Study on Effective Methods and Mechanism of Inhibiting Cobalt Removal Rate in Chemical Mechanical Polishing of GLSI Low-Tech Node Copper Film

Abstract

As the feature size of integrated circuits shrinks down to 20-14 nm and below, cobalt (Co) is identified as a suitable barrier layer material. Copper (Cu) has been widely used as the most basic interconnection metallic material for giant-large scale integrated circuits (GLSI). Cu film chemical mechanical polishing (CMP) has been changed from the traditional two-step polishing to one-step polishing. For Cu film CMP, the slurry having high removal rate selectivity for Cu to barrier material is required to obtain a stop-on-barrier characteristic, which requires the slurry to ensure rapid removal of Cu while ensuring the removal rate of Co close to zero. High removal rate of Co will lead to low removal rate selectivity of Cu and Co, which will further destroy the planarization effect of wafer surface and even lead to device failure. In this paper, several effective methods and mechanism for inhibiting Co removal rate in alkaline Cu film slurry were studied. The results show within a certain range reducing abrasive concentration, increasing the pH value of slurry, increasing the concentration of H2O2 and introducing appropriate corrosion inhibitor can significantly reduce the removal rate of Co, so as to meet the needs of industrial production. A desirable removal rate selectivity (212:1) for Cu to barrier material Co was obtained under the optimized slurry, which can meet the industrial demand. Besides, the surface quality of wafer after CMP are also satisfactory. Several effective methods of inhibiting Co removal rate obtained in this study can be used in fabrication devices of integrated circuits.