Hierarchical Self-Assembly of Thickness-Modulated Block Copolymer Thin Films for Controlling Nanodomain Orientations inside Bare Silicon Trenches

Abstract

We study the orientation and ordering of nanodomains of a thickness-modulated lamellar block copolymer (BCP) thin film at each thickness region inside a topological nano/micropattern of bare silicon wafers without chemical pretreatments. With precise control of the thickness gradient of a BCP thin film and the width of a bare silicon trench, we successfully demonstrate (i) perfectly oriented lamellar nanodomains, (ii) pseudocylindrical nanopatterns as periodically aligned defects from the lamellar BCP thin film, and (iii) half-cylindrical nanostructure arrays leveraged by a trench sidewall with the strong preferential wetting of the PMMA block of the BCP. Our strategy is simple, efficient, and has an advantage in fabricating diverse nanopatterns simultaneously compared to conventional BCP lithography utilizing chemical pretreatments, such as a polymer brush or a self-assembled monolayer (SAM). The proposed self-assembly nanopatterning process can be used in energy devices and biodevices requiring various nanopatterns on the same device and as next-generation nanofabrication processes with minimized fabrication steps for low-cost manufacturing techniques.

Dual Block Copolymer Morphologies in Ultrathin Films on Topographic Substrates: The Effect of Film Curvature

“…The complete absence of PMMA features at the surface of the film cast on 38 nm-deep trenches with similar plateau/trench widths (Figure 5a-d) suggests that the existence of the plateau edges in this system is insufficient to induce the nucleation of PMMA domains. As the local film thicknesses at the center of the plateaus and trenches are rather similar for both 31 and 38 nm-deep trenches (when comparing patterns with identical lateral dimensions), another variable that could explain the difference in morphological behavior is the curvature of the film profile at the plateau edge, which may lead to local frustration of the chains [43]. As we demonstrate hereafter, this variable is directly related to the dimensions of the topographic features.…”

Solvent Vapor Annealing, Defect Analysis, and Optimization of Self-Assembly of Block Copolymers Using Machine Learning Approaches

“…7,45−50 The ideal thickness for a given BCP is unique and depends upon the composition of the BCP and factors such as surface functionalization and energy, the use of a topcoat, and other factors. 4,6,27,44,46,51 Both experimental and computational results strongly link initial film thickness with the resulting self-assembled structure and persistent defects. 11,52,53 Small fluctuations of thickness within a monolayer film can lead to different self-assembled structures as unfavorably thin domain thicknesses frustrate packing due to the buildup of strain.…”

“…To achieve the desired nanopattern via self-assembly, not only are the annealing parameters critical but the initial thickness of the applied BCP monolayer must be precise, typically within one or two nanometers. ,− The ideal thickness for a given BCP is unique and depends upon the composition of the BCP and factors such as surface functionalization and energy, the use of a topcoat, and other factors. ,,,,, Both experimental and computational results strongly link initial film thickness with the resulting self-assembled structure and persistent defects. ,, Small fluctuations of thickness within a monolayer film can lead to different self-assembled structures as unfavorably thin domain thicknesses frustrate packing due to the buildup of strain. , The periodicity of structures formed from self-assembled BCP nanopatterns may be dependent upon film thickness and other processing parameters, as has been recently shown with bottlebrush BCPs. , …”

Non-Bulk Morphologies of Extremely Thin Block Copolymer Films Cast on Topographically Defined Substrates Featuring Deep Trenches: The Importance of Lateral Confinement

“…We have recently demonstrated a simple fabrication process that capitalizes on the combination of substrate topography with thickness confinement to effect the formation of co-existing, dual patterns, where the location of each pattern is dictated in a fully controlled manner by the pre-designed location of the topographic feature [ 71 ]. This behavior was rationalized by the topography-driven variation in film thickness between the film coating the plateaus and the film deposited in the trenches, which is coupled to the extreme sensitivity of the morphology to the local film thickness for films confined to thicknesses lower than half the lamellar period [ 72 , 73 ]. In a follow-up study, we have unraveled the intricate relationship between the trench depth, lateral topographical dimensions, and film surface profile, allowing us to predict the morphology of the film under various experimental conditions while the nominal film thickness remained constant [ 74 ].…”