KR20070025081A - Method for manufacturing gallium nitride substrate - Google Patents

Abstract

A method for manufacturing a GaN substrate is provided to acquire an excellent GaN layer by preventing a silicon substrate from being etched due to a GaN growth source and lessening the interface between the GaN layer and silicon using a substrate surface treatment and a triangle type GaN cluster forming process before a GaN layer growing process. A silicon substrate is loaded into a reaction chamber. A cleaning process is performed on the substrate by flowing a cleaning gas into the reaction chamber(110). A cluster type buffer layer is formed on the substrate by flowing a source gas of Ga and N into the reaction chamber. A single crystal GaN layer is grown on the substrate(140). The GaN layer is separated from the substrate. A damaged portion is then removed from the GaN layer.

Description

Gallium nitride substrate manufacturing method {METHOD FOR MANUFACTURING GALLIUM NITRIDE SUBSTRATE}

1 and 2 are SEM views showing growth of a triangular buffer layer gallium nitride (GaN) film on a silicon substrate according to an embodiment of the gallium nitride substrate manufacturing method according to the present invention.

Figure 3 is a schematic flow chart showing sequentially a gallium nitride substrate manufacturing method according to the present invention.

4 is a cross-sectional view of an HVPE reactor for growing a gallium nitride (GaN) film according to one embodiment of the present invention.

5 is a schematic flowchart sequentially showing a gallium nitride (GaN) film processing method according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10. Reactor

11. Chamber

12. Heater

13. susceptor

14. Silicon substrate

15. First injection

16. Second injection pipe

17. 3rd injection

18. 4th injection

19.Ga metal

21. Exhaust Line

The present invention relates to a method of manufacturing a gallium nitride substrate, and more particularly, to a GaN substrate having a low level of dislocation density by a simpler method, and to significantly shorten the time required for substrate separation using a silicon substrate. The present invention relates to an improved gallium nitride substrate manufacturing method for improving the productivity of the substrate and increasing the substrate yield.

Gallium nitride (hereinafter referred to as GaN) is a nitride semiconductor having a urzite structure, and has a direct energy band gap of 3.4 eV corresponding to the blue wavelength band of visible light at room temperature. It is possible to adjust the prohibition drastically by forming solid solution with InN and AlN, and it is the most popular blue light and light emitting device material because it shows the characteristics of direct transition type semiconductor in the whole composition range of the whole rate solid solution.

GaN films are usually formed on sapphire (Al 2 O 3), silicon carbide (SiC), or silicon (Si) substrates by metal-organic chemical vapor deposition (MOCVD), or hydrogen vapor phase epitaxial (HVPE).

However, in this case, since the lattice constant and the coefficient of thermal expansion are different from each other, it is very difficult to epitaxially grow the GaN film on the substrate due to lattice mismatch. Not only GaN but also GaN-based such as AlN, InN, GaInN, AlGaN, and GaAlInN are all.

As a method to overcome this problem, a buffer layer is first formed on a substrate at a relatively low temperature on a substrate having a similar lattice constant in order to alleviate lattice strain, and then a GaN film is grown on the buffer layer. Has been proposed.

However, this method requires the use of expensive substrates and the inconvenience of using another growth equipment to form the buffer layer, and also allows for epitaxial growth of the GaN film, but the dislocation density in the GaN film is high. Still high, they are limited to applications such as laser diodes and light emitting diodes.

In the case of forming a GaN thin film using a sapphire substrate, it is easy to epitaxially grow a GaN film on a sapphire substrate to the present technical level, but it is very difficult to separate the GaN film from the sapphire in order to use it as a substrate of another device. it's difficult.

In the method described above, after the GaN thick film is grown on the sapphire substrate, the laser is irradiated with the sapphire substrate to separate the GaN thick film from the sapphire substrate, and the pyrolysis and separation of the GaN film is time-consuming, and the yield is high. There is a problem of low.

Although many efforts have been made to obtain GaN substrates by growing and separating GaN thick films on low-cost silicon substrates to overcome the above problems, there are still problems in that silicon substrates are etched or GaN film growth itself is difficult.

The present invention has been made to solve the above problems, it is possible to manufacture a GaN substrate with a low dislocation density on a silicon substrate by a simple method, and after forming a GaN film on the silicon substrate by separating GaN from the substrate GaN substrate It is an object of the present invention to provide a gallium nitride substrate manufacturing method to shorten the process time when obtaining.

The gallium nitride substrate manufacturing method of the present invention for achieving the above object comprises the steps of: (a) charging a silicon substrate in the reactor; (b) flowing a cleaning gas into the reactor to clean the surface of the silicon substrate; (c) flowing a gallium (Ga) source gas and a nitrogen (N) source gas into the reactor to form a buffer layer in a cluster form on the silicon substrate; (d) growing a single crystal gallium nitride (GaN) film on the silicon substrate; (e) separating the gallium nitride (GaN) film from the silicon substrate; (f) removing the damaged layer on the surface of the gallium nitride (GaN) film to form a gallium nitride (GaN) wafer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, in the present invention, a GaN film is grown using a silicon substrate.

FIG. 1 is a scanning electron microscope (SEM) photograph showing that a protective layer in the form of a cluster is grown to prevent etching occurring when a GaN film is grown on a silicon substrate according to the present invention.

As shown in FIG. 1, the cluster-type protective layer formed on the silicon substrate is grown in the form of a triangle by about 90%. In addition, the cluster-type protective layer reduces the lattice mismatch between the silicon substrate and the GaN film.

2 is a scanning electron microscope (SEM) image grown according to the GaN substrate manufacturing method according to the present invention.

In addition, in the GaN substrate manufacturing method according to the present invention, a GaN protective layer having a cluster shape is first grown on a silicon substrate, and a GaN thick film is sequentially grown thereon. As shown in Figure 2, the boundary between the protective layer and the GaN thick film layer is distinguished, which is all made in the HVPE equipment.

This will be described in more detail.

3 is a schematic flowchart showing a GaN substrate manufacturing method according to the present invention in sequence.

Referring to FIG. 3, first, a silicon substrate having a certain orientation is loaded into a reactor, and then the surface of the substrate is treated (steps 100 and 110).

The surface of the single crystal silicon film on which the GaN film is to be grown on the silicon substrate has a surface orientation of (1,1,1), and the H2 gas or HCl gas may be used as the cleaning gas for treating the substrate surface with the cleaning gas. 3 shows the case of using H 2 gas.

When the H2 gas or HCl gas is flowed into the reactor, the surface of the substrate is cleaned by removing the natural oxide film and organic matter. For example, when H2 gas is used, the H2 gas reacts with SiO2, which is a natural oxide film of the silicon substrate, to form Si gas. And H 2 O, wherein Si gas is naturally exhausted and H 2 O is evaporated and blown away by heat, resulting in removal of SiO 2.

In addition, when the substrate surface is treated with a cleaning gas, the substrate surface is cleaned, and the atomic structure of the surface of the silicon substrate becomes a terrace structure. The terrace structure has a stepped surface, and since atoms to be deposited on the substrate surface are easily grown as they adhere to the ends of the steps, the energy barrier required for deposition can be lowered to make deposition easier.

In the process of treating the substrate surface with the cleaning gas as described above, H 2 gas or HCl gas is maintained at 900 to 1100 ° C. while 0.01% of the total amount of gas supplied into the reactor in the GaN film growth process to be performed in step 140 described later. Flow into the reactor in an amount corresponding to 1%.

In this case, when H 2 gas is used as the cleaning gas, H 2 gas is flowed for 0.5 to 10 minutes, and when H H 2 gas is used, HCl gas is flowed for 1 to 30 minutes.

The GaN nucleation process is then performed (step 120).

In this step, in the GaN film growth process, which will be described later, in an amount corresponding to 10 to 30% of the total amount of gas supplied into the reactor, the N source gas is flowed into the reactor for 60 to 90 minutes with NH₃, which is an N source gas. This prevents silicon from being etched when flowing HCl gas as a carrier gas to GaCl 3 gas or Ga metal as a Ga source gas.

As such, the N source gas is first flowed into the reactor, and the substrate is then alternately treated with Ga source gas to generate nuclei of GaN crystals on the silicon substrate. At this time, as described above, since the surface of the silicon substrate has a terrace structure, the nuclei of the generated GaN crystals adhere to the end of the stairs.

For example, when HCl gas is flowed into Ga metal and the silicon substrate is first surface-treated with GaCl gas, GaCl remains on the substrate surface, and then reacts with N in the flowing NH₃ gas to generate GaN nuclei.

After performing the GaN nucleation process of the substrate as described above, a GaN protective layer is grown on the substrate (step 130).

In this step, while maintaining the temperature of the reactor at 300 to 800 ℃ simultaneously flowing the Ga source gas and N source gas in the reactor to grow a protective layer in the form of GaN cluster. In this GaN protective layer growth process, the GaN nuclei generated in the previous step grow gradually and grow into clusters having a certain thickness.

The triangular GaN cluster described above in the present invention plays two roles. In other words, it serves to protect the gas and the source used in the growth of the silicon substrate and the GaN film, and serves as a lattice mismatch caused by different lattice constants and thermal expansion coefficients between the silicon substrate and the GaN film. The total thickness of the grown GaN clusters is about 1-20 μm.

Subsequently, a GaN film is grown on the silicon substrate on which the GaN cluster is grown.

In this step, the GaN film is epitaxially grown by simultaneously flowing a Ga source gas and an N source gas into the reactor while maintaining the temperature of the reactor at 1000 to 1100 ° C.

In the growth process of the GaN film, lateral overgrowth is grown on the GaN cluster generated in the previous step to grow into a film. That is, because the lattice constant and the coefficient of thermal expansion are different between the silicon substrate and the GaN film, the GaN material is more likely to be attached to the GaN protective layer rather than directly stacked on the substrate.

Thereafter, the silicon substrate on which the GaN film is formed is cooled to room temperature to complete formation of the GaN film (step 150).

Next, the mixture of nitric acid (HNO3, 70%) and hydrofluoric acid (HF, 50%) is changed to 0.1 to 10 to remove the silicon substrate at 1 to 100 µm / min, and acetic acid is added to remove residual silicon. (Step 160)

Subsequently, in order to remove the damage layer on the surface of the GaN film, the GaN film is polished, reinserted into the GaN growth equipment, and finally subjected to surface stabilization (step 170).

In general, methods of growing an epi layer may include VPE (Vapor Phase Epitaxial growth), LPE (Liquid Phase Epitaxial growth), and SPE (Solid Phase Epitaxial growth).

Here, the VPE is to grow crystals on the substrate through the decomposition and reaction by heat while flowing the reaction gas on the substrate, depending on the raw material type of the reaction gas hydride VPE (HVPE), halide VPE (halide VPE), Organic metal VPE (MOVPE) and the like.

Among them, the case where the GaN film is grown by HVPE will be described with reference to Examples.

Example

4 is a cross-sectional view showing the structure of a reactor for growing a GaN film by HVPE.

As shown in FIG. 4, the reactor 10 includes a heater 12 installed to surround the growth chamber 11 to heat the chamber 11.

After mounting the silicon substrate 14 on the 3 x 2 "quartz susceptor 13 in the chamber 11, the atmosphere gas is maintained at a temperature of 1000 ° C in the chamber 11 N 2 is injected through the first injection tube 15 as a cleaning gas, and H 2 is injected through the second injection tube 16 as a cleaning gas, and these gases are flowed for 30 minutes.

In this process, the natural oxide film and the organic material on the silicon substrate 14 were removed to clean the surface of the silicon substrate 14, and the surface of the silicon substrate 14 has a terrace structure.

At this time, N2 is used as an atmosphere gas, and also acts as a carrier gas that carries H2. Gases in the chamber 11 are naturally exhausted through the exhaust line 21.

Next, after stopping the supply of H₂ by closing the second inlet tube 16, NH 3 is flowed through the third inlet tube 17 for 70 minutes while maintaining the temperature in the chamber 11 at 1000 ° C. It was. Thereafter, the third injection pipe 17 was closed to stop the supply of NH 3, and then HCl was flowed through the fourth injection pipe 18 for 70 minutes.

At this time, HCl flowing through the fourth injection tube 18 reacts with the Ga metal 19 to generate GaCl gas, as shown in Scheme 1 below, and the GaCl gas is supplied to the silicon substrate 14.

Ga (s) + HCl (g) → GaCl (g) + 1/2 H₂ (g)

Then, alternate supply of NH 3 and GaCl gas is performed once more, and GaN nuclei are grown on the silicon substrate 14 during the alternate supply of NH 3 and GaCl gas.

In addition, NH 3 is simultaneously flowed through the third injection tube 18 while NH 3 is maintained at a temperature of 1050 ° C. in the chamber 11. In this case, NH 3 and GaCl are simultaneously supplied to the silicon substrate 14 to react with each other as shown in Scheme 2 below. As a result, the GaN film is grown to a thickness of 120 μm.

GaCl (g) + NH₃ (g) → GaN (s) + HCl (g) + H₂ (g)

Then, the silicon substrate 14 on which the GaN film was formed is cooled to room temperature.

In order to separate the GaN film from the silicon substrate 14, the silicon substrate 14 is removed by varying the nitric acid (HNO 3, 70%) solution and the hydrofluoric acid (HF, 50%) solution from 0.1 to 10. At this time, the time is 1 to 20 minutes.

In addition, to remove the damaged layer of the remaining GaN film, the front and back surfaces of the GaN film are first lapping and the diamond slurry is changed in size, polished three times, and finally washed and nitrided. A gallium substrate is produced.

Specifically, FIG. 5 shows a detailed flowchart of processing (polishing) the GaN film of step 170 described above.

As shown, the silicon substrate 14 polishes and separates the separated GaN film, thereby bonding the separated GaN film to a plate (step 200).

And lapping to a certain thickness to remove the damage layer of the GaN film (step 210).

The size of the diamond slurry is then changed to first, second and third polishing of the GaN film three times (steps 220, 230 and 240).

Then, the GaN film is finally cleaned (step 250).

As described above, the gallium nitride substrate manufacturing method according to the present invention has the following effects.

By performing the substrate surface treatment and triangular GaN cluster formation process before the GaN film growth, it is possible to grow a high quality GaN film by preventing etching of the silicon substrate from the GaN growth source and relaxing the interface between the GaN film and the silicon.

It is also possible to epitaxially grow and to reduce the dislocation density of the GaN film.

In the step of removing the silicon substrate, the GaN substrate can be easily separated from the GaN film by a chemical method, thereby manufacturing a GaN substrate having a low level of dislocation density by a simpler method.

In addition, since the silicon substrate is used, the time required for separation of the substrate can be significantly shortened compared to the case of obtaining a thick film GaN substrate using a conventional sapphire substrate, thereby improving the productivity of the GaN substrate and increasing the substrate yield. have.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent embodiments are possible. Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

Claims (18)

(a) charging a silicon substrate into a reactor; (b) flowing a cleaning gas into the reactor to clean the surface of the silicon substrate; (c) flowing a gallium (Ga) source gas and a nitrogen (N) source gas into the reactor to form a buffer layer in a cluster form on the silicon substrate; (d) growing a single crystal gallium nitride (GaN) film on the silicon substrate; (e) separating the gallium nitride (GaN) film from the silicon substrate; (f) removing the damaged layer on the surface of the gallium nitride (GaN) film to form a gallium nitride (GaN) wafer. The method of claim 1, In the step (b), the cleaning of the silicon substrate, The HCl gas or the H2 gas is introduced into the reactor in an amount corresponding to a portion of the total amount of gas supplied for the growth of the gallium nitride (GaN) film at a predetermined temperature using the cleaning gas using HCl gas or H2 gas. Flowing to remove the natural oxide film and organic matter from the surface of the silicon substrate, and forming a surface of the silicon substrate in a terrace structure. The method of claim 2, The temperature is a gallium nitride substrate manufacturing method, characterized in that 900 to 1100 ℃. The method of claim 2, The predetermined portion is gallium nitride substrate manufacturing method, characterized in that 0.01 to 1%. The method of claim 2, The HCl gas flows for 1 to 30 minutes, the H2 gas flows for 0.5 to 10 minutes characterized in that the gallium nitride substrate manufacturing method. The method of claim 1, In step (c), Formation of the buffer layer in the form of a cluster on the silicon substrate, The gallium (Ga) source gas is flowed and the gallium nitride (GaN) film is grown on the gallium (Ga) source gas and the nitrogen (N) source gas at a predetermined temperature using the nitrogen (N) source gas. The gallium nitride substrate manufacturing method characterized in that it is made to alternately flow into the reactor for a predetermined time in an amount corresponding to a certain portion of the total amount of gas supplied for. The method of claim 6, The predetermined temperature is a gallium nitride substrate manufacturing method, characterized in that 300 to 800 ℃. The method of claim 6, The predetermined portion is gallium nitride substrate manufacturing method, characterized in that 30 to 50%. The method of claim 6, The predetermined time is gallium nitride substrate manufacturing method, characterized in that 60 to 90 minutes. The method of claim 6, The gallium nitride substrate manufacturing method characterized in that to form a thickness of the buffer layer to 0.1 ~ 20㎛ by adjusting the mixing ratio of the gallium (Ga) and nitrogen (N) up to 10 ~ 100. The method of claim 1, GaCl3 gas is used as the gallium (Ga) source gas or HCl gas is flowed into the gallium (Ga) metal as a carrier gas, The method of manufacturing a gallium nitride substrate, characterized in that for the nitrogen (N) source gas using NH3 gas. The method of claim 1, In step (d), The gallium nitride (GaN) film, the gallium nitride substrate manufacturing method characterized in that the growth of the gallium (Ga) source gas and the nitrogen (N) source gas at the same time in the reactor at 1000 to 1100 ℃. The method of claim 1, In step (d), The gallium nitride (GaN) film is grown to a thickness of 10 to 500㎛ by HVPE (HVPE) method, characterized in that the gallium nitride substrate manufacturing method. The method of claim 1, In the step (e), separation of the gallium nitride (GaN) film, And only the silicon substrate is selectively immersed and removed in an etchant. The method of claim 14, The immersion removal may change the mixing ratio of nitric acid (HNO 3, 70%) and hydrofluoric acid (HF, 50%) to 0.1 to 10 to remove the silicon substrate at 1 to 100 μm / min, and to remove acetic acid solution from 0 to 10%. Method for producing a gallium nitride substrate, characterized in that by adding to remove the residual silicon. The method of claim 1, The gallium nitride (GaN) wafer in the step (f) is, (h) bonding the gallium nitride (GaN) film separated in step (e) to a plate; (i) lapping to a predetermined thickness to eliminate damage of the gallium nitride (GaN) film; (j) polishing the gallium nitride (GaN) film by varying the size of the diamond slurry; (k) cleaning the gallium nitride (GaN) film; At this time, in the step (j), the polishing is gallium nitride substrate manufacturing method, characterized in that carried out three times by changing the size of the diamond slurry. The method of claim 1, Between step (d) and step (e), And cooling the silicon substrate on which the gallium nitride (GaN) film is formed to room temperature. The method of claim 1, The surface of the silicon substrate has a surface orientation of (1,1,1) gallium nitride substrate manufacturing method.

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