Patent Publication Number: US-2022230846-A1

Title: Substrate processing apparatus, method of manufacturing semiconductor device, and recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-005770, filed on Jan. 18, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a substrate processing apparatus, a method of manufacturing a semiconductor device, and a recording medium. 
     BACKGROUND 
     In the related art, a substrate processing apparatus for processing a substrate with a process gas plasma-excited by supplying high frequency power to a coil is known. 
     SUMMARY 
     However, in the substrate processing apparatus as mentioned above, the plasma density in the in-plane direction of the substrate may be biased in the vicinity of a grounding point on the coil, which may cause deterioration of the in-plane uniformity of substrate processing. 
     Some embodiments of the present disclosure provide a technique capable of improving the in-plane uniformity of substrate processing. 
     According to one or more embodiments of the present disclosure, there is provided a technique that includes a process container in which a process gas is plasma-excited; a gas supply system configured to supply the process gas into the process container; and a coil provided with a section between a first grounding point and a second grounding point of the coil so as to be spirally wound a plurality of times along an outer periphery of the process container, the coil being configured to supply high frequency power, wherein the coil is configured so that a coil separation distance, which is a distance from an inner periphery of the coil to an inner periphery of the process container, in a partial section of a first winding section, which is a section where the coil winds once along the outer periphery of the process container in a direction from the first grounding point toward the second grounding point, is longer than a coil separation distance in another partial section of the first winding section continuous with the partial section of the first winding section, and wherein the partial section of the first winding section includes the first grounding point. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure. 
         FIG. 1  is a schematic configuration view of a substrate processing apparatus suitably used in the embodiments of the present disclosure. 
         FIG. 2A  is a view showing a resonance coil according to a comparative example of the present disclosure. 
         FIG. 2B  is an explanatory view showing a relationship between a current and a voltage in the resonance coil of  FIG. 2A . 
         FIG. 3A  is a view showing a state inside a process furnace when a process gas is plasma-excited by using the resonance coil of  FIG. 2A . 
         FIG. 3B  is a horizontal sectional view at the lower end of the resonance coil of  FIG. 3A . 
         FIG. 4A  is a view showing a resonance coil suitably used in the embodiments of the present disclosure. 
         FIG. 4B  is an explanatory view showing a relationship between a current and a voltage in the resonance coil of  FIG. 4A . 
         FIG. 5A  is a view showing a state inside a process furnace when a process gas is plasma-excited by using the resonance coil of  FIG. 4A . 
         FIG. 5B  is a horizontal sectional view at the lower end of the resonance coil of  FIG. 5A . 
         FIG. 6  is a diagram showing the configuration of a control part (control means) of the substrate processing apparatus suitably used in the embodiments of the present disclosure. 
         FIG. 7  is a flow chart showing a substrate-processing process suitably used in the embodiments of the present disclosure. 
         FIG. 8A  is a view showing a state inside a process furnace when a process gas is plasma-excited by using a modification of the resonance coil suitably used in the embodiments of the present disclosure. 
         FIG. 8B  is a horizontal sectional view at the upper end of the resonance coil of  FIG. 8A . 
         FIG. 9A  is a diagram showing a state inside a process furnace when a process gas is plasma-excited by using another modification of the resonance coil suitably used in the embodiments of the present disclosure. 
         FIG. 9B  is a horizontal sectional view at the lower end of the resonance coil of  FIG. 9A . 
         FIG. 10  is a diagram showing a state inside a process furnace when a process gas is plasma-excited by using another modification of the resonance coil suitably used in the embodiments of the present disclosure. 
         FIG. 11  is a diagram showing a state inside a process furnace when a process gas is plasma-excited by using another modification of the resonance coil suitably used in the embodiments of the present disclosure. 
         FIG. 12  is a diagram showing the average film thickness and the in-plane uniformity of a film formed on a substrate when the substrate is processed by using a resonance coil according to an example and a resonance coil according to a comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described in detail so as not to unnecessarily obscure aspects of the various embodiments. 
     One or More Embodiments of the Present Disclosure 
     One or more embodiments of the present disclosure will be now described with reference to  FIGS. 1 to 7 . The drawings used in the following description are all schematic, and the dimensional relationship, ratios, and the like of various elements shown in figures do not always match the actual ones. Further, the dimensional relationship, ratios, and the like of various elements between plural figures do not always match each other. 
     (1) Configuration of Substrate Processing Apparatus 
     A substrate processing apparatus  100  according to one or more embodiments of the present disclosure will be described below with reference to  FIG. 1 . The substrate processing apparatus according to the embodiments of the present disclosure is configured to mainly perform an oxidizing process to a film or a base formed on a substrate surface. 
     (Process Chamber) 
     The substrate processing apparatus  100  includes a process furnace  202  that processes a wafer  200  as a substrate by using plasma. A process container  203  that constitutes a process chamber  201  is provided in the process furnace  202 . The process container  203  includes a dome-shaped upper container  210 , which is a first container, and a bowl-shaped lower container  211 , which is a second container. The process chamber  201  is formed by covering the upper container  210  on the lower container  211 . The upper container  210  is made of quartz. Further, the upper container  210  constitutes a plasma container that forms a plasma generation space in which a process gas is plasma-excited. 
     A gate valve  244  is provided on a lower sidewall of the lower container  211 . When the gate valve  244  is opened, the wafer  200  can be loaded/unloaded in/out of the process chamber  201  via a loading/unloading port  245  by using a transfer mechanism. The gate valve  244  is configured to be a gate valve that maintains airtightness in the process chamber  201  when it is closed. 
     The process chamber  201  has a plasma generation space provided with a resonance coil  212 , which is a coil as an electrode, around the process chamber  201 , and a substrate-processing space communicating with the plasma generation space, as a substrate process chamber in which the wafer  200  is processed. The plasma generation space is a space in which plasma is generated, and refers to a space in the process chamber  201  above the lower end of the coil  212  and below the upper end of the resonance coil  212 . On the other hand, the substrate-processing space is a space in which the substrate is processed by using plasma, and refers to a space below the lower end of the resonance coil  212 . In one or more embodiments of the present disclosure, the diameters of the plasma generation space and the substrate-processing space in the horizontal direction are substantially the same. 
     (Susceptor) 
     A susceptor  217  as a substrate-mounting table on which the wafer  200  is mounted is disposed at the center of the bottom side of the process chamber  201 . The susceptor  217  is provided below the resonance coil  212  in the process chamber  201 . 
     A heater  217   b  as a heating mechanism is integrally embedded inside the susceptor  217 . The heater  217   b  is configured to be able to heat the wafer  200  when electric power is supplied to the heater  217   b.    
     The susceptor  217  is electrically insulated from the lower container  211 . In order to further improve the uniformity of the density of plasma generated on the wafer  200  mounted on the susceptor  217 , an impedance adjustment electrode  217   c  is provided inside the susceptor  217  and is grounded via an impedance variable mechanism  275  as an impedance adjustment part. 
     The susceptor  217  is provided with a susceptor-elevating mechanism  268  including a drive mechanism for raising and lowering the susceptor  217 . Further, the susceptor  217  is provided with through-holes  217   a , and wafer push-up pins  266  are provided on the bottom surface of the lower container  211 . When the susceptor  217  is lowered by the susceptor-elevating mechanism  268 , the wafer push-up pins  266  penetrate through the through-holes  217   a  in a state where the wafer push-up pins  266  is in non-contact with the susceptor  217 . 
     (Gas Supply Part) 
     A gas supply head  236  is provided above the process chamber  201 , that is, in the upper portion of the upper container  210 . The gas supply head  236  includes a cap-shaped lid  233 , a gas introduction port  234 , a buffer chamber  237 , an opening  238 , a shielding plate  240 , and a gas ejection port  239  and is configured to be able to supply a reaction gas into the process chamber  201 . The buffer chamber  237  has a function as a dispersion space for dispersing the reaction gas introduced from the gas introduction port  234 . 
     The downstream end of an oxygen-containing gas supply pipe  232   a  for supplying an oxygen-containing gas, the downstream end of a hydrogen-containing gas supply pipe  232   b  for supplying a hydrogen-containing gas, and an inert gas supply pipe  232   c  for supplying an inert gas are connected to the gas introduction port  234  so that they merge with each other. The oxygen-containing gas supply pipe  232   a  is provided with an oxygen-containing gas supply source  250   a , a mass flow controller (MFC)  252   a  as a flow control device, and a valve  253   a  as an opening/closing valve, sequentially from the upstream side. The hydrogen-containing gas supply pipe  232   b  is provided with a hydrogen-containing gas supply source  250   b , a MFC  252   b , and a valve  253   b , sequentially from the upstream side. The inert gas supply pipe  232   c  is provided with an inert gas supply source  250   c , a MFC  252   c , and a valve  253   c , sequentially from the upstream side. A valve  243   a  is provided on the downstream side where the oxygen-containing gas supply pipe  232   a , the hydrogen-containing gas supply pipe  232   b , and the inert gas supply pipe  232   c  merge with each other, and is connected to the upstream end of the gas introduction port  234 . The valves  253   a ,  253   b ,  253   c , and  243   a  are opened/closed to allow process gases such as the oxygen-containing gas, the hydrogen-containing gas, and the inert gas to be supplied into the process chamber  201  via the gas supply pipes  232   a ,  232   b , and  232   c  while adjusting the flow rate of the gases by the MFCs  252   a ,  252   b , and  252   c , respectively. 
     A gas supply part (gas supply system) according to one or more embodiments of the present disclosure mainly includes the gas supply head  236 , the oxygen-containing gas supply pipe  232   a , the hydrogen-containing gas supply pipe  232   b , the inert gas supply pipe  232   c , the MFCs  252   a ,  252   b , and  252   c , and the valves  253   a ,  253   b ,  253   c , and  243   a . The gas supply part (the gas supply system) is configured to supply the process gases into the process container  203 . 
     Further, an oxygen-containing gas supply system according to one or more embodiments of the present disclosure includes the gas supply head  236 , the oxygen-containing gas supply pipe  232   a , the MFC  252   a , and the valves  253   a  and  243   a . Further, a hydrogen-containing gas supply system according to one or more embodiments of the present disclosure includes the gas supply head  236 , the hydrogen-containing gas supply pipe  232   b , the MFC  252   b , and the valves  253   b  and  243   a . Further, an inert gas supply system according to one or more embodiments of the present disclosure includes the gas supply head  236 , the inert gas supply pipe  232   c , the MFC  252   c , and the valves  253   c  and  243   a.    
     (Exhaust Part) 
     A gas exhaust port  235  for exhausting a reaction gas from the interior of the process chamber  201  is provided on the side wall of the lower container  211 . The upstream end of a gas exhaust pipe  231  is connected to the gas exhaust port  235 . The gas exhaust pipe  231  is provided with an auto pressure controller (APC) valve  242  as a pressure regulator (a pressure adjustment part), a valve  243   b  as an opening/closing valve, and a vacuum pump  246  as a vacuum exhaust device, sequentially from the upstream side. An exhaust part according to one or more embodiments of the present disclosure mainly includes the gas exhaust port  235 , the gas exhaust pipe  231 , the APC valve  242 , and the valve  243   b . The vacuum pump  246  may be included in the exhaust part. 
     (Plasma Generation Part) 
     The resonance coil  212  is provided on the outer peripheral portion of the process chamber  201 , that is, on the outer side of the sidewall of the upper container  210 , so as to be spirally wound a plurality of times along the outer periphery of the upper container  210 . A RF sensor  272 , a high frequency power supply  273 , and a matching device  274  that matches the impedance and output frequency of the high frequency power supply  273 , are connected to the resonance coil  212 . 
     The high frequency power supply  273  supplies high frequency power (RF power) to the resonance coil  212 . The RF sensor  272  is provided on the output side of the high frequency power supply  273  and monitors information of a traveling wave and a reflected wave of the supplied high frequency. The reflected wave power monitored by the RF sensor  272  is input to the matching device  274 , and the matching device  274  controls the frequency of the output high frequency power and the impedance of the high frequency power supply  273  so as to minimize the reflected wave, based on the information of the reflected wave input from the RF sensor  272 . 
     The high frequency power supply  273  includes a power supply control means (control circuit) including a high frequency oscillation circuit and a preamplifier for defining an oscillation frequency and an output, and an amplifier (output circuit) for amplifying the output of the control circuit to a predetermined output. The power supply control means controls the amplifier based on a preset frequency and power output conditions through a control panel. The amplifier supplies constant high frequency power to the resonance coil  212  via a transmission line. 
     The winding diameter, the winding pitch, and the number of turns are set for the resonance coil  212  so as to be resonated at a constant wavelength in order to form a standing wave having a predetermined wavelength. That is, the electrical length of the resonance coil  212  is set to a length corresponding to an integral multiple (1 times, 2 times, . . . ) of one wavelength at a predetermined frequency of the high frequency power supplied from the high frequency power supply  273 . 
     Specifically, in consideration of applied power, a generated magnetic field strength, the outer shape of an applied device, and the like, the resonance coil  212  has the effective sectional area of 50 to 300 mm 2  and the coil diameter of 200 to 500 mm so as to generate a magnetic field of about 0.01 to 10 Gauss with high frequency power of, for example, 800 kHz to 50 MHz and 0.1 to 5 KW, and is wound about 2 to 60 times on the outer peripheral side of a container forming the plasma generation space. 
     As a material of which the resonance coil  212  is made, a copper pipe, a copper thin plate, an aluminum pipe, an aluminum thin plate, a material in which copper or aluminum is vapor-deposited on a polymer belt, etc. are used. The resonance coil  212  is formed in a flat plate shape with an insulating material, and is supported by a plurality of supports (not shown) vertically erected on the upper end surface of a base plate  248 . 
     Both ends of the resonance coil  212  are electrically grounded. One of both ends of the resonance coil  212  is grounded at a first grounding point  302  as a fixed ground. Further, the other end of the resonance coil  212  is grounded at a second grounding point  304 . The second grounding point  304  may be grounded via a movable tap in order to finely tune the electrical length of the resonance coil. Further, in order to finely tune the impedance of the resonance coil  212  at the time of initial installation of the device or at the time of changing the process conditions, a power feeding part is configured by a movable tap  215  between the grounded ends of the resonance coil  212 . Further, the position of the movable tap  215  is adjusted so that the resonance characteristic of the resonance coil  212  is substantially equal to that of the high frequency power supply  273 . Since the resonance coil  212  includes the variable ground portion and the variable power feeding part, the resonance frequency and the load impedance of the process chamber  201  can be adjusted more easily, as will be described later. 
     A shielding panel  223  is provided to shield an electric field outside the resonance coil  212  and to form a capacitance component (C component) necessary for forming a resonance circuit between the shielding panel  223  and the resonance coil  212 . The shielding panel  223  is generally made of a conductive material such as an aluminum alloy and is formed in a cylindrical shape. The shielding panel  223  is arranged at a distance of about 5 to 150 mm from the outer periphery of the resonance coil  212 . 
     A plasma generation part according to one or more embodiments of the present disclosure mainly includes the resonance coil  212 , the RF sensor  272 , and the matching device  274 . The high frequency power supply  273  may be included as the plasma generation part. 
     Here, the plasma generation principle and the properties of the generated plasma of the apparatus according to one or more embodiments of the present disclosure will be described in detail. A plasma generation circuit composed of the resonance coil  212  is configured as an RLC parallel resonance circuit. When the wavelength of the high frequency power supplied from the high frequency power supply  273  is equal to the electrical length of the resonance coil  212 , the reactance condition of the resonance coil  212  is that reactance components created by the capacitive component and the inductive component of the resonance coil  212  are cancelled out to become a pure resistance. However, in the above plasma generation circuit, when plasma is generated, the actual resonance frequency fluctuates slightly depending on a fluctuation in a capacitive coupling between a voltage part of the resonance coil  212  and the plasma, a fluctuation in an inductive coupling between the plasma generation space and the plasma, an excitation state of the plasma, and the like. 
     Therefore, in order to compensate a deviation of resonance in the resonance coil  212  on the power supply side when the plasma is generated, one or more embodiments of the present disclosure provide a function of detecting, by the RF sensor  272 , the reflected wave power from the resonance coil  212  when the plasma is generated, and correcting, by the matching device  274 , the output of the high frequency power supply  273  based on the reflected wave power. 
     Specifically, the matching device  274  increases or decreases the impedance or output frequency of the high frequency power supply  273  so as to minimize the reflected wave power based on the reflected wave power from the resonance coil  212  when the plasma detected by the RF sensor  272  is generated. When controlling the impedance, the matching device  274  is configured by a variable capacitor control circuit that corrects the preset impedance, and when controlling the frequency, the matching device  274  is configured by a frequency control circuit that corrects the preset oscillation frequency of the high frequency power supply  273 . Further, the high frequency power supply  273  and the matching device  274  may be integrally configured. 
     With this configuration, since the resonance coil  212  in one or more embodiments of the present disclosure is supplied with high frequency power at the actual resonance frequency of the resonance coil including plasma (or is supplied with the high frequency power so as to match with the actual impedance of the resonance coil including plasma), a standing wave is formed in which a phase voltage and an anti-phase voltage are always cancelled out. When the electrical length of the resonance coil  212  is equal to the wavelength of the high frequency power, the highest phase current is generated at the electrical midpoint (node of zero voltage) of the coil. Therefore, in the vicinity of the electrical midpoint, since there is almost no capacitive coupling with the process chamber wall or the susceptor  217 , donut-shaped inductive plasma having an extremely low electrical potential is formed. 
     (Winding Diameter of Resonance Coil) 
     Next, the winding diameter of the resonance coil  212  in one or more embodiments of the present disclosure will be described. As described above, the lower end of the resonance coil  212  is grounded at the first grounding point  302 , and the upper end of the resonance coil  212  is grounded at the second grounding point  304 . That is, both ends of the resonance coil  212  are grounded at the first grounding point  302  and the second grounding point  304 , respectively, and the first grounding point  302  is provided below the second grounding point  304 . The resonance coil  212  is configured so that a section between the first grounding point  302  and the second grounding point  304  is provided to be spirally wound a plurality of times along the outer periphery of the process container  203  in order to supply the high frequency power. Here, “along the outer periphery of the process container  203 ” means that the resonance coil  212  and the outer periphery (outer surface or outer wall) of the process container  203  are close to each other to such an extent that a high frequency electromagnetic field generated by the resonance coil  212  substantially plasma-excites the process gas in the process container  203 . 
     &lt;Winding Diameter of Resonance Coil According to Comparative Example&gt; 
     First, in the substrate processing apparatus  100 , an example in which a resonance coil  412  according to a comparative example is used instead of the resonance coil  212  in one or more embodiments of the present disclosure will be described with reference to  FIGS. 2A, 2B, 3A, and 3B . 
     As shown in  FIG. 2A , the resonance coil  412  according to the comparative example has the constant and same winding diameter at any position on the resonance coil  412 . That is, when a distance from the inner wall surface (the surface of the inner periphery) of the upper container  210  to the inner diameter side surface (the surface on the side facing the side wall of the upper container  210 , that is, the inner peripheral surface) of the resonance coil  412  (hereinafter, a coil separation distance) is defined as d 1 , in this comparative example, d 1  is always constant and the winding diameter is the same. 
     The configuration of this comparative example is the same as that of the resonance coil  212  in one or more embodiments of the present disclosure except for the winding diameter. Also in this comparative example, a power feeding point is provided on a line of the resonance coil  412 , and high frequency power is supplied from the high frequency power supply  273  to form a standing wave of a current and a voltage having a length of, for example, one wavelength of high frequency power in the section between the first grounding point  302  and the second grounding point  304  on the line of the resonance coil  412 . Of the waveforms on the left side of  FIG. 2B , a broken line indicates a current and a solid line indicates a voltage. As shown by the waveforms on the left side of  FIG. 2B , the amplitude of the standing wave of the current becomes maximum at the first grounding point  302 , the second grounding point  304 , and the midpoint therebetween (that is, the electrical midpoint) of the resonance coil  412 . 
     A high frequency magnetic field is formed in the vicinity of the midpoint of the resonance coil  412  where the current amplitude becomes maximum, and a high frequency electromagnetic field induced by this high frequency magnetic field generates discharge of a process gas supplied into the plasma generation space in the upper container  210 . When the process gas is excited by this discharge, plasma of the process gas is generated in the vicinity of the midpoint of the resonance coil  412 . Hereinafter, the plasma of the process gas generated by the high frequency electromagnetic field formed in the vicinity of a position (region) where the current amplitude is large is referred to as inductively coupled plasma (ICP). As shown in  FIG. 3A , the ICP is generated in a donut shape in a region of the space along the inner wall surface in the upper container  210  near the midpoint of the resonance coil  412 , thereby generating an ICP with a uniform plasma density in the in-plane direction of the wafer  200 . 
     Here, as shown in  FIGS. 2A and 2B , in the vicinity of the first grounding point  302  on the lower end side of the resonance coil  412  and even in the vicinity of the second grounding point  304  on the upper end side of the resonance coil  412 , the amplitude of the current (magnetic field) becomes maximum to form a high frequency electromagnetic field. However, a section having a large current amplitude (for example, a section having 80% or more of the maximum amplitude) on each of the upper end side and the lower end side of the resonance coil  412  is narrower than a section having a large current amplitude (for example, a section having 80% or more of the maximum amplitude) in the vicinity of the midpoint of the resonance coil  412 . Specifically, for example, on the upper end side and the lower end side of the resonance coil  412 , the length of the section where the current amplitude is 80% or more of the maximum amplitude may be about half of that in the vicinity of the midpoint of the resonance coil  412 . In such a case, on the upper end side and the lower end side of the resonance coil  412 , as shown in  FIGS. 3A and 3B , an ICP having a high plasma density may not be generated to make one round in a donut shape along the inner periphery of the process container  203 , but may be generated in a partial region in the inner peripheral direction of the process container  203 . That is, the ICP having the high plasma density may be generated in a non-uniformly biased state in the inner peripheral direction of the process container  203 . 
     Further, as shown in  FIG. 2B , the distribution of plasma density of the ICP generated on each of the upper end side and the lower end side in the inner peripheral direction of the process container  203  becomes a distribution having a bias that significantly increases the plasma density at a position corresponding to the first grounding point  302  where the current amplitude becomes maximum and a position corresponding to the second grounding point  304  where the current amplitude becomes maximum. This is because the ICP generated in the vicinity of the midpoint is formed so that the distribution of plasma density is substantially uniform over the entire inner peripheral direction of the process container  203  with the midpoint as the center, whereas the ICP generated on each of the upper end side and the lower end side has the maximum plasma density in each of the vicinity of the first grounding point  302  and the vicinity of the second grounding point  304  and has a plasma density distribution in which the plasma density decreases rapidly as a distance increases from there in the inner peripheral direction of the process container  203  along the line of the resonance coil  412 . Further, it is presumed that the formation of the ICP generated in the vicinity of the midpoint so that the plasma density distribution is substantially uniform over the entire inner peripheral direction of the process container  203  is caused by promotion of the formation of the ICP over the entire inner peripheral direction of the process container  203  as a region where the plasma density is high forms a continuous ring along the inner periphery of the process container  203 . 
     That is, when the resonance coil  412  according to the comparative example is used, a grounding point of the resonance coil  412  becomes a singular point, and plasma generated by an induced current at the grounding point causes a bias in the distribution of the plasma density in the inner peripheral direction of the process container  203 , which may deteriorate the in-plane uniformity of a film formed on the wafer  200 . One of the reasons for this is that the plasma density in the circumferential direction becomes non-uniform because the winding diameter of the resonance coil is larger than the wavelength of high frequency power. In particular, it has been confirmed that when a value of the high frequency power supplied from the high frequency power supply  273  is set to 3,500 to 4,800 W, the deterioration of the in-plane uniformity becomes remarkable. 
     &lt;Winding Diameter of Resonance Coil According to One or More Embodiments of the Present Disclosure&gt; 
     Next, the resonance coil  212  in one or more embodiments of the present disclosure will be described with reference to  FIGS. 4A, 4B, 5A, and 5B . 
     In the resonance coil  212  in one or more embodiments of the present disclosure, as shown in  FIGS. 4A and 4B , the winding diameter of the resonance coil  212  is extended at the first grounding point  302  on the lower end side of the resonance coil  212  so as to be different from section other than the first grounding point  302  on the line of the resonance coil  212 . That is, when a distance from the inner wall surface (the inner peripheral surface) of the upper container  210  to the inner diameter side surface (the surface on the side facing the side wall of the upper container  210 , that is, the inner peripheral surface) of the resonance coil  212 , that is, a coil separation distance, which is a distance from the inner periphery of the resonance coil  212  at the midpoint of the resonance coil  212  to the inner periphery of the process container  203 , is defined as d 1 , a coil separation distance at the first grounding point  302  of the resonance coil  212  is defined as d 2  and is longer than d 1 . Here, the midpoint of the resonance coil  212  refers to substantially the center between the first grounding point  302  and the second grounding point  304  in the resonance coil  212 . 
     Specifically, the resonance coil  212  has a first winding section, which is a section where the resonance coil  212  winds once along the outer periphery of the process container  203  in a direction from the first grounding point  302  toward the second grounding point  304 . The first winding section is composed of a first section in which the coil separation distance is constant at d 1 , and a second section continuous with the first section, including the first grounding point  302 , in which the coil separation distance is longer than d 1 . Further, the resonance coil  212  is configured such that the coil separation distance in the second section including the first grounding point  302  in the first winding section is longer than the coil separation distance in the first section. Further, the length of the second section is set to be shorter than half of the first winding section. 
     As shown in  FIGS. 5A and 5B , the coil separation distance d 2  at the first grounding point  302  is set to be longer than the coil separation distance d 1  in the other sections. That is, the resonance coil  212  is configured so that the coil separation distance d 2  at the first grounding point  302  is the longest in the section between the first grounding point  302  and the second grounding point  304 . Further, the resonance coil  212  is configured so that the coil separation distance d 2  at the first grounding point  302  in the first winding section is the longest. In this way, in the first winding section, the vicinity of the first grounding point  302 , which is a singular point, is kept away from the process container  203 , and the other sections are brought closer to d 1  which is a predetermined distance from the process container  203 . Accordingly, while reducing the bias of the plasma density of the ICP formed in the process chamber  201 , it is possible to minimize the decrease in the plasma density and suppress the decrease in the production efficiency of reaction species. 
     Further, the coil separation distance at the second grounding point  304  of the resonance coil  212  in one or more embodiments of the present disclosure is d 1 , and a coil separation distance in a second winding section, which is on the upper end side of the resonance coil  212  and is a section where the resonance coil  212  winds once along the outer periphery of the process container  203  in a direction from the second grounding point  304  toward the first grounding point  302 , is constant as d 1 . As a result, in the vicinity of the second grounding point  304 , an ICP having a higher plasma density than the ICP generated in the vicinity of the first grounding point  302  is generated, thereby improving the production efficiency of the reaction species of a reaction gas. 
     Further, the length of a section from the first grounding point  302  to the second grounding point  304  of the resonance coil  212  is n times or 1/n times (where n is a natural number) the wavelength of the high frequency supplied as high frequency power. Further, the resonance coil  212  is configured so that other sections of the resonance coil  212  are not arranged between the first winding section of the resonance coil  212  and the outer periphery of the process container  203 . That is, the first winding section including the first grounding point  302  of the resonance coil  212  and the second winding section including the second grounding point  304  of the resonance coil  212  are configured to be arranged so as not to overlap other sections in the horizontal direction. If the first winding section and the second winding section overlap other sections in the horizontal direction, a section near the grounding point moves away from the process container  203 , making it difficult to generate an ICP. 
     Further, the length of the first winding section of the resonance coil  212  is set to be longer than a length to the nearest position, which is less than a predetermined ratio with respect to the amplitude at the first grounding point  302 , from the first grounding point  302  where the amplitude of the standing wave of the current flowing through the resonance coil  212  becomes maximum. That is, in the first winding section of the resonance coil  212 , there is a position where the amplitude of the standing wave of the current flowing through the resonance coil  212  is less than the predetermined ratio with respect to the amplitude at the first grounding point  302 . Here, since the plasma density tends to be lower in a section where the amplitude of the standing wave of the current is smaller, a position where the amplitude of the standing wave of the current is less than a predetermined ratio with respect to the amplitude at the first grounding point  302  is present in the first winding section, which makes it easy to cause a bias in the plasma density with the first grounding point  302  as a singular point. Therefore, by using the resonance coil  212  according to the present disclosure, it is possible to remarkably improve the bias of the plasma density. For example, 80% is exemplified as a predetermined ratio at which the bias of the plasma density with the first grounding point  302  as a singular point is likely to occur. If the predetermined ratio exceeds 80%, the distribution of the plasma density of ICP in the first winding section becomes substantially uniform, making it difficult to obtain the effect of improving the uniformity by the disclosed technique. Therefore, it is preferable that the predetermined ratio at which the effect of improving the uniformity by the disclosed technique can be sufficiently obtained is 80% or less. 
     Further, the length of the first winding section of the resonance coil  212  is set to be longer than a length from the first grounding point  302  up to a first position where the amplitude of the standing wave of the current flowing through the resonance coil  212  is minimized (that is, a first position where the amplitude of the standing wave of a voltage is maximized). As described above, when there is a position in the first winding section of the resonance coil  212  where the amplitude of the standing wave of the current is minimized, a point where the amplitude of the standing wave of the current at the first grounding point  302  becomes the maximum and a point where the amplitude thereof becomes the minimum are present in the first winding section, making it easy to cause the bias of the plasma density. Therefore, by using the resonance coil  212  according to the present disclosure, it is possible to remarkably improve the bias of the plasma density. 
     As described above, also in the resonance coil  212  in one or more embodiments of the present disclosure, the power feeding point is provided on the line of the resonance coil  212 , and the high frequency power is supplied from the high frequency power supply  273  to form a standing wave of current and voltage having a length of, for example, one wavelength of the high frequency power supplied on the line of the resonance coil  212 . Therefore, the amplitude of the standing wave of the current becomes maximum at the first grounding point  302 , the second grounding point  304 , and the midpoint therebetween of the resonance coil  212 . That is, the amplitude of the standing wave of the voltage becomes the minimum (ideally zero) at the first grounding point  302 , the second grounding point  304 , and the midpoint therebetween of the resonance coil  212 , and the amplitude becomes the maximum at positions between the first grounding point  302  and the midpoint and between the second grounding point  304  and the midpoint. Further, the power feeding point is provided near the grounding point in order to lower the impedance of the resonance coil  212 . 
     As described above, in one or more embodiments of the present disclosure, the coil winding diameter is set so that the coil separation distance at the first grounding point  302  arranged in the vicinity of the wafer  200  is the longest in the first winding section of the resonance coil  212 . Further, the coil winding diameter is set so that the coil separation distance at the first grounding point  302  of the resonance coil  212  is the longest in the section between the first grounding point  302  and the second grounding point  304  of the resonance coil  212 . In the embodiments, this maximum distance is d 2 . More specifically, in the embodiments, the coil winding diameter is set so that the coil separation distance at the first grounding point  302  of the resonance coil  212  is d 2 , which is longer than d 1 . In one or more embodiments of the present disclosure, the coil winding diameter is set so that the coil separation distance at the grounding point where the amplitude of the standing wave of the current becomes maximum is the maximum distance in the entire section of the resonance coil  212 . 
     Here, the strength of the high frequency electromagnetic field formed by the resonance coil  212  is inversely proportional to a distance from the resonance coil  212 . Therefore, by setting the coil separation distance at the first grounding point  302  to d 2 , which is longer than d 1 , the strength of the high frequency electromagnetic field affected by the amplitude of the current of the resonance coil  212  at the first grounding point  302  arranged in the vicinity of the wafer  200  is reduced. 
     Therefore, by setting the coil separation distance at the first grounding point  302  near the wafer  200 , which is a substrate to be processed, to be the longest in the section between the first grounding point  302  and the second grounding point  304  of the resonance coil  212 , the strength of the high frequency electromagnetic field formed in the vicinity of the first grounding point  302  is reduced. Therefore, it is possible to suppress the bias of the plasma density of the process gas generated in the circumferential direction of the resonance coil  212  by the high frequency electromagnetic field. 
     Further, since the second grounding point  304  is farther from the wafer  200 , which is the substrate to be processed, than the first grounding point  302 , the effect of the bias of the plasma density caused by the second grounding point  304  as a singular point on the in-plane uniformity of processing on the wafer  200  is relatively smaller than that of the first grounding point  302 . Therefore, by setting the coil separation distance at the second grounding point  304 , which is far from the wafer  200  and has a relatively small effect on the in-plane uniformity of the substrate processing, to be a distance (for example, d 1 ) shorter than the coil separation distance d 2  at the first grounding point  302 , it is possible to maintain the production efficiency of the reaction species without causing a decrease in the plasma density due to the increase in the coil separation distance at the second grounding point  304 . As a result, while reducing the bias of the plasma density in the circumferential direction due to the grounding point, it is possible to improve the in-plane uniformity of the wafer  200  while maintaining the plasma processing efficiency. 
     Further, the specific values of the coil separation distances d 1  and d 2  can be appropriately adjusted according to other conditions such as the magnitude of the high frequency power supplied to the resonance coil  212 , the thickness of the resonance coil  212 , the desired degree of uniformity of the plasma density (particularly in the circumferential direction of the upper container  210 ), etc. 
     (Control Part) 
     A controller  221  as a control part is configured to control the APC valve  242 , the valve  243   b , and the vacuum pump  246  via a signal line A, the susceptor-elevating mechanism  268  via a signal line B, a heater-power-adjusting mechanism  276  and the impedance variable mechanism  275  via a signal line C, the gate valve  244  via a signal line D, the RF sensor  272 , the high frequency power supply  273 , and the matching device  274  via a signal line E, and the MFCs  252   a  to  252   c  and the valves  253   a  to  253   c  and  243   a  via a signal line F. 
     As shown in  FIG. 6 , the controller  221 , which is the control part (control means), is configured as a computer including a central processing unit (CPU)  221   a , a random access memory (RAM)  221   b , a memory  221   c , and an I/O port  221   d . The RAM  221   b , the memory  221   c , and the I/O port  221   d  are configured to be capable of exchanging data with the CPU  221   a  via an internal bus  221   e . An input/output device  225  configured as, for example, a touch panel or a display, is connected to the controller  221 . 
     The memory  221   c  is configured by, for example, a flash memory, a hard disk drive (HDD), or the like. A control program for controlling operations of a substrate processing apparatus, a process recipe in which sequences and conditions of substrate processing, which will be described later, are written, etc. are readably stored in the memory  221   c . The process recipe functions as a program for causing the controller  221  to execute each sequence in a substrate-processing process, which will be described later, to obtain a predetermined result. Hereinafter, the process recipe and the control program may be generally and simply referred to as a “program.” When the term “program” is used herein, it may indicate a case of including the process recipe only, a case of including the control program only, or a case of including both the process recipe and the control program. The RAM  221   b  is configured as a memory area (work area) in which a program or data read by the CPU  221   a  is temporarily stored. 
     The I/O port  221   d  is connected to the MFCs  252   a  to  252   c , the valves  253   a  to  253   c ,  243   a , and  243   b , the gate valve  244 , the APC valve  242 , the vacuum pump  246 , the RF sensor  272 , the high frequency power supply  273 , the matching device  274 , the susceptor-elevating mechanism  268 , the impedance variable mechanism  275 , the heater-power-adjusting mechanism  276 , and the like. 
     The CPU  221   a  is configured to read and execute the control program from the memory  221   c . The CPU  221   a  is also configured to read the process recipe from the memory  221   c  according to an input of an operation command from the input/output device  225 . Then, the CPU  221   a  is configured to control the operation of adjusting the opening degree of the APC valve  242 , the opening/closing operation of the valve  243   b , the actuating and stopping of the vacuum pump  246  via the I/O port  221   d  and the signal line A, the elevating operation of the susceptor-elevating mechanism  268  via the signal line B, the operation of adjusting the amount of power supplied to the heater  217   b  (the temperature adjusting operation) by the heater-power-adjusting mechanism  276  and the operation of adjusting the impedance by the impedance variable mechanism  275  via the signal line C, the opening/closing operation of the gate valve  244  via the signal line D, the operations of the RF sensor  272 , the matching device  274 , and the high frequency power supply  273  via the signal line E, the operation of adjusting flow rates of various kinds of gases by the MFCs  252   a  to  252   c  and the opening/closing operation of the valves  253   a  to  253   c  and  243   a  via the signal line F, and the like, according to contents of the read process recipe. 
     The controller  221  may be configured by installing, on the computer, the aforementioned program stored in an external memory (for example, a magnetic tape, a magnetic disk such as a flexible disk or a hard disk, an optical disc such as a CD or a DVD, a magneto-optical disc such as a MO, a semiconductor memory such as a USB memory or a memory card, and the like)  226 . The memory  221   c  and the external memory  226  are configured as a non-transitory computer-readable recording medium. Hereinafter, the memory  221   c  and the external memory  226  may be generally and simply referred to as a “recording medium.” When the term “recording medium” is used herein, it may indicate a case of including the memory  221   c  only, a case of including the external memory  226  only, or a case of including both the memory  221   c  and the external memory  226 . The program may be provided to the computer by using a communication means such as the Internet or a dedicated line, instead of using the external memory  226 . 
     (2) Substrate-Processing Process 
     Next, a substrate-processing process according to one or more embodiments of the present disclosure will be described mainly with reference to  FIG. 7 .  FIG. 7  is a flow chart showing a substrate-processing process according to one or more embodiments of the present disclosure. The substrate-processing process according to one or more embodiments of the present disclosure, which is one of processes of manufacturing a semiconductor device such as a flash memory, is carried out by the above-described substrate processing apparatus  100 . In the following description, the operations of various parts constituting the substrate processing apparatus  100  are controlled by the controller  221 . 
     Although not shown, a trench including an uneven portion having a high aspect ratio is formed in advance on the surface of a wafer  200  to be processed in the substrate-processing process according to one or more embodiments of the present disclosure. In one or more embodiments of the present disclosure, for example, a silicon (Si) layer exposed on the inner wall of the trench is subjected to an oxidation process as a process using plasma. 
     (Substrate-Loading Step S 110 ) 
     First, the wafer  200  is loaded into the process chamber  201 . Specifically, the susceptor-elevating mechanism  268  lowers the susceptor  217  to a transfer position of the wafer  200  to penetrate the wafer push-up pins  266  through the through-holes  217   a  of the susceptor  217 . As a result, the wafer push-up pins  266  protrude by a predetermined height from the surface of the susceptor  217 . 
     Subsequently, the gate valve  244  is opened, and the wafer  200  is loaded into the process chamber  201  from a vacuum transfer chamber adjacent to the process chamber  201  by using a wafer transfer mechanism (not shown). The loaded wafer  200  is supported in a horizontal posture on the wafer push-up pins  266  protruded from the surface of the susceptor  217 . After the wafer  200  is loaded into the process chamber  201 , the wafer transfer mechanism is retracted to the outside of the process chamber  201 , and the gate valve  244  is closed to seal the interior of the process chamber  201 . Then, the susceptor-elevating mechanism  268  raises the susceptor  217  so that the wafer  200  is supported on the upper surface of the susceptor  217 . 
     (Temperature Rise/Vacuum-Exhaust Step S 120 ) 
     Subsequently, the temperature of the wafer  200  loaded into the process chamber  201  is raised. The heater  217   b  is preheated, and by holding the wafer  200  on the susceptor  217  in which the heater  217   b  is embedded, the wafer  200  is heated to a predetermined value in a range of, for example, 150 to 750 degrees C. Further, while the temperature of the wafer  200  is raised, the interior of the process chamber  201  is vacuum-exhausted by the vacuum pump  246  via the gas exhaust pipe  231  to set the internal pressure of the process chamber  201  to a predetermined value. The vacuum pump  246  keeps operated at least until a substrate-unloading step S 160  to be described later is completed. 
     (Reaction Gas Supply Step S 130 ) 
     Next, the supply of an oxygen-containing gas and a hydrogen-containing gas as the reaction gas is started. Specifically, the valves  253   a  and  253   b  are opened, and the oxygen-containing gas and the hydrogen-containing gas are started to be supplied into the process chamber  201  while their flow rates are controlled by the MFC  252   a  and the MFC  252   b , respectively. At this time, the flow rate of the oxygen-containing gas is set to a predetermined value in a range of, for example, 20 to 2,000 sccm. Further, the flow rate of the hydrogen-containing gas is set to a predetermined value in a range of, for example, 20 to 1,000 sccm. 
     Further, the opening degree of the APC valve  242  is adjusted to control the exhaust of the interior of the process chamber  201  so that the internal pressure of the process chamber  201  becomes a predetermined pressure in a range of, for example, 1 to 250 Pa. In this way, while appropriately exhausting the interior of the process chamber  201 , the supply of the oxygen-containing gas and the hydrogen-containing gas is continued until a plasma-processing step S 140  to be described later is completed. 
     Examples of the oxygen-containing gas may include an oxygen (O 2 ) gas, a nitrous oxide (N 2 O) gas, a nitric oxide (NO) gas, a nitrogen dioxide (NO 2 ) gas, an ozone (O 3 ) gas, water vapor (H 2 O gas), a carbon monoxide (CO) gas, a carbon dioxide (CO 2 ) gas, and the like. One or more of these gases can be used as the oxygen-containing gas. 
     Further, examples of the hydrogen-containing gas may include a hydrogen (H 2 ) gas, a deuterium (D 2 ) gas, a H 2 O gas, an ammonia (NH 3 ) gas, and the like. One or more of these gases can be used as the hydrogen-containing gas. When the H 2 O gas is used as the oxygen-containing gas, it is preferable to use a gas other than the H 2 O gas, as the hydrogen-containing gas, and when the H 2 O gas is used as the hydrogen-containing gas, it is preferable to use a gas other than the H 2 O gas, as the oxygen-containing gas. 
     Examples of the inert gas may include a nitrogen (N 2 ) gas and, in addition, a rare gas such as an argon (Ar) gas, a helium (He) gas, a neon (Ne) gas, or a xenon (Xe) gas. One or more of these gases can be used as the inert gas. 
     (Plasma-Processing Step S 140 ) 
     When the internal pressure of the process chamber  201  is stabilized, the application of the high frequency power to the resonance coil  212  from the high frequency power supply  273  via the RF sensor  272  is started. 
     As a result, a high frequency electromagnetic field is formed in the plasma generation space into which the oxygen-containing gas and the hydrogen-containing gas are supplied, and donut-shaped ICP with the highest plasma density is excited at a height position corresponding to the electrical midpoint of the resonance coil  212  in the plasma generation space by this electromagnetic field. Further, as described above, the ICP adjusted so that the distribution of plasma density in the inner peripheral direction of the process container  203  is closer to uniformity by adjusting the coil separation distance is excited at the height position of the lower end of the resonance coil  212 . Further, the ICP is also excited at the height position of the upper end of the resonance coil  212 , but in one or more embodiments of the present disclosure, no adjustment is made to the plasma density distribution in the inner peripheral direction of the process container  203  by adjusting the coil separation distance, unlikely the lower end side. The oxygen-containing gas and the hydrogen-containing gas in the plasma state are dissociated to generate reactive species such as oxygen-containing oxygen radicals (oxygen-active species) or oxygen ions and hydrogen-containing hydrogen radicals (hydrogen-active species) or hydrogen ions. 
     Radicals and unaccelerated ions generated by inductive plasma are uniformly supplied into the trench of the wafer  200  held on the susceptor  217  in the substrate-processing space. The supplied radicals and ions react uniformly with the side wall to modify the surface layer (for example, a Si layer) into an oxide layer (for example, a Si oxide layer) with good step coverage. 
     After that, with the lapse of a predetermined processing time, for example, 10 to 300 seconds, the output of the power from the high frequency power supply  273  is stopped to stop the plasma discharge in the process chamber  201 . Further, the valve  253   a  and the valve  253   b  are closed to stop the supply of the oxygen-containing gas and the hydrogen-containing gas into the process chamber  201 . From the above, the plasma-processing step S 140  is completed. 
     (Vacuum-Exhaust Step S 150 ) 
     When the supply of the oxygen-containing gas and the hydrogen-containing gas is stopped, the interior of the process chamber  201  is vacuum-exhausted through the gas exhaust pipe  231 . As a result, the oxygen-containing gas and the hydrogen-containing gas in the process chamber  201 , an exhaust gas generated by the reaction of these gases, and the like are exhausted to the outside of the process chamber  201 . After that, the opening degree of the APC valve  242  is adjusted to adjust the internal pressure of the process chamber  201  to the same pressure as the vacuum transfer chamber (the unloading destination of the wafer  200 , not shown) adjacent to the process chamber  201 . 
     (Substrate-Unloading Step S 160 ) 
     When the interior of the process chamber  201  reaches a predetermined pressure, the susceptor  217  is lowered to the transfer position of the wafer  200 , and the wafer  200  is supported on the wafer push-up pins  266 . Then, the gate valve  244  is opened, and the wafer  200  is unloaded to the outside of the process chamber  201  by using the wafer transfer mechanism. 
     From the above, the substrate-processing process according to one or more embodiments of the present disclosure is completed. 
     (3) Modifications 
     The resonance coil  212  in the above-described embodiments can be modified as in modifications shown below. Unless stated otherwise, each modification has the same configuration as in the above-described embodiments, and explanation thereof will not be repeated. 
     (First Modification) 
     In a first modification, as shown in  FIGS. 8A and 8B , in addition to the first grounding point  302  on the lower end side of the resonance coil  212 , the coil separation distance at the second grounding point  304  on the upper end side of the resonance coil  212  is made longer than the coil separation distance d 1  at the midpoint of the resonance coil  212 . 
     Specifically, the resonance coil  212  has a second winding section, which is a section where the resonance coil  212  winds once along the outer periphery of the process container  203  in a direction from the second grounding point  304  toward the first grounding point  302 . The second winding section is composed of a third section in which the coil separation distance is constant at d 3 , and a fourth section continuous with the third section, including the second grounding point  304 , in which the coil separation distance is longer than d 3 . Further, the resonance coil  212  is configured such that the coil separation distance in the fourth section including the second grounding point  304  in the second winding section is longer than the coil separation distance d 3  in the third section. Further, the length of the fourth section is set to be shorter than half of the second winding section. 
     As shown in  FIGS. 8A and 8B , the coil separation distance d 4  at the second grounding point  304  in the fourth section is set to be longer than the coil separation distance d 3  in the third section. Further, the resonance coil  212  is configured so that the coil separation distance d 4  at the second grounding point  304  of the coil separation distance in the second winding section is the longest. In this way, similarly to the first winding section, in the second winding section, the vicinity of the second grounding point  304 , which is a singular point, is kept away from the process container  203 , and the other sections are brought closer to d 3  which is a predetermined distance from the process container  203 . Accordingly, while reducing the bias of the plasma density of the ICP formed in the process chamber  201 , it is possible to minimize the decrease in the plasma density and suppress the decrease in the production efficiency of reaction species. 
     In this modification, as the grounding points of the resonance coil  212 , the coil separation distance at the first grounding point  302  of the resonance coil  212  where the amplitude of the standing wave of a current becomes maximum and the coil separation distance at the second grounding point  304  of the resonance coil  212  where the amplitude of the standing wave of the current becomes maximum are set to be longer than the coil separation distance at other sections of the resonance coil  212 . As a result, even when the amplitude of the standing wave of the current becomes maximum at the grounding points of both ends of the first grounding point  302  and the second grounding point  304  of the resonance coil  212 , according to this modification, it is possible to reduce the bias of the plasma density, thereby improving the in-plane uniformity of the wafer  200 . 
     That is, in addition to the first grounding point  302  of the resonance coil  212 , by setting the coil separation distance at the second grounding point  304  to be longer than those at the other sections between the first grounding point  302  and the second grounding point  304 , the strength of the high frequency electromagnetic field formed in the vicinity of the first grounding point  302  and the second grounding point  304  is reduced. 
     Further, the coil separation distance d 4  at the second grounding point  304  may be equal to or different from the coil separation distance d 2  at the first grounding point  302  in the second section. In this modification, the coil separation distance d 2  at the first grounding point  302  is different from the coil separation distance d 4  at the second grounding point  304 . Specifically, the coil separation distance d 2  at the first grounding point  302  is set to be longer than the coil separation distance d 4  at the second grounding point  304 . d 3  and d 1  may be the same distance. 
     As described above, since the second grounding point  304  is farther from the wafer  200 , which is the substrate to be processed, than the first grounding point  302 , the effect of the bias of the plasma density caused by the second grounding point  304  as a singular point on the in-plane uniformity of processing on the wafer  200  is relatively smaller than that of the first grounding point  302 . Therefore, by setting the coil separation distance d 4  at the second grounding point  304 , which is far from the wafer  200  and has a relatively small effect on the in-plane uniformity of the substrate processing, to be shorter than the coil separation distance d 2  at the first grounding point  302 , it is possible to maintain the production efficiency of the reaction species while minimizing a decrease in the plasma density due to the increase in the coil separation distance at the second grounding point  304 . As a result, while reducing the bias of the plasma density in the circumferential direction due to the grounding point, it is possible to improve the in-plane uniformity of the wafer  200  while maintaining the plasma processing efficiency. 
     Further, by setting the coil separation distance d 2  at the first grounding point  302  to be different from the coil separation distance d 4  at the second grounding point  304 , the distribution of plasma density in the first winding section and the distribution of plasma density in the second winding section can be adjusted individually, so that the film thickness distribution of a film formed on the wafer  200  can be controlled. 
     Here, as described above, the plasma generated in the vicinity of the midpoint of the resonance coil  212  tends to be superior in the density uniformity in the circumferential direction of the upper container  210  over the plasmas generated on the upper end side and the lower end side of the resonance coil  212 . Therefore, in this modification, the coil separation distances at the grounding points on the upper end side and the lower end side of the resonance coil  212  are increased to reduce the strength of the high frequency electromagnetic field generated from these positions in the upper container  210 , thereby relatively increasing the ratio of the plasma with excellent uniformity generated in the vicinity of the midpoint of the resonance coil  212 , which contributes to the substrate processing. Therefore, from the viewpoint of improving the uniformity of the plasma density in the circumferential direction of the upper container  210 , this modification is generally preferable over the above-described embodiments. However, from the viewpoint of emphasizing the production efficiency of the reaction species, the above-described embodiments used for the generation of the reaction species without lowering the strength of the high frequency electromagnetic field in the upper container  210  generated from the grounding point on the upper end side of the resonance coil  212  are preferable. 
     (Second Modification) 
     In a second modification, as shown in  FIGS. 9A and 9B , the coil separation distance in the first winding section on the lower end side of the resonance coil  212  is set to be longer than the coil separation distance d 1  at the midpoint of the resonance coil  212 , and the coil separation distance in the second winding section including the second grounding point  304  on the upper end side of the resonance coil  212  is set to be the same d 1  as the coil separation distance at the midpoint of the resonance coil  212 . Further, as shown in  FIG. 9B , the coil separation distance at the start point on the upper end side of the first winding section may be, for example, d 1  or longer than d 1 . 
     In this modification, the first winding section is composed of a sixth section including the first grounding point  302  and a fifth section which is a section other than the sixth section. In the fifth section, the coil separation distance is set to continuously increase from the coil separation distance d 1  to a coil separation distance d 5  in the direction from the second grounding point  304  toward the first grounding point  302 , and in the sixth section, the coil separation distance is set to further continuously increase from d 5 , which is longer than the coil separation distance d 1 , to d 2  in the direction toward the first grounding point  302 . The coil separation distance d 2  at the first grounding point  302  is set to be the longest in the coil separation distance in the first winding section. Further, the resonance coil  212  is configured such that the increase rate of the coil separation distance in the direction from the second grounding point  304  toward the first grounding point  302  in the sixth section is larger than the increase rate in the fifth section. That is, the resonance coil  212  is configured such that the amount of increase of the coil separation distance in the sixth section, which is a section in the vicinity of the first grounding point  302 , changes to be larger than the amount of increase of the coil separation distance in the fifth section. 
     By configuring the resonance coil  212  in this way, as in the above-described embodiments, the coil separation distance on the lower end side is lengthened to decrease the strength of the high frequency electromagnetic field, which is generated near the grounding point in the vicinity of the wafer  200 , in the upper container  210 , thereby improving the uniformity of the plasma density in the circumferential direction of the upper container  210 . 
     (Third Modification) 
     In a third modification, as shown in  FIG. 10 , in addition to the coil separation distance in the first winding section including the first grounding point  302  of the resonance coil  212  in the above-described second modification, a coil separation distance in the entire second winding section including the grounding point  304  of the resonance coil  212  is set to be longer than d 1  which is the coil separation distance in other sections between the first grounding point  302  and the second grounding point  304  of the resonance coil  212  and is the coil separation distance at the midpoint of the resonance coil  212 . Further, in this modification, the coil separation distance in the second winding section including the second grounding point  304  of the resonance coil  212  is d 6  and is set to be constant. In this modification, the coil separation distance of the resonance coil  212  in both the entire first winding section and the entire second winding section is set to be longer than the coil separation distance d 1  which is the coil separation distance in other sections between the first grounding point  302  and the second grounding point  304  of the resonance coil  212  and is the coil separation distance at the midpoint of the resonance coil  212 . With such setting, while maintaining the plasma density (that is, the production efficiency of the reaction species) generated by the other sections between the first grounding point  302  and the second grounding point  304  of the resonance coil  212 , it is possible to more reliably suppress the bias of the plasma density, which is caused by the first grounding point  302  and the second grounding point  304  as singular points, than in the above-described embodiments and first and second modifications. 
     Further, it is preferable that the coil separation distance d 6  is longer than at least d 1  and longer than the coil separation distance d 4  in the second modification. It is more preferable that the coil separation distance d 6  is longer than d 4  and is long enough that ICP is not substantially produced by the high frequency electromagnetic field generated from the second winding section. As a result, it is possible to further reliably suppress the bias of the plasma density caused by the second grounding point  304  as a singular point. 
     In this modification, both the coil separation distance in the first winding section and the coil separation distance in the second winding section of the resonance coil  212  have been described as being longer than the other sections, but the present disclosure is limited thereto. Instead, the coil separation distance of either the first winding section or the second winding section may be set to be longer than that of the other sections. That is, the coil separation distance of the resonance coil  212  in at least one selected from the group of the entire first winding section and the entire second winding section may be set to be longer than d 1  which is the coil separation distance in other sections between the first grounding point  302  and the second grounding point  304  of the resonance coil  212 . 
     Further, in this modification, the configuration in which the coil separation distance in the first winding section is set as in the second modification and the coil separation distance in the second winding section is constant at d 6  has been described, but the present disclosure is not limited thereto. Instead, also for the first winding section, as in the second winding section, the coil separation distance in the entire first winding section may be set to be constant at a distance (for example, d 6 ) longer than d 1 . 
     (Fourth Modification) 
     In a fourth modification, as shown in  FIG. 11 , the coil separation distances in the first winding section and the second winding section are set to be longer than the coli separation distance d 1  at the midpoint of the resonance coil  212 , which is the coil separation distance in the other sections between the first grounding point  302  and the second grounding point  304 , and further, the coil separation distance is set to be gradually shortened from the first winding section and the second winding section toward the midpoint of the resonance coil  212 , so that the coil separation distance is set to be the shortest at the midpoint between the first grounding point  302  and the second grounding point  304 . Further, the coil separation distance may be set to be gradually shortened from either one of the first winding section and the second winding section toward the midpoint of the resonance coil  212 . The coil separation distance in the first winding section and the second winding section can be the same as, for example, the coil separation distance in the third modification. 
     By configuring the resonance coil  212  in this way, it is possible to selectively generate ICP at the midpoint of the resonance coil  212 , which is particularly excellent in the uniformity of plasma density and the generation efficiency of reaction species, and to maximize the coil separation distance at the first grounding point  302  and the second grounding point  304  which are singular points to deteriorate the uniformity of plasma density, thereby further improving the in-plane uniformity of the wafer  200  in plasma processing. Further, a standing wave of voltage is generated in each of a section between the first winding section and the midpoint of the resonance coil  212  and a section between the second winding section and the midpoint of the resonance coil  212 . Plasma (hereinafter referred to as CCP) of a CCP (Capacitively Coupled Plasma) component formed in the vicinity of a section where the amplitude of this standing wave of voltage is large may generate sputtering on the inner wall surface of the process container  203 . However, by configuring the resonance coil  212  so that the coil separation distance in the section where the amplitude of this standing wave of voltage is large as in this modification is longer than d 1 , it is possible to suppress the generation of CCP and also suppress the sputtering due to CCP. 
     Other Embodiments 
     Although various typical embodiments and modifications of the present disclosure have been described above, the present disclosure is not limited to these embodiments and modifications, but may be used in proper combination. 
     For example, in the above embodiments, the example in which the upper end and the lower end of the resonance coil  212  are grounded to be the first grounding point  302  and the second grounding point  304 , respectively, has been described, but without being limited thereto, the grounding point may not be provided at the upper end or the lower end of the resonance coil  212 . That is, the resonance coil  212  may include sections other than the section between the first grounding point  302  and the second grounding point  304 . In this case, it is preferable that at least one selected from the group of the upper end and the lower end belonging to the sections other than the section between the first grounding point  302  and the second grounding point  304  is further grounded. By grounding the end portions belonging to the sections other than the section between the first grounding point  302  and the second grounding point  304  in this way, it is possible to suppress the influence of changes in current and voltage in a section from the first grounding point  302  or the second grounding point  304  up to these end portions on the plasma density distribution, thereby making it easy to control the plasma density distribution. 
     Further, in the above embodiments, the example in which the oxidation process is performed on the substrate surface by using plasma has been described, besides, the present disclosure can also be applied to a nitridation process using a nitrogen-containing gas as the process gas. Further, the present disclosure can be applied not only to the nitridation process and the oxidation process but also to any technique for performing a process to a substrate by using plasma. For example, the present disclosure can be applied to a modification process and a doping process performed by using plasma for a film formed on a substrate surface, a reduction process for an oxide film, an etching process for the film, an ashing process of a resist, and the like. 
     Although the present disclosure has been described in detail with the specific embodiments and modifications, the present disclosure is not limited to such embodiments and modifications, and it is apparent to those skilled in the art that it is possible to take various other embodiments within the scope of the present disclosure. 
     Hereinafter, Examples will be described. 
     Example 1 
     Sample 1 and Sample 2, which are bare wafers (Si substrates), were prepared, and an oxidation process shown below was performed to each of Sample 1 and Sample 2. 
     Sample 1 is one made by forming an oxide film on the bare wafer by performing the oxidation process on the surface of the bare wafer according to the above-described substrate-processing sequence of  FIG. 7  by using the resonance coil  212  shown in  FIGS. 8A and 8B  in the above-described substrate processing apparatus  100 . That is, in Sample 1, high frequency power is supplied to the resonance coil  212 , and an oxygen-containing gas and a hydrogen-containing gas are plasma-excited to perform the oxidation process. The process conditions were set to predetermined conditions within a range of process conditions described in the above-described embodiments. 
     Sample 2 is one made by forming an oxide film on the bare wafer by performing the oxidation process on the surface of the bare wafer according to the above-described substrate-processing sequence of  FIG. 7  by using the resonance coil  412  shown in  FIGS. 3A and 3B  in the above-described substrate processing apparatus  100 . That is, in Sample 2, high frequency power is supplied to the resonance coil  412 , and the same oxidation process as described above is performed. The process conditions were set to predetermined conditions within a range of process conditions described in the above-described embodiments, and were the same process conditions as in Sample 1. 
       FIG. 12  is a diagram showing a comparison in the average film thickness and the in-plane uniformity between the oxide films formed on Sample 1 and Sample 2, respectively. Here, the in-plane uniformity is a numerical value (%) calculated by dividing a difference between the maximum film thickness and the minimum film thickness by the average film thickness. 
     It is confirmed from  FIG. 12  that the oxide film formed on the wafer of Sample 1 is improved in the in-plane uniformity as compared with the oxide film formed on the wafer of Sample 2, although a difference in the average film thickness between the oxide film formed on the wafer of Sample 1 and the oxide film formed on the wafer of Sample 2 is small as about 0.1 nm. That is, it is confirmed that the in-plane uniformity of the wafer is improved by using the resonance coil  212  of the present embodiments. 
     According to the present disclosure in some embodiments, it is possible to improve the in-plane uniformity of substrate processing. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.