Visualization experiments are performed to examine the role of acoustic cavitation bubbles that appear in 0.43-MHz ultrasonic water flow spreading over glass surfaces in the context of physical cleaning. The cleaning performance is evaluated using glass samples on which small silica particles are spin-coated. The visualization suggests that acoustic cavitation bubbles play a major role in particle removal as in the case of conventional cleaning with ultrasonic cleaning baths.

Cleaning tests with ultrasound-superposed water jets are performed to explore the optimal injection distance from the jet nozzle to a glass plate spin-coated with small silica particles (as a cleaning sample). The cleaning performance is evaluated based on particle removal efficiency (PRE) that is calculated using the haze method. Visualization of the water jet and liquid film flow over the cleaning target shows that the jet flow with short injection distance tends to be in a steady state, while the water jet shape instability grows for long injection distance, leading to atomization of the jet. The cleaning tests with varying the injection distance suggest that there exists an optimal injection distance at which the PRE becomes maximal.

The process of quickly removing abrasive particles of silica and ceria slurries is important in the use of CMP equipment. Megasonic cleaning of nozzle injection type is one of a variety of post-CMP cleaning methods and its performance including cleaning efficiency and erosion was explored experimentally with parametric studies. In the cleaning process, it is favorable to achieve both high efficiency and low damage. The cleaning efficiency was defined by particle removal efficiency (PRE) with a glass sample spin-coated with small silica particles; the damage was detected from mass loss of aluminum foils after the cleaning. The cleaning tests show that the performance of nozzle injection megasonic cleaning depends significantly on ultrasound frequency and water temperature. Toward more efficient and less erosive cleaning, the nozzle injection angle is also expected to play a key role.