Nitride crystal substrate manufacturing method and peeling intermediate

Abstract

The invention provides a method for manufacturing a nitride crystal substrate and a peeling intermediate. The manufacturing method comprises the following steps: (a) preparing a base substrate; (b) forming an intermediate layer including an n-type Group III nitride crystal over the base substrate; (c) forming a capping layer on the intermediate layer; (d) forming the intermediate layer into a porous shape through dislocations in the cover layer while maintaining the surface state of the cover layer by an electrochemical treatment; (e) epitaxially growing a regrowth layer formed of a group III nitride crystal on the capping layer; (f) peeling the regrowth layer from the base substrate with at least a portion of the porous intermediate layer as a boundary, (e) having the following steps: (e1) growing a first regrowth layer on the capping layer at a first growth temperature; (e2) growing a second regrowth layer on the first regrowth layer at a second growth temperature, and in (e1), making the first growth temperature lower than the second growth temperature.

Description

Technical Field

[0001] The present application relates to a method for manufacturing a nitride crystal substrate and a peeling intermediate. Background Art

[0002] As a production method for obtaining a nitride crystal substrate formed of a group III nitride crystal, various methods are disclosed (for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2003-178984 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] The purpose of the present application is to enable the regrown layer to grow stably.

[0008] Solutions for solving problems

[0009] According to the present application, a method for manufacturing a nitride crystal substrate is provided, which comprises the following steps:

[0010] (a) a step of preparing a base substrate;

[0011] (b) forming an intermediate layer on the base substrate, the intermediate layer comprising an n-type Group III nitride crystal;

[0012] (c) forming a capping layer on the intermediate layer, the capping layer comprising a Group III nitride crystal having a carrier concentration lower than that of the intermediate layer;

[0013] (d) a step of making the intermediate layer porous by electrochemical treatment while maintaining the surface state of the covering layer and penetrating dislocations in the covering layer;

[0014] (e) a step of epitaxially growing a regrown layer composed of a group III nitride crystal on the cap layer; and

[0015] (f) a step of peeling the regrown layer from the base substrate with at least a portion of the intermediate layer that has become porous as a boundary,

[0016] (e) having the following steps:

[0017] (e1) a step of growing a first regrown layer on the cap layer at a first growth temperature; and

[0018] (e2) a step of growing a second regrown layer on the first regrown layer at a second growth temperature,

[0019] In (e1), the first growth temperature is set lower than the second growth temperature.

[0020] According to another embodiment of the present application, a stripping intermediate is provided.

[0021] It is obtained by the above-mentioned method for manufacturing a nitride crystal substrate,

[0022] The exfoliation intermediate body includes at least the cap layer and the regrown layer.

[0023] Effects of the Invention

[0024] According to the present application, a regrown layer can be stably grown. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flowchart showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0026] Figure 2A This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0027] Figure 2B This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0028] Figure 3A This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0029] Figure 3B This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0030] Figure 4 This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0031] Figure 5 This is a diagram showing temperature changes in a regrowth step according to one embodiment of the present application.

[0032] Figure 6 This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0033] Figure 7 This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0034] Figure 8 This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0035] Fig. 9 This is a schematic cross-sectional view showing a method for manufacturing a nitride crystal substrate according to one embodiment of the present application.

[0036] Fig.10 This is a diagram showing the temperature change in the regrowth step of Modification Example 1.

[0037] Fig.11 It is a diagram showing the temperature change in the regrowth step of the comparative example.

[0038] Fig.12 It is a schematic cross-sectional view showing a state when the temperature is raised to the regrowth temperature of a comparative example.

[0039] Fig.13 This is a picture showing the surface of the seed substrate heated to 883° C. in Experiment 1 observed with an optical microscope.

[0040] Fig.14 This is a picture showing the surface of the seed substrate heated to 963° C. in Experiment 1 observed with an optical microscope.

[0041] Fig.15 This is a picture showing the surface of the seed substrate heated to 1033° C. in Experiment 1 observed with an optical microscope.

[0042] Fig.16 This is a picture showing the surface of the peeled regrown layer in Sample A1 of Experiment 2 observed with an optical microscope.

[0043] Fig.17 This is a picture showing the surface of the peeled regrown layer in Sample C4 of Experiment 2 observed with an optical microscope.

[0044] Description of Reference Numerals

[0045] 10 Seed substrate for nitride crystal growth

[0046] 20 Stripping Intermediates

[0047] 50 substrates

[0048] 100 Base substrate

[0049] 120 main side

[0050] 200 Base layer

[0051] 300 Middle Layer

[0052] 360 empty holes

[0053] 400 Overlay

[0054] 500 Regrowth Layer

[0055] 520 First regrowth layer

[0056] 540 Second regrowth layer

[0057] 510 c side

[0058] 810 Electrolyte

[0059] 820 Processing Tank

[0060] 840 Power Supply

[0061] 842 Anode

[0062] 844 Cathode

[0063] 860 Ammeter DETAILED DESCRIPTION

[0064] <Insights Obtained by the Present Invention>

[0065] The inventors of the present invention have studied the following method as a method for manufacturing a nitride crystal substrate. First, an intermediate layer and a covering layer containing a group III nitride crystal are grown on a base substrate in sequence, and the stack is electrochemically treated. Thus, a seed substrate is prepared in which the intermediate layer becomes porous. Next, using the seed substrate, a thick film of a group III nitride crystal layer is grown again on the seed substrate. Thereafter, a nitride crystal substrate is obtained by cutting the group III nitride crystal layer. In this study, the inventors of the present invention have found the following insights.

[0066] After the cover layer growth step, if the temperature is lowered from the growth temperature to room temperature, the entire laminate will warp in the form of a convex surface of the cover layer due to the difference in linear expansion coefficients between the base substrate, the intermediate layer, and the cover layer (equivalent to the following Figure 3B status).

[0067] If a porous process based on electrochemical treatment is performed in this state, the cover layer and the base substrate are separated with the porous intermediate layer sandwiched therebetween. Therefore, the seed substrate is in a state similar to a thin layer on the base substrate. As a result, the cover layer is in a nearly flat state, and the warpage of the base substrate is reduced (equivalent to the following Figure 4 status).

[0068] Then, if Fig.11 When the temperature is directly raised to the growth temperature TH of the III-nitride crystal in the regrowth step as shown in FIG. Fig.12As shown, as the temperature rises, the base substrate 100 stretches and returns to being flat, whereas the cover layer 940 on the porous intermediate layer 930 warps so that the surface of the cover layer 940 is recessed. Therefore, cracks CRK are generated in the cover layer 940 .

[0069] If the regrown layer is grown thickly in a state where the crack CRK is generated in the cap layer 940 , there is a possibility that at least one of a crack and a pit will be generated in the regrown layer.

[0070] Therefore, the present inventors have made intensive studies and have succeeded in stably growing a regrown layer by adjusting the growth temperature in two stages in the regrowing process.

[0071] The present application below is based on the above-mentioned novel findings found by the present inventors.

[0072] <Details of the embodiments of the present application>

[0073] Next, one embodiment of the present application will be described below with reference to the drawings. It should be noted that the present application is not limited to these examples, and is intended to include all changes within the meaning and scope of the claims and equivalents to the claims.

[0074] <One embodiment of the present application>

[0075] Hereinafter, one embodiment of the present application will be described with reference to the accompanying drawings.

[0076] (1) Method for manufacturing nitride crystal substrate

[0077] Reference Figures 1 to 9 , the method for manufacturing the nitride crystal substrate of this embodiment is described. It should be noted that Figure 2A to Figure 4 , Figure 6 to Figure 9 , hatching of the cross section except for the intermediate layer 300 is omitted.

[0078] In the following, in a III-nitride crystal having a wurtzite structure, <0001> The axis (e.g., the

[0001] axis) is called the "c-axis", and the (0001) plane is called the "c-plane". It should be noted that the (0001) plane is sometimes called the "+c plane (Group III element polar plane)", and the (000-1) plane is called the "-c plane (nitrogen (N) polar plane)". The "carrier concentration" mentioned in this application refers to the free carrier concentration at room temperature (22°C).

[0079] like Figure 1As shown, the manufacturing method of the nitride crystal substrate of the present embodiment includes, for example, a substrate preparation step S10, a base layer forming step S20, an intermediate layer forming step S30, a covering layer forming step S40, a porous step S50, a regrowth step S60, a peeling step S70 and a post-processing step S80.

[0080] (S10: Base substrate preparation step)

[0081] First, if Figure 2A As shown, a base substrate 100 is prepared.

[0082] In this embodiment, for example, a base substrate 100 formed of a material different from the group III nitride is prepared. Specifically, as the base substrate 100, for example, a sapphire substrate, a silicon carbide (SiC) substrate, a silicon (Si) substrate, and a gallium arsenic (GaAs) substrate can be listed. It should be noted that the base substrate 100 can be insulating or conductive. Here, the base substrate 100 is set to a sapphire substrate, for example.

[0083] The diameter of the base wafer 100 may be, for example, 2 inches (50 mm) or more, or 4 inches (100 mm) or more. This allows a large-area regrown layer 500 to be grown.

[0084] The thickness of the base substrate 100 is, for example, not less than 150 μm and not more than 3 mm.

[0085] The base substrate 100 has, for example, a main surface 120 that serves as a growth surface. When the base substrate 100 is a sapphire substrate or a SiC substrate, the low-index crystal plane closest to the main surface 120 is, for example, a c-plane (+c-plane). When the base substrate 100 is a Si substrate or a GaAs substrate, the low-index crystal plane closest to the main surface 120 is, for example, a (001) plane or a (111) plane.

[0086] In this embodiment, the c-plane of the base substrate 100 may be inclined relative to the main surface 120. That is, the c-axis of the base substrate 100 may be inclined at a predetermined off angle relative to the normal to the main surface 120. The off angle of the base substrate 100 is, for example, not less than 0° and not more than 5°.

[0087] The arithmetic mean roughness (Ra) of the main surface 120 of the base substrate 100 is, for example, less than 0.3 nm.

[0088] (S20: Base layer forming step)

[0089] After preparing the base substrate 100, as Figure 2AAs shown, the base layer 200 including the group III nitride crystal is formed on the base wafer 100 by, for example, a vapor phase growth method (forming the base layer 200 formed of the group III nitride crystal).

[0090] Specifically, for example, by the hydride vapor phase epitaxy (HVPE) method, aluminum chloride (AlCl3) gas and ammonia (NH3) gas are supplied to the base substrate 100 heated to a specified growth temperature, thereby growing an aluminum nitride (AlN) buffer layer. Next, gallium chloride (GaCl) gas and NH3 gas are supplied to the base substrate 100 heated to a specified growth temperature, thereby growing a gallium nitride (GaN) layer. It should be noted that the growth temperature of each layer is set to, for example, above 900°C and below 1100°C. Through the above operations, an AlN buffer layer and a GaN layer as a base layer 200 are sequentially formed on the main surface 120 of the base substrate 100. Among them, the base layer 200 may also not have an AlN buffer layer.

[0091] In this embodiment, the base layer 200 is set to be, for example, n-type. Specifically, when growing the GaN layer as the base layer 200, dichlorosilane (SiH2Cl2) gas is further supplied as an n-type dopant gas to grow the Si-doped GaN layer.

[0092] In this embodiment, the carrier concentration in the GaN layer in the base layer 200 is set to be, for example, lower than the carrier concentration in the intermediate layer 300. In other words, the n-type impurity concentration in the GaN layer in the base layer 200 is set to be, for example, lower than the n-type impurity concentration in the intermediate layer 300. Specifically, the carrier concentration (and n-type impurity concentration) in the base layer 200 is set to be, for example, 2×10 18 cm -3 Below or set to 1×10 18 cm -3 As a result, in the porous step S50 of making the intermediate layer 300 porous by electrochemical treatment, which will be described later, the base layer 200 can function as an etching stopper under the intermediate layer 300 .

[0093] The lower limit of the carrier concentration in the GaN layer in the base layer 200 is not limited. However, the carrier concentration in the GaN layer in the base layer 200 can be set to, for example, 1×10 16 cm -3 As described above, by making the base layer 200 itself have a certain degree of conductivity, the intermediate layer 300 can be etched toward the lower portion of the intermediate layer 300 by electrochemical treatment in the porous step S50 described later.

[0094] The thickness of the base layer 200 is not particularly limited. The thickness of the base layer 200 can be set, for example, to be greater than 0 nm and less than 5 μm. By setting the thickness of the base layer 200 to be less than 5 μm, the total thickness of the stack on the base substrate 100 can be adjusted to, for example, less than 15 μm. Thus, cracks caused by differences in linear expansion coefficients between the base substrate 100 and the base layer 200 and other layers can be suppressed.

[0095] In this embodiment, the c-plane of the GaN layer is the closest low-index crystal plane to the surface of the base layer 200. By forming the base layer 200 surface flat with such a crystal plane in advance, the intermediate layer 300 and the cap layer 400 with good crystallinity can be grown on the surface of the base layer 200.

[0096] (S30: Intermediate Layer Formation Step)

[0097] After forming the base layer 200, as Figure 2B As shown, for example, by vapor phase growth method, an intermediate layer 300 including n-type group III nitride crystals is formed on the base layer 200 located above the base substrate 100. (In this step, the intermediate layer 300 composed of group III nitride crystals is formed without pores.)

[0098] Specifically, for example, by the HVPE method, GaCl gas, NH3 gas, and SiH2Cl2 gas as an n-type dopant gas are supplied to the base substrate 100 heated to a predetermined growth temperature, thereby growing a Si-doped GaN layer as the intermediate layer 300 on the base layer 200. It should be noted that the intermediate layer 300 grows with the +c plane as the growth plane.

[0099] In this embodiment, the carrier concentration in the intermediate layer 300 is set to be higher than the carrier concentration of the base layer 200 and the carrier concentration of the cover layer 400. In other words, the n-type impurity concentration in the intermediate layer 300 is set to be higher than the n-type impurity concentration of the base layer 200 and the n-type impurity concentration of the cover layer 400. Specifically, the carrier concentration (and n-type impurity concentration) in the intermediate layer 300 can be set to, for example, 3×10 18 cm -3 Above or set to 1×10 19 cm -3 As described above, in the porous step S50 described later, the intermediate layer 300 can be selectively made porous.

[0100] It should be noted that the upper limit of the carrier concentration in the intermediate layer 300 is not limited. The carrier concentration in the intermediate layer 300 can be set to, for example, 1×10 20 cm -3 Below, or, it can be set to 5×1019 cm -3 Thereby, it is possible to suppress the decrease in the crystallinity of the intermediate layer 300 .

[0101] In this embodiment, the thickness of the intermediate layer 300 can be set to, for example, more than 100 nm or 500 nm or more, or can also be set to 1 μm or more. Thus, in the porous step S50 described later, large pores can be formed in the intermediate layer 300. Thus, in the regrowth step S60 described later, the pores 360 of the intermediate layer 300 can be maintained. As a result, in the peeling step S70 described later, at least a portion of the intermediate layer 300 maintained in a porous state can be used as a boundary to easily and stably peel the regrown layer 500 from the base substrate 100.

[0102] The upper limit of the thickness of the intermediate layer 300 is not limited. The thickness of the intermediate layer 300 can be set to, 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 stack on the base substrate 100 can be adjusted to, for example, 15 μm or less. Thus, cracks caused by differences in linear expansion coefficients between the base substrate 100 and the intermediate layer 300 and other layers can be suppressed.

[0103] (S40: Covering Layer Forming Step)

[0104] After forming the intermediate layer 300, as Figure 3A As shown, the cap layer 400 including the group III nitride crystal is formed on the intermediate layer 300 by, for example, a vapor phase growth method (forming the cap layer 400 formed of the group III nitride crystal).

[0105] Specifically, for example, by the HVPE method, a Si-doped GaN layer as the cap layer 400 is grown on the intermediate layer 300 under the same conditions as the intermediate layer forming step S30, except that the supply amount of SiH2Cl2 gas as the n-type dopant gas is smaller than that in the intermediate layer forming step S30. It should be noted that the cap layer 400 is grown with the +c plane as the growth plane.

[0106] In this embodiment, the carrier concentration in the cap layer 400 is set to be, for example, lower than the carrier concentration in the intermediate layer 300. In other words, the n-type impurity concentration in the cap layer 400 is set to be, for example, lower than the n-type impurity concentration in the intermediate layer 300. Specifically, the carrier concentration (and the n-type impurity concentration) in the cap layer 400 is set to be, for example, 1×10 18 cm -3 Thus, in the porous step S50 described later, etching of the cover layer 400 can be suppressed and the intermediate layer 300 can be selectively made porous. That is, at a predetermined voltage, the size of the pores 360 of the intermediate layer 300 can be increased without increasing the size of the micropores of the cover layer 400.

[0107] The lower limit of the carrier concentration in the cover layer 400 is not limited. However, the carrier concentration in the cover layer 400 can be set to, for example, 1×10 16 cm -3 Or, it can be set to 1×10 17 cm -3 By making the cover layer 400 itself conductive, the intermediate layer 300 can be connected to the anode 842 via the cover layer 400 in the electrochemical treatment step S50 of making the intermediate layer 300 porous, so that the intermediate layer 300 and the anode 842 are at the same potential as a whole.

[0108] Here, in the state where the cover layer forming step S40 is completed, the base layer 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 Above and 1×10 9 cm -2 The dislocations D in the cover layer 400 are utilized in the following porous step S50.

[0109] In the present embodiment, the thickness of the cover layer 400 can be, for example, greater than or equal to 10 nm and less than or equal to 2 μm, or greater than or equal to 50 nm and less than or equal to 1.5 μm.

[0110] By setting the thickness of the cover layer 400 to be 10 nm or more or 50 nm or more, even if exhaust gas such as N2 gas is generated when etching the intermediate layer 300 in the porous step S50 described later, the cover layer 400 can be maintained and the exhaust gas can be released to the outside of the cover layer 400 through the dislocation D of the cover layer 400. Thus, the peeling of the cover layer 400 from the intermediate layer 300 can be suppressed.

[0111] 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 pore forming step S50 described later. Thus, the intermediate layer 300 can be stably pore-formed.

[0112] After the cover layer 400 is grown, the temperature of the base substrate 100 is lowered from the growth temperature of the group III nitride crystal to room temperature. Thus, a stacked body including the base substrate 100 , the base layer 200 , the intermediate layer 300 , and the cover layer 400 is formed.

[0113] At this time, if Figure 3BAs shown in the figure, the stacked body as a whole warps due to the difference in linear expansion coefficients between the base substrate 100 and the group III nitride crystal layer including the base layer 200, the intermediate layer 300 and the cover layer 400. Specifically, since the linear expansion coefficient of sapphire as the base substrate 100 is greater than the linear expansion coefficient of the group III nitride, the stacked body as a whole warps in a manner that the surface of the cover layer 400 is convex.

[0114] The above-mentioned base layer forming step S20, intermediate layer forming step S30 and cover layer forming step S40 are continuously performed in the same chamber without exposing the base substrate 100 to the atmosphere. As a result, it is possible to suppress the unexpected mixing of at least one of oxygen (O) and silicon (Si) as n-type impurities at the interface between the base layer 200, the intermediate layer 300 and the cover layer 400. As a result, it is possible to suppress the influence on the carrier concentration in these layers.

[0115] (S50: Multi-hole process)

[0116] After forming the cover layer 400, as Figure 4 As shown, by the electrochemical treatment, the surface state of the cover layer 400 is maintained and the intermediate layer 300 is made porous through the dislocation D of the cover layer 400 .

[0117] Specifically, the electrochemical treatment is performed, for example, through the following steps.

[0118] like Figure 4 As shown, first, a processing tank 820, a power source 840, and an ammeter 860 are prepared. It should be noted that the power source 840 and the ammeter 860 can be assembled into one device as a current and voltage power source.

[0119] The electrolyte 810 is filled into the treatment tank 820. The electrolyte 810 is a solution containing ions capable of electrochemically etching the group III nitride. Examples of the electrolyte 810 include aqueous solutions containing oxalic acid, nitric acid, hydrofluoric acid, sulfuric acid, sodium sulfate (Na2SO4), sodium chloride (NaCl), sodium hydroxide (NaOH), etc. Here, the electrolyte 810 is an oxalic acid solution.

[0120] In addition, electrodes for electrochemical treatment are prepared. Specifically, in the laminated body after the above-mentioned covering layer forming step S40, an anode 842 is provided on the surface of the covering layer 400, and the anode 842 is connected to the power supply 840. On the other hand, a cathode 844 is prepared, and the cathode 844 is connected to the power supply 840. As the cathode 844, a material having corrosion resistance and easy flow of current is used. As a specific cathode 844, for example, stainless steel (SUS), platinum (Pt), gold (Au), and boron-doped diamond can be listed.

[0121] After the connection of each electrode is completed, the stacked body connected with the anode 842 and the cathode 844 is 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 supply 840. Thus, the electrochemical treatment is performed. At this time, the progress of the electrochemical treatment is confirmed by the change of the current in the ammeter 860.

[0122] At this time, the electrochemical treatment makes the 2- The electrolyte passes through the dislocation D of the cover layer 400 with a relatively low carrier concentration and penetrates toward the intermediate layer 300 with a relatively high carrier concentration. That is, the dislocation D of the cover layer 400 is used as a nano-sized path for the electrolyte to penetrate. In this way, the intermediate layer 300 is selectively etched using the electrolyte that reaches the intermediate layer 300. As a result, a plurality of pores 360 are formed near the plurality of dislocations D in the intermediate layer 300. As a result, the intermediate layer 300 can be made porous.

[0123] On the other hand, according to the following reaction formula, the group III element ions (Ga 3+ ) and nitrogen (N 2 ) gas pass through the dislocation D of the cover layer 400 and are released to the outside compared to the cover layer 400 .

[0124] 2GaN+6h + →2Ga 3+ +N2

[0125] Through the electrochemical treatment, the plurality of pores 360 in the intermediate layer 300 are formed, for example, at positions respectively overlapping with the plurality of dislocations D in the cover layer 400 described later. The plurality of pores 360 in the intermediate layer 300 extend, for example, from the lower surface of the cover layer 400 along the thickness direction toward the base substrate 100. It should be noted that the pores 360 may not reach the base layer 200.

[0126] On the other hand, the partition wall portion of the intermediate layer 300 other than the pores 360 connects the upper portion of the base layer 200 or the lower portion of the intermediate layer 300 to the cover layer 400. Thus, even if the intermediate layer 300 has a plurality of pores 360, it maintains a constant thickness.

[0127] At this time, in the present embodiment, when observing any cross section orthogonal to the main surface 120 of the base substrate 100, the length of each of the plurality of pores 360 in the intermediate layer 300 along the direction of the main surface 120 of the base substrate 100 can be set to, for example, 30 nm or more or 100 nm or more. Thus, in the regrowth step S60 described later, the pores 360 of the intermediate layer 300 can be maintained. As a result, in the peeling step S70 described later, the regrown layer 500 can be easily and stably peeled from the base substrate 100 with at least a portion of the intermediate layer 300 maintained in a porous state as a boundary.

[0128] There is no upper limit to the length of the pores 360 in the intermediate layer 300 along the main surface 120 of the base substrate 100. However, the length of the pores 360 along the main surface 120 of the base substrate 100 can be set to 10 μm or less. Thus, by appropriately adjusting the electrochemical treatment conditions in the porous step S50, it is possible to suppress the peeling of the cover layer 400 caused by the exhaust gas generated when etching the intermediate layer 300.

[0129] At this time, in this embodiment, the depth of each of the plurality of pores 360 in the thickness direction of the intermediate layer 300 can be set to, for example, more than 100 nm, or 500 nm or more, or 1 μm or more. Thus, in the regrowth step S60 described later, the pores 360 of the intermediate layer 300 can be maintained. As a result, in the peeling step S70 described later, the regrown layer 500 can be easily and stably peeled off from the base substrate 100.

[0130] The upper limit of the depth of the void 360 is not limited. However, the depth of the void 360 can be set to be less than the thickness of the intermediate layer 300. Thus, in the peeling step S70 described later, it is possible to suppress excessive spread of peeling from the intermediate layer 300 to other layers.

[0131] On the other hand, in this electrochemical treatment, etching hardly occurs on the surface of the cover layer 400 where the carrier concentration is relatively low. In other words, even if the cover layer 400 has a plurality of dislocations D as described above, excessive etching does not occur on the surface near the dislocations D of the cover layer 400. Thus, the surface state of the cover layer 400 can be maintained flat.

[0132] At this time, in this embodiment, after the porous process S50, the arithmetic mean roughness (Ra) of the surface of the cover layer 400 is set to, for example, 1.0 nm or less, and the root mean square roughness (RMS) of the surface of the cover layer 400 is set to, for example, 2.0 nm or less. Alternatively, the Ra of the surface of the cover layer 400 can be set to, for example, 0.5 nm or less, and the RMS of the surface of the cover layer 400 can be set to, for example, 1.0 nm or less. Here, Ra and RMS are values ​​when the surface of the cover layer 400 is observed in a 5 μm square field of view using an atomic force microscope (AFM).

[0133] As described above, by maintaining the surface roughness of the cap layer 400 at a low level, the thick regrown layer 500 with good crystallinity can be stably grown on the cap layer 400 .

[0134] The lower limits of Ra and RMS of the surface of the cover layer 400 are not limited and may be close to Ra and RMS of the main surface 120 of the base substrate 100. Specifically, the lower limits of Ra and RMS of the surface of the cover layer 400 may be 0.1 nm and 0.2 nm, respectively.

[0135] As described above, etching does not occur near the dislocation D on the surface of the cover layer 400, but etched micro-voids (not shown) may be generated in the region including the dislocation D at a position below the surface of the cover layer 400. In this case, the micro-voids are formed in a manner that expands from a position below the surface of the cover layer 400 as it approaches the intermediate layer 300.

[0136] As specific conditions for the electrochemical treatment that can achieve the selective etching of the intermediate layer 300, for example, the following conditions can be cited. The treatment voltage is adjusted according to the carrier concentration of the intermediate layer 300, etc. The treatment current is adjusted according to the treatment area (the area of ​​the base substrate 100). The treatment time is adjusted according to the thickness of the intermediate layer 300.

[0137] Electrolyte temperature: room temperature (above 10°C and below 30°C)

[0138] Processing voltage: 1V or more and 200V or less, or 10V or more and 20V or less

[0139] Processing current: 0.01mA or more and 60A or less, or 0.1mA or more and 10A or less

[0140] Processing time: 0.1min to 180min, or 1min to 30min

[0141] As the intermediate layer 300 becomes porous based on the electrochemical treatment, Figure 4As shown, the cover layer 400 and the laminated body including the base substrate 100 and the base layer 200 are separated via the porous intermediate layer 300. The separation can be significantly caused by setting the pores 360 of the intermediate layer 300 to have the above-mentioned size.

[0142] Thus, the warping of the covering layer 400 in the porous step S50 can be reduced compared to the warping of the covering layer 400 before the porous step S50. That is, the covering layer 400 can be made to be substantially flat.

[0143] On the other hand, the seed substrate 10 is in a state similar to a configuration in which the group III nitride crystal layer on the base substrate 100 is thin. Thus, the warping of the base substrate 100 in the porous step S50 can be reduced compared to the warping of the base substrate 100 before the porous step S50.

[0144] After the electrochemical treatment, the nitride crystal growth seed substrate 10 is taken out from the electrolyte in the treatment tank 820. Thereafter, the nitride crystal growth seed substrate 10 taken out from the treatment tank 820 is cleaned with pure water or the like and dried. Thus, the electrolyte remaining in the pores 360 of the intermediate layer 300 is removed. The above operation completes the porous step S50.

[0145] In this manner, a seed substrate 10 is obtained. This seed substrate 10 is used in the regrowth step S60 and the peeling step S70 described later.

[0146] (S60: Regrowth Step)

[0147] After the porous step S50 is completed, a regrown layer 500 composed of a group III nitride crystal is epitaxially grown on the cap layer 400. As a method for growing the regrown layer 500, for example, a vapor phase growth method is used.

[0148] like Figure 5 As shown, in the regrowth step S60 of the present 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.

[0149] In the regrowth step S60, first, Figure 5 As shown, the temperature of the seed substrate 10 is raised from room temperature to the first growth temperature T1.

[0150] (S62: First Regrowth Step)

[0151] After the temperature of the seed substrate 10 reaches the first growth temperature T1, Figure 6 As shown, at the first growth temperature T1, the first regrown layer 520 is grown on the capping layer 400 .

[0152] Specifically, for example, by the HVPE method, GaCl gas and NH3 gas are supplied to the seed substrate 10 heated to the first growth temperature T1, thereby growing the GaN layer. Thus, the GaN layer as the first regrown layer 520 is epitaxially grown on the surface of the cap layer 400. It should be noted that various dopants can be added to the GaN layer as the first regrown layer 520.

[0153] At this time, in this embodiment, the first growth temperature T1 of the first regrowth step S62 is set lower than the second growth temperature T2 of the second regrowth step S64 as the main growth described later. That is, the first growth temperature T1 of the first regrowth step S62 is set slightly lower than the growth temperature of a typical group III nitride crystal.

[0154] At this time, as the temperature rises from room temperature to the first growth temperature T1, the base substrate 100 stretches. However, since the first growth temperature T1 is lower than the growth temperature of the base layer 200, etc., the base substrate 100 does not become completely flat, and the main surface 120 of the base substrate 100 is maintained slightly convex.

[0155] In contrast, the linear expansion coefficient of the cover layer 400 is smaller than that of the base substrate 100, and therefore, the elongation of the cover layer 400 is also smaller than that of the base substrate 100. Therefore, the cover layer warps in a manner that the surface of the cover layer 400 is recessed. However, by making the first growth temperature T1 low, excessive warping of the cover layer 400 can be suppressed. Thus, the generation of cracks in the cover layer 400 can be suppressed. As a result, the generation of cracks in the regrown layer 500 on the cover layer 400 can be suppressed.

[0156] At this time, in this embodiment, the first growth temperature T1 is set to, for example, 970° C. or less. Thus, in the first regrowth step S62 , crack generation in the cover layer 400 can be stably suppressed. As a result, crack generation in the regrown layer 500 on the cover layer 400 can be stably suppressed.

[0157] On the other hand, the first growth temperature T1 can be set to, for example, 800° C. or higher. This allows the group III nitride crystal serving as the first regrown layer 520 to be stably grown.

[0158] As described above, by adjusting the first growth temperature T1, the first regrown layer 520 of a predetermined thickness can be grown on the cover layer 400 while suppressing the occurrence of cracks in the cover layer 400. As a result, the total thickness of the group III nitride crystal layer (cover layer 400 and first regrown layer 520) above the porous intermediate layer 300 can be stably thickened. As a result, in the second regrowing 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 break.

[0159] At this time, in this embodiment, by starting the growth of the first regrown layer 520 on the flat surface of the cover layer 400, no crystal plane (the inclined interface 524 described later) other than the c-plane 522 is generated in the initial stage of growth (the stage of thin thickness) of the first regrown layer 520, and the regrown layer 500 can be grown with the c-plane 522 (+c-plane) as the growth plane. In other words, the first regrown layer 520 can be grown in a step flow manner on the entire surface of the cover layer 400. As a result, the crystallinity of the first regrown layer 520 can be improved.

[0160] Thereafter, when the first regrown layer 520 is gradually and slowly grown, an inclined interface 524 other than the c-plane can be generated in at least a portion of the first regrown layer 520. That is, after the first regrown layer 520 of a predetermined thickness is subjected to step flow growth, the first regrown layer 520 can be three-dimensionally grown. Thus, at least a portion of the plurality of dislocations D propagating from the cap layer 400 along the c-axis direction of the first regrown layer 520 can be bent and propagated in a direction substantially perpendicular to the inclined interface 524 at a position where the inclined interface 524 is exposed. Thus, at least a portion of the plurality of dislocations D can be locally gathered. By making the locally gathered dislocations D disappear from each other, the dislocation density can be reduced. As a result, the number of pits on the surface of the regrown layer 500 can be reduced.

[0161] At this time, in this embodiment, the thickness of the first regrown layer 520 can be set to, for example, 1 μm or more, 10 μm or more, or 20 μm or more. Thus, in the second regrowing step S64 as the main growth described later, when the temperature is raised to the second growth temperature, the group III nitride crystal layer above the intermediate layer 300 can be stably prevented from being easily broken. As a result, the generation of cracks and pits in the thick second regrown layer 540 can be stably suppressed.

[0162] On the other hand, the upper limit of the thickness of the first regrown layer 520 is not particularly limited. The thickness of the first regrown layer 520 can be set to, for example, 300 μm or less or 100 μm or less. Here, the first regrown layer 520 grown (three-dimensionally grown) at a low temperature is easily mixed with impurities. Therefore, if the first regrown layer 520 is grown thicker, it is possible to apply stress between the first regrown layer 520 and the second regrown layer 540 described later. In contrast, by setting the thickness of the first regrown layer 520 to 300 μm or less or 100 μm or less, it is possible to suppress excessive stress between the first regrown layer 520 and the second regrown layer 540 described later due to the mixing of impurities in the first regrown layer 520.

[0163] 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. It should be noted that the supply of NH3 gas is continued.

[0164] Afterwards, if Figure 5 As shown, the temperature of the seed substrate 10 is increased from the first growth temperature T1 to the second growth temperature T2.

[0165] (S64: Second Regrowth Step)

[0166] After the temperature of the seed substrate 10 is raised from the first growth temperature T1 to the second growth temperature T2, as shown in FIG. Figure 7 As shown in FIG. 1 , the growth of the regrown layer 500 as the second regrown layer 540 is restarted. That is, at the second growth temperature T2, the thick second regrown layer 540 is grown on the first regrown layer 520 as the main growth.

[0167] 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 on the first regrowth layer 520 as the second regrowth layer 540 under the same conditions as the first regrowth step S62, except that the growth temperature is set to the second growth temperature T2. It should be noted that various dopants may be added to the GaN layer as the second regrowth layer 540.

[0168] At this time, in the present embodiment, as described above, even if the second growth temperature T2 of the second re-growth step S64 as the main growth is set higher than the first growth temperature T1 of the first re-growth step S62, the total thickness of the cap layer 400 and the first re-growth layer 520 as the group III nitride crystal layer above the intermediate layer 300 is made thicker, so that the group III nitride crystal layer above the intermediate layer 300 is not easily broken. Thus, the re-growth layer 500 can be stably grown. Specifically, even if the second re-growth layer 540 is grown thicker, the generation of cracks and pits can be suppressed.

[0169] At this time, in this embodiment, as described above, by making the second growth temperature T2 of the second regrowth step S64 higher than the first growth temperature T1, the second regrowth layer 540 can be step-flow grown (two-dimensional growth, lateral growth) with the c-plane 542 as the growth plane. As a result, the second regrowth layer 540 with good crystallinity and thick film can be grown with improved surface flatness. It should be noted that the normal line of the c-plane 542 of the second regrowth layer 540, that is, the c-axis, can be tilted at an off angle inherited from the c-axis of the base substrate 100 tilted at a predetermined off angle.

[0170] At this time, in this embodiment, the second growth temperature T2 can be set to, for example, 980° C. or above or 1000° C. or above. Thus, the second regrown layer 540 can be stably step-flow grown. As a result, the flatness of the second regrown layer 540 can be improved and the second regrown layer 540 with good crystallinity and thick film can be stably grown.

[0171] On the other hand, the second growth temperature T2 can be set to, for example, 1100° C. or less. This can suppress the surface roughness of the second regrown layer 540 caused by an excessively high growth temperature.

[0172] At this time, in the first regrowing step S62 of the present embodiment, when the inclined interface 524 is generated in at least a portion of the first regrown layer 520 (when the first regrown layer 520 is grown three-dimensionally), the second regrown layer 540 is grown laterally as described above, so that the inclined interface in the second regrown layer 540 can be gradually reduced, that is, the c-plane 542 can be gradually expanded. Thus, the second regrown layer 540 having a mirror-finished surface can be grown.

[0173] At this time, in this embodiment, the total thickness of the regrown layer 500 (the first regrown layer 520 and the second regrown layer 540) can be set to, for example, 600 μm or more or 1 mm or more. The upper limit of the total thickness of the regrown layer 500 is not particularly limited. However, from the perspective of improving productivity, the total thickness of the regrown layer 500 can be set to, for example, 100 mm or less.

[0174] Here, during the growth of the thick regrown layer 500, the dislocations D move in a random walk manner. Thus, during the growth of the regrown layer 500, the dislocations D meet each other or form loops. This phenomenon can reduce the dislocations D reaching the surface of the thick second regrown layer 540.

[0175] Alternatively, in the first regrowing step S62 of the present embodiment, even when the inclined interface 524 is generated in at least a portion of the first regrown layer 520 (when the first regrown layer 520 is grown three-dimensionally), dislocations can be locally collected at the junction of adjacent inclined interfaces during the lateral growth of the second regrown layer 540. In this case, the dislocations D reaching the surface of the thick second regrown layer 540 can also be reduced.

[0176] As a result, the dislocation density of the second regrown layer 540 can be reduced (it should be noted that Figure 7 It is simplified, so Figure 7 The number of dislocations in the .

[0177] Specifically, the dislocation density at the surface of the second regrown layer 540 can be, for example, 3×10 7 cm -2 Below, or can be 1×10 7 cm -2 Below, or can be 5×10 6 cm -2 the following.

[0178] (S70: Peeling Step)

[0179] After the regrowth step S60 is completed, Figure 8 As shown, the regrown layer 500 is peeled off from the base wafer 100 with at least a portion of the intermediate layer 300 that has become porous as a boundary.

[0180] In this embodiment, during the temperature drop after the regrowth step S60, the regrown layer 500 is spontaneously peeled off from the base substrate 100. Thus, a special additional step of peeling off is not required. In other words, the manufacturing method can be simplified.

[0181] 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 base substrate 100 ). This is because, for example, as described above, as the thickness of the regrowth layer 500 increases, the dislocation density decreases.

[0182] Due to the tensile stress in the regrown layer 500 in the direction along the main surface 120 of the base substrate 100 generated by such operation, the c-plane 510 of the regrown layer 500 is warped into a spherical shape with a concave upper side. As a result, the regrown layer 500 is spontaneously and slowly peeled off from the outer periphery to the center of the base substrate 100. That is, by utilizing the warping of the c-plane 510 of the regrown layer 500, the regrown layer 500 can be slowly peeled off from the outer periphery to the center of the base substrate 100. In other words, the regrown layer 500 can be uniformly peeled off in a concentric circle shape relative to the center of the base substrate 100. As a result, the peeling of a large area of ​​the regrown layer 500 can be easily and stably performed.

[0183] Through the above-described peeling step S70 , the peeling intermediate body 20 including at least the cover layer 400 and the regrown layer 500 is formed. A residual piece of the intermediate layer 300 may remain on the lower surface of the cover layer 400 of the peeling intermediate body 20 .

[0184] (S80: post-processing step)

[0185] After the stripping step S70 is completed, Fig. 9 As shown, the regrown layer 500 is cut by a wire saw, for example, along a cross section perpendicular to the normal direction of the center of the surface of the regrown layer 500. Thus, a nitride crystal substrate 50 (hereinafter referred to as "substrate 50") as an in-situ sliced ​​substrate is formed.

[0186] Next, both surfaces of the substrate 50 are polished by a polishing device, thereby making the main surface of the substrate 50 mirror-finished.

[0187] Through the above steps, the substrate 50 formed of a single crystal of a group III nitride according to the present embodiment can be obtained.

[0188] The diameter of the substrate 50 may be, for example, 2 inches or more or 4 inches or more. The thickness of the substrate 50 may be, for example, 150 μm or more and 3 mm or less.

[0189] (2) Summary of this embodiment

[0190] According to the present embodiment, one or more of the following effects can be obtained.

[0191] (a) In the porous step S50 of this embodiment, the intermediate layer 300 is made porous by electrochemical treatment while maintaining the surface state of the cap layer 400 and penetrating the dislocation D of the cap layer 400. In the regrowth step S60, the regrowth layer 500 is epitaxially grown on the cap layer 400.

[0192] In the porous step S50, as described above, the electrochemical treatment is performed in a state where the cover layer 400 with a relatively low carrier concentration covers the intermediate layer 300 with a relatively high carrier concentration. Thus, the intermediate layer 300 can be selectively made porous through the dislocation D of the cover layer 400 while maintaining the surface state of the cover layer 400.

[0193] By maintaining the surface state of the cap layer 400 on the porous intermediate layer 300 to be flat, the cap layer 400 can be used as a regrowth base layer in the regrowth step S60 , and a thick regrowth layer 500 with good crystallinity can be stably grown.

[0194] On the other hand, by covering the plurality of pores 360 of the intermediate layer 300 with the flat cover layer 400, it is possible to suppress the filling of the pores 360 in the intermediate layer 300 and maintain a large number of pores 360 in the intermediate layer 300 in the regrowth step S60. Thereafter, the regrown layer 500 can be easily and stably peeled off from the base substrate 100 using at least a portion of the intermediate layer 300 maintained in a porous state as a boundary.

[0195] As described above, according to the present embodiment, the substrate 50 formed of a single crystal of a group III nitride can be easily obtained from the peeled regrown layer 500 .

[0196] (b) In the regrowth step S60 of this embodiment, the growth temperature is adjusted in two stages. Specifically, the first growth temperature T1 of the first regrowth step S62 is set lower than the second growth temperature T2 of the second regrowth step S64 as the main growth. Thus, in the first regrowth step S62, it is possible to suppress excessive warping in the cover layer 400 and suppress cracking in the cover layer 400.

[0197] In this way, the first regrown layer 520 of a predetermined thickness is grown on the cover layer 400 in a state where crack generation in the cover layer 400 is suppressed. As a result, the total thickness of the group III nitride crystal layer above the porous intermediate layer 300 can be stably increased. As a result, in the second regrowing 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 break.

[0198] As a result, it is possible to stably grow the regrown layer 500. Specifically, even if the second regrown layer 540 is grown thick, the generation of cracks and pits can be suppressed.

[0199] (c) In the present 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 the second growth temperature T2, and then the growth of the regrowth layer 500 is restarted as the second regrowth layer 540.

[0200] Instead of slowly raising the temperature in the first regrowth step S62, the first growth temperature T1 of the first regrowth step S62 is made different from the second growth temperature T2 of the second regrowth step S64 as described above, thereby enabling 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 to be set separately.

[0201] Furthermore, as described above, by growing the first regrown layer 520 of a predetermined thickness on the cap layer 400 in advance, when the growth temperature is raised from the first growth temperature T1 to the second growth temperature T2, cracks in the group III nitride crystal layer above the intermediate layer 300 can be suppressed and the heating rate can be increased. As a result, the manufacturing process can be shortened.

[0202] (3) Modification of one embodiment

[0203] The above-described embodiment can be modified as required as in the following modified examples. Hereinafter, only the elements different from the above-described embodiment will be described, and the 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.

[0204] like Fig.10 As shown, in the first regrowth step S62 of Modification 1, the growth temperature is gradually increased from the first growth temperature T1 toward the second growth temperature T2 while the first regrowth layer 520 is grown.

[0205] According to Modification 1, the heating rate from the first growth temperature T1 to the second growth temperature T2 can be slowed down. As a result, cracking of the group III nitride crystal layer above the intermediate layer 300 caused by the heating process from the first growth temperature T1 to the second growth temperature T2 can be stably suppressed.

[0206] On the other hand, according to Modification 1, in the first regrowth step S62, the growth step of the first regrowth layer 520 and the temperature increase step from the first growth temperature T1 to the second growth temperature T2 are combined. That is, the regrowth step S60 can be transferred from the first regrowth step S62 to the second regrowth step S64 without providing a growth stop period. Therefore, the manufacturing process can also be shortened in the modification.

[0207] <Other embodiments of the present application>

[0208] The embodiments of the present application have been described in detail above, but the present application is not limited to the above embodiments, and various modifications can be made within the scope of the gist thereof.

[0209] In the above embodiment, the base layer forming step S20 is described, but the base layer forming step S20 may not be performed. In other words, there may be no base layer 200. In the intermediate layer forming step S30, the intermediate layer 300 may be formed directly on the base substrate 100.

[0210] In the above embodiment, the upper layer of the base layer 200, the intermediate layer 300, the cap layer 400 and the regrown layer 500 are described as respectively comprising GaN crystals, but the present application is not limited to this case. Each layer is not limited to GaN crystals, and can 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), aluminum indium gallium nitride (AlInGaN), etc., i.e., In x Al y Ga 1-x-y Crystals represented by the composition formula of N (wherein 0≤x≤1, 0≤y≤1, 0≤x+y≤1) are formed.

[0211] In the above embodiment, the Ra of the main surface 120 of the base substrate 100 is less than 0.3 nm, but the main surface 120 of the base substrate 100 may be patterned to have periodic projections and depressions. The base substrate 100 may be a so-called PSS (Patterned Sapphire Substrate).

[0212] In the above embodiment, the case where the base substrate 100 is formed of a material different from the group III nitride is described, but the present application is not limited to this case. The base substrate 100 may be, for example, a self-supporting substrate formed of a group III nitride crystal. In this case, the presence of the pores 360 of the intermediate layer 300 causes a decrease in thermal conductivity above the intermediate layer 300. Therefore, deformation can occur between the layer below the intermediate layer and the layer above the intermediate layer. As a result, in this case, the same problem as the case where the base substrate 100 is a different type of substrate may also occur. Therefore, even in the case of using a self-supporting substrate formed of a group III nitride crystal, by applying the two-stage regrowth process S60, the same effect as the above embodiment can be obtained.

[0213] When the base wafer 100 is a self-supporting wafer formed of a group III nitride crystal, it can be reused after peeling off a functional layer of a semiconductor device grown by so-called GaN on GaN, as in the following Modification 2.

[0214] In the second modification, first, in the substrate preparation step S10, a self-supporting substrate formed of a group III nitride is prepared as a base substrate 100. After the substrate preparation step S10, the process proceeds from the base layer forming step S20 to the porous step S50 in the same manner as in the above-mentioned embodiment. Next, in the regrowth step S60, a functional layer is grown as a regrown layer 500. The "functional layer" mentioned here refers to a layer that functions as at least a part of a semiconductor device. In the stripping step S70, the functional layer as the regrown layer 500 is stripped. Next, after the stripping step S70, a polishing step of polishing the surface of the remaining base substrate 100 is performed. After the polishing step, by reusing the base substrate 100, a cycle from the base layer forming step S20 to the polishing step is repeated. As described above, in the second modification, the self-supporting substrate formed of a group III nitride as the base substrate 100 can be reused, and the manufacturing cost of semiconductor devices and the like can be reduced.

[0215] In the above-mentioned embodiment, the case where the upper layer of the base layer 200, the middle layer 300, the covering layer 400 and the regrown layer 500 contain GaN crystals that are identical to each other is described, but at least one layer among the upper layer of the base layer 200, the middle layer 300, the covering layer 400 and the regrown layer 500 may contain a III-nitride crystal that is different from the other layers.

[0216] In the above embodiment, the case where the upper layer of the base layer 200, the middle layer 300, the covering layer 400 and the regrown layer 500 contain Si as an n-type dopant is described, but at least one layer of the upper layer of the base layer 200, the middle layer 300, the covering layer 400 and the regrown layer 500 may contain, for example, oxygen (O) or germanium (Ge) as an n-type dopant.

[0217] In the above embodiment, the case where the above-mentioned vapor phase growth method is used as the growth method of the base layer 200, the intermediate layer 300, the cover layer 400 and the regrown layer 500 is described, but the present application is not limited to this case. As a growth method for at least any one of the base layer 200, the intermediate layer 300, the cover layer 400 and the regrown layer 500, an organic metal vapor phase epitaxy (MOVPE) method can be used. Alternatively, as a growth method for at least any one of the base layer 200, the intermediate layer 300, the cover layer 400 and the regrown layer 500, a growth method other than the vapor phase growth method can be used.

[0218] In the above embodiment, the case where the first regrown layer 520 is grown three-dimensionally is described, but the present application is not limited to this case. The step flow growth of the first regrown layer 520 can be maintained.

[0219] Example

[0220] Hereinafter, experimental results for verifying the effects of the above-described embodiment will be described.

[0221] (1) Experiment 1

[0222] (1-1) Preparation of seed substrate

[0223] Three seed crystal substrates were prepared under the same conditions through the following steps.

[0224] (Base substrate preparation step)

[0225] As a base substrate for obtaining a seed substrate, the following substrate was prepared.

[0226] Base substrate: sapphire substrate

[0227] The plane orientation of the main surface of the base substrate: +c plane

[0228] Diameter of base substrate: 2 inches (50.8 mm)

[0229] Thickness of base substrate: 430μm

[0230] (Base layer forming step)

[0231] An AlN buffer layer and a GaN layer were sequentially formed as base layers on a base substrate by the HVPE method under the following conditions.

[0232] Growth temperature of substrate layer: 1055℃.

[0233] The thickness of the AlN buffer layer and the GaN layer are 100nm and 4μm respectively.

[0234] Carrier concentration in GaN layer as base layer: about 1×10 18 cm -3

[0235] (Intermediate Layer Formation Step)

[0236] Next, a Si-doped GaN layer as an intermediate layer was grown on the base layer by the HVPE method under the following conditions.

[0237] Growth temperature of the middle layer: 1055°C.

[0238] Thickness of the middle layer: 3000nm

[0239] Carrier concentration in the middle layer: 6×10 18 cm -3

[0240] (Coating Layer Forming Step)

[0241] Next, a GaN layer as a cap layer was grown on the base layer by the HVPE method under the following conditions.

[0242] Growth temperature of the covering layer: 1055°C.

[0243] Thickness of cover layer: 150nm

[0244] Carrier concentration in the cover layer: about 5×10 17 cm -3

[0245] (Porous process)

[0246] Next, the intermediate layer was made porous by electrochemical treatment under the following conditions through the dislocation of the cover layer. Thus, a nitride crystal growth seed substrate was obtained. It should be noted that two nitride crystal growth seed substrates were prepared, one for observation and one for regrowth.

[0247] Electrolyte temperature: room temperature (23°C)

[0248] Processing voltage: 20V

[0249] Processing current: Maximum 100mA

[0250] Processing time: 10 minutes

[0251] (1-2) Heat treatment

[0252] Using the above seed substrates, assuming heating to the growth temperature of the regrown layer, the three seed substrates were heated to 883° C., 963° C., and 1033° C. At this time, the heating atmosphere was set to an atmosphere containing N 2 gas and NH 3 gas, and the heating time was set to 3 minutes.

[0253] (1-3) Evaluation

[0254] The surfaces of the three seed substrates subjected to the above-mentioned heat treatment were observed using an optical microscope.

[0255] (1-4) Results

[0256] Reference Figure 13 to Figure 15 , the evaluation results of Experiment 1 are explained.

[0257] (1033℃)

[0258] like Fig.15As shown in FIG. 1 , a large number of fine cracks are generated on the surface of the cover layer in the seed substrate heated to 1033°C. In this seed substrate, as the temperature rises to 1033°C, the substrate stretches and returns to flatness, while the cover layer on the porous intermediate layer warps. Therefore, it can be considered that cracks are generated in the cover layer during heating at 1033°C.

[0259] (963℃、883℃)

[0260] In contrast, Fig.13 and Fig.14 As shown, in the seed substrates heated to 883° C. and 963° C., the surface of the cover layer did not crack and the surface of the cover layer remained flat. This confirmed that if the heating temperature of the seed substrate is set to 970° C. or less, the generation of cracks in the cover layer can be suppressed.

[0261] (2) Experiment 2

[0262] (2-1) Preparation of seed substrate and peeling intermediate

[0263] In samples A1, A2, B1, B2, C1 to C4, seed substrates were prepared under the conditions described in Table 1 and Table 2 and below. In samples C1 and C3, the seed substrate was used for the regrowth process. In samples A1, A2, B1, B2, and C4, the seed substrate was used for the regrowth process and the peeling process.

[0264] <Sample A1>

[0265] In sample A1, a seed substrate was prepared in the same manner as in Experiment 1.

[0266] (First Regrowth Step)

[0267] Next, a GaN layer as a first regrown layer was grown on the cap layer by the HVPE method under the following conditions.

[0268] First growth temperature: 835°C.

[0269] Thickness of the first regrown layer: 50 μm

[0270] (Second Regrowth Step)

[0271] Next, in the same chamber as the first regrowth step, a GaN layer as a second regrowth layer is grown on the first regrowth layer.

[0272] Second growth temperature: 1055℃.

[0273] Total thickness of the regrown layer: 1mm

[0274] (Peeling process)

[0275] During the temperature drop after the regrowth step, the regrowth layer is peeled off from the base substrate.

[0276] <Sample A2>

[0277] In sample A2, a seed substrate was prepared in the same manner as sample A1 except that the electrochemical treatment time in the porous step was set to 20 minutes. Then, the first regrowth step, the second regrowth step, and the peeling step were performed using the seed substrate of sample A2 under the same conditions as sample A1.

[0278] <Sample B1>

[0279] In sample B1, a seed substrate was prepared in the same manner as sample A1. Thereafter, in sample B1, a first regrowth step, a second regrowth step, and a peeling step were performed under the same conditions as sample A1 except that the first growth temperature was set to 985°C.

[0280] <Sample B2>

[0281] In sample B2, a seed substrate was prepared in the same manner as sample A1. Thereafter, in sample B2, a first regrowth step, a second regrowth step, and a peeling step were performed under the same conditions as sample A1, except that the thickness of the first regrowth layer was set to 0.5 μm.

[0282] <Sample C1>

[0283] In sample C1, a seed substrate was prepared in the same manner as sample A1 except that the cover layer was not provided. In sample C1, a regrowth step was performed in the same manner as sample A1.

[0284] <Sample C2>

[0285] In sample C2, a seed substrate was prepared in the same manner as sample A1 except that the thickness of the cap layer was set to 5 nm. In sample C2, the regrowth step and subsequent steps were not performed.

[0286] <Sample C3>

[0287] In sample C3, a seed substrate was prepared in the same manner as sample A1 except that the thickness of the intermediate layer was set to 50 nm. In sample C3, a regrowth step was performed in the same manner as sample A1.

[0288] <Sample C4>

[0289] In sample C4, a seed substrate was prepared in the same manner as sample A1. Thereafter, in sample C4, a regrowth step and a peeling step were performed under the same conditions as sample A1, except that the first growth temperature was set to 1055° C. (ie, the first regrowth step was not performed).

[0290] (2-2) Evaluation

[0291] Each sample was observed using an optical microscope as follows.

[0292] Cross-section and surface of the laminate after the regrowth process of samples C1 and C3

[0293] ·Surface of the seed substrate of sample C2

[0294] · Cross-section and surface of the peeled intermediate of samples A1, A2, B1, B2, and C4

[0295] In the peeled intermediates of samples A1, A2, B1, B2, and C4, the image of the surface of the regrown layer was binarized in a manner of dividing into pits (dark areas) and other parts (bright areas). Thereafter, in each sample, the ratio of the area of ​​the pits to the unit surface area of ​​the regrown layer (hereinafter also referred to as the "pit area ratio of the regrown layer") was calculated. The unit of the pit area ratio was set to "%". The pits in the measurement of the pit area ratio also include pits that are crack marks of the cover layer.

[0296] As a result, the case where the pit area ratio of the regrown layer exceeds 40% is recorded as "C", the case where the pit area ratio of the regrown layer exceeds 20% and is less than 40% is recorded as "B", and the case where the pit area ratio of the regrown layer is less than 20% is recorded as "A".

[0297] (2-3) Results

[0298] Refer to Table 1, Table 2, Fig.16 and Fig.17 , the evaluation results of Experiment 2 are explained.

[0299] [Table 1]

[0300]

[0301] [Table 2]

[0302]

[0303] <Sample C1>

[0304] In sample C1, no cover layer was formed, so the regrowth process was performed with the porous intermediate layer exposed. Therefore, the pores in the intermediate layer were filled with the regrowth layer, and a bond occurred from the base substrate to the regrowth layer. As a result, after the thick regrowth layer was grown, a large crack reaching the base substrate was generated. Furthermore, the regrowth layer could not be peeled off from the base substrate.

[0305] <Sample C2>

[0306] In sample C2, a portion of the cover layer peeled off after the electrochemical treatment. It is believed that in sample C2, the thickness of the cover layer was less than 10 nm, so the cover layer peeled off due to the outgassing generated during the electrochemical treatment.

[0307] <Sample C3>

[0308] In sample C3, the pores in the intermediate layer disappeared after the regrowth process. This is believed to be because the porous intermediate layer was destroyed at the growth temperature during regrowth. Therefore, a bond occurred in the region from the base substrate to the regrowth layer. As a result, after the thick regrowth layer was grown, a large crack reaching the base substrate was generated. Furthermore, the regrowth layer could not be peeled off from the base substrate.

[0309] <Samples A1, A2, B1, B2 and C4>

[0310] On the other hand, in samples A1, A2, B1, B2, and C4, at least a part of the regrown layer can be peeled off with at least a part of the intermediate layer that has become porous as a boundary.

[0311] The results of samples A1, A2, B1, B2, and C4 confirmed that in the porous step, the surface state of the cover layer can be maintained and the intermediate layer can be made porous, thereby allowing at least a portion of the regrown layer to be peeled off.

[0312] <Comparison of Samples A1, A2, B1 and B2 with Sample C4>

[0313] On the other hand, in samples A1, A2, B1, B2, and C4, the following differences occur depending on the first growth temperature.

[0314] (Sample C4)

[0315] In sample C4, a part of the regrown layer could be peeled off, but a part of the pores in the intermediate layer disappeared under the other part of the regrown layer. Therefore, the other part of the regrown layer could not be peeled off from the substrate.

[0316] Furthermore, if Fig.17 As shown, in sample C4, a plurality of pits exist on the surface of the peeled regrown layer, and the pit area ratio is C.

[0317] In sample C4, as shown in Experiment 1, cracks occurred in the cover layer when the temperature was raised to 1055°C. In the regrowth process of sample C4, the pores in the intermediate layer were maintained and a part of the regrown layer was bonded to the cracks in the cover layer, thereby being able to peel off a part of the regrown layer. However, it can be considered that as crack marks of the cover layer, a plurality of pits were formed in a part of the regrown layer.

[0318] On the other hand, in the regrowth step of sample C4, pores were filled in other parts of the regrowth layer via cracks in the cover layer, so it is considered that other parts of the regrowth layer could not be peeled off from the base substrate.

[0319] (Samples A1, A2, B1 and B2)

[0320] In contrast, in samples A1, A2, B1, and B2, at least a portion of the regrown layer occupying a larger area can be peeled off compared to sample C4. In samples A1, A2, B1, and B2, pits on the surface of the peeled regrown layer are reduced compared to sample C4, and the pit area ratio is A or B.

[0321] The results of samples A1, A2, B1, and B2 confirmed that by setting the first growth temperature of the first regrowth step lower than the second growth temperature of the second regrowth step, the generation of cracks and pits in the thick second regrowth layer can be suppressed.

[0322] <Comparison of Samples A1 and A2 with Samples B1 and B2>

[0323] Furthermore, in samples A1 and A2 and samples B1 and B2, the following differences occurred depending on the conditions of the first regrowth step.

[0324] (Sample B1)

[0325] In sample B1, a portion occupying more than 80% of the area of ​​the regrown layer could be peeled off, but some pores in the intermediate layer disappeared below the other portion of the regrown layer. Therefore, the other portion of the regrown layer could not be peeled off from the base substrate.

[0326] In sample B1, the number of pits can be reduced compared to sample C4. However, a small number of pits exist on the surface of the peeled regrown layer of sample B1, and the pit area ratio is B.

[0327] In sample B1, when the temperature was raised to 985°C, fine cracks occurred in a part of the cover layer. In sample B1, the regrown layer was more easily bonded to the cracks in the cover layer than in sample C4, so that a part of the regrown layer could be peeled off over a large area. However, it can be considered that although the number of pits was reduced in sample B1, a small number of pits were formed in a part of the regrown layer of sample B1 as crack traces of the cover layer.

[0328] On the other hand, it is considered that in Sample B1, similarly to Sample C4, since the pores were filled via the microcracks of the cover layer, the other part of the regrown layer could not be peeled off from the base substrate.

[0329] (Sample B2)

[0330] In sample B2, substantially the same results as those of sample B1 were obtained.

[0331] In sample B2, the thickness of the first regrown layer was less than 1 μm, so microcracks occurred in a part of the first regrown layer when the temperature was raised to the second growth temperature. As a result, it can be considered that sample B2 also obtained substantially the same results as sample B1.

[0332] (Samples A1 and A2)

[0333] In contrast, in samples A1 and A2, the regrown layer occupying a larger area can be peeled off compared to samples B1 and B2. Fig.16 As shown, in samples A1 and A2, the pits at the surface of the peeled regrown layer are less than those in samples B1 and B2, and the pit area ratio is A.

[0334] The results of samples A1 and A2 confirm that in the first regrowth step, by setting the first growth temperature to 970°C or less and the thickness of the first regrowth layer to 1 μm or more, the generation of cracks and pits in the thick second regrowth layer can be stably suppressed.

[0335] <Notes>

[0336] The following is a supplementary note on the method of this application.

[0337] (Note 1)

[0338] A method for manufacturing a nitride crystal substrate comprises the following steps:

[0339] (a) a step of preparing a base substrate;

[0340] (b) forming an intermediate layer on the base substrate, the intermediate layer comprising an n-type Group III nitride crystal;

[0341] (c) forming a capping layer on the intermediate layer, the capping layer comprising a Group III nitride crystal having a carrier concentration lower than that of the intermediate layer;

[0342] (d) a step of making the intermediate layer porous by electrochemical treatment while maintaining the surface state of the covering layer and penetrating dislocations in the covering layer;

[0343] (e) a step of epitaxially growing a regrown layer composed of a group III nitride crystal on the cap layer; and

[0344] (f) a step of peeling the regrown layer from the base substrate with at least a portion of the intermediate layer that has become porous as a boundary,

[0345] (e) having the following steps:

[0346] (e1) a step of growing a first regrown layer on the cap layer at a first growth temperature; and

[0347] (e2) a step of growing a second regrown layer on the first regrown layer at a second growth temperature,

[0348] In (e1), the first growth temperature is set lower than the second growth temperature.

[0349] (Note 2)

[0350] The method for producing a nitride crystal substrate according to Supplementary Note 1, wherein in (a), the base substrate formed of a material different from the Group III nitride is prepared.

[0351] (Note 3)

[0352] The method for producing a nitride crystal substrate according to Supplement 1 or Supplement 2, wherein in (b), the thickness of the intermediate layer is made to exceed 100 nm.

[0353] (Note 4)

[0354] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 3, wherein in (c), the thickness of the cap layer is set to be 10 nm or more.

[0355] (Note 5)

[0356] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 4, wherein in (d), the warping of the cover layer is reduced compared to the warping of the cover layer before (d).

[0357] (Note 6)

[0358] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 5, wherein in (e1), the first growth temperature is set to 970° C. or less.

[0359] (Note 7)

[0360] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 6, wherein in (e1), the thickness of the first regrown layer is set to 1 μm or more.

[0361] (Note 8)

[0362] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 7, wherein in (e2), the second growth temperature is set to 980° C. or higher.

[0363] (Note 9)

[0364] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 8, wherein:

[0365] In (e1), a tilted interface other than the (0001) plane is generated in at least a portion of the first regrown layer.

[0366] In (e2), the inclined interface is gradually reduced to grow the second regrown layer having a mirror-finished surface.

[0367] (Note 10)

[0368] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 9, wherein:

[0369] In (e1), the first growth temperature is maintained, and when the thickness of the first regrown layer reaches a predetermined thickness, the growth of the first regrown layer is terminated.

[0370] In (e2), after the growth temperature is increased from the first growth temperature to the second growth temperature, the growth of the regrown layer is restarted as the second regrown layer.

[0371] (Note 11)

[0372] The method for producing a nitride crystal substrate according to any one of Supplementary Notes 1 to 9, wherein:

[0373] In (e1), while growing the first regrown layer, the growth temperature is gradually increased from the first growth temperature toward the second growth temperature.

[0374] (Note 12)

[0375] A peeling intermediate obtained by the method for producing a nitride crystal substrate according to any one of Appendix 1 to Appendix 11,

[0376] The exfoliation intermediate body includes at least the cap layer and the regrown layer.

Claims

1. A method for manufacturing a nitride crystal substrate, comprising the following steps: (a) a step of preparing a base substrate; (b) forming an intermediate layer on the base substrate, the intermediate layer comprising an n-type Group III nitride crystal; (c) forming a capping layer on the intermediate layer, the capping layer comprising a Group III nitride crystal having a carrier concentration lower than that of the intermediate layer; (d) a step of making the intermediate layer porous by electrochemical treatment while maintaining the surface state of the cover layer and penetrating dislocations in the cover layer; (e) a step of epitaxially growing a regrown layer composed of a group III nitride crystal on the cap layer; and (f) a step of peeling the regrown layer from the base substrate with at least a portion of the intermediate layer becoming porous as a boundary, (e) having the following steps: (e1) a step of growing a first regrown layer on the cap layer at a first growth temperature; and (e2) growing a second regrown layer on the first regrown layer at a second growth temperature, In (e1), the first growth temperature is set lower than the second growth temperature.

2. The method for manufacturing a nitride crystal substrate according to claim 1, wherein: In (b), the thickness of the intermediate layer is set to be more than 100 nm.

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

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

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

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

7. The method for manufacturing a nitride crystal substrate according to claim 1 or 2, wherein: In (e1), at least a portion of the first regrown layer is caused to have an inclined interface other than the (0001) plane, In (e2), the inclined interface is gradually reduced to grow the second regrown layer having a mirror-finished surface.

8. The method for manufacturing a nitride crystal substrate according to claim 1 or 2, wherein: In (e1), the first growth temperature is maintained, and when the thickness of the first regrown layer reaches a predetermined thickness, the growth of the first regrown layer is terminated. In (e2), After the growth temperature is increased from the first growth temperature to the second growth temperature, the growth of the regrown layer is restarted to form the second regrown layer.

9. The method for manufacturing a nitride crystal substrate according to claim 1 or 2, wherein: In (e1), while the first regrown layer is grown, the growth temperature is gradually increased from the first growth temperature toward the second growth temperature.

10. A peeling intermediate obtained by the method for producing a nitride crystal substrate according to claim 1 or 2, The exfoliation intermediate body includes at least the cap layer and the regrown layer.

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