Multiple Self-Aligned Iron Nanowires by a Dual Selective Chemical Vapor Deposition Process

Abstract

We have demonstrated a self-aligned process to fabricate organized iron nanowires on a planarized surface with wire dimensions down to 50 nm. Polishing was used to expose an alternating silicon silicon dioxide edge and a dual selective metal deposition process produced the nanowires. The initial selective deposition produced a tungsten layer on the exposed polysilicon regions. The discovery that selective chemical vapor deposition of iron from Fe͑CO͒ 5 precursor on dielectric surfaces over tungsten surfaces is the key factor that enables the self-alignment of the iron nanowires. Dimensions of the wires are determined by the thickness of the thermal oxide.In semiconductor fabrication, there are various methods that can be used to fabricate patterned nanowires. However, organizing the nanowires into highly ordered arrays can prove extremely challenging. Metallic nanowires can be produced with a combination of advanced lithography and metal etching, chemical mechanical planarization ͑CMP͒, or metal lift-off. However, these techniques may not be the easiest or the most cost effective. With lithographic methods such as ultraviolet ͑UV͒, deep ultraviolet ͑DUV͒, extended ultraviolet ͑EUV͒, E-Beam, and X-ray there are always resolution and alignment issues such as how small a structure can be produced and how closely a structure can be aligned to another. Even when lithography issues are resolved, patterning of very fine metal lines can be a problem. Wet chemical etching is not feasible when trying to produce submicrometer features because of large undercuts due to the isotropic etch. Metal lift-off with sacrificial resist is a more common solution to produce nanostructures, but the process has resistimposed limitations. Deposition must take place below 200°C because of resist thermal stability, preventing its use in a chemical vapor deposition ͑CVD͒ metal process.Selective deposition is an attractive process whereby deposition is preferentially carried out on one surface to the exclusion of the deposition on another. Structures defined by selective CVD are not controlled by resolution of the lithographic tool. Many studies concerning the selective deposition of tungsten using a WF 6 precursor have been reported. [1][2][3][4] The key factor in this work is the discovery of a CVD iron process, which deposits selectively on dielectric surface to the exclusion of tungsten surfaces. This has been reported previously by the authors, 5,6 but to their knowledge has not been investigated by any other group. There are several publications reporting the deposition of Fe by CVD from Fe͑CO͒ 5 . These included the deposition by direct thermal decomposition of Fe͑CO͒ 5 , 6,7 a process which also allows the deposition of epitaxial iron layers on GaAs 8 suggesting a very pure dissociation of the iron precursor. Laser 9 and ion-assisted growth, 10 for the fabrication of magnetic nanostructures have also been reported.In this paper, we demonstrate a self-aligning technique that allows the fabrication of organized parallel iron nanowires o...

Chemical Vapor Deposition of Aluminum Nanowires on Metal Substrates for Electrical Energy Storage Applications

“…24À29 The literature search revealed only reports on CVD growth of Mo NWs on Si, Al 2 O 3 , and steel; 24 Pt NWs on SiO 2 , Ni alloy, and SrTiO 3 (100); 25 Ni NWs on SiO 2 ; 28 Cu NWs on SiO 2 and Si; 26,27 and Fe NWs on SiO 2 . 29 However, for use of metal NWs in energy storage devices, 13,14,16À20 an abundant, low-cost, highly conductive, corrosionresistant, and lightweight Al could be of higher demand. Particularly, if Al NWs are grown on conductive metal foil substrates in order to establish a good electrical contact within an electrode.…”

“…The rapid growth and large-scale synthesis capability of CVD combined with a high precision in controlling the metal NW dimensions makes CVD one of the most promising approaches for metal NW synthesis. Surprisingly, in contrast to the significant progress achieved in CVD growth of CNTs and semiconductor nanowires, very limited studies report the template-free CVD growth of metal NWs. − The literature search revealed only reports on CVD growth of Mo NWs on Si, Al 2 O 3 , and steel; Pt NWs on SiO 2 , Ni alloy, and SrTiO 3 (100); Ni NWs on SiO 2 ; Cu NWs on SiO 2 and Si; , and Fe NWs on SiO 2 . However, for use of metal NWs in energy storage devices, ,,− an abundant, low-cost, highly conductive, corrosion-resistant, and lightweight Al could be of higher demand.…”