Paper NS-MoA7
Directed Assembly of Metal Contacts to Silicon Nanowires using Electrodeposition

Monday, October 15, 2007, 4:00 pm, Room 616

A technique based on electrodeposition for electrically contacting semiconductor nanowires (NWs) is presented. In the majority of exploratory studies electron-beam lithography has been utilized for establishing the metal-nanowire contacts. While useful for laboratory investigation this technique requires a post nanowire-assembly photolithography step and is too slow for large scale assembly. Thus new techniques are needed that are easy to integrate, low cost and involve minimum additional time for integration of nanowires onto device platforms. In the present work we report a process based on electrodeposition for establishing metal contacts to silicon nanowires (SiNWs). In this technique nanowires are first aligned between pairs of planar metal electrodes using dielectrophoresis. These electrodes have been predefined on top of an oxidized silicon substrate using photolithography. After the alignment, the ends of SiNW are resting on top of the metal electrodes and held in place by the Van der Waals attraction with the electrodes. In order to achieve good electrical contacts, metal has to be conformally deposited encapsulating the ends of these nanowires. In the present work this has been achieved via electrodeposition where prefabricated metal electrodes act as selective sites for deposition of metal. As the deposition proceeds the ends of nanowire become encapsulated by the electrodeposited metal. This avoids post NW-assembly photolithography, reducing the associated processing complexity. Metal doesn’t deposit on the SiNW surfaces because of the native oxide present around them. We have demonstrated this process using electrodeposited Ni on electrically doped Si nanowires. Good coverage and control for nanowires aligned between Au/Cr pre-defined electrodes has been achieved and post-electroplating annealing resulted in specific contact resistivities ~10^-6 Ohm-cm². Although native oxide is useful for avoiding metal plating on the surface of NW, it acts as barrier for metal-SiNW reaction during annealing of such contacts. Also Au is not a desirable metal for devices. Therefore we have explored the use of other electrode array metals such as Ni/Ti to replace Au as well as to assist in reducing the native oxide during annealing for good metal-SiNW contacts. The results are promising for development of a general self-assembly technique for the integration of nanostructures on device platforms.