Crystallization process and amorphous state stability of Si-Sb-Te films for phase change memory

Abstract

Crystallization process and amorphous state stability of Si-Sb-Te films with different Si concentration (10, 20 at. %) and Sb/Te ratio (2:3 and 1:1) have been studied and compared with Ge2Sb2Te5 (GST) film by in situ film resistance measurements. The effects of Si concentration and Sb content on crystalline resistivity, crystallization temperature, activation energy of crystallization, and amorphous state stability of films have been studied. The activation energy Ea of crystallization of GST film was confirmed to be 2.34 eV, while the activation energy Ea of Si10Sb36Te54 film increased to 2.99 eV and further reached to 3.65 eV for Si20Sb32Te48 film when the Si content increased to 20 at. %. Si addition increased the crystallization temperature and crystalline resistivity of Si-Sb-Te films largely, and enhanced the amorphous state stability of the films, while Sb revealed contrary effects to Si. The microstructures of Si-Sb-Te films were analyzed through x-ray diffraction and high resolution transmission electron microscopy. Phase separation has been observed in annealed Si-Sb-Te films, and Si-Sb-Te films crystallized into rhombohedral Sb2Te3 phase surrounded by amorphous Si-rich grain boundaries with high resistance, which would be helpful to reduce the writing current of phase change memory.