Method for growing group 13 element nitride crystal layer, nitride semiconductor ingot, and sputtering target

Abstract

A 13-group element nitride crystal layer is grown at a high growth rate to obtain a crystal layer having a large thickness. A 13-group element nitride crystal layer is grown on a base substrate including at least a seed layer. The base substrate is immersed in a melt solution including a flux, and a 13-group element nitride crystal layer is grown two-dimensionally on a nitrogen-polar surface of the seed layer by a flux method.

Description

Technical Field

[0001] This invention relates to a method for cultivating nitride crystal layers of group 13 elements, nitride semiconductor ingots, and sputtering targets. Background Technology

[0002] Nitride semiconductors have a wide bandgap due to their direct transition, as well as a high insulating breakdown electric field and a high saturation electron velocity. Therefore, they have attracted much attention as semiconductor materials for light-emitting devices such as LEDs and LDs, as well as high-frequency / high-power electronic devices.

[0003] It is known that gallium nitride crystals can be grown along the -c axis on the inner wall of a crucible using a so-called flux method (Patent Document 1: Japanese Patent Application Publication No. 2005-206415). In this method, elements such as Mn, Fe, Cr, Co, and Ni are added to the melt to promote the growth of gallium nitride crystals on the N-side of the inner wall of the crucible. However, in the embodiments, only columnar crystals with a length of about 1.5 mm were obtained.

[0004] On the other hand, a method for producing ingots by growing thick gallium nitride crystals was proposed.

[0005] For example, Patent Document 2 (Japanese Patent Application Publication No. 2010-280562) discloses a method in which gallium nitride crystals are grown to a thicker thickness by combining flux method and vapor phase method, and are processed to form an ingot with a surface roughness Ra of less than 5 nm and a warping radius of curvature of more than 2 m.

[0006] In addition, the following technology is disclosed: sputtering target is fabricated by sintering gallium nitride crystalline powder (Patent Document 3: WO2016 / 158651).

[0007] In addition, as a direct bonding method that utilizes surface activation treatment, a method for bonding GaN to a support substrate at room temperature by means of an oxide layer is disclosed (Patent Document 4: (0060) to (0061) of Japanese Patent Application Publication No. 2019-003090).

[0008] In addition, a method was disclosed in which GaN thin film is irradiated with a UV laser to decompose GaN at the interface between GaN and the substrate, and the GaN thin film is peeled off from the substrate (Patent Document 5: Japanese Patent Application Publication No. 2000-101139). Hereinafter, this method will be referred to as the laser ablation method.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2005-206415

[0012] Patent Document 2: Japanese Patent Application Publication No. 2010-280562

[0013] Patent Document 3: WO2016 / 158651

[0014] Patent Document 4: Japanese Patent Application Publication No. 2019-003090

[0015] Patent Document 5: Japanese Patent Application Publication No. 2000-101139

[0016] Patent Document 6: Japanese Patent Application Publication No. 2005-263622 Summary of the Invention

[0017] As can be seen from Patent Document 6 (Japanese Patent Application Publication No. 2005-263622), the upper limit of the growth rate of GaN crystal growth using the flux method is about 100 μm / h.

[0018] Furthermore, Patent Document 3 discloses that when a gallium nitride thin film is formed using a sputtering target obtained by sintering and processing gallium nitride powder, the oxygen concentration of the gallium nitride thin film is greater than 1×10⁻⁶. 20 cm -3 Regarding powdered gallium nitride (GaN), due to its large surface area, it is easily oxidized in the atmosphere. Oxygen is released at the start of the sputtering process, and while a GaN film is formed on the substrate, oxygen is easily introduced into the interior. Therefore, it is considered difficult to form a homogeneous GaN film with low oxygen concentration.

[0019] If GaN is grown to a thicker thickness using methods such as HVPE or fluxing to form bulk GaN materials, rather than sintered GaN powder, it should be possible to form sputtering targets with low impurity concentrations, especially low oxygen concentrations, and to form gallium nitride thin films with low oxygen concentrations using sputtering. However, it can be considered that to achieve a suitable thickness for sputtering targets, the growth time is long, and warping and cracking are prone to occur. Therefore, it is difficult to fabricate sputtering targets using existing methods.

[0020] The objective of this invention is to obtain a thicker nitride crystal layer of group 13 elements by growing the nitride crystal layer at a high cultivation rate.

[0021] Furthermore, the objective of this invention is to obtain a homogeneous sputtering target with a low oxygen concentration.

[0022] This invention relates to a method for cultivating a group 13 element nitride crystalline layer on a substrate containing at least a seed layer, characterized in that...

[0023] The substrate is immersed in a molten liquid containing flux, and a group 13 nitride crystal layer is cultured two-dimensionally on the nitrogen polar surface of the seed layer by means of flux method.

[0024] In addition, the present invention relates to nitride semiconductor ingots, characterized in that they are formed of group 13 element nitrides, with a diameter of 75 mm or more and 200 mm or less, and a thickness of 5 mm or more and 50 mm or less.

[0025] Furthermore, a method for manufacturing a substrate is provided, which manufactures a substrate for cultivating a group 13 element nitride crystal layer, the method being characterized by comprising:

[0026] The process of forming a seed layer on the substrate,

[0027] The process of bonding the group 13 element polar facets of the seed layer to the support substrate, and

[0028] The process of peeling the substrate from the seed layer to obtain a base substrate including the seed layer and the support substrate, wherein the nitrogen polar surface of the seed layer is exposed.

[0029] Invention Effects

[0030] When cultivating group 13 nitride crystal layers using a flux method, the inventors of this invention attempted to place seed crystals in a molten solution and grow the group 13 nitride crystal layers two-dimensionally on the nitrogen polar surface of the seed crystals. As a result, they found that compared to cultivating group 13 nitride crystal layers on the polar surface of group 13 elements (e.g., the gallium polar surface), the group 13 nitride crystal layers could grow at a high cultivation rate.

[0031] As a result, thick films, such as group 13 element nitride crystal layers with a thickness of 5 mm or more, can be grown at a practical speed, thereby enabling the production of nitride semiconductor ingots. It is evident that these nitride semiconductor ingots possess excellent properties as, for example, sputtering targets, particularly providing homogeneous targets with low oxygen concentrations.

[0032] Furthermore, it is known that the nitride semiconductor ingot obtained above can be sliced ​​to produce multiple nitride semiconductor wafers, which is an extremely excellent mass production method.

[0033] Furthermore, regarding the nitride semiconductor ingot obtained above, it is known that the crystal lattice is moderately curved internally, and the lattice orientation (especially the c-plane) is moderately shifted between the nitrogen polar plane and the group 13 element polar plane. In this nitride semiconductor ingot, as crystal growth occurs, the growth facet approaches a single crystal; therefore, the in-plane crystallization strain of the nitride semiconductor wafer obtained by slicing the nitride semiconductor ingot is reduced. Accordingly, a nitride semiconductor wafer with a smaller in-plane deflection angle distribution is obtained. Attached Figure Description

[0034] Figure 1In the diagram, (a) represents the state in which a seed layer 2 is formed on the substrate 1, (b) represents the state in which activation beams A and B are irradiated onto the surface 2a of the seed layer 2 and the surface 3a of the support substrate 3, and (c) represents the state in which the seed layer 2 and the support substrate 3 are directly bonded together.

[0035] Figure 2 In the diagram, (a) represents the state after the substrate 1 is peeled off from the seed layer 2, (b) represents the state after a group 13 nitride crystal layer 4 is grown on the nitrogen polar surface 2b of the seed layer 2, (c) represents the state after the support substrate 3 is peeled off from the group 13 nitride crystal layer 4, and (d) represents the ingot 5 formed from the group 13 nitride crystal layer.

[0036] Figure 3 This is a plan view showing the measurement area in the nitride semiconductor ingot 5 and the nitride semiconductor wafer obtained by slicing the nitride semiconductor ingot. Detailed Implementation

[0037] The present invention will now be described in detail with appropriate reference to the accompanying drawings.

[0038] In preferred examples, such as Figure 1 As shown in (a), a seed layer 2 is formed on surface 1a of substrate 1. At this time, 2b is set as the nitrogen polar surface, and the growth surface 2a is set as the group 13 element polar surface.

[0039] Next, the seed layer 2 is bonded to the separate support substrate. In a preferred embodiment, such as... Figure 1 As shown in (b), the polar surface 2a of the group 13 element in the seed layer 2 is irradiated with an activation beam A to perform surface activation. Additionally, as shown by arrow B, the surface 3a of the support substrate 3 is irradiated with an activation beam to perform surface activation.

[0040] Next, as Figure 1 As shown in (c), the polar surface 2a of the group 13 element of the seed layer 2 is brought into contact with the active surface 3a of the support substrate 3 for direct bonding, thereby obtaining a bond.

[0041] Next, as Figure 2 As shown in (a), the substrate 1 is separated from the seed layer 2 to obtain the substrate 6. At this moment, the nitrogen polar surface 2b of the seed layer 2 is exposed. Next, as... Figure 2 As shown in (b), the group 13 element nitride crystal layer 4 is grown on the nitrogen polar surface 2b of the seed layer 2 by means of flux method.

[0042] Next, the support substrate 3 is removed from the crystal layer 4, thereby... Figure 2 (c) shows a laminate consisting of crystallization layer 4 and seed layer 2. Next, seed layer 2 is removed, thus... Figure 2(d) also shows the nitride semiconductor ingot 5. It should be noted that 4a and 5a are nitrogen polar surfaces, and 4b and 5b are group 13 element polar surfaces.

[0043] In this invention, a group 13 element nitride crystal layer is grown on a substrate containing at least a seed layer. The entire substrate may be composed of the seed layer; however, it is preferable to form the seed layer on a support substrate.

[0044] At this point, a 13-element nitride crystal layer is cultured in two dimensions on the nitrogen polar surface of the seed layer using a flux method.

[0045] It should be noted that two-dimensional cultivation of group 13 element nitride crystal layers refers to crystal growth, in which the nitrogen polarity surface of the seed layer is covered to form a crystal layer.

[0046] In this invention, it is preferable to grow a Group 13 nitride crystal layer to a thickness of 5 mm or more on the nitrogen polar surface of the seed layer, and more preferably to a thickness of 10 mm or more. Furthermore, there is no particular upper limit to the thickness of the Group 13 nitride crystal layer; in practice, thicknesses of 50 mm or less are common.

[0047] It should be noted that when growing a group 13 nitride crystal layer using a flux method, if the group 13 nitride crystal layer is directly epitaxially grown to a relatively thick thickness on the nitrogen polar surface of the substrate, the crystal may crack along with the substrate. However, in the aforementioned preferred embodiment, after forming a seed layer on the substrate, the seed layer is bonded to a separate support substrate. Then, the original substrate is removed, thereby exposing the nitrogen polar surface of the seed layer on the support substrate. When the group 13 nitride crystal layer is grown to a relatively thick thickness on this nitrogen polar surface using a flux method, since delamination occurs at the interface between the support substrate and the crystal before the crystal cracks along with the support substrate, cracking can be prevented, and a thicker crystal can be obtained. Accordingly, a sufficiently thick nitride semiconductor ingot can be obtained.

[0048] Preferably, a low-temperature buffer layer is formed on the substrate before the seed layer is formed. The preferred method for forming the buffer layer is vapor phase growth, such as metal-organic chemical vapor deposition (MOCVD), hydride vapor phase growth (HVPE), or MBE.

[0049] Regarding methods for forming the seed layer, vapor phase growth is a preferred example, including: Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Growth (HVPE), Pulse Excitation Deposition (PXD), MBE, and Sublimation. Metal-Organic Chemical Vapor Deposition is particularly preferred.

[0050] Furthermore, among the group 13 nitrides that constitute the seed layer, the group 13 elements are those in group 13 of the periodic table as defined by IUPAC. Specifically, group 13 elements include boron, gallium, aluminum, indium, and thallium.

[0051] From the viewpoint of preventing melting and disappearance during crystallization cultivation, the thickness of the seed layer is preferably 0.5 μm or more, and more preferably 2 μm or more. Furthermore, from the viewpoint of productivity, the thickness of the seed layer is preferably 15 μm or less.

[0052] While the substrate material is not particularly limited, it needs to be able to crystallize and grow along the direction exposed by the polar facet of the group 13 element in the seed layer. From this perspective, examples of substrate materials include: sapphire, oriented alumina, and single crystals of group 13 nitrides.

[0053] Furthermore, while the material of the support substrate is not particularly limited, examples include sapphire, crystalline oriented alumina, and group 13 nitride single crystals. From an operational point of view, the thickness of the support substrate is preferably 500 μm or more, and more preferably 1000 μm or more.

[0054] Examples of bonding methods that connect the seed layer on the substrate to the support substrate include: direct bonding and bonding using adhesives.

[0055] For example, CBED (converged electron diffraction) can be used to confirm whether the growth surface of a group 13 nitride crystal layer is a nitrogen polar surface. Specifically, an electron beam is focused onto the sample for incident illumination, and a circular diffraction spot from the sample is obtained. This spot is then compared with a simulated diffraction image (CBED image), which confirms that the surface is nitrogen polar.

[0056] When cultivating a group 13 element nitride crystal layer on the nitrogen polar surface of the seed layer, a flux method is used to cultivate the group 13 element nitride crystal layer. In this group 13 element nitride crystal layer, the group 13 element is: a group 13 element in the periodic table established by IUPAC. Specifically, the group 13 element nitride is preferably GaN, AlN, InN, AlGaN, or a mixture thereof.

[0057] The preferred crystal layer for Group 13 nitrides is a single crystal. The definition of a single crystal is given below. A single crystal, as used in textbooks, includes, but is not limited to, a single crystal in general industrial use, where atoms are arranged in a regular pattern throughout the crystal. That is, it means that the crystal may contain some degree of defects, internal strain, or impurities, and is used to distinguish it from polycrystalline (ceramic) crystals.

[0058] When using a flux method to cultivate a group 13 element nitride crystal layer, the type of flux is not particularly limited as long as it can generate gallium nitride crystals. In a preferred embodiment, the flux contains at least one of an alkali metal and an alkaline earth metal, and is particularly preferred to contain a flux containing metallic sodium.

[0059] Metallic raw materials are mixed with flux for use. Metallic raw materials can be elemental metals, alloys, or metal compounds; however, from an operational perspective, elemental metals are preferred.

[0060] The cultivation temperature and holding time of the group 13 nitride crystal layer in the flux method are not particularly limited and can be appropriately modified according to the composition of the flux. In one example, when using a flux containing sodium or lithium to cultivate gallium nitride crystals, the cultivation temperature is preferably 800–950°C, and more preferably 850–900°C.

[0061] According to the flux method, a crystalline layer of group 13 element nitrides is grown in an atmosphere containing a gas containing nitrogen atoms. This gas is preferably nitrogen, but ammonia can also be used. The pressure of the atmosphere is not particularly limited, but from the viewpoint of preventing flux evaporation, it is preferably 10 atmospheres or more, more preferably 30 atmospheres or more. However, if the pressure is higher, the apparatus will be scaled up; therefore, the total pressure of the atmosphere is preferably 2000 atmospheres or less, more preferably 500 atmospheres or less. The gas in the atmosphere other than the nitrogen-containing gas is not limited, but inert gases are preferred, particularly argon, helium, and neon.

[0062] To achieve two-dimensional growth of a group 13 element nitride crystal layer on the nitrogen polarity surface of the seed layer using a flux method, it is preferable to horizontally place the substrate in the crucible, thereby facilitating nitrogen supply to the entire surface of the seed layer on the substrate. Furthermore, it is preferable to sufficiently increase the nitrogen concentration in the flux solution. To increase the nitrogen concentration, the flux solution needs to be thoroughly stirred at a high temperature to dissolve the nitrogen until the entire liquid is supersaturated with nitrogen.

[0063] While there are no particular limitations on the method for separating the substrate and the seed layer, and the method for separating the support substrate from the group 13 nitride crystal layer, examples include grinding, laser ablation, chemical mechanical polishing, etc., with laser ablation being particularly preferred.

[0064] In the case of laser ablation, examples of laser sources include the third, fourth, and fifth harmonics of Nd:YAG lasers, F2 excimer lasers, ArF excimer lasers, KrF excimer lasers, XeCl excimer lasers, XeF excimer lasers, the third and fourth harmonics of YVO4 lasers, and the third and fourth harmonics of YLF lasers. Particularly preferred laser sources include the third and fourth harmonics of Nd:YAG lasers, the third and fourth harmonics of YVO4 lasers, and KrF excimer lasers.

[0065] The shape of laser irradiation can be circular, elliptical, square, or linear.

[0066] The laser profile can be shaped using a beam profiler. The laser profile can be Gaussian, Gaussian-like, circular, or top-hat shaped. A Gaussian distribution or top-hat shape is preferred.

[0067] In order to adjust the irradiation size and energy density of the laser, it can be made to pass through a lens, slit, and aperture before irradiating the substrate.

[0068] In a preferred embodiment, the formation of the protrusion is preferably adjusted by using a pulsed laser. The pulse width of the laser is not particularly limited, but a laser with a pulse width of 100 fs to 200 ns can be used. The pulse width of the laser is preferably 200 ns or less, more preferably 1 ns or less.

[0069] The support substrate can be heated while being irradiated with a laser. Heating reduces warping, thus enabling uniform processing within the substrate surface.

[0070] By slicing nitride semiconductor ingots, multiple nitride semiconductor wafers with nitrogen polar facets and group 13 element polar facets can be fabricated. This significantly improves productivity compared to manufacturing wafers as a single piece. The material of the nitride semiconductor wafer is the same as that of the nitride semiconductor ingot; examples include GaN wafers, AlN wafers, and AlGaN wafers.

[0071] (nitride semiconductor ingot)

[0072] According to the present invention, it is possible to provide nitride semiconductor ingots formed of group 13 element nitrides with a diameter of 75 mm or more and 200 mm or less and a thickness of 5 mm or more.

[0073] The nitride semiconductor ingot is difficult to manufacture and was not previously available.

[0074] (Splash target)

[0075] In the nitride semiconductor ingot of the present invention, the oxygen concentration as an impurity is low, and the oxygen concentration non-uniformity is small in both the thickness direction and in-plane. Specifically, the oxygen concentration on the polar facet of group 13 elements can be 0.8 × 10⁻⁶. 17 cm -3 Above and 2×10 17 cm -3 The oxygen concentration on the nitrogen polar face of the nitride semiconductor ingot can be 0.5 × 10⁻⁶. 17 cm -3 Above and 1.5×10 17 cm -3 the following.

[0076] Conventional nitride semiconductor ingots formed from sintered bodies are only available in ingots with high concentrations of impurities such as oxygen. However, in this invention, high-purity group 13 element nitride crystal layers can be used, and in particular, sputtering targets that can provide sufficiently low oxygen concentrations can be employed.

[0077] Functional element structures can be formed on the obtained group 13 element nitride crystal layer. Alternatively, the same functional element structure can be obtained by sputtering a film using the obtained sputtering target. This functional element structure can be used in high-brightness, high-color-reproducibility white LEDs, high-speed, high-density optical memory blue-violet laser disks, power devices for converters in hybrid electric vehicles, etc.

[0078] Example

[0079] (Example 1)

[0080] (Seed layer film formation)

[0081] according to Figure 1 and Figure 2 The method shown is used to prepare the group 13 element nitride crystal layer and nitride semiconductor ingot of the present invention.

[0082] Specifically, a 3-inch sapphire substrate (substrate 1) with a 0.5-degree offset was placed in a MOCVD (Metal-Organic Chemical Vapor Deposition) furnace. The substrate temperature was raised to 1200°C in a hydrogen atmosphere for cleaning. Next, the temperature was lowered to 520°C, and a 20nm thick gallium nitride layer (buffer layer) was formed using hydrogen as the carrier gas and TMG (trimethylgallium) and ammonia as raw materials. Then, using nitrogen and hydrogen as carrier gases, the substrate temperature was raised to 1100°C, and a 3μm thick GaN seed layer 2 was formed using TMG and ammonia as raw materials. Finally, the substrate with the grown GaN layer was cooled to room temperature in a nitrogen atmosphere and removed from the MOCVD furnace (see reference). Figure 1 (a)).

[0083] (Direct bonding)

[0084] The substrate 1 with the GaN seed layer 2 is removed, and the surface of the GaN seed layer 2 and the support substrate 3 formed of polycrystalline alumina are bonded together at room temperature using direct bonding (surface activation method). For the support substrate 3 formed of polycrystalline alumina, the surface roughness RMS is set to 1 nm by surface polishing. Argon beams A and B are irradiated, and in a vacuum, the polished surfaces are brought into contact with each other and weight is applied, thereby achieving direct bonding.

[0085] (Peeling of substrate 1)

[0086] For joints obtained by direct bonding ( Figure 1 (c) A short-wavelength laser is pulsed from the substrate 1 side to separate the GaN seed layer 2 from the substrate 1, thereby fabricating a substrate 6 on which the GaN seed layer 2 is directly bonded to the support substrate 3. Figure 2 (a)).

[0087] The third harmonic of an Nd:YAG laser (wavelength 355nm) was used as the laser source, and a pulsed laser was employed. The repetition frequency was set to 10Hz, the pulse width to 10ns, and a lens with a focal distance of 700mm was used for focusing. The distance between the lens and the substrate surface was set to 400mm, and the light energy density during laser ablation was set to 500mJ / cm². 2 The entire substrate is scanned by overlapping the irradiation points of pulsed lasers.

[0088] (Thick film growth of nitride semiconductor ingots using flux method)

[0089] A 3-inch polycrystalline alumina support substrate 3 with a GaN seed layer 2 bonded together is used to grow a thick film of GaN crystal layer 4 using a flux method. Figure 2 (b)).

[0090] Specifically, an alumina crucible is prepared. A 3-inch polycrystalline alumina support substrate 3 with a GaN seed layer 2 is placed inside the alumina crucible. Then, 400g of metallic Ga and 800g of metallic Na are filled into the alumina crucible, immersing the 3-inch polycrystalline alumina support substrate 3 with the GaN seed layer 2 in a molten solution containing flux. Next, the alumina crucible is placed in a heat-resistant metal incubation vessel and sealed. The furnace temperature is set to 850°C, and nitrogen gas is introduced to achieve a furnace pressure of 4MPa. Inside the heat- and pressure-resistant crystallization incubation furnace, the incubation vessel is kept in a horizontally rotating state for 35 hours, allowing a GaN crystal layer to grow on the polycrystalline alumina support substrate 3 with the GaN seed layer 2. After cooling to room temperature, the substrate with the grown GaN crystal layer is removed from the alumina crucible. The GaN seed layer 2 and the support substrate 3 naturally peel off, yielding a thick-film GaN crystal layer 4 with a diameter of 3 inches and a thickness of approximately 5.5mm.

[0091] Diamond abrasives were used to grind the surface and back (peeled surface) of the removed thick GaN crystal layer 4 to flatten it and achieve a thickness of 5 mm, resulting in a nitride semiconductor ingot 5 with a diameter of 3 inches. Figure 2 (d)).

[0092] (Example 2)

[0093] The 3-inch sapphire substrate used in Example 1 was modified by changing the offset angle to 0.0 degrees, 0.3 degrees, 1 degree, 2 degrees, and 3 degrees, preparing five different substrates. Using the same method as in Example 1, attempts were made to fabricate nitride semiconductor ingots. The results showed that the growth of the thick GaN crystal layer 4 could not be confirmed with offset angles of 0.0 degrees and 3 degrees. However, the three substrates with offset angles of 0.3 degrees, 1 degree, and 2 degrees yielded nitride semiconductor ingots with a diameter of 3 inches and a thickness of 5 mm, similar to Example 1. These three nitride ingots were designated as #A (0.3 degrees), #B (1 degree), and #C (2 degrees) in ascending order of offset angle. SIMS analysis was performed at 9 points within each of the gallium polar plane and the nitride polar plane. The 9 points within the plane refer to: Figure 3 As illustrated, for the surface 5a of the nitride ingot 5, virtual circles C1 with a radius of 30 mm and C2 with a radius of 60 mm are defined around the center O. Additionally, virtual lines P and H are defined, passing through the center O and orthogonal to each other. Measurement points are: the intersection points A1, A2, A3, and A4 of the center O, virtual circle C1, and virtual lines P and H; and the intersection points B1, B2, B3, and B4 of virtual circle C2 and virtual lines P and H. The average oxygen concentration at depths from 5 μm to 25 μm is calculated at these nine points within the surface, and the maximum and minimum values ​​are determined. The results are shown in Table 1.

[0094] Table 1

[0095]

[0096] (Example 3: Sputtering Target)

[0097] Using the nitride semiconductor ingot of Example 2, and heating a copper plate (backplate), the nitride semiconductor ingot is bonded together using metallic indium to form a sputtering target.

[0098] Using this sputtering target, with Ar at 20 sccm, N2 at 100 sccm, pressure at 1 Pa, and RF power at 400 W as the substrate, a 2-inch sapphire substrate was used. The substrate temperature was set to 250℃, and a GaN film was formed by sputtering. After sputtering, the sapphire substrate was removed, and a uniform GaN film with a thickness of 1 μm was formed. This sputtering process was repeated to fabricate GaN films on 20 sapphire substrates. SIMS analysis showed that the oxygen concentration in all cases was 1 × 10⁻⁶. 17 cm -3 .

[0099] Thus, when using the sputtering target of the present invention for film formation, even if the sputtering target is consumed, a GaN film of the same material can be stably formed.

[0100] (Example 4)

[0101] Similar to Example 1, a 3-inch polycrystalline alumina support substrate with a GaN seed layer was used, and a thick film of GaN crystal layer was grown using a flux method.

[0102] In the flux method, 2000g of metallic Ga and 4000g of metallic Na are filled into an alumina crucible. The alumina crucible is then placed in a heat-resistant metal incubation vessel and sealed. The furnace temperature is set to 850°C, and nitrogen gas is introduced to achieve a furnace pressure of 4MPa. Inside the heat- and pressure-resistant crystallization furnace, the incubation vessel is kept in a horizontally rotating position for 300 hours, thereby allowing a GaN crystalline layer to grow on a 3-inch polycrystalline alumina support substrate with a GaN seed layer. After cooling to room temperature, the substrate with the grown GaN crystalline layer is removed from the alumina crucible, and the GaN crystalline layer and the polycrystalline alumina support substrate naturally peel off, yielding a 3-inch, approximately 52mm thick thick-film GaN crystalline layer.

[0103] Diamond abrasives were used to grind the surface and back of the removed thick GaN crystal layer to flatten it, resulting in a 50 mm thick nitride semiconductor ingot. The nitride semiconductor ingot was then sliced ​​to obtain 50 3-inch GaN wafers (nitride semiconductor wafers) with a thickness of 0.5 mm.

[0104] Three GaN wafers were selected, and their offset angles, distribution, and warpage shapes were measured. The wafer closest to the gallium polarity plane in the pre-slicing ingot was designated #D, the wafer closest to the nitrogen polarity plane was designated #F, and the wafer between #D and #F was designated #E. The offset angles were measured at nine points within the gallium polarity plane of the GaN wafer. The measurement positions of these nine points were defined as follows: Figure 3 The figures O, A1, A2, A3, A4, B1, B2, B3, and B4 are shown. The deflection angle was measured using a Bruker AXS D2Cryso instrument. The difference between the maximum and minimum deflection angles measured at nine points within the plane was defined as the amplitude of the deflection angle. The warpage value was measured using a Nidec FT-17 flatness meter. The results are shown in Table 2. Table 2 shows that the closer the substrate is to the nitrogen polarity surface, the smaller the amplitude of the deflection angle.

[0105] Table 2

[0106]

[0107] (Example 5)

[0108] Using a GaN film obtained by sputtering on a substrate as a seed crystal, a large-diameter GaN wafer is fabricated.

[0109] Specifically, a sapphire substrate with a diameter of 200 mm was used as the substrate, and sputtering was performed using the sputtering target obtained in Example 3. As a result, a GaN film with a thickness of 1 μm was uniformly formed.

[0110] The polarity was determined using the CBED method, and the surface of the GaN film was found to be a gallium polar surface.

[0111] Using this GaN film, a thick-film GaN crystalline layer was grown via a flux method. 2000g of metallic Ga and 4000g of metallic Na were filled into an alumina crucible. The alumina crucible was then placed in a heat-resistant metal cultivation vessel and sealed. The furnace temperature was set to 850°C, and nitrogen gas was introduced to achieve a furnace pressure of 4MPa. The cultivation vessel was kept in a horizontally rotating position for 200 hours within the heat- and pressure-resistant crystallization furnace, thereby allowing the GaN crystalline layer to grow on a sapphire substrate with a GaN film. After cooling to room temperature, the GaN-crystal substrate was removed from the alumina crucible, and the supporting substrate composed of the GaN crystalline layer and polycrystalline alumina naturally peeled off, yielding a thick-film GaN crystalline layer with a diameter of 200mm and a thickness of approximately 6mm.

[0112] Diamond abrasives were used to grind the surface and back of the removed thick GaN crystal layer to planarize it, resulting in a nitride semiconductor ingot with a diameter of 200 mm and a thickness of 5 mm. The nitride semiconductor ingot was then sliced, and the surface and back were ground with diamond abrasives to planarize it, thereby obtaining three GaN wafers with a diameter of 200 mm and a thickness of 1 mm.

Claims

1. A method for cultivating a crystal layer of group 13 element nitrides, wherein, A group 13 nitride crystal layer was grown on a substrate containing a seed layer formed of group 13 nitrides. The cultivation method is characterized by including: The process of forming the seed layer on the substrate, The process of bonding the group 13 element polar facets of the seed layer to the support substrate, and The process of peeling the substrate from the seed layer to obtain the substrate base. The process of immersing the substrate in a molten liquid containing flux and growing a group 13 element nitride crystal layer in two dimensions on the nitrogen polar surface of the seed layer by means of flux method.

2. The method for cultivating a group 13 element nitride crystal layer according to claim 1, characterized in that, The nitride crystal layer of the group 13 elements is grown to a thickness of more than 5 mm.

3. The method for cultivating a group 13 element nitride crystal layer according to claim 1 or 2, characterized in that, A nitride semiconductor ingot formed from the group 13 element nitride crystal layer is obtained by separating the group 13 element nitride crystal layer from the substrate.

4. The method for cultivating a group 13 element nitride crystal layer according to claim 3, characterized in that, The nitride semiconductor ingot has a diameter of 75 mm or more and 200 mm or less, and a thickness of 5 mm or more and 50 mm or less.

5. The method for cultivating a group 13 element nitride crystal layer according to claim 3, characterized in that, A sputtering target formed from the nitride semiconductor ingot is obtained.

6. The method for cultivating a group 13 element nitride crystal layer according to claim 4, characterized in that, A sputtering target formed from the nitride semiconductor ingot is obtained.

7. The method for cultivating a group 13 element nitride crystal layer according to claim 5, characterized in that, The oxygen concentration on the group 13 polar facet of the nitride semiconductor ingot is 0.8 × 10⁻⁶. 17 cm -3 Above and 2×10 17 cm -3 the following, The oxygen concentration on the nitrogen polar facet of the nitride semiconductor ingot is 0.5 × 10⁻⁶. 17 cm -3 Above and 1.5×10 17 cm -3 the following.

8. The method for cultivating a group 13 element nitride crystal layer according to claim 6, characterized in that, The oxygen concentration on the group 13 polar facet of the nitride semiconductor ingot is 0.8 × 10⁻⁶. 17 cm -3 Above and 2×10 17 cm -3 the following, The oxygen concentration on the nitrogen polar facet of the nitride semiconductor ingot is 0.5 × 10⁻⁶. 17 cm -3 Above and 1.5×10 17 cm -3 the following.

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