Novel Process Control with Differentiating STI Micro-scratches leading to Faster Root Cause Analysis

Substantial yield lost was caused by STI micro-scratches. These intermittent micro-scratches excursion was first detected as out of control (OOC) for total defect density (TDD) trend. Total defects were sampled and reviewed to further differentiate micro-scratches from other defects as represented by normalized defect density (NDD) trend. However, NDD excursion did not correlate well to CMP issues alone. Detailed analysis from scanning electron microscope (SEM) review revealed that there are two distinct types of micro-scratches originated from different root causes. Process control based on these two types of micro-scratches was implemented by differentiating these micro-scratches in NDD trend. Faster root cause analysis resulted and the methodology could potentially extend to other types of micro-scratches. In-line correlation showed that micro-scratches was originated from chemical mechanical polishing (CMP) tool, whereas micro-scratches correlates strongly to the upstream rapid thermal process (RTP) STI liner after poly trench etch. Further investigation revealed that TYPE A defects most likely caused by slurry drying; while TYPE B defects was caused by silicon oxide particles generated during growth of STI liner resulted from pre-matured failure of bearings from RTP chambers. These particles were embedded during subsequent gap-fill process but emerged during STI CMP providing as a source to create micro-scratches. Short term solution was implemented for the pre-matured failure of bearings with significant yield recovery and long term solution is currently in beta-testing.