Diamond substrate, method for manufacturing diamond substrate, and diamond semiconductor device produced using diamond substrate

Abstract

The purpose of the present invention is to provide: a label suitable for use in the identification and specification of a diamond substrate and in a manufacturing process of a diamond semiconductor device using the diamond substrate; a method for manufacturing the label; and a diamond semiconductor device manufactured by using the label. The label is present on the main surface of the diamond substrate. The label is provided with a diamond layer that is selectively grown as a crystal on the main surface and that contains impurities.

Description

Diamond substrate, method for manufacturing a diamond substrate, and diamond semiconductor device fabricated using a diamond substrate

[0001] This disclosure relates to a diamond substrate, a method for manufacturing a diamond substrate, and a diamond semiconductor device made using a diamond substrate. [Disclosure of related applications] This application claims priority under Japanese Patent Application No. 2025-067385 (filed on April 16, 2025), and incorporates all the provisions of the said application.

[0002] Patent Document 1 describes a method for recording permanent patterns, such as letters, on the surface of a diamond intended for gemstone use.

[0003] Japanese Patent Publication No. 2022-164940

[0004] When manufacturing semiconductor devices using diamond substrates, it is necessary to identify and distinguish each individual substrate in order to manage the manufacturing process and the resulting semiconductor devices. Therefore, engraving some kind of identification mark, such as a lot number or identification number, at a desired location on the diamond substrate is an effective method. Furthermore, in the semiconductor device manufacturing process, it is essential to superimpose patterns such as the device shape and electrode shape using photolithography, and for this, alignment marks, or similar markings, are necessary for positioning.

[0005] However, unlike conventional semiconductor substrates, diamond substrates are extremely hard, difficult to process, and transparent. Therefore, conventional markings and processing methods are often difficult to see, or even impossible to use. Furthermore, even if metals are deposited, the harsh manufacturing process, including hot acid cleaning, causes the markings to peel off or dissolve during the manufacturing process, rendering them unusable as markings.

[0006] Thus, while technology for imprinting labels onto substrates is highly anticipated for the mass production of diamond semiconductor devices, the aforementioned challenges make it difficult to achieve this simultaneously with substrate cleaning. This difficulty, in turn, has been pointed out to be leading to a decrease in the final yield.

[0007] Therefore, conventionally, it has been difficult to identify or distinguish individual diamond crystals, especially after the manufacturing process. Furthermore, there were no alignment markers that were accurate enough to satisfy the function of the manufacturing process.

[0008] Therefore, the purpose of this disclosure is to provide a diamond substrate that has a label suitable for identifying and distinguishing individual diamond substrates, and also a label suitable for use in the manufacturing process of a diamond semiconductor device using the diamond substrate, a method for manufacturing the diamond substrate, and a diamond semiconductor device manufactured using the diamond substrate.

[0009] The diamond substrate relating to this disclosure is provided with a mark on the main surface of the diamond substrate.

[0010] The method for manufacturing a diamond substrate according to this disclosure involves creating a label on the main surface of the diamond substrate.

[0011] The diamond semiconductor device relating to this disclosure is manufactured using the diamond substrate described above.

[0012] According to this disclosure, it is possible to provide a diamond substrate having a label suitable for identifying and distinguishing individual diamond substrates, and also a label suitable for use in the manufacturing process of a diamond semiconductor device using the diamond substrate, a method for manufacturing the diamond substrate, and a diamond semiconductor device manufactured using the diamond substrate.

[0013] Figure 1 is a schematic cross-sectional view showing a cross-section of a first embodiment of the diamond substrate according to the present disclosure. Figure 2 is a schematic cross-sectional view showing a cross-section of a second embodiment of the diamond substrate according to the present disclosure. Figure 3 is a schematic plan view showing a part of the diamond substrate according to the embodiment and an example of a mark created on the main surface of the diamond substrate. Figure 4 is a schematic cross-sectional view (1) of the mark seen in a cross-section along line A-B in Figure 3. Figure 5 is a schematic cross-sectional view (2) of the mark seen in a cross-section along line A-B in Figure 3. Figure 6 is a schematic cross-sectional view (3) of the mark seen in a cross-section along line A-B in Figure 3. Figure 7 is a schematic cross-sectional view (4) of the mark seen in a cross-section along line A-B in Figure 3. Figure 8 is a schematic cross-sectional view (5) of the mark seen in a cross-section along line A-B in Figure 3. Figure 9 is a schematic cross-sectional view (6) of the mark seen in a cross-section along line A-B in Figure 3. Figure 10 is a schematic perspective view of a hydrogen-terminated field-effect transistor element fabricated using a diamond substrate according to the embodiment. Figure 11 is a graph showing an example of data obtained by varying the gate voltage, relating the drain current to the voltage between the source and drain of a hydrogen-terminated field-effect transistor element fabricated using a diamond substrate according to the embodiment.

[0014] The methods for implementing this disclosure are described below.

[0015] [Description of Embodiments of the Disclosure] Embodiments of the Disclosure are first listed and described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description of them is not repeated.

[0016] (1) In a diamond substrate 20 according to one aspect of the present disclosure, the main surface 25 of the diamond substrate 20 is provided with a mark 30 used for the following purposes: at least one of the following: for the purpose of individually identifying the diamond substrates 20, or for the purpose of being used in the process of manufacturing a diamond semiconductor device on the diamond substrate 20.

[0017] (2) In a diamond substrate 20 according to another aspect of the present disclosure, a label 30 is present on the main surface 25 of the diamond substrate 20, and the label 30 comprises a diamond layer 40 that is selectively and crystallinely grown on the main surface 25, containing impurities.

[0018] (3) In the diamond substrate 20 relating to (2) above, the impurity portion contains boron, and the concentration of boron is 1 × 10 １６ cm ―３ The above 1 x 10 ２２ cm ―３ The range is as follows:

[0019] When boron is added to this extent and selective growth is performed, the label 30 becomes clearly identifiable. The reason for this is that, firstly, the crystal quality of the diamond layer 40 containing impurities due to selective growth tends to be worse, especially on the side portion 41, than on the main surface 25. The label 30, which is composed of the diamond layer 40 containing impurities, has a clear boundary with the main surface 25 due to diffuse reflection of light incident on the side portion 41.

[0020] At the same time, the diamond layer 40 containing impurities undergoes a change in color due to the influence of the impurities (in this case, boron), and a slight difference from the colorless, transparent diamond substrate 20 becomes noticeable. Both of these factors allow the marker 30 to be clearly identified.

[0021] Furthermore, the above trend due to the effect of boron is observed when the boron addition concentration is 1 × 10⁻⁶ １８ cm ―３ This becomes even more pronounced, and as a result, the discriminative power of the marker 30 on the main surface 25 is further improved, making it more preferable.

[0022] (4) In a diamond substrate 20 according to another aspect of the present disclosure, a label 30 is present on the main surface 25 of the diamond substrate 20, and the label 30 comprises a heterocrystalline structure region 50 (hereinafter referred to as the "heterocrystalline structure region 50" in this disclosure) which is a region having a different crystalline structure from the crystalline structure of the main surface 25 (which is the same as the crystalline structure of the diamond substrate 20). Here, in this disclosure, the "heterocrystalline structure region 50" is used as a general term for a crystalline structure region that includes a different crystalline structure when a part of the crystalline structure that the diamond substrate 20 originally had has changed due to some external factor (for example, irradiation with laser light). In other words, it means a region that initially had the same crystalline structure as the diamond substrate 20 but has changed due to an external factor and has become a different crystalline structure. Specifically, this includes graphite, amorphous carbon, DLC (Diamond-Like Carbon), other allotropes of carbon atoms, or mixtures thereof.

[0023] (5) In the diamond substrate 20 relating to (4) above, the heterocrystalline structure region 50 includes the crystalline structure of graphite.

[0024] Graphite is black to the naked eye, and clearly has greater distinguishing power compared to the colorless and transparent diamond substrate 20, making it recognizable and therefore preferable.

[0025] (6) In a diamond substrate 20 according to another embodiment of the present disclosure, a mark 30 is present on the main surface 25 of the diamond substrate 20. The mark 30 includes a recessed region 60 with the main surface 25 as its upper surface, and the recessed region 60 includes a graphite region 62 having a graphite crystalline structure in at least a part of the side wall portion 61.

[0026] (7) A method for manufacturing a diamond substrate 20 according to one aspect of the present disclosure includes the following steps. First, there is a step of preparing the diamond substrate 20 having a main surface 25. Thereafter, a region on the main surface 25 where the marker 30 is to be formed is irradiated with a laser beam, and after the laser beam irradiation, the crystal structure of the region where the marker 30 is to be formed is changed to a crystal structure different from the crystal structure forming the main surface 25. There is a step of changing the structure. Furthermore, there is a step of cleaning the diamond substrate 20, and after cleaning, the marker 30 includes a recessed region 60 with the main surface 25 as the upper surface, and at least a part of at least the side wall portion 61 of the recessed region 60 has a graphite crystal structure. and a graphite region 62 having a structure.

[0027] (8) In the diamond substrate 20 according to the above (7), the central wavelength of the laser beam to be irradiated is in the range of 100 nm to 600 nm.

[0028] The central wavelength of the laser beam is more preferably in the range of 200 nm to 500 nm. Furthermore, it is even more preferably in the range of 300 nm to 400 nm. Within this wavelength range, marking can be performed more efficiently.

[0029] (9) In a diamond substrate 20 according to another aspect of the present disclosure, a marker 30 is present on a main surface 25 of the diamond substrate 20, and the marker 30 includes a recessed structure 70. In the recessed structure 70, the main surface 25 forms the recess upper surface 71, the etched surface of the main surface 25 forms the recess bottom surface 72, and the boundary line between the recess upper surface 71 and the recess side surface 73 forms the recess upper line 74. Here, in the present disclosure, the "recessed structure 70" refers to a structure recessed to a depth of 1 to 100 μm from the surface.

[0030] Even if both the main surface 25 (corresponding to the recess upper surface 71) and the recess bottom surface 72 are colorless and transparent, the recess upper line 74, which is the boundary line between the recess upper surface 71 and the recess side surface 73, exhibits a color due to diffuse reflection of light and becomes visible, whereby the marker 30 can be identified from the main surface 25.

[0031] (10) In a diamond substrate 20 according to another aspect of the present disclosure, a mark 30 is present on a main surface 25 of the diamond substrate 20, and the mark 30 includes a convex structure 80. The convex structure 80 has a structure in which the main surface 25 forms a convex upper surface 81, the etched surface of the main surface 25 forms a convex bottom surface 82, and the boundary line between the convex bottom surface 82 and a convex side surface 83 forms a convex bottom line 84.

[0032] Even if both the main surface 25 (corresponding to the convex upper surface 81) and the convex bottom surface 82 are colorless and transparent, the convex bottom line 84, which is the boundary line between the convex bottom surface 82 and the convex side surface 83, is colored and visible due to diffused reflection of light. As a result, the mark 30 can be distinguished from the convex bottom surface 82 which is the etched surface of the main surface 25.

[0033] (11) In a diamond substrate 20 according to another aspect of the present disclosure, a mark 30 is present on a main surface 25, and the mark 30 includes at least a rough surface region 90.

[0034] Since the rough surface region 90 has poorer crystal quality than the main surface 25, light incident on the rough surface region 90 is diffusely reflected, so that the rough surface region 90 can be distinguished from the main surface 25 of the colorless and transparent diamond substrate 20. Here, in the present disclosure, the "rough surface region 90" refers to a region having a roughness of 1 nm to 1 μm in terms of Ra (arithmetic mean roughness).

[0035] (12) A diamond semiconductor device according to one aspect of the present disclosure is manufactured using the diamond substrate 20 according to the above (1) to (11).

[0036] [Details of Embodiments of the Present Disclosure] Hereinafter, details of the embodiments of the present disclosure will be described.

[0037] (First Embodiment) First, the first embodiment will be described in detail. In the first embodiment, two aspects of the structure of the diamond substrate 20 will be described. However, this is not intended to limit the aspects of the diamond substrate 20 to two types. This is a description of two commonly used aspects, and these two aspects of the diamond substrate 20 can naturally be applied to the embodiments of the substrates in the second and subsequent embodiments.

[0038] [Diamond Substrate (First Aspect)] FIG. 1 is a schematic cross-sectional view showing the first aspect of the diamond substrate 20 used in the present disclosure. As shown in FIG. 1, in the first aspect of the diamond substrate 20 used in the present embodiment, a diamond single crystal substrate 10 cut out from a synthetic diamond single crystal ingot is used as the diamond substrate 20.

[0039] The diamond single crystal substrate 10 is produced from a diamond single crystal ingot artificially synthesized by a high-temperature high-pressure method (HPHT method) or a chemical vapor deposition method (CVD method).

[0040] In the high-temperature high-pressure method (HPHT method), a carbon source is dissolved in a molten metal in a high-temperature high-pressure chamber, and carbon atoms migrate through the metal to a small seed crystal for growth. A parallel plate-shaped diamond single crystal plate is cut out from this bulk synthetic diamond single crystal ingot, and the surface is polished flat to produce the diamond single crystal substrate 10.

[0041] In the chemical vapor deposition method (CVD method), methane (CH ４ ) gas or other carbon-based main component gas is decomposed in a chamber under high-temperature low-pressure conditions, and carbon atoms are deposited on a sliced diamond crystal seed crystal, thereby producing the diamond single crystal substrate 10 having the main surface 25. This technique is also frequently used for epitaxial growth of diamond, as described below.

[0042] [Diamond Substrate (Second Aspect)] FIG. 2 is a schematic cross-sectional view showing the second aspect of the diamond substrate 20 used in the present disclosure. As shown in FIG. 2, the second aspect of the diamond substrate 20 used in the present embodiment is an aspect in which a diamond epitaxial layer 15 is further epitaxially grown on the surface of the diamond single crystal substrate 10 to constitute the diamond substrate 20.

[0043] As a method for epitaxially growing the diamond epitaxial layer 15 on the surface of the diamond single crystal substrate 10, for example, a microwave plasma chemical vapor deposition method (MPCVD method) can be used. The source gas uses hydrogen (H ２ )-diluted methane (CH ４) Gas can be used, but its concentration should be, for example, CH ４ / H ２ This represents a concentration of 0.5%. According to this method, carbon decomposed in a plasma generated by applying microwaves to the raw material gas can be epitaxially grown on the surface of the diamond single crystal substrate 10.

[0044] A diamond epitaxial layer 15, approximately several nanometers to several micrometers thick, is grown on the surface of a diamond single crystal substrate 10 under conditions of a growth temperature of approximately 900°C. If impurities are intentionally not added during this epitaxial growth process, creating an undoped layer, a diamond epitaxial layer 15 with high resistance and insulating properties can be fabricated.

[0045] [Marking] Figure 3 is a schematic plan view showing an example of a marking 30 to be manufactured according to this disclosure, observed from a plan view perpendicular to the surface of the diamond substrate 20. As shown in Figure 3, the marking 30 is formed on a part of the surface of the diamond substrate 20. In Figure 3, a shape with a cross inserted inside a rectangle is shown as an example, but the shape of the marking 30 is not limited to this, and any shape that is recognizable and suitable for the purpose of the marking 30 is acceptable. Letters and numbers can also be used, not just figures.

[0046] The dashed line connecting A and B shown in Figure 3 indicates the position where the schematic cross-sectional diagrams shown in Figure 4 and subsequent figures will be drawn. The schematic cross-sectional diagrams in Figure 4 and subsequent figures show the cross-section between A and B.

[0047] [Selective Growth of Diamond Layer] Figure 4 is a schematic cross-sectional view showing a state in which a marker 30 is fabricated by selectively growing a diamond layer 40 with impurities on the main surface 25 of a diamond substrate 20. As shown in Figure 4, the position and range for forming the marker 30 on a part of the main surface 25 of the diamond substrate 20 are determined, and the diamond layer 40 with impurities is selectively epitaxially grown only in that region.

[0048] The specific method for creating this embodiment is as follows.

[0049] First, a film such as a metal or oxide film is deposited over the entire surface 25 of the diamond substrate 20. Next, the position and area to form a label 30 in a portion of the main surface 25 are determined, and the film such as the metal or oxide film is removed only from that area using a photolithography technique. As a result, only this area of ​​the main surface 25 is exposed.

[0050] The term "photolithography" as used herein refers to the following series of techniques. For example, first, a photoresist is applied to the entire surface of the target, and then the photoresist is selectively exposed to light using a photomask or other exposure methods to form a pattern. There are two types of pattern formation: "positive type," which leaves areas other than the exposed areas intact, and "negative type," which leaves only the exposed areas intact. Furthermore, this photoresist pattern is used as a mask to perform etching or other processes on the symmetrical surface to transfer the pattern, and finally, the photoresist is removed. Hereafter, in this disclosure, the series of techniques following these procedures will be collectively referred to as the photolithography method.

[0051] The diamond layer 40 is epitaxially grown only in the region where the main surface 25 is exposed. For epitaxial growth, for example, hot filament chemical deposition (HFCVD) can be used. The thickness of the selectively grown epitaxial layer may be, for example, in the range of 10 nm to 10 μm.

[0052] Regarding impurities in the diamond layer 40, for example, the boron concentration in the film is 1 × 10⁻⁶. １６ cm ―３ That's 1 x 10 ２２ cm ―３ The following range is adjusted. Adjusting the boron to this extent affects the crystal quality of the diamond layer 40 itself, and the crystal quality in particular on the selectively grown side portion 41 decreases. However, it is not a problem that the crystallinity of the label itself deteriorates. Rather, this creates a difference in crystal quality between the diamond layer 40 and the main surface 25 of the substrate, and the diffuse reflection of light off the diamond layer 40 improves the discriminability, especially around the boundary with the main surface 25 (roughly corresponding to the side portion 41 of the diamond layer 40).

[0053] Furthermore, boron is concentrated in high concentrations (1 × 10⁻⁶). １８ cm －３By adding the above, a slight discoloration is observed in the selectively grown diamond layer 40 itself, and the change in color from the main surface 25 further contributes to improving visibility and distinguishability.

[0054] (Second Embodiment) Next, only the differences from the first embodiment will be described for the second embodiment. [Changes in crystal structure due to laser light irradiation]

[0055] Figure 5 is a schematic cross-sectional view of the area between A and B in Figure 3, showing another aspect of the present disclosure. In this embodiment, a laser beam is directly irradiated onto a part of the main surface 25 of the diamond substrate 20, i.e., the area where the marker 30 is to be formed, and the shape of the marker 30 is drawn while scanning the beam of the laser beam. This takes advantage of the fact that, as a result, the crystal structure of the irradiated area of ​​the laser beam changes from the crystal structure it had before irradiation (which is the same as the crystal structure of the main surface 25) to a heterocrystalline structure area 50 after irradiation. As shown in Figure 5, only the crystal structure of the heterocrystalline structure area 50 changes, and as a result the color and other characteristics of the heterocrystalline structure area 50 change, forming a marker 30 that can be identified from the main surface 25.

[0056] In this embodiment, irradiation with laser light having a specific wavelength is used. In this embodiment, a YAG laser with a wavelength of 355 nm is used. However, the wavelength is not limited to 355 nm; the crystal structure of the diamond substrate 20 can be efficiently changed by using a wavelength within the range of 100 nm to 600 nm of the laser light. Conversely, productivity drops drastically if the wavelength is outside this range. This wavelength range was determined by the inventor after diligently studying multiple wavelengths. If the wavelength falls outside this range, cracks may occur on the main surface 25, or the diamond substrate 20 itself may be damaged.

[0057] Furthermore, it is more preferable that the central wavelength of the laser light is in the wavelength range of 200 nm to 500 nm. Even more preferable is a wavelength range of 300 nm to 400 nm. With this wavelength range, engraving can be performed even more efficiently. Therefore, a YAG laser light with a central wavelength of 355 nm is a very preferable example of a light source.

[0058] However, there is no particular reason to limit the laser light source to the YAG laser used in this embodiment; any laser light source that emits wavelengths within the above range can be used.

[0059] Other energy sources besides lasers include energy beams such as electron beams and ion beams. However, for the purpose of creating labels, an energy source that can focus an energy beam onto a relatively small area and achieve a reasonably high energy density is preferable. Furthermore, it is important for the energy source to be easy to handle, such as being small in size and requiring no complex operation for marking, in order to actually manufacture semiconductor devices. From this perspective, laser light sources are suitable.

[0060] In this embodiment, the heterocrystalline structure region 50 changes into a region having a graphite crystal structure. This material is highly distinguishable from the colorless, transparent diamond substrate 20.

[0061] (Third Embodiment) Next, the third embodiment will be described in detail. [Graphite layer present only on the side walls of the recess]

[0062] Figure 6 is a schematic cross-sectional view of the section between A and B in Figure 3, showing another aspect of the present disclosure. This embodiment utilizes a structure in which a recessed region 60 with the main surface 25 as its upper surface is formed in a part of the main surface 25 of the diamond substrate 20, i.e., in the area where the marker 30 is to be formed, and at least the side wall portion 61 of the recessed region 60 is provided with a graphite region 62 having a graphite crystal structure. As shown in Figure 6, the presence of the graphite region 62 having a graphite crystal structure on the side wall portion 61 of the recessed region 60 makes it the edge of the marker 30, allowing for recognition of the boundary portion between the marker 30 and the main surface 25 and obtaining discriminatory ability.

[0063] The method for manufacturing the structure shown in Figure 6 according to this embodiment will be described below. The method for manufacturing the structure shown in Figure 6 is not necessarily limited to this, but it allows for very efficient formation and is one of the representative manufacturing methods that the inventor has diligently developed.

[0064] First, the structure of the sign 30 according to the second embodiment is fabricated. The fabrication method is the same as that of the second embodiment.

[0065] Next, the diamond substrate 20, which has been fabricated according to the second embodiment, is subjected to hot mixed acid cleaning. Specifically, sulfuric acid (H ２ SO ４ ) and nitric acid (HNO ３ Mix the two chemicals in a deposition ratio of 1:1 to 3, and heat the mixed solution to a temperature of approximately 350°C. Immerse the diamond substrate 20 in this solution and leave it for 5 to 60 minutes. After that, remove the diamond substrate 20 from the solution and rinse it with running water at room temperature to completely wash away the chemical. The process can be stopped here, but afterwards, for example, it may be immersed in an organic solvent such as acetone and ultrasonically cleaned, then rinsed again with pure water and completely dried.

[0066] In this embodiment, a hot mixed acid was used, but other options such as a mixture of hydrofluoric acid and nitric acid, aqua regia, or other strong acid solutions can also be used.

[0067] The inventors of this disclosure have found that when the above procedure is performed appropriately, the region having a graphite crystal structure, which is the heterocrystalline structure region 50 produced according to the second embodiment, is removed except for the graphite region 62 having a graphite crystal structure that is basically present on the surface of the sidewall portion 61. Conversely, they have found that the graphite region 62 having a graphite crystal structure remains only on the sidewall portion 61 without being removed. According to the inventors' investigation, it is sometimes observed that graphite remains discretely on a part of the bottom surface, but it has been confirmed that this does not pose any problem to the identifiability of the label 30. Importantly, because the graphite region 62 always remains on at least a part of the sidewall portion 61, the boundary between the label 30 and the main surface 25 can be clearly identified.

[0068] Furthermore, because it can withstand the aforementioned hot mixed acid cleaning (which is equivalent to a fairly strong acid cleaning), it can also remove organic contaminants, resulting in a significant advantage in the manufacturing process: an increase in final yield.

[0069] (Fourth Embodiment) Next, the fourth embodiment will be described in detail. [Recessed structure formed on the main surface]

[0070] Figure 7 is a schematic cross-sectional view between A and B in Figure 3, showing another aspect of the present disclosure. As shown in Figure 7, in this embodiment, a recessed structure 70 is formed by etching or other carving in a part of the main surface 25 of the diamond substrate 20, i.e., in the area where the mark 30 is to be formed. The main surface 25 becomes the upper surface 71 of the recess, the bottom after carving becomes the bottom surface 72 of the recess, and the boundary line between the upper surface 71 of the recess and the side surface 73 of the recess becomes the upper line 74 of the recess.

[0071] This embodiment primarily utilizes the identifiability provided by the recessed upper line 74. As shown in Figure 7, even if both the main surface 25 (recessed upper surface 71) and the recessed bottom surface 72 are colorless and transparent, the recessed upper line 74, which is the boundary line between the recessed upper surface 71 and the recessed side surface 73, appears colored in a plan view due to diffuse reflection of light. This makes it visible, and thus the marker 30 can be identified from the main surface 25.

[0072] (Fifth Embodiment) Next, the fifth embodiment will be described in detail. [Convex structure formed on the main surface]

[0073] Figure 8 is a schematic cross-sectional view between A and B in Figure 3, showing another aspect of the present disclosure. As shown in Figure 8, in this embodiment, a raised structure 80 is formed by etching or other etching processes on a part of the main surface 25 of the diamond substrate 20, i.e., in the area where the mark 30 is to be formed. The upper surface of the raised portion is made the upper surface 81 of the raised portion (equal to the position of the main surface 25 before etching), the bottom portion after etching is made the bottom surface 82 of the raised portion, and the boundary line between the bottom surface 82 of the raised portion and the side surface 83 of the raised portion is made the bottom line of the raised portion 84.

[0074] This embodiment primarily utilizes the identifiability provided by the protruding bottom line 84. As shown in Figure 8, even if both the protruding bottom surface 82 and the protruding top surface 81 are colorless and transparent after carving, the protruding bottom line 84, which is the boundary line between the protruding bottom surface 82 and the protruding side surface 83, appears colored in a plan view due to diffuse reflection of light. This makes it visible, and thus the mark 30 can be identified from the protruding bottom surface 82 after carving.

[0075] (Sixth Embodiment) Next, the sixth embodiment will be described in detail. [Roughened Surface Region]

[0076] Figure 9 is a schematic cross-sectional view between A and B in Figure 3, showing another aspect of the present disclosure. As shown in Figure 9, this embodiment forms a rough surface region 90 on a part of the main surface 25 of the diamond substrate 20, i.e., the area where the marker 30 is to be formed, and utilizes the identifiability due to the diffuse reflection of light incident on the rough surface region 90. As shown in Figure 9, a rough surface region 90 is formed on the main surface 25 of the diamond substrate 20 used in this embodiment, and identifiability is obtained by the difference in the light reflection state between the main surface 25 and the rough surface region 90.

[0077] For example, etching can be used to form the roughened area 90. By using photolithography, the main surface 25 is masked with a photoresist or metal film, and then only the area of ​​the roughened area 90 is selectively opened, and this area is roughened by etching. After etching, the mask can be removed. Since the diffuse reflection of light increases in the roughened area compared to the flat area, the roughened area 90 becomes distinguishable from the main surface 25.

[0078] (Seventh Embodiment) Next, the seventh embodiment will be described in detail. [Specific Uses of the Embodiment]

[0079] The labels 30 described in Embodiments 1 to 6 above can be used, for example, to individually identify diamond substrates 20. Alternatively, the labels 30 can be used in the process of fabricating diamond semiconductor devices on diamond substrates 20. The present invention exhibits superior effects in this application. However, the present invention is not limited to this application.

[0080] (Eighth Embodiment) Next, the eighth embodiment will be described in detail. [Fabrication of Hydrogen-Terminated Field-Effect Transistor Element]

[0081] Figure 10 is a schematic perspective view showing the basic structure of the hydrogen-terminated field-effect transistor element 100 according to this embodiment. As shown in Figure 10, in this embodiment, a structure in which a diamond epitaxial layer 15 is laminated on a diamond single crystal substrate 10 is used as the diamond substrate 20. A hydrogen-terminated channel layer 101 is fabricated directly below the surface of the diamond epitaxial layer 15 (more precisely, 2 to 5 nm below the outermost surface) between the source electrode 103 and the drain electrode 104. The fabrication method will be described later. A gate insulating layer 102 is placed on top of the hydrogen-terminated channel layer 101. A gate electrode 105 is fabricated directly above this gate insulating layer 102, and an MIS-type hydrogen-terminated field-effect transistor element 100 can be fabricated.

[0082] If impurities are intentionally not added during the epitaxial growth of the diamond epitaxial layer 15, resulting in an undoped layer, a high-resistance, insulating diamond epitaxial layer 15 can be fabricated. Generally, by growing the diamond epitaxial layer 15, the crystal quality of the surface of the diamond epitaxial layer 15 can be improved compared to the crystal quality near the surface of the diamond single-crystal substrate 10. As a result, better results can be obtained in subsequent manufacturing processes and in the characteristics of the final hydrogen-terminated field-effect transistor element 100, which is preferable.

[0083] Next, the hydrogen-terminated channel layer 101 is fabricated. First, the entire surface of the diamond epitaxial layer 15 is exposed to a hydrogen plasma to bond hydrogen atoms to the carbon dangling bonds on the surface, thereby creating a hydrogen-terminated structure across the entire surface (hereinafter referred to as hydrogen plasma treatment).

[0084] Subsequently, for example, by using photolithography to mask the hydrogen-terminated channel layer 101, the parts other than the hydrogen-terminated channel layer 101 are exposed to an oxygen plasma, thereby changing the hydrogen atoms in the hydrogen-terminated structure to an oxygen-terminated structure in which oxygen atoms are replaced. Since the surface of the hydrogen-terminated channel layer 101 exhibits conductivity, while the surface of the oxygen-terminated structure exhibits insulation, electrical isolation between the elements is maintained.

[0085] Subsequently, an electrode layer is fabricated over the entire surface of the diamond epitaxial layer 15. In this embodiment, gold (Au) is used as the electrode material, and electron beam deposition is used as the fabrication method. However, it is not limited to this, and for example, a layered structure such as a gold (Au) layer of 200 nm / platinum (Pt) layer of 30 nm / titanium (Ti) layer of 30 nm from the top layer toward the substrate side may also be used. In addition, a boron (B) doped p+ contact layer may be provided between the diamond epitaxial layer 15 and each electrode to reduce contact resistance. Then, using photolithography, the source electrode 103 and drain electrode 104 of the hydrogen-terminated field-effect transistor element 100 are patterned and fabricated as shown in Figure 9.

[0086] Furthermore, a gate insulating layer 102 is fabricated as shown in Figure 10.

[0087] The material of the gate insulating layer 102 is aluminum oxide (Al ２ O ３ This material is commonly used, and this embodiment also uses this material. When fabricated using atomic layer deposition (ALD), the thickness can be easily controlled and the film quality is good. The thickness is preferably 1 nm to 500 nm.

[0088] Other materials that can be used as the gate insulating layer 102 include SiO ２ CaF ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta2O ５ , TiO ２ WO ３ LaF ３ MgF ２ YF ３ LiF, LiF ３ Any of these can be used. Alternatively, a multilayer structure can be formed by any combination of these materials.

[0089] Furthermore, the gate electrode 105 is fabricated, completing the hydrogen-terminated field-effect transistor element 100.

[0090] Figure 11 is a graph showing an example of data obtained by varying the gate voltage (Vg: unit is volts [V]) applied to the gate electrode 105 of a hydrogen-terminated field-effect transistor element 100 fabricated through the above process, specifically the relationship between the drain voltage (Vd: unit is volts [V]) between the source electrode 103 and the drain electrode 104 and the drain current (Id: unit is milliamperes [mA]), as shown above.

[0091] As shown in Figure 11, the drain current (Id) of the hydrogen-terminated field-effect transistor element 100 is controlled as predetermined by the gate voltage (Vg), and it can be confirmed that it is operating without any problems.

[0092] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description and is intended to include all modifications within the meaning and scope of the claims.

[0093] 10 Diamond single crystal substrate 15 Diamond epitaxial layer 20 Diamond substrate 25 Main surface 30 Label 40 Diamond layer 41 Side surface 50 Heterocrystalline structure region 60 Recessed region 61 Sidewall 62 Graphite region 70 Recessed structure 71 Recessed top surface 72 Recessed bottom surface 73 Recessed side surface 74 Recessed top line 80 Convex structure 81 Convex top surface 82 Convex bottom surface 83 Convex side surface 84 Convex bottom line 90 Rough surface region 100 Hydrogen-terminated field-effect transistor element 101 Hydrogen-terminated channel layer 102 Gate insulating layer 103 Source electrode 104 Drain electrode 105 Gate electrode

Claims

1. A diamond substrate comprising a main surface, wherein the main surface comprises a label, the label serving at least one of the purposes of individually identifying the diamond substrates or for use in a process of manufacturing a diamond semiconductor device on the diamond substrate.

2. A diamond substrate comprising a main surface, the main surface comprising a label, and the label comprising a diamond layer selectively and containing impurities and crystallized on the main surface.

3. The impurity contains boron, and the concentration of boron is 1 × 10⁻⁶ １６ cm ―３ The above 1 x 10 ２２ cm ―３ The diamond substrate according to claim 2, wherein the range is as follows.

4. A diamond substrate comprising a main surface, wherein the main surface comprises a label, and the label comprises a heterocrystalline region having a crystal structure different from that of the main surface.

5. The diamond substrate according to claim 4, wherein the heterocrystalline region includes the crystalline structure of graphite.

6. A diamond substrate comprising a main surface, the main surface comprising a mark, the mark comprising a recessed region with the main surface as its upper surface, and the recessed region comprising a graphite region having a graphite crystalline structure in at least a portion of its side wall.

7. A method for manufacturing a diamond substrate, comprising the steps of: preparing a diamond substrate having a main surface; irradiating a region on the main surface where a mark is to be formed with laser light, and after irradiation with laser light, changing the crystal structure of the region where the mark is to be formed to a crystal structure different from the crystal structure forming the main surface; and cleaning the diamond substrate, wherein after cleaning, the mark has a recessed region with the main surface as its upper surface, and has a graphite region having a graphite crystal structure in at least a part of the side wall of at least the recessed region.

8. The method for manufacturing a diamond substrate according to claim 7, wherein the central wavelength of the laser light is in the range of 100 nm to 600 nm.

9. A diamond substrate comprising a main surface, the main surface comprising a mark, the mark comprising a recessed structure, the recessed structure comprising the main surface forming the upper surface of the recess, the surface of the main surface after etching forming the bottom surface of the recess, and the boundary line between the upper surface of the recess and the side surface of the recess forming the upper line of the recess.

10. A diamond substrate comprising a main surface, the main surface comprising a mark, the mark comprising a convex structure, the convex structure comprising the main surface forming the upper surface of the convex, the surface of the main surface after etching forming the bottom surface of the convex, and the boundary line between the bottom surface of the convex and the side surface of the convex forming the bottom line of the convex.

11. A diamond substrate comprising a main surface, wherein the main surface comprises a mark, and the mark comprises at least a rough surface region including a rough surface.

12. A diamond semiconductor device manufactured using the diamond substrate described in any one of claims 1 to 10.

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