Evolution of the microstructure of sputter deposited TaAlON thin films with increasing oxygen partial pressure

Nina Schalk,Michael Tkadletz,Christian Saringer,Jaakko Julin,Alexander Fian,Velislava L Terziyska

doi:10.1016/j.surfcoat.2021.127237

Abstract

Abstract Recently, quaternary oxynitrides of transition metals and aluminum have attracted increasing interest due to their tunable properties. Within the present work, a series of TaAl(O)N films was sputter deposited using constant nitrogen and varying oxygen partial pressures. The films were grown from single element Ta and Al targets. The deposition parameters were adjusted to obtain a Ta/Al atomic ratio of ~50/50 for the oxygen-free film and were held constant for the following depositions, with the exception of the increasing oxygen partial pressure and compensatory decreasing argon partial pressure. Elastic recoil detection analysis revealed oxygen contents of up to ~26 at.%, while the nitrogen content decreased from ~47 at.% in the oxygen-free film to ~35 at.% in the film with the highest oxygen content, resulting in a significant decrease of the metal/non-metal ratio with increasing oxygen partial pressure. The micro- and bonding structures of the films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. All films exhibited a dominating face-centered cubic TaN-based structure with indications for additional nanocrystalline and amorphous phase fractions in the oxygen containing films. In addition, the mechanical properties were evaluated by nanoindentation, yielding a decreasing hardness and elastic modulus with increasing oxygen content.

Highlights

In recent years, quaternary oxynitrides of transition metals (TM) and aluminum have attracted increasing interest due to the tunability of their properties by adjusting the O/N ratio [1,2,3,4,5,6]
Taking into account the different enthalpies of formation for the respective oxides of Ta and the other TMs mentioned above which have already been used for the deposition of TMAlON discussed in literature, a study of the micro structure and in particular the phase evolution of TaAlON thin films with increasing O content could significantly contribute to the further establishment of a fundamental understanding of the phase formation depending on the involved TM in oxynitrides
A series of TaAl(O)N thin films was deposited by unbalanced d.c. magnetron sputter deposition applying constant nitrogen and increasing oxygen partial pressure, resulting in oxygen contents between 0 and 26 at.%

Summary

Introduction

Quaternary oxynitrides of transition metals (TM) and aluminum have attracted increasing interest due to the tunability of their properties by adjusting the O/N ratio [1,2,3,4,5,6]. For AlN, TiN and ZrN the en thalpies of formation are comparable with − 318, − 338 and − 365 kJ/ mol, respectively, while those for TaN and CrN are with − 251 and − 117 kJ/mol, respectively, even less negative [17,18]. Considering these values, it seems likely that the formation of oxides is governed by thermal activation provided during film growth, while for nitrides additional kinetic activation is necessary, which indicates that the phase formation depends on the involved elements and that compositional variations are present in oxynitrides [1,9,13,19]. The hardness and elastic modulus of the films was determined using nanoindentation

Experimental details

Results and discussion

Conclusion