Understanding photoacid generator distribution at the nanoscale using massive cluster secondary ion mass spectrometry

Abstract. Background: The homogeneity of photoacid generator (PAG) is a critical factor influencing the resolving capability and the sidewall roughness of a photoresist, yet fundamental understanding of the PAG homogeneity lacks at the nanoscale. Aim: We present a methodology, massive cluster secondary ion mass spectrometry (MC-SIMS), to determine PAG homogeneity on a 10- to 15-nm scale at the photoresist film surface. Approach: MC-SIMS bombards the sample with a sequence of massive Au400  +  4 nanoprojectiles, each separated in time and space, collecting and mass analyzing the coemitted secondary ions from each impact. Each sample is analyzed with one million individual projectile impacts. Analysis of coemission of these independent more than one million mass spectra allows for identification of colocalized molecules within nanodomains ∼10- to 15-nm diameter and ∼10  nm in depth from the film surface, therefore revealing spatial molecular distributions at the nanoscale. Results: About 85% to 95% of the measurements showed PAG–PAG coemission and over 90% showed polymer–PAG coemission. Ion-exchanging additive increases polymer–PAG coemission. Conclusions: The majority of PAG molecules exist as small aggregates that are <10  nm in size and such aggregates are highly homogeneously distributed within the polymer matrix. The size of the PAG aggregates can be manipulated by additives through an ion-exchange mechanism.