Nanopatterning via Solvent Vapor Annealing of Block Copolymer Thin Films

Abstract

The self-assembly of block copolymers to generate nanopatterns is of great interest as an inexpensive approach to sub-20 nm lithography. Compared to thermal annealing, solvent vapor annealing has several intriguing advantages with respect to the annealing of thin films of block copolymers, particularly for polymers with high interaction parameters, χ, and high molecular weights. In this methods paper, we describe a controlled solvent vapor flow annealing system with integrated in situ microscopy and laser reflectometry, as well as a feedback loop that automatically controls the solvent vapor flow rate, based upon real-time calculations of the difference between thickness set point and the observed film thickness. The feedback loop enables precise control of swelling and deswelling of the polymer thin film, the degree of swelling at the dwell period, and preprogrammed complex multistep annealing profiles. The in situ microscope provides critical insight into the morphological evolution of the block copolymer thin films over a broad area of the sample, revealing information about terraced phases, on the scale of tens and hundreds of micrometers, during the annealing process. This device could be a powerful tool for understanding and optimizing solvent annealing by providing multiple sources of in situ information, at both the micro- and nanoscales.

Technological strategies for self-assembly of PS-b-PDMS in cylindrical sub-10 nm nanostructures for lithographic applications

“…This makes quite difficult the comparison among the experimental data collected by different research groups. Nevertheless, two main categories, usually referred as static and flow SVA, can be identified depending on the solvent process conditions [82]. [82].…”

“…Nevertheless, two main categories, usually referred as static and flow SVA, can be identified depending on the solvent process conditions [82]. [82]. Top-view seM images of cylindrical Ps-b-PdMs obtained by means of (c) 4 h of svA at room temperature, adapted from [64], (d) 15 min of svA with PvA topcoat at room temperature, adapted from [83], and (e) 5 min of svA at 85 °c in trances, adapted from [77].…”

“…Figure 5(a) shows a simple scheme of a static SVA apparatus [82]. The solvent entrapped in the swollen DBC films promotes the self-assembly of the DBC molecules even at room temperature.…”

“…Two optically transparent windows are usually present on the chamber for real-time measurements of the DBC film thickness by ellipsometry in order to monitor the degree of swelling, determined by the adsorbed solvent. A typical swelling profile of PS-b-PDMS film is reported in Figure 5(b) [82]. Although static SVA represents the simplest SVA method, the control of the processing parameters (swelling rate, annealing time, purging) is very difficult.…”

“…Flow SVA requires a much more sophisticated apparatus (Figure 6(a)) consisting of several interfaced instruments to control the flow of solvent in the chamber and the inert gas in the purge line. Moreover, in situ monitoring of the DBC film thickness is necessary during the sample processing [82]. With this experimental setup, the swelling of the PS-b-PDMS films can be precisely controlled by a feedback loop that adjusts the solvent flow in the chamber as a function of the measured thickness.…”