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 ZnSSiO2 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 100nm on the sample surface. Typical nano-dot height, however, was less than 20nm and this value is not sufficient for the pit height of an optical master disk. To address this problem, a PtOx film was inserted between the TbFeCo and ZnSSiO2 layers. Laser irradiated PtOx decomposed to Pt and oxygen leading to additional surface protrusion due to the combination of the thermally induced interdiffusion of the TbFeCo and ZnSSiO2 region and PtOx decomposition induced compressive stress. Nano-dots of 110nm diameter and 37nm height were successfully fabricated. Transmission electron microscope (TEM) observations of the nano-dot structure are reported.
thermal lithography mastering optical rom disk visible laser light volume change material the diffraction limit