UC Berkeley

The problem of stochastics in photoresist patterning is of significant concern in the commercialization of extreme ultraviolet lithography, especially in patterning of contacts or vias. Traditionally, contact hole critical dimension (CD) variability is characterized as a Gaussian process, however, recent experimental results have demonstrated significant deviations from Gaussian statistics, especially on the small CD side. Modeling results show that this non-Gaussian variation is expected and can be attributed to the non-linear behavior of the contact hole exposure latitude as a function of dose. It is shown that if we consider the noise in the dose or sensitivity domain, it can still be treated as a Gaussian process. The CD statistics are then determined by mapping the Gaussian dose/sensitivity noise through the non-linear and deterministic CD versus dose function.