Experimental investigation of the mechanism for CMP micro-scratch formation

CMP (chemical mechanical planarization) micro-scratches are yield and reliability limiting defects in semiconductor production. Electrical shorts, between vias or metal lines, are the most likely failure modes. As device geometries decrease, the probability of a micro-scratch causing a device failure increases. Therefore, understanding of the mechanisms involved in micro-scratch formation becomes increasingly important for good yield and reliability. A mechanism for the formation of micro-scratches and the experimental results in support of the mechanism are presented. It is proposed that micro-scratches are caused primarily by slurry particles that pack into the polish pad fibers during polish (glazing). Once packed into the pad, the silica particles agglomerate. This is especially true if the silica particles are exposed to pH less than ten at the end of the polish or in between polishes. During ex-situ pad conditioning, the agglomerated silica is fractured and loosened from the pad fibers but not removed from the pad surface. The fractured pieces of silica cause micro-scratches, as they break apart during the first few seconds of polish. The experimental data fully support this mechanism. Based on this mechanism, process changes were made producing an order of magnitude reduction in micro-scratch related failures.