Post-CMP Cleaning Solutions for the Removal of Organic Contaminants with Reduced Galvanic Corrosion at Copper/Cobalt Interface for Advanced Cu Interconnect Applications

Abstract

It has been difficult to remove BTA-related organic residues (BTA, Cu-BTA, and Co-BTA complexes) and silica abrasives from various surfaces during post Cu-CMP cleaning when Co is used as the liner. Here, we investigated the adsorption of these residues and their removal from Cu, Co, TaN and SiO2 films for Cu interconnect applications. A 50 mM aqueous solution of ethylenediamine (En) at pH 11, aided by ultrasonic agitation, almost completely removed these contaminants adsorbed on only Cu and Co films. Cleaning was facilitated by the much higher stability constants of Cu-En/Co-En complexes compared to those of Cu-BTA/Co-BTA complexes, which led to their dissociation via ligand exchange. En also lowered ΔEcorr of the Cu/Co couple to ∼40 mV but their Icorr values remained high. Cysteine (Cys) and uric acid (UA) were effective in controlling the cathodic and anodic reactions of Cu and Co films. An aqueous mixture of 0.75 mM Cys, 9.25 mM UA and 50 mM En at pH 11 not only removed the organic residues and silica particles from Cu and Co films but also lowered ΔEcorr between them to ∼5 mV with an Igc of ∼0.7 μA/cm2, acceptably low Icorr values for both films with excellent surface quality.