Method for manufacturing a GaN substrate

Abstract

To grow crystals of GaN with high crystal quality from a non-semiconductor surface of a base substrate by HVPE method.SOLUTION: A method for producing a GaN substrate includes nitriding a non-semiconductor surface of a base substrate at a temperature higher than 1000°C by using N2 gas and NH3 gas and then growing crystals of GaN from the non-semiconductor surface of the base substrate with the N2 gas as a carrier gas by the HVPE method.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a GaN substrate.

Background Art

[0002] Although the demand for GaN substrates is extremely high, the market size is small. One of the reasons is that the manufacturing cost is high.

[0003] When growing GaN crystals from the surface of a sapphire substrate, from the perspective of reducing the manufacturing cost, it is advantageous to use the HVPE (Hydride Vapor Phase Epitaxy) method with a high crystal growth rate. However, the HVPE method has a problem that it is difficult to obtain GaN with high crystal quality. For example, Non-Patent Document 1 discloses that for XRC-FWHM, which is an index of the crystallinity of GaN, GaN grown on a sapphire substrate by the MOVPE (Metal Organic Chemical Vapor Deposition) method is 200 arcsec, while GaN grown on a sapphire substrate by the HVPE method is 600 arcsec, and the latter is three times the former. Therefore, when manufacturing a GaN substrate, first, GaN is grown on a sapphire substrate by the MOVPE method, and then, GaN is grown on the GaN on the sapphire substrate by the HVPE method, which is a complicated method. And this is the cause of the high manufacturing cost of GaN substrates.

[0004] Therefore, technical studies have been conducted on directly growing GaN crystals on a sapphire substrate. For example, Patent Document 1 discloses coating the surface of a sapphire substrate with a thin film of silicon nitride having a large number of openings formed therein, and growing GaN crystals from the surface of the sapphire substrate exposed from the large number of openings of the thin film at a crystal growth temperature of 400°C or higher and 700°C or lower by the HVPE method to form an LT-GaN layer, and then growing GaN crystals on the LT-GaN layer at a crystal growth temperature of 900°C or higher and 1150°C or lower to form an HT-GaN layer, thereby disclosing a method for manufacturing a GaN substrate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The problem of the present invention is to grow GaN with high crystal quality from the surface of a non-semiconductor of a base substrate by the HVPE method.

Means for Solving the Problems

[0008] The present invention provides a sapphire substrate without a mask for coating the surface, and the surface of the sapphire substrate is Temperature between 1090 °C and 1500 °C nitrided using N2 gas and NH3 gas at a temperature, and then GaN is grown from the surface of the sapphire substrate using N2 gas as a carrier gas by the HVPE method, which is a method for manufacturing a GaN substrate.

Effects of the Invention

[0009] According to the present invention, after nitriding the surface of the non-semiconductor of the base substrate at a temperature exceeding 1000 °C using N2 gas and NH3 gas, GaN is crystal-grown from the surface of the non-semiconductor of the base substrate using N2 gas as a carrier gas by the HVPE method, whereby GaN with high crystal quality can be crystal-grown.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described in detail.

[0012] The method for manufacturing a GaN substrate according to the embodiment is to nitride the surface of the non-semiconductor of the base substrate at a temperature exceeding 1000 °C using N2 gas and NH3 gas, and then crystal-grow GaN from the surface of the non-semiconductor of the base substrate using N2 gas as a carrier gas by the HVPE method.

[0013] According to the method for manufacturing a GaN substrate according to the embodiment, after nitriding the surface of the non-semiconductor of the base substrate at a temperature exceeding 1000 °C using N2 gas and NH3 gas, GaN is crystal-grown from the surface of the non-semiconductor of the base substrate using N2 gas as a carrier gas by the HVPE method, whereby GaN with high crystal quality can be crystal-grown from the surface of the non-semiconductor of the base substrate. Further, since GaN is directly crystal-grown from the surface of the non-semiconductor of the base substrate by the HVPE method, a GaN substrate can be manufactured at low cost.

[0014] Specifically, in the method for manufacturing a GaN substrate according to the embodiment, first, a base substrate with a non-semiconductor surface is prepared. Typical examples of such a base substrate include sapphire substrates. The surface of the base substrate may be a flat surface or a surface subjected to uneven processing such as grooving. The base substrate may have a mask provided on its surface such that a partially non-semiconductor surface is exposed. The surface of the base substrate is preferably a c-plane.

[0015] Subsequently, the base substrate is placed in the chamber of the HVPE apparatus, and while flowing N2 gas and NH3 gas into the chamber, the base substrate is heated, and the non-semiconductor surface of the base substrate is nitrided using N2 gas and NH3 gas at a temperature exceeding 1000°C. The treatment temperature of this nitriding treatment exceeds 1000°C, but from the perspective of crystal-growing high-quality GaN from the non-semiconductor surface of the base substrate, it is preferably 1050°C or higher and 1500°C or lower, more preferably 1090°C or higher and 1200°C or lower. From the same perspective, the flow rate of N2 gas is preferably 1 slm or more and 30 slm or less. The flow rate of NH3 gas is preferably 1 slm or more and 20 slm or less, more preferably 2 slm or more and 15 slm or less, from the same perspective.

[0016] Then, after the nitriding treatment, N2 gas is flowed as a carrier gas into the chamber at the GaN crystal growth temperature, and a Ga source gas and an N source gas are flowed. At this time, the Ga source gas and the N source gas react, and GaN crystal-grows from the non-semiconductor surface of the base substrate by the HVPE method to form a GaN layer. The GaN crystal growth temperature is preferably 1050°C or higher and 1500°C or lower, more preferably 1090°C or higher and 1200°C or lower, from the perspective of crystal-growing high-quality GaN from the non-semiconductor surface of the base substrate. From the same perspective, the GaN crystal growth temperature is preferably the same as the treatment temperature of the previous nitriding treatment. From the same perspective, it is preferable to use only N2 gas as the carrier gas, but it may also be used by containing H2 gas with N2 gas as the main component. From the same perspective, the flow rate of N2 gas is preferably 1 slm or more and 30 slm or less.

[0017] The Ga source gas is GaCl produced by the reaction of HCl gas coming into contact with molten Ga. The N source gas is, for example, NH3 gas. The flow rate of the HCl gas for generating the Ga source gas is, for example, 0.01 slm or more and 2 slm or less. Note that the flow rate of the HCl gas will match the flow rate of the Ga source gas. The flow rate of the N source gas is, for example, 0.1 slm or more and 20 slm or less. The V / III ratio, which is the ratio of the N supply mole to the Ga supply mole, is preferably 1 or more and 50 or less, more preferably 3 or more and 20 or less, from the viewpoint of crystal-growing high-quality GaN from the non-semiconductor surface of the base substrate. The thickness of the GaN layer is preferably 1 μm or more, more preferably 10 μm or more, from the same viewpoint. The growth rate is preferably 10 μm / h or more, more preferably 50 μm / h or more, from the same viewpoint.

[0018] From the viewpoint of crystal-growing high-quality GaN from the non-semiconductor surface of the base substrate, it is preferable that the GaN layer is formed by first crystal-growing N-polarity GaN on the base substrate and then subsequently crystal-growing Ga-polarity GaN thereon. In this case, the film thickness of the N-polarity GaN is preferably 500 μm or less, more preferably 100 μm, from the same viewpoint.

[0019] Finally, the flow of the HCl gas and / or the N source gas is stopped to terminate the crystal growth of GaN, and after stopping the heating of the base substrate and cooling it, the base substrate with the GaN layer formed thereon is taken out from the chamber, and a GaN substrate is obtained by separating the GaN layer from the base substrate. Note that the GaN substrate may be subjected to treatments such as surface polishing as necessary.

[0020] The GaN substrate manufactured as described above has high crystal quality. Its surface state is preferably mirror-like. The dislocation density on the surface is preferably 1×10 8 cm -2 or less, more preferably 1×10 7 cm -2 or less. Here, the dislocation density is the dark spot density measured by the cathodoluminescence (CL) method.

[0021] In addition, this GaN substrate can be suitably used for the production of LEDs, LDs, solar cells, electronic devices, and the like.

Examples

[0022] As in the following Examples 1 and 2 and Comparative Examples 1 and 2, experiments were conducted to grow GaN crystals on a sapphire substrate by the HVPE method.

[0023] (Crystal growth of GaN) <Example 1> A sapphire substrate was prepared as the base substrate. As the sapphire substrate, one having a flat surface with a c-plane and no mask partially covering the surface was used. This sapphire substrate was placed in the chamber of the HVPE apparatus, and GaN was grown on it by the HVPE method.

[0024] Specifically, as shown in FIG. 1, (i) First, the sapphire substrate was heated and the temperature was raised. When the temperature reached 300°C, N2 gas began to flow, and when the temperature reached 500°C, NH3 gas began to flow. At this time, the flow rate of N2 gas was set to 17 slm. The flow rate of NH3 gas was set to 8.0 slm.

[0025] After the temperature of the sapphire substrate reached the crystal growth temperature of 1040°C, the non-semiconductor surface of the sapphire substrate was nitrided at a temperature of 1040°C using N2 gas and NH3 gas by maintaining that state for a predetermined time.

[0026] (ii) After the nitriding treatment, HCl gas began to flow, and GaN was grown on the sapphire substrate for 30 minutes by the HVPE method using N2 gas as the carrier gas. At this time, the flow rate of HCl gas was set to 0.8 slm, the flow rate of NH3 gas was kept at 8.0 slm, and the V / III ratio was set to 10.

[0027] (iii) Starting from the beginning of the HCl gas flow, after 30 minutes, the flow of HCl gas was stopped to terminate the GaN crystal growth, and the heating of the sapphire substrate was stopped and cooled to room temperature. During the cooling process of the sapphire substrate, when it reached 300 °C, the flow of NH3 gas was stopped.

[0028] The sapphire substrate on which GaN was crystal-grown on the substrate was taken out from the chamber of the HVPE apparatus.

[0029] Figure 2 shows the cathode luminescence image of GaN formed on the sapphire substrate obtained in this Example 1. According to this, it can be seen that after the N-polarity GaN of the white part was initially crystal-grown on the sapphire substrate, subsequently, the Ga-polarity GaN of the black part was crystal-grown and formed. The film thickness of the N-polarity GaN was about 40 μm.

[0030] <Example 2> GaN was crystal-grown on the sapphire substrate by performing the same operations as in Example 1 except that the crystal growth temperature was set to 1100 °C.

[0031] <Comparative Example 1> GaN was crystal-grown on the sapphire substrate by performing the same operations as in Example 1 except that the crystal growth temperature was set to 1000 °C.

[0032] <Comparative Example 2> GaN was crystal-grown on the sapphire substrate by performing the same operations as in Example 1 except that H2 was used as the carrier gas.

[0033] (Test method) <Surface state> Regarding the GaN obtained in each of Example 1 and 2 and Comparative Example 1 and 2, the surface state was visually confirmed.

[0034] <Dislocation density> For the GaN obtained in each of Examples 1 and 2, the dislocation density on its surface was determined as the dark spot density measured by the cathodoluminescence (CL) method. Note that for the GaN obtained in Comparative Examples 1 and 2, since the surface shape was poor and the crystal quality was also poor, the measurement of the dislocation density on the surface could not be performed.

[0035] <Growth rate> For the GaN obtained in each of Examples 1 and 2 and Comparative Example 2, its thickness was measured, and based on this, the growth rate was calculated. For the GaN obtained in Comparative Example 1, the measurement of the thickness of GaN could not be performed.

[0036] (Test results) Table 1 shows the test results. According to this Table 1, it can be seen that in Examples 1 and 2, GaN with higher crystal quality was obtained compared to Comparative Examples 1 and 2.

[0037]

Table 1

Industrial applicability

[0038] The present invention is useful in the technical field of a method for manufacturing a GaN substrate.

Claims

1. Prepare a sapphire substrate without a mask covering its surface, The surface of the sapphire substrate is nitrided using N gas and NH gas at a temperature of 1090 °C or higher and 1500 °C or lower, and then GaN is crystal-grown from the surface of the sapphire substrate using N gas as a carrier gas by the HVPE method. A method for manufacturing a GaN substrate. ２ gas and NH ３ After nitriding using gas, by the HVPE method, using N gas as a carrier gas, ２ A method for manufacturing a GaN substrate in which GaN is crystal-grown from the surface of the sapphire substrate.

2. In the method for manufacturing a GaN substrate according to Claim 1, N in the nitriding treatment ２ A method for manufacturing a GaN substrate in which the flow rate of N gas is 1 slm or more and 30 slm or less.

3. In the method for manufacturing a GaN substrate according to Claim 1 or 2, The NH in the nitridation treatment ３ A method for manufacturing a GaN substrate in which the flow rate of the gas is 1 slm or more and 20 slm or less.

4. In the method for manufacturing a GaN substrate according to any one of Claims 1 to 3, A method for manufacturing a GaN substrate using only N ２ gas as the carrier gas.

5. In the method for manufacturing a GaN substrate according to any one of Claims 1 to 4, A method for manufacturing a GaN substrate, wherein the surface of the sapphire substrate is a flat c-plane.

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