A New Slurry for Photocatalysis-Assisted Chemical Mechanical Polishing of Monocrystal Diamond

At a Glance

Metadata	Details
Publication Date	2023-06-20
Journal	Machines
Authors	Junyong Shao, Yanjun Zhao, Jianhui Zhu, Zewei Yuan, Haiyang Du
Institutions	Northeastern University, Shenyang University of Technology
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: Photocatalysis-Assisted Chemical Mechanical Polishing (PCMP) of Monocrystal Diamond

This document analyzes the research paper “A New Slurry for Photocatalysis-Assisted Chemical Mechanical Polishing of Monocrystal Diamond” and outlines how 6CCVD’s advanced MPCVD diamond materials and processing capabilities can support and extend this research.

Executive Summary

The research successfully demonstrates Photocatalysis-Assisted Chemical Mechanical Polishing (PCMP) as an effective, non-toxic method for achieving ultra-smooth surfaces on large-area CVD monocrystal diamond (SCD).

Core Achievement: Achieved ultra-smooth diamond surfaces by combining mechanical abrasion with chemical oxidation driven by UV-activated photocatalysts.
Key Mechanism: Hydroxyl radicals (·OH) generated by UV irradiation of TiO₂ nanoparticles (specifically P25 and 5 nm TiO₂) oxidize the diamond surface at the atomic level.
Surface Quality Improvement: Surface roughness (Ra) was dramatically reduced from an initial 33.6 nm down to 2.6 nm in 8 hours using P25 TiO₂ slurry.
Optimal Performance: The best measured surface quality achieved was Ra 1.6 nm (AFM measurement) using 5 nm TiO₂ particles.
Slurry Composition: The optimized slurry is non-toxic, utilizing P25 TiO₂ (photocatalyst), Al₂O₃ (abrasive), H₂O₂ (electron capture agent), and H₃PO₄ (pH regulator).
Critical Parameters: High Oxidation-Reduction Potential (ORP) and an acidic environment (pH 1.66) were found to be essential for maximizing chemical removal efficiency.
6CCVD Value Proposition: 6CCVD guarantees SCD polishing results (Ra < 1 nm) that surpass the best results achieved in this study, offering immediate, application-ready ultra-smooth diamond wafers.

Technical Specifications

The following hard data points were extracted from the PCMP experiments:

Parameter	Value	Unit	Context
Initial Surface Roughness (Ra)	33.6	nm	Before PCMP
Final Surface Roughness (Ra)	2.6	nm	After 8 h PCMP (P25 TiO₂)
Best Measured Roughness (Ra)	1.6	nm	AFM measurement (5 nm TiO₂)
Polishing Time	8	h	Duration for Ra reduction
Polishing Rotational Speed	60	r/min	PCMP operational parameter
Polishing Pressure	1.09	MPa	PCMP operational parameter
Optimal Slurry pH Range	1.66 - 2.26	N/A	Achieved via H₃PO₄ addition
TiO₂ Band Gap (E_g)	3.2	eV	Anatase crystal type
Required UV Wavelength (λ_g)	< 387.5	nm	Necessary for TiO₂ activation
P25 TiO₂ Particle Size	~25	nm	Mixed crystal (80:20 Anatase:Rutile)
H₂O₂ Concentration (Slurry)	3	mL	Per 100 mL water
Al₂O₃ Concentration (Abrasive)	6	g	Per 100 mL water

Key Methodologies

The PCMP process relies on precise material selection and controlled operational parameters to achieve atomic-level material removal.

Workpiece Pre-Lapping: CVD diamond workpieces were prepared by stepwise lapping using diamond abrasives ranging from 3-6 µm down to 0-0.5 µm to remove initial rough asperities.
Slurry Formulation: The PCMP slurry was prepared using P25 TiO₂ (photocatalyst), Al₂O₃ (abrasive), H₂O₂ (electron capture agent), and H₃PO₄ (pH regulator).
Dispersion and Homogeneity: The slurry underwent a 20 min ultrasonic dispersion treatment to ensure homogeneous distribution of the nano-particles.
pH and ORP Optimization: Phosphoric acid (H₃PO₄) was added to regulate the pH to an acidic range (down to 1.66), significantly increasing the slurry’s Oxidation-Reduction Potential (ORP).
Photocatalytic Activation: A Merc-1000 W mercury lamp was used as the UV light source to activate the TiO₂ particles, generating highly oxidative holes and hydroxyl radicals (·OH).
Process Control: Polishing was conducted using UNIPOL-1202 equipment at 60 r/min and 1.09 MPa pressure.
Activity Maintenance: H₂O₂ was intermittently added during the 8-hour polishing process to prevent electron-hole recombination and maintain high slurry oxidizability.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality CVD diamond materials required for replicating and advancing this PCMP research, particularly for applications demanding superior surface finish and large dimensions.

Applicable Materials

To replicate or extend this research, 6CCVD recommends the following materials:

Material Grade	Description & Application	6CCVD Capability
Optical Grade SCD	High-purity, low-defect Single Crystal Diamond (SCD) wafers, ideal for high-fidelity loudspeakers, optical windows, and semiconductor research requiring the lowest possible surface roughness.	SCD Thickness: 0.1 µm to 500 µm
Electronic Grade PCD	Polycrystalline Diamond (PCD) wafers for large-area semiconductor applications where high thermal conductivity and large size are critical.	PCD Thickness: 0.1 µm to 500 µm
Custom Substrates	SCD or PCD substrates up to 10 mm thick, suitable for high-pressure polishing studies or high-energy accelerator components.	Substrate Thickness: Up to 10 mm

Surface Quality Advantage

The research achieved a best roughness of Ra 1.6 nm. 6CCVD’s standard polishing services exceed this result, providing immediate access to ultra-smooth surfaces, reducing the need for extensive post-processing:

SCD Polishing Guarantee: Guaranteed surface roughness of Ra < 1 nm.
PCD Polishing Guarantee: Guaranteed surface roughness of Ra < 5 nm for inch-sized wafers.

Customization Potential

6CCVD’s in-house manufacturing capabilities allow researchers to move beyond standard dimensions and integrate complex features:

Large-Area Diamond: We provide large-area PCD plates/wafers up to 125 mm in diameter, supporting the paper’s focus on large-area applications.
Custom Dimensions: Wafers can be provided in custom shapes and sizes via precision laser cutting services.
Metalization Services: While not explicitly used in the PCMP process itself, 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for subsequent device fabrication steps (e.g., electrode deposition for electronic semiconductors).

Engineering Support

6CCVD’s in-house PhD team specializes in CVD diamond growth and surface engineering. We offer consultation services to assist researchers in selecting the optimal diamond crystal orientation, material grade, and initial surface preparation required for advanced polishing techniques like PCMP. We can help tailor material specifications to ensure maximum efficiency in photocatalysis-assisted chemical mechanical polishing projects.

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

View Original Abstract

Diamond needs to have a perfectly smooth surface due to the growing requirements in the fields of electronic semiconductors, optical windows and high-fidelity loudspeakers. However, the polishing of diamonds is highly challenging due to their exceptional hardness and chemical stability. In this study, a new polishing slurry is prepared for the proposed photocatalysis-assisted chemical mechanical polishing (PCMP) approach to obtain an ultra-smooth surface for large-area diamond. The analyses and experimental findings revealed the significance of the photocatalyst, abrasive, electron capture agent and pH regulator as essential components of the PCMP slurry. TiO2 with a 5 nm pore size and P25 TiO2 possess improved photocatalysis efficiency. Moreover, diamond removal is smooth under the acidic environment of H3PO4 due to the high oxidation-reduction potential (ORP) of the slurry, and, during the methyl orange test, P25 TiO2 exhibits reasonable photocatalytic effects. Moreover, in 8 h, a smooth surface free of mechanical scratches can be obtained by reducing the surface roughness from Ra 33.6 nm to Ra 2.6 nm.

Tech Support

Original Source

DOI: https://doi.org/10.3390/machines11060664

References

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