Подложки с алмазным теплоотводом для эпитаксиального роста GaN
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | Письма в журнал технической физики |
| Authors | И.О. Майборода, И.А. Черных, Vadim Sedov, A. S. Altakhov, А.А. Андреев |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research details the successful fabrication and characterization of Gallium Nitride (GaN) heterostructures grown on novel substrates featuring an integrated polycrystalline diamond heat sink.
- Core Innovation: Developed Si(111)/Polycrystalline Diamond substrates to enable high-power GaN electronics while managing the severe Coefficient of Thermal Expansion (CTE) mismatch between GaN and diamond.
- Substrate Structure: The substrate consists of a thin 234 nm layer of monocrystalline Si(111) bonded to a 250 µm layer of high-quality polycrystalline diamond.
- Thermal Performance: The diamond heat sink achieved a high thermal conductivity of 1290 ± 190 W/(m·K), which is approximately three times greater than that of Silicon Carbide (SiC).
- Epitaxy Method: GaN heterostructures, designed to host a two-dimensional electron gas (2DEG), were grown using Ammonia Molecular Beam Epitaxy (NH3-MBE).
- Electrical Performance: The resulting 2DEG exhibited high electron mobility (1600 cm2/(V·s)) and low sheet resistance (300 Ω/square).
- Structural Quality: The crystalline quality, measured by the FWHM of the GaN 0002 reflection, was 0.4°, demonstrating quality comparable to structures grown on standard Si substrates.
- Conclusion: This technology provides a viable, high-performance platform for electronic devices requiring high specific heat dissipation, overcoming previous integration challenges.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Thermal Conductivity | 1290 ± 190 | W/(m·K) | Measured via laser flash method |
| Diamond Layer Thickness | 250 | µm | Grown via MPCVD |
| Silicon Layer Thickness | 234 | nm | Final thickness of Si(111) layer |
| Total Nitride Layer Thickness | 1.8 | µm | Sum of all epitaxial layers |
| Electron Mobility (2DEG) | 1600 | cm2/(V·s) | In the HEMT channel |
| Sheet Resistance (2DEG) | 300 | Ω/square | In the HEMT channel |
| FWHM (GaN 0002 Reflection) | 0.4 | ° | X-ray Diffraction rocking curve |
| Saturation Current Density | 0.95 | A/mm | Measured on test structures |
| Diamond Growth Temperature | 840 ± 20 | °C | MPCVD process |
| Diamond Growth Pressure | 75 | Torr | MPCVD process |
| MW Power (Diamond Growth) | 4.5 | kW | Microwave Plasma CVD |
| Diamond Growth Time | 72 | h | Total deposition duration |
| Substrate Size (Epitaxy) | 14 x 14 | mm | Area used for GaN growth |
| Si Substrate Orientation | (111) | N/A | Starting material orientation |
Key Methodologies
Section titled “Key Methodologies”The fabrication process involved three main stages: diamond heat sink deposition, Si layer thinning, and GaN heterostructure epitaxy.
1. Diamond Heat Sink Fabrication (MPCVD)
Section titled “1. Diamond Heat Sink Fabrication (MPCVD)”- Starting Material: Si(111) on insulator (SOI) substrate.
- Deposition Method: Microwave Plasma Chemical Vapor Deposition (MPCVD) using a CH4/H2 gas mixture.
- Growth Parameters:
- Total Gas Flow: 500 sccm.
- Pressure: 75 Torr.
- MW Power: 4.5 kW.
- Temperature: 840 ± 20 °C.
- Growth Recipe:
- Initial Phase (2 hours): 6% CH4/H2 concentration to ensure good adhesion and high film quality.
- Main Phase: Concentration increased to 10% CH4/H2 to maximize the deposition rate.
- Result: A 250 µm thick polycrystalline diamond layer was grown.
- Si Thinning: The Si layer was subsequently thinned to 234 nm using sequential mechanical grinding followed by plasma etching in Xenon Difluoride (XeF2).
2. GaN Heterostructure Epitaxy (NH3-MBE)
Section titled “2. GaN Heterostructure Epitaxy (NH3-MBE)”- Equipment: SemiTeq STE3N Molecular Beam Epitaxy system utilizing an ammonia (NH3) source.
- Interface and Buffer Layer Growth:
- Nitridation: Crystalline Silicon Nitride (Si3N4) was formed on the Si surface using NH3 flow.
- Al Deposition: Two monolayers of Aluminum (Al) were deposited at 600 °C.
- Low-Temp AlN: 10 nm Aluminum Nitride (AlN) layer grown at 900 °C.
- High-Temp Buffer: AlN buffer layer grown at 1200 °C with added Gallium flux to improve surface morphology and reduce defect density.
- Strain Compensation Stack: To manage the compressive stress induced by CTE mismatch during cooling, three sequential AlGaN-AlN-AlGaN layers were grown.
- Final Structure: The growth concluded with a 300 nm GaN channel layer and a 26 nm AlN/AlGaN barrier layer.
3. Characterization
Section titled “3. Characterization”- Thermal: Thermal conductivity measured using the laser flash method.
- Structural: Atomic Force Microscopy (AFM) confirmed a smooth surface relief (RMS roughness 1.8 nm) and X-ray Diffraction (XRD) confirmed crystalline quality (0.4° FWHM for GaN 0002).
- Electrical: Hall measurements confirmed high electron mobility and low sheet resistance.
Commercial Applications
Section titled “Commercial Applications”This technology is highly relevant for applications demanding extreme power density and superior thermal management, where traditional SiC or Si substrates are thermally limiting.
- High Power RF and Microwave Electronics:
- GaN High Electron Mobility Transistors (HEMTs) for 5G/6G infrastructure.
- High-frequency radar and electronic warfare systems.
- Satellite communication amplifiers.
- High-Efficiency Power Conversion:
- Power modules for Electric Vehicles (EVs) and hybrid powertrains.
- Industrial power supplies and motor control systems operating at high switching frequencies.
- Defense and Aerospace:
- Compact, high-power density modules for airborne and space-based systems where weight and heat dissipation are critical constraints.
- Advanced Thermal Management:
- Integration of diamond as a functional heat spreader directly into semiconductor stacks, enabling higher junction temperatures and improved device reliability compared to conventional packaging solutions.
View Original Abstract
Silicon wafers with a polycrystalline diamond heat sink were fabricated; silicon and diamond layers were 300 nm and 250 µm thick, respectively. The thermal conductivity of the diamond was 1290 ± 190 W / m • K. Nitride heterostructures with a two-dimensional electron gas on silicon substrates with a polycrystalline diamond heat sink were grown by ammonia molecular beam epitaxy. Carrier mobility in two-dimensional electron gas and sheet resistance were 1400 cm2 /V•s of 300 Ω/□, respectively.