A diamond-based gan device and method of fabrication

Abstract

The present application relates to a kind of diamond-based GaN device and preparation method.The diamond-based GaN device includes from bottom to top stack: back metal layer, diamond substrate, intermediate metal layer and HEMT layer;HEMT layer uses GaN material, and is equipped with source, gate and drain three electrodes;Diamond substrate is equipped with recess communicating intermediate metal layer, and back metal layer covers the sidewall of recess;HEMT layer is equipped with contact hole for making source and intermediate metal layer communicate, and contact hole is filled with metal for making source and intermediate metal layer contact.The present application solves the problem of wafer yield caused by the self-supporting ability of high-frequency large-size device or circuit after back thinning, and can consider impedance and heat dissipation effect.

Description

Technical Field

[0001] This invention relates to the field of semiconductor devices, and in particular to a diamond-based GaN device and its fabrication method. Background Technology

[0002] Benefiting from its wide bandgap, high electron mobility, high breakdown voltage, and tunable material and device advantages, GaN HEMT has become one of the best candidates for high-power microwave devices. With the increasing demands for frequency, power density, and functionality in microwave devices and circuits, single-chip area is gradually increasing, device substrates are gradually thinning, and high power density is gradually increasing. Substrate thinning leads to a significant increase in dicing fragmentation, especially with larger chip sizes, which limits further frequency increases in GaN devices and circuits; simultaneously, the heat generated by the packaging volume of high-power devices has reportedly exceeded 100 W / cm². -3 Difficulty in dissipating heat during high-throughput operation is one of the main causes of device failure and reliability problems.

[0003] Therefore, this invention is proposed. Summary of the Invention

[0004] The main objective of this invention is to provide a diamond-based GaN device and its fabrication method. This invention not only solves the problem of poor heat dissipation in existing GaN devices, but also addresses the challenge of the mismatch between the crystal properties of diamond and GaN. Furthermore, it resolves issues related to diamond surface roughness, localized protrusions, and warping after substrate thinning when directly bonding diamond and GaN materials. Simultaneously, through multiple activation treatments of the bonding surface, it achieves comprehensive control over interfacial bonding strength, electrical conductivity, thermal conductivity, and impedance. The complete implementation of the above technology will effectively solve the problem of reduced self-support capability in high-frequency, large-size devices or circuits after back-side thinning, leading to low dicing yield, while also considering impedance and heat dissipation effects.

[0005] To achieve the above objectives, the present invention provides the following technical solutions.

[0006] A first aspect of the present invention provides a diamond-based GaN device comprising, from bottom to top, stacked:

[0007] Back metal layer, diamond substrate, intermediate metal layer and HEMT layer;

[0008] The HEMT layer is made of GaN heterojunction material and has three electrodes: source, gate, and drain.

[0009] The diamond substrate has a groove that connects to the intermediate metal layer, and the back metal layer covers the sidewall of the groove; the HEMT layer has a contact hole that connects the source electrode and the intermediate metal layer, and the contact hole is filled with metal that allows the source electrode and the intermediate metal layer to contact each other.

[0010] The diamond-based GaN devices of the present invention have the following characteristics:

[0011] I. An intermediate metal layer is provided between the diamond substrate and the GaNHEMT layer. This metal layer facilitates the transfer of the HEMT layer from a substrate with poor heat dissipation and easy breakage (such as a silicon substrate or a silicon carbide substrate) to the diamond. On the one hand, the high thermal conductivity of diamond solves the problems of poor heat dissipation, high RF loss, and easy breakage during dicing of existing devices. On the other hand, it solves the serious mismatch in crystal structure, lattice constant, and thermal expansion coefficient of GaN directly epitaxially grown on diamond. Furthermore, the buffering effect of the intermediate metal layer reduces the surface roughness and local protrusions of the diamond.

[0012] Second, the sandwich structure of the back metal layer, diamond substrate, and intermediate metal layer can form a capacitor, providing a new way to control the impedance, conductivity, and other electrical properties of GaN devices, thereby expanding the application range of GaN devices. Simultaneously, the grooves in the source and back metal layers can serve as grounding electrodes, increasing the reliability of the device.

[0013] Third, diamond as a support substrate is also suitable for the processing of large-size devices.

[0014] In some embodiments, the intermediate metal layer is doped with a target element and at least one ion selected from O, N, and Ar.

[0015] Doping with the above target elements and ions can activate the metal surface, making bonding easier, and can also reduce the surface roughness and local protrusions of diamond.

[0016] In some embodiments, the target material element includes at least one selected from B, Si, Ge, Fe, Al, Cu, and In.

[0017] In some embodiments, a 10-100 μm non-diamond substrate, preferably 10-50 μm, is further included between the intermediate metal layer and the HEMT layer.

[0018] In some embodiments, the non-diamond substrate is selected from at least one or a multilayer composite of SiC substrate, Si substrate, Al2O3 substrate, and GaN substrate.

[0019] In some embodiments, the diamond substrate has a thermal conductivity ≥800W / (m·K), a roughness ≤10nm, and a warpage ≤20μm.

[0020] In some embodiments, the thickness of the back metal layer is ≥50nm.

[0021] In some embodiments, the thickness of the intermediate metal layer is ≥10 nm.

[0022] In some embodiments, the back metal layer and the middle metal layer are each independently composed of one or more composites of Ti, Au, Cu, and Al.

[0023] A second aspect of the present invention provides a method for fabricating a diamond-based GaN device, comprising the following steps:

[0024] Provide a supporting substrate;

[0025] Then, a HEMT layer is formed on the front side of the supporting substrate. The HEMT layer is made of GaN heterojunction material and has three electrodes: source, gate and drain.

[0026] A temporary protective substrate is placed over the HEMT layer;

[0027] Then, the entire support substrate is thinned or removed from the back side of the support substrate;

[0028] Then, on the side where the support substrate has been thinned or completely removed, a contact hole connecting to the source electrode is etched.

[0029] Then, a first metal layer is formed on one side of the opening of the contact hole, so that the first metal layer covers the sidewall of the contact hole and contacts the source electrode, thereby obtaining a first temporary bonding structure;

[0030] Provide diamond substrates;

[0031] A second metal layer is formed on the front side of the diamond substrate to obtain a second temporary bonding structure;

[0032] Using the first metal layer and the second metal layer as bonding surfaces, the first temporary bonding structure and the second temporary bonding structure are bonded together;

[0033] After the bonding, a groove communicating with the intermediate metal layer is etched on the back side of the diamond substrate;

[0034] A back metal layer is formed on the back side of the diamond substrate and covers the sidewalls of the groove;

[0035] Then the temporary protective substrate is removed.

[0036] The above fabrication method addresses the severe mismatch between GaN material and diamond crystal structure, lattice constant, and thermal expansion coefficient by first forming a HEMT layer on a supporting substrate and then bonding it to a diamond substrate. Simultaneously, forming metal layers (i.e., a first metal layer and a second metal layer) on the two structures to be bonded before bonding improves the bonding strength. Furthermore, a back metal layer with grooves is formed on the back side of the diamond substrate after bonding. This adds a capacitor to adjust the device's electrical characteristics, and both the source electrode and the grooves in the back metal layer can serve as grounding electrodes, increasing the device's reliability.

[0037] In some implementations, the bonding process further includes:

[0038] Both the first metal layer in the first temporary bonding structure and the second metal layer in the second temporary bonding structure are subjected to surface activation treatment and X element implantation.

[0039] The surface activation treatment is: bombarding the surface with an ion beam of at least one of O, N, and Ar, preferably with a bombardment angle of less than 30° and a power of 50W-2kW;

[0040] The X element injection is: bombarding the surface with a target element; the target element preferably includes at least one of B, Si, Ge, Fe, Al, Cu, and In.

[0041] By performing the above treatment on the first and second metal layers, atomic-level direct bonding can be achieved, resulting in strong bonding. At the same time, the thermal resistance, impedance, and other parameters of the metal intermediate layer can be controlled, providing a new approach for the control of the electrical characteristics of the device.

[0042] In some embodiments, the process further includes, after the bonding and before the formation of the groove:

[0043] Annealing is performed at 50–300°C, preferably in an annealing atmosphere of N2, O2, or an inert gas; step annealing is preferred, with each step increasing from a low temperature to a high temperature in increments of 50°C up to 300°C, and each annealing session lasting no less than 30 minutes.

[0044] In some embodiments, the temporary protective substrate is covered by bonding it to the HEMT layer using high-temperature wax, high-temperature adhesive, or molten glass.

[0045] In some embodiments, the back metal layer, the first metal layer, and the second metal layer are each independently composed of one or more composites of Ti, Au, Cu, and Al.

[0046] In some embodiments, the supporting substrate is selected from at least one or a multilayer composite of SiC substrate, Si substrate, Al2O3 substrate, and GaN substrate.

[0047] In some embodiments, the diamond substrate has a thermal conductivity ≥800W / (m·K), a roughness ≤10nm, and a warpage ≤20μm.

[0048] In some embodiments, the thickness of the back metal layer is ≥50nm.

[0049] In some embodiments, the thickness of the intermediate metal layer is ≥10 nm.

[0050] Compared with the prior art, the present invention achieves the following technical effects:

[0051] (1) An intermediate metal layer is provided between the diamond substrate and the GaNHEMT layer of the present invention. This metal layer can facilitate the transfer of the HEMT layer from a substrate with poor heat dissipation and easy breakage (such as a silicon substrate, silicon carbide substrate, etc.) to the diamond. On the one hand, the high thermal conductivity of diamond solves the problems of poor heat dissipation, high radio frequency loss and easy breakage during dicing of existing devices. On the other hand, it solves the serious mismatch in crystal structure, lattice constant and thermal expansion coefficient of GaN directly epitaxially on diamond. Furthermore, the buffering effect of the intermediate metal layer reduces the surface roughness and local protrusion of diamond.

[0052] (2) The sandwich structure of the back metal layer, diamond substrate, and intermediate metal layer in this invention can form a capacitor, providing a new way to control the impedance, conductivity, and other electrical properties of GaN devices, thereby expanding the application range of GaN devices. At the same time, the grooves in the source and back metal layer can be used as grounding electrodes, increasing the reliability of the device.

[0053] (3) The diamond-based GaN device of the present invention, with diamond as the supporting substrate, is also suitable for large-size device processing.

[0054] (4) By performing multiple activation treatments on the first and second metal layers before bonding, atomic-level direct bonding with strong bonding is achieved, and the thermal resistance, impedance and other parameters of the metal intermediate layer are controlled, which increases the way for the electrical characteristics of the device to be controlled.

[0055] (5) The preparation method provided by the present invention has a simple overall process, and there are no strict environmental requirements for all steps, making it easier to implement and with low processing costs. Attached Figure Description

[0056] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0057] Figures 1 to 9 The diagram shows the structure obtained in each step of the diamond-based GaN device fabrication method provided by this invention. Detailed Implementation

[0058] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0059] The accompanying drawings illustrate various structural schematics according to embodiments of the present disclosure. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0060] In the context of this disclosure, when a layer / element is referred to as being "above" another layer / element, the layer / element may be directly above the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "above" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0061] Existing GaN HEMT devices suffer from major problems such as poor heat dissipation, significant video loss, and severe fragmentation during dicing. Diamond, with its high thermal conductivity, electrical insulation, and high hardness, is an ideal heat-conducting substrate, significantly improving heat dissipation efficiency and providing chip self-support. Therefore, replacing silicon and silicon carbide substrates in existing GaN HEMT devices with diamond substrates is a good option. However, the severe mismatch between diamond and GaN in terms of crystal structure, lattice constant, and coefficient of thermal expansion makes their integration extremely challenging.

[0062] To this end, the present invention has discovered that by using a metal-assisted bonding method to achieve direct bonding between GaN and diamond, the problems of diamond surface roughness, local protrusions, and warping after substrate thinning can be overcome. At the same time, by combining surface activation method and X element (target element) compensation technology, atomic-level direct bonding between wafer-level GaN epitaxial layer and diamond self-supporting substrate can be achieved at room temperature. This method has strong bonding performance, good thermal compatibility, and can achieve comprehensive control of interface bonding strength, electrical conductivity, thermal conductivity, and impedance.

[0063] The diamond-based GaN device provided by this invention comprises, from bottom to top, stacked as follows:

[0064] Back metal layer, diamond substrate, intermediate metal layer and HEMT layer;

[0065] The HEMT layer is made of GaN heterojunction material and has three electrodes: source, gate, and drain.

[0066] The diamond substrate has a groove that connects to the intermediate metal layer, and the back metal layer covers the sidewall of the groove; the HEMT layer has a contact hole that connects the source and the intermediate metal layer, and the contact hole is filled with metal that contacts the back metal layer and the intermediate metal layer.

[0067] In the above text, "connection" between the groove and the intermediate metal layer means that the groove penetrates the diamond substrate. The back metal layer covering the sidewalls of the groove means that the surface of the groove is metallized, making it conductive and electrically connected to the intermediate metal layer. The metal filling the contact hole can completely fill it, or only cover the sidewalls of the contact hole, or something in between. Regardless of the filling method, the purpose is to ensure a conductive connection between the source and the intermediate metal layer.

[0068] The metal materials in the back metal layer, the middle metal layer, or the contact holes can be the same or different. In some cases, this is related to the fabrication method; for example, structures formed simultaneously often use the same material. Optional metals include, but are not limited to, one or more composites of Ti, Au, Cu, W, and Al.

[0069] In addition, the intermediate metal layer can also be a composite layer of multiple stacked metal materials, which in some cases is related to the preparation method.

[0070] In some embodiments, the intermediate metal layer is doped with a target element and at least one ion selected from O, N, and Ar.

[0071] The bombardment effect generated by these doping and ion incorporation can activate the metal surface, making bonding easier. It can also reduce problems such as roughness and local protrusions on the diamond surface, and can regulate the electrical conductivity, thermal conductivity, impedance and other properties of the intermediate metal layer, thereby regulating the corresponding electrical properties of the device.

[0072] The target material elements mentioned above include, but are not limited to, at least one of B, Si, Ge, Fe, Al, Cu, and In.

[0073] In some embodiments, a 10–100 μm non-diamond substrate, preferably 10–50 μm, is further included between the intermediate metal layer and the HEMT layer. The non-diamond substrate, as a very thin layer of material, can act as a buffer to prevent damage to the HEMT layer during bonding.

[0074] Additionally, it is understandable that when a non-diamond substrate is present, the contact hole also penetrates the non-diamond substrate in order to achieve electrical connection.

[0075] The aforementioned non-diamond substrate may be selected from, but is not limited to, at least one or a multilayer composite of SiC substrate, Si substrate, Al2O3 substrate, and GaN substrate.

[0076] In some embodiments, the diamond substrate has a thermal conductivity ≥800 W / (mK), a roughness ≤10 nm, and a warpage less than 20 μm. Using a diamond substrate with these characteristics can result in better heat dissipation and lower radio frequency losses.

[0077] In some implementations, the thickness of the back metal layer is ≥50nm. The thickness of the back metal layer is related to the support strength and also affects the electrical characteristics of the device. Taking all factors into consideration, a thickness of 50nm or more is preferred.

[0078] In some embodiments, the thickness of the intermediate metal layer is ≥10nm, which, in conjunction with the thickness of the back metal layer, allows for a wider range of control over the electrical characteristics of the device, such as impedance and conductivity.

[0079] All the diamond-based GaN devices described above can be implemented using a bonding transfer method. This invention provides the following preferred methods.

[0080] The method includes the following steps:

[0081] Provide a supporting substrate;

[0082] Then, a HEMT layer is formed on the front side of the supporting substrate. The HEMT layer is made of GaN heterojunction material and has three electrodes: source, gate and drain.

[0083] A temporary protective substrate is placed over the HEMT layer;

[0084] Then, the entire support substrate is thinned or removed from the back side of the support substrate;

[0085] Then, on the side where the support substrate has been thinned or completely removed, a contact hole connecting to the source electrode is etched.

[0086] Then, a first metal layer is formed on one side of the opening of the contact hole, so that the first metal layer covers the sidewall of the contact hole and contacts the source electrode, thereby obtaining a first temporary bonding structure;

[0087] Provide diamond substrate;

[0088] A second metal layer is formed on the front side of the diamond substrate to obtain a second temporary bonding structure;

[0089] Using the first metal layer and the second metal layer as bonding surfaces, the first temporary bonding structure and the second temporary bonding structure are bonded together;

[0090] After the bonding, a groove communicating with the intermediate metal layer is etched on the back of the diamond.

[0091] A back metal layer is formed on the back of the diamond and covers the sidewalls of the groove;

[0092] Then the temporary protective substrate is removed.

[0093] The above method comprises four main stages: fabrication of the first temporary bond structure, fabrication of the second temporary bond structure, bonding, and post-processing. Each stage employs a specific sequence of steps to achieve the following effects:

[0094] The method of first forming a HEMT layer on a supporting substrate and then bonding and transferring it to a diamond substrate solves the problem of severe mismatch between GaN material and diamond crystal structure, lattice constant and thermal expansion coefficient.

[0095] Meanwhile, metal layers (i.e., the first metal layer and the second metal layer) are formed on the two structures to be bonded before bonding, thereby improving the bonding strength.

[0096] In addition, a back metal layer with grooves is formed on the back of the diamond after bonding. This adds a capacitor to regulate the electrical characteristics of the device, and the grooves in the source and back metal layer can be used as grounding electrodes, increasing the reliability of the device.

[0097] In some implementations, the bonding process further includes:

[0098] Both the first metal layer in the first temporary bonding structure and the second metal layer in the second temporary bonding structure are subjected to surface activation treatment and X element implantation.

[0099] The surface activation treatment is: bombarding the surface with an ion beam of at least one of O, N, and Ar, preferably with a bombardment angle of less than 30° and a power of 50W-2kW;

[0100] The X element injection is: bombarding the surface with a target element; the target element preferably includes at least one of B, Si, Ge, Fe, Al, Cu, and In.

[0101] These two processes enable direct atomic-level bonding with strong bonding strength, while also controlling parameters such as thermal resistance and impedance of the metal interlayer, providing a new approach to the electrical characteristic modulation of devices. Among them, the bombardment angle during surface activation treatment is crucial to surface activation and electrical characteristic modulation; when the bombardment angle is below 30°, better results can be achieved.

[0102] In some embodiments, the process further includes, after the bonding and before the formation of the groove:

[0103] Annealing is performed at 50–300°C, preferably in an annealing atmosphere of N2, O2, or an inert gas; step annealing is preferred, with each step increasing from a low temperature to a high temperature in increments of 50°C up to 300°C, and each annealing session lasting no less than 30 minutes.

[0104] Annealing can further refine the grains and eliminate material defects.

[0105] In some embodiments, the temporary protective substrate is covered by bonding it to the HEMT layer using high-temperature wax, high-temperature adhesive, or molten glass.

[0106] Temporary protective substrates should be made of materials that are less affected by subsequent processes.

[0107] In some embodiments, the back metal layer, the first metal layer, and the second metal layer are each independently composed of one or more composites of Ti, Au, and Cu.

[0108] In some embodiments, the supporting substrate is selected from at least one or a multilayer composite of SiC substrate, Si substrate, Al2O3 substrate, and GaN substrate.

[0109] In some embodiments, the diamond substrate has a thermal conductivity ≥800W / (mK), a roughness ≤10nm, and a warpage ≤20μm.

[0110] In some embodiments, the thickness of the back metal layer is ≥50nm.

[0111] In some embodiments, the thickness of the intermediate metal layer is ≥10 nm.

[0112] The present invention will be described in detail below through specific embodiments.

[0113] Example 1

[0114] A method for fabricating diamond-based GaN devices

[0115] (I) Fabrication of the first temporary bond structure

[0116] Step S11: Provide a support substrate. In this embodiment, a silicon substrate 101 is used as an example.

[0117] Step S12: Then, a HEMT layer 110 is formed on the front side of the silicon substrate 101. The HEMT layer is made of GaN material and has three electrodes: source 105, gate 104 and drain 103.

[0118] Step S13: Bond the temporary protective substrate 107 to the HEMT layer 110 using high-temperature wax 106, as shown. Figure 1 As shown.

[0119] Step S14: Then, the silicon substrate 101 is thinned from the back side to 10–100 μm, such as… Figure 2 As shown.

[0120] Step S15: Then, etch the contact hole 109 connecting the source 105 on the back side of the silicon substrate 101.

[0121] Step S16: Then, a first metal layer 108 is formed on the side of the opening of the contact hole 109 (i.e., the back side of the silicon substrate 101), so that the first metal layer 108 covers the sidewall of the contact hole 109 and contacts the source 105, thereby obtaining a first temporary bonding structure, such as... Figure 3 As shown.

[0122] (II) Fabrication of the Second Temporary Bond Structure

[0123] Step S21: Provide a diamond substrate 201.

[0124] Step S22: A second metal layer 202 is formed on the front side of the diamond substrate 201 to obtain a second temporary bonding structure, as shown below. Figure 4 As shown.

[0125] (III) Bonding

[0126] Step S31: As Figure 5 and 6 The angles indicated by the arrows are used to perform surface activation treatment and X-element implantation on the first metal layer 108 in the first temporary bonding structure and the second metal layer 202 in the second temporary bonding structure.

[0127] The surface activation treatment is as follows: the surface is bombarded with an ion beam of at least one of O, N, and Ar at a bombardment angle of less than 30° and a power of 50W-2kW.

[0128] X-element injection is the process of bombarding the surface with a target element; the target element can be at least one of Si, Ge, and Fe.

[0129] Step S32: Then, using the activated first metal layer 108 and second metal layer 202 as bonding surfaces, the first temporary bonding structure and the second temporary bonding structure are bonded together to obtain the following... Figure 7 The structure shown.

[0130] (iv) Follow-up processing

[0131] Step S32: Etch a groove 204 communicating with the intermediate metal layer on the back side of the diamond substrate 201.

[0132] Step S32: A back metal layer 203 is formed on the back side of the diamond substrate 201, covering the sidewalls of the groove 204, to obtain the following: Figure 8 The structure shown.

[0133] Step S32: Then remove the temporary protective substrate 107 and high-temperature wax 106 to obtain the following: Figure 9 The structure shown.

[0134] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A diamond-based GaN device, characterized in that, Including those stacked from bottom to top: Back metal layer, diamond substrate, intermediate metal layer and HEMT layer; The HEMT layer is made of GaN heterojunction material and has three electrodes: source, gate, and drain. The diamond substrate has a groove that connects to the intermediate metal layer, and the back metal layer covers the sidewall of the groove; the HEMT layer has a contact hole that connects the source electrode and the intermediate metal layer, and the contact hole is filled with metal that allows the source electrode and the intermediate metal layer to contact each other.

2. The diamond-based GaN device according to claim 1, characterized in that, The intermediate metal layer is doped with target material elements and at least one ion selected from O, N, and Ar.

3. The diamond-based GaN device according to claim 2, characterized in that, The target material element includes at least one of B, Si, Ge, Fe, Al, Cu, and In.

4. The diamond-based GaN device according to any one of claims 1-3, characterized in that, The intermediate metal layer and the HEMT layer also include a 10~100μm non-diamond substrate.

5. The diamond-based GaN device according to any one of claims 1-3, characterized in that, The intermediate metal layer and the HEMT layer also include a 10~50μm non-diamond substrate.

6. The diamond-based GaN device according to claim 4, characterized in that, The non-diamond substrate is selected from at least one or a multilayer composite of SiC substrate, Si substrate, Al2O3 substrate, and GaN substrate.

7. The diamond-based GaN device according to claim 5, characterized in that, The non-diamond substrate is selected from at least one or a multilayer composite of SiC substrate, Si substrate, Al2O3 substrate, and GaN substrate.

8. The diamond-based GaN device according to any one of claims 1-3, characterized in that, The diamond substrate has a thermal conductivity ≥800 W / (m·K), a roughness ≤10nm, and a warpage ≤20μm.

9. The diamond-based GaN device according to any one of claims 1-3, characterized in that, The thickness of the back metal layer is ≥50nm; And / or, the thickness of the intermediate metal layer is ≥10nm; And / or, the back metal layer and the middle metal layer are each independently composed of one or more composites of Ti, Au, Cu, and Al.

10. A method for fabricating a diamond-based GaN device, characterized in that, Includes the following steps: Provide a supporting substrate; Then, a HEMT layer is formed on the front side of the supporting substrate. The HEMT layer is made of GaN heterojunction material and has three electrodes: source, gate and drain. A temporary protective substrate is placed over the HEMT layer; Then, the entire support substrate is thinned or removed from the back side of the support substrate; Then, on the side where the support substrate has been thinned or completely removed, a contact hole connecting to the source electrode is etched. Then, a first metal layer is formed on one side of the opening of the contact hole, so that the first metal layer covers the sidewall of the contact hole and contacts the source electrode, thereby obtaining a first temporary bonding structure; Provide diamond substrates; A second metal layer is formed on the front side of the diamond substrate to obtain a second temporary bonding structure; Using the first metal layer and the second metal layer as bonding surfaces, the first temporary bonding structure and the second temporary bonding structure are bonded together; After bonding, the first metal layer and the second metal layer form an intermediate metal layer; After the bonding, a groove communicating with the intermediate metal layer is etched on the back side of the diamond substrate; A back metal layer is formed on the back side of the diamond substrate and covers the sidewalls of the groove; Then the temporary protective substrate is removed.

11. The preparation method according to claim 10, characterized in that, The process includes the following steps prior to the bonding: Both the first metal layer in the first temporary bonding structure and the second metal layer in the second temporary bonding structure are subjected to surface activation treatment and X element implantation. The surface activation treatment is: surface bombardment with an ion beam of at least one of O, N, and Ar; The X element injection is: bombarding the surface with a target element; the target element includes at least one of B, Si, Ge, Fe, Al, Cu, and In.

12. The preparation method according to claim 11, characterized in that, The surface activation treatment is performed at a bombardment angle of less than 30° and a power of 50W-2kW.

13. The preparation method according to claim 11, characterized in that, The process includes the following steps after the bonding and before the formation of the groove: Anneal at 50~300℃.

14. The preparation method according to claim 13, characterized in that, The annealing atmosphere is N2, O2 or an inert gas.

15. The preparation method according to claim 10, characterized in that, The method for covering the temporary protective substrate is to bond the temporary protective substrate to the HEMT layer using high-temperature wax, high-temperature adhesive, or molten glass.

16. The preparation method according to claim 10, characterized in that, The back metal layer, the first metal layer, and the second metal layer are each independently composed of one or more of Ti, Au, Cu, and Al. And / or, The supporting substrate is selected from at least one or a multilayer composite of SiC substrate, Si substrate, Al2O3 substrate, and GaN substrate; And / or, The diamond substrate has a thermal conductivity ≥800 W / (m·K), a roughness ≤10nm, and a warpage ≤20μm. And / or, The thickness of the back metal layer is ≥50nm; And / or, The thickness of the intermediate metal layer is ≥10nm.

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