Effect of Substrate Holder Design on Stress and Uniformity of Large-Area Polycrystalline Diamond Films Grown by Microwave Plasma-Assisted CVD

At a Glance

Metadata	Details
Publication Date	2020-09-30
Journal	Coatings
Authors	Vadim Sedov, Artem Martyanov, A. S. Altakhov, А. Ф. Попович, Mikhail Shevchenko
Institutions	Cascade Technologies (United States), Kurchatov Institute
Citations	44
Analysis	Full AI Review Included

Technical Documentation & Analysis: Low-Stress, Large-Area PCD for Thermal Management

Reference: Sedov et al., Effect of Substrate Holder Design on Stress and Uniformity of Large-Area Polycrystalline Diamond Films Grown by Microwave Plasma-Assisted CVD, Coatings 2020, 10, 939.

Executive Summary

This research successfully demonstrates a method for synthesizing large-area, low-stress Polycrystalline Diamond (PCD) films suitable for high-end electronic heat sink applications, directly addressing a critical need in GaN device thermal management.

Core Achievement: Optimization of MPCVD growth using a novel pedestal substrate holder geometry to achieve highly homogeneous PCD films over 2-inch Si substrates.
Stress Reduction: The pedestal design significantly reduced internal compressive stress in the thick PCD film down to 1.1-1.4 GPa.
Ultra-Low Curvature: This stress control resulted in an extremely low plate displacement ($\Delta h$) of only 50 µm for the 2-inch “diamond-on-Si” plates (Radius R = 6.2 m).
Material Quality: The resulting PCD films (100 µm thick) exhibited high crystalline quality and homogeneity, with no signs of Nanocrystalline Diamond (NCD) formation at the edges, unlike the pocket geometry.
Thermal Performance: Thermal conductivity (TC) reached 10 W/cm·K for 100 µm films and 15 W/cm·K for 200 µm films, confirming suitability for high-performance heat sinks.
Application Focus: The methodology is crucial for improving existing MPCVD reactors aimed at growing large-area, thick, homogeneous PCD layers for advanced electronic applications, such as GaN-on-Diamond devices.

Technical Specifications

The following hard data points were extracted from the optimized MPCVD synthesis using the pedestal substrate holder geometry:

Parameter	Value	Unit	Context
Substrate Material	Si (111)	N/A	Mirror-polished, used as carrier
Substrate Diameter	2 (50.8)	inches (mm)	Large-area target
Si Substrate Thickness	0.35	mm	Thin substrate used for stress testing
Target PCD Film Thickness	100 ± 10	µm	Final average thickness
Substrate Temperature (T_sub)	850 ± 25	°C	Controlled growth temperature
Methane Concentration	3	%	CH₄/H₂ gas mixture
Total Gas Flow Rate	500	sccm	Constant flow rate
Optimized Pressure (Pedestal)	55	Torr	Low-stress growth condition
Optimized MW Power (Pedestal)	4.5	kW	Low-stress growth condition
Compressive Stress ($\sigma$)	1.1-1.4	GPa	Deduced from Raman shift (1335.1 cm^-1)
Plate Displacement ($\Delta h$)	50	µm	Ultra-low curvature achieved (Pedestal)
Radius of Curvature (R)	6.2	m	Resulting curvature (Pedestal)
Thermal Conductivity (TC)	10	W/cm·K	For 100 µm thick PCD
Thermal Conductivity (TC)	15	W/cm·K	For 200 µm thick PCD

Key Methodologies

The experiment focused on optimizing the substrate holder geometry to achieve uniform E-field distribution and low-stress film growth via MPCVD.

Substrate Preparation:
- Mirror-polished monocrystalline silicon (111) plates (2-inch diameter, 0.35 mm thickness) were used.
- Nucleation layer formed by ultrasonic treatment in detonation nanodiamond (DND) slurry (5 nm particle size) for 10 minutes, followed by spin-coating.
Holder Design and Simulation:
- Three molybdenum holder geometries were tested: flat, pocket, and pedestal.
- E-field simulations (Finite Element Method, 2.45 GHz, 5 kW total power) were used to optimize the height of the pedestal stage and pocket protective ring (both set to 2 mm).
MPCVD Synthesis:
- Performed in an ARDIS-100 reactor using CH₄/H₂ gas mixtures (3% CH₄, 500 sccm total flow).
- Substrate temperature maintained at 850 ± 25 °C.
- Growth rate targeted at ~1 µm per hour, requiring 100-hour deposition runs to achieve 100 µm thickness.
In-Situ and Ex-Situ Analysis:
- Thickness/Rate: Monitored in situ using laser interferometry ($\lambda$ = 655 nm).
- Structure/Phase: Analyzed using Scanning Electron Microscopy (SEM) and micro-Raman spectroscopy ($\lambda$ = 473 nm).
- Stress/Curvature: Measured using white light interferometry to determine plate displacement ($\Delta h$) and radius of curvature (R).
- Thermal Conductivity (TC): Measured using the Laser Flash Technique (LFT) on free-standing PCD samples (Si substrate chemically removed). Thin Ti layers (~400 nm) were deposited on the PCD for enhanced laser absorption during LFT.

6CCVD Solutions & Capabilities

The research highlights the critical need for large-area, high-quality, stress-controlled PCD for advanced thermal management. 6CCVD is uniquely positioned to supply materials and services that meet or exceed the specifications required to replicate and extend this work.

Applicable Materials

To replicate the high-quality, low-stress results achieved with the optimized pedestal holder, researchers require premium thermal grade PCD.

Thermal Grade Polycrystalline Diamond (PCD): 6CCVD supplies high-purity PCD wafers specifically engineered for heat sink applications, guaranteeing high thermal conductivity (TC).
Custom Thickness PCD: We offer PCD layers matching the study’s requirements, with thicknesses ranging from 0.1 µm up to 500 µm, allowing for precise thermal budget control in device integration.

Customization Potential

The study utilized 2-inch substrates and required specific metalization for thermal testing. 6CCVD’s capabilities directly address these needs at scale.

Research Requirement	6CCVD Customization Capability	Value Proposition
Large Area Wafers	Plates/wafers available up to 125 mm (5 inches) in diameter.	Exceeds the 2-inch limit, enabling next-generation, larger-scale electronic platforms.
Custom Thickness	SCD and PCD substrates available up to 10 mm thick.	Provides flexibility for both thin-film deposition (0.1 µm) and robust heat spreader applications.
Metalization (Ti layer)	In-House Metalization Services including Ti, Pt, Au, Pd, W, and Cu.	Eliminates the need for external processing steps, streamlining the fabrication of test samples (e.g., LFT) and device integration.
Surface Finish	Precision polishing for inch-size PCD wafers to Ra < 5 nm.	Ensures optimal surface quality for subsequent bonding processes (e.g., GaN-on-Diamond bonding) critical for high-performance electronics.

Engineering Support

The core challenge solved by the authors was reactor optimization to manage stress and uniformity. 6CCVD offers specialized expertise in this area.

Stress and Curvature Control: Our in-house PhD engineering team specializes in optimizing MPCVD growth recipes and reactor parameters to control intrinsic stress, achieving ultra-low curvature and high homogeneity for demanding GaN/SiC Thermal Management projects.
Material Selection Consultation: We provide expert consultation on selecting the optimal diamond material (SCD vs. PCD) and doping (BDD) based on specific application requirements (e.g., balancing thermal conductivity vs. cost and size).

Call to Action

6CCVD provides the high-quality, large-area, stress-controlled PCD materials necessary to advance research in thermal management and high-power electronics.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to ensure timely delivery of your critical materials.

View Original Abstract

In this work, the substrate holders of three principal geometries (flat, pocket, and pedestal) were designed based on E-field simulations. They were fabricated and then tested in microwave plasma-assisted chemical vapor deposition process with the purpose of the homogeneous growth of 100-μm-thick, low-stress polycrystalline diamond film over 2-inch Si substrates with a thickness of 0.35 mm. The effectiveness of each holder design was estimated by the criteria of the PCD film quality, its homogeneity, stress, and the curvature of the resulting “diamond-on-Si” plates. The structure and phase composition of the synthesized samples were studied with scanning electron microscopy and Raman spectroscopy, the curvature was measured using white light interferometry, and the thermal conductivity was measured using the laser flash technique. The proposed pedestal design of the substrate holder could reduce the stress of the thick PCD film down to 1.1-1.4 GPa, which resulted in an extremely low value of displacement for the resulting “diamond-on-Si” plate of Δh = 50 μm. The obtained results may be used for the improvement of already existing, and the design of the novel-type, MPCVD reactors aimed at the growth of large-area thick homogeneous PCD layers and plates for electronic applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings10100939

References

2018 - Thermal conductivity of high purity synthetic single crystal diamonds [Crossref]
2019 - High Power (>27 W) Semiconductor Disk Laser Based on Pre-Metalized Diamond Heat-Spreader [Crossref]
2019 - A diamond made microchannel heat sink for high-density heat flux dissipation [Crossref]
2016 - Multifinger Indium Phosphide Double-Heterostructure Transistor Circuit Technology With Integrated Diamond Heat Sink Layer [Crossref]
2019 - Polycrystalline diamond films with tailored micro/nanostructure/doping for new large area film-based diamond electronics [Crossref]
2016 - Single crystal diamond wafers for high power electronics [Crossref]
1998 - Multilayer diamond heat spreaders for electronic power devices [Crossref]
2012 - Reduced Self-Heating in AlGaN/GaN HEMTs Using Nanocrystalline Diamond Heat-Spreading Films [Crossref]