Defect Annihilation Pathways in Directed Assembly of Lamellar Block Copolymer Thin Films

Abstract

Defects in highly ordered self-assembled block copolymers represent an important roadblock toward the adoption of these materials in a wide range of applications. This work examines the pathways for annihilation of defects in symmetric diblock copolymers in the context of directed assembly using patterned substrates. Past theoretical and computational studies of such systems have predicted minimum free energy pathways that are characteristic of an activated process. However, they have been limited to adjacent dislocations with opposite Burgers vectors. By relying on a combination of advanced sampling techniques and particle-based simulations, this work considers the long-range interaction between dislocation pairs, both on homogeneous and nanopatterned substrates. As illustrated here, these interactions are central to understanding the defect structures that are most commonly found in applications and in experimental studies of directed self-assembly. More specifically, it is shown that, for dislocation dipoles separated by several lamellae, multiple consecutive free energy barriers lead to effective kinetic barriers that are an order of magnitude larger than those originally reported in the literature for tightly bound dislocation pairs. It is also shown that annihilation pathways depend strongly on both the separation between dislocations and their relative position with respect to the substrate guiding stripes used to direct the assembly.

Shear-solvo defect annihilation of diblock copolymer thin films over a large area

“…In other words, for defect annealing, it is not always advantageous to use conventional strategies of increasing defect formation free energy (i.e., high χ BCP) because it increases the kinetic energy barrier ( 15 , 16 ). As suggested by our recent study, guiding strips used in DSA could alter the kinetic path of defect annihilation and stabilize the defects by kinetically trapping them ( 19 ). Thus, the proposed annihilation mechanism of SS annealing needs to be appreciated in the context of free energy paths focused on the variation of kinetic energy barriers.…”

“…In particular, higher segregation strength, χ, between the blocks is believed to enhance the thermodynamic driving force ordering the self-assembly patterns, which also corresponds to the increase in the kinetic energy barrier interfering with defect annihilation ( 15 ). In addition, in the case of the most advanced chemoepitaxy-assisted DSA in terms of long-range ordering and defect control, the guiding stripes were found to yield an additional energy barrier ( 19 ). These studies suggest that thermodynamically optimized DSA is not necessarily in accordance with kinetically optimized defect annihilation.…”

Defect Removal by Solvent Vapor Annealing in Thin Films of Lamellar Diblock Copolymers

“…Here, the defect removal pathway is asymmetric 9 in the sense that the two defect horizontal arms (shown in Fig. 1c) break sequentially, one after the other, by crossing two consecutive free-energy barriers 11,13,14 .…”

“…In order to facilitate the fabrication of defect-free films, further treatments are needed. As examples to techniques that have been developed to tailor the self-assembly behavior of BCP thin films we mentioned electric field alignment 4,5 , shear alignment 6,7 , microwave annealing 8 , and thermal annealing 1,2,[9][10][11][12][13][14][15][16] . Besides these approaches, solvent vapor annealing (SVA) 1,3,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] has been used to enhance the mobility of polymer chains, and to facilitate the annihilation of defects.…”

Solvent Vapor Annealing, Defect Analysis, and Optimization of Self-Assembly of Block Copolymers Using Machine Learning Approaches

“…[34][35][36][37] The self-assembly of a monolayer of a given BCP on a flat, featureless surface results in a polycrystalline morphology with uncorrelated nano-to micron-sized domains, with a significant concentration of defects. 38 The ITRS (now IDRS roadmap) has specified a target of a maximum defectivity of ~1 per 100 cm -2 , [39][40][41][42][43] which is several orders of magnitude lower than that quantified in patterns derived from these monolayers of self-assembled BCPs. Some kinetically trapped non-equilibrium metastable configurations in the free energy landscape persist even through long annealing times, which is an issue for high volume manufacturing on 300 mm wafers.…”