Load locks are vacuum-compatible chambers that transition wafers between atmospheric and vacuum environments. Purpose: Allow wafers to enter vacuum process chambers without breaking vacuum. Cycle between atmosphere and vacuum. Operation cycle: Vent to atmosphere, open atmosphere door, load wafer, close atmosphere door, pump down to vacuum, open vacuum door, transfer wafer. Reverse for unload. Pump down time: Critical for throughput. Large chambers take longer. Optimized for fast cycling. Vacuum level: Pump to base pressure compatible with process chamber requirements (typically 10^-3 to 10^-6 Torr). Slit valves: Doors between load lock and adjacent chambers (atmosphere or vacuum). Sealed when closed. Heating/cooling: Load locks may include wafer heating or cooling stages. Condition wafer for process. Batch load locks: Some load multiple wafers at once to improve throughput. Outgassing: Must pump away gases released from wafer and carrier. May require extended pump time for some wafers. Materials: Vacuum-compatible materials (aluminum, stainless), sealed construction, vacuum pumping system.