Defect dominated charge transport in amorphous Ta2O5 thin films

Abstract

Ta 2 O 5 is a candidate for use in metal-oxide-metal ͑MOM͒ capacitors in several areas of silicon device technology. Understanding and controlling leakage current is critical for successful implementation of this material. We have studied thermal and photoconductive charge transport processes in Ta 2 O 5 MOM capacitors fabricated by anodization, reactive sputtering, and chemical vapor deposition. We find that the results from each of these three methods are similar if one compares films that have the same thickness and electrodes. Two types of leakage current are identified: ͑a͒ a transient current that charges the bulk states of the films and ͑b͒ a steady state activated process involving electron transport via a defect band. The transient process involves either tunneling conductivity into states near the Fermi energy or ion motion. The steady state process, seen most commonly in films Ͻ300 Å thick, is dominated by a large number of defects, ϳ10 19-10 20 cm Ϫ3 , located near the metal-oxide interfaces. The interior of thick Ta 2 O 5 films has a substantially reduced number of defects. Modest heating ͑300-400°C͒ of Ta 2 O 5 in contact with a reactive metal electrode such as Al, Ti, or Ta results in interfacial reactions and the diffusion of defects across the thickness of the film. These experiments show that successful integration of Ta 2 O 5 into semiconductor processing requires a better understanding of the impact of defects on the electrical characteristics and a better control of the metal-Ta 2 O 5 interface.

Identifying and Engineering the Electronic Properties of the Resistive Switching Interface

“…It has three oxygen sites: one interlayer and two intralayer. The GGA band gap is 1.8 eV and is improved by sX-LDA functional to 4.0 eV, in agreement with the experimental value [45]. Crystalline TaO2 has a rutile structure and is shown to be metallic by both GGA and sX-LDA functionals, which is consistent with a recent calculation [19] and the XPS observations [19].…”

Electrochemical behavior assessment of tantalum in aqueous KOH solutions

“…Table 2 shows the calculated donor density of tantalum in KOH solutions. The density of donors (N D ) is in the order of magnitude of 10 20 to 10 22 cm −3 , which is analogous to those reported previously [43]. These high values of the donor densities can be thought as a higher density of oxygen vacancies in the passive film [12,43].…”

“…As long as the thin native oxide on Ta is concerned, however, a depth-profiling study of tantalum metal/oxide interface by combining X-ray photoelectron spectroscopy (XPS) with Ar + ion bombardment has revealed that Ta sub-oxides exist particularly near metal/oxide interface, which have a distribution that is different from the thermally grown oxide films [42]. On the other hand, voltammetry and photoconductivity measurements have shown that point defects are predominantly located near metal/passive film interfaces and their density is vastly reduced moving toward bulk Ta 2 O 5 [43]. Table 2 shows the calculated donor density of tantalum in KOH solutions.…”

Frequency Dependence of C-V Characteristics of MOS Capacitors Containing Nanosized High-κ Ta2O5 Dielectrics

“…Substantial difference in the equivalent oxide thickness is observed. The lowest value of 2.27 nm is obtained for Al gate and is attributed to the known reactivity of Al with Ta 2 O 5 [26].…”