CN216389379U - Gallium nitride epitaxial wafer and semiconductor device - Google Patents

Abstract

The application discloses a gallium nitride epitaxial wafer and a semiconductor device. The gallium nitride epitaxial wafer comprises a substrate, and a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, a loose AlGaN layer, an aluminum gradient layer, a gallium nitride transition layer and a gallium nitride epitaxial layer which are sequentially arranged on the substrate. The low-temperature AlN buffer layer and the high-temperature AlN buffer layer can buffer lattice mismatch between the substrate and the gallium nitride transition layer, the loose AlGaN layer can play a role in relieving stress, the aluminum gradual change layer can improve lattice match of the gallium nitride layer above the aluminum gradual change layer, gallium nitride epitaxy can further reduce stress generated by lattice mismatch between the substrate and the epitaxial layer through the gallium nitride transition layer, and can prevent warping of a large-size epitaxial wafer due to lattice mismatch or stress.

Description

Gallium nitride epitaxial wafer and semiconductor device

Technical Field

The application belongs to the technical field of semiconductors, and particularly relates to a gallium nitride epitaxial wafer and a semiconductor device.

Background

Gallium nitride (GaN) is used as a third-generation wide-band-gap semiconductor material, has high application value in the field of microwave devices due to the characteristics of good physical properties, stability and the like, and is expected to play an important role in the aspects of aviation, high-temperature radiation, radar, communication, automotive electronics and the like. However, the gan single crystal substrate is difficult to prepare, and is usually formed by a heteroepitaxy method, in which the epitaxial wafer is easily warped due to lattice mismatch or stress in a large size, and the problem of warping is more prominent as the size of the substrate increases. Therefore, there is a need to solve the problems of stress and warpage due to lattice mismatch in the prior art.

SUMMERY OF THE UTILITY MODEL

In order to solve the problem that the conventional epitaxial wafer is easy to warp due to lattice mismatch or stress, a gallium nitride epitaxial wafer is provided.

In order to achieve the purpose, the following technical scheme is adopted in the application:

a gallium nitride epitaxial wafer comprises a substrate, wherein a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, a loose AlGaN layer, an aluminum gradient layer, a gallium nitride transition layer and a gallium nitride epitaxial layer are sequentially arranged on the substrate; the thickness of the aluminum gradient layer is 80-150 nm.

The loose AlGaN layer can be formed by depositing an AlInGaN layer on the high-temperature AlN buffer layer and then precipitating all indium.

Preferably, after the formation of the bulk AlGaN layer, the bulk AlGaN layer is purged with nitrogen gas to remove all indium that precipitates from the AlInGaN layer.

Preferably said substrate comprises a sapphire substrate; the thickness of the low-temperature AlN buffer layer is 10-15 nm; the thickness of the high-temperature AlN buffer layer is 40-55 nm; the thickness of the aluminum gradient layer is 80-150 nm; the thickness of the gallium nitride transition layer is 50-100 nm.

Preferably, the gallium epitaxial layer consists of a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer, and the total thickness of the gallium epitaxial layer is 1.5-2 microns.

Further, the present invention also includes a semiconductor device comprising the gallium nitride epitaxial wafer according to any one of the above.

The semiconductor device may be one of a light emitting diode, a laser diode, a photodetector, an avalanche photodiode, a High Electron Mobility Transistor (HEMT), a metal semiconductor field effect transistor (MESFET), a metal oxide field effect transistor (MOSFET), a power metal insulator semiconductor field effect transistor (power MISFET), a Bipolar Junction Transistor (BJT), a metal insulator field effect transistor (MISFET), a Heterojunction Bipolar Transistor (HBT), a power insulated gate bipolar transistor (power IGBT), and a power vertical junction field effect transistor (power vertical JFET).

The preparation method of the gallium nitride epitaxial wafer comprises the following steps: the method comprises the steps that a low-temperature AlN buffer layer, a high-temperature AlN buffer layer and an AlInGaN layer are sequentially arranged on a substrate, indium in the AlInGaN layer is completely separated out to form a loose AlGaN layer, and an aluminum gradient layer, a gallium nitride transition layer and a gallium nitride epitaxial layer are sequentially deposited on the loose AlGaN layer.

The preparation method comprises the following steps:

step S1: placing a substrate into a reaction chamber;

step S2: introducing an aluminum source and a nitrogen source into the reaction chamber, controlling the temperature in the reaction chamber to be a first temperature, and forming a low-temperature AlN buffer layer on the substrate;

step S3: increasing the temperature in the reaction chamber to a second temperature, and continuously introducing an aluminum source and a nitrogen source to form a high-temperature AlN buffer layer on the low-temperature AlN buffer layer; the second temperature is greater than the first temperature;

step S4: keeping the introduction of an aluminum source and a nitrogen source, introducing an indium source and a gallium source into the reaction chamber, and forming an AlInGaN layer on the high-temperature AlN buffer layer; then stopping introducing an aluminum source, a nitrogen source, an indium source and a gallium source at the same time, forming a loose AlGaN layer after indium in the AlInGaN layer is completely separated out, and purging the surface of the loose AlGaN layer by using nitrogen to remove the indium completely separated out from the AlInGaN layer;

step S5: controlling the pressure and the temperature in the reaction chamber to be unchanged, reducing the introduction of an aluminum source, and forming an aluminum gradient layer on the surface of the loose AlGaN layer;

step S6: stopping introducing the aluminum source, and forming a gallium nitride transition layer on the surface of the aluminum gradual change layer;

step S7: and forming a gallium nitride epitaxial layer on the gallium nitride transition layer.

Preferably, the gallium nitride epitaxial layer comprises: a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer; the temperature and the pressure in the reaction chamber in the growth stage of the first gallium nitride epitaxial layer are both higher than the temperature and the pressure in the reaction chamber in the growth stage of the second gallium nitride epitaxial layer, but the growth speed of gallium nitride in the growth stage of the first gallium nitride epitaxial layer is lower than the growth speed of gallium nitride in the growth stage of the second gallium nitride epitaxial layer.

Specifically, the step S2: the nitrogen source is ammonia gas, the aluminum source is trimethylaluminum, the first temperature is 500-650 ℃, and the thickness of the formed low-temperature AlN buffer layer is 10-15 nm;

step S3: the first temperature is 800-1100 ℃, and the thickness of the formed high-temperature AlN buffer layer is 40-55 nm; step S4: the gallium source is trimethyl gallium, the indium source is trimethyl indium, the pressure in the reaction chamber is 150-; controlling the introduction of nitrogen and the direction of the nitrogen, blowing the droplet indium from the surface of the AlInGaN layer, and collecting the blown droplet indium in a recovery device.

Forming a low-temperature AlN buffer layer next to the substrate, wherein when the small and dense grain-shaped aluminum nitride forms the low-temperature AlN buffer layer, certain gaps exist among island-shaped grains; in order to reduce the surface energy and to close the gap by the deformation of crystal grains, a high-temperature AlN buffer layer is provided on the low-temperature AlN buffer layer. The ability to form a dense high temperature AlN buffer layer at high temperatures can improve the quality of epitaxial wafer formation.

The microstructure of the formed loose AlGaN layer presents an irregular porous structure and can play a role in relieving stress, and the aluminum gradual change layer can improve the lattice matching of the gallium nitride layer above the aluminum gradual change layer. And a gallium nitride transition layer is deposited between the upper part of the aluminum gradual change layer and the gallium nitride epitaxial layer, so that the stress generated by lattice mismatch between the substrate and the epitaxial layer can be further reduced, and the warping of a large-size epitaxial wafer caused by lattice mismatch or stress can be prevented.

It should be noted that the "low temperature" and "high temperature" in the "low-temperature AlN buffer layer" and "high-temperature AlN buffer layer" described in the present application are names for the sake of distinguishing the AlN buffer layers formed at two different temperatures, and the high temperature and the low temperature herein do not refer to a temperature range. The low-temperature AlN buffer layer and the high-temperature AlN buffer layer can be replaced by a first AlN buffer layer and a second AlN buffer layer correspondingly, and the forming temperature of the first AlN buffer layer is lower than that of the second AlN buffer layer.

Drawings

Fig. 1 is a schematic cross-sectional structure view of a gallium nitride epitaxial wafer structure according to an embodiment of the present application.

Fig. 2 is a schematic view of a growth process for preparing an epitaxial layer of gallium nitride according to an embodiment of the present disclosure.

Illustration of the drawings: 1-substrate, 2-low temperature AlN buffer layer, 3-high temperature AlN buffer layer, 4-loose AlGaN layer, 5-aluminum gradual change layer, 6-gallium nitride transition layer and 7-gallium nitride epitaxial layer.

Detailed Description

The above-described scheme is further illustrated below with reference to specific examples. It should be understood that these examples are for illustrative purposes and are not intended to limit the scope of the present application. The conditions employed in the examples may be further adjusted as determined by the particular manufacturer, and the conditions not specified are typically those used in routine experimentation.

In the first embodiment, a gallium nitride epitaxial wafer as shown in fig. 1 includes a substrate 1, on which a low-temperature AlN buffer layer 2, a high-temperature AlN buffer layer 3, a loose AlGaN layer 4, an aluminum graded layer 5, a gallium nitride transition layer 6, and a gallium nitride epitaxial layer 7 are sequentially disposed.

The gallium nitride epitaxy can play a role in relieving stress through the loose AlGaN layer, the lattice matching of the gallium nitride layer above the aluminum gradual change layer can be improved, the gallium nitride transition layer can reduce stress generated by lattice mismatch between the substrate and the epitaxy layer, and warping of a large-size epitaxial wafer due to lattice mismatch or stress can be prevented. The gallium nitride epitaxial layer may be prepared by a CVD apparatus.

Embodiment two, a method for preparing a gallium nitride epitaxial wafer, comprising the following steps: the method comprises the steps of sequentially arranging a low-temperature AlN buffer layer, a high-temperature AlN buffer layer and an AlInGaN layer on a substrate, precipitating all indium in the AlInGaN layer to form a loose AlGaN layer, blowing the surface of the loose AlGaN layer by using nitrogen, and then sequentially depositing an aluminum gradient layer, a gallium nitride transition layer and a gallium nitride epitaxial layer on the loose AlGaN layer.

A preferred embodiment: the growth flow diagram of the preparation of the gallium nitride epitaxial layer is shown in fig. 2.

Firstly, a substrate is placed in a reaction chamber, wherein the substrate can be a sapphire substrate, a cleaning step is preferentially carried out before the substrate is placed in the reaction chamber, the cleaning can remove pollution particles and impurities on the surface of the substrate, the cleaning comprises wet cleaning and dry cleaning, the wet cleaning is carried out firstly, deionized water is used for cleaning the surface of the substrate, then dry cleaning is carried out, for example, nitrogen is used for blowing the surface of the substrate, and the substrate is dried, so that the influence possibly brought by moisture is reduced;

secondly, controlling the temperature in the reaction chamber at 650 ℃ of 500-; then, increasing the temperature in the reaction chamber to 800-; in the utility model, a low-temperature AlN buffer layer is firstly formed on the surface of a substrate, because the sapphire substrate is made of alumina and has better lattice matching with AlN, the stress of AlN and the substrate is smaller, and because the AlN layer formed at a lower temperature is in the temperature range of 500-650 ℃, a plurality of fine and dense grain-shaped aluminum nitride is formed, when the aluminum nitride layer is formed, certain gaps exist among island-shaped grains, and the polycrystalline AlN layer is formed. The compact high-temperature aluminum nitride layer can be formed at high temperature and is a single crystal AlN layer, the structure is compact, and the formation quality of the epitaxial wafer can be improved.

After the high-temperature AlN buffer layer is formed, keeping the introduction of an aluminum source and a nitrogen source, introducing an indium source and a gallium source into the reaction chamber, forming an AlInGaN layer on the high-temperature AlN buffer layer, wherein the gallium source is trimethyl gallium, the indium source is trimethyl indium, the pressure in the reaction chamber is 150-. The AlInGaN layer is formed for forming a loose AlGaN layer In the follow-up mode, when the AlInGaN layer with a certain thickness is formed, indium In the AlInGaN layer is difficult to separate out at high temperature when the thickness of the AlInGaN layer is larger than 300nm, In-AlGaN alloy is easy to form, and after the AlInGaN layer with the thickness of being smaller than 100nm is formed into the loose AlGaN layer, stress relief is difficult to achieve through a loose structure. Therefore, when forming the AlInGaN layer in the utility model, the thickness is controlled in the range of 100-300nm, so that the loose AlGaN layer can be conveniently formed, and the loose structure can be utilized to play a role in relieving stress.

Then stopping introducing the aluminum source, the nitrogen source, the indium source and the gallium source at the same time, wherein the time for stopping introducing is 30-60S, when the introduction of the reaction source gas is stopped, because the temperature In the reaction chamber is higher, In is easy to precipitate near the deposition temperature (above 1000 ℃), and In can be precipitated from AlInGaN during the time for suspending introducing, and all indium In the AlInGaN layer can be precipitated during the time;

controlling the pressure and the temperature in the reaction chamber to be unchanged, and reducing the introduction of an aluminum source to form an aluminum gradient layer;

stopping introducing the aluminum source, and forming a gallium nitride transition layer on the surface of the aluminum gradual change layer;

subsequently, a gallium nitride epitaxial layer is formed on the gallium nitride transition layer.

In a preferred embodiment, after all indium in the AlInGaN layer is precipitated, the AlInGaN layer is purged by using nitrogen gas, the introduction of nitrogen gas and the direction of the nitrogen gas are controlled, the precipitated indium in a droplet shape is purged from the surface of the AlInGaN layer, and the purged indium in a droplet shape is collected in a recovery device to prevent other layer structures from being polluted. The indium is precipitated and attached to the surface of the loose AlGaN layer to form liquid drop indium, and the liquid drop indium is easy to form an alloy layer with an indium structure formed later during subsequent deposition, for example, when a GaN layer is formed later, if the indium exists, the indium and the GaN layer form an In-GaN alloy, after the alloy layer is formed, on one hand, an epitaxial wafer is difficult to separate from a substrate wafer, and on the other hand, the existence of the indium can change the conductivity of the GaN layer, and the indium can influence the luminescence performance no matter the indium is used as an LED material or a substrate material of a laser.

Forming an AlInGaN layer on the high-temperature AlN layer, wherein during forming, when AlN is formed, an aluminum source and a nitrogen source are introduced, after the high-temperature AlN layer with a preset thickness is formed, the introduction of the aluminum source and the nitrogen source is kept, an indium source and a gallium source are introduced into the reaction chamber, wherein the aluminum source is trimethylaluminum, the gallium source is trimethylgallium, the indium source is trimethylindium, the nitrogen source is NH3, the pressure in the reaction chamber is 150-200mbar, the temperature is 1050-1100 ℃, forming the AlInGaN layer, then simultaneously stopping the introduction of the aluminum source, the nitrogen source, the indium source and the gallium source, and the introduction time is 30-60S.

The AlInGaN layer stops growing after being deposited, the time of the stop growing is 30-60S, indium is easy to precipitate at high temperature (the temperature for forming the AlInGaN layer is 1050-.

After the reaction source is stopped to be led in for a preset time, controlling the temperature in the reaction chamber to 1150-, wherein x is the content of Al, x is more than or equal to 0 and less than 1, the introduction amount of the Al source is continuously reduced in the introduction process until the aluminum source is not introduced completely, a GaN layer is formed when the aluminum source is not introduced completely, the gallium source is trimethyl gallium, wherein the flow rate of trimethyl gallium is 150-200sccm, the aluminum source is trimethyl aluminum, wherein the flow rate of the trimethylaluminum is 150-200sccm, the nitrogen source is ammonia gas, and the time from the reduction of the introduction of the aluminum source to the complete absence of the introduction of the aluminum source is 10-25min, so that the thickness of the AlxGa1-xN layer is 80-150 nm. After the loose AlGaN layer is formed, although the stress can be relieved, because the AlGaN layer has loose gaps inside, when a gallium nitride layer is epitaxially formed on the AlGaN layer, because the crystal quality of the loose structure below is poor, the crystal quality of an epitaxial layer can be influenced, the quality of an epitaxial wafer can be greatly influenced, the forming temperature of the AlxGa1-xN aluminum gradual change layer is increased, the crystal quality of the aluminum gradual change layer can be improved, the aluminum content is reduced, the formed aluminum gradual change layer has good lattice matching with the gallium nitride epitaxial layer to be formed above, and the stress generated by lattice mismatch is prevented.

After the introduction amount of the aluminum source is gradually reduced until the aluminum source is not introduced completely, when the aluminum source is not introduced, the temperature and the pressure in the reaction cavity are continuously kept, the nitrogen source and the gallium source are continuously introduced to form a gallium nitride transition layer, reaction conditions do not need to be changed at the moment, the reaction conditions only need to be continuously maintained, the reaction sources are continuously introduced, after the introduction of the aluminum source is stopped, the time is kept for 2-10min, the gallium nitride transition layer with the thickness of 50-100nm is formed, the partial gallium nitride transition layer mainly improves the crystallization quality of a subsequent gallium nitride epitaxial wafer, the gallium nitride transition layer is formed at high temperature and high pressure, the epitaxial speed is slow, therefore, the gallium nitride transition layer with a certain thickness can improve the crystallization quality of the epitaxial wafer above, and a thicker thickness is not needed to be formed, and thus the production effect can be improved.

Then, a gallium nitride epitaxial layer is formed on the gallium nitride transition layer, and the following steps of forming the gallium nitride epitaxial layer can refer to the specific steps of the present invention.

And forming a gallium nitride epitaxial layer with the total thickness of 1.5-2 microns on the gallium nitride transition layer. The method comprises the following steps: the formation of the gallium nitride epitaxial layer includes two stages,

forming a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer, wherein the specific forming process comprises the following steps:

the first stage is as follows: controlling the temperature of the reaction chamber, wherein the temperature of the reaction chamber is controlled to 1080-Introducing a gallium source and a nitrogen source at a certain degree, wherein the gallium source is trimethyl gallium, the flow rate of the trimethyl gallium is 150-inch and 200sccm, and the nitrogen source is NH₃Controlling the flow rate of the gallium source and the nitrogen source, controlling the pressure of the reaction chamber at 350mbar, controlling the growth speed of the GaN at 10-15nm/min, controlling the growth time, and controlling the thickness of the GaN at the first stage at 180 nm. In the first stage, the reaction chamber is controlled to be in a high-pressure and high-temperature growth state, and GaN grows at a low speed, so that a dense GaN layer with good lattice constant matching quality can be formed on the transition GaN layer, the stress between the upper epitaxial layer and the lower layer structure can be further reduced, and the quality of the whole external GaN is improved. However, the growth at this stage is slow, and the growth thickness is not too thick, so that the growth time can be saved.

In the method, the GaN epitaxial wafer is formed in two stages, and in the first stage, the temperature and the pressure are higher, the growth speed is slower, so that a bottom epitaxial wafer with higher quality can be formed,

the growth speed is controlled at the second stage, a thicker epitaxial wafer can be quickly formed, and because the quality of the first layer of epitaxial wafer below is higher, the quality of the epitaxial wafer above is also higher, the stress is smaller, the generation of warping is prevented, and the yield of epitaxial wafer products is improved.

The utility model also relates to a semiconductor device, which comprises the gallium nitride epitaxial wafer.

The semiconductor device may be one of a light emitting diode, a laser diode, a photodetector, an avalanche photodiode, a High Electron Mobility Transistor (HEMT), a metal semiconductor field effect transistor (MESFET), a metal oxide field effect transistor (MOSFET), a power metal insulator semiconductor field effect transistor (power MISFET), a Bipolar Junction Transistor (BJT), a metal insulator field effect transistor (MISFET), a Heterojunction Bipolar Transistor (HBT), a power insulated gate bipolar transistor (power IGBT), and a power vertical junction field effect transistor (power vertical JFET).

The utility model has the beneficial effects that: 1. forming a low-temperature AlN buffer layer and a high-temperature AlN buffer layer on a substrate, wherein the two buffer layers can relieve stress generated by lattice mismatch between an upper GaN layer and the substrate, then forming a loose AlGaN layer on the high-temperature AlN buffer layer to further buffer the stress, the loose AlGaN layer is formed after indium is separated out from the AlInGaN layer, and after the loose AlGaN layer is formed, the liquid indium on the surface of the loose AlGaN layer is blown by nitrogen to remove the liquid indium on the surface because the indium is easily separated out to influence the structure of a device;

2. the aluminum gradient layer is formed by raising the temperature of the loose AlGaN layer, so that the crystallization quality of the upper layer structure can be improved, and more crystallization defects caused by the loose layer can be prevented;

3. after the aluminum gradient layer, the forming conditions are kept unchanged, the gallium nitride transition layer is formed, the gallium nitride transition layer formed under high temperature and high pressure has good crystallization quality, the crystallization quality of the epitaxial layer can be improved when the gallium nitride epitaxial layer is formed above, and due to the stress relief of the two buffer layers and the loose AlGaN layer, the stress of the epitaxial wafer can be well reduced, and the epitaxial wafer is prevented from warping.

The above embodiments are merely illustrative of the technical concepts and features of the present application, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present application and implement the present application, and not to limit the protection scope of the present application. All equivalent changes and modifications made according to the spirit of the present application are intended to be covered by the scope of the present application.

Claims (7)

1. A gallium nitride epitaxial wafer comprising a substrate, characterized in that: the substrate is sequentially provided with a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, a loose AlGaN layer, an aluminum gradient layer, a gallium nitride transition layer and a gallium nitride epitaxial layer; the thickness of the aluminum gradient layer is 80-150 nm.

2. A gallium nitride epitaxial wafer according to claim 1, wherein: the thickness of the low-temperature AlN buffer layer is 10-15nm, and the thickness of the high-temperature AlN buffer layer is 40-55 nm.

3. A gallium nitride epitaxial wafer according to claim 1, wherein: the substrate comprises a sapphire substrate.

4. A gallium nitride epitaxial wafer according to claim 1, wherein: the thickness of the gallium nitride transition layer is 50-100 nm.

5. A gallium nitride epitaxial wafer according to any one of claims 1 to 4, wherein: the gallium epitaxial layer consists of a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer, the total thickness of the gallium nitride epitaxial layer is 1.5-2 microns, and the thickness of the first gallium nitride epitaxial layer is 100-180 nm.

6. A semiconductor device comprising the gallium nitride epitaxial wafer according to any one of claims 1 to 5.

7. A semiconductor device according to claim 6, wherein the semiconductor device is one of a light emitting diode, a laser diode, a photodetector, an avalanche photodiode, a high electron mobility transistor, a metal semiconductor field effect transistor, a metal oxide field effect transistor, a power metal insulator semiconductor field effect transistor, a bipolar junction transistor, a metal insulator field effect transistor, a heterojunction bipolar transistor, a power insulated gate bipolar transistor, a power vertical junction field effect transistor.

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