Substrate for silicon carbide epitaxial growth, method for manufacturing same, and method for manufacturing semiconductor device

Abstract

To provide a substrate for silicon carbide epitaxial growth in which warpage or the like caused by a difference in thermal expansion coefficient can be avoided, a support substrate and a seed crystal layer are easily joined, and which can withstand a high temperature in an epitaxial growth process, and to provide a method of manufacturing the same and a method of manufacturing a semiconductor device.SOLUTION: A substrate 1 for SiC epitaxial growth sequentially includes a support substrate 20 having a thermal expansion coefficient approximately equal to that of a SiC epitaxial film, a bonding layer 12 having a melting point of 1800 °C or higher, and a seed crystal layer 14 of single crystal SiC. In the manufacturing method, a bonding layer is formed on a bonding surface of single crystal SiC, ion implantation is performed to form an ion implantation interface, the single crystal SiC and a support substrate are bonded to each other via the bonding layer, and then the single crystal SiC is separated and delaminated at the ion implantation interface to transfer a thin film of a part of the single crystal SiC as a seed crystal layer to the support substrate side. In the method of manufacturing a semiconductor device, a SiC epitaxial film is grown using the growth substrate 1, and a device structure is formed on the SiC epitaxial film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silicon carbide epitaxial growth substrate, a method for manufacturing the same, and a method for manufacturing a semiconductor device, and more particularly to a silicon carbide epitaxial growth substrate that can be used in the manufacture of semiconductor devices such as vertical power devices (MOS-FETs), a method for manufacturing the same, and a method for manufacturing a semiconductor device. [Background technology]

[0002] Currently, single-crystal silicon (Si) substrates are widely used as semiconductor substrates. However, due to their characteristics, they are not necessarily suitable for the recent trend toward higher voltages and higher frequencies. Therefore, although more expensive, single-crystal silicon carbide (SiC) and single-crystal gallium nitride (GaN) substrates are beginning to be used. For example, by using semiconductor elements made of SiC, a semiconductor material with a wider bandgap than silicon, to construct power conversion devices such as inverters and AC / DC converters, it is possible to achieve a reduction in power loss that is not possible with silicon-based semiconductor elements. The use of SiC semiconductor elements not only reduces the losses associated with power conversion compared to conventional devices, but also promotes lighter, more compact, and more reliable devices. Single-crystal SiC substrates are also being considered as a raw material for nanocarbon thin films (including graphene) as a next-generation device material.

[0003] These single-crystal SiC substrates and single-crystal GaN substrates are typically manufactured by (1) using the SiC sublimation method, in which high-purity SiC powder is sublimated at temperatures above 2000°C to grow seed crystals, and (2) using a method in which GaN seed crystals are grown in high-temperature, high-pressure ammonia, or by heteroepitaxially growing GaN on a sapphire or single-crystal SiC substrate. However, the manufacturing process is complex and requires extremely strict conditions, which inevitably results in low substrate quality and yield, resulting in very high costs and hindering practical application and widespread use.

[0004] In any case, the thickness of these substrates that actually exhibits device functions is 0.5 to 100 μm, and the remaining thickness is the so-called handle member (substrate), which mainly serves the role of mechanically holding and protecting the substrate when it is handled.

[0005] In recent years, SiC composite substrates have been investigated, in which a single-crystal SiC layer, relatively thin enough to be handled, is bonded to a polycrystalline SiC substrate via ceramics such as silicon oxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (Zr2O3), silicon nitride (Si3N4), or aluminum nitride (AlN), or metals such as Si, titanium (Ti), nickel (Ni), copper (Cu), gold (Au), silver (Ag), cobalt (Co), zirconium (Zr), molybdenum (Mo), or tungsten (W). However, when using ceramics as the intermediary between the single-crystal SiC layer and the polycrystalline SiC substrate, it is difficult to fabricate electrodes during device fabrication because they are insulators, and when using metals, metal impurities are likely to be mixed into the device, causing degradation of device characteristics, making this method impractical.

[0006] Therefore, various proposals have been made to overcome these drawbacks. For example, Japanese Patent No. 5051962 (Patent Document 1) discloses a method in which a source substrate having, from the surface, an SiO2 bonding layer and a single-crystal SiC thin film, and having been implanted with ions such as hydrogen, is bonded to a polycrystalline AlN intermediate support having an SiO2 bonding layer, with the SiO2 bonding layers bonded together; the single-crystal SiC thin film is transferred to the polycrystalline AlN; polycrystalline SiC is then deposited on the single-crystal SiC thin film, and the substrate is then placed in a hydrogen fluoride (HF) bath to dissolve the SiO2 bonding layer and separate the single-crystal SiC thin film and the polycrystalline AlN.

[0007] Furthermore, Japanese Patent Application Laid-Open Publication No. 2015-15401 (Patent Document 2) discloses a method for providing a semiconductor substrate without forming an oxide film at the bonding interface, even for substrates whose surfaces are difficult to flatten, by modifying the surface of a polycrystalline SiC support substrate to be amorphous using a fast atomic beam and also modifying the surface of a semiconductor single-crystal SiC to be amorphous, and then bringing the two into contact and performing thermal bonding, thereby stacking a single-crystal SiC layer with high bonding strength on the polycrystalline SiC support substrate.

[0008] Furthermore, Japanese Patent No. 6206786 (Patent Document 3) discloses a method in which a single-crystal layer of a single-crystal SiC thin film is integrated onto a polycrystalline SiC support substrate by direct bonding, and the occurrence of non-ohmic conductive properties at the bonding interface is suppressed by doping with impurities. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5051962 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-15401 [Patent Document 3] Patent No. 6206786 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the method of Patent Document 1 has the drawback that the SiO2 bonding layer is usually very tightly bonded, so HF does not easily penetrate the entire surface of the SiO2 bonding layer, especially the center, making separation difficult, requiring a long time, and resulting in extremely poor productivity. Furthermore, when manufacturing large-diameter SiC composite substrates using this method, there is a problem of significant warping due to the difference in thermal expansion coefficients between the polycrystalline SiC in the deposition layer and the aluminum nitride in the intermediate support.

[0011] Furthermore, in the method of Patent Document 2, not only the exfoliated interface of the single-crystal SiC but also some of the interior of the crystal is altered by the high-speed atomic beam, so that the single-crystal SiC does not recover to a good quality even after subsequent heat treatment. This has the drawback that when used as a device substrate or template, it is difficult to obtain a high-performance device or a good-quality SiC epitaxial film.

[0012] The method of Patent Document 3 can reduce costs compared to conventional methods for manufacturing single-crystal SiC substrates, but has the problem that a back-grinding process is required after growing an epitaxial layer on a single-crystal layer and forming a semiconductor device on this epitaxial layer.

[0013] In addition to these drawbacks, the conventional technology described above requires smoothness at the bonding interface, with a surface roughness Ra (arithmetic mean surface roughness) of 1 nm or less, in order to bond single-crystal SiC and polycrystalline SiC. However, SiC is considered to be the second most difficult material to cut after diamond, and even if the surface of single-crystal SiC is modified to be amorphous, the smoothing process, which involves grinding and chemical mechanical polishing (CMP), requires an extremely long time and inevitably increases costs. In addition, because polycrystalline SiC has grain boundaries, it is difficult to uniformly amorphize the surface using a high-speed atomic beam, which causes problems with bonding strength and warping, which are major obstacles to practical application.

[0014] In view of the above problems, the present invention aims to provide a silicon carbide epitaxial growth substrate that can avoid problems of warping and cracking due to differences in thermal expansion coefficients, that facilitates bonding between a support substrate and a seed crystal layer, and that can withstand the high temperatures present in the epitaxial growth process, as well as a method for manufacturing the same and a method for manufacturing a semiconductor device. [Means for solving the problem]

[0015] In order to achieve the above object, one aspect of the present invention is a substrate for silicon carbide epitaxial growth, comprising: a support substrate having a thermal expansion coefficient that is approximately the same as that of a silicon carbide epitaxial film; a bonding layer having a melting point of 1800°C or higher and provided on at least one surface of the support substrate; and a seed crystal layer of single-crystal silicon carbide provided on the surface of the bonding layer.

[0016] The bonding layer preferably comprises aluminum oxide, silicon nitride, aluminum oxynitride, silicon oxynitride, zinc oxide, or a combination thereof.

[0017] The seed crystal layer is preferably made of n-type single crystal silicon carbide, the surface of which is a (0001) Si plane and which has an off angle of 0.5° to 10° relative to the surface.

[0018] The support substrate is preferably made of polycrystalline silicon carbide, and is preferably made of silicon carbide ceramics having crystal grains with an average grain size of 1 μm or less.

[0019] In yet another aspect, the present invention is a method for manufacturing a substrate for silicon carbide epitaxial growth, comprising the steps of: preparing a support substrate having a thermal expansion coefficient substantially matching that of a silicon carbide epitaxial film; forming a bonding layer having a melting point of 1800°C or higher on at least one of a bonding surface of the single crystal silicon carbide and a bonding surface of the support substrate; implanting ions into the bonding surface of the single crystal silicon carbide to form an ion-implanted interface in the single crystal silicon carbide; bonding the bonding surface of the single crystal silicon carbide to the bonding surface of the support substrate via the bonding layer; and separating and peeling the single crystal silicon carbide at the ion-implanted interface to transfer a portion of the single crystal silicon carbide as a seed crystal layer onto the support substrate.

[0020] Preferably, the surface of the bonding layer is polished before the bonding step to have a surface roughness Rms of 0.5 nm or less, and the bonding step is preferably performed by plasma bonding, room temperature bonding, or vacuum bonding.

[0021] In yet another aspect, the present invention is a method for manufacturing a semiconductor device, the method including: a silicon carbide epitaxial growth substrate including a support substrate having a thermal expansion coefficient substantially matching that of a silicon carbide epitaxial film; a bonding layer provided on one surface of the support substrate and having a melting point of 1800°C or higher; and a seed crystal layer of single-crystal silicon carbide provided on the surface of the bonding layer; growing a silicon carbide epitaxial film on the surface of the seed crystal layer; forming a semiconductor device structure including an electrode on the silicon carbide epitaxial film; selectively removing the bonding layer to separate the silicon carbide epitaxial film having the semiconductor device structure from the support substrate; and forming a back surface electrode on the silicon carbide epitaxial film having the semiconductor device structure.

[0022] The separated support substrate is preferably reused in the manufacture of the silicon carbide epitaxial growth substrate. [Effects of the Invention]

[0023] The silicon carbide epitaxial growth substrate according to the present invention uses a support substrate having a thermal expansion coefficient that is approximately the same as that of the silicon carbide epitaxial film, thereby avoiding problems such as warping and cracking due to the difference in thermal expansion coefficients, and can be applied to the manufacturing process of semiconductor devices requiring high precision. Furthermore, by using a bonding layer having a melting point of 1800°C or higher to bond the support substrate and the seed crystal layer, it is not necessary to smooth the bonding surfaces to atomic order (Å order) for bonding, and the bond between the support substrate and the seed crystal layer can be maintained during the epitaxial growth process at temperatures up to 1800°C.

[0024] In addition to the above-described effects, the method for manufacturing a silicon carbide epitaxial growth substrate according to the present invention allows a thin seed crystal layer to be formed by peeling a thin film from a bulk wafer of single crystal SiC and transferring it to a support substrate, thereby significantly reducing costs. Furthermore, the single crystal SiC separated and removed by thin film transfer can be reused to form seed crystal layers, which also significantly reduces costs.

[0025] Furthermore, according to the method for manufacturing a semiconductor device of the present invention, the support substrate can be easily separated from the silicon carbide epitaxial film having the semiconductor device structure by selectively removing the bonding layer by chemical etching or the like, thereby eliminating the need to mechanically remove the support substrate such as a SiC substrate as in the conventional method, and the separated support substrate can be reused to manufacture a growth substrate, thereby significantly reducing costs. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view schematically showing one embodiment of a silicon carbide epitaxial growth substrate according to the present invention. [Figure 2] 1 is a cross-sectional view for schematically explaining one embodiment of a method for manufacturing a silicon carbide epitaxial growth substrate according to the present invention; [Figure 3] 1 is a cross-sectional view for schematically explaining one embodiment of a method for manufacturing a silicon carbide epitaxial growth substrate and a method for manufacturing a semiconductor device according to the present invention. [Figure 4] 1A to 1C are cross-sectional views for schematically explaining an embodiment of a method for manufacturing a semiconductor device according to the present invention. [Figure 5] 1 is a cross-sectional view for schematically explaining the configuration of the bonding layer in Examples 1 and 2. FIG. [Figure 6] 1 is a cross-sectional view for schematically explaining the configuration of the bonding layer in Examples 3 to 5. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of a silicon carbide (SiC) epitaxial growth substrate, a manufacturing method thereof, and a manufacturing method of a semiconductor device according to the present invention will be described with reference to the accompanying drawings, but the present invention is not limited thereto.

[0028] [1. SiC epitaxial growth substrate] Fig. 1 is a cross-sectional view schematically illustrating one embodiment of a SiC epitaxial growth substrate according to the present invention. As shown in Fig. 1, the SiC epitaxial growth substrate 1 (hereinafter simply referred to as "growth substrate") of this embodiment includes a support substrate 20 having a thermal expansion coefficient substantially equal to that of the SiC epitaxial film, a bonding layer 12 provided on one surface of the support substrate 20 and having a melting point of 1800°C or higher, and a seed crystal layer 14 of single-crystal SiC provided on the surface of the bonding layer 12. Note that this embodiment describes a case in which the SiC epitaxial film obtained using the growth substrate 1 is a film for a vertical power device (MOS-FET), but the present invention is not limited thereto.

[0029] The single-crystal SiC of the seed crystal layer 14 can be of various polytypes, such as 4H-SiC, 6H-SiC, and 3C-SiC. The surface of the seed crystal layer 14 on which SiC epitaxial growth is performed is preferably the (0001) Si plane, which facilitates the formation of a SiC epitaxial film and tends to result in a flat SiC epitaxial film, but may also be the (000-1) C plane. The single-crystal SiC of the seed crystal layer 14 preferably has an off-angle of 0.5° to 10° with respect to the main surface. This allows the SiC epitaxial film formed on the seed crystal layer 14 to grow in a step-flow mode. If a smaller off-angle is required, a 10° off-angle substrate may be cut from a 0.5° off-angle substrate. Furthermore, it is preferable to use n-type single-crystal SiC.

[0030] The thickness of the seed crystal layer 14 can be thin without any problem because it is bonded to the support substrate 20 by the bonding layer 12, and is preferably 0.04 μm to 1.0 μm, and more preferably 0.1 μm to 0.8 μm, but can be appropriately set depending on the structure and type of semiconductor device to be formed on the SiC epitaxial film. The size of the seed crystal layer 14, as with the support substrate 20 described below, is set based on the size and cost required for manufacturing the semiconductor device and growing the SiC epitaxial film, and can be, for example, 2 inches to 12 inches in diameter.

[0031] The conductivity of the seed crystal layer 14 can be selected to be conductive or non-conductive depending on the structure and type of device to be formed on the SiC epitaxial film. For example, low resistivity (approximately 20 mΩcm) or high resistivity (approximately 1.0×10 6 Ωcm or more).

[0032] For example, in a vertical MOS-FET, the seed crystal layer 14 is made conductive, an SiC epitaxial film is grown, and the device is formed. After that, the device can be used with the growth substrate 1 attached. In this case, the seed crystal layer 14 is used to form the drain electrode, so the seed crystal layer 14 is preferably thick to reduce lateral resistance, and a thickness of 300 nm or more is suitable. Furthermore, to facilitate ohmic contact, the resistivity of the seed crystal layer 14 is preferably reduced to approximately 0.01 to 0.03 Ω cm.

[0033] On the other hand, in a vertical MOS-FET, the seed crystal layer 14 can be made high resistivity, semi-insulating, or insulating. After forming a device on the SiC epitaxial film, the device layer portion, which is the portion closer to the SiC epitaxial film than the seed crystal layer 14, can be separated and used as a device. In this case, the seed crystal layer is preferably thin since it will be removed, and a thickness of less than 300 nm is suitable, for example. For devices such as RF devices (high frequency devices) where current should not flow below the device, a semi-insulating seed crystal layer 14 is preferred.

[0034] The support substrate 20 is not particularly limited as long as it has a thermal expansion coefficient that is approximately the same as that of the SiC epitaxial film. However, it is preferable that the support substrate 20 is resistant to the thermal process used in the SiC epitaxial growth and is free from the risk of metal contamination. For example, polycrystalline or single-crystalline SiC is preferably used for such a support substrate 20. Various polytypes of polycrystalline SiC may be mixed. For example, polycrystalline SiC is preferably CVD-SiC formed by chemical vapor deposition (CVD) or SiC ceramics made by sintering SiC powder. In the case of SiC ceramics, it is preferable to use one having crystal grains with an average grain size of 1 μm or less. The lower limit of the average grain size is not particularly limited, but it may be, for example, 0.01 μm or more.

[0035] The thickness of the support substrate 20 is preferably 100 μm or more and 650 μm or less, more preferably 200 μm or more and 600 μm or less, and even more preferably 200 μm or more and 500 μm or less.

[0036] The growth substrate 20 is preferably adjusted so that the bow amount is −50 μm or more and 75 μm or less, more preferably −50 μm or more and 50 μm or less. If the bow amount of the growth substrate is −50 μm or more and 75 μm or less, the growth substrate can be fixed to a vacuum chuck or electrostatic chuck in a manufacturing apparatus during a semiconductor device manufacturing process, and if the bow amount is −50 μm or more and 50 μm or less, the growth substrate can be fixed to a vacuum chuck or electrostatic chuck in a manufacturing apparatus during a semiconductor device manufacturing process without any problems.

[0037] The bonding layer 12 must not only firmly bond the support substrate 20 and the seed crystal layer 14, but also be able to withstand the high temperatures of SiC epitaxial growth. Examples of such materials include ceramic materials with a melting point of 1800°C or higher, such as aluminum oxide (Al2O3), silicon nitride (Si3N4), aluminum oxynitride (AlON), silicon oxynitride (SiON), and zinc oxide (ZnO). The upper limit of the melting point of the material used for the bonding layer 12 is not particularly limited, but may be, for example, 2200°C. The bonding layer 12 may be a single layer or multiple layers. In the case of multiple layers, the above materials may be used in combination.

[0038] The thickness of the bonding layer 12 is, for example, preferably 0.010 μm or more and 1.0 μm or less, and more preferably 0.015 μm or more and 0.8 μm or less. Note that, although Fig. 1 shows the case where the bonding layer 12 is provided only between the support substrate 20 and the seed crystal layer 14, i.e., on one surface of the support substrate 20, the present invention is not limited thereto, and the bonding layer 12 may be provided on both surfaces of the support substrate 20, or may be provided so as to enclose the entire support substrate 20.

[0039] [2. Method for manufacturing a SiC epitaxial growth substrate and a semiconductor device] 2 to 4 are cross-sectional views that schematically show an embodiment of a method for manufacturing a SiC epitaxial growth substrate and a method for manufacturing a semiconductor device according to the present invention.

[0040] 2(a) to 3(a), the method for manufacturing a SiC epitaxial growth substrate according to this embodiment includes the steps of preparing single crystal SiC 10 to serve as a seed crystal layer for the growth substrate, forming bonding layers 12 and 22, each having a melting point of 1800°C or higher, on bonding surface 11 of single crystal SiC 10 and bonding surface 20 of support substrate 20, implanting ion species X into bonding surface 11 of single crystal SiC 10 to form separation position 13, bonding single crystal SiC 10 and support substrate 20 via bonding layers 12 and 22 to form bonded substrate 3, and separating and peeling single crystal SiC 10 at separation position 13 to transfer a portion of single crystal SiC 10 to support substrate 20 as seed crystal layer 14, thereby obtaining a SiC epitaxial growth substrate 1. These steps are described below, but the materials of each component have already been described and will not be described here.

[0041] First, as shown in Figure 2(a), single crystal SiC 10 is prepared to serve as the seed crystal layer of the growth substrate. The single crystal SiC 10 can be in the form of either a substrate or an ingot. From the standpoint of handling, it is preferable that the thickness of the single crystal SiC 10 be close to the substrate thickness specified by the SEMI or JEIDA standards. Single crystal SiC 10 can be produced by sublimation, but commercially available SiC substrates, such as those commercially available for power devices, can also be used. It is preferable to use single crystal SiC 10 whose surface has been finish-polished by chemical mechanical polishing (CMP) to ensure a flat and smooth surface.

[0042] 2(b) and 2(c), bonding layers 12 and 22 are formed on the bonding surface 11 of the single crystal SiC 10 and the bonding surface of the support substrate 20, respectively. Note that it is preferable to use the C-plane of the single crystal SiC 10 as the bonding surface 11. The bonding layers 12 and 22 may be formed by any film formation method that can form the layers with good adhesion to the single crystal SiC 10, such as atomic layer deposition (ALD), low pressure chemical vapor deposition (LPCVD), sputtering, etc.

[0043] After forming the bonding layers 12 and 22, it is preferable to perform a thermal stabilization treatment. In the thermal stabilization treatment, the layers are baked at a temperature of, for example, 1000 to 1300°C. Furthermore, it is preferable to perform a planarization treatment on the bonding layers 12 and 22 by polishing the surfaces using a known polishing method such as CMP to make them smooth. The thickness of the bonding layers 12 and 22 after polishing is preferably, for example, 0.010 μm or more and 1.0 μm or less. Furthermore, to improve the adhesion at the bonding interface of the bonding layers 12 and 22, it is preferable to set the surface roughness Rms (root mean square roughness) of the bonding layers 12 and 22 to 0.5 nm or less.

[0044] In Figures 2(b) and (c), bonding layers 12, 22 are formed on both the single crystal SiC 10 and the support substrate 20, but the present invention is not limited to this. For example, the single crystal SiC 10 and the support substrate 20 can be sufficiently bonded together in the same way by simply forming bonding layer 12 on the bonding surface 11 of the single crystal SiC 10 in Figure 2(b) or by simply forming bonding layer 22 on the bonding surface of the support substrate 20 in Figure 2(c).

[0045] As shown in FIG. 2(d), ion species X are implanted into the bonding surface 11 of the single crystal SiC 10. This allows an ion-implanted interface 13 for the thin film transfer method to be formed at the depth of the single crystal SiC 10 where the ion species X is implanted. The ion species X may be, for example, hydrogen ions (H + ) is preferably used. The ion acceleration voltage is preferably 50 KeV to 200 KeV. The ion implantation depth, i.e., the position of the ion implantation interface 13, can be changed by adjusting the acceleration voltage. The ion implantation depth is preferably 100 nm to 2000 nm, and more preferably 100 nm to 1000 nm. This ion implantation depth roughly corresponds to the thickness of the seed crystal layer 14 of the SiC epitaxial growth substrate 1 to be obtained.

[0046] 2, ion implantation is performed after forming bonding layer 12 on single crystal SiC 10, but the present invention is not limited to this, and ion implantation may be performed before forming bonding layer 12. However, performing ion implantation after forming bonding layer 12 on single crystal SiC 10 is preferable because it has the effect of suppressing channeling of implanted ions during ion implantation.

[0047] 2(e), bonding layer 12 formed on bonding surface 11 of ion-implanted single crystal SiC 10 is bonded to bonding layer 22 of support substrate 20 to form bonded substrate 3. Note that, before bonding, surface activation treatment may be performed on both the bonding surfaces of single crystal SiC 10 and support substrate 20. The surface activation treatment is not particularly limited as long as it can activate the bonding surfaces, and examples include plasma activation treatment, vacuum ion beam treatment, ozone water treatment, and UV ozone treatment. The atmosphere for the surface activation treatment can be an inert gas such as nitrogen or argon, or oxygen, either alone or in combination.

[0048] The bonding of the single crystal SiC 10 and the support substrate 20 via the bonding layers 12 and 22 may be performed at room temperature or under heating, or may be performed in air, an inert gas, or a vacuum atmosphere. Preferred bonding methods include plasma bonding, room-temperature bonding, and vacuum bonding, which can eliminate voids. The bonded substrate 3 of the single crystal SiC 10 and the support substrate 20 bonded together via the bonding layers 12 and 22 in this manner may be subjected to a heat treatment, which can increase the bonding strength.

[0049] Next, as shown in FIG. 2(f), the single crystal SiC 10 is separated and peeled at the ion-implanted interface 13, and the remaining portion is thin-film transferred to the support substrate 20 as a seed crystal layer 14. Thin-film transfer can be performed, for example, by heat-treating the bonded substrate 3, which causes separation and peeling of the single crystal SiC 10 starting from the ion-implanted interface 13. The peeling may be performed by applying a mechanical impact with a wedge-shaped blade or the like. The single crystal SiC separated and removed by thin-film transfer can be reused to form a bonding layer and ion-implant the single crystal SiC to form a seed crystal layer by thin-film transfer, which is extremely economical.

[0050] Furthermore, since the ion-implanted interface 13 appears as the surface due to the thin-film transfer, surface polishing such as CMP or etching with a chemical solution or gas such as HF is performed to remove damaged portions caused by the peeling from the seed crystal layer 14 and flatten the surface. As a result, the thickness of the seed crystal layer 14 is set to, for example, 0.04 μm or more and 1.0 μm or less, as described above. In this way, a seed crystal layer 14 of single crystal SiC having the minimum necessary film thickness, which determines the characteristics of the SiC epitaxial growth substrate 1, is obtained, and therefore a SiC epitaxial growth substrate 1 with high characteristics can be produced economically.

[0051] Furthermore, since damaged portions of the seed crystal layer 14 due to ion implantation become crystal defects in the SiC epitaxial film, it is preferable to perform heat treatment to recover them. The heat treatment is preferably performed in an atmosphere of an inert gas such as nitrogen or argon, oxygen, hydrogen, or vacuum, and the temperature is preferably 1000 to 1300°C.

[0052] 3 and 4, the method for manufacturing a semiconductor device according to the present embodiment includes the steps of growing a SiC epitaxial film 30 on the surface of the seed crystal layer 14 of the SiC epitaxial growth substrate 1, forming a semiconductor device structure having an electrode on the SiC epitaxial film 30, selectively removing the bonding layer 12 to separate the SiC epitaxial film 30 having the semiconductor device structure from the support substrate 20, and forming a backside electrode 70 on the silicon carbide epitaxial film having the semiconductor device structure. These steps are described below.

[0053] First, as shown in Fig. 3(g), an SiC epitaxial film 30 is grown on the surface of the seed crystal layer 14 of the growth substrate 1. The SiC epitaxial film 30 can be formed by, for example, a CVD method. The thickness of the SiC epitaxial film 30 varies depending on the structure and type of the device, but can be formed to a thickness of, for example, 5 to 30 µm.

[0054] Then, in order to form a desired semiconductor device structure in the SiC epitaxial film 30, first, the conductivity type is changed by ion implantation or the like into the SiC epitaxial film 30. The conductivity type can be changed, for example, by forming a mask with a predetermined pattern on the outermost surface of the SiC epitaxial film 30 by photolithography and then implanting p-type or n-type ions into the mask openings. After the ion implantation, crystal recovery can be achieved by performing high-temperature heat treatment in an inert gas atmosphere such as argon.

[0055] 3(h), an insulating layer 40 such as a gate insulating film or an interlayer insulating film is formed on the outermost surface of the SiC epitaxial film 30. The insulating layer 40 can be formed, for example, by forming a mask with a predetermined pattern on the outermost surface of the SiC epitaxial film 30 by photolithography, and then forming the insulating layer 40 of SiO2 or the like in the openings of the mask by sputtering or the like.

[0056] 3(i), the insulating layer 40, the SiC epitaxial film 30, and the seed crystal layer 14 are removed in a predetermined pattern to separate the elements. This can be done, for example, by forming a mask with a predetermined pattern by photolithography and removing the insulating layer 40, the SiC epitaxial film 30, and the seed crystal layer 14 in the mask openings by dry etching.

[0057] Then, as shown in FIG. 3(j), an electrode layer 50 including a source electrode and a gate electrode is formed on the surface of the insulating layer 40. The electrode layer 50 can be formed, for example, by forming a mask with a predetermined pattern by photography and forming the source electrode and the gate electrode in the mask openings. These electrodes can be made of, for example, Al or Ti. This allows a semiconductor device structure with electrodes to be formed on the SiC epitaxial film 30.

[0058] In the method for manufacturing a semiconductor device using growth substrate 1 of this embodiment, as described above, the device can be used without separating support substrate 20, and therefore, by the above steps, a vertical MOS-FET semiconductor device 5A including SiC epitaxial film 30 having a semiconductor device structure can be fabricated.

[0059] As described above, the support substrate 20 can be separated and used as a device. In this case, as shown in Fig. 4(k), a temporary support 60 is adhered to the electrode layer 50. As the temporary support 60, for example, a resin film can be used.

[0060] 4(l), the bonding layers 12, 22 can be selectively removed by chemical etching or the like, thereby separating the bonding layers 12, 22 and the support substrate 20 from the device layer portion, which is the portion of the seed crystal layer 14 on the SiC epitaxial film 30 side. There are no particular limitations on the chemical etching method as long as it dissolves the bonding layers 12, 22. For example, immersion in an HF aqueous solution or a potassium hydroxide (KOH) aqueous solution can dissolve the bonding layers 12, 22, allowing the support substrate 20 to be separated from the device layer portion.

[0061] 4(m), an ohmic metal (not shown) such as Ni is formed on the seed crystal layer 14 of the separated device layer portion, and an ohmic electrode is formed by RTA (rapid thermal annealing) in an atmosphere such as argon. Then, a back electrode 70 of Au or Ag is formed on the surface by sputtering, and heat treatment is performed in an atmosphere such as N or H. When separating the support substrate 20, not only the bonding layers 12 and 22 but also the seed crystal layer 14 may be removed. In this case, the ohmic electrode and the back electrode 70 can be formed on the exposed surface of the SiC epitaxial film 30.

[0062] Furthermore, as shown in FIG. 4(n), a device substrate 80 on which an electronic circuit has been formed is bonded to the back electrode 70 side. Then, as shown in FIG. 4(o), the temporary support 60 is removed, thereby fabricating a vertical MOS-FET semiconductor device 5B. Note that although the present embodiment has been described with reference to a vertical MOS-FET, the present invention is not limited to this and can also be applied to the manufacture of, for example, a Schottky barrier diode. [Example]

[0063] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0064] [Example 1] (Fabrication of substrates for SiC epitaxial growth) The support substrate was a 3C-SiC ceramic substrate made by sintering SiC powder with an average particle size of 1 μm. The single-crystal SiC to be bonded to this support substrate was an n-type single-crystal SiC substrate with a 4H-SiC (000-1) C-plane and a 4° bias toward the [11-20] orientation. Hydrogen ions were irradiated onto the C-plane of this single-crystal SiC substrate at 95 keV to a depth of 0.5 μm and a dose of 6 × 10 17 cm -2 The ions were implanted under the following conditions.

[0065] 5, an Al2O3 layer having a thickness of 60 nm was deposited by ALD on both the ion-implanted surface of the single-crystal SiC substrate 10 and the bonding surface of the support substrate 20 as bonding layers 12, 22. After annealing at 1000°C, the surface of the Al2O3 layer was polished by CMP to achieve a planarization process with a thickness of 30 nm and a surface roughness Rms (root mean square roughness) of 0.5 nm.

[0066] The bonding layer of the single-crystal SiC substrate and the bonding layer of the support substrate prepared in this manner were bonded at room temperature in an air atmosphere to obtain a bonded substrate. Then, by peeling and separating at the ion-implanted interface (position at an ion implantation depth of 0.5 μm), a portion of the single-crystal SiC substrate was thin-film transferred to the support substrate as a seed crystal layer. This transferred single-crystal SiC seed crystal layer was thinned to a thickness of 0.38 μm by CMP polishing and HF etching. Furthermore, to repair damage caused by ion implantation to the seed crystal layer, a heat treatment was performed at 1000°C in a hydrogen atmosphere. In this way, a SiC epitaxial growth substrate with an Al2O3 bonding layer was produced.

[0067] When the obtained growth substrate was inspected, it was found that the adhesion between the seed crystal layer and the support substrate was good, and no untransferred defects of the seed crystal layer, known as voids, were found on the surface of the seed crystal layer.

[0068] (Fabrication of semiconductor devices) Onto the SiC epitaxial growth substrate thus prepared, a 20 μm-thick n-type SiC epitaxial film was grown using the CVD method in an epitaxial growth apparatus by spraying high-temperature gas at over 1500°C. During epitaxial growth, the Al2O3 bonding layer did not melt, and a SiC epitaxial film without crystal defects was obtained.

[0069] The growth substrate with this SiC epitaxial film was then processed by the following device process to fabricate a vertical MOS-FET. First, a mask with a predetermined pattern was formed on the top surface of the SiC epitaxial film by photolithography, and a gate oxide film was formed in the mask opening. Next, a mask with a predetermined pattern was formed by photolithography, and p-type ions were implanted into the mask opening. Furthermore, a mask with a predetermined pattern was formed by photolithography, and high-concentration p ions were implanted into the mask opening. + Then, a mask with a predetermined pattern was formed by photolithography, and n-type ions were implanted into the openings of the mask. After that, a high-temperature heat treatment was performed in an inert gas atmosphere such as argon to recover the crystallinity.

[0070] Next, an interlayer insulating film was formed on the surface, planarized by heat treatment, and then a nitride film was formed. Next, a mask with a specified pattern was formed using photolithography, and the gate oxide film, interlayer insulating film, epitaxial film, and seed crystal layer in the mask openings were removed by dry etching to separate the elements. Furthermore, ohmic vias were formed, and ohmic metals such as Al were deposited, followed by heat treatment in an inert gas atmosphere such as argon to establish ohmic contact. Finally, bonding pads were formed using Al or other materials, and a nitride film was then formed as a protective film to create the device layer.

[0071] Next, a temporary support was attached to the bonding pad portion of the device layer, and the bonding layer was then immersed in an HF solution. This dissolved the Al2O3 bonding layer, separating the device layer from the support substrate. Ohmic metal such as Ni was formed on the seed crystal layer of the separated device layer, and RTA (rapid thermal annealing) was performed in an argon atmosphere to form an ohmic electrode. A back electrode such as Au or Ag was then formed on the surface by sputtering, and heat treatment was then performed in an N2 or H2 atmosphere.

[0072] Furthermore, a back electrode was metal-bonded to the surface of a conductive substrate on which a gold film had been sputtered. Each chip, which was the separated device layer, was picked up and soldered to a device substrate on which an electronic circuit had been formed. The temporary support was then removed to produce a vertical power semiconductor device (MOS-FET).

[0073] [Example 2] The experiment and evaluation were carried out under the same conditions as in Example 1, except that a Si3N4 layer was formed as the bonding layer by LPCVD. As a result, a SiC epitaxial film without crystal defects was obtained, as in Example 1. Furthermore, the etching time for the bonding layer when separating the device layer from the support substrate was shorter than in Example 1.

[0074] [Example 3] 6, first, an Al2O3 layer was formed as first bonding layers 12a, 22a to a thickness of 50 nm by ALD on both the ion-implanted surface of single-crystal SiC substrate 10 and the bonding surface of support substrate 20, and then a Si3N4 layer was formed as second bonding layers 12b, 22b to a thickness of 50 nm by LPCVD. Experiments and evaluations were performed under the same conditions as in Example 1. As a result, a SiC epitaxial film without crystal defects was obtained as in Examples 1 and 2, and the bonding layer was similarly etched to obtain a semiconductor device.

[0075] [Example 4] The experiment and evaluation were carried out under the same conditions as in Example 3, except that a 50 nm ZnO layer was formed as the first bonding layer by the ALD method, and a 50 nm Si3N4 layer was formed as the second bonding layer by the LPCVD method. As a result, a SiC epitaxial film without crystal defects was obtained as in Examples 1 to 3, and the bonding layer was similarly etched to obtain a semiconductor device.

[0076] [Example 5] The experiment and evaluation were carried out under the same conditions as in Example 3, except that a 50 nm Si3N4 layer was formed as the first bonding layer by LPCVD, and a 50 nm Al2O3 layer was formed as the second bonding layer by ALD. As a result, a SiC epitaxial film without crystal defects was obtained, as in Examples 1 to 4, and the bonding layer was similarly etched, allowing a semiconductor device to be obtained.

[0077] [Example 6] Except for using a polycrystalline SiC substrate prepared by the CVD method as the support substrate, the experiment and evaluation were carried out under the same conditions as in Example 1. As a result, a SiC epitaxial film without crystal defects was obtained, as in Example 1, and the device layer portion was also able to be separated from the support substrate by etching the bonding layer.

[0078] [Example 7] Except for the fact that the bonding of the bonding layers was performed in a vacuum environment, the experiment and evaluation were carried out under the same conditions as in Examples 1 to 4. As a result, as in Examples 1 to 4, a SiC epitaxial film without crystal defects was obtained, and the device layer portion was also able to be separated from the support substrate by etching the bonding layer.

[0079] [Comparative Example 1] The experiment and evaluation were carried out in the same manner as in Example 1, except that a SiO2 layer with a melting point of 1710°C was formed as a bonding layer by the LPCVD method. As a result, the SiO2 layer melted during the SiC epitaxial growth, and a SiC epitaxial film could not be formed.

[0080] Comparative Example 2 With the exception of using a single crystal SiC substrate with an off-angle of 0° as the seed crystal layer, the experiment and evaluation were carried out in the same manner as in Example 1. As a result, many crystal defects were found in the formed SiC epitaxial film.

[0081] Comparative Example 3 Except for the fact that the single crystal SiC substrate and the support substrate were directly bonded without using a bonding layer, the experiment and evaluation were carried out in the same manner as in Example 1. As a result, since the device layer portion could not be separated from the support substrate by etching, the support substrate had to be shaved to form the vertical power device, which increased the manufacturing cost.

[0082] Comparative Example 4 The experiment and evaluation were carried out in the same manner as in Example 1, except that the surface roughness Rms of the bonding layer after planarization was set to 10 nm and the single-crystal SiC substrate and the support substrate were bonded together. As a result, poor adhesion occurred at the bonding interface of the bonding layer, resulting in bonding defects.

[0083] Comparative Example 5 Except for using a 3C-SiC ceramic substrate made by sintering SiC powder with an average particle size of 5 μm as the support substrate, experiments and evaluations were carried out in the same manner as in Example 1. As a result, when the surface of the seed crystal layer on the growth substrate was inspected, many untransferred defects in the seed crystal layer, called voids, were found. [Explanation of symbols]

[0084] 1. SiC epitaxial growth substrate 3 Bonded substrate 5A, 5B Semiconductor Devices 10 Single crystal SiC 12, 22 Bonding layer 14 Seed layer 20 Support substrate 30 SiC epitaxial film 40 insulating layer 50 electrode layer 60 Temporary support 70 Back electrode 80 Device substrate

Claims

1. A substrate for silicon carbide epitaxial growth comprising: a support substrate having a thermal expansion coefficient substantially equal to that of a silicon carbide epitaxial film; a bonding layer having a melting point of 1800°C or higher and provided on at least one surface of the support substrate; and a seed crystal layer of single-crystal silicon carbide provided on the surface of the bonding layer.

2. 10. The silicon carbide epitaxial growth substrate of claim 1, wherein the bonding layer comprises aluminum oxide, silicon nitride, aluminum oxynitride, silicon oxynitride, zinc oxide, or a combination thereof.

3. 3. The silicon carbide epitaxial growth substrate according to claim 1, wherein the seed crystal layer is an n-type single crystal silicon carbide having a (0001) Si plane as a surface of the seed crystal layer and an off angle of 0.5° to 10° with respect to the surface.

4. 3. The silicon carbide epitaxial growth substrate according to claim 1, wherein the support substrate is made of polycrystalline silicon carbide.

5. 5. The silicon carbide epitaxial growth substrate according to claim 4, wherein the support substrate is made of silicon carbide ceramics having crystal grains with an average grain size of 1 μm or less.

6. providing a support substrate having a thermal expansion coefficient substantially matching that of the silicon carbide epitaxial film; forming a bonding layer having a melting point of 1800°C or higher on at least one of the bonding surfaces of the single crystal silicon carbide and the supporting substrate; implanting ions into the bonding surface of the single crystal silicon carbide to form an ion-implanted interface in the single crystal silicon carbide; bonding a bonding surface of the single crystal silicon carbide to a bonding surface of the support substrate via the bonding layer; a step of separating and peeling off the single-crystal silicon carbide at the ion-implanted interface to transfer a portion of the single-crystal silicon carbide to the support substrate as a seed crystal layer; A method for producing a silicon carbide epitaxial growth substrate, comprising:

7. 7. The method for producing a silicon carbide epitaxial growth substrate according to claim 6, wherein the surface of the bonding layer is polished before the bonding step to have a surface roughness Rms of 0.5 nm or less.

8. 8. The method for producing a silicon carbide epitaxial growth substrate according to claim 6, wherein the bonding step is performed by plasma bonding, room temperature bonding, or vacuum bonding.

9. A silicon carbide epitaxial growth substrate includes a support substrate having a thermal expansion coefficient substantially equal to that of a silicon carbide epitaxial film, a bonding layer provided on one surface of the support substrate and having a melting point of 1800°C or higher, and a seed crystal layer of single-crystal silicon carbide provided on the surface of the bonding layer, the substrate comprising: a step of growing a silicon carbide epitaxial film on the surface of the seed crystal layer; forming a semiconductor device structure with electrodes on the silicon carbide epitaxial film; selectively removing the bonding layer to separate the silicon carbide epitaxial film having the semiconductor device structure from the support substrate; forming a backside electrode on the silicon carbide epitaxial film having the semiconductor device structure; A method for manufacturing a semiconductor device, comprising:

10. The method for manufacturing a semiconductor device according to claim 9, wherein the separated support substrate is reused in manufacturing the silicon carbide epitaxial growth substrate.

Images