Bond pad F-crystal defect control and monitoring

Bonding pad crystal defect was observed on wafers before die saw. To eliminate and monitor the defect, a study was conducted to investigate the effect of humidity and packaging materials (packaging sponge and lint free paper material) on pad crystal defect generation. Ionic content specification of packaging sponge material was defined through the study. A setup for routine monitoring of pad crystal defect was constructed and implemented in wafer fabrication. The pad crystal defects were F rich. Humidity (>55%) was found to be an effective acceleration factor of the defect. With a 70% humidity stress test, a F content limit of 400 ppb in packaging sponge material was concluded to prevent defect generation. Air non-permeable lint free paper was found to provide further protection of the wafers from pad crystal defect.