Precision phase angle control with transmissive etching stop film

Extreme ultraviolet lithography (EUVL) is a main lithographic technology for cutting-edge node. Also, ArF lithography will continue to be used in conjunction with EUVL for advanced node production. Critical ArF imaging layers require photomasks with tight resolution and rigid CD and Positional accuracy. Those specifications are tightening due to the narrow process window. The etching process for phase-shifter has to precisely controlled to achieve the targets. . Various pattern density in PSM (Phase-Shifter Mask) shows phase angle variation due to the digging of the Quartz substrate(QZ). In the high transmittance PSM, the error has larger impact on the lithography due to strong phase shift effects. To prevent phase shift error from the target phase angle, QZ etching stop film is considered. It is possible to obtain a high etching selectivity compared with QZ and to apply an aggressive dry etching condition. In order to control in-plane phase angle distribution due to QZ etching during PSM etching, we proposed a novel high transmission etching stop film for ArF lasers.