Toward energy-efficient physical vapor deposition: Routes for replacing substrate heating during magnetron sputter deposition by employing metal ion irradiation

X Li,B Bakhit,M.P Johansson Jõesaar,L Hultman,I Petrov,G Greczynski

doi:10.1016/j.surfcoat.2021.127120

Abstract

In view of the increasing demand for achieving sustainable development, the quest for lowering energy consumption during thin film growth by magnetron sputtering becomes of particular importance. In addition, there is a demand for low-temperature growth of dense, hard coatings for protecting temperature-sensitive substrates. Here, we explore a method, in which thermally-driven adatom mobility, necessary to obtain high-quality fully-dense films, is replaced with that supplied by effective low-energy recoil creation resulting from high-mass metal ion irradiation of the growing film surface. This approach allows the growth of dense and hard films with no external heating at substrate temperatures Ts not exceeding 130 °C in a hybrid high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) setup involving a high mass (m > 180 amu) HiPIMS target and metal-ion-synchronized bias pulses. We specifically investigate the effect of the metal ion mass on the extent of densification, phase content, nanostructure, and mechanical properties of metastable cubic Ti0.50Al0.50N based thin films, which present outstanding challenges for phase stability control. Ti0.50Al0.50N based thin films are irradiated by group VIB transition metal (TM) target ions generated by Me-HiPIMS discharge, in which Me = Cr (mCr = 52.0 amu), Mo (mMo = 96.0 amu), and W (mW = 183.8 amu). Three series of (Ti1-yAly)1-xMexN films are grown with x = Me/(Me+Al+Ti) varied intentionally by adjusting the DCMS powers, while y = Al/(Al+Ti) also varies as a result of Me+ ion irradiation. Results reveal a strong dependence of film properties on the mass of the HiPIMS-generated metal ions. All layers deposited with Cr+ irradiation exhibit porous nanostructure, high oxygen content, and poor mechanical properties. In contrast, (Ti1-yAly)1-xWxN films are fully-dense even with the lowest W concentration, x = 0.09, show no evidence of hexagonal AlN precipitation, and exhibit state-of the-art mechanical properties typical of Ti0.50Al0.50N grown at 500 °C. The process energy consumption is lowered by 64% with no negative impact on the coating quality. TRIM simulations provide an insight into the densification mechanisms.

Highlights

Physical vapor deposition (PVD) technology is generally considered more environmentally friendly than traditional coating processes such as electroplating or chemical vapor deposition
We further explore the concept of metal-ionsynchronized HiPIMS/DCMS film growth by systematically investi gating the effect of the ion mass on the extent of densification, phase content, nanostructure, and mechanical properties of the resulting thin films
We use group VIB transition metal (TM) target ions generated by Me-HiPIMS discharge, in which Me = Cr, Mo, and W to irradiate Ti0.50Al0.50N films during deposition from two TiAl targets operating in DCMS mode

Summary

Introduction

Physical vapor deposition (PVD) technology is generally considered more environmentally friendly than traditional coating processes such as electroplating or chemical vapor deposition. This is because PVD is clean and dry, with no hazardous materials, and does not generate waste chemicals. PVD consumes appreciable amounts of energy, which is primarily due to the fact that most coatings are deposited at elevated temperatures, Ts/Tm > 0.3 (Ts and Tm : growth and melting temperatures in K) corresponding to Ts > 900 ◦C for TiN, to ensure sufficient adatom mobility. The low-temperature deposition of dense, hard refractory thin films with low residual stress has been a longtime goal in advanced surface engineering [1,2,3,4]

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