Wafer ID is a unique identifier laser-marked or encoded on each wafer for tracking throughout manufacturing. Purpose: Track individual wafer through all processing steps. Traceability for yield analysis and process control. Marking methods: Laser scribing: YAG laser marks alphanumeric code and barcode on wafer edge or front surface. Soft marking: Marks on non-device area, removed later or remains under die seal. Hard marking: Permanent marks on wafer edge or backside. Location: Usually in wafer edge exclusion zone, or dedicated ID area. Away from devices. Standards: SEMI standards specify format, location, and encoding. T7 and related standards. Reading: OCR (optical character recognition) readers at aligners and tools. RFID for some applications. Content: Fab code, lot number, wafer number, carrier slot. Encodes full traceability. Process tracking: Every tool records wafer ID with process data. Enables wafer-level analysis. Yield analysis: Correlate wafer ID to electrical test, defect data, and process history. Critical for fab intelligence.