<title>Volume-change thermal-lithography technique for ultra-high density optical ROM mastering process</title>

Abstract

We have developed a novel lithography technique, which we refer to here as Volume-Change Thermal-Lithography (VCTL), for application to the mastering process in a manufacture of next-generation ultra-high density optical ROM disks. Using a visible laser beam and conventional optics, we have succeeded in fabricating minute dots with diameters of under 100 nm and with interdot spacing far beyond the optical diffraction limit at a practical fabrication speed of 3 m/s. The combination of the temperature distribution induced by a focused laser beam with a Gaussian profile and a specially designed multilayer consisting of TbFeCo and ZnS-SiO₂ was utilized for fabricating the aforementioned nano-structures. A focused laser beam with a Gaussian profile can generate a peak temperature area far smaller than its spot size. TbFeCo and ZnS-SiO₂ undergo mutual diffusion when heated, a result of which is that their volume expands. An incident pulsed laser induces mutual diffusion restricted to the highest heated area. As a result, minute convex structures appear as dots on the sample surface. In addition to fabrication of continuous dot patterns, as a demonstration, small letters with dimensions of approximately 1 μm were drawn by specific dot arrangement, confirming the strong possibility of the technique.