Focused solar annealing for block copolymer fast self-assembly

Abstract

Block copolymer (BCP) self-assembly has tremendous potential applications in next-generation nanolithography. It offers significant advantages, including high resolution and cost-effectiveness, effectively overcoming the limitations associated with conventional optical lithography. In this work, we demonstrate a focused solar annealing (FSA) technique that is facile, eco-friendly, and energy-efficient for fast self-assembly of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films. The FSA principle involves utilizing a common biconvex lens to converge incident solar radiation into a high-temperature spot, which is directly used to drive the microphase separation of PS-b-PMMA thin films. As a result, PS-b-PMMA undergoes self-assembly, forming ordered nanostructures in a vertical orientation at seconds timescales on silicon substrates with a neutral layer. In addition, the FSA technique can be employed for grafting neutral polymer brushes onto the silicon substrate. Furthermore, the FSA's compatibility with graphoepitaxy-directed self-assembly (DSA) of BCP is also demonstrated in the patterning of contact holes. The results of contact hole shrinking show that contact hole prepatterns of ∼60.4 nm could be uniformly shrunk to ∼20.5 nm DSA hole patterns with a hole open yield (HOY) of 100 %. For contact hole multiplication, doublet DSA holes were successfully generated on elliptical templates, revealing an average DSA hole size of ∼21.3 nm. Most importantly, due to the direct use of solar energy, the FSA technique provides many significant advantages such as simplicity, environmental friendliness, solvent-free, low cost, and net-zero carbon emissions, and will open up a new direction for BCP lithography that is sustainable, pollution-free, and carbon-neutral.

Keywords: Block copolymer; Carbon neutrality; Contact hole multiplication; Contact hole shrinking; Fast self-assembly; Focused solar annealing.

Graphical abstract

Fig. 1

Schematic diagram of FSA for BCP fast self-assembly.

Fig. 2

Under different sunlight intensity, (A) temporal variations of the DNI and (B) the relationship between the temperature and the spot diameter of focused sunlight.

Fig. 3

Schematic diagram of vertically oriented (A) lamellae and (D) cylinders of PS-b-PMMA structures. SEM images of the microphase separation morphology of PS-b-PMMA (M_n = 31-b-33 kg/mol) induced by (B) FSA process and (C) conventional thermal annealing process. SEM images of the microphase separation morphology of PS-b-PMMA (M_n = 37-b-16.8 kg/mol) induced by (E) FSA process and (F) conventional thermal annealing process. All scale bars are 200 nm. The inset illustrates the orientation mappings of self-assembled nanostructures.

Fig. 4

(A) XPS C 1s spectra and (B) carbon and oxygen contents of PS-b-PMMA (M_n = 31-b-33 kg/mol) thin films after various annealing processes. (C) XPS C 1s spectra and (D) carbon and oxygen contents of PS-b-PMMA (M_n = 37-b-16.8 kg/mol) thin films after various annealing processes.

Fig. 5

Influence of annealing time over the BCP self-assembly. SEM images of the lamella-forming PS-b-PMMA (M_n = 31-b-33 kg/mol) self-assembled structures by the FSA process at (A) 5 s, (B) 15 s, (C) 30 s, and (D) 45 s. All scale bars are 200 nm. The inset illustrates the orientation mappings of self-assembled nanostructures.

Fig. 6

SEM images of vertically oriented lamellae of PS-b-PMMA (M_n = 31-b-33 kg/mol) structures by (A) FSA process and (C) conventional thermal annealing process, the scale bars are 200 nm. The inset illustrates the orientation mappings of self-assembled nanostructures. (B) The calculation of the bond-order correlation function, ψ₂(r), is derived from SEM image A. (D) The calculation of the bond-order correlation function, ψ₂(r), is derived from SEM image C.

Fig. 7

(A) SEM image of contact hole shrinking templates at 100 k magnification. SEM images of singlet DSA hole per template at (B) 100 k and (C) 30 k magnifications. All scale bars are 100 nm. (D) The CD of the singlet DSA hole and circular guiding templates.

Fig. 8

(A) SEM image of contact hole multiplication templates at 100 k magnification. SEM images of doublet DSA hole per template at (B) 100 k and (C) 30 k magnifications. All scale bars are 100 nm. (D) The CD of the doublet DSA hole and elliptical guiding templates in y-direction.