The directed self-assembly (DSA) of block copolymers (BCPs) is a powerful method for the manufacture of high-resolution features. Critical issues remain to be addressed for successful implementation of DSA, such as dewetting and controlled orientation of BCP domains through physicochemical manipulations at the BCP interfaces, and the spatial positioning and registration of the BCP features. Here, we introduce novel top-coat (TC) materials designed to undergo cross-linking reactions triggered by thermal or photoactivation processes. The cross-linked TC layer with adjusted composition induces a mechanical confinement of the BCP layer, suppressing its dewetting while promoting perpendicular orientation of BCP domains. The selection of areas of interest with perpendicular features is performed directly on the patternable TC layer via a lithography step and leverages attractive integration pathways for the generation of locally controlled BCP patterns and nanostructured BCP multilayers.

Pattern transfer using poly(styrene-block-methyl methacrylate) copolymer films and reactive ion etchingThe best strategies to transfer nanoholes formed from the self-assembly of Polystyren/ Polymethylmethacrylate (PS/PMMA) based block copolymers into a silicon substrate are investigated. The authors show that specific issues are associated with the plasma etching of materials through the PS masks obtained from self-assembly. Indeed, due to the nanometric size of sub-15 nm contact holes and to their inherently high aspect ratio (>5), plasma etching processes typically used to etch SiO 2 and silicon in the microelectronic industry must be revisited. In particular, processes where the etching anisotropy relies on the formation of passivation layer on the feature's sidewalls are not adapted to nanometric dimensions because these layers tend to fill the holes leading to etch stop issues. At the same time, the ion bombarding energy must be increased as compared to a typical process to overcome differential charging effects in high aspect-ratio nanoholes. However, by developing appropriate processes-such as synchronized pulsed plasmas-the authors show that it is possible to etch 70 nm deep holes into silicon by using block copolymers and a hard mask strategy. Another interesting observation resulting from these experiments is that for sub-15 nm holes, a critical dimension (CD)-dispersion of few nm leads to strong aspect ratio dependent etch rates. In addition, a careful analysis of the dispersion of the holes' CD after each plasma steps shows that the CD control is far from satisfying advanced CMOS technology requirements. A critical issue comes from the uncompleted PMMA removal from the PS/PMMA matrix during our self-assembly process: variable amount of PMMA remains in the PS holes, leading to microloading effects during the etching steps, which in turn generates CD-control loss. This problem perhaps can be solved by combining UV exposure to acetic acid treatment to provide PS masks free of PMMA residues before plasma etching.

Directed self-assembly of block copolymers (BCP) is a very attractive technique for the realization of functional nanostructures at high resolution. In this work, we developed full dry-etching strategies for BCP nanolithography using an 18-nm pitch lamellar silicon-containing block copolymer. Both an oxidizing Ar/O2 plasma and a non-oxidizing H2/N2 plasma are used to remove the topcoat material of our BCP stack and reveal the perpendicular lamellae. Under Ar/O2 plasma, an interfacial layer stops the etch process at the top-coat/BCP interface, which provides an etch-stop but also requires an additional CF4-based breakthrough plasma for further etching. This interfacial layer is not present in H2/N2. Increasing the H2/N2 ratio leads to more profound modifications of the silicon-containing lamellas, for which a chemistry in He/N2/O2 rather than Ar/O2 plasma produces a smoother and more regular lithographic mask. Finally, these features are successfully transferred into silicon, silicon-on-insulator and silicon nitride substrates. This work highlights the performance of a silicon-containing block-copolymer at 18 nm pitch to pattern relevant hardmask materials for various applications, including microelectronics.