Silicon Nanowire Growth at Relatively Low Processing Temperature
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Silicon Nanowire Growth at Relatively Low Processing Temperature Joondong Kim, Chunhai Ji and Wayne A. Anderson University at Buffalo, State University of New York, Dept. of Electrical Engineering, Buffalo, NY 14260 USA
ABSTRACT The Metal Induced Growth (MIG) of nanowires has the potential to alter the conventional lithographic techniques to provide an easier fabrication method in nanoelectronics. Our group has studied the MIG technique to synthesize poly-silicon and nano size structures. This work gave silicon nanowires of 20~200 nm diameter, 3~10µm length and single crystal structure. Until now, the growing of silicon nanowires has been understood by two models. One is an oxideassisted mechanism and the other is a metal catalyst assisted mechanism. Both cases need higher growth temperatures above 900 oC. We are now proposing the repeatable growth of silicon nanowires at a low processing temperature, 550~600 oC, which is the lowest silicon nanowire growth temperature without using a gas type silicon source (silane). This novel method to grow silicon nanowires has several advantages: (1) low processing temperature; (2) straight line growth; (3) single crystal structure and (4) repeatability. This Si nanowire growing mechanism is based on NiSi formation.
INTRODUCTION Much interest has been shown in Si nanowires because they have possible applications for quantum wires [1], quantum confinement [2], logic circuits [3], battery cells [4] and nanoscale-interconnects [5]. NiSi has unique and interesting characteristics including lowest resistivity among the nickel silicide materials, less silicon consumption and lower formation temperature than NiSi2 [6] , reduced spiking in shallow junctions [7] and excellent scaling down properties. This new approach to Si nanowires is based on NiSi formation using a relatively low processing temperature. Nickel as a catalyst metal is thermally evaporated onto SiO2 before loading for DC magnetron sputtering. In the metal catalyst-assisted method, metals such as Ni, Fe, Ti and Au, are used as a seed material to produce nanowires. Nanowires may be grown at a low temperature of 300~600 oC using silane and Au catalyst based on the VLS (Vapor Liquid Solid) mechanism. This is based on the easy decomposition of silane gas at low temperature [810]. The MIG method provides nanowires without using a gas type silicon source (silane) and Au catalyst. This has the potential to use the nanowires as a 1 dimensional building block in nanoelectronics. The growth temperature of MIG nanowires of 575 oC is still a low temperature, competitive with other groups, without requiring silane and Au catalyst at 900 ~1200 oC [11-14] or using silane gas at 800 oC [15] On the other hand, an oxide layer takes the role of the catalyst in the oxide-assisted method, which produces silica nanowires, instead of pure Si or Si-alloy nanowires. Usually, a powder type of silicon oxide is a source to generate silicon oxide vapor by heating at around 920 ~ 950 oC and the end result is Si nanowires with a crystal str
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