Observation Result of Chemical Composition Distribution of Resist Thin Film by Photoemission Electron Microscopy

Abstract

The critical issue in EUV resists is the suppression of line width roughness (LWR). The one of the factors contributing to LWR is the aggregation and segregation of chemical compositions in resist thin films. Our group has reported to evaluate the spatial chemical composition distribution inside the resist thin films by resonant soft X-ray scattering (RSoXS). As a result, an aggregation distribution on the order of tens of nanometers was confirmed in the resist thin film due to its chemical composition. However, the scattering information obtained by RSoXS method is average information about the resist thin film, and it was difficult to determine what type of aggregation form the actual aggregation takes, such as spheres or lamellae. We focused on the photoemission electron microscopy (PEEM), which is powerful evaluation tool to observe chemical information on sample surface. Although there have been no reports on PEEM observation of resist surface, that PEEM would allow us to observe the agglomerated structure of the chemical composition on the resist surface.

In this study, we challenged to observe the carbon distribution of polyhydroxystyrene-co-(tert-butyl acrylate) (PHS-TBA), which is used as a base polymer for EUV resists. Two samples with different compositions have been observed by PEEM with UV (5.2 eV) and synchrotron radiation (281, 288, and 301 eV) as light source. With a field of view of 874 µm, we observed the carbon distribution on the resist surface with the synchrotron light.