Plasma Enhanced Atomic Layer Deposition of Tantalum (V) Oxide

Pavel Fedorov,Maxim Yu Maximov,Vladimir Tolmachev,Aleksander Rumyantsev,Anatoly Popovich,Oleg Medvedev,Denis Nazarov,Yury Koshtyal

doi:10.3390/coatings11101206

Abstract

The tantalum oxide thin films are promising materials for various applications: as coatings in optical devices, as dielectric layers for micro and nanoelectronics, and for thin-films solid-state lithium-ion batteries (SSLIBs). This article is dedicated to the Ta-O thin-film system synthesis by the atomic layer deposition (ALD) which allows to deposit high quality films and coatings with excellent uniformity and conformality. Tantalum (V) ethoxide (Ta(OEt)5) and remote oxygen plasma were used as tantalum-containing reagent and oxidizing co-reagent, respectively. The influence of deposition parameters (reactor and evaporator temperature, pulse and purge times) on the growth rate were studied. The thickness of the films were measured by spectroscopic ellipsometry, scanning electron microscopy and X-ray reflectometry. The temperature range of the ALD window was 250–300 °C, the growth per cycle was about 0.05 nm/cycle. Different morphology of films deposited on silicon and stainless steel was found. According to the X-ray diffraction data, the as-prepared films were amorphous. But the heat treatment study shows crystallization at 800 °C with the formation of the polycrystalline Ta2O5 phase with a rhombic structural type (Pmm2). The results of the X-ray reflectometry show the Ta-O films’ density is 7.98 g/cm3, which is close to the density of crystalline Ta2O5 of the rhombic structure (8.18 g/cm3). The obtained thin films have a low roughness and high uniformity. The chemical composition of the surface and bulk of Ta-O coatings was studied by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. Surface of the films contain Ta2O5 and some carbon contamination, but the bulk of the films does not contain carbon and any precursor residues. Cyclic voltammetry (CVA) showed that there is no current increase for tantalum (V) oxide in a potential window of 3–4.2 V and has prospects of use as protective coatings for cathode materials of SSLIBs.

Highlights

Thin films of tantalum oxide are used for antireflection coatings for strongly curved glass lenses [1], as dielectric layers for micro and nanoelectronics [2]
The ability to cover 3D-oriented surfaces with precise thickness control is important. All these tasks can be solved by the Atomic Layer Deposition (ALD) [3]
There was a low growth per cycle at the evaporator temperatures from 70 ◦C to 110 ◦C, indicating that the evaporator temperature is insufficient for the required amount of the reagent enters the reactor (Figure 1a)

Summary

Introduction

Thin films of tantalum oxide are used for antireflection coatings for strongly curved glass lenses [1], as dielectric layers for micro and nanoelectronics [2]. The ability to cover 3D-oriented surfaces with precise thickness control is important All these tasks can be solved by the Atomic Layer Deposition (ALD) [3]. The method makes it possible to obtain uniform films and high-quality coatings on surfaces of both flat and bulk three-dimensional substrates. It allows controlling the thickness of the films with a high accuracy, and provides good reproducibility of the resulting structures characteristics [4]

Methods

Results

Conclusion