Microwave plasma processing device and plasma generation method

Abstract

A microwave plasma processing device according to the present invention comprises: a resonator that includes a container; a first microwave oscillation source that introduces first microwaves that have a first frequency into the resonator; and a second microwave oscillation source that introduces second microwaves that have a second frequency into the resonator. The microwave plasma processing device is configured such that the first microwaves and the second microwaves are superimposed inside the resonator to generate plasma inside the container. The difference between the first frequency and the second frequency causes undulation in the plasma.

Description

Microwave plasma processing apparatus and plasma generation method

[0001] The present invention relates to a microwave plasma processing apparatus and a method for generating plasma.

[0002] Diamond has multiple physical properties of the highest level. Therefore, in recent years, in fields where diamond is used, focusing on its high thermal conductivity, there has been a demand for high-speed deposition of diamond films with a deposition range exceeding 3 inches. Conventional microwave plasma processing equipment for diamond deposition produces diamond substrates by the so-called CVD (Chemical Vapor Deposition) method, in which microwaves are output from a microwave source into a vessel that forms part of a resonator, generating a plasma ball near a substrate placed in the vessel. The size of the generated plasma ball, in other words, the diamond deposition range, correlates with the frequency of the microwaves output.

[0003] In a microwave plasma processing apparatus with a microwave frequency of 2.45 GHz, the diamond deposition area is limited to about 1 to 2 inches, and the position of the generated plasma ball is also fixed. On the other hand, to increase the diamond deposition area, microwaves with a low frequency, for example, about 915 MHz, are sometimes used, but this significantly reduces power efficiency and requires an extremely large device.

[0004] For this reason, a microwave plasma processing apparatus has been proposed that uses multiple phase-controlled power supplies to control the region of strong electric field, thereby controlling the position of the generated plasma ball, as described in Patent Document 1. The microwave plasma processing apparatus of Patent Document 1 can increase the diamond deposition range without using low-frequency microwaves.

[0005] Japanese Patent Application Publication No. 4-230019

[0006] In the microwave plasma processing apparatus, it is difficult to realize, for example, high-speed phase control at high power and the corresponding impedance matching. Note that this problem is not limited to the case of manufacturing diamond substrates, but may also occur when manufacturing other substrates.

[0007] An object of the present invention is to provide a microwave plasma processing apparatus and a plasma processing method that can easily manufacture large-area substrates.

[0008] A microwave plasma processing apparatus according to a first aspect of the present invention comprises a resonator including a container, a first microwave source that introduces a first microwave having a first frequency into the resonator, and a second microwave source that introduces a second microwave having a second frequency into the resonator, wherein the first microwave and the second microwave are superimposed in the resonator to generate plasma in the container, and the difference between the first frequency and the second frequency is such that undulations occur in the plasma.

[0009] A microwave plasma processing apparatus according to a second aspect of the present invention is the microwave plasma processing apparatus according to the first aspect, wherein the absolute value of the difference between the first frequency and the second frequency is less than 0.1 MHz.

[0010] A microwave plasma processing apparatus according to a third aspect of the present invention is the microwave plasma processing apparatus according to the first or second aspect, wherein at least one of the first microwave oscillation source and the second microwave oscillation source is a semiconductor microwave oscillation source or a frequency injection-locked magnetron using the semiconductor microwave oscillation source.

[0011] A plasma processing method according to a fourth aspect of the present invention includes the steps of introducing a first microwave having a first frequency by a first microwave source into a resonator including a container, and introducing a second microwave having a second frequency by a second microwave source into the resonator, wherein the first microwave and the second microwave are superimposed in the resonator to generate plasma in the container, and a difference between the first frequency and the second frequency is a difference that generates undulations in the plasma.

[0012] According to the microwave plasma processing apparatus and plasma processing method of the present invention, large area substrates can be easily manufactured.

[0013] Fig. 1 is a schematic diagram of a microwave plasma processing apparatus according to an embodiment; Fig. 2 is a flowchart showing an example of a processing procedure of a plasma processing method performed using the microwave plasma processing apparatus of Fig. 1; Fig. 3 is a diagram showing the inside of a container of a microwave plasma processing apparatus according to Example 1; Fig. 4 is a diagram showing the inside of a container of a microwave plasma processing apparatus according to Example 2; Fig. 5 is a diagram showing the inside of a container of a microwave plasma processing apparatus according to Example 3; Fig. 6 is a diagram showing the inside of a container of a microwave plasma processing apparatus according to Comparative Example 1; Fig. 7 is a diagram showing the inside of a container of a microwave plasma processing apparatus according to Comparative Example 2; Fig. 8 is a diagram showing the inside of a container of a microwave plasma processing apparatus according to Comparative Example 3; Fig. 9 is a diagram showing the inside of a container of a microwave plasma processing apparatus according to Comparative Example 4.

[0014] Hereinafter, a microwave plasma processing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[0015] <1-1. Overall Configuration of Microwave Plasma Processing Apparatus> Figure 1 is a schematic diagram of a microwave plasma processing apparatus 10 according to this embodiment. The microwave plasma processing apparatus 10 is used to manufacture large diamond substrates, for example, with a diameter of at least 100 mm, by a CVD method. The microwave plasma processing apparatus 10 includes a first microwave source 21, a second microwave source 22, a resonator 30, and a waveguide 60.

[0016] The first microwave source 21 outputs microwaves to be supplied into the container 30A of the resonator 30. The first microwave source 21 is, for example, a magnetron power supply. Hereinafter, the microwaves output by the first microwave source 21 may be referred to as the first microwave. The center frequency of the first microwave is, for example, 2450 MHz (2.45 GHz), 915 MHz, or 10 GHz or higher.

[0017] The second microwave source 22 outputs microwaves to be supplied into the container 30A of the resonator 30. The second microwave source 22 is, for example, a magnetron power supply. Hereinafter, the microwaves output by the second microwave source 22 may be referred to as "second microwaves." The center frequency of the second microwaves is, for example, 2450 MHz (2.45 GHz), 915 MHz, or 10 GHz or higher.

[0018] The microwave plasma processing apparatus 10 is configured so that plasma is generated in the container 30A by superimposing the first microwave and the second microwave in the resonator 30. In the microwave plasma processing apparatus 10, the first frequency, which is the frequency of the first microwave, and the second frequency, which is the frequency of the second microwave, are set to be slightly different so that the plasma generated in the container 30A interferes with each other and generates undulations in the plasma. When undulations occur in the plasma, the plasma emits light (discharges) more strongly over a wider range within the container 30A.

[0019] The absolute value of the difference Δf between the first frequency and the second frequency can be selected arbitrarily as long as it generates undulations in the plasma. For example, the first frequency is 2450 MHz and the second frequency is 2450.001 MHz. That is, the absolute value of the difference Δf is 0.001 MHz. In another example, the first frequency is 2450.001 MHz and the second frequency is 2449.999 MHz. That is, the absolute value of the difference Δf is 0.002 MHz. The first frequency may be greater or smaller than the second frequency. From the viewpoint of suitably generating undulations in the plasma, it is preferable that the absolute value of the difference Δf be in the range of greater than 0 and less than 0.1 MHz. From this viewpoint, it is preferable that at least one of the first microwave source 21 and the second microwave source 22 be a semiconductor microwave source capable of precisely controlling the frequency or a frequency injection-locked magnetron using a semiconductor microwave source.

[0020] The resonator 30 includes a container 30A, a peripheral waveguide 30B, a substrate support table 40, a source gas supply path 51, an exhaust path 52, and an entrance window 80.

[0021] The container 30A is a vacuum container. The pressure inside the container 30A is, for example, in the range of 50 Torr to 200 Torr. The shape of the container 30A can be selected arbitrarily. In this embodiment, the container 30A is cylindrical. An outer circumferential waveguide 30B connected to the waveguide 60 is attached to the peripheral wall 32 of the container 30A. The outer circumferential waveguide 30B has a shape that surrounds the container 30A along the peripheral wall 32 of the container 30A. The substrate support table 40 is accommodated in the internal space 31 of the container 30A. A base material 100 for manufacturing a diamond substrate is placed on the substrate support table 40. The shape of the substrate support table 40 can be selected arbitrarily. In this embodiment, the substrate support table 40 is disk-shaped.

[0022] The material constituting the substrate 100 can be arbitrarily selected as long as it allows a carbon source in the raw material gas described below to form a film on the substrate 100 and grow a diamond having a diamond crystal structure. Examples of the material constituting the substrate 100 include single crystal diamond, polycrystalline diamond, silicon, 3C silicon carbide, gallium nitride, gallium oxide, iridium, platinum, nickel, magnesium oxide, yttrium-stabilized zirconia, and high-melting point metals such as molybdenum.

[0023] The source gas supply line 51 supplies a source gas for forming a diamond substrate to the internal space 31 of the container 30A. The source gas supply line 51 is connected to the peripheral wall 32 of the container 30A, for example, below or above the peripheral waveguide 30B in the height direction of the container 30A. The source gas is, for example, a mixed gas containing carbon, hydrogen, nitrogen, and oxygen.

[0024] The exhaust passage 52 is connected to the peripheral wall 32 of the container 30A, for example, below or above the outer peripheral waveguide 30B in the height direction of the container 30A, so that the gas inside the container 30A can be exhausted. The end of the exhaust passage 52 opposite the container 30A is connected to a vacuum pump (not shown). When the vacuum pump is operated, the gas inside the container 30A passes through the exhaust passage 52 and is exhausted to the outside of the container 30A.

[0025] The waveguide 60 includes a first waveguide 61 and a second waveguide 62. The first waveguide 61 and the second waveguide 62 are, for example, circular waveguides or rectangular waveguides. The first waveguide 61 connects the first microwave source 21 and the outer peripheral waveguide 30B so that the first microwave is introduced into the container 30A. The second waveguide 62 connects the second microwave source 22 and the outer peripheral waveguide 30B so that the second microwave is introduced into the container 30A.

[0026] Holes 32A are formed in the peripheral wall 32 of the container 30A. The number of holes 32A formed in the container 30A can be selected arbitrarily. In this embodiment, eight holes 32A are formed at predetermined intervals around the circumference of the container 30A. The number of holes 32A formed in the container 30A may be two to seven, or nine or more. An entrance window 80 that transmits a microwave mixture of the first microwave and the second microwave is attached to the hole 32A. The entrance window 80 is made of, for example, quartz glass or alumina.

[0027] The first microwave introduced into the outer peripheral waveguide 30B via the first waveguide 61 and the second microwave introduced into the outer peripheral waveguide 30B via the second waveguide 62 travel through the outer peripheral waveguide 30B, are mixed, and are introduced into the container 30A via the multiple holes 32A and the entrance window 80.

[0028] By introducing the first microwave and the second microwave into the peripheral waveguide 30B, the first microwave and the second microwave interfere with each other. As a result, a region of high electric field strength is locally formed within the container 30A. In the region of high electric field strength, molecules of the source gas are separated into electrons and chemically active species, thereby generating a plasma ball. The chemically active species include ions and radicals. The diameter of the generated plasma ball is, for example, 50 mm. The chemically active species contained in the plasma ball react on the surface of the substrate 100, forming diamond crystals, which grow to produce a diamond substrate. The manufactured diamond substrate includes the substrate 100 and the diamond crystals formed on the substrate 100.

[0029] 2, an example of a plasma processing method using the microwave plasma processing apparatus 10 will be described. The plasma processing method includes a first step and a second step.

[0030] In a first step of step S11, a first microwave is output from a first microwave source. In a second step of step S12, a second microwave is output from a second microwave source. Note that the order of steps 1 and 2 may be reversed, or steps 1 and 2 may be performed simultaneously.

[0031] <1-3. Effects of the Microwave Plasma Processing Apparatus> According to the microwave plasma processing apparatus 10, the absolute value of the difference Δf between the first and second frequencies is a value that generates undulations in the plasma, so that the plasma emits (discharges) over a wider area within the container 30A, for example, 10.16 cm (4 inches). In other words, a state equivalent to that achieved when multiple microwaves are phase-controlled and superimposed at a constant speed can be easily achieved. Therefore, the microwave plasma processing apparatus 10 does not require a phase controller, and large-area substrates can be easily manufactured without high-speed phase control and the associated impedance matching. In other words, the microwave plasma processing apparatus 10 can easily increase the processing area relative to the input power.

[0032] Furthermore, in a microwave plasma processing apparatus (hereinafter referred to as "another conventional microwave plasma processing apparatus") configured to introduce microwaves output from a single microwave oscillation source into the resonator 30, the plasma emission (discharge) range is, for example, approximately 2.54 cm (1 inch) to 25.08 cm (2 inches). Therefore, it is not expected that the other conventional microwave plasma processing apparatus will significantly improve the process efficiency of plasma-based film deposition apparatuses and surface processing apparatuses. On the other hand, with the microwave plasma processing apparatus of this embodiment, as described above, emission (discharge) occurs over a range of, for example, 10.16 cm (4 inches), making it easy to manufacture large-area substrates.

[0033] 2. Examples The inventors of the present application conducted tests to observe the plasma emission range PA within the container 30A using the microwave plasma processing apparatuses 10 of Examples 1 to 3 and Comparative Examples 1 to 4. The common specifications of the microwave plasma processing apparatuses 10 of Examples 1 to 3 and Comparative Examples 1 to 4 are as follows.

[0034] The output of the first microwave and the second microwave is 250 W. The pressure inside the container 30A is 6 torr.

[0035] 3 is a diagram showing the inside of the chamber 30A of the microwave plasma processing apparatus 10 of Example 1. In Example 1, the first frequency is 2450 MHz, and the second frequency is 2450.001 MHz. That is, the absolute value of the difference Δf is 0.001 MHz. In Example 1, it was confirmed that the plasma emission range PA was wide.

[0036] 4 is a diagram showing the inside of the chamber 30A of the microwave plasma processing apparatus 10 of Example 2. In Example 2, the first frequency is 2450.001 MHz, and the second frequency is 2449.999 MHz. That is, the absolute value of the difference Δf is 0.002 MHz. In Example 2, it was confirmed that the plasma emission range PA was wide.

[0037] 5 is a diagram showing the inside of the chamber 30A of the microwave plasma processing apparatus 10 of Example 3. In Example 3, the first frequency is 2450 MHz and the second frequency is 2449.99 MHz. That is, the absolute value of the difference Δf is 0.01 MHz. In Example 3, it was confirmed that the plasma emission range PA was wide.

[0038] It was confirmed that the microwave plasma processing apparatus 10 of Examples 1 to 3 could spread plasma to a size of 10.16 cm (4 inches) or more, and that the plasma spread flat. Since the power consumption of plasma is roughly proportional to its volume, the same volume of plasma can be generated with the same power. Furthermore, a flat plasma shape can expand the processing area more than a spherical shape. Therefore, it was confirmed that the microwave plasma processing apparatus 10 of Examples 1 to 3 could increase the processing area relative to the input power.

[0039] 6 is a diagram showing the inside of the vessel 30A of the microwave plasma processing apparatus 10 of Comparative Example 1. In Comparative Example 1, the first frequency is 2450 MHz and the second frequency is 2450 MHz. That is, the absolute value of the difference Δf is 0 MHz. In Comparative Example 1, it was confirmed that the plasma emission range PA is localized, and the emission intensity is very weak, particularly in the center in the left-right direction. This is thought to be because in Comparative Example 1, the first frequency and the second frequency are equal, so the first microwave and the second microwave do not interfere with each other and no swell occurs.

[0040] 7 is a diagram showing the inside of the vessel 30A of the microwave plasma processing apparatus 10 of Comparative Example 2. In Comparative Example 2, the first frequency is 2450 MHz and the second frequency is 2449.9 MHz. That is, the absolute value of the difference Δf is 0.1 MHz. In Comparative Example 2, it was confirmed that the plasma emission range PA is localized, and the emission intensity is very weak, especially in the center in the left-right direction.

[0041] FIG. 8 is a diagram showing the inside of the vessel 30A of the microwave plasma processing apparatus 10 of Comparative Example 3. In Comparative Example 3, the first frequency is 2450 MHz and the second frequency is 2449 MHz. That is, the absolute value of the difference Δf is 1.0 MHz. In Comparative Example 3, it was confirmed that the plasma emission range PA is localized, and the emission intensity is particularly weak in the center in the horizontal direction. Furthermore, it was confirmed that the plasma emission intensity on the right side in the horizontal direction is lower in Comparative Example 3 than in Comparative Example 2.

[0042] FIG. 9 is a diagram showing the inside of the vessel 30A of the microwave plasma processing apparatus 10 of Comparative Example 4. In Comparative Example 4, the first frequency is 2450 MHz and the second frequency is 2448 MHz. That is, the absolute value of the difference Δf is 2.0 MHz. In Comparative Example 4, it was confirmed that the plasma emission range PA is localized, and the emission intensity is particularly weak in the center in the horizontal direction. Furthermore, in Comparative Example 4, it was confirmed that the plasma does not substantially emit light on the right side in the horizontal direction.

[0043] In Comparative Examples 2 to 4, although the first microwave and the second microwave interfere with each other, the absolute value of the difference Δf between the first frequency and the second frequency is large, so the mismatch between the first microwave and the second microwave is larger than in Examples 1 to 3, and the reflected wave is thought to be increased.

[0044] 3. Modifications The above-described embodiments are examples of possible forms of the microwave plasma processing apparatus and plasma processing method according to the present invention, and are not intended to limit the forms. The microwave plasma processing apparatus and plasma processing method according to the present invention may take forms different from those exemplified in the embodiments. Examples include forms in which part of the configuration of the embodiments is replaced, modified, or omitted, or forms in which a new configuration is added to the embodiments. Below are some examples of modifications of each embodiment. Note that the following modifications can be combined with each other as long as there is no technical contradiction.

[0045] <3-1> In the above embodiment, the microwave plasma processing apparatus 10 includes two microwave sources, i.e., the first microwave source 21 and the second microwave source 22. However, the microwave plasma processing apparatus 10 may include three or more microwave sources. For example, if the microwave plasma processing apparatus 10 includes a third microwave source in addition to the first microwave source 21 and the second microwave source 22, the third microwave source may output a third microwave to the resonator 30. The third frequency of the third microwave is preferably different from at least one of the first frequency and the second frequency. The absolute value of the difference Δf between the first frequency and the third frequency is preferably a value that generates undulations in the plasma. The absolute value of the difference Δf between the second frequency and the third frequency is preferably a value that generates undulations in the plasma.

[0046] <3-2> In the above embodiment, the outer circumferential waveguide 30B may be omitted from the microwave plasma processing apparatus 10. In this modification, the first waveguide 61 and the second waveguide 62 may be directly connected to the container 30A.

[0047] <3-3> In the above embodiment, the first waveguide 61, the second waveguide 62, and the outer circumferential waveguide 30B may be omitted. In this modification, the shape of the peripheral wall 32 of the container 30A may be such that it is connected to the first microwave oscillation source 21 and the second microwave oscillation source 22.

[0048] <3-4> The microwave plasma processing apparatus 10 of the above embodiment was used to manufacture diamond substrates, but it can also be applied to the manufacture of other substrates by changing the conditions such as the source gas and the plasma movement period.

[0049] 10: Microwave plasma processing apparatus 21: First microwave source 22: Second microwave source 30: Resonator 30A: Container

Claims

1. A microwave plasma processing apparatus comprising: a resonator including a container; a first microwave oscillation source that introduces a first microwave having a first frequency into the resonator; and a second microwave oscillation source that introduces a second microwave having a second frequency into the resonator; wherein the first microwave and the second microwave are superimposed in the resonator to generate plasma in the container; and the difference between the first frequency and the second frequency is such that undulations occur in the plasma.

2. The microwave plasma processing apparatus according to claim 1, wherein the absolute value of the difference between the first frequency and the second frequency is less than 0.1 MHz.

3. The microwave plasma processing apparatus according to claim 1 or 2, wherein at least one of the first microwave oscillation source and the second microwave oscillation source is a semiconductor microwave oscillation source or a frequency injection locked magnetron using the semiconductor microwave oscillation source.

4. A plasma generation method comprising the steps of: introducing a first microwave having a first frequency by a first microwave oscillation source into a resonator including a container; and introducing a second microwave having a second frequency by a second microwave oscillation source into the resonator, wherein the first microwave and the second microwave are superimposed in the resonator to generate plasma in the container, and the difference between the first frequency and the second frequency is such that undulations occur in the plasma.

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