PROCEEDINGS ARTICLE | April 8, 2011
Proc. SPIE. 7969, Extreme Ultraviolet (EUV) Lithography II
KEYWORDS: Lithography, Phase shifting, Reflection, Electroluminescence, Photomasks, Extreme ultraviolet, Line width roughness, Cadmium sulfide, Extreme ultraviolet lithography, Semiconducting wafers
When compared to a thick absorber mask, a thin absorber EUV mask is expected to have a comparable process
window, a reduced shadowing effect, and lower MEEF. However, regardless of the mask absorber thickness, the
dark-field in EUV lithography is never 100% dark. Using the same absorber stack composition, EUV masks with
thinner absorbers have inherently higher leakage due to the background transmission propagating through the absorber
stack. While this does act to improve resist sensitivity or throughput, the leakage reduces the image contrast and can
cause CD degradation in "double" exposed regions at the edge of adjacent fields. In this study, EUVL lithographic
benchmarking of both thin and thick absorber masks on the ASML Alpha Demo Tool (ADT) at IMEC is presented.
Herein, we experimentally quantify the process window, EL, LWR, MEEF, E<sub>size</sub>, ultimate resolution, and impact of
dark-field background exposures on CDs for both thin and thick absorber masks. There are additional issues when
field edges overlap with adjacent fields, and mitigation strategies for EUV leakage emanating from dark-field regions
are discussed.
