Lanthanum aluminate by atomic layer deposition and molecular beam epitaxy

Abstract

A comparison of physical and electrical characteristics of lanthanum aluminate (LAO) dielectrics formed by atomic layer deposition (ALD) and molecular beam epitaxy (MBE) is investigated in this study. Physical characteristics of LAO deposited with these two deposition methods are compared using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). Capacitors with TaN and TaSiN gate electrodes were fabricated to assess electrical properties of these LAO films. ALD LAO was deposited using La[N(SiMe3)2]3,Al(CH3)3 and water at 225–275 °C. ALD LAO is stable against Pt and TiN∕W metal gates up to 800 °C. After annealing at 900 °C, interactions between metal gates and dielectrics are observed resulting in nonfunctional devices. MBE LAO film was deposited at room temperature or 200–400 °C in two ways: Using single element targets (La, Al) or a compound target. The LAO∕TaN stack deposited with single element targets showed significant Si up diffusion from the substrate to the dielectric and the metal gate electrode. In addition, nitrogen diffusion from the metal gate into the dielectric was detected. The LAO∕TaN stack deposited with a compound target showed improved thermal stability. No metal out-diffusion and only very slight Si out diffusion was detected after a 900 °C anneal. LAO capacitors show well-behaved capacitance-voltage and leakage current density-voltage characteristics. These results indicate that the method by which lanthanum aluminate films are deposited strongly influenced their thermal stability. Of all the films examined, the most stable films are deposited by MBE using a compound target.