Manufacturing method of nitride crystal substrate and peeling intermediate

Abstract

To stably grow a regrowth layer.SOLUTION: A manufacturing method of a nitride crystal substrate includes the steps of: (a) preparing a substrate; (b) forming an intermediate layer including an n-type III-group nitride crystal above the substrate; (c) forming a cover layer including a III-group nitride crystal having a carrier concentration lower than that of the intermediate layer on the intermediate layer; (d) making the intermediate layer porous through a dislocation in the cover layer by electrochemical treatment while a surface state of the cover layer is maintained; (e) epitaxially growing a regrowth layer composed of a III-group nitride crystal on the cover layer; and (f) peeling the regrowth layer from the substrate at least at a part of a porous intermediate layer as a boundary. The step (e) has the steps of: (e1) growing a first regrowth layer on the cover layer at a first growth temperature; and (e2) growing a second regrowth layer on the first growth layer at a second growth temperature. The first growth temperature is lower than the second growth temperature at the step (e1).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a nitride crystal substrate and a peeled intermediate product. [Background technology]

[0002] Various methods have been disclosed as manufacturing methods for obtaining nitride crystal substrates made of Group III nitride crystals (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-178984 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to grow a regrown layer stably. [Means for solving the problem]

[0005] According to an aspect of the present disclosure, (a) providing a substrate; (b) forming an intermediate layer containing n-type Group III nitride crystals above the substrate; (c) forming a cover layer on the intermediate layer, the cover layer including a Group III nitride crystal having a carrier concentration lower than that of the intermediate layer; (d) rendering the intermediate layer porous through dislocations in the cover layer by electrochemical treatment while maintaining the surface state of the cover layer; (e) epitaxially growing a regrowth layer made of a Group III nitride crystal on the cover layer; (f) peeling the regrowth layer from the substrate along at least a portion of the porous intermediate layer; Equipped with (e) is (e1) growing a first regrowth layer on the cover layer at a first growth temperature; (e2) growing a second regrowth layer on the first regrowth layer at a second growth temperature; having In (e1), The first growth temperature is lower than the second growth temperature. A method for producing a nitride crystal substrate is provided.

[0006] According to another aspect of the present disclosure, A peeled intermediate obtained by the above-mentioned method for producing a nitride crystal substrate, At least the cover layer and the re-grown layer are included. A release intermediate is provided. Effect of the Invention

[0007] According to the present disclosure, the regrown layer can be grown stably. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 2A] FIG. 2A is a schematic cross-sectional view illustrating a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 2B] FIG. 2B is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 3A] FIG. 3A is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 3B] FIG. 3B is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic cross-sectional view illustrating a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Diagram 5] FIG. 5 is a diagram showing temperature changes during a regrowth process according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a schematic cross-sectional view illustrating a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a schematic cross-sectional view illustrating a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 8] FIG. 8 is a schematic cross-sectional view illustrating a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 9] FIG. 9 is a schematic cross-sectional view illustrating a method for manufacturing a nitride crystal substrate according to an embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram showing temperature changes in the regrowth process according to the first modification. [Figure 11] FIG. 11 is a diagram showing temperature changes in the regrowth process in the comparative example. [Figure 12] FIG. 12 is a schematic cross-sectional view showing a state when the temperature is raised to the regrowth temperature in the comparative example. [Figure 13] FIG. 13 is a photograph of the surface of the seed substrate heated to 883° C. in Experiment 1, observed with an optical microscope. [Figure 14] FIG. 14 is a photograph of the surface of the seed substrate heated to 963° C. in Experiment 1, observed with an optical microscope. [Figure 15] FIG. 15 is a photograph of the surface of the seed substrate heated to 1033° C. in Experiment 1, observed with an optical microscope. [Figure 16] FIG. 16 is a photograph of the surface of the peeled regrown layer in sample A1 of experiment 2, observed with an optical microscope. [Figure 17] FIG. 17 is a photograph of the surface of the peeled regrown layer in sample C4 of experiment 2, observed with an optical microscope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Knowledge gained by the inventors> The inventors have investigated the following method for manufacturing a nitride crystal substrate. First, an intermediate layer and a cover layer containing a group III nitride crystal are grown in this order on a substrate, and the laminate is subjected to an electrochemical treatment. In this way, a seed substrate having a porous intermediate layer is produced. Next, a thick group III nitride crystal layer is regrown on the seed substrate using the seed substrate. Thereafter, the group III nitride crystal layer is sliced ​​to obtain a nitride crystal substrate. In the investigation, the inventors have found the following.

[0010] After the cover layer growth process, when the temperature was lowered from the growth temperature to room temperature, the entire laminate was warped so that the surface of the cover layer was convex due to the difference in linear expansion coefficient between the substrate and the intermediate layer and cover layer (a state corresponding to Figure 3B described below).

[0011] When the electrochemical process was performed to make the substrate porous, the cover layer and the substrate were separated by the porous intermediate layer. Therefore, the seed substrate was in a state close to a thin layer on the substrate. As a result, the cover layer became almost flat and the warping of the substrate was reduced (a state corresponding to Figure 4 described later).

[0012] Next, when the temperature is directly raised to the growth temperature TH of the Group III nitride crystal in the regrowth step as shown in Fig. 11, while the substrate 100 expands and returns to a flat shape as the temperature is raised, the cover layer 940 warps so that the surface of the cover layer 940 on the porous intermediate layer 930 becomes concave as shown in Fig. 12. This causes cracks CRK to occur in the cover layer 940.

[0013] If the regrown layer is grown thick in a state in which cracks CRK have occurred in the cover layer 940, there is a possibility that at least one of cracks and pits will occur in the regrown layer.

[0014] Therefore, as a result of extensive investigations, the inventors have succeeded in stably growing the regrowth layer by adjusting the growth temperature in two stages in the regrowth process.

[0015] The present disclosure below is based on the above-mentioned new findings discovered by the inventors.

[0016] <Details of the embodiment of the present disclosure> Next, an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0017] <One embodiment of the present disclosure> Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings.

[0018] (1) Method for manufacturing nitride crystal substrate The method for manufacturing a nitride crystal substrate according to this embodiment will now be described with reference to Figures 1 to 9. Note that in Figures 2A to 4 and 6 to 9, hatching of cross sections other than that of intermediate layer 300 has been omitted.

[0019] In the following, in a group III nitride crystal having a wurtzite structure, <0001> The axis (e.g., the <0001> axis) is referred to as the "c-axis" and the (0001) plane is referred to as the "c-plane". The (0001) plane is sometimes referred to as the "+c-plane (III group element polar plane)" and the (000-1) plane as the "-c-plane (nitrogen (N) polar plane)". In this disclosure, "carrier concentration" refers to the free carrier concentration at room temperature (22°C).

[0020] As shown in FIG. 1, the method for manufacturing a nitride crystal substrate according to this embodiment includes, for example, a substrate preparation step S10, a base layer formation step S20, an intermediate layer formation step S30, a cover layer formation step S40, a porous step S50, a regrowth step S60, a peeling step S70, and a post-treatment step S80.

[0021] (S10: Board preparation process) First, as shown in FIG. 2A, a substrate 100 is prepared.

[0022] In this embodiment, for example, a substrate 100 made of a material other than a group III nitride is prepared. Specifically, the substrate 100 may be, for example, a sapphire substrate, a silicon carbide (SiC) substrate, a silicon (Si) substrate, or a gallium arsenide (GaAs) substrate. The substrate 100 may be insulating or conductive. Here, the substrate 100 is, for example, a sapphire substrate.

[0023] The diameter of the substrate 100 is, for example, 2 inches (50 mm) or more, or may be 4 inches (100 mm) or more. This allows a large-area regrown layer 500, which will be described later, to be grown.

[0024] The thickness of the substrate 100 is, for example, not less than 150 μm and not more than 3 mm.

[0025] The substrate 100 has, for example, a primary surface 120 which serves as a growth surface. The closest low-index crystal plane to the primary surface 120 is, for example, the c-plane (+c-plane).

[0026] In this embodiment, the c-plane of the substrate 100 may be inclined with respect to the major surface 120. That is, the c-axis of the substrate 100 may be inclined at a predetermined off angle with respect to the normal to the major surface 120. The off angle of the substrate 100 is, for example, not less than 0° and not more than 5°.

[0027] The arithmetic mean roughness (Ra) of the primary surface 120 of the substrate 100 is, for example, less than 0.3 nm.

[0028] (S20: Base layer formation process) After the substrate 100 is prepared, as shown in FIG. 2A, for example, a vapor phase growth method is used to form an underlayer 200 containing Group III nitride crystals on the substrate 100 (the underlayer 200 made of Group III nitride crystals is formed).

[0029] Specifically, for example, an aluminum nitride (AlN) buffer layer is grown by supplying aluminum chloride (AlCl3) gas and ammonia (NH3) gas to the substrate 100 heated to a predetermined growth temperature by hydride vapor phase epitaxy (HVPE). Next, a gallium nitride (GaN) layer is grown by supplying gallium chloride (GaCl) gas and NH3 gas to the substrate 100 heated to a predetermined growth temperature. The growth temperature of each layer is, for example, 900°C or more and 1100°C or less. In this manner, an AlN buffer layer and a GaN layer are formed in this order as the underlayer 200 on the main surface 120 of the substrate 100. However, the underlayer 200 does not have to have an AlN buffer layer.

[0030] In this embodiment, the underlayer 200 is, for example, an n-type. Specifically, when growing a GaN layer as the underlayer 200, dichlorosilane (SiH2Cl2) gas is further supplied as an n-type dopant gas to grow a Si-doped GaN layer.

[0031] In this embodiment, the carrier concentration in the GaN layer of the underlayer 200 is set to be lower than the carrier concentration in the intermediate layer 300, for example. In other words, the n-type impurity concentration in the GaN layer of the underlayer 200 is set to be lower than the n-type impurity concentration in the intermediate layer 300, for example. Specifically, the carrier concentration (and n-type impurity concentration) in the underlayer 200 is set to be lower than, for example, 2×10 18 cm -3 or less, or 1×10 18 cm -3 This allows the base layer 200 to function as an etching stopper below the intermediate layer 300 in the porous step S50, which will be described later, of making the intermediate layer 300 porous by electrochemical treatment.

[0032] The lower limit of the carrier concentration in the GaN layer of the underlayer 200 is not limited. However, the carrier concentration in the GaN layer of the underlayer 200 is not limited to, for example, 1×10 16 cm -3In this way, since the underlayer 200 itself has some electrical conductivity, etching of the intermediate layer 300 can proceed toward the lower part of the intermediate layer 300 by electrochemical processing in the porous step S50 described later.

[0033] The thickness of the underlayer 200 is not particularly limited. However, the thickness of the underlayer 200 may be, for example, more than 0 nm and 5 μm or less. By setting the thickness of the underlayer 200 to 5 μm or less, the total thickness of the layers on the substrate 100 can be adjusted to, for example, 15 μm or less. This makes it possible to suppress cracks caused by the difference in linear expansion coefficient between the substrate 100 and each layer such as the underlayer 200.

[0034] In this embodiment, the c-plane of the GaN layer is the low-index crystal plane closest to the surface of the underlayer 200. By forming a flat surface of the underlayer 200 having such a crystal plane in advance, the intermediate layer 300 and the cover layer 400 with good crystallinity can be grown on the surface of the underlayer 200.

[0035] (S30: Intermediate layer formation process) After the underlayer 200 is formed, as shown in Fig. 2B, an intermediate layer 300 containing n-type Group III nitride crystals is formed on the underlayer 200 located above the substrate 100 by, for example, a vapor phase growth method. (In this step, an intermediate layer 300 made of Group III nitride crystals that does not contain voids is formed.)

[0036] Specifically, for example, GaCl gas, NH gas, and SiH2Cl2 gas as an n-type dopant gas are supplied to the substrate 100 heated to a predetermined growth temperature by the HVPE method, thereby growing a Si-doped GaN layer as the intermediate layer 300 on the underlayer 200. The intermediate layer 300 is grown with the +c plane as the growth surface.

[0037] In this embodiment, the carrier concentration in the intermediate layer 300 is set to be higher than, for example, the carrier concentration in the underlayer 200 and the carrier concentration in the cover layer 400. In other words, the n-type impurity concentration in the intermediate layer 300 is set to be higher than, for example, the n-type impurity concentration in the underlayer 200 and the n-type impurity concentration in the cover layer 400. Specifically, the carrier concentration (and n-type impurity concentration) in the intermediate layer 300 is set to be higher than, for example, 3×10 18 cm -3 or more, or 1×10 19 cm -3 This allows the intermediate layer 300 to be selectively made porous in the porous step S50 described below.

[0038] The upper limit of the carrier concentration in the intermediate layer 300 is not limited. However, the carrier concentration in the intermediate layer 300 is not limited to, for example, 1×10 20 cm -3 or less, or 5×10 19 cm -3 This can suppress the deterioration of the crystallinity of the intermediate layer 300.

[0039] In this embodiment, the thickness of the intermediate layer 300 may be, for example, more than 100 nm, or may be 500 nm or more, or may be 1 μm or more. This allows large voids to be formed in the intermediate layer 300 in the porous step S50 described below. This allows the voids 360 in the intermediate layer 300 to be maintained in the regrowth step S60 described below. As a result, in the peeling step S70 described below, the regrowth layer 500 can be easily and stably peeled off from the substrate 100 at least a portion of the intermediate layer 300 maintained in a porous state as a boundary.

[0040] The upper limit of the thickness of the intermediate layer 300 is not limited. However, the thickness of the intermediate layer 300 may be, for example, 10 μm or less. By setting the thickness of the intermediate layer 300 to 10 μm or less, the total thickness of the layers on the substrate 100 can be adjusted to, for example, 15 μm or less. This makes it possible to suppress cracks caused by differences in the linear expansion coefficient between the substrate 100 and each layer such as the intermediate layer 300.

[0041] (S40: Cover layer forming process) After the intermediate layer 300 is formed, as shown in FIG. 3A, a cover layer 400 containing Group III nitride crystals is formed on the intermediate layer 300 by, for example, a vapor phase growth method (a cover layer 400 made of Group III nitride crystals is formed).

[0042] Specifically, for example, a Si-doped GaN layer is grown as the cover layer 400 on the intermediate layer 300 by the HVPE method under the same conditions as in the intermediate layer formation step S30, except that the supply amount of SiH2Cl2 gas as an n-type dopant gas is less than that in the intermediate layer formation step S30. The cover layer 400 is grown with the +c plane as the growth surface.

[0043] In this embodiment, the carrier concentration in the cover layer 400 is set to be lower than the carrier concentration in the intermediate layer 300, for example. In other words, the n-type impurity concentration in the cover layer 400 is set to be lower than the n-type impurity concentration in the intermediate layer 300, for example. Specifically, the carrier concentration (and n-type impurity concentration) in the cover layer 400 is set to be lower than, for example, 1×10 18 cm -3 As a result, in the porous step S50 described later, the intermediate layer 300 can be selectively made porous while suppressing etching of the cover layer 400. In other words, under a predetermined voltage, it is possible to increase the size of the voids 360 in the intermediate layer 300 while preventing the microvoids in the cover layer 400 from becoming large.

[0044] The lower limit of the carrier concentration in the cover layer 400 is not limited. However, the carrier concentration in the cover layer 400 is not limited to, for example, 1×10 16 cm -3or more, or 1×10 17 cm -3 In this way, since the cover layer 400 itself has electrical conductivity, in the electrochemical treatment of the porous step S50 for making the intermediate layer 300 porous, the intermediate layer 300 can be connected to the anode 842 via the cover layer 400, and the entire intermediate layer 300 can be made equipotential with the anode 842.

[0045] Here, in a state where the cover layer forming step S40 is completed, the underlayer 200, the intermediate layer 300 and the cover layer 400 have, for example, a plurality of dislocations D penetrating in the thickness direction. The dislocation density on the surface of the cover layer 400 is, for example, 1×10 8 cm -2 More than 1×10 9 cm -2 The dislocations D in the cover layer 400 are utilized in the following porous step S50.

[0046] In this embodiment, the thickness of the cover layer 400 may be, for example, 10 nm or more and 2 μm or less, or 50 nm or more and 1.5 μm or less.

[0047] By making the thickness of the cover layer 400 10 nm or more, or 50 nm or more, even if outgassing such as N2 gas is generated when the intermediate layer 300 is etched in the porous process S50 described later, the cover layer 400 is maintained, and the outgas can be released to the outside of the cover layer 400 through the dislocations D of the cover layer 400. This makes it possible to suppress peeling of the cover layer 400 from the intermediate layer 300.

[0048] On the other hand, by setting the thickness of the cover layer 400 to 2 μm or less, or 1.5 μm or less, the electrolyte can stably reach the intermediate layer 300 through the dislocations D of the cover layer 400 in the porous step S50 described later. This allows void formation in the intermediate layer 300 to be stably performed.

[0049] After the cover layer 400 is grown, the temperature of the substrate 100 is lowered from the growth temperature of the Group III nitride crystal to room temperature, thereby forming a stack including the substrate 100, the underlayer 200, the intermediate layer 300 and the cover layer 400.

[0050] 3B, the entire stack is warped due to the difference in linear expansion coefficient between the substrate 100 and the Group III nitride crystal layer including the underlayer 200, the intermediate layer 300, and the cover layer 400. Specifically, since the linear expansion coefficient of sapphire as the substrate 100 is greater than that of the Group III nitrides, the entire stack is warped such that the surface of the cover layer 400 becomes convex.

[0051] The above-mentioned underlayer forming step S20, intermediate layer forming step S30, and cover layer forming step S40 are performed consecutively in the same chamber without exposing the substrate 100 to the atmosphere. This makes it possible to suppress unintended incorporation of at least one of oxygen (O) and silicon (Si) as n-type impurities at the interfaces between the underlayer 200, intermediate layer 300, and cover layer 400. As a result, it becomes possible to suppress the influence on the carrier concentration in these layers.

[0052] (S50: Porous process) After the cover layer 400 is formed, as shown in FIG. 4, an electrochemical treatment is performed to make the intermediate layer 300 porous through dislocations D in the cover layer 400 while maintaining the surface state of the cover layer 400.

[0053] Specifically, for example, the electrochemical treatment is carried out according to the following procedure.

[0054] 4, first, prepare a treatment tank 820, a power source 840, and an ammeter 860. Note that the power source 840 and the ammeter 860 may be incorporated into one device as a current and voltage power source.

[0055] The treatment tank 820 is filled with an electrolytic solution 810. The electrolytic solution 810 is a solution containing ions capable of electrochemically etching a group III nitride. Examples of the electrolytic solution 810 include aqueous solutions containing oxalic acid, nitric acid, hydrofluoric acid, sulfuric acid, sodium sulfate (Na2SO4), sodium hydroxide (NaOH), and the like. Here, the electrolytic solution 810 is an oxalic acid solution.

[0056] Also, each electrode for performing the electrochemical treatment is prepared. Specifically, in the laminate in which the above-mentioned cover layer forming step S40 is completed, an anode 842 is provided on the surface of the cover layer 400, and the anode 842 is connected to a power source 840. On the other hand, a cathode 844 is prepared, and the cathode 844 is connected to the power source 840. As the cathode 844, a material that has corrosion resistance and allows a current to easily flow is used. Specific examples of the cathode 844 include stainless steel (SUS), platinum (Pt), gold (Au), and boron-doped diamond.

[0057] After completing the connection of each electrode, the laminate with the anode 842 connected and the cathode 844 are immersed in the electrolyte 810 in the treatment tank 820. In this state, a predetermined voltage is applied between the anode 842 and the cathode 844 by the power source 840. This causes the electrochemical treatment to be performed. At this time, the progress of the electrochemical treatment is confirmed based on the change in current in the ammeter 860.

[0058] At this time, the electrochemical treatment causes C2O4 to flow through dislocations D in the cover layer 400, which has a relatively low carrier concentration, toward the intermediate layer 300, which has a relatively high carrier concentration. 2- In other words, the dislocations D in the cover layer 400 are used as nano-sized paths for the electrolyte to penetrate. The electrolyte that reaches the intermediate layer 300 in this manner selectively etches the intermediate layer 300. As a result, a plurality of voids 360 are formed near each of the plurality of dislocations D in the intermediate layer 300. As a result, the intermediate layer 300 can be made porous.

[0059] On the other hand, the Group III element ions (Ga) generated when the intermediate layer 300 is etched are reacted with the following reaction formula: 3+ ) and nitrogen (N 2 ) gas are released to the outside of the cover layer 400 through dislocations D in the cover layer 400. 2GaN + 6h + → 2Ga 3+ + N2

[0060] By the above-mentioned electrochemical treatment, each of the multiple voids 360 in the intermediate layer 300 is formed, for example, at a position overlapping each of the multiple dislocations D in the cover layer 400 described below. The multiple voids 360 in the intermediate layer 300 extend, for example, from the lower surface of the cover layer 400 in the thickness direction toward the substrate 100. Note that the voids 360 do not necessarily need to reach the underlayer 200.

[0061] On the other hand, the partition wall portions of the intermediate layer 300 other than the voids 360 connect the upper part of the foundation layer 200 or the lower part of the intermediate layer 300 to the cover layer 400. As a result, even if the intermediate layer 300 has a plurality of voids 360, it maintains a constant thickness.

[0062] At this time, in this embodiment, the length of each of the multiple voids 360 in the intermediate layer 300 in the direction along the main surface 120 of the substrate 100 may be, for example, 30 nm or more, or 100 nm or more, when viewed in any cross section perpendicular to the main surface 120 of the substrate 100. This makes it possible to maintain the voids 360 in the intermediate layer 300 in the regrowth step S60 described later. As a result, in the peeling step S70 described later, the regrowth layer 500 can be easily and stably peeled off from the substrate 100 at at least a portion of the intermediate layer 300 maintained in a porous state as a boundary.

[0063] The upper limit of the length of the voids 360 in the intermediate layer 300 in the direction along the main surface 120 of the substrate 100 is not limited. However, the length of the voids 360 in the direction along the main surface 120 of the substrate 100 may be 10 μm or less. This makes it possible to suppress peeling of the cover layer 400 caused by outgassing generated when the intermediate layer 300 is etched by appropriately adjusting the electrochemical treatment conditions in the porous step S50.

[0064] At this time, in this embodiment, the depth of each of the multiple voids 360 in the thickness direction of the intermediate layer 300 may be, for example, more than 100 nm, or 500 nm or more, or 1 μm or more. This also makes it possible to maintain the voids 360 in the intermediate layer 300 in the regrowth step S60 described below. As a result, the regrowth layer 500 can be easily and stably peeled off from the substrate 100 in the peeling step S70 described below.

[0065] There is no upper limit to the depth of void 360. However, the depth of void 360 may be equal to or less than the thickness of intermediate layer 300. This makes it possible to suppress excessive spread of peeling from intermediate layer 300 to other layers in the peeling step S70 described below.

[0066] On the other hand, in the electrochemical treatment, the surface of the cover layer 400, which has a relatively low carrier concentration, is hardly etched. In other words, even if the cover layer 400 has a plurality of dislocations D as described above, the surface of the cover layer 400 near the dislocations D is not excessively etched. This makes it possible to maintain the surface state of the cover layer 400 flat.

[0067] In this embodiment, after the porous step S50, the arithmetic mean roughness (Ra) of the surface of the cover layer 400 is, for example, 1.0 nm or less, and the root mean square roughness (RMS) of the surface of the cover layer 400 is, for example, 2.0 nm or less. Alternatively, the Ra of the surface of the cover layer 400 may be, for example, 0.5 nm or less, and the RMS of the surface of the cover layer 400 may be, for example, 1.0 nm or less. Here, Ra and RMS are values ​​obtained when the surface of the cover layer 400 is observed with an atomic force microscope (AFM) in a field of view of 5 μm square.

[0068] As described above, by maintaining the surface roughness of the cover layer 400 small, the regrown layer 500 having good crystallinity and a thick film can be stably grown on the cover layer 400 .

[0069] The lower limit values ​​of Ra and RMS of the surface of cover layer 400 are not limited and may be close to the Ra and RMS of main surface 120 of substrate 100. Specifically, the lower limit values ​​of Ra and RMS of the surface of cover layer 400 may be 0.1 nm and 0.2 nm, respectively.

[0070] As described above, no etching occurs near the dislocation D on the surface of the cover layer 400, but etched microvoids (not shown) may occur in the region including the dislocation D below the surface of the cover layer 400. In this case, the microvoids are formed so as to expand from a position below the surface of the cover layer 400 toward the intermediate layer 300.

[0071] Specific conditions for the electrochemical process that can realize the selective etching of the intermediate layer 300 described above include, for example, the following: The process voltage is adjusted based on the carrier concentration of the intermediate layer 300, etc. The process current is adjusted based on the process area (area of ​​the substrate 100). The process time is adjusted based on the thickness of the intermediate layer 300.

[0072] Electrolyte temperature: Room temperature (10℃ to 30℃) Processing voltage: 1V to 200V or 10V to 20V Processing current: 0.01mA to 60A or 0.1mA to 10A Processing time: 0.1 min to 180 min, or 1 min to 30 min

[0073] As the intermediate layer 300 becomes porous due to the electrochemical treatment described above, the cover layer 400 and the laminate including the substrate 100 and the underlayer 200 are separated from each other by the porous intermediate layer 300, as shown in Fig. 4. When the voids 360 in the intermediate layer 300 have the above-mentioned size, the separation can occur significantly.

[0074] This makes it possible to reduce the warping of the cover layer 400 in the porous step S50 compared to the warping of the cover layer 400 before the porous step S50. That is, the cover layer 400 can be made nearly flat.

[0075] On the other hand, the seed substrate 10 is in a state close to a configuration in which the group III nitride crystal layer on the substrate 100 is thin. This makes it possible to reduce warping of the substrate 100 in the porous step S50 compared to the warping of the substrate 100 before the porous step S50.

[0076] After the electrochemical treatment, the nitride crystal growth seed substrate 10 is taken out of the electrolytic solution in the treatment tank 820. The nitride crystal growth seed substrate 10 taken out of the treatment tank 820 is then washed with pure water or the like and dried. This removes the electrolytic solution remaining in the voids 360 of the intermediate layer 300. This completes the porous step S50.

[0077] In this manner, the seed substrate 10 is obtained. The seed substrate 10 is used in the regrowth step S60 and the peeling step S70 described below.

[0078] (S60: Regrowth process) After the porous step S50 is completed, a regrown layer 500 made of a group III nitride crystal is epitaxially grown on the cover layer 400. The regrown layer 500 is grown by, for example, vapor phase epitaxy.

[0079] 5, in the regrowth step S60 of this embodiment, the growth temperature is adjusted in two stages. Specifically, the regrowth step S60 includes, for example, a first regrowth step S62 and a second regrowth step S64.

[0080] In the regrowth step S60, first, as shown in FIG. 5, the temperature of the seed substrate 10 is increased from room temperature to a first growth temperature T1.

[0081] (S62: 1st regrowth step) When the temperature of the seed substrate 10 reaches the first growth temperature T1, a first regrowth layer 520 is grown on the cover layer 400 at the first growth temperature T1, as shown in FIG.

[0082] Specifically, for example, a GaN layer is grown by supplying GaCl gas and NH3 gas to seed substrate 10 heated to a first growth temperature T1 by the HVPE method. As a result, a GaN layer is epitaxially grown as first regrown layer 520 on the surface of cover layer 400. Various dopants may be added to the GaN layer as first regrown layer 520.

[0083] At this time, in this embodiment, the first growth temperature T1 in the first regrowth step S62 is set lower than the second growth temperature T2 in the second regrowth step S64 as the main growth, which will be described later. In other words, the first growth temperature T1 in the first regrowth step S62 is set slightly lower than a typical growth temperature of a Group III nitride crystal.

[0084] At this time, as the temperature rises from room temperature to the first growth temperature T1, the substrate 100 expands. However, because the first growth temperature T1 is lower (than the growth temperature of the underlayer 200, etc.), the substrate 100 does not become completely flat, and the main surface 120 of the substrate 100 remains slightly convex.

[0085] In contrast, since the linear expansion coefficient of the cover layer 400 is smaller than that of the substrate 100, the expansion of the cover layer 400 is smaller than that of the substrate 100. As a result, the cover layer 400 warps so that the surface of the cover layer 400 becomes concave. However, since the first growth temperature T1 is low, excessive warping of the cover layer 400 can be suppressed. This makes it possible to suppress the occurrence of cracks in the cover layer 400. As a result, it becomes possible to suppress the occurrence of cracks in the regrown layer 500 on the cover layer 400.

[0086] At this time, in this embodiment, the first growth temperature T1 is set to, for example, 970° C. or less. This makes it possible to stably suppress the occurrence of cracks in the cover layer 400 in the first regrowth step S62. As a result, it becomes possible to stably suppress the occurrence of cracks in the regrowth layer 500 on the cover layer 400.

[0087] On the other hand, the first growth temperature T1 may be set to, for example, not less than 800° C. This allows the Group III nitride crystal as the first regrowth layer 520 to grow stably.

[0088] As described above, by adjusting the first growth temperature T1, the first regrowth layer 520 can be grown to a predetermined thickness on the cover layer 400 while suppressing the occurrence of cracks in the cover layer 400. This makes it possible to stably increase the total thickness of the Group III nitride crystal layer (cover layer 400 and first regrowth layer 520) above the porous intermediate layer 300. As a result, in the second regrowth step S64 as the main growth described later, when the temperature is raised to the second growth temperature T2, the Group III nitride crystal layer above the intermediate layer 300 can be made less likely to crack.

[0089] At this time, in this embodiment, by starting the growth of the first regrown layer 520 on the cover layer 400 having a flat surface, in the initial growth stage (thin thickness stage) of the first regrown layer 520, the regrown layer 500 can be grown with the c-plane 522 (+c-plane) as the growth plane without generating any crystal plane (later-described inclined interface 524) other than the c-plane 522. In other words, the first regrown layer 520 can be grown by step-flow growth over the entire surface of the cover layer 400. This can improve the crystallinity of the first regrown layer 520.

[0090] Thereafter, when the first regrowth layer 520 is gradually grown, an inclined interface 524 other than the c-plane may be generated in at least a part of the first regrowth layer 520. That is, the first regrowth layer 520 may be grown three-dimensionally after step-flow growing the first regrowth layer 520 to a predetermined thickness. This allows at least a part of the dislocations D propagating from the cover layer 400 in a direction along the c-axis of the first regrowth layer 520 to be bent and propagated in a direction substantially perpendicular to the inclined interface 524 at the position where the inclined interface 524 is exposed. This allows at least a part of the dislocations D to be locally collected. By eliminating the locally collected dislocations D, the dislocation density can be reduced. As a result, it is possible to reduce the number of pits on the surface of the regrowth layer 500.

[0091] At this time, in this embodiment, the thickness of the first regrowth layer 520 may be, for example, 1 μm or more, or 10 μm or more, or 20 μm or more. This makes it possible to stably prevent the III nitride crystal layer above the intermediate layer 300 from cracking when the temperature is raised to the second growth temperature in the second regrowth step S64 as the main growth described later. As a result, it becomes possible to stably suppress the occurrence of cracks and pits in the thick second regrowth layer 540.

[0092] On the other hand, the upper limit of the thickness of the first re-growth layer 520 is not particularly limited. However, the thickness of the first re-growth layer 520 may be, for example, 300 μm or less, or 100 μm or less. Here, impurities are easily incorporated into the first re-growth layer 520 grown (three-dimensionally grown) at a low temperature. Therefore, if the first re-growth layer 520 is grown thick, stress may be applied between the first re-growth layer 520 and the second re-growth layer 540 described later. In contrast, by setting the thickness of the first re-growth layer 520 to 300 μm or less, or 100 μm or less, it is possible to suppress the application of excessive stress between the first re-growth layer 520 and the second re-growth layer 540 described later, which is caused by the incorporation of impurities into the first re-growth layer 520.

[0093] When the thickness of the first regrown layer 520 reaches a predetermined thickness, the supply of GaCl gas is stopped to terminate the growth of the first regrown layer 520. Note that the supply of NH3 gas is continued.

[0094] Thereafter, as shown in FIG. 5, the temperature of the seed substrate 10 is increased from the first growth temperature T1 to a second growth temperature T2.

[0095] (S64: 2nd regrowth process) After the temperature of the seed substrate 10 is increased from the first growth temperature T1 to the second growth temperature T2, growth of the regrowth layer 500 as the second regrowth layer 540 is resumed as shown in Fig. 7. That is, at the second growth temperature T2, the second regrowth layer 540 as a thick film is grown on the first regrowth layer 520 as main growth.

[0096] Specifically, for example, the second regrowth step S64 is performed in the same chamber as the first regrowth step S62 without exposure to the atmosphere. In the second regrowth step S64, a GaN layer is epitaxially grown as the second regrowth layer 540 on the first regrowth layer 520 under the same conditions as the first regrowth step S62 except that the growth temperature is set to a second growth temperature T2. Various dopants may be added to the GaN layer as the second regrowth layer 540.

[0097] At this time, in this embodiment, as described above, even if the second growth temperature T2 in the second regrowth step S64 as the main growth is set higher than the first growth temperature T1 in the first regrowth step S62, the total thickness of the cover layer 400 and the first regrowth layer 520 as the III nitride crystal layer above the intermediate layer 300 is large, so that the III nitride crystal layer above the intermediate layer 300 is less likely to crack. This makes it possible to stably grow the regrowth layer 500. Specifically, even if the second regrowth layer 540 is grown thick, it is possible to suppress the occurrence of cracks and pits.

[0098] At this time, in this embodiment, as described above, by setting the second growth temperature T2 in the second regrowth step S64 higher than the first growth temperature T1, the second regrowth layer 540 can be grown by step-flow growth (two-dimensional growth, lateral growth) using the c-plane 542 as the growth surface. This allows the second regrowth layer 540 to be grown as a thick film with good crystallinity while improving the flatness of the surface. Note that the c-axis, which is the normal to the c-plane 542 of the second regrowth layer 540, may be inclined at an off-angle inherited from the c-axis of the substrate 100, which is inclined at a predetermined off-angle.

[0099] At this time, in this embodiment, the second growth temperature T2 may be, for example, 980° C. or higher, or 10,000° C. or higher. This allows the second regrown layer 540 to be stably grown by step-flow growth. As a result, the second regrown layer 540 can be stably grown as a thick film with good crystallinity while improving the flatness of the second regrown layer 540.

[0100] On the other hand, the second growth temperature T2 may be, for example, equal to or lower than 1100° C. This makes it possible to suppress the surface roughness of the second regrown layer 540 caused by an excessively high growth temperature.

[0101] At this time, in the first regrowth step S62 of this embodiment, when the inclined interface 524 is generated in at least a part of the first regrowth layer 520 (when the first regrowth layer 520 is grown three-dimensionally), the second regrowth layer 540 is grown laterally as described above, so that the inclined interface in the second regrowth layer 540 can be gradually reduced, that is, the c-plane 542 can be gradually enlarged. This makes it possible to grow the second regrowth layer 540 having a mirror-finished surface.

[0102] At this time, in this embodiment, the total thickness of the regrowth layer 500 (first regrowth layer 520 and second regrowth layer 540) may be, for example, 600 μm or more, or 1 mm or more. The upper limit of the total thickness of the regrowth layer 500 is not particularly limited. However, from the viewpoint of improving productivity, the total thickness of the regrowth layer 500 may be, for example, 100 mm or less.

[0103] Here, dislocations D move like a random walk during the growth process of the thick regrowth layer 500. As a result, dislocations D meet with each other or form loops during the growth of the regrowth layer 500. Due to this phenomenon, it is possible to reduce the number of dislocations D that reach the surface of the second regrowth layer 540 of the thick film.

[0104] Alternatively, even if the inclined interface 524 is generated in at least a part of the first regrowth layer 520 in the first regrowth step S62 of this embodiment (the first regrowth layer 520 is grown three-dimensionally), dislocations can be locally collected at the meeting point of adjacent inclined interfaces in the process of laterally growing the second regrowth layer 540. Even in this case, the dislocations D reaching the surface of the thick second regrowth layer 540 can be reduced.

[0105] As a result, it is possible to reduce the dislocation density in the second regrown layer 540. (Note that because FIG. 7 is simplified, the number of dislocations in FIG. 7 is not significantly reduced.)

[0106] Specifically, the dislocation density on the surface of the second regrowth layer 540 is set to, for example, 3×107 cm -2 can be less than or equal to 1×10 7 cm -2 It can be less than or equal to 5×10 6 cm -2 It can be as follows:

[0107] (S70: Peeling process) After the regrowth step S60 is completed, the regrowth layer 500 is peeled off from the substrate 100 along at least a portion of the porous intermediate layer 300 as a boundary, as shown in FIG.

[0108] In this embodiment, the regrown layer 500 is spontaneously peeled off from the substrate 100 while the temperature is lowered after the re-growth step S60. This makes it possible to eliminate the need for a separate step for performing the peeling, which in turn simplifies the manufacturing method.

[0109] Here, in the regrowth step S60, tensile stress is generated in the regrowth layer 500 (in the direction along the main surface 120 of the substrate 100). This is due to, for example, as described above, the dislocation density decreasing as the thickness of the regrowth layer 500 increases.

[0110] The tensile stress thus generated in the regrown layer 500 warps the c-plane 510 of the regrown layer 500 into a spherical shape with a concave upper side. This causes the regrown layer 500 to spontaneously and gradually peel off from the outer periphery toward the center of the substrate 100. That is, by utilizing the warp of the c-plane 510 of the regrown layer 500, the regrown layer 500 can be gradually peeled off from the outer periphery toward the center of the substrate 100. In other words, the regrown layer 500 can be peeled off evenly in a concentric manner with respect to the center of the substrate 100. As a result, the peeling off of the large-area regrown layer 500 can be easily and stably performed.

[0111] By the above peeling step S70, a peeled intermediate body 20 is formed that includes at least the cover layer 400 and the regrown layer 500. Residual pieces of the intermediate layer 300 may remain on the lower surface of the cover layer 400 of the peeled intermediate body 20.

[0112] (S80: Post-processing process) 9, the regrowth layer 500 is sliced, for example, by a wire saw along a cutting plane perpendicular to the normal direction at the center of the surface of the regrowth layer 500. This forms a nitride crystal substrate 50 (hereinafter abbreviated as "substrate 50") as an as-sliced ​​substrate.

[0113] Next, both sides of the substrate 50 are polished by a polishing device, whereby the main surface of the substrate 50 is made mirror-finished.

[0114] Through the above steps, the substrate 50 made of the single crystal of the Group III nitride of this embodiment is obtained.

[0115] The diameter of the substrate 50 is, for example, 2 inches or more, or may be 4 inches or more. The thickness of the substrate 50 is, for example, 150 μm or more and 3 mm or less.

[0116] (2) Summary of this embodiment According to this embodiment, one or more of the following advantages can be obtained.

[0117] (a) In the porous step S50 of this embodiment, the intermediate layer 300 is made porous through dislocations D in the cover layer 400 by electrochemical treatment while maintaining the surface state of the cover layer 400. In the regrowth step S60, a regrowth layer 500 is epitaxially grown on the cover layer 400.

[0118] In the porous step S50, as described above, electrochemical treatment is performed in a state where the cover layer 400 having a relatively low carrier concentration covers the intermediate layer 300 having a relatively high carrier concentration. This allows the intermediate layer 300 to be selectively made porous through dislocations D of the cover layer 400 while maintaining the surface state of the cover layer 400.

[0119] By maintaining the surface state of the cover layer 400 on the porous intermediate layer 300 flat, the cover layer 400 can be used as a regrowth base layer in the regrowth step S60, allowing a thick regrowth layer 500 with good crystallinity to be stably grown.

[0120] On the other hand, by covering the multiple voids 360 in the intermediate layer 300 with the flat cover layer 400, it is possible to suppress filling of the voids 360 in the intermediate layer 300 in the regrowth step S60, and maintain many of the voids 360 in the intermediate layer 300. Thereafter, the regrowth layer 500 can be easily and stably peeled off from the substrate 100 at at least a portion of the intermediate layer 300 that is maintained in a porous state.

[0121] As described above, according to this embodiment, it is possible to easily obtain the substrate 50 made of a single crystal of a Group III nitride from the peeled regrown layer 500.

[0122] (b) In the regrowth step S60 of this embodiment, the growth temperature is adjusted in two stages. Specifically, the first growth temperature T1 in the first regrowth step S62 is set lower than the second growth temperature T2 in the second regrowth step S64 as the main growth. This makes it possible to prevent the cover layer 400 from excessively warping in the first regrowth step S62, and to prevent the cover layer 400 from cracking.

[0123] In this manner, the first regrowth layer 520 is grown to a predetermined thickness on the cover layer 400 while the occurrence of cracks in the cover layer 400 is suppressed. This makes it possible to stably increase the total thickness of the Group III nitride crystal layer above the porous intermediate layer 300. As a result, in the second regrowth step S64 as the main growth, when the temperature is raised to the second growth temperature T2, the Group III nitride crystal layer above the intermediate layer 300 can be made less likely to crack.

[0124] As a result, it is possible to stably grow the regrown layer 500. Specifically, even if the second regrown layer 540 is grown thick, it is possible to suppress the occurrence of cracks and pits.

[0125] (c) In this embodiment, in the first regrowth step S62, the first growth temperature T1 is maintained, and when the thickness of the first regrowth layer 520 reaches a predetermined thickness, the growth of the first regrowth layer 520 is terminated. In the second regrowth step S64, the growth temperature is increased from the first growth temperature T1 to a second growth temperature T2, and then growth of the regrowth layer 500 is resumed as the second regrowth layer 540.

[0126] Rather than gradually increasing the temperature in the first regrowth step S62, as described above, the first growth temperature T1 in the first regrowth step S62 and the second growth temperature T2 in the second regrowth step S64 are made different, so that the first growth temperature T1 suitable for the first regrowth layer 52 and the second growth temperature T2 suitable for the second regrowth layer 54 can be set separately.

[0127] Furthermore, as described above, by previously growing the first regrowth layer 520 to a predetermined thickness on the cover layer 400, when the growth temperature is increased from the first growth temperature T1 to the second growth temperature T2, it is possible to increase the temperature increase rate while suppressing cracks in the III nitride crystal layer above the intermediate layer 300. As a result, it is possible to shorten the manufacturing process.

[0128] (3) Modifications of the embodiment The above-described embodiment can be modified as necessary as in the following modified examples. Hereinafter, only elements different from the above-described embodiment will be described, and elements substantially the same as those described in the above-described embodiment will be denoted by the same reference numerals and their description will be omitted.

[0129] As shown in FIG. 10, in the first regrowth step S62 of Modification 1, while the first regrowth layer 520 is being grown, the growth temperature is gradually increased from the first growth temperature T1 to the second growth temperature T2.

[0130] According to the first modification, the rate of temperature rise from the first growth temperature T1 to the second growth temperature T2 can be made gentler, and as a result, cracks in the III-nitride crystal layer above the intermediate layer 300 caused by the temperature rise process from the first growth temperature T1 to the second growth temperature T2 can be stably suppressed.

[0131] On the other hand, according to the first modification, the first regrowth step S62 serves both as a step of growing the first regrowth layer 520 and a step of raising the temperature from the first growth temperature T1 to the second growth temperature T2. That is, the regrowth step S60 can be shifted from the first regrowth step S62 to the second regrowth step S64 without providing a growth stop period. This allows the manufacturing process to be shortened even in the modification.

[0132] <Other embodiments of the present disclosure> Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present disclosure.

[0133] In the above embodiment, the case where the underlayer forming step S20 is performed has been described, but the underlayer forming step S20 does not have to be performed. In other words, the underlayer 200 does not have to be provided. In the intermediate layer forming step S30, the intermediate layer 300 may be formed directly on the substrate 100.

[0134] In the above embodiment, the upper layer of the underlayer 200, the intermediate layer 300, the cover layer 400, and the regrown layer 500 each contain GaN crystals, but the present disclosure is not limited to this case. Each layer is not limited to GaN crystals, and may be made of, for example, Group III nitride crystals such as aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN), i.e., In x Al y Ga 1-x-y The crystal may be represented by the composition formula N (where 0≦x≦1, 0≦y≦1, 0≦x+y≦1).

[0135] In the above embodiment, the case where the Ra of the main surface 120 of the substrate 100 is less than 0.3 nm has been described, but the main surface 120 of the substrate 100 may be patterned to have periodic unevenness, for example. The substrate 100 may be, for example, a so-called PSS (Patterned Sapphire Substrate).

[0136] In the above embodiment, the case where the substrate 100 is made of a material different from III-nitride has been described, but the present disclosure is not limited to this case. The substrate 100 may be, for example, a free-standing substrate made of III-nitride crystal. In this case, the presence of the voids 360 in the intermediate layer 300 reduces the thermal conductivity above the intermediate layer 300. For this reason, distortion may occur between the layer below the intermediate layer and the layer above the intermediate layer. As a result, even in this case, the same problem as when the substrate 100 is a heterogeneous substrate may occur. Therefore, even when a free-standing substrate made of III-nitride crystal is used, the same effect as in the above embodiment can be obtained by applying the two-stage regrowth process S60.

[0137] When the substrate 100 is a free-standing substrate made of a group III nitride crystal, it may be reused after peeling off a functional layer of a semiconductor device grown in a so-called GaN on GaN manner, for example, as in the following Modification 2.

[0138] In the second modification, first, in the substrate preparation step S10, a free-standing substrate made of a III nitride is prepared as the substrate 100. After the substrate preparation step S10, the steps from the base layer formation step S20 to the porous step S50 are performed in the same manner as in the above-described embodiment. Next, in the regrowth step S60, a functional layer is grown as the regrowth layer 500. The "functional layer" here means a layer that functions as at least a part of a semiconductor device. In the peeling step S70, the functional layer as the regrowth layer 500 is peeled off. Next, after the peeling step S70, a polishing step is performed to polish the surface of the remaining substrate 100. After the polishing step, the substrate 100 is reused, and the cycle including the base layer formation step S20 to the polishing step is repeated. In this way, in the second modification, the free-standing substrate made of a III nitride as the substrate 100 can be reused, and the manufacturing cost of the semiconductor device and the like can be reduced.

[0139] In the above-described embodiment, the upper layer of the underlayer 200, the intermediate layer 300, the cover layer 400 and the regrowth layer 500 each contain the same GaN crystal. However, at least one of the upper layer of the underlayer 200, the intermediate layer 300, the cover layer 400 and the regrowth layer 500 may contain a Group III nitride crystal different from the other layers.

[0140] In the above-described embodiment, the upper layer of the base layer 200, the intermediate layer 300, the cover layer 400 and the regrown layer 500 contain Si as an n-type dopant. However, at least one of the upper layer of the base layer 200, the intermediate layer 300, the cover layer 400 and the regrown layer 500 may contain, for example, oxygen (O) or germanium (Ge) as an n-type dopant.

[0141] In the above embodiment, the above-mentioned vapor phase epitaxy method is used as the growth method of the underlayer 200, the intermediate layer 300, the cover layer 400, and the regrown layer 500, but the present disclosure is not limited to this case. Metal-organic vapor phase epitaxy (MOVPE) may be used as the growth method of at least one of the underlayer 200, the intermediate layer 300, the cover layer 400, and the regrown layer 500. Alternatively, a growth method other than the vapor phase epitaxy method may be used as the growth method of at least one of the underlayer 200, the intermediate layer 300, the cover layer 400, and the regrown layer 500.

[0142] In the above embodiment, the first regrown layer 520 is grown three-dimensionally, but the present disclosure is not limited to this. The step-flow growth of the first regrown layer 520 may be maintained. EXAMPLES

[0143] Hereinafter, experimental results that support the effects of the above-described embodiment will be described.

[0144] (1) Experiment 1 (1-1) Preparation of seed substrate Three seed crystal substrates were prepared under the same conditions by the following procedure.

[0145] (Substrate preparation process) The following substrates were prepared as substrates for obtaining seed substrates. Substrate: Sapphire substrate Orientation of the main surface of the substrate: +c surface Board diameter: 2 inches (50.8 mm) Substrate thickness: 430μm

[0146] (Underlying layer formation process) An AlN buffer layer and a GaN layer were formed in this order as underlayers on a substrate by HVPE under the following conditions. Growth temperature of the underlayer: 1055°C. The thickness of the AlN buffer layer and the GaN layer are 100 nm and 4 μm, respectively. Carrier concentration in the GaN layer as the underlayer: about 1×10 18 cm -3

[0147] (Intermediate layer formation process) Next, a Si-doped GaN layer was grown as an intermediate layer on the underlayer by HVPE under the following conditions: Intermediate layer growth temperature: 1055°C. Interlayer thickness: 3000nm Carrier concentration in the intermediate layer: 6×10 18 cm -3

[0148] (Cover layer forming process) Next, a GaN layer was grown as a cover layer on the underlayer by HVPE under the following conditions: Cover layer growth temperature: 1055°C. Cover layer thickness: 150nm Carrier concentration in the cover layer: approx. 5×10 17 cm -3

[0149] (Porous process) Next, the intermediate layer was made porous by electrochemical treatment under the following conditions through dislocations in the cover layer. This resulted in a seed substrate for nitride crystal growth. Two seed substrates for nitride crystal growth were produced, one for observation and one for regrowth. Electrolyte temperature: Room temperature (23℃) Processing voltage: 20V Processing current: Maximum 100mA Processing time: 10 minutes

[0150] (1-2) Heat treatment Using the above-mentioned seed substrates, assuming heating to the growth temperature of the regrowth layer, the three seed substrates were heated to temperatures of 883°C, 963°C, and 1033°C, respectively. At this time, the heating atmosphere was an atmosphere containing N2 gas and NH3 gas, and the heating time was 3 minutes.

[0151] (1-3) Evaluation The surfaces of the three seed substrates that had been subjected to the above-mentioned heat treatment were observed under an optical microscope.

[0152] (1-4) Results The evaluation results of Experiment 1 will be described with reference to FIGS.

[0153] (1033℃) As shown in Figure 15, many fine cracks were generated on the surface of the cover layer of the seed substrate heated to 1033°C. In this seed substrate, the substrate stretched and returned to a flat shape as the temperature was increased to 1033°C, but the cover layer on the porous intermediate layer warped. Therefore, it is believed that cracks were generated in the cover layer when heated to 1033°C.

[0154] (963℃, 883℃) In contrast, in the seed substrates heated to 883° C. and 963° C., no cracks were generated on the surface of the cover layer, and the surface of the cover layer was maintained flat, as shown in Figures 13 and 14. From these results, it was confirmed that the generation of cracks in the cover layer can be suppressed by setting the temperature for heating the seed substrate to 970° C. or less.

[0155] (2) Experiment 2 (2-1) Preparation of the seed substrate and peeled intermediate For each of samples A1, A2, B1, B2, and C1 to C4, a seed substrate was prepared under the conditions shown in Tables 1 and 2 and described below. For samples C1 and C3, a regrowth process was performed using the seed substrate. For samples A1, A2, B1, B2, and C4, a regrowth process and a peeling process were performed using the seed substrate.

[0156] <Sample A1> For sample A1, a seed substrate was prepared in the same manner as in experiment 1.

[0157] (1st regrowth process) Next, a GaN layer was grown as a first regrowth layer on the cover layer by HVPE under the following conditions. First growth temperature: 835℃. Thickness of the first regrowth layer: 50 μm

[0158] (Second regrowth process) Next, in the same chamber as the first regrowth step, a GaN layer was grown as a second regrowth layer on the first regrowth layer. Second growth temperature: 1055℃. Total thickness of regrowth layer: 1mm

[0159] (Peeling process) During the temperature drop after the regrowth step, the regrowth layer was peeled off from the substrate.

[0160] <Sample A2> For sample A2, a seed substrate was prepared in the same manner as sample A1, except that the electrochemical treatment time in the porous process was set to 20 minutes. Then, the first regrowth process, the second regrowth process, and the peeling process were performed under the same conditions as sample A1, using the seed substrate of sample A2.

[0161] <Sample B1> For sample B1, a seed substrate was prepared in the same manner as for sample A1. Thereafter, for sample B1, the first regrowth step, the second regrowth step, and the peeling step were performed under the same conditions as for sample A1, except that the first growth temperature was set to 985° C.

[0162] <Sample B2> For sample B2, a seed substrate was prepared in the same manner as for sample A1. Thereafter, for sample B2, the first regrowth step, the second regrowth step, and the peeling step were carried out under the same conditions as for sample A1, except that the thickness of the first regrowth layer was set to 0.5 μm.

[0163] <Sample C1> For sample C1, a seed substrate was prepared in the same manner as for sample A1, except that no cover layer was provided, and for sample C1, a regrowth step was carried out in the same manner as for sample A1.

[0164] <Sample C2> For sample C2, a seed substrate was prepared in the same manner as for sample A1, except that the thickness of the cover layer was set to 5 nm. For sample C2, the steps after the regrowth step were not carried out.

[0165] <Sample C3> For sample C3, a seed substrate was prepared in the same manner as for sample A1, except that the thickness of the intermediate layer was set to 50 nm. For sample C3, a regrowth step was carried out in the same manner as for sample A1.

[0166] <Sample C4> For sample C4, a seed substrate was prepared in the same manner as for sample A1. Thereafter, for sample C4, a regrowth step and a peeling step were performed under the same conditions as for sample A1, except that the first growth temperature was set to 1055° C. (i.e., the first regrowth step was not performed).

[0167] (2-2) Evaluation Each sample was observed under an optical microscope as follows. Cross-sections and surfaces of the laminates after the regrowth process for samples C1 and C3 Surface of the seed substrate of sample C2 Cross sections and surfaces of the peeled intermediates of samples A1, A2, B1, B2, and C4

[0168] For the peeled intermediates of samples A1, A2, B1, B2, and C4, images of the surface of the regrowth layer were binarized to separate pits (dark areas) from the other areas (light areas). Then, for each sample, the ratio of the pit area to the unit surface area of ​​the regrowth layer (hereinafter also referred to as the "pit area ratio of the regrowth layer") was determined. The unit of the pit area ratio was "%." The pits in the measurement of the pit area ratio also include pits that are traces of cracks in the cover layer.

[0169] As a result, cases in which the pit area ratio of the regrowth layer was over 40% were rated as "C", cases in which the pit area ratio of the regrowth layer was over 20% and 40% or less were rated as "B", and cases in which the pit area ratio of the regrowth layer was 20% or less were rated as "A".

[0170] (2-3) Results The evaluation results of Experiment 2 will be described with reference to Tables 1 and 2, and FIGS.

[0171] [Table 1]

[0172] [Table 2]

[0173] <Sample C1> In sample C1, the cover layer was not formed, so the regrowth process was carried out with the porous intermediate layer exposed. As a result, the voids in the intermediate layer were filled with the regrowth layer, and the area from the substrate to the regrowth layer was bonded. As a result, after the thick regrowth layer was grown, a large crack was generated that reached the substrate. Furthermore, the regrowth layer could not be peeled off from the substrate.

[0174] <Sample C2> In sample C2, a part of the cover layer peeled off after the electrochemical treatment. Since the thickness of the cover layer in sample C2 was less than 10 nm, it is believed that the cover layer peeled off due to outgassing generated during the electrochemical treatment.

[0175] <Sample C3> In sample C3, the voids in the intermediate layer disappeared after the regrowth process. This is believed to be because the porous intermediate layer was crushed at the growth temperature during regrowth. As a result, the area from the substrate to the regrowth layer was bonded. As a result, after the thick regrowth layer was grown, a large crack was generated that reached the substrate. Furthermore, the regrowth layer could not be peeled off from the substrate.

[0176] <Samples A1, A2, B1, B2 and C4> In contrast, in samples A1, A2, B1, B2 and C4, at least a portion of the regrown layer could be peeled off along at least a portion of the porous intermediate layer.

[0177] From the results of samples A1, A2, B1, B2 and C4, it was confirmed that in the porous process, by making the intermediate layer porous while maintaining the surface condition of the cover layer, it is possible to peel off at least a part of the regrown layer.

[0178] <Comparison of Samples A1, A2, B1 and B2 with Sample C4> On the other hand, the following differences occurred between samples A1, A2, B1, and B2 and C4 based on the first growth temperature.

[0179] (Sample C4) In sample C4, a part of the regrowth layer could be peeled off, but some of the voids in the intermediate layer had disappeared under the other part of the regrowth layer, so the other part of the regrowth layer could not be peeled off from the substrate.

[0180] Furthermore, as shown in FIG. 17, in sample C4, a large number of pits existed on the surface of the peeled regrown layer, and the pit area ratio was C.

[0181] In sample C4, cracks occurred in the cover layer when the temperature was raised to 1055°C, as shown in experiment 1. In the regrowth process of sample C4, part of the regrowth layer bonded to the cracks in the cover layer while maintaining the voids in the intermediate layer, allowing part of the regrowth layer to peel off. However, it is believed that many pits were formed in part of the regrowth layer as traces of the cracks in the cover layer.

[0182] On the other hand, in the regrowth process of sample C4, voids were filled in the other part of the regrowth layer through the cracks in the cover layer, which is thought to be why the other part of the regrowth layer could not be peeled off from the substrate.

[0183] (Samples A1, A2, B1 and B2) In contrast, in samples A1, A2, B1 and B2, at least a part of the regrowth layer, which occupied a larger area than sample C4, could be peeled off. In samples A1, A2, B1 and B2, the number of pits on the surface of the peeled regrowth layer was reduced compared to sample C4, and the pit area ratio was A or B.

[0184] From the results of samples A1, A2, B1 and B2, it was confirmed that the occurrence of cracks and pits in the second regrowth layer of the thick film could be suppressed by setting the first growth temperature in the first regrowth step lower than the second growth temperature in the second regrowth step.

[0185] <Comparison between Samples A1 and A2 and Samples B1 and B2> Furthermore, the following differences occurred between samples A1 and A2 and samples B1 and B2 based on the conditions of the first regrowth step.

[0186] (Sample B1) In sample B1, a portion of the regrowth layer, which accounted for more than 80% of the area, could be peeled off, but some of the voids in the intermediate layer had disappeared under the remaining portion of the regrowth layer, making it impossible to peel off the remaining portion of the regrowth layer from the substrate.

[0187] In sample B1, the number of pits could be reduced more than in sample C4. However, a small number of pits existed on the surface of the peeled regrown layer in sample B1, and the pit area ratio was B.

[0188] In sample B1, fine cracks were generated in parts of the cover layer when the temperature was raised to 985°C. In sample B1, the regrowth layer bonded to the cracks in the cover layer more easily than in sample C4, allowing parts of the regrowth layer to peel off over a wider area. However, although the number of pits was reduced in sample B1, a small number of pits were formed in parts of the regrowth layer of sample B1 as traces of the cracks in the cover layer.

[0189] On the other hand, in sample B1, as in sample C4, it is believed that the other parts of the regrown layer could not be peeled off from the substrate due to filling of voids via fine cracks in the cover layer.

[0190] (Sample B2) Sample B2 gave results similar to those of sample B1.

[0191] In sample B2, the thickness of the first regrowth layer was less than 1 μm, so fine cracks occurred in parts of the first regrowth layer when the temperature was raised to the second growth temperature. As a result, it is believed that sample B2 also produced results similar to those of sample B1.

[0192] (Samples A1 and A2) In contrast, in samples A1 and A2, the regrown layer occupying a larger area was peeled off than in samples B1 and B2. Furthermore, as shown in Fig. 16, in samples A1 and A2, the number of pits on the surface of the peeled regrown layer was fewer than in samples B1 and B2, and the pit area ratio was A.

[0193] From the results of samples A1 and A2, it was confirmed that by setting the first growth temperature to 970°C or less and setting the thickness of the first regrowth layer to 1 μm or more in the first regrowth process, the occurrence of cracks and pits in the thick second regrowth layer could be stably suppressed.

[0194] <Additional Notes> The following additional notes are given regarding aspects of the present disclosure.

[0195] (Appendix 1) (a) providing a substrate; (b) forming an intermediate layer containing n-type Group III nitride crystals above the substrate; (c) forming a cover layer on the intermediate layer, the cover layer including a Group III nitride crystal having a carrier concentration lower than that of the intermediate layer; (d) rendering the intermediate layer porous through dislocations in the cover layer by electrochemical treatment while maintaining the surface state of the cover layer; (e) epitaxially growing a regrowth layer made of a Group III nitride crystal on the cover layer; (f) peeling the regrowth layer from the substrate along at least a portion of the porous intermediate layer; Equipped with (e) is (e1) growing a first regrowth layer on the cover layer at a first growth temperature; (e2) growing a second regrowth layer on the first regrowth layer at a second growth temperature; having In (e1), The first growth temperature is lower than the second growth temperature. A method for manufacturing a nitride crystal substrate.

[0196] (Appendix 2) In (a), Providing the substrate made of a material other than a III-nitride 2. A method for producing the nitride crystal substrate according to claim 1.

[0197] (Appendix 3) In (b), The thickness of the intermediate layer is more than 100 nm. 3. A method for producing a nitride crystal substrate according to claim 1 or 2.

[0198] (Appendix 4) In (c), The thickness of the cover layer is 10 nm or more. 4. A method for producing a nitride crystal substrate according to any one of claims 1 to 3.

[0199] (Appendix 5) In (d), (d) reducing the warping of the cover layer to a level lower than the warping of the cover layer prior to the step (d); 5. A method for producing a nitride crystal substrate according to any one of claims 1 to 4.

[0200] (Appendix 6) In (e1), The first growth temperature is set to 970° C. or less. 6. A method for producing a nitride crystal substrate according to any one of claims 1 to 5.

[0201] (Appendix 7) In (e1), The thickness of the first regrowth layer is set to 1 μm or more. 7. A method for producing a nitride crystal substrate according to any one of claims 1 to 6.

[0202] (Appendix 8) In (e2), The second growth temperature is set to 980° C. or higher. 8. A method for producing a nitride crystal substrate according to any one of claims 1 to 7.

[0203] (Appendix 9) In (e1), generating an inclined interface other than a (0001) plane in at least a portion of the first regrowth layer; In (e2), Gradually reducing the sloped interface and growing the second regrowth layer having a mirrored surface. 9. A method for producing a nitride crystal substrate according to any one of claims 1 to 8.

[0204] (Appendix 10) In (e1), maintaining the first growth temperature and terminating the growth of the first regrowth layer when the thickness of the first regrowth layer reaches a predetermined thickness; In (e2), After increasing the growth temperature from the first growth temperature to the second growth temperature, growth of the regrowth layer is resumed as the second regrowth layer. 10. A method for producing a nitride crystal substrate according to any one of claims 1 to 9.

[0205] (Appendix 11) In (e1), While growing the first regrowth layer, the growth temperature is gradually increased from the first growth temperature to the second growth temperature. 10. A method for producing a nitride crystal substrate according to any one of claims 1 to 9.

[0206] (Appendix 12) A peeled intermediate obtained by the method for producing a nitride crystal substrate according to any one of Supplementary Note 1 to Supplementary Note 11, At least the cover layer and the re-grown layer are included. Peeling intermediate. [Explanation of symbols]

[0207] 10. Seed substrate for nitride crystal growth 20 Peeling intermediate 50 Substrates 100 Substrates 120 Main surface 200 Base layer 300 Middle Class 360 Void 400 Cover Layer 500 regrowth layer 520 1st regrowth layer 540 Second regrowth layer 510 c-plane 810 Electrolyte 820 Treatment tank 840 power supply 842 Anode 844 Cathode 860 ammeter

Claims

1. (a) providing a substrate; (b) forming an intermediate layer containing n-type Group III nitride crystals above the substrate; (c) forming a cover layer on the intermediate layer, the cover layer including a Group III nitride crystal having a carrier concentration lower than a carrier concentration of the intermediate layer; (d) rendering the intermediate layer porous through dislocations in the cover layer by electrochemical treatment while maintaining the surface state of the cover layer; (e) epitaxially growing a regrowth layer made of a Group III nitride crystal on the cover layer; (f) peeling the regrown layer from the substrate along at least a portion of the porous intermediate layer; Equipped with (e) is (e1) growing a first regrowth layer on the cover layer at a first growth temperature; (e2) growing a second regrowth layer on the first regrowth layer at a second growth temperature; having In (e1), The first growth temperature is lower than the second growth temperature. A method for producing a nitride crystal substrate.

2. In (b), The thickness of the intermediate layer is more than 100 nm. A method for producing the nitride crystal substrate according to claim 1 .

3. In (c), The thickness of the cover layer is set to 10 nm or more. The method for producing the nitride crystal substrate according to claim 1 or 2.

4. In (e1), The first growth temperature is set to 970° C. or less. The method for producing the nitride crystal substrate according to claim 1 or 2.

5. In (e1), The thickness of the first regrown layer is set to 1 μm or more. The method for producing the nitride crystal substrate according to claim 1 or 2.

6. In (e2), The second growth temperature is set to 980° C. or higher. The method for producing the nitride crystal substrate according to claim 1 or 2.

7. In (e1), generating an inclined interface other than a (0001) plane in at least a portion of the first regrowth layer; In (e2), Gradually reducing the sloped interface and growing the second regrowth layer having a mirrored surface. The method for producing the nitride crystal substrate according to claim 1 or 2.

8. In (e1), maintaining the first growth temperature and terminating the growth of the first regrowth layer when the thickness of the first regrowth layer reaches a predetermined thickness; In (e2), After increasing the growth temperature from the first growth temperature to the second growth temperature, growth of the regrown layer is resumed as the second regrown layer. The method for producing the nitride crystal substrate according to claim 1 or 2.

9. In (e1), While growing the first regrowth layer, the growth temperature is gradually increased from the first growth temperature to the second growth temperature. The method for producing the nitride crystal substrate according to claim 1 or 2.

10. A peeled intermediate obtained by the method for producing a nitride crystal substrate according to claim 1 or 2, At least the cover layer and the re-grown layer are included. Peeling intermediate.

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