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.