Mechanism of titanium–nitride chemical mechanical polishing*

During the preparation of the phase change memory, the deposition and chemical mechanical polishing (CMP) of titanium nitride (TiN) are indispensable. A new acidic slurry added with sodium hypochlorite (NaClO) as an oxidizer was developed for the CMP of TiN film. It has achieved a material removal rate of 76 nm/min, a high selectivity between TiN and silica (SiO2) films of 128:1, a selectivity between TiN and tungsten films of 84:1 and a high surface quality. To understand the mechanism of TiN CMP process, X-ray photoelectron spectroscope and potentiodynamic polarization measurement were performed. It was found that the mechanism of TiN CMP process is cyclic reaction polishing mechanism. In addition, both static corrosion rate and the inductively coupled plasma results indicate TiN would not be dissolved. Which means that the mechanical removal process of oxide layer plays a decisive role in the material removal rate. Finally, the mechanism of TiN polishing process is given based on the analysis of surface potential and the description of blocking function.