Plasma generator

Abstract

To provide a plasma generator capable of improving gas decomposition efficiency.SOLUTION: A plasma generator 20 further comprises a second covering body 70 which covers an opening 22c on the other side of a discharge tube 22, and which has a plurality of gas discharge holes 75 for discharging gas that has passed through the discharge tube 22. When a first covering body 26A and the second covering body 70 are viewed along a center axis CL, a gas introduction hole 28 is formed in a first central region C1 including the center axis CL. In a second central region C2 of the second covering body 70 located at a position where the first central region C1 is projected along the center axis CL, there is formed a blocking portion 73 which blocks the discharging of the gas. In a peripheral region R2 located around the second central region C2, there is formed the plurality of gas discharge holes 75 around the center axis CL.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a plasma generator. [Background technology]

[0002] In the semiconductor manufacturing process, inductively coupled plasma (ICP) (hereinafter referred to as ICP) is generated and various processes (cleaning, etc.) are sometimes performed using the ICP. Patent Documents 1 and 2 describe plasma generators that generate ICP.

[0003] ICP is generated using a plasma generator with a coil wound around the outside of a discharge tube. At this time, a high-frequency voltage is output from a high-frequency power supply so that a high-frequency current flows through the coil, and a process gas (hereinafter referred to as gas) is introduced into the discharge tube. The high-frequency current flowing through the coil then ionizes the gas using an induced magnetic field, generating plasma. It is believed that in the initial stage, a plasma called capacitively coupled plasma (CCP) is generated, and then, as the high-frequency current flowing through the coil is increased, ICP occurs.

[0004] When the gas inside the discharge tube is ionized to generate plasma, electrons in the plasma resulting from the ionization collide with the gas, causing it to decompose. For example, NF3 (nitrogen trifluoride) decomposes into N (nitrogen) and 3F (fluorine). The decomposed gas is sent to a plasma processing chamber downstream of the plasma generator, where it is used for cleaning the inside of the plasma processing chamber, for example.

[0005] In this way, gas is decomposed by generating ICP. The decomposed gas is used for cleaning and other processes. Therefore, there is a demand for improving the gas decomposition efficiency. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-161319 [Patent Document 2] Japanese Patent Publication No. 2020-057464 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above, and provides a plasma generator that can increase the efficiency of decomposing gas. [Means for solving the problem]

[0008] In view of the above problems, the present invention provides a plasma generator that introduces a gas into an interior thereof and generates plasma therein, and that includes at least an insulating discharge tube having a cylindrical shape, a conductive coil wound around the outer periphery of the discharge tube with the central axis of the discharge tube as its center, and a first covering that covers one opening of the discharge tube and has at least one gas inlet hole formed therein for introducing a gas into the interior of the discharge tube, and the coil is configured so that a high-frequency current with a frequency in an RF band flows through at least a part of the winding portion of the coil, and the plasma generator is configured to generate plasma in the discharge tube. The lamp further includes a second covering that covers the other opening of the discharge tube and has a plurality of gas exhaust holes formed therein for discharging gas that has passed through the discharge tube, and when the first covering and the second covering are viewed along the central axis, the gas inlet holes are formed in a first central region that includes the central axis, a blocking portion that blocks the discharge of the gas is formed in a second central region of the second covering that is located at a position where the first central region is projected along the central axis, and the plurality of gas exhaust holes are formed around the central axis in a peripheral region that surrounds the second central region.

[0009] According to the present invention, when the first coating and the second coating are viewed along the central axis, the gas inlet holes are formed in a first central region that includes the central axis, and a blocking portion that blocks gas discharge is formed in a second central region of the second coating, which is located at a position obtained by projecting the first central region along the central axis. As a result, gas that is released from the gas inlet holes formed in the first central region and released into the interior of the discharge tube along the central axis of the discharge tube collides with the blocking portion formed in the second central region of the second coating. At the same time, the gas released into the interior of the discharge tube also diffuses to a region (hereinafter referred to as the plasma generation region) close to the winding portion of the coil through which high-frequency current flows.

[0010] When the gas flowing through the discharge tube reaches a steady state, the gas pressure around the central axis at the position where the conductive coil is wound increases, making it easier for the gas to move to the plasma generation region where the gas pressure is low. As a result, undecomposed gas around the central axis also moves to the plasma generation region, so the amount of gas supplied to the plasma generation region can be increased compared to when no blocking portion is provided, and the gas decomposition efficiency can be improved. The decomposed gas (hereinafter referred to as decomposed gas) is discharged from multiple gas exhaust holes formed in the peripheral region surrounding the second central region of the second coating. As a result, more undecomposed gas present along the central axis can be moved to the plasma generation region, thereby improving the gas decomposition efficiency.

[0011] Here, the positions of the gas exhaust holes are not particularly limited as long as they are formed at positions outside the second central region. However, in a more preferred embodiment, when the discharge tube and the second coating are viewed along the central axis, the edges of the gas exhaust holes overlap with part of the periphery of the other opening of the discharge tube.

[0012] According to this aspect, the edges of the multiple gas exhaust holes overlap part of the periphery of the other opening of the discharge tube, so that the decomposition gas that flows from the plasma generation region along the inner surface of the discharge tube can be efficiently exhausted from the multiple gas exhaust holes.

[0013] Here, the shape of the gas discharge holes is not particularly limited as long as it can release a larger amount of decomposition gas, and may be circular, polygonal, etc. However, in a more preferred embodiment, the plurality of gas discharge holes are elongated holes extending around the central axis.

[0014] According to this aspect, the gas decomposed from the plasma generation region flows along the inner surface of the discharge tube around the central axis of the discharge tube. Therefore, by making the multiple gas exhaust holes long holes extending around the central axis, a larger amount of decomposed gas can be stably exhausted from the multiple gas exhaust holes.

[0015] Here, as long as the second covering has a blocking portion and a gas exhaust hole, the configuration of the second covering is not particularly limited, and may be disk-shaped, etc. However, in a more preferred embodiment, a support for supporting a cooling tube that cools the discharge tube is arranged along the outer circumferential surface of the discharge tube at a position closer to the other opening than the coil, the second covering comprising a disk-shaped covering portion in which the blocking portion and the gas exhaust hole are formed, and a cylindrical portion that extends from the periphery of the covering portion in a direction along the central axis so as to surround the outer circumferential surface of the discharge tube and is connected to the support while being connected to the discharge tube, and the covering portion and the cylindrical portion are integrally molded from the same metal material.

[0016] According to this embodiment, the gas heated by passing through the discharge tube comes into contact with the coated portion of the second coating. This heats the coated portion, and the heat is transferred to the cylindrical portion, reaches the annular support, and is absorbed by the cooling tube. This makes it possible to suppress a temperature rise in the coated portion of the second coating. In particular, because the coated portion and the cylindrical portion are integrally molded from the same metal material, thermal stress caused by thermal expansion and contraction does not occur between the coated portion and the cylindrical portion. As a result, heat-induced damage to the second coating can be avoided.

[0017] Here, the number of gas inlet holes formed in the first covering is not particularly limited as long as they are formed in the first central region, and for example, the gas inlet holes may be formed at positions along the central axis. However, in a more preferred embodiment, the first covering has a plurality of gas inlet holes, and the plurality of gas inlet holes have discharge flow paths formed therein through which the gas is discharged into the discharge tube so as to form a swirling flow around the central axis inside the discharge tube.

[0018] According to this aspect, a swirling flow is formed inside the discharge tube by the gas introduced through the plurality of gas inlet holes. As a result, the circumferential gas velocity component of the swirling flow actively guides the gas flowing around the periphery of the swirling flow toward the plasma generation region, allowing the gas to remain in the plasma generation region for a longer period of time. Meanwhile, the central axial gas velocity component of the swirling flow allows the gas around the central axis of the swirling flow to collide with the blocking portion of the second coating, thereby achieving the aforementioned effects. [Effects of the Invention]

[0019] According to the plasma generator of the present invention, the efficiency of decomposing gas can be increased. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing a configuration of a plasma generator according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing the appearance of the plasma generator shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the plasma generator shown in FIG. [Figure 4] 2 is an exploded perspective view of the bottom of the plasma generator. [Figure 5](a) is a bottom view of the second coating showing the positional relationship between the gas exhaust hole and the gas inlet hole when viewed along the central axis shown in Figure 4, (b) and (c) are modified examples of (a), and (d) is a bottom view of the second coating showing the positional relationship between the gas exhaust hole and the gas inlet hole when viewed along the central axis according to the second embodiment described below. [Figure 6] FIG. 10 is a perspective view showing the appearance of a plasma generator according to a second embodiment. [Figure 7] 9(a) is a cross-sectional view for explaining a swirling flow in the plasma generator shown in Fig. 8. FIG. 9(b) is a cross-sectional view of the first covering including a gas introduction hole taken along line AA in FIG. [Figure 8] FIG. 7 is a cross-sectional view of the plasma generator shown in FIG. [Figure 9] 10 is a graph showing the relationship between the flow rate of gas introduced into a discharge tube and the decomposition efficiency of the introduced gas in the plasma generators according to the examples and the comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0021] A plasma generation device 10 including a plasma generator 20 according to an embodiment will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to this embodiment.

[0022] 1. Overall configuration of the plasma generation device 10 and the plasma generator 20 1 is a diagram showing the configuration of a plasma generator 10 according to an embodiment. The plasma generator 10 according to the embodiment is a device that generates inductively coupled plasma (ICP). The plasma generator 10 according to the embodiment includes a high-frequency power supply 12, an impedance matching circuit 14, and a plasma generator 20.

[0023] The high frequency power supply 12 outputs a high frequency voltage having a frequency in the RF (Radio Frequency) band, and supplies the high frequency power to the plasma generator 20 via the impedance matching circuit 14. The impedance matching circuit 14 matches the impedance of the high frequency power output from the high frequency power supply 12 and supplies it to the plasma generator 20.

[0024] Gas is introduced into the plasma generator 20, which generates plasma therein. The plasma generated by the plasma generator 20 is sent to, for example, a plasma processing chamber and used for various processes such as etching.

[0025] Here, the plasma generator 20 receives gas from the upper side in the figure and emits plasma from the lower side in the figure. The upstream side of the gas flowing into the plasma generator 20 is referred to as the upper side, and the downstream side of the gas is referred to as the lower side. However, these upper and lower sides are specified for convenience of explanation, and the components and parts constituting the plasma generator 20 are not limited thereto. Note that in the present embodiment, the upstream side of the flowing gas is referred to as the upper side, and the downstream side of the gas is referred to as the lower side. However, for example, the plasma generator may be arranged upside down with respect to the plasma generator 20 shown in FIG. 3 so that the upstream side of the flowing gas is referred to as the lower side and the downstream side of the gas is referred to as the upper side. Furthermore, the plasma generator 20 shown in FIG. 3 may be placed horizontally so that the upstream and downstream sides of the gas are aligned horizontally. In this way, as long as the plasma generator 20 can achieve the effects described below, the orientation of the plasma generator 20 is not particularly limited.

[0026] The plasma generator 20 includes a discharge tube 22, a coil 24, a first covering 26A, and a second covering 70. The discharge tube 22 has a cylindrical shape and is made of an insulating material such as quartz or alumina.

[0027] Coil 24 is made of a conductive material such as a copper alloy, and is wound around the outer periphery of discharge tube 22, centered on central axis CL of discharge tube 22. High-frequency power is supplied to coil 24 from high-frequency power supply 12 via impedance matching circuit 14. Specifically, coil 24 is configured so that a high-frequency current with a frequency in the RF band flows through at least a portion of the winding portion.

[0028] The first covering body 26A is made of a metal material such as aluminum, and as will be described later, covers and closes one opening 22b of the discharge tube 22. The first covering body 26A includes an upper connecting cylinder 44 that is connected to the discharge tube 22 in a state where it is inserted outside the one opening 22b of the discharge tube 22, and a lid body 26 that covers the opening 44a of the upper connecting cylinder 44 and has a plurality of gas introduction holes 28 formed therein to introduce gas into the inside of the discharge tube 22.

[0029] In such a plasma generator 20, the inside of the discharge tube 22 is maintained in a high vacuum state, and gas is introduced into the interior through a plurality of gas inlet holes 28. The plasma generator 20 ionizes the gas inside the discharge tube 22 to generate plasma by inductive coupling with a fluctuating magnetic field generated by a high-frequency current of an RF band frequency flowing through the coil 24, thereby generating inductively coupled plasma (ICP). The generated plasma is sent out through an opening (other opening 22c) in the discharge tube 22 opposite the gas inlet hole 28 and through a gas outlet hole 75 in the second covering 70, which will be described later, to a plasma processing chamber or the like.

[0030] When the gas inside the discharge tube 22 is ionized to generate plasma, the gas decomposes. For example, if the gas is NF3 (nitrogen trifluoride), it decomposes into N (nitrogen) and 3F (fluorine). The decomposed N (nitrogen) and 3F (fluorine) are sent to a plasma processing chamber (not shown) downstream of the plasma generator 20, for example, where processing such as cleaning of the plasma processing chamber is performed. For example, when cleaning is performed, a chemical reaction between a Si film remaining in the plasma processing chamber and F (fluorine) generates gaseous SiF4, and the Si film can be removed by evacuating it using a vacuum pump.

[0031] Of course, the application of the plasma generator 20 of this embodiment is not limited to cleaning the inside of a plasma processing chamber as described above. For example, it can be applied to the detoxification of harmful gases. When applied to the detoxification of harmful gases, the harmful gas flowing from upstream is ionized and converted into plasma. During this process, the harmful gas is decomposed and made harmless. Furthermore, the gas used is not limited to NF3, and various gases can be used depending on the application (cleaning, detoxification, etc.). For example, O2, etc., can be used. Details of each component are described below.

[0032] The plasma generator 20 will be described in detail below. Fig. 2 is a perspective view showing the appearance of the plasma generator 20 according to the embodiment shown in Fig. 1. Fig. 3 is a cross-sectional view of the plasma generator 20 according to the embodiment shown in Fig. 2.

[0033] 2. First covering body 26A The first covering body 26A is a cover member that covers one opening 22b of the discharge tube 22, and a gas inlet hole 28 that introduces gas into the inside of the discharge tube 22 is formed in the first covering body 26A at a position corresponding to the central axis CL of the discharge tube 22. The first covering body 26A has an upper connecting cylinder (connecting cylinder) 44 and a lid body 26. Note that in this embodiment, the first covering body 26A is composed of the upper connecting cylinder 44 and the lid body 26, but the first covering body 26A may be composed of only the lid body 26 as long as the lid body 26 can be arranged so as to cover one opening 22b of the discharge tube 22.

[0034] The upper connecting cylinder 44 is cylindrical and made of a metal material such as aluminum. It is fitted onto one opening 22b of the discharge tube 22 and connected to the discharge tube 22 via the upper flange 42. The central axis CL of the discharge tube 22 and the (cylindrical) axis of the upper connecting cylinder 44 coincide with each other. The upper connecting cylinder 44 has a substantially cylindrical shape, and its inner circumference coincides with the outer circumference of the discharge tube 22, into which the discharge tube 22 is inserted. A flange portion 46 is formed on the upper connecting cylinder 44 at a position opposite the upper flange 42. A flange portion 48 is formed on the upper portion of the upper connecting cylinder 44, and is connected to a gas supply source (not shown).

[0035] A groove is formed on the inside (discharge tube 22 side) of the lower end position of the upper connecting tube 44, and an O-ring 49 is inserted into the groove. By fixing the flange portion 46 and the upper flange 42 with bolts or the like, the O-ring 49 becomes sandwiched between the flange portion 46 and the upper flange 42. This causes the O-ring 49 to deform, sealing the gap between the discharge tube 22 and the flange portion 46, and maintaining airtightness above the discharge tube 22.

[0036] The cover 26 has a disk shape and is disposed so as to cover the opening 44a formed in the upper connecting cylinder 44. The cover 26 is fixed to the upper connecting cylinder 44 while being placed on a flange portion 48 formed on the upper connecting cylinder 44. This allows the cover 26 to close one opening 22b of the discharge tube 22. Furthermore, with the upper connecting cylinder 44 connected to the discharge tube 22, the cover 26 is disposed at a distance from the end face 22e of one opening 22b of the discharge tube 22 in the direction along the central axis CL of the discharge tube 22. The cover 26 and the flange portion 48 may be integrally formed. This can reduce costs.

[0037] 3. About Coil 24 The coil 24 of the plasma generator 20 is provided in a central region in the direction of the central axis CL of the discharge tube 22. The outer circumferential shape of the cross section of the coil 24 is rectangular, for example, square. The coil 24 is a linear conductor, and is wound around the outer periphery of the discharge tube 22 at a predetermined pitch for a predetermined number of turns, centered on the central axis CL of the discharge tube 22. As a result, the coil 24 is wound around the outer periphery of the discharge tube 22, centered on the central axis CL of the discharge tube 22.

[0038] The coil 24 is hollow and has a cooling channel 52 formed therein through which a refrigerant flows. The coil 24 has a first connection portion 54 at one end and a second connection portion 56 at the other end. One of the first connection portion 54 and the second connection portion 56 is a connection jig for introducing the refrigerant into the cooling channel 52 inside the coil 24, and the other is a connection jig for sending the refrigerant out of the cooling channel 52 of the coil 24. This allows the cooling channel 52 inside the coil 24 to flow through the interior from one end to the other end, cooling the coil 24 and the discharge tube 22. By including such a cooling channel 52, the coil 24 can efficiently cool the heat generated by the coil 24.

[0039] The coil 24 has at least a winding portion 24a that is energized. The winding portion 24a is provided midway between one end and the other end of the coil 24, and a first electrode 62 and a second electrode 64 are provided at both ends of the winding portion 24a. High-frequency power is supplied to the first electrode 62 and the second electrode 64 from the impedance matching circuit 14. This causes a current corresponding to the high-frequency power to flow between the first electrode 62 and the second electrode 64 in the coil 24, allowing the coil 24 to generate a high-frequency magnetic field. Alternatively, the first and second electrodes 62, 64 may be provided from one end to the other of the coil 24, and the entire coil 24 may be energized.

[0040] 4. Discharge tube 22 and cooling and connection structure As described above, the discharge tube 22 of the plasma generator 20 has a cylindrical shape, and gas serving as a plasma material passes through the inside of the discharge tube 22. A disk-shaped upper flange 42 is attached to the discharge tube 22 in a state where it is fitted onto the discharge tube 22. The upper flange 42 is made of a metal material such as aluminum, and is fitted onto the discharge tube 22 between the region of the outer circumferential surface of the discharge tube 22 along the central axis CL, where the coil 24 is wound, and the opening 22b on one side. The upper flange 42 may be fitted onto the discharge tube 22.

[0041] A support 83 having an annular portion 82 supporting a cooling pipe 84 is attached to the discharge tube 22 at a position closer to the other opening 22c than the coil 24, in a state where it is fitted onto the discharge tube 22. As shown in FIG. 4 , an insertion hole 82h for inserting the discharge tube 22 and a groove 82a for accommodating a part of the cooling pipe 84 are formed in the annular portion 82 of the support 83 along the circumferential direction of the annular portion 82. The support 83 is made of a metal material such as aluminum, and is arranged between the coil 24 and a connector 89, which will be described later. The connector 89 may be fitted onto the discharge tube 22.

[0042] The cooling pipe 84 is housed in the groove 82a of the annular portion 82, and is formed so as to surround the discharge tube 22 along the circumferential direction of the annular portion 82 of the support 83. The cooling pipe 84 has a third connection portion 86 at one end and a fourth connection portion 88 at the other end. One of the third connection portion 86 and the fourth connection portion 88 is a connection jig for introducing a refrigerant into the cooling pipe 84, and the other is a connection jig for discharging the refrigerant from the cooling pipe 84. This enables the cooling pipe 84 to cool the discharge tube 22.

[0043] Furthermore, a disk-shaped connector 89 and a second covering 70 (described later) are attached to the discharge tube 22 in a state where they are fitted onto the discharge tube 22. The connector 89 is made of a metal material such as aluminum, and has an insertion hole 89h formed therein through which the discharge tube 22 is inserted. The connector 89 is fitted onto the discharge tube 22 in a region of the outer circumferential surface of the discharge tube 22 along the central axis CL, between the region where the coil 24 is wound and the opening 22c on the other side.

[0044] A groove is formed along the periphery of the insertion hole 89h on the surface of the connector 89 facing the support 83 (see FIGS. 3 and 4), and an O-ring 92 is inserted into this groove. The annular portion 82 of the support 83 and the connector 89 are fixed together with bolts or the like, so that the O-ring 92 is sandwiched between the annular portion 82 and the connector 89. This causes the O-ring 92 to deform, sealing the gap between the discharge tube 22 and the support 83, thereby maintaining airtightness below the discharge tube 22.

[0045] As is generally known, there is a gas density suitable for ionizing a gas to generate plasma. Gas ionization occurs primarily in the plasma generation region PR inside the discharge tube 22, so the gas density in this plasma generation region PR is important. This gas density varies depending on various conditions, such as the type of gas, gas flow rate, coil voltage, coil current, frequency of the high-frequency voltage output from the high-frequency power supply 12, and the inner diameter of the discharge tube. It also varies depending on the progress of the plasma treatment process. Therefore, it is necessary to conduct experiments to determine the conditions, such as the gas flow rate, for each type of gas. For example, before plasma generation, it is necessary to find the conditions suitable for generating CCP, and then it is necessary to find the conditions suitable for generating and maintaining ICP. Furthermore, during the ICP generation and maintenance stage, it is important to improve the gas decomposition efficiency. However, the gas density in the plasma generation region PR inside the discharge tube 22 is a major factor in determining gas decomposition efficiency, but adjusting this density has been difficult in conventional plasma generators. From this perspective, in this embodiment, the plasma generator 20 employs a second coating 70 having the following structure.

[0046] 5. Second covering body 70 4 and 5(a), the second covering 70 is made of a metal material such as aluminum, and is attached to the discharge tube 22 by abutting against the end portion that forms the opening 22c of the discharge tube 22. Specifically, the second covering 70 covers the other opening 22c of the discharge tube 22, and the second covering 70 has a plurality of (for example, four) gas exhaust holes 75 formed therein to exhaust gas that has passed through the discharge tube 22.

[0047] 2 and 5(a), in this embodiment, when the first coating 26A and the second coating 70 are viewed along the central axis CL of the discharge tube 22, the gas inlet hole 28 is formed in a first central region C1 that includes the central axis CL. A blocking portion 73 that blocks gas discharge is formed in a second central region C2 of the second coating 70, which is located at a position where the first central region C1 is projected along the central axis CL. Furthermore, a plurality of (for example, four) gas exhaust holes 75 are formed around the central axis CL in a peripheral region R2 that surrounds the second central region C2 of the second coating 70.

[0048] The first central region C1 is a region including the central axis CL where the gas introduction holes 28 are formed. The first central region C1 is, for example, a region within an imaginary circle centered on the central axis CL. The second central region C2 is a region having the same shape and size as the first central region C1, but is a region where holes such as the gas exhaust holes 75 are not formed. For example, the second central region C2 is a region within an imaginary circle centered on the central axis CL, and a blocking portion 73 is formed in this region. Furthermore, the peripheral region R2 is a region formed to surround the second central region C2. For example, when the second central region C2 is a region within an imaginary circle centered on the central axis CL, the peripheral region R2 is a donut-shaped region surrounding the second central region C2, and the inner periphery of the peripheral region R2 coincides with the outer periphery of the second central region C2, and the outer periphery of the peripheral region R2 coincides with the inner periphery of the discharge tube 22.

[0049] In the plasma generator 20 configured as described above, gas serving as a plasma material is introduced into the interior through the gas inlet 28, and high-frequency power is supplied to the coil 24. First, the plasma generator 20 ionizes the gas inside the discharge tube 22, which is kept in a vacuum state, using the voltage of the coil 24 to generate capacitively coupled plasma (CCP). Then, when the current flowing through the coil 24 increases, the plasma generator 20 generates an induced magnetic field, generating inductively coupled plasma (ICP). The plasma generator 20 according to this embodiment can stably generate and maintain inductively coupled plasma (ICP).

[0050] 3, the gas F1 discharged from the gas inlet hole 28 formed in the first central region C1 and released into the interior of the discharge tube 22 along the central axis CL of the discharge tube 22 collides with the blocking portion 73 formed in the second central region C2 of the second covering 70. At the same time, the gas released into the interior of the discharge tube 22 also diffuses to a region (hereinafter referred to as the plasma generation region PR) inside the discharge tube 22 that corresponds to the winding portion of the coil 24 through which the high-frequency current flows and is close to the winding portion. When the gas flowing through the discharge tube 22 reaches a steady state, the collision of the gas with the blocking portion 73 prevents the undecomposed gas from flowing into the gas exhaust hole 75. As a result, the pressure of the undecomposed gas around the central axis CL at the position where the conductive coil 24 is wound increases, and the gas moves to the plasma generation region PR, where the gas pressure is lower than that around the central axis CL.

[0051] As a result, undecomposed gas around the central axis CL also moves more easily to the plasma generation region PR, so the amount of gas supplied to the plasma generation region PR can be increased compared to when the blocking portion 73 is not provided, thereby improving the gas decomposition efficiency. The decomposed gas (hereinafter, decomposed gas) is discharged from a plurality of gas discharge holes 75 formed in the peripheral region R2 around the second central region C2. As a result, more undecomposed gas present along the central axis CL can be moved to the plasma generation region PR, thereby improving the gas decomposition efficiency.

[0052] In this embodiment, the gas discharge holes 75 are elliptical. The minor axis of each elliptical gas discharge hole 75 is inclined at an angle of, for example, 30° relative to a radial direction passing through the central axis CL, and the major axis of each elliptical gas discharge hole 75 is inclined relative to a circumferential direction about the central axis CL. Furthermore, when the discharge tube 22 and the second covering 70 are viewed along the central axis CL, the edge 75a of each of the multiple gas discharge holes 75 overlaps with part of the periphery of the other opening 22c of the discharge tube 22.

[0053] In this way, the edge 75a of the multiple gas discharge holes 75 overlaps part of the periphery of the other opening 22c of the discharge tube 22, so that the decomposition gas generated from the plasma generation region PR easily flows along the inner circumferential surface 22a of the discharge tube 22. As a result, the decomposition gas can be easily released directly from the gas discharge holes 75, and more decomposition gas can be efficiently discharged from the multiple gas discharge holes 75.

[0054] 5(b), the edges 75a of the multiple gas discharge holes 75 may overlap along the periphery of the other opening 22c of the discharge tube 22. This allows the gas decomposed in the plasma generation region PR to flow along the inner circumferential surface 22a of the discharge tube 22 around the central axis CL of the discharge tube 22, so that a larger amount of decomposed gas can be stably discharged from the multiple gas discharge holes 75.

[0055] 5(a), the gas exhaust holes 75 have an elliptical shape, but as shown in, for example, Figures 5(b) and 5(c), when the discharge tube 22 and the second covering 70 are viewed along the central axis CL, the gas exhaust holes 75 may be elongated holes extending around the central axis CL. The elongated holes have a curved shape in the circumferential direction around the central axis CL, and the ends of the elongated holes are arc-shaped without any corners.

[0056] According to Figures 5(b) and 5(c), the gas decomposed from the plasma generation region PR flows along the inner surface 22a of the discharge tube 22 around the central axis CL of the discharge tube 22. Therefore, by making the multiple gas discharge holes 75 long holes extending around the central axis CL, a larger amount of decomposed gas can be stably discharged from the multiple gas discharge holes 75.

[0057] Here, the shape of the second covering 70 is not particularly limited, and may be, for example, a disk shape, as long as it has the blocking portion 73 and the gas exhaust hole 75 formed therein and can cover the opening 22c of the discharge tube 22. In this embodiment, the second covering 70 has a covering portion 71 and a cylindrical portion 74 formed therein.

[0058] The covering portion 71 has a disk shape, and is formed with a blocking portion 73 and a gas exhaust hole 75. The cylindrical portion 74 extends from the periphery of the covering portion 71 in a direction along the central axis CL so as to surround the outer peripheral surface of the discharge tube 22. Flange portions 76, 78 are formed on both ends of the cylindrical portion 74. The flange portion 76 on one side of the cylindrical portion 74 is connected to the support body 83 via a connector 89 while being connected to the discharge tube 22. The covering portion 71 and the cylindrical portion 74 are integrally formed from the same metal material (e.g., aluminum).

[0059] Here, the gas heated by passing through the discharge tube 22 comes into contact with the coated portion 71 of the second coated body 70. This heats the coated portion 71, and the heat from the coated portion 71 is transferred to the cylindrical portion 74, reaches the connecting body 89 and the annular support 83, and is absorbed by the cooling tube 84. This makes it possible to suppress a temperature rise in the coated portion 71 of the second coated body 70. In particular, because the coated portion 71 and the cylindrical portion 74 are integrally formed from the same metal material, thermal stress caused by thermal expansion and contraction does not occur between the coated portion 71 and the cylindrical portion 74. As a result, heat-induced damage to the second coated body 70 can be avoided.

[0060] Here, the cylindrical portion 74 has a substantially cylindrical shape, and the inner peripheral surface of the cylindrical portion 74 coincides with the outer peripheral surface of the discharge tube 22, and the discharge tube 22 is inserted into the cylindrical portion 74 with the end of the discharge tube 22 abutting against it. A flange portion 76 is formed at one end (upper end) of the cylindrical portion 74, at a position opposite the connector 89, on which a large diameter seal 94 and a small diameter seal 93 are disposed. A flange portion 78 is formed at the other end (lower end) of the cylindrical portion 74, which connects the plasma generator 20 to a plasma processing device (not shown).

[0061] A plurality of (for example, four) notches 76a are formed in the circumferential direction on the periphery of the flange portion 76. The notches 76a are, for example, U-shaped, and by inserting the notches 76a and fastening a fastener 77 to the connector 89, the connector 89 can be connected to the second cover 70. This allows the notches 76a to release stress acting on the fastener 77 even if the flange portion 76 thermally expands and contracts. Furthermore, the fan-shaped portions formed between the notches 76a act as fins, thereby improving the heat dissipation properties of the second cover 70.

[0062] The connector 89 has a ring-shaped protrusion 89a formed on its surface facing the second covering 70, along the inner periphery of an insertion hole 89h through which the discharge tube 22 is inserted. The ring-shaped protrusion 89a protrudes toward the second covering 70. The outer periphery of the ring-shaped protrusion 89a is formed with a fastening hole 89b for fastening to the fastener 77, and an attachment portion 89c protrudes radially from the ring-shaped protrusion 89a. This facilitates the transfer of heat from the second covering 70 from the ring-shaped protrusion 89a of the connector 89 to the cooling pipe 84 disposed in the groove 82a on the inner periphery of the annular portion 82 of the support body 83. This allows for efficient heat dissipation from the second covering 70.

[0063] The plasma generator 20 according to the second embodiment will be described in detail with reference to the following Fig. 5(d) to Fig. 8. The present embodiment differs from the plasma generator 20 according to the first embodiment in the shape of the gas inlet hole of the first covering body 26A and the shape of the gas outlet hole of the second covering body 70. Therefore, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0064] 6 to 8, in this embodiment, a plurality of gas introduction holes 28A are formed in the cover 26 of the first covering 26A. The plurality of gas introduction holes 28A form discharge flow paths 28b through which gas is released into the discharge tube 22 so that the gas introduced through the plurality of gas introduction holes forms a swirling flow F2 around the central axis CL inside the discharge tube 22 (see FIG. 8).

[0065] 7(b), in the present embodiment, lid body 26 has a plurality of gas introduction holes 28A formed therein so as to penetrate circular first surface 26a facing a gas supply source (not shown) and circular second surface 26b facing discharge tubes 22. Gas introduction holes 28A are linear holes formed so as to penetrate lid body 26, and supply ports 28a for supplying gas to gas introduction holes 28A are formed in first surface 26a, and discharge ports 28c for discharging gas from gas introduction holes 28A are formed in second surface 26b.

[0066] The gas inlet hole 28A has a discharge flow path 28b through which the gas is discharged. A discharge port 28c is formed at the end of the discharge flow path 28b. The discharge flow path 28b is a linear path along the direction of gas discharge from the discharge port 28c. In this embodiment, the gas inlet hole 28A is a linear hole, and therefore the extension direction of the discharge flow path 28b coincides with the extension direction of the gas inlet hole 28A. However, as long as a swirling flow can be formed, the gas inlet hole 28A may have a curved gas inlet flow path. The discharge flow path 28b is a flow path that is inclined from the discharge port 28c to the second surface 26b with respect to the thickness direction of the lid 26. In this embodiment and this modified example, the gas inlet hole 28A has a circular shape with the same hole diameter, and the flow path cross section of the discharge flow path 28b is circular.

[0067] In this embodiment, as described above, the plurality of gas introduction holes 28A are arranged so that a swirling flow F2 is formed inside the discharge tube 22 by the gas introduced into the interior of the discharge tube 22 from the plurality of gas introduction holes 28A (specifically, the gas discharged from the discharge port 28c). Specifically, as shown in FIG. 7(a), each gas introduction hole 28A has a discharge flow path 28b formed therein through which the gas is discharged in the same direction around the central axis CL of the discharge tube 22 as the center C when viewed from the direction along the central axis CL of the discharge tube 22. Note that in this embodiment, as an example, the discharge flow path 28b is formed so that the swirling flow F2 is clockwise when viewed from the upstream side, but the discharge flow path 28b may also be formed so that the swirling flow F2 is counterclockwise when viewed from the upstream side.

[0068] In this embodiment, when viewed from a direction along the central axis CL, the multiple gas introduction holes 28A are formed at equal intervals along the same circumference c1 with the central axis CL as the center C. In this embodiment, the multiple gas introduction holes 28A have the same shape, and the supply ports 28a are formed on the circumference c1. The discharge ports 28c are formed on a circumference c3 having a radius slightly larger than the circumference c1. For convenience, the circumferences c1 and c3 are shown as the same circumference in FIG. 7(a).

[0069] In this embodiment, the imaginary line L1 along the direction of the gas discharged from the discharge flow path 28b corresponds to a tangent to the circumference c3 when viewed from the direction along the central axis CL of the discharge tube 22. Therefore, in this embodiment, the imaginary line L1 along the direction of the gas discharged from the discharge flow path 28b of each gas introduction hole 28A and the tangent to the circumference c3 passing through the discharge port 28c of the discharge flow path 28b substantially coincide with each other.

[0070] In the present embodiment, as a preferred example, when viewed from a direction along the central axis CL, the discharge port 28c of the discharge flow path 28b is formed closer to the center C than the center between the center C and the inner circumferential surface 22a in the radial direction connecting the center C and the inner circumferential surface 22a of the discharge tube 22. Here, the "center" refers to the midpoint of the section between the center C and the inner circumferential surface 22a in this radial direction. Specifically, the distance r between the center C and the inner circumferential surface 22a of the discharge tube 22 is the sum of the distance r1 from the center C to the discharge port 28c and the distance r2 from the discharge port 28c to the inner circumferential surface 22a, and in the present embodiment, the distance r1 is preferably shorter than the distance r2.

[0071] 7(a), in this embodiment, the cover 26 is disposed at a distance from the end face 22e that forms one opening 22b of the discharge tube 22 in the direction along the central axis CL. As shown in FIG. 7(b), the discharge flow path 28b of each gas introduction hole 28A is inclined with respect to the direction along the central axis CL so that the gas is discharged toward the inner circumferential surface 22a of the discharge tube 22.

[0072] The covering portion 71 of the second covering 70 covers the other opening 22c of the discharge tube 22, and the covering portion 71 is formed with three gas exhaust holes 75 for exhausting gas that has passed through the discharge tube 22. As shown in FIGS. 7(a) and 5(d), in this embodiment, when the first covering 26A and the second covering 70 are viewed along the central axis CL of the discharge tube 22, the gas inlet hole 28A is formed in a first central region C1 that includes the central axis CL. A blocking portion 73 that blocks gas exhaust is formed in a second central region C2 of the second covering 70, which is located at a position obtained by projecting the first central region C1 along the central axis CL. Furthermore, three gas exhaust holes 75 are formed around the central axis CL in a peripheral region R2 around the second central region C2 of the second covering 70.

[0073] In this embodiment, a swirling flow F2 is formed inside the discharge tube 22 by gas introduced through the multiple gas introduction holes 28A. As a result, the circumferential gas velocity component of the swirling flow F2 actively causes the gas flowing around the periphery of the swirling flow to flow toward the plasma generation region PR, allowing the gas to remain in the plasma generation region PR for a longer period of time. Meanwhile, the gas velocity component in the direction of the central axis CL of the swirling flow F2 causes the gas around the central axis CL of the swirling flow F2 to collide with the blocking portion 73 of the second coating 70, and the same effects as those shown in the first embodiment can be expected. [Example]

[0074] Examples of the present invention are given below. [Example] The plasma generator shown in the first embodiment was prepared. Specifically, a gas inlet hole was provided on the central axis CL of a 4 mm thick lid. The inner diameter of the discharge tube 22 was 73 mm. NF3 gas was introduced into this plasma generator, and the flow rate of the introduced gas and the gas decomposition efficiency of NF3 were measured. The results are shown in Figure 9.

[0075] Comparative Example The difference from the example is that no coating was provided on the second coating. As in the example, NF3 gas was introduced, and the flow rate of the introduced gas and the NF3 gas decomposition efficiency were measured. The results are shown in Figure 9.

[0076] When the plasma generator of the comparative example was used, the maximum gas flow rate at which plasma could be generated was 2.5 slm. In contrast, the plasma generator of the example was able to generate plasma at a maximum gas flow rate of 4.5 slm. Thus, it was confirmed that the plasma generator of the example could generate plasma at a higher gas flow rate than the plasma generator of the comparative example. In the comparative example, when the power supplied to the coil was set to 5.5 W and the gas flow rate was increased to exceed 2.5 slm, the discharge tube 22 was damaged. On the other hand, in the example, even though the power supplied to the coil 24 was limited to 4.5 W, the gas flow rate could be increased to a maximum of 4.5 slm, more than in the example.

[0077] As shown in Figure 8, in the comparative example (▲), as the flow rate of the introduced gas was further increased from 1.5 slm, the gas decomposition efficiency dropped sharply, dropping to below 70% at 2.5 slm. On the other hand, in the example (●), even though the power supplied to the coil 24 was 4.5 kW, it was found that a gas decomposition efficiency of 80% was maintained even at 3.5 slm, and a gas decomposition efficiency of over 70% was obtained at 4.5 slm.

[0078] In the comparative example, the gas introduced into the discharge tube 22 flows linearly downward in the direction of the central axis CL of the discharge tube 22. As the gas flows downward, it gradually diffuses inside the discharge tube 22. However, most of the gas flows around the central axis CL of the discharge tube 22. Therefore, the amount of gas flowing through the plasma generation region PR inside the discharge tube 22, which is closer to the winding portion 24a of the coil through which the high-frequency current flows, is smaller than in the plasma generator 20 of the embodiment. As a result, it is thought that the plasma generator of the comparative example decomposes less gas and has lower gas decomposition efficiency than the plasma generator of the embodiment.

[0079] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0080] 20: plasma generator, 22: discharge tube, 24: coil, 26A: first covering body, 26: lid body, 28, 28A: gas inlet hole, 28b: discharge flow path, 70: second covering body, C1: first central region, C2: second central region, R2: peripheral region, 71: covering portion, 73: blocking portion, 74: cylindrical portion, 75: gas outlet hole, 83: support body

Claims

1. A plasma generator that introduces a gas into an interior and generates plasma therein, an insulating discharge tube having a cylindrical shape; a conductive coil wound around the outer periphery of the discharge tube with the central axis of the discharge tube as the center; a first covering body that covers one opening of the discharge tube and has at least one gas inlet hole formed therein for introducing gas into the discharge tube; The coil is configured so that a high-frequency current having a frequency in an RF band flows through at least a part of a winding portion, the plasma generator further includes a second cover covering the other opening of the discharge tube and having a plurality of gas exhaust holes formed therein for exhausting the gas that has passed through the discharge tube; When the first coating and the second coating are viewed along the central axis, the gas introduction hole is formed in a first central region including the central axis, a blocking portion that blocks the discharge of the gas is formed in a second central region of the second cover, the second central region being located at a position where the first central region is projected along the central axis; The plasma generator, wherein the plurality of gas discharge holes are formed around the central axis in a peripheral region surrounding the second central region.

2. When the discharge tube and the second coating are viewed along the central axis, 2. The plasma generator according to claim 1, wherein edges of the plurality of gas discharge holes overlap a part of the periphery of the other opening of the discharge tube.

3. 2. The plasma generator according to claim 1, wherein the plurality of gas discharge holes are elongated holes extending around the central axis.

4. a support for supporting a cooling tube that cools the discharge tube is disposed along an outer circumferential surface of the discharge tube at a position closer to the other opening than the coil; the second covering body includes a disk-shaped covering portion in which the blocking portion and the gas exhaust hole are formed; a cylindrical portion that extends from the periphery of the covering portion in a direction along the central axis so as to surround the outer circumferential surface of the discharge tube, and that is connected to the support body in a state where the cylindrical portion is connected to the discharge tube, 2. The plasma generator according to claim 1, wherein the covering portion and the cylindrical portion are integrally formed from the same metal material.

5. a plurality of the gas introduction holes are formed in the first covering body, 2. The plasma generator according to claim 1, wherein the plurality of gas introduction holes are formed with a discharge flow path through which the gas is discharged into the discharge tube so that a swirling flow is formed around the central axis inside the discharge tube.

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