Self-Assembled Monolayers as Model Substrates for Atomic Layer Deposition

Our understanding of the role of the initial surface on atomic layer deposition (ALD) of Cu diffusion barrier materials is limited by the complexity of the sequential reactions and the heterogeneous nature of typical dielectric substrates. The atomically controlled surface chemistry of self-assembled monolayers (SAMs) provides a means of creating model substrates for ALD. Here we report on ALD of WCxNy films on SAMs derived from bromoundecyltrichlorosilane adsorbed on silicon dioxide. The as-prepared SAM is macroscopically ordered with the expected Br-termination and has a well-defined chemical composition as determined by contact angle measurements and X-ray photoelectron spectroscopy, respectively. Temperature programmed desorption spectroscopy confirms that the SAM is stable to 550°C. It survives multiple cycles of ALD at 300°C as evidenced by the detection of mass fragments characteristic of the alkyl chain and supported by the persistence of a Br 2p peak at 71 eV. X-ray fluorescence, ellipsometry and atomic force microscopy reveal that the underlying SAM influences WCxNy film coverage, thickness, and morphology.