From pulsed-DCMS and HiPIMS to microwave plasma-assisted sputtering: Their influence on the properties of diamond-like carbon films

Caroline Hain,Robert Weiss,Johann Michler,Alexander Welsh,David Brown,Thomas Nelis,Krzysztof Wieczerzak,Aïcha Hessler-Wyser

doi:10.1016/j.surfcoat.2021.127928

Abstract

The fabrication of high-hardness non-hydrogenated diamond-like carbon (DLC) via standard magnetron sputtering (MS) is often hindered by the low sputtering yields and ionisation rates of carbon, therefore investigations into pulsed alternatives of MS, else sputtered species post-ionisation methods, are of particular interest. This work focuses on investigating the influence of pulsed-direct current MS (pDCMS), high power impulse magnetron sputtering (HiPIMS) and their microwave plasma-assisted (MA-pDCMS, MA-HiPIMS) variants on the properties of the fabricated DLC films. Two setups were used for the pDCMS- and HiPIMS-based methods, respectively. The films were characterised using Raman spectroscopy, nanoindentation, X-ray reflectometry and scanning electron microscopy, where the pDCMS-produced films were additionally characterised by film-stress measurements. Moreover, in situ time-resolved Langmuir probe plasma analysis was performed under HiPIMS and MA-HiPIMS conditions to analyse the influence of the magnetron and microwave plasmas on one another. For both DCMS- and HiPIMS-based procedures, it was found that the addition of microwave plasma did not facilitate attaining hardnesses beyond 30 GPa, however, it did enable modifying the morphology of the films. Furthermore, this study shows the potential of synchronised sputtering with substrate biasing, as well as the importance of microwave plasma source positioning in relation to the substrate. • DLC films produced via pulsed magnetron sputtering and microwave plasma-assisted methods. • In situ plasma diagnostics were used to study magnetron-microwave plasma interactions. • Maximum DLC film hardness did not significantly exceed 30 GPa. • Microwave plasma caused DLC film surface morphology modifications. • Substrate biasing and microwave plasma source positioning affect DLC film tunability.

Highlights

Diamond-like carbon (DLC) is an amorphous carbon material, where its chemical and mechanical properties have made it an attractive choice for films in applications related to automotive and aerospace industries, biomedicine, magnetic storage media and many others [1,2,3,4,5,6]
X-ray reflectivity (XRR) was performed on the pulsed-direct current MS (pDCMS) and MA-pDCMS films to deter mine their thickness and density
diamond-like carbon (DLC) films were produced by means of pDCMS, MApDCMS, high power impulse magnetron sputtering (HiPIMS), MA-HiPIMS with DC substrate biasing and MAHiPIMS with pulsed substrate biasing

Summary

Introduction

Diamond-like carbon (DLC) is an amorphous carbon material, where its chemical and mechanical properties have made it an attractive choice for films in applications related to automotive and aerospace industries, biomedicine, magnetic storage media and many others [1,2,3,4,5,6]. During PVD, the carbon source is can be a pure carbon target, enabling the production of non-hydrogenated amorphous carbon (a-C) and tetrahedral amorphous carbon (ta-C) films Such films exhibit higher hardness, greater temperature [9,10,11] stability and under humid conditions [12,13,14] than their hydrogenated counterparts. Sub plantation occurs through direct carbon ion penetration into the film’s surface and/or indirectly through the displacement of surface atoms into interstitial sites. This entails the penetration of impinging hyperthermal species, ranging from 1 to 1000 eV, into the top layers of the growing film, inducing sp to sp transformations. As graphitic structures exhibit a lower displacement energy than diamond ones (25 eV vs 80 eV), they will be preferentially displaced upon ion bombardment [15]

Results

Discussion

Conclusion