Study on the Mechanism of Nano-Flake Defect during Tungsten Contact Chemical Mechanical Polishing

摘要

Tungsten chemical mechanical polishing (CMP) has been used for metal interconnect formation in semiconductor manufacturing for a long time. Its application continues to the advanced device manufacturing with transistor scaling. However, the defect concerns of the tungsten CMP process have become critical to manufacturing such as metal flake defects that can cause electrical shorts between contacts. Although there are many published studies on tungsten CMP fundamentals, process applications and CMP-induced defects, the mechanism of thin metal flake formation in nanoscale (nano-flake defect) has not been clearly known to industry. In this study, nano-flake defects are identified after tungsten contact CMP, and mechanism of its formation is explored. Significant CMP dishing at wide contact area removes all tungsten and open barrier metal. Friction force by 3-body interaction among wafer, abrasive particle and pad asperity breaks the adhesion of barrier material from intermetallic dielectric material. And it allows re-deposition of barrier metal to the wafer surface. Insufficient CMP in-situ cleaning results in residual nano-flake defects at the end of CMP process. Analysis of device macros, thickness of flake, cross sectional analysis by transmission electron microscope (TEM) and topographical analysis support this suggested mechanism. (C) 2018 The Electrochemical Society.