High aspect ratio PS-b-PMMA block copolymer masks for lithographic applications

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Controlling self-assembly and nanostructure orientation in diblock copolymer (DBC) thick films is critical for technological applications.
• Existing methods for achieving perpendicular nanostructure orientation in poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer films yield limited aspect ratios.

Purpose of the Study:

• To investigate the thickness window for perpendicular orientation of cylindrical structures in asymmetric DBC films at elevated temperatures.
• To optimize annealing conditions for obtaining ordered patterns with high orientational correlation.

Main Methods:

• Utilized rapid thermal processing (RTP) for annealing asymmetric PS-b-PMMA films at temperatures ranging from 190 °C to 310 °C.
• Systematically studied the effect of annealing temperature and time on film thicknesses from 10 to 400 nm.
• Employed a lift-off process to create high-aspect-ratio polystyrene templates and confirmed results with grazing-incidence small-angle X-ray scattering (GISAXS).

Main Results:

• Achieved ordered patterns with a maximum orientational correlation length of 350 nm for film thicknesses up to 200 nm.
• Demonstrated the complete propagation of cylindrical structures through the entire film thickness, yielding high-aspect-ratio PS templates (h/d ≈ 7).
• Fabricated silicon nanopillars with ordering and dimensions matching the DBC lithographic mask.

Conclusions:

• Expanded the achievable thickness window for perpendicular nanostructure orientation in asymmetric DBC films.
• Established a method for creating high-aspect-ratio nanostructures suitable for advanced lithographic applications.
• Validated the use of RTP and lift-off processes for fabricating precise nanostructures from block copolymers.