root cause analysis (rca)

Root Cause Analysis (RCA) is a systematic investigation methodology to identify the fundamental underlying cause of defects, failures, or process excursions, not just symptoms. **Methodology**: Multiple structured approaches used: **5 Whys**: Repeatedly ask why until root cause reached. Simple but effective for straightforward problems. **Fishbone (Ishikawa) diagram**: Categorize potential causes by Man, Machine, Material, Method, Measurement, Environment. **8D problem solving**: Disciplined 8-step process from team formation through permanent corrective action. **Data analysis**: Correlate defect data with process parameters, tool history, material lots, time, and operator data to identify patterns. **Pareto analysis**: Rank potential causes by frequency or impact. Focus on top contributors. **DOE**: Design of Experiments to systematically test hypotheses about cause-effect relationships. **Timeline analysis**: Reconstruct sequence of events leading to problem. Identify what changed. **Common root causes in fab**: Equipment degradation, preventive maintenance gaps, chemical quality variation, recipe errors, environmental excursions, design marginality. **Cross-functional**: RCA often requires expertise from process, equipment, metrology, yield, and quality teams. **Corrective action**: Fix the root cause, not just the symptom. Implement preventive measures to avoid recurrence. **Verification**: Confirm that corrective action resolves the problem. Monitor for recurrence. **Documentation**: Full RCA report with evidence, analysis, root cause, corrective action, and verification results.