Method for manufacturing group III nitride semiconductors

Abstract

This invention provides a method for producing a group III nitride semiconductor with excellent crystal quality and high resistance. [Solution] A method for producing a group III nitride semiconductor, in which a melt obtained by dissolving a group III metal in a flux is held in a crucible 103, and a group III nitride semiconductor is grown by supplying a nitrogen-containing gas to the melt. The crucible 103 used in the method for producing the group III nitride semiconductor mainly consists of alumina and also contains a P-type dopant.

Description

[Technical Field]

[0001] This invention relates to a method for producing a group III nitride semiconductor. [Background technology]

[0002] One known method for growing GaN crystals is the Na flux method. This technique involves introducing nitrogen gas into a molten mixture of Na (sodium) and Ga (gallium), allowing GaN to be grown at relatively low pressures and temperatures of a few MPa and 600-1000°C.

[0003] On the other hand, high-resistance semiconductors are required for power devices that carry large currents. As a method to increase the resistance of GaN crystals, for example, Patent Document 1 discloses a method in which a small amount of Mg is added to a mixed molten state of Na and Ga in the Na flux method. According to this method, a high-resistance GaN crystal can be obtained because Mg functions as a P-type dopant. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International release 2005 / 064661 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the configuration disclosed in Patent Document 1, Mg is weighed and added to the molten metal in the crucible. Since the amount of Mg to be added is very small, it is difficult to weigh it accurately, and there is a risk of adding an excess amount. If an excess amount of Mg is added, it can reduce the growth rate of GaN crystals, promote the generation of miscellaneous crystals, and reduce the uniformity of the in-plane distribution of Mg on the GaN crystal substrate, leading to a decrease in the crystal quality of the GaN crystal. This applies not only to GaN crystals but also to other group III nitride semiconductors. Therefore, there is room for improvement in obtaining high-resistance group III nitride semiconductors with excellent crystal quality.

[0006] This invention has been made in view of the above background, and aims to provide a method for producing a group III nitride semiconductor that can obtain a group III nitride semiconductor with excellent crystal quality and high resistance. [Means for solving the problem]

[0007] One aspect of the present invention is, In a method for producing a group III nitride semiconductor, a melt of a group III metal dissolved in a flux is held in a crucible, and a group III nitride semiconductor is grown by supplying a nitrogen-containing gas to the melt, The crucible is a method for producing a group III nitride semiconductor, in which alumina is the main component and a P-type dopant is also included. [Effects of the Invention]

[0008] In the method for producing a group III nitride semiconductor according to the above embodiment, a melt obtained by dissolving a group III metal in flux is held in a crucible mainly composed of alumina and containing a P-type dopant, causing an extremely small amount of P-type dopant to dissolve into the melt. This prevents the addition of an excess amount of P-type dopant to the melt, making it possible to obtain a group III nitride semiconductor with excellent crystallinity and high resistance.

[0009] As described above, according to the above embodiment, it is possible to provide a method for manufacturing a group III nitride semiconductor that can obtain a group III nitride semiconductor with excellent crystal quality and high resistance. [Brief explanation of the drawing]

[0010] [Figure 1] A conceptual diagram showing the configuration of the crystal growth apparatus in Embodiment 1. [Figure 2] (a) A photograph of a GaN crystal prepared in a crucible that does not contain Mg, and (b) a photograph of a GaN crystal prepared in a crucible that contains Mg. [Figure 3] A figure showing the results of confirmation test 1 in Embodiment 1. [Figure 4] A figure showing the results of the first measurement test in Embodiment 1. [Figure 5] A figure showing the results of the second measurement test in Embodiment 1. [Modes for carrying out the invention]

[0011] The P-type dopant preferably contains at least one of Mg and Zn. In this case, Mg and Zn act effectively as P-type dopants, thereby making the resistance of the group III nitride semiconductor sufficiently high.

[0012] The crucible preferably contains at least one of MgO and MgCO3, and the P-type dopant is Mg derived from at least one of the MgCO3 and MgO contained in the crucible. In this case, MgCO3 or MgO is easy to handle and readily available, and it is easy to disperse Mg, which will become the P-type dopant, in a crucible mainly composed of alumina, making it easy to gradually release Mg into the melt molten in the crucible. Therefore, a high-resistance group III nitride semiconductor with excellent crystal quality can be manufactured at low cost.

[0013] The concentration of MgO in the crucible is 2 mol% or more. In this case, a group III nitride semiconductor with sufficiently high resistance can be manufactured.

[0014] The concentration of the MgCO3 in the crucible is preferably 1 mol% or more. In this case, a group III nitride semiconductor with sufficiently high resistance can be produced.

[0015] The resistance value of the group III nitride semiconductor is 1.00×10 7 Ωcm or more, which is preferable. In this case, the group III nitride semiconductor is suitable for applications requiring high resistance such as power devices.

[0016] The concentration of the P-type dopant in the melt is preferably 0.1 mol% or more. In this case, a group III nitride semiconductor with sufficiently high resistance can be produced.

[0017] The concentration of the P-type dopant in the group III nitride semiconductor is 10 8 cm -3 % or more, which is preferable. In this case, a group III nitride semiconductor with sufficiently high resistance can be produced.

[0018] The concentration of Ca in the melt is preferably less than 0.01 mol%. Since the promotion of crystal growth is ensured by the P-type dopant, there is no need to add Ca for the purpose of promoting crystal growth, and the generation of miscellaneous crystals due to the addition of Ca is prevented, so that the crystal quality of the group III nitride semiconductor can be improved.

[0019] (Embodiment 1) First, the configuration of the crystal growth apparatus 1 used in the method for producing a group III nitride semiconductor according to Embodiment 1 will be described with reference to Figure 1.

[0020] 1. Configuration of the crystal growth apparatus 1 As shown in Figure 1, the crystal growth apparatus 1 has a pressure vessel 100, inside which are a reaction vessel 101 and a heater 102. A crucible 103 is placed inside the reaction vessel 101. A supply pipe 104 for supplying nitrogen gas to the reaction vessel 101 and an exhaust pipe 105 for exhausting the nitrogen gas are also provided. Furthermore, an insulating material 106 is provided inside the pressure vessel 100 so as to surround the reaction vessel 101 and the heater 102.

[0021] The pressure vessel 100 is made of stainless steel and has pressure resistance. The reaction vessel 101 is made of SUS and has heat resistance. The heater 102 heats the reaction vessel 101 by resistance heating, thereby adjusting the growth temperature. Valves are provided on the supply pipe 104 and exhaust pipe 105 connected to the reaction vessel 101, and by adjusting the amount of nitrogen gas supplied and exhausted using these valves, the pressure inside the reaction vessel 101 is adjusted, and the growth pressure is adjusted.

[0022] 2. Composition of Crucible 103 Crucible 103 is a container that holds a seed crystal (GaN self-supporting substrate), Na (flux), Ga (raw material), and other impurities. Crucible 103 is mainly composed of alumina and contains a P-type dopant. The P-type dopant increases the resistance of GaN and can be exemplified by Mg, Zn, Be, Sr, Fe, Mn, etc., with Mg or Zn being preferred. Because crucible 103 is mainly composed of alumina, it has high heat resistance and alkali resistance.

[0023] By including MgO and MgCO3 in crucible 103, the Mg derived from the MgO and MgCO3 can be used as a P-type dopant. While the concentration of MgO in crucible 103 is not limited, it is preferably 2 mol% or higher. Similarly, while the concentration of MgCO3 in crucible 103 is not limited, it is preferably 1 mol% or higher. In either case, Mg can be released into the melt as a P-type dopant necessary to impart high resistance.

[0024] The shape of the crucible 103 is not limited; in this embodiment, the crucible 103 is cylindrical. The size of the crucible 103 is not limited and can be set as appropriate. The crucible 103, installed in the reaction vessel 101, is rotatable by a device (not shown). It is preferable to provide a lid on the crucible 103. This can suppress the evaporation of Na during GaN crystal growth.

[0025] Furthermore, the method of forming the crucible 103 is not limited, but for example, the crucible 103 can be manufactured by casting using a plaster mold. Specifically, it is manufactured as follows: First, a slurry (suspension) is made by mixing alumina powder, water, and MgO or MgCO3 powder, which are the raw materials, and pouring this into a plaster mold made of plaster. A wet jet mill treatment or the like is used to make the slurry. Then, it is left for a predetermined time to allow the plaster mold to absorb the moisture and deposit a certain thickness of alumina powder on the surface of the plaster mold. Next, the liquid slurry remaining in the plaster mold is discarded, leaving only the layer of alumina powder and MgO or MgCO3 powder deposited on the surface of the plaster mold. The remaining layer of alumina powder and MgO or MgCO3 powder is dried for a predetermined time to solidify the deposited layer and obtain a molded body. Then, the molded body is removed from the plaster mold and sintered by firing it in air at 1570°C to produce crucible 103, which is a sintered alumina body containing MgO or MgCO3 powder.

[0026] Furthermore, the various conditions for the casting process may be as follows: When preparing the slurry, it is preferable to use alumina powder with an average particle size of 0.1 to 1 μm. This makes the alumina particles in the crucible more dense, improving its strength.

[0027] Furthermore, although water was used as the solvent for the slurry, any solvent conventionally used for slurries, such as alcohols, ketones, or amines, may be used. However, water is preferred from the standpoint of solvent absorption into the mold, environmental impact, and the absence of solvent residue in the crucible. Distilled water is also preferred from the viewpoint of suppressing the inclusion of impurities.

[0028] Furthermore, while plaster molds are used, any material can be used as long as it can absorb the solvent of the slurry and allow impurities to be mixed into the slurry. Alternatively, if a mold made of a material that does not release many impurities into the slurry is used, impurities can be added to the slurry to artificially induce abnormal grain growth. However, it is preferable to use plaster molds for slip casting because they are inexpensive and allow for easy mixing of impurities into the slurry.

[0029] Furthermore, it is desirable to fire the molded body at a temperature of 1500-1600°C. This is to make the alumina grains dense and prevent them from becoming too large.

[0030] Furthermore, the slurry contains sintering aids to promote sintering, and alumina powder is evenly dispersed in the solvent. Dispersants may be added to achieve this. If a dispersant is added, a heat treatment to remove the dispersant from the molded body may be performed at a temperature lower than the sintering temperature of the molded body before firing.

[0031] 3. Method for manufacturing Group III nitride semiconductors Next, a method for manufacturing a group III nitride semiconductor using the crystal growth apparatus 1 shown in Figure 1 will be described. The method for manufacturing a group III nitride semiconductor in this embodiment is a method of growing a group III nitride single crystal by the flux method. This produces a group III nitride semiconductor. The flux method is a method of supplying a gas containing nitrogen to a melt containing an alkali metal which will be used as a flux and a group III metal which will be used as a raw material, dissolving them, and epitaxially growing a group III nitride semiconductor in the liquid phase.

[0032] In this embodiment, the melt contains Na as an alkali metal flux. The Group III metal raw material is at least one of gallium (Ga), aluminum (Al), and indium (In), and the composition of the Group III nitride single crystal formed can be controlled by the ratio thereof, allowing for the formation of GaN, AlN, InN, AlGaN, InGaN, AlGaInN, etc. The present invention is particularly suitable for the formation of GaN, and this embodiment 1 produces a semiconductor made of a GaN single crystal. Furthermore, Na is used as the flux, and such a flux method is specifically called the Na flux method. The nitrogen-containing gas is a gas of nitrogen molecules or a compound containing nitrogen as a constituent element, such as ammonia, and may also be a mixture of these gases, or the nitrogen-containing gas may be mixed with an inert gas such as a noble gas.

[0033] In this embodiment of the method for manufacturing a Group III nitride semiconductor, first, a GaN freestanding substrate fabricated by the amonothermal method is placed in the crucible 103 as a seed crystal, and then predetermined amounts of Ga, Na, and C are added. C is added for purposes such as suppressing unwanted crystals and improving crystallinity, as well as to ensure that the growing GaN crystal efficiently incorporates the dopant. C acts catalytically and is hardly incorporated into the growing GaN crystal, resulting in a C concentration of 1 × 10⁻¹⁶ in the crystal. 16 / cm 3 The results are as follows:

[0034] Crucible 103 contains MgO or MgCO3. The process of setting the above materials into crucible 103 is carried out in a glove box filled with an inert gas such as Ar. This is to prevent the introduction of impurities due to oxidation of Na, etc.

[0035] Furthermore, the seed crystal is not limited to a GaN freestanding substrate; a template substrate may also be used. The template substrate is a substrate on which GaN has been grown using methods such as MOCVD, HVPE, or MBE, on a substrate different from a group III nitride semiconductor such as sapphire. When using a GaN freestanding substrate, it is advisable to make the thickness 500 μm or more to prevent the GaN freestanding substrate from melting back and disappearing in the early stages of growth. Alternatively, an AlGaN layer may be formed on the surface of the GaN freestanding substrate to prevent meltback.

[0036] Next, the crucible 103 is heated to 845°C by the heater 102, nitrogen gas is introduced into the reaction vessel 101 from the supply pipe 104, and the valves of the supply pipe 104 and exhaust pipe 105 are adjusted to set the pressure inside the reaction vessel 101 to 3 MPa. As a result, a molten mixture of the added Na, Ga, C, and Ge and Mg dissolved from the crucible 103 is formed inside the crucible 103. Then, nitrogen dissolves into the molten mixture, and when the nitrogen in the molten mixture becomes supersaturated, Mg-doped p-GaN crystal growth begins on the seed crystal. This state is maintained for a predetermined time to grow Mg-doped p-GaN on the seed crystal. During growth, the crucible 103 is rotated, and the direction of rotation is reversed at predetermined intervals. This stirs the molten mixture inside the crucible 103. This is to homogenize the molten mixture and improve the crystal quality of the p-GaN being grown. In addition to nitrogen, other gases containing N as a constituent element can be used to introduce into the reaction vessel 101; for example, ammonia may be used.

[0037] The temperature and pressure during cultivation are not limited to the values ​​mentioned above; the temperature should be between 600 and 1000°C, more preferably between 800 and 950°C, and even more preferably between 850 and 900°C. The pressure should be between 1 and 6 MPa, more preferably between 2 and 5 MPa, and even more preferably between 2.5 and 4 MPa.

[0038] Subsequently, heating by heater 102 is stopped, and the supply of nitrogen gas from supply pipe 104 is stopped to return to room temperature and atmospheric pressure. Then, the p-GaN crystals grown on the GaN freestanding substrate are removed from crucible 103, and the Na adhering to the p-GaN crystals is removed using ethanol. This completes the fabrication of the GaN semiconductor.

[0039] Figure 2(a) shows a crystal photograph of a Group III nitride semiconductor produced by a conventional method using crucible 103 that does not contain MgO and MgCO3, as a comparative example, and Figure 2(b) shows a crystal photograph of a Group III nitride semiconductor produced by the method of producing a Group III nitride semiconductor using crucible 103 containing 5 mol% MgO in this embodiment 1, as a test example.

[0040] 4. Amount of P-type dopant incorporation into Group III nitride semiconductors Next, a confirmation test was conducted on the amount of P-type dopant incorporated into the group III nitride semiconductor fabricated by the method for manufacturing group III nitride semiconductors of this embodiment 1. The test conditions were prepared for a GaN semiconductor fabricated by the method for manufacturing group III nitride semiconductors using a crucible containing MgO. Using a SIMS (secondary ion mass spectrometer) (CAMECA, model IMS6F), the MgO concentration in the crucible was changed, and the amount of Mg incorporated into the GaN crystal for each MgO concentration was measured as the Mg incorporation amount.

[0041] As shown in Figure 3, which illustrates the relationship between MgO concentration in the crucible and Mg uptake, a positive correlation was observed between the MgO concentration in the crucible and the amount of Mg uptake. Furthermore, when the MgO concentration in the crucible was approximately 5 mol%, the amount of Mg uptake was 1 × 10⁻⁶. 19 cm -3 This has been confirmed to be the case.

[0042] 5. Measurement of the resistivity of Group III nitride semiconductors Next, the resistivity of the group III nitride semiconductor produced by the method for manufacturing group III nitride semiconductors in this embodiment 1 was measured using a first measurement and a second measurement.

[0043] First, in the first measurement test, two test examples were prepared of a group III nitride semiconductor manufactured by the method for manufacturing a group III nitride semiconductor using crucible 103 containing 5 mol% MgCO3 as described in Embodiment 1 above. Test example 1 was 6 mm square and 1.084 mm thick, and test example 2 was 20 mm × 15 mm and 1.074 mm thick. In addition, two comparative examples were prepared of a group III nitride semiconductor manufactured by the method for manufacturing a group III nitride semiconductor as described above using a crucible that does not contain a dopant. Comparative example 1 was 10 mm square and 0.405 mm thick, and comparative example 2 was 10 mm square and 0.415 mm thick (including the substrate). In comparative examples 1 and 2, Ca was contained in the melt at a predetermined concentration.

[0044] In the first measurement test, the resistivity of Test Examples 1 and 2 and Comparative Examples 1 and 2 was measured using a four-probe testing device (manufactured by Nitto Seikou Analytech Co., Ltd., model number MCP-T600) based on the four-probe testing method. For Comparative Examples 1 and 2, the resistivity was measured using a Hall effect measuring device (manufactured by Toyo Technica Co., Ltd., model number ResiTest8403) based on the Van der Pauw method.

[0045] The resistivity measurement results from the first measurement test are shown in Figure 4. As shown in Figure 4, comparative examples 1 and 2 had resistivity values ​​ranging from approximately 10⁻³ Ω·cm to 10⁻² Ω·cm, while test examples 1 and 2 showed very high resistivity values ​​of 10⁷ Ω·cm or higher.

[0046] Next, in the second measurement test, the resistivity of Comparative Examples 3-6 and Test Example 1, each having the composition shown in Figure 5, was measured. As shown in Figure 5, the second measurement test revealed that Test Example 1 exhibited a significantly higher resistivity compared to Comparative Examples 3-6.

[0047] 6. Effects In the method for producing a group III nitride semiconductor of this embodiment 1, by holding a melt in which a group III metal is dissolved in flux in a crucible 103 mainly composed of alumina and containing a P-type dopant, an extremely small amount of P-type dopant dissolves into the melt. This prevents the addition of an excess amount of P-type dopant to the melt, making it possible to obtain a group III nitride semiconductor with excellent crystallinity and high resistance.

[0048] Furthermore, in this embodiment 1, the P-type dopant includes at least one of Mg and Zn. Since Mg and Zn act effectively as P-type dopants, the resistance of the group III nitride semiconductor can be made sufficiently high.

[0049] Furthermore, in this embodiment 1, the crucible 103 contains at least one of MgO and MgCO3, and the P-type dopant is Mg derived from at least one of the MgO and MgCO3 contained in the crucible 103. MgO and MgCO3 are easy to handle and readily available, and it is easy to disperse Mg, which becomes a P-type dopant, in the crucible 103, which is mainly composed of alumina, so it is easy to gradually release Mg into the melt molten in the crucible 103. As a result, a high-resistance group III nitride semiconductor with excellent crystal quality can be manufactured at low cost.

[0050] Furthermore, in this embodiment 1, the concentration of MgO in crucible 103 is 2 mol% or more. This makes it possible to manufacture a group III nitride semiconductor with sufficiently high resistance.

[0051] Alternatively, instead of the case in this embodiment 1, the concentration of MgCO3 in crucible 103 can be set to 1 mol% or more. In this case as well, a group III nitride semiconductor with sufficiently high resistance can be manufactured.

[0052] Furthermore, in this embodiment 1, the resistance value of the group III nitride semiconductor is 1.00 × 10⁻⁶. 7 The resistance is greater than Ωcm. This makes it a group III nitride semiconductor suitable for applications requiring high resistance, such as power devices.

[0053] Further, in the first embodiment, the concentration of the P-type dopant in the melt is 0.1 mol% or more. Thereby, a group III nitride semiconductor with sufficiently high resistance can be produced.

[0054] Further, in the first embodiment, the concentration of the P-type dopant in the group III nitride semiconductor is 10 8 cm -3 or more. Thereby, a group III nitride semiconductor with sufficiently high resistance can be produced.

[0055] Further, in the first embodiment, the concentration of Ca in the melt is less than 0.01 mol%. Since the promotion of crystal growth is ensured by the P-type dopant, it is not necessary to add Ca for promoting crystal growth, and the generation of miscellaneous crystals due to the addition of Ca is prevented, so that the crystal quality of the group III nitride semiconductor can be improved.

[0056] As described above, according to the above aspect, it is possible to provide a method for producing a group III nitride semiconductor, by which a high-resistance group III nitride semiconductor with excellent crystal quality can be obtained.

[0057] The present invention is not limited to the above respective embodiments and modified examples, and can be applied to various embodiments without departing from the gist thereof.

Description of Reference Signs

[0058] 1: Crystal growth apparatus 100: Pressure vessel 101: Reaction vessel 102: Heater 103: Crucible 104: Supply pipe 105: Exhaust pipe

Claims

1. In a method for producing a group III nitride semiconductor, a melt obtained by dissolving a group III metal in a flux is held in a crucible, and a group III nitride semiconductor is grown by supplying a gas containing nitrogen to the melt, The crucible is a crucible mainly composed of alumina and containing a P-type dopant, and the method for producing a group III nitride semiconductor.

2. The method for producing a group III nitride semiconductor according to claim 1, wherein the P-type dopant comprises at least one of Mg and Zn.

3. The crucible contains MgO and MgCO ３ It includes at least one of the following: The P-type dopant is the MgO and MgCO contained in the crucible. ３ A method for producing a group III nitride semiconductor according to claim 1, wherein the Mg is derived from at least one of the following.

4. The method for producing a group III nitride semiconductor according to claim 3, wherein the concentration of MgO in the crucible is 2 mol% or more.

5. The MgCO in the crucible ３ The method for producing a group III nitride semiconductor according to claim 3, wherein the concentration of is 1 mol% or more.

6. The resistance of the aforementioned Group III nitride semiconductor is 1.00 × 10⁻⁶ ７ A method for producing a group III nitride semiconductor according to any one of claims 1 to 5, wherein the density is Ωcm or greater.

7. The method for producing a group III nitride semiconductor according to any one of claims 1 to 5, wherein the concentration of the P-type dopant in the melt is 0.1 mol% or more.

8. The concentration of the P-type dopant in the group III nitride semiconductor is 10 ８ cm －３ The method for producing a group III nitride semiconductor according to any one of claims 1 to 5.

9. A method for producing a group III nitride semiconductor according to any one of claims 1 to 5, wherein the concentration of Ca in the melt is less than 0.01 mol%.

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