Passivation of metals (Co, Cu) with Self-Assembled Monolayers for area-selective Atomic Layer Deposition

CMOS technology is the most popular and worldwide spread fabrication methodology employed for the construction of integrated circuits, which are used in practically all the electronic applications. Over the last three decades, CMOS technology has undergone an extraordinary evolution characterized by a continuous downward scaling trend, which has led to an increasingly pronounced miniaturization of devices. Unfortunately, sustaining the downscaling tendency nowadays is becoming more and more challenging, because of two main kinds of limitations which arise during fabrication. The first are physical, since the properties of matter below a certain threshold do not scale together with the physical dimensions. The latter are technological, due to the constraints of traditional top-down approaches; the usage of photolithography, for example, entails problems of misalignment which are not acceptable when the dimensions involved are in the order of few tens of nanometers. The research for bottom-up approaches has revealed a good strategy to solve many issues related to the conventional techniques. One of them, Area Selective Atomic Layer Deposition (AS-ALD), has recently gained a lot of attention due to its disruptive potential in allowing self-alignment and thickness control at the nanometric level. Atomic Layer Deposition is a vacuum deposition technique which enables to grow thin, smooth, very conformal and defects-free films onto solid substrates; by the exposition of a substrate to alternated gaseous reactants, in a series of sequential and non-overlapping pulses, ALD builds up a film in a layer-by-layer fashioned way. Area Selective, instead, means that the deposition does not involve the whole surface, but it occurs only in pre-determined regions of interest, feature which turns out to be essential when dealing with patterned samples, as in this study. If, in a patterned sample, one material shows chemical affinity towards the substance to be deposited whereas the others don’t, area selectivity is inherently surface-dependent. If not, the selectivity can be achieved through functionalization of the substrate, either activating the growth areas, or deactivating the non-growth areas. Deactivation consists of passivating the regions where ALD should not take place with something that prevents the deposition. The most widely used materials for this purpose are Self-Assembled Monolayers (SAMs). Self-assembled monolayers are organic molecules which spontaneously assemble in ordered layers on the surfaces of solid materials, as a result of a chemisorption process. The target of this thesis project was to successfully passivate cobalt and copper surfaces by octadecanethiol self-assembled monolayers (ODT SAMs) deposited by spin-coating, in order to block atomic layer deposition of hafnium nitride (HfxNy ALD). The initial part of the work aimed to reach a good passivation of the metals, trying different experimental pathways. Each attempt was followed by the characterization of the samples, performed with Water Contact Angle (WCA), Spectroscopic Ellipsometry (ES), Atomic Force Microscopy (AFM) and Cyclic Voltammetry (CV) techniques. In the second part of the work the most promising samples underwent an ALD, being subsequently analyzed with Spectroscopic Ellipsometry (ES) and Rutherford Backscattering Spectroscopy (RBS) techniques to verify if deposition was effectively prevented.