The present invention relates to a random copolymer comprising repeating units of the following structures (I), (II), (III) and (IV). The present invention also relates to a neutral layer composition consisting of said random copolymer, and also to said crosslinked neutral layer on a substrate which can enable self-assembly of a film of block copolymer overlying said crosslinked neutral layer. to the use of the neutral layer composition, wherein the block copolymer comprises etch-resistant and etchable blocks, wherein the self-assembled pattern is used to create an array of contact holes or posts in the substrate via etching.
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