Ru ALD With Bulk-Like Resistivity for Interconnects

Ruthenium is viewed as a promising alternative to Cu and Co interconnect metals at M0/M1 interconnect layers due to its lower effective resistivity in highly-confined layers and vias, as well as its resistance to diffusion into porous low-k dielectrics and to electromigration. Atomic layer deposition of Ru has been reported with a variety of precursors, but the search for a Ru ALD process with a close-to-bulk (~7 μΩ·cm) resistivity is ongoing, with special interest in a process that can selectively-deposit low-resistance Ru films without passivants. In this work, Ru films with close-to-bulk resistivity deposited using Ru(CpEt)2 were investigated using four-point-probe resistivity measurements, Xray photoelectron spectroscopy (XPS) for chemical analysis, X-ray diffraction/reflectometry (XRD/XRR) for grain size and thicknesses, and scanning electron microscopy (SEM) and atomic force microscopy (AFM) for film morphology.

I. Background and Experiment

Due to its low bulk resistivity and resistance to electromigration, Cu has been used as the interconnect metal of choice since the early 2000s [1] . However, as modern CMOS nodes continue to decrease pitch lengths and via widths decrease, the effective resistivity of Cu in the M0/M1 interconnect layers increases, motivating the use of alternate metals such as Co or Ru. Ru is of special interest owing to its short electron mean-free-path allowing for lower effective resistivity in narrow (<10nm) via widths compared to Co or Cu [2] [3] . While many Ru ALD processes are available, the search for a low-resistivity Ru process is ongoing, with particular interest in a process that can selectively-deposit Ru films without the use of a passivant [4] .