Atomic Layer Deposition of Cobalt Film from Dicobalt-hexacarbonyl-tert-butylacetylene and Hydrogen

Abstract

Thermal atomic layer deposition (ALD) of Co using the highly volatile liquid precursor, dicobalt-hexacarbonyl-tert-butylacetylene (CCTBA) and H2 was examined for application to liner or cap layers in Cu interconnects. The ALD process parameters, including deposition temperature and precursor supply time, were examined, and film properties such as composition and resistivity were investigated. At a deposition temperature of 100 °C, no incubation period was observed on Cu underlayers, and the Co film growth exhibited a self-limiting behavior with a saturated growth per cycle (GPC) of 0.051 nm cycle−1. Conformal deposition was achieved on trench structures with an aspect ratio of 8.4. However, deposition at temperatures above 125 °C resulted in the thermal decomposition of CCTBA and a transition to chemical vapor deposition (CVD) mode. The as-deposited Co film contained 29% C and exhibited a high resistivity of 104 μΩ∙cm. Post-annealing at 300 °C under a hydrogen atmosphere significantly reduced the C impurities to 3%, and decreased the resistivity to 53 μΩ∙cm at a film thickness of 20 nm. Annealing at higher temperatures increased the surface roughness, leading to film agglomeration. Therefore, a two-step process of thermal ALD using CCTBA at 100 °C followed by post-annealing at 300 °C is a suitable approach for fabricating high-quality Co films.