{"id":5266,"date":"2012-07-18T22:29:06","date_gmt":"2012-07-18T22:29:06","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/?p=5266"},"modified":"2012-07-18T22:29:06","modified_gmt":"2012-07-18T22:29:06","slug":"removable-template-for-block-copolymer-directed-self-assembly","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/removable-template-for-block-copolymer-directed-self-assembly\/","title":{"rendered":"Removable Template for Block Copolymer Directed Self-Assembly"},"content":{"rendered":"

Self-assembled block copolymer structures are useful in nanolithography applications, producing patterns with high resolution and throughput. We previously showed control over the direction of in-plane cylindrical microdomains formed by self-assembly of a block copolymer (BCP) using a variety of physical templates made from hydrogen silsesquioxane (HSQ) resist [1<\/a>] <\/sup> [2<\/a>] <\/sup>. The HSQ templates were fabricated by electron-beam lithography and then functionalized with a minority or majority block brush to interact with the BCP and direct the self-assembly (as shown in Figure 1). However, HSQ templates were not easily removed and remained as part of the final pattern. Remaining HSQ caused non-uniform pattern transfer due to dissimilar etch rates between the BCP and HSQ. In this study, we solved this issue by using a removable-resist template coated with an etchable-block brush. We fabricated two- and three-dimensional BCP patterns and then removed the templates. Examples (Figure 2) include three-dimensional bends, junctions and mesh-shaped structures, and the ability to change the BCP morphology through templating.<\/ins><\/p>\n

The negative-tone-post templates were made by electron-beam lithography of poly (methyl methacrylate) (PMMA) resist at high dose (100-600 pC\/pixel). After development of patterns using methyl isobutyl ketone (MIBK) and acetone ultrasonication, the surface of the patterns was coated with hydroxyl-terminated polystyrene (PS) brush (1 kg mol-1<\/sup>). Then poly(styrene-b-dimethylsiloxane) (PS-b-PDMS) BCP (MW=45.5 kg mol-1<\/sup>, f_PDMS=0.32, period 35 nm) was spun and solvent annealed with a mixture of heptane and toluene. CF4 <\/sub>and O2<\/sub> reactive ion etch (RIE) was used to remove the top PDMS layer and the PS matrix.\u00a0 The O2<\/sub> RIE not only removed not only the PS matrix but also removed the PMMA template in the same step. The final results were in-plane oxidized-PDMS cylindrical microdomain patterns in the form of two- and three-dimensional structures devoid of templates. This study provides a path to complex pattern formation for nanolithography with feature sizes below 20 nm.<\/p>\n\n\t\t