Chemical Interactions and Mechanisms of Different pH Regulators on Copper and Cobalt Removal Rate of Copper Film CMP for GLSI

As the feature size of integrated circuits (ICs) shrinks down to 14nm and below, Cobalt (Co) is identified as a suitable barrier layer material. Copper (Cu) has been widely used as the most basic interconnection metallic material for Giant-large scale integrated circuits (GLSI). A higher removal rate (RR) selectivity between Cu and Co is desired to obtain in copper film chemical mechanical polishing (CMP) because the traditional three-step polishing is replaced by two-step polishing of copper and barrier under lower technology nodes. The purpose of copper film polishing is to achieve effective removal of Cu and ultimately stop on the layer of Co. The pH value of slurry is a critical factor affecting the material removal rate and the stability of the slurry. The influence of different kinds of pH regulators and different pH values on the removal rates and the stability of slurries were investigated in this paper. Three pH regulators were chosen in the experiments, containing macromolecular chelating agent FA/OII as organic alkali, KOH as inorganic alkali and KOH mixed with a small amount of tetraethyl ammonium hydroxide (TEAH, C8H21NO) as mixed alkali. According to the investigation of removal rate results and stability experiments results, 10.5 was identified as a suitable pH value and a relatively higher removal rate selectivity was obtained. Meanwhile, using the mixed alkali to adjust slurry pH value can effectively increase the selectivity of Cu and Co and the stability of the copper slurry. The adsorption of TEAH on Cu and Co surface was considered as the critical reason relating to the slight removal rate decline, which was verified by XPS measurements.