Chemically amplified resists are the principal lithographic materials used in the semiconductor industry. The photoacid distribution generated upon exposure and its subsequent evolution during post-exposure bake is one of the most important factors that determine the resolution and lithographic quality of the final, developed resist image. Up to now it has not been possible to measure it. Here we use photoactivation localization microscopy (PALM), with a rhodamine-amide dye that is activated both by ultraviolet light and protonation, to reveal the nanoscale photoacid distribution in a model resist system. By representing the PALM process as a statistical sampling procedure, we derive a maximum likelihood estimator that enables us to extract quantitative values for the photoacid distribution blur to a precision of ± 20 nm, using fluorophores spaced by an average in-plane distance of approx. 330 nm.
Citation: ACS Nano
Pub Type: Journals