Micro-texturing into DLC/diamond coated molds and dies via high density oxygen plasma etching

At a Glance

Metadata	Details
Publication Date	2015-01-01
Journal	Manufacturing Review
Authors	Ersyzario Edo Yunata, Tatsuhiko Aizawa
Institutions	Shibaura Institute of Technology
Citations	14
Analysis	Full AI Review Included

6CCVD Technical Documentation: High-Density Plasma Etching for CVD Diamond Micro-Texturing

Executive Summary

This research demonstrates a highly effective, fast-rate method for micro-texturing Chemical Vapor Deposition (CVD) diamond and Diamond-Like Carbon (DLC) coatings using high-density oxygen plasma etching enhanced by a hollow cathode. This process is crucial for fabricating durable molds/dies and advanced Bio-MEMS/NEMS components.

Fast, Anisotropic Etching: Achieved a high etching rate of 10 µm/h for 20 µm thick CVD diamond films, significantly exceeding conventional CF₄ + O₂ methods (1.8 µm/h).
High Feature Fidelity: The anisotropic nature of the plasma etching created rectangular micro-grooves with exceptionally sharp edges (80° sidewall), confirming the process’s precision.
Material Specificity: The fast etching rate relies on the use of hydrogen-free materials (CVD diamond and a-C DLC), demonstrating resistance to the process when high hydrogen content is present (a-C:H etched 4x slower).
Method Enhancement: Implementation of a hollow cathode device confined the plasma, boosting the activated oxygen atom flux and oxygen ion density (up to 1.41 × 10¹⁷ m^-3), driving the high etching speed.
Dual Mechanism: Etching is driven by efficient chemical oxidation (C + O → CO) augmented by physical bombardment using accelerated oxygen ions (DC bias up to -600 V).
Application Relevance: The demonstrated ability to create deep, precise micro-patterns in hard diamond coatings is a key enabling technology for industrial molds, friction-reducing tools, and complex micro-sensors/actuators.

Technical Specifications

Data extracted from the high-density oxygen plasma etching experiments.

Parameter	Value	Unit	Context / Implication
Target Material Thickness (CVD Diamond)	20	µm	Fully etched depth of micro-grooves.
Diamond Etching Rate (Max)	10	µm/h	Achieved using hollow cathode O₂ plasma.
Conventional Etching Rate (CF₄ + O₂)	1.8	µm/h	Benchmark for slow etching rates.
Etching Anisotropy / Edge Angle	80	°	High fidelity and sharp vertical profiles achieved.
DLC Hydrogen Content (a-C:H)	10-15	at%	Significantly reduced etching rate (2.1 µm/h).
RF Generator Frequency	2	MHz	Standard frequency for plasma generation.
RF Voltage Range	100 to 250	V	Used for generating RF plasma power.
DC Bias Range	-400 to -600	V	Used to accelerate ion flux for physical bombardment.
Operating Pressure Range	25 to 100	Pa	Range for high-density plasma operation.
Base Pressure	< 5 × 10^-3	Pa	High vacuum required for stable plasma.
Maximum Ion Density (Ni)	1.41 × 10¹⁷	m^-3	Measured at 105 Pa using hollow cathode.
Oxygen Gas Purity	99.99	%	Required purity of carrier gas.

Key Methodologies

The following high-density oxygen plasma etching system and process steps were employed to achieve fast-rate micro-texturing:

System Setup: A custom plasma etching system was used, featuring independent RF (2 MHz) and DC biased electrodes, a vacuum chamber, and a specialized hollow cathode device to confine the RF plasma.
Specimen Preparation:
- CVD-diamond films (20 µm thick) were grown onto WC(Co) substrates.
- DLC films (5 µm thick, a-C:H and hydrogen-free a-C) were grown onto silicon substrates via RF-sputtering and un-balanced magnetron sputtering.
Masking: Micro-patterns were defined using resin-type masks (3 µm line-space lattice) for DLC etching, or stainless steel sheet masks (100 µm line width) for CVD diamond etching.
Plasma Excitation: Pure oxygen gas (99.99% purity) was introduced at operating pressures between 25 Pa and 100 Pa. RF voltage (100-250 V) ignited the plasma.
Anisotropy Control: A high negative DC bias (-400 V to -600 V) was applied to the specimen stage, accelerating positively charged oxygen ions (Ni) toward the surface, enhancing the physical bombardment component of etching.
Diagnosis: Plasma state was monitored quantitatively using Emissive-Light Optical Spectroscopy (EOS) to track activated oxygen species (O* at 776.34 nm) and Langmuir probes to measure electron and ion densities.
Result Verification: Etched surfaces were analyzed using SEM, laser-microscopy (for profile measurement), and Raman spectroscopy (to confirm complete removal of diamond/DLC in the etched regions).

6CCVD Solutions & Capabilities

6CCVD provides the high-performance diamond materials and customization services necessary to replicate, optimize, and industrialize the micro-texturing processes demonstrated in this research for mold/die fabrication and advanced Bio-MEMS/NEMS.

Paper Requirement / Research Need	6CCVD Applicable Materials & Services	Technical Specification Match & Sales Advantage
High-Purity CVD Diamond Film (Hydrogen-free base, 20 µm thick)	Polycrystalline Diamond (PCD) Wafers: We offer high-quality MPCVD PCD.	Thickness & Scale: We manufacture PCD wafers up to 125 mm in diameter and films up to 500 µm thick, easily accommodating the 20 µm requirement and enabling large-area mold fabrication.
High-Fidelity Pattern Transfer (Requires smooth starting surface)	Precision Polishing Services: We guarantee surface roughness of Ra < 5 nm for inch-size PCD.	Anisotropy Foundation: An ultra-smooth starting surface is critical for achieving the reported sharp 80° edges and ensuring uniform, high-resolution feature definition after masking and etching.
Conductive Diamond (Bio-NEMS/MEMS) (Reference to BDD applications)	Boron-Doped Diamond (BDD): Available in both SCD and PCD formats, offering high electrical conductivity.	Functional Materials: For sensor/actuator applications referenced in the paper, BDD provides the necessary electro-chemical stability and electrical properties, combined with diamond’s hardness.
Integration & Device Scaling (Transitioning from lab bench to industrial component)	Custom Metalization: In-house deposition of metals including Ti, Pt, Au, W, and Cu.	Integrated Device Readiness: Allows researchers to immediately apply contacts or etch masks (e.g., refractory metal masks for enhanced selectivity) without external processing delays.
Custom Wafer Dimensions (Testing on various substrates/sizes)	Custom Dimensions and Laser Cutting: Plates/wafers up to 125mm, with custom laser cutting and shaping services.	Engineering Flexibility: Provides materials in exact dimensions and shapes required for specific high-density plasma reactors, minimizing material waste and maximizing throughput.
Process Optimization Support (Selecting optimal diamond grade)	Expert Engineering Support: 6CCVD’s in-house PhD team assists with material selection and specification.	Accelerated R&D: Our technical experts can advise on material properties (e.g., nitrogen incorporation, crystalline quality) that affect oxygen plasma etch rate and selectivity, ensuring optimal results for micro-texturing projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures timely delivery worldwide.

View Original Abstract

\n\t\t\t\tDiamond-Like Carbon (DLC) and Chemical Vapor Deposition (CVD)-diamond films have been widely utilized not only as a hard protective coating for molds and dies but also as a functional substrate for bio-MEMS/NEMS. Micro-texturing into these hard coated molds and dies provides a productive tool to duplicate the original mother micro-patterns onto various work materials and to construct any tailored micro-textures for sensors and actuators. In the present paper, the high density oxygen plasma etching method is utilized to make micro-line and micro-groove patterns onto the DLC and diamond coatings. Our developing oxygen plasma etching system is introduced together with characterization on the plasma state during etching. In this quantitative plasma diagnosis, both the population of activated species and the electron and ion densities are identified through the emissive light spectroscopy and the Langmuir probe method. In addition, the on-line monitoring of the plasmas helps to describe the etching process. DLC coated WC (Co) specimen is first employed to describe the etching mechanism by the present method. Chemical Vapor Deposition (CVD) diamond coated WC (Co) is also employed to demonstrate the reliable capacity of the present high density oxygen plasma etching. This oxygen plasma etching performance is discussed by comparison of the etching rates.\n\t\t\t

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Original Source

DOI: https://doi.org/10.1051/mfreview/2015015