JP6974678B2 - Plasma processing equipment and plasma processing method - Google Patents

Description

The present invention relates to a plasma processing apparatus and a plasma processing method.

Conventionally, as a plasma processing device, a device that performs plasma processing by arranging a pair of electrodes on the outer surface of the plasma processing container and inside the plasma processing container and radiating the plasma generated between these electrodes to the object to be processed. Patent Document 1) is known. Further, a device (Patent Document 2) is known in which a dielectric is interposed between a central electrode and a peripheral electrode that define a discharge space, and an object to be processed is introduced into the discharge space between the electrodes to perform plasma treatment. Has been done.

Japanese Unexamined Patent Publication No. 2014-21239 Japanese Unexamined Patent Publication No. 2010-029830

However, in a plasma processing apparatus as in Patent Document 1, when an object to be processed is placed in a discharge space where plasma (discharge) is generated and plasma processing is performed, the object to be processed is introduced into the discharge space and the discharge space. Due to the contact with the electrode, impurities discharged from the electrode during plasma treatment were mixed into the object to be treated, and high-purity plasma treatment could not be performed. That is, the electrode at the time of plasma generation releases impurities by being exposed to plasma or being heated by the resistance due to energization or the temperature of plasma. In addition, the electrode is made of a material that easily reacts with the object to be treated or the gas for discharge (gas for plasma treatment), or the gas for discharge contains a gas (reaction gas) that easily reacts with the electrode (hereinafter, simply for discharge). If it is a gas), impurities are likely to be generated because the electrode reacts with the object to be treated or the gas for discharge (reaction gas), and the purity is lowered by mixing these impurities with the object to be treated. Further, the apparatus of Patent Document 2 has a complicated structure, and it has not been possible to provide a small-sized plasma processing apparatus. Further, in such a device, the object to be processed is likely to be unevenly arranged in the discharge space, and the state of the discharge gas (for example, pressure, concentration, flow velocity) in the discharge space tends to be non-uniform. .. Therefore, the plasma generation start voltage (discharge start voltage), which is a voltage required for dielectric breakdown, becomes unstable, and there is a possibility that plasma generation, that is, plasma processing becomes unstable.

An object of the present invention is to provide a plasma processing apparatus and a plasma processing method capable of performing high-purity plasma treatment without mixing impurities in the object to be treated during plasma treatment.

The plasma processing apparatus of the present invention includes a dielectric and extends in the axial direction, and has a plasma processing container having a tubular tube wall that constitutes a discharge space inside, and a strip of the tubular tube wall along the axial direction. It has a pair of strip-shaped electrodes that are formed and are arranged so as to face each other via the discharge space, and a voltage is applied to the pair of strip-shaped electrodes with an object to be treated introduced into the discharge space. The object to be treated is subjected to plasma treatment by generating plasma, and at least one of the pair of strip-shaped electrodes is embedded in the tubular tube wall so as not to be exposed to the discharge space. And.

Both of the pair of strip-shaped electrodes may be embedded in the tubular tube wall so as not to be exposed to the discharge space.

The pair of strip-shaped electrodes may have a symmetrical shape about an axis of symmetry passing through the central axis of the tubular tube wall.

The pair of strip-shaped electrodes may be bent with a curvature corresponding to the curvature of the tubular tube wall.

The pair of strip-shaped electrodes has a knife edge shape in which the thickness of the central portion is the thickest along the circumferential direction of the tubular tube wall and the thickness is gradually reduced toward both ends to become thinner. good.

The pair of band-shaped electrodes sucks air between the small-diameter tube and the large-diameter tube in a state where the pair of band-shaped electrodes are inserted between the small-diameter tube and the large-diameter tube forming the tubular tube wall. The small-diameter tube and the large-diameter tube may be heat-welded and integrated to be embedded in the tubular tube wall.

The plasma processing method of the present invention is a plasma processing method using any of the above-mentioned plasma processing devices, and includes a step of introducing the object to be processed from an opening into the plasma processing container, and the opening. By supplying a discharge gas from the same opening or different openings and applying a voltage to the pair of band-shaped electrodes, the plasma is generated in the plasma processing container, and the object to be processed is plasma. It is characterized by having a step of processing, a step of stopping application of a voltage to the pair of strip-shaped electrodes, and a step of taking out the object to be processed from the same opening as the opening or a different opening. ..

In the present invention, in a plasma processing apparatus that performs plasma processing on an object to be processed in a plasma processing container, impurities may be generated due to plasma processing by preventing the electrodes from being exposed in the discharge space where plasma processing is performed. Plasma treatment can be performed without impurities being mixed in the object to be treated. Further, by making the electric field strength of the discharge space non-uniform along the circumferential direction of the plasma processing container, it is possible to have a portion where the electric field strength is locally high in the discharge space and generate plasma (discharge) even at a low voltage. can. Therefore, the object to be processed can be reliably plasma-treated.

It is a vertical sectional view which shows the 1st Embodiment of the atmospheric pressure plasma processing apparatus by this invention. FIG. 3 is a cross-sectional view taken along the line II-II of FIG. It is sectional drawing corresponding to FIG. 2 which shows the modification of 1st Embodiment of this invention. It is a vertical sectional view which shows the 2nd Embodiment of the atmospheric pressure plasma processing apparatus by this invention. It is sectional drawing which follows the VV line of FIG. It is sectional drawing corresponding to FIG. 5 which shows the modification of the 2nd Embodiment of this invention.

Hereinafter, embodiments of the atmospheric pressure plasma processing apparatus 100 according to the present invention will be described with reference to the drawings. 1 and 2 show a first embodiment of the atmospheric pressure plasma processing apparatus according to the present invention. As shown in FIGS. 1 and 2, the atmospheric pressure plasma processing apparatus 100 includes a plasma processing container 10 (discharge container). The plasma processing container 10 is made of a dielectric (for example, quartz), and is formed in a cylindrical shape having a perfect circular cross section in the illustrated example. An opening 11 is formed in the radial direction of the plasma processing container 10 at one end in the axial direction of the plasma processing container 10, and an opening 12 is formed in the axial direction of the plasma processing container 10 at the other end. Has been done. The opening 11 is formed in the tube wall 10a of the plasma processing container 10 and communicates with the connecting pipe 11a extending in the radial direction of the plasma processing container 10. One end of the pipe wall 10a is closed by the end wall 10b integral with the pipe wall 10a.

On the other hand, inside the plasma processing container 10, an inner electrode 13a, which is one of the pair of electrodes along the axis of the plasma processing container 10, and an inner tube (inner dielectric) in which the inner electrode 13a is embedded (covered). Body) 13b and 13b are arranged. The inner tube 13b in which the inner electrode 13a is embedded is composed of a dielectric (for example, quartz), and is formed by melt-softening (heat welding) with the inner electrode 13a inserted in the tubular dielectric. .. Further, the inner tube 13b is integrated with the plasma processing container 10 by heat welding (heat molding) at the end wall 10b on the opening 11 side of the plasma processing container 10 to form a part of the plasma processing container 10. .. The tubular space between the inner tube (inner dielectric) 13b and the plasma processing container 10 (tube wall 10a and outer dielectric) constitutes the discharge space (plasma processing space) 14. The tube wall 10a may be an outer dielectric.

In the illustrated embodiment, the inner electrode 13a has a strip shape (foil shape, plate shape) having a uniform cross section in the longitudinal direction (axial direction of the plasma processing container 10, flow direction of the discharge gas in the container) as shown in FIG. ), The thickness of the central portion 13a1 in the width direction is thicker than the thickness of both edge portions 13a2, and the thickness is sharpened toward both edge portions 13a2 (both ends along the width direction). Its thickness is thinner than that of the central portion 13a1, and both edge portions 13a2 have a tapered and pointed knife edge shape. The radial thickness of the plasma processing container 10 of the inner tube 13b in which the inner electrode 13a is embedded is non-uniform along the circumferential direction, and the width direction of the embedded inner electrode 13a (both edges 13a2 along the width direction). The outer thickness d (in the direction of extension) is the thinnest.

On the other hand, on the outer peripheral surface of the plasma processing container 10 (tube wall 10a), an outer electrode 15 serving as the other electrode of the pair of electrodes is disposed. Although the outer electrode 15 is drawn as a metal film-like (foil-like) electrode in the illustrated embodiment, it may be a metal wire wound spirally. The axial length of the outer electrode 15 and the inner electrode 13a facing each other corresponds to the discharge space 14.

The inner electrode 13a and the outer electrode 15 are a pair of electrodes facing each other via the inner tube 13b, the discharge space 14, and the tube wall 10a of the plasma processing container 10, and are electrically connected to a power supply unit (not shown). .. Further, the inner electrode 13a is a high voltage side electrode and the outer electrode 15 is a ground side electrode, but vice versa.

An example of a procedure for plasma-treating an object to be processed by using the atmospheric pressure plasma processing apparatus 100 having the above configuration will be described.

"Introduction of object S to be processed"
The object to be processed S (schematically shown in FIGS. 1 to 6) is introduced into the discharge space 14 from one of the pair of openings 11 and 12 (for example, the openings 11) of the plasma processing container 10. The object S to be processed may be a gas, a solid, or a liquid.

"Supply of gas for discharge"
Discharge gas is supplied from one of the pair of openings 11 and the opening 12 (for example, the opening 11) along the flow path in the discharge space 14 of the plasma processing container 10, and along the flow path in the discharge space 14. To flow the discharge gas. The discharge gas flowing through the discharge space 14 is discharged from the other opening (for example, the opening 12) of the plasma processing container 10. The discharge gas may be not only a highly reactive gas such as oxygen, but also an inert gas such as helium, argon or nitrogen, or a mixed gas of the highly reactive gas and the inert gas. In this way, the discharge gas may flow in the state where the object S to be processed is arranged in the discharge space 14 in advance, but the object to be processed is installed (mixed) in the discharge space 14 with the discharge gas flowing. Alternatively, it may flow into the discharge space 14 as a discharge gas mixed with the object S to be processed.

"Plasma generation and plasma processing"
When a high voltage required for discharge start (dielectric breakdown) is applied between the inner electrode 13a and the outer electrode 15 by the power supply unit, between the inner electrode 13a and the outer electrode 15 in the discharge space 14 of the plasma processing container 10. Dielectric breakdown from the vicinity of both edge portions 13a2 having high electric field strength is the starting point, and plasma (discharge) is generated in the entire discharge space 14. By this plasma, plasma treatment such as surface modification is performed on the object S to be processed in the discharge space 14. It will be described below that the electric field strength in the vicinity of both edge portions 13a2 is locally high as described above. The thickness of the inner electrode 13a decreases from the central portion 13a1 in the width direction toward both edge portions 13a2, and both edge portions 13a2 have a sharp knife edge shape. Electric field concentration is likely to occur. As a result, the electric field strength of the discharge space 14 (the region where the discharge distance is the shortest between the both edge portions 13a2 and the outer electrode 15) along the width direction of the inner electrode 13a is locally increased.

In addition, in the illustrated embodiment, the thickness of the inner tube 13b covering the inner electrode 13a is non-uniform in the circumferential direction, and the thickness is minimized at both edge portions 13a2 (tip of the knife edge shape) of the inner electrode 13a. ing. Since it is known that the electric field strength becomes higher as the thickness of the dielectric becomes thinner, the plasma (in the discharge space 14) is surely generated in at least one of the two spaces X in the width direction of the inner electrode 13a. Discharge) can be generated.

In other words, from the viewpoint of making the distance between the pair of electrodes non-uniform along the circumferential direction of the plasma processing container (discharge tube), either one of the both edge portions 13a2 of the inner electrode 13a is more than the thickness of the central portion. The width of the inner electrode 13a is made non-uniform along the circumferential direction of the plasma processing container, or the thickness of the dielectric between the pair of electrodes is set to the circumference of the plasma processing container. From the viewpoint of making the inner tube 13b non-uniform along the direction, the inner tube 13b is provided with a thin portion (thin wall portion) so that the thickness (outer diameter) of the inner tube 13b can be increased along the circumferential direction of the plasma processing container. By either of the non-uniformity, the electric discharge strength in the plasma processing container can be locally increased, and the electric discharge strength becomes non-uniform along the circumferential direction of the plasma processing container. By applying at least one of these methods, plasma can be generated even at a relatively low discharge start voltage.

The presence of the object S to be processed in the discharge space 14 affects the discharge start voltage. In particular, if the object S to be processed is unevenly arranged in the discharge space 14, the discharge start voltage becomes unstable. Further, the discharge start voltage becomes unstable due to the non-uniform state of the discharge gas (for example, pressure, concentration, flow velocity) in the discharge space. However, as in the present embodiment, by locally generating a portion having a high electric field strength in the discharge space 14, plasma (discharge) can be generated even at a low voltage, and the object S to be processed is arranged. The object S to be processed can be reliably plasma-treated regardless of the state of the discharge gas or the discharge gas. By providing the thin portion of the inner tube 13b on the outside of both edge portions 13a2 having a knife edge shape, the electric field strength in the plasma processing container can be locally increased by the synergistic effect, and the inside of the discharge space 14 can be increased. Even when the bias of the object S to be processed is large, plasma processing can be reliably performed without increasing the discharge start voltage.

"End of plasma treatment and removal of object to be treated"
The power supply between the inner electrode 13a and the outer electrode 15 and the supply of the discharge gas into the discharge space 14 are stopped, and the plasma processing container is stopped from one opening (for example, the opening 12) of the plasma processing container 10. The plasma-treated object S in 10 is taken out. The object S to be processed may be discharged to the outside of the plasma processing container 10 together with the discharge gas.

In the above plasma processing apparatus, the inner electrode 13a and the outer electrode 15 are covered with the inner tube (inner dielectric) 13b and the plasma processing container 10, and neither of them is exposed to the discharge space 14. Therefore, impurities generated from the electrode member or the like (for example, an impure gas discharged from the electrode or a reaction product between the object to be processed and the electrode) are mixed in the object S to be processed or the discharge gas in the discharge space 14. There is no such thing.

Further, in the above first embodiment, since the inner electrode 13a is embedded in the inner tube 13b, the inner electrode 13a is not damaged during plasma discharge. That is, since the inner electrode 13a in the plasma processing container 10 is covered with the inner tube (dielectric) 13b, the discharge gas (the highly reactive gas contained in the discharge gas) does not come into contact with the inner electrode 13a. , The inner electrode 13a is not deteriorated by the discharge gas. Further, since the inner tube (inner dielectric) 13b covering the inner electrode 13a and the plasma processing container 10 are integrally configured, deterioration of the electrode can be prevented more reliably and impurities can be prevented from being mixed. Further, since both edge portions 13a2 of the band-shaped inner electrode 13a in the width direction have a knife edge shape, no gap is formed between the band-shaped inner electrode 13a and the inner tube 13b. As a result, it is possible to prevent the oxygen (atmosphere) that has entered the gap from reacting (oxidizing) with the inner electrode 13a and deteriorating the inner electrode 13a.

Further, FIG. 3 shows a modified example of the first embodiment, in which the inner electrode 13a'has a circular cross section and the inner tube 13b' has an elliptical (elliptical) cross section, whereby the thickness of the dielectric is increased. Is non-uniform in the circumferential direction. Also in this modification, the thickness of the inner tube 13b'which is a dielectric becomes non-uniform along the circumferential direction of the plasma processing container 10, and the thickness of the inner tube 13b' becomes the thinnest in the discharge space 14. The electric field strength of the space X near the inner electrode 13a'that is in contact with the portion can be locally increased. Since the inner electrode 13a'is embedded in the inner tube 13b', the inner electrode 13a'is not damaged and plasma can be reliably generated for a long period of time. Further, impurities generated from the electrode member or the like (for example, an impure gas discharged from the electrode or a reaction product between the object to be processed and the electrode) become the object S to be processed or the gas for discharge arranged in the discharge space 14. It will not be mixed.

4 and 5 show a second embodiment of the atmospheric pressure plasma processing apparatus according to the present invention. In this second embodiment, the arrangement mode of the pair of electrodes and the arrangement mode of the opening are different from those in the first embodiment. The plasma processing container 20 has a tubular tube wall 20a made of a dielectric (for example, quartz), an end wall 20b that closes one end of the plasma processing container 20, and a tube wall substantially in the center of the end wall 20b. An opening 21 formed coaxially with the pipe wall 20a and an opening 22 formed coaxially with the pipe wall 20a at the other end of the pipe wall 20a are provided. A connecting pipe 21a communicating with the opening 21 is integrally formed on the outer surface of the end wall 20b, and forms a part of the plasma processing container 20. The tubular space in the tube wall 20a constitutes the discharge space (plasma processing space) 24.

In this embodiment, as shown in FIG. 5, the pair of electrodes 23 are band-shaped electrodes formed in a band shape (plate shape) having a uniform cross section along the axial direction of the plasma processing container 10, and the tube wall 20a and the tube wall 20a. It is embedded in the tube wall 20a of the plasma processing container 20 so as to face each other via the discharge space 24. The pair of electrodes 23 have a symmetrical shape about an axis of symmetry passing through the central axis of the plasma processing container 20, and are bent at a curvature corresponding to the curvature of the tube wall 20a of the plasma processing container 20. Along the circumferential direction, the central portion 231 has the thickest thickness, and has a knife edge shape that gradually decreases in thickness toward both edge portions 232 and becomes thinner. The pair of electrodes 23 are electrically connected to the power supply device by a feeding member 23a connected to one end in the longitudinal direction.

As a method of burying the pair of electrodes 23 in the tube wall 20a of the plasma processing container 20 by heat molding, a state in which the pair of electrodes 23 are inserted between the small diameter tube (quartz tube) and the large diameter tube (quartz tube). In the above, a manufacturing method in which air between a small diameter pipe and a large diameter pipe is sucked and the small diameter pipe and the large diameter pipe are heat-welded to be integrated can be applied.

In the above-mentioned atmospheric pressure plasma processing apparatus 100, both edges 232 of the pair of electrodes 23 of the plasma processing container 20 have a sharp knife edge shape, and the discharge space 24 and the cylindrical wall surface (dielectric) of the plasma processing container 20 are formed. They are facing each other across the body). Therefore, in the radial cross section of the plasma processing container 20, the distance between the pair of electrodes 23 and the thickness of the dielectric become non-uniform along the axis of symmetry of the pair of electrodes 23 (radial direction of the plasma processing container). Therefore, the electric field strength in the discharge space 24 becomes locally high in the vicinity of both edge portions 232 of the pair of electrodes 23, and becomes non-uniform along the circumferential direction of the plasma processing container 20.

Therefore, as in the first embodiment, when a high voltage required for discharge start (dielectric breakdown) is applied between the pair of electrodes 23 by the power supply unit, the insulation breakdown in the vicinity of both edge portions 232 in the plasma processing container 20 Plasma is generated in the entire discharge space 24, and plasma treatment is performed on the object S to be processed introduced into the discharge space 24 from one of the pair of openings 21 and 22. At this time, impurities generated from the electrode member or the like (for example, the impure gas released from the electrode or the reaction product between the object to be processed and the electrode) are not mixed in the object S to be processed.

In the present embodiment, the strip-shaped electrode 23 is embedded inside the tube wall 20a of the plasma processing container 20 and is not exposed on the outer surface of the tube wall 20a. Therefore, since creeping discharge does not occur on the outer surface of the tube wall 20a of the plasma processing container 20, plasma generation in the discharge space 24 is not hindered by the creeping discharge, and the electrode 23 to which a high voltage is applied is applied. Can provide a safe plasma processing apparatus that is not exposed to the outer surface of the plasma processing container 20.

FIG. 6 shows a modified example of the second embodiment. In this modification, of the pair of electrodes of the second embodiment, the electrode 23'' is embedded in the tube wall 20a of the plasma processing container 20, and the electrode 23'is arranged along the outer surface of the tube wall 20a. It was set up. The pair of electrodes 23'and 23'' in this modification have a symmetrical shape centered on the axis of symmetry, and the central portion 231', 231'' is the thickest along the circumferential direction. It has a knife edge shape that gradually decreases in thickness toward both edges 232', 232'' in the circumferential direction. Therefore, even in this modification, in the radial cross section of the plasma processing container 20, the distance between the pair of electrodes 23'and 23'' and the thickness of the dielectric are the axes of symmetry of the pair of electrodes 23'and 23''. Since it becomes non-uniform along the radial direction of the plasma processing container 20, the electric field strength between the pair of electrodes 23'and 23'is locally increased near both edges 232'and 232''. It becomes non-uniform along the circumferential direction of the plasma processing container 20. Similar to the first embodiment, when a high voltage required for starting discharge (dielectric breakdown) is applied between the pair of electrodes 23'and 23'' by the power supply unit, both edges 232'in the plasma processing container 20 are applied. Plasma is generated in the entire discharge space 24 starting from the dielectric breakdown in the vicinity of and 232'', and the object S to be processed is plasma-treated. At this time, impurities generated from the electrode member or the like (for example, the impure gas discharged from the electrode, or the object to be processed and the electrode) are introduced into the object S to be processed introduced into the discharge space 24 from one of the openings 21 and 22. (Reactant of) is not mixed. Also in this modification, since one of the electrodes 23'' is embedded inside the tube wall 20a of the plasma processing container 20 and is not exposed on the outer surface of the tube wall 20a, creeping discharge may occur on the outer surface of the tube wall 20a. No. This provides a safe plasma processing apparatus in which plasma generation in the discharge space 24 is not hindered by creeping discharge and the electrode 23'' to which a high voltage is applied is not exposed on the outer surface of the plasma processing container 20. can.

In the above embodiment, one and the other of the pair of openings 11 (21) and 12 (22) formed in the plasma processing container 10 (20) are the supply port and the discharge port of the object S to be processed, or the discharge gas, respectively. The inlet and outlet are used, but these may be provided separately. For example, it may be provided independently for the object S to be processed and for the discharge gas.

10 Plasma processing container (discharge container, discharge tube)
10a Tube wall (outer dielectric)
10b End wall 11 Opening 11a Connecting tube 12 Opening 13a, 13a'Inner electrode (one electrode, band-shaped electrode)
13a1 Central part 13a2 Edge part (both edges)
13b, 13b'Inner tube (inner dielectric)
14 Discharge space (plasma processing space)
15 Outer electrode (the other electrode, band-shaped electrode)
20 Plasma processing container (discharge container, discharge tube)
20a Tube wall 20b End wall 21 Opening 22 Opening 23, 23', 23'' Electrode (strip-shaped electrode)
231 231', 231'' Central part 232, 232', 232'' Edge part (both edges)
24 Discharge space (plasma processing space)
100 atmospheric pressure plasma processing equipment

Claims (7)

A plasma processing container that contains a dielectric and extends in the axial direction and has a cylindrical tube wall that constitutes a discharge space inside.
A pair of strip-shaped electrodes formed on the tubular tube wall in a strip shape along the axial direction and arranged so as to face each other via the discharge space.
Have,
The object to be processed is plasma-treated by applying a voltage to the pair of strip-shaped electrodes to generate plasma with the object to be processed introduced into the discharge space.
At least one of the pair of strip electrodes is embedded in the tubular tube wall so as not to be exposed to the discharge space.
A plasma processing device characterized by this. Both of the pair of strip-shaped electrodes are embedded in the tubular tube wall so as not to be exposed to the discharge space.
The plasma processing apparatus according to claim 1. The pair of strip-shaped electrodes have a symmetrical shape about an axis of symmetry passing through the central axis of the tubular tube wall.
The plasma processing apparatus according to claim 2. The pair of strip electrodes are bent with a curvature corresponding to the curvature of the tubular tube wall.
The plasma processing apparatus according to claim 2 or 3, wherein the plasma processing apparatus is characterized in that. The pair of strip-shaped electrodes have a knife edge shape in which the thickness of the central portion is the thickest and the thickness is gradually reduced toward both ends along the circumferential direction of the tubular tube wall.
The plasma processing apparatus according to any one of claims 2 to 4, wherein the plasma processing apparatus is characterized in that. The pair of band-shaped electrodes sucks air between the small-diameter tube and the large-diameter tube in a state where the pair of band-shaped electrodes are inserted between the small-diameter tube and the large-diameter tube forming the tubular tube wall. The small-diameter tube and the large-diameter tube are heat-welded and integrated to be embedded in the tubular tube wall.
The plasma processing apparatus according to any one of claims 2 to 5. A plasma processing method using the plasma processing apparatus according to any one of claims 1 to 6.
The step of introducing the object to be processed into the plasma processing container from the opening, and
A step of supplying a discharge gas from the same opening as the opening or a different opening,
A step of generating the plasma in the plasma processing container by applying a voltage to the pair of strip-shaped electrodes and plasma-treating the object to be processed.
A step of stopping the application of voltage to the pair of strip electrodes, and
The step of taking out the object to be processed from the same opening as the opening or a different opening,
A plasma processing method characterized by having.

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