Tungsten Atomic Layer Deposition on Vertically Aligned Carbon Nanotubes

Vertically Aligned Carbon Nanotubes (VACNTs) can be grown from two-dimensional patterns into three-dimensional structures using lithographic and chemical vapor deposition techniques. These porous, low-density structures can then be filled, or infiltrated, with other materials to impart unique properties to the structure. Depending on the filler material, the resulting composite structure may have many applications such as metal MEMS devices. Many of the challenges of infiltration into nano-porous materials can potentially be overcome through Atomic Layer Deposition (ALD) processes. Tungsten, with its conductivity, high thermal resistance, and high density, is of special interest to us. Tungsten ALD, using Silane and Tungsten Hexafluoride precursors, is used to fill VACNT structures. In contrast to near ideal ALD processes, the tungsten film deposited with each cycle becomes non-self-limiting at large precursor exposures, leading to a larger growth-per-cycle [>5 Å per cycle] than many other ALD processes. The precursor transport and surface reactions occur in the diffusion-limited regime, leading to non-uniform deposition at shorter dose times. With appropriate tuning of three-dimensional feature size and dose times, a near solid structure can be formed.