Spatial Control of the Self-assembled Block Copolymer Domain Orientation and Alignment on Photopatterned Surfaces

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Block copolymer self-assembly is crucial for creating nanoscale patterns.
• Directed self-assembly (DSA) requires precise surface patterning for orientation control.
• Photopatternable surface treatments offer a route to guide block copolymer alignment.

Purpose of the Study:

• To investigate the effectiveness of polarity-switching photopatternable grafting surface treatments (pGSTs) and cross-linkable surface treatments (pXSTs) for directed self-assembly (DSA).
• To evaluate the influence of surface treatment type and film thickness on the alignment and defectivity of poly(styrene-block-4-trimethylsilylstyrene) (PS-b-PTMSS) block copolymers.
• To understand the role of photoacid diffusion in determining the quality of surface patterns and subsequent DSA.

Main Methods:

• Electron beam lithography was used to pattern pGSTs and pXSTs with acid-labile monomer units.
• Fourier transform infrared spectroscopy (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were employed to study photoacid diffusion.
• The self-assembly of PS-b-PTMSS (domain periodicity L0 = 44 nm) was analyzed on the patterned surfaces.

Main Results:

• PS-b-PTMSS exhibited significantly lower defectivity and improved alignment on pXST guidelines compared to pGST guidelines.
• Thinner films of pXST demonstrated slower photoacid diffusion, leading to sharper interfaces between patterned regions.
• Enhanced alignment control of PS-b-PTMSS was achieved on thinner pXST guidelines due to improved interface definition.

Conclusions:

• Polarity-switching photopatternable surface treatments, particularly pXSTs, are effective for directing block copolymer self-assembly.
• Film thickness plays a critical role in controlling photoacid diffusion and the resulting pattern quality for DSA.
• Optimizing surface treatment properties, such as thickness and chemical nature, is key to achieving high-resolution, low-defect block copolymer nanostructures.