Plasma applicator and plasma processing apparatus

Abstract

To provide a plasma applicator and a plasma processing apparatus that provide uniform time average values of electric field strength distribution and can uniformize instantaneous plasma distribution.SOLUTION: A plasma applicator 1 comprises: a wave guide 11 which has a slot and into which a micro wave is to be introduced; a plurality of variable impedance elements 12a that are provided inside the wave guide and are arranged along a tube axis of the wave guide; and a switching element 13a that is electrically connected to each of the variable impedance elements and can electrically switch a magnitude of impedance of each of the plurality of variable impedance elements.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE An embodiment of the present invention relates to a plasma applicator and a plasma processing apparatus. [Background technology]

[0002] Plasma processing is utilized, for example, in the manufacture of microstructures, and various processes such as etching and ashing are performed in the manufacture of semiconductor devices, flat panel displays, photomasks, and the like. Furthermore, in recent years, atmospheric pressure plasma processing, in which plasma processing is performed in an atmosphere at or above atmospheric pressure, and submerged plasma processing, in which plasma processing is performed in liquid, have also been performed.

[0003] In such plasma processing, plasma may be generated using microwaves. High-density plasma can be easily generated using microwaves. For example, a plasma applicator has been proposed that includes a slotted waveguide through which microwaves are introduced.

[0004] In such a plasma applicator, one end of the waveguide is closed. Therefore, a traveling wave propagating inside the waveguide and a reflected wave reflected at the end face of the waveguide overlap each other to form a standing wave inside the waveguide. However, when a standing wave is formed, a part of high electric field intensity and a part of low electric field intensity are generated in the standing wave in the direction along the axis of the waveguide (the direction in which the waveguide extends). When a part of high electric field intensity and a part of low electric field intensity are generated in the microwave radiated outside the slot, the density of the generated plasma becomes non-uniform. If the density of the plasma becomes non-uniform, it becomes difficult to perform uniform processing.

[0005] Therefore, a technique has been proposed in which a reflector that moves in a direction along the axis of the waveguide is provided at the end of the waveguide (see, for example, Patent Document 1). If a reflector that moves in a direction along the axis of the waveguide is provided, the position at which the traveling wave is reflected by the reflector changes, and the phase of the reflected wave can be changed. If the phase of the reflected wave changes, the position of maximum electric field strength of the standing wave can be moved. For example, if the reflector is moved back and forth at a predetermined speed, the position of maximum electric field strength of the standing wave moves back and forth at the same speed. Therefore, even if the standing wave has parts with high electric field strength and parts with low electric field strength, the electric field strength can be made uniform when viewed on a time average. Therefore, the density of the plasma generated by the microwaves irradiated from the waveguide is also made uniform when viewed on a time average.

[0006] However, when processing semiconductor wafers to manufacture electronic devices, if the change in electric field strength is slow, even if the plasma is uniform over time, it is non-uniform when viewed instantaneously. This causes the wafer to be charged up non-uniformly in an instant, and a strong current flows instantaneously between areas with different levels of charge. This results in electrical damage to the electronic devices in the wafer. For this reason, the plasma is required to have not only a high level of uniformity on a time average, but also a high level of uniformity in the instantaneous density distribution. In other words, the plasma must be uniform and have no local fluctuations in plasma density. When the change in electric field strength is slow, the plasma distribution fluctuates according to the electric field strength distribution, and the instantaneous plasma distribution is not uniform. Therefore, in a plasma applicator in which the change in electric field strength is slow, even if the electric field strength distribution can be made uniform on a time average basis, unevenness reflecting standing waves remains in the instantaneous distribution of the electric field strength.

[0007] To eliminate instantaneous unevenness in plasma distribution, the fluctuation of the electric field must be faster than the response time of the plasma, which has a response time of several ms (milliseconds). For this reason, it is difficult to use mechanical methods to move a reflector to a desired position at high speed within a few ms. This leaves unevenness in the instantaneous plasma distribution, which charges the wafer unevenly and causes electrical damage to the device. There was therefore a need to develop technology that could make the instantaneous plasma distribution uniform (suppress the occurrence of unevenness). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2001-203099 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a plasma applicator and a plasma processing apparatus which have a uniform time average value of the electric field strength distribution and can achieve instantaneous uniform plasma distribution. [Means for solving the problem]

[0010] The plasma applicator according to the embodiment includes a waveguide having a slot and into which microwaves are introduced, a plurality of variable impedance elements provided inside the waveguide and aligned along the tube axis of the waveguide, and a switching element electrically connected to each of the plurality of variable impedance elements and capable of electrically switching between high and low impedance of each of the plurality of variable impedance elements. Effect of the Invention

[0011] According to the embodiments of the present invention, a plasma applicator and a plasma processing apparatus are provided that have a uniform time average value of the electric field strength distribution and can instantaneously achieve uniform plasma distribution. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view illustrating a plasma processing apparatus according to an embodiment of the present invention; [Diagram 2] 1 is a schematic plan view illustrating a plasma processing apparatus according to an embodiment of the present invention; [Diagram 3]10A to 10C are schematic cross-sectional views illustrating a waveguide according to a comparative example. [Figure 4] 13A to 13C are schematic cross-sectional views illustrating a waveguide according to another comparative example. [Diagram 5] 13A to 13C are schematic cross-sectional views illustrating a waveguide according to another comparative example. [Figure 6] 11 is a schematic cross-sectional view illustrating a plasma processing apparatus according to another embodiment. FIG. [Figure 7] 11 is a schematic plan view illustrating a plasma processing apparatus according to another embodiment. FIG. [Figure 8] 1A is a schematic cross-sectional view illustrating a plasma processing apparatus according to another embodiment, and FIG. 1B is a schematic plan view illustrating a plasma processing apparatus according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0014] FIG. 1 is a schematic cross-sectional view illustrating a plasma processing apparatus 100 according to this embodiment. FIG. 2 is a schematic plan view illustrating the plasma processing apparatus 100 according to the present embodiment. 1 and 2 is a plasma processing apparatus that performs plasma processing in the atmosphere. That is, the plasma processing apparatus 100 is an example of an atmospheric pressure plasma processing apparatus that performs plasma processing in an atmosphere at atmospheric pressure or higher.

[0015] As shown in FIGS. 1 and 2, a plasma processing apparatus 100 includes, for example, a plasma applicator 1, a power source 2, a microwave generating unit 3, a mounting unit 4, and a controller 5. The plasma applicator 1 includes, for example, a waveguide 11, a reflecting section 12, and a switching section 13.

[0016] Microwaves are introduced into the waveguide 11. For example, the waveguide 11 has a tubular shape extending in one direction. One end of the waveguide 11 is open. The other end of the waveguide 11 is closed. For example, the microwave generating unit 3 described below is connected to the opening of the waveguide 11. The internal space of the waveguide 11 becomes a space through which the microwaves propagate.

[0017] The cross-sectional shape of the waveguide 11 is not particularly limited. The cross-sectional shape of the waveguide 11 can be, for example, a square or a circle. The cross-sectional shape of the waveguide 11 illustrated in FIG. 1 is rectangular. One side surface of the waveguide 11 having a square cross-sectional shape, which is parallel to the tube axis, is a surface (H surface) perpendicular to the electric field direction of the microwave. A surface (E surface) parallel to the tube axis and perpendicular to the H surface is a surface parallel to the electric field direction of the microwave M. In the case of a general waveguide, a surface (end surface) perpendicular to the tube axis is a reflecting surface (short-circuit surface; R surface), but in the case of the plasma applicator 1 according to this embodiment, a reflecting portion 12 provided inside the waveguide 11, which will be described later, functions as the R surface.

[0018] A slot 11a is formed on one of the H faces. The slot 11a penetrates between the outer wall and the inner wall of the waveguide 11. At least one slot 11a can be provided. When one slot 11a is provided, the slot 11a can be provided extending in the direction in which the waveguide 11 extends. When multiple slots 11a are provided, the slots 11a can be arranged side by side in the direction in which the waveguide 11 extends so that the multiple slots 11a form a straight line. In the direction along the axis of the waveguide 11, the slot 11a is provided between the opening of the waveguide 11 and the multiple variable impedance elements 12a. The extending direction (longitudinal direction) of the slot 11a, the extending direction of the waveguide 11, and the direction along the tube axis of the waveguide 11 are all the same direction.

[0019] The waveguide 11 is made of a material that easily reflects microwaves, such as an aluminum alloy.

[0020] In addition, a window 11b covering the slot 11a may be provided on the outer surface of the waveguide 11. The window 11b is plate-shaped and made of a material that transmits microwaves. The window 11b may be made of a dielectric material such as quartz.

[0021] Here, the standing wave formed inside the waveguide 11 will be described. As mentioned above, in the case of a typical waveguide, the surface (end face) perpendicular to the tube axis becomes the reflecting surface (R face). Therefore, the traveling wave that propagates inside the waveguide is reflected at the end face of the waveguide. The reflected wave reflected at the end face of the waveguide propagates inside the waveguide in the opposite direction to the traveling wave.

[0022] FIG. 3 is a schematic cross-sectional view illustrating a waveguide 211 according to a comparative example. Waveguide 211 is a waveguide having a rectangular cross-sectional shape. As shown in Fig. 3, microwaves are introduced into the inside of waveguide 211 from the open end of waveguide 211. The microwaves introduced into the inside of waveguide 211 become a traveling wave toward the end face (R-surface) of waveguide 211. The traveling wave is reflected by the R-surface, and becomes a reflected wave that propagates inside waveguide 211 in the opposite direction to the traveling wave.

[0023] In this case, the traveling wave and the reflected wave have the same wavelength, period (frequency), amplitude, and speed, but travel in opposite directions. Therefore, inside the waveguide 211, the traveling wave and the reflected wave overlap to form a standing wave. When the standing wave is formed, the distribution 210 of the electric field intensity is as shown in FIG. 3. Therefore, in the direction along the tube axis of the waveguide 211, a part 210a with high electric field intensity and a part 210b with low electric field intensity are generated. In addition, since the standing wave is a wave motion that does not progress but appears to be stationary and vibrating, the part 210a with high electric field intensity and the part 210b with low electric field intensity remain in the same position.

[0024] When the portion 210a with high electric field intensity and the portion 210b with low electric field intensity remain in the same position, the energy of the microwave radiated from the slot 211a becomes uneven, as shown in Fig. 3. When the energy of the microwave becomes uneven, the density of the plasma generated outside the slot 211a becomes uneven. When the density of the plasma becomes uneven, it becomes difficult to perform uniform processing.

[0025] FIG. 4 is a schematic cross-sectional view illustrating a waveguide 311 according to another comparative example. Waveguide 311 is a waveguide having a rectangular cross-sectional shape. As shown in Fig. 4, microwaves are introduced into the inside of waveguide 311 from the open end of waveguide 311. The microwaves introduced into the inside of waveguide 311 become a traveling wave toward the R-face. The traveling wave is reflected by the R-face and becomes a reflected wave that propagates inside waveguide 311 in the opposite direction to the traveling wave. Therefore, in waveguide 311 as well, the traveling wave and the reflected wave overlap to form a standing wave, similar to the above-mentioned waveguide 211. When a standing wave is formed, the distribution 310 of the electric field intensity becomes as shown in Fig. 4.

[0026] However, in the case of the waveguide 311, a reflector 311b is provided at the end opposite to the opening side of the waveguide 311. The position of the reflector 311b is movable in the direction along the tube axis of the waveguide 311. For example, the reflector 311b can be moved back and forth in the direction along the tube axis of the waveguide 311 using a driving device such as a solenoid or a motor. If the position of the reflector 311b changes in the direction along the tube axis of the waveguide 311, the position where the traveling wave is reflected changes, and therefore the phase of the reflected wave can be changed. If the phase of the reflected wave changes, the maximum electric field strength position of the standing wave can be moved as shown in FIG. 4.

[0027] For example, if the reflector 311b is moved back and forth at a predetermined speed, the maximum electric field strength position of the standing wave moves back and forth at the same speed. Therefore, even if the standing wave has a part with high electric field strength and a part with low electric field strength, the electric field strength can be made uniform on a time average basis. As a result, it is possible to prevent the density of the plasma generated outside the slot 311a from becoming non-uniform.

[0028] FIG. 5 is a schematic cross-sectional view illustrating a waveguide 411 according to another comparative example. Waveguide 411 is a waveguide having a rectangular cross-sectional shape. As shown in Fig. 5, microwaves are introduced into waveguide 411 from an open end of waveguide 411. The microwaves introduced into waveguide 411 become a traveling wave toward the R-face. The traveling wave is reflected by the R-face and becomes a reflected wave that propagates inside waveguide 411 in the opposite direction to the traveling wave. Therefore, in waveguide 411, similar to waveguide 211 described above, the traveling wave and the reflected wave overlap to form a standing wave. When a standing wave is formed, the distribution 410 of the electric field intensity becomes as shown in Fig. 5.

[0029] However, in the case of the waveguide 411, a plurality of reflectors 411b are provided near the end of the waveguide 411 on the opposite side to the opening side. The plurality of reflectors 411b are arranged side by side in a direction along the tube axis of the waveguide 411. Each of the plurality of reflectors 411b is movable in a direction perpendicular to the tube axis of the waveguide 411. For example, a driving device such as a solenoid or a motor can be used to insert one of the plurality of reflectors 411b into the waveguide 411 or to pull it out from the waveguide 411. For example, the plurality of reflectors 411b can be inserted into the waveguide 411 in sequence or to pull it out from the waveguide 411 in sequence.

[0030] In this way, the position at which the traveling wave is reflected changes in the direction along the tube axis of waveguide 411, and the phase of the reflected wave can be changed. If the phase of the reflected wave changes, the position of maximum electric field strength of the standing wave can be moved, as shown in Fig. 5. Therefore, even if the standing wave has parts with high electric field strength and parts with low electric field strength, the electric field strength can be made uniform on a time average basis. As a result, it is possible to prevent the density of the plasma generated outside the slot 411a from becoming non-uniform.

[0031] Here, if the moving speed of the reflectors 311b and 411b described above increases, the moving speed of the maximum electric field strength position of the standing wave also increases, and therefore the fluctuation speed of the electric field strength distribution also increases. In this case, if the fluctuation in the electric field strength distribution becomes faster than the response speed of the plasma, the momentary non-uniformity of the plasma density distribution can also be suppressed.

[0032] However, in the case of the configuration described with reference to FIGS. 4 and 5, since the reflectors 311b, 411b are moved mechanically, there is a limit to how fast the reflectors 311b, 411b can be moved.

[0033] Therefore, as shown in FIG. 1, plasma applicator 1 according to the present embodiment is provided with reflecting section 12 and switching section 13. As shown in FIG. Each of the multiple reflecting portions 12 includes a variable impedance element 12a, a conductor 12b, and a conductor 12c. A plurality of variable impedance elements 12a are provided inside waveguide 11 near the end opposite to the opening side of waveguide 11. In the direction along the tube axis of waveguide 11, the plurality of variable impedance elements 12a are provided side by side.

[0034] As described later, when switching element 13a is turned on, reflecting portion 12 becomes a reflecting surface (R surface). Therefore, in consideration of controlling the phase of the reflected wave, it is preferable to arrange multiple variable impedance elements 12a at equal intervals.

[0035] Furthermore, in order to allow the comb of the standing wave to be moved at equal intervals in m steps, (m-1) or more variable impedance elements 12a are disposed at intervals L in the direction along the tube axis of waveguide 11, and when the wavelength of the microwave in waveguide 11 is λ, it is preferable that interval L satisfies the following formula: L = (n + 1 / m) × (λ / 2) Note that n is 0, 1, or 2. m is an integer of 2 or greater. By setting the interval L in this way, it is possible to improve the controllability of the phase of the reflected wave.

[0036] The variable impedance element 12a may be, for example, a PIN diode (p-intrinsic-n diode). When a positive voltage of a certain level or more is applied to the anode terminal of the PIN diode, a direct current flows through the PIN diode, and the impedance of the PIN diode to microwaves becomes small. When no voltage is applied, almost no direct current flows through the PIN diode, and the impedance of the PIN diode is high. For this reason, the PIN diode is preferable as a variable impedance element. Since the PIN diode has a distinguished anode and cathode, the following description will use expressions that distinguish between them. However, the variable impedance element is not necessarily limited to an element that has a distinguished anode and cathode. There is no particular limitation on the position of variable impedance element 12a in a cross section perpendicular to the tube axis of waveguide 11. However, in consideration of controllability of the phase of the reflected wave, it is preferable to provide variable impedance element 12a at the position of the tube axis of waveguide 11 (the center of the cross section) or in the vicinity of the tube axis.

[0037] One end of the conductor 12b is electrically connected to the anode side of the variable impedance element 12a. The other end of the conductor 12b is electrically connected to the power source 2 via the switching unit 13 (switching element 13a). The conductor 12b may be, for example, a conductive wire containing a metal such as copper or aluminum.

[0038] One end of the conductor 12c is electrically connected to the cathode side of the variable impedance element 12a. The other end of the conductor 12c is electrically connected to the ground or the negative electrode side of the power supply 2. The conductor 12c illustrated in Fig. 1 is electrically connected to the grounded waveguide 11. The conductor 12c can be, for example, a conductor containing a metal such as copper or aluminum.

[0039] The switching unit 13 is provided outside the waveguide 11. The switching unit 13 has a plurality of switching elements 13a. The switching unit 13 is electrically connected to each of the plurality of variable impedance elements 12a. For example, one switching element 13a is electrically connected to one set of the variable impedance element 12a, the conductor 12b, and the conductor 12c. The switching element 13a may be, for example, a transistor. As will be described later, the switching section 13 can electrically switch between high and low impedances of each of the multiple variable impedance elements 12a.

[0040] The power source 2 is provided outside the waveguide 11. The power source 2 can be, for example, a DC power source. The power source 2 is electrically connected to a plurality of switching elements 13a. For example, the positive electrode of the power source 2 is electrically connected to a plurality of reflecting units 12 (variable impedance elements 12a) via the switching unit 13 (switching element 13a). When the cathode side of the variable impedance element 12a is not grounded, the negative electrode of the power source 2 and the cathode side of the variable impedance element 12a can be electrically connected via a conductor 12c.

[0041] The microwave generating unit 3 is provided outside the waveguide 11. The microwave generating unit 3 can be connected to, for example, the opening side of the waveguide 11. The microwave generating unit 3 introduces microwaves into the waveguide 11. The microwave generating unit 3 can be, for example, a magnetron. The microwave generating unit 3 generates microwaves with a frequency of, for example, 1 GHz to 50 GHz (for example, 2.45 GHz).

[0042] The mounting portion 4 is provided outside the waveguide 11. The workpiece 200 is placed on the upper surface of the mounting portion 4. The upper surface of the mounting portion 4 faces the slot 11a of the waveguide 11. The space between the side of the waveguide 11 where the slot 11a is provided and the upper surface of the mounting portion 4 is the region where plasma P is generated. In addition, the mounting portion 4 can be appropriately provided with a means for holding the workpiece 200. The means for holding the workpiece 200 is, for example, an electrostatic chuck, a vacuum chuck, a mechanical chuck, or the like.

[0043] As shown in FIG. 2, the mounting unit 4 passes below the plasma applicator 1. There are no particular limitations on the workpiece 200 as long as it is a target for plasma processing. The workpiece 200 may be, for example, a semiconductor wafer, a glass substrate, or the like.

[0044] The controller 5 is provided outside the waveguide 11. The controller 5 has, for example, a calculation unit such as a CPU (Central Processing Unit) and a storage unit such as a memory. For example, the controller 5 can be a computer. For example, the calculation unit controls the operation of each element provided in the plasma processing apparatus 100 based on a control program stored in the storage unit.

[0045] Next, the operation of the plasma processing apparatus 100 will be described. The controller 5 controls the microwave generating unit 3 to generate microwaves. The generated microwaves are introduced into the inside of the waveguide 11 from the opening of the waveguide 11. The microwaves introduced into the inside of the waveguide 11 propagate towards the multiple reflecting units 12.

[0046] The controller 5 controls the power supply 2 to apply a voltage to a plurality of variable impedance elements (PIN diodes) 12a via the switching elements 13a. Furthermore, the controller 5 controls the switching unit 13 to change the positions at which the microwaves propagating toward the multiple reflecting units 12 are reflected. For example, the controller 5 controls a plurality of switching elements 13a. The controller 5 sets one of the multiple switching elements 13a to an ON state and sets the remaining switching elements 13a to an OFF state. The controller 5 changes the position at which the microwave is reflected by selecting the switching element 13a to be turned on. The controller 5 switches the multiple switching elements 13a between the ON state and the OFF state, thereby moving the position where the microwave is reflected.

[0047] Next, the switching of the multiple switching elements 13a will be further described. Since a voltage is applied to the multiple switching elements 13a, a current flows through the variable impedance element 12a, the conductor 12b, and the conductor 12c, which are electrically connected to the switching element 13a that is in the ON state. The variable impedance element 12a through which a current flows becomes a conductor, and is therefore able to reflect the incident microwaves.

[0048] On the other hand, no current flows through switching element 13a that is in the OFF state. Therefore, no current flows through variable impedance element 12a, conductor 12b, and conductor 12c that are electrically connected to switching element 13a that is in the OFF state. Variable impedance element 12a, through which no current flows, becomes a nonconductor and can transmit the incident microwaves.

[0049] Therefore, the controller 5 can change the position of the reflection surface (R surface) (the position where the microwave is reflected) by selecting the switching element 13a to be turned on. For example, by sequentially switching the ON and OFF states of the multiple switching elements 13a, it is possible to sequentially switch between conductive and non-conductive properties of the multiple reflection sections 12 arranged in the direction along the tube axis of the waveguide 11. By sequentially switching between conductive and non-conductive properties of the multiple reflection sections 12, it is possible to sequentially change the position of the reflection surface. By sequentially changing the position of the reflection surface, the phase of the reflected wave is sequentially changed, and therefore it is possible to move the maximum electric field strength position 110 of the standing wave, as shown in FIG. 1.

[0050] Therefore, even if the standing wave has parts with high electric field strength and parts with low electric field strength, the electric field strength can be made uniform on a time average basis. Moreover, by switching the ON and OFF states of the multiple switching elements 13a, the position of the reflecting surface can be changed sequentially. Therefore, the moving speed of the reflecting surface can be made faster than when the reflector is moved mechanically as described above. If the moving speed of the reflecting surface is made faster, the moving speed of the maximum electric field strength position 110 of the standing wave will also be made faster. Therefore, the plasma density does not depend on the electric field strength distribution fluctuation, but is determined by the amplitude distribution of the time-averaged electric field strength, and unevenness in the plasma density distribution is suppressed.

[0051] When switching between the ON state and the OFF state of the multiple switching elements 13a, the switching elements 13a can be switched in order along the tube axis of the waveguide 11. Also, the switching elements 13a can be switched at intervals of a predetermined number along the tube axis of the waveguide 11. For example, the switching elements 13a can be switched every other one.

[0052] The microwaves propagating inside the waveguide 11 are radiated to the outside of the waveguide 11 via the slots 11a. The microwaves radiated to the outside of the waveguide 11 excite plasma P near the slots 11a outside the waveguide 11. As described above, the electric field strength of the microwaves radiated to the outside of the waveguide 11 is uniformized on a time average basis, so the density of the generated plasma P is also uniform on a time average basis. Furthermore, by performing the switching sufficiently quickly (faster than the response of the plasma P), fluctuations in the plasma density distribution are suppressed, resulting in uniform plasma P.

[0053] The air contained in the region where the plasma P is generated is excited and activated by the plasma P to generate plasma products such as radicals and ions. When the generated plasma products reach the surface of the workpiece 200, the workpiece 200 is subjected to plasma processing.

[0054] In order to achieve a high processing speed, the distance between the mounting part 4 and the waveguide 11 is shortened. This makes it easier for the plasma P and plasma products to reach the workpiece 200. In addition, it is possible to suppress the plasma products from diffusing to the outside. However, if the distance between the mounting part 4 and the waveguide 11 is shortened when there is an unevenness in the density of the plasma P, processing unevenness is likely to occur.

[0055] As described above, according to the plasma processing apparatus 100 of this embodiment, the moving speed of the maximum electric field strength position 110 of the standing wave can be increased, so that the density of the plasma P can be made uniform. Therefore, even if the distance between the mounting part 4 and the waveguide 11 is shortened, the occurrence of processing unevenness can be suppressed. The distance between the mounting part 4 and the waveguide 11 is preferably several tens of μm or more and several mm or less. In particular, in a pressure atmosphere of several hundred Pa or more, or in the liquid plasma described later, the diffusion of electrons is weakened, and the plasma is concentrated close to the slot 11a. Therefore, it is preferable to bring the mounting part 4 as close to the waveguide 11 as possible.

[0056] FIG. 6 is a schematic cross-sectional view illustrating a plasma processing apparatus 100a according to another embodiment. FIG. 7 is a schematic plan view illustrating a plasma processing apparatus 100a according to another embodiment. As shown in FIGS. 6 and 7, the plasma processing apparatus 100a includes, for example, a plasma applicator 1, a power supply 2, a microwave generating unit 3, a mounting unit 4, a controller 5, a chamber 6, and a gas supply unit .

[0057] The chamber 6 may be, for example, a container having an airtight structure. A mounting unit 4 may be provided on the bottom surface inside the chamber 6. The mounting unit 4 is rotated by a driving unit 4a. A plasma applicator 1 may be provided on the ceiling surface outside the chamber 6. The chamber 6 may be formed from, for example, a metal such as an aluminum alloy.

[0058] 7, the length of the slot 11a of the plasma applicator 1 of the plasma processing apparatus 100a in the direction parallel to the tube axis of the waveguide 11 (hereinafter simply referred to as the length of the slot 11a) is shorter than that of the plasma applicator 1 of the plasma processing apparatus 100. When the workpiece 200 is polygonal, the length of the slot 11a is equal to or shorter than the length of a line connecting the center of rotation of the workpiece 200 and a corner of the outer periphery. When the workpiece 200 is circular, the length of the slot 11a is equal to or shorter than the length of a line connecting the center of rotation of the workpiece 200 and a point on the circumference.

[0059] Moreover, the rotation speed increases from the rotation center to the outer periphery of the workpiece 200. Therefore, it is preferable that the slot 11a has a shape that increases in width from the rotation center to the outer periphery of the workpiece 200. For example, it is preferable that the slot 11a has a sector shape. Alternatively, the curved shape may have a curvature that gradually increases from the rotation center toward the outer periphery. More specifically, the curved shape is formed such that the curvature gradually increases from the rotation center, along the radial direction at the portion closest to the center, and along a direction perpendicular to the radial direction at the portion closest to the outer periphery. By using such a shape, the length that any point on the surface of the rotating workpiece 200 passes through the slot can be made longer toward the outer periphery, thereby obtaining the same effect as the fan shape.

[0060] The gas supply unit 7 supplies the gas G to the space inside the chamber 6 between the mounting unit 4 and the waveguide 11 . The gas supply unit 7 includes, for example, a nozzle 7a, a gas source 7b, and a gas control unit 7c. The nozzle 7a may be provided on, for example, a side wall of the chamber 6. The gas source 7b is provided outside the chamber 6. The gas source 7b may be a high-pressure cylinder containing the gas G, or a factory pipe for supplying the gas G, or the like. The gas control unit 7c is connected between the nozzle 7a and the gas source 7b via a pipe. The gas control unit 7c controls, for example, at least one of the flow rate and pressure of the gas G supplied to the nozzle 7a. The gas control unit 7c can also switch between starting and stopping the supply of the gas G. The gas control unit 7c can be, for example, a mass flow controller (MFC).

[0061] The gas G can be appropriately selected depending on the type of plasma processing and the material of the surface of the workpiece 200. The gas G is, for example, a gas containing fluorine atoms or a gas containing oxygen atoms.

[0062] The plasma processing apparatus 100a can be a plasma processing apparatus that performs plasma processing in an atmosphere with a wide range of gas pressures (from several hundred mPa to several atmospheres). In particular, in the case of atmospheric pressure, an exhaust unit that reduces the pressure inside the chamber 6 to a predetermined pressure is not required.

[0063] The plasma processing apparatus 100a according to this embodiment has the same functions and effects as the plasma processing apparatus 100 described above. In addition, since the gas supply unit 7 is provided, various gases can be used as necessary. In this case, since the chamber 6 is provided, it is possible to prevent highly reactive gases such as gases containing fluorine atoms from diffusing to the periphery of the plasma processing apparatus 100a. This makes it possible to diversify the components of the plasma products, and therefore to diversify the plasma processing. Furthermore, by making the mounting portion 4 rotatable, the plasma applicator 1 can be made smaller in size than the plasma processing apparatus 100 described above. The plasma processing apparatus 100a may be provided with an exhaust section so that the plasma processing can be performed in a reduced pressure atmosphere.

[0064] FIG. 8A is a schematic cross-sectional view illustrating a plasma processing apparatus 100b according to another embodiment. FIG. 8B is a schematic plan view illustrating a plasma processing apparatus 100b according to another embodiment. The plasma processing apparatus 100b is an example of an in-liquid plasma processing apparatus that performs plasma processing in a liquid. As shown in FIGS. 8(a) and 8(b), a plasma processing apparatus 100b includes, for example, a plasma applicator 1, a power source 2, a microwave generating unit 3, a controller 5, a chamber 8, and a transfer unit 9.

[0065] The chamber 8 may be, for example, a container having a liquid-tight structure. The chamber 8 may be provided with an inlet (not shown) through which the workpiece 200 is carried in and an outlet (not shown) through which the workpiece 200 is carried out.

[0066] The inside of the chamber 8 is filled with a liquid 300. There is no particular limitation on the liquid 300. The liquid 300 can be, for example, water, an organic solvent such as alcohol, a chemical liquid, or the like.

[0067] The transfer unit 9 is provided inside the chamber 8. The transfer unit 9 transfers the workpiece 200 in the liquid 300 to a predetermined position. The transfer unit 9 can be, for example, a conveyor.

[0068] In the plasma processing apparatus 100b, the plasma processing can be performed as follows. For example, a carry-in device (not shown) carries the workpiece 200 through a carry-in port into the liquid inside the chamber 8. The transport unit 9 transports the workpiece 200 in the liquid to a position facing the slot 11a.

[0069] The plasma applicator 1 radiates microwaves through the slots 11a to the liquid 300. At this time, the plurality of reflecting sections 12 and the switching section 13 aim to make the electric field intensity uniform when viewed as a time average.

[0070] When microwaves are radiated to the liquid 300, the liquid 300 is heated and bubbles 300a are generated. Then, when the microwaves are incident on the bubbles 300a, plasma is generated, and plasma products are generated by the plasma. For example, the vapor or gas contained in the bubbles 300a, or the liquid 300 at the interface between the bubbles 300a and the liquid 300 or substances contained in the liquid 300 are excited and activated by the plasma, and plasma products such as neutral active species and charged particles such as ions and electrons are generated.

[0071] The generated plasma products diffuse into the liquid 300 , and the workpiece 200 is subjected to plasma processing by the plasma products diffused into the liquid 300 .

[0072] The transport unit 9 transports the plasma-treated workpiece 200 to the position of the unloading port. The workpiece 200 transported to the position of the unloading port is unloaded to the outside of the chamber 8 by a unloading device (not shown).

[0073] In the above, the liquid 300 is heated and boiled to generate the bubbles 300a, but the present invention is not limited to this. For example, the liquid 300 may be depressurized to generate the bubbles 300a. Alternatively, the bubbles 300a may be generated by supplying a gas to the liquid 300.

[0074] In the above, the case where the workpiece 200 is plasma-treated by the plasma products has been exemplified, but the liquid 300 can also be plasma-treated by the plasma products. For example, impurities, bacteria, viruses, etc. contained in the liquid 300 can be decomposed or rendered harmless by the plasma products.

[0075] Although the embodiments have been described above, the present invention is not limited to these descriptions. Any modifications to the above-described embodiments made by those skilled in the art are also encompassed within the scope of the present invention as long as they incorporate the features of the present invention. For example, the shapes, dimensions, materials, arrangements, etc. of the elements provided in the plasma processing apparatus and plasma applicator are not limited to those exemplified, and can be changed as appropriate. Furthermore, the elements provided in each of the above-mentioned embodiments can be combined to the greatest extent possible, and such combinations are also included within the scope of the present invention as long as they include the features of the present invention. [Explanation of symbols]

[0076] 1 plasma applicator, 2 power source, 3 microwave generating section, 5 controller, 11 waveguide, 11a slot, 11b window, 12 reflecting section, 12a variable impedance element, 12b conductor, 12c conductor, 13 switching section, 13a switching element, 100 plasma processing apparatus, 100a plasma processing apparatus, 100b plasma processing apparatus, 110 maximum electric field strength position of standing wave, 200 workpiece, 300 liquid, 300a bubble

Claims

1. A waveguide having a slot and into which microwaves are introduced; A plurality of variable impedance elements are provided inside the waveguide and aligned along a tube axis of the waveguide; a switching element electrically connected to each of the plurality of variable impedance elements and capable of electrically switching between high and low impedance of each of the plurality of variable impedance elements; A plasma applicator comprising:

2. 2. The plasma applicator of claim 1, wherein (m-1) or more of the variable impedance elements are arranged at equal intervals in a direction along the axis of the waveguide, and the intervals between the variable impedance elements satisfy the following formula: L=(n+1 / m)×(λ / 2) L is the spacing of the variable impedance elements. n is 0, 1, or 2. m is an integer of 2 or more. λ is the wavelength of the microwave in the waveguide.

3. One end of the waveguide is open, 3. The plasma applicator according to claim 1, wherein the slot is provided between the opening and the plurality of variable impedance elements in a direction along a tube axis of the waveguide.

4. A plasma applicator according to any one of claims 1 to 3; a microwave generating unit that introduces microwaves into a waveguide provided in the plasma applicator; a power source electrically connected to a plurality of switching elements provided in the plasma applicator; A controller for controlling the plurality of switching elements; Equipped with The controller: One of the plurality of switching elements is turned on; The remaining switching elements are turned off.

5. 5. The plasma processing apparatus according to claim 4, wherein the controller changes the position at which the microwave is reflected by selecting the switching element to be turned on.

6. 6. The plasma processing apparatus according to claim 4, wherein the controller switches the plurality of switching elements between the ON state and the OFF state, thereby moving a position at which the microwaves are reflected.

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