Large-diameter III-nitride epitaxial growth substrate and method for producing same

Abstract

To provide a substrate for group III nitride epitaxial growth capable of manufacturing inexpensively a single crystal of group III nitride in a high quality; and to provide a production method thereof.SOLUTION: A substrate for group III nitride-based epitaxial growth comprises a support substrate having a structure wrapped in a sealing layer in which a core comprising a nitride ceramic has a thickness of 0.05 μm or more and 1.5 μm or less, a flattening layer provided on an upper surface of the support substrate, and having a thickness of 0.5 μm or more and 3.0 μm or less, and a seed crystal layer of a single crystal provided on an upper surface of the flattening layer, including an uneven pattern on the surface, and having a thickness of 0.1 μm or more and 1.5 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a seed substrate for use in epitaxial growth of group III nitride single crystals such as aluminum nitride (AlN), aluminum gallium nitride (Al x Ga 1-x GaN (where 0 < x < 1.0), gallium nitride (GaN), etc.

Background Art

[0002] Substrates of group III nitrides such as crystalline AlN-based and GaN-based have a wide bandgap and excellent short-wavelength light-emitting properties and high-frequency characteristics with high breakdown voltage. For this reason, substrates of group III nitrides are expected to be applied to devices such as light-emitting diodes (LEDs), lasers, Schottky diodes, power devices, and high-frequency devices. In particular, for the emission wavelength in the deep ultraviolet region (UVC; 200 to 280 nm) of LEDs fabricated from single crystals of AlN and Al x Ga 1-x GaN (0.5 < x < 1.0), a bactericidal effect has been reported (Non-Patent Document 1), and further improvement in quality, increase in large diameter, and reduction in price are required.

[0003] Since AlN does not have a melting point under normal pressure, it is difficult to manufacture by a general melt method used for silicon single crystals and the like.

[0004] Non-Patent Document 2 and Non-Patent Document 3 describe methods for manufacturing AlN single crystal substrates by a sublimation method (modified Lely method) using SiC or AlN as a seed crystal at 1700 to 2250 °C in an N2 atmosphere. However, due to equipment limitations such as the requirement of high temperature for crystal growth, it is difficult to reduce the cost, and it is also difficult to increase the large diameter to φ4 inches or more.

[0005] In addition, Patent Document 1 describes a method of growing an AlN layer by hydride vapor phase epitaxy (HVPE) using a silicon substrate or an AlN substrate as a base substrate. However, in this method, when silicon is used as the base substrate, it is difficult to reduce the dislocation density of the AlN layer due to differences in thermal expansion coefficient and lattice constant. On the other hand, when using a sublimation method AlN substrate with good crystallinity as the base substrate, the dislocation density can be reduced. However, since the base substrate itself has a small diameter and is expensive, it is difficult to reduce the cost for large-diameter substrates. To compensate for these drawbacks, Non-Patent Document 4 discloses a method in which an AlN film is laminated by 5 μm in one batch by MOVPE on a sapphire substrate that serves as both a base substrate and a seed substrate, grooves are formed therein by etching, and then a film is formed to a target thickness by HVPE. The voids formed during HVPE film formation due to the above groove structure act as a stress relaxation layer for the thermal expansion difference, and as a result, cracks are prevented. However, this is only effective when the base substrate is φ4 inches or less. When the base substrate is large-diameter such as φ6, φ8, φ12 inches, etc., cracks and large warping occur, which is a problem.

[0006] Patent Document 2 describes a method of epitaxially growing group III nitrides such as GaN single crystals using a composite substrate in which an AlN ceramic with a thermal expansion coefficient close to that of AlN single crystal and low cost is used as a base substrate, the base substrate is sealed with Si3N4 or the like, and a silicon <111> single crystal is thin-film transferred as a seed crystal. However, in this method, for example, when epitaxially depositing a single crystal of AlN or Al x Ga 1-x N(0 < x < 1), it is difficult to reduce the dislocation density due to the difference in lattice constant between the silicon <111> seed crystal and the target AlN or Al x Ga 1-x N(0 < x < 1) single crystal. Also, it is difficult to reduce cracks and warping of the film-forming substrate due to the affinity and thermal expansion coefficient difference with the sealing layer, planarization layer, etc. These have affected the deterioration of characteristics and the reduction of yield in the subsequent device fabrication process, and have consequently hindered the improvement of quality and cost reduction of lasers, LEDs, high-frequency devices, etc. produced.

[0007] Therefore, the inventors of the present invention have conducted intensive studies to eliminate these drawbacks, and as a result, have arrived at the present invention.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above circumstances, and aims to provide a substrate for III-nitride epitaxial growth capable of producing a single crystal of AlN, Al x Ga 1-x N (0.5 < x < 1.0) with a large diameter, high quality, and low cost, and a method for manufacturing the same.

Means for Solving the Problems

[0011] The present invention is based on the results of many trials by the inventors, (1) a support substrate having a structure in which a core made of a nitride ceramic is enclosed in a sealing layer having a thickness of 0.05 μm or more and 1.5 μm or less; a planarization layer provided on an upper surface of the support substrate and having a thickness of 0.5 μm or more and 3.0 μm or less; a single-crystal seed crystal layer having a thickness of 0.1 μm or more and 1.5 μm or less and having a concave-convex pattern on the surface thereof, the single-crystal seed crystal layer being provided on the upper surface of the flattening layer; To have (2) The supporting substrate (base substrate) and the epitaxial film have approximately the same thermal expansion coefficient. (3) Forming a periodic groove or dot structure, or a pattern with an off-angle of 0.1 to 3°, on the seed crystal surface to which the concave-convex pattern has been transferred. The present invention provides a method for producing a Group III nitride epitaxial growth substrate that can grow high-purity, high-quality epitaxial crystals without cracking or warping even with a large diameter and by concentrating crystal defects on the side surfaces during film formation. The present invention provides effects by each of the above elements (1), (2), and (3), but when all three elements are combined, a synergistic effect is achieved, resulting in extremely remarkable effects.

[0012] In order to solve the above problems, a Group III nitride-based epitaxial growth substrate according to an embodiment of the present invention comprises a support substrate having a structure in which a core made of nitride ceramic is surrounded by a sealing layer having a thickness of 0.05 μm or more and 1.5 μm or less, a planarization layer having a thickness of 0.5 μm or more and 3.0 μm or less and provided on the upper surface of the support substrate, and a single-crystal seed crystal layer having a thickness of 0.1 μm or more and 1.5 μm or less and having a concave-convex pattern on its surface and provided on the upper surface of the planarization layer.

[0013] In the present invention, the Group III nitride epitaxial growth substrate may further include a stress adjustment layer on the lower surface of the support substrate.

[0014] In the present invention, the core may be aluminum nitride ceramics, the sealing layer may include silicon nitride, the planarizing layer may include any one of silicon oxide, silicon oxynitride, and aluminum arsenide, and the stress adjustment layer may include elemental silicon.

[0015] In the present invention, the seed crystal layer is Si <111> , SiC, sapphire, aluminum nitride, or aluminum gallium nitride. The uneven pattern of the seed crystal layer is preferably selected from periodic grooves, an off-angle of 0.1 to 3°, and a dot structure. When the seed crystal layer is made of aluminum nitride or aluminum gallium nitride, the resistivity is preferably 1×10 6 It is preferable that the resistivity is Ω·cm or more.

[0016] Furthermore, a method for manufacturing a Group III nitride-based epitaxial growth substrate according to an embodiment of the present invention includes the steps of preparing a core made of nitride ceramics, forming a sealing layer having a thickness of 0.05 μm or more and 1.5 μm or less so as to encase the core to provide a support substrate, forming a planarizing layer having a thickness of 0.5 μm or more and 3.0 μm or less on an upper surface of the support substrate, and providing a single-crystal seed crystal layer having a thickness of 0.1 μm or more and 1.5 μm or less and having an uneven pattern on the upper surface of the planarizing layer.

[0017] The method for producing a Group III nitride epitaxial growth substrate may further include the step of forming a stress adjustment layer on the lower surface of the support substrate.

[0018] In the present invention, the sealing layer is preferably formed by LPCVD, and the planarizing layer is preferably formed by any one of plasma CVD, LPCVD, and low pressure MOCVD.

[0019] In the present invention, the step of providing the seed crystal layer may include the steps of preparing a single crystal substrate of Group III nitride having one surface as an ion-implanted surface, injecting ions from the ion-implanted surface to form a peeling position in the single crystal substrate, bonding the ion-implanted surface and the planarizing layer to form a bonded substrate, separating the bonded substrate at the peeling position into the seed crystal layer and a remainder of the single crystal substrate, and providing a concave-convex pattern on the seed crystal layer obtained as described above.

[0020] In the present invention, in the step of preparing a single crystal substrate, a large-diameter substrate is a commercially available Si substrate. <111> For SiC or sapphire substrates, commercially available substrates can be used as they are. On the other hand, in the case of aluminum nitride or aluminum gallium nitride, which are difficult to obtain in large diameters, a large diameter single crystal substrate can be prepared by stacking aluminum nitride or aluminum gallium nitride on a large diameter sapphire substrate by MOCVD, HVPE, or THVPE. Alternatively, a small diameter single crystal obtained by epitaxially growing an epitaxial layer of aluminum nitride or aluminum gallium nitride by HVPE, HVPE, or THVPE on a small diameter single crystal prepared by sublimation or an AlN substrate prepared by sublimation can be bonded to obtain a single crystal substrate.

[0021] Furthermore, when an epitaxial layer is laminated on the single crystal substrate, the step of forming the separation position may include forming the separation position within the epitaxial layer. In this case, the remaining portion of the single crystal substrate may be reused as a base substrate. Alternatively, the remaining portion of the single crystal substrate may be reused as a single crystal substrate in the manufacture of yet another group III nitride composite substrate.

[0022] In the present invention, the core may be aluminum nitride ceramics, the sealing layer may include silicon nitride, the planarizing layer may include any one of silicon oxide, silicon oxynitride, and aluminum arsenide, and the stress adjustment layer may include elemental silicon.

[0023] In the present invention, the seed crystal layer is a Si <111> , SiC, aluminum nitride, or aluminum gallium nitride. The seed crystal layer may have a concave-convex pattern formed thereon. The concave-convex pattern is preferably selected from periodic grooves, an off-angle of 0.1 to 3°, and a dot structure. The resistivity of the seed crystal layer may be 1×10 6 It is preferable that the resistivity is Ω·cm or more. Effect of the Invention

[0024] According to the present invention, it is possible to provide a substrate for epitaxial growth of III nitrides that enables low-cost production of high-quality, large-diameter single crystals of III nitrides. [Brief description of the drawings]

[0025] [Figure 1] 1 is a diagram showing a cross-sectional structure of a composite substrate 1. FIG. [Diagram 2] 1A to 1C are diagrams illustrating a procedure for manufacturing a composite substrate 1. [Diagram 3] FIG. 2 is a schematic diagram showing a substrate used as a single crystal substrate 20, which is produced by a sublimation method. [Figure 4] 1 is a schematic diagram showing the structure of a single crystal epitaxial layer substrate used as single crystal substrate 20. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to these.

[0027] The cross-sectional structure of a composite substrate 1 according to this embodiment is shown in Fig. 1. The composite substrate 1 shown in Fig. 1 has a structure in which a planarization layer 4 and a single crystal seed crystal layer 2 having a concave-convex pattern on its surface and a thickness of 0.1 µm to 1.5 µm are laminated on a support substrate 3. In addition, a stress adjustment layer 5 is provided on the surface (lower surface) of the support substrate 3 opposite to the surface on which the planarization layer 4 is laminated, as necessary.

[0028] The support substrate (base substrate) 3 includes a core 31 that serves as a core material of the support substrate 3 , and a sealing layer 32 that covers the core 31 .

[0029] The material used for the core 31 is preferably nitride ceramics, which have excellent heat resistance and stability, and are available in large diameter sizes at low cost. As the nitride ceramics, aluminum nitride (AlN), silicon nitride (Si3N4), gallium nitride (GaN), boron nitride (BN), or a mixture of these can be used. AlN is particularly preferable because it has a lattice constant and thermal expansion coefficient close to those of the desired Group III nitride crystal, making it possible to fabricate high-quality Group III nitride crystals with little deformation. In addition, AlN is also preferable in that it has high thermal conductivity and therefore excellent heat transfer in subsequent processes including heating.

[0030] The shape and size of the core 31 is preferably a wafer shape with a thickness of 200 to 1000 μm, since it can be mounted on a normal semiconductor process line. In addition, it is preferable to mirror-finish the surface of the core 31, since this reduces the unevenness of the surface of the support substrate 3.

[0031] When AlN is used as the core 31, there are various methods for manufacturing AlN ceramics, but it is preferable to use the so-called sheet molding / normal pressure sintering method, in which AlN powder is mixed with a sintering aid, an organic binder, a solvent, etc., a wafer-shaped green sheet is produced, and after degreasing, the sheet is sintered in a N2 atmosphere and polished, in order to increase productivity. The sintering aid is selected from Y2O3, Al2O3, CaO, etc., and it is particularly preferable to include Y2O3 as a sintering aid, as this increases the thermal conductivity of the substrate after sintering.

[0032] The sealing layer 32 is a layer that encloses and seals the entire core without any gaps, and has a thickness of 0.05 μm to 1.5 μm. With this structure, it is possible to prevent substances originating from the ceramic material of the core 31 from leaking out of the support substrate 3.

[0033] For example, when AlN ceramics is used as the core 31, there is a possibility that elemental substances resulting from AlN or Y2O3 added as a sintering aid, or substances taken into the ceramics as impurities from the insulation material, furnace material, container, etc. used when sintering the ceramics may leak out. If such substances leak out of the support substrate 3, they will be taken in as impurities when epitaxially growing the target AlN, and will likely become a factor in reducing quality.

[0034] If the sealing layer 32 is too thick, it will not be able to withstand the thermal stress between the surface and interior of the sealing layer 32 when it is repeatedly heated and cooled in the subsequent process, and peeling will easily occur. Therefore, even if various films are selected and combined, a thickness of more than 1.5 μm is not preferable for the sealing layer 32. On the other hand, a thickness of less than 0.05 μm is insufficient in terms of the function of sealing the substances originating from the core 31. For the above reasons, the thickness of the sealing layer 32 is preferably in the range of 0.05 μm to 1.5 μm. A film made of silicon nitride (Si3N4) is preferable as the material for the sealing layer 32, because it is highly effective in sealing the materials originating from nitride ceramics.

[0035] It is preferable that the sealing layer 32 is a dense film, since this enhances the sealing performance. It is also preferable that the sealing layer 32 is a film with high purity, without containing impurities such as sintering aids. In this way, the sealing layer 32 is preferable, since it suppresses the leakage of unintended substances caused by the sealing layer 32 itself to the outside of the support substrate 3.

[0036] Such a high-purity film can be formed by a film formation method such as MOCVD, atmospheric pressure CVD, LPCVD (low pressure CVD), sputtering, etc. In particular, the LPCVD method is preferred because it can form a dense film and has excellent film coverage.

[0037] When silicon nitride is used as the material for the sealing layer 32, silicon oxide (SiO2) or silicon oxynitride (Si x O y N z) may be provided as a part of the sealing layer between core 31. However, even in this case, the overall thickness of sealing layer 32 is preferably set in the range of 0.05 μm to 1.5 μm in order to prevent peeling.

[0038] On the upper surface of the support substrate 3, a planarization layer 3 having a thickness of 0.5 μm to 3.0 μm is laminated on the sealing layer 32. By laminating the planarization layer 4, various voids and irregularities caused by the core 31 and the sealing layer 32 are filled, and sufficient smoothness is obtained for the seed crystal to be transferred. However, if the thickness of the planarization layer 4 is too thick, it may cause warping, which is not preferable. For this reason, the thickness of the planarization layer 4 is preferably 0.5 to 3.0 μm. That is, if the thickness of the planarization layer 4 is less than 0.5 μm, it is not preferable because it cannot sufficiently fill the voids and irregularities generated in the support substrate 3. Also, if the thickness of the planarization layer 4 is 3.0 μm or more, it is not preferable because it is likely to cause warping.

[0039] A stress adjustment layer 5 is provided on the surface (lower surface) opposite to the upper surface of the support substrate 3 on which the planarization layer 4 is laminated. The stress adjustment layer 5 offsets the stress generated by laminating the planarization layer 4, and reduces warpage.

[0040] The planarization layer 4 may be formed only on one side (upper surface) of the support substrate 3 on which the seed crystal layer 2 is to be laminated, but may be formed so as to cover both sides (upper and lower surfaces) of the support substrate or the entire support substrate. In this way, the material laminated on the lower surface acts as a stress adjustment layer 5, and the stress caused by the planarization layer 4 is structurally offset above and below the substrate, further reducing warpage of the substrate.

[0041] Moreover, a single silicon (such as polycrystalline silicon) may be laminated as the stress adjustment layer 5. This has the advantage of providing a composite substrate that can also be attached and detached by an electrostatic chuck.

[0042] The material of the planarization layer 4 is silicon oxide (SiO2), aluminum oxide (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC) or silicon oxynitride (Si x O y Nz ), silicon (Si), gallium arsenide (GaAs), aluminum arsenide (AlAs), etc. In particular, silicon oxide (SiO2), silicon oxynitride (Si x O y N z ) and aluminum arsenide (AlAs) are preferred because they can be easily ground or polished during planarization and can easily become a sacrificial layer for separating the support substrate 3 after epitaxial growth of the desired Group III nitride such as AlN.

[0043] The deposition of the planarization layer 4 can be arbitrarily selected from the plasma CVD method, the LPCVD method, the low pressure MOCVD method, etc., depending on the required film quality and deposition efficiency. Depending on the state of the laminated planarization layer 4 film, a heat treatment for annealing or CMP polishing is performed after deposition in preparation for the formation of the seed crystal layer 2.

[0044] A high-quality Si layer is formed on the planarization layer 4 formed on the upper surface of the support substrate 3. <111> A seed crystal layer 2 made of a single crystal of SiC, sapphire, aluminum nitride, or aluminum gallium nitride is formed. The seed crystal layer 2 has an uneven pattern on its surface. The thickness of the seed crystal layer 2 is preferably 0.1 μm or more and 1.5 μm or less. In this way, it is possible to form a high-quality seed crystal layer 2. That is, a high-quality crystal layer can be thin-film transferred to the above-mentioned single crystal substrate by applying ion implantation peeling. If the thickness of the seed crystal layer 2 is less than 0.1 μm, the damage layer during ion implantation is almost close to that thickness, so it cannot become a good seed crystal. In addition, if the thickness of the seed crystal layer 2 is 1.5 μm or more, the ion implantation device becomes enormously large, requiring a huge investment, which is not realistic.

[0045] The high-quality single crystal used here is preferably a single crystal obtained by any of the general melting methods (CZ method, FZ method), sublimation method, MOCVD method (metal organic chemical vapor deposition method), HVPE (hydride vapor phase epitaxy method), and THVPE (trihalide vapor phase epitaxy method), or an epitaxially grown single crystal. The EPD of the single crystal is 1×10 6 cm -2It is preferable that the crystal has an extremely low dislocation density of 0.1 or less.

[0046] The uneven pattern on the surface of the seed crystal layer 2 is Si <111> After transferring a thin film of SiC, sapphire, aluminum nitride, or aluminum gallium nitride by ion implantation and exfoliation, periodic grooves or dot structures of several μm to several tens of μm are formed on the surface by lithography, or an off-angle of 0.1 to 3 degrees is formed by etching, etc. The pattern is appropriately selected depending on the properties of the seed crystal substrate.

[0047] The seed crystal layer 2 does not need to match the composition of the target film to be epitaxially grown, but it is preferable that the crystal type is similar and that the lattice constant is as close as possible to AlN. On the other hand, the closer the thermal expansion coefficient is to AlN, the better, but since the seed crystal layer 2 is formed extremely thin by thin film transfer, the effect on warping can be almost negligible compared to the core base substrate. In contrast, in the case of a thick seed crystal substrate that also serves as a base substrate and a seed crystal, if there is a difference in the thermal expansion coefficient between the film to be epitaxially grown, the substrate will warp significantly during film formation, causing breakage and cracks.

[0048] In addition, when the seed crystal layer 2 is made of aluminum nitride or aluminum gallium nitride, its resistivity is 1×10 6 It is preferable to set the resistivity to Ω·cm or more. In this way, impurities incorporated into the target material epitaxially formed on the seed crystal layer 2 can be reduced, and coloring of the target material (i.e., light absorption) can be suppressed.

[0049] Next, the steps of the method for manufacturing a Group III nitride-based epitaxial growth substrate according to this embodiment will be described with reference to Fig. 2. First, a core 31 made of nitride ceramic is prepared (S01 in Fig. 2). Next, a sealing layer 32 having a thickness of 0.05 µm or more and 1.5 µm or less is formed so as to encase the core 31, thereby forming a support substrate 3 (S02 in Fig. 2). At this time, the sealing layer 32 is preferably formed by the LPCVD method.

[0050] Next, a planarization layer 4 having a thickness of 0.5 μm to 3.0 μm is formed on the upper surface of the support substrate 3 (S03 in FIG. 2). The planarization layer 4 may be formed by any one of a plasma CVD method, an LPCVD method, and a low-pressure MOCVD method. A stress adjustment layer 5 is further formed on the lower surface of the support substrate 3 (S04 in FIG. 2). The planarization layer 4 and the stress adjustment layer 5 may be formed simultaneously.

[0051] Separately from S01 to S04, a group III nitride single crystal substrate 20 for peeling and transferring the seed crystal layer 2 is prepared (S11 in FIG. 2). A specific method for preparing this single crystal substrate 20 will be described later. Next, ions are implanted from one surface (ion-implanted surface) of the single crystal substrate 20 to form a peeling position (embrittled layer) 21 in the single crystal substrate 20 (S12 in FIG. 2). The ions implanted at this time are, for example, H + , H2 + , Ar + , He + etc.

[0052] Next, the ion-implanted surface of the single crystal substrate 20 is bonded to the planarization layer 4 formed on the support substrate 3 to form a bonded substrate (S21 in FIG. 2). Then, the single crystal substrate 20 is separated at the peeling position 21 of the single crystal substrate 20 in the bonded substrate (S22 in FIG. 2). By doing so, a Si <111> A single crystal film of any one of SiC, sapphire, aluminum nitride, and aluminum gallium nitride is thin-film transferred as a seed crystal layer 2, and after separation into the seed crystal layer 2 and the remainder of the single crystal substrate 20 at a peeling position 21, a concave-convex pattern is provided on the seed crystal layer 2. Through these steps, the support substrate 3, the planarizing layer 4, and the seed crystal layer 2 provided with the concave-convex pattern are laminated to form a Group III nitride-based composite substrate. Meanwhile, the surface of the separated remainder of the Group III nitride single crystal substrate 20 can be polished again to form an ion-implanted surface, so that it can be repeatedly used for thin-film transfer of a seed crystal layer when producing yet another Group III nitride-based composite substrate.

[0053] Alternatively, the ion-implanted surface of the single crystal substrate 20 may be temporarily bonded to another temporary support substrate such as a silicon wafer, and then separated to leave the seed crystal layer 2 bonded to the temporary support substrate, and the seed crystal layer 2 on this temporary support substrate may be bonded to the planarizing layer 4, followed by a step of separating the temporary support substrate from the seed crystal layer. In this manner, the seed crystal layer 2 bonded to the planarizing layer 4 can be turned upside down.

[0054] Next, a method for preparing the single crystal substrate 20 will be described. The single crystal substrate 20 is a Si substrate, which is commercially available and has a large diameter. <111> For SiC or sapphire substrates, commercially available substrates can be used as is. On the other hand, in the case of aluminum nitride or aluminum gallium nitride, for which large-diameter substrates are difficult to obtain, it is preferable to fabricate a large-diameter single crystal substrate by laminating aluminum nitride or aluminum gallium nitride on a large-diameter sapphire substrate using either MOCVD, HVPE, or THVPE (trihalide vapor phase epitaxy). Alternatively, when using a small-diameter substrate (sublimation substrate) fabricated by sublimation, or when using a crystal in which aluminum nitride or aluminum gallium nitride is laminated on an AlN substrate fabricated by sublimation using either MOCVD, HVPE, or THVPE, it is preferable to fabricate a large-diameter substrate by bonding a small-diameter single crystal.

[0055] FIG. 3 is a diagram showing the layer structure of a single crystal substrate 20 when ions are implanted into a large-diameter substrate formed by bonding a plurality of small-diameter sublimation substrates in the same orientation. FIG. 4 is a diagram showing the layer structure of a single crystal substrate 20 when the bonded substrate is used as a base substrate 22, and an epitaxial film is formed thereon by any one of MOCVD, HVPE, and THVPE methods, and this single crystal epitaxial layer substrate is used. In this case, it is preferable to set the peeling position 21 by ion implantation within the epitaxial layer 23. In this way, it is possible to form the seed crystal layer 2 without consuming the expensive AlN substrate produced by the sublimation method, thereby reducing the manufacturing cost. In addition, when Al is formed by any one of MOCVD, HVPE, and THVPE methods, x Ga 1-xWhen epitaxially growing single crystals of AlN, the composition of the source gas can be adjusted to x Ga 1-x The value of x in N can be changed between 0≦x≦1, which has the advantage that an optimum value can be selected for the desired epitaxial growth in the subsequent process.

[0056] Incidentally, AlN substrates produced by the sublimation method are generally small in diameter, expensive, and easily colored, but have excellent crystal properties. As shown in Figure 3, after multiple small-diameter single crystals are bonded together to produce a large-diameter substrate, ion implantation is performed to transfer a thin film with a thickness of 0.1 μm to 1.5 μm, and the remaining portion of the single crystal substrate is reused to produce the next composite substrate, allowing for repeated use, which not only reduces the cost of producing the composite substrate, but also functions as an extremely good seed crystal. In addition, since the substrate produced by the sublimation method is not used as a thick substrate of several hundred μm as in the past, but is used in the form of an extremely thin film of 0.1 μm to 1.5 μm by thin film transfer, coloring does not become an issue as with the original substrate.

[0057] Furthermore, when the peeling position is set within the epitaxial layer as shown in FIG. 4, it is advisable to perform thin film transfer with a thickness of 0.1 μm to 1.5 μm and reuse the remaining portion of the single crystal epitaxial layer substrate for the production of the next composite substrate. In this way, the single crystal epitaxial layer substrate can be used repeatedly, so the cost of producing the composite substrate can be significantly reduced. In addition, if the remaining portion of the single crystal epitaxial layer substrate, in which the epitaxial layer portion has become thin as a result of repeated use, is used as a base substrate, and the epitaxial layer is regenerated by epitaxially forming the epitaxial layer by any of the MOCVD method, HVPE method, and THVPE method, the initial base substrate can be used repeatedly, and the production cost can be further reduced. EXAMPLES

[0058] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0059] [Example 1] (Preparation of the support substrate) (1) 100 parts by weight of AlN powder and 5 parts by weight of Y2O3 as a sintering aid were mixed with an organic binder, solvent, etc. to produce a green sheet, which was then degreased and sintered under N2 at 1900℃ to create a double-sided polished AlN substrate (AlN polycrystalline ceramic substrate) with a diameter of 8 inches and thickness of 725μm. (2) This entire core was covered by the LPCVD method with a 0.2μm thick silicon oxynitride layer, and then covered by another LPCVD device with a 0.6μm thick silicon nitride (Si3N4) layer to completely cover the entire core, sealing it (total thickness of sealing layer = 0.8μm) to form a support substrate.

[0060] (Lamination of planarizing layers) For the purpose of further planarization, a 7μm-thick SiO2 was laminated on the Si3N4 layer on one side (top surface) of the support substrate by plasma CVD (ICP-CVD device). After that, this SiO2 was baked at 1000℃, and then polished and planarized to a thickness of 3μm by CMP polishing, resulting in a surface roughness of Ra = 0.15nm.

[0061] (Seed crystal preparation) φ8 inch silicon pulled by a commercially available CZ method <111> Hydrogen was injected into the substrate at 100 keV to a depth of 0.7 μm (at the peeling position) with a dose of 6 × 10 17 cm -2The ion implantation of AlN was performed. The ion implanted surface of the AlN single crystal substrate after this ion implantation was bonded to the planarization layer of the support substrate prepared in advance. After that, the seed crystal layer of the AlN single crystal was transferred to the support substrate as a thin film by peeling and separating it at the peeling position (0.7 μm part). The damaged part of the Si single crystal of the seed crystal layer during the ion implantation and transfer was lightly polished by CMP, and the thickness of the Si seed crystal layer was set to 0.5 μm. A periodic uneven pattern with a groove depth of 0.3 μm, a groove width of 3 μm, and a terrace width of 5 μm was formed in this Si seed crystal layer. The remaining part of the Si single crystal substrate after the thin film transfer (i.e., the part that was peeled and separated without being transferred to the support substrate) can be used as a large number of seed crystals by repeatedly performing ion implantation, which was extremely economical. As a result, a 3 μm-thick planarization layer and a 0.5 μm-thick Si seed crystal layer were formed on the support substrate having a structure of (1) an AlN ceramic core and (2) a sealing layer. <111> A φ8-inch substrate for III-nitride epitaxial growth provided with a seed crystal layer was obtained.

[0062] (Substrate evaluation) Next, the above substrate was further evaluated as a substrate for AlN epitaxial growth in the following simple manner. That is, a 2 μm AlN film was formed on the above AlN epitaxial substrate by MOCVD, and etch pits were generated by molten alkali (KOH+NaOH) etching to evaluate the dislocation density, and the etch pit density (EPD) was measured. In addition, X-ray rocking curve (XRC) measurements were performed to evaluate the crystallinity. As a result, the EPD was 3×10 5 cm -2 The result showed an extremely low dislocation density. Furthermore, the full width at half maximum (FWHM) of the (0002) surface of the substrate measured by XRC was 321 arcsec, indicating that a high-quality AlN single crystal was obtained. These results demonstrate that the epitaxial substrate of this example is excellent.

[0063] [Comparative Example 1] In Example 1, a concave-convex pattern was not formed on the Si seed crystal layer, and a flat Si <111> In this experiment, a 3 μm-thick flattening layer and a 0.5 μm-thick Si <111> A φ8-inch substrate for III-nitride epitaxial growth provided with a seed crystal layer was obtained.

[0064] (Substrate evaluation) Next, the above substrate was further evaluated as a substrate for AlN epitaxial growth in the following simple manner. That is, a 2 μm AlN film was formed on the above AlN epitaxial substrate by MOCVD, and etch pits were generated by molten alkali (KOH+NaOH) etching to evaluate the dislocation density, and EPD was measured. XRC measurement was also performed to evaluate the crystallinity. As a result, the EPD was 3×10 6 cm -2 The FWHM in the XRC measurement of the (0002) plane of the substrate was 731 arcsec, and the crystal was inferior to Example 1 in both dislocation density and FWHM.

[0065] [Example 2] (Preparation of the support substrate) The structure of the support substrate was as follows: (1) the core was an AlN polycrystalline ceramic substrate similar to that of Example 1. (2) As a sealing layer, the entire AlN ceramic core was first covered with a 0.5 μm thick SiO2 layer formed by LPCVD, and then the entire core was sealed with a 0.8 μm thick Si3N4 layer (total thickness of sealing layer = 1.3 μm) using another LPCVD apparatus to form a support substrate.

[0066] (Lamination of planarizing layer and stress adjustment layer) For the purpose of further planarization, 4 μm of silicon oxynitride was laminated by LPCVD on the Si3N4 layer on one side (top surface) of the support substrate. After that, the silicon oxynitride layer was made 3 μm thick by CMP polishing. Since the entire substrate was significantly warped by about 30 μm, in order to correct the warp, 5 μm of silicon oxynitride was laminated by LPCVD on the bottom surface as a stress adjustment layer. After that, 0.2 μm of polycrystalline silicon was added by LPCVD to accommodate adhesion and desorption by electrostatic chuck. As a result, the warp was almost completely eliminated, and adhesion and desorption to and from the electrostatic chuck became possible.

[0067] (Seed crystal preparation) The AlN crystals used as seed crystals were produced by the sublimation method (modified Lely method) according to the following procedure. First, a TaC crucible was placed inside a growth vessel made of highly purified graphite, and high-purity AlN raw material was placed at the bottom of the TaC crucible, with AlN crystals placed on top. The growth vessel and crucible were heated by high-frequency induction heating, the raw material section was kept at 2000°C, and the raw material was sublimated and decomposed, resulting in the precipitation of AlN single crystals on the AlN crystals on top. This AlN single crystal was sliced ​​and polished to produce a smooth φ2-inch substrate with a thickness of 200 μm. Incidentally, when the resistivity was measured at eight equally spaced points on the surface of this substrate, it was found to be 1×10 6 Ω cm~3×10 11 The optical transmittance at a wavelength of 230 nm was 0.2% at a thickness of 100 μm.

[0068] The 2-inch substrates prepared above were used as regular hexagonal AlN substrates, and several of these were used to align the orientation and bonded to a φ8-inch quartz substrate. The periphery of the quartz substrate was then trimmed by cutting off the excess parts so that it would become an φ8-inch substrate. The φ8-inch AlN single crystal substrate prepared in this way was irradiated with hydrogen at 100 keV to a depth of 0.6 μm (at the peeling position) with a dose of 8 × 10 17 cm -2Ion implantation was carried out. The ion-implanted surface of the AlN single crystal substrate after this ion implantation was bonded to the planarized layer of the support substrate prepared earlier. After that, a thin film of the AlN single crystal seed crystal layer was transferred to the support substrate by peeling and separating at the peeling position (0.6 μm part). Damage caused to the AlN single crystal seed crystal layer during ion implantation and transfer was lightly polished by CMP, and the thickness of the AlN seed crystal layer was set to 0.4 μm.

[0069] This seed crystal layer was etched to form an off-angle of 0.2°. The original substrate for this AlN seed crystal layer was strongly colored and had extremely low light transmittance at a wavelength of 230 nm as described above, but since a thin film was used as the seed crystal as explained in the embodiment of the present invention, no coloring was observed and the light transmittance at a wavelength of 230 nm was 99.9%. The remaining part of the AlN single crystal substrate after this thin film transfer (i.e., the part that was peeled off and separated without being transferred to the support substrate) could be used as a large number of seed crystals by repeatedly performing ion implantation, which was extremely economical. By carrying out this implementation, a φ8-inch III-nitride epitaxial growth substrate was obtained, which was provided with a 2 μm-thick flattening layer and a 0.4 μm-thick AlN seed crystal layer on a support substrate having a structure of (1) an AlN ceramic core and (2) a sealing layer.

[0070] (Substrate evaluation) Next, the Group III nitride epitaxial growth substrate obtained in this example was evaluated as a simple AlN epitaxial growth substrate in the same manner as in Example 1. That is, a 2 μm AlN film was formed on the AlN epitaxial growth substrate by MOCVD, and EPD was measured by molten alkali (KOH+NaOH) etching to evaluate the dislocation density. XRC measurement was also performed to evaluate the crystallinity. As a result, the EPD was 2.3×10 4 cm -2 The result showed an extremely low dislocation density. Furthermore, the full width at half maximum (FWHM) of the (0002) surface of the substrate measured by XRC was 132 arcsec, indicating that a high-quality AlN single crystal was obtained. These results demonstrate that the epitaxial substrate of this example is excellent.

[0071] [Comparative Example 2] The conditions were the same as in Example 2, except that after the AlN crystal was transferred to a thin film, no off-angle was formed and the thin film was used as it was as a seed crystal layer. This epitaxial substrate was used to form a 2 μm AlN film by MOCVD in the same manner as in Example 2, and was evaluated. As a result, the EPD was 6.5 × 10 6 cm -2 The FWHM of the (0002) surface of the substrate was 1950 arcsec in the XRC measurement, and the crystal quality was considerably inferior to that of Example 2. This is thought to be because, in order to increase the size of the seed substrate, multiple AlN substrates were used and bonded together with the orientation aligned, but subtle differences in crystal orientation and the like adversely affected the crystal growth. In contrast, in Example 2, the surface of the seed crystal layer was intentionally provided with an uneven pattern, which is thought to absorb the adverse effects on crystal growth, such as crystal defects and subtle misalignment of orientation. The substrate obtained from this comparative example had poor crystallinity and was unsuitable as an epitaxial substrate for growing a group III nitride single crystal for deep ultraviolet light.

[0072] [Comparative Example 3] A 0.2° off-angle was formed by etching the upper layer of a C-face φ8 inch (725 μm thick) sapphire substrate, which served as both a base substrate and a seed substrate, to prepare an epitaxial substrate. A 2 μm thick AlN film was formed on this substrate by MOCVD in the same manner as in Example 2 and evaluated. As a result, the EPD was 5×10 7 cm -2 The FWHM of the (0002) surface of the substrate measured by XRC was 2500 arcsec, and the crystal quality was considerably inferior to that of Example 2. In addition, the substrate after film formation was significantly warped overall, and could not be attached to a vacuum chuck, making subsequent device processing impossible.

[0073] [Example 3] The conditions were the same as in Example 1, except that the planarization layer was changed from 3 μm thick SiO2 to 2 μm thick AlAs. As a result, a 2 μm thick AlAs planarization layer and a 0.5 μm thick Si <111> A Group III nitride epitaxial growth substrate with a seed crystal layer was obtained. A 50 mm thick layer of AlN was then laminated onto this Group III nitride epitaxial growth substrate by HVPE. The laminate was immersed in a 25% HCl aqueous solution to dissolve the AlAs layer, and a 50 mm thick AlN crystal was separated from the support substrate. The AlN crystal was then cylindrically ground, sliced, and polished to obtain 50 pure φ8 inch AlN single crystal substrates.

[0074] Next, the above substrate was used as an epitaxial substrate for AlN and the same simple evaluation as in Example 1 was carried out. As a result, the EPD was 5.0×10 4 cm -2 The result showed an extremely low dislocation density. Furthermore, XRC measurements of the (0002) surface of the substrate showed a FWHM of 132 arcsec, resulting in a high-quality AlN single crystal. No coloring was observed in this material, and the light transmittance at a wavelength of 230 nm was also good at approximately 90%, making it suitable for use as a device substrate in the deep ultraviolet region.

[0075] As described above, according to the present invention, it is possible to provide an inexpensive substrate for epitaxial growth of III nitrides, which is capable of producing high-quality, large-diameter single crystals of III nitrides. [Explanation of symbols]

[0076] 1 Composite board 2 Seed crystal layer 3 Supporting substrate 4 Planarization layer 5 Stress adjustment layer 20. Single-crystal substrates of group III nitrides 21 Peeling position 22 Underlying substrate 23 Epitaxial layer

Claims

1. A support substrate having a structure in which a core made of a nitride ceramic is enclosed in a sealing layer having a thickness of 0.05 μm to 1.5 μm; a planarization layer provided on an upper surface of the support substrate and having a thickness of 0.5 μm or more and 3.0 μm or less; a single-crystal seed crystal layer having a thickness of 0.1 μm or more and 1.5 μm or less and provided on an upper surface of the planarization layer; a stress adjustment layer provided on the lower surface of the support substrate; A Group III nitride epitaxial growth substrate comprising:

2. 2. The substrate for Group III nitride epitaxial growth according to claim 1, wherein the seed crystal layer has an uneven pattern on its surface.

3. 3. The substrate for III-nitride epitaxial growth according to claim 2, wherein the uneven pattern of the seed crystal layer is selected from the group consisting of periodic grooves, an off-angle of 0.1 to 3 degrees, and a dot structure.

4. 4. The substrate for Group III nitride epitaxial growth according to claim 1, wherein the core is made of aluminum nitride ceramics.

5. 5. The substrate for Group III nitride epitaxial growth according to claim 1, wherein the sealing layer contains silicon nitride.

6. 6. The substrate for Group III nitride epitaxial growth according to claim 1, wherein the planarization layer contains any one of silicon oxide, silicon oxynitride, and aluminum arsenide.

7. 7. The substrate for Group III nitride epitaxial growth according to claim 1, wherein the seed crystal layer is made of Si<111>, SiC, sapphire, aluminum nitride or aluminum gallium nitride.

8. the seed layer is aluminum nitride or aluminum gallium nitride; The resistivity of the seed crystal layer is 1×10 ６ 8. The substrate for Group III nitride epitaxial growth according to claim 1, characterized in that it has a resistivity of Ω·cm or more.

9. 2. The substrate for III-nitride epitaxial growth according to claim 1, wherein the stress adjustment layer contains elemental silicon.

10. Providing a core made of a nitride ceramic; forming a sealing layer having a thickness of 0.05 μm to 1.5 μm inclusive so as to enclose the core, thereby forming a supporting substrate; forming a planarization layer having a thickness of 0.5 μm to 3.0 μm on an upper surface of the support substrate; depositing a stress adjustment layer on a lower surface of the support substrate; providing a single crystal seed crystal layer having a thickness of 0.1 μm or more and 1.5 μm or less on an upper surface of the planarization layer; A method for manufacturing a Group III nitride epitaxial growth substrate comprising the steps of:

11. The method for producing a substrate for III-nitride epitaxial growth according to claim 10, wherein the seed crystal layer is provided so as to have an uneven pattern on its surface.

12. 12. The method for producing a substrate for Group III nitride epitaxial growth according to claim 11, wherein the uneven pattern of the seed crystal layer is selected from the group consisting of periodic grooves, an off-angle of 0.1 to 3°, and a dot structure.

13. 13. The method for producing a substrate for Group III nitride epitaxial growth according to claim 11, wherein the sealing layer is formed by a LPCVD method.

14. 14. The method for producing a Group III nitride epitaxial growth substrate according to claim 11, wherein the planarizing layer is formed by any one of a plasma CVD method, a LPCVD method, and a low-pressure MOCVD method.

15. The step of providing a seed crystal layer includes: providing a single crystal substrate of a group III nitride having one surface as an ion implantation surface; forming a separation position in the single crystal substrate by implanting ions from the ion implantation surface; bonding the ion-implanted surface and the planarization layer to form a bonded substrate; separating the bonded substrate into a seed crystal layer and a remaining portion of the single crystal substrate at the peeling position; providing the seed crystal layer obtained in the separating step with the uneven pattern; The method for producing a Group III nitride epitaxial growth substrate according to any one of claims 11 to 14, comprising:

16. 16. The method for producing a Group III nitride epitaxial growth substrate according to claim 15, characterized in that in the step of preparing a single crystal substrate, an epitaxial layer of aluminum nitride or aluminum gallium nitride is epitaxially grown on a sapphire substrate by any one of MOCVD, HVPE and THVPE methods to produce the single crystal substrate of aluminum nitride or aluminum gallium nitride.

17. 16. The method for producing a Group III nitride epitaxial growth substrate according to claim 15, characterized in that, in the step of preparing a single crystal substrate, the single crystal substrate is obtained by bonding a small-diameter single crystal produced by sublimation deposition or a small-diameter single crystal obtained by epitaxially growing an aluminum nitride or aluminum gallium nitride epitaxial layer by any one of MOCVD, HVPE, and THVPE using an AlN substrate produced by sublimation deposition as a base.

18. 18. The method for producing a Group III nitride epitaxial growth substrate according to claim 16, wherein in the step of forming the separation positions, the separation positions are formed within the epitaxial layer.

19. 19. The method for producing a substrate for Group III nitride epitaxial growth according to claim 17, wherein the remaining portion of the single crystal substrate is reused as a base substrate.

20. The method for producing a Group III nitride-based epitaxial growth substrate according to any one of claims 15 to 19, characterized in that the remainder of the single crystal substrate is reused as a single crystal substrate in the production of yet another Group III nitride-based composite substrate.

21. 21. The method for producing a Group III nitride-based epitaxial growth substrate according to claim 11, wherein the core is made of aluminum nitride ceramics.

22. 22. The method for producing a Group III nitride epitaxial growth substrate according to claim 11, wherein the sealing layer contains silicon nitride.

23. 23. The method for producing a Group III nitride epitaxial growth substrate according to claim 11, wherein the planarization layer contains any one of silicon oxide, silicon oxynitride, and aluminum arsenide.

24. 24. The method for producing a Group III nitride-based epitaxial growth substrate according to claim 12, wherein the seed crystal layer is made of Si<111>, SiC, sapphire, aluminum nitride, or aluminum gallium nitride.

25. The seed crystal layer is made of aluminum nitride or aluminum gallium nitride, and the resistivity of the seed crystal layer is 1×10 ６ The method for producing a Group III nitride epitaxial growth substrate according to any one of claims 11 to 24, characterized in that the resistivity is Ω·cm or more.

26. 11. The method for producing a Group III nitride epitaxial growth substrate according to claim 10, wherein the stress adjustment layer contains elemental silicon.

Images