MTL Annual Research Report 2011

Figure 1: SEM images of the ox-PDMS micro-domains guided by using HSQ template. White and grey colors represent HSQ and ox-PDMS. a) Line frequency doubling happened when using a PS brush and an HSQ template with the same period as the BCP. b) Rectangular lattice shape and dot doubling frequency were achieved by using the PS brush. (Insets: schematic illustrations of the images, in which grey and black colors represent HSQ and ox-PDMS).

In this study, we demonstrated a high-resolution method for doubling the spatial frequency of lines and dots of structures defined by electron-beam lithography, as well as a method for achieving a rectangular lattice in the case of dots. The method used an array of structures defined by electron-beam-lithography (EBL) to template block copolymers. The spatial frequency of the obtained results was half of the original BCP pitch. This method resulted in higher resolution and higher areal density in comparison to previously reported methods for spatial frequency multiplication using templated self-assembly of BCPs, which were limited by the BCP pitch.

In the first step, the templates were fabricated such that the periods of the lines or dots were the same as the period of the BCP. After fabrication of the templates by means of EBL exposure of hydrogen silsequioxane (HSQ) resist, the templates were chemically functionalized with a hydroxyl terminated polystyrene (PS) brush. Then, BCPs of polystyrene-b-polydimethylsiloxane (PS-PDMS) were spin cast onto the substrates with HSQ templates. Annealing of the BCP thin film was done using a cosolvent vapor anneal consisting of 5 parts toluene to 1 part heptane. An oxygen reactive ion etch (RIE) was used to remove the PS block and leave the oxidized-PDMS patterns on the substrate.

Figure 1a shows a scanning electron micrograph (SEM) image of line frequency doubling. The BCP used in this experiment was cylindrical morphology. This result indicates that by using PS functionalized posts; we can template linear spatial-frequency doubling. The period of the resultant lines was half of the period of the HSQ template and the BCP. Figure 1b shows an SEM image of a rectangular lattice obtained by using the above-mentioned method. The HSQ posts formed a centered rectangular lattice as seen in Figure 1b. The BCP used in this experiment was spherical morphology PS-PDMS.