JP7634207B2 - Diamond Substrate - Google Patents

Description

The present invention relates to a method for manufacturing a diamond substrate, a diamond substrate, and a free-standing diamond substrate.

Diamond has a wide band gap of 5.47 eV at room temperature and is known as a wide band gap semiconductor.

Among semiconductors, diamond has an extremely high breakdown field strength of 10 MV/cm, making it possible to operate at high voltages. It also has the highest thermal conductivity of any known substance, making it excellent at dissipating heat. Furthermore, its extremely high carrier mobility and saturated drift velocity make it suitable for use in high-speed devices.

For this reason, diamond has the highest Johnson figure of merit, which indicates the performance of high-frequency, high-power devices, even when compared to semiconductors such as silicon carbide and gallium nitride, and is said to be the ultimate semiconductor.

As such, diamond is expected to be put to practical use as a semiconductor material, and there is a demand for large-area, high-quality diamond substrates. However, diamond substrates of sufficient quality have yet to be obtained.

Currently, type Ib diamonds synthesized by the high-pressure, high-temperature synthesis (HPHT) method are used as diamond substrates. However, type Ib diamonds contain a lot of nitrogen impurities and can only be obtained in a maximum size of about 8 mm square, so they are not very practical.

In Non-Patent Document 1, a Schottky diode is fabricated using diamond synthesized by the HPHT method as a substrate. However, the etch pit density by hydrogen plasma treatment, which is a guideline for the dislocation defect density of the diamond substrate, is about 10 ⁵ cm ^-2 , and it has been reported that even if an electrode is actually formed and operation is attempted, malfunction occurs due to the presence of killer defects near the electrode or in the current path.

In some cases, homoepitaxial diamond is grown epitaxially by chemical vapor deposition (CVD) using diamond synthesized by HPHT as a base.

In Non-Patent Document 2, an attempt is made to create a mosaic-shaped diamond substrate by bonding multiple diamond substrates together in order to obtain a large diamond substrate. However, this technique has problems such as the tendency for cracks to occur along the boundaries of the substrates.

Meanwhile, the creation of diamond substrates by heteroepitaxial growth, in which diamond is grown on a dissimilar material, is also being considered. Heteroepitaxial growth makes it relatively easy to obtain large-area substrates, and is thought to reduce manufacturing costs.

Silicon (Si), platinum (Pt), etc. have been investigated as substrates for heteroepitaxial growth of diamond, and Non-Patent Document 3 reports that iridium (Ir) is suitable as a substrate material. This involves using Ir epitaxially grown on the surface of single crystal magnesium oxide (MgO) as the substrate material, subjecting this surface to a diamond nucleation treatment, and then producing epitaxial diamond by the DC plasma CVD method.

However, heteroepitaxial growth also has the problem that many dislocation defects occur due to the lattice mismatch between diamond and the underlying material. For example, the lattice mismatch between diamond (lattice constant 3.57 Å) and Ir (lattice constant 3.84 Å) is as large as 7%. Non-Patent Document 4 reports that the etch pit density of heteroepitaxial diamond is as high as 10 ⁸ cm ^-2 .

As a method for reducing such dislocation defects, Non-Patent Document 5 proposes a technique called selective growth. This is a method for laterally growing diamonds (ELO: Epitaxial Lateral Overgrowth) from diamond nuclei formed in an arbitrary pattern.

H. Umezawa et al. , Diamond Relat. Mater. , 18, 1196 (2009) H. Yamada et al. , Appl. Phys. Lett. , 104, 102110 (2014) K. Ohtsuka et al. , Jpn. J. Appl. Phys. , 35, L1072 (1996) K. Ichikawa et al. , Proc. 24th NDF-Dia. Sympo. , 226 (2010) Sawabe, A. et al., Journal of the Japanese Society for Crystal Growth, 39, 179 (2012).

Although the selective growth method mentioned above can reduce dislocation defects to some extent, further reduction in defects is required for practical application.

In addition, in heteroepitaxial growth, thermal stress is also generated due to the difference in thermal expansion coefficient between diamond and the base material. For example, the linear expansion coefficient of diamond is 1.1×10 ⁻⁶ K ⁻¹ , that of MgO is 13.8×10 ⁻⁶ K ⁻¹ , and that of Ir is 7.1×10 ⁻⁶ K ⁻¹ . Furthermore, it is known that diamond generates large internal stresses as the crystal grows, and these stresses cause cracks and warping of the diamond substrate.

In fact, many cracks have been generated in heteroepitaxial diamond substrates fabricated by the selective growth method described in Non-Patent Document 5, and it is considered difficult to put the method to practical use in this state.

Therefore, it is expected that thermal stress and internal stress will be reduced in order to put diamond substrates made by epitaxial growth into practical use.

The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing a diamond substrate that can sufficiently reduce defects (including dislocation defects), a high-quality diamond substrate with sufficiently reduced defects, and a free-standing diamond substrate.

In order to solve the above problems, the present invention provides a method for manufacturing a diamond substrate, comprising the steps of:
A first step of providing a pattern of diamonds on a substrate surface;
a second step of growing diamond from the patterned diamond provided in the first step to form diamond in the patterned diamond provided in the first step;
a third step of removing the patterned diamond provided in the first step and forming a patterned diamond made of the diamond formed in the second step;
A fourth step of growing diamond from the patterned diamond formed in the third step to form diamond in the patterned diamond formed in the third step;
The present invention provides a method for producing a diamond substrate, comprising the steps of:

This method of manufacturing diamond substrates can sufficiently reduce defects in diamond substrates, making it possible to produce high-quality diamond.

In this case, the material constituting the base surface can be diamond.

In this way, by using diamond as the material that constitutes the base surface, a diamond substrate can be manufactured by homoepitaxial growth.

The material constituting the base surface can also be a different material other than diamond, such as iridium, rhodium, or platinum.

In this way, by growing diamond heteroepitaxially using a substrate whose surface is made of a different material, it is possible to produce a high-quality, large-area diamond substrate.

In addition, in the method for manufacturing a diamond substrate of the present invention, it is preferable to remove any foreign matter adhering to the walls of the patterned diamond formed on the base surface in the first step prior to the second step.

By removing foreign matter in this way, the occurrence of abnormally grown particles can be suppressed in the second process that follows.

It is also preferable that the ratio D/W, which is the ratio of the depth D to the width W of the pattern gap in the patterned diamond formed in the first process, is 0.1 or more.

In this way, if a pattern of diamonds is provided in the first step so that the ratio of the depth D to the width W of the pattern gap (D/W) is equal, the pattern gaps will close relatively quickly in the second step, so that even if abnormally grown particles occur in the pattern gaps, the impact on the surface of the formed diamond can be reduced.

It is also preferable to penetrate at least a portion of the bottom of the pattern gaps in the patterned diamond provided in the first step.

In addition, when the material constituting the base surface is a different material other than diamond, at least a part of the bottom of the pattern gap in the patterned diamond provided in the first step may be provided below the base surface.

In this way, it is possible to manufacture a diamond substrate in which the internal stress that occurs with crystal growth is alleviated. It is also possible to manufacture a diamond substrate in which the thermal stress that occurs when the base is made of a different material is alleviated.

In addition, in the second step, it is preferable to grow diamond using chemical vapor deposition.

Thus, in the second step, diamond can be grown using various chemical vapor deposition techniques.

It is also preferable to form voids in the diamond grown in the second step.

In this way, forming voids in diamond is preferable because it can relieve internal stress that occurs with crystal growth and thermal stress that occurs when the base is made of a different material.

In addition, it is preferable to remove foreign matter adhering to the wall surface of the patterned diamond formed in the third step before the fourth step.

By removing foreign matter in this way, the occurrence of abnormally grown particles can be suppressed in the fourth step that follows.

In addition, it is preferable that the ratio D/W, which is the ratio of the depth D to the width W of the pattern gap in the patterned diamond formed in the third process, is 0.1 or more.

In this way, the gaps in the pattern are filled relatively quickly in the fourth step, so that even if abnormally grown particles occur in the gaps in the pattern, the impact on the surface of the formed diamond can be reduced.

It is also preferable to penetrate at least a portion of the bottom of the pattern gaps in the patterned diamond formed in the third step.

In addition, when the material constituting the base surface is a different material other than diamond, at least a portion of the bottom of the pattern gap in the patterned diamond formed in the third step may be located below the base surface.

In this way, it is possible to produce a diamond substrate that is free of internal stresses that arise with crystal growth and thermal stresses that arise when the base is made of a different material.

In addition, in the third step, it is preferable to remove the diamond formed in the second step to a position 5 μm to 30 μm from the boundary with the patterned diamond formed in the first step.

By removing the diamond formed in the second step in this way, a higher quality diamond can be grown in the fourth step, and this is also preferable from the standpoint of production efficiency and production costs.

In addition, in the fourth step, it is preferable to grow diamond using chemical vapor deposition.

Thus, in the fourth step, diamond can be grown using various chemical vapor deposition techniques.

It is also preferable to form voids in the diamond grown in the fourth step.

In this way, forming voids in diamond is preferable because it can relieve internal stress that occurs with crystal growth and thermal stress that occurs when the base is made of a different material.

The present invention also provides a diamond substrate having at least one surface made of diamond, the diamond substrate being characterized by having voids inside.

The diamond substrate may also be made of a base and a diamond layer formed on the surface of the base, and may have voids at the boundary between the base and the diamond layer.

The present invention also provides a free-standing diamond substrate, characterized in that one surface of the substrate has voids.

Such diamond substrates with internal voids and freestanding diamond substrates with voids on one surface have sufficiently reduced defects such as dislocation defects. In addition, stress is reduced, making it possible to suppress the occurrence of warping and cracks in the substrate.

The present invention also provides a diamond substrate comprising a base and a diamond layer formed on the surface of the base, the diamond substrate being characterized in that the back surface of the base has an opening.

Such diamond substrates have sufficiently reduced defects, and also have reduced internal stress that occurs with crystal growth and thermal stress that occurs when the base is made of a different material, making it possible to suppress warping and cracking of the substrate.

The present invention also provides a diamond substrate in which at least one surface is made of diamond, and the entirety of at least one surface is made of at least one of laterally grown diamond and diamond grown from a laterally grown diamond layer.

Such diamond substrates have significantly reduced defects and low stress.

The present invention can provide a high-quality diamond substrate with few defects (including dislocation defects) and low stress. By using such a diamond substrate, it is possible to manufacture semiconductor devices that exhibit excellent performance. Furthermore, when diamond is grown heteroepitaxially using a different material as the base, it is possible to simultaneously increase the area of the diamond substrate.

1A to 1C are diagrams illustrating a method for manufacturing a diamond substrate according to the present invention (Example 2). FIG. 2 is a schematic diagram showing lithography and the like performed in the first step in the manufacturing method (Example 2) of the diamond substrate of the present invention. 1A to 1C are diagrams illustrating another method for manufacturing a diamond substrate according to the present invention (Example 1). FIG. 2 is a diagram showing a schematic diagram of lithography and the like carried out in a first step in another method for manufacturing a diamond substrate (Example 1) of the present invention. 1 is a cross-sectional view showing an example of a diamond substrate of the present invention.

As described above, there is a demand for a method for manufacturing a diamond substrate that can sufficiently reduce defects (including dislocation defects), as well as a high-quality diamond substrate and a free-standing diamond substrate with sufficiently reduced defects.

The inventors have discovered that the method for manufacturing a diamond substrate according to the present invention described below makes it possible to manufacture a high-quality diamond substrate with sufficiently reduced defects.

That is, the present invention is a method for producing a diamond substrate,
A first step of providing a pattern of diamonds on a substrate surface;
a second step of growing diamond from the patterned diamond provided in the first step to form diamond in the patterned diamond provided in the first step;
a third step of removing the patterned diamond provided in the first step and forming a patterned diamond made of the diamond formed in the second step;
A fourth step of growing diamond from the patterned diamond formed in the third step to form diamond in the patterned diamond formed in the third step;
The present invention provides a method for producing a diamond substrate, comprising the steps of:

The following describes an embodiment of the present invention with reference to the drawings, but the present invention is not limited to this. The method for manufacturing diamond of the present invention includes at least the four steps described below, but other steps can be added as necessary.

In the first step, a pattern of diamonds 2, 22 is provided on the surface (substrate surface) of the substrate 1, 21 (Fig. 1(A), Fig. 3(A)).

In this case, there is no particular limitation on the material that constitutes the base 1, 21. As shown in Figure 1, if the material that constitutes the base surface is diamond 3, a diamond substrate is produced by homoepitaxial growth.

Examples of such a substrate 1 include diamond 3, such as diamond synthesized by the HPHT method, homoepitaxial diamond, and heteroepitaxial diamond. In particular, if diamond with relatively few defects, such as diamond synthesized by the HPHT method or homoepitaxial diamond, is used as the substrate, a diamond substrate with even fewer defects can be produced.

On the other hand, if the material that makes up the base surface is a different material other than diamond, as shown in Figure 3, a diamond substrate can be produced by heteroepitaxial growth.

The heterogeneous material that constitutes the base surface is preferably a material that is a cubic crystal like diamond, has a small lattice mismatch with diamond, and does not react with carbon to form carbides. Materials that satisfy these conditions include the platinum group metals, such as rhodium (Rh), palladium (Pd), iridium (Ir), and platinum (Pt).

Here, the lattice constant of diamond is 3.57 Å, and the lattice mismatch with Rh (lattice constant 3.72 Å) is 4.2%, with Ir (lattice constant 3.84 Å) is 7.6%, and with Pt (lattice constant 3.92 Å) is 9.8%. It is preferable that the lattice mismatch between diamond and the dissimilar materials that make up the base surface is 10% or less. Also, Ir is preferable from the viewpoint of not reacting with carbon to form carbides.

An example of such a base 21 is a base in which an intermediate layer 24 _made of a material selected from single crystal magnesium oxide (MgO), single crystal strontium titanate ( _SrTiO3 ), α-alumina ( _Al2O3 ), and yttria-stabilized zirconia (YSZ) is provided on a silicon (Si) substrate 23, and further a surface layer 25 made of a material selected from iridium (Ir), rhodium (Rh), and platinum (Pt) is provided on the intermediate layer.

In addition, one or more layers (not shown) made of a material selected from gold (Au), platinum (Pt), titanium (Ti), chromium (Cr), iridium (Ir), rhodium (Rh), silicon (Si), and silicon oxide (SiO ₂ ) may be interposed between the silicon (Si) substrate 23 and the intermediate layer 24.

Heteroepitaxial growth can easily produce large-area diamond substrates at a relatively low cost, so by applying heteroepitaxial growth to the present invention, it is possible to produce high-quality, large-area diamond substrates.

The method for providing the patterned diamonds 2, 22 on the base surface is also not limited. In the present invention, "patterned" refers to a pattern formed by projections and recesses.

When the material constituting the base surface is diamond, for example, the diamond 3 on the base surface can be processed into a pattern of diamond 2 by a known method such as photolithography or electron beam lithography (Figure 1 (A)).

When the material constituting the base surface is a different material, diamond is first grown on the base surface by a known method such as microwave plasma CVD, direct current plasma CVD, hot filament CVD, arc discharge plasma jet CVD, etc. Next, the diamond grown on the base surface is processed into a pattern by a method such as photolithography or electron beam lithography, thereby providing a patterned diamond 22 on the base surface (Figure 3 (A)).

In addition, even if the material constituting the base surface is diamond, a pattern of diamonds can be provided on the base surface by growing diamond on the base surface using a similar technique and processing the grown diamond into a pattern.

The shape of the pattern of diamonds 2, 22 provided on the base surface can be selected arbitrarily. For example, the pattern can be a line, rectangular dot, circular dot, or other pattern of multiple diamonds.

At this time, the position, size, thickness, crystal orientation, etc. of the patterned diamond 2, 22 can be selected arbitrarily, but the ratio D/W of the depth D ( _D11 in FIG. 1, _D21 in FIG. 3) and width W ( _W12 in FIG. 1, _W22 in FIG. 3) of the patterned gap 10, 30 in the patterned diamond 2, 22 is preferably 0.1 or more, more preferably 0.5 or more. Incidentally, _W11 in FIG. 1 and _W21 in FIG. 3 are the widths of the convex parts in the patterned diamond 2, 22. In this way, since the patterned gap 10, 30 is closed relatively quickly in the second step, even if abnormally grown grains are generated from the patterned gap, the influence on the formed diamond surface can be reduced. Incidentally, in the present invention, the "patterned gap" refers to the gap between the convex parts of the patterned diamond.

The material constituting the bottoms 11, 31 of the pattern gaps 10, 30 may be diamond or a different material. However, since materials such as MgO are etched by hydrogen (H ₂ )/methane (CH ₄ ) plasma of CVD when diamond is formed in the pattern gaps in the second step, it is preferable to use a material such as Ir.

In particular, when the material constituting the bottom of the pattern gap is a different material, in the process of processing the diamond into a pattern, a different kind of attachment may adhere to the wall surface of the pattern-shaped diamond 2, 22 provided on the base surface. In addition, a different kind of attachment may adhere due to SiO ₂ used as a mask. It is preferable to remove the different kind of attachment adhered to the wall surface of the pattern-shaped diamond provided on the base surface before the second process. By removing the different kind of attachment adhered to the wall surface of the diamond in this way, the generation of abnormally grown particles can be suppressed in the second process. The removal of the different kind of attachment can be performed, for example, by selective etching or the like.

For example, when foreign deposits such as Ir or _SiO2 are attached to the walls of the patterned diamonds 2, 22 provided on the base surface, they can be removed by etching with _CF4 plasma.

Furthermore, if necessary, at least a portion of the bottoms 11, 31 of the pattern gaps 10, 30 in the patterned diamond provided in the first step may be removed, including the underlying layer, to make them open.

In addition, when the material constituting the substrate surface is a different material other than diamond, at least a part of the bottom 31 of the pattern gap 30 in the patterned diamond provided in the first step may be provided below the substrate surface by removing a part of the substrate as well. In this case, the depth from the substrate surface to the bottom 31 of the pattern gap 30 can be determined as desired.

In this way, it is possible to reduce internal stress and thermal stress that occurs when the base is made of a different material. One method for removing the base as well is etching.

In the second step, diamonds are grown from the patterned diamonds 2, 22 provided in the first step, forming diamonds 12, 32 in the pattern gaps 10, 30 in the patterned diamonds 2, 22 provided in the first step (Figures 1(B), 3(B)).

The method for growing diamonds 12 and 32 from the patterned diamond provided in the first step may be selected from known methods such as microwave plasma CVD, direct current plasma CVD, hot filament CVD, and arc discharge plasma jet CVD.

At this time, diamond grows laterally (ELO: Epitaxial Lateral Overgrowth) using the patterned diamond as a nucleus, so diamonds 12 and 32 with few defects are formed in the gaps between the patterns.

Also, it is not necessary to form diamonds so as to fill all of the pattern gaps.

When growing diamonds 12, 32 in the second step, if the growth rate is made faster from the top of the diamond pattern than from the bottom, it is possible to form voids at the bottom of the gaps in the pattern. By forming such voids, stress can be relieved, and this is particularly preferable because it can relieve thermal stress that occurs when the base is made of a different material. The voids formed can be, for example, approximately triangular voids with a cross section of 0.01 μm to 20 μm on a side.

Specific methods for adjusting the growth rate at the bottom and top of the patterned diamond include adjusting the source gas (e.g., methane) concentration, pressure, input power, etc., to control the ratio of growth rates for each crystal orientation.

Next, in the third step, the patterned diamonds 2 and 22 provided in the first step are removed, and patterned diamonds 13 and 33 made of the diamonds formed in the second step are formed (Figures 1(C) and 3(C)). This step can be performed by using a known method such as photolithography or electron beam lithography.

In addition, it is not necessary to remove all of the patterned diamonds 2, 22 formed in the first step, and it is also possible to remove some of the diamonds 12, 32 formed in the second step, if necessary.

At this time, it is preferable to remove the diamonds 12, 32 formed in the second step to a position 5 μm or more from the boundary with the patterned diamonds 2, 22 provided in the first step. This allows a higher quality diamond to be grown in the fourth step. Also, from the standpoint of manufacturing efficiency and manufacturing costs, it is preferable that the area to be removed is a position 30 μm or less from the boundary with the patterned diamonds 2, 22 provided in the first step.

In the third process, as in the first process, the shape of the pattern of the diamonds 13 and 33 can be selected as desired. For example, the pattern can be one in which multiple diamonds are arranged in a line shape, rectangular dot shape, circular dot shape, etc.

At this time, the position, size, thickness, crystal orientation, etc. of the patterned diamond 13, 33 can be selected arbitrarily, but the ratio D/W of the depth D ( _D12 in FIG. 1, _D22 in FIG. 3) and the width W ( _W14 in FIG. 1, _W24 in FIG. 3) of the patterned diamond 13, 33 is preferably 0.1 or more, more preferably 0.5 or more. Incidentally, _W13 in FIG. 1 and _W23 in FIG. 3 are the widths of the convex portions in the patterned diamond 13, 33. In this way, the patterned diamond 13, 34 is closed relatively quickly in the fourth step, so that even if abnormally grown grains are generated from the patterned diamond 13, 34, the effect on the formed diamond surface is small.

The material constituting the bottoms 15, 35 of the pattern gaps 14, 34 may be diamond or a different material. However, since materials such as MgO are etched by hydrogen (H ₂ )/methane (CH ₄ ) plasma of CVD when diamond is formed in the pattern gaps in the fourth step, it is preferable to use a material such as Ir.

In particular, when the material constituting the bottom of the pattern gap is a different material, the process of processing the diamond into a pattern may cause a different attachment to the wall of the diamond. Also, the different attachment such as _SiO2 used as a mask may be attached. It is preferable to remove the different attachment attached to the wall of the diamond before the fourth process. By removing the different attachment attached to the wall of the diamond in this way, the generation of abnormally grown particles can be suppressed in the fourth process. The removal of the different attachment can be performed, for example, by selective etching or the like.

For example, if Ir or _SiO2 adheres to the wall surface of the diamond, it can be removed by etching with _CF4 plasma.

Furthermore, if necessary, at least a portion of the bottoms 15, 35 of the pattern gaps 14, 34 in the patterned diamonds 13, 33 formed in the third step may be penetrated.

In addition, when the material constituting the base surface is a different material other than diamond, at least a part of the bottom 35 of the pattern gap 34 in the patterned diamond 33 formed in the third step may be located below the base surface by removing part of the base as well.

This is believed to alleviate internal stresses and thermal stresses that occur when the base is made of different materials.

In the fourth step, diamonds are grown from the patterned diamonds 13, 33 formed in the third step, forming diamonds 16, 36 in the pattern gaps 14, 34 in the patterned diamonds 13, 33 formed in the third step (Figures 1(D) and 3(D)).

In the fourth step, as in the second step, the method for growing diamond from the patterned diamond formed in the third step may be selected from known methods such as microwave plasma CVD, direct current plasma CVD, hot filament CVD, and arc discharge plasma jet CVD.

At this time, diamond grows laterally (ELO: Epitaxial Lateral Overgrowth) using the patterned diamond as a nucleus, so diamond with few defects is formed in the gaps between the patterns.

In the fourth step, too, it is not necessary to form diamond so as to completely fill all of the pattern gaps 14 and 34, and it is preferable to form voids at the bottoms of the pattern gaps 15 and 35. In both the second and fourth steps, forming such voids can reduce stress, and can further reduce thermal stress that occurs when the base is made of a different material.

In the present invention, by the first to fourth steps, it is possible to produce diamond substrates 17, 37 whose entire surface is made of laterally grown diamond and/or diamond grown from laterally grown diamond.

That is, the present invention provides a diamond substrate in which the material constituting at least one surface is diamond, and the entirety of at least one surface is made of at least one of laterally grown diamond and diamond grown from laterally grown diamond.

Furthermore, it is not necessary for the entire surface to be made of laterally grown diamonds and/or diamonds grown from laterally grown diamonds by the fourth step. Furthermore, by repeating the formation and growth of patterned diamonds multiple times following the third and fourth steps, a diamond substrate may be produced in which at least one of the entire surfaces is made of at least one of laterally grown diamonds and diamonds grown from laterally grown diamonds.

It is also possible to further reduce defects by forming the entire surface from at least one of laterally grown diamonds and diamonds grown from laterally grown diamonds, and then repeating the formation and growth of patterned diamonds multiple times following the third and fourth steps. This method also makes it possible to form even more voids, which can lead to even lower stress.

The diamond substrate produced by the present invention may be used with the base left on, or may be used as a free-standing substrate with the base removed.

When the base of the diamond substrate is removed to form a free-standing substrate, the free-standing substrate preferably has a thickness of 50 μm or more and 2000 μm or less. If the free-standing substrate has a thickness of 50 μm or more, it is preferable because it is easy to handle and there is no risk of damage during the manufacturing process or the device manufacturing process using the diamond substrate.

On the other hand, if the thickness of the free-standing substrate is 2000 μm or less, there is no risk of the time required to form the diamond being longer, and there is also no risk of the unevenness of the diamond substrate surface becoming larger, so the time required for polishing can be shortened. This makes it possible to reduce manufacturing costs. Furthermore, warping of the substrate can be suppressed, and the occurrence of cracks and breakage can be suppressed.

If the diamond substrate is left with its base layer remaining and the substrate structure includes the base layer, the diamond layer does not need to be formed thicker than necessary. Considering the time required to fabricate the substrate and the effects of internal stress, it is preferable that the thickness from the base surface to the substrate surface be 300 μm or less.

In addition, if voids are formed at the bottom of the pattern gaps in the second and/or fourth steps, a diamond substrate 100 having a void 52 therein and in which the material constituting at least one surface 101 is diamond, is obtained, as shown in FIG. 5.

In this case, the diamond substrate 100 of the present invention is composed of a substrate 50 and a diamond layer 51 formed on the surface of the substrate 50, and can have a void 52 adjacent to the boundary between the substrate 50 and the diamond layer 51.

Furthermore, when the base 50 is removed to form a free-standing substrate, the resulting diamond substrate has a void 52 on one surface.

The diamond substrate having voids inside the substrate and the freestanding diamond substrate having voids on one surface of the present invention have sufficiently reduced defects such as dislocation defects. Furthermore, because stress is reduced, the occurrence of warping and cracks in the substrate can be suppressed.

In addition, when the bottom of the pattern gap is penetrated in the first and/or third steps, a diamond substrate is obtained that is made of a base and a diamond layer formed on the surface of the base, and that has an opening on the back surface of the base.

The diamond substrate of the present invention, which has an opening on the surface of the base, has sufficiently reduced defects and reduces the internal stress and thermal stress that occur with crystal growth, making it possible to suppress the occurrence of warping and cracks in the substrate.

The surface of the diamond substrate produced by the present invention is preferably made of single crystal diamond.

On the surface of the diamond substrate produced by the present invention, a material selected from p-type diamond doped with impurities such as boron (B), n-type diamond doped with impurities such as phosphorus (P), and diamond that is not doped with impurities can be layered. By configuring it in this way, it becomes possible to operate it as a semiconductor device.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1
A diamond substrate was manufactured by the method shown in FIG.

First, as shown in FIG. 3(A), a pattern of diamonds 22 was provided on the surface of the base 21 (first step). Specifically, the pattern of diamonds 22 was provided on the surface of the base 21 through the steps shown in FIG. 4(a) to FIG. 4(f).

The substrate 21 was prepared and the diamond layer 26 was formed on the substrate 21 as follows (Figure 4(a)).

First, a single crystal silicon (Si) substrate 23 was prepared, which had a diameter of 10.0 mm, a thickness of 1.0 mm, and a surface that was (100) plane and was polished on both sides. A layer 24 made of single crystal MgO was formed on one side of the prepared single crystal silicon substrate 23 by electron beam deposition. At this time, the single crystal MgO layer 24 was epitaxially grown to a thickness of 1 μm under conditions of a substrate temperature of 900° C. in a vacuum. Furthermore, a layer 25 made of Ir was formed on the single crystal MgO layer 24. The Ir layer 25 was formed by a radio frequency (RF) magnetron sputtering method (13.56 MHz) using an Ir target with a diameter of 6 inches (150 mm), a thickness of 5.0 mm, and a purity of 99.9% or more. The substrate on which the single crystal MgO layer 24 was formed was heated to 800° C., and after confirming that the base pressure had become 6×10 ⁻⁷ Torr (approximately 8.0×10 ⁻⁵ Pa) or less, Ar gas was introduced at 10 sccm. The opening of the valve connected to the exhaust system was adjusted to set the pressure to 5×10 ⁻² Torr (approximately 6.7 Pa), and then an RF power of 1000 W was input to perform film formation for 15 minutes. The obtained Ir layer 25 had a thickness of 0.7 μm.

The single crystal silicon substrate 23 thus obtained, on which the single crystal MgO layer 24 and the Ir layer 25 were laminated, was used as the base 21 in Example 1.

Next, the substrate 21 was pretreated (bias treated) for diamond nucleation. The substrate was set on a flat electrode with a diameter of 15 mm with the Ir layer 25 facing up. After confirming that the base pressure was 1×10 ⁻⁶ Torr (about 1.3×10 ⁻⁴ Pa) or less, 500 sccm of hydrogen-diluted methane (CH ₄ /(CH ₄ +H ₂ )=5.0 vol.%) was introduced. After adjusting the opening of the valve leading to the exhaust system to set the pressure to 100 Torr (about 1.3×10 ⁴ Pa), a negative voltage was applied to the substrate side electrode and exposed to plasma for 90 seconds, thereby bias treating the substrate surface.

Subsequently, a diamond layer 26 was heteroepitaxially grown on the surface of the substrate by a direct current plasma CVD method. The bias-treated substrate 21 was set in the chamber of a direct current plasma CVD apparatus, and the substrate was evacuated to a base pressure of 10 ^-3 Torr (about 1.3 x 10 ^-1 Pa) or less by a rotary pump, and then hydrogen-diluted methane (CH ₄ /(CH ₄ +H ₂ )=5.0 vol.%), which was a raw material gas, was introduced at 1000 sccm. The pressure in the chamber was adjusted to 110 Torr (about 1.5 x 10 ⁴ Pa) by adjusting the opening degree of the valve connected to the exhaust system, and then a film was formed for 2 hours by passing a direct current of 2.0 A. The substrate temperature during film formation was measured with a pyrometer and found to be 950°C.

The resulting diamond layer 26 was a complete continuous film without any peeling over the entire surface of the 10 mm diameter substrate, with a film thickness of 10 μm. When this diamond layer was subjected to X-ray diffraction measurement (incident X-ray wavelength 1.54 Å), the rocking curve half-width of the diffraction intensity peak at 2θ = 119.5° attributable to diamond (004) was 720 arcsec (approximately 0.2°).

Furthermore, the etch pit density was also evaluated. Using a 2.45 GHz microwave plasma CVD device, the surface of diamond layer 26 was plasma-treated under conditions of 100 vol. % _H2 gas, 0.8 Pa, 2200 W, and 1 hour, and the etch pit density was measured by SEM observation and found to be 8 x ¹⁰⁸ (cm ^-2 ).

Next, the diamond layer 26 was patterned. First, 1000 nm of SiO ₂ film 27 was formed on the diamond layer by RF plasma CVD using tetraethyl orthosilicate (TEOS) as a raw material (FIG. 4(b)). A resist pattern 28 was formed on this SiO ₂ film 27 (FIG. 4(c)). Next, a titanium (Ti) film and a gold (Au) film were formed in order on the SiO ₂ film 27 on which the resist pattern 28 was formed, and then lifted off to form a SiO ₂ film 27 and a titanium (Ti)/gold (Au) pattern 29 in order on the diamond layer 26 (FIG. 4(d)). Next, SiO ₂ etching was performed using CF ₄ gas to form a hard mask for diamond etching (FIG. 4(e)).

Next, the diamond layer was etched using an inductively coupled plasma etching apparatus under the conditions of 100 vol. % _O2 gas, 2.0 Pa, 500 W, and 900 seconds (FIG. 4(f)). In this way, a pattern of diamond 22 was provided on the base surface (FIG. 3(A)).

In this case, the patterned diamond 22 in Fig. 3(A) has a pattern in which rectangular dot-shaped diamonds of 50 µm square (i.e., _W21 is 50 µm) are aligned, and the width _W22 of the pattern gap is 70 µm. In other words, the diamond layer is provided with a plurality of grooves parallel to each other, and further, a plurality of grooves perpendicular to the grooves and parallel to each other are provided. The grooves are oriented in two directions perpendicular to each other, one of which is the same as the [011] direction of the diamond layer.

Since the depth _D21 of the pattern gap was 10 μm, the ratio of the depth _D21 to the width _W22 of the pattern gap ( _D21 / _W22 ) was 0.14. In addition, the bottom of the pattern gap was in a state where the underlying Ir was exposed.

Next, the patterned diamond was cleaned by plasma treatment (FIG. 4(g)). Using an inductively coupled plasma etching device, the treatment was performed under the conditions of _CF4 gas 100 vol.%, 2.0 Pa, 500 W, and 650 seconds. This operation allowed the removal of foreign matter, which was thought to be derived from Ir, adhering to the wall surface of the patterned diamond.

After cleaning, the _SiO2 hard mask was removed with buffered hydrofluoric acid, and then hot mixed acid cleaning was performed (FIG. 4(h)).

Next, in the second step, diamonds 32 were grown from the patterned diamonds 22 provided on the base surface into the pattern gaps 30 in the patterned diamonds provided in the first step by microwave plasma CVD (Figure 3(B)).

The substrate provided with the patterned diamond 22 was set in the chamber of a microwave plasma CVD device, and the chamber was evacuated to ^7x10-8 Torr (about ^9.3x10-6 Pa) using a rotary pump and a turbo molecular pump, after which 500 sccm of hydrogen diluted methane ( _CH4 /( _CH4 + _H2 )=5.0 vol.%), which was the source gas, was introduced. The opening of the valve connected to the exhaust system was adjusted to set the pressure in the chamber to 110 Torr (about ^1.5x104 Pa), and then 3000 W of microwave power was applied to perform film formation for 18 hours. The substrate temperature during film formation was measured with a pyrometer and found to be 1035°C.

The resulting diamond layer had filled the gaps between the patterns. At this time, the thickness from the surface of the base to the surface of the substrate was 103 μm. When this diamond layer was subjected to X-ray diffraction measurement (incident X-ray wavelength 1.54 Å), the rocking curve half-width of the diffraction intensity peak at 2θ = 119.5° attributable to diamond (004) was 340 arcsec (approximately 0.1°).

Furthermore, the etch pit density was also evaluated. Using a 2.45 GHz microwave plasma CVD device, the surface of the diamond layer was plasma-treated under conditions of 100 vol. % _H2 gas, 0.8 Pa, 2200 W, and 1 h, and the etch pit density was measured by SEM observation. The etch pit density was ^1x108 (cm ^-2 ) in the part grown on the patterned diamond, but ^3x106 (cm ^-2 ) in the gaps between the patterns, a decrease of about two orders of magnitude.

When the cross section of the substrate was observed using an SEM, a roughly triangular void with a cross section measuring 5 μm on a side was observed near the center of the area that had previously been a pattern gap, adjacent to the boundary between the Ir layer and the diamond layer.

In order to evaluate the stress of the diamond substrate, the change in warpage of the rear surface of the substrate before and after the formation of the diamond layer was measured using an optical interference type or contact type measuring device.Then, this measured value was divided by the increase in film thickness before and after the formation of the diamond layer, and the calculated value was used as the evaluation value of the stress of the diamond substrate.The evaluation value here was 21× ^10-2 .

Next, the surface of the obtained diamond substrate was polished. After polishing, the thickness from the base surface to the substrate surface was 71 μm, and the surface roughness RMS was 0.3 nm (AFM measurement, 10 μm square area).

Subsequently, as the third step, the second diamond layer was patterned in the same manner as the first patterning, and a patterned diamond 33 was formed from the diamonds 32 formed in the second step (FIG. 3(C)). The pattern shape here was a pattern in which 50 μm square rectangular dot-shaped diamonds (i.e., _W23 was 50 μm) were aligned, as in the first pattern shape, and the width _W24 of the pattern gap was 70 μm. However, the position of the pattern was shifted 60 μm in parallel in the [011] direction of the diamond layer relative to the first pattern.

In other words, here, the diamond 32 formed in the second process is removed up to a position 10 μm from the boundary with the patterned diamond 22 provided in the first process.

Next, in the fourth step, diamonds 36 were grown from the patterned diamond 33 into the patterned gaps 34 in the patterned diamond formed in the third step in a similar manner to the method for growing diamonds from the patterned diamonds provided on the base surface (Figure 3(D)). The pattern gaps of the resulting diamond layer were filled. At this time, the thickness from the base surface to the substrate surface was 164 μm.

When this diamond layer was subjected to X-ray diffraction measurement (incident X-ray wavelength 1.54 Å), the rocking curve half-width of the diffraction intensity peak at 2θ = 119.5°, which is attributed to diamond (004), was 340 arcsec (approximately 0.1°).

Furthermore, the etch pit density was also evaluated. Using a 2.45 GHz microwave plasma CVD device, the surface of the diamond layer was plasma-treated under the conditions of _H2 gas 100 vol. %, 0.8 Pa, 2200 W, and 1 h, and the etch pit density was measured by SEM observation. The etch pit density was 3 x ¹⁰⁶ (cm ^-2 ) both in the part grown on the patterned diamond and in the gaps between the patterns, and the etch pit density was a low value over the entire surface of the diamond substrate 37.

When the cross section of the manufactured diamond substrate 37 was observed with an SEM, a roughly triangular void with a side length of 5 μm was observed near the center of the area that had been the gap in the second pattern, and was in contact with the boundary between the Ir layer and the diamond layer.

To evaluate the stress in the diamond substrate, the ratio (change in warpage of the back surface of the substrate)/(increase in film thickness) was measured before and after the formation of the diamond layer, and the value was 15×10 ⁻² .

Example 2
A diamond substrate was manufactured by the method shown in FIG.

First, as shown in FIG. 1(A), a pattern of diamonds 2 was provided on the surface of a substrate 1 (first step). Specifically, the pattern of diamonds 2 was provided through the steps shown in FIG. 2(a) to FIG. 2(f).

First, a heteroepitaxial diamond substrate (free-standing substrate) 6 with a diameter of 5.0 mm, a thickness of 0.5 mm, and a (100) surface that was polished on both sides was prepared and washed with hot mixed acid to form the base 1 (Figure 2(a)).

Next, the diamond substrate was patterned in the same manner as in Example 1. First, a 1000 nm SiO2 film ₇ was formed on the diamond layer by RF plasma CVD using tetraethyl orthosilicate (TEOS) as a raw material (FIG. 2(b)). A resist pattern 8 was formed on this _SiO2 film 7 (FIG. 2(c)). Next, a titanium (Ti) film and a gold (Au) film were formed in order on the _SiO2 film 7 on which the resist pattern 8 was formed, and then lifted off to form a _SiO2 film 7 and a titanium (Ti)/gold (Au) pattern 9 in order on the diamond substrate 6 (FIG. 2(d)). Next, _SiO2 etching was performed using _CF4 gas to form a hard mask for diamond etching (FIG. 2(e)).

Next, the diamond layer was etched using an inductively coupled plasma etching apparatus under the conditions of 100 vol. % _O2 gas, 2.0 Pa, 500 W, and 900 seconds (FIG. 2(f)). In this way, a pattern of diamond 2 was provided on the base surface (FIG. 1(A)).

In this case, the pattern shape in Fig. 1 (A) is a pattern in which diamonds are arranged in the shape of rectangular dots of 50 µm squares (i.e., _W11 is 50 µm), and the width _W12 of the pattern gap is 70 µm. In other words, the diamond layer is provided with a plurality of grooves parallel to each other, and further, a plurality of grooves perpendicular to the grooves and parallel to each other are provided. The grooves are oriented in two directions perpendicular to each other, one of which is the same as the [011] direction of the diamond layer.

The depth D ₁₁ of the pattern gap in the patterned diamond 2 was set to 10 μm, and the ratio (D ₁₁ /W ₁₂ ) of the depth D ₁₁ to the width W ₁₂ of the pattern gap was 0.14.

Next, the patterned diamond thus obtained was cleaned by plasma treatment (FIG. 2(g)). Using an inductively coupled plasma etching device, the treatment was carried out under the conditions of _CF4 gas 100 vol. %, 2.0 Pa, 500 W, and 650 seconds.

After cleaning, the _SiO2 hard mask was removed with buffered hydrofluoric acid, and then hot mixed acid cleaning was performed (FIG. 2(h)).

Next, in the second step, diamonds 12 were grown from the patterned diamonds 2 provided on the base surface into the pattern gaps 10 in the patterned diamonds provided in the first step by microwave plasma CVD (Figure 1(B)).

The substrate with the patterned diamond 2 was set in the chamber of a microwave plasma CVD device, and the chamber was evacuated to ^7x10-8 Torr (about ^9.3x10-6 Pa) using a rotary pump and a turbo molecular pump, after which 500 sccm of hydrogen diluted methane ( _CH4 /( _CH4 + _H2 )=5.0 vol.%), which was the source gas, was introduced. The opening of the valve connected to the exhaust system was adjusted to set the pressure in the chamber to 110 Torr (about ^1.5x104 Pa), and then 3000 W of microwave power was applied to perform film formation for 15 hours. The substrate temperature during film formation was measured with a pyrometer and found to be 1050°C.

The resulting diamond layer had filled the gaps between the patterns. At this time, the thickness from the surface of the base to the surface of the substrate was 78 μm. When this diamond layer was subjected to X-ray diffraction measurement (incident X-ray wavelength 1.54 Å), the rocking curve half-width of the diffraction intensity peak at 2θ = 119.5°, which is attributed to diamond (004), was 340 arcsec (approximately 0.1°).

Furthermore, the etch pit density was also evaluated. Using a 2.45 GHz microwave plasma CVD device, the surface of the diamond layer was plasma-treated under conditions of 100 vol. % _H2 gas, 0.8 Pa, 2200 W, and 1 h, and the etch pit density was measured by SEM observation. The etch pit density was 2 x ¹⁰⁸ (cm ^-2 ) in the part grown on the patterned diamond, but 4 x ¹⁰⁶ (cm ^-2 ) in the gaps between the patterns, a decrease of about two orders of magnitude.

When the cross section of the board was observed using an SEM, it was found that the gaps between the patterns had been completely filled.

To evaluate the stress in the diamond substrate, the ratio (change in warpage of the back surface of the substrate)/(increase in film thickness) was measured before and after the formation of the diamond layer, and the value was 15×10 ⁻² .

Next, the surface of the obtained diamond substrate was polished. After polishing, the thickness from the base surface to the substrate surface was 56 μm, and the surface roughness RMS was 0.3 nm (AFM measurement, 10 μm square area).

Subsequently, as the third step, the second diamond layer was patterned in the same manner as the first patterning, and a patterned diamond 13 was formed from the diamond formed in the second step (FIG. 1(C)). The pattern shape here is a pattern in which diamonds in the shape of rectangular dots of 50 μm squares (i.e., W ₁₃ is 50 μm) are aligned, as in the first pattern shape, and the width W ₁₄ of the pattern gap is 70 μm. However, the position of the pattern is a pattern that is shifted 60 μm in parallel in the [011] direction of the diamond layer with respect to the first pattern. That is, here, the diamond formed in the second step is removed to a position 10 μm from the boundary with the patterned diamond provided in the first step.

Next, in the fourth step, diamond 16 was grown from patterned diamond 13 in a similar manner to the method used to grow diamond from the patterned diamond on the base surface (Figure 1(D)). The resulting diamond layer had the gaps between the patterns filled. At this time, the thickness from the base surface to the substrate surface was 134 μm.

When this diamond layer was subjected to X-ray diffraction measurement (incident X-ray wavelength 1.54 Å), the rocking curve half-width of the diffraction intensity peak at 2θ = 119.5°, which is attributed to diamond (004), was 340 arcsec (approximately 0.1°).

Furthermore, the etch pit density was also evaluated. Using a 2.45 GHz microwave plasma CVD device, the surface of the diamond layer was plasma-treated under the conditions of 100 vol. % _H2 gas, 0.8 Pa, 2200 W, and 1 h, and the etch pit density was measured by SEM observation. The etch pit density was 3 x ¹⁰⁶ (cm ^-2 ) in the part grown on the patterned diamond, and 4 x ¹⁰⁶ (cm ^-2 ) in the gaps between the patterns, showing low values for the etch pit density over the entire diamond substrate surface.

When the cross section of the resulting diamond substrate 17 was observed using an SEM, it was found that the gaps between the patterns had been completely filled.

To evaluate the stress in the diamond substrate, the ratio (change in warpage of the back surface of the substrate)/(increase in film thickness) was measured before and after the formation of the diamond layer, and the value was 10×10 ⁻² .

(Comparative Example 1)
First, a single crystal silicon (Si) substrate was prepared, which had a diameter of 10.0 mm, a thickness of 1.0 mm, and had its surface polished on both sides to be the (100) plane.

A layer made of single crystal MgO was formed on one side of the prepared single crystal silicon substrate by electron beam deposition. At this time, the single crystal MgO layer was epitaxially grown to 1 μm in a vacuum at a substrate temperature of 900° C. Furthermore, a layer made of Ir was formed on the single crystal MgO layer. The Ir layer was formed by radio frequency (RF) magnetron sputtering (13.56 MHz) using an Ir target with a diameter of 6 inches (150 mm), a thickness of 5.0 mm, and a purity of 99.9% or more. The substrate on which the single crystal MgO layer was formed was heated to 800° C., and after confirming that the base pressure was 6×10 ⁻⁷ Torr (approximately 8.0×10 ⁻⁵ Pa) or less, 10 sccm of Ar gas was introduced. After adjusting the opening of the valve connected to the exhaust system to set the pressure to 5×10 ⁻² Torr (about 6.7 Pa), an RF power of 1000 W was input and film formation was carried out for 15 minutes. The obtained Ir layer had a thickness of 0.7 μm.

The single crystal silicon substrate thus obtained was laminated with a single crystal MgO layer and an Ir layer to form the base in Comparative Example 1.

Next, the substrate was pretreated (bias treated) for diamond nucleation. The substrate was set on a flat electrode with a diameter of 15 mm with the Ir layer facing up. After confirming that the base pressure was 1×10 ⁻⁶ Torr (about 1.3×10 ⁻⁴ Pa) or less, 500 sccm of hydrogen-diluted methane (CH ₄ /(CH ₄ +H ₂ )=5.0 vol.%) was introduced. After adjusting the opening of the valve leading to the exhaust system to set the pressure to 100 Torr (about 1.3×10 ⁴ Pa), a negative voltage was applied to the substrate side electrode and exposed to plasma for 90 seconds to bias treat the substrate surface.

Subsequently, a diamond layer was heteroepitaxially grown on the surface of the substrate by DC plasma CVD. The bias-treated substrate was set in the chamber of a DC plasma CVD apparatus, and the substrate was evacuated to a base pressure of 10 ^-3 Torr (about 1.3 x 10 ^-1 Pa) or less by a rotary pump, and then hydrogen-diluted methane (CH ₄ /(CH ₄ +H ₂ )=5.0 vol.%), which was the raw material gas, was introduced at 1000 sccm. The pressure in the chamber was adjusted to 110 Torr (about 1.5 x 10 ⁴ Pa) by adjusting the opening degree of the valve connected to the exhaust system, and then a film was formed for 2 hours by passing a DC current of 2.0 A. The substrate temperature during film formation was measured with a pyrometer and found to be 950°C.

The diamond layer obtained was a complete continuous film without any peeling over the entire surface of the 10 mm diameter substrate, with a film thickness of 10 μm. When this diamond layer was subjected to X-ray diffraction measurement (incident X-ray wavelength 1.54 Å), the rocking curve half-width of the diffraction intensity peak at 2θ = 119.5° attributable to diamond (004) was 720 arcsec (approximately 0.2°).

Furthermore, the etch pit density was also evaluated. The surface of the diamond layer was plasma-treated using a 2.45 GHz microwave plasma CVD device under conditions of 100 vol. % _H2 gas, 0.8 Pa, 2200 W, and 1 hour, and the etch pit density was measured by SEM observation and found to be 8 x ¹⁰⁸ (cm ^-2 ).

Next, the substrate on which diamond nucleation had been performed was set in the chamber of a microwave plasma CVD device, and after exhausting to ^7x10-8 Torr (about ^9.3x10-6 Pa) with a rotary pump and a turbo molecular pump, 500 sccm of hydrogen diluted methane ( _CH4 /( _CH4 + _H2 )=5.0 vol.%) as the raw material gas was introduced. After adjusting the opening of the valve connected to the exhaust system to set the pressure inside the chamber to 110 Torr (about ^1.5x104 Pa), 3000 W of microwave power was applied to perform film formation for 18 hours. The substrate temperature during film formation was measured with a pyrometer and found to be 1035°C.

The diamond layer obtained was a complete continuous film without any peeling over the entire surface of the 10 mm diameter substrate, with a film thickness of 90 μm. When this diamond layer was subjected to X-ray diffraction measurement (incident X-ray wavelength 1.54 Å), the rocking curve half-width of the diffraction intensity peak at 2θ = 119.5° attributable to diamond (004) was 720 arcsec (approximately 0.2°).

Furthermore, the etch pit density was also evaluated. The surface of the diamond layer was plasma-treated using a 2.45 GHz microwave plasma CVD device under conditions of 100 vol. % _H2 gas, 0.8 Pa, 2200 W, and 1 hour, and the etch pit density was measured by SEM observation, and the value was 4 x ¹⁰⁸ (cm ^-2 ).

To evaluate the stress in the diamond substrate, the (change in warpage of the back surface of the substrate)/(increase in film thickness) was measured before and after the formation of the diamond layer, and the value was 67×10 ⁻² .

The above results show that by manufacturing a diamond substrate using the diamond substrate manufacturing method of the present invention, a high-quality diamond substrate with sufficiently few defects and low stress can be obtained. It is also clear that the diamond substrate of the present invention has sufficiently few defects and reduced stress.

The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

1,21...base, 2,22...patterned diamond formed in the first step, 3...diamond, 23...silicon (Si) substrate, 24...intermediate layer (single crystal MgO layer), 25...surface layer (Ir layer), 6...heteroepitaxial diamond substrate, 26...diamond layer, 7,27... _SiO2 film, 8,28...resist pattern, 9,29...titanium (Ti)/gold (Au) pattern, 10,30...pattern gap in the patterned diamond formed in the first step, 11,31...bottom of the pattern gap in the patterned diamond formed in the first step, 12,32...diamond formed in the second step, 13,33...patterned diamond formed in the third step, 14,34...pattern gap in the patterned diamond formed in the third step, 15,35...bottom of the pattern gap in the patterned diamond formed in the third step, 16, 36: diamond formed in the fourth step; 17, 37, 100: diamond substrate; 50: base; 51: diamond layer; 52: void; 101: surface.

Claims (1)

A diamond substrate comprising a base and a diamond layer formed on a surface of the base,
the surface of the substrate is a different material other than diamond;
A diamond substrate, characterized in that the entire surface of the diamond layer is composed of at least one of laterally grown diamond and diamond grown from the laterally grown diamond.

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