Understanding the Formation of Circular Ring Defects in Post-CMP Cleaning

Ring type defects are considered to come from scratches by large particles or agglomerated particles during brush scrubbing process on wafers in Post Cu CMP (chemical mechanical polishing) cleaning [1]. However, the mechanism for circular ring defects to appear on wafers still remains a puzzle. Our studies indicated that pH variation during the PCMP process might have a significant effect on altering the surface charge and triggering particle agglomeration. The extent and distribution of particle agglomeration were theoretically and experimentally investigated by zeta potential and particle size analyzer. The results from these studies can provide framework for formulation development to reduce or eliminate ring type defects after PCMP process and improve device yield and performance.