(A) study on the $La_2O_3$ and La-Al-O films deposited by plasma-enhanced atomic layer deposition

Abstract

The scaling of complementary metal-oxide-semiconductor (CMOS) has led to the silicon dioxide layer, used as a gate dielectric, being so thin that its leakage current is too high. It is necessary to replace the $SiO_2$ with a physically thicker layer of oxides of higher dielectric constant (k) or ‘high-k’ gate oxides. Recently, rear earth oxides are gaining increasing interest in advance electronics. In particular, $La_2O_3$ is considered among the most promising candidates for high-k gate oxides to substitute for $SiO_2$ in advance CMOS devices because of its high dielectric constant, high breakdown strength and good thermal stability. $La_2O_3$ thin films were deposited by plasma enhanced atomic layer deposition (PEALD) using metal-organic precursor $(La(tmhd)_3)$ and $O_2$ plasma as an oxidant. It was verified that the self-controlled growth mechanism of typical ALD was achieved by examinations of source and reactant saturation condition. The film thickness/cycle saturated at 0.37 $\AA$/cycle, when the source pulse time exceeds 3s and the plasma time is over 5s. $La_2O_3$ films were deposited based on the obtained results. The film characteristics were analyzed by compositional, structural, and electrical points. The crystallinity of a $La_2O_3$ thin film deposited at 350℃ was amorphous and crystallized to hexagonal phase through annealing at 850℃ for 1min. The film deposited by this method has not a stoichiometric composition, the ratio of oxygen to lanthanum was around 2.8 by RBS, resulted from OH- group absorbing water after the film were exposed in air, approved by XPS analysis. The phenomena brought out a lowering dielectric constant (ε=23) and large hysteresis because of mobile ions. ALD $Al_2O_3$ films were deposited in situ as a capping layer for the as-deposited $La_2O_3$ thin film in favor of preventing permeation of water. From XPS analysis, we found out that the $Al_2O_3$ capped films successfully block the water absorption phenomena....