Polycrystalline SiC substrate and SiC bonded substrate equipped therewith

Abstract

The present invention provides a polycrystalline SiC substrate with excellent smoothness of the bonding surface and a SiC bonded substrate equipped therewith. A polycrystalline SiC substrate having a main surface for bonding with a single-crystal SiC substrate, wherein the arithmetic mean height Sa of the main surface is 0.35 nm or less, and the crystal orientation in the direction normal to the main surface satisfies at least one of the following conditions in terms of Miller indices: (i) the orientation index of (111) is 0.50 or more and 0.75 or less, (ii) the orientation index of (200) is 0.45 or more and 3.50 or less, (iii) the orientation index of (220) is 0.60 or more and 1.15 or less, and (iv) the orientation index of (311) is 1.30 or more and 2.75 or less.

Description

[Technical Field]

[0001] The present invention relates to a polycrystalline SiC substrate and a SiC bonded substrate equipped therewith. [Background technology]

[0002] Traditionally, semiconductor devices used as power devices have predominantly utilized silicon as the semiconductor material. In recent years, however, semiconductor devices using silicon carbide (SiC) have gained significant attention as power devices that possess superior characteristics compared to silicon, such as a higher dielectric breakdown voltage, and are capable of low-loss, high-temperature operation.

[0003] An example of SiC used in semiconductor devices is a SiC laminated substrate, which consists of a thin single-crystal SiC layer bonded to a polycrystalline SiC substrate. One of the characteristics of polycrystalline SiC substrates is that they exhibit a variety of crystal orientations.

[0004] The crystal orientation of a polycrystalline SiC substrate can be evaluated by X-ray diffraction measurement. For example, Patent Document 1 specifies the ratio of X-ray diffraction peak intensities considering the warpage of a polycrystalline SiC substrate. Patent Document 2 also specifies the X-ray diffraction peak intensity ratio to control the mechanical strength and thermal conductivity of a polycrystalline SiC molded body. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] WO2023 / 234159 A1 [Patent Document 2] WO2023 / 119874 A1 [Overview of the project] [Problems that the invention aims to solve]

[0006] The bonding process, which involves joining a polycrystalline SiC substrate to a single-crystal SiC substrate, is one of the processes for manufacturing a SiC bonded substrate. In the bonding process, smoothness of the bonding surface (sometimes referred to as the "bonding surface") of both the polycrystalline SiC substrate and the single-crystal SiC substrate is required.

[0007] Accordingly, the present invention aims to provide a polycrystalline SiC substrate with excellent smoothness of the bonding surface and a SiC bonded substrate equipped therewith. [Means for solving the problem]

[0008] Chemical mechanical polishing (CMP) can be used to smooth the bonding surfaces of polycrystalline SiC substrates. However, even when CMP is performed under the same conditions, some polycrystalline SiC substrates can be polished to a smooth bonding surface, while others cannot, and the underlying reason for this was unknown.

[0009] Based on these circumstances, the inventors investigated the properties of polycrystalline SiC substrates that can achieve a bonding surface with excellent smoothness. They found that if the orientation of the crystals in the direction normal to the bonding surface is predetermined, the bonding surface becomes smooth, leading to the invention of this invention.

[0010] In other words, to solve the above problems, the polycrystalline SiC substrate of the present invention has a main surface that is bonded to a single-crystal SiC substrate, the arithmetic mean height Sa of the main surface is 0.35 nm or less, and the orientation of the crystal in the direction normal to the main surface may satisfy at least one of the following in terms of Miller index plane indices: (i) the orientation index of (111) is 0.50 or more and 0.75 or less, (ii) the orientation index of (200) is 0.45 or more and 3.50 or less, (iii) the orientation index of (220) is 0.60 or more and 1.15 or less, and (iv) the orientation index of (311) is 1.30 or more and 2.75 or less.

[0011] The crystallographic orientation in the normal direction to the main surface may have an orientation index of (111) of 0.50 or more and 0.75 or less, an orientation index of (200) of 0.45 or more and 3.50 or less, an orientation index of (220) of 0.60 or more and 1.15 or less, and an orientation index of (311) of 1.30 or more and 2.75 or less, in terms of the plane indices of the Miller indices.

[0012] The polycrystalline SiC substrate may be a substrate for semiconductors. The SiC bonded substrate of the present invention may include the polycrystalline SiC substrate of the present invention and a single-crystalline SiC substrate bonded to the main surface.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a polycrystalline SiC substrate excellent in the smoothness of the bonding surface and a SiC bonded substrate including the same.

Brief Description of the Drawings

[0014] [Figure 1] A diagram showing an outline of a method for manufacturing a SiC bonded substrate. [Figure 2] A scatter diagram plotting the relationship between the arithmetic mean height Sa of the bonding target surface and the orientation index of (111). [Figure 3] A scatter diagram plotting the relationship between the arithmetic mean height Sa of the bonding target surface and the orientation index of (200). [Figure 4] A scatter diagram plotting the relationship between the arithmetic mean height Sa of the bonding target surface and the orientation index of (220). [Figure 5] A scatter diagram plotting the relationship between the arithmetic mean height Sa of the bonding target surface and the orientation index of (311).

Embodiments for Carrying Out the Invention

[0015] Hereinafter, an example of the polycrystalline SiC substrate of the present invention and a SiC bonded substrate including the same will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0016] [Method for Manufacturing SiC Bonded Substrate 210] The polycrystalline SiC substrate can be used as a part constituting the SiC bonded substrate. As an example of the method for manufacturing the SiC bonded substrate, the method for manufacturing the SiC bonded substrate 210 will be described below.

[0017] Fig. 1 shows an overview of the method for manufacturing the SiC bonded substrate 210. In Fig. 1, (A1) to (A4) indicate the steps of preparing a single-crystalline SiC substrate 13 (A1), performing chemical mechanical polishing (CMP) on it (A2), introducing specific elements (A3), and implanting hydrogen ions (A4). Also, (B1) to (B3) indicate the steps of preparing a polycrystalline SiC substrate 22 (B1), performing rough polishing on it (B2), and polishing the bonding target surface 22a (B3). Further, (C1) and (C2) indicate the steps of bonding the single-crystalline SiC substrate 13 and the polycrystalline SiC substrate 22 to form a bonded substrate 100 (C1), and peeling the single-crystalline SiC substrate 13 from the bonded substrate 100 to form a single-crystalline SiC thin film 30 on the polycrystalline SiC substrate 22 to form a bonded substrate 200 (C2). Also, (D1) indicates the step of heat-treating the bonded substrate 200 to obtain the SiC bonded substrate 210.

[0018] 〈Substrate Preparation Step (Fig. 1(A1), (B1))〉 The substrate preparation step is a step of preparing the single-crystalline SiC substrate 13 and the polycrystalline SiC substrate 22, which are necessary to obtain the SiC bonded substrate 210.

[0019] (Single-crystalline SiC Substrate 13) The single-crystal SiC substrate 13 (Figure 1(A1)) is a substrate used to form a single-crystal SiC thin film 30 on a polycrystalline SiC substrate 22. For example, a substrate obtained by performing outer edge grinding, orientation processing, slicing, beveling, lapping, and mechanical polishing on a 4H-SiC single-crystal ingot produced by sublimation can be used. The single-crystal SiC substrate 13 (monocrystalline SiC substrate) after these processing steps has a flat plate-like structure having a bonding surface 11a for bonding with the polycrystalline SiC substrate 22.

[0020] Furthermore, the shape of the single-crystal SiC substrate 13 is, for example, a substantially disc shape with an orientation flat, and a substrate with a diameter of 100 mm to 305 mm can be used. Note that the shape is not limited to a disc (wafer), and may also be polygonal, for example. Also, 6H-SiC may be used as the single-crystal SiC substrate 13 instead of 4H-SiC. Regarding the diameter of the substrate, if an orientation flat is present, it can be represented by the diameter of the arc excluding the orientation flat portion.

[0021] The single-crystal SiC substrate 13 shown in (A2) has the bonding surface 11a shown in (A1) that has been CMP'd. The shape of the bonding surface 11a is approximately disc-shaped (approximately circular), similar to that of the single-crystal SiC substrate 13. The bonding surface 11a may have a V-notch, or it may have an orientation flat.

[0022] Since the bonding surface 11a is the surface that will be bonded to the bonding surface 22a of the polycrystalline SiC substrate 22, it is preferable that it be as smooth as possible. By having a smooth bonding surface 11a, the occurrence of bonding defects with the bonding surface 22a can be suppressed. The arithmetic mean height Sa can be used as a guideline for determining whether the bonding surface 11a is smooth. For example, if Sa is between 0.05 nm and 0.5 nm, the occurrence of bonding defects with the bonding surface 22a can be suppressed. If Sa is greater than 0.5 nm, it may be difficult to suppress the occurrence of bonding defects with the bonding surface 22a. Furthermore, it is not a problem if Sa is less than 0.05 nm, but considering the measurement accuracy of the device that measures Sa, 0.05 nm is a guideline for the lower limit. Note that Sa can be calculated based on the surface roughness value measured using a contact type or non-contact type surface roughness measuring instrument.

[0023] [Polycrystalline SiC substrate 22] The shape of the polycrystalline SiC substrate 22 may be almost the same as that of the single-crystal SiC substrate 13, although its diameter is slightly larger. For example, it may be a disc shape with an orientation flat, and a substrate with a diameter of 100 mm to 305 mm can be used. The shape is not limited to a disc shape; for example, it may be a polygon. The polycrystalline SiC of the polycrystalline SiC substrate 22 may consist of 4H-SiC crystals, 6H-SiC crystals, and 3C-SiC crystals, or a mixture thereof. For example, various polytypes of SiC crystals may be mixed together. Since a polycrystalline SiC substrate 22 containing various polytypes can be manufactured without strict temperature control, it is possible to reduce the cost of manufacturing the polycrystalline SiC substrate 22. 3C-SiC crystals are often used in the manufacture of SiC bonded substrates.

[0024] The polycrystalline SiC substrate 22 is formed in a disc shape, for example, with a thickness of approximately 200 μm to 1000 μm, and the thickness tolerance can be set to ±2.5 μm. While there is no particular upper limit to the thickness of the polycrystalline SiC substrate 22, it can be set to, for example, 1000 μm as described above.

[0025] The polycrystalline SiC substrate 22 has bonding target surfaces 20a, 21a, and 22a that are bonded to the single-crystal SiC substrate 13 via a bonding process (Figure 1(C1)), and these surfaces are the main surfaces. In the polycrystalline SiC substrate 22, the orientation of the crystals in the direction D normal to the main surfaces is such that the orientation index of (111) is 0.50 or more and 0.75 or less in the Miller indices.

[0026] If the orientation index of (111) is 0.50 or more and 0.75 or less, it becomes possible to obtain a joining surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the joining surface polishing process described later. Preferably, if the orientation index of (111) is 0.50 or more and 0.72 or less, it becomes possible to obtain a joining surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the joining surface polishing process described later. Even more preferably, if the orientation index of (111) is 0.54 or more and 0.70 or less, it becomes possible to obtain a joining surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the joining surface polishing process described later.

[0027] Furthermore, the orientation of the crystal in the direction D normal to the main surface is such that, in the Miller index plane index, the orientation index of (200) is between 0.45 and 3.50, which makes it possible to obtain a bonding surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding surface polishing process described later. Preferably, the orientation index of (200) is between 1.50 and 3.50, which makes it possible to obtain a bonding surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding surface polishing process described later. Even more preferably, the orientation index of (200) is between 1.64 and 3.37, which makes it possible to obtain a bonding surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding surface polishing process described later.

[0028] Furthermore, the orientation of the crystal in the direction D normal to the main surface is such that, in the Miller index plane index, the orientation index of (220) is 0.60 or more and 1.15 or less, which makes it possible to obtain a bonding target surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding target surface polishing process described later. Preferably, the orientation index of (220) is 0.60 or more and 1.00 or less, which makes it possible to obtain a bonding target surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding target surface polishing process described later. Even more preferably, the orientation index of (220) is 0.62 or more and 0.96 or less, which makes it possible to obtain a bonding target surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding target surface polishing process described later.

[0029] Furthermore, the orientation of the crystal in the direction D normal to the main surface is such that, in the Miller index plane index, the orientation index of (311) is between 1.30 and 2.75, which makes it possible to obtain a bonding target surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding target surface polishing process described later. Preferably, the orientation index of (311) is between 1.30 and 2.15, which makes it possible to obtain a bonding target surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding target surface polishing process described later. Even more preferably, the orientation index of (311) is between 1.36 and 2.00, which makes it possible to obtain a bonding target surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding target surface polishing process described later.

[0030] Furthermore, the orientation of the crystal in the direction D normal to the main surface is such that, in terms of Miller indices, the orientation index of (111) is 0.50 or more and 0.75 or less, the orientation index of (200) is 0.45 or more and 3.50 or less, the orientation index of (220) is 0.60 or more and 1.15 or less, and the orientation index of (311) is 1.30 or more and 2.75 or less, which also makes it possible to obtain a bonding target surface 22a with an arithmetic mean height Sa of 0.35 nm or less by the bonding target surface polishing process described later.

[0031] The polycrystalline SiC substrate 22 can be used as a substrate for bonded SiC semiconductor substrates (polycrystalline base). A semiconductor substrate is a substrate used in the manufacturing process of semiconductor devices, and the polycrystalline SiC substrate 22 itself or the single-crystal SiC substrate 13 may be semiconductors. An epitaxial growth layer can be formed on the single-crystal SiC thin film 30, and an element can be formed thereon. Examples of SiC elements include electronic devices using the SiC bonded substrate 210 as the substrate, which have been commercialized in the form of SiC-MOSFETs, SiC SBDs (Schottky barrier diodes), and SiC power modules equipped with SiC-MOSFETs and SiC SBDs. The SiC bonded substrate 210 is used as a substrate in these products. The polycrystalline SiC substrate 22 can reinforce the single-crystal SiC substrate 13 as a base substrate by directly bonding it to the single-crystal SiC substrate 13.

[0032] The polycrystalline SiC substrate 22 can be manufactured by depositing a film on a graphite support substrate using a CVD method or the like. After film deposition, the graphite support substrate can be heated or ground off to separate the graphite support substrate from the polycrystalline SiC substrate 22.

[0033] <CMP process (Figure 1 (A2))> To prevent bonding defects with the bonding surface 22a of the polycrystalline SiC substrate 22, the bonding surface 11a of the single-crystal SiC substrate 13 needs to be smooth, and therefore a CMP (Chemical Polishing) process is performed beforehand. The single-crystal SiC substrate 13 with a CMP-polished bonding surface 11a may be obtained by purchasing it, or the bonding surface 11a may be polished by CMP before the specific element introduction process.

[0034] The single-crystal SiC substrate after the delamination process (Figure 1(C2)) can be reused by polishing and removing the damage caused by delamination using CMP (Chemical Polishing).

[0035] For polishing the bonding surface 11a by CMP, polishing methods and equipment known as CMP techniques for single-crystal SiC can be used. For example, as a polishing equipment, a rotary-type CMP device can be used, in which a polishing pad is attached to a circular base plate, and a slurry is dropped onto it while rotating together with a carrier holding the single-crystal SiC substrate 13 in contact with it. The slurry used for polishing can also be any known type as appropriate. Furthermore, the type of polishing pad is not particularly limited, and suede pads, nonwoven fabric pads, or urethane-based pads can be used.

[0036] <Specific element introduction process (Figure 1 (A3))> In this process, in order to prevent the occurrence of interfacial resistance at the bonding interface 110 formed by the bonding of bonding surface 11a and bonding surface 22a, a specific element is introduced into the single-crystal SiC substrate 13. This process may also involve introducing the specific element by performing at least one of the following treatments on the single-crystal SiC substrate 13: ion implantation, neutral element implantation, plasma doping, or thermal diffusion.

[0037] The specified element may be at least one of nitrogen (N), phosphorus (P), boron (B), or aluminum (Al), and the concentration of the specified element after introduction is 1.0 × 10⁻⁶. 19 atoms / cm 3 The above 2.0 × 10 20 atoms / cm 3 The following may also apply. Furthermore, the concentration of a specific element may be higher in regions separated from the bonding interface 110 by 40 nm or more and 60 nm or less.

[0038] <Hydrogen ion implantation process (Figure 1 (A4))> In this process, hydrogen ions are implanted into the single-crystal SiC substrate 13 after the specific element introduction process to form hydrogen ion implantation zones. When hydrogen ions are implanted, they reach a depth corresponding to the incident energy and are distributed at a high concentration. For example, hydrogen ion implantation zones are formed at a depth of approximately 0.9 μm from the bonding target surface 11a.

[0039] For example, the conditions for hydrogen ion implantation include a dose of 10 14 atoms / cm 3 The above 10 16 atoms / cm 3 The following are acceleration voltages: 0.1kV or higher and 170kV or lower.

[0040] <Rough polishing process (Figure 1 (B2))> This process involves rough polishing both sides of a polycrystalline SiC substrate 22 using, for example, a lapping device and polishing fluid. The polycrystalline SiC substrate 22 is placed between the upper and lower plates of the lapping device, and a polishing fluid containing boron carbide (B4C) abrasive grains of grit 100 to 300 (as indicated by ISO 8486) is supplied between the upper and lower plates to roughly polish both sides of the polycrystalline SiC substrate 22. In addition to boron carbide, colloidal silica or diamond may also be used as abrasive grains. The thickness of the polycrystalline SiC substrate will change before and after this process. Before polishing, the thickness of the polycrystalline SiC substrate 22 is approximately 750 ± 250 μm. After polishing, the thickness of the polycrystalline SiC substrate 22 is approximately 500 ± 150 μm. The rough polishing process polishes the bonding surface 20a to form the bonding surface 21a. This process may also involve rough polishing both sides of the polycrystalline SiC substrate 22 using a grinding wheel.

[0041] <Polishing process of the surface to be joined (Figure 1 (B3))> The polycrystalline SiC substrate 22 has bonding target surfaces 20a, 21a, and 22a that become bonding surfaces with the single-crystal SiC thin film 30 after the bonding process (Figure 1(C1)), and these surfaces are the main surfaces. In particular, the smoothness of the bonding target surface 22a that is directly bonded to the single-crystal SiC thin film 30 is important, and the polycrystalline SiC substrate of the present invention is a polycrystalline SiC substrate 22 that has a main surface with improved smoothness after undergoing a bonding target surface polishing process (Figure 1(B3)).

[0042] To prevent bonding defects with the bonding surface 11a of the single-crystal SiC substrate 13, the bonding surface 22a of the polycrystalline SiC substrate 22 needs to be smooth. Therefore, the bonding surface 22a is formed by polishing in advance using this process. Polishing may be performed by CMP in the same manner as the CMP process described above, or by lapping using the smallest possible diamond abrasive grains.

[0043] Specifically, known polishing methods and equipment can be used, similar to the CMP process (Figure 1(A2)). For example, a rotary-type CMP device can be used as the polishing equipment, in which a polishing pad is attached to a circular base plate, and a slurry is dropped onto it while rotating together with a carrier holding the polycrystalline SiC substrate 22 in contact with it. Any known slurry can be used for polishing, such as a permanganate-based slurry or a colloidal silica-based slurry. Furthermore, the type of polishing pad is not particularly limited, and suede pads, nonwoven fabric pads, or urethane-based pads can be used.

[0044] The bonding surface 21a is polished in a bonding surface polishing process so that the arithmetic mean height Sa is 0.35 nm or less, thereby obtaining the bonding surface 22a. If the polycrystalline SiC substrate 22 has a crystal orientation in the direction normal to the main surface that satisfies the above conditions, then an Sa of 0.35 nm or less can be achieved by this process.

[0045] If Sa is 0.35 nm or less, the occurrence of bonding defects with the bonding target surface 11a of the single crystal SiC substrate 13 can be suppressed. A lower limit of Sa is difficult to achieve at 0 nm through polishing, so a value of 0.20 nm or higher is a good guideline.

[0046] Furthermore, Sa can be calculated based on the surface roughness value measured using contact-type or non-contact-type surface roughness measuring instruments.

[0047] In addition, in order to obtain the bonding target surface 22a on the polycrystalline SiC substrate 22 by CMP, it is necessary to polish the bonding target surface 21a by a thickness greater than or equal to the thickness of the polishing damage layer formed thereon.

[0048] 〈Activation Step〉 This step is a step performed before the bonding step. For example, in a vacuum chamber, the bonding target surface 11a of the single crystal SiC substrate 13 and the bonding target surface 22a of the polycrystalline SiC substrate 22 are irradiated with an ion beam and electrons to activate the bonding target surface 11a and the bonding target surface 22a.

[0049] The temperature in the vacuum chamber may be 20°C or higher and 100°C or lower, and the degree of vacuum may be, for example, 1.0×10 -8 Pa or higher and 1.0×10 -5 Pa or lower.

[0050] By this step, the oxide film and impurities on the bonding target surface 11a and the bonding target surface 22a are removed to expose the atoms, so that the bonding hands are exposed to the activated state. In addition, since the irradiation of the ion beam is a process in a vacuum, the bonding target surface 11a and the bonding target surface 22a can be kept in the activated state without being oxidized.

[0051] 〈Bonding Step (Fig. 1(C1))〉 This step is a step of bonding the single crystal SiC substrate 13 and the polycrystalline SiC substrate 22 after the hydrogen ion implantation step to obtain a bonded substrate 100. For example, by bonding the bonding target surface 11a and the bonding target surface 22a activated by the activation step, a bonding interface 110 can be formed to obtain a bonded substrate 100.

[0052] For example, the bonding target surface 11a and the bonding target surface 22a are brought into contact with each other in a vacuum in a vacuum chamber. The bonding hands existing on the activated bonding target surface 11a and the bonding target surface 22a are connected to each other, and the single crystal SiC substrate 13 and the polycrystalline SiC substrate 22 are bonded together to form a bonded substrate 100.

[0053] The conditions for joining are, for example, a temperature of 20°C to 100°C inside the vacuum chamber and a vacuum level of 1.0 × 10⁻⁶. -8 Pa or more 1.0×10 -5 The atmosphere can be set to Pa or less. In a vacuum chamber set to such an atmosphere, the surfaces to be joined 11a and 22a are overlapped and pressed together to bond them. The pressing can be performed under conditions of 3000N or more and 50000N or less, and the pressing time can be 60 seconds or set to approximately 30 seconds to 5 minutes.

[0054] <Peeling process (Figure 1(C2))> This process involves peeling the single-crystal SiC substrate 13 of the bonded substrate 100 in a hydrogen ion implantation section to form a single-crystal SiC thin film 30 on the polycrystalline SiC substrate 22. By heating the bonded substrate 100, a microbubble layer is formed in the hydrogen ion implantation section, and the single-crystal SiC substrate 13 is peeled off using this microbubble layer as the peeling surface, separating the single-crystal SiC thin film 30. The single-crystal SiC substrate 13 after the separation of the single-crystal SiC thin film 30 can be repeatedly used as a single-crystal SiC substrate 13 in the manufacture of the bonded substrate 100 by performing a CMP (Chemical Polishing) process.

[0055] This process involves heating the bonded substrate 100 to approximately 800°C or higher. The atmosphere during delamination may be at least one of the following: an inert gas such as argon (Ar) or nitrogen (N), or a vacuum. Delamination may be performed using rapid thermal annealing (RTA) or a furnace. This allows the single-crystal SiC substrate 13 to be separated in the hydrogen ion implantation section.

[0056] Furthermore, if the single-crystal SiC thin film 30 has a diameter greater than 100% of the diameter of the polycrystalline SiC substrate 22, the single-crystal SiC thin film 30 may crack due to external impacts, potentially causing problems in the formation of the epitaxial layer. Therefore, it is preferable that the single-crystal SiC thin film 30 has a diameter of 100% or less of the diameter of the polycrystalline SiC substrate 22.

[0057] <Heat treatment process (Figure 1 (D1))> This step involves heating and heat-treating the bonded substrate 200 after the delamination step. The heat treatment temperature in the heat treatment step is preferably a temperature at which the introduced specific elements such as phosphorus are activated, and the bonded substrate 200 may be heated to 1100°C to 2200°C (preferably around 1700°C). The atmosphere for the heat treatment may be at least one of the following: an inert gas such as argon (Ar) or nitrogen (N), or a vacuum. The heat treatment step may be performed in the furnace in which the delamination was performed. This causes the specific elements to move to the bonded interface 211 and its vicinity.

[0058] [SiC bonded substrate 210] Next, a SiC bonded substrate 210 will be described as an example of a SiC bonded substrate of this embodiment. The SiC bonded substrate 210 (bonded SiC substrate) is a substrate that can be manufactured by the SiC bonded substrate manufacturing method of the present invention described above.

[0059] The SiC bonded substrate 210 has a laminated structure 40 in which a single-crystal SiC thin film 30 and a polycrystalline SiC substrate 22 are stacked (Figure 1(D1)). The thickness of the single-crystal SiC thin film 30 is approximately 0.5 μm to 1.0 μm, and the thickness of the polycrystalline SiC substrate 22 is approximately 200 μm to 1000 μm.

[0060] The single-crystal SiC thin film 30 has a main surface 30a. The main surface 30a can be smoothed out by performing a CMP process similar to that on the single-crystal SiC substrate 13, thereby creating a surface condition on which an epitaxial growth layer can be formed. In the state of the SiC bonded substrate 210, the main surface 30a is an exposed surface with nothing formed on its surface. In a subsequent process, an epitaxial growth layer is formed on the main surface 30a, and p-type wells, n-type sources, gate electrodes, source electrodes, etc., may also be formed.

[0061] Furthermore, the polycrystalline SiC substrate 22 has a back surface 20b that is opposite to the main surface 30a in the laminated structure 40. In the state of the SiC bonded substrate 210, the back surface 20b is an exposed surface with nothing formed on its surface, and in a later process, the back surface 20b may be plated with electroless plating or the like to form a back surface electrode. In addition, the back surface 20b may be ground down to reduce the overall thickness of the element formed on the main surface 30a.

[0062] The SiC bonded substrate 210 can be used as a bonded SiC semiconductor substrate for semiconductor applications. Because the SiC bonded substrate 210 is a compound semiconductor material with various properties such as heat resistance, wear resistance, chemical resistance, high voltage resistance, and high-frequency characteristics, it can be utilized as a substrate in a wide range of fields, such as power converters, electric vehicle inverters, solar power generation systems, sliding parts like bearings and seals, abrasives, and nozzles, by taking advantage of these properties. [Examples]

[0063] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0064] In the following examples, the orientation index of the polycrystalline SiC substrate 22 was calculated from measurements taken by X-ray diffraction (XRD), and a rough polishing process and a bonding surface polishing process were performed on the polycrystalline SiC substrate 22. The arithmetic mean height Sa of the bonding surface 22a was then measured.

[0065] [Polycrystalline SiC substrate 22] By CVD, a polycrystalline SiC film was deposited on a graphite support substrate. The graphite support substrate was then heated and removed to separate the polycrystalline SiC from the graphite support substrate, thereby obtaining multiple polycrystalline SiC substrates 22, which are 3C-SiC.

[0066] [Evaluation of orientation] For the obtained polycrystalline SiC substrates 22, 2θ / θ scans were performed in the range of 20 to 80° using Cu Kα-ray X-ray diffraction (XRD), and the orientation in the normal direction D was calculated. The orientation was evaluated using the orientation index. The orientation index of the (hkl) plane was calculated using the following equation (1).

[0067] [Formula 1] (hkl) plane orientation index = IF(hkl) / IFR(hkl)···(1)

[0068] Here, IF(hkl) is the diffraction intensity ratio on the (hkl) plane of the sample, calculated using the following equation (2). The diffraction intensity used is the peak area (integrated intensity). Here, Σ(HKL) is the sum of the diffraction intensities of all plane orientations measured within the scan range from the target crystal structure, 3C-SiC.

[0069] [Formula 2] IF(hkl)=I(hkl) / Σ(HKL)...(2)

[0070] Furthermore, the IFR(hkl) was calculated using the same method as in equation (2) from the X-ray diffraction pattern of unoriented polycrystalline SiC powder. The Powder Diffraction File (PDF, PDF number: 00-029-1129) collected by the International Centre for Diffraction Data (ICDD) was used for the calculation.

[0071] [Arithmetic mean height Sa of the joining surface 22a] <Rough polishing process (Figure 1 (B2))> Both sides of the polycrystalline SiC substrate 22 were roughly polished using a lapping device and polishing fluid. Specifically, the polycrystalline SiC substrate 22 was placed between the upper and lower plates of the lapping device, and a polishing fluid containing boron carbide (B4C) abrasive particles of grit 100 to 300 (as indicated by ISO 8486) was supplied between the upper and lower plates to roughly polish both sides of the polycrystalline SiC substrate 22 to form the bonding surface 21a.

[0072] <Polishing process of the surface to be joined (Figure 1 (B3))> Using a permanganate-based slurry (Nanobix, manufactured by Mitsui Mining & Smelting Co., Ltd.), the bonding surface 21a was polished by CMP to form the bonding surface 22a. Specifically, a rotary-type CMP apparatus was used, with a polishing pad attached to a circular base plate, and permanganate slurry was dropped onto the pad while rotating it together with a carrier holding the polycrystalline SiC substrate 22 in contact. A urethane-based pad with a hardness of D66 was used as the polishing pad.

[0073] <Calculation of arithmetic mean height Sa> The surface roughness of the joining surface 22a was measured using a non-contact surface roughness measuring instrument. Based on the measured surface roughness values, the arithmetic mean height Sa of the joining surface 22a was calculated.

[0074] Based on these measurements and calculations, Figures 2 to 5 show scatter plots showing the relationship between the arithmetic mean height Sa of the bonding surface 22a on the polycrystalline SiC substrate 22 and the orientation index for each of the cases (111), (200), (220), and (311).

[0075] From the results in Figure 2, when the orientation index of (111) was between 0.50 and 0.75, Sa was 0.35 nm or less. From the results in Figure 3, when the orientation index of (200) was between 0.45 and 3.50, Sa was 0.35 nm or less. From the results in Figure 4, when the orientation index of (220) was between 0.60 and 1.15, Sa was 0.35 nm or less. From the results in Figure 5, when the orientation index of (311) was between 1.30 and 2.75, Sa was 0.35 nm or less. [Explanation of symbols]

[0076] 11a: Bonding surface, 13: Single crystal SiC substrate, 20a: Bonding surface, 20b: Back surface, 21a: Bonding surface, 21b: Back surface, 22: Polycrystalline SiC substrate, 22a: Bonding surface, 30: Single crystal SiC thin film, 30a: Main surface, 40: Laminated structure, 100: Bonding substrate, 110: Bonding interface, 200: Bonding substrate, 210: SiC bonded substrate, 211: Bonding interface, D: Normal direction

Claims

1. It has a main surface that bonds with a single-crystal SiC substrate, The arithmetic mean height Sa of the main surface is 0.35 nm or less. The orientation of the crystal in the direction normal to the principal surface is, in terms of the Miller indices, (i) The orientation index of (111) is 0.50 or more and 0.75 or less, (ii) The orientation index of (200) is 0.45 or more and 3.50 or less, (iii) The orientation index of (220) is 0.60 or more and 1.15 or less, (iv) The orientation index of (311) is 1.30 or more and 2.75 or less, A polycrystalline SiC substrate that satisfies at least one of the following conditions.

2. The orientation of the crystal in the direction normal to the principal surface is, in terms of the Miller indices, The orientation index of (111) is 0.50 or more and 0.75 or less, The orientation index of (200) is 0.45 or more and 3.50 or less. The orientation index of (220) is 0.60 or more and 1.15 or less, and The polycrystalline SiC substrate according to claim 1, wherein the orientation index of (311) is 1.30 or more and 2.75 or less.

3. A polycrystalline SiC substrate according to claim 1, which is a substrate for semiconductors.

4. A polycrystalline SiC substrate according to any one of claims 1 to 3, The single crystal SiC substrate bonded to the main surface, A SiC bonded substrate comprising the features described above.

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