(A) Study on Effects of Thickness and Preferred Orientation on Dielectric Constant of Hf-Aluminate Film Deposited by PEALD

Abstract

As the size of semiconductor devices continues to shrink to ever smaller dimensions, maintaining cell capacitance (25 ~ 30fF/cell) in DRAM capacitor becomes one of the critical issues. In order to meet this kind of requirement, the development of high-k dielectrics has recently been the focus of intensive efforts to replace $SiO_2$ or silicon oxide-/nitride-based systems for the application of capacitor dielectrics. Of various high-k dielectrics under investigation, $HfO_2$ has displayed many of the promising properties for this purpose, which are primarily due to its high dielectric constant (k = 20-25) and wide band gap (~5.68eV). Along with the development of high-k dielectrics, there is a demand of new deposition technique in order to obtain the controllability of thickness in nanometer scale and superb step coverage. Among various deposition techniques, atomic layer deposition (ALD) is known as the most adequate technique because of its unique feature of the self-limited growth mechanism. This self-limited growth mechanism provides the exact control of the thickness even in ultra-thin film and the conformal deposition for 3-D capacitor structures. In this study, first of all, an experimental approach based on phase transition engineering where the metastable phase of $HfO_2$ with high dielectric constant is stabilized completely by the addition of $Al_2O_3$ was reported. Through the phase transition, the dielectric constant of Hf aluminate films could be enhanced because they had the tetragonal phase with a higher dielectric constant, which are metastable at RT. The relationship between the crystal structure and the dielectric constant in Hf aluminate films were also discussed. When the number of $Al_2O_3$ unit cycles was fixed at 1, Hf aluminate films with below 9 $HfO_2$ unit cycles had the amorphous phase. In the range of 10 to 20 $HfO_2$ unit cycles, the tetragonal phase was observed, which is classified into the (111)-oriented tetragonal phase for ...