Nanometrology for evaluating resists for molecular homogeneity

Abstract

Here we present a methodology for identifying and characterizing nanoscale sites in EUV photoresists which deviate from the mean composition by 3σ. The methodology is based on Nano-Projectile Secondary Ion Mass Spectrometry (SIMS) operating in the in the event-by-event bombardment detection mode. Nanoscale analysis is achieved by probing the surface stochastically with a suite of individual nano-projectile impacts where each nano-projectile samples a volume 10-15 nm in diameter and up to 10 nm in depth. For each impact the coemitted secondary ions are collected, and mass analyzed, allowing for the analysis of co-localized moieties. We applied this method to study the changing film composition in an EUV resist and isolated measurements with a probability below 0.3%. By examining these measurements, we can identify rare sites on the surface that may correspond to molecular aggregations in the surface. In a developed film, the mass spectrometry measurements showed that the photoacid generator, PAG, cation displayed decreased homogeneity on average with increasing exposure dose. The effect was more pronounced in the sites with probabilities below 0.3%, where the measured intensity of the PAG cation in these sites was over 2-fold larger than the mean. Thus, we attribute these nanoscale sites to aggregations of PAG within the top 10 nm of the film. These rare sites may be important in defect production and film stochastics.