Patent ID: 8449684

Claim:
A substrate cleaning system comprising: a cleaning tank that contains a cleaning liquid and accommodates a semiconductor wafer in an upstanding position therein; an ultrasonic generator that generates ultrasonic waves in the cleaning liquid contained in the cleaning tank from below the upstanding semiconductor wafer; a cleaning liquid supply system that supplies the cleaning liquid whose dissolved gas concentration is adjusted to a desired concentration into the cleaning tank; and a control device configured to control the cleaning liquid supply system and the ultrasonic generator such that: the control device causes the cleaning liquid supply system to supply the cleaning liquid into the cleaning tank at a first supply rate in order to fill the tank and adjust a dissolved gas concentration in the liquid to a predetermined value before a semiconductor wafer is immersed in the cleaning liquid within the tank, after the semiconductor wafer is immersed in the tank and maintained in the upstanding position, the control device causes the ultrasonic wave generator to begin generating ultrasonic waves in the cleaning liquid while causing the cleaning liquid supply system to reduce, in a stepwise or stepless manner, the supply rate of the cleaning liquid from the first supply rate to a second supply rate that is less than the first supply rate and greater than zero; thereafter, the control device causes the ultrasonic wave generator to continue generation of ultrasonic waves in the cleaning liquid while causing the cleaning liquid supply system to continue supply of the cleaning liquid at the second supply rate so that cleaning liquid overflows from the tank through an open upper end of the tank; and thereafter, the control device causes the ultrasonic wave generator to continue generation of ultrasonic waves in the cleaning liquid while causing the cleaning liquid supply system to reduce, in a stepwise or stepless manner, the supply rate of cleaning liquid from the second supply rate to a third supply rate that is less than the second supply rate.