Patent Publication Number: US-2022223380-A1

Title: Microwave supply mechanism, plasma treatment apparatus, and plasma treatment method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a microwave supply mechanism, a plasma processing apparatus and a plasma processing method. 
     BACKGROUND 
     In a semiconductor device manufacturing process, plasma processing is often used as an etching process, a film-forming process or the like on a semiconductor substrate. In recent years, a microwave plasma processing apparatus capable of uniformly forming plasma having a high density and a low electron temperature has attracted attention as a plasma processing apparatus that performs such plasma processing. 
     As the microwave plasma processing apparatus, there is known an apparatus that guides microwaves radiated from a microwave supply mechanism having a planar antenna into a chamber to perform microwave plasma processing (see, e.g., Patent Document 1). In such a microwave plasma processing apparatus, a slug tuner is provided in a microwave transmission line of the microwave supply mechanism to adjust the impedance, whereby the impedance of a plasma load is matched with the impedance on the side of the power supply. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: International Publication No. 2008/013112 
     The present disclosure provides some embodiments of a microwave supply mechanism, a plasma processing apparatus and a plasma processing method that can perform both impedance matching and adjustment of an output voltage (output electric field) of an antenna when introducing microwaves from a microwave-generating power supply part to a load side via the antenna. 
     SUMMARY 
     According to an aspect of the present disclosure, a microwave supply mechanism for supplying microwaves from a microwave-generating power supply part to a load includes: a microwave transmission path having a coaxial structure and through which the microwaves from the microwave-generating power supply part are transmitted; an antenna provided at a tip of the microwave transmission path and configured to radiate the microwaves and supply the microwaves to the load; an impedance matching part provided in the microwave transmission path and configured to match impedance on a power supply side and impedance on a load side; and an output voltage adjustment part provided between the impedance matching part and the antenna and configured to adjust a microwave output voltage in the antenna by adjusting impedance. 
     According to the present disclosure, it is possible to provide a microwave supply mechanism, a plasma processing apparatus and a plasma processing method that can perform both impedance matching and adjustment of an output voltage (output electric field) of an antenna when introducing microwaves from a microwave-generating power supply part to a load side via the antenna. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view showing a schematic configuration of a microwave plasma processing apparatus equipped with a microwave supply mechanism according to one embodiment. 
         FIG. 2  is a block diagram showing a configuration of a plasma source used in the plasma processing apparatus of  FIG. 1 . 
         FIG. 3  is a plan view schematically showing a microwave supply part in the plasma source. 
         FIG. 4  is a cross-sectional view showing a microwave supply mechanism according to one embodiment. 
         FIG. 5  is a cross-sectional view showing a power feeding mechanism of the microwave supply mechanism. 
         FIG. 6  is a diagram showing a Smith chart for explaining impedance matching. 
         FIG. 7  is a cross-sectional view showing a microwave supply mechanism according to another embodiment. 
         FIG. 8  is a circuit diagram for explaining a circuit configuration of the microwave supply mechanism according to one embodiment. 
         FIG. 9  is a circuit diagram for explaining a circuit configuration of a conventional microwave supply mechanism. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. 
     &lt;Configuration of Microwave Plasma Processing Apparatus&gt; 
       FIG. 1  is a cross-sectional view showing a schematic configuration of a microwave plasma processing apparatus equipped with a microwave supply mechanism according to one embodiment.  FIG. 2  is a block diagram showing a configuration of a plasma source used in the plasma processing apparatus of  FIG. 1 .  FIG. 3  is a plan view schematically showing a microwave supply part in the plasma source.  FIG. 4  is a cross-sectional view showing a microwave supply mechanism according to one embodiment.  FIG. 5  is a cross-sectional view showing a power feeding mechanism of the microwave supply mechanism. 
     A microwave plasma processing apparatus  100  executes plasma processing, for example, etching processing, on a semiconductor wafer W (hereinafter referred to as wafer W) as a substrate, and performs plasma processing by surface wave plasma. The microwave plasma processing apparatus  100  includes a substantially grounded airtight cylindrical chamber  1  made of a metal material such as aluminum or stainless steel, and a plasma source  2  for radiating microwaves into the chamber  1  to form the surface wave plasma. An opening  1   a  is formed in the upper portion of the chamber  1 , and the plasma source  2  is provided so as to face the interior of the chamber  1  from the opening  1   a.    
     A susceptor  11  which is a support member for horizontally supporting the wafer W is provided inside the chamber  1  in a state in which the susceptor  11  is supported by a cylindrical support member  12  installed upright at the center of the bottom of the chamber  1  via an insulating member  12   a . Examples of the material constituting the susceptor  11  and the support member  12  may include aluminum whose surface is anodized. 
     Although not shown, in the susceptor  11 , there are provided an electrostatic chuck for electrostatically attracting the wafer W, a temperature control mechanism, a gas flow path for supplying a heat transfer gas to the back surface of the wafer W, lift pins configured to move up and down to transfer the wafer W, and the like. Further, a high-frequency bias power source  14  is electrically connected to the susceptor  11  via a matcher  13 . By supplying radio-frequency power from the radio-frequency bias power source  14  to the susceptor  11 , ions in the plasma are drawn to the side of the wafer W. 
     An exhaust pipe  15  is connected to the bottom of the chamber  1 . An exhaust device  16  including a vacuum pump is connected to the exhaust pipe  15 . By operating the exhaust device  16 , the gas in the chamber  1  is discharged so that the interior of the chamber  1  can be depressurized to a predetermined degree of vacuum at high speed. Further, in the sidewall of the chamber  1 , there are provided a loading/unloading port  17  for loading and unloading the wafer W therethrough and a gate valve  18  for opening and closing the loading/unloading port  17 . 
     A ring-shaped gas introduction member  26  is provided along the wall of the chamber  1  at the upper portion of the chamber  1 . The gas introduction member  26  is provided with a large number of gas discharge holes formed in the inner circumference thereof. A gas supply source  27  for supplying a gas such as a plasma-generating gas or a processing gas is connected to the gas introduction member  26  via a pipe  28 . As the plasma-generating gas, a noble gas such as an Ar gas or the like may be preferably used. Further, as the processing gas, an etching gas usually used for etching, for example, a Cl 2  gas or the like, may be used. 
     The plasma-generating gas introduced into the chamber  1  from the gas introduction member  26  becomes plasmarized by the microwave introduced into the chamber  1  from the plasma source  2 . Thereafter, when the processing gas is introduced from the gas introduction member  26 , the processing gas is excited and is plasmarized by the plasma of the plasma-generating gas. The plasma of the processing gas is used to perform plasma processing on the wafer W. 
     &lt;Plasma Source&gt; 
     Next, the plasma source  2  will be described. The plasma source  2  is used for radiating microwaves into the chamber  1  to form a surface wave plasma, and includes a circular top plate  110  supported by a support ring  29  provided on the upper portion of the chamber  1 . A gap between the support ring  29  and the top plate  110  is hermetically sealed. The top plate  110  also functions as an upper wall of the chamber  1 . As shown in  FIG. 2 , the plasma source  2  includes a microwave output part  30  that distributes and outputs microwaves through a plurality of paths, and a microwave supply part  40  that transmits the microwaves outputted from the microwave output part  30  and supplies the microwaves into the chamber  1 . 
     The microwave output part  30  includes a microwave power source  31 , a microwave oscillator  32 , an amplifier  33  that amplifies oscillated microwaves, and a distributor  34  that distributes the amplified microwaves into plural ones. 
     The microwave oscillator  32  oscillates microwaves having a predetermined frequency (e.g., 860 MHz), for example, in a PLL manner. The distributor  34  divides the microwave amplified by the amplifier  33  while maintaining impedance matching between the input side and the output side so that microwave loss does not occur as much as possible. As the microwave frequency, a desired frequency in the range of 700 MHz to 3 GHz may be used in addition to 860 MHz. 
     The microwave supply part  40  includes a plurality of amplifier parts  42  that mainly amplify the microwaves divided by the distributor  34 , and microwave supply mechanisms  41  connected to the respective amplifier parts  42 . 
     As shown in  FIG. 3 , for example, seven microwave supply mechanisms  41  are arranged on the top plate  110 , six along the circumference of the top plate  110  and one at the center of the top plate  110 . The microwave supply mechanisms  41  will be described in detail later. 
     The top plate  110  functions as a vacuum seal and a microwave transmission plate. The top plates  110  includes a metal-made frame  110   a  and a microwave transmission window  110   b , which is fitted into the frame  110   a , provided so as to correspond to a portion where the microwave supply mechanism  41  is arranged, and made of a dielectric material such as quartz or the like. 
     The amplifier part  42  includes a phase shifter  46 , a variable gain amplifier  47 , a main amplifier  48  constituting a solid-state amplifier, and an isolator  49 . 
     The phase shifter  46  is configured to change the phase of the microwave and capable of modulating the radiation characteristics by changing the phase of the microwave. For example, the phase shifter  46  can control directivity to change the plasma distribution by adjusting the phase of each amplifier part  42 , or can obtain a circularly-polarized wave by shifting the phase by 90° between adjacent amplifier parts  42 . Further, the phase shifter  46  may be used for the purpose of spatial synthesis in a tuner by adjusting the delay characteristics between components in the amplifier. However, when it is not necessary to modulate the radiation characteristics or adjust the delay characteristics between the components in the amplifier, the phase shifter  46  may not be provided. 
     The variable gain amplifier  47  is an amplifier for adjusting the power level of microwaves to be input to the main amplifier  48  and adjusting the variation of individual antenna modules or adjusting the plasma intensity. By changing the variable gain amplifier  47  for each amplifier part  42 , it is possible to generate a distribution in the generated plasma. 
     The main amplifier  48  constituting the solid-state amplifier may have, for example, a configuration that includes an input matching circuit, a semiconductor amplifier element, an output matching circuit, and a high-Q resonance circuit. 
     The isolator  49  separates the reflected microwave reflected by the microwave supply mechanism  41  toward the main amplifier  48  and includes a circulator and a dummy load (coaxial terminator). The circulator guides the microwave reflected by the antenna part  45  of the microwave supply mechanism  41 , which will be described later, to the dummy load, and the dummy load converts the reflected microwave guided by the circulator into heat. 
     Each component part of the microwave plasma processing apparatus  100  is controlled by a control part  200  including a microprocessor. The control part  200  includes a storage part that stores a process sequence of the microwave plasma processing apparatus  100  and process recipes as control parameters, an input means, a display, and the like. The control part  200  controls the plasma processing apparatus according to the selected process recipe. 
     &lt;Microwave Supply Mechanism&gt; 
     The microwave supply mechanism  41  supplies the microwave supplied from the amplifier part  42  to the plasma in the chamber  1 . As shown in  FIG. 4 , the microwave supply mechanism  41  includes a microwave transmission path  44  having a coaxial structure, an impedance matching part  61 , an output voltage adjustment part  62 , and an antenna part  45  having a planar slot antenna  81  that radiates microwaves. 
     The microwave transmission path  44  is configured to transmit the microwaves supplied from the amplifier part  42 , and is formed by coaxially arranging a cylindrical outer conductor  52  and a cylindrical inner conductor  53  provided at the center of the outer conductor  52 . The antenna part  45  is provided at the tip of the microwave transmission path  44 . In the microwave transmission path  44 , the inner conductor  53  is on the power supply side and the outer conductor  52  is on the ground side. The upper end of the microwave transmission path  44  is a reflection plate  58 . 
     A power feeding port  54  for feeding microwaves (electromagnetic waves) into the microwave transmission path  44  is provided on the proximal end side of the microwave transmission path  44 . A coaxial line  56  composed of an inner conductor  56   a  and an outer conductor  56   b  is connected to the power feeding port  54  as a power feeding line for supplying the microwave amplified by the amplifier part  42 . A power feeding antenna  90  extending horizontally toward the interior of the outer conductor  52  is connected to the tip of the inner conductor  56   a  of the coaxial line  56 . 
     The power feeding antenna  90  is formed by, for example, cutting out a metal plate of aluminum or the like and then setting the same in a mold of a dielectric member such as Teflon (a registered trademark). A slow-wave member  59  made of a dielectric material is interposed between the reflection plate  58  and the power feeding antenna  90 . When microwaves having a radio frequency such as 2.45 GHz is used, the slow-wave member  59  may be omitted. By reflecting an electromagnetic wave radiated from the power feeding antenna  90  by the reflection plate  58 , the maximum electromagnetic wave is transmitted into the microwaves transmission path  44  having the coaxial structure. In that case, it is preferable to set the distance from the power feeding antenna  90  to the reflection plate  58  to be about half-wavelength of λg/4. However, in microwaves having a low frequency, such a configuration may not be directly applicable due to constraints in the radial direction. In that case, it is preferable to optimize the shape of the power feeding antenna so that the antinode of the electromagnetic wave generated from the power feeding antenna  90  is induced below the power feeding antenna  90 , rather than toward the power feeding antenna  90 . 
     As shown in  FIG. 5 , the power feeding antenna  90  is connected to the inner conductor  56   a  of the coaxial line  56  in the power feeding port  54 . The power feeding antenna  90  includes an antenna main body  91  having a first pole  92  to which an electromagnetic wave is supplied and a second pole  93  from which the supplied electromagnetic wave is radiated, and a ring-shaped reflection part  94  extending from both sides of the antenna main body  91  along the outside of the inner conductor  53 . An electromagnetic wave incident on the antenna main body  91  and an electromagnetic wave reflected by the reflection part  94  form a standing wave. The second pole  93  of the antenna main body  91  is in contact with the inner conductor  53 . 
     The microwave power is fed into the space between the outer conductor  52  and the inner conductor  53  by the microwaves (the electromagnetic waves) emitted from the power feeding antenna  90 . Then, the microwave power supplied to the power feeding port  54  propagates toward the antenna part  45 . 
     The impedance matching part  61  is provided in the microwave transmission path  44  and is configured to match the impedance on the power supply side (transmission cable) with the impedance on the load side (plasma or the like). That is, since the power supply side is usually designed to have a pure resistance output of 50Ω, the impedance matching part  61  is adjusted so that the impedance on the load side including the impedance matching part  61  is 50Ω. As a result, efficient power supply can be performed without reflection. 
     The impedance matching part  61  constitutes a matching circuit which is an LC network (LC circuit). Specifically, the impedance matching part  61  includes two slugs  71  and  72 , motors  73  and  74  for driving the slugs  71  and  72  independently, and a first controller  75  for controlling positions of the slugs  71  and  72 . The slugs  71  and  72  are provided between the outer conductor  52  and the inner conductor  53  of the microwave transmission path  44 , and the impedance is adjusted by moving the slugs  71  and  72 . The motors  73  and  74  are provided on the outside (upper side) of the reflection plate  58 . 
     The slugs  71  and  72  are made of a dielectric material such as alumina or the like. As the dielectric material constituting the slugs  71  and  72 , a dielectric material having an appropriate dielectric constant may be used depending on the impedance adjustment range or the like. Further, the thickness and resistance of each of the slugs  71  and  72  may be appropriately set. The thickness of each of the slugs  71  and  72  may be, for example, λ/4 when the wavelength of the microwave is λ. The resistance of each of the slugs  71  and  72  may be, for example, 15Ω. 
     The vertical movement of the slugs  71  and  72  may be performed by, for example, providing two slug movement shafts (not shown) made of screw rods in an internal space of the inner conductor  53  so as to extend in the longitudinal direction, and rotating the respective slug movement shafts independently by the motors  73  and  74 . 
     The positions of the slugs  71  and  72  are controlled by the first controller  75  that transmits a control signal to the motors  73  and  74  based on the impedance value at the input end detected by an impedance detector (not shown) and position information of the slugs  71  and  72  detected by an encoder or the like. Thus, the impedance is adjusted. The impedance on the load side at this time exists at any position on the Smith chart. The Smith chart is a circular diagram showing complex impedance as shown in  FIG. 6 , in which the horizontal axis indicates the real number (resistance) component of impedance and the vertical axis indicates the imaginary number (reactance) component of impedance. The center (origin) in the diagram corresponds to the case where the impedance on the load side is matched with the impedance on the power supply side. Z LOAD  in  FIG. 6  is the position of the impedance on the load side. As for the impedance, when both slugs are moved at the same time, only the phase is rotated, and when only one of the slugs is moved, a trajectory passing through the origin of the Smith chart is drawn. Therefore, by moving the slugs  71  and  72 , for example, as shown in  FIG. 6 , the phase of Z LOAD  can be rotated to set the imaginary component to 0, and then can be allowed to reach the origin, which is a matching point. In order to correspond to the entire range of the Smith chart, the movement ranges of the slugs  71  and  72  are set to, for example, V 2 , respectively. 
     The output voltage adjustment part  62  is configured to adjust the impedance to adjust the output voltage (output electric field) of the microwave in the planar slot antenna  81  and is provided between the impedance matching part  61  and the antenna part  45 . The output voltage adjustment part  62  constitutes an adjustment circuit which is an LC network (LC circuit). Specifically, the output voltage adjustment part  62  includes a slug  76 , a motor  77  for driving the slug  76 , and a second controller  78  for controlling a position of the slug  76 . The slug  76  is provided between the outer conductor  52  and the inner conductor  53  of the microwave transmission path  44 . The impedance is adjusted by moving the slug  76 . The motor  77  is provided on the outside (upper side) of the reflection plate  58 . The vertical movement of the slug  76  can be performed by, for example, providing a slug movement shaft (not shown) for the slug  76  made of a screw rod in the internal space of the inner conductor  53  so as to extend in the longitudinal direction in parallel with the slug movement shafts of the slugs  71  and  72  described above, and rotating the slug movement shaft by the motor  77 . By moving the slug  76  up and down, the impedance on the input side for inputting microwaves to the plasma can be changed on the Smith chart, whereby the output voltage (output electric field) of the microwaves in the planar slot antenna  81  can be adjusted. Just like the slugs  71  and  72 , the slug  76  is made of a dielectric material such as alumina or the like. As the dielectric material constituting the slug  76 , a dielectric material having an appropriate dielectric constant may be used depending on the impedance adjustment range and the like. As with the slugs  71  and  72 , the thickness and resistance of the slug  76  may be, for example, λ/4 and 15Ω, respectively. However, the thickness and resistance of the slug  76  may be appropriately set. 
       FIG. 4  shows an example in which one slug  76  is provided as the output voltage adjustment part  62 . However, as shown in  FIG. 7 , a slug  79  may be provided in addition to the slug  76 . By providing the two slugs, the impedance on the input side can be adjusted to an arbitrary position on the Smith chart, and the degree of freedom in adjusting the antenna voltage can be increased. However, if the slag is increased, the space required to move the slug increases and the length of the microwave supply mechanism  41  becomes longer. Therefore, the number of slugs may be determined depending on which of the degree of freedom of adjustment or the space is prioritized. 
     The first controller  75  and the second controller  78  are controlled by the control part  200 . 
       FIG. 8  is a circuit diagram for explaining the circuit configuration of the microwave supply mechanism  41  according to the present embodiment described above. As shown in this diagram, each microwave supply mechanism  41  includes the impedance matching part  61  and the output voltage adjustment part  62 , both of which are configured by an LC network. Therefore, prior to the impedance matching in the impedance matching part  61 , the impedance of the output voltage adjustment part  62  can be adjusted to adjust the output voltage (output electric field) of the microwave in the planar slot antenna  81 . After adjusting the output voltage in this manner, the impedance matching can be performed by the LC network of the impedance matching part  61 . 
     The antenna part  45  is arranged at the tip of the microwave transmission path  44  and includes a planar slot antenna  81  and a slow-wave material  82 . The planar slot antenna  81  has a planar shape and has slots  81   a  that radiate microwaves. The slow-wave material  82  is made of a dielectric material and is provided on the back surface (upper surface) of the planar slot antenna  81 . A cylinder member  82   a  made of a conductor connected to the inner conductor  53  penetrates the center of the slow-wave member  82 . The cylinder member  82   a  is connected to the planar slot antenna  81 . The planar slot antenna  81  has a disk shape having a diameter larger than that of the outer conductor  52  of the microwave transmission path  44 . The lower end of the outer conductor  52  extends to the planar slot antenna  81 . The slow-wave material  82  and the planar slot antenna  81  are surrounded by the outer conductor  52 . 
     Microwaves transmitted through the microwave transmission path  44  are radiated from the slots  81   a  of the planar slot antenna  81 . The number, arrangement and shape of the slots  81   a  may be appropriately set so that microwaves are efficiently radiated. A dielectric material may be inserted into the slots  81   a.    
     The slow-wave member  82  has a dielectric constant higher than that of vacuum and is made of, for example, quartz, ceramics, a fluorinated-based resin such as polytetrafluoroethylene or the like, or a polyimide-based resin. The slow-wave member  82  has a function of shortening the antenna by making the wavelength of the microwaves shorter than that in a vacuum. The phase of the microwaves can be adjusted by the thickness of the slow-wave member  82 . The thickness of the slow-wave member  82  is adjusted so that the planar slot antenna  81  becomes the “antinode” of the standing wave. Thus, the reflection can be minimized and the radiant energy of the planar slot antenna  81  can be maximized. 
     The microwave transmission window  110   b  of the top plate  110  is disposed on the leading end side of the planar slot antenna  81 . Then, the microwaves amplified by the main amplifier  48  pass between peripheral walls of the inner conductor  53  and the outer conductor  52 , pass through the microwave transmission window  110   b  via the planar slot antenna  81 , and are radiated into the internal space of the chamber  1 . The microwave transmission window  110   b  may be made of the same dielectric material as the slow-wave member  82 . 
     &lt;Operation of Plasma Processing Apparatus&gt; 
     Next, the operation of the microwave plasma processing apparatus  100  configured as above will be described. First, a wafer W is loaded into the chamber  1  and placed on the susceptor  11 . Then, while a plasma-generating gas, for example, an Ar gas, is introduced from the gas source  27  into the chamber  1  via the pipe  28  and the gas introduction member  26 , microwaves are introduced from the plasma source  2  into the chamber  1  to form microwave plasma. 
     After the plasma is formed, a processing gas, for example, an etching gas such as a Cl 2  gas, is discharged from the gas source  27  into the chamber  1  via the pipe  28  and the gas introduction member  26 . The discharged processing gas is excited by the plasma of the plasma-generating gas and is plasmarized. The wafer W is subjected to a plasma process, for example, an etching process, by the plasma of the processing gas. 
     In generating the plasma, in the plasma source  2 , the microwave power oscillated from the microwave oscillator  32  of the microwave output part  30  is amplified by the amplifier  33  and then is distributed into several pieces by the distributor  34 . Thereafter, the distributed microwave powers are guided to the microwave supply part  40 . In the microwave supply part  40 , the microwave powers distributed into the several pieces in the above manner are individually amplified by the respective main amplifiers  48  constituting solid-state amplifiers and are respectively fed to the microwave supply mechanisms  41 . Then, the microwave supplied to the microwave supply mechanism  41  is radiated into the chamber  1  through the slots  81   a  of the planar slot antenna  81  and the microwave transmission window  110   b  and is spatially synthesized in the chamber  1 . After generating plasma by the microwave supplied into the chamber  1 , the microwave radiated from the planar slot antenna  81  is continuously supplied to the plasma. 
     The feeding of the microwave to the microwave supply mechanism  41  is performed from the side surface of the microwave transmission path  44  via the coaxial line  56 . That is, the microwave (electromagnetic wave) propagating from the coaxial line  56  is fed to the microwave transmission path  44  from the power feeding port  54  provided on the side surface of the microwave transmission path  44 . When the microwave (electromagnetic wave) reaches the first pole  92  of the power feeding antenna  90 , the microwave (electromagnetic wave) propagates along the antenna main body  91  and is radiated from the second pole  93  at the tip of the antenna main body  91 . Further, the microwave (electromagnetic wave) propagating through the antenna main body  91  is reflected by the reflection part  94  and is combined with the incident wave to generate a standing wave. An induced magnetic field is generated along the outer wall of the inner conductor  53  by this standing wave, and an induced electric field is generated by the induced magnetic field. As a result of such linked actions, the microwave (electromagnetic wave) propagates in the microwave transmission path  44  and is guided to the antenna part  45  (planar slot antenna  81 ). 
     At this time, the impedance is automatically matched in the impedance matching part  61 , and the microwave is supplied to the plasma in the chamber  1  in a state in which there is substantially no power reflection. That is, the impedance on the power supply side and the impedance on the load side are matched with each other by the impedance matching part  61  in order to efficiently supply the microwave power from the microwave power source  31  to the plasma in the chamber  1  in a state in which there is substantially no power reflection. 
     Such impedance matching has been performed in the related art. However, in the related art, after impedance matching, the output voltage (output electric field) of the microwave in the antenna becomes a value determined by the load (plasma) state with respect to the microwave power. Since power is determined by two factors, current and voltage, the plasma state can be adjusted by changing the microwave output voltage (output electric field) in the antenna even if the power is the same. However, in the related art, a means for changing an output voltage have not been proposed. Therefore, in the related art, it has been difficult to positively adjust the plasma state when the microwave power is constant. 
     In the related art, only the impedance matching part  61  is provided in the microwave transmission path  44 , and the circuit diagram thereof is shown in  FIG. 9 . The LC network (LC circuit) constituting the impedance matching part  61  is connected to the load (plasma). In order to change the antenna voltage (output voltage) in this circuit configuration, it is conceivable to shift the matching point in the impedance matching part  61 . However, if the matching point is shifted, microwave power cannot be efficiently supplied to the load side due to power reflection. 
     Therefore, in the present embodiment, the output voltage adjustment part  62  composed of an LC network is provided between the impedance matching part  61  and the antenna part  45  (see  FIG. 8 ). As a result, it is possible to adjust the output voltage (output electric field) of the microwave in the planar slot antenna  81  without affecting the impedance matching performed by the impedance matching part  61 . 
     That is, since the impedance on the input side can be adjusted by providing the output voltage adjustment part  62  composed of an LC network separately from the impedance matching part  61 , it is possible to adjust the output voltage (output electric field) of the microwave in the planar slot antenna  81 . Impedance matching can be performed by the impedance matching part  61  on the upstream side after adjusting the output voltage. 
     Since the output voltage (output electric field) of the microwave in the planar slot antenna  81  can be adjusted by the output voltage adjustment part  62  in this manner, the plasma state can be changed even with the same microwave power. That is, the plasma state can be changed by adjusting the output voltage (output electric field) from the power supply side. For example, by lowering the impedance of the output voltage adjustment part  62 , the output voltage becomes low, resulting in a plasma state in which the density is relatively high and the energy is relatively low. Conversely, by increasing the impedance of the output voltage adjustment part  62 , the output voltage becomes high, resulting in a plasma state in which the density is relatively low and the energy is relatively high. 
     Further, in the present embodiment, the impedance of each of the plurality of microwave supply mechanisms  41  can be adjusted by the output voltage adjustment part  62  to adjust the microwave output voltage (output electric field) of the planar slot antenna  81 . This makes it possible to perform multi-zone plasma control. For example, the control for enhancing plasma uniformity and conversely the control for forming a desired plasma distribution can also be performed by adjusting the microwave output voltage (output electric field) in the planar slot antenna  81  for the plurality of microwave supply mechanisms  41 . 
     Further, since the impedance matching part  61  of the microwave supply mechanism  41  is a three-dimensional circuit whose impedance is adjusted by the slug moving along the microwave transmission path  44 , an assembly error becomes an instrument error. On the other hand, in the present embodiment, since the output voltage adjustment part  62 , which is an impedance adjustment tab different from the impedance matcher  61 , is provided in the microwave transmission path  44 , it is possible to adjust the instrument error. 
     [Method of Adjusting Output Voltage Adjustment Part] 
     Next, a specific adjustment method of the output voltage adjustment part  62  will be described. The output voltage adjustment part  62  constitutes an adjustment circuit, which is an LC network (LC circuit) as described above, and adjusts the impedance by the slug  76  or the slugs  76  and  79 . Therefore, for example, the following adjustment methods can be performed. 
     (1) Processes are performed by sequentially changing the position of the slug, to find an impedance point (slug position) where the output voltage of the microwave in the planar slot antenna  81  becomes a value at which the best process result is obtained. 
     (2) Since the impedance value (the position on the Smith chart) and microwave power (electric power) of the LC network constituting the output voltage adjustment part  62  are known, the antenna voltage is obtained therefrom and the slug position is moved to obtain the required antenna voltage and phase position. 
     (3) The electromagnetic field in the vicinity of the planar slot antenna  8 lis measured, the antenna voltage is derived from that value, and the slug position is moved to obtain the required antenna voltage and phase position. 
     Such adjustment of the output voltage can be performed by the control part  200  and the second controller  78 . The adjustment of the output voltage at this time may be performed in advance before the plasma processing is executed or may be performed during the plasma processing if the adjustment time can be secured. When the adjustment is performed during the plasma processing, the adjustment of the output voltage may be prioritized, and then the impedance matching may be performed by the impedance matching part  61 . However, when impedance matching is performed, the output voltage may deviate from the adjusted value. In that case, the output voltage may be adjusted again and impedance matching may be further performed. 
     &lt;Other Applications&gt; 
     Although the embodiments have been described above, it should be considered that the embodiments disclosed herein are exemplary in all respects and not limitative. The above-described embodiments may be omitted, replaced or modified in various forms without departing from the scope of the appended claims and the gist thereof. 
     For example, in the above-described embodiments, there has been described the example in which the impedance is adjusted by using the slug in the output voltage adjustment part and the impedance matching part. However, the present disclosure is not limited thereto, and any existing impedance adjustment means may be used. 
     Further, in the above-described embodiments, there has been described the example in which a plurality of microwave supply mechanisms is provided. However, only one microwave supply mechanism may be used. 
     In the above-described embodiments, there has been described the example in which the slot antenna having slots for radiating microwaves is used as the antenna. However, the present disclosure is not limited thereto. 
     Further, in the above-described embodiments, an apparatus for performing an etching process is exemplified as the plasma processing apparatus. However, the present disclosure is not limited thereto. For example, the plasma process may include another plasma process such as a film forming process, an oxynitride film process or an ashing process. Furthermore, the substrate is not limited to the semiconductor wafer W, but may be another substrate such as an FPD (flat panel display) substrate represented by an LCD (liquid crystal display) substrate, a ceramic substrate or the like. 
     EXPLANATION OF REFERENCE NUMERALS 
       1 : chamber,  2 : plasma source,  41 : microwave supply mechanism,  44 : microwave transmission path,  45 : antenna part,  61 : impedance matching part,  62 : output voltage adjustment part,  71 ,  72 ,  76 ,  79 : slug,  73 ,  74 ,  77 : motor,  75 : first controller,  78 : second controller,  81 : planar slot antenna,  81   a : slot,  82 : slow-wave material,  100 : microwave plasma processing apparatus,  110 : top plate,  110   b : microwave transmission window, W: semiconductor wafer (substrate)