CN103866380B - A kind ofly use graphical annealing loose structure to carry out the method for GaN crystal growth - Google Patents

Abstract

Use graphical annealing loose structure to carry out a method for GaN crystal growth, comprise the following steps: (1) prepares SiO on GaN epitaxial wafer₂Graphic mask; (2) will be with SiO₂GaN epitaxial wafer high annealing in vacuum drying oven of graphic mask; (3) by annealing after with SiO₂The GaN epitaxial wafer of graphic mask forms porous GaN substrate; (4) by porous GaN substrate HVPE epitaxial growth, obtain GaN monocrystalline. The method is by the preparation of GaN epitaxial wafer graphic mask, high annealing, cleaning-drying and the growth of HVPE method, finally obtain high-quality GaN monocrystalline, and be conducive to epitaxially grown GaN monocrystalline from peeling off formation self-supported substrate, this method is made simple, technical maturity, can improve the quality of epitaxial growth GaN monocrystalline, be conducive to realize certainly peeling off of GaN monocrystalline and foreign substrate, be applicable to batch production.

Description

A Method for GaN Single Crystal Growth Using Patterned Annealed Porous Structure

technical field

The invention relates to a method for preparing a GaN growth substrate with a patterned porous structure through an annealing process, and then using a HVPE (Hydride Vapor Phase Epitaxy) method to grow a GaN single crystal, belonging to the technical field of GaN single crystal growth.

Background technique

With the rapid development of the electronic information industry, modern electronic technology puts forward new requirements for the performance of semiconductor materials under high temperature, high frequency, and high voltage conditions. The third-generation semiconductor materials represented by GaN have a large High electric field, high thermal conductivity, high drift velocity of saturated electrons, small dielectric constant, strong radiation resistance, good chemical stability and other properties, it has been widely used in light-emitting diodes (LEDs), laser diodes (LDs) and other fields .

Due to the lack of GaN bulk single crystals, the current commercialized GaN-based devices basically use hetero-epitaxy, but due to the large thermal expansion coefficient and lattice constant mismatch with the heterogeneous substrate, the epitaxially grown devices have The high dislocation density seriously restricts the improvement of device performance. Fabrication of self-supporting GaN substrates followed by fabrication of GaN-based devices on homogenous substrates has become a well-recognized approach to improve device performance. At present, the main method used is to first obtain better bulk or quasi-bulk crystals, and then further process to obtain better quality crystal slices (self-supporting substrates) for homogeneous growth of devices.

The Hydride Vapor-Phase Epitaxy (HVPE) method is considered to be one of the most potential methods to obtain a self-supporting substrate. This method can be traced back to around 1970, and its process is mainly deposited on a heterogeneous substrate. For thicker GaN epitaxial layers, bulk crystals are obtained by laser lift-off or self-lift-off techniques. This method has the advantages of fast growth and low cost. Due to the use of heterogeneous substrate epitaxy, there is lattice mismatch and thermal mismatch between the substrate and the growth layer, so during the growth process and cooling process Various defects will be generated, and the dislocation density will be relatively large.

The current method for HVPE to improve crystal quality is to use buffer layers and insertion layers to reduce the stress caused by lattice mismatch and thermal mismatch between the GaN layer and the substrate. One of the most successful studies is Hitachi's use of void-assisted separation (void-assistedseparation, VAS) [see Y.Oshima, etal, phys.stat.sol. (a), 194 (2002) 554-558], obtained 2-3 inches thick pure GaN layer around 600μm in diameter. This method is to cover a layer of Ti nano-network on the substrate obtained by the MOCVD method, and form a TiN insertion layer after high-temperature annealing and ammoniation to form a porous structure with vacancies. The small mismatch stress effect can realize the self-stripping of the substrate. The porous structure plays a vital role in the preparation of self-stripping GaN single crystals. Foreign researchers have adopted various methods to introduce vacancies to improve the crystal quality [Y.Fu, et al, Applied Physics Letters 86 (4), 043108 (2005), C . Hennig, Journal of Crystal Growth 310(5), 911-915 (2008)]. However, the processes of these methods are complicated, and an independent and simple new method is urgently needed to prepare porous substrates, so as to improve the quality of GaN grown by HVPE.

Contents of the invention

Aiming at the important role of the porous structure substrate on the growth of GaN single crystal and the shortcomings of the existing GaN single crystal growth technology, the present invention provides a simple and efficient method for GaN single crystal growth using a patterned annealed porous structure, which can Improving the quality of epitaxially grown GaN single crystal is beneficial to realize the self-exfoliation of GaN single crystal and heterogeneous substrate.

The method for growing a GaN single crystal using a patterned annealed porous structure of the present invention comprises the following steps:

(1) Prepare a SiO ₂ pattern mask on the GaN epitaxial wafer. The thickness of the GaN epitaxial wafer is 2 μm-5 μm. The SiO ₂ mask has openings arranged in a square or hexagonal arrangement. The thickness of the SiO ₂ mask is 50nm-100nm , the opening period is 60μm-150μm, and the opening diameter is 10μm-15μm;

(2) Anneal the GaN epitaxial wafer with a SiO ₂ pattern mask in a vacuum furnace at 1200-1300°C for 60-90 minutes at high temperature;

(3) Ultrasonic clean the annealed GaN epitaxial wafer with a SiO ₂ pattern mask in deionized water for 5 minutes, and then rinse it in concentrated phosphoric acid (phosphoric acid with a mass ratio of more than 80%) for 1 to 5 minutes. Rinse with deionized water; then wash in acetone at 25°C-53°C and ethanol at 25°C-73°C for 1 minute to 5 minutes, rinse with deionized water, and rinse with hydrofluoric acid (mass ratio 40%) for 20 Seconds to 5 minutes to remove the SiO ₂ layer, rinse it with deionized water, and dry it with nitrogen to form a porous GaN substrate;

(4) The porous GaN substrate is grown by HVPE epitaxy to obtain a GaN single crystal.

The present invention obtains a high-quality GaN single crystal through the preparation of a GaN epitaxial wafer pattern mask, high-temperature annealing, cleaning and drying, and HVPE growth, and is conducive to the self-exfoliation of the epitaxially grown GaN single crystal to form a self-supporting substrate. The method is simple to manufacture and has a mature process, can improve the quality of epitaxially grown GaN single crystals, is beneficial to realizing self-stripping of GaN single crystals and heterogeneous substrates, and is suitable for mass production.

Description of drawings

FIG. 1 is a flow chart of the method for GaN single crystal growth using patterned annealing to obtain a porous structure in the present invention.

Fig. 2 is a cross-sectional SEM (scanning electron microscope) image of a porous structure substrate prepared on a sapphire substrate.

Fig. 3 is a cross-sectional SEM (scanning electron microscope) image of a GaN single crystal grown by HVPE using a porous structure substrate.

Fig. 4 is the PL (photoluminescence) spectrum of the sample prepared by using pattern annealed GaN substrate with porous structure and GaN substrate grown by MOCVD method in the present invention.

Fig. 5 is a photomicrograph (×200) of the back side of the self-peeling substrate prepared in the present invention.

detailed description

Example 1

Figure 1 shows the process of GaN single crystal growth using a patterned annealed porous structure in the present invention. The growth process includes three stages: SiO ₂ pattern mask preparation, high temperature annealing and cleaning, and HVPE growth of GaN single crystal. Specific steps are as follows:

(1) On the GaN epitaxial wafer prepared by MOCVD (metal organic compound chemical vapor deposition), the SiO ₂ pattern mask is prepared by photolithography and wet etching. The SiO ₂ pattern is a square arrangement of openings, and the GaN epitaxial wafer The thickness of the SiO2 mask is 2 μm, the thickness of the SiO ₂ mask is 50 nm, the opening period is 60 μm, and the opening diameter is 10 μm;

(2) Anneal the GaN epitaxial wafer with a SiO ₂ pattern mask in a vacuum furnace at a high temperature of 1200 ° C for 90 min;

(3) Ultrasonic the annealed GaN epitaxial wafer with a SiO ₂ pattern mask in deionized water for 5 minutes, then rinse it in concentrated phosphoric acid (phosphoric acid with a mass ratio of more than 80%) for 5 minutes, rinse it with deionized water, and then in Wash in 50°C acetone and 50°C ethanol solutions for 2 minutes, rinse with deionized water, then rinse with hydrofluoric acid (commercially available hydrofluoric acid with a mass ratio of 40%) for 1 minute to remove the SiO ₂ layer, and rinse with deionized water , nitrogen drying to form a porous GaN substrate;

(4) Put the cleaned porous GaN substrate into a HVPE (Hydride Vapor Phase Epitaxy) growth system for epitaxial growth to obtain a GaN single crystal.

Fig. 2 is a cross-sectional SEM (scanning electron microscope) image of a porous structure substrate prepared on a sapphire substrate. Figure 3 is a cross-sectional SEM (scanning electron microscope) image of a GaN single crystal prepared by HVPE growth using a porous substrate. It can be seen from the figure that there are so-called vacancies (voids) at the growth interface. These vacancies effectively prevent the upward extension of dislocations, improve the crystal quality, and at the same time facilitate the stress release caused by thermal mismatch to produce self-stripping.

Fig. 4 is the PL (photoluminescence) spectrum of GaN single crystal prepared by using patterned annealed GaN substrate with porous structure and GaN substrate grown by MOCVD method prepared by the present invention. It can be seen that both the pattern annealed porous GaN substrate and the GaN substrate grown by the ordinary MOCVD method have a luminescence peak at 363nm. Under the same test conditions, the GaN single crystal prepared using the porous substrate emits stronger. There is no luminescence peak in the yellow region of 600nm, which shows that the use of pattern annealing porous structure can effectively improve the quality of GaN single crystal; There is an obvious pattern structure on the back of the bottom, which shows that the patterned annealed porous structure used in the present invention plays a very good role in the self-stripping process.

Example 2

The difference between this embodiment and embodiment 1 is:

In step (1), the thickness of the GaN epitaxial wafer is 3 μm, the pattern of the SiO ₂ pattern mask is a hexagonal arrangement of openings, the thickness of the SiO ₂ mask is 100 nm, the opening period is 150 μm, and the opening diameter is 12 μm;

The high-temperature annealing temperature in step (2) is 1300°C, and the annealing time is 70 minutes;

In step (3), the rinsing time of concentrated phosphoric acid is 1 min; the rinsing time is 1 min in 53°C acetone and 73°C ethanol solutions respectively; the rinsing time of hydrofluoric acid is 20 seconds.

Example 3

The difference between this embodiment and embodiment 1 is:

In step (1), the thickness of the GaN epitaxial wafer is 5 μm, the thickness of the SiO ₂ pattern mask is 60 nm, the opening period is 120 μm, and the opening diameter is 15 μm;

The high-temperature annealing temperature in step (2) is 1250°C, and the annealing time is 80 minutes;

In step (3), the rinsing time of concentrated phosphoric acid is 4 minutes; the rinsing time is 5 minutes respectively in 25°C acetone and 25°C ethanol solutions; the rinsing time of hydrofluoric acid is 5 minutes.

Example 4

The difference between this embodiment and embodiment 1 is:

In step (1), the thickness of the GaN epitaxial wafer is 4 μm, the pattern of the SiO ₂ pattern mask is a hexagonal arrangement of openings, the thickness of the SiO ₂ mask is 85 nm, the opening period is 80 μm, and the opening diameter is 13 μm;

The high-temperature annealing temperature in step (2) is 1300°C, and the annealing time is 60 minutes;

In step (3), the rinsing time of concentrated phosphoric acid is 2 minutes; the rinsing time is 3 minutes in 35°C acetone and 40°C ethanol solutions respectively; the rinsing time of hydrofluoric acid is 3 minutes.

Within the scope of each parameter given by the present invention, GaN single crystal substrates with different patterned annealed porous structures can be obtained by changing the specific values of each parameter, and the various patterned annealed structure GaN substrates obtained are utilized HVPE method High-quality GaN single crystal can be obtained by epitaxial growth, and the grown GaN can be self-exfoliated from the substrate.

Claims (1)

1. a method that uses graphical annealing loose structure to carry out GaN crystal growth, is characterized in that, comprises the following steps:

(1) on GaN epitaxial wafer, prepare SiO₂Graphic mask, the thickness of GaN epitaxial wafer is 2 μ m-5 μ m, SiO₂FigureMask is the perforate of Square array or the perforate of Hexagonal array, SiO₂Graphic mask thickness is 50nm-100nm, the perforate cycleBe 60 μ m-150 μ m, opening diameter is 10 μ m-15 μ m;

(2) will be with SiO₂The GaN epitaxial wafer of graphic mask in vacuum drying oven, high annealing 60 minutes at 1200-1300 DEG C-90 minutes;

(3) by annealing after with SiO₂The GaN epitaxial wafer of graphic mask cleans 5 minutes in deionized water for ultrasonic, thenRinsing 1 minute-5 minutes in SPA at mass ratio more than 80%, rinses well by deionized water; Then at 25 DEG C-53 DEG C thirdIn ketone and 25 DEG C of-73 DEG C of ethanolic solutions, clean respectively 1 minute-5 minutes, rinse well by deionized water, then use hydrofluoric acid rinsingWithin 20 seconds-5 minutes, remove SiO₂Layer, rinses well by deionized water, and nitrogen is dried, and forms porous GaN substrate;

(4) porous GaN substrate is passed through to HVPE epitaxial growth, obtain GaN monocrystalline.