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.