Using scaling laws to understand the growth mechanism of atomic layer deposited WN_xC_y films on methyl-terminated surfaces

Atomic layer deposition (ALD) of tungsten nitride carbide (WN_xC_y) on methyl-terminated self-assembled monolayers (SAMs) is investigated. SAM substrates provide extended transient regimes of different lengths, during which the WN_xC_y film growth is nonlinear. The extent of this offset from linear growth depends on the alkyl chain length. The film morphology is characterized by atomic force microscopy, which reveals island growth and fractal behavior. During the transient regime, WN_xC_y deposition shows nonconservative growth, as revealed by the low film density and a roughness exponent α of ∼0.4–0.5. During the linear growth regime, a conservative mechanism is observed, characterized by a higher, constant film density and α∼0.7. These observations do not apply to all ALD deposited films. In particular, ALD HfO₂ films follow a conservative-type mechanism during the entire range of growth.