Planarization of Bit-Patterned Surface Using Gas Cluster Ion Beams

The planarization of the bit-patterned surface using gas cluster ion beams (GCIBs) was studied. By applying the features of gas cluster ions, such as low-energy irradiation and surface smoothing effects, it is possible to carry out effective smoothing of a patterned surface. We fabricated a dot pattern on the Si substrate as a model structure for bit-patterned media by electron beam lithography and inductive coupled plasma etching. A carbon overcoat covered the Si dots. On Ar-GCIB irradiation at an acceleration voltage of 20 kV, the Si dots with a diameter of 150 nm were planarized. The required ion dose for planarization was 5 times 10¹⁴ ions/cm². The cross-sectional transmission electron microscope images showed that only the carbon overcoat layer was planarized without a change in the structure of Si dots. Etching depth of the overcoat increased linearly with the ion dose, indicating good reproducibility of the method with precise control of residual thickness.