Metal Silicide Nanowires Grown in Catalyst Free Method for Nanoelectronic and Nanophotonic Applications Developed by UW Scientistss

University of Wisconsin-Madison Chemistry Professor Song Jin with Andrew Schmitt and Yipu Song has developed a method of manufacturing  metal silicide nanowires, including metallic, semiconducting, and ferromagnetic semiconducting transition metal silicide nanowires.

According to the scientists in Patent Application 20100164110, the nanowires are grown using either chemical vapor deposition (CVD) or chemical vapor transport (CVT) on silicon substrates covered with a thin silicon oxide film, the oxide film desirably having a thickness of no greater than about 5 nm and, desirably, no more than about 2 nm (e.g., about 1-2 nm). The metal silicide nanowires and heterostructures made from the nanowires are well-suited for use in CMOS compatible wire-like electronic, photonic, and spintronic devices.

FIG. 1 illustrates a method of producing FeSi nanowires in accordance with the Wisconsin invention. 

FIG. 2 shows SEM images of nanowires having secondary structures branching from their surfaces. 

The metal silicide nanowires and heterostructures made from the nanowires are well-suited for use in CMOS compatible wire-like electronic, photonic, and spintronics devices. 

As MOSFET devices are scaled down smaller and smaller in ultra large scale integration (ULSI) processes, all aspects of the MOSFET device structures, including semiconductor channels, source and drain electrical contacts, gate stacks, and interconnects, need to be scaled. Increasingly, the now famous Moore's law has also become applicable to novel materials. Very prominent among these novel materials are metal silicides. Metal silicides are already of paramount importance as integral parts of silicon microelectronics, mainly because of the low resistivity ohmic contact to CMOS transistors provided by metallic silicides such as NiSi, CoSi₂, and TiSi₂ in the now dominant SALICIDE (Self-Aligned Silicides) process. In the last few years, metallic silicides, particularly nickel silicides (NiSi, Ni₂Si, Ni₃Si) have also been successfully explored in the FUSI (Full Silicidated Gate) process for the state-of-art MOSFET at 45 nm node, which is superior to the traditionally poly-silicon gates.

Often overlooked is the fact that many silicides are direct bandgap semiconductors (e.g., .beta.-FeSi₂, CrSi₂) that are promising for photonic applications as well, though a host of materials issues have prevented their application so far. Most significantly, the recent discovery of group IV ferromagnetic semiconductors, such as alloys of Fe_xCo_1-xSi, suddenly brings into sight the exciting prospects of silicon-based spintronics. Furthermore, because silicides are omnipresent at the interfaces between semiconductor (e.g., Si) and ferromagnetic metals (such as Fe), silicides inevitably dictate the success or failure of any silicon-based spintronic devices. Therefore, silicide materials are critically important both by choice and by necessity

The Wisconsin methods provide a general synthetic approach for the production of single crystalline metal silicide nanowires. In one method, free-standing, single crystal, metal silicide nanowires are grown on a thin (e.g., 1-2 nm thick) silicon oxide film over an underlying silicon substrate via a chemical vapor deposition (CVD) process using single source or multiple (e.g., double) source precursors. In another method, free-standing single crystal, metal silicide nanowires are grown on the thin silicon oxide film via a chemical vapor transport (CVT) process using solid metal silicide precursors. The CVT process may be employed for the growth of transition metal silicides for which organometallic precursors are not readily available.

The nanowire growth mechanisms provided by the Wisconsin inventors are different from the well known vapor-liquid-solid (VLS) growth mechanism, due to the absence of metal catalysts. As a result, the metal nanowires are free from metal catalyst impurities and lack the catalyst caps or tips that are characteristic of VLS-grown nanowires.

Potential applications for the metal silicide nanowires include, but are not limited to, extremely small and low resistivity silicide gate lines to nanowire or traditional MOSFET devices, integrated ohmic contacts and low resistivity interconnects for nanoelectronics, highly efficient, highly stable, and CMOS compatible field emission tips for vacuum electronics and field emission displays, nanophotonic devices based on semiconducting silicide nanowires, and finally, nanospintronic devices based on ferromagnetic semiconducting silicide nanowires.