Roles and mechanism analysis of chitosan as a green additive in low-tech node copper film chemical mechanical polishing

Abstract As a natural macromolecule organic compound, chitosan (CTS, (C6H11NO4)n) was used as a green additive in low-tech node copper (Cu) chemical mechanical polishing (CMP), which has many functions and can improve the performance of Cu CMP in some aspects. Firstly, CTS has strong bactericidal properties under neutral or acidic conditions, so it can be used as a fungicide. Besides, CTS molecules have free amino and hydroxyl groups, which can coordinate with metal ions. At pH = 10.00, Ultraviolet-visible (UV-vis) and X-ray photoelectron spectroscopy (XPS) measurements were used to analyze the reaction mechanism of Cu ions and CTS. The results showed that there was a complexation reaction between Cu ions and CTS, and Cu-CTS complexes with parallel bridge structure was formed. In addition, CTS can also be applied to the field of corrosion inhibition of metals for the forming of a passive protective film on the surface of metals to prevent further corrosion within a certain concentration range. Using this property, CTS was introduced into Cu film CMP to improve the removal rate selectivity of Cu to barrier materials cobalt (Co) and ruthenium (Ru) in low-tech node. Specifically, there was a synergistic effect between fatty alcohol polyoxyethylene ether (JFCE, C12H25O.(C2H4O)n) and CTS. With the existence of JFCE, the complexation or inhibition effect of CTS can be improved. Finally, with the introduction of CTS, a lower surface roughness after CMP can be obtained. Therefore, it can be concluded that the green additive CTS with multiple roles can be introduced to the slurries of Cu and other materials used in integrated circuits.