A dummy wafer is a blank or non-product wafer used to fill empty slots in batch processing equipment or stabilize process conditions during single-wafer processing. Purpose in batch tools: LPCVD and diffusion furnaces require full loads for uniform gas flow and temperature distribution. Empty slots cause non-uniformity. Dummy wafers fill unused positions. Purpose in single-wafer tools: Some tools process several dummy wafers before product to stabilize chamber conditions (seasoning, thermal equilibration). Types: Bare silicon wafers, oxide-coated wafers, or previously processed wafers. Quality requirements lower than product wafers. Seasoning: After chamber cleaning or maintenance, dummy wafers processed to coat chamber walls with target film, reducing particle shedding from bare chamber surfaces. Cost control: Dummy wafers are reused multiple times until film buildup or contamination requires replacement. Tracks usage count. Thermal stability: In furnaces, dummy wafers at front and back of boat stabilize temperature for product wafers in the middle. Equipment protection: Some processes require wafer on chuck for proper RF coupling or to protect chuck surface. Dummy wafer serves this role when no product available. Inventory management: Fabs maintain inventory of dummy wafers by type. Automated wafer handling systems track dummy wafer locations and usage. Contamination risk: Heavily used dummy wafers can outgas contaminants. Replacement schedules prevent cross-contamination to product wafers. Reclaim: Used dummy wafers periodically reclaimed (re-polished) to extend useful life.