| AVS 64th International Symposium & Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | Zhejun Zhang, University of Illinois at Urbana-Champaign |
| Authors: | Z. Zhang, University of Illinois at Urbana-Champaign E. Mohimi, University of Illinois at Urbana-Champaign T.K. Talukdar, University of Illinois at Urbana-Champaign G.S. Girolami, University of Illinois at Urbana-Champaign J.R. Abelson, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
A major challenge in nanoscale device fabrication is to fill a deep via or trench with material without leaving a low density ‘seam’ along the centerline. We previously demonstrated two variants of low temperature chemical vapor deposition (CVD) that afford superconformal coating, in which film growth is faster deep in the feature that near to the opening. This affords a ‘V’ shaped coating profile, and as deposition proceeds, the apex of the V moves upwards until the feature is completely filled. Our first method, suitable for the growth of metallic films such as CrB2, involves the use of a highly reactive inhibitor, such as H atoms, in conjunction with the CVD precursor to suppress the growth rate in the upper portion of the feature. Our second method, suitable for dielectric deposition such as MgO, takes advantage of the intrinsic competition between two reactants, such as the precursor and water, on the film growth surface for adsorption sites. In both cases, the kinetic results are successfully modeled using Langmuir-Hinshelwood (LH) adsorption theory in combination with molecular transport of the reactants inside the feature.
In this interpretation, the suppression of film growth rate corresponds to a situation in which a significant fraction of the surface binding sites are occupied (blocked) by a species that does not lead to film growth, either the inhibitor in the first case or an excess of one reactant in the second case. However, we have not had any direct proof of this assumed mechanism. To obtain direct insight, we have implemented reflection FTIR spectroscopy in order to measure the surface coverage in adsorbates in real time during film growth. This is very challenging experimentally, however, the use of a thin dielectric on metal substrate at high angle of incidence provides enough signal enhancement in p-polarization to observe sub-monolayer coverages. In addition, the intrinsic cancellation of the absorption signal in s-polarization means that the contribution of gas phase absorption can be cancelled out by subtraction of the p and s signals.
We report the absorption competition for surface sites for the growth of MgO and HfO2 by low temperature CVD, and we compare the measurements with the range of values estimated from LH theory in view of the molecular fluxes to the surface and the measured film growth rates. As expected, the data reveal surprises such as a low total surface coverage in adsorbates even under competitive kinetics, indicating that the density of binding sites is significantly smaller than the geometric density of sites for these oxides.