Growth method of GaN thick film for improving laser lift-off efficiency

Abstract

The application relates to a GaN thick film growth method for improving laser stripping efficiency. The method comprises the following steps: (1) adopting an oxalic acid solution to perform etching on a sapphire substrate with GaN seeds, and forming uniform nanometer-sized hollows; (2) introducing ammonia gas, and heating to a GaN thick film growth temperature under the protection of the ammonia gas; (3) growing a GaN thick film on the sapphire substrate with the GaN seeds through a metal organic chemical vapor deposition method or a hydride vapor phase epitaxy method, bonding the GaN thick film to a silicon wafer, stripping the substrate through laser, and obtaining the GaN thick film. The application forms nanometer-sized sponge branch-shaped hollows on the sapphire substrate with the GaN seeds through electrochemical etching, forms weak connection between lattices at the interface, effectively reduces laser threshold energy during laser stripping, significantly improves laser stripping efficiency by 50%, and meanwhile, the GaN thick film which is stripped off has good toughness, high quality and is not easy to be broken, and the qualified rate is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a GaN thick film growth method for improving laser stripping efficiency, and belongs to the field of optoelectronic power devices. BACKGROUND

[0002] GaN material is an ideal material for making optoelectronic devices, especially blue-green LED and LD. Such light sources have broad application prospects and huge market potential in high-density optical information storage, high-speed laser printing, full-color dynamic high-brightness light display, solid-state lighting light source, high-brightness signal detection, communication, etc. In addition, GaN semiconductor material is also an ideal material for making high-temperature, high-frequency and high-power devices. GaN is a representative of nitride materials, and is one of the excellent wide-bandgap III-V compound semiconductor materials, and is one of the advanced semiconductor materials in the world today.

[0003] Laser stripping technology is one of the important methods to obtain GaN thick film. Laser stripping technology uses ultraviolet waveband laser light source (EgIaser>EgGaN) to irradiate the sample through the sapphire substrate, so that the GaN at the sapphire and GaN interface absorbs the laser energy, the temperature of the GaN material rises rapidly, and thermal decomposition occurs to generate metal Ga and N2. N2 escapes, and the sample is heated to the melting point of metal Ga (30℃), so that Ga melts, and the sapphire and GaN thick film are separated.

[0004] The GaN-based epitaxial wafer is bonded to other high-conductivity and high-thermal-conductivity substrates before stripping, and then combined with laser stripping technology, GaN-based optoelectronic and electronic devices without sapphire substrate can be obtained. Since laser stripping technology can fundamentally solve the adverse effects of sapphire substrate on GaN-based LED, and has high efficiency and low damage, it has become a new research hotspot.

[0005] Chinese patent document CN102418143A discloses a method for preparing self-stripping GaN single crystal by H3PO4 etching substrate, comprising the following steps: (1) using metal organic chemical vapor deposition method to epitaxially grow 2-10 mu m thick GaN film on sapphire substrate, forming GaN epitaxial wafer; (2) immersing GaN epitaxial wafer into H3PO4 solution with temperature of 220-280 DEG C and concentration of 70%-90% for 3-30 minutes; (3) quickly taking out the etched GaN epitaxial wafer from H3PO4 solution and putting into cold water to stop etching; (4) after cleaning and drying the etched GaN epitaxial wafer, putting into hydride vapor phase epitaxy growth system to epitaxially grow GaN single crystal; (5) after epitaxially growing GaN single crystal, through the cooling process of hydride vapor phase epitaxy growth system, GaN single crystal realizes self-stripping from sapphire substrate, and self-supporting GaN single crystal is obtained. However, the acid etching ability of the patent is too strong, although it can make GaN single crystal self-stripping, but the self-stripped GaN single crystal is very easy to crack, resulting in very low yield of GaN thick film product.

[0006] In the current laser stripping technology, since the epitaxial gallium nitride on sapphire has good density, a higher laser stripping energy is required, and the higher laser stripping energy will lead to cracking or fragmentation of the epitaxial wafer. Under the current technical conditions, the laser stripping power density is required to be higher, and the stripping efficiency is lower, so it is necessary to propose a GaN thick film growth method for improving the laser stripping efficiency. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a GaN thick film growth method for improving the laser stripping efficiency. The method includes the following steps:

[0008] The technical scheme of the present application is as follows:

[0009] A GaN thick film growth method for improving the laser stripping efficiency, comprising the following steps:

[0010] (1) using oxalic acid solution to etch the sapphire substrate with GaN seed crystal, forming uniform nanometer cavities;

[0011] (2) introducing ammonia gas, and heating to GaN thick film growth temperature under the protection of ammonia gas;

[0012] (3) growing GaN thick film on the sapphire substrate with GaN seed crystal by metal organic chemical vapor deposition or hydride vapor phase epitaxy, bonding the GaN thick film to the silicon wafer, laser peeling the substrate to obtain the GaN thick film.

[0013] According to the application, preferably, the concentration of the oxalic acid solution in step (1) is 0.3-2 mol / L.

[0014] According to the application, preferably, the corrosion in step (1) is electrochemical corrosion, the corrosion voltage is 15 V, and the corrosion time is 5-30 min; further preferably, the corrosion time is 15 min.

[0015] According to the application, preferably, the nano-hollows in step (1) are in the shape of sponge branches and are uniformly distributed on the surface of the sapphire substrate.

[0016] According to the application, preferably, the GaN seed crystal in step (1) has a growth thickness of 0.5-5 μm.

[0017] According to the application, preferably, the ammonia flow in step (2) is 10-100 L, and the growth temperature is 1050-1150 ℃.

[0018] According to the application, preferably, in step (2), when the organic chemical vapor deposition method is used, the growth pressure is controlled to be between 20-300 mbar, and the V / III ratio is controlled to be between 150-1500.

[0019] According to the application, preferably, in step (2), when the hydride vapor phase epitaxy method is used, the growth pressure is controlled to be between 800-1000 mbar, and the V / III ratio is controlled to be between 20-200.

[0020] According to the application, preferably, in step (3), the material used for bonding is epoxy resin or graphite glue, the bonding pressure is 0.01 MP-0.02 MP, the bonding temperature is 50-200 ℃, and the thickness of the bonding material is 2-10 μm.

[0021] Further preferably, the material used for bonding is graphite glue, and the thickness of the graphite glue is 5 μm. The graphite glue has better thermal conductivity and can reduce the cracking of the thick film GaN.

[0022] According to the application, preferably, in step (3), the thickness of the GaN thick film before bonding is 500-700 μm, and the thickness of the GaN thick film obtained after peeling is 495-695 μm.

[0023] The details of the application can be implemented by using the existing technology.

[0024] The application has the following beneficial effects:

[0025] The application provides a GaN thick film growth method for improving laser stripping efficiency, wherein nano-sized sponge dendritic cavities are etched out on a sapphire substrate with GaN seed crystals through an electrochemical etching scheme, the nano-sized sponge dendritic cavities are uniformly distributed, then a GaN thick film is grown on the sapphire substrate with the GaN seed crystals and the cavities to 500-700 μm, a weak connection between lattices is formed at the interface, the laser threshold energy is effectively reduced when laser stripping, the laser stripping efficiency is significantly improved by 50%, meanwhile, the GaN thick film peeled off has good toughness and high quality and is not easy to break, the qualified rate is significantly improved and reaches 70%, and the production cost is effectively reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The figure is a schematic diagram of laser stripping of the GaN thick film of the application.

[0027] Figure 2 The figure is a schematic diagram of the sapphire substrate after oxalic acid etching of the application.

[0028] Figure 3 The figure is a schematic diagram of the nano-sized sponge dendritic cavities of the application. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and advantages of the application more clear, the application is further described below through embodiments and in conjunction with the drawings, but is not limited thereto, and the application not described in detail is according to the conventional technology in the field.

[0030] Embodiment 1

[0031] As shown in the figure, a GaN thick film growth method for improving laser stripping efficiency comprises the following steps: Figures 1 to 3

[0032] (1) an oxalic acid solution with a concentration of 1.5 mol / L is used to electrochemically etch a sapphire substrate with 3 μm GaN seed crystals, and nano-sized sponge dendritic cavities are formed on the surface of the sapphire substrate; the etching voltage is 15 V, and the etching time is 15 min;

[0033] (2) 20 L of ammonia gas is introduced, and the temperature is raised to 1100 ℃ under the protection of the ammonia gas;

[0034] (3) a 500 μm GaN thick film is grown on the sapphire substrate with the GaN seed crystals through a metal organic chemical vapor deposition method, the GaN thick film is bonded to a silicon wafer through graphite glue, the substrate is laser stripped, and a 498 μm GaN thick film is obtained.

[0035] ​The growth pressure of the metal organic chemical vapor deposition method is 200 mbar, the V / III ratio is 800, the thickness of the graphite glue is 5 μm, the bonding pressure is 0.01 MP, and the bonding temperature is 100 °C.

[0036] Example 2

[0037] A GaN thick film growth method for improving laser stripping efficiency comprises the following steps:

[0038] (1) An oxalic acid solution with a concentration of 0.8 mol / L is used to perform electrochemical etching on a sapphire substrate with a 3 μm GaN seed crystal, to form uniform nanometer-sized sponge dendritic cavities on the surface of the sapphire substrate; the etching voltage is 15 V, and the etching time is 15 min;

[0039] (2) 20 L of ammonia gas is introduced, and the temperature is raised to 1100 °C under the protection of the ammonia gas;

[0040] (3) A 500 μm GaN thick film is grown on the sapphire substrate with the GaN seed crystal by using a hydride vapor phase epitaxy method, and then the GaN thick film is bonded to a silicon wafer by using graphite glue, the substrate is laser stripped, and a 498 μm GaN thick film is obtained.

[0041] The growth pressure of the hydride vapor phase epitaxy method is 900 mbar, the V / III ratio is 100, and the thickness of the graphite glue is 3 μm.

[0042] The bonding pressure is 0.01 MP, and the bonding temperature is 100 °C.

[0043] Example 3

[0044] A GaN thick film growth method for improving laser stripping efficiency comprises the following steps:

[0045] (1) An oxalic acid solution with a concentration of 0.3 mol / L is used to perform electrochemical etching on a sapphire substrate with a 1 μm GaN seed crystal, to form uniform nanometer-sized sponge dendritic cavities on the surface of the sapphire substrate; the etching voltage is 15 V, and the etching time is 15 min;

[0046] (2) 50 L of ammonia gas is introduced, and the temperature is raised to 1100 °C under the protection of the ammonia gas;

[0047] (3) A 600 μm GaN thick film is grown on the sapphire substrate with the GaN seed crystal by using a metal organic chemical vapor deposition method, and then the GaN thick film is bonded to a silicon wafer by using graphite glue, the substrate is laser stripped, and a 598 μm GaN thick film is obtained.

[0048] The growth pressure of the metal organic chemical vapor deposition method is 150 mbar, the V / III ratio is 300, and the thickness of the graphite glue is 5 μm.

[0049] Bonding pressure 0.015 MP, bonding temperature 150℃.

[0050] Example 4

[0051] A GaN thick film growth method for improving laser lift-off efficiency, comprising the following steps:

[0052] (1) Using a 2 mol / L oxalic acid solution to electrochemically etch a sapphire substrate with a 1 μm GaN seed crystal, forming a uniform nanometer-sized sponge branch-shaped cavity on the surface of the sapphire substrate; etching voltage 10 V, etching time 20 min;

[0053] (2) Introducing 80 L of ammonia, and under ammonia protection, heating to 1100℃;

[0054] (3) Growing a 600 μm GaN thick film on the sapphire substrate with the GaN seed crystal by metal organic chemical vapor deposition, and then bonding the GaN thick film to a silicon wafer by graphite glue, laser lifting off the substrate to obtain a 598 μm GaN thick film.

[0055] The growth pressure of the metal organic chemical vapor deposition is 100 mbar, and the V / III ratio is 1000; the thickness of the graphite glue is 5 μm.

[0056] Bonding pressure 0.02 MP, bonding temperature 200℃.

[0057] Comparative Example 1

[0058] A GaN thick film growth method, comprising the following steps:

[0059] Introducing 80 L of ammonia, and under ammonia protection, heating to 1100℃; growing a 600 μm GaN thick film on the sapphire substrate with the GaN seed crystal by metal organic chemical vapor deposition, and then bonding the GaN thick film to a silicon wafer by graphite glue, laser lifting off the substrate to obtain a 598 μm GaN thick film.

[0060] The growth pressure of the metal organic chemical vapor deposition is 200 mbar, and the V / III ratio is 800; the thickness of the graphite glue is 5 μm. Bonding pressure 0.01 MP, bonding temperature 100℃.

[0061] Comparative Example 2

[0062] A GaN single crystal was prepared according to the method disclosed in Chinese patent document CN102418143A.

[0063] Test Example

[0064] The same thickness of 600 μm GaN thick film is respectively grown by the method of embodiment 1, the comparative example 1 and the comparative example 2 of the present application, the growth sample is 10, and the laser stripping threshold energy of the GaN thick film and the qualified rate of the GaN thick film are counted, as shown in Table 1.

[0065] Table 1

[0066] Method Threshold energy (mJ / cm) Pass rate (%) Example 1 170 70％ Comparative Example 1 340 5％ Comparative Example 2 Self-stripping 10％

[0067] As shown in Table 1, the GaN thick film growth method provided by the present application can effectively reduce the laser stripping threshold energy of the GaN thick film, which is reduced by 50% compared with the comparative example 1, that is, the laser stripping efficiency is improved by more than 50%. At the same time, the GaN thick film peeled off by the GaN thick film growth method provided by the present application has good toughness and high quality, and is not easy to break, and the qualified rate reaches 70%, which is significantly improved compared with 5% of the comparative example 1 and 10% of the comparative example 2.

Claims

1. A GaN thick film growth method for improving laser lift-off efficiency, characterized by, The method comprises the following steps: (1) using oxalic acid solution to etch the sapphire substrate with GaN seed crystal to form uniform nanometer cavities; wherein the nanometer cavities are in the shape of sponge branches and are uniformly distributed on the surface of the sapphire substrate; (2) introducing ammonia gas, and heating to the GaN thick film growth temperature under the protection of the ammonia gas; (3) growing GaN thick film on the sapphire substrate with GaN seed crystal by metal organic chemical vapor deposition or hydride vapor phase epitaxy, bonding the GaN thick film to a silicon wafer, and laser peeling the substrate to obtain GaN thick film; wherein the material used for the bonding is epoxy resin or graphite glue, the bonding pressure is 0.01-0.02 MP, the bonding temperature is 50-200 DEG C, and the thickness of the bonding material is 2-10 microns; the thickness of the GaN thick film before the bonding is 500-700 microns, and the thickness of the obtained GaN thick film after the peeling is 495-695 microns.

2. The GaN thick film growth method for improving laser liftoff efficiency according to claim 1, wherein In step (1), the concentration of the oxalic acid solution is 0.3-2 mol / L, and the growth thickness of the GaN seed crystal is 0.5-5 microns.

3. The method for growing a GaN thick film with improved laser liftoff efficiency according to claim 1, wherein In step (1), the etching is electrochemical etching, the etching voltage is 15 V, and the etching time is 5-30 min.

4. The GaN thick film growth method for improving laser lift-off efficiency according to claim 3, wherein In step (1), the etching time is 15 min.

5. The method for growing a GaN thick film with improved laser liftoff efficiency according to claim 1, wherein In step (2), the ammonia gas flow is 10-100 L, and the growth temperature is 1050-1150 DEG C.

6. The method for growing a GaN thick film with improved laser liftoff efficiency according to claim 1, wherein In step (2), when the organic chemical vapor deposition method is used, the growth pressure is controlled to be 20-300 mbar, and the V / III ratio is controlled to be 150-1500.

7. The method for growing a GaN thick film with improved laser liftoff efficiency according to claim 1, wherein In step (2), when the hydride vapor phase epitaxy method is used, the growth pressure is controlled to be 800-1000 mbar, and the V / III ratio is controlled to be 20-200.

8. The method for growing a GaN thick film with improved laser liftoff efficiency according to claim 1, wherein The material used for the bonding is graphite glue, and the thickness of the graphite glue is 5 microns.

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