5-Phenyl-1-H-Tetrazole as a Low-pH Passivating Agent for Copper Chemical Mechanical Planarization

The introduction of porous low-k dielectric materials into semiconductor devices requires the development of low downforce Cu chemical mechanical planarization (CMP). An alternative passivation agent, 5-phenyl-lH-tetrazole (PTA), is proposed here that is effective at lower pH than the traditional CMP passivation agent, benzotriazole (BTA). PTA has previously been reported as a low-pH Cu corrosion inhibitor, but has not been explored for Cu CMP. Cu CMP removal rates and Cu static etch rates are measured for slurries containing 3 wt % H 2 O 2 , 1 wt % glycine, 3 wt % colloidal silica, and PTA concentrations ranging from 0.5 to 3 mM. At pH 3 and PTA concentrations of 0.5-2 mM, PTA provides both effective passivation and Cu removal rates of > 1400 nm/min. Fourier transform-infrared and electrochemical studies are consistent with the formation of an effective passivation layer on Cu in CMP slurries containing PTA concentrations ranging from 0.5 to 2 mM, with the effectiveness of passivation increasing with PTA concentration. The improved low-pH passive film formation for PTA in Cu CMP slurries relative to BTA is most likely due to its much lower pKa (4.3), with a much larger fraction of PTA in the anionic form at low pH.