6 December 2004 Printability of topography in alternating aperture phase-shift masks
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Abstract
Alternating aperture phase-shift mask (AAPSM) technology in combination with conventional illumination enables the imaging needed in the 65nm node and beyond, thanks to its high image contrast and small mask error factor (MEF). It is a known point of attention that AAPSM topography induces an image intensity imbalance between the light propagating through the zero and pi-shifted space. There are several ways to compensate for such imbalance in the mask making process. The most common approaches are applying an undercut or a bias of the pi-shifted space. The guaranteed quartz etch depth of the pi-shifted space through pitch is another challenge in the mask making process of an AAPSM. This paper reports on the methodology to evaluate the mask making quality of AAPSM for both 193nm and 157nm lithography through printability. For this purpose rigorous electro-magnetic field simulations through the 3D mask topography using Solid-CM (software from Sigma-C) are performed. The parameter for the quantification of the image imbalance is the difference between the measured width of neighbouring zero and pi-shifted spaces on the wafer print. As a first step in the methodology the amount of undercut or bias applied on the mask is deduced from the correlation between the experimentally measured and simulated space difference. Once the amount of undercut or bias is known, the phase error for the evaluated structure is estimated by evaluating the through focus behaviour of the space difference. This gives an indication of the quality of the etch process through pitch during mask making. For the 193nm lithography the wafers are exposed on an ASML PAS5500/1100 ArF scanner working with a 0.75NA projection lens. The 157nm AAPSM masks are printed with an ASML Micrascan VII equipped with a 0.75NA projection lens. The wafers and masks are evaluated on a top-down mask-compatible CD-SEM (KLA-Tencor 8250XR).
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Vicky Philipsen, Vicky Philipsen, Rik Jonckheere, Rik Jonckheere, } "Printability of topography in alternating aperture phase-shift masks", Proc. SPIE 5567, 24th Annual BACUS Symposium on Photomask Technology, (6 December 2004); doi: 10.1117/12.568699; https://doi.org/10.1117/12.568699
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