Fundamental phenomena affecting the cleaning process have been studied for 65 nm Si3N4 particles, where 300 mm p-type Czochralski silicon wafers are used. The removal ratio of particles is similar to 0.05 by the conventional mixed cleaning process, which employs NH4OH:H2O2:H2O=1:2:50 (APM) with pH 9.2. Most particles are firmly reattached to the surface after the etching is finished because particles are attractive to the surface. When higher ultrasonic power is applied for removal of particles, peeling occurs at a high ratio in 34 nm wide patterns. However, a higher removal ratio can be attained by utilizing a sequential cleaning process. After etching of the surface in APM, removal of floating particles is performed in highly alkaline media without including APM. Because higher repulsive forces are formed in this highly alkaline media, the removal ratio increases to 0.93 at ultrasonic powers of 1.0 W/cm(2). Peeling is not a serious problem at this power. (C) 2008 The Electrochemical Society.