lot

A lot in semiconductor manufacturing is a group of wafers that are processed together as a unit through the fabrication sequence, serving as the fundamental unit of production tracking, scheduling, and quality control. The lot concept provides a practical framework for managing the thousands of process steps required to manufacture integrated circuits, enabling batch tracking, statistical process control, and efficient fab scheduling. Lot characteristics include: lot size (typically 25 wafers for 300mm fabs — matching FOUP capacity, and 25 or 50 wafers for 200mm fabs — matching cassette capacity), lot identity (unique lot ID assigned at wafer start and tracked through every process step via the manufacturing execution system), and lot type (production lots for customer orders, engineering lots for process development, qualification lots for tool certification, monitor lots for process monitoring, and hot lots for expedited priority processing). Lot tracking through the fab records: every process step performed (recipe, tool, chamber, time, operator), inline measurement results (film thickness, CD measurements, defect counts, overlay), lot hold and release events (engineering dispositions for out-of-spec measurements), and lot genealogy (split and merge operations when lots are combined or divided). Lot operations include: lot start (new wafers entering the fab), lot split (dividing a lot for parallel processing experiments or to separate good/bad wafers after wafer sort), lot merge (combining split lots back together), lot scrap (removing defective wafers — tracked for yield analysis), and lot hold (pausing processing for engineering investigation). Lot-based manufacturing has evolved toward more flexible approaches: some advanced fabs use single-wafer tracking (each wafer tracked individually rather than as part of a lot) for tighter process control and adaptive processing where recipe parameters are adjusted wafer-by-wafer based on upstream measurements. Lot priority schemes (hot lots running at 2-3× normal velocity through the fab) enable rapid learning cycles but disrupt normal production flow.