Combined HF+MW CVD Approach for the Growth of Polycrystalline Diamond Films with Reduced Bow

At a Glance

Metadata	Details
Publication Date	2023-02-07
Journal	Coatings
Authors	Vadim Sedov, А. Ф. Попович, Stepan Linnik, Artem Martyanov, Junjun Wei
Institutions	Prokhorov General Physics Institute, University of Science and Technology Beijing
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: Combined HF+MW CVD Diamond Films

Executive Summary

This research demonstrates a highly effective, cost-optimized approach for producing high-performance polycrystalline diamond (PCD) films suitable for advanced thermal management applications, such as GaN-on-Diamond devices.

Performance Breakthrough: A combined Microwave Plasma (MW) CVD and Hot Filament (HF) CVD process yielded 110 µm-thick PCD films with a thermal conductivity (TC) of 210 W/m·K.
Significant TC Improvement: This TC value represents a 60% increase compared to films grown purely by the cost-effective HF CVD method (130 W/m·K).
Stress Management: The bi-layer approach successfully leveraged the opposing stress trends of MW CVD (compressive) and HF CVD (tensile) materials, resulting in a 57% reduction in plate bow (19 µm) compared to the pure HF CVD sample (45 µm).
Structural Control: The initial 25 µm high-quality MW CVD layer acts as a template, promoting larger grain size and superior structural quality in the subsequent, cost-effectively grown HF CVD bulk layer.
Cost Efficiency: The methodology provides a path to high-quality, large-area PCD substrates by utilizing the high-rate, cost-effective HF CVD for the majority of the film thickness, while mitigating its typical performance limitations.
Application Focus: The resulting low-bow, high-TC PCD films are ideal for integration as heat spreaders in high-power electronics, photonics, and GaN-on-Diamond heterostructures.

Technical Specifications

The following hard data points were extracted from the comparative analysis of the as-grown PCD samples.

Parameter	Value	Unit	Context
Combined Film Thickness	110	µm	MW (25 µm) + HF (85 µm)
Thermal Conductivity (TC)	210 ± 25	W/m·K	Combined MW+HF PCD
TC Improvement	≈60	%	Relative to pure HF CVD film
Film Bow (Δh)	-19	µm	Combined MW+HF PCD on Si
Bow Reduction	57	%	Relative to pure HF CVD film
Surface Roughness (Rrms)	1.8	µm	Combined MW+HF PCD
Pure MW CVD TC	870 ± 104	W/m·K	112 µm thick film
Pure HF CVD TC	130 ± 15	W/m·K	93 µm thick film
Raman FWHM (Combined)	7.8	cm^-1	Diamond peak width (Indicator of quality)
Substrate Size (Initial)	19 x 19 x 0.5	mm³	Si (111)
CVD Synthesis Temperature	850 ± 25	°C	MW and HF processes

Key Methodologies

The experiment successfully combined two distinct CVD techniques to optimize material properties and cost efficiency.

Substrate Preparation:
- Si (111) plates (19 x 19 x 0.5 mm³) were used, suitable for GaN-on-Diamond structures.
- Substrates were seeded using an aqueous suspension of nanodiamond particles (≈5 nm) via 10 minutes of ultrasound treatment.
Initial Layer Growth (MW CVD):
- Reactor: ARDIS-100 (2.45 GHz, 4.8 kW power).
- Gas Mixture: CH₄/H₂ (3% methane concentration).
- Pressure/Temperature: 55 Torr, 850 ± 25 °C.
- Growth Rate/Thickness: ≈1 µm/h, grown to 25 µm thickness. (This layer provides the high-quality template.)
Bulk Layer Growth (HF CVD):
- Reactor: Laboratory-built HF reactor using tungsten filaments (d = 0.16 mm).
- Gas Mixture: H₂/CH₄ (6 vol.% methane concentration).
- Pressure/Temperature: 20 ± 1 Torr, 850 ± 20 °C.
- Growth Rate/Thickness: ≈1.1 µm/h, grown to ≈85 µm thickness. (This layer provides the bulk material cost-effectively.)
Post-Processing & Characterization Preparation:
- Samples were laser-cut to 17 x 17 mm² to minimize edge effects.
- The Si substrate was removed via wet etching (HNO₃-HF acid mixture) prior to thermal measurement.
- Thin Ti layers (≈400 nm) were deposited on both sides of the freestanding PCD film to enhance laser absorption and IR emissivity for Laser Flash Technique (LFT) measurement.

6CCVD Solutions & Capabilities

The research highlights the critical need for high-quality, customized PCD films with precise thickness control and advanced post-processing for thermal management applications. 6CCVD is uniquely positioned to supply and enhance the materials required for this research field.

Applicable Materials

To replicate or extend this research, engineers require high-purity, high-TC polycrystalline diamond grown via MPCVD.

Material Recommendation: Optical Grade Polycrystalline Diamond (PCD).
- 6CCVD specializes in high-quality MPCVD PCD, which is essential for achieving the high thermal conductivity (TC) demonstrated by the initial MW CVD layer (870 W/m·K for the pure MW CVD sample).
- Our MPCVD process ensures minimal non-diamond sp² phase contamination, crucial for maximizing phonon transport and TC.
Advanced Option (SCD): For ultimate thermal performance, 6CCVD offers Single Crystal Diamond (SCD) plates (up to 500 µm thick) which provide TC values up to 24 W/cm·K (2400 W/m·K) at room temperature, exceeding the performance of even the best PCD films mentioned in the literature (2000-2200 W/m·K).

Customization Potential

The success of the combined approach relies on precise control over layer thickness, substrate size, and interface preparation—all core competencies of 6CCVD.

Research Requirement	6CCVD Capability	Value Proposition
Custom Thickness Control	SCD and PCD films available from 0.1 µm up to 500 µm. Substrates up to 10 mm.	We can precisely control the thickness ratio (e.g., 25 µm MW layer) to optimize stress compensation and thermal performance.
Large Area Substrates	Plates/wafers available up to 125 mm diameter (PCD).	Surpassing the 2-inch (≈50 mm) limit of standard 2.45 GHz MW CVD reactors mentioned in the paper, enabling industrial scale-up for high-volume electronics.
Substrate Removal	Expertise in handling and processing freestanding diamond films after substrate removal (e.g., Si, SiC).	We provide high-quality, freestanding diamond heat spreaders ready for bonding to GaN or other active layers.
Custom Metalization	Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu layers.	We can replicate the Ti (≈400 nm) layers used for LFT measurement or provide custom Ti/Pt/Au stacks required for high-reliability bonding in GaN-on-Diamond devices.
Surface Finish	Polishing services available for PCD (Ra < 5 nm for inch-size wafers) and SCD (Ra < 1 nm).	Ensures optimal thermal contact resistance (TCR) at the diamond/device interface, critical for maximizing heat dissipation efficiency.

Engineering Support

The successful demonstration of stress compensation and TC enhancement through bi-layer growth opens new avenues for optimizing diamond heat spreaders.

Application Expertise: 6CCVD’s in-house PhD team specializes in material selection and optimization for Power Electronics, GaN-on-Diamond, and High-Frequency Communications projects.
Stress Management Consultation: We offer consultation on tuning intrinsic stress in MPCVD films by adjusting growth parameters (e.g., methane concentration, nitrogen doping) to achieve the desired compressive/tensile balance, eliminating the need for complex, multi-reactor setups (MW CVD + HF CVD).
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) for sensitive, high-value diamond materials.

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

View Original Abstract

A combination of two methods of chemical vapor deposition (CVD) of diamond films, microwave plasma-assisted (MW CVD) and hot filament (HF CVD), was used for the growth of 100 µm-thick polycrystalline diamond (PCD) layers on Si substrates. The bow of HF CVD and MW CVD films showed opposite convex\concave trends; thus, the combined material allowed reducing the overall bow by a factor of 2-3. Using MW CVD for the growth of the initial 25 µm-thick PCD layer allowed achieving much higher thermal conductivity of the combined 110 µm-thick film at 210 W/m·K in comparison to 130 W/m·K for the 93 µm-thick pure HF CVD film.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings13020380

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]
2022 - Surface Etching Evolution of Mechanically Polished Single Crystal Diamond with Subsurface Cleavage in Microwave Hydrogen Plasma: Topography, State and Electrical Properties [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]