The Effects of Tin Underlays on the Stability of Gold Thin Films during Isothermal Annealing

Abstract

An investigation is undertaken to study the influence of thin layers of tin, which are sandwiched between gold films and SiO2 substrates, on the thermal stability of gold (as used for metallizations in microelectronic devices). It is found that tin has, similarly as indium, a stabilizing influence on the gold grain structure when the Au/Sn composite film is annealed between 300 and 500 °C in air. The tin from the underlayer is found to diffuse through the gold film to form SnO2 on the free surface and near the grain boundaries, which contributes to the prevention of hole and hillock formation and to an only minimal grain growth during thermal treatment. No preferred orientation of the gold films is found.

Properties of Tin Oxide Films Prepared by MOCVD

“…The composition of as-deposited tin oxide films could be an oxygen deficient state like SnO 2-x , SnO, or Sn [5] and the respective grains of the film can have little stress between the crystallites or the cauliflower grains and the alumina substrate. Annealing in air atmosphere at high temperature can cause the oxygen deficient tin oxide move near the stoichiometric composition of SnO 2 leading to the volume expansion of film [6]. The cauliflower grains on substrate can have high stress due to the volume expansion related to the increase of oxygen The cauliflower grain under higher stress and high temperature could migrate from bottom to the surface to release the stress leading to the formation of hillocks.…”