Morphology of Diamond Layers Grown on Different Facets of Single Crystal Diamond Substrates by a Microwave Plasma CVD in CH4-H2-N2 Gas Mixtures

At a Glance

Metadata	Details
Publication Date	2017-06-06
Journal	Crystals
Authors	E. E. Ashkinazi, Р. А. Хмельницкий, Vadim Sedov, Andrew Khomich, А. В. Хомич
Institutions	Troitsk Institute for Innovation and Fusion Research, Prokhorov General Physics Institute
Citations	33
Analysis	Full AI Review Included

6CCVD Technical Documentation: Analysis of Facet-Dependent MPCVD Diamond Growth Morphology

This document summarizes the findings of the research paper “Morphology of Diamond Layers Grown on Different Facets of Single Crystal Diamond Substrates by a Microwave Plasma CVD in CH₄-H₂-N₂ Gas Mixtures” and details how 6CCVD’s capabilities support and enhance this area of advanced diamond engineering, particularly for high-rate epitaxy and multilayer coating development.

Executive Summary

This study successfully demonstrates high-rate homoepitaxial growth of Single Crystal Diamond (SCD) on {100} substrates using Microwave Plasma CVD (MPCVD) with a high concentration of nitrogen (4%).

Facet Specificity: Homoepitaxial growth was exclusively sustained on the {100} face. All other facets ({110}, {111}, {211}, {311}) resulted in the immediate formation of Nanocrystalline Diamond (NCD) films.
High-Rate Epitaxy: The addition of 4% nitrogen (N₂) increased the SCD epitaxial growth rate on the {100} face to 42 µm/h, an order of magnitude increase compared to N₂-free processes.
Defect Analysis: The {100} surface exhibited hillocks (likely around screw dislocations) often associated with polycrystalline aggregates, indicating structural limitations at high growth rates.
Stress Quantification: High-resolution Photoluminescence (PL) mapping of nitrogen-vacancy (NV) optical centers was successfully used to quantify localized internal stress within growth defects, measuring up to 0.4 GPa (tensile) and 0.25 GPa (compressive).
Industrial Relevance: These findings are critical for controlling morphology in the manufacturing of bilayer/multilayer NCD-on-Microcrystalline Diamond (MCD) coatings, essential for advanced tooling applications requiring low roughness and high wear resistance.

Technical Specifications

Extracted physical and process parameters from the experimental analysis:

Parameter	Value	Unit	Context
Substrate Type	IIa Synthetic SC Diamond	-	HPHT Gradient Method, Multifaceted Sample
Sustained Epitaxy Facet	{100}	-	Only plane supporting homoepitaxial growth
N₂ Concentration	4	%	High concentration in gas mixture
Total Gas Flow Rate	500	sccm	H₂:460 / CH₄:20 / N₂:20
Chamber Pressure	130	Torr	-
Microwave Frequency	2.45	GHz	ARDIS-100 system
Microwave Power	2.8	kW	-
Substrate Temperature	~800	°C	Measured through plasma
{100} Epitaxial Growth Rate	42	µm/h	Achieved in N₂-rich environment
Homoepitaxial Film Thickness	3.5	µm	Measured after 5 min growth on {100} lacuna
Maximum Tensile Stress (Hillocks)	0.4	GPa	Measured via NV ZPL shift (575 nm)
Maximum Compressive Stress	0.25	GPa	Measured via NV ZPL shift (575 nm)
Diamond Raman FWHM ({100})	2.7	cm^⁻1	Indicates high crystallinity
Diamond Raman FWHM ({311})	4.3	cm^⁻1	Indicates higher disorder (NCD)

Key Methodologies

The experiment successfully combined high-concentration MPCVD growth with advanced structural and spectroscopic characterization to link process parameters to resulting film morphology and internal strain.

Substrate Preparation:
- A multifaceted Type IIa SC diamond (HPHT produced) was used, incorporating low-index facets: {100}, {110}, {111}, {211}, and {311}.
- The primary {100} planes were polished to a roughness Ra < 10 nm; other facets remained unpolished (Ra 90-180 nm).
MPCVD Growth Recipe:
- Synthesis was performed in an ARDIS-100 system (2.45 GHz, 5 kW).
- Gas mixture: H₂/CH₄/N₂ (460/20/20 sccm), resulting in a high nitrogen concentration (4%).
- Deposition times: Short (5 min) and Prolonged (70 min) to examine initial nucleation vs. long-term morphology evolution.
Morphological Characterization:
- Scanning Electron Microscopy (SEM) (JEOL JSM7001F) was used to analyze surface morphology, crystallite size (tens to hundreds of nanometers for NCD), and the formation of hillocks/step bunching on the {100} face.
Spectroscopic and Stress Analysis:
- Confocal Raman and Photoluminescence (PL) spectroscopy (Horiba Jobin-Yvon LabRam HR840) was used (473 nm excitation).
- Phase Determination: Raman spectroscopy confirmed high-quality SCD on {100} (sharp 1332.4 cm^⁻1 peak) and the presence of disordered/non-diamond carbon (D and G bands, trans-polyacetylene TPA bands) characteristic of NCD on other facets.
- Stress Mapping: High-resolution spatial mapping of the PL spectra of the nitrogen-vacancy (NV) optical centers (ZPL at 575 nm and 637 nm) was used. The shift ($\Delta \nu_r$) of the ZPL position served as a proxy to calculate internal mechanical stress ($\sigma$ [GPa] = $\Delta \nu_r [0.38 GPa/cm^{⁻1}]$).

6CCVD Solutions & Capabilities

The successful replication and extension of this high-rate, morphology-controlled epitaxy research hinges on access to high-quality substrates, precise doping control, and advanced metrology. 6CCVD is uniquely positioned to supply the required materials and services.

Applicable Materials for Replication and Extension

Research Requirement	6CCVD Solution & Material	Engineering Advantage
High-Quality {100} Substrates	Optical Grade SCD Wafers	SCD substrates up to 500 µm thick and large dimensions (up to 125mm) providing a low-defect, primary {100} growth surface necessary for homoepitaxy.
NCD/MCD Layering	Polycrystalline Diamond (PCD)	We offer both SCD (microcrystalline foundation) and control over the MPCVD parameters to deposit precise NCD layers on top, facilitating the production of industrial bilayer superhard coatings.
N-Doping Control	Custom Doped SCD	The study highlighted the critical role of N₂ (4%) in increasing growth rate. 6CCVD provides custom doping capabilities, including precise N-doping during growth, to optimize deposition efficiency and material properties.
Custom Wafer Structuring	Laser Cutting Services	The research utilized a multifaceted substrate ({100}, {110}, {111}, etc.). 6CCVD offers precision laser cutting and shaping to create custom facet designs or substrates for replication of this morphology study.

Customization Potential

Dimension and Scale-up: The paper demonstrates a high growth rate (42 µm/h) which is vital for producing thick layers economically. 6CCVD manufactures plates and wafers up to 125mm (PCD), allowing partners to scale this high-rate process to industrial dimensions while maintaining thickness control (SCD/PCD up to 500 µm).
Polishing for PL Analysis: Accurate PL/Raman stress mapping requires extremely flat, low-damage surfaces. 6CCVD provides industry-leading polishing services, achieving Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring optimal surface preparation for high-resolution spectroscopic analysis of defects like hillocks and NV centers.
Metalization Support: If subsequent device integration (e.g., thermal management or electrical contacts) requires metal features, 6CCVD offers in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu, to complete the device stack.

Engineering Support

The ability to control the morphology transition between homoepitaxy ({100}) and NCD formation (other facets) based on gas chemistry (N₂ concentration) is crucial for advanced tool coating development. 6CCVD’s in-house PhD team can assist with material selection, recipe optimization, and stress management for similar NCD-on-MCD Multilayer Coating projects, ensuring uniformity and adhesion across complex geometries.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Epitaxial growth of diamond films on different facets of synthetic IIa-type single crystal (SC) high-pressure high temperature (HPHT) diamond substrate by a microwave plasma CVD in CH4-H2-N2 gas mixture with the high concentration (4%) of nitrogen is studied. A beveled SC diamond embraced with low-index {100}, {110}, {111}, {211}, and {311} faces was used as the substrate. Only the {100} face is found to sustain homoepitaxial growth at the present experimental parameters, while nanocrystalline diamond (NCD) films are produced on other planes. This observation is important for the choice of appropriate growth parameters, in particular, for the production of bi-layer or multilayer NCD-on-microcrystalline diamond (MCD) superhard coatings on tools when the deposition of continuous conformal NCD film on all facet is required. The development of the film morphology with growth time is examined with SEM. The structure of hillocks, with or without polycrystalline aggregates, that appear on {100} face is analyzed, and the stress field (up to 0.4 GPa) within the hillocks is evaluated based on high-resolution mapping of photoluminescence spectra of nitrogen-vacancy NV optical centers in the film.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst7060166

References

2012 - Advances in the Deposition of Diamond Coatings on Co-Cemented Tungsten Carbides [Crossref]
2015 - Engineered CVD Diamond Coatings for Machining and Tribological Applications [Crossref]
2017 - Application of Raman spectroscopy for the analysis of the structure of diamond coatings on a hard alloy [Crossref]
2008 - Run-in behavior of nanocrystalline diamond coatings studied by in situ tribometry [Crossref]
2009 - Fabrication and application of nano-microcrystalline composite diamond films on the interior hole surfaces of Co cemented tungsten carbide substrates [Crossref]
2006 - The versatility of hot-filament activated chemical vapor deposition [Crossref]
2004 - The effect of nitrogen addition during high-rate homoepitaxial growth of diamond by microwave plasma CVD [Crossref]
2013 - Growth of large size diamond single crystals by plasma assisted chemical vapour deposition: Recent achievements and remaining challenges [Crossref]