A HEMT device based on a composite substrate and its fabrication method

Abstract

This invention relates to a HEMT device based on a composite substrate and its fabrication method. The device, from bottom to top, comprises: a composite substrate, a GaN high-resistivity layer, a GaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN passivation layer. The composite substrate is a germanium-molybdenum composite substrate, a germanium-tungsten composite substrate, or a germanium-hafnium composite substrate, with an AlN layer sputtered on its surface. The AlN layer has a thermal expansion coefficient 0.95 to 1.05 times that of GaN. This invention also provides a method for fabricating the HEMT device based on the composite substrate. This invention grows and fabricates HEMT devices on a composite substrate with high thermal conductivity. The sputtering of an AlN layer on the composite substrate completely solves the heat dissipation problem of existing HEMT devices, while also addressing the lattice mismatch between the substrate and the HEMT device, reducing stress, overcoming the problem of easy cracking at the growth interface, and improving the performance and yield of the HEMT device.

Description

Technical Field

[0001] This invention relates to a HEMT device based on a composite substrate and its fabrication method, belonging to the field of optoelectronic power devices. Background Technology

[0002] GaN material is ideal for fabricating optoelectronic devices, especially blue-green LEDs and LDs. These light sources have broad application prospects and huge market potential in high-density optical information storage, high-speed laser printing, full-color dynamic high-brightness light displays, solid-state lighting sources, high-brightness signal detection, and communications. Furthermore, GaN semiconductor materials are also ideal for fabricating high-temperature, high-frequency, and high-power devices. GaN is a representative of nitride materials and one of the best wide-bandgap III-V compound semiconductor materials, making it one of the most advanced semiconductor materials in the world today.

[0003] Magnetron sputtering is a physical vapor deposition technique used to fabricate various special-function thin films, such as superconducting thin films, magnetic thin films, and superhard films. Sputtering involves bombarding the surface of a solid with particles of a certain energy. Molecules or atoms on the solid surface are ejected after being bombarded. Magnetron sputtering, on the other hand, introduces a magnetic field between two electrodes. Electrons are simultaneously subjected to different electric and magnetic fields, causing their trajectories to follow a cycloidal pattern. This results in uniform sputtering onto the desired substrate surface, leading to good film consistency and a fast deposition rate.

[0004] However, as the power density and size of GaN-based HEMT devices continue to increase, heat dissipation also increases, leading to performance degradation, reduced output power, and increased failure rates, even resulting in complete failure. To address this issue, researchers both domestically and internationally have proposed various heat dissipation methods to improve the high-temperature stability of devices. Nevertheless, more than half of electronic product failures are still caused by temperature-related issues.

[0005] Furthermore, existing GaN-based HEMT devices mainly use sapphire substrates, Si substrates, silicon nitride substrates, aluminum nitride substrates, gallium nitride substrates, or zinc oxide substrates. These substrates have significant differences in expansion coefficients with nitride materials, resulting in lattice mismatch. This leads to high stress during the epitaxial growth of nitrides in HEMT devices, making it easy for cracks to form at the interface during growth, which seriously affects device performance and yield.

[0006] In view of this, there is an urgent need to find a new type of HEMT device and its fabrication method that can solve both problems at the same time. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a HEMT device based on a composite substrate and its fabrication method. An AlN layer is sputtered onto the composite substrate, and a GaN high-resistivity layer, a GaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN passivation layer are grown on the sputtered AlN composite substrate. This composite substrate design not only solves the thermal mismatch problem but also addresses the heat dissipation problem of the HEMT device. The epitaxial structure of this device is perfectly matched with the novel substrate, making it suitable for applications in power electronics, radio frequency, power devices, blue lasers, etc., meeting the application needs of high-efficiency, novel high-power power electronics, optoelectronics, and other fields.

[0008] The technical solution of the present invention is as follows:

[0009] A HEMT device based on a composite substrate comprises, from bottom to top: a composite substrate, a GaN high-resistivity layer, a GaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN passivation layer.

[0010] The composite substrate is a germanium-molybdenum composite substrate, a germanium-tungsten composite substrate, or a germanium-hafnium composite substrate, and its surface is sputtered with an ALN ​​layer, the coefficient of thermal expansion of which is 0.95 to 1.05 times that of GaN.

[0011] According to a preferred embodiment of the present invention, the thickness of the composite substrate is 400–8000 μm.

[0012] According to a preferred embodiment of the present invention, the thickness of the ALN layer is 10-500 nm.

[0013] According to a preferred embodiment of the present invention, the thicknesses of the GaN high-resistivity layer, GaN buffer layer, GaN channel layer, AlN insertion layer, AlGaN barrier layer and GaN passivation layer are 500–2000 nm, 500–2000 nm, 10–300 nm, 0.5–2 nm, 10–40 nm and 1–5 nm, respectively.

[0014] The above-mentioned method for fabricating HEMT devices based on composite substrates includes the following steps:

[0015] (1) The surface of the composite substrate is mirror polished, and then an ALN ​​layer is prepared on the surface of the composite substrate;

[0016] (2) Place the composite substrate obtained in step (1) in the growth chamber of the MOCVD equipment, introduce 10-50L of ammonia gas, and heat it to 1000-1300℃ under the protection of ammonia gas.

[0017] (3) Keep the temperature at 1000-1300℃, introduce TMGa and ferrocene, and grow a GaN high-resistivity layer on the ALN layer of the composite substrate.

[0018] (4) Keep the temperature at 1000-1300℃, introduce TMGa, and grow a GaN buffer layer on the GaN high resistivity layer;

[0019] (5) Keep the temperature at 1100-1300℃, introduce TMGa, and grow GaN channel layer on GaN buffer layer;

[0020] (6) Keep the temperature at 1100-1300℃, introduce TMGa, TMAl and TMIn, and grow an AlN insertion layer on the GaN channel layer.

[0021] (7) Keep the temperature at 1100-1300℃, introduce TMGa, TMAl and TMIn, and grow an AlGaN barrier layer on the AlN insertion layer.

[0022] (8) Keep the temperature at 1100-1300℃, introduce TMGa, TMAl and TMIn, grow a GaN passivation layer on the AlGaN barrier layer, and obtain a HEMT device based on a composite substrate.

[0023] According to a preferred embodiment of the present invention, in step (1), the AlN layer is prepared by vapor phase epitaxy, pulsed laser deposition or magnetron sputtering; more preferably, magnetron sputtering.

[0024] According to a preferred embodiment of the present invention, in step (3), the flow rate of TMGa is 50-500cc, the flow rate of ferrocene is 10-300cc, the growth pressure is 100-500mbar, and 5-50L of ammonia gas is continuously and uniformly introduced during the growth process.

[0025] According to a preferred embodiment of the present invention, in steps (4) and (5), the flow rate of the TMGa is 50-500cc, the growth pressure is 100-500mbar, and 5-50L of ammonia gas is continuously and uniformly introduced during the growth process.

[0026] According to a preferred embodiment of the present invention, in steps (6) to (8), the flow rate of TMGa is 20-100cc, the flow rate of TMAl is 100-300cc, the flow rate of TMIn is 50-300cc, the growth pressure is 50-150mbar, and 15-50L of ammonia gas is continuously and uniformly introduced during the growth process.

[0027] In this invention, the GaN high-resistivity layer, GaN buffer layer, GaN channel layer, AlN insertion layer, AlGaN barrier layer, and GaN passivation layer are all prepared and grown using metal-organic chemical vapor deposition. For any other aspects not detailed herein, existing technologies can be employed.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention employs metal-organic chemical vapor deposition to innovatively grow and fabricate HEMT devices on germanium-molybdenum composite substrates, germanium-tungsten composite substrates, or germanium-hafnium composite substrates. The germanium composite substrates have high thermal conductivity, thus completely solving the heat dissipation problem of existing HEMT devices.

[0030] 2. The HEMT device fabrication method provided by the present invention sputters an ALN ​​layer on a composite substrate with a thermal expansion coefficient that is 0.95 to 1.05 times that of GaN, thereby making the thermal expansion coefficient of the composite substrate closer to, or even the same as, that of GaN. This solves the problem of lattice mismatch between the substrate and the HEMT device, reduces stress, overcomes the problem of easy cracking at the growth interface, and improves the performance and yield of the HEMT device.

[0031] 3. In the preparation of the AlN insertion layer, AlGaN barrier layer and GaN passivation layer, the present invention introduces TMIn, which improves the surface flatness of HEMT devices and the device mobility, carrier concentration and current collapse performance. It can be applied to power electronics, radio frequency, power devices, blue lasers and other fields to meet the application needs of high-efficiency new high-power power electronics, optoelectronics and other fields. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the growth structure of the HEMT device based on a composite substrate according to the present invention. Detailed Implementation

[0033] To make the technical problems, technical solutions and advantages of the present invention clearer, the present invention will be further described below through embodiments and in conjunction with the accompanying drawings. However, the present invention is not limited thereto. All matters not described in detail in the present invention are based on conventional techniques in the art.

[0034] Example 1

[0035] A HEMT device based on a composite substrate comprises, from bottom to top: a composite substrate, a GaN high-resistivity layer, a GaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN passivation layer.

[0036] The composite substrate is a germanium-molybdenum composite substrate with a thickness of 2000 μm. Its surface is sputtered with an ALN ​​layer, and its coefficient of thermal expansion is 0.95 to 1.05 times that of GaN.

[0037] The method for fabricating the HEMT device based on the composite substrate includes the following steps:

[0038] (1) The surface of the germanium-molybdenum composite substrate was mirror polished, and then a 200 nm ALN layer was prepared by magnetron sputtering.

[0039] (2) Place the composite substrate obtained in step (1) in the growth chamber of the MOCVD equipment, introduce 40L of ammonia gas, and raise the temperature to 1200℃ under the protection of ammonia gas.

[0040] (3) Maintain the temperature at 1200℃, introduce 200cc TMGa and 100cc ferrocene, and grow a GaN high-resistivity layer with a thickness of 1500nm on the ALN layer of the composite substrate at a growth pressure of 300mbar; continuously and uniformly introduce 20L of ammonia gas during the growth process.

[0041] (4) Maintain the temperature at 1200℃, introduce 200cc of TMGa, and grow a GaN buffer layer with a thickness of 1500nm on the GaN high resistivity layer at a growth pressure of 300mbar; continuously and uniformly introduce 20L of ammonia gas during the growth process.

[0042] (5) Maintain the temperature at 1200℃, introduce 200cc of TMGa, and grow a GaN channel layer with a thickness of 200nm on the GaN buffer layer at a growth pressure of 300mbar; continuously and uniformly introduce 20L of ammonia gas during the growth process.

[0043] (6) Maintain the temperature at 1200℃, introduce 50cc TMGa, 200cc TMAl and 200cc TMIn, and grow an AlN insertion layer with a thickness of 1nm on the GaN channel layer at a growth pressure of 100mbar; continuously and uniformly introduce 30L of ammonia gas during the growth process.

[0044] (7) Maintain the temperature at 1200℃, introduce 50cc TMGa, 200cc TMAl and 200cc TMIn, and grow an AlGaN barrier layer with a thickness of 20nm on the AlN insertion layer at a growth pressure of 100mbar; continuously and uniformly introduce 30L of ammonia gas during the growth process.

[0045] (8) Maintain the temperature at 1200℃, introduce 50cc TMGa, 200cc TMAl and 200cc TMIn, and the growth pressure is 100mbar. During the growth process, continuously and uniformly introduce 30L of ammonia gas. Grow a GaN passivation layer with a thickness of 2nm on the AlGaN barrier layer to obtain a HEMT device based on a composite substrate.

[0046] Example 2

[0047] A HEMT device based on a composite substrate, with the structure and fabrication method as described in Example 1, except that:

[0048] The composite substrate is a germanium-tungsten composite substrate with a thickness of 800 μm.

[0049] In step (1), the thickness of the ALN layer is 10 nm;

[0050] In step (3), 50cc of TMGa and 10cc of ferrocene are introduced, the growth pressure is 100mbar, and the thickness of the GaN high-resistivity layer is 500nm.

[0051] In steps (4) and (5), 50c TMGa is introduced, the growth pressure is 100mbarr, the GaN buffer layer thickness is 500nm, and the GaN channel layer thickness is 10nm.

[0052] In steps (6) to (8), 20cc TMGa, 100cc TMAl and 500cc TMIn are introduced, the growth pressure is 50mbar, the AlN insertion layer thickness is 0.5nm, the AlGaN barrier layer thickness is 10nm and the GaN passivation layer thickness is 1nm.

[0053] Example 3

[0054] A HEMT device based on a composite substrate, with the structure and fabrication method as described in Example 1, except that:

[0055] The composite substrate is a germanium-hafnium composite substrate with a thickness of 8000 μm.

[0056] In step (1), the thickness of the ALN layer is 500 nm;

[0057] In step (3), 500cc of TMGa and 300cc of ferrocene are introduced, the growth pressure is 500mbar, and the thickness of the GaN high-resistivity layer is 2000nm.

[0058] In steps (4) and (5), 500c TMGa is introduced, the growth pressure is 500mbar, the GaN buffer layer thickness is 2000nm, and the GaN channel layer thickness is 300nm.

[0059] In steps (6) to (8), 100cc TMGa, 300cc TMAl and 300cc TMIn are introduced, the growth pressure is 150mbar, the AlN insertion layer thickness is 2nm, the AlGaN barrier layer thickness is 40nm and the GaN passivation layer thickness is 5nm.

[0060] Example 4

[0061] A HEMT device based on a composite substrate, with the structure and fabrication method as described in Example 1, except that:

[0062] In steps (3) and (4), the reaction temperature is 1000℃.

[0063] In steps (5) to (8), the reaction temperature is 1300℃.

[0064] Comparative Example 1

[0065] HEMT devices are fabricated using existing Si substrates, specifically:

[0066] An AlN nucleation layer was grown at a growth temperature of 800℃, and then the temperature was increased to 1300℃ to grow a high-temperature AlN layer with a height of 300nm. Then, a GaN high-resistivity layer, a GaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN passivation layer were grown sequentially according to the scheme in Example 1.

[0067] Test case

[0068] Using the methods of Example 1 and Comparative Example 1 of the present invention, 10 HEMT devices were grown respectively. The presence or absence of cracks at the growth interface of the HEMT devices and the heat dissipation of the prepared HEMT devices were statistically analyzed. The results are shown in Table 1.

[0069] Heat dissipation test: The HEMT devices prepared in Example 1 and Comparative Example 1 were powered on and used to 100°C, and then allowed to cool down naturally at room temperature. The cooling time was recorded.

[0070] Table 1

[0071] Growth interface crack ratio Time required to cool from 100℃ to 30℃ Example 1 0％ 100s Comparative Example 1 80％ 500s

[0072] As shown in Table 1, the HEMT device provided in Example 1 is uniquely fabricated on a germanium-molybdenum composite substrate. The germanium-molybdenum composite substrate has a high thermal conductivity, requiring only 100 seconds to cool from 100°C to 30°C, compared to 500 seconds in Comparative Example 1. Example 1's cooling time is only 1 / 5 of Comparative Example 1, completely solving the heat dissipation problem of existing HEMT devices. Furthermore, the HEMT device fabrication method provided in Example 1 sputters an ALN ​​layer onto a composite substrate with a thermal expansion coefficient 0.95 to 1.05 times that of GaN, further bringing the composite substrate's thermal expansion coefficient closer to, or even equal to, that of GaN. This solves the lattice mismatch problem between the substrate and the HEMT device, reducing stress. The HEMT devices prepared in Example 1 show no cracking at the growth interface, while Comparative Example 1 shows an 80% cracking rate at the growth interface. This demonstrates that the fabrication method of this invention overcomes the problem of easy cracking at the growth interface, improving the performance and yield of the HEMT device.

Claims

1. A HEMT device based on a composite substrate, characterized in that, From bottom to top, it includes: a composite substrate, a GaN high-resistivity layer, a GaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN passivation layer; The composite substrate is a germanium-molybdenum composite substrate, a germanium-tungsten composite substrate, or a germanium-hafnium composite substrate, and its surface is sputtered with an ALN ​​layer; the thermal expansion coefficient of the composite substrate is 0.95 to 1.05 times that of GaN. The thickness of the composite substrate is 400~8000μm; the thickness of the ALN layer is 10~500nm; and the thicknesses of the GaN high-resistivity layer, GaN buffer layer, GaN channel layer, AlN insertion layer, AlGaN barrier layer and GaN passivation layer are 500~2000nm, 500~2000nm, 10~300nm, 0.5~2nm, 10~40nm and 1~5nm, respectively.

2. The method for fabricating the HEMT device based on a composite substrate as described in claim 1, characterized in that, The steps include the following: (1) The surface of the composite substrate is mirror polished, and then an ALN ​​layer is prepared on the surface of the composite substrate; (2) Place the composite substrate obtained in step (1) in the growth chamber of the MOCVD equipment, introduce 10-50L of ammonia gas, and heat it to 1000-1300℃ under the protection of ammonia gas. (3) Keep the temperature at 1000-1300℃, introduce TMGa and ferrocene, and grow a GaN high-resistivity layer on the ALN layer of the composite substrate. (4) Keep the temperature at 1000-1300℃, introduce TMGa, and grow a GaN buffer layer on the GaN high resistivity layer; (5) Keep the temperature at 1100-1300℃, introduce TMGa, and grow GaN channel layer on GaN buffer layer; (6) Keep the temperature at 1100-1300℃, introduce TMGa, TMAl and TMIn, and grow an AlN insertion layer on the GaN channel layer; (7) Keep the temperature at 1100-1300℃, introduce TMGa, TMAl and TMIn, and grow an AlGaN barrier layer on the AlN insertion layer; (8) Keep the temperature at 1100-1300℃, introduce TMGa, TMAl and TMIn, grow GaN passivation layer on AlGaN barrier layer, and obtain HEMT device based on composite substrate.

3. The preparation method according to claim 2, characterized in that, In step (1), the AlN layer is prepared by vapor phase epitaxy, pulsed laser deposition or magnetron sputtering.

4. The preparation method according to claim 3, characterized in that, The AlN layer was prepared by magnetron sputtering.

5. The preparation method according to claim 2, characterized in that, In step (3), the flow rate of TMGa is 50-500cc, the flow rate of ferrocene is 10-300cc, the growth pressure is 100-500mbar, and 5-50L of ammonia is continuously and uniformly introduced during the growth process.

6. The preparation method according to claim 2, characterized in that, In steps (4) and (5), the flow rate of the TMGa is 50-500cc, the growth pressure is 100-500mbar, and 5-50L of ammonia gas is continuously and uniformly introduced during the growth process.

7. The preparation method according to claim 2, characterized in that, In steps (6) to (8), the flow rate of TMGa is 20-100cc, the flow rate of TMAl is 100-300cc, the flow rate of TMIn is 50-300cc, the growth pressure is 50-150mbar, and 15-50L of ammonia gas is continuously and uniformly introduced during the growth process.

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