatus  300  monitors the impedance and the like of the plasma processing apparatus  400  during plasma processing. The high frequency measurement apparatus  300  is connected to an input terminal of the plasma processing apparatus  400  and includes sensors for detecting the high frequency voltage and the high frequency current at the input terminal. The high frequency measurement apparatus  300  also calculates various types of high frequency parameters for the impedance and the like based on the detected values of the high frequency voltage and the high frequency current. 
     In general, with high frequency measurement apparatuses, the detected values obtained by the sensors can deviate from correct values due to errors in the sensor sensitivity and the like. In light of this, a measurement object serving as a reference is measured by the measurement apparatus in advance, and a calibration parameter is acquired based on the measurement results. 
     In actual measurement, the detected values obtained by the sensors are converted into correct values using the calibration parameter, and the converted values are output (e.g., see JP 2004-309132A and JP 2007-163308A). 
     With the high frequency measurement apparatus  300  shown in  FIG. 8 , SOLT (Short-Open-Load-Thru) calibration, for example, is used for correction of the high frequency voltage and the high frequency current. In SOLT calibration, a load simulator (dummy load)  500  (see  FIG. 9 ) for which the real impedance value has been specified in advance is connected to the high frequency measurement apparatus  300 , and impedance measurement is performed by the high frequency measurement apparatus  300 . Three types of load simulators having mutually different impedances are used when performing this measurement. Specifically, the load simulators that are used are a load simulator having the characteristic impedance of the measurement system (the characteristic impedance of the transmission line that transmits a high frequency for measurement, which is generally 50Ω or 75Ω), a load simulator having the open condition impedance (substantially infinite), and a load simulator having the short circuit condition impedance (substantially zero). Next, a calibration parameter for correcting the high frequency voltage and the high frequency current is calculated from the measured impedance values of the load simulators that were measured by the high frequency measurement apparatus  300  and the real impedance values of the load simulators, and the calibration parameter is recorded in a memory of the high frequency measurement apparatus  300 . 
     In the actual measurement, the detected high frequency voltage and high frequency current are corrected using the calibration parameter recorded in the memory, and various types of high frequency parameters are calculated based on the corrected values. 
     With the calibration method described above, the high frequency measurement apparatus  300  is directly connected to each of the load simulators  500  when the calibration parameter is calculated. The calibration parameter is therefore for correcting the values at the output terminal of the high frequency measurement apparatus  300 . The impedance that is corrected based on such a calibration parameter is the impedance obtained when the load side is viewed from the output terminal of the high frequency measurement apparatus  300 . However, monitoring the plasma processing apparatus  400  requires measurement of the impedance between electrodes provided inside the chamber of the plasma processing apparatus  400 . 
     In the case where the high frequency measurement apparatus  300  and the plasma processing apparatus  400  are directly connected to each other as shown in  FIG. 8 , the impedance obtained when the load side is viewed from the output terminal of the high frequency measurement apparatus  300  can be thought to correspond to the impedance between the electrodes in the plasma processing apparatus  400 . However, the precision of the measured value obtained by the high frequency measurement apparatus  300  decreases since these two impedances are not completely the same. 
     SUMMARY OF THE INVENTION 
     The present invention was conceived in light of the above-described circumstances, and an object thereof is to provide a load simulator used for performing calibration so as to raise the precision of measured values obtained by a high frequency measurement apparatus as high as possible. 
     A load simulator provided by a first aspect of the present invention includes: a passive element; two electrode plates that are connected to the passive element; and a bias applier that biases at least one of the two electrode plates in a predetermined direction. 
     It is preferable that the two electrode plates are substantially parallel with each other, and the bias applier biases the two electrode plates in a direction of separation from each other. 
     It is preferable that the bias applier biases the two electrode plates so as to respectively be pressed against two electrodes in a chamber of a plasma processing apparatus. 
     It is preferable that the bias applier is a coil spring disposed between the two electrode plates. 
     It is preferable that the load simulator of the present invention further includes: a circuit having wiring that connects the passive element and the two electrode plates; and an insulator. The passive element and the circuit are disposed between the two electrode plates, and the insulator is disposed so as to surround the circuit. 
     It is preferable that the two electrode plates are each a copper plate. 
     It is preferable that the load simulator of the present invention further includes a flexible conductor for electrically connecting the passive element and at least one of the two electrode plates. 
     It is preferable that the conductor is copper foil. 
     It is preferable that the load simulator of the present invention further includes a coaxial connector electrically connected to the two electrode plates. 
     According to the present invention, at least one of the electrode plates is biased by the bias applier, thus enabling the electrode plate to be pressed in the predetermined direction. The load simulator of the present invention can be used when disposed between two electrodes in the chamber of a plasma processing apparatus. Accordingly, in a case such as the case of calibrating a high frequency measurement apparatus to be disposed at the input terminal of the plasma processing apparatus, it is possible to dispose the load simulator of the present invention between the two electrodes of the plasma processing apparatus, determine the impedance using the high frequency measurement apparatus, and then calculate a calibration parameter based on the measured impedance value obtained through the measurement and the real impedance value of the load simulator. The calibration parameter can be used to correct a detected value obtained by the high frequency measurement apparatus to the value between the electrodes of the plasma processing apparatus. Using this calibration parameter therefore enables raising the precision of the measured value obtained by the high frequency measurement apparatus. 
     Also, since the electrode plate is pressed against an electrode of the plasma processing apparatus by the bias applier, the load simulator can also be used in plasma processing apparatuses having different inter-electrode distances. 
     Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating the case of using a load simulator according to the present invention in processing for calibrating a high, frequency measurement apparatus. 
         FIG. 2  is a plan view of the configuration of the load simulator of the present invention. 
         FIG. 3  is a cross-sectional view taken along line B-B′ shown in  FIG. 2 . 
         FIG. 4  is a diagram illustrating the structure of a coil spring portion of the load simulator according to the present invention. 
         FIG. 5  is a circuit diagram showing the load simulator of the present invention. 
         FIG. 6  is a diagram for describing a calibration parameter. 
         FIG. 7  is a flowchart showing a procedure of calibration of the high frequency measurement apparatus. 
         FIG. 8  is a block diagram showing the configuration of a general plasma processing system. 
         FIG. 9  is a diagram illustrating the case of using a conventional load simulator in processing for calibrating a high frequency measurement apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A specific description of an embodiment of the present invention will be given below with reference to the attached drawings. 
       FIGS. 1 to 5  are diagrams for describing a load simulator based on an embodiment of the present invention. 
     As shown in  FIG. 2 , a load simulator  1  includes passive elements such as a resistor  21  and a capacitor  22 . The impedance of the load simulator  1  is set to a predetermined value. The load simulator  1  can therefore be used to simulate a load having that impedance value. 
     As shown in  FIG. 1 , the chamber of a plasma processing apparatus  400  is provided with two electrodes, namely a positive electrode  401  and a ground electrode  402 . The load simulator  1  is disposed between these two electrodes, and is used to calibrate a high frequency measurement apparatus  300 . The high frequency measurement apparatus  300  is connected to an input terminal c of the plasma processing apparatus  400 , and a calibration parameter is calculated based on a measured impedance value obtained by the high frequency measurement apparatus  300  and the real impedance value set in the load simulator  1 . A method for calculating the calibration parameter will be described later. 
       FIG. 2  is a plan view of the load simulator  1 . A positive electrode plate  70 , which will be described later, is not shown in  FIG. 2 .  FIG. 3  is a cross-sectional view of the load simulator  1  taken along line B-B′ shown in  FIG. 2 .  FIG. 4  is a diagram for describing the structure of a coil spring  40  portion of the load simulator  1 . 
     As shown in  FIGS. 2 and 3 , the load simulator  1  includes a printed circuit board  10 , the resistor  21 , the capacitor  22 , insulating resin  30 , four coil springs  40 , a coaxial connector  50 , a ground electrode plate  60 , and the positive electrode plate  70 . 
     The printed circuit board  10  is obtained by forming predetermined wiring on a substantially rectangular substrate made up of an insulating material such as glass epoxy, and passive elements such as the resistor  21  and the capacitor  22  are mounted on the printed circuit board  10 . As shown in  FIG. 2 , the printed circuit board  10  is provided with ground wiring  11 , connection wiring  12 , and positive-side wiring  13 . 
     The ground wiring  11  electrically connects a first terminal of the capacitor  22  and a negative-side terminal of the coaxial connector  50 . The printed circuit board  10  is fixed to the ground electrode plate  60  using four screws  14 . The screws  14  are electrically conductive, and one of them is fixed to the ground electrode plate  60  above the ground wiring  11 . The ground wiring  11  and the ground electrode plate  60  are therefore electrically connected via that screw  14 . The ground electrode plate  60  is electrically connected to the ground electrode  402  when the load simulator  1  is disposed in the plasma processing apparatus  400  (see  FIG. 1 ). The ground electrode  402  is grounded and is at the reference potential (ground potential) of 0 V. The potential of the ground wiring  11  is therefore also the reference potential. Note that in the case where the printed circuit board  10  is not fixed to the ground electrode plate  60  using the screw  14 , the ground wiring  11  and the ground electrode plate  60  may be electrically connected via through-holes (holes penetrating the substrate that have been subjected to plating or the like in order to electrically connect the two surfaces of the substrate) provided in the printed circuit board  10 . Also, another method may be used to electrically connect the ground wiring  11  and the ground electrode plate  60 . 
     The connection wiring  12  electrically connects a first terminal of the resistor  21  and a second terminal of the capacitor  22 . The resistor  21  and the capacitor  22  are therefore connected to each other in series. 
     The positive-side wiring  13  electrically connects a second terminal of the resistor  21  and a positive-side terminal of the coaxial connector  50 . The positive-side wiring  13  and the positive electrode plate  70  are electrically connected via a connection conductor  72  that will be described later. The positive electrode plate  70  is electrically connected to the positive electrode  401  when the load simulator  1  is disposed in the plasma processing apparatus  400 . The high frequency power supplied to the positive electrode  401  of the plasma processing apparatus  400  is therefore supplied to the positive-side wiring  13 . 
     Note that the configuration of the printed circuit board  10  is not limited to this. For example, the shape of the printed circuit board  10  is not limited to being rectangular, and there are also no limitations on the disposition of the resistor  21  and the capacitor  22 , as well as the shapes of the various wiring. 
     The resistor  21  has a resistance value of approximately 50Ω. The resistance value of the resistor  21  is set such that the overall resistance value of the load simulator resistance value 1 is 50Ω, including parasitic resistance resulting from the various wiring and the like. The resistor  21  is fixed to the ground electrode plate  60  so as to be in direct contact therewith. Heat generated by the resistor  21  can therefore be efficiently dissipated by the ground electrode plate  60 . Note that in the case where there is no need to dissipate heat generated by the resistor  21 , the resistor  21  does not need to be fixed to the ground electrode plate  60 . For example, the resistor  21  may be fixed to the printed circuit board  10 . 
     The capacitor  22  is a passive element that has a predetermined capacitance. The capacitance of the capacitor  22  is capacitance for canceling out parasitic inductance resulting from the various wiring and the like, and is set such that the overall reactance of the load simulator  1  is j0Ω (j being an imaginary unit) when high frequency power is supplied from the high frequency power source apparatus  100  (see  FIG. 1 ). 
       FIG. 5  is a circuit diagram showing the load simulator  1 . As shown in  FIG. 5 , the resistor  21 , and the capacitor  22  are connected in series by the connection wiring  12  between the positive electrode plate  70  and the ground electrode plate  60 . 
     The load simulator  1  is designed such that the overall impedance is 50+j0Ω. Three load simulators are used in the later-described calibration of the high frequency measurement apparatus  300 . The load simulator  1  is a load simulator having the characteristic impedance (50±j0Ω), and will be referred to as the load simulator  1   a  when there is a need to distinguish between the three load simulators in the description. Also, a load simulator  1   b  is a load simulator having the open condition impedance (substantially infinite), and a load simulator  1   c  is a load simulator having the short circuit condition impedance (substantially zero). The configurations of the load simulators  1   b  and  1   c  are similar to the configuration of the load simulator  1   a , but the resistance value of the resistor  21  and the capacitance of the capacitor  22  are different from those in the case of the load simulator  1   a . Note that it is sufficient that the resistance value of the resistor  21  and the capacitance of the capacitor  22  in the load simulators  1   b  and  1   c  are designed appropriately. 
     It should also be noted that the passive elements used in the load simulators  1   a ,  1   b , and  1   c  are not limited to being the resistor  21  and the capacitor  22 . An inductor may be used instead of the capacitor  22 , or inductors may be used instead of the resistor  21  and the capacitor  22 . Also, there is no limitation to the case where the passive elements are connected to each other in series, and they may be connected to each other in parallel. It is sufficient that the arrangement of the passive elements and the method for connecting them are designed appropriately such that the load simulators  1   a  to  1   c  can artificially realize loads having predetermined impedances. 
     The insulating resin  30  is for insulating the positive electrode plate  70  and the ground electrode plate  60  so that a short circuit does not occur. In the present embodiment, polytetrafluoroethylene (commercial name “Teflon”) is used as the material of the insulating resin  30 . Note that the material of the insulating resin  30  needs only be a material having insulating properties, and may be another synthetic resin or the like. As shown in  FIG. 2 , the insulating resin  30  is configured as an enclosure made up of four linear portions, and is shaped such that a portion is missing from the enclosure. Note that the shape of the insulating resin  30  is not limited to this. A configuration is possible in which the shape of the insulating resin  30  is not missing a portion (i.e., a fully closed rectangular shape in a plan view), and a hole for the disposition of the coaxial connector  50  is provided in a portion of the insulating resin  30 . Also, the insulating resin  30  may be annular in a plan view, or a configuration is possible in which the outer shape is rectangular and the inner shape is circular in a plan view. Furthermore, the insulating resin  30  may be box-shaped in which the upper face side in  FIG. 3  is closed. 
     As shown in  FIGS. 2 and 3 , the insulating resin  30  is fixed to the ground electrode plate  60  such that the outer circumference extends along the outer circumference of the ground electrode plate  60 . The printed circuit board  10 , the resistor  21 , and the capacitor  22  are disposed in a hollow portion in the center in a plan view. Accordingly, the printed circuit board  10 , the resistor  21 , and the capacitor  22  are surrounded by the insulating resin  30 . If the printed circuit board  10 , the resistor  21 , and the capacitor  22  are not surrounded by the insulating resin  30 , when the load simulator  1  is disposed in the plasma processing apparatus  400 , there are cases where a floating capacitance is generated between the various wiring on the printed circuit board  10  and the walls of the chamber of the plasma processing apparatus  400 . The impedance changes if a floating capacitance is generated. The impedance of the load simulator  1  would therefore be different before and after being disposed in the plasma processing apparatus  400 . The insulating resin  30  also has the function of suppressing the generation of such a floating capacitance so as to suppress a change in the impedance of the load simulator  1 . 
     Also, a hole  31  is provided at each of the four corners of the upper face of the insulating resin  30 . A coil spring  40  is inserted into each of the holes  31  (see  FIG. 4 ). The insulating resin  30  also serves the role of fixing the coil springs  40 . Note that the number of holes  31  that are provided is not limited to being four. 
     The configuration of the insulating resin  30  is not limited to this. If the floating capacitance that is generated when the load simulator  1  is disposed in the plasma processing apparatus  400  can be ignored, there is no need to cover the printed circuit board  10  and the like with the insulating resin  30 . For example, instead of providing the insulating resin  30 , columns of an insulator may be provided at the four corners of the ground electrode plate  60 . Also, a column of an insulator may be provided in the center of the ground electrode plate  60 , and the printed circuit board  10  and the like may be provided around the column. 
     The coil springs  40  are for biasing the positive electrode plate  70  and the ground electrode plate  60  in the direction of separation from each other using elastic force. When the load simulator  1  is disposed in the plasma processing apparatus  400 , the elastic force of the coil springs  40  presses the positive electrode plate  70  against the positive electrode  401 , and presses the ground electrode plate  60  against the ground, electrode  402  (see  FIGS. 1 and 3 ). Note that another elastic body may be used instead of the coil springs  40 . It is sufficient that the positive electrode plate  70  and the ground electrode plate  60  are biased in the direction of separation from each other using elastic force, and therefore a configuration is possible in which plate springs, rubber, or the like are used. 
     Also, there is no need for a biasing configuration such as the coil springs  40  if a distance H between the positive electrode  401  and the ground electrode  402  of the plasma processing apparatus  400  (hereinafter, referred to as the “inter-electrode distance”; see  FIG. 1 ) matches a height h of the load simulator  1  (the distance between the upper face of the positive electrode plate  70  and the lower face of the ground electrode plate  60 ; see  FIG. 3 ). Accordingly, the load simulator  1  may be designed such that the height h and the inter-electrode distance H match each other, or a configuration for adjusting the height h may be provided. Note that there are cases where the inter-electrode distance H differs for each plasma processing apparatus  400 . Also, if the positive electrode  401  is disposed on the lid of the chamber, there are cases where the inter-electrode distance H changes due to the opening and closing of the lid. In consideration of this, it is desirable that the load simulator  1  is provided with a bias applier such as the coil springs  40 . 
     The coaxial connector  50  is used when the impedance of the load simulator  1  is measured using an impedance analyzer. The load simulator  1  is designed so as to have a predetermined impedance value. Specifically, selection of the passive elements and adjustment of the various wiring are performed while measuring the impedance, such that the measured impedance arrives at a target impedance value. When the impedance is to be measured, the connector of the measurement terminal of the impedance analyzer is connected to the coaxial connector  50 . Note that there is no need to provide the coaxial connector  50  if the impedance is measured using another method. 
     The ground electrode plate  60  is for electrical connection to the ground electrode  402  when the load simulator  1  is disposed in the plasma processing apparatus  400 . The ground electrode plate  60  is a rectangular copper plate that is electrically conductive and thermally conductive. In the present embodiment, the ground electrode plate  60  also functions as a heat dissipating plate and dissipates heat generated by the resistor  21  fixed to the ground electrode plate  60 . When the load simulator  1  is disposed in the plasma processing apparatus  400 , the ground electrode plate  60  is pressed against the ground electrode  402  by the coil springs  40 . The ground electrode plate  60  and the ground electrode  402  are therefore in close contact, thus enabling the potential of the ground electrode plate  60  to be set to the reference (ground) potential. Note that the shape of the ground electrode plate  60  is not limited to this. For example, the ground electrode plate  60  may be shaped so as to conform to the shape of the ground electrode  402  of the plasma processing apparatus  400 . Also, the material of the ground electrode plate  60  is not limited to being copper, and needs only be an electrically conductive material. 
     The positive electrode plate  70  is for electrical connection to the positive electrode  401  when the load simulator  1  is disposed in the plasma processing apparatus  400 . In the present embodiment, the positive electrode plate  70  is a copper plate with a shape similar to that of the ground electrode plate  60 . When the load simulator  1  is disposed in the plasma processing apparatus  400 , the positive electrode plate  70  is pressed against the positive electrode  401  by the coil springs  40 . The positive electrode plate  70  and the positive electrode  401  are therefore in close contact, thus enabling high frequency power input from the high frequency power source apparatus  100  to the plasma processing apparatus  400  to be appropriately supplied to the load simulator  1 . Note that the shape of the positive electrode plate  70  is not limited to this. For example, the positive electrode plate  70  may be shaped so as to conform to the shape of the positive electrode  401  of the plasma processing apparatus  400 . Also, the material of the positive electrode plate  70  is not limited to being copper, and needs only be an electrically conductive material. 
     The position of the positive electrode plate  70  relative to the ground electrode plate  60  is defined by guides  71  (see  FIGS. 3 and 4 ). In the present embodiment, screws are screwed into holes provided at the four corners of the positive electrode plate  70 , and the portions of the screws that project out from the lower face of the positive electrode plate  70  (the bottom face in  FIG. 3 ) serve as the guides  71 . The guides  71  are provided so as to conform to the positions of the holes  31  at the four corners of the upper face of the insulating resin  30 . The four guides  71  are inserted into the coil springs  40  and holes  31  (see  FIG. 4 ) such that the positive electrode plate  70  is disposed substantially parallel to the ground electrode plate  60  over the insulating resin  30  (“over” as viewed in  FIGS. 3 and 4 ). The guides  71  restrict change in the horizontal position (position in the up-down and left-right directions in  FIG. 2 ) of the positive electrode plate  70  relative to the ground electrode plate  60 . Note that the coil springs  40  may be fixed to the positive electrode plate  70  instead of providing the guides  71 . 
     Also, the positive electrode plate  70  is electrically connected to the positive-side wiring  13  by the connection conductor  72  (see  FIG. 3 ). Since the distance between the positive electrode plate  70  and the ground electrode plate  60  can change due to the coil springs  40 , the distance between the positive electrode plate  70  and the printed circuit board  10  fixed to the ground electrode plate  60  also changes. A flexible conductor is therefore used as the connection conductor  72 . In the present embodiment, copper foil that has been processed so as to be able to be employed as the connection conductor  72  is used. For example, it is sufficient for the connection conductor  72  to be a conductor formed by preparing copper foil tape by applying an electrically conductive adhesive to one face of elongated copper foil, and then folding the copper foil tape such that the face to which the electrically conductive adhesive was applied is on the inner side. Note that since the distance between the printed circuit board  10  and the positive electrode plate  70  changes as described above, it is sufficient that the length and shape of the connection conductor  72  are designed taking this fact into consideration. 
     Also, the connection conductor  72  is not limited to this, and needs only be a member obtained by processing an electrically conductive material so as to be flexible. For example, a copper wire or the like may be used. Note that the resistance value of the connection conductor  72  rises as the cross-sectional area of the connection conductor  72  decreases and the length thereof increases. It is therefore preferable that the connection conductor  72  has a larger cross-sectional area and a shorter length. Also, a configuration is possible in which, instead of providing the connection conductor  72 , the coil springs  40  are formed using an electrically conductive material, one end of each coil spring  40  is fixed to the positive electrode plate  70 , and the other end is connected to the positive-side wiring  13 . 
     The height of the load simulator  1  can change due to the coil springs  40 . Specifically, the height of the load simulator  1  changes in the range between the height h when pressure is not applied to the load simulator  1  (only gravity due to the positive electrode plate  70  is in effect) and the height when the lower face of the positive electrode plate  70  comes into contact with the upper face of the insulating resin  30  (hereinafter, referred to as the height h′). The load simulator  1  therefore can be used with any plasma processing apparatus  400  as long as the inter-electrode distance H falls within this range of change (h′&lt;H&lt;h). Also, it is sufficient that the load simulator  1  is designed such that the height of the insulating resin  30  (vertical dimension in  FIG. 3 ), the length of the coil springs  40 , and the like are adjusted according to the inter-electrode distances H of the plasma processing apparatuses  400  with which the load simulator  1  will possibly be used. 
     It is sufficient that the horizontal size of the load simulator  1  (in  FIG. 2 , the size in the up-down direction and the size in the left-right direction), that is to say, the size of the positive electrode plate  70  and the ground electrode plate  60 , is designed according to the size of the electrodes  401  and  402  of the plasma processing apparatus  400  with which the load simulator  1  will be used. For example, the positive electrode plate  70  and the ground electrode plate  60  may be formed smaller than the electrodes  401  and  402  as shown in  FIG. 1 . 
     Next, a method for calibrating the high frequency measurement apparatus  300  using the load simulators  1   a ,  1   b , and  1   c  will be described. 
     The high frequency measurement apparatus  300  is a so-called RF sensor that measures high frequency parameters for the impedance, reflection coefficient, high frequency voltage, high frequency current, traveling wave power, reflected wave power, and the like in the chamber of the plasma processing apparatus  400  in order to monitor the state of the plasma processing apparatus  400  during plasma processing. As shown in  FIG. 1 , the high frequency measurement apparatus  300  is disposed at the input terminal of the plasma processing apparatus  400 . The high frequency measurement apparatus  300  detects the high frequency voltage and the high frequency current at the input terminal of the plasma processing apparatus  400  using a sensor, and calculates high frequency parameters for the impedance and the like from the detected values using an arithmetic operation. Note that a detailed description of the high frequency measurement apparatus  300  will not be given. 
     In the calibration of the high frequency measurement apparatus  300 , first the load simulators  1   a ,  1   b , and  1   c  are disposed between the electrodes  401  and  402  of the plasma processing apparatus  400  in the stated order, and the impedance of each load simulator is measured by the high frequency measurement apparatus  300 . The load simulators  1   a ,  1   b , and is are designed so as to each have a predetermined impedance. Next, a calibration parameter for correcting the high frequency voltage and the high frequency current is calculated from the measured impedance values of the load simulators  1   a ,  1   b , and  1   c  that were obtained by the high frequency measurement apparatus  300  and the real impedance values of the load simulators  1   a ,  1   b , and  1   c . In the actual measurement performed by the high frequency measurement apparatus  300 , the detected high frequency voltages and high frequency currents are corrected using the calibration parameter before various types of high frequency parameters are calculated. 
     If the relationship that a current signal I 0  and a voltage signal V 0  detected and output by the high frequency measurement apparatus  300  have with a current signal I 1  flowing between the electrodes of the plasma processing apparatus  400  and a voltage signal V 1  generated between the electrodes is replaced with a two-port network, a calibration parameter X for correcting the current signal I 0  and the voltage signal V 0  to the current signal I 1  and the voltage signal V 1  can be thought of as the two-dimensional square matrix shown in  FIG. 6 . 
     Elements X 11 , X 12 , X 21 , and X 22  of the calibration parameter X can be calculated from the real impedance values of the load simulators  1   a ,  1   b , and  1   c , and the measured impedance values of the load simulators  1   a ,  1   b , and  1   c  that were obtained by the high frequency measurement apparatus  300 . Note that the absolute values of a voltage value and a current value that are to serve as a reference are needed in order to perform this calculation. Highly precise measured power values are necessary in order to use the absolute values of a voltage value and a current value as reference values. In order to measure highly precise measured power values, it is best to connect a load for which the reflected power is “0” when performing measurement. Accordingly, in order to realize a reflected power of “0” in the present embodiment, the load simulator  1   a  that is used is a load having the same impedance as the characteristic impedance (i.e., 50+j0Ω). 
     The calculated calibration, parameter X can be used to convert the current signal I 0  and voltage signal V 0  into the corrected current signal I 1  and voltage signal V 1  as shown in  FIG. 6 . Specifically, the corrected current signal I 1  and voltage signal V 1  can be calculated using the following Expressions (1) and (2) that are derived from  FIG. 6 . 
     
       
         
           
             
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                                 22 
                               
                             
                           
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                           X 
                           12 
                         
                       
                       · 
                       
                         I 
                         0 
                       
                     
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                           X 
                           22 
                         
                         
                           X 
                           12 
                         
                       
                       · 
                       
                         V 
                         0 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
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     Next, a description of a procedure for calibrating the high frequency measurement apparatus  300  will be given with reference to the flowchart shown in  FIG. 7 . 
       FIG. 7  is a flowchart for describing a procedure for calibrating the high frequency measurement apparatus  300 . This flowchart shows a procedure of processing for correcting the current signal I 0  and voltage signal V 0  that are detected in the case where the impedance between the electrodes in the chamber of the plasma processing apparatus  400  is measured by the high frequency measurement apparatus  300 . 
     First, the load simulators  1   a ,  1   b , and  1   c  are disposed between the electrodes  401  and  402  of the plasma processing apparatus  400  in the stated order (see  FIG. 1 ), and the impedances thereof are measured by the high frequency measurement apparatus  300  (step S 1 ). Next, the calibration parameter X is calculated from the measured impedance values of the load simulators  1   a ,  1   b , and  1   c  that were obtained by the high frequency measurement apparatus  300  and the real impedance values of the load simulators  1   a ,  1   b , and  1   c , and the calibration parameter X is recorded in a memory of the high frequency measurement apparatus  300  (step S 2 ). In the present embodiment, an arithmetic circuit (not shown) of the high frequency measurement apparatus  300  records the measured impedance values of the load simulators  1   a ,  1   b , and  1   c  in the memory, and after the three measured impedance values have been obtained, the arithmetic circuit calculates the elements of the calibration parameter X using the real impedance values of the load simulators  1   a ,  1   b , and  1   c  that were recorded in advance, and records the elements of the calibration X in the memory. Note that there is no limitation to the case where an arithmetic circuit of the high frequency measurement apparatus  300  performs the calculation of the calibration parameter X, and a configuration is possible in which, for example, the calibration parameter X is calculated separately by a worker. In this case, it is sufficient that the worker inputs the calibration parameter X using an input device of the high frequency measurement apparatus  300  in order for the calibration parameter X to be recorded in the memory. 
     Next, the impedance between the electrodes in the chamber of the plasma processing apparatus  400  is measured when plasma processing is actually being performed (step S 3 ). At this time, the high frequency measurement apparatus  300  corrects the detected current signal I 0  and voltage signal V 0  using the calibration parameter X recorded in the memory, and calculates the impedance based on the corrected current signal I 1  and voltage signal V 1 . 
     Note that the above-described calibration processing procedure is a processing procedure in the case where the calibration parameter X has not been recorded in the memory of the high frequency measurement apparatus  300 . Steps S 1  and S 2  of the above processing procedure do not need to be performed every time, and it is sufficient that the calibration parameter X is recorded after performing these steps one time. This processing may be performed by the manufacturer when manufacturing the high frequency measurement apparatus  300 . 
     According to the present embodiment, the positive electrode plate  70  and the ground electrode plate  60  of the load simulator  1  are disposed so as to be parallel to each other. Accordingly, the load simulator  1  is disposed between the positive electrode  401  and the ground electrode  402  of the plasma processing apparatus  400  such that the positive electrode plate  70  is connected to the positive electrode  401  of the plasma processing apparatus  400 , and the ground electrode plate  60  is connected to the ground electrode  402 . Accordingly, in the calibration of the high frequency measurement apparatus  300 , the load simulator  1  can be disposed between the two electrodes  401  and  402  of the plasma processing apparatus  400 , and the impedance thereof can be measured by the high frequency measurement apparatus  300 . The calibration parameter X is then calculated from the measured value and the real impedance value of the load simulator  1 . The calibration parameter X can be used to correct a detected value obtained by the high frequency measurement apparatus  300  to the value between the electrodes in the chamber of the plasma processing apparatus  400 . Using this calibration parameter X therefore enables raising the precision of measured values obtained by the high frequency measurement apparatus  300  compared to the case of using a calibration parameter that is based on a measured impedance value obtained by directly connecting the load simulator  500  to the high frequency measurement apparatus  300 . 
     Also, when the load simulator  1  is disposed in the plasma processing apparatus  400 , the positive electrode plate  70  and the ground electrode plate  60  of the load simulator  1  are respectively pressed against the positive electrode  401  and the ground electrode  402  of the plasma processing apparatus  400  by the coil springs  40 . This enables bringing the positive electrode plate  70  and the positive electrode  401  into close contact, and bringing the ground electrode plate  60  and the ground electrode  402  into close contact. Also, since the height h of the load simulator  1  can change, it can be disposed in any plasma processing apparatus  400  in which the inter-electrode distance H is in a predetermined range. 
     Note that although the case of performing calibration using the three load simulators  1   a ,  1   b , and  1   c  is described in the above embodiment, the present invention is not limited to this. A configuration is possible in which switching between three types of impedances is made possible by providing a variable resistor and a variable capacitor as the resistor  21  and the capacitor  22  of the load simulator  1 . In this case, loads having various impedances can be realized through the switching of the impedance, without the load simulator  1  being removed from the chamber and exchanged. 
     In the above embodiment, the case is described in which the impedances of the load simulators  1   a ,  1   b , and  1   c  are set to an impedance value close to limit values so as to enable performing calibration with a wide range of impedances, but the present invention is not limited to this. The impedances of the load simulators  1   a ,  1   b , and  1   c  may be set in accordance with the range of impedances to be measured by the high frequency measurement apparatus  300 . 
     Although the case where the positive electrode  401  and the ground electrode  402  of the plasma processing apparatus  400  are parallel plate electrodes is described in the above embodiment, the present invention is not limited to this. In the case where the positive electrode  401  or the ground electrode  402  is not a flat plate, or the case where the positive electrode  401  and the ground electrode  402  are not parallel with each other, it is sufficient to change the shape and manner of fixing the positive electrode plate  70  or the ground electrode plate  60 . For example, if the positive electrode  401  is a curved plate instead of a flat plate, it is sufficient to form the face of the positive electrode plate  70  that opposes the positive electrode  401  so as to be a similar curved face.