At least one recessed region having two parallel edges is formed in an
insulator layer over a semiconductor layer such that the lengthwise
direction of the recessed region coincides with optimal carrier mobility
surfaces of the semiconductor material in the semiconductor layer for
finFETs to be formed. Self-assembling block copolymers are applied within
the at least one recessed region and annealed to form a set of parallel
polymer block lines having a sublithographic width and containing a first
polymeric block component. The pattern of sublithographic width lines is
transferred into the semiconductor layer employing the set of parallel
polymer block lines as an etch mask. Sublithographic width semiconductor
fins thus formed may have sidewalls for optimal carrier mobility for
p-type finFETs and n-type finFETs.