Growth kinetics of amorphous interlayers and formation of crystalline silicide phases in ultrahigh vacuum deposited polycrystalline Er and Tb thin films on (001)Si

Abstract

The growth kinetics of amorphous interlayer (a-interlayer) and formation of crystalline silicide phases in ultrahigh vacuum deposited polycrystalline Er and Tb thin films on (001)Si have been investigated by cross-section transmission electron microscopy. The growth of the amorphous interlayer in both Er/Si and Tb/Si systems was observed to exhibit similar behaviors. The growth was found to follow a linear growth law initially in samples annealed at 190–240 °C. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be 0.5 eV, 15.5 nm, and 0.35 eV, 16 nm in Er/Si and Tb/Si systems, respectively. Crystalline silicides (ErSi2−x or TbSi2−x) were found to form at the amorphous interlayer/Si interfaces in samples after prolonged and/or high-temperature annealing. Simultaneous growth of the a-interlayer and crystalline phase was observed and the growth rate of a-interlayer was faster than the growth of epitaxial ErSi2−x and TbSi2−x phases in samples annealed at 270–300 °C in Er/Si and Tb/Si systems, respectively. The competitive growth can be understood from energetic consideration. A high density of recessed amorphous regions were found to form between isolated epitaxial silicide regions which led to uneven silicide/Si interfaces and eventually pinholes in the silicide films at high temperatures. The formation mechanism of rough silicide/Si interface is discussed.