Impact of MegaSonic process conditions on PRE and sub-resolution assist feature damage

The use of MegaSonic energy is widely accepted in photomask cleaning. For the advanced technology nodes, beyond 65nm, the problem of damaged sub resolution assist features (SRAF) becomes highly prevalent. Such feature damages are often related to the application of MegaSonic energy. We investigated the influence of common cleaning media and MegaSonic parameters for damaging SRAF patterns. A special option of our cleaning tool was utilized to test a large number of different settings with low resources for test mask and defect inspections. In this paper we will present the results of our investigations and present conditions for MegaSonic cleaning which will enable the wide use of this technology beyond the 45nm technology node.