Laminate with a single-crystal substrate of a group 13 nitride

Abstract

The task is to suppress the reduction of the layer support density and the support mobility in a laminate comprising a buffer layer provided on a first principal surface of a single crystal substrate of a group 13 nitride, a channel layer provided on the buffer layer having a thickness of 700 nm or less, and a barrier layer provided on the channel layer. The laminate 1 comprises a single-crystal substrate 2 of a group 13 nitride, which is composed of a single crystal of a group 13 nitride and has a first principal face 2a and a second principal face 2b, a buffer layer 3 provided on the first principal face 2a of the single-crystal substrate 2 of a group 13 nitride, a channel layer 4 provided on the buffer layer 3, and a barrier layer 5 provided on the channel layer 4. The channel layer 4 has a thickness of 700 nm or less, and the first principal face 2a of the single-crystal substrate 2 of a group 13 nitride has an off angle of 0.4° or more and 1.0° or less.

Description

Technical area

[0001] The present invention relates to a laminate comprising a single crystal substrate made of a Group 13 nitride. TECHNICAL BACKGROUND

[0002] Nitride semiconductor devices are widely used in both optical and electronic components such as high electron mobility transistors (HEMTs). For example, an epitaxial substrate is known that contains a buffer layer, a channel layer, and a barrier layer formed on a freestanding substrate made of a semi-insulating, zinc-doped gallium nitride single crystal.

[0003] For example, Patent Document 1 discloses that the thickness of a channel layer in a HEMT structure on a silicon carbide substrate is less than 500 nm to suppress leakage current and current collapse.

[0004] Furthermore, there is the problem that many defects arise in gallium nitride films grown heteroepitaxially on a substrate made of a different material due to the different lattice constants or thermal expansion coefficients of gallium nitride and the substrate made of the different material. Therefore, the homoepitaxial growth of a gallium nitride film on a gallium nitride substrate was investigated.

[0005] When using a gallium nitride substrate, it is preferable to use a gallium nitride substrate with semi-insulating properties to prevent leakage current between the source-drain electrodes when operating a HEMT device at a high voltage. It is known that doping an element capable of forming a deep acceptor level, such as a transition metal element, in the gallium nitride single crystal is effective for realizing a semi-insulating gallium nitride substrate. Patent Documents 2, 3, and 4 describe the use of zinc, manganese, or iron as such a doping element.

[0006] According to Patent Documents 5 and 6, a semi-insulating and free-standing gallium nitride substrate doped with zinc is disclosed as an epitaxial substrate for a HEMT device. (Previous technical documents)(Patent documents) (Patent Document 1) Japanese Patent Publication No. 2021-002616A (Patent Document 2) Japanese Patent No. 5039813B (Patent Document 3) Japanese Patent Publication No. 2006-024597A (Patent Document 4) Japanese Patent Publication No. 2007-534580A (Patent Document 5) Japanese Patent No. 6730302B (Patent Document 6) Japanese Patent No. 6705831B SUMMARY OF THE INVENTION (Problems to be solved by the invention)

[0007] According to Patent Document 1, it is disclosed that the thickness of the channel layer is less than 500 nm to prevent both leakage current and current collapse in the HEMT structure on the silicon carbide substrate. When the HEMT device operates in a high frequency band, for example, tens of GHz or higher, it is considered effective to reduce the film thickness of the channel layer to prevent property deterioration due to parasitic capacitance of the channel layer.

[0008] When the inventors then fabricated and evaluated an epitaxial substrate with the channel layer of the thin film on a single crystal substrate made of a Group 13 nitride to improve the properties of the HEMT device, the problem arose that the characteristic indices of high carrier density and carrier mobility were reduced.

[0009] An object of the present invention is to suppress the reduction of the layer carrier density and the carrier mobility in a laminate including a buffer layer provided on a first main surface of a Group 13 nitride single crystal substrate, a channel layer provided on the buffer layer and having a thickness of 700 nm or less, and a barrier layer provided on the channel layer. (Solution to the tasks)

[0010] The present invention provides a laminate comprising: a group 13 nitride single crystal substrate comprising a group 13 nitride single crystal and having a first major surface and a second major surface; a buffer layer provided on the first main surface of the Group 13 nitride single crystal substrate; a channel layer provided on the buffer layer; and a barrier layer provided on the channel layer, wherein the channel layer has a thickness of 700 nm or less, and wherein the first major face of the group 13 nitride single crystal has an off-angle of 0.4° to 1.0°. (Effects of the invention)

[0011] The inventors found that the reduction in carrier density and carrier mobility can be suppressed in the laminate including the buffer layer provided on the first main surface of the Group 13 nitride single-crystal substrate, the channel layer provided on the buffer layer and having a thickness of 700 nm or less, and the barrier layer provided on the channel layer, and thus the present invention was carried out. Although the reason for such effects is not clear, the off-angle of the first main surface of the Group 13 nitride single-crystal substrate is set to 0.4° to 1.0°, so that the surface flatness of the thinned channel layer is improved, and it is believed that this improvement contributes to the improvement in carrier density and carrier mobility. BRIEF DESCRIPTION OF THE DRAWINGS Fig.Fig. 1(a) is a diagram schematically showing a laminate 1 according to an embodiment of the present invention, and Fig. 1(b) is a diagram schematically showing a composite substrate 8 for depositing an epitaxial growth layer. Fig. Fig. 2(a) is a representative schematic and perspective view showing a Group 13 nitride single crystal substrate according to a preferred embodiment, and Fig. (b) is a diagram schematically showing the plane orientation and crystalline planes of the crystalline structure of a Group 13 nitride single crystal substrate according to a preferred embodiment. Fig. Figure 3 is a graph showing the dependence of the support density of a channel layer on the off-angle of a zinc-doped group 13 nitride single crystal substrate. Fig.Figure 4 is a graph showing the carrier mobility of a channel layer on the off-angle of a zinc-doped Group 13 nitride single crystal substrate. Fig. Figure 5 is a photograph showing the surface morphology of a channel layer when the off angle of the first major face of a zinc-doped group 13 nitride single crystal substrate is 0.66°. Fig. Figure 6 is a photograph showing the surface morphology of a channel layer when the off angle of the first principal face of a zinc-doped group 13 nitride single crystal substrate is 0.09°. Fig. Figure 7 is a photograph showing the surface morphology of a channel layer when the off angle of the first major face of a zinc-doped group 13 nitride single crystal substrate is 1.15°. Fig.8 is a diagram showing an example of the relationship between the off angle of the first principal surface of a zinc-doped Group 13 nitride single crystal substrate and the carbon concentration of a channel layer. EMBODIMENTS OF THE INVENTION

[0012] Fig. Fig. 1(a) is a diagram schematically showing a laminate 1 according to an embodiment of the present invention.

[0013] A Group 13 nitride single-crystal substrate 2 has a first main surface 2a and a second main surface 2b. The first main surface 2a of the Group 13 nitride single-crystal substrate 2 is selected as the film-forming surface, and epitaxial growth layers are deposited on the first main surface 2a. Specifically, according to the present invention, a buffer layer 3 is formed on the first main surface 2a of the Group 13 nitride single-crystal substrate 2, a channel layer 4 is formed on the main surface 3a of the buffer layer 3, and a barrier layer 5 is formed on the main surface 4a of the channel layer 4. A predetermined electrode or the like may be formed on the main surface 5a of the barrier layer 5.

[0014] A group 13 nitride single crystal substrate 2 is constructed from a group 13 nitride single crystal and has a first main surface 2a and a second main surface 2b.

[0015] The Group 13 element is a Group 13 element according to the IUPAC definition and can particularly preferably be gallium, aluminum, and / or indium. Furthermore, the Group 13 nitride single crystal can preferably be a Group 13 nitride single crystal selected from gallium nitride, aluminum nitride, indium nitride, or their mixed crystals. More specifically, GaN, AlN, InN, Ga x A1 1-x N (1>x>0), Ga x In 1-x N (1>x>0), Al x ln 1-x N (1>x>0) and Ga x Al y In z N (1>x>0, 1>y>0, x+y+z=1) are listed.

[0016] The definition of a single crystal is described. Although it is a single crystal described in textbooks, in which the atoms are regularly arranged throughout the crystal, it is not limited to this type of crystal, but also includes single crystals commonly offered in industry. This means that the crystal may contain defects to some degree, or there may be deformation, or an impurity may be incorporated.

[0017] Furthermore, the Group 13 nitride single-crystal substrate can be a freestanding substrate. The term "freestanding substrate" refers to a substrate that is not deformed or broken under its own weight during handling and can be handled as a solid. The freestanding substrate of the present invention can be used as a substrate for various types of semiconductor devices, such as light-emitting devices.

[0018] In a preferred embodiment, the thickness of the freestanding substrate after polishing may preferably be 300 µm or greater, and preferably 1000 µm or less.

[0019] Although the size of the freestanding substrate is not particularly limited, the size is preferably 2 inches, 4 inches or 6 inches and can be 8 inches or larger.

[0020] As in Fig.As shown in Figure 1(b), an underlying substrate 7 composed of a material whose thermal conductivity is higher than that of a Group 13 nitride single crystal is directly bonded to the second main surface 2b side of the Group 13 nitride single crystal substrate 2, thereby obtaining a composite substrate 8 for depositing an epitaxial growth layer. The material of the underlying substrate may preferably be SiC, AlN, or diamond. Furthermore, the thermal conductivity of the underlying substrate may preferably be 200 W / mK or higher, and more preferably 500 W / mK or higher.

[0021] According to a preferred embodiment, the Group 13 nitride single crystal contains one or two or more elements selected from the group consisting of zinc, manganese, and iron as dopants. For the purposes of the present invention, the total concentration of one or two or more elements selected from the group consisting of zinc, manganese, and iron in the Group 13 nitride single crystal substrate is preferably 1×10 18 atoms / cm 3 up to 1×10 21 atoms / cm 3 and preferred 1×10 19 atoms / cm 3 up to 1×10 21 atoms / cm 3 The concentrations of the elements in the single-crystal Group 13 nitride substrate are measured using SIMS (secondary ion mass spectrometry).

[0022] Furthermore, the Group 13 nitride single crystal may contain an element in addition to the dopant. The element may be, for example, hydrogen (H), oxygen (O), silicon (Si), or the like.

[0023] The off-angle of the first principal surface of the Group 13 nitride single-crystal substrate is 0.4° or more and 1.0° or less. The standard axis of the off-angle can be the a-axis, c-axis, or m-axis of the wurtzite structure.

[0024] Fig. Figure 2(a) is a representative and schematic perspective view showing a single crystal substrate 100 made of a Group 13 nitride according to a preferred embodiment. As shown in Fig.As shown in Fig. 2(a), in the Group 13 nitride single crystal substrate 100 of the embodiment, the plane orientation <0001> (c-axis) is inclined relative to the normal vector A of the first surface. That is, the Group 13 nitride single-crystal substrate 100 of the present embodiment is an off-angle substrate having an off-angle that is inclined relative to the plane orientation <0001> is inclined.

[0025] Fig. Figure 2(b) is a diagram schematically showing the plane orientation and crystal planes of the crystalline structure of the Group 13 nitride single crystal substrate according to a preferred embodiment. Fig.The crystalline structure shown in Figure 2(b) is <0001> Orientation is the c-axis orientation, the <1-100> orientation is the m-axis orientation, and the <11-20> orientation is the a-axis orientation. The top surface of the hexagonal crystal, considered a regular hexagonal prism, corresponds to the c-plane, and the sidewall surface of the regular hexagonal prism corresponds to the m-plane.

[0026] According to the Group 13 nitride single crystal substrate of the present embodiment, the c-plane is inclined with respect to the orientation of the first surface. In other words, according to the Group 13 nitride single crystal substrate of the present embodiment, the <0001> -Orientation (orientation of the c-axis) with respect to the normal vector of the first surface (normal vector “A”, shown in Fig. 2(a)). The direction of the inclination can be the a-axis or the m-axis.

[0027] When the off-angle is 0.4° or more, the reduction in the characteristics of the channel layer can be suppressed even when the channel layer is thinned, and in particular, the reduction in the layer carrier density and the carrier mobility of the secondary electron gas can be suppressed. From this point of view, the off-angle may more preferably be 0.5° or more. When the off-angle exceeds 1.0°, step bunching is generated in micro-regions on the surface of the channel layer, and the distortion at an interface of the channel layer, for example, at an interface between the barrier layer and the channel layer, is changed so that the reduction in the characteristic, in particular, the reduction in the layer carrier density, is observed. With respect to the layer carrier density and the carrier mobility, the off-angle is 1.0° or less, preferably 0.9° or less, and more preferably 0.7° or less.

[0028] According to a preferred embodiment, the single-crystal substrate made of a group 13 nitride has a specific resistance at room temperature of 1×10 7 Ωcm or higher. This means that the Group 13 nitride single-crystal substrate is semi-insulating, effectively preventing the leakage current between the source-drain electrodes in a semiconductor device, such as a HEMT device. From this point of view, the resistivity of the Group 13 nitride single-crystal substrate at room temperature may more preferably be 1×10 9 Ωcm or higher. In addition, the specific resistance of the single-crystal substrate made of a group 13 nitride at room temperature is in many cases 1×10 13 Ωcm or less. (Production of single crystal from a group 13 nitride)

[0029] The method for producing the Group 13 nitride single crystal substrate may be a vapor-phase method such as the MOCVD (Metal Organic Chemical Vapor Deposition) method, the HVPE (Hydride Vapor Phase Epitaxy) method, the PXD (Pulse Excited Deposition) method, the MBE method, the sublimation method, or the like, or a liquid-phase method such as the ammothermal method, the flux method, or the like. More preferably, the Group 13 nitride single crystal is produced by the flux method.

[0030] In the fluxing method, preferably, a seed crystal film is provided on the surface of a supporting substrate such as sapphire, a group 13 nitride single crystal, or the like, and the group 13 nitride single crystal is grown thereon by the fluxing method.

[0031] Al x Ga 1-x N (0≦x≦1) or In x Ga 1-xN (0≦x≦1) can be mentioned as preferred examples of the material of the seed crystal film, and gallium nitride is particularly preferred.

[0032] The method for forming the seed crystal film can preferably be a vapor deposition method, and examples include the MOCVD (metal organic chemical vapor deposition) method, the HVPE (hydride vapor phase deposition) method, the PXD (pulse excited deposition) method, the MBE method, and the sublimation method. The metal organic chemical vapor deposition method is the most preferred method. Furthermore, the growth temperature can preferably be 950 to 1200°C.

[0033] If the single crystal of a Group 13 nitride is grown by a fluxing process, the type of flux is not particularly limited as long as the single crystal can be produced. In a preferred embodiment, the flux contains at least one alkali metal and one alkaline earth metal, with the flux containing sodium metal being particularly preferred.

[0034] A metallic raw material substance is mixed with the flux and applied. The metal raw material substrate can be a single metal, an alloy, or a metal compound, and the single metal is preferred from a handling perspective.

[0035] The growth temperature and holding time for growing a Group 13 nitride single crystal by the fluxing method are not particularly limited and can be adjusted accordingly depending on the composition of the flux. For example, when growing a gallium nitride crystal using a flux containing sodium or lithium, the growth temperature may preferably be 800 to 950°C, and more preferably 850 to 900°C.

[0036] In the fluxing method, the Group 13 nitride single crystal is grown in an atmosphere containing a gas containing nitrogen. The gas may preferably be nitrogen gas and may be ammonia. Although the atmospheric pressure is not particularly limited, it may preferably be 10 atoms or more, and more preferably 30 atoms or more, to prevent the evaporation of the flux. However, the higher the pressure, the larger the scale of the system becomes. Thus, the total pressure of the atmosphere may preferably be 2000 atoms or less, and more preferably 500 atoms or less. Although the gas other than the nitrogen atom in the atmosphere is not limited, an inert gas is preferred, and argon, helium, or neon is particularly preferred.

[0037] According to a particularly preferred embodiment, an MOCVD GaN template is placed in a crucible, and 10 to 60 parts by mass of Ga metal, 15 to 90 parts by mass of Na metal, 0.1 to 5 parts by mass of a total amount of one or more elements selected from the group consisting of zinc metal, manganese metal, and iron metal, and 10 to 500 mg of C are then filled into the crucible. The crucible is placed in a heating furnace, the temperature in the furnace is set at 800°C to 950°C, the pressure in the furnace is set at 3 MPa to 5 MPa, heating is carried out for 20 hours to 400 hours, and the temperature is then cooled to room temperature. After cooling is complete, the crucible is withdrawn from the furnace.

[0038] The resulting gallium nitride single crystal is polished with diamond abrasives to smooth the surface. The gallium nitride single crystal is then formed on the MOCVD GaN template. (Formation of epitaxial growth layers)

[0039] According to the present invention, for example as in Fig. As shown in Fig. 1(a), the respective epitaxial growth layers of a buffer layer 3, a channel layer 4 and a barrier layer 5 are formed on a first main surface 2a of a single crystal substrate 2 made of a group 13 nitride.

[0040] For example, gallium nitride, aluminum nitride, indium nitride, or their mixed crystals are used as epitaxial growth layers grown on the single-crystal substrate made of a group 13 nitride. In particular, gallium nitride (GaN), aluminum nitride (AIN), indium nitride (InN), aluminum gallium nitride (Ga x Al 1-x N) (1>x>0), indium gallium nitride (Ga x In 1-x N) (1>x>0), aluminum indium nitride (Al x In 1-x N) (1>x>0) or aluminum indium gallium nitride (Ga x Al y In zN) (1>x>0, 1>y>0, x+y+z=1).

[0041] The formation of the buffer layer 3, the channel layer 4, and the barrier layer 5 can be performed, for example, by metal-organic chemical vapor deposition (MOCVD). In the formation of the layers by the MOCVD method, organometallic raw material gases (TMG (trimethylgallium), TMA (trimethylaluminum), TMI (trimethylindium), or the like) depending on the target composition, ammonia gas, hydrogen gas, and nitrogen gas are introduced into a reactor of an MOCVD furnace. Group 13 nitride single crystals are then formed by the vapor-phase reaction of the organometallic raw material gases corresponding to the respective layers and ammonia gas, while the group 13 nitride single crystal substrate mounted in the reactor is heated to a predetermined temperature.

[0042] The buffer layer can prevent the diffusion of a metal element doped into the single crystal of a group 13 nitride into the channel layer.

[0043] In a preferred embodiment, the buffer layer is composed of aluminum nitride or aluminum gallium nitride. Since the composition of the buffer layer is such that it has a high aluminum concentration, it is possible to further suppress the diffusion of the metal element into the channel layer. The thickness of the buffer layer is 1 nm or greater and 20 nm or less, so it can act as a back barrier for the electrons of the channel layer, and the layer carrier density and carrier mobility can be improved.

[0044] The preferred growth conditions for the buffer layer in the MOCVD process are as follows. Growth temperature: 700°C to 1200°C Pressure in the reactor: 5 kPa to 30 kPa Carrier gas: hydrogen Ratio of nitrogen gas / element gas of group 13: 5000 to 20000 Ratio of raw material gas for aluminum / raw material gas for element of group 13: 0.7 to 1.0

[0045] The thickness of the channel layer is set to 700 nm or less. This can prevent a degradation of a property due to the parasitic capacitance of the channel layer. The thickness of the channel layer may preferably be 500 nm or less, and more preferably 300 nm or less. Furthermore, the thickness of the channel layer may preferably be 50 nm or more.

[0046] In a preferred embodiment, the channel layer is made of gallium nitride.

[0047] In a preferred embodiment, the carbon content in the epitaxial growth layer is lower. In this case, the carbon concentration of the epitaxial growth layer may preferably be 5×10 16 Atom / cm 3 or less and preferably 2×1016 Atom / cm 3 or less. The carbon concentration in the epitaxial growth layer is measured using SIMS (secondary ion mass spectroscopy).

[0048] According to a preferred embodiment, when the channel layer is grown by MOCVD on the Group 13 nitride single-crystal substrate whose first major surface has an off-angle of 0.4 to 1.0°, the growth temperature is set to 1000°C or less and the growth rate to 1 μm / hour or less. The growth temperature is 1000°C or less so that the diffusion of the metal element doped into the Group 13 nitride single-crystal substrate into the channel layer is suppressed, and the reduction in the layer carrier density and carrier mobility is suppressed when the channel layer is thinned.

[0049] That is, in the case where the channel layer is thinned, the method for preventing the increase in resistance and deterioration of the crystallinity of the channel layer due to the diffusion and contamination of the dopant element, particularly Zn, Fe, or Mn, of the Group 13 nitride single-crystal substrate into the channel layer is investigated. As a result, it is found that the diffusion of the dopant element into the channel layer can be suppressed and high crystallinity can be achieved by setting the growth temperature of the channel layer to 1000°C or less and the growth rate to 1 μm / hour or less.Although there is a risk of deterioration in the surface flatness or an increase in the carbon concentration of the channel layer when the channel layer is grown at 1000°C or less, high surface flatness can be achieved when the growth rate is 1 µm / hour or less and the off angle of the first main surface of the Group 13 nitride single-crystal substrate is 0.4° or more. According to a preferred embodiment, it is possible to use a carbon concentration of 2×10 10 / cm 3 or less.

[0050] From this point of view, the growth temperature of the channel layer may preferably be 990°C or lower. Furthermore, the growth temperature of the channel layer may preferably be 950°C or higher. At a growth temperature of 950°C or lower, pits are more likely to be formed on the surface of the epitaxial growth layer. The growth temperature may preferably be set to 960°C or higher.

[0051] From the above-described perspectives, the growth rate of the channel layer may preferably be 0.8 μm / hour or less. Furthermore, the growth rate of the channel layer may preferably be 0.3 μm / hour or higher, and more preferably 0.5 μm / hour or higher. At a growth rate of less than 0.3 μm / hour, the surface flatness of the channel layer tends to deteriorate.

[0052] The preferred fabrication conditions for the channel layer are as follows: Growth temperature: as described above Pressure in the reactor: 30 kPa to 105 kPa Carrier gas: hydrogen Ratio of nitrogen gas / gas for the element(s) of group 13: 1000 to 10000

[0053] In a preferred embodiment, the barrier layer is composed of indium aluminum gallium nitride, indium aluminum nitride or aluminum gallium nitride.

[0054] If the barrier layer is made of aluminum gallium nitride by MOCVD, the following manufacturing conditions are preferred. Growth temperature: 1000°C to 1200°C Pressure in the reactor: 1 kPa to 30 kPa Ratio of nitrogen gas / raw material gas for the element(s) of Group 13: 5000 to 20000 Carrier gas: hydrogen Ratio of raw material gas for aluminum / raw material gas the element(s) of group 13: 0.1 to 0.4

[0055] If the barrier layer is made of aluminum indium nitride by MOCVD, the following manufacturing conditions are preferred. Growth temperature: 700°C to 900°C Pressure in the reactor: 1 kPa to 30 kPa Ratio of nitrogen gas / raw material gas for the element(s) of Group 13: 2000 to 20000 Carrier gas: nitrogen Ratio of raw material gas for indium / raw material gas the element(s) of group 13: 0.1 to 0.9

[0056] If the barrier layer is made of aluminum indium gallium nitride by MOCVD, the following manufacturing conditions are preferred. Growth temperature: 700°C to 1000°C Pressure in the reactor: 1 kPa to 30 kPa Ratio of nitrogen gas / raw material gas for the element(s) of Group 13: 2000 to 20000 Carrier gas: nitrogen Raw material gas for aluminum / raw material gas for the element(s) of Group 13: 0.1 to 0.9 Raw material gas for indium / raw material gas for the element(s) of group 13: 0.1 to 0.9 EXAMPLES (Experiment A) (Preparation of a zinc-doped gallium nitride single-crystal substrate) Preparation of the GaN template

[0057] A 2 µm-thick seed film composed of gallium nitride was deposited by MOCVD on the surface of a 2-inch diameter c-plane sapphire substrate to obtain an MOCVD GaN template suitable for use as a seed substrate. At this time, the off-angle of the c-plane sapphire substrate was adjusted accordingly so that the off-angle of the deposition surface of the MOCVD GaN template was between 0 and 1.2°, allowing the fabrication of a variety of GaN templates with different off-angles of the deposition surfaces. Formation of zinc-doped gallium nitride single crystal by fluxing

[0058] By applying a variety of the resulting MOCVD-GaN templates as seed substrates and the Na fluxing process, zinc-doped gallium nitride single crystals were formed. Specifically, gallium metal and sodium metal as raw materials, and powdered zinc as a dopant, were placed in an alumina crucible, and the crucible was sealed with an alumina lid. The ratio of gallium metal to sodium metal was set at 15 mol% Ga / (Ga+Na) (mol%). The crucible was placed in a heating furnace. The temperature inside the furnace was set at 850°C, the pressure inside the furnace was set at 4.5 MPa, and heating was carried out for 100 hours, followed by cooling to room temperature. After cooling, the alumina crucible was withdrawn from the furnace to confirm that a gallium nitride single crystal with a thickness of approximately 1000 µm had deposited on the surface of the seed substrate. Flattening of the surface

[0059] The resulting gallium nitride single crystal was polished with diamond abrasives to flatten the surface, resulting in a total thickness of 700 µm of the gallium nitride single crystal formed on the c-plane substrate. In this way, the GaN single crystal was formed on the MOCVD GaN template. Since the resulting underlying substrate and the gallium nitride single crystal were observed visually, cracks were not observed in all of them. Separation of the seed crystal substrate

[0060] The seed crystal substrate was separated from the gallium nitride single crystal by laser lift-off method to obtain a gallium nitride single crystal substrate. Processing the wafer

[0061] The first main surface and the second main surface of the gallium nitride single crystal substrate were subjected to polishing treatment to obtain a zinc-doped gallium nitride single crystal substrate with a thickness of 400 µm. Measurement of specific resistance

[0062] The resistivity of the zinc-doped gallium nitride single crystal substrate was measured using the electrical capacitance method and yielded a value of 5×10 7 up to 2×10 11 Ωcm. Formation of epitaxial growth layers

[0063] The buffer layer 3, the channel layer 4 and the barrier layer 5 were grown on the first main surface 2a of the zinc-doped gallium nitride single crystal substrate 2 by MOCVD to manufacture the laminate 1.Regarding the formation of the layers by MOCVD, in the case where the buffer layer is formed of aluminum nitride or aluminum gallium nitride, the channel layer is formed of gallium nitride, and the barrier layer is formed of aluminum gallium nitride, an MOCVD furnace is used in which the respective organic metal (MO) raw material gases of gallium and aluminum (trimethylgallium (TMG): trimethylaluminum (TMA)), ammonia gas, hydrogen gas, and nitrogen gas can be fed into a reactor, a zinc-doped gallium nitride single crystal substrate mounted in the reactor is heated to a predetermined temperature, and a gallium nitride crystal and an aluminum gallium nitride crystal are generated by vapor-phase reaction of ammonia gas and the organic metal raw material gases corresponding to the respective layers, and are sequentially deposited on the free-standing substrate.If the barrier layer is made of aluminum indium nitride or aluminum indium gallium nitride, an organic metal raw material gas (trimethylindium) containing indium is also used.

[0064] The following manufacturing conditions apply in detail. (Buffer layer: AIN) Growth temperature: 980°C Pressure in the reactor: 5 kPa Ratio of gas for group 15 / gas for group 13: 15000 Al raw material gas / raw material gas for group 13: 1.0 Thickness: 20 nm (Channel layer: GaN) Growth temperature: 980°C Pressure in the reactor: 100 kPa Ratio of gas for group 15 / gas for group 13: 6800 Growth rate: 0.7 µm / hour Thickness: 200 nm (Barrier layer: AlGaN) Growth temperature: 1050°C Pressure in the reactor: 5 kPa Ratio of gas for group 15 / gas for group 13: 12000 Ratio of Al raw material gas / raw material gas for Group 13 element: 0.25 Thickness: 25 nm Manufacturing a device for measuring the Hall effect

[0065] A device for measuring the carrier density and carrier mobility of the thus-obtained epitaxial substrate for a semiconductor device was fabricated. As a measuring device, a plurality of chips, each 6 mm square, were cut out of the epitaxial substrate for a semiconductor device, and ohmic electrodes were formed near the ends at the four corners of the chips. A 1 mm square pattern of Ti / Al / Ni / Au was fabricated by vacuum deposition and photolithography as an electrode for Hall measurement. The respective thicknesses of the metal layers of Ti, Al, Ni, and Au can preferably be fabricated in a range of 5 nm to 50 nm, a range of 40 nm to 400 nm, a range of 4 nm to 40 nm, and a range of 20 nm to 200 nm, in this order.Thereafter, a heat treatment is preferably carried out at 600°C to 1000°C under a nitrogen atmosphere for 10 seconds to 1000 seconds to improve the ohmic properties of the source electrode 500 and the drain electrode 600. Measurement of carrier density and carrier mobility

[0066] The carrier density and room-temperature carrier mobility of the epitaxial growth layer of the as-fabricated Hall measurement device were measured using the Hall effect measurement (van der Pauw method). The Hall effect measurement was performed using a Hall effect measurement system ("ResiTest 8300," manufactured by TOYO Corporation). The measurement results are shown in Table 1. Fig. 3 further shows the relationship between the off-angle and the substrate density, and Fig. Figure 4 shows the relationship between the off-angle and carrier mobility.

[0067] Based on the Al composition and film thickness of the barrier layer investigated according to the present embodiment, a substrate density of 8.5×10 12 / cm 3 or higher and an electron mobility of 1400cm 2 / Vs or higher is considered good. Measuring the off-angle

[0068] To investigate the relationship between carrier density, carrier mobility, and off-angle, the off-angle of the first principal surface of the zinc-doped gallium nitride single-crystal substrate of the Hall measurement device was measured using X-ray diffraction. The X-ray diffraction measurement was performed using a multipurpose X-ray diffraction system ("D8 DISCOVER," manufactured by Bruker AXS Corporation). The measurement results for the respective examples are listed in Table 1.

[0069] The relationship between the off-angle and the substrate density is shown in Fig.3 and the relationship between the off-angle and the wearer mobility was shown in Fig. 4 shown. Table 1 Off-angle of substrate [degrees] Substrate density [ / cm] 2 Carrier mobility [cm 2 / V*s] Comparison example 1,15 8,30E+12 1452 Comparison example 1,09 8,49E+12 1468 Comparison example 1,05 8,61E+12 1482 Invention example 0,98 9,02E+12 1497 Invention example 0,81 9,15E+12 1495 Invention example 0,66 9,22E+12 1498 Invention example 0,52 9,13E+12 1496 Invention example 0,42 9,01E+12 1493 Comparison example 0,37 8,56E+12 1437 Comparison example 0,23 7,72E+12 1259 Comparison example 0,09 5,95E+12 940

[0070] As can be seen from Table 1, the carrier density and carrier mobility are high when the off-angle of the first major surface (epitaxial growth surface) of the zinc-doped gallium nitride single-crystal substrate is in the range of 0.4 to 1.0°. Conversely, when the off-angle of the first major surface of the zinc-doped gallium nitride single-crystal substrate is less than 0.4° or more than 1.0°, the carrier density and carrier mobility are demonstrably lower. Assessment of surface morphology

[0071] The surface morphology of the epitaxial growth layer was observed using an infinite interference optical microscope ("DM8000M", manufactured by LEICA Corporation). The observation magnification was 100x. As a result, according to the inventive examples, in which the off-angle of the first main surface 2a of the zinc-doped gallium nitride single-crystal substrate 2 was 0.4° to 1.0°, a good surface morphology with low surface roughness of the channel layer was confirmed. Fig. For example, Figure 5 shows the surface morphology of the channel layer in the case where the off-angle of the first main face of the zinc-doped Group 13 nitride single crystal substrate is 0.66° and a smooth surface morphology with low roughness is observed.

[0072] On the other hand, in the comparative examples where the off-angles were outside the range, the surface roughness of the channel layer was found to be large. That is, in the case where the off-angle was below 0.4°, a morphology was observed in which many island-like fine protrusions were scattered on the surface of the channel layer. Fig. For example, Figure 6 shows the surface morphology of the channel layer for the case where the off-angle is 0.09°.

[0073] If the off-angle is large, step bunching also occurs. Fig. For example, Figure 7 shows the surface morphology of the channel layer for the case where the off-angle is 1.15°, indicating that many fine and elongated steps are formed. Assessment of carbon concentration in the channel layer

[0074] The carbon concentration in the channel layer was measured using SIMS. The results are shown in Fig. 8. For samples with an angle of 0.4° or more, the carbon concentration in the channel layer is proven to be 1×10 10 / cm 3 or below. On the other hand, an increase in the carbon concentration in the channel layer was observed for samples with an off-angle below 0.4°. (Experiment B)

[0075] The off-angle described above was set to 0.6° in Experiment A. Furthermore, the thickness of the channel layer was changed to 1000 nm, 700 nm, 500 nm, 200 nm, 100 nm, 50 nm, or 30 nm by adjusting the growth time. Subsequently, the layer carrier density and carrier mobility of the channel layer were measured at room temperature by Hall effect measurement (van der Pauw method). Furthermore, the parasitic capacitance of the channel layer was measured using the CV method. In the CV method, a shot-key electrode with a length of φ 1 cm was formed and a measurement frequency of 100 kHz was applied. The parasitic capacitance at an application of -3 V was measured, and the results are listed in Table 2. Table 2 Thickness of the channel layer (nm) Capacitance (pF) Substrate density ( / cm 2 ) Carrier mobility (cm 2 / V*s) 1000 1415 9,15E+12 1492 700 138 9,16E+12 1495 500 21,5 9,20E+12 1496 200 11,8 9,22E+12 1498 100 3,5 9,17E+12 1496 50 1,5 9,19E+12 1498 30 1,3 4,20E+12 853

[0076] When the channel layer thickness is in the range of 50 nm to 700 nm, the parasitic capacitance can be reduced. At the same time, the carrier density and carrier mobility are good at a channel layer thickness in the range of 50 nm to 700 nm. At a channel layer thickness of 30 nm, the carrier density is demonstrably low. It is assumed that carrier generation in the 2DEG layer is suppressed. (Experiment C: Mn doping)

[0077] Mn-doped gallium nitride single-crystal substrates were grown under the same conditions as in Experiment A. However, the dopant added to the flux was replaced with powdered manganese. As a result, a variety of Mn-doped gallium nitride single-crystal substrates with different off-angles were obtained. The room-temperature resistivity of the Mn-doped gallium nitride single-crystal substrate was measured using an electron capacitance system and was 8×10 7 up to 3×10 11 Ωcm.

[0078] Then, the buffer layer, the channel layer, and the barrier layer were deposited on the first major surface of the Mn-doped gallium nitride single-crystal substrate under the same conditions as in Experiment A. The substrate carrier density and the room-temperature carrier mobility of the channel layer were measured by Hall effect measurement (van der Pauw method). The measurement results are shown in Table 3.

[0079] As a result, good results for the support density and support mobility were obtained when the off-angle was in the range of 0.4 to 1.0°. Table 3 Off-angle of substrate [degrees] Substrate density [ / cm 2 ] Carrier mobility [cm 2 / V*s] Comparison example 1,10 7,87E+12 1402 Invention example 0,95 8,59E+12 1445 Invention example 0,67 8,86E+12 1472 Invention example 0,50 8,74E+12 1469 Invention example 0,42 8,56E+12 1460 Comparison example 0,36 8,00E+12 1370 Comparison example 0,24 7,15E+12 1322 (Experiment D: Fe doping)

[0080] Fe-doped gallium nitride single-crystal substrates were grown under the same conditions as in Experiment A. However, the dopant added to the flux was replaced with powdered iron. As a result, a variety of Fe-doped gallium nitride single-crystal substrates with different off-angles were obtained. The specific resistance of the Fe-doped gallium nitride single-crystal substrate at room temperature was measured using the electrical capacitance method and yielded a value of 1×10 7 up to 2×10 9 Ωcm.

[0081] Then, the buffer layer, the channel layer, and the barrier layer were deposited on the first major surface of the Mn-doped gallium nitride single-crystal substrate under the same conditions as in Experiment A. The carrier density and the carrier mobility at room temperature of the epitaxial growth layer were measured using the Hall effect measurement method (van der Pauw method). The measurement results are shown in Table 4.

[0082] As a result, good results were obtained for the support density and support mobility when the off-angle is in the range of 0.4 to 1.0°. Table 4 Off-angle of substrate [degrees] Substrate density [ / cm 2 ] Carrier mobility [cm 2 / V*s] Comparison example 1,07 8,03E+12 1395 Invention example 0,92 8,32E+12 1422 Invention example 0,70 8,37E+12 1443 Invention example 0,63 8,40E+12 1440 Invention example 0,43 8,21E+12 1417 Comparison example 0,33 7,62E+12 1328 Comparison example 0,20 7,21E+12 1310 QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2021-002616A

[0006] JP 5039813B

[0006] JP 2006-024597A

[0006] JP 2007-534580A

[0006] JP 6730302B

[0006] JP 6705831B

[0006]

Claims

[1] Laminate, comprising: a group 13 nitride single crystal substrate comprising a group 13 nitride single crystal and having a first major surface and a second major surface; a buffer layer provided on the first main surface of the Group 13 nitride single crystal substrate; a channel layer provided on the buffer layer; and a barrier layer provided on the channel layer, wherein the channel layer has a thickness of 700 nm or less, and wherein the first main surface of the Group 13 nitride single crystal substrate has an off angle of 0.4° or more and 1.0° or less. [2] The laminate according to claim 1, wherein the Group 13 nitride single crystal contains one or more elements selected from the group consisting of zinc, manganese and iron as a dopant. [3] The laminate according to claim 1 or 2, wherein the single crystal substrate made of a Group 13 nitride has a specific resistance of 1 × 10 7 Ωcm or higher. [4] The laminate according to any one of claims 1 to 3, wherein the channel layer has a thickness of 50 nm or greater. [5] A laminate according to any one of claims 1 to 4, wherein the buffer layer comprises aluminum nitride or aluminum gallium nitride. [6] The laminate according to any one of claims 1 to 5, wherein the buffer layer has a thickness of 1 nm or greater and 20 nm or less, and wherein the buffer layer comprises aluminum nitride or aluminum gallium nitride. [7] A laminate according to any one of claims 1 to 6, wherein the channel layer has a carbon concentration of 2 × 10 10 / cm 3 or less. [8] A laminate according to any one of claims 1 to 7, wherein the barrier layer comprises indium aluminum gallium nitride, indium aluminum nitride or aluminum gallium nitride. [9] A laminate according to any one of claims 1 to 8, wherein the channel layer comprises gallium nitride. [10] The laminate according to any one of claims 1 to 9, wherein the first major surface has an off-angle of 0.5° or more and 0.7° or less. [11] A laminate according to any one of claims 1 to 10, wherein the single crystal of a Group 13 nitride is produced by a fluxing process.

Images