JP2020035556A - Plasma processing apparatus - Google Patents

Abstract

SOLUTION: There is provided a plasma processing apparatus 10 that includes a voltage electrode 2 to which a voltage is applied, a ground electrode 3 that is electrically connected to a ground potential, and a workpiece holder 4 that holds the workpiece, and when the voltage is not applied to the voltage electrode, the workpiece is in an electrically floating state in which the potential is independent of the voltage electrode and the ground electrode, such that plasma is generated in at least one of between the voltage electrode and the workpiece and between the ground electrode and the workpiece by applying the voltage to the voltage electrode.EFFECT: A workpiece can be plasma-processed without conducting the workpiece to a ground potential.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plasma processing apparatus.

  2. Description of the Related Art Conventionally, a technique of generating plasma by reducing the pressure inside an airtight container and performing plasma processing on a work disposed in the airtight container has been widely used. However, in recent years, a technique for stably performing plasma discharge under atmospheric pressure has been established, and plasma processing in an open space has been put to practical use. This eliminates the need for a strong closed container that can withstand reduced pressure, and realizes an inexpensive plasma processing apparatus.

  An example of a plasma processing apparatus that performs such an atmospheric pressure plasma process is disclosed in Patent Document 1. In the plasma processing apparatus disclosed in Patent Document 1, a power supply is connected to a cylindrical HOT electrode. The inner surface of the HOT electrode is covered with a dielectric. A continuous linear workpiece is inserted through the HOT electrode, and the outer surface of the workpiece faces the inner surface of the HOT electrode. The workpiece is grounded.

  A voltage is applied to the HOT electrode by a power source, and a discharge is generated in a discharge space between the HOT electrode and the object to be processed, whereby the outer surface of the object to be processed is plasma-processed.

JP 2007-115616 A

  However, conventionally, it has been difficult or undesirable in some cases to conduct the object to be grounded to the ground potential, as in Patent Document 1 described above.

  In view of the above situation, an object of the present invention is to provide a plasma processing apparatus which can perform plasma processing on an object without conducting the object to ground potential.

  An exemplary plasma processing apparatus of the present invention includes a voltage electrode to which a voltage is applied, a ground electrode that is electrically connected to a ground potential, and a workpiece holder that holds a workpiece, and the voltage electrode includes: When no voltage is applied, the object to be processed is in an electrically floating state in which the potential is independent of the voltage electrode and the ground electrode, and the voltage is applied to the voltage electrode, whereby the voltage is applied. Plasma is generated in at least one of between the electrode and the object and between the ground electrode and the object.

  According to the exemplary plasma processing apparatus of the present invention, it is possible to perform plasma processing on an object without conducting the object to ground potential.

FIG. 1 is a longitudinal sectional view schematically showing a plasma processing apparatus according to the first embodiment. FIG. 2 is a top view showing a first arrangement configuration example of electrodes. FIG. 3 is a top view illustrating a second arrangement configuration example of electrodes. FIG. 4 is a top view showing a third arrangement configuration example of the electrodes. FIG. 5 is a longitudinal sectional view schematically showing a plasma processing apparatus according to the second embodiment. FIG. 6 is a longitudinal sectional view schematically showing a plasma processing apparatus according to the third embodiment. FIG. 7 is a sectional view taken along line VII-VII in FIG. FIG. 8 is a top sectional view showing a modification of the configuration shown in FIG. FIG. 9 is an enlarged view schematically showing the vicinity of the processing object in a state where the processing object is set in the plasma processing apparatus according to the first modification. FIG. 10 is an enlarged view schematically showing the vicinity of a processing target in a state where the processing target is set in the plasma processing apparatus according to the second modification. FIG. 11 is an enlarged view schematically showing the vicinity of a processing target in a state where the processing target is set in the plasma processing apparatus according to the third modification.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following, the direction in which the central axis C extends is referred to as “axial direction”, and the X1 side in the axial direction is “upper”, and the X2 side in the axial direction is “lower”. The direction around the central axis is referred to as “circumferential direction”, and the radial direction of the central axis is referred to as “radial direction”.

<First embodiment>
A plasma processing apparatus according to a first embodiment of the present invention will be described. FIG. 1 is a longitudinal sectional view schematically showing a plasma processing apparatus 10 according to the first embodiment.

  A plasma processing apparatus 10 illustrated in FIG. 1 is an apparatus that generates plasma under atmospheric pressure and performs plasma processing on a metal processing target 1 that is a processing target. The plasma processing apparatus 10 includes a voltage electrode 2, a ground electrode 3, a workpiece holder 4, and a high-voltage power supply unit 5.

  The workpiece 1 has an upper column 11 and a lower column 12. The upper column 11 and the lower column 12 both have a columnar shape extending in the axial direction about the central axis C. The upper column 11 is arranged above the lower column 12. The diameter of the cross section perpendicular to the axial direction of the upper column 11 is smaller than the diameter of the cross section perpendicular to the axis of the lower column 12. The upper column 11 and the lower column 12 are made of metal.

  The workpiece holder 4 holds the workpiece 1. The workpiece holder 4 is formed in a cylindrical shape with a bottom extending in the axial direction about the central axis C, and has a concave portion 4A opened upward. The recess 4A is a columnar space extending in the axial direction with the center axis C as the center. The workpiece 1 is held by the workpiece holder 4 because the lower portion of the lower column 12 is accommodated in the recess 4A. The workpiece holder 4 is made of an insulating material.

  The voltage electrode 2 has a metal electrode part 21 and a dielectric 22. With the workpiece 1 held by the workpiece holder 4, the inner wall surface 211 of the metal electrode portion 21 faces the outer peripheral surface of the upper column 11 of the workpiece 1. The dielectric 22 covers the inner wall surface 211. A gap S2 is arranged between the dielectric 22 and the upper column 11.

  As the dielectric 22, a ceramic material such as alumina or zirconia, or a free-cutting ceramic is preferably used. The same applies to a dielectric 32 described later.

  The high-voltage power supply unit 5 applies a high-frequency high voltage to the metal electrode unit 21. That is, a voltage is applied to the voltage electrode 2. The frequency of the voltage applied by the high-voltage power supply unit 5 is, for example, 1 kHz to 100 kHz. The waveform of the voltage applied by the high-voltage power supply unit 5 is desirably a pulse waveform, but may be a sine wave, a rectangular wave, or the like, and may be a known waveform used in atmospheric pressure plasma discharge. The voltage applied by the high-voltage power supply unit 5 is, for example, 5 kVpp to 20 kVpp, and depends on the gap between the voltage electrode 2 and the workpiece 1 and the gap between the ground electrode 3 and the workpiece 1. It is set appropriately.

  The ground electrode 3 has a metal electrode part 31 and a dielectric 32. With the workpiece 1 held by the workpiece holder 4, the inner wall surface 311 of the metal electrode portion 31 faces the outer peripheral surface of the upper column 11 of the workpiece 1. The dielectric 32 covers the inner wall surface 311. A gap S3 is arranged between the dielectric 32 and the upper column 11.

  The metal electrode portion 31 is electrically connected to the ground potential. That is, the ground electrode 3 is electrically connected to the ground potential.

  The workpiece 1 made of metal is held by a workpiece holder 4 made of an insulating material. Therefore, when a high voltage is not applied to the voltage electrode 2 by the high-voltage power supply unit 5, the workpiece 1 has a floating potential. That is, when no voltage is applied to the voltage electrode 2, the object 1 is in an electrically floating state in which the potential is independent of the voltage electrode 2 and the ground electrode 3.

  Thus, by applying a high-frequency high voltage to the voltage electrode 2 from the high-voltage power supply unit 5, a current path is formed through the voltage electrode 2, the upper column 11, and the ground electrode 3, and the gaps S2, S3 , A dielectric barrier discharge occurs, and the processing gas in the gaps S2 and S3 is turned into plasma to generate plasma P. Since the plasma P directly contacts the outer peripheral surface of the upper cylindrical portion 11, the outer peripheral surface of the upper cylindrical portion 11 is subjected to plasma processing.

  If necessary, a desired gas may be externally supplied to the gaps S2 and S3 by a gas supply unit (not shown). For example, in the case of removing residues such as cutting oil adhering to an object to be processed, it is desirable to use a gas in which a small amount of oxygen is added to nitrogen, but the present invention does not limit the type of gas.

  That is, when a voltage is applied to the voltage electrode 2, plasma is generated both between the voltage electrode 2 and the workpiece 1 and between the ground electrode 3 and the workpiece 1.

  As described above, according to the present embodiment, even when it is difficult or undesirable to conduct the object 1 to the ground potential, the voltage electrode 2 and the object , And a current path via the ground electrode 3 to generate plasma P both between the voltage electrode 2 and the workpiece 1 and between the ground electrode 3 and the workpiece 1. . When the generated plasma P comes into direct contact with the processing target 1, the processing target 1 can be subjected to plasma processing.

  Note that, for example, even if the workpiece holder 4 is made of metal and an insulator (not shown) is arranged outside the workpiece holder 4, the workpiece 1 can be floated.

  Even if only one of the dielectric 22 and the dielectric 32 is provided, the dielectric barrier discharge can be performed. Further, in a case where the arc discharge can be suppressed by controlling the waveform of the voltage applied to the voltage electrode 2 by the high voltage power supply unit 5, a configuration without using the dielectrics 22 and 32 is also possible. That is, the dielectric is not essential.

<Arrangement of electrodes in first embodiment>
Next, an example of a specific arrangement of the voltage electrode 2 and the ground electrode 3 in the plasma processing apparatus 10 according to the first embodiment will be described. In the following, for convenience of description of each configuration example, reference numerals such as “A” are added to reference numerals of the voltage electrode 2 and the ground electrode 3.

  FIG. 2 is a top view showing a first arrangement configuration example of electrodes. In the configuration of FIG. 2, the voltage electrode 2A and the ground electrode 3A are arranged on the workpiece 1 held in the workpiece holder 4. The voltage electrode 2A has a metal electrode part 21A and a dielectric 22A. The ground electrode 3A has a metal electrode part 31A and a dielectric 32A.

  The inner wall surface 211A of the metal electrode portion 21A extends planarly in a tangential direction at one intersection point PI1 between the diameter D1 extending in the radial direction through the central axis C and the outer peripheral surface of the upper column portion 11. The dielectric 22A covers the inner wall surface 211A, extends parallel to the inner wall surface 211A, and is formed in a flat plate shape. Therefore, the inner wall surface 221A of the dielectric 22A has a planar shape extending in parallel with the inner wall surface 211A.

  When viewed from above, in the gap S2, the gap between the outer peripheral surface of the upper cylindrical portion 11 and the inner wall surface 221A of the dielectric 22A increases with distance from the intersection PI1 to both sides along the outer peripheral surface of the upper cylindrical portion 11. Therefore, in the gap S2, the plasma P is generated in a predetermined range extending from the intersection PI1 to both sides along the outer peripheral surface of the upper cylindrical portion 11, and no plasma is generated outside the predetermined range.

  The inner wall surface 311A of the metal electrode portion 31A extends planarly in the tangential direction at the other intersection point PI2 between the diameter D1 and the outer peripheral surface of the upper columnar portion 11. The dielectric 32A covers the inner wall surface 311A, extends parallel to the inner wall surface 311A, and is formed in a flat plate shape. Therefore, the inner wall surface 321A of the dielectric 32A has a planar shape extending in parallel with the inner wall surface 311A.

  When viewed from above, in the gap S3, the gap between the outer peripheral surface of the upper cylindrical portion 11 and the inner wall surface 321A of the dielectric 32A increases as the distance from the intersection PI2 to both sides increases along the outer peripheral surface of the upper cylindrical portion 11. Therefore, in the gap S3, the plasma P is generated in a predetermined range extending from the intersection PI2 to both sides along the outer peripheral surface of the upper column portion 11, and no plasma is generated outside the predetermined range.

  The inner wall surface 221A of the dielectric 22A and the inner wall surface 321A of the dielectric 32A face each other via the upper column 11 in the radial direction in which the diameter D1 extends. That is, the voltage electrode 2A and the ground electrode 3A face each other. As a result, the distance between the voltage electrode 2A and the ground electrode 3A can be lengthened, so that discharge between them can be suppressed, and between the voltage electrode 2A and the object 1 or between the voltage electrode 2A and the object 1 Plasma is easily generated between the object 1 and the ground electrode 3A.

  It should be noted that in the configuration of FIG. 2, the length of the voltage electrode 2A in the tangential direction and the length of the ground electrode 3A in the tangential direction are shortened so that the range in which the voltage electrode 2A and the ground electrode 3A are provided is within the predetermined range. Then, plasma can be generated over the entire circumference in the gaps S2 and S3.

  FIG. 3 is a top view illustrating a second arrangement configuration example of electrodes. In the configuration shown in FIG. 3, the voltage electrode 2B and the ground electrode 3B are arranged on the workpiece 1 held by the workpiece holder 4. The voltage electrode 2B has a metal electrode part 21B and a dielectric 22B. The ground electrode 3B has a metal electrode part 31B and a dielectric 32B.

  The inner wall surface 211B of the metal electrode portion 21B has an arc-shaped surface extending from the radially outer position of the intersection point PI1 to both sides in the circumferential direction of the upper columnar portion 11 when viewed from above. The inner wall surface 221B of the dielectric 22B has an arc-shaped surface that extends from the position radially inside the radially outer position of the intersection point PI1 to both circumferential sides of the upper cylindrical portion 11 when viewed from above.

  Thereby, it is possible to suppress a change in the circumferential direction of the gap between the outer peripheral surface of the upper columnar portion 11 and the inner wall surface 221B of the dielectric 22B in the gap S2, and to generate the plasma P all around the gap S2. it can.

  The inner wall surface 311B of the metal electrode portion 31B has an arcuate surface extending from the radially outer position of the intersection point PI2 to both circumferential sides of the upper columnar portion 11 when viewed from above. The inner wall surface 321B of the dielectric 32B has an arc-shaped surface extending from the position radially inward of the radially outer position of the intersection point PI2 to both circumferential sides of the upper column 11 when viewed from above.

  Thereby, it is possible to suppress a change in the circumferential direction of the gap between the outer peripheral surface of the upper cylindrical portion 11 and the inner wall surface 321B of the dielectric 32B in the gap S3, and it is possible to generate the plasma P all around the gap S3. it can.

  Note that one of the inner wall surfaces 221B and 321B may be an arc-shaped surface, and the other may be other than an arc-shaped surface (for example, FIG. 2).

  That is, at least one of the electrode surface (the inner wall surface 221B) of the voltage electrode 2B facing the object 1 and the electrode surface (the inner wall surface 321B) of the ground electrode 3 facing the object 1 It has a shape along the outer peripheral surface.

  Thereby, the region where plasma P is generated on the outer peripheral surface of the workpiece 1 can be increased. Further, since the distance between the workpiece 1 and the electrode surface becomes uniform, the plasma P is easily generated uniformly. In particular, when the voltage electrode 2B and the ground electrode 3B are enlarged in order to expand the generation region of the plasma P, the distance between the two electrodes tends to be short. However, since the voltage electrode 2B and the ground electrode 3B face each other, the distance Can be made as long as possible.

  The shape along the outer peripheral surface of the object 1 is a curved surface. Thereby, the area to be processed in the object to be processed 1 having the curved outer peripheral surface can be increased.

  FIG. 4 is a top view showing a third arrangement configuration example of the electrodes. This configuration example is a modification of the above-described second arrangement configuration example shown in FIG. In the configuration of FIG. 4, as a configuration difference from FIG. 2, the radial direction in which the voltage electrode 2 </ b> A faces the outer peripheral surface of the upper column 11, and the outer peripheral surface of the ground electrode 3 </ b> A and the upper column 11 face each other. The radial direction is orthogonal. Thereby, plasma P can be generated at radial positions orthogonal to each other on the outer peripheral surface of the upper cylindrical portion 11, and a desired portion of the outer peripheral surface can be subjected to plasma processing.

<Second embodiment>
Next, a plasma processing apparatus according to a second embodiment of the present invention will be described. FIG. 5 is a longitudinal sectional view schematically showing a plasma processing apparatus 101 according to the second embodiment.

  The plasma processing apparatus 101 according to the present embodiment includes a rotation mechanism 6 as a configuration difference from the above-described first embodiment (FIG. 1). The rotation mechanism 6 drives the workpiece holder 4 to rotate in the circumferential direction about the center axis C as a rotation axis. The rotation mechanism 6 includes a motor, a speed reducer, a control device, and the like (not shown).

  With the rotation of the workpiece holder 4, the workpiece 1 rotates around the rotation axis. At this time, the arrangement configuration of the electrodes is, for example, the configuration shown in FIGS. 2 to 4 described above. As a result, the outer peripheral surface of the upper cylindrical portion 11 of the workpiece 1 sequentially passes through the processing position where the plasma processing is performed by the voltage electrode 2 or the ground electrode 3 in the circumferential direction. Can be processed.

  That is, the plasma processing apparatus 101 moves the workpiece holder 4 relative to the voltage electrode 2 and the ground electrode 3 around the rotation axis whose circumferential direction is the direction along the circle where the voltage electrode 2 and the ground electrode 3 are arranged. And a rotation mechanism 6 for rotating the rotation. This makes it possible to perform plasma processing on the entire surface of the processing target 1 in the circumferential direction. The circle on which the voltage electrode 2 and the ground electrode 3 are arranged is a circle having a radius equal to each line segment having the same distance from the position of the voltage electrode 2 or the position of the ground electrode 3 to the same point. 6 is a circle centered on the center axis C which is also the rotation center.

  Further, the workpiece holder 4 may be fixed, and a rotation mechanism for rotating the voltage electrode 2 and the ground electrode 3 around the central axis C may be provided. However, it is desirable that the rotating mechanism 6 rotates the workpiece holder 4 as in the configuration shown in FIG. Thereby, the configuration of the rotation mechanism can be simplified as compared with the case where the electrode side is rotated.

<Third embodiment>
Next, a plasma processing apparatus according to a third embodiment of the present invention will be described. FIG. 6 is a longitudinal sectional view schematically showing a plasma processing apparatus 102 according to the third embodiment.

  The plasma processing apparatus 102 illustrated in FIG. 6 includes a cover 7 as a configuration difference from the second embodiment (FIG. 5) described above. The cover 7 is a cover member extending in the axial direction and opening downward, and accommodates the voltage electrode 2 and the ground electrode 3 therein. Thereby, the plasma generation region PR1 disposed between the voltage electrode 2 and the upper column 11 and the plasma generation region PR2 disposed between the ground electrode 3 and the upper column 11 are moved upward by the cover 7. Covered from.

  The cover 7 is connected to one end of the flow meter 9 via the connection section 8. The other end of the flow meter 9 is connected to the ejector 110.

  The ejector 110 is a negative pressure generator connected to the cover 7. The ejector 110 generates a high-speed airflow of the air supplied from the air supply unit 111, and generates a negative pressure in a direction orthogonal to the airflow by the Venturi effect. When the negative pressure is generated by the ejector 110, the processing gas G is sucked from the outside air into the gaps S2 and S3, plasma is generated in the plasma generation regions PR1 and PR2, and the gas inside the cover 7 is discharged from the connection portion 8 to the outside. Exhausted to That is, the ejector 110 functions as an exhaust mechanism. Note that, for example, a vacuum pump or a diaphragm pump may be employed instead of the ejector 110.

  That is, the plasma processing apparatus 102 at least covers the cover 7 that covers the plasma generation regions PR1 and PR2 between the voltage electrode 2 and the object 1 and between the ground electrode 3 and the object 1. Prepare. The cover 7 is connected to the exhaust mechanism 110. Thereby, the predetermined gas by the plasma generated in the plasma generation regions PR1 and PR2 can be exhausted by the exhaust mechanism 110.

  The predetermined gas is, for example, ozone or the like. When exhausting ozone, it is desirable to arrange an ozone filter in the middle of the exhaust path.

  In addition, by measuring the flow rate of the gas flow flowing through the exhaust path by the flow meter 9, it can be detected whether the exhaust is performed normally.

  The upper portion of the outer peripheral surface of the upper column portion 11 faces the voltage electrode 2 and the ground electrode 3, and the lower portion of the outer peripheral surface does not face the voltage electrode 2 and the ground electrode 3. Therefore, no discharge is generated below the outer peripheral surface. Then, active species are generated in the plasma generation regions PR1 and PR2 based on the sucked processing gas G. Connection portion 8 is arranged above voltage electrode 2 and ground electrode 3. Therefore, the generated active species moves upward and is exhausted to the outside from the connection portion 8. That is, the movement of the active species to the lower part of the outer peripheral surface is suppressed, and it is possible to prevent the lower part where the plasma processing is not desired to be performed.

  That is, one part in the axial direction of the outer peripheral surface of the columnar workpiece 1 extending in the axial direction faces the voltage electrode 2 and the ground electrode 3, and the part of the outer peripheral surface excluding the one part in the axial direction is , Voltage electrode 2 and ground electrode 3. The connection portion 8 where the exhaust mechanism 110 and the cover 7 are connected is disposed on one axial side of the voltage electrode 2 and the ground electrode 3. Thereby, the active species generated in the plasma generation regions PR1 and PR2 move to the other side in the axial direction on the outer peripheral surface of the workpiece 1, and the other side in the axial direction that is not desired to be plasma-processed is processed. Can be suppressed.

  Here, FIG. 7 is a cross-sectional view taken along line VII-VII of the plasma processing apparatus 102 shown in FIG. In FIG. 7, the arrangement of the electrodes shown in FIG. 3 described above is adopted. As shown in FIG. 7, adjacent members 13A and 13B made of an insulating material are accommodated inside the cover 7. The adjacent members 13A and 13B are arranged adjacent to the voltage electrode 2 and the ground electrode 3 in the circumferential direction. Gaps SA and SB are arranged between the adjacent members 13A and 13B and the outer peripheral surface of the upper column 11, respectively.

  If the adjacent members 13A and 13B are not arranged, the processing gas may easily pass through the non-arranged portions, and the processing gas may not easily pass through the plasma generation regions PR1 and PR2. Therefore, by providing the adjacent members 13A and 13B, the processing gas can easily pass through the plasma generation regions PR1 and PR2.

  That is, the plasma processing apparatus 102 includes adjacent members 13 </ b> A and 13 </ b> B arranged adjacent to the voltage electrode 2 and the ground electrode 3 in a circumferential direction around the axial direction in which the workpiece 1 extends. This makes it easier to flow gas into the plasma generation regions PR1 and PR2, and can improve the efficiency of plasma processing.

  The adjacent members 13A and 13B radially oppose the workpiece 1 via the gaps SA and SB. Thereby, a part of the active species generated in the plasma generation regions PR1 and PR2 can be moved to the gaps SA and SB, and the outer peripheral surface of the workpiece 1 facing the gap can be processed. In particular, when the workpiece 1 can be rotated by the rotating mechanism 6 as in the present embodiment, it becomes easy to move a part of the active species generated in the plasma generation regions PR1 and PR2 to the gaps SA and SB. In a case where the processing target 1 is not rotated, the gaps SA and SB may not be provided.

<Fourth embodiment>
Next, a plasma processing apparatus according to a fourth embodiment of the present invention will be described. FIG. 8 is a modified example of the configuration shown in FIG. 7 described above, and shows a top cross-sectional view of the cover 7 cut at an intermediate position in the axial direction.

  The configuration shown in FIG. 8 is different from the configuration shown in FIG. 7 in that the area of the inner wall surface 221 of the dielectric 22 facing the outer peripheral surface of the upper cylindrical portion 11 and the inner wall surface of the dielectric 32 facing the outer peripheral surface are different. 321 is different.

A capacitor constituted by the voltage electrode 2 and the upper column 11 is denoted by C _H , and a capacitor formed by the upper column 11 and the ground electrode 3 is denoted by C _L. The ratio of the area of the inner wall surface 221 of the capacitor C _{H to} the area of the inner wall surface 321 of the capacitor C _L is set to 1: n (n> 1). Then, the capacitance becomes C _L = nC _H.

Then, the impedance of the capacitor C _H becomes Z _H = 1 / jωC _H
The impedance of the capacitor C _L is Z _L = 1 / njωC _H = 1 / n · Z _H
Becomes

Therefore, the voltage drop at the capacitor C _L is 1/1 / the voltage drop at the capacitor C _H.
n.

For example, assuming that a voltage of 10 kV is applied between the voltage electrode 2 and the ground electrode 3 and n = 3,
10 × the capacitor C _H 3/4 = 7.5kV,
10 × 1/4 = 2.5kV in the capacitor C _L is applied, respectively.
Accordingly, the discharge start voltage if 7 kV, preferentially discharge is performed in the capacitor C _H. Thereby, as shown in FIG. 8, the plasma is preferentially generated in the plasma generation region PR1 on the side of the voltage electrode 2.

  Here, when the area of the inner wall surface 221 is equal to the area of the inner wall surface 321 as shown in FIG. 7, if the discharge starting voltage is 7 kV, a voltage of 14 kV is applied between the voltage electrode 2 and the ground electrode 3. However, in this embodiment, discharge can be performed at 10 kV.

When the size relationship of the area of the inner wall surface is reversed from that in FIG. 8, the capacitor C _L (ground electrode 3 side) can discharge preferentially.

  That is, when a voltage is applied to the voltage electrode 2, plasma is generated between one of the voltage electrode 2 and the workpiece 1 and one between the ground electrode 3 and the workpiece 1.

  In addition, the embodiment shown in FIG. 1 and the like described above is also included. In other words, by applying a voltage to the voltage electrode 2, the space between the voltage electrode 2 and the object 1 and the ground electrode 3 and the object 1 Plasma is generated in at least one of the states. Thus, even when it is difficult or undesirable to conduct the object 1 to the ground potential, the object 1 can be connected to the ground potential without passing through the voltage electrode 2, the object 1, and the ground electrode 3. Thus, the plasma P can be generated in at least one of between the voltage electrode 2 and the workpiece 1 and between the ground electrode 3 and the workpiece 1. When the generated plasma P comes into direct contact with the processing target 1, the processing target 1 can be subjected to plasma processing.

  In the present embodiment, the capacitance generated when the voltage electrode 2 faces the workpiece 1 and the capacitance generated when the ground electrode 3 faces the workpiece 1 are unequal. . Thereby, even if the voltage applied to the voltage electrode 2 is suppressed, it is possible to cause a discharge to occur between the voltage electrode 2 and the object 1 and between the ground electrode 3 and the object 1. Becomes

  Further, the area of the electrode surface (inner wall surface 221) of the voltage electrode 2 facing the workpiece 1 is different from the area of the electrode surface (inner wall surface 321) of the ground electrode 3 facing the workpiece 1. As a result, even if the distance between the processing target 1 and the electrode surface 221 of the voltage electrode 2 is the same as the distance between the processing target 1 and the electrode surface 321 of the ground electrode 3, the capacitance is not reduced. Since it can be made uniform, it is effective when the workpiece 1 is rotated.

  The method of changing the capacitance is an area and a gap. When it is desired to set a large capacitance for the purpose of avoiding discharge, if the gap is narrowed, the electric field strength between the gaps increases when the potential difference between the gaps is the same, so that a situation in which discharge is likely to occur is caused. May not be able to create the intended situation. If the capacitance is increased by increasing the area while maintaining the gap, the capacitance is increased without changing the electric field intensity, so that the impedance can be reduced and the effect of avoiding discharge can be further ensured.

<Other modifications>
Next, other modified embodiments will be described. FIG. 9 is an enlarged view schematically showing the vicinity of the workpiece W1 in a state where the workpiece W1 is set in the plasma processing apparatus according to the first modification. In the configuration shown in FIG. 9, a rod-shaped voltage electrode EH and a rod-shaped ground electrode EL are used for the plate-shaped workpiece W1.

  The voltage electrode EH and the ground electrode EL are arranged to face the same surface WS on one side of the workpiece W1. The workpiece W1 is in an electrically floating state when a high voltage is not applied to the voltage electrode EH. Thus, by applying a high voltage to the voltage electrode EH, a current path is formed through the voltage electrode EH, the workpiece W1, and the ground electrode EL, and the tip of the voltage electrode EH and the same surface of the workpiece W1 are formed. WS, and between the tip of the ground electrode EL and the same surface WS of the workpiece W1, plasma can be processed on the same surface WS.

  FIG. 10 is an enlarged view schematically showing the vicinity of the workpiece W1 in a state where the workpiece W1 is set in the plasma processing apparatus according to the second modification. In the configuration shown in FIG. 10, unlike FIG. 9, the voltage electrode EH is arranged so as to face one surface WS1 of the object W1, and the ground electrode EL is opposed to the surface WS2 on the other side of the object W1. Placed.

  Thus, by applying a high voltage to the voltage electrode EH, a current path is formed through the voltage electrode EH, the workpiece W1, and the ground electrode EL, and between the tip of the voltage electrode EH and the surface WS1, and Plasma is generated between the tip of the ground electrode EL and the surface WS2, and the surfaces WS1 and WS2 can be subjected to plasma processing.

  FIG. 11 is an enlarged view schematically showing the vicinity of the workpiece W2 in a state where the workpiece W2 is set in the plasma processing apparatus according to the third modification. In the configuration shown in FIG. 11, the voltage electrode EH and the ground electrode EL are arranged on the workpiece W2 having a closed cylindrical shape. The workpiece W2 is in an electrically floating state when a high voltage is not applied to the voltage electrode EH.

  The voltage electrode EH and the ground electrode EL are arranged to face an annular end surface WS21 located on the outer peripheral side of the opening end of the workpiece W2. Thus, by applying a high voltage to the voltage electrode EH, a current path is formed through the voltage electrode EH, the workpiece W2, and the ground electrode EL, and between the tip of the voltage electrode EH and the end face WS21, and Plasma is generated between the tip of the ground electrode EL and the end face WS21, and the end face WS21 can be subjected to plasma processing. At this time, if a rotation mechanism for rotating the voltage electrode EH and the ground electrode EL along the end face WS21 is provided, the end face WS21 can be processed over the entire circumference.

  Although the embodiment of the present invention has been described above, the embodiment can be variously modified within the scope of the gist of the present invention.

  INDUSTRIAL APPLICATION This invention can be utilized for the plasma processing of a to-be-processed object.

  DESCRIPTION OF SYMBOLS 1 ... Workpiece, 11 ... Upper column part, 12 ... Lower column part, 2A, 2B ... Voltage electrode, 21, 21A, 21B ... Metal electrode part, 22, 22A , 22B ... dielectric, 211A, 211B ... inner wall surface, 221 221A, 221B ... inner wall surface, 3, 3A, 3B ... ground electrode, 31, 31A, 31B ... metal electrode part , 32, 32A, 32B ... dielectric, 311A, 311B ... inner wall surface, 321, 321A, 321B ... inner wall surface, 4 ... workpiece holder, 5 ... high voltage power supply unit, 6 ... Rotating mechanism, 7 ... Cover, 8 ... Connecting part, 9 ... Flow meter, 110 ... Ejector, 111 ... Air supply part, 13A, 13B ... Adjacent member, 10, 101, 102: plasma processing apparatus, S2, S3: gap, PR , PR2: plasma generation area, SA, SB: gap, P: plasma, G: processing gas, C: central axis, EH: voltage electrode, EL: ground electrode , W1, W2 ... Workpiece

Claims (12)

A voltage electrode to which a voltage is applied;
A ground electrode electrically connected to a ground potential;
A workpiece holder for holding the workpiece,
With
When the voltage is not applied to the voltage electrode, the object is in an electrically floating state in which the potential is independent of the voltage electrode and the ground electrode,
By applying the voltage to the voltage electrode, between the voltage electrode and the object to be processed, plasma is generated in at least one of between the ground electrode and the object to be processed,
Plasma processing equipment.   The plasma processing apparatus according to claim 1, wherein the voltage electrode and the ground electrode face each other.   At least one of an electrode surface of the voltage electrode facing the object to be processed and an electrode surface of the ground electrode facing the object to be processed has a shape along an outer peripheral surface of the object to be processed. The plasma processing apparatus according to claim 2.   The plasma processing apparatus according to claim 3, wherein the shape along the outer peripheral surface of the workpiece is a curved surface.   A rotation mechanism that rotates the workpiece holder around a rotation axis whose circumferential direction is a direction along a circle where the voltage electrode and the ground electrode are arranged, relative to the voltage electrode and the ground electrode; The plasma processing apparatus according to claim 1, further comprising:   The plasma processing apparatus according to claim 5, wherein the rotation mechanism rotates the workpiece holder. At least, further comprising a cover that covers a plasma generation region that is a region between the high voltage electrode and the object, and between the ground electrode and the object,
The plasma processing apparatus according to claim 1, wherein the cover is connected to an exhaust mechanism. A part in one axial direction of the outer peripheral surface of the columnar workpiece to be extended in the axial direction faces the voltage electrode and the ground electrode,
A portion of the outer peripheral surface except a part on one side in the axial direction does not face the voltage electrode and the ground electrode,
8. The plasma processing apparatus according to claim 7, wherein a connection part where the exhaust mechanism and the cover are connected is disposed on one axial side with respect to the voltage electrode and the ground electrode. 9.   The plasma processing apparatus according to claim 7, further comprising: an adjacent member disposed adjacent to the voltage electrode and the ground electrode in a circumferential direction around the axial direction in which the object extends.   The plasma processing apparatus according to claim 9, wherein the adjacent member radially opposes the workpiece through a gap.   2. The capacitance generated when the voltage electrode faces the object to be processed and the capacitance generated when the ground electrode faces the object to be processed are unequal. The plasma processing apparatus according to claim 10.   The plasma processing apparatus according to claim 11, wherein an area of an electrode surface of the voltage electrode facing the object to be processed is different from an area of an electrode surface of the ground electrode facing the object to be processed.

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