Scalable fabrication of high-quality, ultra-thin single crystal diamond membrane windows

At a Glance

Metadata	Details
Publication Date	2016-01-01
Journal	Nanoscale
Authors	Afaq Habib Piracha, Kumaravelu Ganesan, Desmond W. M. Lau, Alastair Stacey, Liam P. McGuinness
Institutions	Center for Integrated Quantum Science and Technology, RMIT University
Citations	55
Analysis	Full AI Review Included

Technical Documentation & Analysis: Scalable Ultra-Thin SCD Membranes

This document analyzes the research paper, “Scalable fabrication of high-quality, ultra-thin single crystal diamond membrane windows,” and maps the material requirements and processing steps to the advanced capabilities offered by 6CCVD.

Executive Summary

The research successfully demonstrates a robust, scalable, and reproducible method for fabricating large-area, ultra-thin Single Crystal Diamond Membrane Windows (SCDMW) suitable for advanced quantum and photonic applications.

Scalable Fabrication: A multi-step process combining ion implantation, MPCVD overgrowth, fusion bonding, and ICP-RIE thinning enables the production of high-quality SCDMW arrays.
Sub-Micron Thickness: Membranes were reliably fabricated as thin as ~300 nm, meeting the critical thickness requirements for single- mode optical waveguides and quantum information processing (QIP).
Quantum Readiness: The SCDMWs successfully hosted in situ created single Nitrogen-Vacancy (NV) centers, exhibiting single-photon emission (g²(0) = 0.3) and low strain (Raman FWHM 2.1 cm⁻¹).
Mechanical Robustness: The membranes are supported by a thick diamond frame (~150 µm), minimizing breakage, bowing, and handling difficulties, and demonstrating high mechanical quality (Q factor ~400 in air).
High Material Quality: The final membranes exhibited excellent surface quality (RMS roughness ~3 nm), comparable to the original bulk SCD substrate.
6CCVD Value Proposition: 6CCVD specializes in supplying the necessary high-purity SCD substrates, custom PCD/SCD frame materials, and controlled nitrogen doping required to replicate and scale this fabrication process.

Technical Specifications

The following hard data points were extracted from the research paper detailing the material properties and process parameters.

Parameter	Value	Unit	Context
Membrane Thickness (Minimum)	~300	nm	Achieved via ICP-RIE thinning
Membrane Lateral Dimension (Max)	4 x 4	mm	Large size SCDMW array
Individual Window Size (Max)	1 x 1	mm	Used in arrays
Frame Thickness	150 - 300	µm	Used for mechanical support
Surface Roughness (RMS)	~3	nm	AFM scan of thin membrane (Ra < 5 nm)
Raman FWHM (Thin SCDMW)	2.1	cm⁻¹	Indicative of high crystallinity/low strain
NV Center Density	~5	µm⁻²	Optically active defects
Single Photon Emission (g²(0))	0.3	N/A	After background subtraction
Mechanical Q Factor (in air)	~400	N/A	Drum head resonator (f₁₁ = 247 kHz)
Ion Implantation Energy	1	MeV	Helium ions
Damage Layer Depth	~1.7	µm	SRIM simulation result

Key Methodologies

The fabrication relies heavily on precise control of MPCVD growth and subsequent etching processes.

Substrate Selection: Use of high-quality, low-dislocation SCD substrates (HPHT Type Ib or CVD Type IIa, 300-500 µm thick).
Damage Layer Creation: High-energy Helium ion implantation (1 MeV, flux 5 x 10¹⁶ ions per cm²) to create a subsurface damage layer at ~1.7 µm depth.
Graphitization: Vacuum annealing (5 x 10^-6 mbar) at 1300 °C for 1 hour to convert the damage layer into an etchable graphite-like carbon layer.
High-Quality MPCVD Overgrowth:
- Microwave Power: 3000 W.
- Pressure: 100 Torr.
- Gas Mixture: 2% Methane (CH₄) in Hydrogen (H₂).
- Substrate Temperature: 950 °C to 1000 °C.
- Growth Rate: ~20 nm min^-1.
Frame Integration: Laser-micromachined diamond frames (SCD or PCD, 150 µm thick) are aligned and fused to the overgrown substrate using a second MPCVD fusion growth step.
Lift-off: Electrochemical etching in boric acid solution (~300 V) to selectively remove the graphite layer, lifting off the fused SCD membrane/frame assembly.
Final Thinning: Inductive Coupled Plasma Reactive Ion Etching (ICP-RIE) using alternating Ar/Cl₂ and O₂/Ar plasma sequences to remove the remaining damage layer and achieve the final target thickness (down to 300 nm).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the specialized diamond materials and processing required to replicate and advance the scalable fabrication of ultra-thin SCDMWs for quantum and photonic engineering.

Applicable Materials

To achieve the high crystallinity, low strain, and specific thickness profiles demonstrated in this research, 6CCVD recommends the following materials:

Component	6CCVD Material Recommendation	Key Specification Match
Starting Substrate	Optical Grade SCD (Type IIa)	High purity, low dislocation density, essential for minimizing strain and maximizing NV center coherence.
Membrane Material	SCD, Nitrogen-Doped (Controlled)	Controlled in situ nitrogen incorporation during MPCVD for high-density, high-quality NV center creation.
Support Frame	High-Purity PCD or SCD Plates	Available in thicknesses up to 10 mm (Substrates) or standard plates (0.1 µm - 500 µm). PCD offers a cost-effective frame solution.
Thin Membranes	SCD Plates (0.1 µm - 500 µm)	We supply pre-thinned SCD plates, reducing the RIE time required by the end user.
Alternative Doping	Boron-Doped Diamond (BDD)	For applications requiring conductive membranes or electrodes (N/MEMS, electrochemical sensing).

Customization Potential

The success of this fabrication method relies on precise dimensional control and surface quality, areas where 6CCVD excels:

Custom Dimensions: 6CCVD provides SCD and PCD plates/wafers up to 125 mm in diameter, significantly exceeding the 4 x 4 mm scale demonstrated in the paper, enabling true industrial scalability.
Ultra-Low Roughness Polishing: We guarantee surface roughness of Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD frames, ensuring optimal conditions for subsequent CVD overgrowth and minimizing scattering losses in photonic devices.
Custom Frame Fabrication: 6CCVD offers precision laser cutting and micromachining services for fabricating complex frame geometries, micro-channels, and apertures (as shown in Fig. 1d) in both SCD and PCD materials.
Metalization Services: While the paper did not detail metal contacts, 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) crucial for integrating these SCDMWs into N/MEMS or electronic devices.

Engineering Support

The complex nature of ion implantation, annealing, and subsequent MPCVD overgrowth requires deep material expertise. 6CCVD’s in-house PhD team provides comprehensive engineering support:

Material Selection for QIP: Assistance in selecting the optimal nitrogen concentration and substrate type (e.g., Type IIa vs. Type Ib) to maximize NV center yield and coherence time for similar Quantum Sensing and Integrated Photonics projects.
Process Optimization: Consultation on CVD parameters (pressure, temperature, gas ratios) to ensure low-strain, high-crystallinity homoepitaxial growth, critical for achieving the reported Raman FWHM of 2.1 cm⁻¹.
Global Logistics: We ensure reliable global shipping (DDU default, DDP available) for sensitive, high-value diamond materials.

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

View Original Abstract

High quality, ultra-thin single crystal diamond (SCD) membranes that have a thickness in the sub-micron range are of extreme importance as a materials platform for photonics, quantum sensing, nano/micro electro-mechanical systems (N/MEMS) and other diverse applications. However, the scalable fabrication of such thin SCD membranes is a challenging process. In this paper, we demonstrate a new method which enables high quality, large size (∼4 × 4 mm) and low surface roughness, low strain, ultra-thin SCD membranes which can be fabricated without deformations such as breakage, bowing or bending. These membranes are easy to handle making them particularly suitable for fabrication of optical and mechanical devices. We demonstrate arrays of single crystal diamond membrane windows (SCDMW), each up to 1 × 1 mm in dimension and as thin as ∼300 nm, supported by a diamond frame as thick as ∼150 μm. The fabrication method is robust, reproducible, scalable and cost effective. Microwave plasma chemical vapour deposition is used for in situ creation of single nitrogen-vacancy (NV) centers into the thin SCDMW. We have also developed SCD drum head mechanical resonator composed of our fully clamped and freely suspended membranes.