Effects of Interfacial Organic Layers on Nucleation, Growth, and Morphological Evolution in Atomic Layer Thin Film Deposition

Atomic layer deposition (ALD) of titanium nitride, TiN, from the reaction of Ti[N(CH 3 ) 2 ] 4 and NH 3 on silicon dioxide, and silicon dioxide modified by interfacial organic layers with different structures (straight-chain vs branched) and functional terminations (−OH, −NH 2, and −CH 3 ), has been investigated employing molecular beam techniques, atomic force microscopy (AFM), X-ray photoelectron spectroscopy, and scanning transmission electron microscopy (STEM). We find that the interfacial organic layers have a profound effect on subsequent growth of TiN via ALD. For organic layers possessing unreactive end groups (−CH 3 ), the initial rate of growth (thickness deposited per cycle) is strongly attenuated, and growth on these surfaces is 3-D and severely islanded, emanating from defects in the adlayer. Roughness builds quickest on the organic layers that are the thickest. For organic layers that possess reactive end groups (−NH 2 and −OH), growth is also attenuated, but less so, and the degree of attenuation is essentially independent of the layer thickness and structure. The dependence of the attenuation on the substrate temperature (decreased at higher values) suggests that some degradation of the interfacial layer may occur in these cases, where fragments of the decomposition reaction(s) are retained at the surface, leading to attenuation of the rate of deposition. Results from AFM suggest that even on these reactive surfaces growth is not fully 2-D, but involves initially the formation of a high density of small islands. High-resolution STEM did show that the films that were eventually formed are continuous and very conformal. Finally, we find an excellent correlation between the saturation density of adsorbed Ti species and the degree of attenuation of the initial rate of deposition.