The Molecular Foundry, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, USA.
ACS Nano. 2011 Nov 22;5(11):8523-31. doi: 10.1021/nn201391d. Epub 2011 Oct 26.
Directed self-assembly (DSA) of block copolymers (BCPs), either by selective wetting of surface chemical prepatterns or by graphoepitaxial alignment with surface topography, has ushered in a new era for high-resolution nanopatterning. These pioneering approaches, while effective, require expensive and time-consuming lithographic patterning of each substrate to direct the assembly. To overcome this shortcoming, nanoimprint molds--attainable via low-cost optical lithography--were investigated for their potential to be reusable and efficiently template the assembly of block copolymers (BCPs) while under complete confinement. Nanoimprint directed self-assembly conveniently avoids repetitive and expensive chemical or topographical prepatterning of substrates. To demonstrate this technique for high-resolution nanofabrication, we aligned sub-10 nm resolution nanopatterns using a cylinder-forming, organic-inorganic hybrid block copolymer, polystyrene-block-polydimethylsiloxane (PS-b-PDMS). Nanopatterns derived from oxidized PDMS microdomains were successfully transferred into the underlying substrate using plasma etching. In the development phase of this procedure, we investigated the role of mold treatments and pattern geometries as DSA of BCPs are driven by interfacial chemistry and physics. In the optimized route, silicon molds treated with PDMS surface brushes promoted rapid BCP alignment and reliable mold release while appropriate mold geometries provided a single layer of cylinders and negligible residual layers as required for pattern transfer. Molds thus produced were reusable to the same efficacy between nanoimprints. We also demonstrated that shear flow during the nanoimprint process enhanced the alignment of the BCP near open edges, which may be engineered in future schemes to control the BCP microdomain alignment kinetics during DSA.
定向自组装（DSA）的嵌段共聚物（BCP），无论是通过表面化学预图案的选择性润湿，还是通过与表面形貌的图形外延对准，都为高分辨率纳米图案化开创了一个新时代。这些开创性的方法虽然有效，但需要昂贵且耗时的光刻图案化每个基底以指导组装。为了克服这一缺点，人们研究了纳米压印模具——通过低成本的光刻技术获得——它们是否具有可重复使用的潜力，并能在完全限制的情况下有效地模板组装嵌段共聚物（BCP）。纳米压印定向自组装方便地避免了对基底进行重复且昂贵的化学或形貌预处理。为了证明这种用于高分辨率纳米制造的技术，我们使用形成圆柱的有机-无机杂化嵌段共聚物聚苯乙烯-嵌段-聚二甲基硅氧烷（PS-b-PDMS）对齐了亚 10nm 分辨率的纳米图案。通过等离子体刻蚀，成功地将源自氧化 PDMS 微区的纳米图案转移到基底中。在该程序的开发阶段，我们研究了模具处理和图案几何形状的作用，因为 BCP 的 DSA 由界面化学和物理驱动。在优化的路线中，用 PDMS 表面刷处理的硅模具促进了快速 BCP 对准和可靠的模具脱模，而适当的模具几何形状提供了一层圆柱和几乎可以忽略不计的残余层，这是图案转移所需要的。因此，生产的模具可以在相同的效果之间重复使用纳米压印。我们还证明，纳米压印过程中的剪切流增强了 BCP 在开口边缘附近的对准，这可能在未来的方案中用于控制 DSA 期间 BCP 微区对准动力学。
