Single Step Process for Self-Assembled Block Copolymer Patterns via in Situ Annealing during Spin-Casting

Abstract

We demonstrated a simple and time-efficient processing method for facilitating a microphase separation of block copolymers (BCPs) based on a single step of spincasting with low volatile solvent and in situ annealing. Wellordered lamellar patterns of poly(styrene-b-methyl methacrylate) BCP films having wide range of molecular weights (51− 235 kg/mol) were fabricated by a single 3 min process of spincasting, even without the conventional pretreatment of substrate neutralization. The formation of this well-ordered lamellar structure is attributed to a synergetic effect between slow solvent evaporation and thermal energy that may provide an efficient cooling profile for the BCP film during the spincasting process. P atterning via self-assembly of block copolymers (BCPs)can be regarded as one of the promising alternatives that overcome the technological and economical limitations associated with photolithographic approaches. 1−6 For instance, with a number of advantages intrinsic to polymer materials, this cost-effective patterning method is expected to replace in part conventional lithographic process for nanoelectronics applications. 7−11 However, despite this potential usability, many technological issues regarding the pattern fidelity and high throughput still remain unresolved, bottlenecking the viability of BCP patterning technology to be used in the actual applications.Low throughput, which is basically due to the slow ordering kinetics of BCPs in molten state, is one of the main obstacles preventing the practical commercialization for BCP patterning. The most common and traditional process for the pattern formation of BCPs relies on the sequential process consisting of substrate neutralization, spin-casting, and thermal annealing (TA), which undesirably takes several hours or days for achieving sufficient phase separation. 12−18 Many works have been done to facilitate the ordering kinetics of BCP thin film, which commonly employs the solvent vapor annealing (SVA) method to infiltrate solvent vapor into the BCP film in the course of phase-separation. 11,19−21 These works have demonstrated that BCPs under SVA become phase-separated more rapidly with enhanced order than under TA, possibly due to lowered local free energy barriers on the ordering pathway as well as the drastic increase in chain mobility in the solventswollen film. In particular, recent SVA approaches suggested that the ordering kinetics is even more facilitated when additional stimuli are combined with SVA. 22−26 Buriak and coworkers demonstrated the ultrafast formation of the BCP pattern using microwaves that instantaneously elevated the solvent vapor pressure and the annealing temperature accelerating ordering kinetics. 25 Ross and co-workers employed a solvothermal annealing setup combining TA and SVA for BCP film accomplishing excellent order within few minutes, 23 which indicates a synergetic effect on facilitating BCP ordering kinetics. While these combined approaches based on SVA is certainly promising for high-throughput BCP patterning in ...

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

“…Similar effects were seen with cylinder‐forming PS‐ b ‐PMMA . Other interesting annealing methods that promote vertical microdomains have been reported as well, including zone casting, electrospray deposition, and in situ annealing during spin coating . However, these techniques will not be discussed since the ordering mechanism is based on solvent evaporation, much like solvent vapor annealing.…”

“…[162] Other interesting annealing methods that promote vertical microdomains have been reported as well, including zone casting, [163,164] electrospray deposition, [165,166] and in situ annealing during spin coating. [167] However, these techniques Figure 19. TEM cross-section images for star-block PS-PDMS thin film A) without and B) with air plasma treatment.…”

Self-Assembly in ultrahigh molecular weight sphere-forming diblock copolymer thin films under strong confinement

“…The as-prepared film (Fig. 3a) displays a surface structure with large-sized continuous PMMA domains, since DMF is used for dissolving PS- b -PMMA, which is a good solvent for PMMA and a poor solvent for PS 9 . However, with increasing annealing time from 0 h to 0.5 h, the PMMA domain size decreases while the PS phase increases.…”

Large-Grained Cylindrical Block Copolymer Morphologies by One-Step Room-Temperature Casting

“…Jung et al have combined nonvolatile solvent spin-casting with in situ heating with a high-power IR lamp to evaporate diphenyl and dibenzyl ethers to order lamellar PS- b -PMMA without the need for neutral-brush grafting typically required for obtaining vertically oriented BCP lamellae. 73 …”