Study of cracks formation in HIGHLY – low boron-doped epitaxial (113) diamond bilayers
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | NANOCOM … |
| Authors | V. Mortet, Ladislav Klimša, N. Lambert, Marina Davydova, Jaromı́r Kopeček |
| Institutions | Czech Academy of Sciences, Institute of Physics, Czech Technical University in Prague |
| Citations | 1 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Epitaxial Boron-Doped Diamond Bilayers
Section titled “Technical Documentation & Analysis: Epitaxial Boron-Doped Diamond Bilayers”Executive Summary
Section titled “Executive Summary”This research investigates the critical material science challenge of crack formation in highly boron-doped (p+) / undoped (i) epitaxial diamond bilayers grown on (113) substrates, a structure essential for high-performance Schottky diodes.
- Core Achievement: Successful growth of highly boron-doped (p+) diamond layers achieving 1021 cm-3 concentration and low resistivity (2 mΩ·cm), suitable for ohmic contacts in electronic devices.
- Critical Limitation Identified: A critical thickness (tcrit) of approximately 3.5 µm was observed for the undoped layer, above which severe cracking occurs, independent of methane concentration.
- Root Cause: Crack formation is attributed to the relaxation of elastic energy due to a significant lattice mismatch (ca. 0.8%) between the heavily doped (p+) and the subsequently grown undoped (i) epitaxial layers.
- Orientation Advantage: The (113) orientation was selected for its superior surface morphology, higher growth rate, and enhanced boron incorporation efficiency compared to conventional (100) and (111) orientations.
- Application Focus: The resulting bilayer structure is a necessary precursor for fabricating semi-vertical diamond Schottky diodes, requiring precise control over layer thickness and doping profiles.
- 6CCVD Value Proposition: 6CCVD specializes in providing custom, high-quality Boron-Doped Diamond (BDD) and Electronic Grade Single Crystal Diamond (SCD) substrates and epitaxial layers necessary to overcome these strain engineering challenges.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental results and deposition parameters:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Orientation | (113) | N/A | High-Pressure High-Temperature (HPHT) Diamond |
| Highly Boron-Doped Layer Thickness (1st step) | ca. 5 | µm | Base epitaxial layer thickness |
| Highly Boron Concentration ([B]) | 1021 | cm-3 | Determined by Raman analysis (p+ layer) |
| Highly Boron Resistivity | 2 | mΩ·cm | Suitable for low ON resistance ohmic contact |
| Critical Undoped Layer Thickness (tcrit) | ca. 3.5 | µm | Thickness threshold for crack formation |
| Lattice Mismatch (p+ vs. i) | ca. 0.8 | % | Source of elastic strain/cracking |
| Growth Pressure | 100 | mbar | MPCVD reactor setting (AX5010) |
| Microwave Power | 700 | W | MPCVD reactor setting |
| B/C Ratio (1st step, p+) | 2000 | ppm | Gas phase concentration using Trimethylborane |
| B/C Ratio (2nd step, i) | 0 | ppm | Gas phase concentration (undoped layer) |
| Methane Concentration (2nd step, i) | 0.3 to 1 | % | Varied parameter for undoped layer growth |
| Undisturbed Zone Center Phonon Line Width | 12.32 | cm-1 | Used to determine 1021 cm-3 boron concentration |
Key Methodologies
Section titled “Key Methodologies”The epitaxial diamond bilayers were grown using a two-step process in a commercial Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) reactor.
- Substrate Selection: Use of (113) oriented High-Pressure High-Temperature (HPHT) diamond substrates, chosen for optimal surface quality and boron incorporation.
- Step 1: Highly Boron-Doped Layer (p+):
- Thickness: ca. 5 µm.
- Gas Phase: B/C ratio of 2000 ppm (using Trimethylborane precursor).
- Methane Concentration: 1%.
- Conditions: 100 mbar pressure, 700 W microwave power, 700 sccm total gas flow.
- Step 2: Undoped Layer (i):
- Gas Phase: Boron precursor flow was immediately stopped (B/C = 0 ppm).
- Methane Concentration: Varied between 0.3% and 1% to study growth rate effects.
- Thickness Variation: Deposition time was varied to achieve undoped layer thicknesses ranging from 1.4 µm up to 10.1 µm.
- Characterization Techniques:
- Boron Concentration: Evaluated via Raman spectroscopy (488 nm excitation laser) by analyzing the width of the zone center phonon line.
- Thickness: Estimated using known deposition rates, verified by Secondary Ion Mass Spectroscopy (SIMS) on reference samples.
- Defect Analysis: Optical microscopy and Scanning Electron Microscopy (SEM) were used to observe crack formation and surface defects.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research highlights the critical need for precise control over doping, thickness, and crystalline orientation to manage lattice mismatch strain in advanced diamond electronic devices. 6CCVD is uniquely positioned to supply the materials and engineering support required to replicate and advance this work, specifically addressing the challenges of strain mitigation and high-quality epitaxial growth.
Applicable Materials
Section titled “Applicable Materials”To replicate or extend this research, 6CCVD recommends the following materials, available with custom specifications:
| Material Requirement | 6CCVD Solution | Key Specification Match |
|---|---|---|
| Heavily Doped Layer (p+) | Heavy Boron-Doped Diamond (BDD) | Achievable concentrations up to 1021 cm-3 (metallic regime) for low-resistance ohmic contacts. |
| Intrinsic Layer (i) | Electronic Grade Single Crystal Diamond (SCD) | High-purity, low-defect SCD epitaxial layers with thickness control from 0.1 µm to 500 µm. |
| Substrate Orientation | Custom Oriented SCD Substrates | We supply high-quality SCD substrates specifically oriented to (113), (100), or (111) to meet specific epitaxial growth requirements. |
| Bilayer Structure | Custom Epitaxial Stacks | Capability to grow complex, multi-layer epitaxial structures (p+/i/n) with abrupt interfaces and precise thickness control necessary for Schottky or PIN diodes. |
Customization Potential for Advanced Device Fabrication
Section titled “Customization Potential for Advanced Device Fabrication”The paper demonstrates that the success of the Schottky diode fabrication hinges on managing layer thickness and strain. 6CCVD offers the following capabilities to overcome these limitations:
- Precision Thickness Control: We can supply both the 5 µm p+ layer and the critical undoped layer with thickness control far exceeding the 3.5 µm critical limit, allowing researchers to precisely engineer strain relaxation.
- Large Area Epitaxy: While the paper focuses on small samples, 6CCVD offers Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, enabling future scale-up of (113) oriented devices if required.
- Advanced Polishing: We guarantee ultra-low surface roughness (Ra < 1 nm for SCD) essential for high-quality epitaxial growth and minimizing surface defects (like those observed in sample 3-063).
- Integrated Metalization: For the final Schottky diode fabrication, 6CCVD offers in-house metalization services, including deposition of Au, Pt, Pd, Ti, W, and Cu, allowing for seamless integration of ohmic and Schottky contacts onto the finished bilayer structure.
Engineering Support
Section titled “Engineering Support”The core challenge—lattice mismatch strain—is a complex engineering problem. 6CCVD’s in-house PhD team provides expert consultation:
- Strain Mitigation Strategies: Assistance in designing alternative doping profiles (e.g., graded doping layers) or optimizing growth recipes to mitigate the 0.8% lattice mismatch and increase the critical thickness threshold for similar Diamond Schottky Diode projects.
- Recipe Optimization: Support for fine-tuning gas phase parameters (B/C ratio, [CH4] %) and reactor conditions to achieve specific growth rates and material quality on non-standard orientations like (113).
- Global Supply Chain: We offer reliable global shipping (DDU default, DDP available) ensuring rapid delivery of custom materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
In this work, we present the study of the formation of cracks in high and low boron-doped diamond epitaxial bilayers necessary in the fabrication process of Schottky diodes.Epitaxial diamond layers were grown on (113) oriented diamond substrates by Microwave Plasma Enhanced Chemical Vapor Deposition.The effect of the thickness and the methane concentration during the growth of the undoped diamond layer on the crack formation have been studied using optical and scanning electron microscopy (SEM).We experimentally observed a critical thickness of ca.3.5 µm above which all undoped layers are cracked.The formation of these cracks is attributed to the relaxation of the elastic energy stored in the epitaxial undoped layer due to the significant lattice mismatch (ca.0.8 %) between the undoped and highly boron-doped diamond layers with a boron concentration of 10 21 cm -3 as determined by Raman spectroscopy analysis.