Thinner absorber structure in EUVL mask is supposed to be applied in 2x HP node since it shows several advantages including H-V bias reduction. Here, lithographic performances of EUVL masks as a function of absorber stack height are investigated using ADT exposure experiments. Wafer SEM images show that minimum resolution is almost identical at ~27.5 nm with absorber thickness ranging from 45 to 70 nm. Simulations also exhibit that NILS and contrast become maximized and saturated in those ranges. However, thinner absorber structure using 50-nm-thick absorber shows much lower H-V bias than conventional structure using 70-nm-thick absorber. MEEF, EL, DOF, and LWR are also slightly improved with thinner absorber. One of the noticeable issues in thin absorber is low OD which results in pattern damages and CD reduction at shot edges due to light leakage from the neighboring exposures. To overcome these issues, appropriate light shielding process during mask fabrication as well as minimizing OoB radiation in EUVL scanner are required. Another item to prepare for 2x HP node is to increase defect detection sensitivity with 19x nm inspection tools. Thus, absorber stacks with new ARC layer optimized for 19x nm inspection should be developed and applied in EUVL mask blanks.

Date Published: 20 March 2010
PDF: 9 pages
Proc. SPIE 7636, Extreme Ultraviolet (EUV) Lithography, 76360X (20 March 2010); doi: 10.1117/12.847955

Published in SPIE Proceedings Vol. 7636:
Extreme Ultraviolet (EUV) Lithography
Bruno M. La Fontaine, Editor(s)