Elsevier

Applied Surface Science

Volume 438, 30 April 2018, Pages 14-19
Applied Surface Science

Full Length Article
In-situ XRD vs ex-situ vacuum annealing of tantalum oxynitride thin films: Assessments on the structural evolution

https://doi.org/10.1016/j.apsusc.2017.10.220Get rights and content

Highlights

  • The structural evolution of TaNxOy films was studied under ex-situ and in-situ annealing.

  • The highest structural stability was observed for atomic ratios (N + O)/Ta  0.5 and (N + O)/Ta  1.0.

  • For (N + O)/Ta ≈ 0.5, the fcc-Ta(O,N) polycrystalline structure is maintained at all annealing temperatures.

  • The films with (N + O)/Ta  1.0 maintain the amorphous structure, at all temperatures, on both processes.

  • Films with other atomic ratios exhibit structural evolution differences, between the ex-situ and in-situ annealing.

Abstract

The purpose of this work is to discuss the main structural characteristics of a group of tantalum oxynitride (TaNxOy) thin films, with different compositions, prepared by magnetron sputtering, and to interpret and compare the structural changes, by X-ray diffraction (XRD), when the samples are vacuum annealed under two different conditions: i) annealing, followed by ex-situ XRD: one sample of each deposition run was annealed at a different temperature, until a maximum of 800 °C, and the XRD patterns were obtained, at room temperature, after each annealing process; ii) annealing with in-situ XRD: the diffraction patterns are obtained, at certain temperatures, during the annealing process, using always the same sample. In-situ XRD annealing could be an interesting process to perform annealing, and analysing the evolution of the structure with the temperature, when compared to the classical process.

A higher structural stability was observed in some of the samples, particularly on those with highest oxygen content, but also on the sample with non-metal (O + N) to metal (Ta) ratio around 0.5.

Introduction

Tantalum (Ta) thin films and tantalum ceramic thin films (oxides, nitrides and oxynitrides) have extraordinary properties allowing them to be used in several interesting applications. Tantalum (refractory metal with melting temperature around 3050 °C) and tantalum nitride can be used as resistors and heaters, in the case of Ta, but also diffusion barriers, pressure sensors and protective layers [1], [2], [3], [4], [5], [6], [7]. Particularly, the formation of a tantalum oxide layer on the surface of Ta or Ta-nitrides allows them to have high resistance to chemical attacks [2].

The potential of these materials as thin films to be used in high temperature applications is significant. Several publications can be found where the behaviour of tantalum and tantalum nitride films under annealing is studied. To the best of our knowledge, the number of studies referring the behaviour of tantalum oxynitride subjected to thermal treatments is limited. The authors have published a study about the structural stability of a set of tantalum oxynitride films [8], while J.H. Hsieh et al. [9] discussed the behaviour of TaNxOy thin films with and without rapid thermal annealing.

Generally, concerning the structural stability with the temperature of any material, most of the studies follow the same pattern: annealing execution, generally in vacuum, followed by structural evaluation, normally by XRD, at room temperature. Only a few studies refer to the study of the structure evolution, obtaining the XRD patterns at specific temperatures, simultaneously with the annealing process. In this work, the differences concerning the structural evolution of magnetron sputtered TaNxOy films are discussed, after vacuum annealing, in two conditions: the diffraction patterns were captured at room temperature, after vacuum annealing, and compared to in-situ annealing and structural evaluation by XRD.

Section snippets

Experimental details

TaNxOy thin films were deposited onto silicon (100) substrates by DC reactive magnetron sputtering. Before being inserted in the chamber, the substrates were cleaned with ethanol. Prior to the etching process and subsequent deposition, the chamber was evacuated to a base pressure of 1.1÷1.3 × 10−3 Pa. The substrates were plasma etched for a period of 500 s, using pure argon with a partial pressure of ∼0.3 Pa (60 sccm) and a pulsed current of approximately 0.6 A.

The substrate holder was positioned at 70

Tantalum oxynitride film produced with (N + O)/Ta  0.1 (P(N2 + O2) = 0.02 Pa (B1))

The Ta content of the B1 film is around 90 at.% (Table 2). Fig. 1 reveals the XRD pattern of the as-deposited sample and of the samples that suffered ex-situ annealing at 400 °C, 600 °C and 800 °C. The XRD pattern of the as-deposited samples evidences a quasi-amorphous structure with evidences of poorly developed β–Ta or Ta2N crystallites, revealed by a broad peak, in the range 33° <  < 42°. The peak detected at 2θ = 36.1°, may be assigned to the (410) planes of the β–Ta structure or, more probably, to

Conclusions

TaNxOy thin films were deposited by magnetron sputtering. The structural evolution as function of the annealing temperature was studied under two different conditions: i) vacuum annealing, at specific temperatures, and registration of XRD patterns at room temperature after annealing (ex-situ process); ii) vacuum annealing, at specific temperatures, and registration of XRD patterns at those specific temperatures (in-situ process). The general observations of the structural behaviour of the

Acknowledgement

This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013.

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