Alignment and reordering of a block copolymer by solvent-enhanced thermal laser direct write

Block copolymer (BCP) thin films have shown high potential as a pattern transfer medium for ultra-fine (<20 nm) features. We introduce an effective approach for performing rapid local annealing of BCP films by focused laser spike (FLaSk) zone annealing, using a moving highly-focused circularly polarized visible wavelength laser spot. A poly(styrene-b-dimethylsiloxane) BCP was transformed from a metastable spherical micelle morphology to the bulk equilibrium cylindrical morphology aligned along the write direction within a region controlled by manipulation of the laser focal plane, even for curved paths. This simultaneous microdomain reordering and alignment was accomplished on the tens of millisecond time scale by creating a very large driving thermal gradient (estimated as 100–750 K/μm or, temporally, 3000–75,000 K/s), enhanced by incorporation of solvent vapor (here toluene) swelling of the BCP film. The extent of the thermal effects suggests that the role of solvent may extend beyond increasing the mobility of the BCP film to enhancing both the thermal gradient and also potentially the surface energy gradients, providing a thermocapillary shear mechanism. Further, enhanced domain alignment is greatest at higher scan speed, indicating as well the importance of the temporal thermal gradient.