An electrostatic chuck (ESC) wafer stage with a built-in thin acoustic emission (AE) sensor has been developed for in situ detection of anomalies around a wafer, such as wafer movement and micro-arc discharge. The thin AE sensor is made of aluminum nitride piezoelectric films and is installed on an ESC wafer stage. The built-in sensor has a detector less than 1 mm thick and can detect acoustic waves propagating through the wafer stage that are abruptly generated by the anomalies occurring during the plasma etching process. The sensor detects acoustic waves caused by wafer movement and micro-arc discharges with high sensitivity, and furthermore identifies these anomalies based on the frequency characteristics of the detected acoustic waves. The effectiveness of the ESC wafer stage has been clearly demonstrated. This in situ detection method is expected to contribute to improving production yield and overall equipment effectiveness in semiconductor manufacturing.