Abstract
Extreme-ultraviolet free-electron lasers (EUVFELs) producing intense femtosecond pulse are able to superimpose ion-pair formation induced by a single photon onto the other in the resist polymer degradation. Electron beam resist (ZEP520A) sensitivity was obtained by using 61 nm EUVFEL at different dose densities in order to observe the multiple spur effect in a well-controlled environment. A higher ionization density has been identified to suppress the resist-degradation effectiveness due to the multiple spur effect for the first time. This is explained by two competing effects, namely, spatiotemporal overlap reducing the effectiveness, and high radical concentration enhancing cross-linking efficiency.