Fabrication of ridge-and-groove servo pattern consisting of self-assembled dots for high-density bit patterned media

Bit patterned media (BPM) is a candidate for high-density magnetic recording. One of the critical issues concerning high-density BPM is a fine pattern drawing process for an etching mask. A self-assembled polymer is a solution for the fine etching mask material realizing a density of more than several Tb/in2. The remaining issue concerning the self-assembled mask is servo pattern formation with the self-assembled dots. This paper reports fabrication of a ridge-and-groove servo pattern with arrays of 35nm-pitch self-assembled CoPt magnetic dots and signal properties of the servo pattern are estimated. Dot size and alignment was not uniform in the servo pattern because of the deviation of the guide width and the taper at the guide edge. This feature will result in a distorted servo signal profile. However, the numerical estimation based on the fabricated servo patterns revealed that the linearity of the position error signal was fairly good. The distortion in waveform does not degrade the phase information of the servo signal, provided the guide is positioned with high precision. Thus the ridge-and-groove servo is suitable for self-assembled bit patterned media.