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The focused ion beam (FIB) milling tool is an important component of reference metrology and process characterization,
both as a supporting instrument for bulk sample preparation before forwarding to the transmission electron microscope
(TEM) and other instruments and as an in situ measurement instrument using angled scanning electron microscopy. As
features grow denser, deeper and more demanding, full-profile reference metrology is needed, and this methodology will
only grow in importance. Thus, the ability to extract accurate dimensional and profile information out of the crosssectional
faces produced by FIB milling is critical.
For features that demonstrate perfect symmetry in the plane of the cross section, analyzing images and extracting
metrology data are straightforward. However, for industrial materials, symmetry is not a safe assumption: as features
shrink, the line edge and sidewall roughness increases as a percentage of the overall feature dimension. Furthermore,
with the introduction of more complex architectures such as 3D memory and FinFETs, the areas of greatest interest, such
as the intersections of wrap-around gates, cannot be assumed to be symmetrical in any given plane if cut placement is
not precisely controlled. Therefore it is important to establish the exact location and repeatability of the cross-section
plane, both in terms of coordinate placement and effective angle of the milled surface.
To this end, we prepared designed-in line edge roughness samples in the Albany Nanotech facility using SEMATECH's
AMAG6 metrology reticle. The samples were thoroughly characterized before being milled by a non-destructive,
sidewall-scanning atomic force microscope (AFM). These samples are then milled and measured under varying process
and setup parameters using a single-beam FIB with angled SEM. We established methodologies that allow precise
alignment of the cut planes of slice-and-view FIB milling to 3D-AFM scan lines to compare repeated sections
throughout a feature. This gives us a large amount of data to test the accuracy and repeatability of cut placement using
various alignment and recipe setup schemes.
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