Role of 1,2,4-Triazole as a Passivating Agent for Cobalt during Post-Chemical Mechanical Planarization Cleaning

Cobalt (Co) has been considered as one of the candidates for the barrier material in copper (Cu) interconnects. As a metal that is less noble than copper, Co poses two challenges to the integration scheme. For example, during the post-chemical mechanical planarization (CMP) cleaning step, corrosion of Co and galvanic corrosion between Co and Cu may occur. To minimize such corrosion, a corrosion inhibitor is often added into the post-CMP cleaning solution. The present study investigates the interaction between these metals and a representative corrosion inhibitor 1,2,4-triazole (TAZ). More specifically, this study uses various analytical techniques to elucidate the mechanism with which TAZ reduces the corrosion density of Co and Cu and prevents galvanic corrosion between the two metals. Furthermore, it is found that TAZ preferentially forms a passivating film on the relative stable Co surface containing cobalt hydroxide (Co(OH) 2 ) whereas the instability of Co reduces the effectiveness of TAZ inhibition. The corrosion protection for cobalt at pH 10 in presence of TAZ is mainly attributed to the physisorption and chemisorption of TAZ molecules on oxide covered Co surface, which follows Langmuir adsorption isotherm. It is anticipated that the same passivation mechanism may also be applicable to other structurally similar corrosion inhibitors.