Methods and apparatus for cleaning substrates

An apparatus for cleaning a semiconductor wafer comprising features of patterned structures, the apparatus comprising:

• a wafer holder configured to hold the semiconductor wafer;
• an inlet configured to apply liquid on the semiconductor wafer;
• a transducer configured to deliver acoustic energy to the liquid;
• a power supply of the transducer;
• and
• a controller for the power supply comprising a timer, the controller being configured to control the transducer based on the timer to:
• deliver acoustic energy to the liquid at a first frequency and a first power level for a predetermined first time period, wherein sizes of bubbles inside the features increase during the first time period, and
• deliver acoustic energy to the liquid at a second frequency and a second power level for a predetermined second time period, wherein sizes of bubbles inside the features decrease during the second time period,
• wherein the controller is configured to alternately apply the first and second time periods one after another for a predetermined number of cycles.

A controller for a power supply of a transducer comprising a timer, the controller being configured to control the transducer based on the timer to:

• deliver acoustic energy to liquid applied on a semiconductor wafer at a first frequency and a first power level for a predetermined first time period, wherein sizes of bubbles inside features of patterned structures of the semiconductor wafer increase during the first time period;
• and
• deliver acoustic energy to the liquid at a second frequency and a second power level for a predetermined second time period, wherein sizes of bubbles inside features decrease during the second time period,
• wherein the controller is configured to alternately apply the first and second time periods one after another for a predetermined number of cycles.