High-Precision Solvent Vapor Annealing for Block Copolymer Thin Films.

Gunnar Nelson,Ryan Gnabasik,Chloe Drapes,Andrew Baruth,Jeffrey Wong,Meagan Grant

doi:10.3390/mi9060271

Abstract

Despite its efficacy in producing well-ordered, periodic nanostructures, the intricate role multiple parameters play in solvent vapor annealing has not been fully established. In solvent vapor annealing a thin polymer film is exposed to a vapor of solvent(s) thus forming a swollen and mobile layer to direct the self-assembly process at the nanoscale. Recent developments in both theory and experiments have directly identified critical parameters that govern this process, but controlling them in any systematic way has proven non-trivial. These identified parameters include vapor pressure, solvent concentration in the film, and the solvent evaporation rate. To explore their role, a purpose-built solvent vapor annealing chamber was designed and constructed. The all-metal chamber is designed to be inert to solvent exposure. Computer-controlled, pneumatically actuated valves allow for precision timing in the introduction and withdrawal of solvent vapor from the film. The mass flow controller-regulated inlet, chamber pressure gauges, in situ spectral reflectance-based thickness monitoring, and low flow micrometer relief valve give real-time monitoring and control during the annealing and evaporation phases with unprecedented precision and accuracy. The reliable and repeatable alignment of polylactide cylinders formed from polystyrene-b-polylactide, where cylinders stand perpendicular to the substrate and span the thickness of the film, provides one illustrative example.

Highlights

Techniques to achieve periodic nanostructures via traditional “top down” methods, including photolithography, have become increasingly challenging within the semiconductor industry
The directed self-assembly of block polymer (BP) thin films has become a strong candidate to achieve sub-20 nm dimensions, where the size and morphology is controlled by varying the molecular weight of the constituent polymer blocks
It is increasingly clear that annealing BP thin films is critical to achieving self-assembled nanostructures with a given morphology and lateral order

Summary

Introduction

Techniques to achieve periodic nanostructures via traditional “top down” methods, including photolithography, have become increasingly challenging within the semiconductor industry. In 2007, directed self-assembly was first considered as a potential scaling solution, according to the International Technology Roadmap for Semiconductors (ITRS) [11]. In their 2013 report, the directed self-assembly of complex structures with low anneal time, low defect density, and high reproducibility was identified as one of the “Grand Challenges” to extend Moore’s law [11]. The directed self-assembly of block polymer (BP) thin films has become a strong candidate to achieve sub-20 nm dimensions, where the size and morphology is controlled by varying the molecular weight of the constituent polymer blocks

Methods

Results

Conclusion