Characterization of transport of titanium neutral atoms sputtered in Ar and Ar/N₂ HIPIMS discharges

Abstract

10We report in this work the investigation of the transport behavior of Ti neutral atoms 11 sputtered in reactive high power impulse magnetron sputtering (R-HiPIMS) device 12 used for TiN coating deposition. The time resolved tunable diode laser induced 13 fluorescence (TR-TDLIF), previously developed to study the transport of tungsten 14 atoms, was improved to measure Ti neutral atoms velocity distribution functions. We 15 find that the TR-TDLIF signal has to be fitted using three Gaussian distributions, 16 corresponding to the energetic (EN), thermalized (TH) and quasi-thermalized (QTH: 17 TH atoms with non-zero mean velocity) atoms populations. Then, the ability to 18 distinguish populations of atoms and to determine their corresponding deposited flux 19 and energy may be of great interest to control film properties as desired for targeted 20 applications. From the fitting, the vapor transport parameters (flux and energy) are 21 calculated and studied as function of distance from the target, pressure and percentage 22 of nitrogen in Ar/N2 gas mixture. The study focuses on the effect of added nitrogen on 23 the transport of sputtered atoms. 24 Keywords: time resolved tunable diode laser induced fluorescence, reactive 25 magnetron sputtering, high power impulse magnetron sputtering (HiPIMS), atoms 26 velocity distribution function, transport of sputtered atoms, titanium, nitrogen 27 I. Introduction 28 Since the 1970s, magnetron sputtering (MS) process has been developed for the growth of 29 thin films by physical vapor deposition (PVD) [1]. The developments of conventional reactive 30 direct current (R-dcMS) and radiofrequency (R-rfMS) magnetron sputtering methods allow 31 the deposition of a wide range of thin films of materials such as metals, oxides, nitrides, 32 ceramics, etc. [2]. Consequently, MS is a widely used deposition technology in many 33 industrial applications.34 2 In conventional magnetron sputtering discharges, sputtered species are mainly emitted by 35 the cathode as neutral particles and ions of the sputtered material do not contribute 36 significantly to the deposition process. Ionized Physical Vapor Deposition (IPVD) reactors 37have then been developed since the 1990s to improve the quality of deposited films in terms 38 of mechanical properties (higher density, reduced porosity, better resistance to corrosion) and 39 of conformity for deposition on complex substrate geometry [3][4][5][6][7][8]. The main goal of IPVD is 40 to ionize a fraction of neutral species sputtered from the magnetron target in order to transfer 41 potential energy to ions, and to collimate and control the obtained ion particle fluxes by 42 applying a negative bias voltage to the substrate. IPVD reactors consist of a magnetron 43 discharge assisted by an additional plasma source, located in the area between the substrate 44 and the magnetron cathode, which ionizes the sputtered vapor flowing from the magnetron. 45Reactors using helicon [9], electron cyclotron resonance (ECR) coupled discharge [10] or 46 microw...

Ionized particle transport in reactive HiPIMS discharge: correlation between the energy distribution functions of neutral and ionized atoms

“…In addition, in such a discharge, the sputtered atoms are highly ionized (usually >50%), possibly modifying the electron density [3]. In our previous work, the measurements by means of time average mass spectrometry (for Ti + ions) and TR-TDLIF (for Ti neutral atoms) revealed a strong decrease of Ti + and Ti fluxes when 1% N2 is added to gas mixture (see figures 8 and 13 in [14]). For this strong decrease of both species, the poisoning target was identified as the main cause because the surface effect on sputtering dominates that of the plasma in our conditions.…”

“…TiN film was chosen for its good mechanical and optical properties, excellent chemical resistance, and good biocompatibility, but we note that film properties are not the specific focus of this work. In our previous work on the transport of sputtered neutral titanium atoms in Ar/N2 HiPIMS discharge, we observed that the deposited flux and energy remain constant with increasing N2 content (≥1%) in the gas mixture [14]. This surprising behaviour with increasing fraction of reactive gas raises the need to characterize the ions by time-resolved mass spectrometry.…”

“…The discharge was powered by a MELEC SIPP 2000 HiPIMS generator (Umax =1 kV, Imax_peak = 200 A). To correlate mass spectrometry measurements with previous TR-TDLIF results [14], the HiPIMS discharge power was fixed at P = 350 W cm −2 (U = 500 V, I = 20 A) during discharge (td = 10 μs) and A HIDEN EQP 300 instrument was used to measure the time-resolved IEDFs (TR-IEDFs) of Ti + , Ar + , N + , Ti ++ , and N ++ . The grounded 100-µm-diameter orifice of the mass spectrometer was placed in the virtual position of the substrate.…”

“…Pop1 and Pop2 exhibit collisional transport more similar to diffusion (see figure 3 in [14]), as in the case of thermalized neutral (TH) atoms. Notably, Pop3 seems to evolve quite differently from the other three populations.…”

Diagnostics of a high-pressure DC magnetron argon discharge with an aluminium cathode

“…In planar magnetron discharges, magnetic fields created by permanent magnets positioned behind the cathode, trap electrons near the cathode region allowing plasma production at relatively low pressures [2,3], therefore favouring cathode material sputtering by energetic ions [4]. For the deposition of metallic coating (copper, aluminium, tungsten, etc), inert gases such as argon (Ar) or krypton (Kr) are usually used [1,[5][6][7][8].…”