Hollow cathode plasma electron source for low temperature deposition of cobalt films by electron-enhanced atomic layer deposition

Abstract

The development of a hollow cathode plasma electron source (HC-PES) facilitated the rapid nucleation and low temperature deposition of thin cobalt films using electron-enhanced atomic layer deposition (EE-ALD). The Co EE-ALD was performed near room temperature (30–60 °C) using sequential exposures of cobalt tricarbonyl nitrosyl and low energy (100–200 eV) electrons. Electron-stimulated desorption of CO and NO surface species creates open sites for precursor adsorption to facilitate the low temperature film growth. The HC-PES displayed high electron currents, rapid ALD cycling, and low susceptibility to chemical interference. Electron steering optics were also used to mitigate the effects of sputtering in the HC-PES. The high electron currents from the HC-PES yielded rapid nucleation of cobalt films in as few as four EE-ALD cycles with Co growth rates over 2 Å/cycle on areas >4 cm2. In high aspect ratio structures, transmission electron microscopy and energy dispersive spectroscopy analyses revealed a 4:1 topographical selectivity in favor of horizontal compared with vertical surfaces. This selectivity was attributed to the directional electron flux from the HC-PES. This topographical area selective deposition suggests that Co EE-ALD may be successful in achieving bottom-up fill of trenches and vias.