EUV lithography for resolution below 8 nm half pitch requires the numerical aperture (NA) of the projection lens to be
significantly larger than the current state-of-the-art 0.33NA. In order to be economically viable, a throughput in the range
of 100 wafers per hour is needed.
As a result of the increased NA, the incidence angles of the light rays at the mask increase significantly. Consequently
the shadowing and the variation of the multi-layer reflectivity deteriorate the aerial image contrast to unacceptably low
values at the current 4x magnification.
The only solution to reduce the angular range at the mask is to increase the magnification. Simulations show that we
have to double the magnification to 8x in order to overcome the shadowing effects. Assuming that the mask
infrastructure will not change the mask form factor, this would inevitably lead to a field size that is a quarter of the field
size of current 0.33NA step and scan systems. This would reduce the throughput of the high-NA scanner to a value
significantly below 100 wafers per hour unless additional measures are taken.
This paper presents an anamorphic step and scan system capable to print fields that are half the field size of the current full
field. The anamorphic system has the potential to achieve a throughput in excess of 150 wafers per hour by increasing
the transmission of the optics as well as increasing the acceleration of the wafer stage and mask stage. This makes it an
economically viable lithography solution.
The proposed 4x/8x magnification is not the only logical solution. There are potentially other magnifications to increase
the scanner performance while at the same time reducing the mask requirements.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jan van Schoot ; Koen van Ingen Schenau ; Gerardo Bottiglieri ; Kars Troost ; John Zimmerman, et al.
EUV High-NA scanner and mask optimization for sub 8 nm resolution
", Proc. SPIE 9635, Photomask Technology 2015, 963503 (November 16, 2015); doi:10.1117/12.2202258; http://dx.doi.org/10.1117/12.2202258