KR100461505B1 - Method for manufacturing a nitride semiconductor substrate - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a group III nitride single crystal semiconductor substrate used as a material for blue and ultraviolet (UV) light emitting devices, wherein a surface of a silicon nitride (AlN) thin film, which serves as a buffer layer, is grown on a silicon substrate. Thermal oxidation and a gallium nitride (GaN) thin film formed by a halide vapor deposition (HVPE) method on the aluminum nitride (AlN) thin film whose surface is protected by the thermal oxidation film can obtain a high purity nitride film single crystal. Compared to sapphire substrates, the thermal expansion coefficient difference with gallium nitride (GaN) is small and inexpensive. In particular, since the nitride film is grown on a silicon substrate that can obtain a large-area substrate, it can be applied industrially and economically. The effect can be obtained.

Description

Method for manufacturing a nitride semiconductor substrate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a nitride semiconductor substrate, and more particularly, to a method for producing a group III nitride single crystal semiconductor substrate used as a material for blue and ultraviolet (UV) light emitting devices.

Nitride-based semiconductors of group III are materials for blue and ultraviolet (UV) light emitting devices, and their applicability has been expected since the 1970s, and research has been focused on making optical devices emitting blue and green light using them. . As a result, from 1994, about 20 years later, light emitting devices (LEDs) using gallium nitride (GaN) -based nitride semiconductors were developed and commercialized by Nakamura et al.

When blue and ultraviolet (UV) laser diodes (LDs), which have shorter wavelengths than red laser diodes (GaAs) with gallium arsenide (GaAs), are developed and commercialized, they are four times more than optical disks, such as compact discs (CDs). Information can be aggregated. Furthermore, the use of gallium nitride (GaN) -based nitride semiconductors enables the implementation of electronic devices that can operate stably in extreme environments and communication devices that can operate stably in the gigahertz (GHz) frequency band. However, until now, there is no suitable substrate for growing a gallium nitride (GaN) nitride semiconductor, and the defect concentration is increased by deformation due to lattice mismatch. Therefore, excellent properties are obtained by using a gallium nitride (GaN) nitride semiconductor. It is difficult to implement an optical device and an electronic device having. Therefore, efforts have been made to reduce the defect density by using a silicon carbon (SiC) substrate having a small lattice mismatch, but have not yet shown a great effect.

Recently, gallium nitride (GaN) is rapidly grown on a substrate by a method of halide vapor phase epitaxy (HVPE) to produce a low crystal defect thickness, and then the substrate is removed by mechanical polishing to have a constant thickness. Although research has been conducted to replace gallium nitride (GaN) based nitride semiconductor substrates by producing gallium nitride (GaN) single crystals, sapphire substrates stable at high temperatures are currently used. However, the sapphire substrate has a large difference in the coefficient of thermal expansion from gallium nitride (GaN), which is expensive and cannot produce a large-area substrate. Therefore, the sapphire substrate is expensive to produce a gallium nitride (GaN) single crystal substrate. It takes

Accordingly, an object of the present invention is to provide a method for manufacturing a nitride semiconductor substrate, which is capable of producing a large-area nitride film single crystal substrate at a low cost and to solve the problems caused by the disadvantages of the sapphire substrate.

1A to 1D are cross-sectional views of devices for explaining a method of manufacturing a nitride semiconductor substrate according to one embodiment of the present invention.

2A and 2B are graphs showing photographs of an aluminum nitride (AlN) thin film grown on a silicon substrate, followed by atomic force microscope and transmission electron microscope.

Figure 3a is a graph of the analysis of the characteristics of the aluminum nitride (AlN) thin film grown on a silicon substrate by X-ray.

3B is a partial cross-sectional view showing the results of observing a cross section of a silicon substrate, an aluminum nitride thin film, and a gallium nitride thin film with a transmission electron microscope;

3C is a diagram showing a transmission electron diffraction pattern of gallium nitride (GaN) crystals.

FIG. 3D is a diagram showing a transmission electron diffraction pattern of an interface between aluminum nitride (AlN) and a silicon substrate. FIG.

4 is a graph showing the results of film quality analysis when gallium nitride (GaN) is grown on a silicon substrate.

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

10: silicon substrate 10a: silicon oxide film

11: aluminum nitride (AlN) thin film 11a: aluminum nitride (AlN) oxide film

12: nitride film

The present invention for achieving the above object is to form a buffer layer for buffering the lattice mismatch with the substrate on the silicon substrate, the step of thermal oxidation process to grow an oxide film on the surface of the buffer layer, the oxide film Forming a nitride film on the substrate; and removing the silicon substrate.

The buffer layer is an aluminum nitride (AlN) thin film, is grown by a molecular beam epitaxy method, the nitride film is made of GaN, InN, AlN, AlGaN or InGaN.

The silicon substrate has a merit that the difference in coefficient of thermal expansion with the nitride film is smaller than that of the sapphire substrate, which is inexpensive, and in particular, a substrate having a large area can be obtained. Therefore, if the nitride film single crystal is grown on a silicon substrate, it is expected that industrially many effects can be obtained. However, when the nitride film is grown directly on the silicon substrate, first, the surface lattice mismatch is about 17% (Si (111) substrate) and about 33% (Si (100) substrate), and second, it becomes unstable at high temperature.

As a method for solving the problem of lattice mismatch, a method of forming an aluminum nitride (AlN) thin film serving as a buffer layer on a silicon substrate has been proposed. However, an experimental result has been reported that the stability of silicon (Si) itself is a problem when forming an aluminum nitride (AlN) thin film on a silicon substrate by a halide vapor deposition (HVPE) method. That is, chlorine gas is used at a high temperature when growing the nitride film. The silicon substrate is decomposed by reacting with the chlorine gas, and the decomposed silicon is added as an impurity during the nitride film growth.

Therefore, the present invention proposes the following method to solve the above problems. The present invention first uses a molecular beam epitaxy process to grow a high quality aluminum nitride (AlN) thin film, and to prevent the silicon substrate from reacting with chlorine gas at high temperature to decompose during gallium nitride (GaN) film growth. A pre-oxidation process is performed. Finally, a gallium nitride (GaN) film is grown by a halide vapor phase growth (HVPE) method to obtain a single crystal substrate.

Next, the present invention will be described in more detail with reference to the accompanying drawings.

1A to 1D are cross-sectional views of devices for describing a method of manufacturing a nitride semiconductor substrate according to the present invention.

Referring to FIG. 1A, the aluminum nitride (AlN) thin film 11 is grown to a thickness of several tens to several hundred nm on the silicon substrate 10 at a low temperature by physical vapor deposition or chemical vapor deposition. Natural oxide film present on the surface of the silicon substrate 10 by continuously washing in a 4: 1 mixed H ₂ SO ₄ / H ₂ O solution and 100: 1 mixed H ₂ O / HF solution before charging the chamber 10 And impurities. After the silicon substrate 10 is charged into the chamber, it is heat-treated to remove the natural oxide film adsorbed on the surface very thinly within a short time. The aluminum nitride (AlN) thin film 11 is grown on the silicon substrate 10 using aluminum (Al) and nitrogen (N ₂ ) plasma. The grown aluminum nitride (AlN) thin film 11 serves as a buffer layer for buffering lattice mismatch with the silicon substrate 10, and the surface roughness may be changed to prevent the mixture of silicon (Si) and aluminum (Al) from forming. It should be low below nm and have good crystallinity

Referring to FIG. 1B, a thermal oxidation process is performed at a temperature of 800 to 1100 ° C., and a silicon oxide film 10a is grown on the bottom surface of the silicon substrate 10, and aluminum nitride (AlN) thin film 11 is formed on the surface of aluminum nitride. The (AlN) oxide film 11a is allowed to grow. Surface oxidation for stabilization at high temperature may use both wet and dry oxidation methods, in which only the silicon oxide film 10a may be grown. As well as forming the oxide film 11a on the surface, a dense thermal oxide film is formed by the penetration of oxygen through microdefects such as microtubes present in the aluminum nitride (AlN) thin film 11. In the case of the aluminum nitride (AlN) thin film 11, complex phases such as Al ₂ O ₃ / AlON are controlled according to thermal oxidation temperature and time. At the same time, since the oxide film 10a grows faster on the back surface of the silicon substrate 10, the reaction of group III metals such as Ga, In, Al, and silicon (Si) during subsequent growth of nitride semiconductor thin films such as GaN, InN, AlGaN, InGaN This is avoided.

Referring to FIG. 1C, the nitride film 12 is formed on the oxide film 11a grown on the surface of the aluminum nitride (AlN) thin film 11 by physical vapor deposition or chemical vapor deposition. The nitride film 12 is deposited on the aluminum nitride (AlN) thin film 11 whose surface is protected by the oxide film 11a at a high temperature by physical vapor deposition or chemical vapor deposition, and the physical vapor deposition, molecular beam deposition, sputtering, and electron beam deposition are performed. Etc. are used, and chemical vapor deposition includes organometallic chemical vapor deposition, halide vapor phase growth (HVPE), and the like.

At this time, GaN, InN, AlN, AlGaN, InGaN are applied to the nitride film 12. When the nitride is grown on the silicon substrate 10 at a high temperature, silicon (Si) atoms are formed such as Ga, Al, In, or the like. Since it is difficult to form a high quality nitride semiconductor by reacting with metals, the oxide film 10a must be formed on the surface of the silicon substrate 10 by heat treatment in an oxygen atmosphere before the nitride film 12 is grown. In fact, when the nitride film is grown on the silicon substrate, the result of analysis through the Secondary Ion-Mass Spectrometer (SIMS) shows that the silicon film contains a large amount of silicon (Si).

Referring to FIG. 1D, by removing the silicon oxide film 10a and the silicon substrate 10, a nitride semiconductor substrate composed of the nitride film 12 and the oxide film 11a is obtained. The silicon oxide film 10a and the silicon substrate 10 may be removed by a mechanical method or a chemical method. In this case, it is important to prevent stress from being applied to the nitride film 12. Therefore, the removal of the silicon substrate 10 by wet etching, which is one of chemical methods, does not apply stress to the nitride film 12 than the removal by the chemical mechanical polishing (CMP) method. This removal method is not applicable to the sapphire substrate, and is applicable only to the silicon substrate.

2A and 2B illustrate, as an example, an atomic force microscope when the aluminum nitride (AlN) thin film 11 is grown on a silicon substrate 10 by a molecular beam epitaxy (MBE) method. It is a partial sectional view (FIG. 2A) and a partial sectional view (FIG. 2B) observed with the transmission electron diffraction microscope. The surface roughness of the aluminum nitride (AlN) thin film 11 is 1.8 nm, which is very dense and smooth. The epitaxial relationship of AlN [1-100] // Si [112] and AlN [0001] // Si [111] provides a substrate made of aluminum nitride (AlN) and silicon (Si) having excellent characteristics. It can be seen that manufactured.

3A to 3D illustrate, as an example, a double crystal X when a gallium nitride (GaN) thin film is formed by a halide vapor deposition (HVPE) method on an oxide film 11a grown on an aluminum nitride (AlN) thin film 11 surface. Partial cross-sectional view (FIGS. 3B-3D) observed with a -ray diffraction rocking curve (FIG. 3A) and a transmission electron diffraction microscope. The full width half maximum (FWHM) value of the gallium nitride (GaN) (0002) peak was 389 areseconds, indicating excellent crystallinity. GaN [1-100] // AlN [1-100] // Si [112] has an epitaxial relationship and is a defect of gallium nitride (GaN) compared to a defect in an aluminum nitride (AlN) thin film serving as a buffer layer. This is shown to be small. As a result, it can be seen that a gallium nitride (GaN) film having excellent characteristics in terms of crystallinity was grown.

FIG. 4 is a graph showing the results of SIMS analysis when a gallium nitride (GaN) thin film is grown on an aluminum nitride (AlN) thin film 11 by a halide vapor deposition (HVPE) method. The reaction of (Ga) occurred very seriously, and a large amount of silicon (Si) was detected in the gallium nitride (GaN) thin film. Therefore, in this case, a useful nitride film could not be obtained. On the other hand, in the present invention, a nitride film having high purity can be obtained by growing an oxide film 11a on the surface of the aluminum nitride (AlN) thin film 11 to completely protect the surface and then growing gallium nitride (GaN).

As described above, the present invention grows an aluminum nitride (AlN) thin film serving as a buffer layer on a silicon substrate, and thermally oxidizes the surface, and halide vapor phase growth on an aluminum nitride (AlN) thin film whose surface is protected by a thermal oxide film. By forming a gallium nitride (GaN) thin film by the (HVPE) method, a nitride film having high purity can be obtained.

The present invention uses a silicon substrate having a low thermal expansion coefficient difference from gallium nitride (GaN) compared to a sapphire substrate and having a low cost, in particular, a large area substrate. Therefore, by growing the nitride film single crystal on the silicon substrate having such an advantage, it is possible to apply industrially to create a large market economically with the technical ripple effect. For example, short wavelength laser diodes (LDs) such as blue and ultraviolet (UV), electronic devices applicable to the ultra high frequency band, and the like can be manufactured at low cost.

Claims (7)

Forming a buffer layer on the silicon substrate to buffer lattice mismatch with the substrate; Performing a thermal oxidation process to grow an oxide film on the surface of the silicon substrate and the buffer layer, respectively; Forming a nitride film on the oxide film grown on the surface of the buffer layer; And Removing the silicon substrate and the oxide film grown on the surface thereof. The method of manufacturing a nitride semiconductor substrate according to claim 1, wherein the buffer layer is an aluminum nitride (AlN) thin film and grown by molecular beam epitaxy. The silicon substrate of claim 1, wherein the silicon substrate is washed with H ₂ SO ₄ / H ₂ O solution mixed at 4: 1 and H ₂ O / HF solution mixed at 100: 1 before forming the buffer layer. The manufacturing method of the nitride semiconductor substrate. The method of claim 1, wherein the thermal oxidation step is performed at a temperature of 800 to 1100 ℃. The method of claim 1, wherein the nitride film is formed by any one of molecular beam deposition, sputtering, electron beam deposition, organometallic chemical vapor deposition, and halide vapor phase growth (HVPE). The method of claim 1, wherein the nitride film is one of GaN, InN, AlN, AlGaN, and InGaN. The method of claim 1, wherein the silicon substrate is removed by wet etching.