Investigation of the barrier slurry with better defect performance and facilitating post-CMP cleaning

Abstract

It becomes very critical for yield enhancement to accomplish defect free global planarization during barrier CMP. Conventional commercial barrier chemical mechanical polishing (CMP) slurries usually contain benzotriazole (BTA) and oxidizer (most frequently H2O2) which could cause organic defects and oxide particles on the copper surface for post-CMP cleaning. In this paper, we present a kind of weakly alkaline barrier slurry with lower defect occurrence than conventional ones, and a key feature of the slurry is facilitating post-CMP cleaning. The experimental results obtained from the defect map show it is hard for a simple cleaning solution containing nothing but deionized water and surfactants to completely remove oxide particles and the organic residue on the wafer surface polished with the commercial barrier slurry. On the contrary, the defect map of the wafer polished with the weakly alkaline barrier slurry indicates that there is no surface contamination after cleaning with this simple cleaning solution, but there are still many defects. AFM (atomic force microscopy) graphs demonstrate these defects are scratches, and the tool views them as defects. The polishing results indicate that the root causes for scratches are the large particles exceeding 0.5μm size in the slurry, and micro-scratches are remarkably reduced after installation of a 0.2μm size filter without affecting the CMP performance, including dishing, resistance, capacitance and leakage current. Compared with the conventional commercial barrier CMP slurry, the alkaline barrier slurry can also control copper line corrosion due to galvanic reaction.