Microstructures Manufactured in Diamond by Use of Laser Micromachining

At a Glance

Metadata	Details
Publication Date	2020-03-06
Journal	Materials
Authors	Mariusz Dudek, Adam Rosowski, Marcin Kozanecki, Malwina Jaszczak, W. Szymański
Institutions	Oxford Lasers (United Kingdom), Lodz University of Technology
Citations	8
Analysis	Full AI Review Included

Advanced Technical Documentation: High-Precision Diamond Micromachining for Microfluidics and MEMS

6CCVD Analysis of “Microstructures Manufactured in Diamond by Use of Laser Micromachining”

Executive Summary

This study demonstrates the feasibility and precision of nanosecond (ns) pulsed laser micromachining on Microwave Plasma-Enhanced Chemical Vapor Deposition (MW PECVD) polycrystalline diamond (PCD) plates for applications requiring complex 3D structures, such as Microelectromechanical Systems (MEMS) and advanced microfluidics.

Ultra-High Precision Achieved: Optimal laser parameters resulted in narrow, deep grooves (12.8 µm narrowness, 245 µm depth) with excellent wall perpendicularity (< 88.9° slope).
Superior Surface Quality: Optimal processing conditions yielded exceptionally low surface roughness (Ra) values down to 0.135 µm, crucial for functional microfluidic channels.
Material Integrity Maintenance: The research successfully identified parameters (e.g., low scan speed of 100 mm/s at 9.5 W power) that minimize laser-induced phase transition, preventing the conversion of diamond (sp³) to graphite/amorphous carbon (sp²).
Methodology: Micromachining utilized a 355 nm UV Diode-Pumped Solid State (DPSS) nanosecond laser system operating at a 50 kHz pulse repetition rate.
Critical Parameter Correlation: Raman spectroscopy confirmed that increased scanning speed, due to local heating and rapid re-scanning, significantly promotes graphitization, necessitating precise control over the processing recipe.
Application Potential: The demonstrated precision and surface quality validate PCD as a superior material for complex diamond microfluidic and photonic devices.

Technical Specifications

Parameter	Value	Unit	Context / Observation
Substrate Material	Polycrystalline Diamond (PCD)	N/A	MW PECVD grown on Si substrate (seeded with nanodiamond)
Substrate Thickness (Initial)	530	µm	Typical thickness used for bulk machining
Diamond Growth Rate	1	µm/h	Deposition condition
Deposition Temperature	820	°C	Substrate temperature during MW PECVD
Material Hardness (HV)	85.1 ± 10.2	GPa	High intrinsic mechanical stability
Young’s Modulus	1114.5 ± 183.8	GPa	High intrinsic mechanical stability
Laser Wavelength	355	nm	UV (Suitable for high absorption by diamond)
Laser Type	DPSS (Diode Pumped Solid State)	N/A	Nanosecond pulsed regime
Pulse Repetition Rate	50	kHz	Constant parameter
Average Power (Tested Range)	5 to 11 (Optimal 9.5)	W	Power directly impacts graphitization severity
Scan Speed (Tested Range)	50 to 400	mm/s	Directly impacts surface temperature and phase transition
Hatching Distance (Scan Spacing)	5 to 20	µm	Used for area filling / volumetric removal
Focused Spot Size	21	µm	Determined by 163 mm F-Theta lens
Achieved Groove Narrowness	12.8	µm	Optimal structure result
Achieved Groove Depth	245	µm	Deep channel structure result
Achieved Groove Slope	< 88.9	°	Excellent perpendicularity
Achieved Surface Roughness (Ra)	0.135	µm	Optimal result, suitable for microfluidic channel interiors
Diamond Raman Peak (Undisturbed)	1332.9	cm^-1	Reference sp³ bond signature
Graphite Raman D Peak (Disorder)	~1350	cm^-1	Appears with high power/speed (sp² transformation)
Graphite Raman G Peak (Graphite)	~1580	cm^-1	Appears with high power/speed (sp² transformation)

Key Methodologies

The study involved two primary stages: material synthesis via MW PECVD and subsequent high-precision laser micromachining.

I. PCD Substrate Synthesis (MW PECVD)

Substrate Preparation: Silicon (Si) substrate was seeded with a detonation nanodiamond suspension via treatment in an ultrasonic bath.
PECVD Parameters: Growth was conducted in a DF-100 system using the following recipe:
- Microwave Power: 3.6 kW
- Methane (CH₄) Content: 2% (in H₂ gas mixture)
- Total Gas Flow Rate: 800 sccm
- Pressure: 87 Torr
- Substrate Temperature: 820 °C

II. Nanosecond Laser Micromachining

Laser System: A 355 nm UV DPSS laser (50 kHz pulse rate, 25/35 ns pulse duration) was utilized via a galvanometer scanning system with a 163 mm F-Theta lens (21 µm spot size).
Hatching Technique: Material removal was achieved by filling defined shapes using linear scanning lines (hatching). Both single pattern (0°) and double-pattern (0° and 90°) techniques were employed.
Process Optimization: Parameters were varied to assess geometry and material integrity:
- Average Laser Power: Tested from 5 W to 11 W.
- Scanning Speed: Tested from 50 mm/s (low pulse overlap) to 400 mm/s (high pulse overlap).
- Hatching Distance: Tested from 5 µm (high overlap) to 20 µm (low overlap).
Graphitization Control: Low scanning speeds (e.g., 100 mm/s) were found necessary to allow adequate heat dissipation from the modified surface, preventing the formation of sp² (graphite/amorphous carbon) phases confirmed by Raman spectroscopy.
Microstructure Analysis: Machined structures were characterized using SEM, Confocal Laser Scanning Microscopy (CLSM) for geometry (depth, roughness, slope), and Raman spectroscopy (514.5 nm excitation) for detecting material phase changes.

6CCVD Solutions & Capabilities

The findings confirm that ultra-precision microstructures—critical for advanced thermal, fluidic, and photonic devices—can be reliably manufactured in MPCVD diamond, provided the substrate quality and processing control are exceptional. 6CCVD is uniquely positioned to supply the foundational materials and specialized engineering services required to replicate and scale this research.

Applicable Materials for Microfluidic/MEMS Applications

To achieve the lowest possible roughness (Ra 0.135 µm achieved in the paper) and maintain structural integrity post-machining, the quality of the starting diamond material is paramount.

6CCVD Recommended Material	Specification	Relevance to Research Needs
Optical Grade PCD	Wafers up to 125mm in size; low impurity concentration.	Offers the balance of low cost and suitable thermal properties for scaling large microfluidic arrays.
High Purity Single Crystal Diamond (SCD)	Ra < 1nm Polishing achievable; superior defect density control.	Ideal for replicating the sharpest grooves and highest geometric fidelity, especially in photonic or biological fluidics where surface roughness is critical.
Polished Substrates	Standard PCD or SCD plates with Ra < 5nm (PCD) or Ra < 1nm (SCD).	Providing pre-polished material reduces subsequent post-processing steps and aids in achieving the final low Ra surface reported in the paper (0.135 µm).
Custom Thickness Wafers	SCD/PCD from 0.1 µm up to 500 µm (or substrates up to 10mm).	The paper used 530 µm; 6CCVD provides custom thickness to match specific device requirements (e.g., thinner membranes for high-sensitivity MEMS sensors).

Customization Potential

The research highlights the need for precise, custom structural features in diamond. 6CCVD offers extensive in-house services to transition research findings into scalable engineering solutions:

Custom Machining & Shaping: 6CCVD can provide laser cutting, dicing, and highly controlled CNC shaping to deliver substrates ready for micro-machining, including the precise dimensions (e.g., 10 µm narrowness) required by the end application.
Precision Metalization Services: Many diamond microfluidic and MEMS devices require integrated electrodes, heaters, or sensor contacts. 6CCVD provides in-house metalization using thin film deposition of: Ti, Pt, Au, Pd, W, and Cu. This is essential for converting passive microstructures (grooves) into active microchips (e.g., electrophoretic or resistive heating devices).
Dimensional Scaling: While the research focused on small test structures, 6CCVD can provide large-area PCD substrates up to 125 mm diameter, enabling the scale-up of microfluidic platforms and photonic integrated circuits.

Engineering Support

The core challenge of this research was optimizing laser parameters (power, scan speed, pulse overlap) to prevent thermal degradation and graphitization (sp² carbon).

6CCVD’s in-house PhD-level engineering team specializes in the interaction of energy systems (such as lasers) with MPCVD diamond structure. We assist clients in modeling thermal effects and selecting materials to minimize undesirable phase transitions, ensuring maximum sp³ quality remains after processing.
We offer technical consulting on achieving specific mechanical or optical properties (Hardness 85.1 GPa, high Young’s Modulus) required for robust Microfluidic Devices and MEMS components.
Global Shipping Assurance: 6CCVD provides reliable global shipping (DDU default, DDP available) to ensure timely delivery of high-value diamond substrates anywhere in the world.

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

View Original Abstract

Different microstructures were created on the surface of a polycrystalline diamond plate (obtained by microwave plasma-enhanced chemical vapor deposition—MW PECVD process) by use of a nanosecond pulsed DPSS (diode pumped solid state) laser with a 355 nm wavelength and a galvanometer scanning system. Different average powers (5 to 11 W), scanning speeds (50 to 400 mm/s) and scan line spacings (“hatch spacing”) (5 to 20 µm) were applied. The microstructures were then examined using scanning electron microscopy, confocal microscopy and Raman spectroscopy techniques. Microstructures exhibiting excellent geometry were obtained. The precise geometries of the microstructures, exhibiting good perpendicularity, deep channels and smooth surfaces show that the laser microprocessing can be applied in manufacturing diamond microfluidic devices. Raman spectra show small differences depending on the process parameters used. In some cases, the diamond band (at 1332 cm−1) after laser modification of material is only slightly wider and shifted, but with no additional peaks, indicating that the diamond is almost not changed after laser interaction. Some parameters did show that the modification of material had occurred and additional peaks in Raman spectra (typical for low-quality chemical vapor deposition CVD diamond) appeared, indicating the growing disorder of material or manufacturing of the new carbon phase.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13051199

References

2011 - Diamond electrophoretic microchips—Joule heating effects [Crossref]
1999 - Pulsed laser surface modifications of diamond thin films [Crossref]
1998 - Ablation of CVD diamond with nanosecond laser pulses of UV-IR range [Crossref]
2000 - Antireflection structures written by excimer laser on CVD diamond [Crossref]
2009 - Femtosecond laser writing of buried graphitic structures in bulk diamond [Crossref]
2008 - Microstructuring of diamond bulk by IR femtosecond laser pulses [Crossref]
2009 - Femtosecond laser microstructuring in the bulk of diamond [Crossref]
2011 - Three-dimensional laser writing in diamond bulk [Crossref]
2011 - Laser Induced Nanoablation of Diamond Materials [Crossref]