Investigation of block depth distribution in PS-b-PMMA block copolymer using ultra-low-energy cesium sputtering in ToF-SIMS

Directed self-assembly of block copolymers (BCPs) is a promising candidate for next generation nanolithography. In order to validate a given pattern, the lateral and in-depth distributions of the blocks should be well characterized; for the latter, time-of-flight (ToF) SIMS is a particularly well-adapted technique. Here, we use an ION-TOF ToF-SIMS V in negative mode to provide qualitative information on the in-depth organization of polystyrene-b-polymethylmethacrylate (PS-b-PMMA) BCP thin films. Using low-energy Cs+ sputtering and Bi-3(+) as the analysis ions, PS and PMMA homopolymer films are first analyzed in order to identify the characteristic secondary ions for each block. PS-b-PMMA BCPs are then characterized showing that self-assembled nanodomains are clearly observed after annealing. We also demonstrate that the ToF-SIMS technique is able to distinguish between the different morphologies of BCP investigated in this work (lamellae, spheres or cylinders). ToF-SIMS characterization on BCP is in good agreement with XPS analysis performed on the same samples. Copyright (c) 2013 John Wiley & Sons, Ltd.