Interactions of Higher Order Tip Effects in CD-AFM Linewidth Metrology
Ronald G. Dixson, Boon Ping Ng, Xavier Bonnaud, Ndubuisi G. Orji
A major challenge in critical dimension atomic force microscope (CD-AFM) width metrology is accounting for the effects of the tip on the apparent features in an image. The overall effect of the tip is to broaden the apparent width of lines and narrow the apparent width of trenches as a result of the geometrical interaction of the tip with the surface. To a first approximation, this effect can be well-modeled as a constant bias in width measurements, independent of the specific feature characteristics, by the width of the tip. Beyond this approximation there are a number of smaller tip effects related to the measurement details. Some of these result from the details and interactions of the tip shape and feature shape, resulting in small variations of the tip bias from feature to feature and measurement to measurement. These effects are sometimes called shape effects, secondary effects, or higher order tip effects. One source of higher order effects is due to the lateral dithering of the tip, which increases the effective tip width. However, in addition to this known effect, the tip dither may also affect the apparent edge heights of the tip flare. Although the apparent tip width is expected to depend on lateral dither, the apparent edge height, at least in principle, would not be expected to depend on lateral dither. Our analysis suggest that this apparent dependence results from the interaction of the fine details of the tip flare shape and the dither envelope with the specific algorithm used to estimate the edge height. Consequently, both the sign and the magnitude of the dependence are specific to every tip. This is one example of the inter-dependencies that can be present when evaluating higher-order tip effects. Although these are often small, accurate metrology in some applications may require consideration of possible interactions between such smaller, secondary tip effects.
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, Bonnaud, X.
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Interactions of Higher Order Tip Effects in CD-AFM Linewidth Metrology, Journal of Vacuum Science and Technology B, [online], https://doi.org/10.1116/1.4919090
(Accessed December 7, 2023)