In this work the damage added on gate stack features after batch megasonic cleaning is identified and classified by SEM review. To understand if damaging is a random or a clustered process, damage clustering distributions are compared with a theoretical random distribution of damage sites. In the damaged areas, defect clusters are observed that we explain by the presence of so-called weak spots in the neighborhood of a damaging event. Only a limited influence of the megasonic cleaning settings was found on the damage-size distributions. This suggests that, for the cleaning conditions investigated in this work, the number of added defects varied with the amount of the damage events but the event strength remains the same.