di water (deionized water)

DI water (deionized water) is ultra-pure water with ions removed, used extensively for wafer cleaning, rinsing, and chemical dilution. **Purity level**: 18.2 megohm-cm resistivity (theoretically pure). Measured continuously. **Ion removal**: Multi-stage process - RO (reverse osmosis), then ion exchange (mixed bed), then electrodeionization (EDI), then polishing. **Uses in fab**: Wafer rinsing after wet processes, chemical dilution, tool cleaning, CMP slurry makeup, humidification. **Quality parameters**: Resistivity, TOC (total organic carbon), particles, bacteria, silica, dissolved oxygen. **Point of use**: Final polishing at tool to ensure maximum purity at wafer surface. **Contamination sources**: Piping, storage, ambient exposure. Must minimize residence time. **System components**: RO units, DI tanks, circulation pumps, UV sterilizers, filters, resistivity monitors. **Consumption**: Modern fabs use millions of gallons per day. Major utility. **Environmental**: Wastewater from DI production requires treatment before discharge. **Criticality**: DI water quality directly affects device yield. Tight specifications enforced.