Metal silicide nanowires for nanoscale contacts and polycrystalline silicon thin films for solar cells by metal-induced growth
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The metal-induced growth method (MIG) has been used to grow metallic nanowires for nanoscale interconnections and Si thin films for solar cell applications. Metal-induced growth (MIG) is a spontaneous reaction of metal and Si. MIG nanowires were grown at 575 °C, which is the lowest nanowire growth temperature in the solid state. Three types of catalysts, such as Ni, Co, and Pd were demonstrated to establish the growth mechanism concluding that metal should be a major diffuser to grow nanowires. Ni-induced growth is the most successful to form nickel monosilicide (NiSi) nanowires, 20--100 nm in diameter and 1--10 μm in length. The nanowire growth mechanism is based on the formation of the NiSi phase and Ni diffuses inside the nanowire body as well as the bottom layer as shown by TEM studies. Nanowires are attractive 1-dimensional building blocks to use in nanoelectronics and nanoscale connections. It may be a breakthrough to the "Red Brick Wall", which is a potential barrier of device scaling. The MIG nanowires have been utilized to form a nanoscale interconnection in a tiny space-nanobridge. It differs from the conventional methods which are assisted by external factors, such as electric or magnetic field, and focused ion or electron beam lithography. This MIG nanobridge is independent from complex fabrication requirements. Electrical measurement was directly performed from the nanowire as-grown state and gave a metallic transport characteristic with a low resistance of 148 Ω. Resistivity of the NiSi nanowire was calculated to be 10.6 Ωm, close to the NiSi film. The self-assembled nanobridge is practical for use in nanoscale interconnection with a reduced thermal budget. MIG poly-Si films were grown at 600--620 °C with 2--5 um thickness. Ni, Co, or Co coated Ni were used as a catalyst to provide a seed layer of NiSi 2 and CoSi 2 . These catalysts form a good template to grow an epitaxial Si film due to their low lattice mismatch to Si by 0.4 % and 1.23 %, respectively. The MIG Si films were fabricated for solar cells. X-ray photoelectron spectroscopy investigation was performed to investigate the depth of the silicide layer. The formation of silicide phases was traced by X-ray diffraction. The grain size and surface morphology were studied by atomic force microscopy analysis. The Ni-induced case showed metal contamination of the Si film resulting in a poor Schottky junction. The Co-induced case was stable but the poly-Si grain size is small. The coated Ni case was motivated by taking advantage of large grain size by Ni and stability by Co. It enhanced the short circuit current density by one order higher than that of the single Co use. The Co coating successfully prevented Ni contamination and improved the quality of the Si film at the same time.