CN104060323A - Method for obtaining self-supported GaN monocrystal by preparing substrate with N-sided conical structure - Google Patents

Abstract

The invention provides a method for realizing the self-stripping and obtaining self-supported GaN monocrystal by preparing a substrate with an N-sided conical structure. The method comprises the following steps: (1) epitaxially growing a GaN membrane on the substrate to form a GaN epitaxial wafer; (2) conducting Ga side corrosion of the GaN epitaxial wafer by adopting chemical wet-process corrosion to form a corrosion pit reaching the substrate; (3) preparing a substrate for which a conical structure with an apex facing towards the substrate is on the N side of the GaN; (4) placing the prepared GaN epitaxial wafer into water so as to stop the formation of the conical structure; (5) epitaxially growing GaN monocrystal on the GaN epitaxial wafer through a hydride vapor phase; and (6) after finishing the growing of the GaN monocrystal, conducting cooling to realize the self-stripping from the substrate, thus obtaining the self-supported GaN monocrystal. The method has the characteristics of being low in cost and simple and easy, and the high-quality GaN monocrystal can be obtained.

Description

Method for Obtaining Self-supporting GaN Single Crystal by Preparing N-face Tapered Structure Substrate

technical field

The invention relates to a method for obtaining a self-exfoliating gallium nitride (GaN) single crystal. The method is to grow a self-supporting GaN single crystal by preparing an N-face GaN tapered structure substrate, and belongs to the field of semiconductor materials.

Background technique

Gallium Nitride (GaN), as a typical third-generation semiconductor material, has received widespread attention due to its excellent properties such as wide direct bandgap and high thermal conductivity. The most important physical feature that distinguishes gallium nitride from the first-generation and second-generation semiconductor materials is that it has a wider forbidden band (at room temperature, its forbidden band width is 3.4eV), which can emit blue light with a shorter wavelength; It has the characteristics of high breakdown voltage, high electron mobility, stable chemical properties, high temperature resistance, corrosion resistance, etc., so it is very suitable for making radiation-resistant, high-frequency, high-power and high-density integrated electronic devices as well as blue, green and ultraviolet optoelectronics device. Therefore, the research and application of GaN semiconductor materials has become the frontier and hotspot of global semiconductor research.

Due to the current lack of GaN single crystal substrate materials, GaN-based devices are generally grown on heterogeneous substrates, and the resulting lattice mismatch and thermal mismatch lead to residual stress in the device that affects its performance. In order to further improve device performance, it is necessary to obtain high-quality self-supporting GaN single crystal substrate materials, and the HVPE (Hydride Vapor Phase Epitaxy) growth method is considered to be a suitable GaN single crystal growth method. The commonly used method to remove the HVPE grown GaN single crystal substrate is to use laser lift-off technology to lift the thicker GaN from the sapphire substrate. However, this method requires large-thickness, high-quality, crack-free HVPE-GaN, which is difficult for heteroepitaxial GaN on sapphire and other substrates. By preparing a substrate with a certain structure, the stress caused by the mismatch can be reduced, and the HVPE-GaN can be detached from the substrate during the cooling process. This idea is also widely used. Generally speaking, the purpose of common processing methods is to add a flexible buffer layer between the substrate and HVPE grown GaN [Hyun-Jae Lee, et al, Applied Physics Letter91(2007) 192108], or leave a gap [Y. Oshima, et al, phys.stat.sol.(a), 194(2002) 554-558], or the use of periodic nano-patterned substrates to reduce the contact area between GaN and the substrate [C.L.Chao, Appl.Phys.Lett .95(2009)051905]. These methods can help the GaN single crystal grown by HVPE to be self-exfoliated from the substrate during the cooling process to obtain a self-supporting GaN single crystal substrate, but these methods involve complex photolithography, Epitaxy and other processes.

Contents of the invention

The present invention aims at the deficiencies in the existing self-exfoliating substrate preparation technology for obtaining self-supporting GaN single crystals, and provides a self-exfoliating substrate with a simple preparation process and self-exfoliating effect by preparing N-face GaN tapered substrates to obtain self-supporting GaN single crystals. crystal method.

The method for obtaining a self-supporting GaN single crystal by preparing an N-face tapered substrate of the present invention comprises the following steps:

(1) Epitaxially grow GaN thin films with a thickness of 2 μm to 5 μm on c-plane sapphire substrates or 6H-SiC substrates by metal organic chemical vapor deposition (MOCVD) to obtain GaN epitaxial wafers.

(2) The Ga surface of the GaN epitaxial wafer is etched by a wet etching method to form an etching pit reaching the substrate. The wet etching adopts one of the following methods:

a. Etching the GaN epitaxial wafer at 180-220°C with a H ₃ PO ₄ solution with a mass concentration of 70%-85%, and the etching time is 10 minutes-15 minutes;

b. Using a mixed acid of concentrated phosphoric acid and concentrated sulfuric acid in a volume ratio of 1:1-1:5, etch the GaN epitaxial wafer at 170-270°C for 10-20 minutes;

(3) The epitaxial wafer processed in step (2) is prepared to have a conical structure with an apex facing the substrate on the N surface, using one of the following methods:

a. Immerse in H ₃ PO ₄ solution with a mass concentration of 50%-70%, heat to 80-100°C for 60-120 minutes;

b. Immerse in a KOH solution with a concentration of 2-8mol/L, heat to 80-100°C and keep for 60-180 minutes.

(4) taking out the GaN epitaxial wafer processed in step (3) from the solution and putting it into water to stop the formation of the tapered structure, and ending the preparation process of the N-face tapered structure;

(5) After cleaning and drying the epitaxial wafer treated in step (4), put it into a hydride vapor phase epitaxy (HVPE) growth system to grow GaN single crystal;

(6) After the GaN single crystal growth is completed, the GaN single crystal is self-stripped from the sapphire substrate through the cooling process of the hydride vapor phase epitaxy (HVPE) growth system, and a self-supporting GaN single crystal is obtained.

The above process uses step (1) to use wet etching to form hexagonal etching pits on the Ga surface of the GaN layer on epitaxial wafers of different substrates (sapphire or 6H-SiC) to penetrate the GaN film. When step (3) is performed, the N surface of the GaN thin film forms a cone-shaped structure because of its low surface energy. After HVPE growth, there are gaps between the conical structures, which block the extension of dislocations and leave gaps for stress release. At the same time, since the apex of the tapered structure faces the sapphire substrate, the contact area between GaN and the sapphire substrate is reduced. When the thickness of HVPE-GaN is large enough, self-exfoliation after cooling can be achieved to obtain a self-supporting GaN single crystal.

The invention has the characteristics of low cost, simple operation, high-quality GaN single crystal can be obtained, and is suitable for mass production.

Description of drawings

Fig. 1 is a flow chart of the method for obtaining a self-supporting GaN single crystal by preparing an N-face tapered substrate in the present invention.

Fig. 2 is a schematic diagram of preparing an N-face conical substrate and obtaining a self-supporting GaN single crystal according to the present invention.

Fig. 3 is a scanning electron microscope (SEM) image of a dodecahedron-shaped structure formed by the N surface of the GaN film in contact with the sapphire substrate.

Fig. 4 is a scanning electron microscope (SEM) image of the obtained self-supporting GaN single crystal N-face morphology.

Among them: 1. Sapphire substrate, 2. GaN film, 3. GaN film after wet etching Ga surface, 4. GaN film with tapered structure formed on N surface, 5. GaN single crystal grown by HVPE.

Detailed ways

In the present invention, a method for obtaining a self-supporting GaN single crystal by preparing an N-face cone-shaped substrate is shown in FIG. 1 and FIG. 2 . The specific preparation process is as described in the following examples.

Example 1

(1) Epitaxially grow a GaN thin film 2 with a thickness of 2 μm-5 μm on the c-plane sapphire substrate 1 by MOCVD method, see (a) figure in FIG. 2 to form a GaN epitaxial wafer;

(2) Immerse the GaN epitaxial wafer grown by MOCVD in an H ₃ PO ₄ solution with a concentration of 80% at 200° C. for 10 minutes;

(3) Immerse the epitaxial wafer treated in the previous step in a H ₃ PO ₄ solution with a concentration of 60%, and heat it to 100° C. for 80 minutes;

(4) Take the etched GaN epitaxial wafer out of the H ₃ PO ₄ solution quickly and put it into water to stop its corrosion, and obtain a GaN thin film 4 with a tapered structure (see (c) in FIG. 2 ). The N-face of the GaN thin film in contact with the sapphire substrate (the N-face of the GaN thin film refers to the face connected to the sapphire substrate 1) forms a dodecahedral pyramid structure, and the structural morphology is shown in FIG. 3 .

(5) After the etched GaN epitaxial wafer is washed and dried with deionized water, it is put into a HVPE growth system to epitaxially grow GaN single crystal 5, see (d) in FIG. 2 .

(6) After the epitaxial growth of the GaN single crystal 4 is completed, the GaN single crystal is self-stripped from the sapphire substrate 1 through the HVPE cooling process to obtain a self-supporting GaN single crystal, as shown in (e) in FIG. 2 . The scanning electron microscope (SEM) image of the N surface of the self-supporting GaN single crystal is shown in Fig. 4.

Example 2

The difference between this embodiment and embodiment 1 is:

In step (1), a GaN thin film is epitaxially grown on a 6H-SiC substrate to form a GaN epitaxial wafer.

In step (2), the GaN epitaxial wafer is etched in a 180°C 85% H ₃ PO ₄ solution for 12 minutes, or immersed in a 220°C 70% H ₃ PO ₄ solution for 15 minutes.

In step (3), the epitaxial wafer is immersed in a H ₃ PO ₄ solution with a mass concentration of 50%, heated to 80°C for 120 minutes, or immersed in a 70% H ₃ PO ₄ solution, heated to 90°C for 60 minutes .

Example 3

The difference between this embodiment and embodiment 1 is:

In step (2), the GaN epitaxial wafer is immersed in the mixed acid of concentrated phosphoric acid and concentrated sulfuric acid in a volume ratio of 1:1, and etched at 220 ° C for 15 minutes, or the GaN epitaxial wafer is immersed in concentrated phosphoric acid and concentrated sulfuric acid according to the volume ratio. In a mixed acid with a ratio of 1:2.5, etch at 170°C for 20 minutes, or immerse the GaN epitaxial wafer in a mixed acid with a volume ratio of 1:5 between concentrated phosphoric acid and concentrated sulfuric acid, and etch at 270°C for 10 minutes. This allows the bottom of the etch pit to reach the substrate surface.

In step (3), the epitaxial wafer is immersed in a KOH solution with a concentration of 5mol/L and heated to 90°C for 120 minutes, or the epitaxial wafer is immersed in a KOH solution with a concentration of 2mol/L and heated to 100°C for 180°C. minutes, or immerse the epitaxial wafer in a KOH solution with a concentration of 8 mol/L, and heat it to 80°C for 60 minutes. In this way the N-face can form a cone-shaped structure with six triangular faces, the vertices of which face the substrate.

It can be seen from the above specific examples that changing the wet etching process and the formation process of the N-face conical structure can obtain conical structures with different shapes, and perform HVPE growth of GaN monolayer on the substrate with the top-down conical structure on the N-face. crystal, which reduces the contact area between GaN and the heterogeneous substrate, leaving a gap to release the stress, and obtain a high-quality GaN single crystal with complete stress release. When the thickness of the GaN single crystal grown by HVPE is large, by reducing the GaN single crystal The interface between the crystal and the substrate is self-stripping, and a self-supporting GaN single crystal is obtained.

Claims (5)

1. a method that obtains Free-standing GaN monocrystalline by preparing N face cone shape structured substrate, is characterized in that, comprises the following steps:

(1) method thick GaN film of epitaxy 2 μ m-5 μ m on c surface sapphire substrate or 6H-SiC substrate of employing metal organic chemical vapor deposition, obtains GaN epitaxial wafer.

(2) adopt the method for wet etching to carry out the corrosion of Ga face to GaN epitaxial wafer, form the corrosion pit that arrives substrate;

(3) epitaxial wafer of processing through step (2) is carried out to N mask and have the preparation of summit towards the pyramidal structure of substrate;

(4) GaN epitaxial wafer after treatment step (3) is taken out and puts into water to stop the formation of pyramidal structure from solution, finish N face pyramidal structure preparation process;

(5) after epitaxial wafer after treatment step (4) is cleaned, dried up, put into hydride vapor phase epitaxy growth system and carry out the growth of GaN monocrystalline;

(6) GaN single crystal growing finish after through the temperature-fall period of perhydride vapor phase epitaxial growth system, GaN monocrystalline from peeling off, obtains Free-standing GaN monocrystalline Sapphire Substrate.

2. the method that obtains according to claim 1 Free-standing GaN monocrystalline by preparing N face cone shape structured substrate, is characterized in that, in described step (2), the method for wet etching is the H of functional quality concentration 70%-85% ₃pO ₄solution corrodes GaN epitaxial wafer at 180-220 DEG C, etching time 10 minutes-15 minutes.

3. obtain according to claim 1 the method for Free-standing GaN monocrystalline by preparing N face cone shape structured substrate, it is characterized in that, in described step (2), the method for wet etching is to use strong phosphoric acid and the vitriol oil mixing acid of 1:1-1:5 ratio by volume, at 170-270 DEG C, GaN epitaxial wafer is corroded 10 minutes-20 minutes.

4. obtain according to claim 1 the method for Free-standing GaN monocrystalline by preparing N face cone shape structured substrate, it is characterized in that, in described step (3), carrying out N mask has summit towards the method for the preparation of the pyramidal structure of substrate to be, the H that immersion mass concentration is 50%-70% ₃pO ₄solution, is heated to 80-100 DEG C and keeps 60 minutes-120 minutes.

5. obtain according to claim 1 the method for Free-standing GaN monocrystalline by preparing N face cone shape structured substrate, it is characterized in that, in described step (3), carrying out N mask has summit towards the method for the preparation of the pyramidal structure of substrate to be, immersing concentration is the KOH solution of 2-8mol/L concentration, is heated to 80-100 DEG C and keeps 60 minutes-180 minutes.