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

摘要

As the semiconductor industry continuously pursues smaller and more advanced device nodes, improving thelithographic performance of photoresists becomes more critical and challenging. The homogeneity of the photoresistformulation components within the thin film, such as the distribution of photoacid generator (PAG) molecules, arecritical factors influencing resolving capability and the sidewall roughness after development. However, there is stilllack of fundamental experimental approaches to probe the distribution of these components at the nanoscale throughoutthe photoresist film. Herein, we present the use of a new methodology, namely, massive cluster secondary ion massspectrometry (MC-SIMS), to determine PAG homogeneity on a 10-15 nm scale within a photoresist film. In comparisonto conventional SIMS, of which the detection spatial resolution is limited to large domains and the data is aggregatedprior to analysis, MC-SIMS bombards the sample with a sequence of massive Au_(400)~(+4) nanoprojectiles, each separated intime and space, collecting and mass analyzing the co-emitted secondary ions from each projectile impact. Each sample isanalyzed with a large quantity (10~6-107) of individual projectile impacts within an analysis area 125 μm in diameter.Analysis of co-emission of these independent 10~6-10~7 mass spectra allows for identification of co-localized moleculeswithin nanodomains ～10-15 nm diameter and ～10 nm in depth (the emission area of a single impact) from the filmsurface. This unique method therefore reveals spatial distributions of molecules at the nanoscale.Using MC-SIMS methodology, we directly measured key factors influencing the PAG homogeneity at the nanoscaleincluding (1) PAG concentration, (2) the nature of the polymer matrix, (3) the nature of the PAG, and (4) additives. Wediscovered that 85-95% of PAG salts aggregate at the nanoscale. The majority of the PAG aggregates are less than 10nm in size and are highly homogeneously distributed within the polymer matrix in the film. Furthermore, the size of thePAG aggregates can be manipulated by additives through an ion-exchange mechanism.