A method for fabricating a wide bandgap semiconductor and diamond hetero-integrated substrate

Abstract

The application discloses a preparation method of a wide-bandgap semiconductor and diamond hetero-integrated substrate; the preparation method comprises the following steps: taking a wide-bandgap semiconductor material as a functional layer substrate, firstly depositing / adhering a transition layer and a bearing layer on the top of the wide-bandgap semiconductor material, then thinning and removing the wide-bandgap semiconductor original substrate, depositing a polycrystalline diamond thick film on the back surface of the wide-bandgap semiconductor original substrate by adopting a chemical vapor deposition method, and finally stripping the top transition layer and the bearing layer to obtain a complete wide-bandgap semiconductor-diamond composite substrate. The process of the application has strong compatibility with a semiconductor device manufacturing process, and can realize large-scale preparation; the prepared polycrystalline diamond thick film has high thermal conductivity, and forms a close interface combination with the wide-bandgap semiconductor, so that the boundary thermal resistance is small, and the thermal transport limitation of a traditional substrate is effectively broken; the composite substrate can be widely applied to scenes with strict heat dissipation performance requirements, and provides core support for device power density improvement and long-term reliability guarantee.

Description

Technical Field

[0001] This invention relates to the field of wide bandgap semiconductor substrate fabrication technology, and more specifically, to a method for fabricating a wide bandgap semiconductor and a diamond heterogeneous integrated substrate. Background Technology

[0002] Wide bandgap semiconductor materials, with silicon carbide (SiC) and gallium nitride (GaN) as the core and gallium oxide (Ga2O3) and diamond as emerging directions, have a bandgap much larger than that of silicon (silicon's bandgap is only 1.12 eV, while wide bandgap materials generally exceed 3 eV). Compared with traditional silicon-based materials, they have achieved a fundamental breakthrough in electrical and thermal physical properties and have demonstrated strong adaptability and application value in many strategic emerging fields.

[0003] Despite the numerous advantages and broad application prospects of wide-bandgap semiconductors, their industrialization and full performance realization still face a core bottleneck—heat dissipation. This issue has become a key factor restricting their large-scale application. Although SiC material itself has a thermal conductivity of 350-490 W / m²... -1 ·K -1 GaN's thermal conductivity far exceeds that of silicon-based materials (130-230 W / m²). -1 ·K -1 While similar to silicon, wide-bandgap devices exhibit high power density, high frequency operation, and high-temperature characteristics, along with challenges in packaging and interface compatibility, amplifying the heat dissipation pressure. From a heat conduction perspective, heat from wide-bandgap devices must be conducted through the chip, solder layer, substrate, and housing to the heat sink. However, traditional silicon-based packaging materials lack sufficient temperature resistance and thermal conductivity. Low-thermal-resistance packaging solutions such as silver sintering and active metal brazing substrates are costly and require improved process yields. Furthermore, the mismatch in thermal expansion coefficients between different materials easily leads to interface cracks and voids during temperature cycling, resulting in a significant increase in thermal resistance. In addition, micron-level localized hot spots easily form inside the device at high frequencies, with temperatures far exceeding the average junction temperature, posing a risk of thermal runaway. The heteroepitaxial structure (GaN-on-Si / SiC) commonly used in GaN devices introduces additional interface thermal resistance, further hindering heat dissipation. This heat dissipation challenge is evident in various application scenarios. It is worth noting that the heat dissipation problem is not an inherent defect of the material, but a systemic problem caused by the combined effects of material properties, packaging processes, and application scenarios. The progress of solving this problem is directly related to the efficiency of converting wide-bandgap semiconductor devices from laboratory performance to industrial value.

[0004] Diamond, as an emerging ultra-wide bandgap material, has emerged as a potential solution to the heat dissipation bottleneck of wide bandgap semiconductors due to its exceptional heat dissipation performance. Its advantages in the field of heat dissipation are truly revolutionary. Diamond's thermal conductivity exceeds 2000 W / m². -1 ·K -1Diamond thermal conductivity is more than 5 times that of copper and 4-6 times that of SiC, reaching the highest level among known semiconductor materials. It can effectively reduce near-junction thermal resistance and chip junction temperature, making it particularly suitable for the high heat flux density heat dissipation requirements of wide-bandgap devices under high-frequency, high-power conditions. However, to achieve efficient integration of diamond with wide-bandgap semiconductors and fully leverage its heat dissipation advantages, two core technical challenges remain: bonding and heteroepitaxial growth. The bottlenecks in these two technologies mainly focus on four aspects: interface compatibility, process control, thermal resistance balance, and cost compatibility. Firstly, the coefficient of thermal expansion (CTE) is severely mismatched with the lattice, making the interface prone to failure. Diamond's CTE is only 1 ppm / K, significantly different from SiC (4-6 ppm / K) and GaN (5-7 ppm / K). This easily generates thermal stress during bonding and high-temperature operating cycles, leading to interface cracks and delamination, which can only be alleviated, not completely eliminated, by the intermediate layer. During heteroepitaxial growth, thermal stress can also cause epitaxial layer cracking and substrate damage. Meanwhile, diamond has a high lattice mismatch with GaN and Ga2O3, resulting in numerous defects in the epitaxial layer and degrading device performance. Secondly, the quality of the bonding layer and epitaxial layer is difficult to control, leading to high interfacial thermal resistance. Bonding is prone to producing porosity and voids, and even advanced processes suffer from insufficient thermal stability. The transition intermediate layer has extremely low thermal conductivity, creating a dilemma in thickness selection. Uneven nucleation during epitaxy leads to inconsistent grain sizes and increased grain boundary thermal resistance. Improper protective layer design can also increase interfacial thermal resistance, making it difficult to achieve ideal levels. Thirdly, process compatibility is poor and the process is challenging. Diamond has high hardness, making it difficult to meet bonding standards in terms of surface roughness and warpage. The high-temperature, high-vacuum conditions for bonding are incompatible with existing packaging processes, and large-size wafer bonding technology is immature. Mainstream epitaxial processes have low growth rates and insufficient thickness control precision, parameter fluctuations easily increase defects, plasma easily damages the substrate, and large-size epitaxial technology has not yet been mastered. Fourthly, doping characteristics restrict device integration and fabrication. Diamond N-type doping efficiency is extremely low, pn junction fabrication has not yet been achieved, and its electrical performance is mismatched with that of SiC and GaN after bonding. Furthermore, doping during epitaxy is uneven, boron doping at room temperature limits carrier concentration, and dopants easily form impurities and defects. Fifth, it is costly and difficult to scale up. Bonding requires high-purity diamond, specialized materials and equipment, resulting in low process yields. The high cost of epitaxial substrates, precursors, and equipment, coupled with slow growth and low yields, further increases costs. Currently, it is only being explored and validated in high-end, niche applications. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, the present invention aims to provide a method for fabricating a wide-bandgap semiconductor-diamond composite substrate with high heat dissipation efficiency for high-efficiency heat dissipation scenarios. The fabrication process of this invention is highly compatible with semiconductor device manufacturing processes, enabling large-scale fabrication. The polycrystalline diamond thick film prepared by this invention exhibits high thermal conductivity and forms a tight interface bond with the wide-bandgap semiconductor, resulting in low boundary thermal resistance. The resulting composite substrate can improve the thermal transport efficiency of devices, thereby enhancing device performance and lifespan, effectively overcoming the thermal transport limitations of traditional substrates. The composite substrate of this invention can be widely applied in scenarios with stringent heat dissipation requirements, such as high-power RF devices, AI accelerator chips (GPUs / TPUs), automotive power modules, and high-density integrated circuits, providing core support for improving device power density and ensuring long-term reliability. The technical solution of this invention is described in detail below.

[0006] A method for fabricating a wide-bandgap semiconductor and a diamond heterostructure substrate includes the following steps: Step 1: Deposit a transition layer on a wide bandgap semiconductor material; Step 2: Using a wafer / carrier as a carrier layer, the carrier layer is bonded to a wide bandgap semiconductor material by growth or adhesion methods, and then edge impurities are removed; Step 3: Remove the original substrate of the wide bandgap semiconductor material, and deposit a nucleation layer on the surface of the wide bandgap semiconductor material where the original substrate has been removed; Step 4: Deposit a thick film of polycrystalline diamond on the nucleation layer; Step 5: Remove the transition layer and carrier layer on the wide bandgap semiconductor material to obtain the wide bandgap semiconductor and diamond heterostructure substrate.

[0007] In this invention, in step one, the wide bandgap semiconductor material is selected from any one of gallium nitride (GaN), gallium oxide (Ga2O3), silicon carbide (SiC), aluminum nitride (AlN), or diamond; the wide bandgap semiconductor material is grown on a primary substrate, which includes any one of Si, SiC, sapphire, or GaN.

[0008] In this invention, in step one, the transition layer is selected from any one of silicon nitride (SiN), silicon oxide (SiO), or silicon (Si); the thickness of the transition layer is between 100 nm and 500 nm, and the deposition is performed by plasma chemical vapor deposition or atomic layer deposition; the temperature range of plasma chemical vapor deposition or atomic layer deposition is 250 °C to 300 °C.

[0009] In this invention, in step two, diamond is grown on the transition layer as a support layer, or silicon or silicon carbide is bonded as a support layer by adhesive bonding.

[0010] In this invention, in step three, the original wide-bandgap semiconductor material substrate is removed by laser substrate stripping, hydrogen ion implantation stripping, polishing, and plasma dry etching.

[0011] In this invention, in step three, the expansion coefficient of the nucleation layer material is between that of semiconductor materials and polycrystalline diamond, and its thermal conductivity is higher than that of semiconductor materials, with a thickness ranging from 5nm to 100nm.

[0012] In this invention, in step four, a thick polycrystalline diamond film is deposited on the nucleation layer using chemical vapor deposition (CVD). The thickness of the deposited polycrystalline diamond film is between 300 μm ± 20 μm. CVD includes, but is not limited to, hot filament chemical vapor deposition (HFCVD), microwave plasma chemical vapor deposition (MPCVD), direct current arc jet chemical vapor deposition (DC Arc Jet CVD), direct current hot cathode chemical vapor deposition (DC-HC CVD), and combustion flame chemical vapor deposition (CFCVD). In a specific embodiment, a thick polycrystalline diamond film is deposited on the nucleation layer using microwave plasma chemical vapor deposition, with methane as the carbon source and hydrogen as the activator. The methane concentration is between 1 vol% and 3 vol%, and the growth temperature is between 800℃ and 900℃.

[0013] In this invention, in step five, the transition layer and the support layer are removed by chemical etching, chemical mechanical polishing, or laser ablation.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: Diamond substrates possess extremely high thermal conductivity compared to pristine substrates, enabling rapid heat transport during the operation of GaN HEMT (High Electron Mobility Transistor) devices. This effectively improves the power density and lifespan of GaN HEMT devices. The core value of this invention, which directly grows diamond after removing the original substrate, lies in fundamentally solving the bottlenecks of thermal resistance, stress, and reliability in the bonding path at the interface. Through metallurgical-grade bonding and in-situ stress control, it maximizes the high thermal conductivity of diamond, making it particularly suitable for the industrialization needs of next-generation high-power-density GaN devices. This invention offers significant advantages in both overall performance and cost, representing the mainstream direction for heat dissipation technology in future GaN HEMT devices. This invention can solve the heat dissipation bottleneck problems in scenarios such as RF chips, high-power electronic devices, and AI computing chips. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the fabrication process of the wide bandgap semiconductor and diamond heterostructure integrated substrate of the present invention.

[0016] Figure 2This is a cross-sectional SEM image of the diamond-GaN sample after laser cutting in Example 1.

[0017] Figure 3 This is a cross-sectional SEM image of the sample after laser cutting or hydrogen ion implantation and plasma dry etching in Example 1.

[0018] Figure 4 This is a cross-sectional SEM image of the sample after high thermal conductivity diamond was deposited at the bottom of GaN in Example 1.

[0019] Figure 5 This is a cross-sectional SEM image of the GaN-diamond composite substrate obtained after removing the top diamond sacrificial layer of GaN in Example 1. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and examples. The embodiments of the present invention include, but are not limited to, the following examples.

[0021] Example 1

[0022] A method for preparing a GaN-diamond composite substrate, such as... Figure 1 As shown, it includes the following steps: (1) A 200 nm silicon dioxide layer is deposited on GaN on a silicon substrate as a transition layer; (2) A 100 μm diamond layer was deposited on the transition layer as a sacrificial layer; after depositing the diamond sacrificial layer, the sample was cut around it using a laser, such as... Figure 2 As shown, the cut samples, from top to bottom, are diamond-gallium nitride-silicon; (3) The original substrate of the sample was removed by laser lift-off and plasma dry etching (at this time, the cross-sectional SEM image of the material is as follows). Figure 3 As shown, a 5nm silicon nitride layer is deposited on the surface of the removed original substrate as a nucleation layer; (4) A 100 μm polycrystalline diamond was deposited in a 3 vol% CH4 environment (CH4+H2), and its cross-sectional SEM image is shown below. Figure 4 As shown; (5) Wet etching with 6% HF was used to remove the transition layer and the diamond sacrificial layer to obtain the GaN-diamond composite substrate; the cross-sectional SEM image of the GaN-diamond composite substrate after removing the diamond sacrificial layer is shown in Figure 1. Figure 5 As shown.

[0023] The GaN-diamond composite substrate prepared in Example 1 was tested using the time-domain thermal reflectometry method. The results showed that the thermal conductivity of the composite substrate was as high as 1800 W / m. -1 K -1 The interfacial thermal resistance is only 7 μm. 2K GW -1 .

[0024] Example 2

[0025] A method for preparing a GaN-diamond composite substrate, such as... Figure 1 As shown, it includes the following steps: (1) A 200 nm silicon dioxide layer is deposited on GaN on a SiC substrate as a transition layer; (2) A diamond layer with a thickness of 100 μm was deposited as a support layer; after depositing the diamond sacrificial layer, the sample was cut around it with a laser. The cut sample was diamond-gallium nitride-silicon carbide from top to bottom. (3) The original silicon carbide substrate was removed by laser lift-off and plasma dry etching; 5 nm silicon nitride was deposited on the surface of the removed original substrate as a nucleation layer; (4) Deposit 100 μm polycrystalline diamond in an environment of 2 vol% CH4 (CH4+H2); (5) Use 6% HF for wet etching to remove the support layer and obtain GaN-diamond composite substrate.

[0026] The GaN-diamond composite substrate prepared in Example 2 was tested using the time-domain thermal reflectometry method. The results showed that the thermal conductivity of the composite substrate was as high as 1800 W / m. -1 K -1 The interfacial thermal resistance is only 5 μm. 2 K GW -1 .

Claims

1. A method for fabricating a wide-bandgap semiconductor and a diamond heterostructure substrate, characterized in that, Includes the following steps: Step 1: Deposit a transition layer on a wide bandgap semiconductor material; Step 2: Using a wafer / carrier as a carrier layer, the carrier layer is bonded to a wide bandgap semiconductor material by growth or adhesion methods, and then edge impurities are removed; Step 3: Remove the original substrate of the wide bandgap semiconductor material, and deposit a nucleation layer on the surface of the wide bandgap semiconductor material where the original substrate has been removed; Step 4: Deposit a thick polycrystalline diamond film on the nucleation layer; Step 5: Remove the transition layer and carrier layer on the wide bandgap semiconductor material to obtain the wide bandgap semiconductor and diamond heterostructure substrate.

2. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, In step one, the wide bandgap semiconductor material is selected from gallium nitride (GaN), gallium oxide (Ga2O3), silicon carbide (SiC), aluminum nitride (AlN), or diamond; the wide bandgap semiconductor material is grown on the original substrate, which is selected from Si, SiC, sapphire, or GaN.

3. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, In step one, the transition layer is selected from any one of silicon nitride (SiN), silicon oxide (SiO), or silicon (Si); the thickness of the transition layer is between 100 nm and 500 nm, and the deposition is performed by plasma chemical vapor deposition or atomic layer deposition; the temperature range of plasma chemical vapor deposition or atomic layer deposition is 250 °C to 300 °C.

4. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, In step two, diamond is grown on the transition layer as a support layer, or silicon or silicon carbide is bonded as a support layer by adhesive bonding.

5. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, In step three, the original wide-bandgap semiconductor material substrate is removed by laser substrate stripping, hydrogen ion implantation stripping, polishing, and plasma dry etching.

6. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, In step three, the expansion coefficient of the nucleation layer material is between that of semiconductor materials and polycrystalline diamond, and its thermal conductivity is higher than that of semiconductor materials, with a thickness ranging from 5nm to 100nm.

7. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, In step four, the thickness of the deposited polycrystalline diamond film is between 300 μm ± 20 μm; a polycrystalline diamond film is deposited on the nucleation layer by microwave plasma chemical vapor deposition, with methane as the carbon source and hydrogen as the activator, the methane concentration between 1 vol% and 3 vol%, and the growth temperature between 800℃ and 900℃.

8. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, In step five, the transition layer and the carrier layer are removed by chemical etching, chemical mechanical polishing, or laser ablation.

9. The method for fabricating a wide bandgap semiconductor and a diamond heterojunction substrate according to claim 1, characterized in that, The fabricated wide-bandgap semiconductors and diamond heterostructure substrates are designed for heat dissipation applications.

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