CN1176483C - Method for preparing self-supporting gallium nitride substrate by laser lift-off - Google Patents

Abstract

The present invention relates to a method for preparing a self support gallium nitride substrate by laser stripping. An excimer laser is adopted. The energy corresponding to a laser wavelength is smaller than the band gap energy of sapphire, but larger than the band gap energy of GaN. The laser irradiation penetrates a sapphire substrate and irradiates GaN at a sapphire-gallium nitride interface; afterwards, the heating or the weak acid corrosion is carried out; the GaN is separated from the sapphire, and a GaN self support substrate is obtained; particularly, a gallium nitride surface is firstly stuck on a base sheet, and then, the laser irradiation is carried out; after the GaN is separated from the sapphire, base sheet bonding layers are separated by a heating method.

Description

Method for preparing self-supporting gallium nitride substrate by laser lift-off

1. Technical field

The invention relates to a method and technology for obtaining a crack-free self-supporting GaN substrate by using a laser lift-off technique to lift gallium nitride (GaN) from a sapphire substrate.

2. Technical background

Group III-V nitride materials (also known as GaN-based materials) mainly based on GaN, InGaN, and AlGaN alloy materials are new semiconductor materials that have attracted much attention in the world in recent years. Its 1.9-6.2eV continuously variable direct band gap, excellent physical and chemical stability, high saturation electron drift velocity, high breakdown field strength and high thermal conductivity and other superior properties make it the best choice for the preparation of short-wavelength semiconductor optoelectronic devices and high-frequency, high-voltage, high-temperature microelectronic devices Material.

Due to the limitations of the physical properties of GaN itself, the growth of GaN bulk single crystal is very difficult and has not been put into practical use. However, the homoepitaxial growth of III-nitride thin film materials with GaN substrates shows extremely superior performance, so GaN homoepitaxial growth with low dislocation density substrates is a better way to improve the quality of III-nitride epitaxial layers. Method.

At present, large-area GaN substrates are usually obtained by gas-phase growing GaN thick films on heterogeneous substrates (such as sapphire, SiC, Si, etc.), and then separating the original heterogeneous substrates. Among them, GaN growth on sapphire substrates is the most common and of the highest quality. In order to obtain a free-standing GaN substrate, the sapphire substrate must be removed. Because sapphire is extremely stable, it is difficult to use chemical etching methods. The general method is mechanical grinding, but because sapphire is very hard, it not only consumes a lot of diamond abrasives, but also costs a lot and the speed is extremely slow. The method of laser irradiation is used to heat the GaN thick film and the interface region of the substrate to melt it, so as to obtain a self-supporting GaN substrate. The advantage of the laser lift-off method is that the time is fast and the sapphire substrate can be recycled.

In the present invention, we use laser scanning irradiation technology to peel off the GaN film from the sapphire substrate to obtain a self-supporting GaN substrate without cracks.

3. Technical content

The purpose of the invention is to peel off the GaN thin film from the sapphire substrate by laser scanning irradiation technology to obtain the self-supporting GaN substrate without cracks.

The technical solution of the present invention is: adopt the method of laser irradiation, utilize the laser to pass through the sapphire substrate to heat the GaN thick film and the interface area of sapphire substrate to decompose GaN at the interface, heat or weak hydrochloric acid above Ga melting point By etching, GaN and sapphire can be separated to obtain a self-supporting GaN substrate.

The further improvement of the present invention is: first stick the gallium nitride surface on a substrate, such as a silicon wafer as the substrate, then irradiate the laser, separate GaN and sapphire, and then bond the substrate by heating Layer separation.

Mechanism and technical characteristics of the present invention are:

In the laser lift-off technology, the energy corresponding to the laser wavelength is smaller than the band gap energy of sapphire, but larger than the band gap energy of GaN. When the laser penetrates the sapphire substrate and reaches the sapphire/GaN interface, GaN absorbs its energy and decomposes as follows.

GaN and sapphire can be separated by heating or corrosion with weak hydrochloric acid above the melting point of Ga to obtain a GaN self-supporting substrate.

4. Description of drawings

Fig. 1 is the schematic diagram of laser lift-off GaN technology from sapphire substrate according to the present invention

Fig. 2 is a schematic diagram of pressure generation at the sapphire-GaN interface during the laser lift-off process of the present invention, and Sappire is sapphire.

5. Specific implementation

The present invention scheme mainly comprises the following steps:

1. GaN films are grown on sapphire substrates by metal organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE) or other methods.

2. Use Si(111) as support material. A silicon wafer is attached to GaN to form a sapphire/GaN/Si structure.

3. Select a suitable laser, and vertically incident the laser with a certain energy density through the sapphire to irradiate the sapphire/GaN interface. The energy corresponding to the laser wavelength is smaller than the bandgap energy of sapphire, but larger than that of GaN. For example, using Lambda Physik LPX 205i KrF ultraviolet excimer laser (wavelength 248nm, pulse width 38ns), the laser energy density varies from 200 to 5000mJ/cm ² .

4. Heating the sapphire/GaN/Si structure at a temperature higher than metal Ga (29°C), or corroding the metal at the sapphire/GaN interface with a weak HCl solution, the sapphire substrate can be peeled off. A GaN/Si structure is obtained.

5. Heat the GaN/Si structure at 500°C, or put the GaN/Si structure in an appropriate organic solvent, and remove the silicon wafer. A self-supporting GaN substrate can be obtained.

Using the laser irradiation lift-off technique, we successfully obtained a crack-free self-supporting GaN substrate. Before and after laser lift-off, the structure and optical properties of GaN did not change much. By carefully controlling the laser lift-off conditions, we can achieve the lift-off of large-area (>2 inches in diameter) GaN films.

Claims (1)

1, laser lift-off prepares the method for self-standing gan substrate, it is characterized in that earlier gallium nitride surface being bonded on the substrate, carry out laser irradiation again, after GaN and sapphire separated, with heating means the substrate adhesive linkage is separated again, institute's employing excimer laser such as following: the pairing energy of optical maser wavelength is less than the sapphire band-gap energy, but band-gap energy greater than GaN, laser irradiation sees through Sapphire Substrate, irradiation sapphire-gallium nitride GaN at the interface, GaN and sapphire are separated in heating or weak acid corrosion then, obtain GaN self-supporting substrate.

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