Chemical-mechanical planarization of copper/tantalum for microelectronic applications

With copper emerging fast as the interconnect metal and with CMP becoming the only viable technique to inlay copper, various aspects of copper CMP were investigated in this work. Mechanical aspect of copper CMP was investigated by polishing copper in the absence of slurry chemicals with alumina particles of various bulk densities. It was observed that the copper polish rate increased significantly above a certain threshold bulk density which correlated with the measured nano-hardness of the material being polished. The chemical aspect of copper CMP was investigated by measuring the copper dissolution rate in ferric nitrate, ammonium persulfate, and hydrogen peroxide. Copper does not passivate in ferric nitrate and ammonium persulfate and dissolves readily in both the chemistries. An inhibitor, benzo triazole (BTA), was used to minimize the isotropic dissolution. Unlike ammonium persulfate and ferric nitrate, hydrogen peroxide was found to passivate copper surface.; Chemical-Mechanical aspect of copper CMP was studied by polishing copper in ferric nitrate and ammonium persulfate with and without added BTA and in hydrogen peroxide using alumina particles of various bulk densities. In the absence of BTA, the overall polish rate in ferric nitrate was the sum of chemical and mechanical removal rates. In the presence of BTA, the Cu-BTA inhibition layer decreased the copper dissolution rate and, hence, the polish rate. In the case of hydrogen peroxide based slurries, the polish rates were lower than DI water rates due to the formation of a harder oxide film on the copper surface.; The effect of pressure and velocity on copper polish rate was determined in DI water and in the presence of several slurry chemistries with alumina particles as the abrasives. Copper CMP in DI water followed the Preston equation. However, an empirical model, R = KPV + BV + R_c, where K, B, and R_c are constants, was used to describe the polish rate data in the presence of slurry chemicals.; Since copper integration requires a barrier layer (Ta/TaN), various aspects of Ta CMP were also investigated. Ta polish rate showed a significant variation with the pH of the slurry. For polishing in DI water, the variation in polish rate with pH was attributed to the electrostatic interactions between the particles and the tantalum surface.