Improvement in the aspect ratio of fabricated minute dots by the volume change thermal lithography technique

Volume change thermal lithography has been developed as a low cost and simple lithography technique for application in optical mastering. The combination of the temperature distribution induced by a focused laser spot with a Gaussian distribution and a special multilayer consisting of TbFeCo and ZnS-SiO₂ are utilized. Application of heat to these materials induces interdiffusion and as a result local volume expansion leading to the formation of a convex surface region. This technique was used to fabricate nano-dots with dimensions less them 100 nm on the sample surface. Typical nano-dot height, however, was less than 20 nm and this value is not sufficient for the pit height of an optical master disk. To address this problem, a PtO_x film was inserted between the TbFeCo and ZnS-SiO₂ layers. Laser irradiated PtO_x decomposed to Pt and oxygen leading to additional surface protrusion due to the combination of the thermally induced interdiffusion of the TbFeCo and ZnS-SiO₂ region and PtO_x decomposition induced compressive stress. Nano-dots of 110 nm diameter and 37 nm height were successfully fabricated. Transmission electron microscope (TEM) observations of the nano-dot structure are reported.