AVS 56th International Symposium & Exhibition
    Thin Film Wednesday Sessions
       Session TF-WeA

Paper TF-WeA11
The Role of Ammonia as an Inhibitor Species in Low Temperature CVD to Reduce Film Growth Rate and Enhance Conformal Coverage

Wednesday, November 11, 2009, 5:20 pm, Room B4

Session: ALD/CVD: Novel Applications, Mechanical Properties
Presenter: S. Babar, University of Illinois, Urbana-Champaign
Authors: S. Babar, University of Illinois, Urbana-Champaign
P. Zhang, University of Illinois, Urbana-Champaign
W. Wang, University of Illinois, Urbana-Champaign
N. Kumar, University of Illinois, Urbana-Champaign
J.R. Abelson, University of Illinois, Urbana-Champaign
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Our group recently demonstrated the phenomenon of growth inhibition in low temperature chemical vapor deposition of TiB2: a neutral molecule is added to the flow of precursor in order to reduce the growth rate and enhance the degree of conformal coverage; the atoms contained in the inhibitor are not incorporated into the film [JACS 130, 52 (2008)]. Here, we demonstrate the inhibition behavior of ammonia on HfB2 growth using Hf(BH4)4. The growth rate and surface roughness are measured in-situ by spectroscopic ellipsometry. At substrate temperatures below 350oC, ammonia reduces the growth rate of HfB2, down to zero at an ammonia pressure of ~ 1 mTorr. Upon cessation of the ammonia injection, growth resumes after 1-2 minutes. When ammonia is delivered as short pulses, the surface roughness appears to increase, then declines again after the ammonia is pumped out. We explore the origins of this phenomenon, which may involve the formation of a dielectric surface layer or re-nucleation of HfB2 growth. We explain the role of ammonia using a site-blocking model in which ammonia adsorbs reversibly on the surface sites and reduces the rate of precursor adsorption. This simple rate model fits the data well. We show that growth inhibition by ammonia can be used to greatly enhance the degree of conformal coverage in a deep trench.