CN113235047B

CN113235047B - Preparation method of AlN thin film

Info

Publication number: CN113235047B
Application number: CN202110781721.0A
Authority: CN
Inventors: 不公告发明人
Original assignee: Zhixin Semiconductor Hangzhou Co Ltd
Current assignee: Zhixin Semiconductor Hangzhou Co Ltd
Priority date: 2020-12-25
Filing date: 2021-07-12
Publication date: 2021-10-01
Anticipated expiration: 2041-07-12
Also published as: CN112795871A; CN113235047A

Abstract

The invention relates to a preparation method of an AlN thin film, which relates to the technical field of semiconductors and comprises the following steps: (1) depositing a first AlN layer on the surface of the substrate by adopting a physical vapor deposition method; (2) carrying out high-temperature annealing treatment on the first AlN layer at 1500-1800 ℃ in a flowing nitrogen atmosphere; (3) annealing the first AlN layer in the step (2) at 700-1000 ℃ in a constant nitrogen atmosphere; (4) moving the annealed first AlN layer to metal organic chemical vapor deposition equipment, and introducing hydrogen and ammonia gas at 1100-1300 ℃ to remove impurity atoms on the surface of the annealed first AlN layer; (5) and growing a second AlN layer at 1300-1400 ℃ under the condition of 30-100 mbar. The invention adopts a multiple annealing technology and is matched with subsequent epitaxial growth, thereby not only effectively reducing the dislocation density of the obtained AlN epitaxial film, but also improving the stress state of the AlN film, solving the cracking behavior in the AlN film epitaxial process and finally obtaining the high-quality AlN film with smooth surface, low dislocation density and no crack.

Description

Preparation method of AlN thin film

Technical Field

The invention relates to the technical field of semiconductors, in particular to a preparation method of an AlN thin film with the characteristics of low dislocation density and atom-level flat surface.

Background

The deep ultraviolet LED is taken as a typical third-generation wide bandgap semiconductor product, has the advantages of small volume, long service life, no toxicity and the like, can effectively kill bacteria, has a high-speed and high-efficiency killing function on viruses such as anthrax spores, escherichia coli, influenza, malaria and the like, and is widely used for surface, air and water sterilization and the like. The AlGaN is taken as a typical material of the deep ultraviolet LED, the forbidden bandwidth of the AlGaN is continuously adjustable between 3.4eV and 6.2eV along with the change of Al components from 0 to 1, the corresponding wave band covers 200-365 nm, most of the ultraviolet wave band is covered, and the AlGaN is an ideal material for preparing an ultraviolet light emitting and detecting device.

From the perspective of growth strain and light transmittance, it is an ideal choice to use an AlN homogeneous substrate and an AlN/sapphire template substrate in order to prepare high-quality AlGaN materials and related devices. Due to the lack of low-cost, high-quality and large-size AlN single crystal substrates in the conventional technology, compared with AlN homogeneous substrates, growing AlN thin films on cheap and mature sapphire substrates is a mainstream technical development route in the field.

Therefore, in order to ensure the unique advantages of the AlGaN-based high-performance deep ultraviolet device, one of the key bases is to prepare a high-quality AlN epitaxial film. However, due to the large lattice mismatch and thermal mismatch between the AlN epitaxial layer and the foreign substrate, the AlN film is not only severely stressed, but also has a high density of threading dislocations, particularly those threading dislocations that typically extend into the active region of the device. These defects can act as non-radiative recombination sites or leakage current paths, adversely affecting device performance (e.g., efficiency, reliability, and lifetime). Therefore, how to prepare the AlN thin film with relatively low dislocation density on the substrate has great significance for ensuring the unique advantages of the AlGaN-based high-performance deep ultraviolet device.

In order to improve the quality of AlN thin films, researchers have proposed various growth approaches, including the use of buffer layers, insertion layer methods, superlattice methods, epitaxial lateral overgrowth methods, and the like. Although the crystal quality of the AlN thin film is improved to a certain extent by the methods, the methods still have a gap from the expected level.

Disclosure of Invention

The method adopts a multiple annealing technology and is matched with a preparation method for the subsequent epitaxial growth of the AlN thin film, so that the crystallization quality of the AlN epitaxial layer on the foreign substrate can be improved, the AlN thin film which is free of cracks, smooth in atomic level and low in dislocation density is obtained, and a high-quality AlN template is provided for the subsequent AlGaN epitaxial growth.

The technical scheme of the invention is as follows:

a preparation method of an AlN thin film comprises the following steps:

(1) depositing a first AlN layer on the surface of the substrate by adopting a physical vapor deposition method;

preferably, the thickness of the first AlN layer is 10-500 nm; the thick AlN single crystal layer is difficult to fuse into the AlN single crystal layer with high quality by subsequent high-temperature annealing, and the thin AlN single crystal layer is lost in the high-temperature annealing process without forming a continuous film;

preferably, the substrate is one of sapphire, silicon carbide or a patterned substrate;

preferably, the physical vapor deposition method is one of magnetron sputtering, radio frequency sputtering or electron beam evaporation;

(2) carrying out high-temperature annealing treatment on the first AlN layer at 1500-1800 ℃ in a flowing nitrogen atmosphere; because the mobility of Al is very low, the first AlN layer grown in the step (1) may be poor in quality, possibly even in a polycrystalline state, and the annealing treatment at this temperature enables the AlN thin film in the polycrystalline state to become a high-quality single-crystal AlN thin film;

the flow rate of the flowing nitrogen is 20-1000 sccm;

the high-temperature annealing time is 60-200 min;

preferably, the annealing temperature is 1650-1800 ℃;

the selection of the range of the parameters in the step can ensure the formation of the AlN single crystal and prevent the loss of the AlN, and finally, the quality of the AlN crystal is better, and the loss of the AlN is more caused by too long time or too high temperature;

(3) annealing the first AlN layer in the step (2) at 700-1000 ℃ in a constant nitrogen atmosphere; annealing at the temperature of 700-1000 ℃ can well eliminate stress, and meanwhile, AlN crystals are not affected;

preferably, the annealing time is 20-120 min;

preferably, the annealing temperature is 750-950 ℃;

in the step, the range of the parameters is selected, so that the obtained AlN has good stress relief, the time can be shortened, and the productivity can be improved; in addition, when annealing is carried out at high temperature, AlN small grains are fused and grow up, more stress can be generated, and the stress can be eliminated by high-temperature annealing in use, so that cracking in the subsequent growth process is avoided;

(4) moving the annealed first AlN layer to metal organic chemical vapor deposition equipment, and introducing hydrogen and ammonia gas at 1100-1300 ℃ to remove impurity atoms on the surface of the annealed first AlN layer; at the temperature, the impurity atoms can be effectively removed by matching with the introduction of hydrogen and ammonia;

the flow ratio of the hydrogen to the ammonia is 5-50;

the time for simultaneously introducing the hydrogen and the ammonia is 1-10 min;

preferably, the time for simultaneously introducing the hydrogen and the ammonia is 3-5 min;

because hydrogen and ammonia are corrosive, the ranges of the parameters in the step are selected to ensure that AlN losses are very little, otherwise, AlN losses are possibly much;

(5) growing a second AlN layer at 1300-1400 ℃ under the condition of 30-100 mbar; because the mobility of Al atoms is low, the mobility of the Al atoms can be increased by using high temperature, and the formation of AlN single crystals is facilitated; under lower pressure, the pre-reaction of trimethylaluminum and ammonia gas can be reduced, the raw material consumption is avoided to be more, and the pollution of impurity carbon particles to AlN is reduced;

the growth thickness of the second AlN layer is 1000-5000 nm; with the increase of the AlN thickness, the stress in the AlN epitaxial layer is gradually increased, so that cracks are generated, and the thickness range can ensure that the AlN crystal has high quality and is not easy to generate cracks;

preferably, when the second AlN layer is epitaxially grown by a metal organic compound vapor deposition method, the metal organic source is trimethylaluminum or triethylaluminum, the carrier gas is nitrogen, hydrogen, or a mixture thereof, and the nitrogen source is ammonia;

as described above, the method for preparing a high-quality AlN film according to the present invention has the following beneficial effects:

the method comprises the steps of growing an aluminum nitride film on a substrate by using a physical vapor deposition method, forming a first AlN layer by using physical sputtering by using a mode of combining high-temperature annealing and low-temperature annealing in different gas states, wherein impurities may be generated, the impurities can be released when the AlN crystal is fused at high temperature, the impurities can be taken away by flowing nitrogen, meanwhile, the constant nitrogen can play a protective role in stress relief annealing, and when the AlN crystal is annealed at high temperature in use, a plurality of small crystal grains are not fused into a large crystal grain to release the impurities; and removing impurity atoms from the annealed first AlN layer in a metal-organic chemical vapor deposition device, and then growing a second AlN layer. The AlN thin film has low cost, no pollution and stability.

In addition, the first AlN obtained by physical sputtering may be amorphous or polycrystalline, and high-temperature annealing enables the sputtered AlN to recrystallize into a single crystal; the stress formed by fusion of high-temperature annealing AlN grains can be eliminated by low-temperature annealing, the stress and the effect are different, and the stress state of the AlN thin film is improved and the cracking behavior of the AlN thin film in the epitaxial process is solved by using the high-temperature annealing and low-temperature annealing treatment in a matched mode, so that the dislocation generated by lattice mismatch between the heterojunction substrate and the epitaxial layer is effectively reduced. The annealed AlN is cleaned by introducing hydrogen and ammonia gas into metal organic chemical vapor deposition equipment at the same time and controlling the flow ratio, so that surface oxygen, carbon and aluminum-containing oxides can be effectively removed, the crystal quality of the AlN thin film is improved, the flatness of the AlN surface is improved, and a larger effect is provided for subsequently growing a second AlN layer and obtaining a high-quality AlN epitaxial thin film with an atomically smooth surface. The method has the advantages of simple operation flow, easy realization of process effect, remarkable improvement of AlN crystal quality and the like, has wide application prospect, and has important significance for preparation and large-scale application of wide-bandgap III-nitride semiconductor devices.

Drawings

FIG. 1 is a flow chart of the AlN thin film preparation method of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be appreciated by those of ordinary skill in the art that numerous technical details are set forth in order to provide a better understanding of the present application in various embodiments of the present invention. However, the technical solution claimed in the present application can be implemented without these technical details and various changes and modifications based on the following embodiments. The following embodiments are divided for convenience of description, and should not constitute any limitation to the specific implementation manner of the present invention, and the embodiments may be mutually incorporated and referred to without contradiction.

The method of the invention utilizes a high-temperature and low-temperature heat treatment method under the nitrogen atmosphere to cause the AlN material extending on the foreign substrate to generate a recrystallization process, so as to rearrange crystal grains. In the process, the AlN crystal grains are arranged more uniformly, so that the density of screw dislocation generated by crystal grain inclination (tilt) and edge dislocation generated by crystal grain mutual torsion (twist) is greatly reduced, and the crystallization quality of the material can be improved. The high-temperature heat treatment enables the sputtered polycrystal even amorphous AlN to be recrystallized to form small grains, the small grains can be recombined at high temperature to grow into large grains, the dislocation density is reduced, the small grains are orderly arranged to form a single crystal, meanwhile, stress can be generated in the process of grain fusion, and the stress can be eliminated by reducing temperature annealing. Meanwhile, in the heat treatment process, the stress state of the AlN film is improved, the AlN film is changed from a tensile stress state to a compressive stress state, and the cracking behavior in the AlN film epitaxy process is solved. The annealed AlN is cleaned by introducing hydrogen and ammonia gas simultaneously and controlling the flow ratio in metal organic chemical vapor deposition equipment, so that surface oxygen, carbon and aluminum-containing oxide can be effectively removed, the crystal quality of the AlN thin film is improved, and the flatness of the AlN surface is improved.

The invention is described in detail below with reference to the drawings and specific examples.

In this embodiment, the substrate is sapphire, the metal organic source is trimethylaluminum, and the nitrogen source is one or more of nitrogen and ammonia.

Example 1

1. Growing a first AlN layer on the sapphire substrate by adopting physical vapor deposition equipment, wherein the target material is simple substance aluminum, the deposition environment is mixed gas of argon and nitrogen, the temperature is controlled to be 600 ℃, and the deposition thickness is 200 nm; where the temperature is suitable for the formation of the first AlN layer, the temperature is too low or too high and the AlN film may not be dense enough or defective.

2. Transferring the substrate deposited with the first AlN layer to a high-temperature annealing furnace, introducing 50sccm flowing nitrogen in a pure nitrogen atmosphere, and annealing at 1750 ℃ for 150 min; the flowing nitrogen of 50sccm can not only take away excessive heat to lower the temperature and make the annealing effect poor, but also can take away some impurities. The temperature and the time are set in consideration of the AlN thickness, and are proper, so that a better single crystal can be obtained, and AlN is not lost.

3. Reducing the temperature of the annealing furnace to 800 ℃, closing flowing nitrogen, annealing for 90min, and then cooling along with the furnace; wherein the flowing nitrogen is closed to prepare for the second stress relief annealing, and the constant nitrogen is kept in the annealing furnace.

4. And moving the annealed first AlN layer to metal organic chemical vapor deposition equipment, heating to 1250 ℃, and introducing a solution with a flow ratio of 20: 1, baking for 4min to remove impurities on the surface of the first AlN layer.

5. Controlling the pressure of the equipment to be 50mbar, heating to 1350 ℃, introducing trimethylaluminum and ammonia gas, and growing a 3000nm second AlN layer.

The obtained AlN thin film has no crack under the optical microscope detection; the surface has an atomic level flat surface under the detection of an atomic force microscope; the half width in the (002) direction was 130arcsec by XRD, and the half width in the (102) direction was 300 arcsec. Wherein (002) and (102) represent two different crystal plane directions of the crystal; the two half-width values are related to dislocation density, the larger the value, the more dislocations, the poorer the crystal quality, typically the (002) half-width value represents threading dislocations and the (102) half-width value represents edge dislocations.

Example 2

1. And growing a first AlN layer on the sapphire substrate by adopting physical vapor deposition equipment, wherein the target material is simple substance aluminum, the deposition environment is mixed gas of argon and nitrogen, the temperature is controlled to be 600 ℃, and the deposition thickness is 300 nm.

2. And transferring the substrate deposited with the first AlN layer to a high-temperature annealing furnace, introducing flowing nitrogen of 50sccm in a pure nitrogen atmosphere, and annealing for 180min at 1750 ℃.

3. And reducing the temperature of the annealing furnace to 800 ℃, closing the flowing nitrogen, annealing for 90min, and then cooling along with the furnace.

The obtained AlN thin film has no crack under the optical microscope detection; the surface has an atomic level flat surface under the detection of an atomic force microscope; the half width in the (002) direction was 110arcsec by XRD, and the half width in the (102) direction was 270 arcsec.

Example 3

1. And growing a first AlN layer on the sapphire substrate by adopting physical vapor deposition equipment, wherein the target material is simple substance aluminum, the deposition environment is mixed gas of argon and nitrogen, the temperature is controlled to be 600 ℃, and the deposition thickness is 400 nm.

5. Controlling the pressure of the equipment to be 50mbar, heating to 1350 ℃, introducing trimethylaluminum and ammonia gas, and growing a 4000nm second AlN layer.

The obtained AlN thin film has no crack under the optical microscope detection; the surface has an atomic level flat surface under the detection of an atomic force microscope; XRD showed that the half width in the (002) direction was 90arcsec, and the half width in the (102) direction was 225 arcsec.

Example 4

1. And growing a first AlN layer on the sapphire substrate by adopting physical vapor deposition equipment, wherein the target material is simple substance aluminum, the deposition environment is mixed gas of argon and nitrogen, the temperature is controlled to be 600 ℃, and the deposition thickness is 500 nm.

2. And transferring the substrate on which the first AlN layer is deposited to a high-temperature annealing furnace, introducing flowing nitrogen of 50sccm in a pure nitrogen atmosphere, and annealing at 1800 ℃ for 150 min.

5. Controlling the pressure of the equipment to be 50mbar, heating to 1350 ℃, introducing trimethylaluminum and ammonia gas, and growing a 5000nm second AlN layer.

The obtained AlN thin film has no crack under the optical microscope detection; the surface has an atomic level flat surface under the detection of an atomic force microscope; the half width in the (002) direction was 75arcsec by XRD, and the half width in the (102) direction was 180 arcsec.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. A preparation method of an AlN thin film is characterized by comprising the following steps:

(2) carrying out high-temperature annealing treatment on the first AlN layer at 1500-1800 ℃ in a flowing nitrogen atmosphere;

(3) annealing the first AlN layer treated in the step (2) at the temperature of 700-1000 ℃ and under the constant nitrogen pressure;

(4) moving the annealed first AlN layer to metal organic chemical vapor deposition equipment, and introducing hydrogen and ammonia gas at 1100-1300 ℃ to remove impurity atoms on the surface of the annealed first AlN layer;

(5) and growing a second AlN layer at 1300-1400 ℃ under the condition of 30-100 mbar.

2. The method according to claim 1, wherein the substrate is one of sapphire, silicon carbide, zinc oxide, and quartz glass.

3. The method of claim 1, wherein the physical vapor deposition method is one of magnetron sputtering, radio frequency sputtering, or electron beam evaporation.

4. The method of claim 1, wherein the first AlN layer in the step (1) has a thickness of 10 to 500 nm.

5. The method according to claim 1, wherein a flow rate of the flowing nitrogen gas is 20 to 1000 sccm.

6. The method for preparing an AlN thin film according to claim 1 or 5, wherein the high-temperature annealing time is 60 to 200 min; the annealing temperature is 1650-1800 ℃.

7. The method according to claim 1, wherein the annealing pressure is atmospheric pressure.

8. The method for preparing an AlN thin film according to claim 1, wherein the annealing time in the step (3) is 20 to 120 min; the annealing temperature is 750-950 ℃.

9. The method according to claim 1, wherein the flow ratio of hydrogen to ammonia is 5 to 50.

10. The method for preparing an AlN thin film according to claim 1, wherein the time for simultaneously introducing the hydrogen gas and the ammonia gas is 1 to 10 min.

11. The method according to claim 1, wherein the second AlN layer is grown to a thickness of 1000 to 5000 nm.