(The) microstructure and electrical property of $HfO_2/Al_2O_3$ films deposited by atomic layer deposition

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, the growth of $HfO_2$ films by plasma-enhanced ALD (PEALD) using oxygen plasma as an oxygen reactant of tetrkis(ethylmethylamino) hafnium (TEMAHf) on p-Si(100) substrate was presented and compared with the ones formed by conventional ALD using $H_2O$. The saturated film thickness/cycle in PEALD $HfO_2$ deposited with oxygen plasma was higher than that of ALD $HfO_2$ deposited with $H_2O$ because the number of TEMAHf molecules adsorbed during one deposition cycle increased by the oxygen plasma. The carbon concentration of PEALD $HfO_2$ films was lower than that of ALD $HfO_2$ films at the same deposition temperature. The interfacial oxide layers, generated between $HfO_2$ and Si substrates during the initial stage of ALD, have been also investigated with oxygen plasma and water. In th...