Synthesis and Characterization of Silicon-Containing Block Copolymers from Nitroxide-Mediated Living Free Radical Polymerization

Abstract

High etch resistance to oxygen plasma for silicon-containing polymers, and the high thermal and mechanical robustness of the etching product, silicon oxide, make it attractive to design novel silicon-containing block copolymers for direct patterning of nanostructures on a desired substrate. Here, we report the synthesis of a series of block copolymers from silicon-containing styrenic monomers and styrene (St) or 4-acetoxystyrene (AcOSt) using living free radical polymerization via a α-hydride nitroxide-mediated unimer (α-H unimer). Controlled polymerization with narrow polydispersity (PDI < 1.25) and high yield (up to 80%) were achieved by optimizing polymerization time and temperature, addition of solvents, use of rate accelerants, monomer addition sequence, and solvent polarity. Block copolymer morphologies before and after O2 plasma were studied using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). When silicon-containing block formed the major phase and silicon concentration was greater than 12 wt %, the morphology and domain size were maintained after O2 plasma.

Block Copolymer Orientation Control Using a Top-Coat Surface Treatment

“…Si containing BCPs such as poly(styreneb-dimethylsiloxane) (PS-b-PDMS) [11][12], poly(4-(pentamethyl disiloxymethyl) -b-styrene) [13], polyhedral oligomeric silsesquioxane (POSS) containing block copolymers [14] or oligosaccharide -block-p-trimethylsilylstyrene [15] which has higher χ parameters than PS-b-PMMA and much higher etch selectivity. Unfortunately, it is difficult to get perpendicular pattern orientation with BCPs of this sort by thermal annealing because the Si containing block has a low surface energy, and tends to segregate to the top surface of a BCP film where it can associate with air, which has a low dielectric constant.…”

One‐Step Direct‐Patterning Template Utilizing Self‐Assembly of POSS‐Containing Block Copolymers

“…The first approach is via sol-gel chemistry [20][21][22] which is essentially a post-functionalization method and the second approach is direct incorporation of monomers containing metals or inorganic moieties into the block during polymerization. [23,24] In the former approach, it is difficult to predictably control the resulting BCP composite morphology since the addition of inorganic monomer into the BCP changes the volume fraction, whereas, the later approach is simpler.…”

Fabrication of Hierarchically Ordered Hybrid Structures over Multiple Length Scales via Direct Etching of Self-Organized Polyhedral Oligomeric Silsesquioxane (POSS) Functionalized Block Copolymer Films

“…Among various block copolymers, silicon-containing block copolymers have been successfully used as a template for direct patterning of ordered nanostructures by oxygen plasma treatment. [17][18][19] The silicon-containing segments in the block copolymer offer high etch resistance to oxygen plasma compared to hydrocarbon segments due to the stability of silicon oxide, which is the product of the oxygen plasma etching. Thus, the phase-separated silicon-containing structures selectively remain as nano-patterns after the oxygen plasma treatment.…”