Enhanced Lateral Growth of Homoepitaxial (001) Diamond by Microwave Plasma Chemical Vapor Deposition with Nitrogen Addition

At a Glance

Metadata	Details
Publication Date	2025-10-30
Journal	Coatings
Authors	Tzu-I Yang, Chia-Yen Chuang, Junbin Huang, Cheng‐Jung Ko, Wei-Lin Wang
Institutions	National Yang Ming Chiao Tung University, National Chung Shan Institute of Science and Technology
Analysis	Full AI Review Included

Enhanced Lateral Growth of High-Quality (001) Single Crystal Diamond via Nitrogen-Assisted MPCVD

Executive Summary

This research validates a high-rate, single-step Microwave Plasma Chemical Vapor Deposition (MPCVD) strategy utilizing nitrogen incorporation to achieve substantial lateral expansion of high-quality (001) Single Crystal Diamond (SCD) substrates. This technique is critical for advancing diamond-based electronic and quantum applications requiring large-area, low-defect material.

Maximized Lateral Growth: Optimal nitrogen concentration (180 ppm N₂) achieved a balanced growth rate ratio (λ ≈ 1.1), resulting in a lateral growth rate of 52.5 µm/h.
Significant Area Expansion: The process yielded a 1.6 times increase in SCD surface area (from 5.5 mm to 7.6 mm edge length) in a short 20 h growth duration, reaching a final thickness of 0.95 mm.
High Crystalline Quality: The grown layer maintained excellent structural integrity, confirmed by a narrow X-ray rocking curve (XRC) Full Width at Half Maximum (FWHM) of 11 arcsec for the (004) reflection.
Defect Reduction: Etch Pit Density (EPD) analysis demonstrated that the laterally expanded regions exhibited a threading dislocation density approximately one order of magnitude lower (6.7 x 10⁴ cm⁻²) than the central substrate area.
PCD Suppression: The optimized nitrogen addition effectively suppressed the formation of Polycrystalline Diamond (PCD) rims, maximizing the usable SCD area.
Industrial Relevance: This single-step method provides an effective, scalable strategy for fabricating large-area, high-quality SCD substrates essential for next-generation high-power and quantum devices.

Technical Specifications

The following hard data points were extracted from the optimal growth condition (N180 sample) and subsequent characterization:

Parameter	Value	Unit	Context
Optimal N₂ Concentration	180	ppm	Maximizing lateral growth rate (GR[100])
Vertical Growth Rate (GR[001])	47.3	µm/h	N180 sample
Lateral Growth Rate (GR[100])	52.5	µm/h	N180 sample
Growth Rate Ratio (λ)	1.1	N/A	GR[100] / GR[001]
Growth Duration	20	h	Total growth time
Final Thickness	0.95	mm	SCD layer thickness
Initial Substrate Size	5.5 x 5.5 x 0.5	mm³	(001) SCD
Final Edge Length	7.6	mm	Along [100] direction
Surface Area Gain	1.6	times	Relative to initial substrate area
Substrate Temperature	1180	°C	Measured during N180 growth
XRC FWHM (004)	11	arcsec	High crystalline quality of grown layer
EPD (Lateral Region)	6.7 x 10⁴	cm⁻²	10x lower than central region
Raman FWHM (Center)	2.8-3.0	cm⁻¹	Confirms high phase purity

Key Methodologies

The homoepitaxial growth was conducted using a high-power MPCVD system under tightly controlled gas phase chemistry:

Substrate: Polished (001)-oriented synthetic CVD diamond substrates (5.5 x 5.5 x 0.5 mm³) with miscut angle ≤1°.
Pre-Treatment: Two-step acid cleaning (H₂O₂:H₂SO₄ at 200 °C, followed by HNO₃:H₂SO₄ at 300 °C) to remove sp² carbon and surface damage.
System: 6 kW/2.45 GHz ASTeX-type MPCVD reactor.
Base Pressure: 1.33 x 10⁻⁴ Pa (prior to plasma ignition).
Pre-Growth Plasma: Hydrogen plasma pre-treatment at 5000 W and 1.67 x 10⁴ Pa (125 Torr) for 20 min.
Source Gases: High purity H₂ (5N5) and CH₄ (5N), purified using heated zirconium-based getter purifiers.
Gas Mixture: 10% CH₄ in H₂.
Total Flow Rate: 500 sccm.
Growth Pressure: 1.87 x 10⁴ Pa (140 Torr).
Microwave Power: 5600 W.
Doping: Nitrogen gas introduced in concentrations ranging from 0 to 2000 ppm. Optimal lateral growth achieved at 180 ppm N₂.
Post-Growth Treatment: Hydrogen plasma post-treatment (5000 W, 1.67 x 10⁴ Pa) for 20 min to stabilize the surface.

6CCVD Solutions & Capabilities

The findings of this research—specifically the need for high-quality, large-area SCD substrates and precise control over doping and growth geometry—align perfectly with 6CCVD’s core capabilities in advanced MPCVD diamond manufacturing.

Applicable Materials for Replication and Extension

To replicate and extend this high-rate lateral growth technique, researchers require the highest quality starting materials and precise control over doping:

Optical Grade SCD (001) Substrates: The success of ELO relies on low-dislocation density seeds. 6CCVD provides high-purity, low-defect SCD substrates up to 500 µm thick, ensuring minimal substrate-originated threading dislocations (TDs) propagate into the grown layer.
Custom Nitrogen Doping (N-Doped SCD): This study demonstrates the critical role of N₂ concentration (180 ppm) in balancing vertical and lateral growth. 6CCVD offers custom SCD growth recipes, allowing precise control over nitrogen incorporation for optimizing growth kinetics, crystalline quality, and NV center formation (for quantum applications).
Heavy Boron Doped PCD (BDD): While not the focus of this paper, the high-rate, high-power MPCVD conditions used here are analogous to those required for synthesizing BDD films for electrochemical or high-power electronic applications. 6CCVD provides custom BDD materials up to 500 µm thick.

Customization Potential for Advanced Research

The paper highlights the need for precise material processing and large dimensions, areas where 6CCVD excels:

Research Requirement	6CCVD Capability	Technical Advantage
Large Area Expansion	Plates/wafers up to 125 mm (PCD) and large-format SCD substrates.	Enables scaling of the 1.6x area gain demonstrated in the paper to industrially relevant sizes.
Precision Thickness	SCD and PCD thickness control from 0.1 µm up to 500 µm (Substrates up to 10 mm).	Allows researchers to grow the required 0.95 mm thick layers or thinner membranes for specific device fabrication.
Surface Quality	Polishing capability to achieve Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD).	Essential for minimizing polishing-induced damage (flat-bottomed EPs) and ensuring a smooth surface for subsequent device processing.
Post-Growth Processing	Custom laser cutting and precision dicing services.	Facilitates the removal of the underlying substrate (as performed on sample N-X) for membrane fabrication or XRC analysis without compromising the grown surface.
Metalization	Internal capability for Au, Pt, Pd, Ti, W, Cu metalization.	Supports the integration of SCD layers into high-power electronic devices or quantum circuits requiring ohmic contacts or specific bonding layers.

Engineering Support

The successful implementation of this lateral growth technique requires expert knowledge in gas phase chemistry, plasma dynamics, and defect engineering.

6CCVD’s in-house PhD engineering team specializes in optimizing MPCVD recipes to control growth kinetics (GR[100]/GR[001] ratio) and defect incorporation. We offer consultation services to assist clients in selecting the optimal material and process parameters for similar large-area, low-dislocation SCD fabrication projects, particularly those targeting high-power integrated electronic devices or quantum information processing.

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

View Original Abstract

Diamond, as an exceptional material with many superior properties, requires a single crystal in a reasonably large size for practical industrial applications. However, achieving large-area single-crystal diamond (SCD) growth without the formation of polycrystalline rims remains challenging. Microwave plasma chemical vapor deposition (MPCVD) using a gas mixture of 10% CH4-H2 was used for the homoepitaxial growth of (001) SCD. The effect of nitrogen gas addition in the range of 0-2000 ppm on lateral growth was investigated. Deposition with 180 ppm N2 over a growth duration of 20 h to reach a thickness of 0.95 mm resulted in significantly enhanced lateral growth without the appearance of a polycrystalline diamond (PCD) rim for the grown diamond, and the total top surface area of SCD increased by an area gain of 1.6 relative to the substrate. The corresponding vertical and lateral growth rates were 47.3 µm/h and 52.5 µm/h, respectively. Characterization by Raman spectroscopy and atomic force microscopy (AFM) revealed uniform structural integrity across the whole surface from the laterally grown regions to the center, including the entire expanded area, in terms of surface morphology and crystalline quality. Moreover, measurements of the etch pit densities (EPDs) showed a substantial reduction in the laterally grown regions, approximately an order of magnitude lower than those in the central region. The high quality of the homoepitaxial diamond layer was further verified with (004) X-ray rocking curve analysis, showing a narrow full width at half maximum (FWHM) of 11 arcsec.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings15111256

References

2019 - Diamond power devices: State of the art, modelling, figures of merit and future perspective [Crossref]
2024 - Applications of diamond films: A review [Crossref]
2025 - Optical-grade diamond: Characteristics, synthesis, and recent research progress [Crossref]
2004 - Application of diamond in high technology [Crossref]
2012 - Homoepitaxial growth of single crystal diamond membranes for quantum information processing [Crossref]
2020 - Large-scale integration of artificial atoms in hybrid photonic circuits [Crossref]
2021 - Polishing and planarization of single crystal diamonds: State-of-the-art and perspectives [Crossref]
2013 - Diamond polishing [Crossref]
2023 - CVD diamond: A review on options and reality [Crossref]