Microwave Mode Converter

Abstract

To provide a microwave mode converter for suppressing abnormal discharge even when a large-power microwave is introduced, achieving simplification and miniaturization, and arbitrarily enlarging an aperture of a cylindrical waveguide or coaxial waveguide in a conversion part.SOLUTION: A microwave mode converter 41 includes a rectangular waveguide 411, a ring-shaped resonator 412 coupled to the waveguide 411, a coaxial structure 413 coupled to the resonator 412. A microwave TE mode transmitting through the rectangular waveguide 411 is converted into a TEM mode transmitting through the coaxial structure 413 through the ring-shaped resonator 412.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a microwave mode converter. [Background technology]

[0002] Most artificial diamonds used in industry as cutting tool materials and abrasive particles have been produced by ultra-high pressure synthesis, but in recent years, the use of vapor phase synthesis has become more common. The main vapor phase synthesis devices used in industry are hot filament CVD (Chemical Vapor Deposition) devices and microwave plasma CVD devices. In microwave plasma CVD devices, microwaves at a frequency of 2.45 GHz or 915 MHz are used to generate microwave discharge in a gas primarily composed of methane and hydrogen at a pressure (vacuum level) of 10 to 300 Torr, generating plasma to grow diamond on a substrate.

[0003] This microwave plasma CVD apparatus is equipped with a mode converter that converts the mode of the microwaves transmitted into the chamber. For example, there is a mode converter that has a TE-mode rectangular waveguide and a TM-mode cylindrical waveguide (Patent Documents 1 to 3). In addition, there is a mode converter that converts a TE rectangular waveguide to a TE cylindrical waveguide, first converts the waveguide to a TM cylindrical waveguide, divides it into four, and then combines it again to convert it into a large-diameter cylindrical waveguide (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 02-009202 [Patent Document 2] Japanese Patent Application Publication No. 10-126101 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-5533 Summary of the Invention [Problem to be solved by the invention]

[0005] The rapid growth of large-area diamond using a microwave plasma CVD apparatus requires the introduction of high-power microwaves. However, in the microwave mode converter described above, abnormal discharges can occur in the waveguide when high-power microwaves are introduced. This abnormal discharge is particularly noticeable in high-humidity environments. Furthermore, in Patent Document 1, the waveguide has a multi-stage structure of rectangular → cylindrical → 4-rectangular → 4-twisted tube → 4-rectangular → cylindrical, resulting in a large and complex mode converter. Patent Document 2 has the advantage of being able to increase the diameter without using a tapered tube, but the mode converter is still large and complex. Furthermore, in recent years, research and development of the structure and shape of mode converters has been progressing to meet the need for larger bulk. However, in Patent Document 3, the diameter of the cylindrical waveguide is approximately the same as the long side of the rectangular waveguide, and in order to increase the diameter, it is necessary to connect an additional tapered tube of a certain length, resulting in a complex structure. Thus, when high-power microwaves are introduced into the chambers of microwave plasma CVD equipment and etching equipment, radar antennas, etc., there is a need to suppress abnormal discharge in the mode converter, and to simplify and miniaturize the mode converter.

[0006] The present invention has been proposed in view of the above-mentioned conventional circumstances, and aims to provide a microwave mode converter that suppresses abnormal discharge even when high-power microwaves are introduced, and that allows the diameter of the cylindrical waveguide or coaxial waveguide in the conversion section to be expanded as desired while achieving simplification and miniaturization. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides the following means.

[0008] [1] A waveguide having a rectangular shape, a ring-shaped resonator coupled to the waveguide, and a coaxial structure coupled to the resonator, A microwave mode converter in which the TE mode of microwaves propagating through the rectangular waveguide is converted, via the ring-shaped resonator, into a TEM mode propagating through the coaxial structure portion.

[0009] [2] The microwave mode converter according to [1] above, wherein the resonator has an outer peripheral side wall and an inner peripheral side wall, and has a plurality of microwave introduction ports arranged in a line along the circumferential direction of the inner peripheral side wall.

[0010] [3] The microwave mode converter according to [2] above, wherein the opening faces of the plurality of microwave introduction ports are arranged parallel to the axial direction of the axis of symmetry of the resonator, and are arranged in a row so as to be rotationally symmetrical along the circumferential direction of the inner side wall with the axis of symmetry of the resonator as a reference.

[0011] [4] The microwave introduction port is a linear or rectangular slit, The microwave mode converter according to [2] or [3] above, wherein the slit is arranged so that its long side is parallel to the magnetic field direction at the slit in accordance with the resonance mode in the resonator, and so that the direction of the magnetic field formed in the coaxial structure by the slit is the same as the magnetic field direction in the coaxial structure. [Effects of the Invention]

[0012] According to the present invention, it is possible to realize a microwave mode converter that can suppress abnormal discharge even when high-power microwaves are introduced, and that can optionally expand the diameter of the cylindrical waveguide or coaxial waveguide in the conversion section while achieving simplification and miniaturization of the microwave mode converter.When this is applied to a microwave plasma CVD apparatus, it is possible to ensure sufficient space required for manufacturing objects to be processed, such as large bulk objects. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a partial cross-sectional perspective view showing an example of the configuration of a microwave plasma CVD apparatus to which a microwave mode converter according to an embodiment of the present invention is applied. [Figure 2] FIG. 2 is a side view showing the configuration of the microwave plasma CVD apparatus of FIG. [Figure 3] FIG. 3(A) is a cross-sectional view that schematically shows an example of the configuration of the microwave plasma CVD apparatus of FIG. 1, and FIG. 3(B) is a cross-sectional view taken along line AA. [Figure 4] FIG. 4 is a perspective view showing the configuration of a microwave mode converter provided in the coaxial structure of FIG. [Figure 5] FIG. 5(A) is a plan view of the microwave mode converter of FIG. 4, and FIG. 5(B) is a cross-sectional view taken along line BB. [Figure 6] 6(A) and 6(B) are cross-sectional views that schematically show modifications of the microwave plasma CVD apparatus of FIG. 3(A). [Figure 7] 7(A) to 7(C) are cross-sectional views that schematically show other modifications of the microwave plasma CVD apparatus of FIG. 3(A). [Figure 8] FIG. 8(A) is a side view that schematically shows an example in which the ring-shaped resonator of FIG. 7(A) is replaced with a plurality of waveguides, and FIG. 8(B) is a cross-sectional view along line CC. [Figure 9] FIG. 9 is a diagram showing the distribution of the electric field intensity by the simulation of the first embodiment. [Figure 10] FIG. 10(A) is a diagram showing the distribution of electric field strength in the simulation of Example 2, and FIG. 10(B) is a diagram showing the distribution of magnetic field strength in the cross section along the line DD. [Figure 11] FIG. 11 is a perspective view showing the configuration of a microwave mode converter in a conventional microwave plasma CVD apparatus. [Figure 12] FIG. 12 is a diagram showing the distribution of electric field intensity by simulation of Comparative Example 1. In FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0015] In the drawings used in the following description, the dimensions of the components may be shown at different scales to make them easier to see, and the dimensional ratios of the components may not necessarily be the same as in reality. Furthermore, the materials exemplified in the following description are merely examples, and the present invention is not necessarily limited to them, and can be implemented with appropriate changes within the scope of the present invention.

[0016] Fig. 1 is a partial cross-sectional perspective view showing an example of the configuration of a microwave plasma CVD apparatus according to an embodiment of the present invention, and Fig. 2 is a side view showing the configuration of the microwave plasma CVD apparatus of Fig. 1. The microwave plasma CVD apparatus 1 is an apparatus that generates plasma to precipitate or deposit a substance such as diamond on a workpiece such as a substrate.

[0017] As shown in Figures 1 and 2, the microwave plasma CVD apparatus 1 includes a chamber 10A, a mounting table 110A provided in the center of the chamber 10A in a plan view of the chamber 10A, a coaxial structure 80A located in the center of the chamber 10A in a plan view of the chamber 10A and including a central conductor 81 parallel to the axial direction of a symmetry axis Z1 of an internal resonance mode of the chamber 10A and an outer conductor 82 located around the central conductor 81, a plurality of microwave introduction ports 20, 20, ... provided in the coaxial structure 80A of the chamber 10A and coupled to match the internal resonance mode of the chamber 10A, a microwave introduction window 30A that transmits microwaves while pressure-compartmentalizing the chamber 10A and a waveguide described later, a waveguide 40A connected to the plurality of microwave introduction ports 20, 20, ..., and a microwave oscillation source 50 connected to the waveguide 40A.

[0018] The mounting table 110A may be provided at the axial upper end of the central conductor 81, or may be installed, for example, on the upper surface of the chamber 10A opposite the axial upper end of the central conductor 81. The axial upper end of the central conductor 81 is preferably located above the bottom surface of the chamber 10A to prevent the microwave introduction window 30A from being exposed to plasma. The mounting table 110A is not particularly limited as long as it can stably support the workpiece W. However, it is preferably made of molybdenum (Mo) or the like, from the viewpoint of being a conductive and heat-resistant material that is resistant to etching by plasma. The mounting table 110A may also have a multilayer structure composed of multiple layers made of different materials. The multilayer structure is not particularly limited, but may be, for example, a two-layer structure in which the lower layer is made of copper (for water cooling) and the upper layer is made of molybdenum. Alternatively, it may be a three-layer structure in which the bottom layer is made of copper (for water cooling), the middle layer is made of SUS, and the top layer is made of molybdenum.

[0019] The chamber 10A is a sealed container having at least a bottom wall 11 and a side wall 12 shown in FIGS. 2 and 3, and an enclosed space S1 shown in FIGS. 1 to 3 inside. The chamber 10A is made of a metal such as stainless steel or an aluminum alloy, and is provided with a viewing window (quartz, heat-resistant glass) as needed. In this embodiment, the chamber 10A has a uniaxially symmetric shape, that is, a shape that is rotationally symmetric with respect to a symmetry axis Z1 parallel to the z direction. The chamber 10A has, for example, a substantially cylindrical shape in a plan view, but is not limited thereto.

[0020] The microwave plasma CVD apparatus 1 includes a source gas inlet 60 for introducing source gas into the chamber 10A and a gas outlet 70 for discharging gas from the chamber 10A. The source gas inlet 60 supplies source gas, which is the raw material for forming a coating on the workpiece W, into the sealed space S1 of the chamber 10A. The source gas is, for example, a mixed gas primarily composed of methane (CH4) and hydrogen (H2). The source gas may further contain argon (Ar), oxygen (O2), or, for the purpose of intentional doping, compounds containing nitrogen (N2), phosphorus (P), boron (B), or the like as impurities. The gas outlet 70 includes a pump for discharging gas from the sealed space S1 and an exhaust resistance controller (not shown). By driving the pump, the sealed space S1 can be maintained in a reduced pressure state (preferably a vacuum state) at a constant pressure.

[0021] FIG. 3(A) is a cross-sectional view that schematically shows an example of the configuration of the microwave plasma CVD apparatus of FIG. 1, and FIG. 3(B) is a cross-sectional view taken along line AA.

[0022] In this embodiment, a coaxial opening 13 is provided in the bottom wall 11 of the chamber 10A, which communicates with the multiple microwave introduction ports 20, 20, ... provided in the coaxial structure 80A. The opening surface of the coaxial opening 13 is arranged around the central conductor 81 in a plan view of the chamber 10A, and is provided perpendicular to the axial direction (z direction) of the central conductor 81. The coaxial opening 13 has, for example, a ring shape, and is provided so that its axial direction is parallel to the axial direction (z direction) of the central conductor 81.

[0023] The opening surface of the coaxial opening 13 is arranged coaxially with respect to the central axis of the central conductor 81 of the chamber 10A in a plan view of the chamber 10A. The coaxial opening 13 has a circumferential direction and a radial direction, and the circumferential direction is arranged along the circumferential direction of the chamber 10A.

[0024] In this embodiment, the microwave introduction window 30A is placed on the bottom wall 11 of the chamber 10A so as to cover the coaxial opening 13. The microwave introduction window 30A is installed between the chamber 10A (reduced pressure region) and the waveguide 40A (atmospheric pressure region) (see FIGS. 1 and 2). The microwave introduction window 30A is preferably made of a material (dielectric) that transmits microwaves without loss, such as quartz.

[0025] Similar to the coaxial opening 13, the microwave introduction window 30A is also provided parallel to the axial direction of the symmetry axis of the internal resonance mode of the chamber 10A or the axial direction of the central conductor 81 in a plan view of the chamber 10A. The microwave introduction window 30A is not limited to a ring shape, and may have a shape other than a ring shape, as long as it is axially symmetric and can close the coaxial opening 13.

[0026] The waveguide 40A shown in Fig. 2 transmits microwaves from the microwave oscillation source 50 to the chamber 10A via a plurality of microwave introduction ports 20, 20, .... In this embodiment, as shown in Fig. 3, the waveguide 40A is coupled to a rectangular waveguide 411 and has a ring-shaped resonator 412 provided in the coaxial structure 80A of the chamber 10A. The coaxial structure 80A and the ring-shaped resonator 412 constitute the microwave mode converter 41. The ring-shaped resonator 412 is coupled to the coaxial structure 80A via a plurality of microwave introduction ports 20, 20, ... provided in the resonator.

[0027] In the configuration shown in FIG. 3 , the internal resonance mode is axially symmetric, and the introduction direction of microwaves introduced from the multiple microwave introduction ports 20 is perpendicular to the axial direction of the symmetry axis of the internal resonance mode of the chamber 10A or the axial direction of the central conductor 81. In other words, a normal to the center of the opening surfaces of the multiple microwave introduction ports 20 is perpendicular to the symmetry axis. Furthermore, the opening surfaces of the multiple microwave introduction ports 20 are arranged around the central conductor 81 in a plan view of the chamber 10A and are arranged parallel to the axial direction of the central conductor 81. When microwaves are introduced from the multiple microwave introduction ports 20 to the coaxial structure 80A (described later) in a direction perpendicular to the symmetry axis, the microwaves then pass through the microwave introduction window 30A of the coaxial opening 13 and travel to the upper part of the chamber 10A.

[0028] FIG. 4 is a perspective view showing the configuration of the microwave mode converter 41 provided in the coaxial structure part 80A of FIG. 1, FIG. 5(A) is a plan view of the microwave mode converter 41 of FIG. 4, and FIG. 5(B) is a cross-sectional view along line BB. The microwave mode converter 41 has a rectangular waveguide 411, a ring-shaped resonator 412 coupled to the waveguide 411, and a coaxial structure 413 coupled to the resonator 412. Since the microwave mode converter 41 has the rectangular waveguide 411 and the coaxial structure 413, it can also be called an applicator, which is a mode conversion joint. However, the applicator of this embodiment is significantly different from conventional applicators in that it has a ring-shaped resonator.

[0029] Waveguide 411 has one end 411a connected to circulator 90 (microwave oscillation source 50 side), and the other end 411b connected to resonator 412. Waveguide 411 has a rectangular shape in a cross section perpendicular to the propagation direction of the microwave, and has a straight shape in a plan view.

[0030] The resonator 412 has an outer peripheral sidewall 412A and an inner peripheral sidewall 412B, and the other end 411b of the waveguide 411 is connected to the outer peripheral sidewall 412A. The resonator 412 has a rectangular shape in a cross section perpendicular to the propagation direction of the microwaves and a perfect circle in a plan view. The resonator 412 also has a plurality of microwave introduction ports 412C, 412C, ... arranged side by side along the circumferential direction of the inner peripheral sidewall 412B. In this embodiment, the plurality of microwave introduction ports 412C, 412C, ... constitute the plurality of microwave introduction ports 20, 20, ..., but this is not limiting, and the plurality of microwave introduction ports 412C, 412C, ... and the plurality of microwave introduction ports 20, 20, ... may be provided separately and directly connected to each other.

[0031] The opening surfaces of the microwave introduction ports 412C are arranged parallel to the axial direction of the symmetry axis of the resonator 412 (z direction), for example, the axial direction of the central conductor 81, and are arranged side by side in a rotational symmetric manner along the circumferential direction of the inner side wall 412B with respect to the symmetry axis of the resonator 412. For example, the opening surfaces of the four microwave introduction ports 412C are arranged side by side in a 90-degree rotational symmetric manner along the circumferential direction of the inner side wall 412B. The opening surfaces of the microwave introduction ports 412C have, for example, long sides and short sides, with the long sides extending along the circumferential direction of the inner side wall 412B and the short sides extending along the axial direction of the central conductor 81. The opening surfaces of the microwave introduction ports 412C preferably have the same shape, but may have different shapes as long as they do not affect microwave radiation.

[0032] The microwave introduction port 412C is typically a linear or rectangular slit. The slit has a long side that corresponds to the resonance mode in the resonator 412 and is aligned with the magnetic field at or near the slit. place The slits are arranged so that they are parallel to the direction of the magnetic field formed in the coaxial structure 413 by the slits and so that the direction of the magnetic field is the same as the direction of the magnetic field in the coaxial structure 413. The slits are, for example, rectangular in shape, but may also have an elongated hole shape or the like.

[0033] The coaxial structure 413 has an outer peripheral sidewall 413A and an inner peripheral sidewall 413B, and forms the coaxial structure 80A of the chamber 10A. One end 413a of the coaxial structure 413 is connected to the resonator 412 via multiple microwave introduction ports 20, 20, ..., and the other end 413b forms the coaxial opening 13 of the chamber 10A (see FIG. 3(A)). In this embodiment, the inner peripheral sidewall 413B forms the central conductor 81, and the outer peripheral sidewall 413A forms the outer conductor 82. The coaxial structure 413 has a ring shape when viewed in cross section perpendicular to the microwave propagation direction. In this embodiment, the outer peripheral sidewall 413A of the coaxial structure 413 and the inner peripheral sidewall 412B of the resonator 412 form the same plane. In other words, the plurality of microwave introduction ports 412C, 412C, . . . are provided on the outer peripheral side wall 413A of the coaxial structure portion 413, and are arranged side by side along the circumferential direction thereof.

[0034] In the microwave mode converter 41 configured as described above, microwaves introduced from one end 411a of the waveguide 411 are introduced from the other end 411b into the resonator 412, and are further transmitted to the coaxial structure 413 from a plurality of microwave introduction ports 412C, 412C, ... provided on the inner circumferential side wall 412B of the resonator 412. As a result, the TE (Transverse Electric) mode of the microwaves transmitted through the rectangular waveguide 411 is converted into a TEM (Transverse Electromagnetic) mode transmitted through the coaxial structure 413 via the ring-shaped resonator 412. Note that the TE mode is generally a propagation mode in which the electric field direction is perpendicular to the traveling direction of the electromagnetic wave, and the TEM mode is generally a propagation mode in which the electric field direction and the magnetic field direction are perpendicular to each other. place In this embodiment, the TE mode refers to, for example, the fundamental mode TE10. In this case, the magnetic field in the chamber 10A place The distribution is axially symmetric (circular).

[0035] As described above, the microwave mode converter 41 has a ring-shaped resonator 412, which has a plurality of microwave introduction ports 412C, 412C, ... arranged in a line along the circumferential direction of the inner peripheral side wall 412B. Therefore, microwaves in a resonant mode are introduced into the coaxial structure 413 from the plurality of microwave introduction ports 412C, 412C, .... This suppresses concentration of electric field strength within the microwave mode converter 41 and reduces the probability of abnormal discharge occurring within the waveguide. Furthermore, the configuration of the microwave mode converter 41 can be simplified and made more compact than existing microwave mode converters. Furthermore, because the microwave mode converter 41 has a ring-shaped resonator 412, the diameter of the coaxial structure 413 (particularly the inner peripheral side wall 413B) can be increased. As a result, sufficient space can be secured below the workpiece (crystal) to install mechanisms for cooling, automatically elevating, and controlling the temperature distribution of the workpiece, which are necessary when manufacturing workpieces such as large bulk objects.

[0036] The microwave plasma CVD apparatus 1 also includes a circulator 90 and an EH tuner 100 provided in the waveguide 40A. The circulator 90 has a first port 91 connected to the microwave oscillation source 50, a second port 92 connected to the chamber 10A, and a third port 93 different from the first port 91 and the second port 92. The circulator 90 receives microwaves from the microwave oscillation source 50 at the first port 91 and propagates the microwaves to the second port 92. The circulator 90 also propagates the microwaves received at the second port 92, i.e., the microwaves reflected from a microwave propagation component connected to the second port 92, to the third port 93. A non-reflecting absorbing end called a dummy load is connected to the third port 93, and the microwaves propagated to the third port 93 are completely absorbed and converted into heat. As a result, microwaves reflected from the microwave propagation component connected to second port 92 are completely absorbed by the dummy load, preventing these microwaves from returning to microwave source 50. The circulator 90 and dummy load can be used in a common manner to prevent a microwave source (such as a magnetron) from being thermally damaged by reflected microwaves. This allows microwaves generated by microwave source 50 to be unidirectionally supplied to waveguide 40A. EH tuner 100 has E tuner section 101 and H tuner section 102, and impedance is adjusted by extending and retracting the plungers of E tuner section 101 and H tuner section 102. EH tuner 100 is one example of a method for adjusting impedance; other methods, such as a three-stub tuner, can also be used.

[0037] The microwave source 50 generates microwaves at a predetermined frequency, for example, 2.45 GHz or 915 MHz, which is in the ISM band. A magnetron or a semiconductor oscillator, for example, is used as the microwave source 50. Furthermore, in the microwave plasma CVD apparatus 1 of this embodiment, cooling paths using a medium such as cooling water or air may be provided above, to the sides, and below the chamber 10A.

[0038] In the microwave plasma CVD apparatus 1 configured as described above, microwaves supplied from the microwave oscillation source 50 are introduced into the chamber 10A through a plurality of microwave introduction ports 20, 20, ... provided in the coaxial structure 80A of the chamber 10A. The microwaves are irradiated onto the source gas in the chamber 10A, causing discharge, thereby generating plasma in the chamber 10A. Then, a coating of diamond or the like is formed on the surface of the workpiece W placed near the plasma from the source gas decomposed by the plasma.

[0039] As described above, according to this embodiment, the multiple microwave introduction ports 20, 20, ... are provided in the coaxial structure 80A of the chamber 10A and are coupled to match the internal resonance mode of the chamber 10A including the coaxial structure 80A. Therefore, by introducing microwaves into the chamber 10A from the multiple microwave introduction ports 20, 20, ..., electric field concentration in the waveguide 40A (FIG. 2) and the coaxial structure 80A is alleviated, and abnormal discharge and the associated heating can be suppressed even when high-power microwaves are introduced, thereby improving power efficiency.

[0040] Furthermore, since the central conductor 81 below the workpiece W can be made thicker as needed, mechanisms necessary for managing the crystal growth environment, such as raising and lowering the large-area workpiece W and controlling the temperature (distribution) by cooling and heating, can be incorporated below the substrate electrode, improving crystal quality and enabling the uniform synthesis of large-area substrates and the synthesis of thick bulk crystals.

[0041] Furthermore, because the plasma is generated above the mounting table 110A and the microwave introduction window 30A is positioned so that it is not exposed to the plasma generated in the chamber 10A, etching of the microwave introduction window 30A by the plasma can be prevented. As a result, contamination of the workpiece W with elements constituting the microwave introduction window, such as silicon, is prevented, enabling the synthesis of high-purity thin films of, for example, diamond, thereby improving the quality of the workpiece, such as bulk. Furthermore, because the plasma does not approach the microwave window even when high-power microwaves are supplied, high-power microwaves can be supplied, allowing for an increased film formation area on the workpiece W. This makes it possible to manufacture workpieces, such as large bulks, without increasing the size of the equipment.

[0042] 6(A) and 6(B) are cross-sectional views schematically showing a modified example of the microwave plasma CVD apparatus 1 of FIG. 3(A). FIGS. 7(A) to 7(C) are cross-sectional views schematically showing other modified examples of the microwave plasma CVD apparatus 1 of FIG. 3(A). The microwave introduction method in the configurations of FIGS. 6(A) and 6(B) is the same as that in the configurations of FIGS. 1 to 5. That is, the microwave introduction direction from the ring-shaped resonator 412 provided in the coaxial structure 80B or 80C is perpendicular to the axis of each coaxial structure. Also, FIGS. 7(A) to 7(C) show configurations in which the microwave introduction direction from the ring-shaped resonator 412 provided in the coaxial structure 80D, 80E, or 80F is parallel to the axis of each coaxial structure.

[0043] 6(A), the microwave introduction window 30A is disposed below the mounting table 110B. That is, it is preferable that the mounting surface of the mounting table 110B, i.e., the mounting position of the workpiece W, and the installation position of the microwave introduction window 30A are offset in the axial direction of the symmetry axis of the chamber 10B (z-axis direction).

[0044] 6(B), the mounting table 110C may have an outer diameter larger than the outer diameter of the center conductor 81 of the coaxial structure 80C of the chamber 10C, and the microwave introduction window 30B may be disposed below the mounting table 110C and extend along the axial direction of the axis of symmetry of the chamber 10C. In this case, the microwave introduction window 30B may have, for example, a cylindrical shape, and form a pressure barrier between the sealed space S1 of the chamber 10C and the space S2 below the mounting table 110C. Plasma is generated above the mounting table 110C, and the microwave introduction window 30B is located below the mounting table 110C and is shielded by the mounting table 110C so as not to be exposed to the plasma. This prevents the microwave introduction window 30B from being etched by the plasma.

[0045] In FIG. 7A, multiple microwave introduction ports 20 are provided in a coaxial structure 80D of the chamber 10D and coupled to match the internal resonance mode of the chamber 10D. The introduction direction of microwaves from the multiple microwave introduction ports 20 is parallel to the axial direction of the symmetry axis of the internal resonance mode of the chamber 10D or the axial direction of the central conductor 81. In this case, the opening faces of the multiple microwave introduction ports 20 are arranged around the central conductor 81 in a plan view of the chamber 10D and are provided perpendicular to the axial direction of the central conductor 81. The multiple microwave introduction ports 20 are provided in a part of the coaxial structure 80, i.e., the bottom wall 11 of the chamber 10D. The multiple microwave introduction ports 20 are provided directly above multiple microwave introduction ports 412C, 412C, provided in the ring-shaped resonator 412. A mounting table 110D is provided on the upper end of the central conductor 81.

[0046] Furthermore, the ring-shaped resonator 412 is disposed directly below the chamber 10D. The ring-shaped resonator 412 has a plurality of microwave introduction ports 412C, 412C, ... provided on the upper surface of the ring-shaped resonator 412. The plurality of microwave introduction ports 412C, 412C, ... are directly connected to the plurality of microwave introduction ports 20. The opening surface of the microwave introduction port 412C of the ring-shaped resonator 412 and the opening surface of the microwave introduction port 20 are provided perpendicular to the axial direction (z direction) of the central conductor 81. In this embodiment, the plurality of microwave introduction ports 412C, 412C, ... and the plurality of microwave introduction ports 20, 20, ... are provided separately, but the plurality of microwave introduction ports 412C, 412C, ... may form the plurality of microwave introduction ports 20, 20, ...

[0047] 7(B), the mounting table 110E may have an outer diameter larger than the outer diameter of the central conductor 81, and the microwave introduction window 30B may be disposed below the chamber 10E and extend along the axial direction of the axis of symmetry of the chamber 10E. In this case, the microwave introduction window 30B may have, for example, a cylindrical shape, and form a pressure partition between the sealed space S1 of the chamber 10E and the space S2 below the mounting table 110E. Plasma is generated above the mounting table 110E, and the microwave introduction window 30B is located below the mounting table 110E and is shielded by the mounting table so as not to be exposed to the plasma, thereby preventing the microwave introduction window 30B from being etched by the plasma.

[0048] 7(C), the central conductor 81 supporting the mounting table 110F may extend downwardly in the chamber 10F. In this case, the ring-shaped resonator 412 is disposed in the lower part of the chamber 10F, and the microwave introduction port 20 is provided on the radial side (x-direction) of the central conductor 81. By changing the length of the coaxial structure 80F extending downwardly, the resonance mode in the chamber 10F can be adjusted.

[0049] 7A, plasma is generated above the mounting table 110D, and the microwave introduction window 30A is provided below the mounting table 110D, thereby preventing the microwave introduction window 30B from being etched by the plasma. Also, according to the embodiments shown in FIGS. 7B and 7C, plasma is generated above the mounting table 110E, and the microwave introduction window 30B is provided below the mounting table 110E and is shielded by the mounting table 110E so as not to be exposed to the plasma. This further prevents the microwave introduction window 30B from being etched by the plasma. Similarly, plasma is generated above the mounting table 110F, and the microwave introduction window 30B is provided below the mounting table 110F and is shielded by the mounting table 110F so as not to be exposed to the plasma. This further prevents the microwave introduction window 30B from being etched by the plasma.

[0050] In the microwave plasma CVD apparatus shown in FIGS. 3 to 6, instead of a ring-shaped resonator for introducing microwaves from a plurality of ports, a waveguide may be connected to each microwave introduction port individually.

[0051] FIG. 8 shows an example in which the ring-shaped resonator in FIG. 7(A) is replaced with a plurality of waveguides.

[0052] Figure 8(A) is a side view schematically showing a modified example of the microwave plasma CVD apparatus of Figure 6(A), and Figure 8(B) is a cross-sectional view taken along line CC. The configuration of the microwave plasma CVD apparatus of Figures 8(A) and 8(B) is basically the same as the configuration of the microwave plasma CVD apparatus of Figure 6(A), and common parts are designated by the same reference numerals and their explanations are omitted, with the following explanation focusing on the differences.

[0053] As shown in Figures 8(A) and 8(B), the microwave plasma CVD apparatus 1 includes a plurality of microwave introduction ports 20, 20, ... provided in a coaxial structure 80G of a chamber 10G and coupled to match the internal resonance mode of the chamber 10G, and a plurality of microwave introduction windows 30C, 30C, ... that transmit microwaves while providing a pressure barrier between the chamber 10G and a waveguide 40B. The waveguide 40B is composed of, for example, a plurality of rectangular waveguides, and in this embodiment, four rectangular waveguides are arranged around the axis of symmetry of the chamber 10G. In the configuration shown in Figures 8(A) and 8(B), microwaves are introduced from the plurality of microwave introduction ports 20, 20, ... in a direction parallel to the axis of symmetry of the internal resonance mode of the chamber 10G. Near the opening surfaces of the multiple microwave introduction ports 20, 20, ..., the waveguide 40B is coupled to the chamber 10G so that the direction M of the magnetic field of the internal resonance mode of the chamber 10G coincides with the direction M of the magnetic field within each rectangular waveguide of the TE mode waveguide 40B.

[0054] In this embodiment, the internal resonance mode of the chamber 10G is axially symmetric, and the introduction direction of microwaves introduced from the multiple microwave introduction ports 20 is parallel to the symmetry axis of the internal resonance mode of the chamber 10G. In other words, the normal at the center of the opening surface of the multiple microwave introduction ports 20 is parallel to the symmetry axis. In this case, the opening surfaces of the multiple microwave introduction ports 20 are arranged perpendicular to the axial direction (z direction) of the symmetry axis of the internal resonance mode of the chamber 10G in a plan view of the chamber 10G. The opening surfaces of the multiple microwave introduction ports 20 have, for example, long and short sides, and the in-plane direction of the opening surface defined by the long and short sides is arranged perpendicular to the axial direction (z direction) of the symmetry axis of the internal resonance mode. The multiple microwave introduction ports 20 preferably have the same shape, but may have different shapes as long as they do not affect microwave radiation.

[0055] The opening faces of the multiple microwave introduction ports 20, 20, ... are arranged along the circumferential direction of the chamber 10G with the axis of symmetry of the internal resonance mode of the chamber 10G as a reference when viewed from above the chamber 10G. For example, the opening faces of the four microwave introduction ports 20, 20, ... are arranged side by side along the circumferential direction of the chamber 10G so as to be rotationally symmetrical by 90°. The opening face of the microwave introduction port 20 has, for example, a long side and a short side, with the long side extending along the circumferential direction of the chamber 10G and the short side extending along the axial direction of the axis of symmetry of the internal resonance mode.

[0056] The microwave introduction port 20 is typically a linear or rectangular slit. The long side of the slit is place The slit is arranged so as to be parallel to the direction of M. This generates an electric field parallel to the short side of the slit, and the slit functions as an antenna that radiates electromagnetic waves from its opening. The slit is, for example, arc-shaped, but may also be rectangular, elongated, or the like.

[0057] In this embodiment, the plurality of microwave introduction windows 30C, 30C, ... are placed on the bottom wall 11 of the chamber 10G so as to cover the plurality of microwave introduction ports 20, 20, .... The plurality of microwave introduction windows 30C, 30C, ... are installed between the chamber 10G (reduced pressure region) and the waveguide 40B (atmospheric pressure region).

[0058] Similar to the multiple microwave introduction ports 20, 20, the multiple microwave introduction windows 30C, 30C, ... are arranged along the circumferential direction of the chamber 10G with reference to the axis of symmetry of the internal resonance mode of the chamber 10G in a plan view of the chamber 10G. For example, four microwave introduction windows 30C, 30C, ... are arranged side by side with 90° rotational symmetry along the circumferential direction of the chamber 10G. The microwave introduction window 30C is not limited to an arc shape as long as it can close the microwave introduction port 20, and may have a rectangular shape, an elongated hole shape, or the like, or may be a single ring shape without being divided.

[0059] In this way, the microwave plasma CVD apparatus 1 may be configured such that microwaves are introduced into the chamber 10G via a waveguide 40B consisting of, for example, multiple rectangular waveguides. In this case, microwaves are introduced into each microwave introduction port at the same phase. This configuration also suppresses abnormal discharge in the waveguide 40B and ensures good access to the crystal, thereby improving crystal quality and enabling the production of large bulk objects to be processed.

[0060] Fig. 9 is a diagram showing the distribution of electric field strength by simulation of Example 1. Fig. 10(A) is a diagram showing the distribution of electric field strength by simulation of Example 2, and Fig. 10(B) is a diagram showing the distribution of magnetic field strength in a cross section along line DD. Fig. 11 is a perspective view showing the configuration of a microwave mode converter in a conventional microwave plasma CVD apparatus. Fig. 12 is a diagram showing the distribution of electric field strength by simulation of Comparative Example 1.

[0061] As Example 1, a structure equivalent to the configuration shown in Fig. 6(A) was designed in a simulation, and numerical calculations were performed to calculate the electric field intensity distribution. The simulation software used was JMAG-Studio (manufactured by JSOL Corporation). The calculation method used was the finite element method and iterative method, with approximately 1 million elements (tetra mesh), a model size of 1 m x 0.4 m x 0.3 m, an input microwave frequency of 2.45 GHz, a mode of TE10, and boundary conditions of perfect conductors except for the input / output port (the end of the rectangular waveguide) for inputting the microwave and the microwave introduction window. The electric field strength calculated by the simulation is shown as grayscale shading in Figure 9. The electric field strength was measured in region A in Figure 9, which corresponds to the substrate placement area, and in region B, which corresponds to the waveguide or coaxial structure area.

[0062] As Example 2, a structure (FIG. 10(A)) was designed in which the radial width of the coaxial structure portion was made larger than that of Example 1, and numerical calculations were performed in the same manner as in Example 1 to calculate the electric field intensity distribution. Figure 10(B) shows the calculated magnetic field strength distribution in the DD cross section of the ring-shaped resonator in Figure 10(A), with arrows indicating the general direction of the magnetic field lines within the ring resonator and coaxial structure. Multiple microwave introduction ports are provided on the inner periphery of the ring-shaped resonator, and are arranged at the boundary between the ring-shaped resonator and the coaxial structure so that the directions of the magnetic field lines are aligned. This allows the TE mode of microwaves propagating through the rectangular waveguide to be converted to TEM mode, which propagates through the coaxial structure, via the ring-shaped resonator.

[0063] Furthermore, as Comparative Example 1, a microwave mode converter installed in a conventional microwave plasma CVD apparatus was used. In the conventional ASteX6500 microwave plasma CVD apparatus, microwaves are introduced into a resonator-type chamber via a microwave mode converter 300 (Fig. 11) located below the chamber, and a predetermined electric field strength is obtained at the substrate placement section. That is, the conventional microwave mode converter has a structure that includes a rectangular waveguide and a coaxial line, and does not include a ring-shaped resonator. As Comparative Example 1, a structure corresponding to this conventional microwave mode converter (Fig. 12) was designed, and numerical calculations were performed to calculate the electric field strength distribution. Table 1 shows the electric field strengths in regions A and B in Examples 1 and 2 and Comparative Example 1, and the calculation results of the ratio of the electric field strength in region A to the electric field strength in region B (specific strength).

[0064] [Table 1]

[0065] The results in Table 1 show that in Example 1, when microwaves were introduced into the chamber from a rectangular waveguide via a ring-shaped resonator with multiple slits on the sidewall, a high electric field strength equivalent to that of Comparative Example 1 could be obtained in Region A, i.e., the substrate placement area. In addition, the ratio (specific strength) of the electric field strength in Region A to the electric field strength in Region B was 0.2 to 0.3, and it was found that the probability of abnormal discharge occurring in Region B, i.e., the waveguide, could be reduced compared to Comparative Example 1.

[0066] Furthermore, in Example 2, even though the radial width of the coaxial structure portion was made larger than in Example 1, it was possible to obtain a high electric field strength in region A, i.e., the substrate placement portion, equivalent to that of Comparative Example 1. Furthermore, the ratio (specific strength) of the electric field strength in region A to the electric field strength in region B was 0.7 to 2.5, which was significantly larger than the specific strength in Example 1, and it was found that the probability of abnormal discharge occurring in region B, i.e., the waveguide, could be further reduced.

[0067] On the other hand, in Comparative Example 1, when microwaves were introduced into the coaxial line from a rectangular waveguide without passing through a resonator, the ratio (specific intensity) of the electric field strength in region A to the electric field strength in region B was 0.05 to 0.3, and it was found that the probability of abnormal discharge occurring was higher than in either Example 1 or Example 2.

[0068] The present invention is not necessarily limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0069] For example, in the present embodiment, in the configuration shown in FIG. 3 , the coaxial structure 80A is provided on the bottom wall 11 of the chamber 10A. However, the present invention is not limited to this. As long as the coaxial structure is coupled to the chamber 10A in a manner that matches the internal resonance mode, and the microwave introduction window 30A is located in a position that is not exposed to the plasma generated within the chamber 10A, the locations of the coaxial structure and the microwave introduction window 30A are not particularly limited. The microwave introduction window 30A may be located, for example, in a position other than on or near an extension of the in-plane direction of the workpiece W. Alternatively, the microwave introduction window 30A may be located in a position on the bottom wall 11 that is not visually visible from the workpiece W, or in a position on the bottom wall 11 that is not visible from the workpiece W. This suppresses etching of the microwave introduction window by the plasma generated on the workpiece W, while increasing the purity of the diamond deposited or grown on the workpiece W.

[0070] Alternatively, the waveguide 40A may not have the coaxial structure 413, but may instead have a rectangular waveguide 411 and a ring-shaped resonator 412 coupled to the waveguide 411. In this case, the resonator 412 may have one or more microwave introduction ports on the upper surface of the resonator 412, and may also function as a coaxial waveguide. More specifically, in the configuration of Fig. 7(A), the microwave plasma CVD apparatus 1 may not have the coaxial structure 80D, and the mounting table 110D may be provided on the bottom wall 11 of the chamber 10D. In this case, the microwave plasma CVD apparatus 1 may include a raw material gas inlet section 60 (see FIGS. 1 and 2) that introduces a raw material gas into the chamber 10D, a plurality of microwave introduction ports 20, 20, ... coupled to match the internal resonance mode of the chamber 10D, a microwave introduction window 30A (see FIGS. 1 and 2) that transmits microwaves while providing a pressure barrier between the chamber 10D and the waveguide, a waveguide 40A (see FIGS. 1 and 2) connected to the plurality of microwave introduction ports 20, 20, ..., and a microwave oscillation source 50 (see FIGS. 1 and 2) connected to the waveguide 40A.

[0071] Furthermore, although the workpiece W is placed on both the bottom wall and the top wall of the chamber 10A, this is not limiting, and the workpiece W may be placed on either the bottom wall or the top wall of the chamber 10A. [Explanation of symbols]

[0072] 1. Microwave plasma CVD equipment 10A Chamber 10B Chamber 10C Chamber 10D Chamber 10E Chamber 10F Chamber 10G Chamber 11 Bottom wall 12 Side wall 13 Coaxial opening 20 Microwave introduction port 30A microwave introduction window 30B Microwave introduction window 30C Microwave introduction window 40A Waveguide 40B Waveguide 41 Microwave mode converter 50 Microwave Source 60 Raw material gas inlet 70 Gas exhaust section 80A coaxial structure 80B coaxial structure 80C coaxial structure 80D coaxial structure 80E coaxial structure 80F coaxial structure 80G coaxial structure 81 Center conductor 82 outer conductor 90 Circulator 91 Port 1 92 Second Port 93 Third Port 100 EH Tuner 101 E-tuner section 102 H tuner section 110A Mounting stand 110B Mounting stand 110C Mounting stand 110D Mounting Table 110E Mounting Table 110F Loading table 110G loading table 411 Waveguide 411a One end 411b Other end 412 resonator 412A Outer peripheral side wall 412B Inner side wall 412C Microwave introduction port 413 Coaxial structure 413A Peripheral side wall 413B Inner side wall

Claims

1. a rectangular waveguide, a ring-shaped resonator coupled to the waveguide, and a coaxial structure coupled to the resonator; A microwave mode converter in which the TE mode of microwaves propagating through the rectangular waveguide is converted, via the ring-shaped resonator, into a TEM mode propagating through the coaxial structure portion.

2. 2. The microwave mode converter according to claim 1, wherein the resonator has an outer circumferential side wall and an inner circumferential side wall, and has a plurality of microwave introduction ports arranged side by side along the circumferential direction of the inner circumferential side wall.

3. 3. The microwave mode converter according to claim 2, wherein opening faces of the plurality of microwave introduction ports are provided parallel to an axial direction of an axis of symmetry of the resonator, and are arranged side by side in rotational symmetry along a circumferential direction of the inner peripheral side wall with the axis of symmetry of the resonator as a reference.

4. the microwave introduction port is a linear or rectangular slit; 4. The microwave mode converter according to claim 2, wherein the slit is arranged so that its long side is parallel to the magnetic field direction at the slit in accordance with a resonance mode in the resonator, and so that the direction of the magnetic field formed in the coaxial structure by the slit is the same as the magnetic field direction in the coaxial structure.

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