A new imprint directed self-assembly (DSA) route is developed for creating high resolution line patterns consisting of in-plane polystyrene-block-polydimethylsiloxane (PS-b- PDMS) cylinders. Resist line prepatterns are prepared by nanoimprint and trimmed by oxygen plasma to proper feature geometry and dimension. Registered block copolymer line patterns with exceptional long-range order are generated after DSA then, with the smallest half-pitch of 6 nm or so. Excellent stretching capability of PS-b-PDMS polymer chains indicates a broad process window for DSA. Initial pattern transfer results at 16.5 nm pitch imply the potential of this approach for future nanodevice fabrication at ultra-high pattern resolution.
Directed self-assembly (DSA) of block copolymers (BCPs) proves to be a viable solution for the ultrahigh density bit-patterned media (BPM) application. However, servo design integration is still extremely challenging since the servo layouts require more complex patterns than the simple arrays naturally achieved by the DSA process. We present an integration scheme to create BPM servo patterns by utilizing the BCP dot-array patterns. This proposed method is based on an imprint guided two-step DSA process, combined with conventional optical lithography to define two separate zones. Both the data zone and servo zone consist of self-assembled hexagonal dot arrays: a regular pattern in the data zone and an arbitrary pattern in the servo zone. This method was successfully used to fabricate a servo-integrated BPM template with an areal density of 1.5 Teradot/inch2 (Td/in.2) (Lo=22.3 nm). Using the fabricated quartz template, CoCrPt BPM media has been successfully patterned by nanoimprint lithography and subsequent ion-beam etching process on a 2.5 in. disk. Further, using patterned-in servo wedges on 1.5 Td/in.2 patterned CoCrPt media, we are able to close the servo control loop for track-following on a spin-stand test. The standard deviation of repeatable run-out over the full revolution is calculated to be about 4% of the 38.6 nm track pitch. This method is currently being used to fabricate a template at a much higher density of 3.2 Td/in.2 (Lo=15.2 nm).
Bit-patterned media (BPM) fabrication sets a high bar for nanopatterning especially in the aspects of lithography resolution and pattern transfer. Directed self-assembly (DSA) of spherical block copolymers (BCPs) provides promising pattern resolution extendibility and pattern layout flexibility as long as proper pre-pattern designs are provided. Polystyrene-block-polydimethylsiloxane in the form of monolayered spheres is used as a vehicle to form either globally densely packed nanodot arrays in the data zone or locally densely packed nanodot arrays in the servo zone on a BPM template. Skew compatibility of spherical BCPs is also discussed. The BCP dot template is then applied as the scaffold for pattern transfer into quartz to make a nanoimprint mold and further into magnetic storage media. Distributions of both dot sizes and dot spacings are closely monitored after DSA pattern formation and pattern transfer.
KEYWORDS: Electron beam lithography, Optical simulations, Magnetism, Scattering, Point spread functions, Electron beams, Laser scattering, Head, Photoresist processing, Monte Carlo methods
The drive for higher magnetic storage density is correspondingly pushing to minimize the lithographic critical dimensions of the read/write components of thin film magnetic recording heads while maximizing the aspect ratio. Electron beam lithography can provide adequate resolution for research and development of magnetic heads. In this work, we present the experimental results of high aspect ratio trench patterning in 1.0-4.0 μm thick single-layer CAR resists with Leica VB6 operating at 50 keV. Although the maximum achievable aspect ratio in thick resist is limited by the forward scattering of the primary electron beam as it passes through the resist towards the resist-substrate interface, a sub-50 nm isolated top pole trench structure with an aspect ratio about 20:1 has been achieved by using e-beam SAFIER shrink process. To better understand the electron beam proximity effect on the resist profile in thick resists, electron beam simulation has been implemented. The theoretical limit of resist profiles has been predicted by simulation.
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