Surface Morphology and Spectroscopic Features of Homoepitaxial Diamond Films Prepared by MWPACVD at High CH4 Concentrations

At a Glance

Metadata	Details
Publication Date	2022-10-22
Journal	Materials
Authors	Javier Sierra Gómez, José Vieira, Mariana Amorim Fraga, E.J. Corat, Vladimir Jesús Trava-Airoldi
Institutions	Universidade Presbiteriana Mackenzie, National Institute for Space Research
Citations	4
Analysis	Full AI Review Included

Technical Analysis and Documentation: High-Rate Homoepitaxial SCD Growth

Executive Summary

This research successfully demonstrates high-rate homoepitaxial growth of Single Crystal Diamond (SCD) films using Microwave Plasma-Assisted Chemical Vapor Deposition (MWPACVD) by optimizing methane (CH$_{4}$) concentration.

High Growth Rate Achieved: SCD films were grown at rates up to 27 µm/h, resulting in films up to 270 µm thick in a 10-hour run, significantly advancing large-area, thick SCD production.
Material Quality: Films exhibited excellent crystalline quality, confirmed by High-Resolution X-ray Diffractometry (HRXRD) FWHM values ranging from 0.014° to 0.028°, comparable to commercial HPHT substrates.
Surface Morphology Control: Increasing CH$_{4}$ concentration (from 6% to 12%) inversely correlated with surface roughness (Ra), achieving a minimum Ra of 171.59 nm, crucial for subsequent device fabrication.
Defect Analysis: Photoluminescence (PL) spectroscopy identified Nitrogen-Vacancy (NV) and Silicon-Vacancy (SiV) centers, highlighting the need for ultra-high purity gas and reactor components for quantum and optical applications.
Application Relevance: The ability to produce thick, high-quality SCD at high rates is critical for emerging high-demand fields, including microelectronics, high-power devices, and wide-spectrum optical communication systems.

Technical Specifications

The following hard data points were extracted from the experimental results, focusing on the optimal growth conditions and resulting material quality.

Parameter	Value	Unit	Context
Substrate Orientation	<100>	N/A	HPHT Type Ib seed
Maximum Growth Rate	26.6	µm/h	Achieved at 12% CH$_{4}$ concentration
Maximum Film Thickness	270	µm	Grown over 10 hours
Growth Temperature	1060 ± 10	°C	Constant parameter
Reactor Pressure	150	Torr	Constant parameter
Microwave Power	3.62	kW	Constant parameter (2.45 GHz system)
Lowest Surface Roughness (Ra)	171.59	nm	Achieved at 12% CH$_{4}$
Best Crystalline FWHM (HRXRD)	0.014	°	Measured at 6% CH$_{4}$
Best Structural FWHM (Raman)	4.6	cm⁻¹	Measured at 8% CH$_{4}$
Nitrogen Contamination (Leakage)	46.6	ppm	Estimated vacuum system leakage
Identified Defects (PL)	575, 637, 737	nm	NV⁰, NV⁻, and SiV centers

Key Methodologies

The experiment utilized a high-power MWPACVD system to achieve homoepitaxial growth on commercial HPHT substrates.

Substrate Preparation:
- Substrates (3 x 3 x 1.1 mm³) were <100> oriented HPHT Type Ib diamond.
- Cleaning involved effervescent aqua regia (100 °C, 60 min), followed by ultrasonic washing in acetone, isopropyl alcohol, and deionized water.
Pre-Growth Etching:
- Substrates were etched in H$_{2}$ plasma for 40 minutes at 1040 °C to remove surface damage.
MWPACVD Growth Parameters:
- Reactor Type: Cylindrical cavity MWPACVD reactor (6 kW, 2.45 GHz system).
- Power: 3.62 kW.
- Pressure: 150 Torr.
- Temperature: 1060 ± 10 °C (monitored by two-color infrared pyrometer).
- Gas Flow: Total flow of 200 sccm (H$_{2}$ balance).
- Key Variable: Methane (CH$_{4}$) concentration varied from 6% to 12%.
Post-Growth Processing:
- Bottom faces were cleaned by grinding with 3 µm diamond paste.
- Samples were boiled again in aqua regia and cleaned ultrasonically.
Characterization Techniques:
- Structural Quality: Raman and Photoluminescence (PL) spectroscopy (514.5 nm Nd:YAG laser).
- Crystalline Quality: High-Resolution X-ray Diffractometry (HRXRD) using a PANalytical X’Pert setup with a four-crystal Ge(220) monochromator (Cu Kα$_{1}$ radiation, λ = 1.5406 Å).
- Morphology: Scanning Electron Microscopy (SEM) and Optical Profilometry (Veeco WYKO NT1100).

6CCVD Solutions & Capabilities

The reported research highlights the critical need for high-quality, thick SCD material with controlled surface morphology and minimal defect incorporation for advanced applications. 6CCVD is uniquely positioned to supply and enhance the materials required for this type of research.

Applicable Materials

To replicate or extend this research, particularly focusing on minimizing NV and SiV defects for quantum or high-power electronics, 6CCVD recommends the following materials:

Electronic Grade SCD: Ideal for high-power devices and microelectronics, offering superior thermal management and elevated breakdown voltage. We provide <100> oriented substrates matching the experimental setup.
Optical Grade SCD: Essential for applications sensitive to defects (like the NV and SiV centers identified in the paper). Our optical grade material is grown under ultra-low nitrogen conditions to minimize NV incorporation, crucial for high-coherence time applications.
Custom Thick SCD Substrates: The paper achieved 270 µm thickness. 6CCVD routinely supplies SCD films up to 500 µm thick, allowing researchers to explore even thicker device layers or freestanding diamond fabrication.

Customization Potential

The research utilized small (3x3 mm²) substrates and focused on surface roughness control. 6CCVD’s advanced manufacturing capabilities directly address the scaling and finishing challenges presented:

Research Requirement	6CCVD Capability	Technical Advantage
Size Limitation	Plates/wafers up to 125 mm (PCD) and large-area SCD.	Enables scaling of high-rate growth to commercial dimensions.
Thickness	SCD up to 500 µm; Substrates up to 10 mm.	Supports fabrication of robust, freestanding diamond devices.
Surface Finish	Polishing to Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD).	Significantly surpasses the 171.59 nm Ra achieved in the paper, providing device-ready surfaces without requiring extensive post-processing.
Metalization	Internal capability for Au, Pt, Pd, Ti, W, Cu.	Allows researchers to immediately integrate diamond films into device architectures (e.g., Schottky contacts, ohmic contacts) without external processing.
Custom Dimensions	Precision laser cutting and shaping services.	Provides custom geometries beyond standard squares, necessary for complex optical or thermal management systems.

Engineering Support

The paper noted challenges related to unintentional contamination (46.6 ppm N$_{2}$ leakage and Si incorporation from reactor components), which led to the formation of NV and SiV defects.

Defect Control Consultation: 6CCVD’s in-house PhD team specializes in optimizing MPCVD recipes to minimize specific point defects. We offer consultation on material selection and growth parameters to achieve ultra-low nitrogen (N) and silicon (Si) concentrations required for high-coherence quantum and high-purity electronic projects.
Process Optimization: We assist engineers in selecting the optimal CH$_{4}$ concentration and growth temperature balance to achieve both high growth rate (up to 27 µm/h demonstrated here) and superior surface quality (Ra < 1 nm).
Global Logistics: 6CCVD ensures reliable global shipping (DDU default, DDP available) for time-sensitive research projects worldwide.

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

View Original Abstract

Single crystal diamond (SCD) is a promising material to satisfy emerging requirements of high-demand fields, such as microelectronics, beta batteries and wide-spectrum optical communication systems, due to its excellent optical characteristics, elevated breakdown voltage, high hardness and superior thermal conductivity. For such applications, it is essential to study the optically active defects in as-grown diamonds, namely three-dimensional defects (such as stacking faults and dislocations) and the inherent defects arising from the cultivation method. This paper reports the growth of SCD films on a commercial HPHT single-crystal diamond seed substrate using a 2.45 GHz microwave plasma-assisted chemical vapor deposition (MWPACVD) technique by varying the methane (CH4) gas concentration from 6 to 12%, keeping the other parameters constant. The influence of the CH4 concentration on the properties, such as structural quality, morphology and thickness, of the highly oriented SCD films in the crystalline plane (004) was investigated and compared with those on the diamond substrate surface. The SCD film thickness is dependent on the CH4 concentration, and a high growth rate of up to 27 µm/h can be reached. Raman spectroscopy, high-resolution X-ray diffractometry (HRXRD), scanning electron microscopy (SEM), surface profilometry and optical microscopic analyses showed that the produced homoepitaxial SCD films are of good quality with few macroscopic defects.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15217416

References

2005 - Growing Diamond Crystals by Chemical Vapor Deposition [Crossref]
2016 - Homoepitaxial growth of single crystalline CVD-diamond [Crossref]
2020 - Investigation of homoepitaxial growth by microwave plasma CVD providing high growth rate and high quality of diamond simultaneously [Crossref]
2022 - Chemical Vapor Deposition Single-Crystal Diamond: A Review [Crossref]
2022 - Homoepitaxial lateral growth of single-crystal diamond with eliminating PCD rim and enlarging surface area [Crossref]
2017 - Express in situ measurement of epitaxial CVD diamond film growth kinetics [Crossref]
2008 - Single crystal CVD diamond growth strategy by the use of a 3D geometrical model: Growth on (113) oriented substrates [Crossref]