Dry etching of single-point cutting tool made of nano-polycrystalline diamond using oxygen plasma (Shapeable cutting edge radius)

At a Glance

Metadata	Details
Publication Date	2022-01-01
Journal	Transactions of the JSME (in Japanese)
Authors	Takuya Semba, Yoshifumi Amamoto, Hitoshi Sumiya
Institutions	Fukuoka Institute of Technology, Sumitomo Electric Industries (United States)
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Ultra-Precision Diamond Tool Sharpening via Oxygen Plasma Dry Etching

Reference: Semba, Amamto, and Sumiya, Transactions of the JSME (in Japanese), Vol.88, No.907 (2022). Topic: Dry etching of single-point cutting tool made of nano-polycrystalline diamond using oxygen plasma (Shapeable cutting edge radius).

Executive Summary

This research successfully demonstrates the use of oxygen plasma dry etching to achieve unprecedented sharpening of Nano-Polycrystalline Diamond (NPD) cutting tools, pushing the limits of ultra-precision machining (UPC).

Ultra-Sharp Edges Achieved: Oxygen plasma dry etching successfully sharpened NPD single-point cutting tools, achieving a final converged Cutting Edge Radius (CER) of less than 0.1 nm.
Precision Limit Defined: The shapeable CER limit achievable by this method was determined to be less than 0.5 nm, significantly surpassing the 25-45 nm limits of conventional Single Crystal Diamond (SCD) tools.
Mechanism Verified: The process relies on the oxygen plasma generating a conductive graphite layer on the non-conductive NPD surface, which is then efficiently removed by ion bombardment (RIE), enabling continuous etching and sharpening.
Differential Etching Rates: The flank face removal rate (2.04 µm/h) was significantly higher than the rake face rate (0.95 µm/h), confirming the mechanism sharpens the edge by preferentially removing material orthogonal to the original surface.
Standard Fabrication Tool: The study utilized the convergence phenomenon (r_m ≈ r_p) to fabricate a standard tool with a CER variation of less than 0.1 nm, suitable for calibrating AFM probe tip radii.
Application: This technique is critical for advancing Ultra-Precision Cutting (UPC) technology, where minimum undeformed chip thickness requires sub-nanometer tool sharpness.

Technical Specifications

The following hard data points were extracted from the dry etching experiments and AFM measurements:

Parameter	Value	Unit	Context
Achievable Cutting Edge Radius (CER)	< 0.5	nm	Shapeable CER limit via O₂ plasma dry etching
Converged CER (Average)	< 0.1	nm	CER achieved after prolonged etching (6+ hours)
CER Variation (Standard Deviation)	< 0.5	nm	Variation in converged CER
Flank Face Removal Rate (∆f/∆t)	2.04	µm/h	Etching rate measured at ±20°, ±40°, ±60°
Rake Face Removal Rate (∆r/∆t)	0.95	µm/h	Etching rate measured at 0°
Bias Voltage (V)	1,000	V	Applied to the NPD holder to attract O₂⁺ ions
Antenna Power (RF)	120	W	Inductively Coupled Plasma (ICP) source
Target Power (RF)	20	W	Applied to the target electrode
Vacuum Pressure (P)	0.3	Pa	Standard dry etching condition for NPD tools
Etching Gas Flow Rate	10	sccm	Oxygen (O₂) gas flow
AFM X, Y Resolution	0.2	nm	Atomic Force Microscopy measurement resolution
AFM Z Resolution	0.01	nm	Atomic Force Microscopy measurement resolution

Key Methodologies

The dry etching process utilized Inductively Coupled Plasma (ICP) Reactive Ion Etching (RIE) with oxygen gas to sharpen pre-formed Nano-Polycrystalline Diamond (NPD) R-bites.

Tool Pre-Processing: NPD R-bites (Nose R=0.4 mm, Rake 0°, Flank 10°) were initially shaped using a combination of Laser Machining (LM), Electrochemical Machining (ECM), and Dry Lapping.
Etching Apparatus: An ICP dry etching system (SP-HC1FS) was employed, featuring a stainless steel target electrode and a copper ring antenna.
Sample Mounting: The NPD tool was brazed onto a cemented carbide substrate, which was then clamped into an S45C holder. The holder was rotated at 10 rpm to ensure uniform etching.
Plasma Conditions: Oxygen (O₂) was used as the etching gas at a flow rate of 10 sccm. The chamber vacuum was maintained at 0.3 Pa.
Energy Input: RF power was applied (120 W Antenna, 20 W Target). A negative bias voltage of 1,000 V was applied to the holder, accelerating positively charged oxygen ions toward the diamond surface.
Etching Mechanism: The high-temperature plasma collision with the NPD surface generated a thin, conductive layer of graphite (confirmed by EPMA). This conductive layer allowed the non-conductive diamond to be etched by the accelerated O₂⁺ ions, removing initial chips (< 1 µm) and rounding.
Measurement: Cutting Edge Radius (CER) was measured using an AFM (SPM-9500J3) in Dynamic mode, compensating for the cantilever tip radius (r_p) using the relationship: r = r_m - r_p.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, precisely manufactured diamond materials for achieving sub-nanometer cutting edges. 6CCVD is uniquely positioned to supply the foundational materials and custom engineering required to replicate and advance this ultra-precision dry etching technique.

Applicable Materials

The study utilized Nano-Polycrystalline Diamond (NPD), a material classification within the broader Polycrystalline Diamond (PCD) family.

Research Requirement	6CCVD Material Solution	Technical Rationale
Nano-Polycrystalline Diamond (NPD)	High-Purity MPCVD PCD Wafers/Plates	6CCVD supplies high-density, high-purity MPCVD PCD material up to 125 mm in diameter, providing the necessary fine-grain structure required for ultra-sharp tool fabrication.
Single Crystal Diamond (SCD) Comparison	Optical Grade SCD (Ra < 1 nm)	For applications requiring the ultimate in material uniformity and zero grain boundaries, 6CCVD offers SCD plates up to 500 µm thick, polished to an industry-leading roughness of Ra < 1 nm.
Conductive Diamond (BDD)	Boron-Doped Diamond (BDD) Substrates	While the paper relied on plasma-induced graphitization to enable RIE on non-conductive NPD, 6CCVD can supply BDD material, which is inherently conductive, potentially simplifying the RIE setup or enabling electrochemical processes without pre-treatment.

Customization Potential

The fabrication of R-bites requires precise geometry and integration onto a holder. 6CCVD offers comprehensive services to meet these needs:

Custom Dimensions and Shaping: The NPD tools used had specific rake (0°) and flank (10°) angles and a 0.4 mm nose radius. 6CCVD provides custom laser cutting and shaping services to fabricate complex diamond geometries directly from our SCD or PCD wafers, ensuring precise initial angles and dimensions, minimizing subsequent material removal steps (LM/ECM/Lapping).
Metalization for Brazing: The NPD chip was brazed onto a cemented carbide substrate. 6CCVD offers in-house metalization capabilities (including Ti, W, Pt, Au, Cu) to apply robust adhesion layers directly onto the diamond material, ensuring reliable bonding to the tool holder for high-stability etching and machining.
Thick Substrates: We can supply diamond substrates (SCD or PCD) up to 10 mm thick, providing the necessary mechanical stability for mounting and high-precision processing, such as the 10 rpm rotation used in the dry etching setup.

Engineering Support

The achievement of a CER < 0.5 nm is highly dependent on precise material selection and post-processing optimization.

6CCVD’s in-house PhD team specializes in diamond material science and can assist researchers and engineers with:

Material Selection: Consulting on the optimal PCD grain size or SCD orientation required for specific ultra-precision cutting (UPC) applications.
Process Optimization: Providing guidance on how the initial surface quality (e.g., 6CCVD’s Ra < 5 nm PCD polishing) impacts the required dry etching time and plasma parameters (Bias, Power) needed to reliably achieve sub-nanometer CERs.
Tool Integration: Assisting with the design and application of custom metalization schemes for robust tool mounting and electrical biasing during plasma processing.

Call to Action: For custom specifications or material consultation regarding ultra-precision cutting tools, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Dry etching using oxygen plasma was conducted on a single-point cutting tool made of nano-polycrystalline diamond to clarify the shapeable cutting edge radius (CER). The CER of the tool was measured by atomic force microscopy (AFM). The cantilever employed was made of single crystal silicon and had a tetrahedral shape with a probe tip radius of 4 to 10 nm. The CER can be identified by subtracting the probe tip radius from a measured CER when the probe tip radius is fixed at a certain value. Dry etching tests revealed that the measured CER decreased and converged to a constant value equivalent to the probe tip radius with increasing etching time. Utilizing this phenomenon, a standard tool suitable for calibrating the probe tip radius was fabricated. The CER and the variation in the CER of the standard tool were less than 0.1 nm. This calibration using the standard tool made it possible to identify the CER from the measured CER. It became clear that the CER converged to less than 0.1 nm, and the variation in converged CER was less than 0.5 nm. Hence, it can be concluded that the shapeable CER that can be formed by dry etching using oxygen plasma is less than 0.5 nm.

Tech Support

Original Source

DOI: https://doi.org/10.1299/transjsme.21-00354