Device for forming diamond film or the like, and method for forming the same

Abstract

To provide a diamond formation device capable of suppressing electrode melting caused in a case of using a DC power supply as a power source for generating plasma in a liquid, and a method for forming the same.SOLUTION: A device for forming at least a diamond film on a surface of a base material 30 includes: a container 10 for holding a raw material liquid 20 and installing a base material in the raw material liquid; an electrode part 40 that includes a positive electrode 41 and a negative electrode 42 and generates plasma in the raw material liquid; a raw material gas supply part and a carrier gas supply part, each of which is connected to the electrode part; and a power source 70 for applying a voltage on the electrode part. The power source is a DC power supply. The electrode part further includes an additional member 43. The additional member is attached to an electrode positioned in a generation region of the plasma P of the electrode part.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a device for forming a diamond film or the like and a method for forming the same.

Background Art

[0002] As a method for forming a diamond film, a vapor phase synthesis method has been known heretofore. In this vapor phase synthesis method, there have been technical problems such as "slow growth rate of the diamond film" and "requirement for diamond formation in a chamber under high pressure conditions". Therefore, attempts have already been made to generate plasma P' in a raw material liquid under the use conditions of a high-frequency power source 70' and thereby form a diamond film on a substrate 30' (see FIG. 4).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventors of the present application have noticed that there are still problems to be overcome when using a conventional device for forming a diamond film, and have found a need for measures therefor. Specifically, the inventors of the present application have found the following problems.

[0005] In a mode of generating plasma P' in a raw material liquid 20' under the use conditions of a high-frequency power source 70' (a component of a diamond film forming device), the structure of the forming device becomes complicated, and it is necessary to supply relatively large power at high cost. Therefore, the introduction of a DC power source is desired from the viewpoints of simplifying the structure of the forming device and supplying large power at low cost.

[0006] However, when using a DC power supply, the plasma formed by applying a voltage to the electrodes can reach a very high temperature compared to when using a high-frequency power supply 70' (when using a high-frequency power supply: 4000K, when using a DC power supply: 7000K - 10000K).

[0007] When the plasma is in a very high temperature state, the electrodes (especially the positive electrode) may be overheated and the electrodes may melt. If the electrodes melt, there is a risk that the target substance (diamond) formed on the substrate by plasma irradiation cannot be obtained suitably due to this.

[0008] For the above reasons, avoiding the use of a DC power supply as a power source for generating plasma in a liquid can be recognized by those skilled in the art. However, DC power supplies have the advantages of simplifying the structure of the forming device and being able to supply large power at low cost as described above. Therefore, effective utilization of such a DC power supply with such advantages can be considered.

[0009] Therefore, an object of the present invention is to provide a diamond forming device and a forming method thereof that can suppress electrode melting that may occur when using a DC power supply.

Means for Solving the Problems

[0010] To achieve the above object, in one embodiment of the present invention, A device for forming at least a diamond film on the surface of a substrate, A container for holding a raw material liquid and installing a substrate in the raw material liquid, An electrode part having a positive electrode and a negative electrode and generating plasma in the raw material liquid, A raw material gas supply part and a carrier gas supply part respectively connected to the electrode part, A power supply for applying a voltage to the electrode part And having, The power supply is a DC power supply, and A device is provided, wherein the electrode part further includes an additional member, and the additional member is attached to an electrode located in the plasma generation region of the electrode part.

[0011] Moreover, in order to achieve the above object, in one embodiment of the present invention, A method for forming at least a diamond film on the surface of a substrate, comprising: placing a substrate in a container and holding a raw material liquid in the container in which the substrate is placed; supplying a raw material gas and a carrier gas into an electrode part having a positive electrode and a negative electrode and positioned with its tip side in the raw material liquid; and applying a voltage to the electrode part using a power source to generate plasma at the tip side of the electrode part. The method includes: using a DC power source as the power source, and using an electrode part further including an additional member, the additional member being attached to an electrode located in the plasma generation region of the electrode part.

Advantages of the Invention

[0012] According to the present invention, it is possible to suppress the above-mentioned electrode melting that may occur when using a DC power source. Therefore, even when using a DC power source as the power source, a diamond film can be suitably formed on the surface of the substrate.

Brief Description of the Drawings

[0013]

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DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a diamond film forming device according to an embodiment of the present invention will be described. Prior to the description of the configuration of the diamond film forming device of the present invention, the background leading to the invention of the present invention will be described.

[0015] (Background Leading to the Invention of the Present Invention) As described above, the inventors of the present application have found that in conventional diamond film forming devices, it is common for those skilled in the art to use a high-frequency power source as a power supply component, and it is not common for those skilled in the art to use a DC power source. Such matters are based on the following content. When a DC power source is used as the power supply, compared with the case of using a high-frequency power source, the plasma formed by applying a voltage to the electrode becomes extremely hot, whereby the electrode is overheated and there is a risk of the electrode melting. Such melting of the electrode can inhibit suitable diamond formation on the substrate by plasma irradiation. Therefore, the inventors of the present application recognize that avoiding the use of a DC power source as a power supply for generating plasma in a liquid is the recognition of those skilled in the art. In this regard, the DC power source has the advantage that it is possible to simplify the structure of the forming device and supply high power at low cost.

[0016] Therefore, the inventors of the present application have "deliberately" focused on the availability of effectively using a DC power source, which is considered not common for those skilled in the art, and have devised the present invention in order to embody that focus point. That is, the present invention has been devised based on the idea of how to realize the use of a DC power source, which is considered not common for those skilled in the art. On the other hand, conventionally, as described above, the use of a DC power source as a power supply has led to the idea that it can result in inhibiting suitable diamond formation. That is, the conventional idea and the idea of "how to realize the use of a DC power source" are fundamentally in a contradictory relationship. From the above, it can be said that the present invention has been newly devised by the inventors of the present application despite the existence of a contradictory relationship. In this regard, the present invention has technical significance.

[0017] As can be seen from the above, the very fact that the "usability of a DC power source" is newly considered, which runs counter to the thinking of conventional persons skilled in the art, itself has technical significance. On the other hand, in order to realize it, it is necessary to overcome the newly found technical problem of "electrode melting due to exposure to a plasma atmosphere in a very high temperature state". The inventors of the present application have intensively studied to overcome the newly found technical problem, and as a result, have come up with the present invention. From the viewpoint of overcoming the above technical problem, the inventors of the present application have found that an additional member (or an added member) is newly introduced to the electrode portion.

[0018] (Specific Configuration of the Present Invention) Hereinafter, the configuration of a diamond film forming device according to an embodiment of the present invention will be described with reference to the drawings.

[0019] FIG. 1 shows a cross-sectional view schematically showing a diamond film forming device according to an embodiment of the present invention. FIG. 2 shows an enlarged cross-sectional view schematically showing an electrode portion and its peripheral member which are components of a diamond film forming device according to an embodiment of the present invention. FIG. 3 shows an enlarged cross-sectional view schematically showing an electrode portion which is a component of a diamond film forming device according to an embodiment of the present invention.

[0020] A diamond film forming device 100 according to an embodiment of the present invention comprises the following components as shown in FIG. 1. Specifically, a diamond film forming device 100 according to an embodiment of the present invention comprises a container 10, an electrode portion 40, a raw material gas supply portion 50, a carrier gas supply portion 60, a power source 70, a gas cooling portion 80, and a liquid tank 90.

[0021] The container 10 is for holding the raw material liquid 20 and installing the base material 30 in the raw material liquid 20. From the viewpoint of more preferably providing the carbon source necessary for forming the diamond film described later, the raw material liquid 20 can be a liquid having the same composition as the raw material gas 50X. Without being limited to this, the raw material liquid 20 may be composed of water from the viewpoint of only cooling the tip 40X of the electrode portion 40 positioned in the raw material liquid 20. The base material 30 is a member serving as a base for forming the diamond film described later on its surface (upper surface), and is composed of cemented carbide, silicon, or the like. The cemented carbide mentioned here is, for example, obtained by mixing and sintering tungsten carbide (WC) and cobalt (Co) functioning as a binder. Note that titanium carbide (TiC) or the like can be added from the viewpoint of further improving the material characteristics.

[0022] The electrode part 40 includes a positive electrode 41 and a negative electrode 42, and is for generating plasma P in the raw material liquid 20 in a state where a voltage is applied. The constituent material of the positive electrode 41 may be a Cu-based material, and the constituent material of the negative electrode 42 may be a W-based material. The electrode part 40 for generating plasma P in the raw material liquid 20 is configured such that its tip is positioned at least within the raw material liquid 20. Although not particularly limited, the positive electrode 41 may adopt a cylindrical structure having an internal space region 41X. When a cylindrical structure can be adopted, a receiving member for receiving a part of the positive electrode 41 having the cylindrical structure may be further provided. Although not particularly limited, the receiving member and the raw material gas supply part 50 may be connected via a raw material gas supply pipe. Also, the receiving member and the carrier gas supply part 60 may be connected via a carrier gas supply pipe. On the other hand, the negative electrode 42 may adopt a rod-shaped (columnar) structure that can extend within the internal space region 41X of the positive electrode 41. When such a structure is adopted, the generation region of plasma P is provided between the cylindrical positive electrode 41 and the rod-shaped negative electrode 42 that extends within the internal space region 41X of the positive electrode 41. Also, from the viewpoint of more preferably facilitating the supply of at least the carbon source necessary for forming the diamond film described later to the substrate 30 by plasma P, the electrode part 40 is positioned adjacent to the upper vertical side of the substrate 30 so that the electrode part 40 and the substrate 30 face each other. In other words, the substrate 30 is positioned adjacent to the lower vertical side (in the direction of gravity) of the electrode part 40. Note that the distance between the electrode part 40 and the substrate 30 may be 0.5 mm to 3.0 mm, preferably 1.0 mm to 2.5 mm, and more preferably 1.5 mm to 2.0 mm from the viewpoint of directly irradiating the generated plasma P to the substrate 30.

[0023] The raw material gas supply part 50 is connected to the electrode part 40, and is configured to be able to supply the raw material gas 50X to the electrode part 40. The raw material gas supply part 50 corresponds to a pressure vessel for heating and vaporizing a solution that is the source of the raw material gas. The carrier gas supply part 60 is connected to the electrode part 40, and is configured to be able to supply the carrier gas 60X to the electrode part 40. The power supply 70 is for applying a voltage to the electrode part 40, and in the present invention, a DC power supply 71 is used as the power supply 70.

[0024] When the raw material gas 50X and the carrier gas 60X are supplied into the electrode part 40 in a state where a voltage is applied to the electrode part 40 (i.e., a potential difference generation state), a plasma state is formed based on each gas. Specifically, when each gas is supplied into the electrode part 40 in a state where a voltage is applied to the electrode part 40, the molecules of the raw material gas 50X and the molecules of the carrier gas 60X are each ionized between the electrodes and enter a moving state in which they are separated into ions and electrons. In such a moving state, plasma P is generated. In one embodiment, as the carrier gas 60X, helium gas, neon gas, argon gas, nitrogen gas, or the like can be used. As the solution serving as the source of the raw material gas 50X, a liquid containing a carbon source can be used.

[0025] (Method for forming a diamond film or the like) When using the diamond film or the like forming device 100 having the above components, at least the following steps can be passed through to form at least a diamond film on the surface of the substrate 30. ● Step of installing the substrate 30 in the container 10 and holding the raw material liquid 20 in the container 10 in which the substrate 30 is installed ● Step of supplying the raw material gas 50X and the carrier gas 60X into the electrode part 40 provided with the positive electrode 41 and the negative electrode 42 and having the tip 40X side positioned in the raw material liquid 20, and ● Step of applying a voltage to the electrode part 40 using the power source 70 (DC power source 71) to generate plasma P on the tip 40X side of the electrode part 40

[0026] As described above, when the raw material gas 50X and the carrier gas 60X are supplied into the electrode portion 40 with a voltage applied to the electrode portion 40, the molecules of the raw material gas 50X and the molecules of the carrier gas 60X are each ionized between the electrodes and enter a moving state in which they are separated into ions and electrons. In such a moving state, plasma P is generated. When plasma P is generated based on the carrier gas 60X and the raw material gas 50X, at least the carbon source (C source) in the raw material gas 50X is extracted by the heat of the plasma P. Since the plasma P can be directly irradiated onto the base material 30 as described above, accordingly, the extracted carbon source is provided to the surface (particularly the upper surface) side of the base material 30 located adjacent to the vertical lower side of the electrode portion 40. Due to the supply of the carbon source to the surface (particularly the upper surface) side of such a base material 30, diamond film formation on the base material 30 becomes possible.

[0027] As can be seen from the following examples, from the viewpoint of finally suitably obtaining a diamond film, as the liquid containing the carbon source, for example, a combination of methanol (90% by volume or more) and ethanol (10% by volume or less) can be used. Without being limited thereto, water may be contained in the liquid containing the carbon source. As also shown in the following examples, when a base material made of cemented carbide is used as the base material 30, a diamond film is formed on most of the main surface of the base material 30 due to the carbon source, and it has been newly discovered that fibrous carbon nanotubes (CNTs) are also formed in part on the main surface of the base material 30. It is known that the carbon nanotubes (CNTs) can be synthesized using Co particles as a catalyst. Regarding this, as described above, the cemented carbide contains Co as a binder. Therefore, the inventors of the present application understand that when the plasma P is irradiated onto the base material 30, Co is dissolved and atomized from the base material 30, and carbon nanotubes (CNTs) are formed from the carbon source of the raw material gas 50X taken out by the plasma P using the Co as a catalyst.

[0028] In addition, in the above formation method, it is preferable to adopt the following aspects.

[0029] In one aspect, it is preferable to supply a first plasma based on the carrier gas 60X and a second plasma based on the raw material gas 50X from the generation region of the plasma P to the substrate 30, and to supply the first plasma to the substrate 30 prior to the supply of the second plasma.

[0030] When irradiating the surface (upper surface) of the substrate 30 with the plasma P, it has already been known that it is preferable that the substrate 30, which is the irradiated member, is also preheated from the viewpoint of preferably forming the obtained diamond film. In this regard, the recognition of those skilled in the art in the past has been "heating the substrate using an external heat source". Regarding such common sense of those skilled in the art in the past, an aspect without using an external heat source has been intensively studied from the viewpoint of "overall dimensional reduction and configuration simplification of the diamond film forming device 100 and the like". As a result, the inventors of the present application have devised an aspect in which, instead of simultaneously supplying the raw material gas 50X and the carrier gas 60X as in the past, a plasma based on the carrier gas is intentionally formed earlier in time, and the high-temperature heat of the plasma is transmitted to the substrate 30 side. According to such an aspect, it becomes possible to heat the substrate 30 without using an external heat source prior to supplying the carbon source resulting from the raw material gas to the substrate 30 side for diamond film formation. From the above, it becomes possible to preferably form a diamond film obtained without using an external heat source. In this regard, this aspect is characteristic from the viewpoint of the manufacturing process.

[0031] (Introduction of additional member) Here, the inventors of the present application have earnestly studied in order to overcome the above-mentioned technical problem that "when using the DC power supply 71 as the power supply 70, the electrode may melt due to the electrode part 40 being exposed to the plasma P in a very high temperature state". As a result, the inventors of the present application have devised to give characteristics to the electrode part 40 which is a component of the diamond film forming device 100. Specifically, as shown in FIG. 2, as a component of the electrode part 40 exposed to the atmosphere of the plasma P in a very high temperature state, in addition to the positive electrode 41 and the negative electrode 42, an additional member 43 is newly introduced. The "additional member" as used in this specification refers to a member additionally or additionally provided as a component of the electrode part. As shown in FIG. 2, the additional member 43 is attached to the electrode located in the plasma P generation region of the electrode part 40. That is, it can be said that the additional member 43 is an attachment member 43X additionally attached to the electrode located in the plasma P generation region. On the other hand, in the conventional diamond film forming device, there is no technical idea of "deliberately" newly introducing an additional member in addition to the positive electrode and the negative electrode as components of the electrode part. In this regard, it can be said that the configuration of the diamond film forming device of the present invention is characteristic compared with the conventional aspect.

[0032] (Function of additional member: Protection of the electrode itself located in the plasma generation region) The fact that the additional member 43 is additionally attached to the electrode located in the plasma P generation region means that the electrode located in the plasma P generation region is covered by the additional member 43. That is, by performing such covering, the additional member 43 can function as a protection member for the electrode itself located in the plasma P generation region. Thereby, due to the presence of the additional member 43, it becomes possible to suitably avoid the electrode located directly below the additional member 43 from being directly exposed to the plasma P. Therefore, due to such avoidance, it becomes possible to suitably suppress the melting of the electrode due to the electrode part 40 being exposed to the plasma P in a very high temperature state.

[0033] (Function of additional member: Prevention of melting of electrode located in plasma generation region) Based on the above-described technical effect of "preferably suppressing electrode melting caused by exposing the electrode portion 40 to the plasma P in a very high-temperature state", the additional member 43 can function as an electrode melting prevention member 43Y. Note that the "electrode melting prevention member" as used in this specification refers to a member for preventing the melting of the electrode which is a component of the electrode portion. In contrast, in a conventional diamond film forming device, there is no such technical concept of "deliberately" further introducing an electrode melting prevention member as a component of the electrode portion in the first place. Also in this regard, the configuration of the diamond film forming device of the present invention is characteristic as compared with the conventional aspect.

[0034] (Function of additional member: impurity supply) Furthermore, the inventors of the present application recognize that when the additional member 43 is newly introduced as a component of the electrode portion 40, since the additional member 43 itself is also exposed to the high-temperature thermal atmosphere of the plasma, partial melting of the additional member 43 may occur. When partial melting of the additional member 43 occurs, in addition to the carbon source (C source) in the source gas 50X being extracted by the heat of the plasma P due to this, it is conceivable that impurities caused by the constituent material of the additional member 43 may be generated. In this case, the additional member 43 can function as an impurity supply source member 43Z. Note that the "impurity supply source member" as used in this specification refers to a member that can be a source for supplying impurities to the surface side of the base material. Since the generated plasma P can be directly irradiated onto the base material 30, the carbon source extracted due to this and the impurities caused by the constituent material of the additional member 43 are provided to the surface (particularly the upper surface) side of the base material 30.

[0035] Here, for example, when a small amount of impurities (such as phosphorus) is added to a Si film, the physical properties of the film can be changed, and thereby a desired Si semiconductor can be formed. That is, the understanding of those skilled in the art is that adding a small amount of impurities to the film is necessary to obtain a desired semiconductor. In recent years, in place of Si-based materials, diamond-based materials with strong resistance to the external environment have begun to be used as the film (substrate). From the above, there is a possibility that by adding a small amount of impurities (such as phosphorus) to a diamond film, the physical properties of the film can be changed, and thereby a desired diamond semiconductor can be formed.

[0036] In the present invention, since the plasma P generated as described above can be directly irradiated onto the substrate 30 serving as a base, impurities resulting from the carbon source taken out due to this and the constituent materials of the additional member 43 are provided on the surface side of the substrate 30. That is, in the present invention, not only the carbon source that can directly contribute to the formation of the diamond film, but also impurities resulting from the constituent materials of the additional member 43 are supplied to the substrate 30 side at "the same timing". This means that it is possible to form a film due to the fact that the carbon source and impurities can be supplied to the substrate 30 at "the same timing" without providing a conventional step of separately adding a small amount of impurities to the diamond film. That is, without providing a conventional step of separately adding a small amount of impurities to the diamond film, there is a possibility that the physical properties of the obtained diamond film can be changed by the presence of impurities at "the same timing" as the carbon source. Therefore, according to the present invention, there is a possibility that a diamond semiconductor having semiconductor characteristics can be finally formed without providing a step of separately adding a small amount of impurities to the diamond film. Incidentally, the impurities required for forming a suitable semiconductor can also be referred to as "dopants". In this case, although not particularly limited, it is also possible to use phosphorus, arsenic, antimony, boron, gallium, etc., which can be semiconductor dopants, as the constituent materials contained in the additional member 43.

[0037] Incidentally, the above additional member 43 preferably adopts the following aspect.

[0038] In one aspect, it is preferable that the additional member 43 is disposed on the tip 40X side of the electrode portion 40.

[0039] Plasma P can be generated relatively more on the tip 40X side of the electrode portion 40. In view of this point, it is preferable that the additional member 43 is disposed on the tip 40X side of the electrode portion 40. With such an arrangement, the tip 40X of the electrode portion 40 is covered. Therefore, the additional member 43 can function as a protective member for the tip 40X itself of the electrode portion 40 located in the plasma P generation region. Thereby, due to the presence of the additional member 43, it is possible to suitably avoid the tip 40X of the electrode portion 40 located directly below the additional member 43 from being directly exposed to the plasma P. Therefore, due to such avoidance, it is possible to suitably suppress the melting of the tip 40X of the electrode portion 40 caused by the tip 40X of the electrode portion 40 being exposed to the plasma P that can be generated relatively more in a very high temperature state.

[0040] Also, since plasma P can be generated relatively more on the tip 40X side of the electrode portion 40, if the additional member 43 is disposed on the tip 40X side, a part of the additional member 43 covering the tip 40X can be melted due to the heat of the plasma P. When such partial melting of the additional member 43 occurs, impurities caused by the constituent material of the additional member 43 can occur as described above. Since the generated plasma P can be directly irradiated onto the base material 30, impurities caused by the constituent material of the additional member 43 in addition to the carbon source can also be supplied to the surface side of the base material 30 due to this. As a result, ultimately, the impurities may be present at the same timing as the carbon source, and it may be possible to form a diamond semiconductor having semiconductor characteristics.

[0041] In one aspect, it is preferable that the additional member 43 is positioned on the surface of the positive electrode 41 located in the plasma P generation region.

[0042] In the relationship between the melting point and boiling point of the constituent elements between one electrode and the other electrode, which are components of the electrode unit 40, it is a matter technically recognized by those skilled in the art that the melting point and boiling point of the constituent elements of one electrode are different from those of the other electrode. As an example, the melting point and boiling point of the constituent elements of one electrode may be lower than those of the other electrode. In this case, when both electrodes are directly exposed to the plasma P, due to the fact that the melting point and boiling point of the constituent elements of one electrode are lower than those of the constituent material of the other electrode, one electrode may melt and / or vaporize compared to the other electrode.

[0043] For example, as described above, when a Cu-based material can be used as the constituent material of the positive electrode 41 and a W-based material is used as the constituent material of the negative electrode 42, the metal element Cu contained in the Cu-based material has a lower melting point and boiling point compared to the metal element W contained in the W-based material. Specifically, the melting point of Cu is 1085 °C, and the boiling point of Cu is 2562 °C. On the other hand, the melting point of W is 3422 °C, and the boiling point of W is 5555 °C. In this case, when both electrodes are directly exposed to the plasma P, it can be said that the positive electrode 41 for which a Cu-based material can be used is more likely to melt and / or vaporize compared to the negative electrode 42 for which a W-based material can be used due to its low melting point and boiling point. Based on such matters, it is preferable that the additional member 43 is positioned on the surface of the positive electrode 41 located in the generation region of the plasma P. When the additional member 43 is provided on the surface of the positive electrode 41 located in the generation region of the plasma P, it becomes possible to suitably avoid the positive electrode 41 for which a "readily meltable and / or vaporizable" Cu-based material can be used from being directly exposed to the plasma P.

[0044] Further, when an additional member 43 is provided on the surface of the electrode on the lower melting point and boiling point side of the constituent elements, for example, the positive electrode 41, the following technical effects can also be achieved. That is, due to the presence of the additional member 43, melting of the positive electrode 41 itself located directly below the additional member 43 can be avoided. Therefore, it is possible to preferably avoid the melt resulting from the positive electrode 41 being supplied into the plasma P. Accordingly, it is possible to avoid the melt resulting from the positive electrode 41 functioning as an impurity on the substrate 30 side. On the other hand, since the additional member 43 is directly exposed to the plasma P, it is conceivable that a part of the additional member 43 may melt due to the properties of its constituent material. In this case, the melt resulting from the additional member 43 may be supplied into the plasma P. This means that the melt resulting from the additional member 43 may function as an impurity on the substrate 30 side. Therefore, in addition to the carbon source based on the source gas 50X in the presence of the plasma P, impurities resulting from the constituent material of the additional member 43 are also supplied to the surface side of the substrate 30 at the same timing, and thereby there is a possibility that a diamond semiconductor having semiconductor characteristics is provided.

[0045] Note that, as described above, when the positive electrode 41, which is a component of the electrode unit 40, can adopt a cylindrical structure, the additional member 43 of the cylindrical structure is provided at the tip of the inner wall surface that forms the internal space region of the positive electrode 41 having the cylindrical structure. Here, since the plasma P generated on the tip side of the electrode unit 40 is extremely hot, as the number of occurrences of the plasma P increases, there is a possibility that the resistance of the positive electrode 41, the negative electrode 42, and the additional member 43, which are components of the electrode unit 40, to the plasma P cannot be suitably maintained continuously. Therefore, it is desirable to adopt a structure that can sequentially supply the positive electrode 41, the negative electrode 42, and / or the additional member 43, which are the components. In order to enable such sequential supply, a receiving member having a function of receiving a part of the positive electrode 41 having a cylindrical structure is preferably structured to be able to suitably supply the cylindrical member of the positive electrode 41 and the additional member 43 of the cylindrical structure provided at the tip of the inner wall surface of the positive electrode 41 from the side of the receiving member to the installation side of the positive electrode 41 (that is, from the upper side direction to the lower side direction). Thereby, even when the number of occurrences of the plasma P increases and the resistance of the positive electrode 41 and the additional member 43 to the plasma P cannot be suitably maintained continuously, it is possible to sequentially supply the positive electrode 41, the negative electrode 42, and / or the additional member 43.

[0046] The additional member 43 may adopt the following aspects.

[0047] In one aspect, the additional member 43 may be an alloy member including the constituent materials of the positive electrode 41 and the negative electrode 42.

[0048] As described above, if the additional member 43 functions at least as a protective member for the electrode located in the plasma P generation region, its constituent material is not particularly limited. For example, the constituent material of the additional member 43 may be an alloy material including the constituent materials of the positive electrode 41 and the negative electrode 42. That is, the additional member 43 may be an alloy member including the constituent materials of the positive electrode 41 and the negative electrode 42.

[0049] Here, as described above, it is a matter technically recognized by those skilled in the art that the melting point and boiling point of the constituent elements of the positive electrode are different from those of the negative electrode. For example, when the melting point and boiling point of the constituent elements of the positive electrode are lower than those of the negative electrode, the melting point and boiling point of the alloy part including the constituent materials of the positive electrode 41 and the negative electrode 42 generally tend to be lower than those of the electrode with the higher melting point and boiling point (for example, the negative electrode side made of W). Based on such a tendency, in the atmosphere of the high-temperature plasma P, as described above, the alloy member as the additional member 43 can protect the positive electrode 41, thereby avoiding the melting of the positive electrode 41 itself. On the other hand, the alloy member and the negative electrode 42 will be directly exposed to the plasma P. In this case, based on the above tendency, the alloy member will melt while the negative electrode 42 with a higher melting point and boiling point is less likely to melt or cannot melt at all.

[0050] From the above, the melting of the positive electrode 41 itself located directly below the alloy member can be avoided, so that the melt caused by the positive electrode 41 is not supplied into the plasma P, thereby avoiding the possibility that the melt caused by the positive electrode 41 functions as an impurity on the substrate 30 side. On the other hand, since a part of the additional member 43 can melt due to the nature of the alloy member directly exposed to the plasma P, the melt caused by the additional member 43 is supplied into the plasma P, and thereby the melt can function as an impurity on the substrate 30 side. Note that as described above, since the negative electrode 42 is less likely to melt or cannot melt at all, the possibility that the melt caused by the negative electrode 42 is supplied into the plasma P and thereby the melt functions as an impurity on the substrate 30 side is lower than that of the alloy member. From the above, in the presence of the plasma P, in addition to the carbon source based on the raw material gas 50X, the impurities caused by the constituent material of the additional member 43 are also supplied to the surface side of the substrate 30 at the same timing, and thereby there is a possibility that a diamond semiconductor having semiconductor characteristics is provided.

[0051] Taking as an example the case where the positive electrode 41 is made of a Cu-based material and the negative electrode 42 is made of a W-based material, the alloy member as the additional member will be made of a Cu-W-based material. In this case, from the viewpoint of reducing the degree of melting as much as possible for the alloy member directly exposed to the plasma P, it is more preferable that the above alloy member contains relatively more W, which has a higher melting point and boiling point than Cu, which has a lower melting point and boiling point in terms of the metal element ratio. This is based on the recognition of those skilled in the art that in order to suitably obtain a semiconductor, impurities (corresponding to the melt caused by the alloy member) should preferably be supplied in a small amount only, and it is not preferable to supply them in a large amount.

Example

[0052] Using the following device, a diamond film or the like was formed.

[0053] Example 1 (Configuration of the diamond film forming device 100 used) ● Container 10: It consists of a cylindrical quartz glass and a stainless steel flange, and its airtightness is maintained by a silicon packing and an O-ring. The inside of the container 10 is filled with the raw material liquid 20 and the carrier gas 60X (Ar gas). ● Raw material liquid 20: Methanol solution (97% by volume) and ethanol solution (3% by volume) ● Substrate 30: Cemented carbide substrate (dimensions 8 mm × 27 mm × 0.5 mm, a sintered body obtained by mixing tungsten carbide (WC) and cobalt (Co) (weight ratio 5:1)) ● Positive electrode 41 (a component of the electrode part 40): Cylindrical Cu-based positive electrode (inner diameter: 6.0 mm) ● Negative electrode 42 (a component of the electrode part 40): Columnar W-based negative electrode (diameter: 2.4 mm) ● Additional member 43 (a component of the electrode part 40): Cu-W-based alloy member provided at the end of the cylindrical Cu-based positive electrode (metal element ratio: W (84%), Cu (14%), other metals, etc. (2%)) ● Raw material gas supply unit 50: A pressure vessel for supplying a raw material gas 50X obtained by heating and vaporizing a mixed solution of a methanol solution (97% by volume) and an ethanol solution (3% by volume) up to 170°C ● Carrier gas supply unit 60: A cylinder for supplying argon gas ● Power supply 70: A DC power supply (TIG welding machine MT-200WA, manufactured by Maito Kogyo Co., Ltd.) (input current: 10 A) ● Gas cooling unit 80 ● Liquid tank 90

[0054] (Implementation process) (1) First, a cemented carbide substrate (dimensions: 8 mm × 27 mm × 0.5 mm) was placed on the substrate holder in the container 10, and the inside of the container 10 where the cemented carbide substrate was placed was filled with a mixed solution of a methanol solution (97% by volume) and an ethanol solution (3% by volume) and argon gas. At this time, the tip 40X of the electrode part 40 was positioned in the mixed solution, and the height was adjusted using a micrometer so that the distance between the cemented carbide substrate and the tip 40X of the electrode part 40 was 1.0 mm. The airtightness of the container 10 was maintained by a silicon packing and an O-ring. Also, as a pretreatment of the cemented carbide substrate, its surface was roughed with sandpaper for 2 minutes, ultrasonic polishing treatment was performed with colloidal water (the weight ratio of methanol to diamond powder serving as nuclei is 5:1) for 30 minutes, and the surface was washed with methanol.

[0055] (2) Next, argon gas used as the carrier gas 60X was supplied into the internal space region of the electrode part 40 at a rate of 5 L / min, and a voltage was applied to the electrode part 40 using a DC power supply (TIG welding machine MT-200WA, manufactured by Maito Kogyo Co., Ltd.) to generate plasma P based on argon gas at the arc discharge part on the tip 40X side of the electrode part 40. Then, the cemented carbide substrate was heat-treated with the plasma jet based on argon gas for 60 seconds to raise the temperature of the substrate board. The temperature of the cemented carbide substrate after heating with argon gas plasma was 690 - 860°C (used thermometer: infrared radiation thermometer).

[0056] (3) Next, a raw material gas 50X based on a mixed solution of a methanol solution (97% by volume) and an ethanol solution (3% by volume) was supplied to the internal space region of the electrode portion 40 at a rate of 5 L / min. A voltage was applied to the electrode portion 40 using a DC power source (TIG welding machine MT-200WA, manufactured by Mite Industry Co., Ltd.) to generate plasma P based on the raw material gas 50X at the arc discharge portion on the tip 40X side of the electrode portion 40.

[0057] (4) By irradiating the generated plasma P onto the cemented carbide substrate for a total of 260 seconds, film formation on the substrate was carried out for 200 seconds. Note that in the 200-second film formation process, the film formation had not been completed and was in the middle of the film formation process. Also, the film formation behavior was observed when the current output from the DC power source was 12 A and the voltage was between 19.8 and 24.0 V.

[0058] (Results) Equipment Used The quality of the obtained film was analyzed using the following equipment. · Scanning electron microscope (SEM) (manufactured by JEOL Ltd. / product name: JSM-6060) · Microscopic Raman spectroscopic analyzer (manufactured by Renishaw / pl product name: inVia Reflex, excitation light (150 mW), spot diameter: 1.4 μm, YAG laser wavelength: 532 nm)

[0059] The results are shown in FIGS. 5 to 7.

[0060] As shown in FIG. 5 (SEM image of the surface of the cemented carbide substrate), the precipitation of diamond crystals (during film formation) was confirmed. Wide-ranging irregularities were confirmed on the surface of the diamond crystals. Also, as shown in FIG. 6 (Raman spectrum of the surface of the cemented carbide substrate: vertical axis Intensity [count], horizontal axis Raman Shift [cm -1 ), near 1332 cm -1 the sp of diamond 3Sharp peaks due to the bonding were confirmed. The crystal was a unique one that grew in a spiral shape (growing while generating spiral dislocations) from a single crystal with a polyhedral structure as a whole (see the SEM image of the surface of the cemented carbide substrate at 5000 times magnification in the lower right of Fig. 5).

[0061] Also, as shown in Fig. 7 (SEM image of the surface of the cemented carbide substrate), fibrous composites considered to be carbon nanotubes (CNTs) were confirmed at other points on the surface of the cemented carbide substrate.

[0062] It is known that carbon nanotubes (CNTs) can be synthesized using Co particles as a catalyst. Regarding this, the cemented carbide substrate used as the substrate 30 contains Co. Therefore, it is understood that when the plasma P is irradiated onto the cemented carbide substrate, Co is dissolved and atomized from the cemented carbide substrate, and carbon nanotubes (CNTs) are formed from the carbon source of the source gas 50X taken out by the plasma P using the Co as a catalyst.

[0063] Example 2 (Configuration of the diamond film forming device 100 used) Different from Example 1, the following Si substrate was used as the substrate 30. Since the other components are under the same conditions as in Example 1, the description of the overlapping parts will be omitted. ● Substrate 30: Si substrate (dimensions: 8 mm × 27 mm × 0.5 mm)

[0064] (Implementation process) Except for using an Si substrate as the substrate 30, the process is substantially the same as that carried out in Example 1, so the description of the overlapping parts will be omitted.

[0065] (1) First, place a Si substrate (dimensions: 8 mm × 27 mm × 0.5 mm) on the substrate holder in container 10, and fill the inside of container 10 with a mixed solution of a methanol solution (97 vol%) and an ethanol solution (3 vol%) and argon gas. At this time, the tip 40X of electrode part 40 is positioned within the mixed solution, and the height is adjusted using a micrometer so that the distance between the Si substrate and the tip 40X of electrode part 40 is 1.5 mm. Also, the Si substrate was pretreated in the same manner as in Example 1.

[0066] (2) Generate plasma P based on argon gas, and perform heat treatment of the Si substrate for 60 seconds with a plasma jet based on argon gas to raise the temperature of the substrate substrate. The temperature of the Si substrate after heating by argon gas plasma was 680 - 750°C.

[0067] (3) Next, supply a source gas 50X based on a mixed solution of a methanol solution (97 vol%) and an ethanol solution (3 vol%) into the internal space region of electrode part 40 at 5 L / min, and generate plasma P based on source gas 50X using a DC power supply.

[0068] (4) By irradiating the generated plasma P onto the Si substrate for 360 seconds, a film formation process on the substrate was carried out for 300 seconds. Note that in the 300 - second implementation, film formation had not ended and was in a state during film formation. Also, the film formation behavior was observed when the current output from the DC power supply was 12 A and the voltage was between 24.4 - 28.9 V (average voltage: 26.7 V, average output: 319.8 W).

[0069] (Results) Equipment Used Regarding the quality of the obtained film, analysis was performed using the same scanning electron microscope (SEM) and microscopic Raman spectroscopic analyzer as those used in Example 1.

[0070] The results are shown in FIGS. 8 and 9.

[0071] As shown in Fig. 8 (SEM image of the Si substrate surface), the deposition of diamond crystals (during film formation) was confirmed. Wide-ranging irregularities were confirmed on the surface of the diamond crystals. Also, as shown in Fig. 9 (Raman spectrum of the Si substrate surface: vertical axis Intensity [count], horizontal axis Raman Shift [cm -1 ), a sharp peak attributed to the sp -1 bond of diamond was confirmed near 1332 cm 3 . From the above, it was found that diamond crystals can be produced as long as a carbon source based on the supplied gas is provided even without a carbon source on the substrate side. The single crystal structure had a substantially cubic structure compared to the structure of a normal hexahedron or the like. Also, in Example 2, it was found that the substantially cubic structure can become more prominent compared to the case of Example 1 (using a cemented carbide substrate as the substrate 30) (refer to the SEM image of the cemented carbide substrate surface at 5000 times magnification in the lower right of Fig. 5 and the SEM image of the Si substrate surface at 5000 times magnification in the lower right of Fig. 8). That is, in order to more preferably obtain the substantially cubic structure of diamond crystals, it is considered preferable to use a Si substrate as the substrate 30 rather than a cemented carbide substrate.

[0072] Example 3 Since it is under substantially the same conditions as Example 2, descriptions of overlapping parts will be omitted. The differences are as follows. ● The temperature of the Si substrate after heating by argon gas plasma in the implementation process (2) is 710 - 940 °C ● In the implementation process (4), the film formation process was carried out on the Si substrate for 134 seconds. In the implementation for 134 seconds, the film formation had not ended and was in a state during film formation. Also, the film formation behavior was observed when the current output from the DC power supply was 12 A and the voltage was between 16.2 - 22.4 V (average voltage: 19.3 V, average output: 231.6 W).

[0073] (Results) Equipment used Regarding the quality of the obtained film formation, analysis was carried out using the same scanning electron microscope (SEM) and microscopic Raman spectroscopic analyzer as those used in Example 1 and Example 2.

[0074] The results are shown in FIGS. 10 and 11.

[0075] As shown in FIG. 10 (SEM image of the Si substrate surface), deposition of diamond crystals (during film formation) was confirmed. Wide-ranging irregularities were confirmed on the surface of the diamond crystals. Also, as shown in FIG. 11 (Raman spectrum of the Si substrate surface: vertical axis Intensity [count], horizontal axis Raman Shift [cm -1 ), a sharp peak due to the sp -1 bond of diamond was confirmed near 1332 cm 3 . From the above, it was found that diamond crystals can be produced as long as a carbon source based on the supplied gas is provided even if there is no carbon source on the substrate side.

[0076] Example 4 Since the conditions are substantially the same as in Example 2, descriptions of overlapping parts will be omitted. The differences are as follows. ● In the implementation step (2), the temperature of the Si substrate after heating by argon gas plasma is 670 to 740 °C ● In the implementation step (4), the plasma P generated was irradiated onto the Si substrate for 200 seconds to perform a film formation process on the substrate. Also, the film formation behavior was observed when the current output from the DC power supply was 22 A (input current 20 A) and the voltage was between 19.4 and 23.2 V (average voltage: 21.3 V, average output: 468.6 W).

[0077] (Results) Equipment used Regarding the quality of the obtained film, analysis was performed using the same scanning electron microscope (SEM) and microscopic Raman spectroscopic analyzer as those used in Examples 1 to 3.

[0078] The results are shown in FIGS. 12 and 13.

[0079] Fig. 13 (Raman spectrum of the Si substrate surface: vertical axis Intensity [count], horizontal axis Raman Shift [cm -1 ) shows that, as shown near 1332 cm -1 , a sharp peak due to the sp 3 bond of diamond was confirmed. From the above, it was found that diamond crystals can be produced if a carbon source based on the supply gas is provided even without a carbon source on the substrate side. Also, as shown in Fig. 12 (SEM image of the Si substrate surface, particularly refer to the SEM image of the Si substrate surface at 5000 times magnification in the lower right of Fig. 12), the precipitation of diamond crystals (during film formation) was confirmed. More specifically, under the conditions of Example 4 of the present embodiment, it was found that the diamond crystals (polycrystals) were formed by stacking a large number of single crystals with a cubic structure in a brick-like manner. Therefore, it was found that the overall structure of the polycrystal and the structure of the single crystal can have a pseudo (similar) relationship due to the brick-like arrangement.

[0080] When the structure of the polycrystal and the structure of the single crystal have a pseudo (similar) relationship, it is considered that the polycrystal can be converted into a single crystal by slightly heating the polycrystal to induce atomic diffusion at the grain boundary. From the common general knowledge of those skilled in the art, it is known that polycrystalline semiconductors generally have poor device efficiency, while single-crystalline semiconductors generally have good device efficiency. In view of such circumstances, when the diamond film can function as a diamond semiconductor, single-crystal conversion is essential for using the diamond semiconductor as various devices. From the above, "the structure of the polycrystal and the structure of the single crystal having a pseudo (similar) relationship" that can enable conversion into a single crystal can be said to be effective in using the diamond film (diamond semiconductor) as various devices.

[0081] The above describes Examples 1 to 4. In the above Examples 1 to 4, an alloy member including the constituent materials of the positive electrode 41 and the constituent materials of the negative electrode 42 is provided as the additional member 43 in the electrode portion 40. Specifically, a Cu-W alloy member (metal element ratio: W (84%), Cu (14%), other metals, etc. (2%)) is provided at the end of a cylindrical Cu-based positive electrode.

[0082] According to such a configuration, melting of the positive electrode 41 itself located directly below the alloy member can be avoided. Therefore, it is possible to avoid the melt due to the positive electrode 41 from being supplied into the plasma P. On the other hand, since the alloy member (in some cases, the negative electrode 42) is directly exposed to the plasma P, a part of it can melt. Therefore, the melt due to the constituent material of the alloy member (in some cases, the negative electrode 42) is supplied into the plasma P, and thereby the melt can function as an impurity to the substrate 30 side. Note that since the melting point and boiling point of W, which is the constituent material of the negative electrode 42, are considerably higher than those of Cu, which is the constituent material of the positive electrode 41, it is understood that it is difficult to melt in a high-temperature plasma or does not melt at all. Therefore, the possibility that the melt due to the negative electrode 42 is supplied into the plasma P and thereby the melt functions as an impurity to the substrate 30 side is considered to be lower than that of the alloy member. From the above, in addition to the carbon source based on the source gas 50X in the presence of the plasma P, the impurities due to the constituent material of the alloy member can also be supplied to the surface side of the substrate 30 at the same timing. Thereby, there is a possibility of forming a diamond semiconductor having semiconductor characteristics.

[0083] Note that as the metal element ratio of the Cu-W alloy member, W was 84% and Cu was 14%. That is, the Cu-W alloy member relatively contains more W having a higher melting point and boiling point than Cu having a lower melting point and boiling point in terms of the metal element ratio. In order to preferably obtain a semiconductor, generally, impurities are preferably supplied in a small amount as much as possible and not in a large amount. Therefore, since the Cu-W alloy member relatively contains more W having a higher melting point and boiling point than Cu having a lower melting point and boiling point in terms of the metal element ratio, the degree of melting of the Cu-W alloy member directly exposed to the high-temperature plasma is relatively small, and thereby it is understood that the impurities due to the constituent material of the alloy member can also be made small.

[0084] The above has described one embodiment of the present invention, but it merely exemplifies typical examples within the scope of application of the present invention. Therefore, it will be easily understood by those skilled in the art that the present invention is not limited thereto and various modifications can be made.

Industrial Applicability

[0085] According to the present invention, the obtained diamond film can be a diamond semiconductor film. In this case, the diamond semiconductor film can be used for airplanes, ships, artificial satellites, rockets, etc. due to its properties. Cross-reference to related applications

[0086] This application claims priority under the Paris Convention based on Japanese Patent Application No. 2017-253939 (filing date: December 28, 2017, title of the invention: "Device for forming diamond film, etc. and method for forming the same"). All the contents disclosed in the application are hereby incorporated herein by reference.

Explanation of Reference Numerals

[0087] 100 Device for forming diamond film, etc. 10 Container 20, 20' Raw material liquid 30, 30' Substrate 40 Electrode part 40X Tip of the electrode part 41 Positive electrode 41X Internal space region of the positive electrode 42 Negative electrode 43 Additional member 43X Mounting member 43Y Electrode melting prevention member 43Z Impurity supply source member 50 Raw material gas supply part 50X Raw material gas 60 Carrier gas supply part 60X Carrier gas 70 Power supply 70' High-frequency power supply 71 DC power supply 80 Gas cooling part 90 Liquid tank P, P' plasma

Claims

1. 1. A device for forming at least a diamond film on a surface of a substrate, comprising: a container for holding a raw material liquid and for placing a substrate in the raw material liquid; an electrode unit including a positive electrode and a negative electrode for generating plasma in the raw material liquid; a raw material gas supply unit and a carrier gas supply unit respectively connected to the electrode unit; A power source for applying a voltage to the electrode portion; and the power source is a DC power source; and A device, wherein the electrode portion further comprises an additional member, the additional member being attached to an electrode located in the plasma generation region of the electrode portion.

2. The device according to claim 1 , wherein the additional member is a member for preventing melting of the electrode in a region where the plasma is generated.

3. The device according to claim 1 or 2, wherein the additional member is an impurity supply source member in a region where the plasma is generated.

4. The device according to any one of claims 1 to 3, wherein the additional member is provided on a tip side of the electrode portion which generates the plasma.

5. The device according to any one of claims 1 to 4, wherein the additional member is positioned on a surface of the positive electrode located in a region where the plasma is generated.

6. 6. The device according to claim 1, wherein the additional member is an alloy member comprising a constituent material of the positive electrode and a constituent material of the negative electrode.

7. the positive electrode has a tubular structure having an interior space region, the negative electrode extends within the interior space region of the positive electrode; and The device according to any one of claims 1 to 6, wherein the plasma generation region is provided between the positive electrode and the negative electrode extending within the interior spatial region of the positive electrode.

8. The device according to any one of claims 1 to 7, wherein the positive electrode is made of a Cu-based material, the negative electrode is made of a W-based material, and the additional member is made of a Cu-W-based material.

9. The device according to claim 8 , wherein the additional member contains W in a relatively larger amount than Cu in terms of metal element ratio.

10. The device according to any one of claims 1 to 9, wherein the electrode portion is positioned vertically above the substrate so that the electrode portion and the substrate face each other.

11. 1. A method for forming at least a diamond film on a surface of a substrate, comprising: placing a substrate in a container and holding a raw material liquid in the container in which the substrate is placed; supplying a raw material gas and a carrier gas into an electrode unit having a positive electrode and a negative electrode and a tip side of which is positioned in the raw material liquid; Applying a voltage to the electrode portion using a power source to generate plasma at the tip side of the electrode portion. Including, A DC power supply is used as the power supply, and A method using an electrode portion further comprising an additional member, the additional member being attached to an electrode located in a region of the electrode portion where the plasma is generated.

12. The method according to claim 11 , wherein the additional member is a member for preventing melting of the electrode in a region where the plasma is generated.

13. The method according to claim 11 or 12, wherein the additional member is an impurity supply source member in a region where the plasma is generated.

14. The method according to any one of claims 11 to 13, wherein the additional member is provided on the tip side of the electrode portion which generates the plasma.

15. The method according to any one of claims 11 to 14, wherein the additional member is positioned on a surface of the positive electrode located in a region where the plasma is generated.

16. The method according to any one of claims 11 to 15, wherein an alloy member containing a constituent material of the positive electrode and a constituent material of the negative electrode is used as the additional member.

17. The method according to any one of claims 11 to 16, wherein the positive electrode is made of a Cu-based material, the negative electrode is made of a W-based material, and the additional member is made of a Cu-W-based material.

18. The method according to claim 17, wherein the additional member contains W in a relatively larger amount than Cu in terms of metal element ratio.

19. supplying a first plasma based on the carrier gas and a second plasma based on the raw material gas from a plasma generation region to the substrate; The method of any one of claims 11 to 18, wherein the first plasma is applied to the substrate prior to the application of the second plasma.

20. The method according to any one of claims 11 to 19, wherein the electrode portion is positioned vertically above the substrate so that the electrode portion and the substrate face each other.

21. The method according to any one of claims 11 to 20, further comprising forming carbon nanotubes on the surface of the substrate in addition to the diamond film.

22. A single crystal which is a unit component of a diamond film formed on a surface of a substrate, The single crystal is a unitary component of a diamond film, the single crystal having a cubic shape.

23. A polycrystal constituting a diamond film formed on a surface of a substrate, The polycrystals constituting the diamond film are in the form of brick-like stacks having a plurality of single crystals each having a cubic shape, and the brick-like stacks as a whole form a pseudo-single crystal structure.

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