stocker

A stocker is an automated high-density storage system in semiconductor fabs that stores, organizes, and retrieves FOUPs (Front Opening Unified Pods) containing wafers, functioning as the automated warehouse that buffers work-in-progress between process steps and manages the flow of material through the factory. Stockers are essential components of the automated material handling system (AMHS) that enables lights-out factory operation by eliminating manual wafer carrier transport. Stocker architecture includes: storage shelves (multi-level racking systems holding hundreds to thousands of FOUPs — typical stockers hold 200-1,000+ FOUPs organized on shelves accessible by internal robots), internal crane/robot (a high-speed retrieval mechanism — typically a stacker crane or gantry robot that traverses vertically and horizontally to pick and place FOUPs on shelves and I/O ports), input/output ports (interfaces where overhead hoist transport vehicles deliver and retrieve FOUPs — including conveyor-based load/unload ports for high throughput), and integrated controller (managing inventory, optimizing storage locations, and coordinating with the fab's manufacturing execution system and material control system). Stocker placement strategy: stockers are positioned throughout the fab at interbay locations (between major process bays) and intrabay locations (within process bays near tool groups), creating a distributed storage network that minimizes transport time between storage and process tools. Advanced stockers feature: nitrogen purge capability (maintaining inert atmosphere inside stored FOUPs to prevent native oxide growth and moisture absorption — critical for sensitive process steps), environmental monitoring (temperature, humidity, particle counts within the stocker), RFID tracking (automatic FOUP identification upon entry), seismic bracing (earthquake protection for the tall racking structures), and predictive analytics (optimizing FOUP placement based on anticipated process flow to minimize retrieval time). Stocker throughput is measured in FOUP moves per hour — modern stockers achieve 100-200+ moves per hour to support high-volume manufacturing.