Development and Characterization of a Thinner Binary Mask Absorber for 22 nm node and Beyond
2010
The lithography challenges posed by the 22 nm node continue to place stringent requirements on photomasks.
The dimensions of the mask features continue to shrink more deeply into the sub-wavelength scale. In this
regime residual mask electromagnetic field (EMF) effects due to mask topography can degrade the imaging
performance of critical mask patterns by degrading the common lithography process window and by magnifying
the impact of mask errors or MEEF. Based on this, an effort to reduce the mask topography effect by
decreasing the thickness of the mask absorber was conducted. In this paper, we will describe the results of our
effort to develop and characterize a binary mask substrate with an absorber that is approximately 20-25% thinner
than the absorber on the current Opaque MoSi on Glass (OMOG) binary mask substrate.
For expediency, the thin absorber development effort focused on using existing absorber materials and deposition
methods. It was found that significant changes in film composition and structure were needed to obtain a
substantially thinner blank while maintaining an optical density of 3.0 at 193 nm. Consequently, numerous
studies to assess the mask making performance of the thinner absorber material were required and will be
described. During these studies several significant mask making advantages of the thin absorber were
discovered. The lower film stress and thickness of the new absorber resulted in improved mask flatness and up
to a 60% reduction in process-induced mask pattern placement change. Improved cleaning durability was
another benefit. Furthermore, the improved EMF performance of the thinner absorber [1] was found to have the
potential to relieve mask manufacturing constraints on minimum opaque assist feature size and opaque corner to
corner gap.
Based on the results of evaluations performed to date, the thinner absorber has been found to be suitable for use
for fabricating masks for the 22 nm node and beyond.
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