Solvothermal Vapor Annealing of Lamellar Poly(styrene)- block -poly( d , l -lactide) Block Copolymer Thin Films for Directed Self-Assembly Application

International audienceSolvo-thermal vapor annealing (STVA) was employed to induce microphase separation in a lamellar forming semicrystalline block copolymer (BCP) thin film containing a rapidly degradable block. Directed self-assembly of poly(styrene)-block-poly(D,L-lactide) (PS-b-PLA) BCP films via topographically patterned silicon nitride was demonstrated with alignment over macroscopic areas. Interestingly, we observed lamellar patterns aligned parallel as well as perpendicular to graphoepitaxial guiding patterns . PS-b-PLA BCP microphase separated with high a degree of order in an atmosphere of tetrahydrofuran (THF) with an elevated vapor pressure (at ca. 40-60°C). Grazing incidence small angle X-ray scattering (GISAXS) measurements of PS-b-PLA films reveals the through-film uniformity of perpendicular domains after STVA. Perpendicular lamellar orientation was observed on both hydrophilic and relatively hydrophobic surfaces with a periodicity (L0) of ~ 32.5 nm. The rapid removal of the PLA domains is demonstrated using a mild basic solution for the development of a well-defined PS mask template. GISAXS data reveals the through-film uniformity is retained following wet etching. The experimental results in this article demonstrate highly oriented PS-b-PLA microdomains after a short annealing period and facile PLA removal forming porous on-chip etch masks for nanolithography application