Fracture properties of thin film TiN at elevated temperatures

J Buchinger,L Löfler,J Ast,A Wagner,Z Chen,J Michler,Z.L Zhang,P.H Mayrhofer,D Holec,M Bartosik

doi:10.1016/j.matdes.2020.108885

Abstract

We provide an experimental and theoretical description of the high temperature fracture behaviour of TiN thin films. For this, we employ molecular dynamics and density functional theory, to show that the surface energies drop insignificantly between 0 and 1000 K. We utilise these results to predict a slight decrease of the fracture toughness over the aforementioned temperature range.For the experimental perspective, we use unbalanced DC reactive magnetron sputtering to synthesise a TiN film, on which we perform in situ high temperature microcantilever bending tests. Upon increasing the testing temperature from room temperature to 773 K our results present a slight, irreversible decrease of KIC, once the deposition temperature of the film (~653 K) is exceeded.Based on our theoretical groundwork, as well as complementary data produced by X-ray diffraction, nanoindentation, transmission electron microscopy, and wafer curvature measurements, we identify growth defect recovery as the main reason behind the decrease of KIC. We observe no change in the deformation and/or fracture mechanism of TiN across the experimentally investigated temperature range. Using an analytical model based on continuum mechanics, we estimate the influence of macro residual stresses on the temperature-dependent fracture toughness of TiN attached to a Si (100) wafer.

Highlights

The energies calculated by Density Functional Theory (DFT) do not perfectly match those provided by molecular dynamics (MD), they are of similar magnitude
As an example for the effect of residual stresses within the realistic configuration of a thin film attached to a semi-infinite substrate, we present the system fracture toughness values gained by the analytical model for an initial crack with an a/t ratio of 0.2, where a refers to the initial crack length and t to the film thickness (2.8 μm)
A noteworthy change occurred only once the deposition temperature of the TiN film had been surpassed, which led to a decrease of the fracture toughness from 2.9 ± 0.1 to 2.5 ± 0.1 MPa√m

Summary

Introduction

In the case of ceramic thin films, the high temperature (HT) fracture behaviour in particular presents itself as rather uncharted territory Among this family of materials, TiN has garnered widespread popularity within the field of microelectronics [10,11,12], fuel cells & batteries [13,14], and as protective coatings against harsh environments [15,16]. In many of these applications, TiN is exposed to severe thermally and/or mechanically-induced stresses [17]. TiN is commonly consulted as a reference material for the family of refractory nitride and carbide thin films and may serve as a basis to elucidate the fracture mechanisms of other isostructural representatives of this class of materials

Methods

Results

Conclusion