Epitaxial growth of CuAl₂ films as conductor for high conductivity interconnects

This study explores the potential of tetragonal CuAI$_2$ as alternative conductor for narrow high-conductivity interconnect lines. Epitaxial and polycrystalline 46-350 nm thick CuAl$_2$ films are deposited on MgO(001) and SiO$_2$/Si substrates at T$_s$ = 100-400 °C. Figure 1 shows typical x-ray diffraction (XRD) patterns from three films deposited at T$_s$ = 100, 200, and 300 °C, demonstrating a transition from 110 orientation to 001 orientation with increasing T$_s$. XRD φ scans and pole figures indicate a single in-plane orientation where CuAl$_2$[110]‖MgO[100] for T$_s$ ≥ 300 °C while CuAl$_2$ 110 films grown at T$_s$ = 100 °C exhibit a two domain epitaxy.

In situ and ex situ transport measurements at 295 and 77 K quantify the effect of film thickness, deposition temperature, annealing, and compositional variations on the resistivity. CuAl$_2/$SiO$_2$/Si films have 6-10% higher room temperature resistivity than CuAl$_2$/MgO(001) due to electron scattering at grain boundaries in polycrystalline CuAl$_2$. Annealing reduces the resistivity of as-deposited films from 19.4-22.6 $\mu\Omega$.cm to 7.2-8.5 $\mu\Omega$.cm by improving crystallinity.