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Microstructural and Surface Morphological Evolution at the Atomic Scale during the Growth of Polycrystalline TiN: a HR-TEM, XRD, STM, and Modeling Study

Joe Greene
Frederick Seitz Materials Research Laboratory
Dept. Materials Science, Univ. Illinois, Urbana, IL 61801, USA

 TiN and related transition-metal (TM) nitrides are used as diffusion barriers in microelectronics as well as hard, wear, and corrosion resistant coatings in mechanical and optical applications. Since all TM nitrides are highly anisotropic, control of preferred orientation is essential. We have used a combination of XRD, TEM, and HR-XTEM analyses to show that TiN layers grown by reactive evaporation or sputter deposition at low temperatures (Ts < 450 °C) exhibit competitive texture evolution with a columnar 111 "kinetically-limited" texture eventually becoming dominant. The columns are narrow and facetted with inter- and intracolumn porosity. Higher Ts or the use of high incident N2+/Ti flux ratios (> 5) with low N2+ energies (20 eV) result in non-competitive growth with a fully dense complete 002 orientation from the initial monolayer. The columns are broad-based with flat surfaces. Kinetic Monte Carlo (KMC) modeling, assuming that the activation energy Es for surface diffusion and the Ehrlich barrier Eb at descending step edges are larger on 111 than on 002, provide a qualitative understanding. Quantitative modeling requires transport activation energies (Es, Eedge, Ef, and Eb) and island line tensions vs orientation. To obtain these parameters, we have grown single-crystal TiN(001) and TiN(111) layers at Ts = 700-950 °C under conditions resulting in large (> 1500 Å) atomically-flat terraces. Partial TiN monolayers (qTiN = 0.1-0.4 ML) were then deposited and in-situ high-temperature STM used to following the coarsening and decay kinetics of single and multiple islands (Ostwald ripening) on flat terraces and in single-atom deep vacancy pits. From the results, combined with solutions of the Gibbs-Thompson and diffusion equations, we obtain the atomic transport parameters listed above which are then used as input into higher level KMC and level-set models for predicting microstructural and surface morphological evolution as a function of growth parameters. The simulated and experimentally-determined microstructures and surface morphologies are in good agreement and provide detailed atomic scale understanding of complex surface interactions during reactive film growth.

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