Study of Nb2O5 High-k Dielectric Material Deposited By Atomic Layer Deposition for Metal-Insulator-Metal Capacitor

Abstract

Metal-Insulator-Metal (MIM) capacitors are important components in many electronic devices, including memory devices, filters, and oscillators. The performance of these devices depends strongly on the electrical properties of the dielectric layer. The application of new high-k materials can improve the properties of modern capacitors such as leakage current and capacitance density. However, it is necessary to understand the deposition conditions of both electrode and dielectric materials in order to master the dielectric properties in future MIM capacitors.One potentially interesting high-k material is niobium pentoxide (Nb2O5) with a wide band gap (3.6 eV) and high refractive index (n=2.3 @633 nm) deposited by Atomic Layer Deposition (ALD) using niobium (V) ethoxide as niobium precursor at 180°C and H2O as reaction agent and oxygen source. Nb2O5 films were deposited directly on a silicon (Si 100) substrate or on a 10nm of titanium nitride (deposited by ALD on Si substrate, n=1.4@633 nm). The Nb2O5 films were deposited with a good film thickness uniformity on the 6-inches of the wafers with a thickness ranging from 20 to 60 nm on each sample. The deposition was done under a suitable ALD temperature of 200-300 °C. In order to investigate the film growth, structure, morphology and optical properties, the samples were characterized by spectroscopic ellipsometry (SE), scanning electron microscopy (SEM), X-Ray diffraction (XRD) and atomic force microscopy (AFM). The as-deposited films were then annealed in a furnace at temperature ranging from 500 to 650°C under N2 atmosphere.Subsequently, a MIM structure (Al/Nb2O5/TiN) was produced by adding a second aluminum layer deposited at 250°C on a Nb2O5/TiN/Si stack by the sputtering method. The surface of the second electrodes was aimed to have 0.1-1.0 mm2 to confirm the surface dependency of the capacitance value. The electrical properties of Nb2O5 dielectric layer such as dielectric constant, breakdown voltage and leakage current at possible user voltage were measured on this last structure. The low leakage current density is desirable for MIM capacitors as it helps to minimize energy loss and increase the energy storage capabilities of the capacitors. The obtained J-E curve was compared to some electrical conduction mechanisms to identify its electrical conduction behaviors. The barrier height of the F-N tunneling mechanism was determined by fitting the experimental data to the F-N equation. These measurements indicate that the electrical properties of the Nb2O5 material produced by ALD with specific settings are promising for the application in capacitors. These results provide new insight into our understanding of the application of Nb2O5 realized by ALD for the MIM capacitor.