CN113299553B - Growth method of nitride high electron mobility transistor epitaxial material - Google Patents

Abstract

The invention discloses a growth method of a nitride high electron mobility transistor epitaxial material, which comprises the steps of sequentially growing a buffer layer, a GaN channel layer and an AlGaN barrier layer on a substrate, wherein the AlGaN barrier layer grows by adopting a two-step method, the first AlGaN barrier layer grows by adopting at least one group III source flow gradient process, the second AlGaN barrier layer grows by adopting a group III source flow constant process, and the thickness of the first AlGaN barrier layer is 0-4 nm. The invention adopts the two-step growth method, overcomes the problem of Al component reduction at the position of the AlGaN barrier layer close to the heterojunction interface caused by Ga atom diffusion, improves the consistency of the Al component along the growth direction, realizes a steep AlGaN/GaN heterojunction interface, and thus improves the two-dimensional electron gas mobility of the channel.

Description

A kind of growth method of nitride high electron mobility transistor epitaxial material

technical field

The invention belongs to the technical field of semiconductor materials, and particularly relates to a growth method of a nitride high electron mobility transistor epitaxial material.

Background technique

Gallium Nitride (GaN)-based High Electron Mobility Field Effect Transistor (HEMT) is a new type of electronic device based on nitride heterostructures. The commonly used material system, thanks to the strong polarization characteristics and band gap difference of the AlGaN/GaN heterojunction, the two-dimensional electron gas (2DEG) surface density in the heterojunction quantum well reaches the order of 10 ¹² . The base gate voltage controls the channel electrons to work. The device has excellent characteristics of high frequency and high power, and is widely used in wireless communication base stations, power electronic devices and other fields of information sending and receiving, energy conversion, etc., in line with the current development concept of energy saving, environmental protection, green and low carbon.

The two-dimensional electron gas mobility of AlGaN/GaN heterojunction is one of the key factors affecting the power characteristics of HEMT devices, and higher carrier mobility is beneficial to improve the operating current of the device. The two-dimensional electron gas mobility in AlGaN/GaN heterojunctions is restricted by various scattering mechanisms, including lattice scattering, interface scattering, and alloy disorder scattering. At room temperature, the mobility of AlGaN/GaN heterojunction 2DEG is generally 1400-1600 cm ² /Vs.

Studies have shown that the 2DEG mobility of AlGaN/GaN HEMT materials is closely related to the steepness of the heterojunction interface composition. The higher the Al composition on the AlGaN side of the heterojunction interface, the deeper the potential well formed and the stronger the 2DEG confinement. The probability of entering the AlGaN layer through the potential barrier is smaller, thereby reducing the random scattering of the alloy and improving the 2DEG mobility. However, in the early stage of growing the AlGaN barrier layer, due to the high growth surface temperature above 1000 degrees, the Ga atoms decomposed by the GaN buffer layer may diffuse into the AlGaN barrier layer near the heterojunction interface, reducing the Al composition. As the AlGaN thickness increases, the Ga diffusion decreases, and the Al composition gradually increases to the design value and stabilizes. Due to the diffusion of Ga atoms, the Al composition of the AlGaN barrier layer near the channel is lower than the designed value, and the depth of the heterojunction potential well decreases, resulting in increased channel electron overflow, increased alloy scattering, and decreased 2DEG mobility.

By inserting a layer of 1-2 nm AlN between AlGaN/GaN heterojunctions, the 2DEG mobility can be increased to over 2000 cm ² /Vs. However, the introduction of the AlN intercalation layer significantly increases the barrier height of the AlGaN/GaN heterojunction surface and increases the difficulty of the contact process during the fabrication of HEMT devices. Ohmic contact resistance is the most important parasitic resistance of HEMT devices and one of the key factors affecting the frequency characteristics of devices.

Therefore, for HEMT materials for GaN high-frequency power devices, how to effectively improve the two-dimensional electron gas mobility in the channel without affecting the barrier height of the AlGaN/GaN heterojunction surface is an important issue in material design and epitaxy process.

SUMMARY OF THE INVENTION

In order to solve the technical problem mentioned in the above background art, that is, the Al composition of the heterojunction interface of the AlGaN/GaN HEMT epitaxial material is lower than the design value, and the closer the interface is to the larger the deviation, the present invention proposes a nitride high electron mobility. The growth method of high-rate transistor epitaxial materials overcomes the problem of the reduction of Al composition at the AlGaN/GaN heterojunction interface, and significantly improves the consistency of the Al composition of the AlGaN barrier layer along the growth direction.

In order to realize the above-mentioned technical purpose, the technical scheme of the present invention is:

A method for growing a nitride high electron mobility transistor epitaxial material. A buffer layer, a GaN channel layer and an AlGaN barrier layer are sequentially grown on a substrate. The AlGaN barrier layer is grown by a two-step method. A first layer of AlGaN barrier layer is grown by at least one group III source flow rate gradient process, and the second step is to use a group III source flow rate constant process to grow a second layer of AlGaN barrier layer, and the thickness of the first layer of AlGaN barrier layer is 0 ~4nm.

Based on the preferred solution of the above technical solution, the flow rate of the constant III source flow process used in the second step is equal to the flow final value of the at least one group III source flow rate gradient process used in the first step.

Based on the preferred solution of the above technical solution, the at least one Group III source flow rate gradient process used in the first step includes three combinations: the first one is the aluminum source flow rate gradient, the gallium source flow rate is constant; the second one is the aluminum source flow rate The flow rate is constant, and the flow rate of the gallium source is gradual; the third type is the simultaneous gradual change of the flow rate of the aluminum source and the gallium source.

Based on the preferred solution of the above technical solution, the flow rate gradient process of at least one group III source used in the first step, for the aluminum source, adopts the process of gradually reducing the flow rate, and the initial value is 1-5 times the final value; Source, using the process of increasing flow gradually, the initial value is 0.2-1 times the final value.

Based on the preferred solution of the above technical solution, the at least one Group III source flow rate gradient process used in the first step, and the gradient mode includes linear change and non-linear change.

Based on the preferred solution of the above technical solution, the material of the substrate is sapphire, Si or SiC.

Based on the preferred solution of the above technical solution, the material of the buffer layer is AlN, GaN or AlGaN.

The beneficial effects brought by the above technical solutions:

The invention adopts this two-step method to grow the AlGaN potential barrier, which can overcome the problem of reducing the Al composition of the AlGaN/GaN heterojunction caused by the diffusion of Ga atoms to the greatest extent, improve the steepness of the composition of the heterojunction interface, and reduce the disorder of the 2DEG alloy. scattering, thereby increasing the 2DEG mobility. By optimizing the first-layer AlGaN barrier process, including III-group source gradient method, initial value, and the first layer of AlGaN thickness and other parameters, the consistency of the Al composition of the barrier layer along the growth direction is improved, and the two-dimensional electron gas migration in the channel is improved. rate increased to 1800-2000 cm ² /Vs.

Description of drawings

Fig. 1 is the structure schematic diagram of the epitaxial material of nitride high electron mobility transistor in the present invention;

Numeral descriptions in FIG. 1: 1, substrate layer; 2, buffer layer; 3, channel layer; 4, first layer of AlGaN barrier layer; 5, second layer of AlGaN barrier layer;

FIG. 2-FIG. 4 are graphs showing flow changes of gallium source and aluminum source in the growth of AlGaN barrier layer in the present invention.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings.

The present invention designs a growth method of a nitride high electron mobility transistor epitaxial material. As shown in FIG. 1 , a buffer layer 2 , a GaN channel layer 3 and a first layer are sequentially grown on the substrate layer 1 by MBE or MOCVD technology. The AlGaN barrier layer 4 and the second AlGaN barrier layer 5 .

The AlGaN barrier layer is grown by a two-step method. In the first step, at least one group III source flow rate gradient process is used to grow the first layer of the AlGaN barrier layer, and the second step is to use the III group source flow constant process to grow the second layer of AlGaN potential barrier layer, the thickness of the first layer of AlGaN barrier layer is 0-4 nm.

Preferably, the flow rate of the constant group III source flow rate process used in the second step is equal to the flow rate final value of the at least one group III source flow rate gradient process used in the first step. The at least one Group III source flow rate gradient process adopted in the first step includes three combination modes: the first one is that the aluminum source flow rate is gradual, and the gallium source flow rate is constant; the second type is that the aluminum source flow rate is constant, and the gallium source flow rate is gradual; The third is the simultaneous gradient of the aluminum source and the gallium source flow. The at least one III source flow rate gradient process used in the first step, for aluminum sources, adopts the process of gradually decreasing the flow rate, and the initial value is 1-5 times the final value; for gallium sources, the flow rate gradually increases. Process, the initial value is 0.2-1 times the final value. The at least one Group III source flow rate gradient process used in the first step, and the gradient mode includes linear change and non-linear change.

Preferably, the material of the substrate is sapphire, Si or SiC. The material of the buffer layer is AlN, GaN or AlGaN.

Example 1

1) Select SiC substrate and use MOCVD technology to grow;

2) 1100 ℃ and 100 Torr, baking in hydrogen atmosphere for 10 minutes;

3) At 1100°C, ammonia gas and aluminum source were introduced to grow a 100nm-thick AlN nucleation layer on the surface of the substrate;

4) Cool down to 1000°C, turn off the aluminum source, pass in the gallium source, and grow a 1.5um thick GaN buffer layer;

5) The temperature is raised to 1050℃, and the 0.5um thick GaN channel layer is grown;

6) Turn on the aluminum source and grow the first layer of AlGaN barrier layer with a thickness of 2nm. The flow rate of the aluminum source gradually changes from 150ml/min to 50ml/min, and the flow rate of the gallium source is constant at 10ml/min;

7) Keep the flow rate of the aluminum source at 50 ml/min and the flow rate of the gallium source at 10 ml/min, and grow a second AlGaN barrier layer with a thickness of 18 nm;

8) Turn off the aluminum source and gallium source and bring it down to room temperature.

Example 2

1) Select a sapphire substrate and grow it by MOCVD technology;

2) 1050 ℃ and 100 Torr, baking in hydrogen atmosphere for 5 minutes;

3) 1050 ℃ and 100 Torr, nitriding with ammonia gas for 10 minutes;

4) Cool down to 550°C, feed ammonia and gallium sources, and grow a 20nm-thick GaN nucleation layer on the surface of the substrate;

5) The temperature is raised to 1000℃, and a 1.5um thick GaN buffer layer is grown;

6) The temperature is raised to 1050°C, and a 0.5um thick GaN channel layer is grown;

7) Turn on the aluminum source, grow the first layer of AlGaN barrier layer, the thickness is 2nm, the flow rate of the aluminum source is constant at 50ml/min, and the flow rate of the gallium source changes linearly from 5ml/min to 10ml/min;

8) Keep the flow rate of the aluminum source at 50 ml/min and the flow rate of the gallium source at 10 ml/min, and grow a second AlGaN barrier layer with a thickness of 18 nm;

9) Turn off the aluminum source and gallium source and bring it to room temperature.

Example 3

1) Select Si substrate and use MOCVD technology to grow;

2) 1100 ℃ and 100 Torr, baking in hydrogen atmosphere for 10 minutes;

3) 1100 ℃, pass through the aluminum source, and pre-deposit aluminum on the surface of the substrate for 10 seconds;

4) At 1100°C, ammonia gas was introduced to grow a 300nm-thick AlN nucleation layer on the surface of the substrate;

5) Pass the gallium source to grow the 1.2um thick AlGaN buffer layer;

6) Turn off the aluminum source and grow a 0.5um thick GaN channel layer;

7) Turn on the aluminum source and grow the first layer of AlGaN barrier layer with a thickness of 2nm. The flow rate of the aluminum source gradually changes from 150ml/min to 50ml/min, and the flow rate of the gallium source is constant at 10ml/min;

8) Keep the flow rate of the aluminum source at 50 ml/min and the flow rate of the gallium source at 10 ml/min, and grow a second AlGaN barrier layer with a thickness of 18 nm;

9) Turn off the aluminum source and gallium source and bring it to room temperature.

In terms of process control, by setting the three parameters of the initial value, final value and gradient mode of the aluminum source and gallium source flow, the gradual change of the III source flow is realized, as shown in Figure 2-Figure 4. (a) in Figure 2 keeps the flow rate of the gallium source unchanged, and the flow rate of the aluminum source changes linearly; (b) in Figure 2 keeps the flow rate of the gallium source unchanged, and the flow rate of the aluminum source changes nonlinearly; (a) in Figure 3 In order to keep the flow rate of the aluminum source constant, the flow rate of the gallium source changes linearly; (b) in Figure 3 is to keep the flow rate of the aluminum source unchanged, and the flow rate of the gallium source changes nonlinearly; (a)-(d) in Figure 4 are the aluminum source The flow rate and the flow rate of the gallium source change at the same time.

The invention adopts a two-step method to grow the AlGaN barrier layer, and the purpose is to improve the consistency of the Al composition of the barrier layer along the growth direction. The gradient mode and initial value of the first layer of AlGaN need to be optimized according to different types of epitaxy equipment and growth processes, and the consistency of the Al composition of the AlGaN barrier layer along the growth direction is used as the evaluation standard.

The embodiment is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention all fall within the protection scope of the present invention. .

Claims (7)

1. A growth method of nitride high electron mobility transistor epitaxial material grows buffer layer, GaN channel layer and AlGaN barrier layer on substrate in turn, which is characterized in that: the AlGaN barrier layer grows by adopting a two-step method, the first AlGaN barrier layer grows by adopting at least one group III source flow gradient process, the second AlGaN barrier layer grows by adopting a group III source flow constant process, the thickness of the first AlGaN barrier layer is 0-4 nm, and the Al component in the first AlGaN barrier layer is gradually reduced from bottom to top.

2. The method of claim 1, wherein the step of growing the nitride high electron mobility transistor epitaxial material comprises: the flow of the group III source flow constant process adopted in the second step is equal to the flow final value of at least one group III source flow gradual change process adopted in the first step.

3. The method of claim 1, wherein the step of growing the nitride high electron mobility transistor epitaxial material comprises: the at least one group III source flow gradual change process adopted in the first step comprises three combination modes: the first method is characterized in that the flow of an aluminum source is gradually changed, and the flow of a gallium source is constant; the second method is that the flow of the aluminum source is constant and the flow of the gallium source is gradually changed; and the third is that the flow rates of the aluminum source and the gallium source are gradually changed simultaneously.

4. The method for growing nitride high electron mobility transistor epitaxial material according to any of claims 1-3, wherein: the first step adopts at least one group III source flow gradual change process, and for an aluminum source, the flow gradual change process is adopted, and the initial value is 1-5 times of the final value; for the gallium source, a process of gradually increasing the flow is adopted, and the initial value is 0.2-1 times of the final value.

5. The method for growing the epitaxial material of the nitride high electron mobility transistor according to any of claims 1 to 3, wherein: the first step adopts at least one group III source flow gradual change process, and the gradual change mode comprises linear change and nonlinear change.

6. The method of claim 1, wherein the step of growing the nitride high electron mobility transistor epitaxial material comprises: the substrate is made of sapphire, Si or SiC.

7. The method of claim 1, wherein the step of growing the nitride high electron mobility transistor epitaxial material comprises: the buffer layer is made of AlN, GaN or AlGaN.

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