Effect of Cleaning Chemistries on Cobalt: Surface Chemistries and Electrical Characterization

Abstract

The etching characteristics of ECD cobalt in different cleaning solutions were characterized using four-point probe, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. 0.05% HF solution with saturated dissolved oxygen concentration was found to result in a substantial etch of ECD cobalt (~5 nm/min). In contrast, cleaning in the SC1 1:4:100 mixture and the formulated mixture led to a significantly lower etch amount, which could be explained by the formation of a passivation layer at the surface. XPS characterization indicated the formation of a cobalt hydroxide at the surface. The electrical evaluation of the DD structure carried out after cleaning using the formulated chemical mixture and subsequent metallization showed good yield for the 22 nm Kelvin vias, testifying an efficient cleaning of the Co surface at the via bottom.

X-Ray Photoelectron Spectroscopy Estimation of Cobalt Seed Layer Reactivity Toward Air Exposure: A Challenge?

“…It is evident that for both, solutions immersion induced an important decay of the oxide region, so a decay of its initial thickness which must be associated to an oxide etching obviously related to a mass loss of the Co layer. This point must be critical when ultra thin Co seed layers are considered [9,10].…”

“…In the same way, A.Pacco et al [10], have proposed a study which considers a wet chemical process for a recess engineering. Based on a self limiting Co oxide thickness manipulation, they showed the interest of digital etching cyclic process for managing the thickness of ultra thin Co films.…”