Keywords: nanolithography, self–assembly, block copolymers, nanodots, bit patterned media, BPM, magnetic storage, nanotechnology, nanopatterns, magnetic recording media, quantum devices, PV cells, photovoltaic cells, battery cells
Attempts to form the 10–nm–order pitch of self–assembled nanodots using PS–PDMS block copolymer
Block copolymer (BCP) self–assembly exhibits its ability to form various nanostructures with a size down to 3 nm, which is particularly attractive for emerging technologies such as bit patterned media (BPM). Poly(styrene–b–dimethyl siloxane) (PS–PDMS) has been acknowledged as the most promising block copolymer for self–assembly fabrication due to its possibility to form nanopattern with a fine pitch, high etching selectivity, and its characteristic of robustness for pattern transfer. Here, we attempt to form PS–PDMS self–assembled nanodot array with a 10–nm–order pitch in order to satisfy the demand of low cost technique to form ultrahigh density nanodot array for BPM, which is regarded as the next–generation magnetic recording media, and for quantum devices such as the third–generation quantum dot photovoltaic cell and future battery cell. In this study, self–assembled nanodot array on a large area with pitches of 11 nm (σ = 2.08 nm) and 10 nm (σ = 1.61 nm) was formed using PS–PDMS with molecular weights of 5600-1300 g/mol (minority block volume fraction fPDMS = 19.8%) and 4700-1200 g/mol (fPDMS = 21.4%), respectively. In experiments, it was shown that some critical parameters, such as the thickness of PS–PDMS film, the treatment of the substrate surface, and annealing condition, played crucial roles in forming 10–nm–order size of self–assembled nanodot array using PS–PDMS. The relationships between pitches of PS–PDMS nanodot array and the product of the total number of segments and the Flory–Huggins segmental interaction parameter (χN) obtained by calculations and experiments will be discussed. Based on the position of PS–PDMS on mean–field phase diagram for BCP melts, the possibility to form nanodot array with a pitch of less than 10 nm is described. This study promises to open way toward the fabrication of more than 7.45 Tbit/in.² storage devices and the application of quantum devices.