Effect of low-damage inductively coupled plasma on shallow nitrogen-vacancy centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-08-17 |
| Journal | Applied Physics Letters |
| Authors | Felipe FĂĄvaro de Oliveira, S. Ali Momenzadeh, Ya Wang, Mitsuharu KONUMA, Matthew Markham |
| Institutions | University of Stuttgart, Element Six (United Kingdom) |
| Citations | 66 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Low-Damage Plasma Etching for Shallow NV Centers
Section titled âTechnical Documentation & Analysis: Low-Damage Plasma Etching for Shallow NV CentersâThis document analyzes the research paper âEffect of Low-Damage Inductively Coupled Plasma on Shallow NV Centers in Diamondâ and aligns its material requirements and technical achievements with the advanced capabilities of 6CCVD.
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates a critical surface engineering technique for quantum applications, directly benefiting engineers requiring ultra-high-purity diamond substrates.
- Nanometric Precision Etching: A novel oxygen Inductively Coupled Plasma (ICP) âsoft plasmaâ process achieved nanometric etching precision (1-2 nm removal depth) essential for controlling shallow Nitrogen-Vacancy (NV) center depth.
- Damage-Free Surface: Unlike standard Reactive Ion Etching (RIE), the soft plasma process completely removed the amorphous carbon (a-spÂł) damage layer without introducing new sub-surface defects, confirmed by XPS and PL microscopy.
- Enhanced Spin Coherence (Tâ): The low-damage treatment resulted in a threefold increase in Tâ coherence times for NV centers located < 4 nm from the surface, achieving values up to ~35 ”s.
- Material Requirement: The success relied on high-purity, electronic grade, 12C isotopically purified Single Crystal Diamond (SCD) substrates with ultra-low initial surface roughness (Ra < 1 nm).
- Application Relevance: This technique is vital for scaling quantum sensing applications, enabling precise depth control and preservation of optical/spin properties in near-surface NV centers used as atomic-sized magnetic field sensors.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research detailing the material properties and process outcomes:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | 12C purified SCD | N/A | Electronic grade, [100] orientation. |
| Substrate Thickness | > 50 | ”m | Overgrown layer thickness. |
| Initial RMS Roughness (AFM) | < 1 | nm | As-polished surface quality required. |
| Etching Rate (180 W ICP) | 1.5 ± 1.0 | nm/min | Oxygen soft plasma process. |
| Damage Layer Thickness Removed | 1-2 | nm | RIE-induced amorphous carbon (a-spÂł). |
| Nitrogen Implantation Energy (Tâ Test) | 2.5 | keV | Used for single NV center creation. |
| Nitrogen Implantation Energy (Profiling) | 5.0 | keV | Used for depth distribution analysis. |
| Annealing Temperature | 950 | °C | Post-implantation high vacuum (< 10-6 mbar). |
| Maximum Tâ Coherence Time | ~35 | ”s | Achieved for NV centers < 2.5 nm depth post-treatment. |
| Tâ Improvement Factor | Threefold | N/A | Compared to initial WCO-treated surface. |
| NV Conversion Yield | 1.7 ± 0.3 | % | Conversion from implanted N atoms to NV centers. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise MPCVD material selection, controlled plasma processing, and high-temperature annealing.
- Substrate Selection: High-purity, [100]-oriented Single Crystal Diamond (SCD) with an as-polished surface (Ra < 1 nm) was used. For Tâ measurements, 12C isotopically purified SCD (> 50 ”m thick) was utilized to minimize 13C spin bath noise.
- Masking and RIE Damage: Samples were masked using lithography (AZ 5214 E photoresist). A control region was exposed to Ar/Oâ RIE plasma (70 W RIE power, 37.5 mTorr) to introduce a known sub-surface damage layer.
- Oxygen Soft Plasma Etching (ICP):
- Ignition: RIE source used briefly (a few seconds) at 30 W power, 10 mTorr pressure.
- Sustained Etch: RIE switched off; plasma sustained only by the remote ICP source (180 W or 300 W power). This configuration exposed the sample primarily to neutral chemical radicals, minimizing ion bombardment damage.
- NV Center Creation: Nitrogen ions (2.5 keV or 5.0 keV) were implanted, followed by high-temperature annealing (950 °C in high vacuum, < 10-6 mbar, 2 hours) and subsequent Wet Chemical Oxidation (WCO).
- Characterization: Surface quality was monitored via Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). Spin properties (Tâ) and depth profiling were measured using optically detected magnetic resonance (ODMR) via Hahn echo and NMR sequences.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe success of this low-damage etching technique hinges entirely on the quality and purity of the starting diamond material. 6CCVD is uniquely positioned to supply the necessary substrates and engineering support to replicate and advance this research.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the reported Tâ coherence times and minimize decoherence sources, the highest purity materials are mandatory.
| Research Requirement | 6CCVD Material Solution | Technical Specification |
|---|---|---|
| High Purity, Low Strain | Electronic Grade SCD | [100] or [111] orientation available; thickness up to 500 ”m. |
| Maximum Spin Coherence (Tâ) | Isotopically Purified SCD | 99.999% 12C purity available, essential for minimizing 13C spin bath noise. |
| Surface Preparation | Ultra-Low Roughness Polishing | Guaranteed Ra < 1 nm polishing on SCD, matching the initial surface quality used in the study. |
| Depth Profiling Substrates | Custom Thickness SCD Wafers | Plates/wafers up to 125mm in diameter, allowing for large-scale processing and multiple test regions. |
Customization Potential
Section titled âCustomization PotentialâThe precise control over surface preparation and integration is critical for quantum device fabrication. 6CCVD offers comprehensive customization services that exceed standard commercial offerings.
- Custom Dimensions and Orientation: We provide [100]-oriented SCD wafers up to 125mm, allowing researchers to scale up the soft plasma etching process for larger device arrays.
- Precision Polishing: The paper highlights the necessity of an initial RMS roughness < 1 nm. 6CCVD guarantees this level of polishing quality on our SCD substrates, ensuring minimal polishing-induced defects prior to implantation.
- Metalization Services: While the paper focuses on etching, future integration of NV centers requires microwave delivery structures. 6CCVD offers in-house custom metalization (e.g., Ti/Pt/Au, W, Cu) for creating microwave striplines or electrodes directly on the diamond surface, compatible with ODMR setups.
- Laser Cutting and Shaping: We offer precision laser cutting services to create custom shapes or features required for specific plasma chamber holders or device geometries.
Engineering Support
Section titled âEngineering SupportâThe optimization of plasma recipes (like the two-step RIE/ICP process) and subsequent high-temperature annealing requires deep material science expertise.
- Plasma Compatibility Consultation: 6CCVDâs in-house PhD team specializes in CVD diamond growth and post-processing. We provide expert consultation on material selection (e.g., nitrogen concentration, orientation) to ensure optimal compatibility with complex surface treatments like low-damage ICP etching and high-temperature annealing for Shallow NV Center Engineering projects.
- Process Integration: We assist clients in selecting the appropriate diamond grade (e.g., electronic grade vs. optical grade) and thickness for projects involving ion implantation, thermal oxidation, and plasma processing, ensuring maximum NV center yield and Tâ preservation.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Near-surface nitrogen-vacancy (NV) centers in diamond have been successfully employed as atomic-sized magnetic field sensors for external spins over the last years. A key challenge is still to develop a method to bring NV centers at nanometer proximity to the diamond surface while preserving their optical and spin properties. To that aim we present a method of controlled diamond etching with nanometric precision using an oxygen inductively coupled plasma process. Importantly, no traces of plasma-induced damages to the etched surface could be detected by X-ray photoelectron spectroscopy and confocal photoluminescence microscopy techniques. In addition, by profiling the depth of NV centers created by 5.0 keV of nitrogen implantation energy, no plasma-induced quenching in their fluorescence could be observed. Moreover, the developed etching process allowed even the channeling tail in their depth distribution to be resolved. Furthermore, treating a 12C isotopically purified diamond revealed a threefold increase in T2 times for NV centers with &lt;4 nm of depth (measured by nuclear magnetic resonance signal from protons at the diamond surface) in comparison to the initial oxygen-terminated surface.