A bonded structure of a mosaic diamond wafer and a dissimilar semiconductor, a method for manufacturing the same, and a mosaic diamond wafer for a bonded structure of a dissimilar semiconductor.

Abstract

To provide a joined body of a mosaic diamond wafer and a heterogeneous semiconductor that has excellent heat dissipation characteristics and can be increased in size.SOLUTION: A joined body 10 of a mosaic diamond wafer and a heterogeneous semiconductor is a joined body in which a mosaic diamond wafer 1 having a joined boundary part B1 between single crystal diamond substrates 1A and 1B is joined to a heterogeneous semiconductor 2. The largest step in a joined surface 1aa of the mosaic diamond wafer 1 to the heterogeneous semiconductor 2 is 10 nm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a bonded body of a mosaic diamond wafer and a heterogeneous semiconductor, a method for manufacturing the same, and a mosaic diamond wafer for a bonded body with a heterogeneous semiconductor.

Background Art

[0002] Power devices such as GaN devices require cooling, but a sufficient cooling method has not yet been developed. In such a situation, it has been considered to use a diamond material having a high thermal conductivity as a heat dissipation base material.

[0003] Patent Document 1 describes a wafer having a polycrystalline diamond layer grown or bonded on GaN.

[0004] Non-Patent Document 1 discloses a GaN-HEMT (high electron mobility transistor) using a single crystal diamond substrate as a heat dissipation substrate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0006]

Non-Patent Document 1

[0007] Polycrystalline diamond generally has lower thermal conductivity than single-crystal diamond due to the presence of grain boundaries. While adjustments to growth conditions are necessary to achieve thermal conductivity comparable to single crystals, the growth rate remains at less than one-tenth that of single crystals. Furthermore, while mechanical polishing is required to flatten the growth surface, the high anisotropy of diamond polishing speeds means that the polishing speed is significantly slower for polycrystalline diamonds compared to single crystals. For these reasons, using polycrystalline diamond as a bonding wafer is expected to result in significantly higher manufacturing costs compared to single-crystal diamonds. Moreover, polycrystalline diamonds are prone to warping due to grain orientation and particle size distribution resulting from non-uniformity of the growth atmosphere, and reducing these warps is technically difficult. Additionally, the aforementioned anisotropy makes it difficult to obtain a surface suitable for wafer bonding through mechanical polishing. As a result, a thick intermediate layer is required to bond GaN wafers and polycrystalline wafers, which acts as a thermal barrier, significantly reducing the heat dissipation effect of the device.

[0008] On the other hand, while single-crystal diamond substrates can be bonded virtually directly to GaN wafers via an extremely thin intermediate layer (<5nm), the lack of inch-sized single-crystal diamond wafers prevents wafer-level bonding, resulting in high costs, which is a significant challenge.

[0009] This disclosure is made in view of the above circumstances and aims to provide a bonded structure of a mosaic diamond wafer and a dissimilar semiconductor that has high heat dissipation characteristics and can be scaled up, a method for manufacturing the same, and a mosaic diamond wafer for use in bonded structures with dissimilar semiconductors. [Means for solving the problem]

[0010] A mosaic diamond wafer is a mosaic-shaped diamond wafer formed by bonding multiple single-crystal diamond substrates arranged on the same surface to each other by growing diamond crystals on them using a vapor phase method (see, for example, Non-Patent Document 2).

[0011] Figure 9 shows an optical microscope image of the vicinity of the bonding boundary of a typical mosaic diamond wafer obtained by the method described in Patent Document 2. In Figure 9, the area indicated by the arrow is the bonding boundary between single-crystal diamond substrates. In mosaic diamond wafers, even when multiple single-crystal diamond substrates are arranged in a crystal growth apparatus so that their crystal orientations are aligned, the bonding boundaries tend to undergo abnormal growth (polycrystallization), resulting in anisotropic crystal orientations. Figure 9 shows that the bonding boundaries differ significantly from the rest of the wafer, reflecting the abnormal growth (polycrystallization).

[0012] Figure 10 shows a cathodoluminescence mapping image near the bonding boundary of a mosaic diamond wafer. The length of one side of the cathodoluminescence mapping image is 125 μm. In cathodoluminescence mapping images, non-emitting regions are areas where crystal defects exist (non-emitting centers). The cathodoluminescence mapping images reveal that complex non-emitting centers are concentrated near the junction boundary.

[0013] Mosaic diamond wafers possess quality close to that of single-crystal diamonds, while being relatively easier to produce in large areas compared to single-crystal diamonds. Therefore, if mosaic diamond wafers can be used as a heat dissipation substrate, the problems associated with single-crystal diamond substrates described above can be solved. However, since the bonding boundaries between the single-crystal diamond substrates constituting the mosaic diamond wafer correspond to the grain boundaries of polycrystalline diamonds, those skilled in the art would assume that, like polycrystalline diamonds, they cannot be directly bonded to GaN wafers. In addition, as shown in Figures 9 and 10, there is a problem unique to mosaic diamond wafers in that defects and strains are concentrated at the bonding boundaries, making it unimaginable to those skilled in the art that mosaic diamond wafers could be directly bonded to GaN wafers.

[0014] After diligent research, the inventors have achieved direct bonding between a mosaic diamond wafer and a GaN wafer, thereby completing this disclosure.

[0015] This disclosure provides the following means to solve the above problems.

[0016] A bonded structure of a mosaic diamond wafer and a dissimilar semiconductor according to a first aspect of this disclosure is a bonded structure in which a mosaic diamond wafer having bonding boundaries between a plurality of single-crystal diamond substrates is bonded to a dissimilar semiconductor, wherein the maximum step difference at the bonding surface of the mosaic diamond wafer with the dissimilar semiconductor is 10 nm or less.

[0017] In the above embodiment, the bond between the mosaic diamond wafer and the dissimilar semiconductor may be one selected from the group consisting of gallium nitride, gallium oxide, silicon, and silicon carbide.

[0018] The bonded structure of the mosaic diamond wafer and the dissimilar semiconductor according to the above embodiment may be one in which the mosaic diamond wafer and the dissimilar semiconductor are directly bonded.

[0019] The bonded body of the mosaic diamond wafer and the heterogeneous semiconductor according to the above aspect may be one in which the mosaic diamond wafer and the heterogeneous semiconductor are bonded via an intermediate layer.

[0020] The method for manufacturing a bonded body of a mosaic diamond wafer and a heterogeneous semiconductor according to the second aspect of the present disclosure includes a step of selecting a mosaic diamond wafer having a bonding boundary portion between a plurality of single crystal diamond substrates, wherein the maximum step on the bonding surface of the mosaic diamond wafer with the heterogeneous semiconductor is 10 nm or less.

[0021] The method for manufacturing a bonded body of a mosaic diamond wafer and a heterogeneous semiconductor according to the third aspect of the present disclosure includes a step of preparing a mosaic diamond wafer having a bonding boundary portion between a plurality of single crystal diamond substrates, and a step of polishing the surface of the mosaic diamond wafer until the maximum step at the bonding boundary portion becomes 10 nm or less.

[0022] The method for manufacturing a bonded body of a mosaic diamond wafer and a heterogeneous semiconductor according to the above aspect includes a step of producing an epitaxial substrate in which a heterogeneous semiconductor layer is epitaxially grown on the main surface of a growth substrate, a step of bonding the epitaxial substrate to a support substrate via an adhesive layer, a step of removing the growth substrate to expose the heterogeneous semiconductor layer, a step of bonding the heterogeneous semiconductor layer and the polished surface of the mosaic diamond wafer, and a step of removing the adhesive layer to obtain a bonded body of the mosaic diamond wafer and the heterogeneous semiconductor.

[0023] The mosaic diamond wafer for a bonded body of a mosaic diamond wafer and a heterogeneous semiconductor according to the fourth aspect of the present disclosure is a mosaic diamond wafer used in a bonded body in which a mosaic diamond wafer having a bonding boundary portion between a plurality of single crystal diamond substrates and a heterogeneous semiconductor are bonded, and the maximum step on the bonding surface of the mosaic diamond wafer with the heterogeneous semiconductor is 10 nm or less.

Advantages of the Invention

[0024] The bond between a mosaic diamond wafer and a dissimilar semiconductor according to this disclosure provides a bond between a mosaic diamond wafer and a dissimilar semiconductor that has high heat dissipation characteristics and can be scaled up. [Brief explanation of the drawing]

[0025] [Figure 1] This is a schematic cross-sectional diagram conceptually illustrating the configuration of a bond between a mosaic diamond wafer and a dissimilar semiconductor according to one embodiment of the present disclosure. [Figure 2] These are schematic perspective diagrams conceptually illustrating the manufacturing method of mosaic diamond wafers, with (a) showing the first step, (b) showing the second step, and (c) showing the third step. [Figure 3] This is a schematic cross-sectional diagram showing the general configuration of a polishing apparatus used for polishing mosaic diamond wafers. [Figure 4] This is a schematic cross-sectional diagram illustrating each step in an example of a manufacturing method for a bonded structure of a mosaic diamond wafer and a dissimilar semiconductor. [Figure 5] This is a schematic cross-sectional diagram illustrating each step in an example of a manufacturing method for a bonded structure of a mosaic diamond wafer and a dissimilar semiconductor. [Figure 6] This is a schematic cross-sectional diagram illustrating each step in an example of a manufacturing method for a bonded structure of a mosaic diamond wafer and a dissimilar semiconductor. [Figure 7] This is a schematic cross-sectional diagram illustrating each step in an example of a manufacturing method for a bonded structure of a mosaic diamond wafer and a dissimilar semiconductor. [Figure 8] (a) is a scanning white-light interference microscope image of the vicinity of the bonding boundary of the mosaic diamond wafer used in the example, and (b) is a scanning white-light interference microscope image of the vicinity of the bonding boundary of the mosaic diamond wafer used in the comparative example. [Figure 9] This is an optical microscope image of the vicinity of the bonding boundary of a mosaic diamond wafer. [Figure 10] This is a cathodoluminescence mapping image of the vicinity of the bonding boundary of a mosaic diamond wafer. [Modes for carrying out the invention]

[0026] The following description will explain, with reference to figures, a bonded structure of a mosaic diamond wafer and a dissimilar semiconductor, a method for manufacturing the same, and a mosaic diamond wafer for bonding with a dissimilar semiconductor. Note that the drawings are schematic representations, and the relative sizes and positions of images shown in different drawings are not necessarily accurately depicted. The relationships and ratios of dimensions in the length, depth, and height directions may differ from those in reality. Furthermore, in the following description, similar components are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed explanations of these components may be omitted. Also, the materials, dimensions, etc., exemplified in the following description are examples only, and the disclosure is not limited to them. It is possible to modify and implement the disclosure as appropriate within the scope of achieving its effects. The configuration shown in one embodiment can also be applied to other embodiments.

[0027] (Bonding of a mosaic diamond wafer and a dissimilar semiconductor) Figure 1 is a schematic cross-sectional view conceptually showing the configuration of a bond between a mosaic diamond wafer and a dissimilar semiconductor according to one embodiment of the present disclosure. The bonded structure 10 of a mosaic diamond wafer and a dissimilar semiconductor shown in Figure 1 is a bonded structure in which a mosaic diamond wafer 1 having bonding boundaries B1 between multiple single-crystal diamond substrates 1A and 1B is bonded to a dissimilar semiconductor 2, and the maximum step height at the bonding surface 1aa between the mosaic diamond wafer 1 and the dissimilar semiconductor 2 is 10 nm or less.

[0028] <Mosaic Diamond Wafer> In the bonded structure of this disclosure, as described above, the mosaic diamond wafer is a mosaic-shaped diamond wafer obtained by bonding multiple single-crystal diamond substrates arranged on the same plane to a large diamond single-crystal wafer by growing diamond crystals on them using a vapor phase method.

[0029] <Method for manufacturing mosaic diamond wafers> Mosaic diamond wafers can be manufactured as follows: Multiple single-crystal diamond substrates are prepared and arranged in a crystal growth apparatus so that their crystal orientations are aligned, and diamond crystals are grown on them. There are no particular restrictions on the crystal growth conditions as long as the method and conditions are suitable for diamond crystal growth. For example, if microwave plasma CVD is used, the microwave power should be 5kW, the raw material gas pressure 16kPa, the flow rate ratio of hydrogen to methane constituting the raw material gas should be around 10:0.1 to 1, and the substrate temperature should be maintained at around 800 to 1200°C. The crystal-grown layers will integrate the installed single-crystal diamond substrates, resulting in a mosaic diamond wafer.

[0030] Typically, in methods for fabricating mosaic diamond wafers, the threshold for considering the off-angles of the single-crystal diamond substrates to be bonded as identical is set at a minimum of 1°. However, even a 1° difference in off-angle results in different quality growth layers under the same conditions, leading to the growth of single-crystal layers of varying quality in each bonded single-crystal region on mosaic diamond wafers bonded using this method. Conventional mosaic diamond wafers suffer from abnormal growth along the bonding boundaries, which is difficult to suppress. To address these problems, a method for manufacturing mosaic diamond wafers using an ion implantation method for creating self-supporting films is known (see, for example, Patent Document 2). Using such a method, substrates with aligned off-angles and off-directions can be joined together.

[0031] This manufacturing method will be explained with reference to Figure 2. This method allows for the production of mosaic diamond wafers through the following steps; (1) A step of ion implanting into a parent substrate made of single-crystal diamond (hereinafter sometimes referred to as "single-crystal diamond parent substrate" or simply "parent substrate") to form a graphitized non-diamond layer near the surface of the parent substrate, and etching the non-diamond layer to separate the single-crystal diamond layer above the non-diamond layer (hereinafter sometimes referred to as "single-crystal diamond child substrate" or simply "child substrate") (2) The operation of step (1) is repeated on the parent substrate used in step (1) above, and further a step is performed to separate multiple single-crystal diamond layers (substrates) 1a, 1b, 1c, and 1d (see Figure 2(a)). (3) A step of placing the multiple single-crystal diamond layers separated in steps (1) and (2) above onto a flat support base, with their sides in contact with each other, their crystal planes aligned, and the surfaces separated from the parent substrate in contact with the surface of the support base (see Figure 2(b)). (4) A step in which single crystal diamond is grown on a plurality of single crystal diamond layers (substrates) 1a, 1b, 1c, 1d placed on a support base in step (3) above by vapor phase synthesis, thereby bonding the plurality of single crystal diamond layers (substrates) 1a, 1b, 1c, 1d together, and a mosaic diamond wafer 1 is obtained consisting of portions 1A, 1B, 1C, 1D derived from each substrate, which are integrated via bonding boundaries B1, B2, B3, B4 (see Figure 2(c)). Furthermore, (5) after inverting the single-crystal diamond layer bonded in step (4) above on a support stand, a step may be performed to grow single-crystal diamond on a surface separated from the parent substrate by a vapor phase synthesis method.

[0032] In this manufacturing method, each sub-substrate constituting the mosaic diamond wafer 1 is obtained from the same single-crystal diamond parent substrate, and therefore each sub-substrate has the same crystallographic properties as the parent substrate. In other words, having the same crystallographic properties means that the orientation of the crystal planes, such as the off-angle and off-direction, as well as the distribution of strain and defects, are uniform. For this reason, there is no need to change the diamond growth conditions for each sub-substrate, and the same processed layer can be obtained for the set conditions. Consequently, single-crystal diamond can be easily and accurately grown on this surface by vapor phase synthesis, and the properties of the large-area substrate made of single-crystal diamond, which is fabricated by joining these, are also homogeneous.

[0033] Furthermore, the sub-substrates having the same crystallographic properties are not limited to those obtained by the method described in Patent Document 2. Multiple single-crystal diamond substrates having the same crystallographic properties may be selected from commercially available single-crystal diamond substrates, or single-crystal diamond substrates having the same crystallographic properties may be manufactured by appropriately employing known diamond manufacturing methods.

[0034] A crucial difference between mosaic diamond wafers and polycrystalline diamond is that many areas at the bonding boundaries have the same crystal orientation. In contrast, polycrystalline diamond is thought to be difficult to bond directly to GaN wafers because its surface consists of regions where the crystal orientations are in different directions.

[0035] <Method for polishing mosaic diamond wafers> Any polishing method capable of smoothing the diamond surface can be used to polish mosaic diamond wafers. Known polishing methods include the skif polishing method, which involves friction between diamond particles embedded in a metal platen and the diamond workpiece; a method using a thermochemical reaction between a quartz platen and diamond; a method combining etching with oxygen plasma and chemical mechanical polishing; and a polishing method using active radicals generated by a catalytic reaction between a transition metal and hydrogen peroxide. These polishing methods may be used individually or in combination.

[0036] In the polishing process of the mosaic diamond wafer surface, polishing is continued until the maximum step difference on the surface is 10 nm or less. Here, the "maximum step difference" on the surface is the maximum value of the local height difference in the surface shape measured by a white light interference microscope, at least in the area including each bonding boundary (for example, the bonding boundaries indicated by symbols B1, B2, B3, and B4 in Figure 2). This is because a bonded structure directly bonded between a mosaic diamond wafer and a dissimilar semiconductor has only been obtained when using a mosaic diamond wafer in which the maximum step difference at the bonding surface is 10 nm or less. Note that a surface roughness of about 10 nm, as indicated by Ra, is too rough for a polished surface, and direct bonding with a dissimilar semiconductor is not possible. For direct bonding with a dissimilar semiconductor, the step difference at the bonding boundary, which is the joint between single-crystal diamond substrates, must be 10 nm or less.

[0037] Regardless of the polishing method used, the polishing apparatus includes, schematically as shown in Figure 3, a polishing platen 120 mechanically coupled to a rotating mechanism, a sample holding platen 130 for holding a sample S (mosaic diamond wafer) on the polishing platen 120, a pressurizing member 140 for applying a constant load to the sample S, and a substrate rotating mechanism 150 for rotating the sample S while pressing it against the polishing platen 120 via the sample holding platen 130. In addition, if necessary, members for supplying or holding chemical solutions such as polishing agents to the polishing platen surface and around the workpiece, and a mechanism for heating the platen surface may also be provided. When using the skife polishing method, which involves friction between diamond particles embedded in a metal polishing plate and the diamond workpiece, the polishing plate 120 is, for example, a polishing plate made of cast iron with diamond microparticles embedded on it. It is desirable that the diamond microparticles are dispersed in a machining oil or the like beforehand and then fixed onto the polishing plate. Furthermore, in order to perform high-quality polishing, it is desirable that the particles be fixed so that each particle is arranged at approximately uniform height and density. When using a diamond polishing method that utilizes thermochemical reactions, a polishing platen 120 made of synthetic quartz can be used. Since the essence of this method lies in the thermochemical reaction that occurs between the diamond and the quartz surface, it is desirable to provide a mechanism for heating the polishing platen surface in order to improve the reaction rate. When using a method that combines etching by oxygen plasma with chemical mechanical polishing, it is desirable to use a polishing plate surface that incorporates multiple plasma generating electrodes equipped with oxygen gas supply paths, and a path for supplying chemically active species generated in the plasma generation section to the polishing surface, in order to enable uniform supply of active radicals generated in the oxygen plasma to the polishing surface. Furthermore, it is desirable to equip the plate surface with a polishing pad made of urethane, nonwoven fabric, or the like. In addition, it is desirable to equip the plate surface with a polishing solution supply device for dropping the polishing solution onto the plate surface at a constant rate. When using a polishing method that utilizes active radicals generated by a catalytic reaction between a transition metal and hydrogen peroxide, a metal polishing platen 120 made of a transition metal element is used. For example, iron, nickel, etc., can be used as the platen material. Furthermore, it is desirable to have a chemical solution tank around the platen 120, holding an oxidizing agent solution in the tank so that the polishing platen 120 is immersed in the oxidizing agent solution. Alternatively, instead of a chemical solution tank, a structure may be provided with an oxidizing agent solution supply device that drops the oxidizing agent solution onto the polishing platen surface at a constant rate. As these oxidizing agents, for example, hydrogen peroxide diluted to about 0.5 to 10 weight percent can be used. The conditions for the platen rotation speed, polishing pressure, etc., in the diamond polishing process using each of these methods can be any conditions, as long as the maximum step height on the mosaic diamond wafer surface can be sufficiently reduced.

[0038] (Manufacturing method for bonding mosaic diamond wafers and dissimilar semiconductors) In the following section, using Figures 4 to 7, we will explain the manufacturing method of a bond between a mosaic diamond wafer and a dissimilar semiconductor, using the case where the dissimilar semiconductor is GaN as an example.

[0039] First, as shown in Figure 4, an epitaxial substrate ES is prepared by forming a GaN layer 12 on the main surface of a growth substrate 11 such as a Si substrate by heteroepitaxial growth. Electronic elements such as diodes, transistors, and resistors may be formed in the GaN layer 12 beforehand. Then, a support substrate BS selected from a glass substrate, sapphire substrate, Si substrate, and SiC substrate is prepared, and the epitaxial substrate ES and the support substrate BS are bonded together with an adhesive such as an adhesive so that the main surface of the epitaxial substrate ES on the side where the GaN layer 12 is formed faces the main surface of the support substrate BS for bonding (first main surface). This results in the epitaxial substrate ES and the support substrate BS being bonded together by an adhesive layer AH.

[0040] As the adhesive layer AH, known adhesive materials such as resin adhesives including acrylic resin, epoxy resin, silicone resin, modified silicone resin, and alumina adhesive, or inorganic adhesives mainly composed of water glass, alumina, etc., can be used. However, from the viewpoint of suppressing substrate warping after bonding and ensuring ease of final removal, it is preferable to use a non-solvent diluted resin-based adhesive that hardens through a chemical reaction. For example, acrylic resin, epoxy resin, and silicone resin are suitable.

[0041] After bonding, a curing treatment is performed to improve the mechanical strength of the adhesive layer AH. While any curing conditions can be used depending on the adhesive layer AH used, for example, a heat treatment is performed in a 70-degree Celsius forced-air drying oven for 6 hours.

[0042] Since the role of the support substrate BS is to support the GaN layer 12 in subsequent processes, any material can be used, not limited to the substrate described above, as long as it can withstand the process in terms of heat resistance, mechanical strength, and resistance to chemicals used in the manufacturing process.

[0043] Next, as shown in Figure 5, the growth substrate 11 is removed. The growth substrate 11 can be removed from the main surface (back surface) opposite to the main surface on which the GaN layer 12 is formed, using methods such as mechanical polishing, dry etching, or wet etching with a solution. However, from the viewpoint of removal speed, mechanical polishing is preferred.

[0044] Next, the surface (back surface) of the GaN layer 12 on the side from which the growth substrate 11 was removed is polished and smoothed. Known methods such as mechanical polishing, chemical mechanical polishing (CMP), dry etching, and wet etching with a solution can be used for smoothing, but since high smoothing quality is required to improve the bonding quality in the subsequent bonding process, chemical mechanical polishing is preferred.

[0045] Next, as shown in Figure 6, a mosaic diamond wafer 20, in which the maximum step height at the bonding surface 20aa is 10 nm or less, is bonded to the back surface of the GaN layer 12.

[0046] While any direct bonding method between dissimilar materials can be used to directly bond the mosaic diamond wafer 20 to the GaN layer 12, it is desirable to reduce the interfacial thermal resistance between the GaN layer 12 and the mosaic diamond wafer 20 as much as possible in order to improve the performance and reliability of the nitride semiconductor device. Furthermore, in order to prevent warping of the substrate after bonding, it is desirable to bond the GaN layer 12 and the mosaic diamond wafer 20 without heating. For this reason, bonding using a room temperature bonding method is most preferable. An example of a room temperature bonding method is surface-activated room temperature bonding, which is a method of bonding in which the bonding surface is surface-treated in a vacuum to make the atoms on the surface in an active state that is easily chemically bonded.

[0047] In addition, atomic diffusion bonding and hydrophilic pressure bonding can also be used as room-temperature bonding methods. Atomic diffusion bonding is a method in which a metal film is formed on the surface of the objects to be bonded by sputtering or the like, and the metal films are brought into contact with each other in a vacuum to bond them.

[0048] Hydrophilic pressure bonding is a method of bonding surfaces that have been treated to become hydrophilic by attaching a large number of hydroxyl groups to each surface, and then joined together by overlapping the treated surfaces and applying pressure.

[0049] Finally, as shown in Figure 7, the support substrate BS and adhesive layer AH on the opposite side of the mosaic diamond wafer 20 are removed to obtain a bonded body 30 on which GaN2 is formed on the mosaic diamond wafer 20. The method for removing the support substrate is determined according to the material of the adhesive layer AH. For example, known methods can be used, such as mechanically peeling the adhesive layer AH together with the support substrate BS from the mosaic diamond wafer 20, immersing the adhesive layer AH in a solvent to make its physical properties brittle and then mechanically peeling it from the mosaic diamond wafer 20, removing the support substrate BS by heat-treating and burning the adhesive layer AH, or removing the support substrate BS by treating the adhesive layer AH with sulfuric acid and burning it.

[0050] The above explanation has used GaN as an example of the case where the heterogeneous semiconductor is gallium oxide, but the heterogeneous semiconductor may also be one selected from the group consisting of gallium oxide, silicon, and silicon carbide.

[0051] Furthermore, while we have described the case of directly bonding a mosaic diamond wafer and a GaN wafer, bonding may also be done via an intermediate layer. The intermediate layer can be made of a material selected from amorphous silicon, amorphous carbon, germanium, metals, and oxides thereof. [Examples]

[0052] (Examples) <Preparing Mosaic Diamond Wafers> The mosaic diamond wafer was fabricated using the method shown in Figure 2. The mosaic diamond wafer sample used in this study consisted of four 10mm x 10mm sub-substrates bonded together, with the crystal plane of the main surface being the (100) plane.

[0053] Figure 8(a) shows a scanning white-light interference microscope image of the vicinity of the bonding boundary of a polished mosaic diamond wafer sample. No steps or irregularities were observed.

[0054] Next, using the methods shown in Figures 4 to 7, the mosaic diamond wafer and the GaN wafer were directly bonded using a surface activation room-temperature bonding method, and a bonded body of the mosaic diamond wafer and the GaN wafer was obtained.

[0055] (Comparative example) Except for preparing a mosaic diamond wafer sample by joining sub-substrates obtained from different parent substrates, we attempted to fabricate a bonded body of a mosaic diamond wafer and a GaN wafer using the same method as in the example, but the bonding was unsuccessful.

[0056] Figure 8(b) shows a scanning white-light interference microscope image of the vicinity of the bonding boundary of a polished mosaic diamond wafer sample. Steps and irregularities were observed at the bonding boundary, with the largest step being 50 nm or more.

[0057] Based on the interference microscope images in Figures 8(a) and 8(b), it is believed that differences in the smoothness of the bonding surfaces of the mosaic diamond wafers influenced the success or failure of the direct bonding between the mosaic diamond wafers and the GaN wafers. [Explanation of Symbols]

[0058] 1.20 Mosaic Diamond Wafer 1a 1a, 1b, 1c, 1d Single crystal diamond substrate 1aa, 20aa joint surface 2. Heterogeneous semiconductors 10, 30 Bonding of mosaic diamond wafers and dissimilar semiconductors 12 GaN layer (GaN wafer)

Claims

1. A bonded body is formed by bonding a mosaic diamond wafer having bonding boundaries between multiple single-crystal diamond substrates to a dissimilar semiconductor, The maximum step height at the bonding surface between the mosaic diamond wafer and the dissimilar semiconductor is 10 nm or less. A bonded body of a mosaic diamond wafer and a dissimilar semiconductor, wherein the step difference near the bonding boundary on the bonding surface of the mosaic diamond wafer is 10 nm or less.

2. The bonded body of a mosaic diamond wafer and a dissimilar semiconductor according to claim 1, wherein the dissimilar semiconductor is one selected from the group consisting of gallium nitride, gallium oxide, silicon, and silicon carbide.

3. The bonded body of a mosaic diamond wafer and a dissimilar semiconductor according to claim 1 or 2, wherein the mosaic diamond wafer and the dissimilar semiconductor are directly bonded together.

4. The bonded body of a mosaic diamond wafer and a dissimilar semiconductor according to claim 1 or 2, wherein the mosaic diamond wafer and the dissimilar semiconductor are bonded via an intermediate layer.

5. A method for manufacturing a bonded body of a mosaic diamond wafer having bonding boundaries between multiple single-crystal diamond substrates and a dissimilar semiconductor, A method for manufacturing a bond between a mosaic diamond wafer and a dissimilar semiconductor, comprising the step of selecting a mosaic diamond wafer in which the maximum step difference at the bonding surface with the dissimilar semiconductor is 10 nm or less, and the step difference near the bonding boundary at the bonding surface of the mosaic diamond wafer is 10 nm or less.

6. A process for preparing a mosaic diamond wafer having bonding boundaries between multiple single-crystal diamond substrates, A method for manufacturing a bond between a mosaic diamond wafer and a dissimilar semiconductor, comprising the step of polishing the surface of the mosaic diamond wafer until the maximum step difference at the bonding boundary is 10 nm or less.

7. A process for fabricating an epitaxial substrate by epitaxially growing a different semiconductor layer on the main surface of a growth substrate, The process of bonding the epitaxial substrate to a support substrate via an adhesive layer, A step of removing the growth substrate and exposing the dissimilar semiconductor layer, A step of joining the dissimilar semiconductor layer and the polished surface of the mosaic diamond wafer, A method for manufacturing a bond between a mosaic diamond wafer and a dissimilar semiconductor according to claim 5 or 6, comprising the step of removing the adhesive layer to obtain a bond between a mosaic diamond wafer and a dissimilar semiconductor.

8. A mosaic diamond wafer used in a bonded body in which a mosaic diamond wafer having bonding boundaries between multiple single-crystal diamond substrates is bonded to a dissimilar semiconductor, The maximum step height at the bonding surface between the mosaic diamond wafer and the dissimilar semiconductor is 10 nm or less. A mosaic diamond wafer for bonding a mosaic diamond wafer to a dissimilar semiconductor, wherein the step difference near the bonding boundary on the bonding surface of the mosaic diamond wafer is 10 nm or less.

Images