rework

Rework is reprocessing failed wafers or devices to recover yield — stripping and redoing defective layers or steps, typically recovering 50-90% of failures, but adding cost and cycle time, making prevention preferable to rework.

What Is Rework?

• Definition: Reprocessing to fix defects and recover yield.
• Methods: Strip and redo layers, laser repair, reprogramming.
• Recovery: 50-90% of reworked units can be recovered.
• Cost: Adds processing cost and cycle time.

Why Rework Matters

• Yield Recovery: Salvage value from failed wafers/devices.
• Cost: Cheaper than scrapping but more expensive than first-pass success.
• Cycle Time: Adds days or weeks to manufacturing flow.
• Capacity: Consumes equipment capacity.

Common Rework Types

• Photoresist Strip/Redo: Fix lithography defects.
• Metal Strip/Redeposit: Fix metal layer defects.
• Laser Repair: Fix memory bit failures with redundancy.
• Reprogramming: Fix soft errors in non-volatile memory.

Economics: Rework is economical when recovery value exceeds rework cost, typically for expensive wafers or late-stage failures.

Best Practice: Minimize rework through defect prevention and first-pass quality (high FPY).

Rework is yield recovery — salvaging value from failures, but prevention through robust processes is always preferable to rework.