WO2011122422A1

WO2011122422A1 - Plasma processing apparatus, and dielectric window

Info

Publication number: WO2011122422A1
Application number: PCT/JP2011/057037
Authority: WO
Inventors: 清隆石橋
Original assignee: 東京エレクトロン株式会社
Priority date: 2010-03-30
Filing date: 2011-03-23
Publication date: 2011-10-06
Also published as: TW201210412A

Abstract

Disclosed is a plasma processing apparatus (11), which has a bottom (21) disposed on the underside, and a side wall (22) that extends in a cylindrical shape from the outside of the bottom (21) toward the upper side. On the inside of the same are provided a processing container (12) for plasma processing on the unprocessed substrate, and a dielectric window (16), for mounting to the upper edge of the side wall (22) so as to cover the opening of the processing container (12) and seal the processing container (12), and also for transmitting microwaves to the inside of the processing container (12). A dielectric window recess (63) is disposed on the dielectric window (16) as a wavelength adjustment means, for, when mounted to the upper edge of the side wall (22), adjusting the wavelength of the microwaves that are transmitted in a radial direction in the dielectric window (16), in a region farther outward radially than the inner wall surface (51) of the side wall (22).

Description

Plasma processing apparatus and dielectric window

The present invention relates to a plasma processing apparatus and a dielectric window, and more particularly to a plasma processing apparatus using a microwave as a plasma source and a dielectric window used in such a plasma processing apparatus.

Some semiconductor devices perform processing such as etching and CVD (Chemical Vapor Deposition) using plasma when manufacturing semiconductor devices. A conventional plasma processing apparatus for performing such plasma processing will be briefly described. FIG. 12 is a schematic cross-sectional view showing a conventional plasma processing apparatus 100. FIG. 13 is an enlarged view of a region indicated by XIII in FIG. 12 and 13, the vertical direction of the paper surface is the vertical direction of the apparatus.

Referring to FIGS. 12 and 13, a plasma processing apparatus 100 includes a processing container 101 that performs plasma processing on a substrate to be processed therein, and a disk-shaped dielectric window 102 that transmits microwaves into the processing container 101. With. The processing container 101 is configured to include a bottom portion 108 located on the lower side and a cylindrical side wall 109 extending upward from the outer peripheral portion of the bottom portion 108.

When the microwave is radiated to the dielectric window 102, it propagates in the dielectric window 102 in the radial direction from the center side toward the outer diameter side. Further, the microwave propagated from the center side toward the outer diameter side is reflected by the side surface 102c of the dielectric window 102 and the wall surface 110a of the side wall 109 facing the side surface 102c of the dielectric window 102 and is centered from the outer diameter side. Propagates radially toward the side. Here, the microwave traveling from the center side to the outer diameter side and the microwave traveling from the outer diameter side to the center side overlap, and a standing wave is formed in the dielectric window 102.

Here, techniques for adjusting a standing wave formed in a dielectric window are disclosed in WO03 / 105544A1 (Patent Document 1) and JP-A-2001-223171 (Patent Document 2).

WO03 / 105544A1 publication JP 2001-223171 A

According to Patent Document 1, the dielectric window is provided with a reflecting member for reflecting the microwave propagating in the dielectric window. The reflecting member is provided in a region on the inner diameter side of the dielectric window, specifically, a region on the inner diameter side from the inner wall surface of the side wall. Thereby, the position where the microwave is reflected by the reflecting member and the standing wave is formed is set as a region on the outer diameter side of the dielectric window.

According to Patent Document 2, an electromagnetic wave absorber is provided between the dielectric window and the processing container. As a result, the microwave is absorbed to suppress the reflection of the microwave, and the formation of the standing wave itself is suppressed.

Here, referring again to FIGS. 12 and 13, on the inner diameter side of the upper end portion of the side wall 109, a support portion 110 that is recessed downward from the upper end portion is provided so as to support the dielectric window 102. . The dielectric window 102 is supported by the support portion 110 such that the outer diameter side of the lower surface 102 b of the dielectric window 102 is placed on the support portion 110.

Here, a standing wave formed in the dielectric window 102 is considered. First, in the region of the dielectric window 102 that is not placed on the support portion 110, that is, in the region 103 on the inner diameter side of the inner wall surface 109b of the side wall 109, plasma is generated below it. Then, since energy is absorbed by the plasma, the strength of the formed standing wave is weakened, and the formed electromagnetic field is relatively weak.

On the other hand, in the region of the dielectric window 102 that is placed on the support portion 110, that is, in the region 104 on the outer diameter side of the inner wall surface 109 b of the side wall 109, the support portion 110 is positioned below the lower portion. No plasma is generated. Then, since energy is not absorbed by the plasma, the strength of the standing wave formed is increased, and the formed electromagnetic field is relatively increased. FIG. 14 is a view showing a part of the plasma processing apparatus 100 shown in FIG. 12 and showing a strong electromagnetic field region in the dielectric window 102. Referring to FIG. 14, the strong electromagnetic field 111 formed in the outer diameter side region of the dielectric window 102 is shown as an image. In FIG. 14, the hatching of the dielectric window 102 is omitted from the viewpoint of easy understanding.

Then, in the processing vessel 101, in the vicinity of the contact P between the inner wall surface 109b of the side wall 109 and the lower surface 102b of the dielectric window 102 shown in FIG. As a result, in the vicinity of the contact P, erosion due to plasma and adhesion of reaction products occur.

Here, the technique disclosed in Patent Document 1 is insufficient to solve the above-described problem.

Further, in the technique disclosed in Patent Document 2, the microwave is absorbed to suppress the reflection of the microwave and the formation of the standing wave itself is suppressed, so that plasma is hardly generated in the processing container. There is a fear. Moreover, it is necessary to provide an electromagnetic wave absorber in the apparatus, and there is a possibility that the assembly of the apparatus becomes complicated.

An object of the present invention is to reduce the influence of a standing wave formed in a dielectric window and generate a plasma appropriately, and the dielectric window used in such a plasma processing apparatus Is to provide.

The plasma processing apparatus according to the present invention has an opening on the upper side, a bottom portion disposed on the lower side, and a cylindrical side wall extending from the outer side of the bottom portion toward the upper side. A processing container that performs plasma processing on a processing substrate, a gas supply unit that supplies a plasma processing gas into the processing container, a holding base that is disposed in the processing container and holds a substrate to be processed, and plasma excitation A microwave generator for generating microwaves for use, and a dielectric window placed on the upper end of the side wall so as to cover the opening of the processing container to seal the processing container and allow microwaves to pass through the processing container A plurality of slot holes, which are disposed above the dielectric window, and a slot antenna plate for radiating the microwave to the dielectric window; and the microwave generated by the microwave generator And a microwave supply means for supplying to the window. Wavelength changing means for changing the wavelength of the microwave propagating in the radial direction in the dielectric window in a region on the outer diameter side of the inner wall surface of the side wall when the dielectric window is placed on the upper end of the side wall Is provided.

Such a plasma processing apparatus includes wavelength changing means for changing the wavelength of the microwave propagating in the radial direction in the dielectric window in a region on the outer diameter side of the inner wall surface of the side wall of the dielectric window. The wavelength changing means changes the wavelength of the microwave in a region on the outer diameter side of the inner wall surface of the side wall in the dielectric window. Thereby, the position where a strong standing wave is formed can be changed in the dielectric window. Therefore, it is possible to reduce the possibility that a strong electromagnetic field is formed in a region of the dielectric window on the outer diameter side of the inner wall surface of the side wall. As a result, erosion or the like in the vicinity of the contact between the inner wall surface of the side wall and the lower surface of the dielectric window can be prevented. As a result, the influence of the standing wave formed in the dielectric window can be mitigated, and plasma can be generated appropriately. In other words, the inventor of the invention of the present application has found that the dielectric window has an inner wall surface of the side wall and the dielectric window caused by the formation of strong standing waves in the outer diameter side region of the inner wall surface of the side wall. Focusing on problems such as erosion in the vicinity of the contact point with the lower surface, by adjusting the position where a strong standing wave is formed by providing wavelength changing means, the above-described problems are solved. .

Preferably, the wavelength changing means is a concave portion recessed inward from at least one of the upper side, the lower side, and the side surface of the dielectric window, and the dielectric wall is formed with the wall surface forming the concave portion as a boundary. Change the wavelength of the microwave that propagates radially in the body window. By doing so, the wavelength of the microwave can be changed with a simple configuration.

Preferably, a plurality of wavelength changing means are provided in the circumferential direction, and as one embodiment, the plurality of wavelength changing means are provided so that the radial distance from the center of the dielectric window is the same. Yes. By doing so, the radial position where the standing wave is formed can be made uniform in the circumferential direction. Then, for example, when the plasma processing apparatus is assembled, if the center of the dielectric window may be displaced from the center of the cylindrical side wall, the radial length from the center through which the microwave is propagated to the side wall However, they are different at the circumferential positions. As a result, the strength of the standing wave may be different at the circumferential position. In particular, the deviations that occur when assembling the plasma processing apparatus are different among the apparatuses. Therefore, the strength of the standing wave at the circumferential position may be different between devices. Even in such a case, by providing a plurality of wavelength changing means so that the radial distance from the center of the dielectric window is the same, the radial position where the standing wave is formed is made uniform in the circumferential direction. can do.

As another embodiment, the plurality of wavelength changing means are equally arranged in the circumferential direction. Thereby, the circumferential direction position where a standing wave is formed can be made uniform in the circumferential direction.

In yet another embodiment, the plurality of wavelength changing means are provided so as to have rotational symmetry about the radial center of the dielectric window.

More preferably, the wavelength changing means is provided within a half length of the microwave wavelength from the side surface of the dielectric window. Thus, when the microwave reflected from the side surface of the dielectric window propagates from the outer diameter side toward the center side, the wavelength of the microwave can be appropriately changed by the wavelength changing means.

More preferably, a member having a dielectric constant different from that of the dielectric window is provided in the inner region of the recess. By doing so, the wavelength of the microwave can be changed efficiently.

As an embodiment, a metal member is provided in the inner region of the recess.

Preferably, the metal member is grounded.

More preferably, the metal member is provided so that the radial position of the metal member can be changed.

In another aspect of the present invention, the present invention relates to a dielectric window. The dielectric window has an opening on the upper side, a bottom portion disposed on the lower side, and a cylindrical side wall extending from the outer side of the bottom portion toward the upper side, and plasma processing is performed on the substrate to be processed therein. In the processing container, the processing container is placed on the upper end of the side wall so as to cover the opening of the processing container to seal the processing container, and the microwave is transmitted into the processing container. The dielectric window has a recess that changes the wavelength of the microwave that propagates radially in the dielectric window in a region on the outer diameter side of the inner wall surface of the side wall when placed on the upper end of the side wall. Are provided. The plurality of recesses are provided at positions within half the length of the microwave wavelength from the side surface of the dielectric window. The plurality of recesses are equally arranged in the circumferential direction.

Such a dielectric window includes a recess for changing the wavelength of the microwave propagating in the radial direction in the dielectric window in a region on the outer diameter side of the inner wall surface of the side wall. The recess changes the wavelength of the microwave in a region on the outer diameter side of the inner wall surface of the side wall in the dielectric window. Thereby, the position where a strong standing wave is formed can be changed in the dielectric window. Therefore, it is possible to reduce the possibility that a strong electromagnetic field is formed in a region of the dielectric window on the outer diameter side of the inner wall surface of the side wall. As a result, erosion or the like in the vicinity of the contact between the inner wall surface of the side wall and the lower surface of the dielectric window can be prevented.

The plasma processing apparatus according to the present invention includes wavelength changing means for changing the wavelength of the microwave propagating in the radial direction in the dielectric window in a region on the outer diameter side of the inner wall surface of the side wall of the dielectric window. The wavelength changing means changes the wavelength of the microwave in a region on the outer diameter side of the inner wall surface of the side wall in the dielectric window. Thereby, the position where a strong standing wave is formed can be changed in the dielectric window. Therefore, it is possible to reduce the possibility that a strong electromagnetic field is formed in a region of the dielectric window on the outer diameter side of the inner wall surface of the side wall. As a result, erosion or the like in the vicinity of the contact between the inner wall surface of the side wall and the lower surface of the dielectric window can be prevented. As a result, the influence of the standing wave formed in the dielectric window can be mitigated, and plasma can be generated appropriately.

The dielectric window according to the present invention includes a recess for changing the wavelength of the microwave propagating in the radial direction in the dielectric window in a region on the outer diameter side from the inner wall surface of the side wall. The recess changes the wavelength of the microwave in a region on the outer diameter side of the inner wall surface of the side wall in the dielectric window. Thereby, the position where a strong standing wave is formed can be changed in the dielectric window. Therefore, it is possible to reduce the possibility that a strong electromagnetic field is formed in a region of the dielectric window on the outer diameter side of the inner wall surface of the side wall. As a result, erosion or the like in the vicinity of the contact between the inner wall surface of the side wall and the lower surface of the dielectric window can be prevented.

It is a schematic sectional drawing which shows an example of the plasma processing apparatus which concerns on one Embodiment of this invention. It is a figure which shows a slot antenna board. It is the figure which expanded a part of plasma processing apparatus shown in FIG. It is the figure which looked at the dielectric material window shown in FIG. 1 from the upper direction. It is the figure which expanded a part of plasma processing apparatus shown in FIG. It is the figure which expanded a part of plasma processing apparatus shown in FIG. 1, Comprising: It is a figure which shows the strong electromagnetic field area | region in a dielectric material window. It is the figure which looked at the dielectric window which provided the dielectric window recessed part in other embodiment from the upper direction. It is a figure which shows the dielectric material window recessed part in other embodiment. It is a figure which shows the dielectric material window recessed part in other embodiment. It is the figure which looked at the dielectric material window shown in FIG. 9 from the upper direction. It is a figure which shows an example of the structure which made changeable the radial direction position of a metal member. It is a schematic sectional drawing shown about the conventional plasma processing apparatus. It is the figure which expanded the area | region shown by XIII in FIG. It is the figure which showed a part of plasma processing apparatus shown in FIG. 12, Comprising: It is a figure which shows the strong electromagnetic field area | region in a dielectric material window.

Hereinafter, a plasma processing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of a plasma processing apparatus 11 according to an embodiment of the present invention. FIG. 2 is a view showing the slot antenna plate 18.

First, referring to FIG. 1, the plasma processing apparatus 11 is open on the upper side, in which a processing container 12 that performs plasma processing on the substrate W to be processed, a gas for plasma excitation in the processing container 12, and A gas supply unit 13 that supplies a gas for plasma processing, a holding base 14 that is disposed in the processing container 12 and holds the substrate W to be processed, and is disposed outside the processing container 12 for plasma excitation. A microwave generator 15 that generates a microwave; a dielectric window 16 that is disposed so as to cover the opening of the processing container 12 to seal the processing container 12 and transmits the microwave into the processing container 12; A slot hole 17 is provided. The slot antenna plate 18 is disposed above the dielectric window 16 and radiates microwaves to the dielectric window 16. A dielectric plate 19 that is disposed above the na plate 18 and propagates the microwave in the radial direction; a microwave supply means 20 that supplies the microwave generated by the microwave generator 15 into the processing vessel 12; And a control unit (not shown) for controlling the entire plasma processing apparatus 11.

The processing container 12 includes a bottom portion 21 located at the lower portion of the holding table 14 and a side wall 22 extending upward from the outer peripheral portion of the bottom portion 21. An exhaust port 23 for exhaust is provided on the radial center side of the bottom portion 21. The upper side of the processing container 12 is open, and is provided by a dielectric window 16 disposed on the upper side of the processing container 12 and an O-ring 24 as a seal member interposed between the dielectric window 16 and the processing container 12. The processing container 12 is configured to be sealable.

The side wall 22 has a cylindrical shape and includes a cylindrical portion 22a extending upward from the outer peripheral portion of the bottom portion 21 and a dielectric window support member 10 positioned above the cylindrical portion 22a. The dielectric window support member 10 is provided so as to be placed on the cylindrical portion 22a. Although not shown, a seal member is provided between the cylindrical portion 22a and the dielectric window support member 10. The inner wall surface 55 of the dielectric window support member 10 and the inner wall surface 51 of the cylindrical portion 22a are provided so as to be straightly connected in the vertical direction. That is, a step is not formed between the inner wall surface 55 of the dielectric window support member 10 and the inner wall surface 51 of the cylindrical portion 22a, and is provided flush. The material of the dielectric window support member 10 is a metal. Specific examples of the material for the dielectric window support member 10 include aluminum. Further, in this embodiment, a support portion 52 that is recessed downward from the upper end portion is provided on the inner diameter side of the upper end portion of the dielectric window support member 10 so as to support the dielectric window 16. The support portion 52 is provided in an annular shape and supports the dielectric window 16. That is, the dielectric window 16 is placed on the support portion 52 that is the inner diameter side of the upper end portion of the dielectric window support member 10. Note that a part of the gas supply unit 13 described above is provided so as to be embedded in the cylindrical portion 22 a and supplies gas into the processing container 12 from the outside of the processing container 12.

The slot antenna plate 18 has a thin plate shape and a disc shape. The slot antenna plate 18 is provided with a plurality of slot holes 17 penetrating in the plate thickness direction. As shown in FIG. 2, the plurality of slot holes 17 are provided such that a pair of slot holes 17 are orthogonal to each other in a substantially letter C shape, and the pair of slot holes 17 have a predetermined interval in the circumferential direction. Open and provided. Also in the radial direction, a plurality of pairs of slot holes 17 are provided at predetermined intervals. In this embodiment, a plurality of pairs of slot holes 17 are provided so as to have rotational symmetry. The rotation axis in this case is an eight rotation axis, and the same shape is obtained when the slot antenna plate 18 is rotated 45 degrees about the radial center 28.

The dielectric plate 19 has a flat disk shape. In the center of the dielectric plate 19, an opening for arranging an inner conductor 32 provided in a coaxial waveguide 31 described later is provided.

Here, when manufacturing the plasma processing apparatus 11, the radial center 64 of the dielectric window 16, the radial center 28 of the slot antenna plate 18, and the radial center of the dielectric plate 19, Manufactured to match each other. In this way, in the microwave propagated from the center side toward the outer diameter side, the propagation degree of the microwave in the circumferential direction is made the same, and the plasma generated in the lower side of the dielectric window 16 is uniform in the circumferential direction. We are trying to ensure sex. Here, the radial center 28 of the slot antenna plate 18 is used as a reference.

The microwave supply means 20 includes an inner conductor 32 having a substantially round bar shape whose one end 35 is connected to the center 28 of the slot antenna plate 18, and an outer diameter of the inner conductor 32 by opening a radial gap 34 with the inner conductor 32. A coaxial waveguide 31 including a substantially cylindrical outer conductor 33 provided on the side is provided. That is, the coaxial waveguide 31 is configured by combining the inner conductor 32 and the outer conductor 33 so that the outer peripheral surface 36 of the inner conductor 32 and the inner peripheral surface 37 of the outer conductor 33 face each other. The inner conductor 32 and the outer conductor 33 are combined so that the radial center of the inner conductor 32 coincides with the radial center of the outer conductor 33.

Further, the microwave supply means 20 includes a waveguide 39 whose one end 38 is connected to the microwave generator 15 and a mode converter 40 for converting the mode of the microwave. The waveguide 39 is provided so as to extend in the horizontal direction, specifically, in the left-right direction in FIG. As the waveguide 39, a waveguide having a circular cross section or a rectangular cross section is used.

The microwave generated in the microwave generator 15 is propagated into the processing container 12 through the waveguide 39 and the coaxial waveguide 31. As the frequency of the microwave generated by the microwave generator 15, for example, 2.45 GHz is selected.

For example, microwaves of TE mode which is generated by the microwave generator 15 propagates in the left direction in the drawing showing the the waveguide 39 by the arrow A ₁ in FIG. 1, the mode converter 40 is converted into a TEM mode The Then, the microwave is converted into a TEM mode propagates through the coaxial waveguide 31 to the paper surface under the direction indicated by arrow A ₂ in Fig. Specifically, the microwave propagates between the inner conductor 32 and the outer conductor 33 where the gap 34 is formed, and between the inner conductor 32 and the inner diameter side end portion 47 of the cooling plate 43 described later. The microwave propagated through the coaxial waveguide 31 propagates in the radial direction in the dielectric plate 19 and is radiated to the dielectric window 16 from a plurality of slot holes 17 provided in the slot antenna plate 18. The microwave transmitted through the dielectric window 16 generates an electric field immediately below the dielectric window 16 and generates plasma in the processing container 12.

Further, the plasma processing apparatus 11 is disposed on the upper side of the dielectric window support member 10 and is disposed on the upper side of the dielectric window pressing ring 41 and the dielectric window pressing ring 41 for pressing the dielectric window 16 from the upper side. An antenna holder 42 that holds the slot antenna plate 18 and the like from above, a cooling plate 43 that is disposed above the dielectric plate 19 and cools the dielectric plate 19 and the like, and between the antenna holder 42 and the cooling plate 43. An electromagnetic shielding elastic body 44 that shields an electromagnetic field inside and outside the processing container 12, a center fixing plate 46 that fixes the center of the slot antenna plate 18, and an outer peripheral portion of the cooling plate 43. At the radial position where the dielectric plate positioning portion 48 that projects in the shape of a ring on the body window 16 side and positions the dielectric plate 19 in the radial direction, and the dielectric plate positioning portion 48 is provided. And a periphery fixing ring 45 for fixing the slot antenna plate 18.

The dielectric window pressing ring 41 has a cylindrical shape and is provided so as to contact the upper end surface of the dielectric window support member 10. The dielectric window pressing ring 41 is provided so that the inner diameter side surface 61 of the dielectric window pressing ring 41 is positioned on the inner diameter side of the side surface 62 of the dielectric window 16. As a result, the dielectric window 16 is pressed from the upper side at the inner diameter side end portion 66 of the dielectric window pressing ring 41.

FIG. 3 is an enlarged view of a part of the plasma processing apparatus 11 shown in FIG. FIG. 4 is a view of the dielectric window 16 shown in FIG. 1 as viewed from above. The details of the dielectric window 16 will be described with reference to FIGS. The dielectric window 16 has a disk shape, and the lower surface 25 of the dielectric window 16 is flat. The dielectric window 16 is supported by the support portion 52 such that the outer diameter side of the lower surface 25 of the dielectric window 16 is placed on the support portion 52. Further, the dielectric window 16 is provided with a radial gap 54 between the wall surface 53 of the dielectric window support member 10 facing the side surface 62 of the dielectric window 16. The material of the dielectric window 16 is a dielectric. Specific materials for the dielectric window 16 include quartz and alumina. For example, in an apparatus that processes a substrate to be processed such as a wafer having a diameter of 300 mm, the diameter of the dielectric window 16 is set to 500 mm.

Further, the upper surface 58 of the dielectric window 16 is recessed at the center in the radial direction so as to reduce the plate thickness from the upper surface 58 of the dielectric window 16 so as to receive the center fixing plate 46. A central recess 49 is provided. Further, of the upper surface 58 of the dielectric window 16, the outer diameter side end portion is recessed so as to reduce the plate thickness from the upper surface 58 of the dielectric window 16 so as to receive the outer peripheral fixing ring 45. A dielectric window upper end surface 59 is provided.

Here, the dielectric window 16 is provided with a recess as a wavelength changing means for changing the wavelength of the microwave propagating in the radial direction in the dielectric window 16. In this embodiment, the recess is a dielectric window recess 63 having a shape that is recessed straight downward from the dielectric window upper end surface 59.

The dielectric window recess 63 includes a recess bottom surface 56 that is located on the lower side and serves as a bottom, and a recess wall surface 57 that is located on the upper side of the recess bottom surface 56 and serves as a wall. The concave wall surface 57 has a substantially perfect circle shape when viewed from above. The size of the perfect circle shape is arbitrarily determined by the frequency of the microwave, the size of the dielectric window 16 itself, and the like. For example, when the frequency of the microwave used for processing is 2.45 GHz, the diameter of the recess wall surface 57 is 15 mm.

Dielectric window recess 63, for example, if the distance L ₁ from the dielectric window upper surface 59 to the surface 25 of the lower side of the dielectric window 16 is 25mm, until the recess bottom surface 56 of the dielectric window upper surface 59 The distance L ₀ is 15 mm. That is, the ratio of the distance L ₀ from the dielectric window upper end surface 59 to the recess bottom surface 56 is 0.6 with respect to the distance L ₁ from the dielectric window upper end surface 59 to the lower surface 25 of the dielectric window 16. It is provided so that L ₁ : L ₀ = 5: 3.

The dielectric window recess 63 is provided such that the outer diameter side end 67 of the recess wall surface 57 is positioned on the outer diameter side of the inner wall surface 55 of the dielectric window support member 10. Specifically, the outer diameter side end portion 67 is provided so as to be located within a half length of the microwave wavelength from the side surface 62 of the dielectric window 16. That is, with reference to FIG. 3, when the side surface 62 of the dielectric window 16 is used as a reference, the dielectric window recess 63 has a distance L ₃ from the side surface 62 to the outer diameter side end portion 67. The support member 10 is provided so as to be shorter than the distance L ₂ to the inner wall surface 55. Then, the length of half the wavelength of the microwave is longer than L _3. Further, in this embodiment, the dielectric window recess 63 is such that the inner diameter side end portion 68 of the recess wall surface 57 is on the inner diameter side of the inner wall surface 55 of the dielectric window support member 10 and the dielectric window upper end surface. It is provided so as to be positioned on the outer diameter side from the inner diameter side end portion 59 of 59. That is, referring to FIG. 3, when the side surface 62 of the dielectric window 16 is used as a reference, the dielectric window recess 63 has a distance L ₄ from the side surface 62 to the inner diameter side end portion 68. It is provided so as to be longer than the distance L ₂ to the inner wall surface 55 of the member 10. Here, for example, a distance _{L 2} from the side surface 62 to the inner wall surface 55 of the dielectric window support member 10 is a 20 mm, the distance _{L 3} from the side surface 62 to the outer diameter side end portion 67 is a 10 mm, side distance _{L 4} to the inner diameter

side end portion

68 and 62 is 25 mm. That is, the ratio of the distance L ₃ from the side surface 62 to the outer diameter side end 67 is ½ with respect to the distance L ₂ from the side surface 62 to the inner wall surface 55 of the dielectric window support member 10. And L ₂ : L ₃ = 2: 1.

In addition, eight dielectric window recesses 63 are provided at equal intervals in the circumferential direction. Specifically, the dielectric window recesses 63 adjacent in the circumferential direction are provided at an interval of about 45 degrees. That is, referring to FIG. 4, the angle θ formed by the center 63 a of the adjacent dielectric window recess 63 and the center 64 of the dielectric window 16 is set to about 45 degrees. The eight dielectric window recesses 63 have rotational symmetry, and the rotation axis in this case is eight rotation axes. That is, when the dielectric window 16 is rotated 45 degrees about the radial center 64 of the dielectric window 16, the same shape is obtained. The plurality of dielectric window recesses 63 are provided such that the radial distances from the center 64 of the dielectric window 16 are the same. That is, the distance L ₅ from the center 64 of the dielectric window 16 to the center 63a of the dielectric window recess 63 are provided so that each is the same.

Here, the operation of the dielectric window recess 63 will be described. FIG. 5 is an enlarged view of a part of the plasma processing apparatus 11 shown in FIG. In FIG. 5, for ease of understanding, hatching is omitted from some members. Referring to FIG. 5, when microwaves are supplied from the microwave supply means 20, the microwaves are propagated in the radial direction through the dielectric plate 19 and radiated from the slot holes of the slot antenna plate 18 to the dielectric window 16. . When the microwave is radiated into the dielectric window 16, it propagates in the dielectric window 16 in the radial direction from the center side toward the outer diameter side as indicated by an arrow B ₁ indicated by a dotted line in FIG. 5. The microwave propagated in the radial direction from the center side toward the outer diameter side reaches the position where the dielectric window recess 63 is provided. Here, air exists in the inner region of the dielectric window recess 63. The dielectric constant of the air is significantly different from the dielectric constant of the dielectric window 16 and is lower than that of the dielectric window 16. Then, the microwave that has reached the position where the dielectric window recess 63 is provided is separated from the arrow B ₁ with the recess wall surface 57 of the dielectric window recess 63 as a boundary, as indicated by the arrow B ₂ indicated by the solid line in FIG. Propagate toward the outer diameter side at different wavelengths. Specifically, the microwave propagates toward the outer diameter side at a wavelength longer than the wavelength propagating in the dielectric window 16. That is, the wavelength of the microwave changes long with the recess wall surface 57 of the dielectric window recess 63 as a boundary. If it does so, the part of the belly | groove of the microwave which is a location with the strong microwave intensity | strength will decrease with the recessed part wall surface 57 of the dielectric material window recessed part 63 as a boundary. Also, some of the microwaves, such as the arrow B ₃ shown by a solid line in FIG. 5, in the recess wall 57 of the dielectric window recess 63, reflected toward the center side. In this way, in the dielectric window 16, the propagation wave and the reflected wave overlap each other in the region on the outer diameter side from the inner wall surface 55 of the dielectric window support member 10 with the dielectric plate recess 63 as a boundary. Reduce the risk of standing waves. Even when a strong standing wave is formed in the dielectric window 16, the dielectric window 16 has a region on the inner diameter side of the inner wall surface 55 of the dielectric window support member 10 and has a strong electromagnetic field. The position to be formed is a region on the inner diameter side of the inner wall surface 55 of the dielectric window support member 10. Referring to FIG. 6, the position where strong electromagnetic field 65 is formed is closer to the inner diameter than FIG. FIG. 6 is an enlarged view of a part of the plasma processing apparatus 11 shown in FIG. 1 and shows a strong electromagnetic field region in the dielectric window 16. In FIG. 6, only the electromagnetic field 65 is shown, but it is naturally formed in a region near the center.

As described above, the plasma processing apparatus 11 changes the wavelength of the microwave that propagates in the radial direction in the dielectric window 16 in the region on the outer diameter side of the inner wall surface 51 of the side wall 22 in the dielectric window 16. It includes a dielectric window recess 63 as changing means. The wavelength changing unit changes the wavelength of the microwave in a region of the dielectric window 16 on the outer diameter side of the inner wall surface 51 of the side wall 22. Thereby, the position where a strong standing wave is formed in the dielectric window 16 can be changed. Therefore, in the dielectric window 16, it is possible to reduce the possibility that a strong electromagnetic field is formed in a region on the outer diameter side of the inner wall surface 51 of the side wall 22. As a result, erosion or the like in the vicinity of the contact between the inner wall surface 51 of the side wall 22 and the lower surface 25 of the dielectric window 16 can be prevented. As a result, the influence of the standing wave formed in the dielectric window 16 can be mitigated, and plasma can be generated appropriately.

Further, such a dielectric window 16 includes a dielectric window recess 63 that changes the wavelength of the microwave propagating in the radial direction in the dielectric window 16 in a region on the outer diameter side of the inner wall surface 51 of the side wall 22. . The dielectric window recess 63 changes the wavelength of the microwave in the region on the outer diameter side of the inner wall surface 51 of the side wall 22 in the dielectric window 16. Thereby, the position where a strong standing wave is formed in the dielectric window 16 can be changed. Therefore, in the dielectric window 16, it is possible to reduce the possibility that a strong electromagnetic field is formed in a region on the outer diameter side of the inner wall surface 51 of the side wall 22. As a result, erosion or the like in the vicinity of the contact between the inner wall surface 51 of the side wall 22 and the lower surface 25 of the dielectric window 16 can be prevented.

Further, in this embodiment, the outer diameter side end portion 67 of the dielectric window recess 63 as the wavelength changing means is provided at a position within half the length of the microwave wavelength from the side surface 62 of the dielectric window 16. It is said. Thereby, when the microwave is reflected from the side surface 62 of the dielectric window 16 and propagates from the outer diameter side toward the center side, the wavelength of the microwave is appropriately changed by the dielectric window recess 63. Can do. Thereby, a possibility that a strong standing wave may be formed in a region on the outer diameter side of the inner wall surface 55 of the dielectric window support member 10 can be reduced.

Also, a plurality of dielectric window recesses 63 are provided in the circumferential direction, and a plurality of dielectric window recesses 63 are provided so that the radial distance from the center of the dielectric window 16 is the same, thereby forming a standing wave. The radial position can be made uniform in the circumferential direction. For example, when the plasma processing apparatus 11 is assembled, if there is a case where the center of the dielectric window 16 is displaced from the center of the cylindrical side wall 22, the radial direction from the center through which the microwave is propagated to the side wall 22. The length is different at each circumferential position. As a result, the strength of the standing wave may be different at the circumferential position. In particular, the deviations that occur when assembling the plasma processing apparatus 11 are different between the apparatuses. Therefore, the strength of the standing wave at the circumferential position may be different between devices. Even in such a case, by providing the plurality of dielectric window recesses 63 so that the radial distance from the center of the dielectric window 16 is the same, the radial position where the standing wave is formed is set in the circumferential direction. Can be made uniform.

In the above-described embodiment, the example in which the eight dielectric window recesses 63 are provided at equal intervals in the circumferential direction has been described, but the rotational symmetry of the slot hole 17 is not limited thereto. Is preferably a common multiple of the order of, for example, 24 may be provided as shown in FIG. Alternatively, a plurality of gaps may be provided in the circumferential direction with an interval smaller than half the length of the microwave wavelength. FIG. 7 is a view of the dielectric window 83 provided with the dielectric window recess 82 in another embodiment as viewed from above.

In the above embodiment, the example has been described in which the concave wall surface 57 of the dielectric window concave portion 63 is provided so that the shape viewed from above is a substantially perfect circle shape. Instead, it may be provided in the shape of a long hole extending in the radial direction, may be provided in the shape of a long hole extending in the circumferential direction, or may be provided in an annular shape. Moreover, you may provide in rectangular shapes, such as square shape.

In the above-described embodiment, the dielectric window recess 63 has the outer diameter side end portion 67 positioned on the outer diameter side of the inner wall surface 55 of the dielectric window support member 10 and the inner diameter side end portion 68. Although the example provided so as to be located on the inner diameter side from the inner wall surface 55 of the dielectric window support member 10 has been described, without being limited thereto, both the outer diameter side end portion 67 and the inner diameter side end portion 68 are You may provide so that it may be located in the outer diameter side from the inner wall face 55 of the dielectric material window support member 10. FIG. That is, the dielectric window recess 63 may be provided so as to include a region on the outer diameter side of the dielectric window 16 from the inner wall surface 55 of the dielectric window support member 10. FIG. 8 is a view showing a dielectric window recess 88 according to still another embodiment, in which both the outer diameter side end 86 and the inner diameter side end 87 of the dielectric window recess 88 are connected to the dielectric window support member 10. It is a figure which shows the case where it provides so that it may be located in the outer-diameter side from the inner wall surface 55 of this. Referring to FIG. 8, with reference to side surface 89 of dielectric window 90, distance L ₆ from side surface 89 to outer diameter side end portion 86 and distance L ₇ from side surface 89 to inner diameter side end portion 87 are side surfaces. It is provided so as to be shorter than a distance L ₈ from 89 to the inner wall surface 55 of the dielectric window support member 10.

In the above embodiment, the dielectric window recess 63 has been described as an example of a shape recessed downward from the dielectric window upper end surface 59. However, the present invention is not limited to this, and the lower side of the dielectric window 16 is not limited thereto. It may be a shape that is recessed upward from the side surface 25, or may be a shape that is recessed in the radial direction from the side surface 62 of the dielectric window 16 toward the center 64 of the dielectric window 16. FIG. 9 is a diagram showing a dielectric window recess 71 according to still another embodiment, in which the dielectric window recess 71 is formed in a radial direction from the side surface 72 of the dielectric window 70 toward the center 78 of the dielectric window 70. It is a figure which shows the case where it is set as the concave shape. FIG. 10 is a view of the dielectric window 70 shown in FIG. 9 as viewed from above.

9 and 10, the dielectric window recess 71 has a shape recessed in the radial direction from the side surface 72 of the dielectric window 70 toward the center side of the dielectric window 70. The dielectric window recess 71 is provided so as to be positioned at the center of the dielectric window 70 in the plate thickness direction. The dielectric window recess 71 includes a recess bottom surface 75 positioned on the inner diameter side and serving as a bottom, and a recess wall surface 80 serving as a wall positioned on the outer diameter side of the recess bottom surface 75. The concave wall surface 80 has a substantially perfect circle shape when viewed from the lateral direction.

For example, when the distance L ₁₂ from the dielectric window upper end surface 73 to the lower surface 79 of the dielectric window 70 is 30 mm, the dielectric window recess 71 is formed from the upper end 76 to the lower end 77. distance _{L 14} to is provided so as to be 10 mm. That is, the ratio of the distance L ₁₄ from the upper side end portion 76 to the lower side end portion 77 with respect to the distance L ₁₂ from the dielectric window upper end surface 73 to the lower surface 79 of the dielectric window 70 is 1/3. It is provided to become. Further, the ratio of the distance L ₁₅ from the dielectric window upper end surface 73 to the upper side end portion 76 with respect to the distance L ₁₂ from the dielectric window upper end surface 73 to the lower surface 79 of the dielectric window 70 is 1 /. 3 and is provided so as to be provided such that the ratio of the distance L ₁₆ from the lower side surface 79 of the dielectric window 70 to the lower end portion 77 is 1/3.

The dielectric window recess 71 is such that the distance from the side surface 72 of the dielectric window 70 to the bottom surface 75 of the recess is on the inner diameter side of the inner wall surface 55 of the dielectric window support member 10 and the inner diameter of the upper end surface 73 of the dielectric window. It is provided so as to be positioned on the outer diameter side from the side end portion 74. That is, with reference to FIG. 9, when the side surface 72 of the dielectric window 70 is used as a reference, the dielectric window recess 71 has a distance L ₁₁ from the side surface 72 to the recess bottom surface 75. It provided to be longer than the distance L ₁₀ to the inner wall surface 55 of the. Here, for example, the distance _{L 10} from the side surface 72 to the inner wall surface 55 of the dielectric window support member 10 is a 20 mm, the distance _{L 11} from the side surface 72 to the bottom surface of the recess 75 is 25 mm. That is, the distance L ₁₀ from the side surface 72 to the inner wall surface 55 of the dielectric window support member 10 is set such that the ratio of the distance L ₁₁ from the side surface 72 to the recess bottom surface 75 is 1.25. Further, the diameter 500mm of the dielectric window 70, the ratio of the distance _{L 11} from the side surface 72 to the bottom surface of the recess 75 is provided so as to be 0.05.

Further, eight dielectric window recesses 71 are provided at equal intervals in the circumferential direction. The eight dielectric window recesses 71 are provided so as to have rotational symmetry. The plurality of dielectric window recesses 71 are provided such that the radial distances from the center 78 of the dielectric window 70 are the same. For example, the distance L ₁₃ from the center 78 of the dielectric window 70 to the bottom surface 75 of the recess is provided to be the same.

As described above, even when the dielectric window recess 71 is provided, the wavelength of the microwave can be changed by the dielectric window recess 71, so that the standing wave formed in the dielectric window 70 can be separated from the side wall 22. The inner wall surface 51 can be positioned on the inner diameter side.

It should be noted that the dielectric window recess 71 may be provided in the shape of a slot viewed from the lateral direction of the recess wall surface 80 in the shape of a long hole extending in the circumferential direction, or may be provided in an annular shape. Moreover, you may provide in rectangular shapes, such as square shape. Further, the concave bottom surface 75 may be provided on the outer diameter side of the inner wall surface 55 of the dielectric window support member 10.

Further, in the above-described embodiment, the example in which the wavelength changing unit is the dielectric window concave portion 63 has been described. It is good. By doing so, the microwave can be reflected by the wall surface of the metal member. And the standing wave formed in the dielectric window 16 can be made into the position of an inner diameter side.

In this case, the metal member may be grounded. Specifically, since the members constituting the processing container 12 such as the dielectric window supporting member 10 and the dielectric window pressing ring 41 are grounded, the dielectric window supporting member 10 and the dielectric window pressing ring 41 such as this. The metal member may be grounded by electrically connecting the metal member. By doing so, the standing wave formed in the dielectric window 16 can be controlled more effectively.

Moreover, it is good also as a structure which can change the radial direction position of a metal member. FIG. 11 is a diagram illustrating an example of a configuration in which the radial position of the metal member 94 can be changed. Referring to FIG. 11, dielectric window recess 91 has a shape recessed in the radial direction from side surface 93 of dielectric window 92 toward the center side of dielectric window 92, as shown in FIGS. 9 and 10 described above. It is. A metal member 94 is provided in the inner region of the dielectric window recess 91. The metal member 94 is provided by a drive mechanism 95 so as to be movable in the radial direction.

The drive mechanism 95 is inserted into a through-hole 96a that penetrates the dielectric window support member 96 in the radial direction, and is disposed on the outer diameter side of the dielectric window support member 96, a holding portion 95a that holds the metal member 94, And a drive unit 95b that moves the holding unit 95a in a direction toward the inner diameter side or the outer diameter side (arrow C _{1 in} FIG. 11). The holding portion 95a holds the metal member 94 so that the metal member 94 can move in the radial direction within the dielectric window recess 91.

The metal member 94 is provided to extend in the radial direction so as to straddle the outer diameter side end portion of the dielectric window 92 and the dielectric window support member 96. In this embodiment, the dielectric window recess 91 is provided so as not to contact the recess wall surface 91a and the recess bottom surface 91b. An electrical contact member 97 that electrically connects the dielectric window support member 96 and the metal member 94 is provided between the dielectric window support member 96 and the metal member 94. The electrical contact member 97 is provided so as to cover the entire circumference of the side surface 94a of the metal member 94. Since the dielectric window support member 96 is grounded, the metal member 94 is also grounded. Thereby, leakage of microwaves and the like can be prevented.

Here, when the radial position of the metal member 94 is changed, the drive unit 95b is driven to move the metal member 94 in the radial direction via the holding unit 95a. For example, when the metal member 94 reaches the radial position where the standing wave state is appropriate, the movement of the metal member 94 is stopped.

By doing so, the metal member 94 can be moved in the radial direction by using the drive mechanism 95 to change the radial position of the metal member 94. Then, the size of the space surrounded by the concave wall surface 91a or the concave bottom surface 91b of the dielectric window concave portion 91 and the metal member 94, that is, the size of the inner region of the dielectric window concave portion 91 can be adjusted. In this case, the state of the standing wave formed in the dielectric window 92 can be controlled in the plasma processing apparatus 11 in accordance with a change in process conditions, a change in plasma excitation state, or the like. As a result, the substrate to be processed W can be processed uniformly.

The drive unit 95b of the drive mechanism 95 may be configured to move the metal member 94 in the radial direction by a manual operation by the user, or may be configured to move the metal member 94 in the radial direction by automatic operation by an apparatus. May be. When automatic operation is performed, a reflected wave detection means for detecting the reflected wave of the microwave is provided, and feedback such as moving the metal member 94 in the radial direction according to the reflected wave detected by the reflected wave detection means. Control may be performed.

In addition, the configuration in which the radial position of the metal member 94 can be changed by using the drive mechanism 95 in this way is, for example, as shown in FIG. When eight are opened, they may be applied to all eight or a part of the eight. In this case, the through hole 96a that penetrates the dielectric window support member 96 in the radial direction may be provided according to the dielectric window recess 91 to which the drive mechanism 95 is applied.

Also, the wavelength changing means may be a member formed so that the dielectric constant is lower than that of the dielectric window 16, specifically, the dielectric constant is lower than that of the dielectric window 16.

In the above-described embodiment, the wavelength changing unit has been described with respect to the upper surface 58 of the dielectric window 16 and the concave portion recessed inward from the side surface 62 of the dielectric window 16. However, the present invention is not limited thereto, and the wavelength of the microwave may be changed depending on the space by forming a space inside the dielectric window 16.

Moreover, in said embodiment, although the side wall 22 is the structure containing the dielectric material window support member 10 and the cylindrical part 22a, Comprising: Although the example comprised from a some member was demonstrated, it does not restrict to this. The dielectric window support member 10 and the cylindrical portion 22a may be integrated.

Further, in the above embodiment, on the inner diameter side of the upper end portion of the dielectric window support member 10, the support portion 52 that is recessed downward from the upper end portion is provided so as to support the dielectric window 16. Although the example in which the dielectric window 16 is placed on the support portion 52 has been described, the upper end portion of the dielectric window support member 10 has a flat shape, and the support portion 52 is not limited to this. The structure which is not provided may be sufficient. In this case, the dielectric window 16 may be placed on the inner diameter side of the upper end portion of the dielectric window support member 10. For example, in the upper end portion of the dielectric window support member 10, from the inner diameter side to the outer diameter side. You may comprise so that it may be mounted over a near position.

In the above-described embodiment, the plasma processing apparatus 11 has been described with respect to an example of a configuration including the dielectric plate 19. However, the present invention is not limited thereto, and the plasma processing apparatus 11 may be applied to an apparatus having a configuration without a dielectric plate. Can do.

As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

The plasma processing apparatus according to the present invention is effectively used when a uniform processing is required within the surface of the substrate to be processed during plasma processing.

10, 96 dielectric window support member, 11 plasma processing apparatus, 12 processing vessel, 13 gas supply unit, 14 holding base, 15 microwave generator, 16, 70, 83, 90, 92 dielectric window, 17 slot hole, 18 slot antenna plate, 19 dielectric plate, 20 microwave supply means, 21 bottom part, 22 side wall, 22a cylindrical part, 23 exhaust port, 24 O-ring, 25, 58, 79 face, 28, 63a, 64, 78 center, 31 coaxial waveguide, 32 inner conductor, 33 outer conductor, 34, 54 gap, 36 outer peripheral surface, 37 inner peripheral surface, 35, 38, 47, 66, 67, 68, 69, 74, 76, 77, 86, 87 end, 39 waveguide, 40 mode converter, 41 dielectric window pressing ring, 42 antenna pressing, 43 cooling plate, 44 electromagnetic shielding elasticity , 45 outer periphery fixing ring, 46 center fixing plate, 48 dielectric plate positioning portion, 49 central recess, 51, 55 inner wall surface, 52 support portion, 53 wall surface, 56, 75, 91b recess bottom surface, 57, 80, 91a recess wall surface 59, 73 Dielectric window upper end surface, 62, 72, 89, 93, 94a side surface, 63, 71, 82, 88, 91 Dielectric window recess, 65 electromagnetic field, 94 metal member, 95 drive mechanism, 95a holding part 95b driving part, 96a through hole, 97 electrical contact member.

Claims

A process having an opening on the upper side, a bottom part disposed on the lower side, and a cylindrical side wall extending from the outer side of the bottom part toward the upper side, and performing plasma processing on the substrate to be processed therein A container,
A gas supply unit for supplying a plasma processing gas into the processing container;
A holding table disposed in the processing container and holding the substrate to be processed thereon;
A microwave generator for generating microwaves for plasma excitation;
A dielectric window that is placed on the upper end of the side wall so as to cover the opening of the processing container to seal the processing container, and allows microwaves to pass through the processing container;
A plurality of slot holes, disposed on the upper side of the dielectric window, and a slot antenna plate for radiating microwaves to the dielectric window;
A plasma processing apparatus comprising: a microwave supply means for supplying a microwave generated by the microwave generator to the dielectric window;
When the dielectric window is placed on the upper end of the side wall, the wavelength of the microwave propagating in the radial direction in the dielectric window is changed in a region on the outer diameter side of the inner wall surface of the side wall. A plasma processing apparatus provided with wavelength changing means.
The wavelength changing means is a recess that is recessed inward from at least one of the upper side, the lower side, and the side surface of the dielectric window, with the wall surface constituting the recess as a boundary, The plasma processing apparatus according to claim 1, wherein the wavelength of the microwave propagating in the radial direction in the dielectric window is changed.
The plasma processing apparatus according to claim 1, wherein a plurality of wavelength changing units are provided in a circumferential direction.
The plasma processing apparatus according to claim 3, wherein the plurality of wavelength changing units are provided so that radial distances from a center of the dielectric window are the same.
The plasma processing apparatus according to claim 3, wherein the plurality of wavelength changing units are equally arranged in a circumferential direction.
The plasma processing apparatus according to claim 3, wherein the plurality of wavelength changing units are provided so as to have rotational symmetry about a radial center of the dielectric window.
The plasma processing apparatus according to claim 1, wherein the wavelength changing unit is provided at a position within a half length of a wavelength of the microwave from a side surface of the dielectric window.
The plasma processing apparatus according to claim 2, wherein a member having a dielectric constant different from that of the dielectric window is provided in an inner region of the recess.
The plasma processing apparatus according to claim 2, wherein a metal member is provided in an inner region of the recess.
The plasma processing apparatus according to claim 9, wherein the metal member is grounded.
The plasma processing apparatus according to claim 9, wherein the metal member is provided so that a radial position of the metal member can be changed.
A processing container having an opening on the upper side, a bottom portion disposed on the lower side, and a cylindrical side wall extending from the outer side of the bottom portion toward the upper side, and performing plasma processing on the substrate to be processed therein A dielectric window that is placed on the upper end of the side wall so as to cover the opening of the processing container and seals the processing container, and transmits microwaves into the processing container,
When the dielectric window is placed on the upper end of the side wall, the wavelength of the microwave propagating in the radial direction in the dielectric window is changed in a region on the outer diameter side of the inner wall surface of the side wall. A plurality of recesses are provided,
The plurality of recesses are provided at a position within half the length of the microwave wavelength from the side surface of the dielectric window,
The plurality of recesses are dielectric windows arranged equally in the circumferential direction.