Low temperature growth of high-k Hf-La oxides by remote-plasma atomic layer deposition: Morphology, stoichiometry, and dielectric properties

In this work, we investigated the growth of Hf oxide, La oxide, and alloyed Hf-La oxide films using remote-plasma atomic layer deposition at temperatures ranging from ∼80 to ∼250 C. The relative composition and atomic bonding structure of the film were determined by in situ x ray photoelectron spectroscopy (XPS). Atomic force microscopy and transmission electron microscopy were implemented to characterize the morphology and crystalline structure. The XPS results indicated that for low temperature Hf oxide growth, a significant amount of excess oxygen species was observed in the deposited film. This oxygen could lead to instabilities and adversely affect the function of thin film transistors. The authors established that a He plasma post deposition treatment can partially remove the excess oxygen. In addition, the pure Hf oxide films show a surface morphology with protruding islands over a smooth surface which reflects the crystallized nature of the Hf oxide domains. In order to suppress the crystallization of the Hf oxide and to obtain a smooth morphology, 1-3 cycles of La-oxide were employed between adjacent Hf-oxide cycles. The Hf-La oxide films showed reduced roughness compared with that of the pure Hf oxide film. Carbon residue in the alloyed film is also reduced compared with that of the La oxide film. Finally, the electrical properties of the deposited films were characterized by capacitance-voltage (C-V) and current-voltage (I-V) measurement. The I-V curves show that the alloyed Hf-La oxide films have a higher break down field than that of pure Hf oxide films.