Selective growth of horizontally-oriented carbon nanotube bridges on patterned silicon wafers by electroless plating Ni catalysts

Abstract

The main purpose of this research was to develop an Integrated Circuit compatible process to grow the horizontally-oriented carbon nanotubes (CNTs) across the trenches of the patterned Si wafer, which was produced by conventional photolithography technique. The selectivity of tile process is based oil the difference ill electrical conductivity between amorphous silicon (a:Si) and silicon nitride (Si3N4), where the catalyst can be much easier deposited by electroless plating on the a:Si part of the pattern. The selectivity is also based oil greater chemical reactivity of the catalyst with a:Si to form silicides, instead of with Si3N4. Furthermore, the Si3N4 barrier layer of the pattern was designed oil top of tile a:Si layer to guide the growth of CNTs in horizontal direction to bridge tile trenches of tile pattern. The as-deposited catalysts were examined by Auger electron spectroscopy (AES). The catalyst-coated pattern was pretreated in hydrogen plasnia and followed by CNT growth in a microwave plasina chemical vapor deposition (MPCVD) system. The CNT bridges were characterized by scanning electron microscopy (SEM), transmission electron rnicroscopy (TEM), high-resolution TEM (HRTEM), and I-V measurements. Under tile present deposition conditions, TEM and HRTEJM examinations indicate that the deposited nanostructures are bamboo-like InUltiwalled carbon nanOtLibes (MWNTs) with a wall thickness of 20 similar to 30 graphene layers. Electrical conductivity of the as-deposited MWNTs call be greatly improved by subjecting to 760 degrees C heat treatment under nitrogen atmosphere. The results demonstrate that the amounts of' CNTs and bridges are tunable with tile Ni catalyst plating time. Under the present experimental configuration and at a catalyst plating time of 20 s, countable numbers of bridges call be obtained, which are selectively and horizontally grown oil the areas of the pattern with Ni catalyst. This process call be a step approaching the application of CNTs in electronic devices. (c) 2005 Elsevier B.V. All rights reserved.