Investigation of the effect of different cleaning forces on Ce-O-Si bonding during oxide post-CMP cleaning

Abstract

Ceria removal during the STI post-CMP cleaning process has recently become a serious concern to the semiconductor industries. It is known that ceria forms a strong Ce-O-Si bonding with the oxide surface that causes the difficulty in ceria removal. In this study, the bond formation and their removal were studied by polishing the oxide surface at pH 4 and pH 8 conditions, i.e. the pH of commercially formulated slurries. Ceria removal mechanisms were investigated through the use of different physical cleaning methods (megasonic and brush scrubbing) and chemical cleaning solutions such as standard cleaning solution 1 (SC1, a mixture solution of NH4OH, H2O2 and H2O), sulfuric acid, and hydrogen peroxide mixture (SPM), and diluted HF (DHF). It was found that ceria particles were removed easily at pH 4 polishing conditions as the electrostatic attraction is dominant than Ce-O-Si bond formation. However, at pH 8 conditions, particles were not removed due to strong bond formation. Only DHF and SPM cleaning conditions were able to remove the ceria particles due to the strong undercutting of oxide and dissolution of ceria particles, respectively. SPM could be the better choice as DHF would cause the surface roughness issues.