Extending Ru capping layer durability under physical force cleaning

Abstract

Physical force wet cleaning technologies (MegaSonic & Droplet Spray) are considered the supreme challenge in 193i reticle cleaning due to smaller critical dimension, high feature aspect ratio, and sensitive interfaced fragile features. However this was not considered equally challenging in EUV masks. Recently, MegaSonic cavitation has been linked to Ru (capping layer) pitting issues; making the use of acoustic based cleaning questionable for EUVL reticles. Nevertheless, acoustic energy is necessary to remove particles trapped in deep and congested trenches. This strengthens the need to control the physical force energy within the damage free regime even further. In this study we have investigated method to control MegaSonic cavitation as well as established a link between pattern damage observed in optical mask and Ru pitting in EUV masks. Effect of different cleaning chemistries typically used in mask cleaning is compared with a new cleaning chemistry (referred to as chemical A). A new POR (Process of Record) based on chemical A is qualified and its effects on PRE, absorber CD and EUV-reflectivity are discussed.