Investigation of block depth distribution in PS- b-PMMA block copolymer using ultra-low- energy cesium sputtering in ToF-SIMS T. Terlier, a R. Tiron, a A. Gharbi, a X. Chevalier, b M. Veillerot, a E. Martinez a and J.-P. Barnes a * 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 © 2013 John Wiley & Sons, Ltd. Keywords: ToF-SIMS; PS-b-PMMA; depth profile; block-copolymers self-assembly Introduction The study of polymeric materials has long been the subject of intense research for many applications. More recently, block copolymers (BCPs) are becoming increasingly targeted in lithography for the future technology nodes because of their processing simplicity, low manufacturing costs, low critical dimension and high density of achievable features. [1] Suitable characterization techniques are needed in order to monitor the chemical distribution of each block, both laterally and in-depth. Time-of-flight (ToF) SIMS seems to be a particularly well- adapted technique as it has recently shown significant progress in depth profiling of polymers with the use of gas cluster ion beams (GCIBs). [2] Development of low-energy monoatomic ion beams for sputtering and energetic cluster ion for analysis has allowed similar progression. [3] The dual- beam analysis approach allows fast, highly depth-resolved profiles with low fragmentation sputtering using ultra-low- energy cesium and high ionization yield analysis due to the pulsed Bi 3 + ion beam. In this paper, we study polystyrene-b-polymethylmethacrylate (PS-b-PMMA) BCP system for nanolithography applications. This kind of polymer is able to form various self-assembled nanoscopic features depending on the volume fraction of both blocks. [4,5] In our case, the PS-b-PMMA BCP system is also interesting because of the different photoresistive properties of these chemical species: PMMA is a good positive photoresist, and polystyrene is a negative resist. The PS-b-PMMA BCP studied here is expected to form different domains of PMMA in a PS matrix after thermal annealing. Experimental section Materials Three PS-b-PMMA BCPs of different PS : PMMA volume ratios are used: Symmetric PS-b-PMMA (M n = 48 kg/mol for PS and M n = 46 kg/mol for PMMA, M w /M n = 1.09) and asymmetric PMMA cylinder forming PS-b-PMMA (M n = 46 kg/mol for PS and M n = 21 kg/mol for PMMA, M w /M n = 1.09) were purchased from Polymer Source Inc. (Dorval, Quebec), and asymmetric PMMA spheres forming PS-b-PMMA (M n = 52 kg/mol for PS and M n = 11 kg/mol for PMMA, M w /M n = 1.08) was provided by ARKEMA (ARKEMA - Lacq, France) under the trade name Nanostrength® EO. These BCPs are referred to as L, C and S, respec- tively. PS and PMMA homopolymers of M n = 12 kg/mol that were provided by ARKEMA are used and referred to as h-PS and h-PMMA, respectively. All these polymers were used as received and were dissolved in propylene glycol monomethyl ether acetate (PGMEA) to obtain 2 wt.% solutions. Sample preparation The polymer solutions are spin coated on bare silicon leading to film thicknesses of 50–90 nm. BCPs are baked at 230 °C for 5 min * Correspondence to: J.-P. Barnes, CEA, LETI, MINATEC Campus, 17 rue des Mar- tyrs, 38054 Grenoble Cedex 9, France. E-mail: jean-paul.barnes@cea.fr a CEA, LETI, MINATEC Campus, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France b ARKEMA – Groupement de Recherches de Lacq, RN 117, BP34, 64170 Lacq, France Surf. Interface Anal. 2014, 46, 83–91 Copyright © 2013 John Wiley & Sons, Ltd. Research article Received: 25 June 2013 Revised: 8 October 2013 Accepted: 25 October 2013 Published online in Wiley Online Library: 26 December 2013 (wileyonlinelibrary.com) DOI 10.1002/sia.5353 83