Photomask technology has attained feature sizes of about 50nm and below. Whereas the main feature size is still above 70-80nm at 20nm technology node recently reported e.g. by Toppan Printing Company as developed, assist features for this node are in the range of 50-60nm. One of the critical aspects of this technology development is the cleaning process. Processes are supposed to clean off contamination and particles down to a defect size of about 40nm and at the same time prevent damage to assist features in the same size range. Due to obvious trade offs between cleaning power and Feature Damage Probability (FPD), this task becomes tricky. Improvement of cleaning processes by raising the power of megasonic (MS) cleaning, or adjusting the speed and size of droplets for spray cleaning occurs at the expense of increased feature damage. Prolongation of physical cleaning steps does not necessarily leads to improvement of the cleaning as shown previously. Susceptibility to feature damage occurs predicatively according to dimension and orientation. This allows us to extrapolate a Feature Damage Limit (FDL) which approximates the smallest feature size for which a process has an acceptable probability of success. In a practical sense, the most advantageous approach seems to be to adjust the cleaning power to the maximum allowed by the FDP and then optimize to the lowest process time necessary to reach expected cleaning efficiency. Since there are several alternative physical cleaning principles, we have to pick the best one for a given application. At this point we have to raise the question of how to compare the cleaning efficiency of processes. The goal of this work is to provide a method for evaluation and comparison of cleaning efficiency between physical cleaning processes and demonstrate the method on an example. We will focus on comparing two physical cleaning processes 1MHz megasonic and binary spray process.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.