Microscopic Evaluation of Al<sub>2</sub>O<sub>3</sub>/p-Type Diamond (111) Interfaces Using Scanning Nonlinear Dielectric Microscopy

At a Glance

Metadata	Details
Publication Date	2022-05-31
Journal	Materials science forum
Authors	Yu Ogata, Kohei Yamasue, Xufang Zhang, Tsubasa Matsumoto, Norio Tokuda
Institutions	Kanazawa University, Tohoku University
Citations	3
Analysis	Full AI Review Included

Microscopic Evaluation of Al₂O₃/p-Type Diamond (111) Interfaces: Technical Analysis and 6CCVD Solutions

This document analyzes the research concerning the microscopic evaluation of Al₂O₃/p-type diamond (111) interfaces, focusing on interface defect density ($D_{it}$) and its impact on diamond MOSFET performance. This analysis highlights how 6CCVD’s advanced MPCVD diamond materials and customization capabilities directly support and enable the replication and advancement of this critical power device research.

Executive Summary

The following points summarize the core findings and technical relevance of the study for diamond power device engineering:

Application Focus: The research addresses the critical challenge of low channel mobility in inversion channel diamond MOSFETs, directly linked to high interface defect density ($D_{it}$).
Nanoscale Characterization: Scanning Nonlinear Dielectric Microscopy (SNDM), local CV profiling, and local DLTS were successfully used to map $D_{it}$ distribution at the Al₂O₃/diamond interface at the nanoscale.
Termination Impact: Interface defect density was found to be lowest for H-terminated diamond (111), followed by OH-terminated, and highest for O-terminated interfaces.
Surface Flatness is Critical: The study confirms that the flattening process of the diamond surface strongly affects the spatial distribution and clustering of interface defects, with atomically flat areas showing distinct, line-shaped $D_{it}$ features.
Material Requirements: Successful device fabrication relies on high-quality, p-type Boron-doped Single Crystal Diamond (SCD) (111) substrates with precise CVD layer control and ultra-low surface roughness.
6CCVD Value Proposition: 6CCVD specializes in providing the necessary highly-controlled, Boron-Doped SCD (111) substrates and custom metalization/polishing services required to optimize these critical interfaces.

Technical Specifications

The following table extracts key material and performance parameters achieved in the study:

Parameter	Value	Unit	Context
Substrate Material	p-type Diamond (111)	N/A	HTHP synthesized
Substrate Doping (Boron)	10¹⁷	cm^-3	Required for p-type conductivity
p⁺ CVD Layer Thickness	200	nm	Used for ohmic contact formation
Dielectric Material	Al₂O₃	N/A	Deposited via ALD
Dielectric Thickness	50	nm	Insulating layer
Electrode Material	Gold (Au)	N/A	Vacuum deposited
Electrode Thickness	200	nm	Top contact layer
SNDM Tip Radius	2	µm	Pt-Ir coated conductive cantilever
Lowest Max dC/dV Slope	68	aF/V	Al₂O₃/H-Diamond (111) interface
Highest Max dC/dV Slope	10	aF/V	Al₂O₃/O-Diamond (111) interface
Average Interface Defect Density ($D_{it}$)	10¹³	cm^-2eV^-1	Measured by local DLTS
Flat Area Roughness (RMS)	~1	nm	After Al₂O₃ deposition
Rough Area Roughness (RMS)	~10	nm	After Al₂O₃ deposition

Key Methodologies

The experimental success hinges on precise material preparation and advanced nanoscale characterization techniques:

Substrate Selection and Growth: High-pressure high-temperature (HTHP) synthesized p-type diamond (111) substrates were used, followed by the deposition of a high Boron concentration p⁺ CVD diamond layer (200 nm) to facilitate low-resistance ohmic contact.
Surface Planarization: Anisotropic diamond etching, based on a carbon solid solution reaction into Ni, was employed to achieve atomically flat (111) surfaces with step-terrace regions, minimizing plasma-induced damage.
Surface Termination: Three distinct surface terminations were prepared for comparison: Hydrogen (H), Oxygen (O), and Hydroxyl (OH) groups, which critically influence the interface properties.
Dielectric and Electrode Deposition: A 50 nm Al₂O₃ insulating layer was deposited using Atomic Layer Deposition (ALD), followed by vacuum deposition of a 200 nm Gold (Au) electrode.
Nanoscale Characterization: Scanning Nonlinear Dielectric Microscopy (SNDM) was utilized in contact mode, combining conventional dC/dV imaging, local CV profiling, and time-resolved local Deep Level Transient Spectroscopy (DLTS) to achieve microscopic mapping of $D_{it}$.

6CCVD Solutions & Capabilities

6CCVD provides the foundational diamond materials and precision engineering services necessary to replicate and advance the high-performance diamond MOSFET structures described in this research.

Applicable Materials

To achieve the high carrier mobility and low $D_{it}$ demonstrated, researchers require highly controlled, high-quality diamond materials:

Boron-Doped Single Crystal Diamond (BDD-SCD) (111): This is the core material required. 6CCVD offers BDD-SCD with precise doping control, essential for achieving the $10^{17}$ cm^-3 concentration specified for the p-type substrate.
High-Purity SCD (111) for Epitaxy: We supply high-quality SCD substrates suitable for subsequent epitaxial growth of the p⁺ CVD layer, ensuring minimal defects propagate to the active interface.
Custom CVD Layer Growth: 6CCVD can grow the required highly Boron-doped p⁺ layer (200 nm thickness) via MPCVD, ensuring excellent crystalline quality and controlled doping for optimized ohmic contact formation.

Customization Potential

The study emphasizes the critical role of precise dimensions, layer thickness, and surface quality. 6CCVD’s capabilities are perfectly aligned with these needs:

Research Requirement	6CCVD Customization Capability
Ultra-Low Roughness (Ra ~1 nm)	Precision Polishing: We guarantee SCD polishing to Ra < 1 nm, directly supporting the need for atomically flat (111) surfaces crucial for minimizing $D_{it}$ clustering.
Custom Layer Thicknesses	Thickness Control: We offer SCD and PCD layers from 0.1 µm up to 500 µm, allowing precise control over the 50 nm dielectric and 200 nm p⁺ CVD layers.
Specific Metal Stacks (Au Electrode)	In-House Metalization: 6CCVD offers custom metal stacks including Au, Pt, Pd, Ti, W, and Cu. We can deposit the required 200 nm Au electrode or complex Ti/Pt/Au stacks for enhanced adhesion and reliability.
Custom Dimensions	Wafer Size and Cutting: While the paper used small 2 mm x 2 mm samples, 6CCVD can supply SCD or PCD wafers up to 125 mm, and offers precise laser cutting services for specific R&D dimensions.

Engineering Support

The optimization of diamond/dielectric interfaces for power devices is a complex challenge. 6CCVD’s in-house PhD team specializes in diamond surface chemistry and material science.

Interface Optimization: Our experts can assist researchers in selecting the optimal BDD-SCD orientation ((111) vs. (100)) and material specifications to achieve desired carrier mobility and breakdown voltage targets for similar Inversion Channel MOSFET projects.
Surface Termination Guidance: We provide consultation on pre-processing steps, including surface cleaning and termination methods (H, O, or OH), to ensure the starting material is optimized for subsequent ALD processes.
Global Logistics: We offer reliable global shipping (DDU default, DDP available) to ensure timely delivery of sensitive, high-value diamond materials worldwide.

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

View Original Abstract

Improvement of channel mobility is required to improve the performance of the inversion channel MOSFETs using diamond. The previous studies have suggested that high interface defect density ( D it ) at the Al 2 O 3 /diamond (111) interface has a significant impact on the carrier transport property on a channel region. To investigate the physical origins of the high D it , especially from microscopic point of view, here we investigate Al 2 O 3 /p-type diamond (111) interfaces using scanning nonlinear dielectric microscopy (SNDM). We find the high spatial fluctuations of Al 2 O 3 /hydroxyl (OH)-terminated diamond (111) interface properties and their difference by the flatness of the diamond surface.

Tech Support

Original Source

DOI: https://doi.org/10.4028/p-n0z51t

References

**** - Development of diamond-based power devices [Crossref]
**** - High Carrier Mobility in Single-Crystal Plasma-Deposited Diamond [Crossref]
2016 - Inversion channel diamond metal-oxide-semiconductor field-effect transistor with normally off characteristics [Crossref]
2021 - Inversion-type p-channel diamond MOSFET issues [Crossref]
**** - Formation of atomically flat hydroxyl-terminated diamond (1 1 1) surfaces via water vapor annealing [Crossref]
**** - Inversion channel mobility and interface state density of diamond MOSFET using N-type body with various phosphorus concentrations [Crossref]
2017 - Nanosecond microscopy of capacitance at SiO2/4H-SiC interfaces by time-resolved scanning nonlinear dielectric microscopy [Crossref]