Mitigation of EUV mask blank substrate pit and scratch defects by Accelerated Neutral Atom Beam (ANAB) processing

EUV mask blank substrates will be subject to extraordinarily demanding requirements upon flatness, smoothness and absence of residual defects. To date, no combination of available surface preparation techniques has been able to produce essentially perfect substrates with zero residual defect populations. A critical problem yet to be resolved involves small numbers of nanoscale divots and scratches which are generated by the operations used to meet smoothness requirements. A new non-contact surface sputtering technique known as accelerated neutral atom beam (ANAB) shows promise for mitigating the divot and scratch defects without increasing surface roughness and without altering flatness and planarity. This paper describes a mask blank substrate study which has been conducted to demonstrate the ANAB defect mitigation capability.