Focused electron beam-induced deposition (FEBID) and focused ion beam-induced deposition (FIBID) are direct-write techniques with advantages in the three-dimensional (3D) fabrication of nanostructures. However, only a few reports have discussed the differences between these depositions using the same precursor species.
Study: Focused Ion Beam vs Focused Electron Beam Deposition of Cobalt Silicide Nanostructures Using Single-Source Precursors: Implications for Nanoelectronic Gates, Interconnects, and Spintronics. Image Credit: Unwind/Shutterstock.com
An article published in the journal ACS Applied Nano Materials presented a report on the deposition of cobalt silicide by using two single-source precursors in gallium (Ga)-ion beam writing and revealed that silylene bis(tetracarbonylcobalt) (H2Si(Co(CO)4)2) was a suitable precursor for the direct-write technique, with 2:1 ratio of cobalt (Co): silicon (Si) retention in the deposit.
FIBID deposits resulted in a 90 atom% of metal/metalloid contents with (H2Si(Co-(CO)4)2) precursor, while FEBID deposits with the same precursor provided material with less than 60 atom% of metal/metalloid content. Thus, a dense deposition was obtained using FEBID, which showed electric properties and paramagnetic behavior like granular metal.
Furthermore, the FIBID material was porous and showed anticipated temperature-dependent electric and ferromagnetic properties of dicobalt silicide. Further investigation suggested various prevailing material conversion paths based on the discovered microstructural properties, such as the formation of bubbles in FIBID-derived materials. Thus, the application of cobalt silicides in nanoelectronics and spintronics may be affected by variations in material characteristics that depend on the deposition process.
Fabrication of Nanostructures via FEBID/FIBID
Nanomaterials are often fabricated and integrated via top-down methods using high-resolution nanofabrication techniques to construct nanopatterns and manufacture nanodevices. Among these methods, focused beams of charged particles are frequently employed to generate nanopatterns with extremely high resolution and to produce two-dimensional (2D) nanostructures either by focused ion beam (FIB) milling or electron beam lithography (EBL).
Additionally, nanostructure’s site-selective writing with appropriate form and dimensions is possible via focused electron/ion beams. Hence, these direct-write methods have been developed for direct applications in non-specialist environments. Surface-adsorbed precursors must be fragmented for both FEBID and FIBID writings.
Non-destructive FEBID and FIBID vary primarily because the ions in the latter deposition method are incorporated into the growing material, implanted in the substrate, and damage the substrate material by amorphization or localized sputtering because of ion momentum transfer.
During FIBID, lighter elements, which are byproducts of precursor fragmentation and partial ligand stripping, are eliminated. In this regard, new research in surface science on precursor fragmentation suggests that ion bombardment creates deposits with significantly larger metal concentrations. The number of ion or electrons and the concentration of the precursor during the deposition process distinguishes the deposition regimes for both FEBID and FIBID.
While metal silicides are intermetallic compounds with a wide range of magnetic, electronic, catalytic, optical, and mechanical properties, cobalt silicides are promising materials in nanoelectronics as gates in integrated devices, interconnects, and spintronic applications.
FEBID versus FIBID of Cobalt Silicide Nanostructures
Previous reports have mentioned the creation of deposits of better purity using ion-based direct writing techniques instead of electrons. Energetic ions incident on a surface for the adsorption of molecules produced several effects, including dissociation or desorption of the molecules or reaction between molecules and substrate material.
In this study, two single-source precursors were evaluated for cobalt silicides for feasibility in FIBID. Owing to the slow growth rates, associated high Ga concentrations, and strong sputtering effects that usually lead to the variation in metal/metalloid stoichiometry, silylene tetracarbonyl cobalt (H3SiCo(CO)4) did not function well under the specified circumstances.
However, H2Si(Co(CO)4)2 was shown to be a suitable precursor for FIBID due to rapid growth rates with high metal/metalloid concentrations of up to 90 atom% and retention of the metal/metalloid ratio offered by the precursor, while using the same precursor in FEBID-derived material revealed substantial differences in the physical properties and microstructures of the deposits.
The FIBID material was porous and ferromagnetic and temperature-dependent electric characteristics like cobalt silicides were observed. In contrast to the FIBID material, the FEBID produced a dense deposit with paramagnetic and electrical characteristics of a granular metal.
Thus, based on the direct-write approach, the present work demonstrated that identical precursor molecules could produce deposits with different physical characteristics. The composition, microstructure, and physical characteristics of materials vary based on the direct-write deposition method, affecting their use in applications, such as interconnects or gates in nanoelectronics and spintronics.
In summary, two single-source precursors for cobalt silicides were tested for the first time for their feasibility in FIBID. The effects of the current, precursor pressure and acceleration voltage on the composition of the deposits were evaluated.
Moreover, the magnetic and electric transport properties of the nanodeposits were investigated and compared with those of the same precursor-based FEBID material. The results revealed that the microstructure and physical properties of the deposits relied on the technique used for molecule-to-material conversion. This study offered substantial information suggesting different reaction channels for FEBID and FIBID, leading to unique microstructural features.
Jungwirth, F et al. (2022). Focused Ion Beam vs Focused Electron Beam Deposition of Cobalt Silicide Nanostructures Using Single-Source Precursors: Implications for Nanoelectronic Gates, Interconnects, and Spintronics. ACS Applied Nano Materials.
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