Square arrays of holes and dots patterned from a linear ABC triblock terpolymer.

Microphase separation of a polyisoprene-b-polystyrene-b-polyferrocenylsilane (PI-b-PS-b-PFS) triblock terpolymer film during chloroform solvent-annealing formed a 44 nm period square-symmetry array of alternating PI and PFS cylinders in a PS matrix. This nanostructure was converted to either a positive pattern of posts or a negative pattern of holes with tunable diameter by oxygen reactive ion etching or by surface reconstruction in a solvent, respectively, and coexisting post and hole patterns were also formed. Square arrays of silicon posts, pits, and inverted pyramids were fabricated by pattern transfer from the triblock terpolymer film into silicon substrates. The morphology of the triblock terpolymer film varied with the chloroform vapor pressure during solvent annealing, which was explained by selective swelling of the PI block at high vapor pressures. This triblock terpolymer system provides a convenient block copolymer lithography process for generation of nanoscale posts or holes with square symmetry.