Method for preparing aln / gan heterojunction with nucleation layer optimization on single crystal diamond substrate

Abstract

The application discloses a preparation method of an AlN / GaN heterojunction with a nucleation layer optimized on a single-crystal diamond substrate, and mainly solves the problem of low crystal quality of the heterojunction prepared on the single-crystal diamond substrate in the prior art, which affects the heat dissipation capacity and working performance of a device. The preparation method comprises a substrate (1), a GaN epitaxial layer (4) and an AlN epitaxial layer (5) from bottom to top. The substrate is single-crystal diamond treated by plasma bombardment, so as to improve the nucleation capacity of the GaN epitaxial layer. Meanwhile, an h-BN layer (2) and a sputtering B x Al 1‑x N layer (3) are sequentially arranged between the substrate and the GaN epitaxial layer, the h-BN layer provides a nucleation point for GaN growth, and the sputtering B x Al 1‑x N layer is used for buffering the lattice difference between the h-BN layer and the GaN layer. The application improves the crystal quality of the GaN epitaxial layer, and can be used for manufacturing power devices, so as to improve the heat dissipation capacity and working performance of the device.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microelectronics, and particularly relates to a method for manufacturing an AlN / GaN heterojunction on a single-crystal diamond substrate, which can be used for preparing a GaN-based device with high power. BACKGROUND

[0002] With the rapid development of new energy vehicles, wireless charging and 5G technology, the band gap and power density of traditional semiconductors such as Si and GaAs are not sufficient to support the progress of information and power technology. GaN material has been used in high-voltage and high-frequency high-power application scenarios due to its high band gap, high breakdown field strength and high electron saturation velocity. GaN-based electronic devices have been widely used in wireless power transmission and conversion fields, and have great application potential.

[0003] However, due to the limitations of material properties and growth technology, current GaN-based electronic devices are mainly prepared by heteroepitaxy technology. In addition to reducing the material quality, this heteroepitaxy also seriously affects the heat dissipation capacity of the device, thereby limiting the performance of the device under high-power working conditions. Taking mature sapphire substrates, Si substrates and SiC substrates as examples, their thermal conductivities are 45, 150 and 390 W·m -1 ·K -1 , which are not sufficient to meet the stable heat dissipation capacity of the device under high-power working conditions. Diamond material is currently the best material for heat dissipation in nature, and the thermal conductivity of high-quality single-crystal diamond substrate can reach 2300 W·m -1 ·K -1 , and the heat dissipation capacity is nearly 6 times that of SiC material. Therefore, the industry believes that single-crystal diamond material can be well applied to GaN-based electronic devices under high-power working conditions. Therefore, the preparation of GaN devices on single-crystal diamond substrates has become a popular direction and gradually attracted attention.

[0004] In recent years, the combination of single-crystal diamond substrates and GaN-based electronic devices has undergone a large amount of research, with multiple technical routes, mainly including low-temperature bonding technology, GaN-based diamond epitaxy technology, and diamond substrate GaN thin film epitaxy technology. The technical route of epitaxially growing GaN thin film on single-crystal diamond substrate is the best in performance, because the interface bonding strength, interface thermal resistance and overall device thermal resistance can be the best, and it is more conducive to taking advantage of the strong heat dissipation capacity of single-crystal diamond substrate. However, due to the differences in crystal system and lattice constant, the dislocation density and carbon impurity content of the GaN material epitaxially grown on the single-crystal diamond substrate by the existing technology are very high, and the crystal quality is poor, which leads to the degradation and instability of the device performance, and cannot meet the requirements of high thermal conductivity and high crystal quality at the same time, thereby limiting the development and application of GaN-based microwave power devices with high performance and high heat dissipation capacity. SUMMARY

[0005] The AlN / GaN heterojunction of the present application comprises, from bottom to top, a substrate, a GaN epitaxial layer and an AlN epitaxial layer, and is characterized in that:

[0006] To achieve the above-mentioned purpose, the AlN / GaN heterojunction of the present application comprises, from bottom to top, a substrate, a GaN epitaxial layer and an AlN epitaxial layer, and is characterized in that:

[0007] The substrate is a single-crystal diamond substrate treated by plasma surface bombardment, which is used to improve the heat dissipation capacity of the AlN / GaN heterojunction and improve the nucleation ability of the GaN epitaxial layer;

[0008] A magnetron sputtering B x Al 1-x N layer and a h-BN layer are additionally arranged between the GaN epitaxial layer and the single-crystal diamond substrate, the h-BN layer is used to improve the nucleation ability of the epitaxial layer, and the magnetron sputtering B x Al 1-x N layer is used to transition and buffer the material difference between the h-BN layer and the GaN epitaxial layer.

[0009] Further, the thickness of the h-BN layer is 20-70 nm;

[0010] Further, the thickness of the magnetron sputtering B x Al 1-x N layer is 20-80 nm, and the adjustment range of the B content is 0.3-0.5;

[0011] Further, the thickness of the GaN epitaxial layer is 500-800 nm;

[0012] Further, the thickness of the AlN epitaxial layer is 100-300 nm.

[0013] To achieve the above-mentioned purpose, the AlN / GaN heterojunction of the present application comprises, from bottom to top, a substrate, a GaN epitaxial layer and an AlN epitaxial layer, and is characterized in that:

[0014] 1) Select a single-crystal diamond substrate and clean and dry it;

[0015] 2) Perform surface bombardment on the cleaned and dried substrate using CF4 plasma, with a bombardment power of 120-150 W and a bombardment time of 10 min-30 min;

[0016] 3) Transfer the h-BN with thickness of 20-70nm to the surface bombarded substrate, and place it in the drying oven, and bake at 130-190℃ for 1-2 hours to complete the preparation of h-BN layer;

[0017] 4) Sputter the B x Al 1-x N layer with thickness of 20-80nm on the h-BN layer by using standard magnetron sputtering process, to complete the magnetron sputtering B x Al 1-x N layer;

[0018] 5) Prepare AlN / GaN heterojunction:

[0019] 5a) Grow the GaN layer with thickness of 500-800nm on the B x Al 1-x N layer by using MOCVD process;

[0020] 5b) Grow the AlN layer with thickness of 100-300nm on the GaN layer by using MOCVD process.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] Firstly, the present application uses single crystal diamond as the substrate material, which enhances the heat dissipation capacity of the device; at the same time, the single crystal diamond substrate is subjected to surface plasma bombardment, and compared with the conventional single crystal diamond substrate, the substrate surface is more conducive to the nucleation growth of GaN material, and the crystal quality of GaN material is improved.

[0023] Secondly, the present application introduces the h-BN layer and the magnetron sputtered B x Al 1-x N layer, which further improves the nucleation ability of GaN material on the surface of single crystal diamond substrate; at the same time, the introduction of the magnetron sputtered B x Al 1-x N layer can serve as a transition layer between h-BN and GaN epitaxial layer, which improves the crystal quality of GaN epitaxial layer, further improves the crystal quality of heterojunction and enhances the reliability of the device. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of the AlN / GaN heterojunction of the present application on the single crystal diamond substrate for optimizing the nucleation layer;

[0025] Figure 2 is a flowchart for preparing Figure 1 structure. DETAILED DESCRIPTION

[0026] The application will be further described in detail below with reference to the accompanying drawings.

[0027] Referring to Figure 1 , the AlN / GaN heterojunction of the application comprises: a single crystal diamond substrate 1, an h-BN layer 2, a magnetron sputtering B x Al 1-x N layer 3, a GaN epitaxial layer 4, and an AlN epitaxial layer 5. Among them:

[0028] The single crystal diamond substrate 1 is subjected to CF4 plasma bombardment to increase the nucleation ability of GaN material;

[0029] The h-BN layer 2 is located on the single crystal diamond substrate 1 after the bombardment treatment, and has a thickness of 20-70 nm to increase the nucleation ability of the GaN epitaxial layer;

[0030] The magnetron sputtering B x Al 1-x N layer 3 is located on the h-BN layer 2, and has a thickness of 20-80 nm and a B content adjustment range of 0.3-0.5 to increase the nucleation ability of the GaN epitaxial layer;

[0031] The GaN epitaxial layer 4 is located on the magnetron sputtering B x Al 1-x N layer 3, and has a thickness of 500-800 nm;

[0032] The AlN epitaxial layer 5 is located on the GaN epitaxial layer 4, and has a thickness of 100-300 nm;

[0033] The AlN epitaxial layer 5 and the GaN epitaxial layer 4 form an AlN / GaN heterojunction.

[0034] Referring to Figure 2 , the application provides three embodiments of AlN / GaN heterojunction on single crystal diamond based on substrate processing.

[0035] Embodiment 1: The single crystal diamond substrate is subjected to CF4 plasma treatment for 30 min, and then an h-BN layer with a thickness of 70 nm, a magnetron sputtering B 0.3 Al 0.7 N layer with a thickness of 80 nm, a GaN epitaxial layer with a thickness of 500 nm, and an AlN epitaxial layer with a thickness of 300 nm are prepared.

[0036] Step one: clean and plasma bombard the substrate, such as Figure 2 (a).

[0037] 1a) ultrasonic cleaning the substrate in acetone solution for 50 min;

[0038] 1b) Put the cleaned substrate into a drying oven and perform a drying treatment at a temperature of 90°C;

[0039] 1d) Put the dried substrate into a dilute hydrochloric acid solution and soak for 50s;

[0040] 1e) Put the soaked substrate into a drying oven and perform a drying treatment at a temperature of 150°C again;

[0041] 1f) Perform bombardment on the dried substrate using CF4plasma, with a bombardment power of 120W and a bombardment time of 30min.

[0042] Step two, preparation of the h-BN layer, as Figure 2 (b).

[0043] Transfer the h-BN with a thickness of 70nm to the processed and cleaned substrate 1, and put it into a drying oven and bake at 190°C for 2 hours to complete the preparation of the h-BN layer.

[0044] Step three, preparation of the magnetron sputtered B 0.3 Al 0.7 N layer, as Figure 2 (c).

[0045] Set the reaction chamber temperature to 320°C, the pressure to 1.8Pa, and the sputtering power to 260W, and use the magnetron sputtering process to prepare a B 0.3 Al 0.7 N layer on the surface of the h-BN layer 2 with a thickness of 80nm, to complete the preparation of the magnetron sputtered B 0.4 Al 0.6 N layer 3.

[0046] Step four, growth of AlN / GaN heterojunction.

[0047] 4a) After the preparation of the magnetron sputtered B 0.4 Al 0.6 N layer, put it into the reaction chamber of the MOCVD equipment, set the temperature of the reaction chamber to 1100°C and the pressure of the reaction chamber to 100Torr, and simultaneously introduce ammonia gas with a flow rate of 5600sccm and gallium source with a flow rate of 100sccm into the reaction chamber, to grow a GaN epitaxial layer with a thickness of 500nm on the magnetron sputtered B 0.4 Al 0.6 N layer, as Figure 2 (d);

[0048] 4b) The temperature of the reaction chamber is set to 1100°C, the pressure of the reaction chamber is set to 80 Torr, the reaction chamber is supplied with ammonia gas at a flow rate of 4000 sccm and the aluminum source at a flow rate of 150 sccm, and an AlN epitaxial layer with a thickness of 300 nm is grown on the GaN epitaxial layer, thereby completing the fabrication of the AlN / GaN heterojunction, as shown in FIG. 4b. Figure 2 (e).

[0049] Example 2, a single crystal diamond substrate is subjected to CF4plasma bombardment for 20 min, an h-BN layer with a thickness of 50 nm is prepared on the substrate, and the B 0.4 Al 0.6 N layer has a thickness of 50 nm, the GaN epitaxial layer has a thickness of 700 nm, and the AlN epitaxial layer has a thickness of 200 nm.

[0050] Step A, the substrate is treated and cleaned, as shown in Figure 2 (a).

[0051] First, the substrate is subjected to ultrasonic cleaning in an acetone solution for 40 min, and then the cleaned substrate is placed in a drying oven and subjected to drying treatment at a temperature of 70°C. Then, the dried substrate is immersed in a dilute hydrochloric acid solution for 40 s and then placed in a drying oven and subjected to drying treatment again at a temperature of 130°C.

[0052] Then, the dried substrate is subjected to bombardment using CF4plasma, the bombardment power is 140 W, and the bombardment time is 20 min.

[0053] Step B, the h-BN layer is prepared, as shown in Figure 2 (b).

[0054] The h-BN layer with a thickness of 50 nm is transferred to the treated and cleaned substrate 1, and then placed in a drying oven and baked at a temperature of 160°C for 1.5 hours, thereby completing the preparation of the h-BN layer.

[0055] Step C, the B 0.4 Al 0.6 N layer is prepared by magnetron sputtering, as shown in Figure 2 (c).

[0056] The B 0.4 Al 0.6 N layer with a thickness of 50 nm is prepared on the h-BN layer 2 by the magnetron sputtering process, and the process parameters of the magnetron sputtering are as follows: the temperature of the reaction chamber is 350°C, the pressure is 1.9 Pa, and the sputtering power is 280 W.

[0057] Step D, the AlN / GaN heterojunction is grown.

[0058] First, the B 0.4Al 0.6 The sample of the N layer is put into the reaction chamber of the MOCVD device, the temperature of the reaction chamber is set to 1050°C, the pressure of the reaction chamber is set to 75 Torr, the ammonia gas with a flow rate of 4500 sccm and the gallium source with a flow rate of 80 sccm are simultaneously introduced into the reaction chamber, and the B 0.4 Al 0.6 The GaN epitaxial layer with a thickness of 700 nm is grown on the N layer, and then Figure 2 (d);

[0059] Then, the process conditions are changed, i.e., the temperature of the reaction chamber is set to 1050°C, the pressure of the reaction chamber is set to 60 Torr, the ammonia gas with a flow rate of 3500 sccm and the aluminum source with a flow rate of 125 sccm are simultaneously introduced into the reaction chamber, and the AlN epitaxial layer with a thickness of 200 nm is grown on the GaN epitaxial layer to complete the fabrication of the AlN / GaN heterojunction, as shown in Figure 2 (e).

[0060] In Example 3, the single crystal diamond substrate is subjected to CF4 plasma bombardment for 10 min to prepare the h-BN layer with a thickness of 20 nm, the B 0.5 Al 0.5 The heterojunction with the N layer with a thickness of 20 nm, the GaN epitaxial layer with a thickness of 500 nm, and the AlN epitaxial layer with a thickness of 100 nm.

[0061] Step one, the substrate is treated and cleaned, as shown in Figure 2 (a).

[0062] 1.1) The substrate is placed in an acetone solution for ultrasonic cleaning for 30 min, and the cleaned substrate is placed in a drying oven for drying treatment at a temperature of 60°C;

[0063] 1.2) The dried substrate is immersed in a dilute hydrochloric acid solution for 35 s, and then taken out and placed in a drying oven for drying treatment again at a temperature of 110°C

[0064] 1.3) The dried substrate is subjected to CF4 plasma bombardment at a power of 150 W for 10 min to complete the pretreatment of the substrate.

[0065] Step two, the h-BN layer is prepared, as shown in Figure 2 (b).

[0066] The h-BN layer is prepared on the pretreated substrate, i.e., the h-BN with a thickness of 50 nm is transferred to the cleaned and bombarded substrate 1, and is placed in a drying oven for baking at a temperature of 130°C for 1 hour to complete the preparation of the h-BN layer.

[0067] Step three, the B 0.5Al 0.5 N layer, such as Figure 2 (c).

[0068] The reaction chamber temperature was set to 370℃, the pressure was set to 2.0 Pa, and the sputtering power was set to 300 W. A 20 nm thick B 0.5 Al 0.5 N layer was sputtered on the surface of the h-BN layer 2. 0.5 Al 0.5 N layer 3 was prepared.

[0069] Step four, growing AlN / GaN heterojunction.

[0070] 4.1) After the preparation of the B 0.5 Al 0.5 N layer, it was placed in the reaction chamber of the MOCVD equipment. The temperature of the reaction chamber was set to 1000℃, the pressure of the reaction chamber was set to 50 Torr, and the flow rate of the ammonia gas was set to 3400 sccm, and the flow rate of the gallium source was set to 50 sccm. The two gases were simultaneously introduced into the reaction chamber to grow a 500 nm thick GaN epitaxial layer on the B 0.5 Al 0.5 N layer, as shown in Figure 2 (d);

[0071] 4.2) The temperature of the reaction chamber was kept unchanged, the pressure of the reaction chamber was reduced to 30 Torr, and the flow rate of the ammonia gas was set to 3000 sccm, and the flow rate of the aluminum source was set to 100 sccm. The two gases were simultaneously introduced into the reaction chamber to grow a 100 nm thick AlN epitaxial layer on the GaN epitaxial layer, thereby completing the fabrication of the AlN / GaN heterojunction, as shown in ​ (e).

[0072] The above description is only three specific examples of the present application and does not constitute any limitation on the present application. Obviously, for those skilled in the art, after understanding the content and principles of the present application, various modifications and changes in form and details can be made without departing from the principles and structures of the present application. However, these modifications and changes based on the idea of the present application are still within the scope of protection of the claims of the present application.

Claims

1. An AlN / GaN heterojunction with nucleation layer optimization on a single crystal diamond substrate, comprising from bottom to top: The substrate (1), GaN epitaxial layer (4) and AlN epitaxial layer (5) are characterized in that: The substrate (1) is a single crystal diamond substrate treated by plasma surface bombardment, which is used to improve the heat dissipation capacity of the AlN / GaN heterojunction and improve the nucleation ability of the GaN epitaxial layer; The magnetic sputtering B x Al 1-x N layer (3) and h-BN layer (2) are added between the GaN epitaxial layer (4) and the single crystal diamond substrate (1), the h-BN layer is used to improve the nucleation ability of the epitaxial layer, the magnetic sputtering B x Al 1-x N layer is used to transition and buffer the material difference between the h-BN layer and the GaN epitaxial layer; the thickness of the h-BN layer (2) is 20-70nm; the magnetic sputtering B x Al 1-x N layer (3), the thickness is 20-80nm, and the adjustment range of B content is 0.3-0.

5.

2. The heterojunction according to claim 1, characterized in that: The thickness of the GaN epitaxial layer (4) is 500-800 nm, The thickness of the AlN epitaxial layer (5) is 100-300 nm.

3. A method for preparing an AlN / GaN heterojunction with nucleation layer optimization on a single crystal diamond substrate, characterized in that: The method comprises the following steps: 1) Select a single crystal diamond substrate and clean and dry it; 2) Perform surface bombardment on the cleaned and dried substrate using CF4 plasma, with a bombardment power of 120-150 W and a bombardment time of 10-30 min; 3) Transfer a h-BN layer with a thickness of 20-70 nm to the surface-bombarded substrate (1) and place it in a drying oven for baking at 130-190°C for 1-2 hours to complete the preparation of the h-BN layer (2); 4) A B layer with a thickness of 20nm-80nm is sputtered on the h-BN layer (2) using a standard magnetron sputtering process. x Al 1-x N layers, completing magnetron sputtering of B x Al 1-x N layer (3); the B x Al 1-x The growth condition parameters for layer N are set as follows: The reaction chamber temperature is 320-370°C, The pressure is 1.8-2.0 Pa, The sputtering power is 260-300 W, and the target material is aluminum and boron, The sputtering gas is nitrogen; 5) Fabricate an AlN / GaN heterojunction: 5a) depositing a B layer (2) by magnetron sputtering B x Al 1-x On the AlN layer (3), a GaN layer (4) with a thickness of 500-800 nm is grown by MOCVD process. 5b) Grow an AlN layer (5) with a thickness of 100-300 nm on the GaN layer (4) using MOCVD process.

4. The method of claim 3, wherein, In step 1), the substrate is cleaned and dried using standard cleaning process, which achieves the following: 1a) Place the substrate in acetone solution for ultrasonic cleaning for 30-50 min; 1b) Place the cleaned substrate in a drying oven for drying treatment at a temperature of 60-90°C; 1c) Soak the dried substrate in dilute hydrochloric acid solution for 35-50 s; 1d) Take out the soaked substrate and place it in a drying oven for drying treatment at a temperature of 110-150°C.

5. The method of claim 3, wherein, In step 5a), the MOCVD process for growing the GaN layer is set as follows: The reaction chamber temperature is 1000-1100°C, and the pressure is 50-100 Torr; Simultaneously introduce ammonia gas with a flow rate of 3400-5600 sccm and gallium source with a flow rate of 50-100 sccm into the reaction chamber.

6. The method of claim 3, wherein, In step 5b), the MOCVD process for growing the AlN layer is set as follows: The reaction chamber temperature is 1000-1100°C, and the pressure is 30-80 Torr; Simultaneously introduce ammonia gas with a flow rate of 3000-4000 sccm and aluminum source with a flow rate of 100-150 sccm into the reaction chamber.

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