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 |
Technical Documentation & Analysis: GaN HEMT on Si/Diamond Substrates
Section titled “Technical Documentation & Analysis: GaN HEMT on Si/Diamond Substrates”Executive Summary
Section titled “Executive Summary”This research successfully demonstrates the fabrication of high-performance GaN HEMT heterostructures on novel Silicon-on-Polycrystalline Diamond (Si/PCD) substrates, addressing critical thermal management challenges in high-power electronics.
- Thermal Advantage: The integration of a 250 µm Polycrystalline Diamond (PCD) heat spreader achieved a thermal conductivity (k) of 1290 ± 190 W/(m·K), significantly exceeding that of standard SiC substrates.
- Structural Quality: Despite the large Coefficient of Thermal Expansion (CTE) mismatch between GaN and diamond, the use of a thin Si layer (234 nm) and AlGaN/AlN buffer layers resulted in crack-free epitaxy and excellent structural quality (GaN 0002 FWHM of 0.4°).
- Device Performance: The resulting heterostructures exhibited high 2DEG mobility (1600 cm²/(V·s)) and low sheet resistance (300 Ω/□), matching performance achieved on standard Si substrates.
- Methodology: The PCD layer was deposited via Microwave Plasma Chemical Vapor Deposition (MPCVD), followed by precise mechanical and plasma thinning of the Si layer to achieve the required nanometer thickness.
- Core Value Proposition: This Si/PCD platform is highly promising for next-generation electronic devices requiring high power density and superior heat dissipation capabilities.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the analysis of the Si/Diamond substrate and the resulting GaN heterostructure.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Thermal Conductivity (k) | 1290 ± 190 | W/(m·K) | Measured via Laser Flash Method |
| Polycrystalline Diamond (PCD) Thickness | 250 | µm | MPCVD deposited heat spreader |
| Silicon (Si) Layer Thickness | 234 | nm | Final thinned layer on PCD |
| Nitride Layer Total Thickness | 1.8 | µm | Sum of all GaN/AlGaN/AlN layers |
| Electron Mobility (2DEG) | 1600 | cm²/(V·s) | In the GaN HEMT structure |
| Sheet Resistance (Rsheet) | 300 | Ω/□ | In the GaN HEMT structure |
| GaN (0002) Rocking Curve FWHM | 0.4 | ° | Structural quality metric |
| RMS Surface Roughness (Si/Diamond) | 1.8 | nm | Measured via AFM on the final surface |
| Substrate Size Used | 14 x 14 | mm | Sample dimensions |
Key Methodologies
Section titled “Key Methodologies”The fabrication of the high-quality Si/PCD substrate and subsequent epitaxy involved precise, multi-step processing, highlighting the need for specialized MPCVD and thinning capabilities.
- PCD Deposition (MPCVD):
- Reactor: WT-100 (2.45 GHz) plasma-chemical setup.
- Gas Mixture: Methane (CH4) / Hydrogen (H2).
- Gas Flow: Total flow 500 sccm.
- Pressure: 75 Torr.
- Microwave Power: 4.5 kW.
- Growth Profile: Initial 2 hours at 6% CH4/H2 (for adhesion/quality), then increased to 10% CH4/H2 (for increased growth rate).
- Temperature: Substrate maintained at 840 ± 20 °C.
- Duration: 72 hours, yielding 250 µm thickness.
- Substrate Thinning and Preparation:
- The initial Si substrate was thinned to the required 234 nm thickness.
- This was achieved through sequential mechanical grinding/polishing followed by plasma etching in Xenon Difluoride (XeF2).
- Nitride Epitaxy (NH3-MBE):
- System: SemiTeq STE3N using ammonia (NH3) source.
- Buffer Stack: Complex 3-fold AlGaN-AlN-AlGaN stack used to manage compressive strain and compensate for CTE mismatch during cooling.
- Growth Temperatures: Initial AlN layer at 900 °C, subsequent buffer layers up to 1200 °C.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the advanced diamond materials and custom processing required to replicate, scale, and extend this critical research into commercial high-power GaN devices.
Applicable Materials
Section titled “Applicable Materials”To achieve the high thermal performance demonstrated (k = 1290 W/(m·K)), researchers require high-quality, thermal-grade diamond.
- Material Recommendation: Thermal Grade Polycrystalline Diamond (PCD).
- 6CCVD provides MPCVD PCD wafers optimized for thermal management, ensuring high thermal conductivity necessary for GaN HEMT heat spreading.
- Substrate Thickness: The paper used 250 µm PCD. 6CCVD offers PCD thickness control from 0.1 µm up to 500 µm, allowing precise tuning for specific thermal budgets and mechanical stability requirements.
Customization Potential for Scaling
Section titled “Customization Potential for Scaling”The research utilized small 14 x 14 mm samples. 6CCVD’s capabilities enable immediate scaling to industry-standard formats, reducing R&D costs and accelerating commercialization.
| Research Requirement | 6CCVD Capability | Value Proposition |
|---|---|---|
| Substrate Size | Custom plates/wafers up to 125 mm (PCD). | Enables large-scale, high-volume manufacturing of Si/Diamond composite wafers. |
| Surface Finish | Polishing capability for PCD down to Ra < 5 nm (inch-size wafers). | Ensures the ultra-smooth surface finish (1.8 nm RMS achieved in the paper) required for subsequent high-quality MBE/MOCVD epitaxy. |
| Composite Fabrication | Expertise in thin-film diamond growth and substrate processing. | We can supply the high-quality PCD layer or assist in the bonding/thinning process required to create the Si-on-Diamond composite structure. |
| Device Integration | Internal Metalization Services (Au, Pt, Pd, Ti, W, Cu). | Future device fabrication (Ohmic and Schottky contacts) can be streamlined by utilizing 6CCVD’s in-house metal deposition capabilities. |
Engineering Support
Section titled “Engineering Support”The primary technical hurdle identified in the paper is managing the extreme Coefficient of Thermal Expansion (CTE) mismatch between diamond, silicon, and GaN, which necessitates complex buffer layers and precise strain engineering.
- CTE Mismatch Mitigation: 6CCVD’s in-house PhD team specializes in the material science of diamond interfaces. We offer consultation on optimizing diamond surface termination and material selection to improve adhesion and reduce interfacial stress for similar high-power GaN projects.
- Custom Recipe Development: We can tailor MPCVD growth parameters (gas flow, pressure, temperature) to optimize PCD grain structure and thermal properties specifically for integration with Si or SiC layers.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
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.