Interface Modulation for the Heterointegration of Diamond on Si
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2024-03-13 |
| Journal | Advanced Science |
| Authors | Xing Li, Li Wan, Chaonan Lin, Wentao Huang, Jing Zhou |
| Institutions | Macau University of Science and Technology, Dalian University of Technology |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive SummaryāThis research focuses on optimizing the diamond-silicon (Si) interface via Microwave Plasma Chemical Vapor Deposition (MPCVD) to resolve the critical heat dissipation bottleneck in Si-based power electronics.
- Interface Mechanism Discovery: The study reveals that the initial MPCVD process forms an epitaxial beta-SiC (Ī²-SiC) interlayer through the reaction between anisotropically sputtered Si atoms and deposited amorphous carbon (a-C) nanostructures.
- Epitaxial Relationship: The Ī²-SiC interlayer maintains a ācube-on-cubeā orientation relationship with the Si substrate, which is essential for subsequent high-quality diamond growth.
- Grain Size Enhancement: The presence of the epitaxial Ī²-SiC interlayer significantly promotes the formation of larger diamond grain sizes compared to randomly oriented SiC interlayers (e.g., those formed on SiO2/Si).
- Interface Modulation Strategy: The thickness of the epitaxial Ī²-SiC layer can be precisely reduced by increasing the CH4/H2 ratio from 3% to 10%. This modulation is governed by the competitive reaction rates between H/H+ etching and non-diamond carbon phase formation.
- Epitaxy Breakdown: Further increasing the CH4/H2 ratio to 20% enhances non-diamond carbon formation, interrupting the epitaxial growth of Ī²-SiC and resulting in a thick amorphous interlayer containing randomly embedded Ī²-SiC nanocrystals.
- Engineering Impact: These findings provide crucial interfacial design strategies necessary to reduce thermal boundary resistance and enable the full potential of diamond-integrated Si devices.
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| SiC Thermal Conductivity (Target) | approx 400 | W m-1 K-1 | Crystalline SiC interlayer potential for reducing thermal boundary resistance. |
| Diamond Deposition Rate (3% CH4) | 1.5 | Āµm h-1 | Growth rate of polycrystalline diamond film. |
| Diamond Film Thickness (5h growth) | approx 6.03 | Āµm | Synthesized film thickness at 3% CH4/H2. |
| Substrate Temperature (Growth) | approx 880 | Ā°C | Standard MPCVD growth temperature. |
| Si Lattice Constant | 5.43 | A | Reference value for Si substrate. |
| Ī²-SiC Lattice Constant | 4.35 | A | Reference value for Ī²-SiC (significant lattice mismatch exists). |
| Epitaxial Ī²-SiC Size (3% CH4) | approx 20 | nm | Size of triangular nanoislands observed at the interface. |
| Epitaxial Ī²-SiC Size (10% CH4) | approx 10 | nm | Reduced size due to increased CH4 concentration. |
| Epitaxial Ī²-SiC Thickness (20% CH4) | approx 5 | nm | Thin epitaxial layer observed before amorphous layer formation. |
| Si Vacancy Formation Energy (Si(111)) | 5.94 | eV | Highest energy barrier, indicating Si(111) is most resistant to plasma etching. |
| Si Vacancy Formation Energy (Si(100)) | 3.19 | eV | Lowest energy barrier. |
| C2 Binding Energy | 7.16 | eV | Theoretical calculation; C2 prefers reaction over SiC or Si2 formation. |
Key Methodologies
Section titled āKey MethodologiesāThe study utilized Microwave Plasma Chemical Vapor Deposition (MPCVD) for synthesis, coupled with advanced electron microscopy and Density Functional Theory (DFT) calculations for analysis.
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Diamond Film Synthesis (MPCVD):
- Substrates: Si (001), Si (111), mechanically scratched Si (001), and Si (001) with a pre-deposited amorphous SiO2 layer.
- Gases: High-purity (7N) H2 and CH4 (reactant gases).
- Process Parameters: Substrate temperature maintained at approx 880 Ā°C; total pressure at 228 mbar.
- Modulation Parameter: CH4/H2 concentration ratios were varied at 3%, 10%, and 20% to study interfacial reaction competition.
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Structural and Compositional Analysis:
- Cross-Sectional Preparation: Focused Ion Beam (FIB) was used to fabricate precise cross-sectional samples.
- Microscopy: Scanning Electron Microscopy (SEM) was used for morphology and thickness measurement.
- Interface Analysis: High-Resolution Transmission Electron Microscopy (HRTEM) and Scanning Transmission Electron Microscopy Energy-Dispersive X-ray (STEM-EDX) mapping were critical for identifying the ācube-on-cubeā orientation, elemental distribution (C and Si), and interlayer thickness.
- Diffraction: Selected Area Electron Diffraction (SAED) and X-ray Diffraction (XRD) confirmed the crystalline phases (diamond, Ī²-SiC, graphite).
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Theoretical Modeling (DFT):
- Software: Vienna ab initio Simulation Package (VASP) was used for spin-polarized DFT calculations.
- Calculations: Determined the formation energies of Si vacancy defects on various Si surfaces (Si(111), Si(110), Si(100)) to explain anisotropic etching.
- Kinetic Analysis: Climbing-Image Nudged Elastic Band (CI-NEB) method was employed to investigate the thermodynamic and kinetic properties of the etching process.
Commercial Applications
Section titled āCommercial ApplicationsāThe ability to control the diamond-SiC interface quality and thickness directly impacts the thermal performance and reliability of high-power electronic devices integrated with diamond.
- High-Power Electronics:
- High-Flux Heat Sinks: Utilizing diamondās superior thermal conductivity (greater than 2000 W/mK) to manage heat in high-density power modules, especially those based on Si, SiC, or GaN.
- CMOS Integration: Enabling robust heterointegration with established Complementary Metal-Oxide Semiconductor (CMOS) technology, overcoming the thermal bottleneck at the interface.
- Advanced Sensing Technology:
- Deep UV Detectors: Fabrication of high-performance diamond-based deep ultraviolet detectors.
- Gas and Temperature Sensors: Improving the stability and performance of diamond-based sensors by controlling the underlying Si interface.
- Micro/Nano Devices:
- Large-Scale Diamond Applications: Providing a scalable, low-cost method (MPCVD) for synthesizing large-area, high-quality diamond films compatible with Si wafers.
- Industrial Materials:
- Abrasive Tools: Production of high-quality diamond films for industrial abrasive applications where grain size and uniformity are important.
View Original Abstract
Abstract Along with the increasing integration density and decreased feature size of current semiconductor technology, heterointegration of the Siābased devices with diamond has acted as a promising strategy to relieve the existing heat dissipation problem. As one of the heterointegration methods, the microwave plasma chemical vapor deposition (MPCVD) method is utilized to synthesize largeāscale diamond films on a Si substrate, while distinct structures appear at the Siādiamond interface. Investigation of the formation mechanisms and modulation strategies of the interface is crucial to optimize the heat dissipation behaviors. By taking advantage of electron microscopy, the formation of the epitaxial Ī² āSiC interlayer is found to be caused by the interaction between the anisotropically sputtered Si and the deposited amorphous carbon. Compared with the randomly oriented Ī² āSiC interlayer, larger diamond grain sizes can be obtained on the epitaxial Ī² āSiC interlayer under the same synthesis condition. Moreover, due to the competitive interfacial reactions, the epitaxial Ī² āSiC interlayer thickness can be reduced by increasing the CH 4 /H 2 ratio (from 3% to 10%), while further increase in the ratio (to 20%) can lead to the broken of the epitaxial relationship. The above findings are expected to provide interfacial design strategies for multiple largeāscale diamond applications.