Unbiased estimation of linewidth roughness

Linewidth roughness (LWR) is usually estimated simply as three standard deviations of the linewidth. The effect of image noise upon this metric includes a positive nonrandom component. The metric is therefore subject to a bias or "systematic error" that we have estimated can be comparable in size to the roughness itself for samples as smooth as required by the industry roadmap. We illustrate the problem using scanning electron microscope images of rough lines. We propose simple changes to the measurement algorithm that, if adopted by metrology instrument suppliers, would permit estimation of LWR without bias caused by image noise.

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