800 kHz Femtosecond Laser Cleaning of Microwave Plasma Chemical Vapor Deposition Diamond Growth Substrate

At a Glance

Metadata	Details
Publication Date	2025-05-28
Journal	Crystals
Authors	Xiwang Wu, Xin Chen
Institutions	Xuchang University
Analysis	Full AI Review Included

Technical Documentation & Analysis: Femtosecond Laser Cleaning for High-Quality MPCVD Diamond Substrates

Executive Summary

This research validates a critical process improvement for manufacturing high-quality Single Crystal Diamond (SCD) by addressing substrate contamination. 6CCVD utilizes and supports such advanced techniques to ensure the superior quality of our diamond materials.

Problem Addressed: MPCVD growth residues (polycrystalline diamond, graphite, amorphous carbon) adhere strongly to high-temperature molybdenum alloy growth substrates, severely degrading subsequent SCD growth quality and morphology.
Solution Implemented: Non-contact, high-efficiency cleaning using an 800 kHz high-repetition-rate femtosecond laser (250 fs pulse width).
Optimal Parameters: Cleaning was optimized at 2.38 W average power, 800 kHz repetition rate, 1800 mm/s scanning speed, and 10 µm scanning interval.
Cleaning Mechanism: Residue removal relies on a combination of vaporization, thermoelastic expansion, and acoustic forces, ensuring a “cold processing” effect that minimizes thermal damage to the Mo substrate.
Key Achievement: Effective removal of thick, layered SCD/PCD residues (30-50 µm thick) from complex geometries (Foundation Trench and Inwall Regions).
Surface Quality Improvement: Substrate surface roughness (Sa) was significantly reduced from an average of approximately 6.557 µm to 5.231 µm, restoring substrate cleanliness and reusability.
6CCVD Value: This cleaning method is essential for maintaining the pristine substrate conditions required for 6CCVD to produce large-area, ultra-high purity SCD and PCD materials.

Technical Specifications

The following hard data points were extracted from the study detailing the laser parameters and material characteristics.

Parameter	Value	Unit	Context
Laser Repetition Rate	800	kHz	Optimized cleaning frequency
Laser Average Power	2.38	W	Optimal power for non-destructive cleaning
Laser Pulse Width	250	fs	Ultra-short pulse duration
Laser Wavelength	1035	nm	Used with F-theta lens
Laser Spot Diameter	15	µm	Focused spot size
Scanning Speed	1800	mm/s	Optimized cleaning speed
Scanning Interval	10	µm	Step size between scans
Initial Substrate Roughness (Sa)	~6.557	µm	Average before cleaning (high fluctuation)
Final Substrate Roughness (Sa)	~5.231	µm	Average after cleaning (reduced fluctuation)
Single Crystal Diamond Ablation Threshold	8.80	J/cm²	Single-pulse threshold
Residue Layer Thickness (IR)	30 to 50	µm	Thick layered structure on Inwall Region
Substrate Base Material (Mo Alloy)	74.33	wt.%	Molybdenum content

Key Methodologies

The experiment focused on optimizing high-repetition-rate femtosecond laser parameters for non-destructive cleaning of complex MPCVD growth substrate geometries.

Substrate Material: Molybdenum alloy growth substrates (35 mm radius, 6 mm height) were used, featuring Foundation Trench Regions (FTR) and Inwall Regions (IR) where residues accumulated.
Contaminant Analysis: Residues were identified primarily as single-crystal diamond particles (Raman peak at 1304 cm^-1, close to pure diamond’s 1332 cm^-1 peak) mixed with small amounts of graphite and oxides.
Laser System: A femtosecond laser (1035 nm, 250 fs pulse width) with a maximum average power of 40 W was utilized, though optimized cleaning was performed at 2.38 W.
FTR Cleaning: The substrate was placed flat. Multiple scans were performed using the optimized parameters (2.38 W, 800 kHz, 1800 mm/s) to remove aggregated residues via vaporization and thermoelastic expansion.
IR Cleaning (Complex Geometry): A special processing substrate was used to incline the sample at a 45° angle. The laser focus was positioned at the midpoint of the IR to compensate for the 0.7 mm Rayleigh length, ensuring uniform energy density across the inclined surface.
Crack Repair: The same laser parameters were successfully used to clean and smooth strip-shaped cracks (width of 3 µm) on the Mo substrate, further enhancing reusability.
Post-Cleaning Characterization: EDS confirmed the removal of carbon residues (C content dropped from 98.62 wt.% to 0 wt.%) and the restoration of the Mo content (increased to 86.24 wt.%). Confocal microscopy verified the reduction in surface roughness (Sa).

6CCVD Solutions & Capabilities

This research underscores the critical importance of substrate quality in achieving high-performance SCD. 6CCVD’s expertise in MPCVD growth and post-processing directly supports the requirements and advancements demonstrated in this paper.

Applicable Materials

To replicate or extend this research into high-volume manufacturing of advanced diamond products, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): The goal of the cleaning process is to enable the growth of high-quality, low-defect SCD. 6CCVD provides SCD plates with thicknesses ranging from 0.1 µm to 500 µm, essential for applications requiring superior optical transparency and minimal internal stress.
High Purity Polycrystalline Diamond (PCD): For applications requiring large-area coverage or specific thermal management, 6CCVD offers PCD wafers up to 125 mm in diameter. Maintaining a clean substrate is crucial for ensuring the uniform grain structure and high thermal conductivity of these materials.
Custom Substrates (Up to 10 mm): While the paper used Mo alloy, 6CCVD can supply and process various substrate materials (e.g., SCD, Si, Mo) up to 10 mm thick, ensuring the foundation for your MPCVD growth is optimized.

Customization Potential

The successful implementation of this femtosecond laser cleaning technique requires precise control over substrate geometry and subsequent material handling—areas where 6CCVD excels.

6CCVD Service	Technical Advantage for Researchers
Custom Dimensions & Shaping	We offer plates and wafers up to 125 mm (PCD) and can provide custom laser cutting and shaping services to match complex substrate geometries (like the FTR/IR grooves) used in advanced MPCVD reactors.
Ultra-Low Roughness Polishing	Post-cleaning roughness was reduced to 5.231 µm. 6CCVD guarantees final diamond surface finishes of Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD), ensuring optimal epitaxy and device performance.
Advanced Metalization	For subsequent device integration, 6CCVD provides in-house metalization services (Au, Pt, Pd, Ti, W, Cu) tailored to the cleaned substrate or the final diamond film, ensuring robust electrical contacts and thermal interfaces.
Global Logistics Support	We ensure reliable, timely delivery of custom diamond materials worldwide, with DDU (Delivered Duty Unpaid) as the default and DDP (Delivered Duty Paid) available upon request.

Engineering Support

The successful integration of high-repetition-rate femtosecond laser cleaning into a production environment requires deep material science expertise. 6CCVD’s in-house PhD team can assist clients in:

Material Selection: Advising on the optimal SCD or PCD grade required for specific electronic or optical applications enabled by high-quality growth.
Process Integration: Consulting on the necessary substrate preparation and post-growth processing steps to maximize yield and quality in similar MPCVD Diamond Growth projects.
Quality Assurance: Utilizing advanced characterization techniques (Raman, SEM/EDS, AFM) to verify the quality and cleanliness of both the growth substrate and the final diamond product.

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

View Original Abstract

Microwave Plasma Chemical Vapor Deposition (MPCVD) plays a crucial role in the growth of high-quality diamonds. However, during the MPCVD process, residues such as polycrystalline diamond, and graphite often adhere to the high-temperature growth substrate surfaces, potentially degrading diamond growth quality. To effectively remove these contaminants and improve the quality of diamond growth, this study employed an 800 kHz femtosecond laser to clean growth substrates with residual deposits. We assessed the effects of multiple cleaning cycles on residue removal from the Foundation Trench Region (FTR) and Inwall Region (IR) and on substrate quality. The results indicate that multiple scans at a laser power of 2.38 W, a repetition rate of 800 kHz, a scanning speed of 1800 mm/s, and a scan spacing of 10 μm significantly removed residues, reduced substrate surface roughness, and restored substrate cleanliness. This approach enhances the quality and efficiency of diamond growth via MPCVD. The application of high-repetition-rate femtosecond laser cleaning techniques for growth substrates significantly improves the quality of regenerated diamond films, providing crucial support for the preparation of high-quality diamond materials.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst15060517

References

2021 - Diamond as the heat spreader for the thermal dissipation of GaN-based electronic devices [Crossref]
2008 - Diamond as an electronic material [Crossref]
2009 - High quality, large surface area, homoepitaxial MPACVD diamond growth [Crossref]
2006 - High rate homoepitaxial growth of diamond by microwave plasma CVD with nitrogen addition [Crossref]
2009 - Recent advances in high-growth rate single-crystal CVD diamond [Crossref]
2020 - Nanosecond-millisecond combined pulse laser drilling of alumina ceramic [Crossref]