Onset of material alterations and damage -free nanoparticle removal utilizing laser induced plasma for nanofilms on lithography photomasks

Removal of sub-100 nm particles without damage is a challenge in semiconductor industry and nanotechnology, to assure nano-scale substrate cleanliness on lithography photomasks. Laser induced plasma (LIP) shockwave cleaning is an emerging technology for nanoparticle removal. In the current study, the onset of material alterations on EUVL masks and photomasks have been identified for LIP in air, LIP utilizing shock tubes and wet-LIP. Material alteration mechanisms for EUVL masks due to varying LIP exposure in air have been identified. Based on fully-coupled transient thermo-mechanical analyses, radiation heating was determined as the major LIP damage source. Further, the film surface radial stress component was identified as the most critical damage concern. Furthermore, as a manufacturing level solution, pre-tension on the films of these lithography masks is suggested to reduce the damage-risk from LIP exposure. Based on a mathematical model, LIP process parameters have been optimized and the threshold limits for nanoparticle removal in air for lithography masks have been obtained. For particles smaller than this threshold, pressure amplification techniques, such as pressurized chambers, shock tubes and wet-LIP, can be utilized. Shock tubes and wet-LIP have been utilized for maximizing LIP pressure, and safe firing distances for nanoparticle removal have been obtained. Damage-free nanoparticle removal from lithography masks have been successfully conducted using LIP in air, shock tubes (in-air) and wet-LIP. Successful detachment of native particles on a photomask was demonstrated with the laser shock cleaning (LSC) research tool built for semi-automated cleaning of full-length lithography masks.