Effect of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on Cu/Ta chemical mechanical planarization (CMP) in the barrier layer: A novel complexing agent and the dual role on Cu

Abstract

Tantalum and its nitrides are used in barrier layers in copper interconnected ultra-large-scale integrated circuits. However, due to the different physical and chemical properties of copper (Cu) and tantalum (Ta), the difference in removal rates is a problem. This study developed an acidic barrier layer slurry with better Cu/Ta rate-selective properties. During the research and development process, it is found that the introduced novel complexing agent, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), has a bisexual effect on Cu while effectively enhancing the Ta removal rate. Therefore, the detailed analysis was carried out on the mechanism of PBTCA on Cu/Ta. In this study, the effects of the slurry fundamental composition, include pH value, oxidant H2O2 and complexing agent PBTCA, on Cu/Ta removal rate were firstly investigated by electrochemical and chemical mechanical planarization (CMP) experiments. Subsequently, XPS, SEM and AFM tests were utilized for in-depth analysis of the micro-activity mechanism of PBTCA. The concentration of PBTCA between 0.2 wt% and 0.3 wt% was found to have complexation effect on Cu, and the concentration between 0.3 wt% and 0.8 wt% was found to have corrosion inhibition effect on Cu, which verified that PBTCA has a dual effect on Cu. This phenomenon effectively reduces the difference of Cu/Ta removal rate and facilitates surface flattening. In addition, PBTCA is an environmentally friendly and biodegradable organophosphate condensate. Finally, the slurry stability experiments were carried out by average particle size and zeta potential tests. CMP experiments and atomic force microscopy (AFM) tests were employed to verify the performance of the slurry. It was concluded that the slurry was well stabilized with the oxidant addition, and the storage time had almost no effect on the removal rate and surface morphology of Cu and Ta. The results of the study provide a feasible method for barrier layer CMP.