Plasma-assisted atomic layer deposition and post-annealing enhancement of low resistivity and oxygen-free nickel nano-films using nickelocene and ammonia precursors

Abstract

Oxygen-free and low resistivity nickel (Ni) thin films are successfully prepared by plasma-assisted atomic layer deposition using nickelocene (NiCp₂) as a metal precursor and ammonia (NH₃) as a reactant. The properties of the deposited films are characterized by means of X-ray photoelectron spectroscopy, X-ray diffraction, ultraviolet photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy and four-point-probe measurements. The results indicate that the as-deposited films are Ni-dominated materials with small quantities of C and N, containing Ni–Ni, Ni–C, Ni–N, C–N and C–C bonds. Moreover, the films also exhibit excellent conformality on Si nano-pillars with an aspect ratio of ∼13. As the deposition temperature increases from 160 to 280 °C, the film resistivity reduces from ∼127 to ∼71 μΩ cm, which is related to the gradually enhanced Ni₃C phase in the films. However, the work function of the film shows a weak dependence on the deposition temperature, increasing from 4.003 to 4.046 eV. After being annealed at 400 °C in the forming gas (N₂/4%-H₂), the resistivity is reduced significantly down to 11.8 μΩ cm, and the work function increases up to 4.136 eV. These are ascribed to an increase in the purity of the films, as demonstrated by the disappearance of N and the loss of C in the post-annealed films. Such a preparation technique of high quality Ni nano-films is very promising for advanced integrated circuits.