Dry etching of single-point cutting tool made of nano-polycrystalline diamond using oxygen plasma (Shapeable cutting edge radius)
At a Glance
Section titled âAt a Glanceâ| 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 |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the use of oxygen plasma dry etching to sharpen nano-polycrystalline diamond (NPD) single-point cutting tools, focusing on achieving sub-nanometer cutting edge radii (CER).
- Core Achievement: Demonstrated the capability to form a shapeable CER of less than 0.5 nm on NPD tools using O2 plasma dry etching.
- Mechanism Confirmation: The non-conductive NPD is etched by first forming a conductive graphite layer on the surface, which is then attacked by positively charged O2 plasma ions attracted by a 1,000 V negative bias applied to the tool holder.
- Sharpening Effect: Dry etching removes initial chipping and roundness by proceeding normal (perpendicular) to the rake and flank faces. The removal depth is linear with time, reaching 2.04 ”m/h on the flank face.
- Metrology Innovation: A standard NPD tool was fabricated via prolonged etching, achieving a CER of less than 0.1 nm (with variation less than 0.1 nm), enabling accurate calibration of the AFM probe tip radius ($r_p$).
- Convergence Limit: The measured CER ($r_m$) converged to a constant value equivalent to the calibrated probe tip radius ($r_p$) after approximately 6 hours of etching, confirming the actual CER ($r$) approached 0 nm.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Shapeable CER (Achieved Limit) | < 0.5 | nm | Maximum variation in converged CER |
| Converged CER (Minimum) | < 0.1 | nm | Actual cutting edge radius after prolonged etching |
| AFM X, Y Resolution | 0.2 | nm | Measurement precision |
| AFM Z Resolution | 0.01 | nm | Measurement precision |
| AFM Cantilever Tip Radius ($r_p$) | 4 to 10 | nm | Typical range for silicon tetrahedral probe |
| Dry Etching Vacuum (Optimal) | 0.2 | Pa | Condition for successful NPD etching |
| Bias Voltage | 1,000 | V | Applied to the tool holder |
| Oxygen Gas Flow Rate | 10 | sccm | Etching gas parameter |
| Antenna Power | 120 | W | Used for dry-lapped tool etching |
| Flank Face Removal Rate ($\Delta f/\Delta t$) | 2.04 | ”m/h | Linear removal speed (higher rate) |
| Rake Face Removal Rate ($\Delta r/\Delta t$) | 0.95 | ”m/h | Linear removal speed (lower rate) |
| Standard Tool CER ($r$) | 0.1 | nm | Fabricated tool for AFM probe calibration |
Key Methodologies
Section titled âKey MethodologiesâThe dry etching process utilized an inductively coupled plasma (ICP) system to sharpen pre-formed NPD cutting tools.
- Tool Pre-forming: NPD single-point cutting tools (0.4 mm nose radius) were initially shaped using a sequence of Laser Machining (LM), Electrochemical Machining (ECM), and Dry Lapping to achieve initial rough edges.
- Etching Setup: The tool was mounted on an S45C steel holder (10 mm diameter, 6 mm curvature radius, 10 mm extension) and rotated at 10 rpm within the ICP chamber.
- Plasma Conditions: Oxygen (O2) gas was introduced at 10 sccm. The chamber vacuum was maintained at a low pressure (0.2 Pa) to prevent iron contamination from the holder masking the diamond surface.
- Plasma Generation and Bias: High-frequency RF power (up to 120 W Antenna power) generated the O2 plasma. A negative bias voltage of 1,000 V was applied to the tool holder, attracting positively charged plasma ions.
- Etching Mechanism: The plasma collision induced the formation of a conductive graphite layer on the non-conductive NPD surface (verified by EPMA). The positively charged plasma ions then collided with this conductive layer, etching the diamond material.
- Sharpening Geometry: Etching was confirmed to occur normal to the original rake and flank faces, resulting in the removal of initial roundness and chipping. The flank face etched faster (2.04 ”m/h) than the rake face (0.95 ”m/h).
- Metrology and Calibration: Cutting Edge Radius (CER) was measured using Atomic Force Microscopy (AFM) in dynamic mode. A standard tool was etched until its measured radius ($r_m$) converged (e.g., 4.9 nm), defining the probe tip radius ($r_p$). The actual CER ($r$) was calculated as $r = r_m - r_p$.
Commercial Applications
Section titled âCommercial ApplicationsâThis dry etching technology enables the fabrication of ultra-sharp diamond tools necessary for achieving the highest levels of precision in manufacturing.
- Ultra-Precision Machining (UPC): Essential for achieving mirror-like surface finishes (Rz < 10 nm) on non-ferrous materials (e.g., pure aluminum, copper) by minimizing the minimum undeformed chip thickness to the sub-nanometer scale.
- Micro-Optics and Molds: Used in the production of high-quality optical components and molds where surface integrity and form accuracy are paramount, as sub-nanometer CER reduces subsurface damage.
- Advanced Tool Manufacturing: Provides a reliable, non-mechanical method for sharpening robust Nano-Polycrystalline Diamond (NPD) tools, expanding their use in applications traditionally reserved for more fragile Single-Crystalline Diamond (SCD) tools.
- Industrial Metrology: The technique allows for the fabrication of highly precise, low-variation standard tools (CER < 0.1 nm), which are critical for the accurate calibration of high-resolution AFM probes used in quality control and research environments.
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.