No abstract

The contamination behavior of ceria particles (50 and 100 nm) with oxide surfaces at pH 4 and 8 was studied using dipping and polishing conditions. Higher contamination at pH 4 than pH 8 was observed for dipping cases. In contrast, pH 8 conditions produced higher contamination than pH 4 for polishing cases. The difference in the contamination between dipping and polishing could be attributed to electrostatic attraction and chemical bonding. During polishing, weak or no chemical bonding may occur at pH 4, whereas the Ce–O–Si bond may form due to the surface charges of ceria and silica at pH 8. XPS analysis revealed that strong additional peaks related to Ce–O–Si bonding were detected for O 1s spectra at a binding energy of around 532 eV for surfaces polished at pH 8. Similar results were observed for 50 nm as well as 100 nm ceria particles. Based on the results, we concluded that ceria particles would have different adhesion behaviors for dipping and polishing at the same pH value. Also, higher ceria adhesion was observed at higher pH compared to lower pH during the CMP process, which was correlated to strong Ce–O–Si chemical bond formation due to the CMP conditions.

Ceria removal during STI post-CMP cleaning has become a significant concern to the semiconductor industries. Understanding of ceria adhesion and removal mechanisms is very important. In this work, ceria slurries at pH 4 and pH 8 were used to polish oxide surfaces. Their adhesion behavior was affected by the pH of the slurry and the removal behavior was varied as a function of cleaning methods and chemistry used. Different physical cleaning (megasonic and PVA brush) methods and chemical cleaning (SC1, SPM, DHF) methods were compared. During polishing, the particles may attach to the oxide surface electrostatically at pH 4 and through Ce-O-Si bonds at pH 8 conditions. It was found that electrostatically attached particles could be easy to remove whereas Ce-O-Si bonded particles could be removed by strong acidic chemistry such as SPM or DHF.