KR20210085889A - Crystal growth method - Google Patents

Abstract

The present invention relates to a crystal growing method. As a crystal growing method for growing GaN on a substrate in a hydride vapor phase epitaxy (HVPE) manner, provided is a crystal growing method which comprises a step of forming a GaN layer or a 3-5 family compound semiconductor layer on an AlN dot after the AlN dot is formed on a substrate, and forming a double layer of dot seeds for growing GaN, thereby improving growing speed and crystallinity of a GaN thick film.

Description

Crystal growth method {Crystal growth method}

The present invention relates to a crystal growth method, and more particularly, to a crystal growth method capable of improving the growth rate and crystallinity of GaN.

In general, GaN single-crystal wafers have high charge mobility, so they are suitable materials for high-output, high-frequency power devices using Schottky diodes, etc., and have been conventionally used as substrates for laser diodes. It is also used as a substrate.

Such a GaN wafer is usually manufactured by growing a GaN thick film with hydride vapor phase epitaxy (HVPE) on a sapphire (Al ₂ O ₃ ) substrate and then laser or physically separating sapphire and GaN.

When growing GaN with HVPE, growth parameters are very complex and diverse, such as growth temperature, ammonia flow rate, Ga flow rate, growth rate, carrier gas flow rate, _{and initial surface treatment of sapphire (Al 2} O ₃ ) substrate, and these growth parameters are optimal. The growth of single crystal GaN with few defects is possible only when combined with

In particular, among the growth parameters described above, the surface treatment of the sapphire substrate is performed at the initial stage of GaN growth, and the surface treatment process of the substrate is very important enough to influence the final quality of GaN.

Specifically, the initial surface treatment of the sapphire substrate is made by flowing a _{trace amount of ammonia (NH 3} ) onto the substrate at a high temperature of 500°C to 900°C. When the sapphire substrate is surface treated in this way, Al of the sapphire substrate and N of ammonia react to form nano-sized AlN dots having a diameter of several tens of nm on the surface of the sapphire substrate, and these AlN dots enable GaN growth It is known to act as a seed.

However, when GaN is grown after forming AlN dots on a sapphire substrate by the above-described method in an actual HVPE reactor, GaN grows at a very slow rate of 10 μm or less per hour, making it difficult to obtain a thick GaN film of the desired thickness, which It means that there is a limit to promoting the growth of GaN with AlN dots alone due to the low reactivity of the AlN dots.

The present invention has been devised to solve the problems of the prior art, and an object of the present invention is to provide a crystal growth method capable of promoting the growth of GaN when manufacturing a GaN single crystal wafer using HVPE.

As a means for solving the above technical problem,

The present invention relates to a crystal growth method for growing GaN on a substrate with hydride vapor phase epitaxy (HVPE). After forming an AlN dot on the substrate, a GaN layer or a group 3-5 compound semiconductor layer is formed on the AlN dot to grow GaN. It provides a crystal growth method comprising the step of forming a dot seed of a double layer for

In this case, the diameter and height of the AlN dots may be 10 to 100 nm.

In this case, the thickness of the GaN layer may be 1.5 to 20 nm.

In this case, the AlN dots may contain 10 at% or less of Ga.

In this case, the GaN layer may contain 50 at% or less of Al.

In this case, the AlN dots may contain 10at% or less of Ga, and the GaN layer may contain 50at% or less of Al.

In this case, the group 3-5 compound semiconductor layer may be made of InN.

In this case, the substrate may be any one selected from a sapphire substrate, an oxide substrate, a sulfide substrate, a fluoride substrate, and a Si substrate.

In this case, the oxide substrate is a _{Ga 2 O 3, TiO 2,} LaAlO 3, MgO, NdCaAlO 4, NdGaO 3, BaTiO 3, SCAM, and any one substrate is selected from SrTiO ₃ substrate, and the sulfide substrate ZnS or ZnSe a substrate, the fluoride substrate may be a CaF ₂ substrate, and the Si substrate may be a surface-treated Si substrate.

According to the present invention, when GaN is grown by HVPE, by surface-treating the substrate so that an AlN/GaN double layer is formed on the substrate, the GaN layer acts as a seed to improve the growth rate and crystallinity of the GaN thick film.

1 is a view showing a state in which AlN dots are formed on a substrate according to the present invention;
2 is a view showing a state in which a GaN layer is formed on the AlN dots shown in FIG. 1;
3 and 4 are photographs showing AFM surface images of AlN dots and AlN/GaN double-layer dots, respectively;
5 and 6 are photographs showing the results of Synchrotron XRD mapping of AlN dots and AlN (28 nm)/GaN (4.3 nm) double-layer dots, respectively;
7 and 8 are graphs showing the Synchrotron XRD omega scan results in H scan of AlN dots and AlN (28 nm)/GaN (4.3 nm) double-layer dots, respectively;
9 and 10 are graphs showing L scan for obtaining the thickness of the AlN layer and the GaN layer,
11 is a diagram illustrating a scan direction in a reciprocal lattice space.

Hereinafter, the crystal growth method according to the present invention will be described in detail.

FIG. 1 is a diagram illustrating a state in which AlN dots are formed on a substrate according to the present invention, and FIG. 2 is a diagram illustrating a state in which a GaN layer is formed on the AlN dots illustrated in FIG. 1 .

1 and 2, in the crystal growth method according to a preferred embodiment of the present invention, when a GaN single crystal wafer is manufactured by hydride vapor phase epitaxy (HVPE), the substrate is surface treated to promote the growth of a GaN thick film. As a technical feature, each process will be sequentially described below.

First, AlN dots 20 are formed on the sapphire substrate 10 .

Specifically, the sapphire substrate 10 is mounted on the inside of the HVPE reactor, and the temperature inside the reactor is raised to about 500 to 1000°C. After that, when HCL and NH _{3 gas are mixed with N 2} gas at a ratio of 1:10 and injected into the reactor for about 5 minutes and flowed, Al of the sapphire substrate 10 and N of ammonia react with the sapphire substrate 10. AlN dots 20 are formed on the surface. For reference, unexplained reference numeral 40 in FIGS. 1 and 2 denotes an AlN layer.

The diameter and height of the AlN dots 20 are preferably 10 to 100 nm. This is because, if the diameter and height of the AlN dot 20 is less than 10 nm, it cannot act as a seed for GaN growth, and if it exceeds 100 nm, it may cause deterioration of the surface flatness of the final product and warpage of the substrate.

In addition, the AlN dots 20 may contain Ga of 10 at% or less, preferably 5 at% or less. As such, when the AlN dots 20 contain a small amount of Ga, the lattice mismatch between the GaN and AlN thick films can be reduced. However, when forming the AlN dots 20, the amount of Ga included in the formation is preferably 5 at% or less, which is a very small amount for the formation of the AlN dots 20.

Meanwhile, although the sapphire substrate 10 will be described as an example, the substrate applicable to the present invention is not limited to the sapphire substrate, and Ga ₂ O ₃ , TiO _{2 , LaAlO 3} , MgO, NdCaAlO ₄ , NdGaO ₃ , BaTiO ₃ , SCAM, _{and an oxide substrate such as SrTiO 3} , a sulfide substrate such as ZnS or ZnSe, a _{fluoride substrate such as CaF 2} , or a surface-treated Si substrate may also be used.

Thereafter, a GaN layer 30 is formed on the AlN dots 20 .

Specifically, when a small amount of GaCl, HCl gas, and NH ₃ gas are injected into the reactor, a GaN layer 30 having a thickness of several nm is formed on the AlN dot 20 . In this case, the GaCl gas and the NH ₃ gas are adjusted to an amount of 5% or less than the amount input during the GaN thick film growth, and are input at a ratio of 0.1 or less (GaCl/NH ₃ ).

Since the GaN layer 30 has crystallinity as the same material as the GaN thick film and has a high degree of activation even in the raw material reaction gas, it is possible to promote the growth of the GaN thick film and improve the crystallinity of the GaN thick film.

The thickness of the GaN layer 30 is preferably 1.5 to 20 nm. If the thickness of the GaN layer 30 is less than 1.5 nm, it is difficult to act as a seed for the growth of GaN due to interdiffusion of the composition with the lower layer. In addition, the GaN layer 30 should have a thickness of 1.5 nm or more, which is a thickness that can partially absorb strain with the AlN layer by repeating at least three or more GaN lattice constants (0.45 nm). On the other hand, if the thickness of the GaN layer 30 is more than 20 nm, even if the thickness of the GaN layer 30 is increased, the activity with the reactive gas is rather decreased, so that the growth rate decreases or the growth rate does not increase anymore. It cannot be expected to improve the speed and crystallinity.

In addition, the GaN layer 30 may include Al through interdiffusion with Al of the sapphire substrate 10 . In this case, since Al is based on mutual diffusion by the growth temperature, it may be included in the GaN layer 30 at a maximum of 50 at% or less.

Meanwhile, the same effect can be obtained even when a group III-V compound semiconductor layer is formed instead of the GaN layer 30 . InN may be used as the group 3-5 compound semiconductor material. _{Formation of InN can be formed on AlN dots through a process in which In metal vaporizes and reacts with NH 3} gas in the same manner as in GaN formation. InN is similar to GaN with lattice constants of 0.35 nm and 0.32 nm, respectively, and InN is also The high degree of activation with the reaction gas improves the growth rate.

After forming the GaN layer 30 as described above, GaN is grown using a conventional crystal growth method.

For example, GaCl may be formed by reacting the previously injected HCl with Ga, and a GaN thick film having a thickness of several μm may be formed on the sapphire substrate 10 by reacting _{GaCl and NH 3 gas.} That is, in the present invention, if a GaN thick film is grown after forming a GaN layer of 1 to 20 nm on a substrate for growth of the GaN thick film, the growth conditions or methods are not particularly limited, and various known methods can be applied.

In order to confirm the effect of the crystal growth method described above, a GaN thick film was grown using a sapphire substrate surface-treated with AlN dots and AlN/GaN double-layer dots, and the effect of the dots on the GaN thick film growth was confirmed.

As a result, when the surface was treated with AlN dots, the GaN thick film grew limited, and the growth rate was very slow at 10 µm or less per hour, making it difficult to grow a thick film of 300 µm or more, and the consumption of raw material gas was very high. However, in the case of surface treatment with AlN/GaN double-layer dots, the growth rate was very fast (20 μm or more), and thick films of 300 μm or more could be easily grown. From these results, it can be seen that the GaN layer with a thickness of several nm laminated on the AlN dots serves to promote the growth of the GaN thick film.

In this regard, FIGS. 3 and 4 show AFM surface images of AlN dots and AlN/GaN double-layer dots, respectively. It can be seen from FIGS. 3 and 4 that AlN dots exist in a very distinct dot shape with a height of 30 nm, whereas AlN/GaN double-layer dots exist in a dot shape grown in the horizontal direction rather than a sharp dot shape. It is seen that the GaN layer formed on the AlN dots promoted the dot formation in the lateral direction.

5 and 6 show the results of Synchrotron XRD mapping of AlN dots and AlN (28 nm)/GaN (4.3 nm) double-layer dots, respectively. An AlN (0002) pattern and a GaN (0002) pattern can be confirmed from FIGS. 5 and 6 .

7 and 8 show the results of Synchrotron XRD omega scan in H scan of AlN dots and AlN (28 nm)/GaN (4.3 nm) double-layer dots, respectively. In FIG. 7 , a sharp AlN peak at the interface reflecting the crystallinity of the sapphire substrate is observed. In this case, the broad component seen around the sharp AlN component is due to strain due to a lattice mismatch of 13.2% between the AlN and the lattice of the sapphire substrate. In addition, it can be seen from FIG. 8 that the omega scan half width of H scan of AlN and GaN is very small as 0.012, so that AlN/GaN double-layer dots of high crystallinity reflecting the single crystallinity of the sapphire substrate are formed. On the other hand, the observation of a broad component in the AlN peak in FIG. 8 as in FIG. 7 means that the AlN layer was formed at the interface with the sapphire substrate and the GaN layer was formed on the AlN layer. The thickness of each layer was obtained by L scan of FIGS. 9 and 10 , and specifically, the thickness was 23 nm for AlN dots, and AlN (28 nm)/GaN (4.3 nm) for GaN/AlN double-layer dots. 11 is a diagram illustrating the above-described H scan, L scan, and Omega scan in a reciprocal lattice space.

10: sapphire substrate 20: AlN dot
30: GaN layer 40: AlN layer

Claims (9)

In the crystal growth method of growing GaN on a substrate with hydride vapor phase epitaxy (HVPE),
A crystal growth method, comprising: forming an AlN dot on a substrate and then forming a GaN layer or a Group 3-5 compound semiconductor layer on the AlN dot to form a double-layer dot seed for GaN growth. The method of claim 1,
A crystal growth method, characterized in that the diameter and height of the AlN dots are 10 to 100 nm. The method of claim 1,
The thickness of the GaN layer is a crystal growth method, characterized in that 1.5 ~ 20nm. The method of claim 1,
The AlN dot crystal growth method, characterized in that it contains 10at% or less of Ga. The method of claim 1,
The GaN layer is a crystal growth method, characterized in that it contains 50 at% or less of Al. The method of claim 1,
The AlN dot contains 10at% or less of Ga, and the GaN layer contains 50at% or less of Al. The method of claim 1,
The group 3-5 compound semiconductor layer is a crystal growth method, characterized in that made of InN. 8. The method according to any one of claims 1 to 7,
The substrate is a crystal growth method, characterized in that any one selected from a sapphire substrate, an oxide substrate, a sulfide substrate, a fluoride substrate, and a Si substrate. 9. The method of claim 8,
The oxide substrate is _{Ga 2 O 3, TiO 2,} LaAlO 3, MgO, NdCaAlO 4, NdGaO 3, BaTiO 3, and any one substrate is selected from the SCAM, SrTiO ₃ substrate, and the sulfide substrate is ZnS or ZnSe substrate, The fluoride substrate is a CaF ₂ substrate, the Si substrate is a crystal growth method, characterized in that the surface-treated Si substrate.

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