Plasma generator

Abstract

A uniform curtain-like plasma is ejected from the slit-shaped plasma ejection port. The plasma generating device 100 of the present invention comprises: the anode plate 1 having on its surface 11 a plurality of ridges 1a and a plurality of grooves 1b extending in the gas flow direction X; a front-side dielectric plate 31 covering the surface 11 of the anode plate 1 with gaps between it and the ridges 1a; a plate-shaped back-side dielectric plate 32 covering the back surface of the anode plate 1; a cathode 2 including at least a front-side cathode plate 21 facing the anode plate 1 across the front-side dielectric plate 31; a process space 4 consisting of the space between the anode plate 1 and the front-side dielectric plate 31; a gas inlet 41 for introducing a process gas into the process space 4; a power source for applying a voltage between the anode plate 1 and the cathode 2; and a slit-shaped plasma outlet 42 formed at the downstream end of the process space 4 for discharging the process gas that has been made into a plasma state by the voltage applied to the process space 4.

Description

[Technical Field]

[0001] The present invention relates to a plasma generator that generates plasma at room temperature and atmospheric pressure, and more particularly to a plasma generator that has irregularities on the electrode surface to promote discharge. [Background technology]

[0002] Conventionally, plasma generating devices have been widely used to irradiate plasma onto resin or metal surfaces to etch the surfaces, for example, to improve their wettability. Such plasma generating devices are configured to apply a high-frequency voltage between electrodes facing each other across a dielectric while flowing a process gas such as argon, thereby turning the process gas into a plasma state (see Patent Documents 1 and 2).

[0003] For example, Patent Document 1 discloses a plasma generator that discharges plasma in a straight line from a discharge port at the tip of a cylindrical torch. The plasma generator in Patent Document 1 is configured such that a cylindrical outer electrode faces a rod-shaped inner electrode provided at the center of the internal space of the torch, with a dielectric sandwiched between them, and the outer electrode is cooled by the flow of process gas coming into contact with the irregularities provided on the outer peripheral surface of the outer electrode.

[0004] When performing high-speed surface treatment on a large area, a plasma treatment apparatus is used in which multiple torches that spray plasma in a straight line are arranged in a row. However, this type of plasma treatment apparatus has the problem of uneven treatment occurring between the areas where the torches pass.

[0005] In contrast to this, Patent Document 2 describes a method in which a pulsed electric field is applied to a process gas introduced between opposing plate-shaped electrodes to generate plasma, and the plasma is discharged in a curtain-like manner from a slit-shaped outlet formed at the edge between the opposing electrodes, thereby processing a large area of ​​the target surface at high speed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-48185 [Patent Document 2] Patent Publication No. 2021-101153 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the plasma processing apparatus of Patent Document 2 has a problem in that the horizontal protrusions on the surface of the plate-shaped electrode to promote discharge disrupt the flow of process gas, preventing the plasma from being uniformly ejected from the slit-shaped outlet. The present invention has been made in view of the above-mentioned problems, and has an object to provide a plasma generating device capable of uniformly discharging plasma from a slit-shaped discharge port. [Means for solving the problem]

[0008] The invention made to solve the above problem is a plasma generation device that generates plasma by applying a high voltage between electrodes while flowing a process gas into a process space provided between the electrodes, comprising: the anode plate having a surface with a plurality of ridges extending along the gas flow direction of a process gas and aligned in a width direction perpendicular to the gas flow direction, and a plurality of recesses respectively provided between the plurality of ridges; a front-side dielectric plate covering the surface of the anode plate with gaps formed between the ridges and the front-side dielectric plate; a cathode including at least a front-side cathode plate facing the anode plate with the front-side dielectric plate interposed therebetween; a process space formed by the space between the anode plate and the front-side dielectric plate; a gas inlet port for introducing a process gas into the process space from the upstream side in the gas flow direction; a power source for applying a voltage between the anode plate and the cathode; and a slit-shaped plasma outlet port formed at the downstream end of the process space in the gas flow direction, for discharging a process gas that has been put into a plasma state by the voltage applied to the process space by the power source.

[0009] In this way, in the plasma generating device of the present invention, a plurality of convex and concave ridges extending in the flow direction (gas flow direction) of the process gas are provided on the surface of the anode, and a gap is provided between the convex ridges and the front-side dielectric, thereby preventing the process gas from being biased in the width direction of the process space and preventing the plasma from being discharged unevenly in the longitudinal direction of the slit-shaped outlet.

[0010] The cathode preferably further includes a rear cathode plate facing the anode plate across the rear dielectric plate, thereby enabling more efficient generation of discharge and more efficient conversion of the process gas into plasma.

[0011] The cathode preferably connects the front cathode plate and the back cathode plate on both sides in the width direction and surrounds the entire periphery of the anode plate, thereby enabling more efficient generation of discharge and conversion of the process gas into plasma.

[0012] It is preferable that a pair of spacers made of resin plate-like members are provided on both sides of the process space in the width direction, the spacers being in contact with the outermost convex stripes of the anode plate in the width direction from the outside in the width direction, thereby preventing the plasma discharged from collecting at both ends of the slit-shaped discharge port.

[0013] It is preferable that the spacer is made of a hard resin, and the front dielectric plate and the back dielectric plate are made of a soft resin that is softer than the spacer, thereby making it possible to shield both ends of the process space in the width direction while ensuring a gap between the anode plate and the front dielectric plate.

[0014] Preferably, the front dielectric plate has an inclined portion at its upstream end in the gas flow direction that inclines so as to move away from the anode plate as it moves upstream, and the gas inlet is a space having a substantially triangular cross section formed between the inclined portion and the anode plate. This allows the process gas to be accelerated by the gas inlet and introduced downstream into the process space, thereby enabling powerful plasma to be ejected from the ejection port.

[0015] In the plasma discharge port, it is preferable that the downstream end of the anode plate in the gas flow direction is hidden upstream of the edges of the front dielectric plate and the back dielectric plate in the gas flow direction, thereby preventing the plasma discharged from the plasma discharge port from going around to the outside of the front dielectric plate or the back dielectric plate and scattering sparks. [Effects of the Invention]

[0016] As described above, according to the plasma generation device of the present invention, it is possible to prevent the plasma from being unevenly discharged from the slit-shaped plasma discharge port. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view of a plasma generation device according to an embodiment of the present invention, viewed from the plasma discharge side. [Figure 2] 2 is a partially transparent perspective view showing the plasma generating device of FIG. 1 with appropriate portions cut away. FIG. [Figure 3] 2 is a perspective view showing a horizontal step surface around an end portion in the width direction of the anode plate of the gas cutting device shown in FIG. 1. FIG. [Figure 4] 4A is an enlarged cross-sectional view of the cross section shown in FIG. 3 as seen from the plasma discharge port side, and FIG. 4B is an enlarged cross-sectional view of the main part, further enlarging the periphery of the process space in FIG. [Figure 5] 2 is a perspective view showing a vertical cross section of the plasma generating device shown in FIG. 1 taken at a position near an end in the width direction. [Figure 6] 2A and 2B are a bottom view and a front view, respectively, of the plasma generating device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described. However, the present invention is not limited to the following embodiment, and appropriate modifications can be made without departing from the spirit of the present invention.

[0019] Fig. 1 shows a plasma generator 100 according to one embodiment of the present invention, and Fig. 2 shows it partially cut away and partially cut away. As shown in Fig. 2, the plasma generator 100 mainly comprises a plate-shaped anode plate 1, a cathode 2 in the shape of a flat rectangular box surrounding the anode plate 1, a dielectric 3 interposed between the anode plate 1 and the cathode 2 and surrounding the anode plate 1, a process space 4 defined by the space between the anode plate 1 and the dielectric 3, a gas inlet 41 for introducing process gas G into the process space 4, a power supply (not shown) for applying a voltage between the anode plate 1 and the cathode 2, a slit-shaped plasma outlet 42 for discharging the process gas G in a plasma state from the process space 4, and a distributor 6 for distributing the process gas G introduced from a gas hose connection port 43 in the width direction Y of the process space 4. The plasma generating device 100 is configured to apply a high-voltage, high-frequency pulse voltage between the anode plate 1 and the cathode 2 to generate plasma from the process gas G flowing within the process space 4 .

[0020] The anode plate 1 is formed by drilling a copper plate, and as shown in Fig. 2, the surface 11 is provided with a number of ridges 1a and a number of grooves 1b, 1b, ... that extend along the gas flow direction X (see the upward arrow in Fig. 2) in which the process gas G flows and are alternately arranged one by one in a width direction Y perpendicular to the gas flow direction X. The ridges 1a and grooves 1b both have rectangular cross sections and are provided over the entire length of the anode plate 1 in the gas flow direction, and the grooves 1b are open at both end edges of the anode plate 1 in the gas flow direction. In this embodiment, the back surface 12 of the anode plate 1 is flat and has no irregularities, as shown in Fig. 4, but the back surface 12 may also be provided with ridges 1a, ... and grooves 1b, ...

[0021] The cathode 2 is made of stainless steel and has a flattened rectangular tube shape. The cathode 2 surrounds the entire periphery of the anode plate 1 with the anode plate 1 inserted inside. In this embodiment, as shown in Figs. 3 and 4 , the cathode 2 is formed by connecting, with screws, a front-side cathode plate 21 facing the front surface 11 of the anode plate 1 with a front-side dielectric plate 31 interposed therebetween, a back-side cathode plate 22 facing the back surface 12 of the anode plate 1 with a back-side dielectric plate 32 interposed therebetween, and a pair of cathode side plates 23, 23 (only one of which is shown in Fig. 4 ) that connect the front-side cathode plate 21 and the back-side cathode plate 22 on both sides in the width direction of the anode plate 1 (the left-right direction in Fig. 4 ).

[0022] The front-side cathode plate 21 of the cathode 2 is made of a plate material having a width spanning the entire width of the cathode 2, and the back-side cathode plate 22 is made of a plate material that is shorter in the width direction than the front-side cathode plate 21 by the thickness of the cathode side plate 23. As shown in Fig. 4 , the cathode side plate 23 has a substantially T-shaped cross section formed by a long plate-shaped side wall portion 23a that forms the side wall of the cathode 2 and a rib-like portion 23b that extends from the side wall portion 23a toward the inside of the cathode 2, and is configured to engage with both widthwise ends of the back-side cathode plate 22.

[0023] As shown in FIG. 4(a), the dielectric 3 includes a front-side dielectric plate 31 covering the front surface 11 of the anode plate 1, a back-side dielectric plate 32 covering the back surface of the anode plate 1, and a pair of spacers 33, 33 (only one of which is shown in FIG. 4(a)) sandwiched between the front-side dielectric plate 31 and the back-side dielectric plate 32 on both sides in the width direction. The front-side dielectric plate 31 is a rectangular plate spanning substantially the entire inner width of the flat rectangular parallelepiped cathode 2. The back-side dielectric plate 32 is made of a plate-like member with substantially the same length and width as the front-side dielectric plate 31, and has a pair of stepped portions 32a, 32a (only one of which is shown in FIG. 4(a)) at both widthwise ends that are stepped from the center portion in the width direction toward the front side by the thickness of the rib-shaped portion 23b of the cathode side plate 23.

[0024] The spacer 33 has a rectangular thin plate shape and is sandwiched between the front dielectric plate 31 and the step portion 32a of the back dielectric plate 32 so that both end edges in the width direction Y abut against the side wall portion 23a of the cathode side plate 23 and the outermost convex strip 1aA in the width direction Y of the anode plate 1 from the outside in the width direction Y. According to experiments by the inventors, if there is a gap between the outermost ridge 1aA and the spacer 33 through which the process gas can flow, plasma flows back into this gap against the flow of the process gas G at the plasma inlet. This causes a short circuit due to the conductivity of the plasma gas at the short distance between the anode plate 1 and the cathode 2, making it impossible to discharge plasma uniformly in the longitudinal direction of the plasma outlet 42. Furthermore, if the anode plate 1 is not provided with irregularities, plasma will gather at both ends in the longitudinal direction, making it impossible to discharge plasma uniformly in the longitudinal direction of the plasma outlet 42. However, by providing irregularities on the anode plate 1 and abutting the spacer 33 against the outermost ridge 1aA from the outside to eliminate the gap between the ridge 1aA and the spacer 33, and by providing irregularities on the anode plate 1, it is possible to discharge plasma uniformly in the longitudinal direction of the plasma outlet 42.

[0025] The spacer 33 is made of a hard resin such as polycarbonate, and the front dielectric plate 31 and the back dielectric plate 32 are made of a soft resin such as silicone rubber that is softer than the spacer 33. This ensures a sufficient distance between the anode plate 1 and the front dielectric plate 31, while also bringing the spacer 33 into close contact with the front dielectric plate 31 and the back dielectric plate 32, thereby providing sufficient shielding from the process gas.

[0026] The process space 4 is a flat, plate-like space having a generally comb-like cross section perpendicular to the gas flow direction X, formed by the surface 11 of the anode plate 1 and the inner surface of the front dielectric plate 31. A gas inlet 41 for introducing a process gas such as argon into the process space 4 is provided on the upstream side (lower side in FIG. 3 ) of the process space 4 in the gas flow direction X, and a slit-shaped plasma outlet 42 is provided on the downstream side.

[0027] The power supply (not shown) is preferably one that can apply a high-frequency pulsed electric field to the process space 4, but this can be changed as appropriate depending on the type of process gas, etc., and may be, for example, a high-frequency AC power supply.

[0028] As shown in FIG. 3 , the distributor 6 is a box made of a hard resin such as polyvinyl chloride, and is disposed on the upstream side (lower side in FIG. 3 ) of the gas flow direction X so as to cover the upstream opening of the cathode 2. The distributor 6 is formed into a flattened rectangular box shape with an opening toward the downstream side of the gas flow direction X by screwing together a front member 61 that forms the front surface of the distributor 6 and a rear member 62 that forms the back surface 6a, both left and right surfaces 6b, 6b, and bottom surface 6c. The opening of the distributor 6 is closed with the cathode 2 and the dielectric 3, forming a roughly rectangular parallelepiped gas distribution chamber 63 inside. Process gas G is introduced into the gas distribution chamber 63 through six gas hose connection ports 43, 43, ..., each consisting of a hose joint penetrating the back surface 6a. The upstream ends of the anode plate 1 and the front dielectric plate 31 in the gas flow direction X extend into the gas distribution chamber 63. This end of the front dielectric plate 31 has an inclined portion 31a that slopes away from the anode plate 1 as it moves upstream, and a wedge-shaped gas inlet 41 with an approximately triangular cross section is formed between the inclined portion 31a and the anode plate 1.

[0029] At the plasma outlet 42, the downstream end 1c of the anode plate 1 in the gas flow direction X (upper side in FIG. 2) is hidden upstream of the downstream edge 3b of the dielectric 3 in the gas flow direction X. This prevents the plasma emitted from the plasma outlet 42 from being attracted to the cathode 2 and spreading. The edge 3a of the dielectric 3 is made up of the edge 31b of the front dielectric plate 31, the edge 32b of the back dielectric plate 32, and the edge 33b of the spacer 33.

[0030] Furthermore, the downstream edge 2a of the cathode 2 in the gas flow direction X is located upstream of the edge 3b of the dielectric 3 in the gas flow direction X. In other words, the edge 3a of the dielectric 3 protrudes from the inside of the edge 2a of the rectangular cathode 2 to the outside of the plasma discharge port (upper side in FIG. 2). This makes it possible to prevent discharge from bypassing the downstream edge 3a of the dielectric 3 and occurring between the anode plate 1 and the cathode 2.

[0031] (How to use the plasma generator 100 and the functions and effects of each part) When using the plasma generator 100 to irradiate plasma onto the surface of a resin or the like to perform surface treatment such as improving wettability, first, a process gas G such as argon gas is supplied at an appropriate pressure higher than atmospheric pressure from the gas hose connection port 43 into the gas distribution chamber 63 inside the distributor 6. The process gas G supplied to the gas distribution chamber 63 is introduced into the process space 4 between the anode plate 1 and the front dielectric plate 31 from the gas inlet 41. At this time, since the gas inlet 41 becomes narrower downstream, the process gas G is accelerated and introduced into the process space 4.

[0032] In this state, a high frequency pulse electric field is applied between the anode plate 1 and the cathode 2 by a power supply (not shown), and plasma is generated from the process gas G. The generated plasma is discharged from the plasma discharge port 42. The discharged plasma is irradiated onto the surface to be treated, thereby performing a process such as etching.

[0033] At this time, since the plasma generator 100 has a slit-shaped plasma outlet 42, the plasma can be discharged in a curtain shape. Furthermore, the plasma generating device 100 has a large number of ridges 1a, 1a, ... and a large number of recesses 1b, 1b, ... on the surface of the anode plate 1, and a gap 4a is provided between the ridges 1a, 1a, ... and the front dielectric plate 31, so that plasma can be emitted uniformly over the entire length of the plasma outlet 42.

[0034] Furthermore, the cathode 2 is arranged to surround the entire periphery of the anode plate 1 with the dielectric 3 surrounding the entire periphery of the anode plate 1 in between, so that discharge occurs evenly throughout the entire process space, and plasma can be generated throughout the entire process space 4.

[0035] Furthermore, since the spacer 33 is formed from a hard resin and the front dielectric plate 31 and the back dielectric plate 32 are formed from a soft resin that is softer than the spacer 33, gas leakage from both ends in the width direction of the process space 4 can be suppressed while maintaining the gap 4a between the anode plate 1 and the front dielectric plate 31.

[0036] Furthermore, at the plasma outlet 42, the dielectric 3 is made to protrude further than the anode plate 1 and the cathode 2, which prevents the discharged plasma from spreading and from bypassing the edge 3a of the dielectric 3 and causing a discharge between the anode plate 1 and the cathode 2.

[0037] As described above, the plasma generator of the present invention is not limited to the above-described embodiment. For example, protrusions and recesses may also be provided on the rear surface of the anode plate. The cathode is not limited to one that surrounds the entire periphery of the anode, and may be provided only on the front surface of the anode plate, or two anode plates that are not laterally connected may be provided on the front and back sides. Two or all of the spacer, front dielectric, and back dielectric may be provided integrally, or all may be made of the same material, or may be made of a dielectric other than resin. The dielectric at the plasma outlet does not need to protrude beyond the edge of the anode or cathode. [Explanation of symbols]

[0038] 100 Plasma Generator 1 Anode plate 1a Convex stripe 1aA Outermost ridge 1b groove 11 Surface 2 cathode 3 Dielectrics 31 Front dielectric plate 31a Slope 32 Back dielectric plate 33 Spacer 4 Process Space 4a Gap 4b Gas inlet 41 Gas inlet 42 Plasma outlet X Gas flow direction Y: Width direction perpendicular to the gas flow direction G Process gas

Claims

1. 1. A plasma generating apparatus that generates plasma by applying a high voltage between electrodes while flowing a process gas into a process space provided between the electrodes, comprising: a plate-like anode plate having a surface including a plurality of ridges extending along a gas flow direction of a process gas and aligned in a width direction perpendicular to the gas flow direction, and a plurality of recesses respectively provided between the plurality of ridges; a front dielectric plate covering the front surface of the anode plate with a gap between the protrusion and the front dielectric plate; and a plate-shaped back dielectric plate covering the back surface of the anode plate. a cathode including at least a front cathode plate facing the anode plate with the front dielectric plate interposed therebetween; a process space defined by the space between the anode plate and the front dielectric plate; a gas inlet port for introducing a process gas into the process space from an upstream side in the gas flow direction; a power source that applies a voltage between the anode plate and the cathode; a slit-shaped plasma outlet formed at a downstream end of the processing space in the gas flow direction, for discharging a process gas that has been made into a plasma state by a voltage applied to the processing space by the power source; A plasma generating device comprising:

2. 2. The plasma generating device according to claim 1, wherein the cathode further comprises a rear cathode plate facing the anode plate with the rear dielectric plate interposed therebetween.

3. 3. The plasma generating device according to claim 2, wherein the cathode connects the front cathode plate and the rear cathode plate on both sides in the width direction and surrounds the entire periphery of the anode plate.

4. spacers each made of a pair of resin plate-like members sandwiched between the front dielectric plate and the rear dielectric plate on both sides of the processing space in the width direction, 3. The plasma generator according to claim 1, wherein the spacer abuts against an outermost ridge in the width direction of the anode plate from outside in the width direction.

5. 5. The plasma generating device according to claim 4, wherein the spacer is made of a hard resin, and the front dielectric plate and the rear dielectric plate are made of a soft resin that is softer than the spacer.

6. 3. The plasma generating device according to claim 1, wherein the front dielectric plate has an inclined portion at its upstream end in the gas flow direction, the inclined portion inclining away from the anode plate as it moves upstream, and the gas inlet is a space having a substantially triangular cross section formed between the inclined portion and the anode plate.

7. 3. The plasma generating device according to claim 1, wherein at the plasma outlet, the downstream end of the anode plate in the gas flow direction is hidden upstream of the edges of the front dielectric plate and the back dielectric plate in the gas flow direction.

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