yield excursion
**Yield Excursion** is a sudden, unexpected drop in manufacturing yield below historical baselines, indicating a process problem requiring immediate investigation.
## What Is a Yield Excursion?
- **Definition**: Yield drops >3σ below historical mean
- **Duration**: May affect single lots or persist for days/weeks
- **Root Causes**: Equipment drift, contamination, material variation
- **Response**: Stop production, quarantine affected lots, investigate
## Why Yield Excursion Response Matters
Every hour of delayed response multiplies affected wafers. Fast detection and root cause analysis minimize financial impact ($100K+ per hour in modern fabs).
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**Excursion Investigation Steps**:
1. Split data by equipment, chamber, recipe
2. Check inline metrology trends
3. Review PM logs and part changes
4. Compare defect signatures to known patterns
5. Run DOE to confirm hypothesis