Low-Temperature Deposition of Diamond Films by MPCVD with Graphite Paste Additive

At a Glance

Metadata	Details
Publication Date	2024-04-16
Journal	C – Journal of Carbon Research
Authors	Stephen Yang-En Guu, Fu‐Cheng Lin, Yu-Sen Chien, Alen Jhang, Yonhua Tzeng
Institutions	National Cheng Kung University
Citations	1
Analysis	Full AI Review Included

Executive Summary

This research demonstrates a novel Microwave Plasma Chemical Vapor Deposition (MPCVD) technique utilizing a graphite paste additive to achieve high-quality, large-grain diamond films at low temperatures (450 °C), critical for advanced Integrated Circuit (IC) fabrication.

Low-Temperature Feasibility: Successful deposition of diamond films on silicon at 450 °C, mitigating thermal degradation risks for pre-fabricated IC structures.
Enhanced Growth Rate: Achieved a rapid deposition rate exceeding 200 nm/h, significantly higher than conventional low-temperature MPCVD.
Improved Morphology: The graphite paste additive promoted large grain growth, increasing average grain size from 15-25 nm (without paste) to approximately 80 nm (with repetitive paste application).
High Material Quality: Raman analysis confirmed the formation of sp³-bonded diamond (1332 cm^-1 peak) and an enhanced sp³/sp² ratio, crucial for maximizing thermal conductivity and dielectric properties.
IC Compatibility: Films were deposited in the required thickness range (tens to a few hundred nanometers), positioning MPCVD diamond as a promising dielectric and thermal management material for 3D nanostructure ICs.
Methodology: The paste, containing nanoscale graphite, binder, and solvent, vaporized in the plasma, supplying additional C, O, and H radicals to dominate and accelerate the initial diamond growth phase.

Technical Specifications

Parameter	Value	Unit	Context
Substrate Temperature	450	°C	Low-temperature requirement for IC compatibility
Deposition Rate (Max)	>200	nm/h	Achieved using graphite paste additive
Film Thickness (Max)	197	nm	After three repetitive 20 min growth periods (Gas #1)
Average Grain Size (Max)	80	nm	After three repetitive 20 min growth periods
Average Grain Size (Baseline)	15-25	nm	Without graphite paste additive
Microwave Power	950	W	2.45 GHz Astex AX5010 reactor
Gas Pressure	30	torr	Operating pressure during deposition
Total Gas Flow Rate	160	sccm	Total flow rate of H₂, CH₄, and CO₂
Gas Composition #1	5% CH₄, 1% CO₂	in H₂	Primary gas mixture used
Gas Composition #2	5% CH₄	in H₂	Comparison gas mixture used
Seeding Particle Size	3.7	nm	Commercial nanodiamond solution used for seeding
Diamond Raman Peak	1332	cm^-1	Confirms sp³-bonded diamond formation

Key Methodologies

The low-temperature, high-rate diamond deposition was achieved through the following steps:

Substrate Preparation: P-type (001) silicon wafers were seeded using a commercial nanodiamond solution (nominal 3.7 nm particles) via an ultrasonic electrostatic seeding method for 50 min.
Substrate Mounting: Seeded wafers were adhered to a molybdenum plate using a specific graphite paste (30% methyl ethyl ketone, 30% propylene glycol methyl ether acetate, 30% modified epoxy resin, 10% synthetic graphite) for temperature uniformity.
Plasma Ignition: Pure hydrogen (H₂) plasma was ignited at approximately 1 torr.
Process Stabilization: Gas pressure was adjusted to 30 torr, and the microwave power was set to 950 W.
Growth Initiation: CH₄ and CO₂ were introduced (5% CH₄, 1% CO₂ in H₂). The vaporization of the graphite paste supplied additional C, O, and H radicals, dominating the initial 10-20 minutes of growth.
Repetitive Growth (for thicker films): To sustain the graphite paste effect, the process was terminated every 20 minutes, the substrate was removed, 0.018 g of fresh graphite paste was reapplied, and the growth cycle was repeated up to three times to achieve films approaching 200 nm thickness.
Characterization: Films were analyzed using Optical Emission Spectroscopy (OES) to monitor plasma radicals (CH, C₂), Scanning Electron Microscopy (SEM) for grain size and thickness, and Raman Spectroscopy (458 nm laser) for carbon phase content (sp³/sp² ratio).

6CCVD Solutions & Capabilities

The research successfully demonstrated the critical need for high-quality, thin diamond films for thermal management and dielectric isolation in advanced ICs. 6CCVD is uniquely positioned to supply the specialized materials required to replicate and scale this novel low-temperature MPCVD process.

Applicable Materials

To replicate or extend this research, engineers require high-purity, highly controlled polycrystalline diamond (PCD) films with precise thickness control, optimized for dielectric and thermal performance.

6CCVD Material Solution	Specification Match	Value Proposition
Optical Grade PCD Wafers	High sp³ content, low defect density.	Provides the high thermal conductivity (TC) and dielectric strength required for IC applications.
Thin PCD Films (0.1 µm - 500 µm)	Matches the required thickness range (tens to hundreds of nanometers).	Allows precise control over film thickness for integration into 3D nanostructures and interconnects.
Custom Substrates	Silicon (001) used in the paper.	6CCVD can deposit PCD films directly onto customer-supplied silicon or other semiconductor substrates.
Boron-Doped Diamond (BDD)	Not used in the paper, but relevant for IC electrodes.	Available for extending research into conductive diamond electrodes or sensors integrated into the same IC platform.

Customization Potential

The success of this low-temperature process relies on precise material control, which is a core competency of 6CCVD.

Custom Dimensions: While the paper used standard silicon wafers, 6CCVD offers PCD plates/wafers up to 125mm in diameter, enabling seamless scaling to industry-standard wafer sizes.
Thickness Control: 6CCVD guarantees thickness control for PCD films from 0.1 µm up to 500 µm, ensuring the ability to produce the exact few-hundred-nanometer films demonstrated in this study.
Surface Finish: Achieving optimal interface quality is crucial for thermal performance. 6CCVD offers advanced polishing services:
- PCD polishing to Ra < 5 nm (for inch-size wafers).
Metalization Services: For subsequent IC processing steps (e.g., contact formation), 6CCVD offers in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu deposition, eliminating the need for external processing steps.

Engineering Support

The novel use of graphite paste highlights the importance of optimizing precursor chemistry and plasma parameters for low-temperature growth.

In-House PhD Team: 6CCVD’s material scientists specialize in advanced MPCVD recipes and can provide consultation on optimizing precursor delivery, gas ratios (H₂/CH₄/CO₂), and power levels to maximize growth rate and sp³/sp² ratio for similar high-thermal-conductivity dielectric projects.
Global Logistics: 6CCVD ensures reliable, global delivery of custom diamond materials, with DDU (Delivered Duty Unpaid) as the default and DDP (Delivered Duty Paid) available upon request.

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

View Original Abstract

Modern integrated circuits (ICs) take advantage of three-dimensional (3D) nanostructures in devices and interconnects to achieve high-speed and ultra-low-power performance. The choice of electrical insulation materials with excellent dielectric strength, electrical resistivity, strong mechanical strength, and high thermal conductivity becomes critical. Diamond possesses these properties and is recently recognized as a promising dielectric material for the fabrication of advanced ICs, which are sensitive to detrimental high-temperature processes. Therefore, a high-rate low-temperature deposition technique for large-grain, high-quality diamond films of the thickness of a few tens to a few hundred nanometers is desirable. The diamond growth rate by microwave plasma chemical vapor deposition (MPCVD) decreases rapidly with lowering substrate temperature. In addition, the thermal conductivity of non-diamond carbon is much lower than that of diamond. Furthermore, a small-grain diamond film suffers from poor thermal conductivity due to frequent phonon scattering at grain boundaries. This paper reports a novel MPCVD process aiming at high growth rate, large grain size, and high sp3/sp2 ratio for diamond films deposited on silicon. Graphite paste containing nanoscale graphite and oxy-hydrocarbon binder and solvent vaporizes and mixes with gas feeds of hydrogen, methane, and carbon dioxide to form plasma. Rapid diamond growth of diamond seeds at 450 °C by the plasma results in large-grained diamond films on silicon at a high deposition rate of 200 nm/h.

Tech Support

Original Source

DOI: https://doi.org/10.3390/c10020039

References

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1991 - Towards a general concept of diamond chemical vapour deposition [Crossref]
2018 - Morphology and mechanical behavior of diamond films fabricated by IH-MPCVD [Crossref]
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