Modification of electrokinetic behavior of CeO2 abrasive particles in chemical mechanical polishing for shallow trench isolation

Ceria (CeO2) slurry stability and oxide-to-nitride Selectivity in the shallow trench isolation chemical mechanical polishing (STI CMP) process were manipulated with the modification of ceria surface potentials. The electrophoretic mobility Of CeO2 particles is strongly dependent oil suspension pH as well as ionizable acrylic polymer. With modification of surface potentials, the isoelectric point (pH(iep)) of ceria shifted toward acidic pH values. resulting in ail increasing negative surface potential at pH values between 5 and 7. This surface modification resulted in ail increase of oxide removal rate due to mutually repulsive electrostatic forces between modified CeO2 abrasive particle and SiO2 film. When modified ceria particles are dispersed at a pH near the pH(iep) of silicon nitride, where the surface potential of silicon nitride is minimal, the removal rate of nitride is sharply reduced and thus oxide-to-nitride selectivity is improved by a factor of roughly 1:50.