SiC POLYCRYSTALLINE SUBSTRATE, SiC AFFIXED SUBSTRATE, AND METHOD FOR MANUFACTURING SiC AFFIXED SUBSTRATE

Abstract

The present invention improves the manufacturing yield of a SiC bonded substrate.　The present invention is characterized by comprising a bonding surface that is bonded to an SiC single crystal substrate, and is also characterized in that the stacking fault density of the bonding surface is 1.0% or less.

Description

SiC polycrystalline substrate, SiC bonded substrate, and method for manufacturing SiC bonded substrate

[0001] The present invention relates to a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing a SiC bonded substrate.

[0002] Silicon carbide semiconductors (hereinafter sometimes referred to as "SiC") are expected as materials for power devices. However, it is difficult to obtain large-area silicon carbide single crystal substrates for silicon carbide semiconductors, and mass production is difficult and expensive compared to conventionally used silicon semiconductors.

[0003] In order to inexpensively manufacture SiC single crystal substrates, a technique of bonding a SiC single crystal ingot (SiC single crystal substrate) and a SiC polycrystalline substrate has been proposed (for example, Patent Document 1). The SiC polycrystalline substrate of the SiC bonded substrate functions as a supporting substrate. Therefore, the single crystal attached onto the SiC polycrystalline substrate may be a thin film. After bonding the SiC single crystal ingot and the SiC polycrystalline substrate, the SiC single crystal ingot is peeled off leaving a thin SiC single crystal layer on the SiC polycrystalline substrate. A SiC polycrystalline substrate (SiC bonded substrate) having a thin SiC single crystal layer attached thereto allows a SiC thin film to be formed on the surface SiC single crystal layer, and elements such as power devices can be further formed thereon.

[0004] On the other hand, the peeled SiC single crystal ingot is repeatedly used to manufacture other SiC bonded substrates. Therefore, since a plurality of SiC bonded substrates can be produced from one SiC single crystal ingot, the cost of SiC semiconductors can be reduced.

[0005] Japanese Unexamined Patent Application Publication No. 2009-117533

[0006] From the viewpoint of preventing impurity contamination in processes such as element formation, it is desirable that the bonding interface between the SiC single crystal layer and the SiC polycrystalline layer of a SiC bonded substrate composed of a SiC single crystal substrate and a SiC polycrystalline substrate has no adhesive layer composed of any material other than SiC. Therefore, it is desirable that the SiC polycrystalline substrate and the SiC single crystal substrate are directly bonded.

[0007] In direct bonding, since there is no adhesive layer, the bonding surface between the SiC polycrystalline layer and the SiC single-crystal layer must be as flat as possible. If there are localized depressions (scratches or holes) on the bonding surface, unbonded areas will occur at the bonding interface where the SiC polycrystalline substrate and the SiC single-crystal layer cannot be partially bonded. These unbonded areas at the bonding interface can cause irregularities on the surface of the SiC single-crystal layer, inducing crystal defects when forming the SiC thin film on the SiC single-crystal layer, which can lead to a decrease in device performance and yield.

[0008] Grinding and polishing are performed to flatten the substrate surface before bonding. For the final polishing of the SiC single crystal layer surface, chemical mechanical polishing (CMP) is performed. CMP flattens the substrate surface by simultaneously performing chemical reactions and mechanical polishing with abrasive grains.

[0009] On the other hand, a SiC polycrystalline substrate is an aggregate of crystal grains with irregular crystal orientations. Therefore, the crystal orientation exposed on the surface of the SiC polycrystalline substrate differs depending on the location on the substrate. Different crystal orientations mean different arrangements of atoms, resulting in different chemical reactivity. Consequently, when a SiC polycrystalline substrate is polished using a CMP process, the chemical reaction progresses differently for each crystal grain, making it difficult to achieve a completely flat surface across the entire SiC polycrystalline substrate.

[0010] One proposed solution to improve this is to weaken the chemical reaction during the CMP process for SiC polycrystalline substrates and polish them using mechanical action. However, even with this measure, localized irregularities occur on the surface of the SiC polycrystalline substrate. These irregularities can cause areas where the SiC polycrystalline layer and the SiC single crystal layer are not bonded together at the interface in SiC bonded substrates, where a SiC polycrystalline substrate and a SiC single crystal substrate are bonded together.

[0011] Thus, it is necessary to reduce defects (unbonded areas) at the bonding interface between the SiC single-crystal layer and the SiC polycrystalline layer of a SiC bonded substrate. However, it has not been clarified how to evaluate the properties of the bonding interface, such as the density of defects at the bonding interface, in order to avoid a decrease in the manufacturing yield of the SiC bonded substrate.

[0012] Therefore, in order to solve the above problems, the present invention aims to improve the manufacturing yield of SiC bonded substrates.

[0013] To solve the above problems, the SiC polycrystalline substrate of the present invention is characterized by having a bonding surface for bonding with a SiC single crystal substrate, and the stacking fault density of the bonding surface is 1.0% or less. Furthermore, the SiC bonded substrate of the present invention is characterized by comprising the above-mentioned SiC polycrystalline substrate and a SiC single crystal substrate bonded to the bonding surface of the above-mentioned SiC substrate.

[0014] Furthermore, in order to solve the above problems, the present invention provides a method for manufacturing a SiC bonded substrate, characterized by including a heating step of heating the SiC polycrystalline substrate in an inert atmosphere by holding it at a temperature of 1750°C to 1950°C for 15 to 30 hours, or at a temperature of 1980°C to 2100°C for 5 to 15 hours; a polishing step of polishing one side of the SiC polycrystalline substrate, which is the bonding surface; and a bonding step of removing the oxide film on the surface of the polished bonding surface and bonding it with a SiC single crystal substrate in a vacuum atmosphere.

[0015] The present invention makes it possible to improve the manufacturing yield of SiC bonded substrates.

[0016] This graph shows the results of an investigation into the impact of stacking fault density on product yield.

[0017] The following describes an example of an embodiment of the SiC polycrystalline substrate, SiC bonded substrate, and method for manufacturing the SiC bonded substrate according to the present invention.

[0018] [SiC Single Crystal Substrate] For the SiC single crystal substrate, a 4H-SiC single crystal substrate, for example, manufactured by sublimation, can be used. The shape of the SiC single crystal substrate is generally disc-shaped, and in addition to being circular, it may have indicator parts that show the orientation of the substrate, such as an orientation flat or a notch. It is preferable to use a substrate with a diameter of 100 mm to 305 mm (4 inches to 12 inches). Note that the shape is not limited to a generally disc shape such as a circle, and may also be polygonal, for example.

[0019] [SiC Polycrystalline Substrate] A SiC polycrystalline substrate is a substrate that can reinforce a SiC single-crystal substrate by directly bonding it to the SiC single-crystal substrate, thereby using the SiC single-crystal substrate as a support substrate. By reinforcing the SiC single-crystal substrate, for example, warping of the SiC single-crystal substrate can be suppressed, and by suppressing warping, it becomes possible to hold and transport the SiC single-crystal substrate.

[0020] <Stacking Faults> SiC is a material that exhibits polymorphism. The polymorphism of SiC appears due to the stacking method along the c-axis of the crystal, and it takes on structures such as hexagonal and cubic crystal systems. In the structure of SiC, regular tetrahedra formed by silicon (or carbon) share vertices and form bases, and are stacked. The period of this stacking differs for each crystal structure.

[0021] This disruption in the stacking period is called a stacking fault. Stacking faults occur, for example, when synthesizing SiC powder, when depositing SiC polycrystalline substrates by chemical vapor deposition (CVD), when stress is applied to a SiC polycrystalline substrate, or when heat treatment is performed. Stacking faults also occur in SiC single crystals during the growth of SiC single crystal substrates, and when growing SiC single crystal thin films on SiC single crystal substrates by epitaxial growth using CVD. Stacking faults in SiC single crystals are known to adversely affect the operation of silicon carbide devices.

[0022] The effect of stacking faults occurring in a SiC polycrystalline substrate is on the flatness (surface irregularities) of the polished surface. Since stacking faults represent disruptions in the stacking period, in extreme cases, the crystal structure of the faulty area differs from that of the surrounding area. This results in a difference in polishing speed between the surrounding area and the faulty area. Consequently, the surface of the stacking fault area becomes uneven after polishing. Therefore, in SiC polycrystalline substrates where flatness is strictly required (for example, SiC polycrystalline substrates for bonding), fewer stacking faults are desirable.

[0023] The SiC polycrystalline substrate in this embodiment has a bonding surface that bonds with a SiC single crystal substrate, and the stacking fault density Y of the bonding surface is 1.0% or less. By having a stacking fault density Y of 1.0% or less, defects (unbonded portions) at the bonding interface between the SiC polycrystalline layer and the SiC single crystal layer of the SiC bonded substrate, which is formed by bonding a SiC single crystal substrate and a SiC polycrystalline substrate, are reduced. When forming a SiC single crystal thin film on the SiC single crystal layer of the SiC bonded substrate by epitaxial growth using the CVD method, the yield of the device can be improved by reducing defects at the bonding interface, which are the starting points for crystal defects.

[0024] In particular, a stacking fault density Y of 0.55% to 1.0% can further improve the yield of the devices.

[0025] The stacking fault density (%) of a SiC polycrystalline substrate can be calculated, for example, by X-ray diffraction. In this case, the diffraction intensity ratio X = a / b is determined based on the peak intensity at 2θ = 33.6° (a) and the peak intensity at 2θ = 41.4° (b) in the X-ray diffraction profile using CuKα rays, and the stacking fault density Y of the SiC polycrystalline layer that forms the junction can be determined based on the diffraction intensity ratio X using the following equation (1).

[0026] [Formula 1] Y=X / (0.0682X+0.0227)+1.7X ３ (1)

[0027] In other words, in equation (1), X is the diffraction intensity ratio obtained from X = a / b, a is the peak intensity at 2θ = 33.6° in the X-ray diffraction profile of the SiC polycrystalline substrate using CuKα rays, and b is the peak intensity at 2θ = 41.4° in the X-ray diffraction profile of the SiC polycrystalline substrate using CuKα rays.

[0028] <Crystal Structure> Considering the difference in thermal expansion with the SiC single crystal substrate, heat resistance, and high rigidity, 3C-SiC, in which the crystal structure of the SiC polycrystalline substrate is a zincblende structure, can be adopted.

[0029] <Thickness of SiC Polycrystalline Substrate> Furthermore, if the thickness of the SiC polycrystalline substrate is reduced, the reinforcing effect that mitigates the warping of the SiC single crystal substrate weakens, which may result in problems such as transport errors that prevent the SiC bonded substrate from being transported. For this reason, the thickness of the SiC polycrystalline substrate used for the SiC bonded substrate is preferably 300 μm or more, more preferably 350 μm or more. The upper limit of the thickness of the SiC polycrystalline substrate is not particularly limited and does not affect the solution of the problems of the present invention, but it can be set to, for example, 1000 μm or less.

[0030] The SiC polycrystalline substrate 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 is removed and polishing or lapping is performed. Since the thickness of the SiC polycrystalline substrate varies before and after polishing, for example, to match the thickness of the SiC polycrystalline substrate mentioned above, the thickness before polishing (after film deposition) is approximately 750 ± 250 μm. After lapping, the thickness is approximately 400 ± 50 μm. The SiC polycrystalline substrate may be manufactured by the CVD method in an unpolished state, after polishing, or after lapping. A SiC single crystal substrate is bonded to the polished or lapped SiC polycrystalline substrate at the bonding surface, and a portion of the bonded SiC single crystal substrate, peeled or cut parallel to the bonding surface (i.e., perpendicular to the thickness direction), is transferred to the bonding surface as a SiC single crystal layer to manufacture a SiC bonded substrate having a SiC single crystal layer.

[0031] <Shape of SiC Polycrystalline Substrate> The shape of the SiC polycrystalline substrate is approximately the same as that of a SiC single crystal substrate, roughly a disc shape, and may include indicator parts that show the orientation of the substrate, such as an orientation flat or a notch. Substrates with a diameter of 100 mm to 305 mm (4 inches to 12 inches) can be used. Note that the shape is not limited to a disc shape, and may also be polygonal, for example.

[0032] [SiC Bonded Substrate] The SiC bonded substrate according to this embodiment is formed by bonding a SiC single crystal substrate to a SiC polycrystalline substrate by directly bonding it to the bonding surface. The SiC bonded substrate may also be provided on the SiC polycrystalline substrate as a SiC single crystal layer, which is obtained by peeling or cutting a portion of the bonded SiC single crystal substrate parallel to the bonding surface (perpendicular to the thickness direction).

[0033] [Method for Manufacturing SiC Bonded Substrates] The method for manufacturing the SiC bonded substrate of the present invention will now be described. This method includes the following heating, grinding, and bonding steps, and the SiC bonded substrate of the present invention can be manufactured by this method.

[0034] <Heating Process> The substrate to be heated is a SiC polycrystalline substrate before bonding with a SiC single crystal substrate. The heating process rearranges dislocations within the SiC substrate, causing relaxation of internal stress and stabilizing the SiC polycrystalline substrate. On the other hand, stacking faults are introduced due to the rearrangement of dislocations and the thermal stability of polymorphisms. If the relaxation of internal stress is insufficient, the warping of the SiC polycrystalline substrate will increase. Also, if the stacking fault density increases, defects (unbonded areas) are more likely to occur at the bonding interface of the SiC bonded substrate, as described above. Therefore, it is necessary to set heating conditions that relax internal stress and do not increase the stacking fault density.

[0035] Specifically, a SiC polycrystalline substrate is placed in a heating furnace or the like, and the SiC polycrystalline substrate is heated in an inert atmosphere to a temperature of 1750°C to 1950°C for 15 to 30 hours, or to a temperature of 1980°C to 2100°C for 5 to 15 hours.

[0036] The purpose of using an inert atmosphere is to prevent oxidation of the SiC polycrystalline substrate, and it is preferable to thoroughly remove oxygen from the heated atmosphere using argon gas, nitrogen gas, or the like.

[0037] By performing the heating step, dislocations in the SiC polycrystalline substrate rearrange, internal stress is relaxed, and the substrate is stabilized. On the other hand, while stacking faults are generated by the heating step, the stacking fault density Y can be suppressed to 1.0% or less if the temperature and time are within the above ranges.

[0038] Note that as the SiC polycrystalline substrate to be subjected to the heating step, a substrate manufactured by chemical vapor deposition may be used. Further, as described in the section [Thickness of SiC polycrystalline substrate], the SiC polycrystalline substrate can be manufactured by forming a film on a graphite support substrate, but as the SiC polycrystalline substrate to be subjected to the heating step, either before or after removing the graphite support substrate is acceptable.

[0039] As described in the item [SiC polycrystalline substrate], a disk-shaped substrate having a diameter of 100 mm or more and 305 mm or less can be used as the SiC polycrystalline substrate to be subjected to the heating step.

[0040] As described in the item [SiC polycrystalline substrate], a disk-shaped substrate having a thickness of 750±250 μm can be used as the SiC polycrystalline substrate to be subjected to the heating step. Note that the thickness of the SiC polycrystalline substrate can be set based on the thickness reduced by polishing. For example, when the thickness reduced by polishing is 100 μm, a SiC polycrystalline substrate having a thickness of 750±150 μm can be used.

[0041] Further, when heated, sublimation of the SiC polycrystalline substrate starts from around 1800°C, and a damaged layer due to sublimation is formed on the surface of the SiC polycrystalline substrate. In a state where this damaged layer remains, the surface of the SiC polycrystalline substrate before bonding to the SiC single crystal substrate becomes rough, which causes bonding defects in the bonded substrate. However, for a SiC polycrystalline substrate with a thickness of 750±250 μm, the amount of grinding of the substrate by grinding or lapping step after the heating step is large, and the damaged layer can be sufficiently removed. Therefore, it is possible to perform the heating step under a higher temperature condition than the sublimation temperature of SiC polycrystal.

[0042] Furthermore, in a SiC polycrystalline substrate with a 3C-SiC crystal structure, the peak at 2θ = 33.6° in X-ray diffraction originates from stacking faults, and the peak height increases as the number of stacking faults increases. Conversely, it is known that the peak height of the peak at 2θ = 41.4° decreases as the number of stacking faults increases. Therefore, by using a SiC polycrystalline substrate with a 3C-SiC structure, it becomes easier to determine the stacking fault density of the junction surface by performing X-ray diffraction after the heating process.

[0043] <Polishing Process> In the polishing process, the surface of at least one of the bonding surfaces of the SiC polycrystalline substrate, whose stacking fault density has been reduced to 1.0% or less by the heating process, is polished. Polishing may be performed on both the bonding surface and the other surface opposite the bonding surface. Furthermore, the polishing process may be divided into multiple steps, such as rough grinding, precision polishing, and lapping.

[0044] <Bonding Process> In the bonding process, first, the oxide film on the surface of the SiC polycrystalline substrate polished in the polishing process and the SiC single crystal substrate to be bonded is removed. The oxide film can be removed by washing the SiC polycrystalline substrate and the SiC single crystal substrate with various liquids. After the oxide film has been removed by washing, the SiC polycrystalline substrate and the SiC single crystal substrate are dried and then placed in a bonding apparatus under a vacuum atmosphere. In the bonding process, a neutral Ar atomic beam is irradiated onto the bonding surface of the SiC polycrystalline substrate and the bonding surface of the SiC single crystal substrate to remove surface contamination and oxide film, modify the bonding surface of both substrates into an amorphous layer, and create bonding bonds. Ion beams can be used instead of neutral Ar atomic beams to similarly remove surface contamination and oxide film, modify the bonding surface of both substrates into an amorphous layer, and create bonding bonds. Subsequently, the bonding surfaces of both substrates are brought into contact in the bonding apparatus and a load is applied to bond the bonding surface of the SiC polycrystalline substrate and the bonding surface of the SiC single crystal substrate. In this way, the bonded substrate according to the embodiment is manufactured.

[0045] (Other Steps) The method for producing a SiC polycrystalline substrate according to the present invention may include additional steps besides the heating step. Examples thereof include a film forming step of forming a SiC polycrystalline film on a Si supporting substrate or a graphite supporting substrate by CVD or the like, a supporting substrate removing step of removing the supporting substrate after the film forming step, and a peripheral offset chamfering step of adjusting the shape of the SiC polycrystalline substrate obtained after removing the supporting substrate. These steps may be performed before the heating step, or may be performed starting from the middle of these steps.

[0046] Hereinafter, the present invention will be described in further detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited in any way by these Examples.

[0047] In the following examples, a heating step was performed on SiC polycrystalline substrates, and the stacking fault density was measured and the product yield was evaluated.

[0048] [Heat Treatment of SiC Polycrystalline Substrate] <Specimen> The specimen used in the heating step is 3C-SiC formed by CVD, and a disk-shaped SiC polycrystalline substrate having a diameter of 6 inches and a thickness of 750±250 μm, which had no heat history such as annealing after the supporting substrate removing step, was used.

[0049] <Example 1> Three specimens were held at 1800°C for 24 hours in an annealing furnace set to an inert atmosphere with argon gas to prevent oxidation (heating step). Thereafter, the specimens were left to cool to room temperature and taken out from the annealing furnace.

[0050] <Example 2> A heating step was performed in the same manner as in Example 1 except that the holding temperature was set to 1900°C, and the specimen was taken out from the annealing furnace.

[0051] <Example 3> A heating step was performed in the same manner as in Example 1 except that the holding temperature was set to 2000°C and the holding time was set to 6 hours, and the specimen was taken out from the annealing furnace.

[0052] <Example 4> A heating step was performed in the same manner as in Example 1 except that the holding temperature was set to 2000°C and the holding time was set to 12 hours, and the specimen was taken out from the annealing furnace.

[0053] <Comparative Example 1> The heating process was carried out in the same manner as in Example 1, except that the holding time was set to 2000°C, and the product was removed from the annealing furnace.

[0054] [Stacking fault density] The stacking fault density of the test specimens of Examples 1 to 4 and Comparative Example 1 after heat treatment was calculated by X-ray diffraction measurement under the following conditions.

[0055] <X-ray diffraction measurement conditions, etc.> Measurements were performed using the 2θ / θ method with a Rigaku SmartLab. The measurement conditions were as follows: CuKα rays (Cu target), step size: 0.0070°, scanning range: 20-80°, current / voltage: 200mA, 45kV.

[0056] <Calculation of stacking fault density> Based on the X-ray diffraction profile obtained by measurement, the diffraction intensity ratio X = a / b was determined based on the peak intensity at 2θ = 33.6° (a) and the peak intensity at 2θ = 41.4° (b), and the stacking fault density Y of the junction was calculated using the above formula (1).

[0057] [Evaluation of Product Yield] Following the procedure below, the test specimens of Examples 1 to 4 and Comparative Example 1 (hereinafter sometimes collectively referred to as "SiC polycrystalline substrates") after heat treatment were polished to form bonding surfaces, and a SiC single crystal substrate was bonded to these bonding surfaces to obtain a SiC bonded substrate as a SiC single crystal layer. The product yield was then evaluated.

[0058] <Polishing of test specimens, etc.> The bonding surfaces (C-planes) of the 6-inch SiC single crystal substrate and the bonding surfaces of the 6-inch SiC polycrystalline substrate were polished to a surface roughness suitable for bonding. The surface roughness (Sa) was 0.2 nm for the bonding surface of the SiC single crystal substrate and 0.3 nm for the bonding surface of the SiC polycrystalline substrate.

[0059] The surface roughness (Sa) can be calculated from the surface roughness measured using a white light interferometer (Nexview, manufactured by Zygo). The orientation flat of the bonding surface was set to the 6 o'clock position, and the surface roughness was measured at nine points in the plane (coordinate positions X: 0 mm Y: 70 mm, X: 0 mm Y: 35 mm, X: 0 mm Y: 0 mm (center of the substrate), X: 0 mm Y: -35 mm, X: 0 mm Y: -60 mm, X: -70 mm Y: 0 mm, X: -35 mm Y: 0 mm, X: 35 mm Y: 0 mm, X: 70 mm Y: 0 mm). The average of the nine measured values ​​was calculated and this was defined as the surface roughness (Sa).

[0060] <Cleaning Process> The SiC single-crystal substrate and SiC polycrystalline substrate after polishing were cleaned according to the following procedure to remove the oxide film from the surface.

[0061] (Sulfuric acid hydrolysis) A mixture of concentrated sulfuric acid and hydrogen peroxide in a deposition ratio of 10:1 was heated to 140°C, and then the SiC single crystal substrate and SiC polycrystalline substrate were immersed in the liquid for 950 seconds.

[0062] (Warm pure water washing) After washing with sulfuric acid, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the above liquid and immersed in warm pure water at 70°C for 750 seconds.

[0063] (Pure water washing) After washing with warm pure water, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the warm pure water and immersed in pure water at room temperature (15°C to 30°C) for 600 seconds.

[0064] (Drying) After washing with pure water, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the pure water and dried by IPA vapor drying.

[0065] (SC-1 Cleaning) After drying, the SiC single crystal substrate and SiC polycrystalline substrate were immersed in SC-1 cleaning solution at 75°C for 300 seconds and ultrasonically cleaned. The SC-1 cleaning solution consisted of NH4OH water (29% by mass) and H4OH water by volume ratio. ２ O ２ It is a mixture of water (31% by mass) and DIW (ultrapure water) in a ratio of 1:4:40.

[0066] (Warm pure water washing) After SC-1 washing, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the SC-1 washing solution and immersed in 50°C warm pure water for 600 seconds.

[0067] (HF cleaning) After washing with warm pure water, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the warm pure water and immersed in HF (0.25 mass%) water at room temperature (15°C to 30°C) for 345 seconds.

[0068] (SC-2 cleaning) After HF cleaning, the SiC single crystal substrate and SiC polycrystalline substrate were immersed in SC-2 cleaning solution at 75°C for 600 seconds and ultrasonically cleaned. The SC-2 cleaning solution was a mixture of HCl water (29% by mass): H2O2 water (31% by mass): DIW (ultrapure water) in a volume ratio of 1:1:6.

[0069] (Warm pure water washing) After SC-2 washing, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the SC-2 washing solution and immersed in 50°C warm pure water for 600 seconds.

[0070] (Pure water washing) After washing with warm pure water, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the warm pure water and immersed in pure water at room temperature (15°C to 30°C) for 300 seconds.

[0071] (Drying) After washing with pure water, the SiC single crystal substrate and SiC polycrystalline substrate were removed from the pure water and dried by IPA vapor drying.

[0072] <Manufacturing of bonded substrates> Bonded substrates were manufactured according to the following procedure.

[0073] <Hydrogen Ion Implantation> After polishing, the oxide film was washed away, and hydrogen ion implantation was performed on the first bonding surface (C-plane) of the SiC single crystal substrate. The implantation energy was controlled to form an implanted layer at a depth of approximately 0.6 μm from the surface of the first bonding surface.

[0074] <Irradiation Process> After storage in the atmosphere, the SiC single-crystal substrate and SiC polycrystalline substrate were placed in a bonding apparatus (MWB-06-AX-FAB, manufactured by NIDEK Machine Tools Co., Ltd.) and vacuumed. After vacuuming, a neutral Ar atomic beam was irradiated onto the bonding surface of both substrates using a Fast Atom Beam gun (hereinafter abbreviated as FAB gun) inside the bonding apparatus to remove contamination and oxide films from their surfaces, modify the bonding surface of both substrates into an amorphous layer, and create bonding bonds. The amount of neutral Ar atomic beam irradiation was controlled by the acceleration voltage, current value, and irradiation time of the FAB gun, with the following parameters: acceleration voltage: 0.9 kV, current value: 30 mA, and irradiation time: 150 seconds, respectively.

[0075] <Bonding Process> After irradiation with a neutral Ar atomic beam, the bonding surfaces of both substrates were brought into contact within the bonding apparatus, and a load of 45 kN was applied to bond them. The vacuum level in the process chamber of the bonding apparatus from immediately before irradiation with the neutral Ar atomic beam until during the bonding process was 0.7E. －５ Pa (0.7 × 10) －５ The temperature was Pa, and the time lag from the completion of irradiation with a neutral Ar atomic beam to the contact of the bonding surfaces was 30 seconds.

[0076] <Removal process> The substrate after bonding is N ２ The substrate was heat-treated at 1100°C in an atmosphere to recrystallize the amorphous layer at the bonding interface, and then exfoliated using a hydrogen ion implantation layer to obtain a bonded substrate in which a SiC single crystal layer approximately 0.6 μm thick was formed (transferred) onto a SiC polycrystalline support substrate.

[0077] <Heat Treatment Process> The bonded substrates after the delamination process were further heat-treated at 1700°C in an Ar atmosphere.

[0078] <Surface Polishing> The surface of the SiC single crystal layer on the bonded substrate was polished to make it smooth so that the surface on which the epitaxial film would be deposited in a later process would be smooth.

[0079] [Evaluation Results of Product Yield] Table 1 shows the evaluation results of the heat treatment conditions, stacking fault density Y, and product yield. Figure 1 shows a graph illustrating the effect of stacking fault density on product yield when held at 1800°C, 1900°C, and 2000°C for 24 hours (Example 1, Example 2, Comparative Example 1). Product yield is the ratio of good products to the total number of products manufactured. The result for Example 2, which had the highest product yield, is set to 100%, and the other examples are shown as relative values.

[0080]

[0081] Table 1 and Figure 1 show that when the stacking fault density Y of the SiC polycrystalline substrate was 1.0% or less, the product yield was good. On the other hand, when the stacking fault density Y of the SiC polycrystalline substrate exceeded 1.0%, the number of bonding defects in the SiC bonded substrate increased, resulting in a decrease in product yield.

Claims

1. A SiC polycrystalline substrate characterized by having a bonding surface for bonding with a SiC single crystal substrate, wherein the stacking fault density of the bonding surface is 1.0% or less.

2. The SiC polycrystalline substrate according to claim 1, characterized in that the stacking fault density is determined based on the ratio of the first peak intensity at 2θ = 33.6° and the second peak intensity at 2θ = 41.4° in the X-ray diffraction profile of the SiC polycrystalline substrate using CuKα rays.

3. The SiC polycrystalline substrate according to claim 1, wherein the crystal structure is 3C-SiC.

4. The SiC polycrystalline substrate according to claim 1, having a disc shape with a diameter of 100 mm or more and 305 mm or less.

5. The SiC polycrystalline substrate according to claim 1, wherein the thickness is 300 μm or more and 1000 μm or less.

6. A SiC bonded substrate comprising: a SiC polycrystalline substrate as described in claim 1; and a SiC single crystal substrate bonded to the bonding surface.

7. A method for manufacturing a SiC bonded substrate, comprising: a heating step of heating the SiC polycrystalline substrate in an inert atmosphere by holding it at a temperature of 1750°C to 1950°C for 15 to 30 hours, or at a temperature of 1980°C to 2100°C for 5 to 15 hours; a polishing step of polishing one side of the SiC polycrystalline substrate, which is the bonding surface; and a bonding step of removing the oxide film from the surface of the polished bonding surface and bonding it with a SiC single crystal substrate in a vacuum atmosphere.

8. The method for manufacturing a SiC bonded substrate according to claim 7, wherein the SiC polycrystalline substrate subjected to the heating step is disc-shaped with a diameter of 100 mm or more and 305 mm or less.

9. The method for manufacturing a SiC bonded substrate according to claim 7, wherein the SiC polycrystalline substrate subjected to the heating step has a thickness of 750 ± 250 μm.

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