Effects of metal layers on chemical vapor deposition of diamond films
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-09-01 |
| Journal | Journal of Electrical Engineering |
| Authors | Tibor Izsák, G. Vanko, Oleg Babčenko, Bohumír Zaťko, Alexander Kromka |
| Institutions | Institute of Chemistry of the Slovak Academy of Sciences, Institute of Electrical Engineering of the Slovak Academy of Sciences |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research investigates the technological compatibility of thin metal layers (Ni, Ir, Au) with Microwave Plasma Chemical Vapor Deposition (MWCVD) for creating hybrid diamond/metal structures, specifically targeting 3D immersed electrodes for radiation detectors.
- Core Achievement: Defined a suitable metal multilayer system (Au/Ir) capable of stabilizing metallization while preventing diamond growth directly on the metal surface, crucial for buried electrodes.
- Ni Incompatibility: Nickel (Ni, 15 nm) was found unsuitable, promoting high carburization and resulting in amorphous carbon formation instead of diamond crystals, even at low deposition temperatures (~330°C).
- Ir Stability (Concept 1): Thin Iridium (Ir, 15 nm) proved stable and allowed successful overgrowth by a fully closed diamond film when deposited on a flat GaN substrate at low temperature (~330°C).
- Ir Instability (Concept 2): In the hybrid diamond/metal/diamond structure (Concept 2), the thin Ir layer was unstable at high temperatures (~1000°C), transferring into isolated clusters that were subsequently overgrown.
- Stabilized Metallization: The Au/Ir (30/15 nm) bilayer system successfully stabilized the metal layer in Concept 2, preventing clustering and inhibiting diamond growth on the metal surface.
- Conclusion for Detectors: The Au/Ir bilayer system provides a strong basis for fabricating diamond-based radiation detectors with built-in and/or buried metal electrodes.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Ni Layer Thickness | 15 | nm | Tested in Concept 1 |
| Ir Layer Thickness | 15 | nm | Tested in Concept 1 and 2 |
| Au/Ir Bilayer Thickness | 30/15 | nm | Tested in Concept 2 for stabilization |
| Concept 1 Deposition Temp (Low T) | ~330 | °C | Linear Antenna MWCVD (Ni, Ir on GaN) |
| Concept 2 Deposition Temp (Standard T) | ~1000 | °C | Focused Plasma CVD (Ir, Au/Ir hybrid) |
| Concept 2 Deposition Temp (Low T) | 460-520 | °C | Focused Plasma CVD (Ir, Au/Ir hybrid) |
| Diamond Base Layer Thickness (D-basis*) | Approx. 70 | nm | Initial layer for Concept 2 |
| Standard Diamond Film Thickness | 400 | nm | Grown on Si reference (Standard T) |
| Diamond Raman Peak (sp3) | ~1332 | cm-1 | Typical broadened peak |
| Graphitic G-band Raman Peak | ~1560 | cm-1 | Observed on Ni and Ir (low T) layers |
| Trans-Polyacetylene Raman Peak | ~1140 | cm-1 | Detected in low temperature deposition |
| LA-MWCVD Power | 2 x 1700 | W | Used for Concept 1 |
| Focused Plasma CVD Power (Standard T) | 3 | kW | Used for Concept 2 |
| Focused Plasma CVD Pressure (Standard T) | 70 | mbar | Used for Concept 2 |
Key Methodologies
Section titled “Key Methodologies”The study employed two distinct concepts using Microwave Plasma Chemical Vapor Deposition (MWCVD) systems (Linear Antenna and Focused Plasma) to test metal layer compatibility.
Concept 1: Metal on Flat Substrate (Low Temperature Deposition)
Section titled “Concept 1: Metal on Flat Substrate (Low Temperature Deposition)”- Substrate Preparation: Flat GaN substrate was used.
- Metallization: A thin metal layer (15 nm Ni or 15 nm Ir) was coated onto the GaN.
- CVD System: Linear Antenna MWCVD (LA-MWCVD) was used.
- Deposition Parameters:
- MW Power: 2 x 1700 W
- Pressure: 0.1 mbar
- Gas Mixture: H2/CH4/CO2 (200/5/20 sccm)
- Substrate Temperature: ~330°C
- Result: Ni resulted in amorphous carbon; Ir resulted in fully closed diamond film overgrowth.
Concept 2: Hybrid Diamond/Metal/Diamond Composite
Section titled “Concept 2: Hybrid Diamond/Metal/Diamond Composite”- Base Layer Formation: A thin nanocrystalline diamond film (D-basis*, approx. 70 nm) was formed using LA-MWCVD.
- Metallization: The base layer was overcoated with the metal layer (15 nm Ir or 30/15 nm Au/Ir bilayer).
- CVD System: Focused Plasma CVD was used for the second growth step.
- Standard Temperature Deposition (~1000°C):
- Power: 3 kW
- Pressure: 70 mbar
- Gas Mixture: 5% CH4 and 1.5% CO2 in H2
- Result: Thin Ir layer was unstable (clustered); Au/Ir layer was stable (no diamond growth).
- Low Temperature Deposition (460-520°C):
- Power: 2.5 kW
- Pressure: 30 mbar
- Gas Mixture: 5% CH4 and 1.5% CO2 in H2
- Result: Thin Ir layer was unstable (amorphous carbon grown on clusters); Au/Ir layer was stable (no diamond growth).
Commercial Applications
Section titled “Commercial Applications”The successful integration of stable, buried metal electrodes within diamond films opens pathways for advanced devices utilizing diamond’s extreme properties.
- Diamond Radiation Detectors: Direct application for fabricating 3D lateral electrode structures, improving charge collection efficiency and defining sensitive volume for high-resolution dosimetry.
- High-Power Electronics: Utilizing diamond as a wide bandgap semiconductor substrate with integrated, stable metal contacts (like Ir/Au) for high-frequency or high-power switching devices.
- Microdosimetry: Fabrication of high-resolution detectors for small field dosimetry by overcoming volume averaging effects inherent in traditional planar detectors.
- Ohmic/Schottky Contacts: Optimization of metal multilayer systems (e.g., Ir/Au) to achieve specific electrical behaviors (ohmic or Schottky) required for various diamond-based electronic devices.
- MEMS/NEMS Devices: Creation of robust micro- and nano-electromechanical systems where buried, stable conductive layers are necessary for sensing or actuation.
View Original Abstract
Abstract Diamond is recognized as one of the most promising wide bandgap materials for advanced electronic applications. However, for many practical uses, hybrid diamond growth combining metal electrodes is often demanded. Here, we present the influence of thin metal (Ni, Ir, Au) layers on diamond growth by microwave plasma chemical vapor deposition (MWCVD) employing two different concepts. In the first concept, a flat substrate (GaN) was initially coated with a thin metal layer, then exposed to the diamond MWCVD process. In the second concept, the thin diamond film was firstly formed, then it was overcoated with the metal layer and finally, once again exposed to the diamond MWCVD. It should be mentioned that this concept allows the implementation of the metal electrode into the diamond bulk. It was confirmed that the Ni thin films (15 nm) hinder the formation of diamond crystals resulting in the formation of an amorphous carbon layer. Contrary to this finding, the Ir layer resulted in a successful overgrowth by the fully closed diamond film. However, by employing concept 2 ( ie hybrid diamond/metal/diamond composite), the thin Ir layer was found to be unstable and transferred into the isolated clusters, which were overgrown by the diamond film. Using the Au/Ir (30/15 nm) bilayer system stabilized the metallization and no diamond growth was observed on the metal layer.