Laminated substrate and laminated substrate with circuit

Abstract

To provide, at low cost, a laminated substrate having not only a desired function (for example, a heat sink function) of a support substrate, but also functionality in high thermal conductivity application, such as a heat spreader. This laminated substrate has a two-layer configuration comprising: a support substrate that comprises a material that is selected from a group consisting of ceramics and metals, and that is other than diamond; and a diamond film that is provided on the support substrate and that comprises oriented polycrystalline diamond.

Description

Laminated substrate and laminated substrate with circuit

[0001] The present disclosure relates to a laminated substrate and a laminated substrate with circuit.

[0002] Diamond is a material having an extremely high thermal conductivity (about 22 W / cm·K), and is expected to be applied to heat spreaders and the like for semiconductor devices. Applications such as heat spreaders require a diamond film or substrate of a certain size.

[0003] As a method for producing a diamond substrate, Non-Patent Document 1 (Makoto Kasu, Ryota Takaya, and Seong-Woo Kim, Diamond & Related Materials 126 (2022) 109086) discloses that after forming a 1 μm-thick Ir buffer layer on a sapphire substrate by sputtering, diamond nuclei are formed on the Ir buffer layer by a bias-enhanced nucleation (BEN) process using a direct current plasma CVD apparatus, and a diamond layer is grown on the BEN-treated Ir buffer layer by microwave plasma CVD, thereby producing a sapphire / Ir buffer layer / diamond layer laminate. This document also describes that a microneedle process is essential for obtaining a free-standing diamond layer without damage from the laminate.

[0004] Meanwhile, a bonded substrate in which a supporting substrate and a group 13 element nitride crystal substrate are bonded together has been proposed. For example, Patent Document 1 (Japanese Patent No. 7295351) discloses a bonded substrate including a supporting substrate such as silicon carbide and a group 13 element nitride crystal substrate, and discloses that a neutral atomic beam is irradiated to a bonding surface of the group 13 element nitride crystal substrate and a bonding surface of the supporting substrate to activate the surfaces, thereby directly bonding the supporting substrate and the group 13 element nitride crystal substrate.

[0005] Japanese Patent No. 7295351, Japanese Unexamined Patent Application Publication No. 2014-086400, WO2022 / 190465

[0006] Makoto Kasu, Ryota Takaya, and Seong-Woo Kim, "Growth of high-quality inch-diameter heteroepitaxial diamond layers on sapphire substrates in comparison to MgO substrates", Diamond & Related Materials 126 (2022) 109086

[0007] Self-supporting diamond single-crystal substrates are difficult to manufacture in large quantities and are very expensive. Similarly, self-supporting polycrystalline diamond substrates are also costly. Therefore, there is a need for inexpensive alternatives to diamond single-crystal and polycrystalline self-supporting substrates.

[0008] The present inventors have now discovered that by employing a two-layer structure consisting of a support substrate and an oriented polycrystalline diamond film, it is possible to provide a laminated substrate that not only has the desired function of the support substrate (e.g., heat sink function) but also functions as a high thermal conductivity application such as a heat spreader, at a low cost.

[0009] Therefore, the object of the present invention is to provide a laminated substrate at low cost that combines a desired function of the support substrate (e.g., heat sink function) with a function for high thermal conductivity applications such as a heat spreader.

[0010] The following embodiments are provided according to this disclosure: [Embodiment 1] A two-layer laminated substrate comprising: a support substrate made of a material other than diamond, selected from the group consisting of ceramics and metals; and a diamond film made of oriented polycrystalline diamond provided on the support substrate. [Embodiment 2] The laminated substrate according to Embodiment 1, wherein the oriented polycrystalline diamond is biaxially oriented. [Embodiment 3] The laminated substrate according to Embodiment 1 or 2, wherein carbon and dissimilar metallic elements other than the constituent elements of the support substrate are not present at the interface between the diamond film and the support substrate. [Embodiment 4] The support substrate is made of ceramics, and the ceramics are AlN, SiC, and Si ３ N ４The multilayer substrate according to any one of Aspects 1 to 3, which is at least one selected from the group consisting of. [Aspect 5] The multilayer substrate according to any one of Aspects 1 to 4, wherein the support substrate is made of metal, and the metal is Cu or a Cu-containing alloy. [Aspect 6] The multilayer substrate according to any one of Aspects 1 to 5, wherein the diamond film has a thickness of 0.5 to 100 µm. [Aspect 7] The multilayer substrate according to any one of Aspects 1 to 6, wherein the support substrate has a thickness of 300 µm to 2 mm. [Aspect 8] The thickness T of the diamond film １ of the support substrate with respect to thickness T ２ ratio T ２ / T １ The multilayer substrate according to any one of Aspects 1 to 7, wherein is 3 to 4000. [Aspect 9] The multilayer substrate according to any one of Aspects 1 to 8, wherein the diamond film has (100) plane orientation. [Aspect 10] The multilayer substrate according to any one of Aspects 1 to 9, wherein the oriented polycrystalline diamond includes a plurality of diamond single crystal particles each having a single crystal structure substantially in a direction normal to a surface of the diamond film. [Aspect 11] (111) plane peak intensity I measured by X-ray diffraction (XRD) with respect to the surface of the diamond film １ (400) plane peak intensity I with respect to ２ ratio I ２ / I １A laminated substrate according to any one of embodiments 1 to 10, wherein the ratio is 5.5 or higher. [Embodiment 12] A laminated substrate according to any one of embodiments 1 to 11, wherein the (100) crystal orientation of each diamond single crystal particle, measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD), is distributed tilted at various tilt angles from a reference (100) crystal orientation, and the average tilt angle is 0.5 to 10°. [Embodiment 13] A laminated substrate according to any one of embodiments 1 to 12, wherein 80% or more of the diamond single crystal particles measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD) have a tilt angle in the range of 0.5 to 10°. [Aspect 14] A laminated substrate according to any one of aspects 1 to 13, wherein the (110) crystal orientation of each diamond single crystal particle, measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD), is distributed rotated at various twist angles from a reference (110) crystal orientation, and the average twist angle is 0.5 to 15°. [Aspect 15] A laminated substrate according to any one of aspects 1 to 14, wherein 80% or more of the diamond single crystal particles measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD) have a twist angle in the range of 0.5 to 15°. [Aspect 16] The average cross-sectional diameter D at the outermost surface of the diamond single crystal particles exposed on the surface of the diamond film. Ｔ The thickness T of the diamond film relative to the thickness of the diamond film. １ The aspect ratio T is defined as the ratio of １ / D Ｔ A laminated substrate according to any one of embodiments 1 to 15, wherein the ratio is 1.0 or greater. [Embodiment 17] The diamond film is 19.625 cm ２ A laminated substrate according to any one of embodiments 1 to 16 having the above area. [Embodiment 18] A laminated substrate according to any one of embodiments 1 to 17, wherein the laminated substrate is a heat dissipation substrate for power semiconductors. [Embodiment 19] A laminated substrate with a circuit, comprising: a laminated substrate according to any one of embodiments 1 to 18; and a circuit for device mounting formed on the diamond film.

[0011] This is a conceptual cross-sectional view of the laminated substrate of this disclosure. This is a diagram of ICDD card #01-071-3649. The average cross-sectional diameter D on the surface of the diamond film. Ｔ This is a schematic cross-sectional view illustrating the calculation of [the value]. This is a schematic cross-sectional view showing an example of the manufacturing process of the laminated substrate of this disclosure. This is a schematic cross-sectional view showing the HEMT element fabricated in Example 1.

[0012] Figure 1 conceptually shows the laminated substrate 10 of this disclosure. The laminated substrate 10 is a two-layer substrate consisting of a support substrate 12 and a diamond film 14 provided on the support substrate 12. Therefore, there may be no dissimilar metallic elements other than carbon and the constituent elements of the support substrate at the interface between the diamond film 14 and the support substrate 12. The support substrate 12 is made of a material other than diamond, and this material is selected from the group consisting of ceramics and metals. The diamond film 14 is made of oriented polycrystalline diamond. By adopting this two-layer structure consisting of a support substrate 12 and an oriented polycrystalline diamond film 14, it is possible to provide a laminated substrate 10 at low cost that combines the desired function of the support substrate 12 (e.g., heat sink function) with a function for high thermal conductivity applications such as a heat spreader (provided by the diamond film 14).

[0013] As mentioned above, self-supporting diamond single-crystal substrates are difficult to manufacture in large sizes and are very expensive. Even self-supporting polycrystalline diamond substrates are expensive. To address these problems, by adopting a film form (which does not necessarily require a self-supporting substrate form) as the diamond product, constructing the film from oriented polycrystalline diamond, and combining it with a support substrate 12 (for example, by direct bonding), a laminated substrate 10 with an oriented polycrystalline diamond film 14 can be provided at low cost. Therefore, in addition to the desired function of the support substrate 12 (e.g., heat sink function), this laminated substrate 10 can also possess functions for high thermal conductivity applications such as a heat spreader (provided by the diamond film 14). Thus, typically, the diamond film 14 functions as a heat spreader, and the support substrate 12 functions as a heat sink, providing a mounting substrate for devices with a heat spreader. Therefore, it is preferable that the laminated substrate 10 is a heat dissipation substrate for power semiconductors. Furthermore, the laminated substrate 10 may be in the form of a laminated substrate with circuits. Such a circuit-equipped laminated substrate may comprise the laminated substrate 10 of this disclosure and a circuit for device mounting formed on the diamond film 14.

[0014] The support substrate 12 is a substrate made of a material other than diamond, and this material is selected from the group consisting of ceramics and metals. If the support substrate 12 is made of ceramics, this ceramic is AlN, SiC, and Si ３ N ４ It is preferable that the support substrate 12 is at least one selected from the group consisting of the following. If the support substrate 12 is made of metal, it is preferable that this metal is Cu or a Cu-containing alloy. A support substrate 12 made of such ceramics or metal can exhibit excellent thermal conductivity, and thus can impart good performance as a heat sink to the laminated substrate 10. From this viewpoint, the thickness of the support substrate 12 is preferably 300 μm to 2 mm, more preferably 500 μm to 1.5 mm, and even more preferably 1000 μm to 1.5 mm.

[0015] The diamond film 14 is composed of oriented polycrystalline diamond. That is, the oriented polycrystalline diamond film 14 can be manufactured inexpensively on a substrate such as a silicon substrate, and it has the advantage that the diamond film 14 can be easily enlarged by using a large Si substrate or the like as the substrate. In other words, by adopting the oriented polycrystalline diamond film 14, the laminated substrate 10 can be provided at a low cost and in a configuration suitable for large-scale enlargement. Therefore, the diamond film 14 can be used as an inexpensive alternative to diamond single-crystal substrates and diamond polycrystalline freestanding substrates. Moreover, because the diamond film 14 is an oriented polycrystalline diamond film, it also has the advantage of improved thermal conductivity and polishability compared to random polycrystalline diamond films. Therefore, the diamond film 14 is particularly advantageous for applications that diffuse heat in the direction of the film surface (especially heat spreaders for semiconductor devices).

[0016] The oriented polycrystalline diamond constituting the diamond film 14 contains a plurality of diamond single crystal particles 14a, and it is preferable that these diamond single crystal particles 14a have a single crystal structure in a direction substantially normal to the surface 14b of the diamond film 14. In this case, the diamond film 14 is composed of a plurality of diamond single crystal particles 14a (typically columnar particles) linked two-dimensionally in the horizontal plane, and therefore has a single crystal structure in a direction substantially normal to the surface. Thus, although the diamond film 14 as a whole is not a single crystal, it has a single crystal structure at the local domain level, and can therefore have sufficient crystallinity to ensure device characteristics. Nevertheless, the diamond film 14 of this disclosure is not a diamond single crystal film, much less a diamond single crystal self-supporting substrate.

[0017] As described above, the diamond film 14 is composed of oriented polycrystalline diamond. This oriented polycrystalline diamond typically contains multiple diamond single crystal particles 14a having a single crystal structure in a direction approximately normal to the surface 14b of the diamond film 14. Therefore, the diamond single crystal particles 14a exposed on the surface of the diamond film 14 are typically in communication with the back surface of the diamond film 14 without grain boundaries. The presence of grain boundaries hinders heat transfer in the thickness direction, thus reducing the thermal conductivity in the thickness direction, but this configuration avoids such a reduction in thermal conductivity. The diamond single crystal particles 14a are typically columnar particles, and more typically prismatic particles. The top view shape or cross-sectional shape of the prismatic particles is typically a quadrilateral, or a polygon formed by the fusion of multiple quadrilaterals.

[0018] The diamond film 14 is preferably (100) plane oriented. Although diamond is known as a hard material, the (100) plane of diamond is relatively easy to polish compared to other planes such as the (110) plane and the (111) plane, which is advantageous when polishing the surface 14b of the diamond film 14 to form a flat surface. The (100) plane orientation can be confirmed by analyzing the surface 14b of the diamond film 14 with an electron backscatter diffraction (EBSD) and obtaining an inverse pole figure orientation mapping. Since diamond is an isotropic crystal, the (100) plane is equivalent to the (001) plane and the (010) plane. Therefore, the evaluation of the (100) plane orientation can be substituted by evaluating the (001) plane orientation or the (010) plane orientation of the diamond film 14 with EBSD.

[0019] The degree of (100) plane orientation in the diamond film 14 is preferably evaluated by comparing the peak intensity of the (400) plane, which is equivalent to the (100) plane, with the peak intensity of the (111) plane using X-ray diffraction (XRD). When measuring diamond with XRD, as shown in the information on ICDD card #01-071-3649 in Figure 2, the crystal plane with the strongest diffraction intensity is the (111) plane, while the (400) plane has a relatively weaker intensity. Therefore, the peak intensity of the (111) plane measured by X-ray diffraction (XRD) for the surface 14b of the diamond film 14 is １ Peak intensity I of the (400) plane relative to ２ Ratio I ２ / I １ However, it is preferably 5.5 or higher, more preferably 10 or higher, and even more preferably 25 or higher. Within these ranges, it is possible to provide a diamond film 14 that is highly oriented to the (100) plane equivalent to the (400) plane. Peak intensity ratio I ２ / I １ Since a higher value is always better, there should be no particular upper limit, but typically it is 100 or less, and more typically 50 or less.

[0020] The (100) crystal orientation of each diamond single crystal particle 14a, measured on the surface 14b of the diamond film 14 by inverse pole figure mapping using electron beam backscatter diffraction (EBSD), is distributed tilted at various tilt angles from a reference (100) crystal orientation. A small average tilt angle is desirable, preferably 10° or less, more preferably 5.0° or less, even more preferably 2.5° or less, and particularly preferably 1.0° or less. Such a tilt angle aligns the crystal orientation of the polished surface, which has the advantage of shortening the polishing time when polishing the film surface. From the viewpoint of shortening the polishing time, there should be no lower limit on the average tilt, but typically the average tilt angle is 0.5° or more. The reference (100) crystal orientation is identified as pointing to the (100) axis, which coincides with the direction normal to the film surface of the diamond film 14. As mentioned above, in diamond, the (100) plane is equivalent to the (001) plane and the (010) plane. Therefore, the evaluation of the (100) plane orientation can be substituted by evaluating the (001) plane orientation or the (010) plane orientation of the diamond film 14 using EBSD. Furthermore, it is preferable that 80% or more of the diamond single crystal grains 14a measured by EBSD inverse pole figure mapping on the surface 14b of the diamond film 14 have a tilt angle within the range of 0.5 to 10°, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more have a tilt angle within the above range. Such a tilt angle distribution has the advantage that the crystal orientation of the polished surface is aligned, and the time required for polishing is shortened.

[0021] It is preferable that the diamond single crystal particles 14a have a crystal orientation that is generally aligned in the in-plane direction of the diamond film 14. In this case, the diamond film 14 can be said to be a biaxially oriented film having a crystal orientation that is generally aligned not only in the approximate normal direction but also in the in-plane direction, particularly in the rotational direction (hereinafter referred to as the twist direction) centered on a normal oriented approximately perpendicular to the film surface of the diamond film 14. That is, it is preferable that the oriented polycrystalline diamond is biaxially oriented. Specifically, the (110) crystal orientation of each diamond single crystal particle measured by EBSD inverse pole figure mapping on the surface 14b of the diamond film 14 is distributed rotated at various twist angles (in the twist direction) from the reference (110) crystal orientation, and it is desirable that the average twist angle be small, preferably 15° or less, more preferably 5° or less, even more preferably 2.5° or less, and particularly preferably 1.0° or less. Such an average twist angle has the advantage that the crystal orientation of the polished surface is aligned, and the time required for polishing is shortened. From the perspective of reducing polishing time, there should be no lower limit on the average twist angle, but typically the average twist angle is 0.5° or greater. There are no particular limitations on the method for determining the average twist angle, but it can be determined using methods such as EBSD or the euhedron of oriented single crystal grains.

[0022] The following describes a method for determining the average twist angle from the euhedron of oriented single crystal grains. (100) oriented diamond grains have a square crystal shape, and the sides of this square are in the (110) crystal orientation. Therefore, a straight line L is drawn in the plane of the observation image (e.g., SEM image), and the average value A of the angles between line L and the sides of the square of each oriented single crystal grain is calculated. Next, a straight line L' is drawn from line L at an angle A. The absolute value of the angle between this line L' and the sides of the square of each oriented single crystal grain is the twist angle. The average twist angle is calculated from the twist angles of multiple oriented single crystal grains. Alternatively, by using EBSD, the average twist angle can also be determined by using the direction that most frequently shows the (110) crystal orientation as the reference line.

[0023] Furthermore, it is preferable that 80% or more of the diamond single crystal grains 14a, measured by EBSD inverse pole figure mapping on the surface 14b of the diamond film 14, have a twist angle in the range of 0.5 to 15°, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more have a twist angle within the above range. Such a twist angle distribution has the advantage that the crystal orientation of the polished surface is aligned, and the time required for polishing is shortened.

[0024] The diamond film 14 easily achieves a high degree of smoothness on its surface 14b. One reason for this is that while diamond has different growth rates depending on its crystal orientation, the diamond film 14 is an oriented polycrystalline diamond film. As a result, each diamond single crystal particle 14a grows at a more uniform rate than in a random polycrystalline diamond film, making it easier for the upper surfaces of the diamond single crystal particles 14a exposed on the surface 14b to be aligned. Another reason is that, because it is an oriented polycrystalline diamond film, it has improved polishability compared to a random polycrystalline diamond film, and this tendency is particularly true in the case of (100) plane orientation. Specifically, the surface 14b of the diamond film 14 preferably has an arithmetic mean roughness Ra of 5 nm or less, more preferably 1 nm or less, and even more preferably 0.6 nm or less. The lower limit of the arithmetic mean roughness Ra of the surface 14b is not particularly limited, but is typically 0.1 nm or more. The arithmetic mean roughness Ra can be measured in accordance with JIS B 0601 (2001).

[0025] Thickness T of the diamond film 14 １ The thickness of the diamond film 14 is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, particularly preferably 10 μm or more, and most preferably 30 μm or more, for example 50 μm or more, 70 μm or more, or 100 μm or more. Therefore, there should be no upper limit specified for the thickness T of the diamond film 14. On the other hand, from the viewpoint of manufacturing cost, a thickness T of 70 μm or less is practical for the diamond film 14, and 50 μm or less is preferable.

[0026] The average cross-sectional diameter D at the outermost surface of the diamond single crystal grains 14a exposed on the surface 14b of the diamond film 14.Ｔ The thickness T of the diamond film 14 relative to this. １ The aspect ratio T is defined as the ratio of １ / D Ｔ A larger T / D ratio is preferable because it improves abrasiveness. Ｔ The average cross-sectional diameter D is preferably 1 or more, more preferably 10 or more, and even more preferably 30 or more. Ｔ This can be determined using a band contrast diagram based on the inverse pole figure orientation mapping of the cross-section of the diamond film 14, as illustrated in Figure 3. That is, a straight line S parallel to the substrate 12 or bonding surface 14c is located at a predetermined distance (e.g., 3 μm) below the surface 14b (outermost surface) of the diamond film 14, as shown in Figure 3. Ｔ Draw a line S. Ｔ Let n be the number of intersection points X between the diamond film 14 and the grain boundaries, and let L be the distance between intersection points X that contain at least 10 intersection points X. Ｔ Defined as, D Ｔ = L Ｔ The value calculated by the formula / (n-1) represents the average cross-sectional diameter D of the diamond single crystal grains 14a on the surface 14b of the diamond film 14. Ｔ This is how you should decide. On the other hand, aspect ratio T / D Ｔ If the ratio is too large, the thermal conductivity within the film surface may decrease. Therefore, T / D Ｔ The T / D ratio is preferably 50 or less, more preferably 10 or less, and even more preferably 5 or less. Ｔ A preferred range is 1 to 50, and more preferably 2 to 20.

[0027] As mentioned above, by employing the oriented polycrystalline diamond film 14, the laminated substrate 10 can be provided at a low cost and in a configuration suitable for large-scale applications. The area of ​​the diamond film 14 is 19.625 cm². ２ Preferably, it is 78.5 cm² or larger (corresponding to a circular area with a diameter of 5 cm (approximately 2 inches)), and more preferably 78.5 cm². ２ (corresponding to a circular area of ​​10 cm (approximately 4 inches) or larger in diameter), more preferably 176.625 cm². ２This corresponds to a circular area of ​​15 cm (approximately 6 inches) or more in diameter. Therefore, when the plan view shape of the diamond film 14 is circular or includes a circular portion, the diameter of the diamond film 14 is preferably 5 cm or more, more preferably 10 cm or more, and even more preferably 15 cm or more. However, the plan view shape of the diamond film 14 does not have to be circular or include a circular portion. In any case, the larger the area of ​​the diamond film 14, the more useful it is as a heat spreader, so there should be no upper limit on its area, but from the viewpoint of manufacturing cost, the area of ​​the diamond film 14 is 706.5 cm². ２ The following (corresponding to a circular area with a diameter of 30 cm (approximately 12 inches) or less) is realistic.

[0028] However, although the diamond film 14 of this disclosure can be provided at a low cost, forming a large-area diamond film 14 still incurs considerable costs. Therefore, multiple diamond films 14 smaller than the support substrate 12 may be bonded to the support substrate 12. In this case, it is preferable to perform the bonding in a tiling manner, where the multiple diamond films 14 are bonded to the support substrate 12 like tiles. With this configuration, even while using multiple smaller, less expensive diamond films 14, performance equivalent to that of a large diamond film 14 (for example, thermal conductivity as a heat spreader) can be provided. In other words, the laminated substrate 10 (especially the large-sized laminated substrate 10) can be provided at an even lower cost.

[0029] The diamond single crystal particles 14a may be doped with an n-type dopant or a p-type dopant. In this case, the diamond film 14 can be used as a component or layer such as a p-type electrode, an n-type electrode, a p-type layer, or an n-type layer.

[0030] Thickness T of the diamond film 14 １ The thickness T of the support substrate 12 relative to the support substrate 12 ２ Ratio T ２ / T １ It is preferable that the value is 3 to 4000, and more preferably 10 to 1000.

[0031] Manufacturing Method The laminated substrate 10 of this disclosure can preferably be manufactured by following the steps of (a) forming a diamond film 14 on a single crystal substrate 8, (b) polishing the diamond film 14 and the support substrate 12, (c) directly bonding the diamond film 14 and the support substrate 12, and (d) removing the single crystal substrate 8, as shown in Figure 4. Each of steps (a) to (d) will be described below.

[0032] (a) Formation of the diamond film First, a diamond film 14 is formed on a single crystal substrate 8, which is a single crystal Si substrate or a single crystal SiC substrate. The diamond film 14 can be formed by first performing a bias-enhanced nucleation (BEN) process (hereinafter referred to as bias treatment) as a pretreatment for forming diamond nuclei on the single crystal substrate 8, and then depositing the diamond film 14 by known deposition methods such as chemical vapor deposition (CVD) or physical vapor deposition (PVD). It is particularly preferable to use a (100)-oriented, double-sided polished Si single crystal substrate 8 with no off-angle. The pretreatment for forming diamond nuclei can preferably be carried out by setting the single crystal substrate 8 in a bias treatment device, evacuating it, heating the single crystal substrate 8 to a temperature of 800 to 1100°C, and performing bias treatment at a pressure of 50 to 200 Torr in the presence of hydrogen-diluted methane gas. The diamond film 14 can preferably be formed by heteroepitaxial growth of the diamond film 14 on the bias-treated side of the single crystal substrate 8 at 800 to 1100°C for 2 to 40 hours using microwave plasma CVD.

[0033] (b) Polishing of the diamond film and support substrate Next, the exposed surface of the diamond film 14 (the bonding surface 14c which will be bonded to the support substrate 12) is polished to make it smooth. At this time, it is preferable to polish the bonding surface 14c of the diamond film 14 until the arithmetic mean roughness Ra is 0.6 nm or less. On the other hand, as the support substrate 12, a substrate made of a material other than diamond, selected from the group consisting of ceramics and metals, is prepared. The bonding surface 12a of this support substrate 12 (which will be bonded to the diamond film 14) is also polished to make it smooth. At this time, it is preferable to polish the bonding surface 12a of the support substrate 12 until the arithmetic mean roughness Ra is 0.6 nm or less.

[0034] (c) Direct bonding of the diamond film and the support substrate The diamond film 14 and the support substrate 12 after polishing are directly bonded so that their bonding surfaces 14c and 12a are in contact. Direct bonding of the diamond film 14 and the support substrate 12 can be performed by known methods, but it is preferable to increase the bonding strength by activating the surface of each bonding surface of the diamond film 14 and the support substrate 12 by irradiation with a neutral atomic beam such as an Ar beam (see, for example, Patent Document 1 (Japanese Patent No. 7295351)). Surface activation with a neutral atomic beam is preferably performed by generating a neutral atomic beam using a known apparatus such as the one disclosed in Patent Document 2 (Japanese Patent Application Publication No. 2014-086400) and irradiating each bonding surface. That is, a saddle field type high-speed atomic beam source is used as the beam source. Then, an inert gas is introduced into the chamber and a high voltage is applied to the electrodes from a DC power supply. As a result, electrons move due to the saddle field type electric field generated between the electrode (positive electrode) and the housing (negative electrode), and a beam of atoms and ions from the inert gas is generated. Of the beam that reaches the grid, the ion beam is neutralized at the grid, so a beam of neutral atoms is emitted from the high-speed atomic beam source. The atomic species constituting the beam are preferably inert gases (argon, nitrogen, etc.). The voltage during activation by beam irradiation is preferably 0.5 to 2.0 kV, and the current is preferably 50 to 200 mA. Next, the diamond film 14 and the support substrate 12 are joined by bringing the activated bonding surfaces into contact with each other in a vacuum atmosphere. The bonding temperature can be room temperature, but specifically, it is preferably 40°C or lower, more preferably 30°C or lower, and even more preferably 20 to 25°C. The pressing load during bonding is preferably 100 to 20000 N. Furthermore, the flatter the bonding surfaces 14c and 12a of the diamond film 14 and the support substrate 12, the higher the bonding strength can be, which is preferable. Alternatively, the bonding strength may be increased by surface activation of each bonding surface by irradiation with a plasma such as nitrogen gas plasma (plasma activation method), as proposed in Patent Document 3 (WO2022 / 190465).

[0035] (d) Removal of the base substrate The single crystal substrate 8 (i.e., single crystal Si substrate or single crystal SiC substrate) is removed from the three-layer bonded body of single crystal substrate 8 / diamond film 14 / support substrate 12 obtained by direct bonding. Examples of methods for removing the single crystal substrate 8 include cleaning with hydrofluoric acid and plasma etching. Cleaning with hydrofluoric acid is particularly preferred. It is preferable to polish the surface 14b of the exposed diamond film 14 until the arithmetic mean roughness Ra is 0.6 nm or less. In this way, a two-layer laminated substrate 10 of diamond film 14 / support substrate 12 is obtained.

[0036] The present invention will be further described in detail by the following examples. However, the present invention is not limited to the following examples.

[0037] Example 1 (1) Fabrication of a diamond film A double-sided polished Si single crystal substrate with a diameter of 50.8 mm and a thickness of 1 mm, oriented in a (100) plane and without an off-angle, was prepared as a single crystal substrate 8 for diamond film deposition. Pretreatment such as bias treatment was performed on this Si single crystal substrate 8 to form diamond nuclei. Specifically, the Si single crystal substrate 8 was set on the negative voltage application electrode (cathode) of a bias treatment device and evacuated. Next, the Si single crystal substrate 8 was heated to 800°C, then 3 volume% hydrogen-diluted methane gas was introduced to set the pressure to 130 Torr and bias treatment was performed. This bias treatment was performed by applying a DC voltage between the two electrodes and passing a predetermined DC current. Finally, a diamond film 14 was obtained by heteroepitaxial growth of a diamond film 14 on the bias-treated side of the Si single crystal substrate 8 at 1000°C for 8 hours using microwave plasma CVD.

[0038] (2) Fabrication of the support substrate and polishing of the diamond film and support substrate A support substrate 12 with a thickness of 0.5 mm was prepared, consisting of an aluminum nitride sintered body. Next, the bonding surface 14c of the diamond film 14 and the bonding surface 12a of the support substrate 12 were polished, and both surfaces were smoothed so that the arithmetic mean roughness Ra was 0.5 nm (see Figure 4(b)). The thickness of the support substrate 12 after polishing was 0.45 mm.

[0039] (3) Bonding of the diamond film and the support substrate Next, the bonding surface 14c of the diamond film 14 and the bonding surface 12a of the support substrate 12 were irradiated with a neutralizing beam to activate each bonding surface and directly bond them (see Figures 4(b) and (c)). Specifically, after cleaning each of the bonding surfaces 12a and 14c to remove dirt, the diamond film 14 and the support substrate 12 were set in a vacuum chamber. The inside of the vacuum chamber was 10 －６ After evacuating to a Pa-level vacuum, each bonding surface was irradiated with a high-speed atomic beam (acceleration voltage: 1 kV, Ar flow rate: 27 sccm) for 120 seconds. Then, the bonding surface 14c of the diamond film 14 and the bonding surface 12a of the support substrate 12 were brought into contact, and the diamond film 14 and the support substrate 12 were bonded by applying pressure of 10,000 N for 2 minutes. In this way, a laminated substrate with a three-layer structure of Si single crystal substrate 8 / diamond film 14 / support substrate 12 was obtained (see Figure 4(c)).

[0040] (4) Removal of Si single crystal substrate and polishing of diamond film The Si single crystal substrate 8 was removed from the obtained laminated substrate by hydrofluoric acid cleaning, exposing the diamond film 14. Next, the exposed surface 14b of the diamond film 14 was polished to smooth it until the arithmetic mean roughness Ra was 0.5 nm, and a laminated substrate 10 with a two-layer structure of diamond film 14 / support substrate 12 was obtained (see Figure 4(d)).

[0041] (5) Analysis of the diamond film The following various analyses were performed on the prepared diamond film 14.

[0042] (5a) Surface XRD An XRD profile was measured in the range of 2θ = 10 to 140° when X-rays were irradiated onto the surface 14b (the surface opposite to the bonding surface 14c) of the diamond film 14 using an XRD device (Rigaku Corporation, RINT-TTR III). This XRD measurement was performed under the following conditions: X-ray source: Cu-Kα rays, voltage: 50kV, current: 300mA, step angle: 0.020°, scan speed: 2.00° / min. As a result, the diamond (400) plane was detected as the main phase, and the (111) plane and (110) plane were detected as secondary phases. To evaluate the degree of diamond orientation, the ratio of the maximum peak intensity of the (400) plane to the maximum peak intensity of the (111) plane was calculated. Specifically, the maximum peak intensity near the (400) plane peak was calculated.２ The maximum peak intensity near the (111) plane peak is I １ Peak intensity ratio I ２ / I １ The peak intensity ratio I in this example was calculated. ２ / I １ The intensity ratio was 6.6, indicating that it is an oriented polycrystalline film oriented on the (400) plane (which is equivalent to the (100) plane). Note that when measuring diamond with XRD, the crystal plane with the strongest diffraction intensity is the (111) plane, while the (400) plane has relatively weak intensity (see ICDD card #01-071-3649 shown in Figure 2). Nevertheless, the intensity ratio I ２ / I １ The fact that the value is 6.6 suggests that the diamond film 14 in this example is a strongly (100) plane-oriented film.

[0043] (5b) Surface EBSD An electron backscatter diffraction (EBSD) spectrometer (Nordlys Nano, Oxford Instruments) was attached to a SEM (SU-5000, Hitachi High-Technologies Corporation) to perform inverse pole figure orientation mapping of the diamond film 14 in a field of view of 797 μm × 1061 μm. The conditions for this EBSD measurement were as follows: <EBSD Measurement Conditions> - Acceleration voltage: 15 kV - Spot intensity: 70 - Working distance: 22.5 mm - Step size: 0.5 μm - Sample tilt angle: 70° - Measurement program: Aztec (version 3.3) - Analysis program: HKL Channel 5

[0044] From the inverse pole figure orientation mapping obtained by adjusting the angles of pole figures {001} and {110}, it was found that the diamond film 14 is a biaxially oriented polycrystalline film, oriented in the (100) axis direction normal to the surface 14b of the film, as well as in the in-plane direction of the film. The average tilt angle of the diamond single crystal grains 14a from the (100) axis was 6.0°. This average tilt angle was obtained by loading the measurement results from EBSD as the Diamond space group m3m into the results analysis software HKL CHANNEL 5 (Oxford Instruments), adjusting the plot in the analysis application Mambo included with HKL CHANNEL 5 so that it is four times symmetric to the center of pole figure {001}, and then quantifying the deviation (tilt angle) in the 100 axis direction in the analysis application Tango included with HKL CHANNEL 5 and calculating the average value. Furthermore, the proportion (frequency) of diamond single crystal grains with a tilt angle of 0.5 to 10° was 90%.

[0045] Each diamond single crystal grain constituting the diamond was oriented in the in-plane direction (horizontal direction) parallel to the surface of the diamond film. The average twist angle of the diamond single crystal grains relative to the (110) axis was 4.8°, and the twist angle distribution approximated a Gaussian distribution. The EBSD measurement results were loaded as the Diamond space group m3m into the results analysis software HKL CHANNEL 5 (Oxford Instruments). After adjusting the plots in the analysis application Mambo, included with HKL CHANNEL 5, so that they were four times symmetric to the center of the pole figure {001}, the deviation in the 110 axis direction (twist angle) was quantified and the average value was calculated using the analysis application Tango, also included with HKL CHANNEL 5. Furthermore, the proportion (frequency) of diamond single crystal grains with a twist angle of 0.5 to 15° was 90%.

[0046] (5c) Cross-sectional EBSD Next, the laminated substrate 10 containing the diamond film 14 was cut to expose the surface perpendicular to the plate surface, and after polishing using a CP polishing machine (manufactured by JEOL Ltd., IB-09010CP), the cross-section of the diamond film 14 was observed using EBSD under the same measurement conditions as in (5b) above. From the obtained inverse pole figure mapping and band contrast diagram, it was found that (i) the shape of the diamond single crystal particles 14a is columnar, (ii) the diamond film 14 is composed of a plurality of diamond single crystal particles 14a having a single crystal structure in the approximately normal direction, and (iii) these diamond single crystal particles 14a are biaxially oriented particles that are (100) oriented in the approximately normal direction to the film surface and also oriented in the in-plane direction of the film.

[0047] Furthermore, as shown in Figure 3, a straight line S is located 3 μm below the outermost surface 14b of the diamond film 14 in the band contrast diagram. Ｔ Draw a line S Ｔ Let n be the number of intersection points X between the diamond film 14 and the grain boundaries, and let L be the distance between intersection points X that contain at least 10 intersection points X. Ｔ This was defined as follows. And, as shown in Figure 3, D Ｔ = L Ｔ The value calculated by the formula / (n-1) represents the average cross-sectional diameter D of the diamond single crystal grains 14a on the surface 14b of the diamond film 14. Ｔ This was determined. As a result, the average cross-sectional diameter D in this example is Ｔ The thickness of the diamond film 14 was 7.4 μm. １ The diameter is 20 μm, and the average cross-sectional diameter D is as described above. Ｔ The thickness T of the diamond film 14 relative to the diamond film 14. １ The aspect ratio T is defined as the ratio of １ / D Ｔ The value was 2.7. The thickness T of the diamond film 14. １ The thickness T of the support substrate 12 relative to the support substrate 12 ２ Ratio T ２ / T １ The value was 22.5.

[0048] (6) Analysis of the interface between the diamond film and the support substrate After polishing the diamond film 14 to a thickness of approximately 2 μm and partially removing it, a depth analysis for positive ions was performed on a region of approximately 5 μm thickness including the interface between the diamond film 14 and the support substrate 12 using D-SIMS (dynamic SIMS) under the following measurement conditions. <D-SIMS measurement of positive ions> - Measurement device: SIMS4550 manufactured by FEI - Primary ion species: O ２ ＋ • Primary ion acceleration energy: 3 keV • Secondary ion polarity: Positive

[0049] As a result, the only metallic elements detected from the diamond film 14, the support substrate 12, and their interface were Al and Y contained in the support substrate 12, and other metallic elements were below the detection limit.

[0050] (7) Evaluation of heat dissipation performance when HEMT element is driven A HEMT element 20 having a HEMT structure as shown in Figure 5 was fabricated on a commercially available semi-insulating 4H-SiC single crystal using the MOCVD method. The HEMT element 20 consists of a SiC single crystal substrate 22 (thickness 350 μm), a GaN buffer layer 24 (thickness 500 nm), a GaN channel layer 26 (thickness 150 nm), and Al ０．２ Ga ０．８ N barrier layers 28 (thickness 20 nm) are stacked in sequence, Al ０．２ Ga ０．８ The HEMT element 20 has a layer configuration in which a source electrode 30, a gate electrode 32, and a drain electrode 34 are formed on the surface of the N barrier layer 28, spaced apart from each other. After the HEMT element 20 was cut into small pieces using a dicer, the SiC single crystal substrate 22 of the HEMT element 20 was polished to a thickness of 50 μm, and the surface of the HEMT element 20 on the SiC single crystal substrate 22 side was directly bonded to the surface 14b of the diamond film 14 of the laminated substrate 10 using the same method as in (3) above.

[0051] The temperature change ΔT of the HEMT element 20, to which the laminated substrate 10 is directly bonded, was measured using the thermoreflectance method when it was operated in DC under the conditions of drain voltage: 20V, gate voltage: 4V, and drain current: 0.5A. As a result, ΔT was approximately 30°C, indicating that the laminated substrate 10 has high heat dissipation capabilities when the HEMT is driven.

[0052] Example 2 (Comparison) Except for not forming the oriented polycrystalline diamond film 14, a support substrate 12 with a thickness of 0.5 mm made of aluminum nitride sintered body and a HEMT element 20 were prepared in the same manner as in Example 1, and the HEMT element 20 was directly bonded to the support substrate 12 (aluminum nitride sintered body). The temperature change ΔT when the HEMT element 20 was operated in DC in the same manner as in Example 1 was approximately 200°C, indicating that the heat dissipation during operation was insufficient.

[0053] 8 Single crystal substrate 10 Multilayer substrate 12 Support substrate 12a, 14c Bonding surface 14 Diamond film 14a Diamond single crystal particles 14b Surface 20 HEMT element 22 Si single crystal substrate 24 GaN buffer layer 26 GaN channel layer 28 Al ０．２ Ga ０．８ N barrier layer 30 Source electrode 32 Guard electrode 34 Drain electrode L Ｔ Length S Ｔ Straight line X Intersection T １ , T ２ thickness

Claims

1. A two-layer laminated substrate comprising: a support substrate made of a material other than diamond, selected from the group consisting of ceramics and metals; and a diamond film made of oriented polycrystalline diamond provided on the support substrate.

2. The laminated substrate according to claim 1, wherein the oriented polycrystalline diamond is biaxially oriented.

3. The laminated substrate according to claim 1 or 2, wherein no dissimilar metallic elements other than carbon and the constituent elements of the support substrate are present at the interface between the diamond film and the support substrate.

4. The support substrate is made of ceramics, and the ceramics are AlN, SiC, and Si ３ N ４ The laminated substrate according to claim 1 or 2, which is at least one selected from the group consisting of the following.

5. The laminated substrate according to claim 1 or 2, wherein the support substrate is made of metal, and the metal is Cu or a Cu-containing alloy.

6. The laminated substrate according to claim 1 or 2, wherein the diamond film has a thickness of 0.5 to 100 μm.

7. The laminated substrate according to claim 1 or 2, wherein the support substrate has a thickness of 300 μm to 2 mm.

8. Thickness T of the diamond film １ The thickness T of the support substrate relative to the thickness T ２ Ratio T ２ / T １ A laminated substrate according to claim 1 or 2, wherein the value is 3 to 4000.

9. The laminated substrate according to claim 1 or 2, wherein the diamond film is (100) oriented.

10. The laminated substrate according to claim 1 or 2, wherein the oriented polycrystalline diamond comprises a plurality of diamond single crystal particles having a single crystal structure in a direction substantially normal to the surface of the diamond film.

11. The peak intensity I of the (111) plane measured by X-ray diffraction (XRD) on the surface of the diamond film １ to the peak intensity I of the (400) plane ２ the ratio I ２ / I １ is 5.5 or more, the laminated substrate according to claim 1 or 2.

12. The laminated substrate according to claim 1 or 2, wherein the (100) crystal orientation of each diamond single crystal particle, measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD), is distributed tilted at various tilt angles from a reference (100) crystal orientation, and the average tilt angle is 0.5 to 10°.

13. The laminated substrate according to claim 12, wherein more than 80% of the diamond single crystal particles measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD) have a tilt angle in the range of 0.5 to 10°.

14. The laminated substrate according to claim 1 or 2, wherein the (110) crystal orientation of each diamond single crystal particle, measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD), is distributed rotated at various twist angles from a reference (110) crystal orientation, and the average twist angle is 0.5 to 15°.

15. The laminated substrate according to claim 14, wherein more than 80% of the diamond single crystal particles measured on the surface of the diamond film by inverse pole figure mapping of electron backscatter diffraction (EBSD) have a twist angle in the range of 0.5 to 15°.

16. The average cross-sectional diameter D at the outermost surface of the diamond single crystal particles exposed on the surface of the diamond film. Ｔ The thickness T of the diamond film relative to the thickness of the diamond film. １ The aspect ratio T is defined as the ratio of １ / D Ｔ A laminated substrate according to claim 1 or 2, wherein the coefficient is 1.0 or greater.

17. The diamond film is 19.625 cm ２ A laminated substrate according to claim 1 or 2, having the above area.

18. The laminated substrate according to claim 1 or 2, wherein the laminated substrate is a heat dissipation substrate for power semiconductors.

19. A circuit-equipped laminated substrate comprising: a laminated substrate according to claim 1 or 2; and a circuit for device mounting formed on the diamond film.

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