Determining the validity domain of roughness measurements as a function of CD-SEM acquisition conditions
Résumé
In the effort of continuously improving patterning strategies for increasing circuit density while reducing dimensions, several challenges regarding patterning fidelity emerge. In recent years, stochastic effects had their relative importance increased, and therefore the need for closely monitoring those effects is also increasing [1]. Among other stochastic effects, within-feature roughness is significant as it can impact circuit electrical behavior, decreasing time and power performance, and even lead to failures. The workhorse method of the industry for measuring roughness is based on topdown CD-SEM (Critical Dimension Scanning Electron Microscopy) image. In recent years, methods have been proposed as a way to improve and standardize the roughness measurement [2, 3]. Those methods rely on the obtention of the power spectral density (PSD) from the detected edges of the features in CD-SEM images, in order to determine their roughness. However, one important aspect is the impact of the CD-SEM image acquisition conditions on the limitation of the observed PSD. As the acquisition parameters changes, different frequencies may be more or less observable in a CD-SEM image, potentially leading to errors in the metrology evaluation [4].
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