Selectivity enhancement in the removal of SiO2 and Si3N4 films with addition of triethanolamine in a ceria slurry during shallow trench isolation chemical mechanical polishing

Abstract

Effects of the triethanolamine (TEA) concentration in a ceria slurry oil the removal rates and the removal selectivity of SiO2 and Si3N4 films were investigated by performing shallow trench isolation chemical mechanical polishing (STI-CMP). At a higher concentration of TEA in the polishing slurry, the removal rate of the Si3N4 film significantly decreased while maintaining a high removal rate of the SiO2 film with a high removal selectivity of the SiO2-to-Si3N4 films during the CMP process. We found that the adsorption behavior between TEA and the surface of the Si3N4 film was determined by the electrokinetic behavior, where the zeta-potential measurement depended oil the suspension's pH. Adsorption results demonstrated that as the TEA concentration was increased, the force of attraction between negatively charged hydroxyl groups along the backbone of the TEA and the surface of the Si3N4 film Was enhanced due to all electrostatic attraction force. Through these reactions, the zeta potential of the Si3N4 film's surface became more positive because of the amine functional group of TEA in the slurry. In addition, with increasing zeta potential of the Si3N4 film, a denser passivation layer was formed oil the Si3N4 film with an anionic surfactant, which led to suppression of the removal of the Si3N4 film with a higher SiO2-to-Si3N4 removal selectivity in the STI CMP.