High quality NH₂SAM (self assembled monolayer) diffusion barrier for advanced copper interconnects

Abstract

In this work, the quality of an amino-terminated SAM barrier (NH₂SAM) is tested. A high density and the absence of pinholes in the barrier layer are essential for a good barrier performance in the copper interconnects. The quality of the NH₂SAM layer has been assessed by water contact angle (C.A) and High resolution AFM (HR-AFM). The density and the closure of the film have been monitored by X-Ray Reflectivity (XRR), Ellipsometry and Cylic Voltametry (CV). Already for 1min deposition, the C.A value changes from <10^o typical of a clean silicon oxide surface, to 51^o. A 15min deposited NH₂SAM (thickness <1nm, measured by XRR), results in a pinhole-free layer, as observed by HR-AFM. The refraction index (η) calculated from ellipsometry data, indicates an increase in the density of the layer with the deposition time. On the other hand, cyclic voltametry shows inhibition of the electrochemical reduction of Fe³⁺ to Fe²⁺ when NH₂SAM are grafted on a 2 nm SiO₂/Si electrodes. A decrease in the capacitive current is observed by increasing the layer thickness and density. The intrinsic barrier performance has been extracted from planar capacitor structures that allow measuring the leakage/Cu diffusion through the barrier in the vertical direction. The Time-Dependent Dielectric Breakdown (TDDB) lifetime results in an increase of 10 orders of magnitude of the capacitor lifetime with respect to the no-barrier control system.