Diameter-Reduced Islands for Nanofabrication Toward Bit Patterned Magnetic Media

Thin films deposited on a flat substrate, if the adhesion is not strong, can be made to ball up and form discrete islands upon heating to elevated temperatures due to the surface energy difference. We have applied this useful process to electron beam lithography (EBL) and nano-imprinting lithography (NIL). By combining the ball-up processes of Ni thin film with e-beam lithography followed by reactive ion etching, Si nano islands and vertical nanopillars as small as 10 nm in diameter have been realized. There is a strong correlation between the initial thickness of Ni mask layer and final Ni island diameter obtained after ball-up. The smallest island diameter is obtained using ~ 5-nm initial Ni layer thickness. Below 3-nm initial layer thickness, the intended ball-up reaction does not occur. With more than ~ 15-nm initial metal film thickness, the Ni layer is broken up into nonspherical and highly irregular structures. [Co/Pd]_n multilayer magnetic thin films deposited on prepatterned substrate by nano imprinting lithography with versus without island ball-up process have been investigated for bit patterned media studies. The coercivity of magnetic islands can be enhanced by island diameter reduction using the ball up process.