Ion-milling method for aperture fabrication in GaP probes for near-field optical memory application

New optical memory system is urgently required to realize high memory capacity and fast data transfer rate in the coming high-speed internet era. To overcome the current capacity barrier of far-field techniques, a novel near-field optical memory using near-field optics has been proposed using vertical cavity surface emitting laser (VCSEL) microprobe array. Arrays of up to 625 microprobes were prepared successfully using newly developed micro-fabrication process, which includes the photolithography and dry etching by ion-milling method. Since etching rate depends on the incident angle of ion beam to etching surface, it is possible to realize higher etching rate for metal layer deposited on top surface compared to side plane by adjusting the angle of ion beam to both surfaces. In case of GaP microprobes, the relative etching rate of top surface to side plane shows maximum value when top surface is exposed to ion beam with 25 degree. After forming apertures on top surface, GaP probe shows triangle surface of around 200 nm in each edge, which strongly depends on its original size of flat-tip surface before the aperture formation. We believe that ion-milling method developed in this research is very effective to prepare all apertures simultaneously in the array system and can be applied to other microprobes prepared in batch process.