wafer chuck

A wafer chuck is the component that holds the wafer in position and provides thermal control during CVD and other semiconductor processing. **Types**: **Electrostatic chuck (ESC)**: Uses electrostatic force to clamp wafer. No mechanical contact points. Dominant in modern tools. **Mechanical clamp**: Physical ring presses wafer edges. Older technology. Causes edge exclusion. **Vacuum chuck**: Vacuum channels hold wafer by suction. Common in lithography. **Heating**: Resistive heaters embedded in chuck body provide wafer temperature control. Zones for uniformity (center/edge). **Temperature range**: Room temperature to 700+ C depending on application and chuck material. **Material**: Aluminum (to ~400 C), AlN ceramic (to 700 C), graphite (higher temperatures). **Thermal uniformity**: Multiple heating zones controlled independently. Target <1% temperature variation across wafer. **RF function**: In PECVD/etch, chuck serves as electrode. RF power may be applied through chuck for bias. **Backside gas**: Helium between wafer and chuck improves thermal contact (see backside gas). **Lift pins**: Pins through chuck raise wafer for robot handoff. **Maintenance**: Chuck surface degrades over time. Cleaning and eventual replacement. **Wafer sensing**: Thermocouples or fiber optic sensors in chuck monitor temperature.