With shrinking pattern size, mask 3D effects are estimated to become stronger, such as horizontal/vertical shadowing, best
focus shifts through pitch and pattern shift through focus. To reduce these mask 3D effects, we have proposed etched
multilayer EUV mask structure and have also reported on the fabrication process of etched multilayer EUV mask, in which
line and space mask patterning has been demonstrated. And by using etched multilayer EUV mask, the reduction of mask 3D
effects is experimentally demonstrated. In our previous study, we have shown etched multilayer EUV mask has enough
durability against chemical erosion in suitable cleaning process.
In this work, to meet the demands of different variation on pattern in etched multilayer mask, especially fabrication process
for sub-60nm pattern based on effective mirror width in dark-field exposure is studied. 60 nm pillar pattern on mask is
obtained using negative tone resist with keeping resolution of line and space pattern. We also examined CD characteristics 60
nm line and space pattern in consideration of effective mirror width. This work represents that etched multilayer EUV mask
is ready for dark-field exposure of 15 nm pattern in wafer.
With shrinking pattern size at 0.33NA EUV lithography systems, mask 3D effects are expected to become stronger, such
as horizontal/vertical shadowing, best focus shifts through pitch and pattern shift through focus. Etched multilayer EUV mask
structures have been proposed in order to reduce mask 3D effects. It is estimated that etched multilayer type mask is also
effective in reducing mask 3D effects at 0.33NA with lithographic simulation, and it is experimentally demonstrated with
NXE3300 EUV Lithography system. We obtained cross-sectional TEM image of etched multilayer EUV mask pattern. It is
observed that patterned multilayer width differs from pattern physical width. This means that effective reflecting width of
etched multilayer pattern is smaller than pattern width measured by CD-SEM.
In this work, we evaluate mask durability against both chemical and physical cleaning process to check the feasibility of
etched multilayer EUV mask patterning against mask cleaning for 0.33NA EUV extension. As a result, effective width can be
controlled by suitable cleaning chemicals because sidewall film works as a passivation film. And line and space pattern
collapse is not detected by DUV mask pattern inspection tool after mask physical cleaning that includes both megasonic and
binary spray steps with sufficient particle removal efficiency.
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