scrap rate

**Scrap rate** is the **percentage of wafers discarded due to defects or process failures** — representing total loss with no recovery possible, typically <5% for mature processes, with high scrap rates indicating serious process or equipment problems requiring immediate attention. **What Is Scrap Rate?** - **Definition**: (Scrapped wafers / Total wafers) × 100%. - **Typical**: <5% for stable processes, <1% for mature. - **Impact**: Complete loss of wafer value and processing cost. - **Causes**: Catastrophic defects, equipment failures, handling damage. **Why Scrap Rate Matters** - **Cost**: Total loss of wafer and all processing costs. - **Capacity**: Scrapped wafers reduce effective output. - **Process Health**: High scrap indicates serious problems. - **Yield Impact**: Scrapped wafers don't contribute to yield. **Common Causes** - **Equipment Failure**: Tool malfunctions causing wafer damage. - **Process Excursion**: Parameters out of spec, unusable wafers. - **Contamination**: Severe contamination requiring scrap. - **Handling**: Wafer breakage, severe scratches. - **Metrology Failure**: Wafers outside measurement limits. **Prevention**: Robust equipment maintenance, process control, and handling procedures minimize scrap rate. Scrap rate is **the worst yield loss** — complete write-off with no recovery, making scrap prevention a top priority for manufacturing efficiency.