Resist Free Patterning of Nonpreferential Buffer Layers for Block Copolymer Lithography

We report the design of a direct electron beam patternable buffer layer to spatially control the orientation of the microdomains in an overlaying polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer (BCP) film. The buffer layer consists of a surface anchored low molecular weight PS-b-PMMA, with the PMMA segment anchored to the surface and a short PS block at the buffer layer/BCP interface. The block architecture of the buffer layer combines the essential features of "bottom up" and "top down" approaches as it functions as a nonpreferential layer to dictate perpendicular orientation of BCP domains from the substrate interface and as an e-beam resist to allow top-down lithographic process to spatially define the buffer layer on the substrate. The composition of the buffer layer can be tuned by changing the relative block lengths to create a nonpreferential surface which effectively induces perpendicular orientation of domains in an overlying BCP film. The grafted block copolymer can be locally shaved by e-beam lithography resulting in spatial control of domain orientation in the BCP film. The direct patterning approach reduces the number of steps involved in forming chemical patterns by conventional lithography.