Co contamination of Si: Plating & aging

Cobalt has emerged as a vital material in 10 nm technology for localized interconnect layers, potentially offering a compelling alternative to Cu-based interconnects. In this study, we subjected the contamination arising from the presence of cobalt atoms in silicon to comprehensive investigation, employing electron transmission electron microscopy (TEM) observations in conjunction with first-principles calculations. The results show that a dense CoSi layer with a thickness of a few nanometers is formed at the interface of cobalt and Si. The CoSi layer blocks the diffusion of Co atoms into Si. This is due to the semiconducting nature of the covalent bond formed between Co and Si, leading to the emergence of a forbidden zone at the Co/CoSi interface. The diffusion of Co into CoSi is governed by the atomic exchange mechanism, however, the local distortion of the periodic atomic potential due to the presence of the forbidden zone at the Co/CoSi interface hinders the diffusion of Co into Si. Therefore, the deposition of a Co metal layer on a Si chip does not require an additional barrier layer.