High thermal conductivity in wafer-scale cubic silicon carbide crystals
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-11-23 |
| Journal | Nature Communications |
| Authors | Zhe Cheng, Jianbo Liang, Keisuke Kawamura, Hao Zhou, Hidetoshi Asamura |
| Institutions | Air Water (Japan), Georgia Institute of Technology |
| Citations | 125 |
| Analysis | Full AI Review Included |
Technical Analysis: High Thermal Conductivity in Wafer-Scale Cubic Silicon Carbide Crystals
Section titled âTechnical Analysis: High Thermal Conductivity in Wafer-Scale Cubic Silicon Carbide CrystalsâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates the exceptional thermal performance of high-purity, wafer-scale cubic silicon carbide (3C-SiC), positioning it as a leading material for next-generation power electronics and thermal management.
- Record Thermal Conductivity: Isotropic thermal conductivity ($\kappa$) exceeding $500 \text{ W m}^{-1}\text{K}^{-1}$ was achieved at room temperature in bulk 3C-SiC crystals, resolving a long-standing puzzle regarding its theoretical potential.
- Second Highest Among Large Crystals: This $\kappa$ value is the second highest among all large crystals, surpassed only by single crystal diamond (SCD).
- High Purity & Quality: The high $\kappa$ is attributed to exceptional crystal quality (FWHM 158 arcsec) and ultra-low boron impurity concentration (< $3 \times 10^{13} \text{ atoms cm}^{-3}$), which minimizes defect-phonon scattering.
- Wafer Scale Potential: The demonstrated 2-inch free-standing wafers are scalable up to 6-inch, addressing a key limitation of other high-$\kappa$ materials like boron arsenide (BAs) and boron phosphide (BP).
- Superior Thin Films: Corresponding 3C-SiC thin films exhibited record-high in-plane and cross-plane $\kappa$, exceeding diamond thin films of equivalent thickness.
- Exceptional Integration: Thermal Boundary Conductance (TBC) at the 3C-SiC/Si interface ($\sim 620 \text{ MW m}^{-2}\text{K}^{-1}$) is among the highest reported for semiconductor interfaces, facilitating heterogeneous integration.
- 6CCVD Value Proposition: While 3C-SiC is a strong competitor, 6CCVDâs Single Crystal Diamond (SCD) offers intrinsic thermal conductivity exceeding $2000 \text{ W m}^{-1}\text{K}^{-1}$, providing the ultimate solution for extreme heat flux management where 3C-SiC performance is insufficient.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the analysis of the high-quality 3C-SiC crystals:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Bulk Thermal Conductivity ($\kappa$) | > 500 | W m-1K-1 | Room Temperature (RT), Isotropic |
| Wafer Scalability (Potential) | Up to 6 | inch | Free-standing 3C-SiC |
| Demonstrated Wafer Size | 2 | inch | Free-standing 3C-SiC |
| Bulk Thickness (Free-standing) | $\sim 100$ | ”m | Used for TDTR measurements |
| Thin Film Thickness Range | 0.93 to 2.52 | ”m | Epitaxial 3C-SiC on Si |
| Growth Temperature (LT-CVD) | 1300 | K | Low-Temperature Chemical Vapor Deposition |
| XRD FWHM ((111) Peak) | 158 | arcsec | High Crystal Quality |
| Stacking Fault Density | $\sim 1000$ | cm-1 | Observed on the growth face |
| Boron (B) Impurity Concentration | < $3 \times 10^{13}$ | atoms cm-3 | Below SIMS detection limit (Key to high $\kappa$) |
| Nitrogen (N) Impurity Concentration | $5.8 \times 10^{15}$ | atoms cm-3 | Measured on the growth face |
| Thermal Boundary Conductance (TBC) | $\sim 620$ | MW m-2K-1 | 3C-SiC/Si interface |
| TBC Comparison (Diamond/Si) | $\sim 62$ | MW m-2K-1 | 3C-SiC TBC is 10x higher than diamond/Si interfaces37 |
Key Methodologies
Section titled âKey MethodologiesâThe high thermal conductivity 3C-SiC crystals were fabricated and characterized using advanced CVD and ultrafast thermal metrology techniques:
- Growth Method: Low-Temperature Chemical Vapor Deposition (LT-CVD) was used in a customized CVD reactor.
- Substrate and Orientation: Growth occurred on (111) Si substrates. The specific orientation and low growth temperature (1300 K) were critical for achieving high crystal quality 3C-SiC layers with low stacking fault density.
- Bulk Crystal Fabrication: Free-standing bulk 3C-SiC crystals ($\sim 100 \text{ ”m}$ thick) were obtained by etching away the Si substrate using HNA (HF: HNO3: H2O).
- Thermal Characterization (Bulk/Cross-Plane): Time-Domain Thermoreflectance (TDTR) was used to measure $\kappa$ and TBC. Measurements utilized a $90 \text{ nm}$-thick Al transducer layer.
- TDTR Parameters: $5\times$ objective (spot size $10.7 \text{ ”m}$) and $9.3 \text{ MHz}$ modulation frequency were primarily used for bulk $\kappa$.
- Thermal Characterization (In-Plane): Beam-Offset Time-Domain Thermoreflectance (BO-TDTR) was employed to measure the in-plane $\kappa$ of 3C-SiC thin films, utilizing an offset pump beam relative to the probe beam.
- Structural Analysis: Crystal quality was confirmed using X-ray Diffraction (XRD) rocking curves (FWHM 158 arcsec) and High-Resolution Scanning Transmission Electron Microscopy (HR-STEM) with Selected Area Electron Diffraction (SAED).
- Purity Analysis: Secondary Ion Mass Spectrometry (SIMS) was used to confirm ultra-low concentrations of critical impurities (Boron, Nitrogen, Oxygen), validating the high-purity requirement for high $\kappa$.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights 3C-SiC as a powerful thermal management material, second only to diamond. For engineers and scientists requiring the absolute highest thermal performance, 6CCVD provides MPCVD diamond solutions that surpass 3C-SiCâs capabilities, particularly in high-power density applications where heat flux is critical.
Applicable Materials: The Diamond Advantage
Section titled âApplicable Materials: The Diamond AdvantageâWhile 3C-SiC achieves $500 \text{ W m}^{-1}\text{K}^{-1}$, 6CCVDâs CVD diamond offers significantly higher intrinsic thermal conductivity, making it the definitive choice for extreme thermal management:
| 6CCVD Material | Application Focus | Thermal Conductivity ($\kappa$) | 3C-SiC Comparison |
|---|---|---|---|
| Optical Grade Single Crystal Diamond (SCD) | Ultimate Heat Spreaders, Active Devices, Quantum | > $2000 \text{ W m}^{-1}\text{K}^{-1}$ | 4x higher than 3C-SiC |
| Thermal Grade Polycrystalline Diamond (PCD) | Large-Area Substrates, Cost-Effective Heat Sinks | $\sim 1000 - 1800 \text{ W m}^{-1}\text{K}^{-1}$ | 2x to 3.6x higher than 3C-SiC |
| Boron-Doped Diamond (BDD) | Electrochemical, Sensing, Active Device Electrodes | Tunable (Semiconducting) | Used where electrical conductivity is required |
Customization Potential for Heterogeneous Integration
Section titled âCustomization Potential for Heterogeneous IntegrationâThe paper emphasizes the challenge of integrating high-$\kappa$ materials with high TBC. 6CCVD directly addresses this integration challenge through comprehensive customization services:
- Custom Dimensions and Thickness:
- 6CCVD offers SCD plates/wafers in thicknesses ranging from $0.1 \text{ ”m}$ up to $500 \text{ ”m}$, matching or exceeding the bulk and thin-film dimensions used in this 3C-SiC study ($\sim 100 \text{ ”m}$).
- For large-area thermal management, 6CCVD provides PCD wafers up to $125 \text{ mm}$ in diameter, addressing the scalability requirement noted in the research.
- Advanced Metalization Services:
- TBC measurements rely heavily on the metal transducer layer (Al in this study) and subsequent device metalization (e.g., Ti/Pt/Au mentioned in related TBC literature).
- 6CCVD provides in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to optimize TBC for diamond/SiC or diamond/Si interfaces, crucial for replicating or extending the high TBC findings observed with 3C-SiC.
- Surface Preparation:
- The high quality of the 3C-SiC was achieved partly through careful polishing. 6CCVD guarantees ultra-smooth surfaces: Ra < $1 \text{ nm}$ for SCD and Ra < $5 \text{ nm}$ for inch-size PCD, ensuring optimal interface quality for TBC maximization.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in optimizing CVD diamond properties for extreme applications. We can assist researchers and engineers with material selection for similar Wide-Bandgap Semiconductor Thermal Management projects, ensuring the correct balance between thermal performance, electrical properties, and integration compatibility.
Global Logistics
Section titled âGlobal Logisticsâ6CCVD supports global research efforts with reliable worldwide shipping (DDU default, DDP available), ensuring prompt delivery of custom diamond materials to meet demanding research timelines.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.