Optimization Design of MPCVD Single Crystal Diamond Growth Based on Plasma Diagnostics

At a Glance

Metadata	Details
Publication Date	2023-01-01
Journal	Journal of Inorganic Materials
Authors	Yicun LI, Xiaobin Hao, Bing Dai, Dongyue Wen, Jiaqi Zhu
Institutions	Harbin Institute of Technology
Citations	2
Analysis	Full AI Review Included

Executive Summary

This research presents a systematic, diagnostic-driven methodology for optimizing Microwave Plasma Chemical Vapor Deposition (MPCVD) parameters for single crystal diamond (SCD) growth, addressing the complexity and diversity of industrial requirements.

Systematic Optimization: A quantitative framework was established linking core input parameters (Pressure P, MW Power W) to critical plasma characteristics (effective size, energy density ρ, and precursor concentration).
Diagnostic Tools: Plasma imaging (H_α filtered) and Optical Emission Spectroscopy (OES) were used to quantitatively diagnose the plasma state, enabling precise control over the growth environment.
Predictive Process Map: A comprehensive P-W-Size-Temperature (T) process map was generated based on fitted experimental data, allowing engineers to select parameters based on desired SCD size and growth temperature.
High Accuracy: Experimental validation confirmed the map’s strong predictive capability, with parameter errors consistently measured at less than 5% of the predicted values.
Enhanced Efficiency: The study demonstrated that high plasma energy density (up to 148.5 W/cm³) can be achieved at relatively low power (2600 W) by utilizing plasma contraction at high pressure.
High Growth Rate: Optimized conditions (high energy density, high C₂/CH precursor concentration) resulted in a high SCD growth rate of 8.9 µm/h.

Technical Specifications

The following specifications detail the optimized growth conditions (Sample 2) and the performance achieved using the HITLH-2450M MPCVD system.

Parameter	Value	Unit	Context
MPCVD System Type	HITLH-2450M	N/A	Home-made, 2.45 GHz, TM₀₂₁ mode
Substrate Size	5 x 5 x 0.5	mm	CVD SCD (100) seed
Predicted Growth Temperature	850	°C	Target setpoint
Actual Growth Temperature	860	°C	Sample 2 (Verification)
Predicted Pressure (P)	15.6	kPa	Sample 2 (Verification)
Predicted MW Power (W)	2600	W	Sample 2 (Verification)
Actual Plasma Energy Density (ρ)	148.5	W/cm³	Sample 2 (Highest density achieved)
Actual Growth Rate	8.9	µm/h	Sample 2 (Highest rate achieved)
Actual Major Axis (X_e)	41.2	mm	Effective deposition diameter
Gas Flow (H₂)	192	sccm	Standard condition
Gas Flow (CH₄)	8	sccm	Standard condition
Parameter Prediction Error	Less than 5	%	Verified accuracy of the process map

Key Methodologies

The systematic optimization process relied on coupling macroscopic input parameters with microscopic plasma diagnostics to generate a predictive process map.

Equipment and Setup: Experiments were conducted using a custom-built HITLH-2450M MPCVD system (2.45 GHz, 6 kW source) utilizing a stainless steel TM₀₂₁ resonant cavity.
Input Parameter Variation: The primary input variables, Reaction Chamber Pressure (P, 3-21 kPa) and Microwave Power (W, 900-4500 W), were varied according to three established matching modes: Uniform Increase, Optimal Absorption (minimum reflected power), and Saturated Input.
Plasma Imaging and Sizing: A SCMOS camera equipped with an H_α filter (656 nm) was used to image the atomic hydrogen distribution. The effective plasma boundary was defined using the 1/e intensity contour.
Plasma Quantification: The plasma was approximated as an ellipsoid (defined by major axis X_e and minor axis Z_e). Effective plasma volume (V_p) and energy density (ρ = W_a / V_p) were calculated, where W_a is the absorbed power.
Spectroscopic Analysis (OES): An Ocean Optics Maya 2000 spectrometer was used to monitor the relative concentrations of key growth species (Atomic Hydrogen H, Carbon dimer C₂, and Methylidyne CH) by measuring their emission line intensities.
Temperature Correlation: Substrate temperature (T) was measured via infrared thermometry and correlated with P and W inputs, accounting for the fixed water-cooling temperature.
Process Map Generation: Quantitative relationships derived from the diagnostic data (P-W-X_e, P-W-T) were integrated to construct a comprehensive MPCVD process map, enabling predictive parameter selection based on desired SCD size and temperature.
Optimization Strategy: For high growth rate, parameters were selected from the map that maintained the required size (X_e) and temperature (T), while maximizing energy density (moving toward higher P and lower W along the selected isotherm).

Commercial Applications

The ability to precisely control and predict SCD growth parameters based on plasma diagnostics is crucial for scaling up production and tailoring diamond properties for specific high-tech markets.

High-Power Electronics: Producing electronic-grade SCD with controlled thickness and high thermal conductivity for use in high-frequency, high-power devices (e.g., 5G/6G communication, power switching).
Quantum Technology: Precise tuning of plasma conditions (especially temperature and purity) is essential for incorporating specific color centers (like NV centers) into diamond for quantum sensing, metrology, and computing applications.
Optical Windows: Manufacturing large-area, high-purity optical-grade diamond for high-power laser systems and extreme environment optics.
Tooling and Industrial Wear: Optimizing growth rate and thickness for tool-grade diamond applications where material volume and mechanical robustness are key requirements.
Synthetic Gemstones: Achieving high, predictable growth rates (8.9 µm/h demonstrated) for the efficient, large-scale production of high-quality lab-grown diamonds.

View Original Abstract

Microwave plasma chemical vapor deposition, MPCVD)技术是制备大尺寸、高品

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Original Source

DOI: https://doi.org/10.15541/jim20230164