Cleaning apparatus, measurement method and calibration method

An apparatus for cleaning a substrate comprising:

• a cleaning tank configured to hold a cleaning liquid for cleaning the substrate;
• an ultrasonic generating unit configured to irradiate the cleaning liquid with ultrasonic waves, the ultrasonic generating unit being connected to the cleaning tank via a medium capable of transmitting the ultrasonic waves to the cleaning liquid in the cleaning tank;
• a luminescence intensity measuring device configured to measure, as a measured value, an intensity of luminescence produced when the cleaning liquid is irradiated with the ultrasonic waves;
• and
• a processing unit configured to derive a concentration of the gas dissolved in the cleaning liquid from the measured value and a predetermined correlation between the concentration of the gas dissolved in the cleaning liquid and the intensity of the luminescence.