Onset of Material Alterations Due to Laser-Induced Plasma Exposure in Nanofilms Deposited on Photomasks

Damage-free removal of sub-100 nm particles from photomasks with deposited nanofilms is a challenge in lithography. Laser-induced plasma (LIP) is an emerging noncontact, chemical-free, dry, and selective nanoparticle removal technique. Investigation of the onset of material alterations on bonded nanofilms for optimizing LIP particle removal process is the objective of this paper. Shockwave thermomechanical excitation and radiation heating from the plasma core are major potential sources of damage. Computational analyses reported here indicate radiation heating as the chief damage source. Damage thresholds for the critical nanofilm surface temperature rise and radial stress component have been identified for a given nanosecond pulsed laser.