PUTRANTO Achmad's PhD thesis defence

High Resolution Nano-Patterning via Block Copolymer Lithography for Microelectronic and Sensing Applications

Achieving high-resolution nanostructures at sub-10 nm scale is paramount for technological advancements, especially in the field of microelectronics, where the continuous reduction in transistor size plays a crucial role, but also in other fields like in photonics for the fabrication of metasurfaces or in the field of bio/chemical sensors for example. In this context, the directed self-assembly (DSA) of high-χ block copolymers (BCPs) is a promising nanofabrication technique. A higher value of the Flory-Huggins parameter χ, measuring the chemical incompatibility between the blocks, enables the formation of higher resolution features (sub-10 nm).

In this PhD thesis, the focus revolves around investigating the DSA of a high-χ lamellar Si-containing material, polystyrene -block- poly(1,1-dimethylsilacyclobutane) (PS-b-PDMSB) with a 9 nm half pitch, on topographic substrates for BCP lithography (a so-called graphoepitaxy process), with the ultimate goal of addressing applications in microelectronics and surface-enhanced Raman spectroscopy (SERS).

To attain a lithography-compatible configuration i.e., long-range ordered out-of-plane lamellae, precise control of the wetting interaction between the BCP and its environment (e.g., substrate’s bottom and sidewalls, as well as polymeric top-coat) is required. In the first part of the work, we evaluated various plasma chemistry treatments on the topographic substrates, composed of spin-on-carbon (SOC) guiding lines and a Si base substrate, to favour this vertical alignment within trenches. Notably, a HBr/O2 plasma-treatment achieves both neutral wetting at the bottom interface and strong PS-affine wetting at the SOC trench sidewalls, effectively guiding vertical BCP lamellae along the trenches. On the other hand, a grafted neutral underlayer is shown to induce isotropic wetting, resulting in a ladder-like structure (perpendicular alignment along the guiding lines). Experimental observations are in good agreement with a free energy configurational model developed to describe the systems. The selective removal of one of the BCP domains, for example by plasma etching, results in open out-of-plane structures that serve as lithographic templates for further applications.

Additionally, the potential of these dense sub-10 nm structures for SERS-based sensing is evaluated. Metal deposition on these BCP templates yields various nanoscopic gold line structures, which are evaluated through the detection of grafted thiophenol. In particular, long-range aligned anisotropic patterns exhibit a strong polarization-dependent signal. Finite-different-time-domain simulations (FDTD) are also carried out to explain these nano-plasmonic behaviours.