Measuring the Structure of Epitaxially Assembled Block Copolymer Domains with Soft X-ray Diffraction
Gila Stein, James A. Liddle, Andrew Aquila, Eric M. Gullikson
The size, shape, and roughness of poly(styrene-b-methyl methacrylate) block copolymer domains assembled on an epitaxial template are characterized with soft x-ray diffraction. The domain size and shape are deformed when the dimensions of the epitaxial template are incommensurate with the equilibrium dimensions of the block copolymer, producing sidewall angles in the range of 1 deg. to 2 deg. (+/-0:2 deg.). The average width of the copolymer interface is (4.9 +/- 0.08) nm. Comparison with mean-field theoretic predictions for the structure of block copolymer interfaces suggests a low-frequency variance in the copolymer interface position of 0.3 nm^2,or a low-frequency line-edge roughness of approximately 1.7 nm. This roughness magnitude is less than predicted by capillary wave models for copolymer interfaces, and may indicate suppression of longer-wavelength fluctuation modes due to substrate pinning or block connectivity.