Batch tools process multiple wafers simultaneously in a single run, providing high throughput for processes where uniformity across many wafers can be maintained. Types: (1) Horizontal furnaces—legacy, wafers loaded horizontally into quartz tube; (2) Vertical furnaces—modern, wafers stacked vertically in quartz boat (100-150 wafers); (3) Wet benches—chemical processing of multiple wafers in baths (25-50 wafers per carrier). Vertical furnace processes: thermal oxidation, LPCVD (Si₃N₄, poly-Si, TEOS oxide), diffusion (dopant drive-in), anneal. Batch advantages: very high throughput (amortize process time over many wafers), excellent uniformity achievable with proper gas flow and temperature control, lower cost per wafer for suitable processes. Batch disadvantages: long cycle times (hours for furnace), large lots-in-process, difficult to implement wafer-to-wafer APC, single wafer failure risk affects entire batch. Uniformity control: gas injector design, rotation, temperature zone control, boat position optimization. Loading effects: pattern-dependent depletion requires spacing and recipe optimization. Wet bench types: overflow rinse, quick dump rinse (QDR), megasonic cleaning, chemical etch baths. Transition trend: many processes moving from batch to single-wafer for better control at advanced nodes, but batch tools remain essential for high-volume thermal processes where uniformity and throughput justify batch approach.