Property study of phase change materials for nanopatterning

Abstract

Metallic glass, Al-Ni-Gd, was explored for its potential as a phase change thermal absorption medium for application in ultra-high density read only memory (ROM) storage disk mastering process. Thermal analysis showed that Al-Ni-Gd film has high activation energy. Optical analysis confirmed the material undergoes phase change transition from amorphous when as-deposited to crystalline state after annealed, making it a suitable material as the phase change thermal absorption layer in this study. A specially designed laser thermal lithography (LTL) structure combining with the proposed LTL technique was used to study the fabrication of nano-dots on the dependence on incident laser peak power, laser pulse width and phase change thickness. Al-Ni-Gd was used as the phase change layer in the LTL structure which performed as a thermal absorption material. By using a focused beam (blue laser of wavelength 405 nm) with numerical aperture of 0.9, a Gaussian distribution of light intensity produced an effective hot spot when absorbed by the Al-Ni-Gd phase change layer. The hot area induced thermal cross-linking reaction to the top active dielectric layer, with the result that nano-dots were fabricated after etching. In this project, nano-dots of 200 nm dimensions were successfully fabricated using the proposed LTL technique, which was very close to the diffraction limit of 225 nm given by the optical set-up. We found that the size and height of the nano-dots increased with increasing laser pulse width and power. However, with increasing phase change layer thickness, both size and height of nano-dots were observed to decrease. With the results, LTL technique has demonstrated to have the potential as a simple and low-cost lithography technique for application in optical disk mastering process.