JP7161158B2 - Method for manufacturing diamond substrate layer - Google Patents

Description

The present invention relates to a single-crystal diamond substrate that has not undergone surface processing such as grinding or polishing.

Conventionally, diamond has been expected to be the ultimate semiconductor device due to its excellent properties. As an example, a structure in which an n-type diamond layer or a p-type diamond layer is laminated on a diamond substrate serving as a base substrate has been proposed. With such a structure, the quality of the laminated diamond depends on the quality and surface condition of the diamond substrate used as the base substrate. That is, the underlying substrate for fabricating a semiconductor device is required not only to have crystal quality, but also to be flat and free of a work-affected layer with respect to the growth surface of the underlying substrate. For this reason, flattening techniques such as etching and CMP polishing described in Japanese Patent Application Laid-Open No. 01-062484 (hereinafter referred to as Patent Document 1) are used as methods for processing the surface of the substrate. In addition, regarding the underlying substrate before the planarization, a technology for increasing the diameter using heteroepitaxial growth, such as International Publication No. WO 2015/046294 (hereinafter referred to as Patent Document 2), is used, and mass production is possible due to the increase in diameter. It was possible to improve the chip unit price and reduce the chip unit price.

JP-A-01-062484 WO2015/046294

While having the above-mentioned effects, in recent years, regarding the substrate, which has been increased in diameter according to Patent Document 2, etc., the processing method described in Patent Document 1 can obtain the high-precision surface roughness necessary for vapor phase growth on the crystal surface. However, there is a problem that it is not possible to suppress the formation of hillocks (microscopic protrusions) during the vapor phase growth of diamond using the crystal surface. In addition, other processing methods, such as laser cutting and mechanical polishing using diamond abrasive grains, which have been used for jewelry processing for a long time, roughen the processed surface and produce a process-affected layer.

In view of the above problems, the object of the invention described in the present application is to provide a method for manufacturing a diamond substrate layer using a single-crystal diamond substrate having high precision and smooth surface roughness without forming a work-affected layer on the surface. .

For the above purpose, the invention described in the present application uses any of MgO single crystal, α-Al ₂ O ₃ , Si, quartz, platinum, iridium, strontium titanate (SrTiO ₃ ) as a base substrate for growing a single crystal diamond substrate. A base substrate having a surface roughness Ra of 10 nm or less is prepared , an iridium single crystal film is formed on the surface of the base substrate, the base substrate is placed in a growth furnace, and hydrogen, As a gas containing carbon, methane is introduced into the growth furnace at a methane/hydrogen gas flow rate ratio of 0.001% to 30%, and the pressure inside the growth furnace is set to 1.3×10 ³ Pa to 1.3×10 ⁵ Pa. , and a microwave with a frequency of 2.45 GHz (±50 MHz) or 915 MHz (±50 MHz) is supplied with power of 100 W to 60 kW to generate plasma, and the temperature is kept at 700 ° C. to 1300 ° C. by heating with the plasma. An active species is deposited on one side of the base substrate, a single crystal diamond substrate is vapor-grown on the iridium single crystal film to a thickness of 30 μm or more and 500 μm or less, and the base substrate and the iridium single crystal film are removed by wet etching, The single-crystal diamond substrate has no work-affected layers on its front and back surfaces, and the back surface has a surface roughness Ra of 10 nm or less. The technical feature of the present invention is that it is a method for manufacturing a diamond substrate layer using a grown single-crystal diamond substrate.

Further, the invention according to the second aspect of the present invention is technically characterized in that the back surface of the manufacturing method has a surface roughness Ra of 5 nm or less.

The technical features described above enable the invention described in the present application to form a highly accurate growth surface using only vapor phase growth. That is, since the growth surface of a conventional heteroepitaxially grown single crystal diamond substrate is rough in an unpolished state and needs to be flattened using a conventional processing technique, it is possible to finish the surface to be flat and free of a work-affected layer. It was impossible. On the other hand, the rear surface separated from the base substrate for diamond layer growth after vapor deposition is in a state where the diamond layer can be grown in a highly accurate and smooth state due to the growth method. Along with this, in the method of manufacturing a diamond substrate layer using a single-crystal diamond substrate described in the present application, the grown surface is used as the bottom surface, and vapor phase growth is performed again on the back surface side separated from the underlying substrate. It is possible to provide a single-crystal diamond substrate that has both the front and back surfaces without a work-affected layer and that has a smooth surface roughness without polishing by means of vapor phase epitaxy using the back surface. Become. More specifically, after vapor phase epitaxy is performed so that the state of the back surface has a surface roughness Ra of 10 nm or less, the underlying substrate is removed by wet etching to make the growing surface the bottom surface and the back surface. By carrying out vapor phase epitaxy, it is possible to provide a homoepitaxial single-crystal diamond substrate having no damaged layer and a highly precise and smooth crystal surface. This is because diamond has no polarity and can be grown on the back surface. In addition, since the above-described surface processing is not required in the present invention, high quality without the hillocks is achieved by diamond vapor phase growth using a homoepitaxial single crystal diamond substrate that does not generate a work-affected layer on both the front and back surfaces. A single crystal diamond substrate can be obtained.

In addition to the effects described above, the invention according to the second aspect of the present invention can further improve the surface roughness of the vapor-grown rear surface. That is, in the vapor phase epitaxy, it is possible to control the surface roughness up to a certain value depending on the surface of the underlying substrate and growth conditions. More specifically, when the single crystal diamond substrate obtained by the heteroepitaxial growth is used to grow the single crystal diamond substrate again, the surface roughness Ra can be smoothed to a certain value depending on the growth conditions and the thickness of the growth. . The single-crystal diamond substrate according to the present invention is such that the roughness of the crystal surface grown in the crystal growth stage on the back surface is 5 nm or less, and the single-crystal diamond homoepitaxially grown on the back surface is a thick-film diamond with good crystallinity. It allows the growth of single crystals.

As described above, by using the invention described in the claims of the present application, it is possible to provide a single-crystal diamond substrate having high precision and smooth surface roughness without forming a work-affected layer on the surface.

FIG. 2 is an explanatory diagram of a manufacturing method for a single-crystal diamond substrate used in the best embodiment of the present invention; AFM measurement images of the front surface (a) and back surface (b) of the single crystal diamond substrate produced in FIG.

BEST MODE FOR CARRYING OUT THE INVENTION The best embodiment of the present invention is shown below with reference to FIGS. 1 and 2. FIG. In addition, regarding symbols and part numbers in the drawings, common symbols or numbers are given to parts that function as the same parts.

FIG. 1 shows a diagram for explaining the manufacturing method of the single-crystal diamond substrate used in this embodiment, and FIG. 2 shows AFM measurement images on the front surface (a) and back surface (b) of the same substrate. Note that growth devices such as a growth stage, a chamber, and a target are omitted from the drawing.

As can be seen from FIGS. 1(a) to 1(g), in the present embodiment, first, a single-crystal diamond layer 3 is vapor-grown on a base substrate 1 made of MgO single crystal using a CVD method or the like. A homoepitaxial diamond single crystal substrate ( 4, which will be described below as a homo-epi substrate, was obtained.

A detailed description is given below. _In this embodiment, MgO _single crystal is used for the underlying substrate 1 on which the initial diamond layer is formed. Iridium, strontium titanate (SrTiO ₃ ), and the like are included. Of these, MgO single crystal substrates and aluminum oxide (sapphire) single crystal substrates are extremely stable thermally, and substrates with a diameter of up to 8 inches (approximately 203.2 mm) are available. Because it is possible, it is preferable as a substrate for the diamond layer used when producing the homo-epitaxial substrate.

Further, as the base substrate 1, one having at least one surface mirror-polished is used. This is because the diamond layer 3 is grown on the mirror-polished surface side in the step of growing the diamond layer 3, which will be described later. The mirror polishing should be performed so that at least one side is smooth enough to allow the diamond layer to grow, and as a guideline, polishing to a surface roughness Ra of 10 nm or less is preferable. This is because if Ra exceeds 10 nm, the quality of the single-grown diamond layer is degraded. It is assumed that there are no cracks on the one side. Moreover, the measurement of Ra can be performed with a surface roughness measuring machine. As for the substrate, if necessary, a substrate having both sides mirror-polished may be used, and in this case, either side can be arbitrarily used as the growth surface of the diamond layer.

When an MgO single crystal substrate is used as the base substrate 1, it is preferable to use the (001) plane as the growth plane of the diamond layer, but planes other than the (001) plane can also be used. Further, the shape of the substrate for the diamond layer in the planar direction is not particularly limited, and may be, for example, circular or rectangular. In addition, when the substrate is circular, the diameter is preferably 2 inches (about 50.8 mm) or more, more preferably 3 inches (about 76.2 mm) or more, and 6 inches from the viewpoint of increasing the size. (about 152.4 mm) or more is more preferable. Although the upper limit of the diameter of the substrate is not particularly limited, it is preferably 8 inches or less from a practical viewpoint. In the present application, considering the dimensional tolerance of substrates, the range of 49.8 mm or more to 50.8 mm in diameter is defined as 2 inches by subtracting 1.0 mm, which is 2% of 50.8 mm, from 2 inches in diameter.

While the size of the underlying substrate 1 is specified in the case of a circular shape, the size of the base substrate 1 is preferably 50 mm×50 mm or more, more preferably 75 mm×75 mm or more, from the viewpoint of increasing the size of the square substrate. . Moreover, the upper limit of the dimension is preferably 200 mm×200 mm or less from a practical viewpoint. The substrate for the diamond layer therefore has a surface area of at least 20 cm ² . Furthermore, from the viewpoint of increasing the size, it is more preferable to have a surface area of up to 1297 cm ² .

The thickness of the base substrate 1 is preferably 3.0 mm or less, more preferably 1.5 mm or less, and even more preferably 1.0 mm or less. Although the lower limit of the thickness is not particularly limited, it is preferably 0.05 mm or more, more preferably 0.4 mm or more, from the viewpoint of ensuring rigidity. When the shape in the planar direction is circular and the diameter is 50 mm or more and 150 mm or less, the thickness is preferably 0.3 mm or more, and when the diameter exceeds 150 mm, the thickness is preferably 0.6 mm or more.

In this embodiment, the iridium (Ir) single crystal film 2 is formed on the surface of the underlying substrate 1 as a pretreatment, and the diamond layer is grown on the Ir single crystal film.

Next, a diamond layer 3 made of a diamond single crystal is grown on one side to form it. A method for growing the diamond layer is not particularly limited, and a known method can be used. Specific examples of growth methods include vapor deposition methods such as a pulsed laser deposition (PLD) method and a chemical vapor deposition (CVD) method.

When using the CVD method, a substrate for a diamond layer is placed in a CVD growth furnace, and a CVD diamond single crystal is grown on one side of the substrate. As a growth method, a direct current plasma method, a hot filament method, a combustion flame method, an arc jet method, or the like can be used, but a microwave plasma method is preferable in order to obtain high-quality diamond with less contamination.

In the epitaxial growth of the diamond layer by the microwave plasma CVD, a gas containing hydrogen and carbon is used as a raw material gas. As a gas containing hydrogen and carbon, methane is introduced into the growth furnace at a methane/hydrogen gas flow rate ratio of 0.001% to 30%. The pressure in the furnace is maintained at about 1.3×10 ³ Pa to 1.3×10 ⁵ Pa, and the microwave frequency of 2.45 GHz (±50 MHz) or 915 MHz (±50 MHz) is supplied with power of 100 W to 60 kW. Generate plasma. Active species are deposited on one side of the substrate, which is kept at a temperature of 700° C. to 1300° C. by heating with the plasma, to grow CVD diamond. The thickness of the diamond layer is preferably 30 μm or more and 500 μm or less.

After forming the diamond layer 3, the underlying substrate 1 is separated. In this embodiment, the underlying substrate 1 is removed by wet etching using nitric acid or the like, and the remaining Ir film 2 is removed by the same method after being alloyed with solder.

1 manufactured by the above-described method, the grown surface O was used as the bottom surface, and the back surface U was subjected to vapor phase epitaxy of the diamond substrate layer again in this embodiment. (Refer to (e) in FIG. 1) The conditions for the growth are the same as those for the vapor phase growth of the diamond substrate layer. By the second vapor phase epitaxy, a high-quality single crystal diamond substrate could be obtained by homoepitaxial growth on the same material in the present embodiment.

FIG. 2 shows a surface AFM measurement image of the homo-epi substrate 4 obtained in this embodiment. Here, FIG. 2(a) is the crystal surface of the surface O, and FIG. 2(b) is the crystal surface for growth of the back surface U. 0 nm. As can be seen from FIG. 2, the homo-epitaxial substrate obtained in this embodiment has a smoother surface roughness on the back surface than on the front surface. This is because the surface of the underlying substrate affects the crystal surface on the separated back surface. Observation of the back surface using a transmission electron microscope shows that there is no atomic disturbance due to processing, that is, there is no process-affected layer. I was able to confirm that.

As described above, by using the homo-epitaxial substrate according to the embodiments of the present application, it is possible to provide a single-crystal diamond substrate having high precision and smooth surface roughness without forming a work-affected layer on the surface.

REFERENCE SIGNS LIST 1 base substrate 2 Ir layer 3 diamond substrate layer 4 single crystal diamond substrate for homoepitaxial growth O surface U back surface

Claims (2)

A base substrate for growth of a single crystal diamond substrate is made of any one of MgO single crystal, α-Al ₂ O ₃ , Si, quartz, platinum, iridium, and strontium titanate (SrTiO ₃ ), and has a surface roughness Ra of 10 nm. preparing the base substrate having the following surfaces;
forming an iridium single crystal film on the surface of the underlying substrate;
placing the underlying substrate in a growth furnace;
introducing methane as a gas containing hydrogen and carbon into the growth furnace at a methane/hydrogen gas flow rate ratio of 0.001% to 30%;
keeping the pressure in the growth furnace at 1.3×10 ³ Pa to 1.3×10 ⁵ Pa,
Plasma is generated by applying microwaves with a frequency of 2.45 GHz (±50 MHz) or 915 MHz (±50 MHz) with power of 100 W to 60 kW,
Depositing active species on one side of the base substrate which is kept at a temperature of 700° C. to 1300° C. by heating with the plasma,
vapor-growing a single-crystal diamond substrate to a thickness of 30 μm or more and 500 μm or less on the iridium single-crystal film;
removing the base substrate and the iridium single-crystal film by wet etching to make the front and back surfaces of the single-crystal diamond substrate free from work-affected layers and to make the back surface have a surface roughness Ra of 10 nm or less;
A method for producing a diamond substrate layer using the single crystal diamond substrate, wherein vapor phase epitaxy is performed again on the back side of the single crystal diamond substrate to grow the diamond substrate layer homoepitaxially. Surface roughness of the back surface Ra=5 nm or lessto faceA method for producing a diamond substrate layer according to claim 1.

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