Relationship between Emission Spectrum and B Content in B Doped Diamond Synthesis using Mode Conversion Type Microwave Plasma CVD
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-06-26 |
| Journal | Journal of The Surface Finishing Society of Japan |
| Authors | Asuka Suzuki, Takuya Maruko, Yoshihiro Takahashi, Yukihiro Sakamoto |
| Institutions | Chiba Institute of Technology |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research investigates the critical relationship between plasma composition, monitored via Optical Emission Spectroscopy (OES), and the resulting electrical resistivity of Boron-Doped Diamond (BDD) films synthesized using Mode Conversion Type Microwave Plasma CVD.
- Core Achievement: Demonstrated that BDD resistivity can be effectively controlled and predicted by monitoring the intensity ratio of specific B-containing plasma species (BH/Hβ) during growth.
- Resistivity Control: Achieved ultra-low volume resistivity of 0.3 Ω·cm under optimized plasma conditions (Pattern 1).
- Monitoring Superiority: OES monitoring provided a more reliable correlation to final film resistivity than traditional methods based solely on the molar quantity of the supplied B source.
- Key Plasma Species: Resistivity decreased significantly as the intensity of B-related emission peaks (B at 249.7 nm, BH at 433.1 nm, BO at 436.3 nm) increased relative to atomic hydrogen (Hβ).
- Mechanism Insight: The results suggest that the degree of B source decomposition and the resulting concentration of active B species in the plasma directly dictate the incorporation rate and electrical properties of the BDD film.
- Methodology: Used a relatively safe liquid B source (B(CH3O)3) delivered via a bubbling method, making the process suitable for industrial scaling compared to highly toxic gaseous B sources.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minimum Volume Resistivity | 0.3 | Ω·cm | Achieved using Pattern 1 conditions (highest B incorporation). |
| Microwave Frequency | 2.45 | GHz | Mode Conversion Type CVD system. |
| Microwave Power | 1.0 | kW | Fixed synthesis parameter. |
| Synthesis Pressure | 20 | kPa | Fixed synthesis parameter. |
| Substrate Material | Si (100) P-type | N/A | Initial resistivity 0.8 to 12 Ω·cm. |
| Target Film Thickness | 16 ± 4 | µm | Achieved by adjusting growth time for each pattern. |
| B Source Material | B(CH3O)3 | N/A | Liquid source (0.01 g/ml in CH3OH). |
| Key OES Correlation | BH/Hβ Ratio | N/A | Resistivity decreases as this intensity ratio increases. |
| B Atomic Emission Peak | 249.7 | nm | Monitored B species in OES spectra. |
| BH Molecular Emission Peak | 433.1 | nm | Monitored Boron Hydride species. |
| Diamond Raman Peak Shift | 1333 (Broadened/Shifted) | cm-1 | Indicates high B incorporation (BDD characteristic). |
Key Methodologies
Section titled “Key Methodologies”The BDD films were synthesized using a Mode Conversion Type Microwave Plasma CVD system, allowing for uniform electric field distribution and substrate temperature control.
- Substrate Preparation: Si (100) P-type wafers were pre-treated using diamond powder scratching followed by ultrasonic cleaning.
- Gas Mixture and Flow Rates (Fixed):
- Main H2 flow: 100 sccm.
- CH4 flow: 15 sccm.
- Pressure: 20 kPa.
- Microwave Power: 1.0 kW.
- Boron Source Delivery: A liquid B source (B(CH3O)3 dissolved in CH3OH, 0.01 g/ml) was introduced via a bubbling method using H2 as the carrier gas.
- B Incorporation Control (Pattern Variation): The H2 carrier gas flow rate was varied across three patterns to control the amount of B source introduced into the plasma:
- Pattern 1 (Low Resistivity): 3 to 5 sccm.
- Pattern 2: 1 to 3 sccm.
- Pattern 3 (High Resistivity): 1 to 3 sccm.
- In-situ Plasma Monitoring (OES): Optical Emission Spectroscopy was performed continuously during growth to measure the intensity of key plasma species, including B (249.7 nm), BH (433.1 nm), BO (436.3 nm), and Hβ (486.1 nm).
- Electrical Characterization: Resistivity was measured using the four-point probe method (JIS K 7194 standard).
- Structural Analysis: Raman spectroscopy was used to confirm B incorporation (shift and broadening of the 1333 cm-1 diamond peak) and SEM was used for surface and cross-section morphology.
Commercial Applications
Section titled “Commercial Applications”Highly conductive BDD films, particularly those achieving resistivity in the 0.3 Ω·cm range, are critical for advanced electrochemical and electronic applications where chemical stability and high conductivity are simultaneously required.
- Electrochemical Anodes: Used in advanced oxidation processes (AOPs) for industrial wastewater treatment and purification due to their extreme chemical inertness, wide potential window, and resistance to fouling.
- Electrochemical Sensors: High-sensitivity detection of heavy metals, organic pollutants, and biological molecules (e.g., glucose, dopamine) in harsh environments.
- High-Power Electronics: Utilizing diamond’s superior thermal conductivity (W/mK) combined with controlled electrical conductivity for heat dissipation and active device layers in high-frequency or high-temperature applications.
- Energy Storage: Potential use as electrode materials in supercapacitors and batteries due to high surface area stability and charge transfer kinetics.
- Quantum Device Architectures: BDD layers can serve as conductive contacts or specific structural components in devices utilizing Nitrogen-Vacancy (NV) centers for quantum sensing and computing.
- Microelectromechanical Systems (MEMS): Fabrication of robust, chemically resistant micro-devices requiring conductive diamond components.
View Original Abstract
As described herein, we investigate the effects of the plasma state on boron（B）-doped diamond（BDD）resistivity. Preparing BDD of various volume resistivities is difficult. Various studies have examined control of the BDD resistance value, necessitating systematic investigations of the relation between resistivity and B contents in plasma. Therefore, plasma during growth was measured using optical emission spectroscopy （OES）to clarify the relation between emission species and resistance values. For each condition, OES revealed peaks of B（249.7 nm）, BH （433.1 nm）, BO（436.3 nm）, Hα, Hβ, CH, and C2. Electrical resistivity measurements obtained using the four-point probe method with mini mum volume resistivity of 0.3 Ω·cm were obtained. With increasing B-containing emission species such as B, BH, and BO intensity in OES spectra, resistivity was decreased. Results suggest that B-containing emission species in OES spectra influence the resistivity of BDD.