WO2018012529A1

WO2018012529A1 - Single-crystal diamond substrate

Info

Publication number: WO2018012529A1
Application number: PCT/JP2017/025393
Authority: WO
Inventors: 英雄會田; 聖祐金; 豊木村; 友喜川又; 憲次朗池尻
Original assignee: 並木精密宝石株式会社
Priority date: 2016-07-14
Filing date: 2017-07-12
Publication date: 2018-01-18
Also published as: JP7161158B2; JPWO2018012529A1

Abstract

[Problem] To provide a single-crystal diamond substrate having high precision and low surface roughness, and in which a work-affected layer does not occur on the surface thereof. [Solution] In the present invention, a back surface of a diamond layer vapor-phase grown by heteroepitaxial growth is formed so as to have a surface roughness in a specific range as a surface for fostering homoepitaxial growth, whereby a single-crystal diamond layer formed by additional vapor-phase growth is formed on the back surface of a diamond single-crystal after the vapor-phase growth is completed, and a single-crystal diamond substrate having high precision and low surface roughness can be obtained without a work-affected layer occurring thereon.

Description

Single crystal diamond substrate

The present invention relates to a single crystal diamond substrate which is not subjected to surface processing such as grinding and polishing.

Conventionally, diamond is expected as an ultimate semiconductor device due to its excellent characteristics, and as an example, a configuration in which an n-type diamond layer or a p-type diamond layer is laminated on a diamond substrate as a base substrate has been proposed. In such a configuration, the quality of the diamond to be laminated depends on the quality and surface state of the diamond substrate used as the base substrate. That is, the base substrate for manufacturing the semiconductor device is required not only to have crystal quality, but also to have a flat surface and no work-affected layer on the surface to be a growth surface of the base substrate. For this reason, planarization techniques such as etching and CMP polishing described in JP-A-01-062484 (hereinafter referred to as Patent Document 1) and the like are used as the surface processing method of the substrate. For the base substrate before the planarization, a technique for increasing the diameter using heteroepitaxial growth such as International Publication No. 2015/046294 (hereinafter described as Patent Document 2) is used, and mass productivity due to the increase in diameter is used. It was possible to improve the cost and reduce the chip unit price.

Japanese Patent Laid-Open No. 01-062484 International Publication No. 2015/046294

While having the effects described above, in recent years, with respect to the substrate whose diameter has been increased by Patent Document 2 or the like, the processing method described in Patent Document 1 provides high-precision surface roughness necessary for vapor phase growth on the crystal surface. It cannot be applied, and there is a problem that generation of hillocks (Hillocks) cannot be suppressed during vapor phase growth of diamond using the crystal surface. In addition, with respect to other processing methods, laser cutting and mechanical polishing using diamond abrasive grains, which have been used for jewelry processing for a long time, result in a roughened processing surface and a work-affected layer.

In view of the above problems, the invention described in the present application aims to provide a single crystal diamond substrate having a highly accurate and smooth surface roughness without causing a work-affected layer on the surface.

For the above-mentioned purpose, the invention described in the present application is that the single crystal diamond substrate that is not subjected to grinding or polishing on the growth surface has no technically altered layer on the surface and the surface roughness Ra = 10 nm or less. It is a feature. More specifically, the technical feature of the raw homoepitaxial diamond single crystal substrate for which crystal growth has been completed is that the surface roughness Ra is 10 nm or less.

Further, the invention described in the second aspect of the present invention is characterized in that the surface roughness Ra of the substrate is formed with 5 nm or less.

Due to the technical features described above, the invention described in the present application can form a highly accurate growth surface using only vapor phase growth. That is, the growth surface of a conventional single crystal diamond substrate that has been heteroepitaxially grown is rough in an unpolished state and needs to be flattened using conventional processing techniques, so that it can be finished to a flat surface without a work-affected layer. It was impossible. On the other hand, the rear surface separated from the base substrate for growing the diamond layer after vapor phase growth is in a state in which the diamond layer can be grown with high accuracy and smoothness due to its growth method. Along with this, the single crystal diamond substrate described in the present application uses the grown surface as a bottom surface, and performs vapor phase growth again on the back surface side separated from the base substrate, so that both the front surface and the back surface are processed alteration layers. It is possible to provide a single crystal diamond substrate having a smooth surface roughness without being polished by vapor phase growth using the back surface. More specifically, after vapor phase growth is performed so that the state of the back surface is a surface roughness Ra = 10 nm or less, the base substrate is removed by wet etching to make the growth surface the bottom surface, By performing vapor phase growth, it is possible to provide a single crystal diamond substrate for homoepitaxial that has no work-affected layer and has a highly accurate and smooth crystal surface. This is due to the fact that diamond has no polarity and it is possible to grow diamond on the back surface. In addition, since the surface processing described above is not required in the present invention, high quality without the above hillocks is obtained by diamond vapor phase growth using a single crystal diamond substrate for homoepitaxial that does not cause a work-affected layer on the front and back surfaces. A simple single crystal diamond substrate can be obtained.

In addition to the effects described above, the surface roughness of the vapor-grown back surface can be further improved by the invention described in the second aspect of the present invention. That is, in the vapor phase growth, the surface roughness can be controlled by the surface of the base substrate and the growth conditions up to a certain value. More specifically, when the single crystal diamond substrate is grown again using the single crystal diamond obtained by the heteroepitaxial growth, the surface roughness Ra can be smoothed to a constant value depending on the growth conditions and the thickness to be grown. . The single crystal diamond substrate according to the present invention is a thick film diamond having good crystallinity, which is obtained by homoepitaxially growing single crystal diamond on the back surface by setting the roughness of the crystal surface grown in the crystal growth stage on the back surface to 5 nm or less. It is possible to grow into a single crystal.

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

Explanatory drawing of the manufacturing method of the single crystal diamond substrate used in the best embodiment of this invention. The AFM measurement image of the single crystal diamond substrate surface (a) and back surface (b) manufactured in FIG.

Hereinafter, the best embodiment of the present invention will be described with reference to FIGS. In addition, about the symbol and component number in a figure, the common symbol or number is provided to what functions as the same component.

FIG. 1 is an explanatory diagram of a method for producing a single crystal diamond substrate used in this embodiment, and FIG. 2 shows AFM measurement images on the substrate front surface (a) and back surface (b) of the substrate. In addition, about the growth apparatuses, such as a growth stage, a chamber, and a target, description in a figure is abbreviate | omitted.

As can be seen from FIGS. 1A to 1G, in this embodiment, the single crystal diamond layer 3 is first vapor-deposited on the base substrate 1 made of MgO single crystal using a CVD method or the like. A diamond single crystal substrate for homoepitaxial growth that can grow the diamond single crystal substrate having the above-mentioned high-precision surface roughness by using the back surface of the diamond substrate obtained by separating the base substrate and the like from the diamond layer as a growth layer ( 4) was obtained.

Detailed description will be given below. For the base substrate 1 for forming the first diamond layer, MgO single crystal is used in this embodiment, but other materials include aluminum oxide (α-Al ₂ O ₃ : sapphire), Si, quartz, platinum, iridium, and strontium titanate (SrTiO ₃₎ or the like. Of these, the MgO single crystal substrate and the aluminum oxide (sapphire) single crystal substrate are extremely stable thermally and have a diameter of up to 8 inches (about 203.2 mm). For the reason that it is possible, it is preferable as a substrate for a diamond layer used when the above-mentioned homoepi substrate is prepared.

Further, the base substrate 1 is a substrate whose at least one surface is mirror-polished. This is because the diamond layer 3 is grown and formed on the mirror-polished surface side in the later-described diamond layer 3 growth step. The mirror polishing may be performed so that at least one side is smooth enough to grow a diamond layer. As a guideline, the surface roughness Ra is preferably 10 nm or less. This is because when the Ra exceeds 10 nm, the quality of the diamond layer to be grown on one piece is deteriorated. It is assumed that there is no crack on the one side. Further, Ra can be measured with a surface roughness measuring machine. As the substrate, a substrate whose both surfaces are mirror-polished may be used as necessary. In this case, any one surface can be arbitrarily used as a growth surface of the diamond layer.

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

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

Further, the thickness of the base substrate 1 is preferably 3.0 mm or less, more preferably 1.5 mm or less, and further preferably 1.0 mm or less. Although the lower limit of thickness is not specifically limited, It is preferable that it is 0.05 mm or more from a viewpoint of ensuring rigidity, and it is more preferable that it is 0.4 mm or more. In addition, when the planar shape 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, as a pretreatment, an iridium (Ir) single crystal film 2 is formed on the surface of the base substrate 1, and a diamond layer is grown on the Ir single crystal film.

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

When the CVD method is used, a diamond layer substrate is placed in a CVD growth furnace, and a CVD diamond single crystal is grown on one surface 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 little contamination.

In the epitaxial growth of the diamond layer by the microwave plasma CVD, a gas containing hydrogen and carbon is used as a source gas. Methane is introduced into the growth furnace as a gas containing hydrogen and carbon at a methane / hydrogen gas flow rate ratio of 0.001% to 30%. By maintaining the pressure in the furnace at about 1.3 × 10 ³ Pa to 1.3 × 10 ⁵ Pa and applying microwaves with a frequency of 2.45 GHz (± 50 MHz) or 915 MHz (± 50 MHz) to a power of 100 W to 60 kW Generate plasma. CVD diamond is grown by depositing active species on one side of the substrate maintained at a temperature of 700 ° C. to 1300 ° C. by heating with the plasma. The thickness of the diamond layer is set so as to be equal to the height of the columnar diamond to be formed, and it is preferable to grow with a thickness of 30 μm or more and 500 μm or less.

After the diamond layer 3 is formed, the base substrate 1 is separated. In the present embodiment, the base substrate 1 is removed by wet etching using nitric acid or the like, and the remaining Ir film 2 is alloyed with solder and then removed by the same method.

With respect to the homoepitaxial substrate 4 shown in FIG. 1 manufactured by the above-described method, in this embodiment, the grown surface O is the bottom surface, and the diamond substrate layer is vapor-phase grown again on the back surface U where the pillars remain. went. (See (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 this second vapor phase growth, a high quality single crystal diamond substrate could be obtained by homoepitaxial growth on the same material in this embodiment.

FIG. 2 shows a surface AFM measurement image of the homoepitaxial substrate 4 obtained in this embodiment. 2A shows the crystal surface of the surface O, and FIG. 2B shows the growth crystal surface of the back surface U. The surface roughness Ra = 19.1 nm and the surface roughness Ra = 4. 0 nm. As can be seen from FIG. 2, the homoepitaxial substrate obtained in the present embodiment has the surface roughness of the back surface smoother than the front surface. This is because the surface of the base substrate has an influence on the separated back crystal surface, and there is no disorder of the atoms caused by processing, that is, no work-affected layer by observing the back surface using a transmission electron microscope. I was able to confirm that.

As described above, a single crystal diamond substrate having a high precision and smooth surface roughness can be provided without producing a work-affected layer on the surface by using the homoepitaxial substrate described in the present embodiment.

DESCRIPTION OF SYMBOLS 1 Base substrate 2 Ir layer 3 Diamond substrate layer 4 Single crystal diamond substrate for homoepitaxial growth O Surface U Back surface

Claims

A single crystal diamond substrate that has no work-affected layer on the surface, has a surface roughness Ra of 10 nm or less, and has not been subjected to grinding or polishing on the surface.
2. The single crystal diamond substrate according to claim 1, wherein there is no work-affected layer on the surface, the surface roughness Ra is 5 nm or less, and the surface is not ground or polished.