Damage-free highly efficient plasma-assisted polishing of a 20-mm square large mosaic single crystal diamond substrate

At a Glance

Metadata	Details
Publication Date	2020-11-10
Journal	Scientific Reports
Authors	Nian Liu, Kohki Sugawara, Naoya Yoshitaka, Hideaki Yamada, Daisuke Takeuchi
Institutions	The University of Osaka, National Institute of Advanced Industrial Science and Technology
Citations	54
Analysis	Full AI Review Included

Technical Documentation & Analysis: Damage-Free Polishing of Large Single Crystal Diamond

This document analyzes the research paper detailing the Plasma-Assisted Polishing (PAP) of large mosaic Single Crystal Diamond (SCD) substrates. This analysis is designed to provide technical insight while highlighting 6CCVD’s superior material supply and customization capabilities for advanced diamond applications.

Executive Summary

Core Value Proposition: Validation of Plasma-Assisted Polishing (PAP) as a highly efficient, damage-free method for processing large-area Single Crystal Diamond (SCD) substrates.
Material & Size: Successful polishing of a 20 mm x 20 mm mosaic SCD (100) substrate synthesized via Microwave Plasma Chemical Vapor Deposition (MPCVD).
High Efficiency: Achieved a high Material Removal Rate (MRR) of 13.3 µm/h, significantly exceeding conventional mechanical polishing rates.
Ultra-High Surface Quality: Resulting surface demonstrated excellent flatness (≤ 0.5 µm) and ultra-low roughness (Sq < 0.5 nm, measured by AFM).
Damage-Free Confirmation: Micro-Raman spectroscopy confirmed the complete absence of residual stress and non-diamond (sp²) components, which is critical for high-power electronic device fabrication.
Application Relevance: The technique is ideal for processing large, fragile mosaic SCD substrates where high mechanical stress from traditional methods (e.g., scaife polishing) can cause breakage or subsurface damage (SSD).

Technical Specifications

The following hard data points were extracted from the experimental results and methodology:

Parameter	Value	Unit	Context
Substrate Material	Mosaic SCD (100)	N/A	MPCVD grown, clone method
Substrate Dimensions	20 x 20 x 1	mm	Large-area sample size
Material Removal Rate (MRR)	13.3	µm/h	Achieved during initial 3 h of PAP
Final Flatness	≤ 0.5	µm	Measured by Laser Interferometer
Final Roughness (Sq, SWLI)	< 0.5	nm	Measured over 84-µm square area
Final Roughness (Sq, AFM)	0.4	nm	Measured over 5-µm square area
Polishing Pressure	401	kPa	Calculated average contact pressure (initial 3h)
Relative Sliding Speed	1.2	m/s	Between polishing plate and SCD
SCD Substrate Rotation Speed	20	rpm	During mechanical removal phase
Plasma Gas Composition	Ar-based O₂	N/A	Used to modify quartz glass surface
RF Frequency	13.56	MHz	Plasma generation frequency
RF Power	100	W	Plasma generation power
Chamber Pressure	0.8	kPa	Vacuum environment
Diamond Raman FWHM (PAP)	2.2	cm^-1	Indicates high crystallinity (damage-free)

Key Methodologies

The Plasma-Assisted Polishing (PAP) process combines plasma surface modification with mechanical removal under controlled conditions.

Material Synthesis: Mosaic SCD (100) substrate (21 mm x 19 mm x 1 mm) was prepared using the clone method via MPCVD, followed by a lift-off process to obtain a free-standing substrate.
PAP Setup: The SCD substrate was fixed on an upper rotary table and pressed against a quartz glass polishing plate installed on a lower rotary table within a vacuum chamber.
Plasma Generation: An Argon-based oxygen plasma was generated by applying an RF electric field (13.56 MHz) to aluminum alloy electrodes.
Recipe Parameters:
- RF Power: 100 W
- Gas Pressure: 0.8 kPa
- Argon Flow Rate: 200 sccm
- Oxygen Flow Rate: 30 sccm
Mechanical Action: The polishing plate and the SCD substrate were rotated in opposite directions. The relative sliding speed was maintained at 1.2 m/s (SCD holder rotation: 20 rpm).
Surface Analysis: Flatness, roughness, and crystallinity were evaluated using Laser Interferometer, SWLI, AFM, and Confocal Raman Microscopy.

6CCVD Solutions & Capabilities

This research demonstrates the critical need for large-area, high-quality, and structurally robust SCD substrates that can withstand advanced post-processing techniques like PAP. 6CCVD is uniquely positioned to supply the necessary materials and customization required to replicate and scale this research for commercial applications in high-power electronics and optics.

Requirement from Research Paper	6CCVD Solution & Capability	Technical Advantage for Customer
Large-Area SCD Substrate (20 mm square)	Custom Dimensions & Scale: 6CCVD supplies high-quality SCD plates in custom sizes. For maximum scalability, we offer Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter.	Enables immediate scaling of device fabrication (e.g., high-power switches, heat spreaders) beyond the 20 mm scale demonstrated.
High-Quality CVD Diamond (Mosaic/Clone)	Applicable Materials: We recommend Electronic Grade SCD or Optical Grade SCD grown via MPCVD, ensuring high purity, controlled (100) orientation, and low defect density required for high-performance devices.	Guarantees the necessary material integrity to achieve ultra-low defect density and high thermal/electrical performance after PAP.
Ultra-Smooth Surface Finish (Sq < 0.5 nm)	Advanced Polishing Services: 6CCVD provides standard polishing services achieving Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD. We can supply pre-polished substrates ready for final damage-free processing like PAP.	Reduces preparation time and ensures an atomically smooth starting surface, minimizing the required MRR during the final PAP step.
Need for Robust Substrates (1 mm thick)	Thickness Control: 6CCVD offers SCD and PCD layers up to 500 µm thick, with robust diamond substrates available up to 10 mm thick.	Provides flexibility for engineers requiring robust handling or specific thermal management solutions for high-power applications.
Custom Interface Layers (e.g., Metalization)	Internal Metalization Capability: While PAP is a final polish, device integration requires metal contacts. 6CCVD offers in-house deposition of Au, Pt, Pd, Ti, W, and Cu layers.	Streamlines the supply chain by providing polished, metalized, and ready-to-use diamond components for device assembly.
Material Selection for Low-Stress Processing	Engineering Support: 6CCVD’s in-house PhD team specializes in material integrity analysis and can assist researchers in selecting materials optimized for low-stress post-processing techniques like Plasma-Assisted Polishing (PAP) for high-voltage applications.	Ensures material integrity is maintained throughout the fabrication chain, maximizing device yield and reliability by avoiding subsurface damage (SSD).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

View Original Abstract

Abstract Plasma-assisted polishing (PAP) as a damage-free and highly efficient polishing technique has been widely applied to difficult-to-machine wide-gap semiconductor materials such as 4H-SiC (0001) and GaN (0001). In this study, a 20-mm square large mosaic single crystal diamond (SCD) substrate synthesized by microwave plasma chemical vapor deposition (CVD) was polished by PAP. Argon-based plasma containing oxygen was used in PAP to modify the surface of quartz glass polishing plate, and a high material removal rate (MRR) of 13.3 μm/h was obtained. The flatness of SCD polished by PAP measured by an interferometer was 0.5 μm. The surface roughness measured by both scanning white light interferometer (SWLI) (84-μm square) and atomic force microscope (AFM) (5-μm square) was less than 0.5 nm S q. The micro-Raman spectroscopy measurement results of mosaic SCD substrate processed by PAP showed that residual stress and non-diamond components on the surface after PAP processing were below the detection limit.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-020-76430-6