Electrochemical Mechanical Polishing of Copper with High Permittivity Abrasives

Abstract

Electro-Chemical Mechanical Polishing (ECMP) is a promising low-pressure copper planarization method for the interconnection containing low-k material. ECMP utilizes anodic dissolution of copper to raise the material removal rate. However, the surface roughness is usually not acceptable in ECMP because the selective removal ability of electrochemical dissolution is poor. Different permittivity abrasives have different influence on surface quality in ECMP. High permittivity abrasives can enhance selective removal ability to get better polishing results through aggrandizing the potential drop in electrode/electrolyte interface. In this article, three abrasives with different permittivity are compared using polishing experiments. The results show that rutile TiO₂, permittivity of which is larger than anatase TiO₂ and SiO₂, gets the best surface quality among the three abrasives. The composition of electrolyte with rutile TiO₂ was also optimized to improve polishing performance. The chosen electrolyte contains 0.5 mol/L glycine, 0.1 mol/L TSA, 1 wt% rutile TiO₂. The material removal rate got by using this electrolyte is 0.06 mg/min and the surface roughness is Ra8.9 nm.

Keywords:

• Abrasives
• CMP
• Copper
• ECMP
• Electrochemistry
• Permittivity
• SiO₂
• TiO₂