Basal Plane Bending of Homoepitaxial MPCVD Single-Crystal Diamond

At a Glance

Metadata	Details
Publication Date	2020-10-12
Journal	Materials
Authors	Xiaotong Han, Peng Duan, Yan Peng, Xiwei Wang, Xuejian Xie
Institutions	State Key Laboratory of Crystal Materials, Jinan Institute of Quantum Technology
Citations	3
Analysis	Full AI Review Included

Executive Summary

This study investigates the factors controlling basal plane bending (BPP) in homoepitaxial single-crystal diamond (SCD) grown by Microwave Plasma Chemical Vapor Deposition (MPCVD), a critical quality metric for semiconductor applications.

Primary Mechanism Identified: Basal plane bending is fundamentally caused by thermal stress resulting from an uneven temperature distribution across the substrate surface during MPCVD growth.
Substrate Dominance: The curvature radius (R) of the SCD epilayer is closely related to the substrate quality; BPP is inherited from the substrate, necessitating the use of high-quality, flat substrates (R > 50 m for HTHP substrates).
Temperature Sensitivity: Increasing the growth temperature severely exacerbates BPP. Raising the temperature from 900 °C to 1150 °C reduced the radius of curvature from 358.17 m to 23.40 m (increased bending).
Time Dependence: Longer growth time leads to more severe BPP. At 1100 °C, increasing the growth duration from 4 h to 16 h reduced the radius of curvature to a minimum of 10.20 m.
Thermal Gradient Quantification: A significant temperature gradient of 40 °C/mm was measured on the substrate surface at 1100 °C, confirming the source of the thermal stress that induces bending.
Measurement Technique: High-Resolution X-ray Diffraction (HRXRD) was successfully used to quantify BPP by measuring the linear shift in the ω(400) rocking curve peak position across the sample surface.

Technical Specifications

Parameter	Value	Unit	Context
CVD System Model	ARDIS-300	N/A	Optosystems Ltd. MPCVD reactor
Microwave Frequency	2.45	GHz	MPCVD operation
Standard Growth Pressure	275	torr	Typical operating condition
Methane Concentration (CH₄/H₂)	3.00	%	Standard gas ratio
X-ray Source	Cu Kα1	N/A	HRXRD measurement radiation
X-ray Operation	40 kV / 40 mA	N/A	HRXRD power settings
Substrate Orientation	(100)	N/A	Defined base plane for bending analysis
Temperature Gradient (1100 °C)	40	°C/mm	Measured surface gradient (main cause of BPP)
Curvature Radius (R) (Lowest Bending)	358.17	m	Grown at 900 °C, 4 h (HTHP substrate)
Curvature Radius (R) (Highest Bending)	10.20	m	Grown at 1100 °C, 16 h (Maximum BPP observed)
Curvature Radius (R) (High Temp)	23.40	m	Grown at 1150 °C, 4 h
Substrate Curvature (MPCVD Source)	8.47	m	Curvature of the substrate before growth (high initial bending)

Key Methodologies

The study utilized MPCVD for diamond growth and HRXRD for structural characterization, focusing on controlled variations of substrate type, temperature, and growth duration.

I. MPCVD Growth Setup and Control

Reactor: ARDIS-300 MPCVD system (2.45 GHz, 6 kW).
Substrates: (100)-oriented SCD from two sources: High-Pressure High-Temperature (HTHP) diamond and MPCVD diamond.
Temperature Measurement: Substrate surface temperature was monitored and maintained using a double interference infrared radiation thermo pyrometer (emissivity 0.1).
Temperature Distribution Mapping: The pyrometer was mounted on a three-dimensional displacement platform to measure the spatial temperature distribution across the substrate surface.
Standard Recipe: Pressure fixed at 275 torr; CH₄/H₂ ratio fixed at 3.00%.

II. Experimental Variations

Experiment Group	Variable Parameter	Range/Conditions	Purpose
Substrate Quality	Substrate Source	HTHP vs. MPCVD diamond	Determine inheritance of BPP from substrate.
Temperature Dependence	Growth Temperature	900 °C, 1000 °C, 1100 °C, 1150 °C	Investigate thermal stress effects on BPP.
Time Dependence	Total Growth Time	4 h, 8 h, 16 h	Investigate accumulation of stress/bending over time (at 1100 °C).
Holder Design	Pocket Holder Height (d)	1.0 mm, 1.3 mm	Simulation/measurement of holder effect on temperature gradient.

III. Basal Plane Bending Measurement (HRXRD)

Instrument: Bruker D8 Discover HRXRD, operating with Cu Kα1 radiation.
Principle: Bending is detected by scanning the X-ray beam across the sample surface (1 mm steps) and measuring the shift in the incidence angle (ω) required to maintain the (400) rocking curve peak.
Quantification: The radius of curvature (R) was calculated from the slope of the incidence angle (ω) versus the scanning distance (x), R = (dω/dx)^-1. A linear change in ω indicates an approximately spherical bending surface.

Commercial Applications

The successful growth of large-size, high-quality SCD with minimal basal plane bending is essential for realizing diamond’s potential in extreme electronics and optical applications.

High-Power and High-Voltage Electronics:
- SCD is used for high-frequency, high-power devices (e.g., RF transistors, power switches). Low BPP is mandatory to prevent the introduction of dislocations and cracks that degrade breakdown voltage and carrier mobility.
Deep Ultraviolet (DUV) Detectors:
- SCD’s wide band gap makes it ideal for solar-blind DUV detection. High crystal quality (low BPP) ensures high quantum efficiency and low dark current.
Particle and Radiation Detectors:
- Used in harsh environments (e.g., accelerators, nuclear facilities). Minimizing BPP ensures structural integrity and consistent performance under high radiation flux.
Advanced Substrate Manufacturing:
- The findings provide critical process control parameters (temperature uniformity, substrate selection) necessary for scaling up the production of 2-inch mosaic SCDs and larger wafers for the semiconductor industry.
Thermal Management Solutions:
- While not the primary focus, high-quality SCD is used as a superior heat spreader. Controlling BPP ensures the structural integrity of thick diamond films used in demanding thermal applications.

View Original Abstract

We report herein high-resolution X-ray diffraction measurements of basal plane bending of homoepitaxial single-crystal diamond (SCD). We define SCD (100) as the base plane. The results revealed that growth parameters such as temperature, growth time, and basal plane bending of the substrate all affect the basal plane bending of SCD. First, the basal plane bending of SCD depends mainly on the substrate and becomes severe with increasing basal plane bending of the substrate. The SCD growth experiments show that the basal plane bending increases with elevated growth temperature and increased growth time. Finally, to understand the mechanism, we investigated the substrate-surface temperature distribution as a function of basal plane bending of SCD fabricated by chemical vapor deposition (CVD). This allowed us to propose a model and understand the origin of basal plane bending. The results indicate that an uneven temperature distribution on the substrate surface is the main cause of the base-plane bending of CVD diamond.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13204510

References

2005 - Diamond semiconductor technology for RF device applications [Crossref]
1982 - Semiconductors for high-voltage, vertical channel field-effect transistors [Crossref]
2004 - New Unipolar Switching Power Device Figures of Merit [Crossref]
2014 - Large-area high-quality single crystal diamond [Crossref]
2009 - Chemical vapour deposition synthetic diamond: Materials, technology and applications [Crossref]
2015 - Prospects for the synthesis of large single-crystal diamonds [Crossref]
2003 - Oxidation of ethane over vanadia-alumina-based catalysts: Co-feed and redox experiments [Crossref]
2006 - Silicon carbide and diamond for high temperature device applications [Crossref]
2017 - Exploring constant substrate temperature and constant high pressure SCD growth using variable pocket holder depths [Crossref]
2014 - A 2-in. mosaic wafer made of a single-crystal diamond [Crossref]