AVS 63rd International Symposium & Exhibition
    Thin Film Wednesday Sessions
       Session TF+MI+NS-WeM

Paper TF+MI+NS-WeM6
Tungsten ALD in Porous Carbon Nanotube Forests

Wednesday, November 9, 2016, 9:40 am, Room 105A

Session: ALD and Nanostructures
Presenter: Richard Vanfleet, Brigham Young University
Authors: K. Hinton, Brigham Young University
N. Hollingworth, Brigham Young University
D.D. Allred, Brigham Young University
R.R. Vanfleet, Brigham Young University
Correspondent: Click to Email
We have deposited tungsten on carbon nanotube (CNT) forests by CVD (WF6 & H2) and ALD -the silane reduction of WF6. Resulting structures are studied by scanning electron and transmission electron microscopy. We observed that the CNT forest provides a scaffolding for the nucleation and growth of the tungsten. Such structures may be a useful avenue for metal MEMS that does not require extensive etching. The present study may provide insight into the mechanisms of ALD in highly porous structures. In conventional ALD on surfaces which are largely planar, the amount of reactants needed to completely cover the surface does not change much from step-to-step. In contrast the surfaces of carbon nanotube forests consist of cylindrical tubes largely oriented perpendicular to the sample surface. Thus, the surface area increases with deposition. This is in addition to the changes in surface area associated with incubating early stage nucleation sites. When beginning with adequate tungsten or silane one might expect to move to starvation mode as the number of cycles increases if the amount of each reactant is kept constant. We see evidence for tungsten starvation in our research results. For low number of cycles the CNT fibers have a spatially uniform nucleation of tungsten. For low amounts of WF6 or low “soak” times, as cycles increase, growth on the top surface and sidewalls of the carbon nanotube forest outpaces growth within the structure. Post deposition cross-sections show distinct bands witnessing the starvation of tungsten growth in the interior as more of the tungsten is deposited on regions that have direct access to the WF6 gas. EDX analysis across such a cross-section shows distinct plateaus in the amount of tungsten present corresponding to the bands.