Understanding the impact of Cu surface pre-treatment on Octadecanethiol-derived self-assembled monolayer as a mask for area-selective deposition

Abstract

Atomic layer deposition (ALD) combined with self-assembled monolayer (SAM) passivation allows selective deposition on patterned substrates at the nanoscale, enabling bottom-up material fabrication for various applications. Selective chemisorption of 1-octadecanethiol (ODT) on Cu over SiO2 is exploited to achieve area selective deposition (ASD). Although the essential role played by SAM in preserving a confined material growth at higher ALD cycles is largely accepted, studies elucidating the influence of substrate properties on SAM's ALD inhibition are lacking. In this work, Cu is treated either with acids or oxidizing agents to produce a multiplicity of surfaces, which differ in terms of composition and morphology. Using water contact angle, atomic force microscopy, x-ray photoelectron spectroscopy and cyclic voltammetry measurements, Cu substrates are characterized before and upon ODT deposition. The ODT layers formed on Cu are tested as a passivation means towards Hf3N4 ALD. The results stress the essential contribution of interface properties in forming dense thiol-SAM on metals, which is fundamental to a successful ASD process. It is here demonstrated that ODT on clean Cu cannot block Hf3N4 ALD at 150 degrees C, whereas on oxidized Cu the same organic layer prevents up to 19 nm Hf3N4 film growth before the Cu passivation is affected.