CN117894661A - Plasma processing equipment and plasma processing method - Google Patents

Abstract

The invention provides plasma processing equipment and a plasma processing method, comprising a processing chamber containing a cavity, an upper electrode and a substrate support positioned in the processing chamber, wherein the substrate support is used for placing a substrate to be processed, a space between the substrate support and the upper electrode is used for generating plasma, the cavity is provided with a first part of side wall, the first part of side wall comprises a side wall of the cavity, which is higher than the substrate support, the first part of side wall is made of insulating materials, the first part of side wall comprises a first surface and a second surface, the first surface is closer to the inside of the processing chamber than the second surface, the second surface is provided with a side wall electrode, the side wall electrode is coupled with a first impedance adjusting circuit, the side wall electrode can be arranged for adjusting and controlling a flow path of plasma so as to influence the uniformity of a plasma process, and the side wall electrode is arranged on the surface of the first part of side wall, which is not facing the inside of the processing chamber, so that abnormal discharge in the processing chamber is prevented, and the reliability of the plasma processing equipment is improved.

Description

Plasma processing equipment and plasma processing method

Technical Field

The present invention relates to the field of semiconductor devices and their manufacture, and more particularly to a plasma processing apparatus and a plasma processing method.

Background

In the manufacturing process of a semiconductor device, plasma treatment is a process of promoting a reaction using the activity of plasma to realize thin film treatment. In a typical plasma processing process, a process gas (e.g., CF ₄、O₂, etc.) is excited by Radio Frequency (RF) to form a plasma. The plasmas perform physical bombardment and chemical reaction with the surface of the wafer after the electric field (capacitive coupling or inductive coupling) between the upper electrode and the lower electrode acts, so that the surface of the wafer is treated, for example, the deposition of a film layer can be realized through chemical reaction at a low temperature through the activity of the plasmas, or the deposition of the film layer can be realized through the fact that particles are easily adsorbed to the surface at a lower temperature, and the etching of the film layer can be realized through the activity of the plasmas.

The uniformity of process conditions has been very important for semiconductor manufacturing and how to improve the uniformity of process conditions is an important research direction for those skilled in the art.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a plasma processing apparatus and a plasma processing method, which can improve uniformity of process conditions and ensure reliability of the plasma processing apparatus.

In order to achieve the above purpose, the invention has the following technical scheme:

an embodiment of the present invention provides a plasma processing apparatus including:

a processing chamber comprising a cavity;

An upper electrode;

A substrate support in the processing chamber, the substrate support for positioning a substrate to be processed, a space between the substrate support and the upper electrode for generating plasma;

The chamber has a first portion of sidewalls including sidewalls of the chamber that are higher than the substrate support, the first portion of sidewalls being of an insulating material, the first portion of sidewalls including a first surface and a second surface, the first surface being closer to the interior of the processing chamber than the second surface, the second surface being provided with sidewall electrodes, the sidewall electrodes being coupled with a first impedance adjustment circuit.

Optionally, the first part of side wall includes a first layer structure and a second layer structure sequentially arranged from the processing chamber to the outside, a gap is formed between the first layer structure and the second layer structure, and the side wall electrode is located in the gap; the cavity is provided with a second part side wall which is lower than the first part side wall, and the bottom of the second layer structure is connected with the second part side wall.

Optionally, the second surface is a side surface of the first layer structure close to the second layer structure.

Optionally, a bottom of the first portion sidewall is lower than the substrate support.

Optionally, the first impedance adjusting circuit is located outside the processing chamber, and the second layer structure has an opening for providing a connection between the sidewall electrode and the first impedance adjusting circuit, and the opening is sealed by a seal.

Optionally, the second portion side wall has an exhaust passage therein, the exhaust passage being located below the gap.

Optionally, the first impedance adjusting circuit comprises an electronic sensor and an electronic controller connected in series between the sidewall electrode and a first power supply.

Optionally, the first impedance adjusting circuit further comprises at least one of a first inductor connected in series between the sidewall electrode and the first power supply and a second inductor connected in parallel with the electronic controller.

Optionally, the substrate support includes a bias electrode coupled to a second power source and a conditioning electrode coupled to a second impedance conditioning circuit.

Optionally, the upper polar plate is a gas shower head or an inductance coupling coil above the processing chamber.

The embodiment of the invention also provides a plasma processing method which is applied to the plasma processing equipment and comprises the following steps:

Controlling, by the first impedance adjustment circuit, a voltage of the sidewall electrode to be a preset voltage for adjusting a density of plasma in a space between the substrate support and the upper electrode;

and adjusting the position of the side wall electrode.

The embodiment of the invention provides plasma processing equipment and a plasma processing method, wherein the plasma processing equipment comprises a processing chamber containing a cavity, an upper electrode and a substrate support piece positioned in the processing chamber, the substrate support piece is used for placing a substrate to be processed, a space between the substrate support piece and the upper electrode is used for generating plasma, the cavity is provided with a first part side wall, the first part side wall comprises a side wall of the cavity, which is higher than the substrate support piece, the first part side wall is made of insulating materials, the first part side wall comprises a first surface and a second surface, the first surface is closer to the inside of the processing chamber than the second surface, the second surface is provided with a side wall electrode, the side wall electrode is coupled with a first impedance adjusting circuit, that is, a side wall electrode can be arranged on the surface of the first part side wall, which is not oriented to the inside of the processing chamber, so that the side wall electrode can be contacted with the plasma as little as possible, abnormal discharge in the processing chamber is prevented, the reliability of the plasma processing equipment is improved, the number of vacuum sealing rings required by the cavity is reduced, and the cost is reduced.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are needed in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are some embodiments of the invention and that other drawings may be obtained from these drawings without inventive effort for a person skilled in the art.

Fig. 1 and fig. 2 are diagrams showing a plasma processing apparatus for performing a plasma processing process according to an embodiment of the present invention;

Fig. 3 and fig. 4 are schematic diagrams of an adjusting circuit according to an embodiment of the present application;

FIG. 5 is a schematic view of a plasma density distribution according to an embodiment of the present application;

FIG. 6 is a schematic view of another plasma density distribution according to an embodiment of the present application;

FIG. 7 is a schematic view of another plasma density distribution according to an embodiment of the present application;

fig. 8 is a flowchart of a plasma processing method according to an embodiment of the present application.

Detailed Description

In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to the appended drawings.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present invention is not limited to the specific embodiments disclosed below.

In the following detailed description of the embodiments of the present invention, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration only, and in which is shown by way of illustration only, and in which the scope of the invention is not limited for ease of illustration. In addition, the three-dimensional dimensions of length, width and depth should be included in actual fabrication.

For a better understanding of the technical solutions and technical effects of the present invention, specific embodiments will be described in detail below with reference to the accompanying drawings.

In the plasma treatment process, the process gas can form plasmas under the action of radio frequency excitation, and the plasmas perform physical bombardment and chemical reaction with the surface of the wafer after the plasmas are subjected to the action of an electric field between the upper electrode and the lower electrode, so that the surface of the wafer is treated at a low temperature, for example, a required film layer is formed on the surface of the wafer, or the surface of the wafer is cleaned or etched. Referring to fig. 1 and 2, a plasma processing apparatus for performing a plasma processing process according to an embodiment of the present invention includes: a processing chamber comprising a cavity, an upper electrode 140, and a substrate support 120 positioned in the processing chamber.

Wherein in a capacitively coupled plasma (CAPACITIVELY COUPLED PLASMA, CCP) processing apparatus, the upper electrode 140 may be a gas showerhead connected with a gas supply for supplying process gas to the processing chamber. A mounting substrate may be provided above the gas shower head and may be fixed with a top cover of the process chamber such that the upper electrode 140 is fixed at an upper portion of the process chamber. In the inductively coupled plasma (Inductive Coupled Plasma, ICP) processing apparatus, an insulating window may be provided at the top of the reaction chamber, an inductive coupling coil (not shown) is provided above the insulating window, the inductive coupling coil is bonded to a radio frequency power source, and a gas injection port is provided at the side wall or top of the reaction chamber, and these inductive coupling coils may serve as the upper electrode 140.

The substrate support 120 is used to place a substrate to be processed, the space between the substrate support 120 and the upper electrode 140 is used as a processing space for generating the plasma 130, and it is difficult for the current plasma reaction chamber to adjust the plasma density distribution at the center and edge of the substrate to be processed, thereby making the plasma process less uniform at different locations. The chamber has a first portion of sidewall 160, the first portion of sidewall 160 includes a sidewall of the chamber above the substrate support, a sidewall electrode 180 may be disposed at the first portion of sidewall 160, the sidewall electrode 180 is coupled with a first impedance adjusting circuit 190, plasma enters a processing space of the reaction chamber according to an expected flow plan, the plasma has a certain potential while in the processing space, and a voltage difference is provided between the plasma and the sidewall electrode 180, and by setting a current property of the first impedance adjusting circuit 190, a distribution characteristic of the plasma may be adjusted, thereby affecting a process characteristic of the plasma.

If the sidewall electrode 180 is disposed on the inner wall of the processing chamber, the sidewall electrode 180 is in direct contact with the plasma, there may be abnormal discharge in the processing chamber, and the cavity of the current processing chamber is usually made of a metal material, which affects the power-on of the sidewall electrode 180. In this embodiment of the present application, the sidewall of the chamber higher than the substrate support may be used as the first portion sidewall 160, the material of the first portion sidewall 160 is an insulating material, the first portion sidewall 160 includes a first surface and a second surface, the first surface is closer to the inside of the processing chamber than the second surface, and the sidewall electrode 180 may be disposed on the second surface, so that the sidewall electrode 180 is not directly disposed on the inner wall of the processing chamber, contact between the sidewall electrode 180 and plasma is reduced, abnormal discharge in the processing chamber is reduced, and because the material of the first portion sidewall 160 is an insulating material, even if the first portion sidewall 160 exists between the sidewall electrode 180 and plasma, the electric field provided by the sidewall electrode 180 may still act on the plasma, so as to realize regulation of local concentration of the plasma, thereby realizing regulation of uniformity of the plasma process.

The sidewall electrode 180 may be a ring-shaped or ring-like construction and may be a ring-shaped electrode, the sidewall electrode 180 may be a continuous ring around the periphery of the process chamber, or may be discontinuous at selected locations. The sidewall electrode 180 may also be an electrode with perforations, such as a ring or mesh electrode with perforations.

As a possible embodiment, the first portion of the sidewall 160 includes a first layer structure, and referring to fig. 1, the inner sidewall of the first layer structure is used as a first surface, and the outer sidewall is used as a second surface, that is, the sidewall electrode 180 may be disposed on the outer side of the first portion of the sidewall 160, so that the position of the sidewall electrode 180 on the outer sidewall may be adjusted according to practical situations, thereby improving the degree of freedom of adjustment of the uniformity of the plasma process.

As another possible embodiment, the first portion of the sidewall 160 includes a first layer structure 161 and a second layer structure 162 sequentially arranged outward from the processing chamber, as shown with reference to fig. 2, that is, the second layer structure 162 may be disposed at the periphery of the first layer structure 161 and surround the first layer structure 161, a gap 164 may be formed between the first layer structure 161 and the second layer structure 162, and the sidewall electrode 180 may be disposed in the gap 164. The first layer structure 161 and the second layer structure 162 may be connected at the top of the first portion sidewall 160 through the connection part 163 such that the first layer structure 161 and the second layer structure 162 constitute an integrated structure, and the first layer structure 161, the connection part 163 and the second layer structure 162 may be composed of the same material and may be formed through the same process. The cavity has the second part lateral wall 170 of relative first part lateral wall 160 lower, the bottom of second layer structure 162 and the second part lateral wall 170 of cavity connect, constitute complete lateral wall, that is to say, under the circumstances that second layer structure 162 and second part lateral wall 170 constitute the lateral wall of complete processing chamber, can increase first layer structure 161, keep apart the plasma in lateral wall electrode 180 and the processing chamber, under the circumstances that does not influence the regulation and control effect of lateral wall electrode 180 to the plasma, reduce the contact of lateral wall electrode 180 and plasma as far as possible, reduce the abnormal discharge in the processing chamber, the development degree of difficulty is little.

Specifically, the second surface may be a side surface of the first layer structure 161 near the second layer structure 162, or may be a side surface of the second layer structure 162 near the first layer structure 161, where the second surface is a side surface of the first layer structure 161 near the second layer structure 162, and the sidewall electrode 180 is as close to the plasma as possible, so as to improve the regulation efficiency of the sidewall electrode 180. When the first impedance adjusting circuit 190 is located outside the processing chamber, the second layer structure 162 has an opening for providing a connection 191 between the sidewall electrode 180 and the first impedance adjusting circuit 190, and the opening is sealed by the sealing member 165, so that only one sealing member is used for sealing, and the number of the required sealing members is small, which is beneficial to improving the sealing performance of the processing chamber, reducing the risk of vacuum leakage and reducing the cost.

In the embodiment of the present application, the bottom of the first portion of the sidewall 160 may be higher than the substrate support 120, may be flush with the substrate support 120, may be lower than the substrate support 120, and the first portion of the sidewall 160 is used to isolate the plasma from the sidewall electrode 180, so that the more downward the first portion of the sidewall 160 is extended, the more effectively the plasma is blocked, so that the plasma is not contacted with the sidewall electrode 180 as much as possible, i.e., the bottom of the first portion of the sidewall 160 is lower than the substrate support 120, and a better isolation effect can be obtained.

In the embodiment of the present application, the second portion of the sidewall 170 connected to the first portion of the sidewall 160 is located below the first portion of the sidewall 160, and the material may be a conductive material or an insulating material, and the conductive material may be a metal material, for example. In the first part of the side wall 160, there may be an exhaust channel 171, which is located below the gap 164 between the first layer 161 and the second layer 162, the exhaust channel 171 being adapted to exhaust the gas in the process chamber, circulating the gas in the process chamber, the plasma being pumped away by a pumping device connected to the exhaust channel 171 when the gas in the process chamber is exhausted through the exhaust channel 171, further reducing the concentration of the plasma entering the gap 164 between the first layer 161 and the second layer 162.

In an embodiment of the present application, the first impedance adjusting circuit 190 includes the electronic sensor 130 and the electronic controller 134 connected in series between the sidewall electrode 180 and the first power source, and the electronic sensor 130 and the electronic controller 134 may be variable capacitors, and are shown with reference to fig. 3 and 4, which are schematic diagrams of the adjusting circuit provided in the embodiment of the present application. The first impedance adjusting circuit 190 may be an LLC circuit, which may include one or more inductors, e.g., the first impedance adjusting circuit 190 further includes at least one of a first inductor 132B connected in series between the sidewall electrode 180 and the first power supply and a second inductor 132A connected in parallel with the electronic controller, and referring to fig. 4, the first impedance adjusting circuit 190 further includes a first inductor 132B connected in series between the sidewall electrode 180 and the first power supply and a second inductor 132A connected in parallel with the electronic controller. Wherein the first power source may be a ground power source providing zero potential to the first impedance adjusting circuit 190.

The substrate support 120 includes a bias electrode coupled with a second power supply and a conditioning electrode coupled with a second impedance conditioning circuit. The second impedance adjusting circuit may be composed with reference to the first impedance adjusting circuit, and may include an electronic sensor and an electronic controller connected in series between the adjusting electrode and the third power supply, and the electronic sensor and the electronic controller may be variable capacitors. The second impedance adjusting circuit may be an LLC circuit, which may include one or more inductors, e.g. the second impedance adjusting circuit further includes at least one of a third inductor connected in series between the adjusting electrode and the third power supply and a fourth inductor connected in parallel with the electronic controller. The third power supply can be a ground power supply and provides zero potential for the second impedance adjusting circuit. The bias electrode may be coupled to the second power supply via a filter, which may be an impedance matching circuit, and the second power supply may be at least one of a dc power supply, a pulsed dc power supply, a radio frequency power supply, a pulsed radio frequency power supply, and the like.

When the plasma has a certain potential in the processing space, a voltage difference is provided between the plasma and the sidewall electrode 180 and a voltage difference is also provided between the plasma and the adjusting electrode, the distribution characteristics of the plasma can be adjusted by providing the current properties of the first impedance adjusting circuit 190 and the second impedance adjusting circuit. Specifically, the impedance of the first and second impedance adjusting circuits 190 and 190 may be adjusted, and when the impedance of the first impedance adjusting circuit 190 is high, the generated plasma has a minimum surface coverage, and by minimizing the impedance of the first impedance adjusting circuit 190, the surface coverage of the plasma may be grown to a maximum value, thereby effectively covering the entire working area of the substrate support 120. Similarly, there is a similar effect in adjusting the impedance of the second impedance adjusting circuit.

Fig. 5 is a schematic diagram of a plasma density distribution of a plasma chamber without using a first impedance adjusting circuit, wherein the abscissa is a horizontal position in the processing chamber, the ordinate is a plasma density distribution, a dark gray area continuous in an upper area indicates a higher plasma concentration, a dark gray area continuous in a lower right area indicates a lower plasma concentration, and plasma concentrations of other light gray areas are between the two areas, and a ratio of A1 point plasma density to a center B1 point plasma density at 150mm is 110.7%.

Referring to fig. 6, another schematic diagram of plasma density distribution provided in an embodiment of the present application is shown, when the first impedance adjusting circuit 190 is used, the variable capacitance is adjusted to make the impedance of the first impedance adjusting circuit 10 ohms, the plasma density distribution is shown in the dark gray area continuous in the upper area, the plasma density is higher, the plasma density is shown in the dark gray area continuous in the lower right area, the plasma density in other light gray areas is between the two areas, and the ratio of the plasma density at the point A1 to the plasma density at the point B1 is 104.3%.

Referring to fig. 7, a schematic diagram of a plasma density distribution according to another embodiment of the present application is shown, wherein when the first impedance adjusting circuit 190 is used, the variable capacitance is adjusted such that the impedance of the first impedance adjusting circuit is 2 ohms, the plasma density distribution is shown in the dark gray area continuous in the upper area, the plasma density is higher, the plasma density is shown in the dark gray area continuous in the lower right area, the plasma density in the other light gray areas is between the two areas, and the ratio of the plasma density at the point A1 to the plasma density at the point B1 is 102.7%. As can be seen from the above, the first impedance adjusting circuit 190 can make the plasma distribution on the substrate more uniform.

The embodiment of the invention provides plasma processing equipment, which comprises a processing chamber containing a cavity, an upper electrode and a substrate support piece positioned in the processing chamber, wherein the substrate support piece is used for placing a substrate to be processed, a space between the substrate support piece and the upper electrode is used for generating plasma, the cavity is provided with a first part of side wall, the first part of side wall comprises a side wall of the cavity, which is higher than the substrate support piece, the first part of side wall is made of insulating materials, the first part of side wall comprises a first surface and a second surface, the first surface is closer to the inside of the processing chamber than the second surface, the second surface is provided with a side wall electrode, the side wall electrode is coupled with a first impedance adjusting circuit, that is, a side wall electrode can be arranged on the surface of the first part of side wall, which is not oriented to the inside of the processing chamber, so that the side wall electrode can be less contacted with the plasma, abnormal discharge in the processing chamber is prevented, the reliability of the plasma processing equipment is improved, the number of vacuum sealing rings required by the cavity is reduced, and the cost is reduced.

Based on the plasma processing apparatus provided by the embodiment of the present application, the embodiment of the present application further provides a plasma processing method, where the method is applied to the foregoing plasma processing apparatus, and referring to fig. 8, a flowchart of the plasma processing method provided by the embodiment of the present application is shown, and the method may include:

S101, controlling the voltage of the side wall electrode to be a preset voltage by the first impedance adjusting circuit, wherein the preset voltage is used for adjusting and controlling the density of plasma in a space between the substrate support and the upper electrode.

S102, adjusting the positions of the side wall electrodes.

In the embodiment of the application, the preset voltage can be determined for the side wall electrode, and the voltage of the side wall electrode is controlled to be the preset voltage through the first impedance adjusting circuit, so that the voltage difference between the side wall electrode and the plasma can influence the distribution of the plasma, and the process characteristics of the plasma can be improved. The control of the voltage to the sidewall electrode can be achieved by regulating the capacitance value of the variable capacitor in the first impedance adjusting circuit.

In addition, the position of the sidewall electrode may be adjusted, and the adjustment of the position of the sidewall electrode may include upward or downward adjustment, so that the density distribution of the plasma can be adjusted to be more uniform. For example, the sidewall electrode may be moved to a position where the plasma density is low or moved to a position where the plasma density is high according to the actual voltage of the sidewall electrode, so that the plasma density is more uniform.

The adjustment of the voltage of the sidewall electrode may be performed after the position adjustment of the sidewall electrode, may be performed before the position adjustment of the sidewall electrode, or may be performed simultaneously with the position adjustment of the sidewall electrode.

In addition, the regulating voltage can be determined for the regulating electrode, and the voltage of the regulating electrode is controlled to be the regulating voltage through the second impedance regulating circuit, so that the distribution of the plasma is influenced through the voltage difference between the regulating electrode and the plasma, and the process characteristics of the plasma are improved. The control of the voltage of the tuning electrode may be achieved by a regulation of the capacitance of a variable capacitor in the second impedance tuning circuit.

It should be noted that, in the present description, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different manner from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the method disclosed in the embodiment, since it corresponds to the device disclosed in the embodiment, the description is relatively simple, and the relevant points are referred to the device part description.

The foregoing is merely a preferred embodiment of the present invention, and the present invention has been disclosed in the above description of the preferred embodiment, but is not limited thereto. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention or modifications to equivalent embodiments using the methods and technical contents disclosed above, without departing from the scope of the technical solution of the present invention. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.

Claims (11)

1. A plasma processing apparatus, comprising:

a processing chamber comprising a cavity;

An upper electrode;

A substrate support in the processing chamber, the substrate support for positioning a substrate to be processed, a space between the substrate support and the upper electrode for generating plasma;

The chamber has a first portion of sidewalls including sidewalls of the chamber that are higher than the substrate support, the first portion of sidewalls being of an insulating material, the first portion of sidewalls including a first surface and a second surface, the first surface being closer to the interior of the processing chamber than the second surface, the second surface being provided with sidewall electrodes, the sidewall electrodes being coupled with a first impedance adjustment circuit.

2. The apparatus of claim 1, wherein the first portion of the sidewall comprises a first layer structure and a second layer structure arranged in sequence outward from the process chamber, the first layer structure and the second layer structure having a gap therebetween, the sidewall electrode being located in the gap; the cavity is provided with a second part side wall which is lower than the first part side wall, and the bottom of the second layer structure is connected with the second part side wall.

3. The apparatus of claim 2, wherein the second surface is a side surface of the first layer structure proximate to the second layer structure.

4. The apparatus of claim 2, wherein a bottom of the first portion sidewall is lower than the substrate support.

5. The apparatus of claim 2, wherein the first impedance adjusting circuit is located outside the processing chamber, the second layer structure having an opening for providing a connection between the sidewall electrode and the first impedance adjusting circuit, the opening being sealed by a seal.

6. The apparatus of claim 2, wherein the second portion sidewall has an exhaust passage therein, the exhaust passage being located below the gap.

7. The apparatus of any one of claims 1-6, wherein the first impedance adjustment circuit comprises an electronic sensor and an electronic controller connected in series between the sidewall electrode and a first power source.

8. The apparatus of claim 7, wherein the first impedance adjustment circuit further comprises at least one of a first inductor connected in series between the sidewall electrode and the first power source and a second inductor connected in parallel with the electronic controller.

9. The apparatus of any of claims 1-6, wherein the substrate support comprises a bias electrode coupled to a second power source and a conditioning electrode coupled to a second impedance conditioning circuit.

10. The apparatus of any of claims 1-6, wherein the upper plate is a gas showerhead or an inductive coupling coil located above the process chamber.

11. A plasma processing method, characterized by being applied to the plasma processing apparatus according to any one of claims 1 to 10, comprising:

Controlling, by the first impedance adjustment circuit, a voltage of the sidewall electrode to be a preset voltage for adjusting a density of plasma in a space between the substrate support and the upper electrode;

and adjusting the position of the side wall electrode.