Synergistic Effect of Composite Complex Agent on BTA Removal in Post-Cu-CMP: Experimental and Theoretical Analysis

Abstract

Nowadays the development of nanoscale-interconnected integrated circuit chips makes the chemical mechanical polishing (CMP) and post-CMP cleaning more challenging. In general, organic residues such as benzotriazole (BTA) can adsorb on the wafer surface after CMP process and form thin films to prevent the contact between cleaning solution and the wafer surface, which thus can seriously affect the post-CMP cleaning process. And the efficient removal of BTA remains problematic due to the potential introduction of additional impurities. Therefore, a new alkaline cleaning solution based on citric acid (CA) was proposed to improve the removal efficiency of BTA. Results exhibit that the cleaning efficiency of BTA residues can reach 98.86% with 400 ppm tetraethyl ammonium hydroxide (TEAH) and 0.6 wt% CA (pH = 10.5). X-ray photoelectron spectroscopy (XPS) measurements show that the cleaning solution can coordinate with copper ions to break the ionization balance of Cu-BTA. In addition, the electronic properties and reaction sites on copper surface were determined by quantum chemical calculation and density functional theory (DFT). The theoretical analysis indicates that CA has hydroxyl and carboxyl functional groups, and its presence with TEAH can promote the complexation of Cu ions, which accelerates the breakage of Cu-BTA and the desorption of BTA from the copper surface.