Effect of the substrate crystalline orientation on the surface morphology and boron incorporation into epitaxial diamond layers

At a Glance

Metadata	Details
Publication Date	2020-01-01
Journal	NANOCOM …
Authors	J. Voves, Alexandr Pošta, Marina Davydova, Alexandr Laposa, Vojtěch Povolný
Institutions	Czech Academy of Sciences, Institute of Physics, Czech Technical University in Prague
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Efficiency Boron Doping in MPCVD Diamond

Executive Summary

This research confirms that the crystalline orientation of the diamond substrate is the dominant factor governing boron incorporation efficiency (BIE), surface morphology, and growth rate for heavily doped epitaxial layers, critical for next-generation vertical power devices.

Optimal Orientation: Epitaxial growth on (113) vicinal surfaces yielded superior material quality compared to conventional (100) and (111) orientations.
High Growth Rate: The (113) layer achieved a deposition rate of 3-5 µm/h, significantly faster than (100) (1.8-2 µm/h) and (111) (0.9-1 µm/h).
Ultra-Smooth Surface: The (113) layer exhibited a flat, homogeneous surface with an RMS roughness of approximately 1 nm, essential for device fabrication.
Homogeneous Doping: (113) layers showed excellent spatial homogeneity of boron concentration, avoiding the inhomogeneous incorporation and pyramidal hillocks observed on (100) substrates.
Maximum BIE: The (113) orientation achieved the highest BIE (approx. 2%), resulting in a high boron concentration of 7.2 x 10²⁰ cm^-3 at a low B/C ratio (2,000 ppm).
Core Application: These results provide a promising pathway for developing thick, highly boron-doped templates required for high-performance vertical diamond power electronics.

Technical Specifications

The following table summarizes the key growth parameters and resulting material properties for the heavily boron-doped homo-epitaxial diamond layers investigated.

Parameter	(111) Orientation	(100) Orientation	(113) Orientation (Optimal)	Context
Microwave Power	575	700	700	W
Pressure	60	100	100	mbar
Methane Concentr.	0.1	1	1	%
B/C Ratio	10,000	4,000	2,000	ppm
Boron Concentr.	5.3 x 10²⁰	1.3 x 10²⁰	7.2 x 10²⁰	cm^-3
Deposition Rate	0.9 - 1	1.8 - 2	3 - 5	µm/h
BIE	0.28	< 1	~2	%
RMS Roughness	~50	Inhomogeneous (Hillocks)	~1	nm
Surface Defects	Line defects, trenches	Pyramidal hillocks	Few linear defects, flat	Morphology
B Homogeneity	Good (small variations)	Very Inhomogeneous	Very Good	Raman Mapping

Key Methodologies

The epitaxial diamond layers were grown using a resonance cavity Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) system (AX5010, Seki Diamond Systems).

Substrate Preparation (Cleaning): All polished diamond substrates underwent a multi-step cleaning procedure to remove surface contaminants:
- Cleaning in hot H₂SO₄ + KNO₃ (10 min).
- Rinsing in deionized water in an ultrasound bath (2 x 10 min).
- Cleaning in acetone with ultrasound (10 min).
- Cleaning in isopropyl alcohol with ultrasound (10 min).
Pre-Growth Etching: The substrate was exposed to pure hydrogen microwave plasma at high temperature (10 min) prior to precursor gas introduction.
Growth Parameters: Specific parameters (Microwave Power, Pressure, Methane concentration, B/C ratio) were optimized for each orientation, as detailed in the Technical Specifications table above.
Morphology Analysis: Surface morphology was studied using Optical Microscopy (Olympus BX60) and Atomic Force Microscopy (AFM) (NT-MDT Ntegra Prima).
Boron Concentration & Homogeneity Analysis:
- Raman Spectroscopy Mapping (Renishaw inVia Qontor, 532 nm laser) was used.
- Boron concentration was determined from the width of the diamond’s zone-center phonon peak (1332 cm^-1).
- Boron homogeneity was mapped using the shift of the Raman wideband centered around 500 cm^-1.

6CCVD Solutions & Capabilities

The successful fabrication of high-quality, thick, heavily boron-doped diamond templates hinges on precise control over crystalline orientation, doping concentration, and surface finish—all core competencies of 6CCVD.

Applicable Materials

To replicate or extend this critical research into vertical diamond power devices, 6CCVD recommends the following materials:

Material Specification	6CCVD Product Line	Relevance to Research
Heavily Boron-Doped SCD	BDD (Boron-Doped Diamond)	Required for high conductivity (metallic regime) and high BIE (7.2 x 10²⁰ cm^-3).
Custom Oriented Substrates	SCD (Single Crystal Diamond)	Essential for replicating the high-performance (113) growth. 6CCVD offers custom orientation substrates beyond standard (100).
Thick Templates	SCD/PCD Substrates	The application requires “thick highly boron-doped templates.” 6CCVD provides SCD/PCD layers up to 500 µm thick and substrates up to 10 mm.

Customization Potential

6CCVD’s advanced MPCVD and post-processing capabilities directly address the engineering challenges highlighted by this study:

Custom Crystalline Orientation: We specialize in providing custom-oriented SCD substrates, including (113) vicinal surfaces, necessary to achieve the high BIE and smooth morphology demonstrated in the paper.
Ultra-Low Roughness Polishing: The success of the (113) layer relies on achieving Ra < 1 nm. 6CCVD guarantees Ra < 1 nm polishing for Single Crystal Diamond (SCD) wafers, ensuring the ideal starting surface for subsequent epitaxial growth.
Large Area Doping: While this study used small samples, 6CCVD can scale production to PCD plates/wafers up to 125 mm in diameter, enabling large-scale device manufacturing.
Device Metalization: For subsequent device fabrication (e.g., ohmic contacts for vertical devices), 6CCVD offers in-house metalization services including Au, Pt, Pd, Ti, W, and Cu deposition, streamlining the manufacturing process.

Engineering Support

The complexity of optimizing BIE and surface morphology across different crystalline planes requires deep material science expertise. 6CCVD’s in-house PhD team can assist engineers and scientists with material selection, custom recipe development, and process optimization for similar vertical diamond power device projects. We ensure that the starting material specifications (orientation, doping profile, and surface finish) are perfectly matched to your application requirements.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

View Original Abstract

Epitaxial growth of diamond is critically important for the fabrication of diamond-based electronic devices.The emerging study of the epitaxial diamond growth on the (113) vicinal surfaces evidences highly needed high growth rates and low structural defects concentrations with both p-and n-type doping.In this work, we compare the morphology and dopant concentration incorporation of heavily boron-doped (113) epitaxial diamond layers with conventionally studied (100) and ( 111) epitaxial layers.Epitaxial layers were grown using resonance cavity Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) system.The surface morphology of epitaxial layers was studied by optical microscopy and atomic force microscopy, whereas the boron incorporation homogeneity was determined by Raman spectroscopy mapping.Heavily boron-doped (113) epitaxial diamond layers can be grown at a high growth rate with a smooth surface, without pyramidal hillocks or non-epitaxial crystallite defects, and with homogeneous boron concentration.These results confirm that epitaxial diamond growth on (113) vicinal surfaces is a promising solution for the development and fabrication of diamond-based electronic devices.

Tech Support

Original Source

DOI: https://doi.org/10.37904/nanocon.2020.3683