We report a method to fabricate high-quality patterned magnetic dot arrays using block copolymer lithography, metal deposition, and a dry lift-off technique. Long-range order of cylindrical domains oriented perpendicular to the substrate and in hexagonal arrays was induced in the block copolymer films by prepatterning the substrate with topographic features and chemically modifying the surface to exhibit neutral wetting behaviour towards the blocks of the copolymer. The uniformity of the domain size and row spacing of block copolymer templates created in this way was improved compared to those reported in previous studies that used graphoepitaxy of sphere-forming block copolymers. The pattern of block copolymer domains was transferred to a pattern of magnetic metal dots, demonstrating the potential of this technology for the fabrication of patterned magnetic recording media.

The application of block copolymers (BCPs) for the fabrication of ultra-high-density addressable arrays, such as bit-patterned media (BPM), has been hampered by the poor intrinsic limit of thin film technology for long-range lateral ordering and orientation control over microdomains. [1][2][3][4][5][6] Chemically patterned substrates have been used to induce lateral ordering and to control the orientation of microdomains. [7][8][9][10] However, the resolution scalability, defined here as the ratio of the period patterned onto the surface and the natural period of the BCP, was limited to about a factor of 2. Additionally, when anisotropic BCP microdomains, such as cylinders or lamellae, are used, their orientation normal to the film surface (necessary for pattern transfer) requires the use of surfaces having balanced interfacial interactions with the blocks of the BCP and the use of BCPs with blocks having near-equal surface energies. Alternatively, the BCPs must be in nonequilibrium states that are susceptible to relaxation during thermal conditioning. In addition, to achieve small features, the microdomains of the BCP must be small, requiring the BCP to be in the strong segregation limit. This restricts the number of BCPs that are useful in achieving such small size scales; otherwise, additives must be used to enhance the microphase separation. It would be far more desirable to develop a process using BCPs with symmetric microdomains (spherical), so that it would be possible to take advantage of the differences in the interaction of the blocks with the substrate and in the surface energies of the blocks. This would make the process far more versatile and applicable to many different BCPs.Here, we used a BCP with spherical microdomains and a patterned substrate comprising a semidense hole-tone pattern in an ultrathin preferential wetting layer. As shown in Figure 1, the substrate was pretreated with a preferential wetting layer with a thickness of <10 nm consisting of a polymer brush with selective affinity for the major block of the copolymer. The surface energy of the minor component is lower than that of the major component, forcing a preferential segregation of the minor component to the free surface. The minor component also has a preferential affinity for the shallow patterned hole areas, which were formed by selectively removing the brush layer via an electron-beam lithography (EBL) process. Under these conditions, the equilibrium, and thus thermodynamically stable, structure of a film having a thickness 1.5 times the centerto-center distance of the spherical microdomains in the bulk (1.5 L 0 ), will consist of the lower surface energy component at its surface, pinned spherical microdomains of the minor component block covering the patterned features, and an array of spherical microdomains imbedded within the thin film. The pinned spherical microdomains may be spherelike, hemispherical, or even pancakelike, depending on the relative sizes of the patterned features and the natural BCP spherical domains. The...

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The directed self-assembly of block copolymer (BCP) offers a new route to perfect nanolithographic patterning at sub-50 nm length scale with molecular scale precision. We have explored the feasibility of using the BCP approach versus the conventional electron beam (e-beam) lithography to create highly dense dot patterns for bit-patterned media (BPM) applications. Cylinder-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) directly self-assembled on a chemically prepatterned substrate. The nearly perfect hexagonal arrays of perpendicularly oriented cylindrical pores at a density of approximately 1 Terabit per square inch (Tb/in.(2)) are achieved over an arbitrarily large area. Considerable gains in the BCP process are observed relative to the conventional e-beam lithography in terms of the dot size variation, the placement accuracy, the pattern uniformity, and the exposure latitude. The maximum dimensional latitude in the cylinder-forming BCP patterns and the maximum skew angle that the BCP can tolerate have been investigated for the first time. The dimensional latitude restricts the formation of more than one lattice configuration in certain ranges. More defects in BCP patterns are observed when using low molecular weight BCP materials or on non-hexagonal prepatterns due to the dimensional latitude restriction. Finally, the limitations and challenges in the BCP approach that are associated with BPM applications will be briefly discussed.

Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots∕in.2) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist ZEP520 and 12 nm for a negative-tone resist silsesquioxane, corresponding to the areal density of ∼2.0 and ∼4.5 Tdots∕in.2, respectively. Using the ZEP520 resist process, a Cr dot array with a pitch of 21 nm (∼1.5 Tdots∕in.2) for template fabrication is demonstrated. High-quality scanning electron microscopy and atomic force microscopy images were used as primary metrology for both the dot size uniformity and the placement accuracy analysis.