Cu$_x$Al$_{1-x}$ films as Alternatives to Copper for Advanced Interconnect Metallization

TL;DR

This study explores Cu$_x$Al$_{1-x}$ thin films as promising alternatives to copper for advanced interconnects, combining first-principles simulations and experimental deposition to evaluate their electrical properties and challenges.

Contribution

It provides a comprehensive analysis of Cu$_x$Al$_{1-x}$ films, including electronic structure, resistivity, and phase stability, highlighting their potential and challenges for interconnect applications.

Findings

Lowest resistivity of 9.5 μΩcm for 28 nm CuAl and CuAl$_2$ after annealing

Phase separation issues observed in off-stoichiometric films

Surface oxide formation affects film stability

Abstract

Cu$_x$Al$_{1-x}$ thin films with $0.2 \le x \le 0.7$ have been studied as potential alternatives for the metallization of advanced interconnects. First-principles simulations were used to obtain the Cu$_x$Al$_{1-x}$ electronic structure and cohesive energy to benchmark different intermetallics and their prospects for interconnect metallization. Next, thin Cu$_x$Al$_{1-x}$ films were deposited by PVD with thicknesses in the range between 3 and 28 nm. The lowest resistivities of 9.5 $\mu\Omega$cm were obtained for 28 nm thick stochiometric CuAl and CuAl$_2$ after 400$^\circ$C post-deposition annealing. Based on the experimental results, we discuss the main challenges for the studied aluminides from an interconnect point of view, namely the control of the film stoichiometry, the phase separation observed for off-stoichiometric CuAl and CuAl$_2$, as well as the presence of a nonstoichiometric surface oxide.