Correlation of atomic force microscopy sidewall roughness measurements with scanning electron microscopy line-edge roughness measurements on chemically amplified resists exposed by x-ray lithography

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As critical dimensions of resist features shrink, roughness of the features may contribute significantly to the variation in critical dimension. Measuring and understanding the causes of this roughness will become increasingly important with smaller sizes. To date, mainly two techniques have been used to measure the roughness: atomic force microscopy (AFM) and scanning electron microscopy (SEM). Topdown SEM measurements provide an easy and expedient measure of the variation in the profile of the resist feature. These measurements are often called “line-edge roughness” (LER). AFM measurements are considerably more time consuming, but provide information on the entire sidewall surface of the resist, rather than just the profile in line-edge roughness. Our recent AFM measurements on the positive-tone resist APEX-E and UV5 have shown that the sidewall roughness of the resist is depth dependent; resist near the substrate is smoother than resist at the top surface of the resist. For instance, APEX-E may have a roughness on the order of 3 nm rms near the substrate, which may increase to 7 or so nm rms at the top of the resist line. This article will correlate measurements made by both AFM and SEM and explore how the depth-dependent roughness in AFM data may affect the magnitude of the roughness measured by topdown SEM.