Study of Gas Cluster Ion Beam Planarization for Discrete Track Magnetic Disks

We studied planarization of carbon overcoat by gas cluster ion beam (GCIB) for discrete track magnetic disks. We fabricated discrete tracks with variant pitches by focused ion beam on a 30-nm-thick carbon overcoat deposited on magnetic disks, and we planarized them with an Ar GCIB using lateral sputtering effect. It was found that planarization by GCIB was more effective for lower wavelengths than for those with a few hundreds nanometers. On the discrete tracks with 100-nm pitch and 20-nm depth, the initial peaks and valleys were removed by GCIB; however, on the ones with over 200-nm pitch, the initial peaks and valleys remained though the heights were drastically decreased. These results indicate the capability of GCIB planarization as a process for the discrete track media. Furthermore, cross sections were observed by transmission electron microscopy. The GCIB with relatively low dose could also planarize the 120-nm-pitch carbon tracks without etching the magnetic layer.