Mechasnistic studies of nucleation and growth during the atomic layer deposition of metals
Keywords: Chemical Engineering.

Nanotechnology has enabled major advancements in numerous fields such as renewable energy, semiconductor device fabrication, biomedicine, and waste treatment, among others. Precise patterning of features on the nanometer scale is imperative for further development of these technologies. Namely, the development of deposition techniques that are capable of depositing uniform thin films with precise stoichiometry and high uniformity over complex structures is essential. Atomic layer deposition (ALD), a deposition technique that relies on self-limiting surface reactions, has the potential to meet all these requirements. Although many ALD processes have been reported in the literature, many of the chemical and physical phenomena that govern film nucleation during ALD are still unknown. As the properties of ALD films are highly affected by the nucleation stage of film growth, this work aims to better understand how precursor chemistry and surface functionality relate to nucleation and growth for a subset of ALD processes. In the first part of this thesis, we present a study of surface modification techniques to tailor the nucleation properties of Pt ALD. Firstly, we investigate Pt nucleation enhancement through a small molecule surface pretreatment. We find that dosing small organometallic molecules at submonolayer coverage on a SiO2 surface significantly enhances Pt ALD nucleation. We find that the origin of this enhancement is a combination of enhanced chemisorption of the Pt precursor to the SiO2 surface and an increase in the adhesion energy between the Pt and the surface. Secondly, we combine this nucleation enhancement strategy on SiO2 with a well-known self-assembled monolayer growth inhibitor on Co to provide proof of concept for the case of area-selective ALD (AS-ALD) of Pt on Co vs. SiO2. We demonstrate that this combination of enhancement and inhibition in the AS-ALD process yields higher Pt coverages on the growth surface (SiO2) while maintaining high selectivity on the non-growth surface (Co). The combination of activation with inhibition could be expanded to other AS-ALD systems and help tackle current limitations in device patterning. In the second part of this thesis, we investigate the chemisorption mechanism of Ru(DMBD)(CO)3, a precursor that has been shown to be an exceptional candidate for Ru ALD. However, other studies have shown that ruthenium carbonyl derivatives spontaneously decarbonylate post chemisorption, and therefore have been widely implemented in continuous deposition schemes. We therefore aimed to gain deeper insight on the chemisorption mechanism of this precursor and understand the surface functionality that renders it suitable for ALD. Using in situ and ex situ characterization techniques to probe surface chemistry, we find that the deposition mechanism follows a thermally driven spontaneous decarbonylation scheme. Although at high temperatures the decarbonylation is efficient, at low temperatures carbonyl impurities are incorporated into the film. Together with findings from literature reports, we conclude that self-limiting decarbonylation mechanisms are often unsuitable for ALD, due to their continuous, kinetically driven nature. Overall, this work demonstrates the importance of understanding both the chemical and physical mechanisms that govern ALD nucleation and growth, and how these mechanisms affect the resultant film properties