Diamond crystal substrate and diamond crystal substrate manufacturing method

Abstract

Provided are: a diamond crystal substrate that tends not to crack during manufacture and that is obtained at a good yield even with a large diameter; and a manufacturing method for same. The diamond crystal substrate comprises a diamond crystal 31 in which the main plane is the {111} plane or a plane having an off-angle with respect to the {111} plane. In the diamond crystal 31, there is a direction at which the radius of curvature is at least 1500 cm.

Description

Diamond Crystal Substrate and Method for Manufacturing Diamond Crystal Substrate

[0001] The present invention relates to a diamond crystal substrate and a method for manufacturing a diamond crystal substrate.

[0002] Diamond with a {111} plane is expected for applications such as quantum devices, and a diamond substrate with good crystallinity is required. For example, in Patent Document 1, as an example, by using a base substrate in which an Ir intermediate layer is formed on a sapphire (α - Al2O3) substrate having an off-angle of 8°, 16°, and 24° with respect to the {0001} plane, it is described that a high-quality {111} plane diamond self-supporting structure substrate without twins can be obtained.

[0003] International Publication No. 2024 / 048357

[0004] However, when growing diamond on a base substrate made of a material different from diamond as in Patent Document 1, since the materials are different, there are differences in the crystal lattice and linear expansion coefficient between the base and diamond, and diamond is likely to crack, resulting in a very low yield. For example, in Patent Document 1, although it is described that both the examples with an off-angle and the comparative examples without an off-angle can obtain a continuous film without peeling on the entire surface with a diameter of 150 mm, when the applicant verified this by experiments, simply setting the off-angle appropriately could not suppress the cracking of diamond. In fact, in Patent Document 1, no photograph of diamond or the like is specifically shown, and since the film thickness and crystallinity of both the examples and comparative examples in Patent Document 1 can only be evaluated with a 2 mm square sample, it is difficult to obtain a large-diameter diamond crystal without cracks by the method of Patent Document 1, and even if it is obtained accidentally, the yield is poor.

[0005] The present invention has been made to solve the above problems, and provides a diamond crystal substrate that is difficult to crack during manufacturing and can be obtained with a high yield even for a large diameter, and a method for manufacturing the same.

[0006] To achieve the above objective, the diamond crystal substrate disclosed below comprises a diamond crystal whose main surface is a {111} plane or a plane having an off-angle with respect to the {111} plane, wherein the diamond crystal has a direction in which the radius of curvature is 1500 cm or more.

[0007] According to the above-described diamond crystal substrate, since it has a direction in which the radius of curvature is 1500 cm or more, the warping during diamond crystal growth is small, and it is less likely to crack during manufacturing. Therefore, this diamond crystal substrate can be obtained with a good yield even in large diameters.

[0008] Figure 1 is a schematic diagram showing a method for manufacturing a diamond crystal substrate according to an embodiment of the present invention. Figure 2 is an optical microscope image of a diamond crystal 30. Figure 3 is a table showing examples and comparative examples. Figure 4 is a graph showing the relationship between the radius of curvature [perpendicular] and the FWHM of the (111) plane. Figure 5 is a graph showing the relationship between the growth temperature and the FWHM of the (111) plane. Figure 6 is a graph showing the relationship between the FWHM of the (220) plane and the FWHM of the (111) plane.

[0009] One embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and design modifications can be made as appropriate within the scope of satisfying the configuration of the present invention. Furthermore, the configurations described in the embodiments and modified examples may be combined or modified as appropriate. Also, for the sake of clarity, the configurations in the drawings referenced below are simplified or schematic, or some configurations are omitted.

[0010] First, an overview of the method for manufacturing a diamond crystal substrate according to the embodiment of the present invention will be described. Figure 1 is a schematic diagram showing the method for manufacturing a diamond crystal substrate according to the embodiment of the present invention.

[0011] In the method for manufacturing a diamond crystal substrate according to an embodiment of the present invention, first, a sapphire substrate 10 is prepared as shown in Figure 1(a). The main surface 101 of this sapphire substrate 10 has an off-angle in the <11-20> direction (hereinafter referred to as the "a-axis direction") with respect to the (0001) plane of the sapphire (hereinafter referred to as the "c-plane").

[0012] Next, as shown in Figure 1(b), an intermediate layer 20 is grown on the main surface 101 of the sapphire substrate 10. This intermediate layer 20 is made of a metal selected from the group consisting of Group 8, Group 9, and Group 10 elements, and is preferably composed of iridium (Ir), platinum (Pt), ruthenium (Ru), palladium (Pd), or rhodium (Rh), with iridium or ruthenium being particularly preferred. The intermediate layer 20 may also be made of an alloy consisting of multiple of these metallic elements.

[0013] The surface 21 of the intermediate layer 20 is a {111} plane in the case of iridium and a {0001} plane in the case of ruthenium. However, depending on the off-angle θ1 of the sapphire substrate 10, the surface 201 of the intermediate layer 20 may also be tilted with respect to these planes.

[0014] The intermediate layer 20 can be formed, for example, by a magnetron sputtering method targeting the above-mentioned metal. In particular, the intermediate layer 20 can be formed by high-frequency (RF) magnetron sputtering or direct-current (DC) magnetron sputtering. The thickness of the intermediate layer 20 to be formed may be, for example, 1.0 μm or more and 2.0 μm or less.

[0015] Next, as shown in Figure 1(c), a diamond crystal 30 is grown on the surface of the intermediate layer 20. At this time, the diamond crystal 30 is grown using step flow growth. Step flow growth is a growth mode in which, for example, an off-angle is provided in the underlying layer, the surface of the crystal growth becomes staircase-like (step-like) at the atomic level, and the ends of these steps become the starting points of crystal growth, so that the crystal growth direction is aligned in one direction.

[0016] The step flow growth process of the diamond crystal 30 will be explained with reference to Figure 2. Figure 2 is an optical microscope image of the diamond crystal 30. As shown in Figure 2, when the diamond crystal 30 is grown using step flow growth, triangular steps S are formed on the surface, and crystal growth occurs in the direction of the vertex of this triangle (upward in the figure).

[0017] The diamond crystal 30 can be grown using, for example, the CVD (Chemical Vapor Deposition) method in a step-flow manner. In particular, the diamond crystal 30 can be grown using, for example, microwave plasma CVD, DC plasma CVD, or hot filament CVD. For example, when growing the diamond crystal 30 using DC plasma CVD, if the CVD furnace pressure is 100 Torr, the hydrogen gas flow rate is 475 sccm, and the methane gas flow rate is 25 sccm, the diamond crystal 30 can be grown using a step-flow manner.

[0018] The surface 301 of the diamond crystal 30 is a {111} plane. However, depending on the off-angle θ1 of the sapphire substrate 10, the surface 301 of the diamond crystal 30 is also tilted by θ2 with respect to the {111} plane.

[0019] Finally, as shown in Figure 1(d), the sapphire substrate 10 and the intermediate layer 20 are lifted off from the diamond crystal 30, and the diamond crystal 30 is polished as appropriate to produce a substrate consisting only of the diamond crystal 31. At this time, the surface 311 of the diamond crystal 31 may be a surface with the same orientation as the surface in Figure 1(c), or it may be a surface whose orientation has been adjusted by polishing, etc. (for example, a just {111} surface with no off-angle).

[0020] Furthermore, the diamond crystal substrate does not necessarily have to be a substrate consisting solely of diamond crystals 31 as shown in Figure 1(d); a substrate with an intermediate layer 20 or sapphire substrate 10 remaining may also be used as a diamond crystal substrate. Alternatively, after creating a state consisting only of diamond crystals 31 as shown in Figure 1(d), diamond may be further grown on the surface of these diamond crystals 31 to create a diamond crystal substrate, or a substrate cut from the grown diamond may be used as a diamond growth substrate.

[0021] Next, the examples and comparative examples will be described with reference to the drawings. Figure 3 is a table showing the examples and comparative examples. Figures 4 and 5 are graphs of the values ​​listed in the table in Figure 3. Figure 4 is a graph showing the relationship between the radius of curvature [perpendicular] and the FWHM of the (111) plane, and Figure 5 is a graph showing the relationship between the growth temperature and the FWHM of the (111) plane.

[0022] Figure 3 shows Example 1 and Comparative Examples 1 and 2, along with their respective optical microscope images, growth temperatures, full width at half maximum (FWHM) of the X-ray diffraction peaks, and radius of curvature. Note that Example 1 and Comparative Examples 1 and 2 shown in Figure 3 were all fabricated using a sapphire substrate 10 with an off-angle θ1 of 10° and an iridium intermediate layer 20, with different growth temperatures for the diamond crystals 30. The growth temperature for Example 1 was 850°C, for Comparative Example 1 it was 950°C, and for Comparative Example 2 it was 1150°C.

[0023] In Figure 3, the growth temperature is the substrate temperature during the growth of the diamond crystal 30. FWHM is the full width at half maximum of the X-ray diffraction peaks from the (111) plane and the (220) plane of the diamond crystal 30, measured by X-ray rocking curve measurement, and the unit is "seconds" (also called "arcsec"). For the (111) plane, the diffraction peak was measured by incident X-rays from the direction normal to the surface 301 of the diamond crystal 30, and for the (220) plane, the diffraction peak was measured by incident X-rays from a direction inclined with respect to the normal to the surface 301 of the diamond crystal 30. As shown in Figure 3, Example 1, Comparative Examples 1 and 2 are all square in shape, and the full width at half maximum of the X-ray diffraction peaks of the (111) plane and the (220) plane shown in the figure was measured by incident X-rays at their respective central positions.

[0024] The radius of curvature [perpendicular] is the radius of curvature perpendicular to the growth direction of step flow growth, and the radius of curvature [parallel] is the radius of curvature parallel to the growth direction of step flow growth. The growth direction of step flow growth is the direction along the a-axis of the sapphire substrate 10 when viewed from above from the surface 301 side of the diamond crystal 30. The radius of curvature is the warp of the crystal, and in this case, when measuring the rocking curve of the (111) plane, the X-ray diffraction peak angle of the (111) plane within the surface 301 of the diamond crystal 30 is measured sequentially along specific directions (directions perpendicular to and parallel to the growth direction of step flow growth) near the center position of Example 1, Comparative Examples 1 and 2, and the radius of curvature can be calculated from the amount of shift of the X-ray diffraction peak angle.

[0025] As shown in the optical microscope image in Figure 3, in Example 1, a nearly crackless diamond crystal 30 with sides of approximately 20 mm was obtained, but in Comparative Examples 1 and 2, the diamond crystal 30 was cracked. At this time, the radius of curvature [parallel] of Example 1 and Comparative Examples 1 and 2 were all around several tens of cm, with no significant difference. On the other hand, regarding the radius of curvature [perpendicular], Example 1 had 2204 cm, Comparative Example 1 had 1364 cm, about half of Example 1's, and Comparative Example 2 had an even smaller radius of curvature of 385 cm, about one-sixth of Example 1's.

[0026] Furthermore, a smaller FWHM value indicates better crystallinity (fewer crystal defects such as dislocations). In Example 1, the values ​​were 266 seconds on the (111) plane and 171 seconds on the (220) plane, while in Comparative Example 1, the values ​​were 1278 seconds on the (111) plane and 527 seconds on the (220) plane. Comparative Example 2 was even higher, with 1753 seconds on the (111) plane and 1933 seconds on the (220) plane.

[0027] Thus, the larger the radius of curvature [perpendicular], the less likely the diamond crystal 30 is to crack during manufacturing. In particular, as shown in Figure 3, even when the size of the diamond crystal 30 is increased to a diameter of about 20 mm on each side, it is possible to obtain a diamond crystal 30 that is almost crack-free. Specifically, by making the radius of curvature [perpendicular] 1500 cm or more, more preferably 2000 cm or more, it is possible to obtain a large-diameter diamond crystal 30 that is crack-free with good reproducibility.

[0028] Furthermore, as shown in Figure 4, increasing the radius of curvature [perpendicular] can improve the FWHM, i.e., crystallinity, of the diamond crystal 30. For example, if the radius of curvature [perpendicular] is set to 1500 cm or more, the FWHM of the (111) plane becomes approximately 1000 seconds or less, and a diamond crystal 30 with sufficiently good crystallinity can be obtained with good reproducibility. Furthermore, if the radius of curvature [perpendicular] is set to 2000 cm or more, the FWHM of the (111) plane becomes approximately 500 seconds or less, and a diamond crystal 30 with extremely good crystallinity can be obtained with good reproducibility.

[0029] As described above, the diamond crystal substrate according to the embodiment of the present invention exhibits minimal warping during diamond crystal growth and is less prone to cracking during manufacturing. Therefore, this diamond crystal substrate can be produced with a high yield even in large diameters.

[0030] Furthermore, if the surface 301 of the diamond crystal 30 in Figure 1(c) is polished, for example, as shown in the diamond crystal 31 in Figure 1(d), the growth direction of step flow growth becomes difficult to discern from its appearance. However, in the diamond crystal 31, the radius of curvature can be large only in the direction perpendicular to the growth direction of step flow growth. Therefore, if there is a direction within the surface 311 of the diamond crystal 31 where the maximum value of the radius of curvature is 1500 cm or more, it is nothing other than a crystal manufactured by the manufacturing method according to the embodiment of the present invention described above, and thus achieves the effects described above.

[0031] Furthermore, as shown in Figure 5, increasing the growth temperature of the diamond crystal 30 reduces the radius of curvature [perpendicular] and increases the FWHM of the (111) plane. To make the radius of curvature [perpendicular] of the diamond crystal 30 1500 cm or more, it is preferable to set the growth temperature to 925°C or lower, and even more preferable to set it to 900°C or lower.

[0032] <Modifications, etc.> The embodiments described above are merely examples for carrying out the present invention. The present invention is not limited to the embodiments described above, and it is possible to carry out the present invention by appropriately modifying the embodiments described above without departing from the spirit of the invention.

[0033] For example, in the above-described embodiment 1, the off-angle θ1 of the sapphire substrate 10 was set to 10°, but a sapphire substrate 10 with an off-angle θ1 other than 10° may also be used. However, if the off-angle θ1 is made too small, it becomes prone to cracking and twinning. On the other hand, if the off-angle θ1 is made too large, the radius of curvature [perpendicular] tends to become small. Therefore, it is preferable to set the off-angle θ1 of the sapphire substrate 10 to 5° or more and 15° or less, as this prevents cracking and twinning while also increasing the radius of curvature [perpendicular].

[0034] Furthermore, in the embodiments described above, we focused on the radius of curvature [perpendicular] of the diamond crystal 30 and explained conditions such as reducing warping and making it less prone to cracking during manufacturing. On the other hand, since the FWHM of the (220) plane is a value that indicates the magnitude of the in-plane strain of the diamond crystal 30, it is also possible to focus on this and find conditions that reduce the warping of the diamond crystal 30 and make it less prone to cracking during manufacturing.

[0035] Figure 6 is a graph showing the relationship between the FWHM of the (220) plane and the FWHM of the (111) plane. As shown in Figure 6, when the FWHM of the (220) plane is 500 seconds or less, the FWHM of the (111) plane becomes approximately 1000 seconds or less, and as described above, a diamond crystal 30 with low warping, low cracking during manufacturing, and sufficient high-quality crystallinity can be obtained with good reproducibility. Furthermore, when the FWHM of the (220) plane is 250 seconds or less, the FWHM of the (111) plane becomes approximately 500 seconds or less, and a diamond crystal 30 with extremely high-quality crystallinity can be obtained with good reproducibility.

[0036] Furthermore, the diamond crystal 30 may be grown such that both the radius of curvature [perpendicular] of the diamond crystal 30 and the FWHM of the (220) plane satisfy the above conditions, or the diamond crystal 30 may be grown focusing only on the FWHM of the (220) plane, such that the FWHM of the (220) plane satisfies the above conditions.

[0037] Furthermore, the diamond crystal substrate and the method for manufacturing the diamond crystal substrate described above can be explained as follows.

[0038] The diamond crystal substrate comprises a diamond crystal whose main surface is a {111} plane or a plane having an off-angle with respect to the {111} plane, and the diamond crystal has a direction in which the radius of curvature is 1500 cm or more (first configuration). Therefore, this diamond crystal substrate exhibits less warping during diamond crystal growth and is less prone to cracking during manufacturing. Consequently, this diamond crystal substrate can be produced with good yield even in large diameters.

[0039] In the first configuration, the diamond crystal may have a direction in which the radius of curvature is 2000 cm or more (second configuration). Also, in the first or second configuration, the diamond crystal may have a full width at half maximum of 500 arcseconds or less of the X-ray diffraction peak of the (220) plane (third configuration). These configurations make it possible to more effectively reduce warping during crystal growth and make the crystal less prone to cracking during manufacturing.

[0040] Furthermore, the method for manufacturing a diamond crystal substrate comprises a first step of forming an intermediate layer made of metal on a sapphire substrate with a main surface having an off-angle in the a-axis direction with respect to the c-plane, and a second step of growing a diamond crystal in a step flow on the intermediate layer, wherein the radius of curvature in the direction perpendicular to the crystal growth direction in the step flow growth is 1500 cm or more (fourth configuration). With this configuration, warping during diamond crystal growth can be reduced and cracking during manufacturing can be prevented. Therefore, this method for manufacturing a diamond crystal substrate can be obtained with a good yield even in large diameters.

[0041] Furthermore, in the fourth configuration, the diamond crystal grown in the second step may have a radius of curvature of 2000 cm or more in a direction perpendicular to the crystal growth direction in the step-flow growth (fifth configuration). Also, in the fourth or fifth configuration, the diamond crystal grown in the second step may have a full width at half maximum of 500 arcseconds or less of the X-ray diffraction peak of the (220) plane (sixth configuration). These configurations make it possible to more effectively reduce warping during crystal growth and make the crystal less prone to cracking during manufacturing.

[0042] Furthermore, in any one of the fourth to sixth configurations, the growth temperature in the second step may be 925°C or lower (seventh configuration). This configuration makes it possible to increase the radius of curvature in the direction perpendicular to the crystal growth direction in step flow growth of a diamond crystal.

[0043] Also, in any one of the fourth to seventh configurations, the second step may have a growth temperature of 900°C or lower (eighth configuration). According to this configuration, the radius of curvature in a direction perpendicular to the crystal growth direction in step-flow growth can be made larger more effectively.

[0044] Also, in any one of the fourth to eighth configurations, the off-angle of the sapphire substrate may be 5° or more and 15° or less (ninth configuration). According to this configuration, it is possible to prevent the coexistence of cracks and twins and increase the radius of curvature in a direction perpendicular to the crystal growth direction in step-flow growth.

[0045] 10... Sapphire substrate, 101... Main surface, 20... Intermediate layer, 201... Surface, 30, 31... Diamond crystal, 301, 311... Surface, S... Step

Claims

1. A diamond crystal substrate comprising a diamond crystal whose main surface is a {111} plane or a plane having an off-angle with respect to a {111} plane, wherein the diamond crystal has a direction in which the radius of curvature is 1500 cm or more.

2. The diamond crystal substrate according to claim 1, wherein the diamond crystal has a direction in which the radius of curvature is 2000 cm or more.

3. The diamond crystal substrate according to claim 1 or 2, wherein the diamond crystal has a full width at half maximum of the X-ray diffraction peak of the (220) plane of 500 arcseconds or less.

4. A method for manufacturing a diamond crystal substrate, comprising: a first step of forming an intermediate layer made of metal on a sapphire substrate with a main surface having an off-angle in the a-axis direction with respect to the c-plane; and a second step of growing a diamond crystal in step flow growth on the intermediate layer, wherein the second step is such that the radius of curvature in the direction perpendicular to the crystal growth direction in step flow growth is 1500 cm or more.

5. The method for manufacturing a diamond crystal substrate according to claim 4, wherein the diamond crystal grown by the second step has a radius of curvature of 2000 cm or more in a direction perpendicular to the crystal growth direction in the step flow growth.

6. The method for manufacturing a diamond crystal substrate according to claim 4, wherein the diamond crystal grown by the second step has a full width at half maximum of 500 arcseconds or less for the X-ray diffraction peak of the (220) plane.

7. The method for manufacturing a diamond crystal substrate according to claim 4, wherein the second step is a growth temperature of 925°C or less.

8. The method for manufacturing a diamond crystal substrate according to claim 4, wherein the second step is a growth temperature of 900°C or less.

9. The method for manufacturing a diamond crystal substrate according to any one of claims 4 to 8, wherein the off-angle of the sapphire substrate is 5° or more and 15° or less.

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