Synthesis of Polycrystalline Diamond Films in Microwave Plasma at Ultrahigh Concentrations of Methane

At a Glance

Metadata	Details
Publication Date	2023-04-08
Journal	Coatings
Authors	Artem Martyanov, Ivan Tiazhelov, Sergey Savin, В. В. Воронов, В. И. Конов
Institutions	MIREA - Russian Technological University, Prokhorov General Physics Institute
Citations	21
Analysis	Full AI Review Included

Technical Documentation and Analysis: Ultrahigh Methane Concentration MPCVD PCD

Executive Summary

This research demonstrates critical advancements in the synthesis of Polycrystalline Diamond (PCD) films using Microwave Plasma Chemical Vapor Deposition (MPCVD) under ultrahigh methane concentrations ($v_c$ up to 100%). The findings are essential for engineers requiring precise control over diamond morphology and phase composition.

Ultrahigh Concentration Growth: Diamond growth is confirmed possible even in pure methane ($v_c = 100%$), provided the substrate temperature ($T_s$) is maintained below 800 °C.
Morphology Control: The critical transition point between Microcrystalline Diamond (MCD) and Nanocrystalline Diamond (NCD) is highly dependent on $T_s$. The transition shifts from $v_c = 20%$ (at $T_s = 900$ °C) to $v_c = 70%$ (at $T_s = 800$ °C).
Non-Linear Growth Rates: The growth rate exhibits a non-linear trend, peaking at intermediate ultrahigh concentrations (e.g., 4.1 µm/h at $T_s = 900$ °C and $v_c = 40%$).
Texture Manipulation: Films grown at ultrahigh methane concentrations show a preference for (220) crystallographic texture, deviating from the standard (111) orientation typically observed at low $v_c$.
Quality vs. Rate Trade-off: Lower $T_s$ facilitates higher-quality PCD films (lower sp²/sp³ ratio, narrower FWHM) but results in reduced growth rates, confirming the need for precise process optimization.
Application Relevance: The ability to precisely manipulate the MCD/NCD structure at high growth rates is crucial for flexible production of diamond materials used in heat sinks, hard coatings, and protective layers.

Technical Specifications

The following hard data points were extracted from the experimental results detailing the MPCVD synthesis parameters and resulting material properties.

Parameter	Value	Unit	Context
Methane Concentration ($v_c$) Range	4 - 100	%	Full range investigated, including pure CH₄
Substrate Temperature ($T_s$) Range	700 - 1050	°C	Range used for synthesis
Fixed Total Gas Flow	500	sccm	Constant flow rate (CH₄ + H₂)
Final Film Thickness	2	µm	Controlled by laser interferometer
Peak Growth Rate (Max)	4.1	µm/h	Achieved at $T_s = 900$ °C, $v_c = 40%$
Minimum Growth Rate	0.6	µm/h	Observed at $T_s = 800$ °C, $v_c = 4%$ and $v_c = 100%$
MCD-to-NCD Critical $v_c$ ($T_s = 900$ °C)	20	%	Threshold for morphology transition
MCD-to-NCD Critical $v_c$ ($T_s = 800$ °C)	70	%	Threshold for morphology transition
Annealing Temperature (sp² removal)	590	°C	Used for 10 hours in air
Standard Diamond Raman Peak	1333	cm^-1	Used for quality assessment
Texture Preference at High $v_c$	(220)	N/A	Observed shift from standard (111) texture

Key Methodologies

The PCD films were synthesized using a high-power MPCVD reactor, focusing on the complex relationship between gas composition, temperature, and pressure.

Substrate Preparation: Polished single-crystal (100) silicon wafers (10 x 10 x 0.35 mm³) were used as substrates.
Seeding: Substrates were seeded via spin coating using an aqueous suspension of nanodiamond particles (3-7 nm).
CVD Reactor: Synthesis was performed in an ARDIS 100 MPCVD reactor (2.45 GHz, 5 kW).
Gas Flow Control: A fixed total gas flow of 500 sccm (CH₄ + H₂) was maintained. Methane concentration ($v_c$) was varied from 4% to 100%.
Temperature Control (Series 1): $v_c$ was fixed at 40%. $T_s$ was varied (700-1050 °C) by adjusting pressure (54-86 Torr) and microwave power (3.5-5 kW).
Concentration Control (Series 2): $T_s$ was fixed at 800 °C or 900 °C. $v_c$ was varied (4%-100%). Pressure (73 → 45 Torr) and power (4.5 → 2.2 kW) were adjusted dynamically to maintain constant $T_s$.
Thickness Monitoring: Film thickness was controlled to a final value of 2 µm using a laser interferometer during synthesis.
Post-Synthesis Treatment: Samples were annealed in air at 590 °C for 10 hours to remove non-diamond (sp²) carbon phases.
Characterization: Morphology (SEM), phase composition (Raman spectroscopy, sp²/sp³ ratio), and crystallographic texture (XRD, texture coefficient $T_c(hkl)$) were analyzed.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and custom engineering services required to replicate and extend this research into industrial applications, particularly those demanding precise control over PCD morphology (MCD/NCD) and crystallographic texture.

Applicable Materials

This research focuses exclusively on the synthesis and characterization of Polycrystalline Diamond (PCD) films. 6CCVD offers high-purity PCD tailored for applications requiring high thermal conductivity and wear resistance.

6CCVD Material Grade	Description & Relevance to Research
Standard PCD	High-quality, high-purity polycrystalline diamond suitable for hard coatings and heat sinks. Directly addresses the material synthesized in the paper.
Custom Morphology PCD	We offer precise control over the MCD-to-NCD transition. Our engineers can replicate the specific $v_c$ and $T_s$ recipes identified (e.g., $v_c = 20%$ at $900$ °C for NCD transition) to deliver films with tailored grain sizes (microcrystalline, nanocrystalline, or layered structures).
Optical Grade PCD	For applications requiring low optical absorption, 6CCVD can optimize growth conditions (lower $v_c$ and $T_s$) to minimize internal defects and sp² content, ensuring superior optical quality compared to the high-$v_c$ films studied here.

Customization Potential

The paper highlights the necessity of manipulating complex CVD parameters (power, pressure, gas flow) to achieve specific material properties (texture, growth rate, morphology). 6CCVD’s in-house capabilities directly address these customization needs.

Large Area PCD: While the paper used 10 x 10 mm substrates, 6CCVD specializes in producing large-area PCD plates and wafers up to 125 mm in diameter, enabling scaling for industrial applications like large-format heat spreaders.
Thickness Precision: The research targeted 2 µm films. 6CCVD offers PCD films with thickness control ranging from 0.1 µm to 500 µm, allowing for optimization in thin-film protective coatings or thick-plate thermal management solutions.
Texture Engineering: The shift from (111) to (220) texture at ultrahigh $v_c$ is a key finding. 6CCVD can engineer specific crystallographic textures, providing films optimized for directional properties (e.g., enhanced thermal transport or specific mechanical wear characteristics).
Metalization Services: Although not the primary focus of this paper, future integration of these PCD films into electronic or sensor devices requires metal contacts. 6CCVD offers internal metalization capabilities, including deposition of Ti, Pt, Au, Pd, W, and Cu, ensuring seamless integration of the custom PCD material.

Engineering Support

The complex, non-linear relationship between methane concentration, temperature, and resulting material quality (sp²/sp³ ratio, FWHM) necessitates expert guidance.

6CCVD’s in-house team of PhD material scientists specializes in optimizing MPCVD recipes for specific performance metrics. We offer consultation services to assist researchers and engineers in:

Recipe Optimization: Developing custom growth recipes to balance high growth rates (up to 4.1 µm/h demonstrated) with the required material quality (low defect concentration).
Thermal Management Projects: Selecting the optimal PCD grade and morphology (MCD vs. NCD) for specific heat sink or protective layer applications, leveraging the precise MCD-to-NCD transition data provided by this research.
Defect Mitigation: Designing synthesis conditions to minimize the internal structural defects observed in ultrahigh $v_c$ films, thereby improving resistance to post-growth processing like annealing.

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

View Original Abstract

Polycrystalline diamond (PCD) films are usually grown by chemical vapor deposition (CVD) in hydrogen-methane mixtures. The synthesis conditions determine the structure and quality of the grown material. Here, we report the complex effect of the microwave plasma CVD conditions on the morphology, growth rate and phase composition of the resulting PCD films. Specifically, we focus on the factors of (i) increased methane concentrations (νc) that are varied over a wide range of 4%-100% (i.e., pure methane gas) and (ii) substrate temperatures (Ts) varied between 700-1050 °C. Using scanning electron microscopy, X-ray diffraction and Raman spectroscopy, we show that diamond growth is possible even at ultrahigh methane concentrations, including νc = 100%, which requires relatively low synthesis temperatures of Ts < 800 °C. In general, lower substrate temperatures tend to facilitate the formation of higher-quality PCD films; however, this comes at the cost of lower growth rates. The growth rate of PCD coatings has a non-linear trend: for samples grown at Ts = 800 °C, the growth rate increases from 0.6 µm/h at νc = 4% to 3.4 µm/h at νc = 20% and then falls to 0.6 µm/h at νc = 100%. This research is a step toward control over the nature of the CVD-grown PCD material, which is essential for the precise and flexible production of diamond for various applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings13040751

References

2020 - Hierarchically structured diamond composite with exceptional toughness [Crossref]
2018 - Thermal conductivity of high purity synthetic single crystal diamonds [Crossref]
2023 - Thermal conductivity of pink CVD diamond: Influence of nitrogen-related centers [Crossref]
2019 - Co-deposition of diamond and β-SiC by microwave plasma CVD in H2-CH4-SiH4 gas mixtures [Crossref]
2022 - Diamond-germanium composite films grown by microwave plasma CVD [Crossref]
2023 - Microporous poly- and monocrystalline diamond films produced from chemical vapor deposited diamond-germanium composites [Crossref]
2023 - Chip-level thermal management in GaN HEMT: Critical review on recent patents and inventions [Crossref]
2022 - GaN-based heterostructures with CVD diamond heat sinks: A new fabrication approach towards efficient electronic devices [Crossref]
2022 - Luminescent diamond composites [Crossref]