SNOM imaging of very fine pits formed by EB lithography for ultrahigh density optical recording

The possibility to optically image the very fine pit structure formed by electron beam (EB) writing has been researched using scanning near-field optical microscopy (SNOM). Fine test pit samples were formed in an electron resist (ZEP520) with a minimum pit size of 30 nm × 160 nm. From experimental results using the pits, a conventional reflection SNOM could not image fine pit structures with a size of less than 100 nm. The technique was improved by coating the metal film on the optical probe and adopting an optical depolarization technique in the SNOM optics efficiently to detect near-field light reflected from the sample surface. We demonstrated that very fine pits with a minimum size of 30 nm were imaged and discussed that reflection type depolarization SNOM has a potential to achieve an ultrahigh density optical reading with 1.2 Tb/in.², which is limited by EB fabrication of the pits.