Microstructure Development and Evolution of Sputter Deposited Indium Thin Films in Cryogenics

Abstract

Low melting temperature materials have been deposited on amorphous substrate using DC magnetron sputter system. Process parameters such as power, pressure, and temperature have been investigated to improve surface morphology based on kinetic concept of condensation film mechanisms. Very rough surface was produced in thin films whose thickness was less than 1 micrometer deposited at room temperature, and it seems to correlate with intrinsic stress induced by sputter deposition. Since intrinsic stress is influenced by the diffusion of atoms, microstructure of films could be modified by changing process parameters. Low diffusivity and high nucleation rate created smoother surface with small grain size. Temperature is the most critical parameter that affects nucleation and diffusion of adatoms, so that microstructure could be dramatically modulated at low homologous (Ts/Tm) temperature with nano-granular structure. Indium vi films were deposited on cooled substrate by flowing liquid nitrogen to obtain low homologous temperature of indium which has low melting temperature as 156 oC. A structure zone model was proposed with revision for a very thin film of low melting temperature materials, and the boundary between zone 1 and zone 2 was shifted to higher homologous temperature. Properties due to modulated microstructure were also studied. Sheet resistance and reflectance were dramatically improved in 200 nm thickness films by improved surface roughness. This study provides a better understanding of very thin film deposition, and the wide selection of materials for various applications such as metallic narrow band pass filters, electrodes in flexible display, and so on.