Passivation of copper–hafnium thin films using self-forming hafnium oxide

The structural changes and electrical properties of copper hafnium (Cu(Hf)) thin films have been investigated. After annealing the Cu(Hf) film in an oxygen atmosphere, the surface of the film was capped with a self-formed HfO2 layer to diminish copper oxidation and reduce the electrical resistivity of the films. The outward diffusion of Hf atoms from the Cu(Hf) matrix was confirmed by X-ray diffraction, four-point probe measurements, Auger electron spectroscopy, and transmission electron microscopy. A Cu film with high Hf content exhibited superior passivation characteristics when the film was annealed in an oxygen atmosphere, but it also had high resistivity because of the high Hf content. The leakage current of the Cu(Hf) film was also markedly improved, revealing that Hf is a promising doping element for Cu interconnects and thin-film transistors.

► Cu(Hf) film will be potentially applied on TFT-LCD and IC.
► The surface of Cu(Hf) film was capped with a self-forming HfO2 layer after annealing.
► The self-forming HfO2 layer protects the underlying Cu film from further oxidization.
► The Cu(1.1 at.% Hf) film reaches the lowest resistivity of 2.71 μΩcm after annealing.
► Cu(Hf)/SiO2/Si/Al structure has a much lower leakage current than for a pure Cu film.