Block Copolymer Lithography in the Magnetic Storage Industry
Block copolymer directed self-assembly continues to make advances that place this technology as a potential candidate for sub-20nm lithography. The naturally periodic features found in block copolymer films display superior size uniformity atultra-high densities, making them ideal lithographic masks to define the highly periodic data bits in the data sectors of hard disk drives for bit patterned media (BPM) technology at densities beyond 1Tbit/in2.
Nanofabrication challenges towards bit-patterned media, however, reach far beyond pattern formation at small length scales. We explore two potential architectures amenable to directed self assembly: arrays of hexagonal close packed (hcp) circular dots and arrays of rectangular bits with a high aspect ratio. On the one hand, hcp patterns maximize feature density for a given lithographic dimension while, on the other hand, rectangular patterns support wider write head poles in order to achieve the high write fields needed to write high-coercivity media. In both cases a combination of e-beam lithography with block copolymer self assembly ensures the small dimensions required for high density media together with the flexibility to achieve accurate translational placement over circular tracks with constant angular pitch.
Looking forward, extendibility towards higher areal densities remains very much dependent on the ability of block copolymer lithography to deliver high image quality and high etch-contrast features for single-digit lithography at full-wafer scale. I will review the current challenges in pattern transfer at these small dimensions and evaluate some potential solutions that may enable the fabrication of patterned media templates beyond 1Tb/in2.