CN100359636C

CN100359636C - Laser Lift-off Method for Fabricating Free-Supporting Gallium Nitride Substrates

Info

Publication number: CN100359636C
Application number: CNB2005100952458A
Authority: CN
Inventors: 修向前; 张�荣; 陈琳; 谢自力; 韩平; 顾书林; 江若琏; 胡立群; 朱顺明; 施毅; 郑有炓
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2005-11-04
Filing date: 2005-11-04
Publication date: 2008-01-02
Anticipated expiration: 2025-11-04
Also published as: CN1794419A

Abstract

The present invention relates to an improved laser stripped method for preparing a self-supporting gallium nitride substrate. An ultraviolet laser which has suitable wave length is directly used to emit a laser to penetrate through a GaN/sapphire sample irradiated by a sapphire in air of which the temperature is from 650 to 800 DEG C. After GaN of an interface is resolved, the sapphire is easy to remove to get a GaN self-supporting substrate. The laser emits the laser to penetrate through the irradiation of the sapphire under the protection of an ammonia atmosphere when temperature is over 800 DEG C. The present invention is stripped by the laser of which the temperature is over 650 DEG C to make GaN and the sapphire easily separated to get the GaN self-supporting substrate. Stress between the sapphire and the substrate is completely released. The GaN substrate which is obtained is smooth without warp.

Description

The method of the laser lift-off of preparation self-standing gan substrate

One, technical field

The present invention relates to improve the laser lift-off technique of stripping gallium nitride on the Sapphire Substrate (GaN), and reduce the method and the technology of stress in the free from flaw self-supporting GaN substrate that obtains simultaneously.

Two, background technology

III-V group nitride material (claiming the GaN sill again) based on GaN and InGaN, AlGaN alloy material is the novel semiconductor material of extremely paying attention in the world in recent years, the direct band gap of its 1.9-6.2eV continuous variable, excellent physics, chemical stability, high saturated electron drift velocity, superior functions such as high disruptive field intensity and high heat conductance make it become the most preferably material of short wavelength's semiconductor photoelectronic device and high frequency, high pressure, the preparation of high temperature microelectronic component.

Because the restriction of the physical property of GaN own, the growth of GaN body monocrystalline has very big difficulty, as yet practicability not.Yet, carry out homoepitaxy with the GaN substrate and obtain III group-III nitride thin-film material and but demonstrated extremely superior performance, therefore with the low-dislocation-density substrate carry out GaN homoepitaxy be improve III nitride epitaxial layers quality than good method.

At present, large tracts of land GaN substrate all is to go up vapor phase growth GaN thick film in foreign substrate (as sapphire, SiC, Si etc.) usually, obtains after then former foreign substrate being separated.Sapphire is that present growing GaN uses the most general foreign substrate.In order to obtain self-supporting GaN substrate, must remove Sapphire Substrate.Because sapphire is extremely stable, is difficult to adopt chemical corrosion method.General method is a mechanical grinding, but because of sapphire is very hard, not only will consume a large amount of diamond abrasives, and cost is very high and speed is extremely slow.The method of laser irradiation is to utilize laser that the boundary zone heating of GaN thick film and substrate is made it fusing, thereby obtains the GaN substrate of self-supporting.The advantage of laser-stripping method is that the time is fast, and Sapphire Substrate is recyclable.

Adopt laser-stripping method, need at first sample to be bonded on other the substrate, i.e. the GaN transfer techniques.Binding agent commonly used is organic gel (as silicon rubber, epoxy resin etc.) or metal alloy.But after Sapphire Substrate is removed,, also need organic gel or alloy are removed in order to obtain the GaN substrate of self-supporting.Organic gel is owing to after solidifying, be difficult to be dissolved in the solvent; Even adopt the organic gel (as organic glass) that to dissolve, in the process of dissolving,, be easy to make GaN cracked, thereby have influence on the integrality of GaN substrate because change in volume can take place glue itself.The method that the organic gel oxidation is burned in employing, the change in volume in the course of reaction and the gas of generation also can be cracked with the GaN substrate, are difficult to obtain complete GaN substrate.And alloy is removed the general method that adopts acid corrosion, and the gas that produces in the process (as hydrogen) can make that equally also GaN is cracked, has reduced productive rate.That adopts in addition sticks substrate (as silicon chip and sapphire etc.), also needs to remove simultaneously, can increase technology difficulty and cost.

In the present invention, we adopt the laser scanning irradiation technique, directly on Sapphire Substrate the GaN film are stripped down, and obtain self-supporting free from flaw GaN substrate.

Three, summary of the invention

The present invention seeks to: need not to adopt the method for substrate-transfer, but directly the GaN film is stripped down from Sapphire Substrate, obtain free from flaw self-supporting GaN substrate with the laser scanning irradiation technique.

Technical solution of the present invention is: the method for the laser lift-off of improved preparation self-standing gan substrate, directly the ultraviolet laser with suitable wavelength sees through sapphire irradiation GaN/ sapphire samples in 650-800 ℃ of following air atmosphere, after GaN at the interface is decomposed, sapphire can be removed easily, can obtain GaN self-supporting substrate.Only need in normal air atmosphere, heat the GaN/ Sapphire Substrate under the temperature at 650-800 ℃, adopt the method for laser irradiation, utilize laser to see through Sapphire Substrate and the boundary zone of GaN thick film and Sapphire Substrate is heated the GaN decomposition that makes at the interface, just GaN and sapphire can be separated, thus the GaN substrate of acquisition self-supporting.Owing to peel off under the temperature more than 650 ℃ and carry out, the stress among the GaN can obtain discharging at this moment, thereby has reduced the warpage of self-supporting GaN, obtains smooth stressless GaN substrate.The GaN film thickness here should be not less than 100 microns, preferably more than 300 microns, can obtain almost hundred-percent success.

This method also can be more than 800, as carrying out at 800-900 ℃, but since GaN under high like this temperature, decompose easily, so laser irradiation this moment will be carried out under protection of ammonia atmosphere.

Mechanism of the present invention and technical characterstic are:

The pairing energy of optical maser wavelength is less than the sapphire band gap in laser lift-off technique, but greater than the band gap of GaN.When the laser penetration Sapphire Substrate arrived sapphire/GaN interface, GaN absorbed its energy, and following decomposition takes place.

Laser lift-off technique of the present invention is to carry out being higher than under 650 ℃, and far above the Ga fusing point, GaN and sapphire are easy to just separate, thereby obtain GaN self-supporting substrate.Owing to be not less than under 650 ℃, the stress between sapphire and the substrate obtains discharging fully, so the smooth no warpage of the GaN substrate that obtains in addition.

Four, embodiment

The present invention program mainly comprises following step:

1, adopts gas phase epitaxy of metal organic compound (MOCVD), molecular beam epitaxy (MBE), hydride gas-phase epitaxy (HVPE) or additive method growing GaN film on Sapphire Substrate.

2, GaN film/sapphire structures is placed on the heater, GaN faces down.Under air atmosphere, heter temperature generally remains on and is not less than 650 ℃, and is not higher than 800 ℃.When being higher than 800 ℃, under protection of ammonia atmosphere, carry out.

3, select suitable laser, carry out on the scanning platform in computer-controlled stepping when laser scanning irradiation, the speed of scanning platform motion and the frequency of laser irradiation have relation.Sapphire is passed in the laser vertical incident that will have certain energy density, irradiation sapphire/GaN interface.The pairing energy of optical maser wavelength is less than the sapphire band gap, but greater than the band gap of GaN.As adopting Lambda Physik LPX 205i KrF ultraviolet light excimer laser (wavelength 248nm, the wide 38ns of pulse), laser energy density is from 200～5000mJ/cm ²Change.The time of laser scanning irradiation is being carried out (on computer-controlled two-dimensional scan platform) according to certain frequency and speed on the scanning platform of a stepping.The speed of scanning platform motion and the frequency of laser irradiation have relation, and the speed of motion should be less than the effective diameter of each laser facula irradiation.

4, laser irradiation finishes, and Sapphire Substrate can be disposed easily.Can obtain self-supporting GaN substrate.

Utilize improved laser irradiation lift-off technology, we have successfully obtained, and large scale (〉=2 inches) is smooth, free from flaw self-supporting GaN substrate.Owing to be higher than under 650 ℃, the stress that is caused by sapphire among the GaN discharges fully, and the GaN substrate of acquisition is very smooth, and the warpage situation that stress causes has greatly been improved.

Claims

1. The laser lift-off method for preparing a self-supporting gallium nitride substrate, which is characterized in that the GaN/sapphire sample is irradiated directly through the sapphire with an ultraviolet laser in an air atmosphere at 650-800 ° C, and after the GaN at the interface is decomposed, the sapphire is removed, a GaN self-supporting substrate can be obtained.

2. A laser lift-off method for preparing a self-supporting gallium nitride substrate, which is characterized in that the GaN/sapphire sample is irradiated through the sapphire with an ultraviolet laser under the protection of an ammonia atmosphere at a temperature above 800°C, and the GaN at the interface is decomposed , the sapphire is removed to obtain a GaN self-supporting substrate.

3. The laser lift-off method for preparing a self-supporting gallium nitride substrate as claimed in claim 1, wherein the thickness of the GaN film is more than 100 microns before laser lift-off.

4. The laser lift-off method for preparing a self-supporting gallium nitride substrate as claimed in claim 1, wherein the thickness of the GaN film is more than 300 microns before laser lift-off.