WO2008117571A1

WO2008117571A1 - Process for producing nitride single crystal

Info

Publication number: WO2008117571A1
Application number: PCT/JP2008/051894
Authority: WO
Inventors: Yusuke Mori; Mikiya Ichimura; Katsuhiro Imai; Takayuki Hirao; Takatomo Sasaki; Fumio Kawamura
Original assignee: Ngk Insulators, Ltd.
Priority date: 2007-03-26
Filing date: 2008-01-30
Publication date: 2008-10-02
Also published as: JPWO2008117571A1

Abstract

A seed crystal substrate is immersed in a melt containing a flux and a single crystal raw material in a growth vessel, and a nitride single crystal is grown on the growth surface of the seed crystal substrate. The process comprises the preparatory step for dissolving nitrogen in the above melt at temperature T1 (K) under pressure P1 (MPa) and the principal growing step for growing a nitride single crystal on the growth surface of the seed crystal substrate at temperature T2 (K) under pressure P2 (MPa). These P1, P2, T1 and T2 satisfy the formulae: T2-10 ≤ T1 ≤ T2+60 (1) P2-0.5 ≤ P1 ≤ P2+5.0 (2), and P1 ≥ 1.1 x P2 x (T1/T2)0.5exp[(E/k)•[(1/T1)-(1/T2)]] (3).

Description

Specification

TECHNICAL FIELD The present invention relates to a method for producing a nitride single crystal. Background art

Gallium nitride III-V nitride is attracting attention as an excellent blue light emitting device, and has been put to practical use as a material for light emitting diodes and semiconductor laser diodes. : A method for growing a group III nitride single crystal using 7 Lux has been reported by each organization (Japanese Patent Laid-Open No. 2000-29, 6 9-6, Japanese Patent Laid-Open No. 2000-29) No. 24 00, WO 2 0 0 5—0 9 5 6 8 2 Al, WO 2 0 0 6—0 3 0 7 1 8). In Japanese Patent Laid-Open No. 2000-29 24 0 0, the temperature and pressure are classified into four regions A to D according to the growth mode of the GaN single crystal, and a plurality of regions among the four regions are used to make III A method for growing a group nitride crystal is claimed [claim 9]. By growing using a plurality of regions, it is possible to grow a crystal having a plurality of forms [0068].

In addition, a method for controlling the nucleation site by using a GaN thin film or an A1N thin film deposited on a substrate as a seed crystal has been reported (Japanese Patent Laid-Open No. 2000-0-3 2 7 4 9 5)

In the method described in Japanese Patent Laid-Open No. 2 00 0-3-2 7 4 9 5, the ratio of Na + Na + Ga) is 0.4, the temperature holding time is 24 hours, the nitrogen pressure is 100 atm, and the growth temperature is 800 ° C, 700C, 600 ° C, 500 As a result of growth at ° C, GaN crystal growth occurred on the A1N thin film at 600 ° C or higher. It is described. However, this temperature and pressure range is a region D where the plate-like GaN crystal grows predominantly as described in Japanese Patent Laid-Open No. 2000-29-2400, and the seed crystal It is not region B where GaN crystals grow predominantly only on the top. For this reason, it has been confirmed that many miscellaneous crystals are generated in addition to seed crystals.

In view of this, the present inventor has kept the growth temperature and pressure in the region B in Japanese Patent Laid-Open No. 2 0 0 3-2 924 00, and Japanese Patent Laid-Open No. 2 0 3-2 9 2 4 0 0 As claimed in the gazette, the generation of miscellaneous crystals was suppressed, and it was confirmed that GaN crystals grew only on the seed crystals. However, the start of GaN crystal growth was confirmed more than 50 hours after holding the temperature and pressure in region B, and no clear growth was confirmed only by holding for 24 hours. As described above, the growth of GaN crystals that do not generate miscellaneous crystals requires a long period of time, so the productivity is low.

Japanese Patent Laid-Open No. 2 00 3-2 924 0 0 describes that crystal growth having a plurality of forms is possible by using a plurality of regions among the four regions A to D. However, there is no description of what form of crystal can be obtained by using multiple regions. Moreover, there is no description about the growth rate in addition to the crystal form.

An object of the present invention is to suppress the generation of miscellaneous crystals and improve the productivity per unit time of a nitride single crystal when growing a nitride single crystal on a seed crystal substrate.

The present invention is a method of immersing a seed crystal substrate in a melt containing a flux and a single crystal raw material in a growth vessel, and growing a nitride single crystal on the growth surface of the seed crystal substrate,

A nitrogen dissolution process for dissolving nitrogen in the melt at temperature T l (K) and pressure PI (MP a), and Full growth process of growing a nitride single crystal on the growth surface of the seed crystal substrate at temperature T 2 (Κ) and pressure Ρ 2 (MP a)

And P 1, P 2, T 1 and Τ 2 satisfy the following relational expressions (1), (2) and (3).

Τ 2— 1 0 ≤ Τ 1 ≤ Τ 2 + 6 0 (1)

Ρ 2-0. 5 ≤ Ρ 1 ≤ Ρ 2 + 5. 0 (2)

Ρ 1 ≥ 1. 1 X Ρ 2 X (Τ 1 / Ύ 2) ⁰ ' ⁵ exp [(Ε / k) · [(1 / Τ 1) one (1 / T 2)]] (3)

(E is 2.8 e V,

k is Boltzmann constant (1. 3 8 X 1 0— "J / K)

The present inventor has conceived of performing the main growth process after the initial process for dissolving nitrogen. In the nitrogen dissolving step, the melting is performed at a higher temperature, a higher pressure, or a higher temperature and pressure than in the main growing step, and the dissolution of nitrogen into the melt is advanced. At this stage, the growth of GaN crystals should not start when the nitrogen concentration is saturated (see Figure 5). In this growth process, the growth of single crystals is carried out at a temperature and pressure at which no miscellaneous crystals are generated. As a result, the production of single crystals per unit time required for growth was significantly improved while suppressing the generation of miscellaneous crystals.

In the conventional technology, as shown in Fig. 4, it takes time to saturate the nitrogen gas in the melt, and until then, precipitation of nitrides does not start, so the effective growth time is short and productivity is low. It was low.

Here, the horizontal axis of FIG. 1 is 100 K / T, and T is the absolute temperature of the melt (unit is K). The vertical axis is P / MPa, and P is the pressure of nitrogen applied to the melt (unit: MPa).

In FIG. 1, O indicates the temperature T 2 and the pressure P 2 in the main growth process. (T 2—1 0), (T 2 +6 0). (P 2— 0. 5), (P 2 + 5. 0) is shown. Furthermore, the straight line V in Fig. 1 shows the condition of Eq. (3). Equation (3) corresponds to the condition of R≥l.1, where R is (Nitrogen dissolution rate in the melt in the nitrogen dissolution process) / (Nitrogen in the melt in this growth step) Dissolution rate). Specifically, R is expressed by the following formula. Also, the nitrogen dissolution rate X increases as the pressure and temperature increase.

However,

E: Activation energy of dissociation and dissolution of nitrogen-: Pollmmann constant

Nitrogen dissolution rate X increases at high temperature and pressure <

(T 1−T 2) must be at least 10 ° C and (PI—P 2) must be at least 0.5 MPa, and by satisfying equation (3), It is necessary to make the nitrogen dissolution rate larger than the nitrogen dissolution rate in this growth process. As a result, the amount of nitrogen dissolved in the melting step can be increased and the productivity of single crystals can be improved. At the same time, it is necessary to set (T 1−T 2) to 60 ° C or less and (P 1−P 2) to 5. OMPa or less. If (T 1 – T 2) exceeds 60 ° C, a mechanism to prevent evaporation and diffusion of flux materials such as Na is required, which complicates equipment and processes. If (1? 2) exceeds 5.0 MPa, a container with high pressure resistance is required, which is a cost-up factor.

From the above viewpoint, it is more preferable that P1, P2, T1, and T2 satisfy the following relational expressions (4) and / or (5).

Τ 2 ≤ Τ 1 ≤ Τ 2 + 4 0 (4)

Ρ 2 ≤ Ρ 1 ≤ Ρ 2 + 3.0 (5) Brief description of the drawings

Figure 1 1,? 2 is a graph schematically illustrating the relationship between Ding 1 and Ding 2. Figure 2 1,? 2 is a graph schematically illustrating the relationship between Ding 1 and Ding 2. Figure 3 1,? 2 is a graph schematically illustrating the relationship between Ding 1 and Ding 2. Fig. 4 is a diagram schematically showing the relationship between the growth time and the nitrogen dissolution amount of GaN growth in the prior art.

FIG. 5 is a diagram schematically showing the relationship between the growth time and the amount of growth of nitrogen dissolving gan in the present invention.

FIG. 6 is a schematic block diagram of a single crystal growth apparatus that can be used in the present invention.

FIG. 7 is a schematic diagram showing single crystal growth in a growth vessel.

Fig. 8 is a photograph of the growth container taken out from the atmosphere control container observed from above.

Fig. 9 is a photograph showing the GaN single crystal taken out from the growth vessel.

Figure 10 is a photograph showing the surface of a GaN single crystal observed with a microscope. The

Figure 11 is a graph showing the relationship between the total growth time and the G a N weight. FIG. 12 is a graph showing the relationship between the temperature and pressure in Examples and Comparative Examples and the regions A to D in Patent Document 2. BEST MODE FOR CARRYING OUT THE INVENTION

The holding time in the nitrogen dissolving step is preferably 5 hours or more and 60 hours or less. If the holding time is too short, the amount of nitrogen dissolved in the melt is small, and it becomes difficult to improve the productivity of the single crystal. On the other hand, there is no particular upper limit. However, since there is a tendency for single crystal growth to start in about 60 hours from the start of the growth process even without the nitrogen dissolution process, if the holding time in the nitrogen dissolution process exceeds 60 hours, the production according to the present invention The benefits of improved performance are reduced.

The growth temperature and pressure in this growth process should be determined according to the type of nitride single crystal to be grown. Should be selected.

In a preferred embodiment, the temperature T 2 and the pressure P 2 in the main growing process satisfy the following relational expressions (6) and (7).

l o g P 2≥ (-5. 4 0 Χ10 / T 2 + 4. 8 3

(6) log P 2≤ (-5.5 9 X10 ³ ) / T 2 + 5. 4 7

(7)

This temperature and pressure range is illustrated in Figs. L 1 is equivalent to Eq. (6) and L 2 is Eq. (7). Region B is between (6) and (7). Yes, this growth process is carried out at the temperature and pressure in area B. The example in Fig. 2 shows an example of P 2 = 3.9 MPa, T 2 = 1 1 6 3 K (8 90 ° C), and in the example in Fig. 3, P 2 = 2.5 MPa, T An example of 2 = 1 1 7 3 K (9 0 0 ° C) is shown. Regions A, B, and C are the same as in Patent Document 2.

In this embodiment, the temperature T 1 and the pressure P 1 of the nitrogen dissolving step may exist in the region C or may exist in the region B. But especially preferred is 1 chopstick 1 also satisfies the following equations (8) and (9). That is, it exists in area B.

log P 1≥ (— 5. 4 0 X10 ³ ) / T 1 + 4. 8 3

(8)

log P 1≤ (one 5. 5 9 X 10 ³ ) / T 1 + 5. 4 7

In a preferred embodiment, as schematically shown in FIG. 6, a plurality of heating elements 6 Α, 6 Β, and 6 C are installed in the vertical direction, and the heating value is controlled independently for each heating element. In other words, multi-zone control is performed in the vertical direction. When each heating element is heated, a nitrogen-containing atmosphere flows through the gas tank 1, the pressure control device 2, and the piping 3 to the growth vessel 7 in the atmosphere control vessel 4, and when heated and pressurized, the inside of the growth vessel 7 All the mixed raw materials are melted to produce a melt.

The material of the heating element is not particularly limited, but alloy heating elements such as iron-chromium-aluminum and nickel-chromium, refractory metal heating elements such as platinum, molybdenum, tantalum and tandastain, silicon carbide, molybdenum silicate Non-metallic heating elements such as carbon can be exemplified.

In the single crystal growth apparatus of the present invention, an apparatus for heating the raw material mixture to generate a melt is not particularly limited. This device is a hot isostatic press However, other atmospheric pressure heating furnaces may be used.

The flux for producing the melt is not particularly limited, but one or more metals selected from the group consisting of Al-rich metal and Al-rich earth metal or alloys thereof are preferable. Examples of the metal include lithium, sodium, potassium, norevidium, cesium, beryllium, magnesium, calcium, strontium, and palium, and lithium, sodium, and calcium are particularly preferable. Sodium is most preferred.

The material of the growth vessel for carrying out the reaction is not particularly limited as long as it is a material that is durable under the intended heating and pressurizing conditions. These materials include high melting point metals such as metal tantalum, tungsten, and molybdenum, oxides such as alumina, sapphire, and yttrium, nitride ceramics such as aluminum nitride, titanium nitride, zirconium nitride, and boron nitride, Examples include carbides of refractory metals such as tungsten carbide and tantanore carbide, and pyrolysis products such as p-BN (pyrolytic BN) and p-Gr (pyrolytic graphite).

By using the present invention, a single crystal of gallium nitride can be grown using a flux containing at least sodium metal. This flux dissolves the gallium source material. As the raw material of gallium, gallium simple metal, gallium alloy and gallium compound can be applied, but gallium simple metal is also preferable in terms of handling.

This flux can contain metals other than sodium, such as lithium. The usage ratio of the raw material of the gallium and the flux raw material such as sodium may be appropriate, but in general, the use of an excess amount of sodium is considered. Of course, this is not limiting.

Gas other than nitrogen in the atmosphere is not limited, but inert gas is preferable, Argon, helium and neon are particularly preferred.

The material of the growth substrate for epitaxial growth of gallium nitride crystal is not limited, but sapphire, A 1 N template, GaN template, silicon single crystal, SiC single crystal, MgO single Perovsky such as crystals, spinel (Mg A l ₂ 0 ₄ ), L i A 1 0 ₂ , L i G a 0 ₂ , L a A 1 O ₃ , L a G a O 3, N d G a 0 ₃ Can be exemplified. In addition, the composition formula [A 丄 ichi, (S r! _ _X B a _x ), J

_{! C (! A 1 _ z} G a z) _ u - D u) O 3 (A is a rare earth element; D is one or more elements Der selected from the group consisting of niobium Contact Yopi tantalum Y = 0. 3 to 0.98; x = 0 to l; z = 0 to l; u = 0. 1 5 to 0.49; X + z = 0.1 to 2) Perovskite structure complex oxides can also be used. Further, SCAM (ScAlMg0 ₄₎ can also be used. Example

(Example 1)

GaN single crystals were grown according to the method described with reference to Figs. 1, 2, and 5.

Specifically, 3 g of metal gallium (Ga) as a Group III material, 4 g of metal sodium (Na) as a flux, and a seed crystal 9 were weighed in a growth vessel 7 as shown in FIG. The seed crystal 9 was a gallium nitride single crystal thin film epitaxially grown on sapphire. This growth vessel 7 was placed and sealed in an atmosphere control vessel 4 having a gas inlet. A series of operations were performed in an inert gas atmosphere to prevent oxidation of raw materials and flux. 5 is a melt. After the sealed container was placed in an electric furnace having heating elements 6 A to 6 C, the gas tank 1 was connected to the gas inlet through the pressure controller 2. After maintaining the initial process temperature at 920 ° C for 20 hours, GaN single crystals were grown at the main growth process temperature of 890 ° C. The nitrogen gas pressure was kept constant at 3 · 9 MPa. The total training time (initial process 20 hours + main training process time) was 150 hours. After the growth process was completed, the growth container was taken out of the cooled atmosphere control container, and the flux was reacted with ethanol to remove the GaN single crystal grown on the seed crystal.

Figure 8 shows the observation of the growth container taken out from the atmosphere control container from above. Figure 9 shows the GaN single crystal taken out from the growth vessel. Fig. 10 shows the surface of a GaN single crystal observed with a microscope. There were no miscellaneous crystals at the gas-liquid interface, and no miscellaneous crystals adhered to the GaN single crystal. The crystal surface was smooth. The weight of the grown GaN single crystal was 1.08 g.

(Example 2)

The training preparation was performed in the same manner as in Example 1. After maintaining the initial process pressure at 4.3 MPa for 20 hours, GaN single crystals were grown at the main growth process pressure of 3.9 MPa. The temperature was kept constant at 890 ° C. The total training time (initial process 20 hours + main training process time) was 150 hours. After the growth process was completed, GaN single crystals were collected. The GaN single crystal weight was 0.98 g.

(Comparative Example 1)

The training preparation was performed in the same manner as in Example 1. A GaN single crystal was grown at a constant temperature of 890 ° C and a pressure of 3.9 MPa. The training time was 150 hours. After the growth was completed, GaN single crystals were collected. The GaN single crystal weight was 0.54 g.

(Example 3)

Under the same conditions as in Example 1, only the total growth time (initial process 20 hours + main growth process time) was changed, and a GaN single crystal was grown. The weight of the grown GaN single crystal grown at the total growth time of 50, 75, 100, 125 hours is They were 0.11, 0.28, 0.55, and 0.73 g, respectively.

(Comparative Example 2)

A GaN single crystal was grown under the same conditions as in Comparative Example 1 while changing only the growth time. The weight of the grown GaN single crystal grown at the growth time of 25, 50, 75, 100, and 125 hours is 0.0C! 0.00, 0.02, 0.10, 0.30g

The results of Examples 1, 2, and 3 and Comparative Examples 1 and 2 are collectively shown in FIG. By using an initial process of high temperature and high pressure, we succeeded in shortening the time to start the growth of GaN crystals. As a result, the total growth increased when the total time for GaN growth was constant.

FIG. 12 is a graph showing the relationship between the temperature and pressure in each example and the regions A to D in Patent Document 2. The temperature and pressure conditions in the examples and comparative examples are all within the region B.

Table 1 shows the range where R (nitrogen dissolution rate in the melt in the nitrogen dissolution process) / (nitrogen dissolution rate in the melt in the main growth process) is 1.1 or more. In this example, T 2 = 8 90 ° C and P 2 = 3.9 MPa. The activation energy E of nitrogen dissociation and dissolution was used after calculating a value of 2.8 eV by cluster model simulation. As a result, it can be seen that R is 1.1 or more within the range of Eq. (3).

Although specific embodiments of the present invention have been described, the present invention is not limited to these specific embodiments and can be implemented with various changes and modifications without departing from the scope of the claims. .

Claims

The scope of the claims

1. A method in which a seed crystal substrate is immersed in a melt containing flatts and a single crystal raw material in a growth vessel, and a nitride single crystal is grown on a growth surface of the seed crystal substrate,

A nitrogen dissolving step for dissolving nitrogen in the melt at temperature T l (K) and pressure P I (MP a); and

A main growth step of growing a nitride single crystal on the growth surface of the seed crystal substrate at a temperature T 2 (K) and a pressure P 2 (MP a)

And P 1, P 2, T 1, and 満足 2 satisfy the following relational expressions (1), (2), and (3):

Τ 2-1 0 ≤ Τ 1 ≤ Τ 2 + 6 0 (1)

Ρ 2-0. 5 ≤ Ρ 1 ≤ Ρ 2 + 5. 0 (2)

Ρ 1≥ 1. 1 X Ρ 2 X (Τ 1 / Τ 2) 0 - 5 exp [(E / k) - [(1 / T - (1 / T 2)]] (3)

(E is 2.8 e V,

k is the Boltzmann constant (1. 3 8 X 1 0— ^{2 3} J / K)

2. The method according to claim 1, wherein T 1 and 、 2 satisfy the following relational expression (4). '

Τ 2 ≤ Τ 1 ≤ Τ 2 + 4 0 (4)

3. The method according to claim 1, wherein P 1 and Ρ 2 satisfy the following relational expression (5).

Ρ 2 ≤ Ρ 1 ≤ Ρ 2 + 3. 0 (5)

4. The method according to any one of claims 1 to 3, wherein a time of the nitrogen dissolving step is 5 hours or more and 60 hours or less.

5. The temperature T 2 and the pressure P 2 in the main growth process satisfy the following relational expressions (6) and (7), according to any one of claims 1 to 4: The method described.

l o g P 2 ≥ (— 5. 4 0 Χ10 °) / Ύ 2 + 4. 8 3

(6) l o g P 2 ≤ (one 5.59 X10 °) / Ύ 2 + 5. 4 7

(7)