Tuning the stress in TiN films by regulating the doubly charged ion fraction in a reactive HiPIMS discharge

Rommel Paulo B Viloan,Daniel Lundin,Ulf Helmersson,Julien Keraudy

doi:10.1063/1.5134003

Abstract

In the present study, we investigate the impact of pulse power (Ppulse) on the ion flux and the properties of TiN films using reactive high-power impulse magnetron sputtering. Ppulse was adjusted in the range of 5–25 kW, while keeping the total average power constant through regulating the pulsing frequency. It is found that the required N2 flow, to produce stoichiometric TiN, decreases as Ppulse is increased, which is due to a decrease in the deposition rate. The plasma conditions when stoichiometric TiN is formed were investigated in detail. In situ ion mass spectrometry measurements of the ion energy distribution functions reveal two distinct ion populations, ions originating from sputtered atoms (Ti+, Ti2+, and N+) and ions originating from the working gas (Ar+, Ar2+, and N2+). The average ion energies (Eave) of the sputtered ions show an increase with increasing Ppulse, while Eave for the gas ions remains almost unaffected. The relative flux intensity Ti2+/Ti+ showed an increasing trend, from 0.28 to 0.47, as Ppulse was increased from 5 to 25 kW. The ion flux changes affect the growth of the TiN film such that 111-textured films are grown for low Ppulse while higher Ppulse results in mixed orientations. In addition, the hardness of the deposited film increases with increasing Ppulse, while the compressive film stress increases significantly at a higher Ppulse. In this way, optimum deposition conditions were identified at Ppulse = 8.3 kW, where a relatively low compressive stress of 0.89 GPa and high hardness of 22.67 GPa were measured.

Highlights

High-power impulse magnetron sputtering (HiPIMS) is a deposition technique initially introduced by Kouznetsov et al.[1] as a way to deposit dense coatings inside via-structures
We investigate the impact of pulse power (Ppulse) on the ion flux and the properties of TiN films using reactive highpower impulse magnetron sputtering
High power and high current densities, of several kW/cm[2] and several A/cm[2], are supplied to the cathode in pulses of low duty cycles resulting in a time-averaged power comparable to dc magnetron sputtering, but with electron densities up to 1019 m−3.2,3 The result is a flux of ionized material from the cathode with an ionization fraction vastly superior to dcMS4–6 and with a broader ion energy distribution.[7,8,9]

Summary

Introduction

High-power impulse magnetron sputtering (HiPIMS) is a deposition technique initially introduced by Kouznetsov et al.[1] as a way to deposit dense coatings inside via-structures. Despite the potential of HiPIMS for growing high quality thin films, there are examples in the literature demonstrating the adverse effects of using high-power pulses due to the development of high film stress.[15,16,17,18] Greczynski et al.[19] measured compressive stresses up to 6 GPa when using HiPIMS on the Ti target during deposition of Ti1 − xAlxN coatings in a hybrid HiPIMS/dcMS co-sputtering setup. Viloan et al.[18] deposited TiN coatings without the use of substrate bias but still yielding a relatively high scitation.org/journal/jap compressive stress of 2.1 GPa. The compressive stress further increased when a reversed, positive, pulse (150 V) was applied to the target after the HiPIMS pulse, resulting in a compressive stress reaching 4.7 GPa

Results

Discussion

Conclusion