Sunday, March 30, 2014

Texas Instrument and University of Texas reports a new route to HfO2 ALD on Graphene

ALD HfO2 dielectric has since the introduction of Intels 45 nm technology become the material of choise for most modern scaled trasistor technologies. As reported yesterday SIMIT in Shanghai reports HfO2 growth directly on graphene by ALD  using a H2O/TEMAHf ALD process. Now Texas Instruments and University of Texas Dallas, Department of Materials Science and Engineering reports an alternative rout how to grow ALD HfO2 on the inert graphene surface. In a recent publication in Applied Surface Science, the researchers use reactive E-beam evaporation to create an HfO2 seed ayer on graphene for ALD HfO2 growth. ALD of HfO2 was performed using a Cambridge Nanotech Inc., Savannah 100 ALD reactor (TDMAHf and H2O). Please find the abstract below:

Picture from Wikipedia

Scaling of HfO2 dielectric on CVD graphene

S. McDonnell, A. Azcatl, G. Mordi, C. Floresca, A. Pirkle, L. Colombo, J. Kim, M. Kim, R.M. Wallace

Applied Surface Scienece, Vol. 294, 1 March 2014, Pages 95–99
The deposition of ultra-thin metal oxides on graphene is challenging due to the inert nature of the sp2 bonded graphene lattice. The feasibility of e-beam deposition of hafnium and hafnium oxide layers as seeds for further growth by atomic layer deposition on graphene CVD graphene is presented here. It is shown that metallic hafnium deposited in an ultra high vacuum environment readily reacts with graphene, forming a metal-carbide, rendering it unsuitable as a seed layer for the deposition of gate oxide materials. The deposition of HfO2 by reactive e-beam under an O2 partial pressure on the other hand eliminates the reaction with the underlying graphene. The uniformity of the e-beam HfO2 seed layers is found to control the uniformity of the subsequent films deposited by atomic layer deposition. Contrary to previous studies on graphite and exfoliated graphene substrates it is found that the uniformity and thickness scalability of atomic layer deposited thin films is limited on CVD graphene, most likely due to transfer induced residues on the graphene surface.

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