Mechanical Properties and Diffusion Barrier Performance of Crwn Coatings Fabricated Through Hybrid Hipims/RFMS

coatings

Article Mechanical Properties and Diffusion Barrier Performance of CrWN Coatings Fabricated through Hybrid HiPIMS/RFMS

Li-Chun Chang 1,2,*, Cheng-En Wu 1 and Tzu-Yu Ou 1

1 Department of Materials Engineering, Ming Chi University of Technology, New Taipei City 24301, Taiwan; [email protected] (C.-E.W.); [email protected] (T.-Y.O.) 2 Center for Plasma and Thin Film Technologies, Ming Chi University of Technology, New Taipei City 24301, Taiwan * Correspondence: [email protected]; Tel.: +886-2-2908-9899

Abstract: CrWN coatings were fabricated through a hybrid high-power impulse magnetron sputtering/radio-frequency magnetron sputtering technique. The phase structures, mechanical properties,

and tribological characteristics of CrWN coatings prepared with various nitrogen ﬂow ratios (f N2s) were investigated. The results indicated that the CrWN coatings prepared at f N2 levels of 0.1 and 0.2 exhibited a Cr2N phase, whereas the coatings prepared at fN2 levels of 0.3 and 0.4 exhibited a CrN phase. These CrWN coatings exhibited hardness values of 16.7–20.2 GPa and Young’s modulus levels of 268–296 GPa, which indicated higher mechanical properties than those of coatings with similar residual stresses prepared through conventional direct current magnetron sputtering. Face-

centered cubic (fcc) Cr51W2N47 coatings with a residual stress of −0.53 GPa exhibited the highest wear and scratch resistance. Furthermore, the diffusion barrier performance of fcc CrWN ﬁlms on Cu metallization was explored, and they exhibited excellent barrier characteristics up to 650 ◦C.

Citation: Chang, L.-C.; Wu, C.-E.; Ou, T.-Y. Mechanical Properties and Keywords: diffusion barrier; HiPIMS; mechanical properties; RFMS Diffusion Barrier Performance of CrWN Coatings Fabricated through Hybrid HiPIMS/RFMS. Coatings 2021, 11, 690. https://doi.org/10.3390/ 1. Introduction coatings11060690 Transition metal nitride ﬁlms such as TiN [1], CrN [2,3], TaN [4,5], and W2N[6,7] have been widely utilized as protective coatings in versatile applications, such as hard Academic Editor: coatings, diffusion barriers, and corrosion-resistant and wear-resistant layers. Moreover, Alexander Tolstoguzov ternary nitride ﬁlms such as TiAlN [8], TaZrN [9,10], and CrWN [11] have been developed to enhance the characteristics of the above binary nitride materials. CrWN coatings have Received: 15 May 2021 been applied as hard coatings [11–15] and protective coatings on die materials for precision Accepted: 7 June 2021 Published: 9 June 2021 molding glass technology [16–19]. In a previous study [15], CrWN coatings manufactured using direct current magnetron sputtering (DCMS) exhibited a wide hardness range of

Publisher’s Note: MDPI stays neutral 10.8–27.6 GPa depending on their chemical composition and crystalline structure. The with regard to jurisdictional claims in operation of precision molding glass requires molding dies and protective coatings against ◦ published maps and institutional affil- repeated thermal cycles at 200–600 C under a low oxygen content atmosphere, implying iations. that CrWN possesses the potential to function as a diffusion barrier for Cu metallization. Cu is the most favorable material for interconnecting ultra-large-scale integrated circuits because of its higher conductivity and superior electromigration resistance compared to Al [20]. Cu diffuses easily into Si and SiO2, which compromises device performance [21,22]. Barrier materials that have been reported to prohibit the diffusion of Cu into Si include Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. transition metals (Cr, Ti, Nb, Ta, and W) [23], bilayers (Ta/Ti) [24], alloys (TiW) [25,26], This article is an open access article binary and ternary nitrides (TiNx, TaNx, WNx, RuWN, and WTiN) [26–32], thin film metallic distributed under the terms and glass (Zr–Cu–Ni–Al–N) [33], and high entropy alloys [34]; and the failure temperatures of ◦ conditions of the Creative Commons these barrier layers exhibited distinct variations in the range of 400–850 C. Therefore, the Attribution (CC BY) license (https:// successful exploration of new barrier materials is essential in the field of integrated circuits. creativecommons.org/licenses/by/ A qualifying barrier material should exhibit good adhesion to Cu, prevent the diffusion of 4.0/). Cu into Si or the interlayer dielectric (ILD), and be inactive on both Cu and ILD at high

Coatings 2021, 11, 690. https://doi.org/10.3390/coatings11060690 https://www.mdpi.com/journal/coatings Coatings 2021, 11, 690 2 of 14

temperatures. CrN has been extensively used for mechanical and corrosion resistance purposes; however, previous reports on its use as a diffusion barrier are scarce [35,36]. ◦ CrN can decompose to Cr2N by releasing N2 at temperatures of 500–700 C because of stress relaxation [37]. W can also be added to CrN to increase oxidation resistance and thermal stability [16,18]. Therefore, the goal of this study was to investigate the mechanical properties and diffusion barrier performance of CrWN coatings. High-power impulse magnetron sputtering (HiPIMS) exhibits a main feature of a high degree of ionization of sputtered material through the development of a highly dense plasma (~1013 ions/cm3)[38–41]. The HiPIMS technique is typiﬁed by a low duty cycle of <10%, low repetition frequency of <10 kHz, and high-power densities in the order of kW/cm2 [42]. Therefore, HiPIMS helps to produce coatings with a dense structure and high hardness [43,44]. Moreover, a hybrid HiPIMS/radio-frequency magnetron sputtering (RFMS) process has been previously employed to simultaneously improve the deposition rate and coating quality [45,46]. In this paper, CrWN ﬁlms were prepared by hybrid HiP- IMS/RFMS, the Cu/CrWN/Cr/Si structures were annealed in a vacuum (7 × 10−4 Pa) at elevated temperatures for 1 h, and the thermal stability and diffusion barrier characteristics of the CrWN barriers were studied.

2. Materials and Methods In a hybrid HiPIMS/RFMS apparatus, a target of W (99.95%, 50.8 mm in diameter) was linked to a RF power generator, whereas the target of Cr (99.99%, 76.2 mm in diameter) was attached to a pulse power supply (SPIK 2000A; Shen Chang Electric Co., Ltd., Taipei, Taiwan). The distance between substrates and targets was 12 cm. The substrate holder was rotated at 10 rpm and grounded. In the first part of this study, a Cr interlayer of 100 nm was deposited at 200 W for 10 min under an Ar flow of 30 sccm. Then, CrWN coatings were co-sputtered on Cr interlayers, after flowing N2 and Ar into the vacuum chamber. The total flow rate of N2 and Ar was 30 sccm. The nitrogen flow ratio (f N2 = N2/(N2+Ar)), ranging from 0.1 to 0.4, was the main process variable. The working pressure was maintained at 0.4 Pa. The power applied to the W (WW) and Cr (WCr) targets was 50 and 500 W, respectively. The deposition times were controlled to form coatings of approximately 1000 nm in thickness. The substrates were silicon and stainless-steel (SUS420) plates. The samples prepared on SUS420 substrates were adopted to evaluate the tribological characteristics, adhesion properties, and wear behavior. Adhesion was tested via a scratch test (Scratch Tester, J & L Tech. Co., Gyeonggi-do, Korea) with a diamond tip 0.2 mm in diameter at a moving speed of 0.01 mm/s. Wear behavior was examined through a pin-on-disc test method with a pin of cemented carbide (WC-6 wt.% Co) and a ball 6 mm in diameter under a normal load of 2 N. The sliding speed was 126 mm/s, the wear track diameter was 4 mm, and the wear length was 200 m. In the second part of this work, two CrWN thin films of 100 nm with a Cr interlayer of 10 nm were fabricated by shortening the deposition times to evaluate their diffusion barrier characteristics, including sheet resistance, phase stability, and elemental diffusion. These samples were covered with a Cu layer (100 nm thick) prepared through DCMS and annealed in a vacuum (7 × 10−4 Pa) at 550–650 ◦C for 1 h. The elemental compositions were analyzed using a field-emission electron probe microanalyzer (FE-EPMA, JXA-8500F, JEOL, Akishima, Japan). The phases were identified through grazing-incident X-ray diffraction (GIXRD) using an X-ray diffractometer (X’Pert PRO MPD, PANalytical, Almelo, the Netherlands). Coating thicknesses were examined via cross-sectional images using a field emission scanning electron microscope (FE-SEM, JSM-6701F, JEOL, Akishima, Japan). The nanostructure was observed using transmission electron microscopy (TEM, JEM-2010F, JEOL, Akishima, Japan). The mechanical properties, hardness (H), and Young’s modulus (E) of the coatings were evaluated using a nanoindentation tester (TI-900 Triboindenter, Hysitron, Minneapolis, MN, USA) and determined using the Oliver and Pharr method [47]. An atomic force microscope (AFM, DI 3100, Bruker, Santa Barbara, CA, USA) recorded the average roughness (Ra) and root-mean- Coatings 2021, 11, 690 3 of 14

square roughness (Rq). The residual stress of coatings was estimated using the curvature method [48], 2 EShS σftf = , (1) 6(1 − νS)Rf

where σf is the in-plane stress component in the film, tf is the film thickness, ES is the Young’s modulus of the Si substrate (130.2 GPa), νS is the Poisson’s ratio for the Si substrate (0.279), hS is the substrate thickness (525 µm), and Rf is the curvature radius of the film. Wear scars and elemental mapping were observed using SEM (S3400N, Hitachi, Tokyo, Japan) equipped with energy dispersive spectroscopy (EDS, Inca x-sight, Oxford Instruments, Tokyo, Japan). The sheet resistance of the Cu/CrWN/Cr/Si samples was determined using a four-point probe. The sheet resistance can be derived by:

4.53 V R = , (2) I where I is the applied current, and V is the measured voltage. The elemental diffusion was examined using an Auger electron spectroscopy (AES, PHI700, ULVAC-PHI, Kanagawa, Japan).

3. Results and Discussion 3.1. CrWN Coatings Co-Sputtered Using Various Nitrogen Flow Rates

Table1 lists the atomic compositions of the CrWN coatings prepared with an f N2 of 0.1–0.4. These samples were denoted as Cr65W4N31, Cr62W3N35, Cr58W2N40, and Cr51W2N47 in accordance with their atomic compositions. The N content of the CrWN coatings were increased from 31.0 to 35.0, 39.4, and 46.9 at.% by increasing the nitrogen ﬂow ratio (f N2) from 0.1 to 0.2, 0.3, and 0.4, whereas the Cr content exhibited a tendency to decrease from 64.7 to 61.9, 58.1, and 50.6 at.%, and the W content decreased from 4.0 to 2.8, 2.2, and 2.0 at.%. The O contents of these coatings were 0.3 at.%. The deposition rate increased from 12.1 to 14.6 nm/min and then decreased to 11.4 and 10.9 nm/min as f N2 increased from 0.1 to 0.4 (Table1).

Table 1. Co-sputtering parameters, atomic compositions, and thicknesses of CrWN coatings.

N Flow Atomic Compositions (at.%) Thickness Rate Sample 2 f 1 (sccm)N2 Cr W N O (nm) (nm/min)

Cr65W4N31 3 0.1 64.7 ± 0.6 4.0 ± 0.0 31.0 ± 0.6 0.3 ± 0.1 954 12.1 Cr62W3N35 6 0.2 61.9 ± 0.5 2.8 ± 0.1 35.0 ± 0.4 0.3 ± 0.2 1180 14.6 Cr58W2N40 9 0.3 58.1 ± 0.8 2.2 ± 0.1 39.4 ± 0.7 0.3 ± 0.1 947 11.4 Cr51W2N47 12 0.4 50.6 ± 0.6 2.0 ± 0.6 46.9 ± 0.5 0.3 ± 0.0 933 10.9 1 f N2: nitrogen ﬂow ratio.

Figure1 shows the GIXRD patterns of the CrWN coatings. The coatings prepared with an f N2 of 0.1 and 0.2 exhibited a hexagonal Cr2N phase, whereas the coatings prepared with an f N2 of 0.3 and 0.4 displayed a face-centered cubic (fcc) CrN phase. As the formation 0 enthalpy of W2N(∆H298 = −72 kJ/mol) is lower than that of CrN (−118 kJ/mol) and Cr2N (−126 kJ/mol) [6,49], and the W content is low compared to the Cr content, the evolution of the crystalline phase is dominated by the compositions of Cr and N. The phase evolution from Cr2N to CrN was accompanied by a decrease in the atomic ratio of Cr/N from 2.09, to 1.77, 1.47, and 1.08 when the f N2 increased from 0.1, to 0.2, 0.3, and 0.4. Moreover, the reﬂection Cr2N (111) of the Cr62W3N35 coatings shifted toward a lower value compared to that of the Cr65W4N31 coatings, which implies that higher amounts of N atoms were incorporated into the lattice, resulting in an increase in lattice constants. A similar variation was observed in the reﬂections CrN (111) and (200) of the Cr51W2N47 coatings compared to those of the Cr58W2N40 coatings. Coatings 2021, 11, x FOR PEER REVIEW 4 of 14

Coatings 2021, 11, 690 incorporated into the lattice, resulting in an increase in lattice constants. A similar varia-4 of 14 tion was observed in the reflections CrN (111) and (200) of the Cr51W2N47 coatings compared to those of the Cr58W2N40 coatings.

FigureFigure 1. 1. GIXRDGIXRD patterns patterns of of (a (a) )Cr Cr6565WW4N4N31,31 (b,() bCr) Cr62W623WN353N, (35c),( Crc)58 CrW582NW40,2 Nand40, ( andd) Cr (d51)W Cr2N5147W coatings.2N47 coatings.

FigureFigure 22 shows the the cross-sectional cross-sectional FE-SEM FE-SEM images images of ofthe the CrWN CrWN coatings. coatings. The The CrCr6565WW4N431N coatings31 coatings revealed revealed an evident an evident columnar columnar structure, structure, whereas whereas the Cr62W the3N35 Cr coat-62W3N35 ingscoatings displayed displayed a much a fine much column finear columnar structure. structure.By contrast, By the contrast, Cr58W2N40 the, and Cr Cr58W51W2N2N4047, and costingsCr51W2 withN47 costingsa CrN phase with exhibited a CrN phase short and exhibited disordered short grains, and disordered similar to those grains, reported similar to bythose Lin et reported al. [50]. byFigure Lin 3a et displays al. [50]. Figurea cross-sectional3a displays TEM a cross-sectional (XTEM) image TEMof the (XTEM) Cr51W2N image47 coatings,of the Cr which51W2N exhibited47 coatings, a dense which and exhibited granular structure. a dense and The granulargrain size structure. was tens of The na- grain nometers.size was tensThe ofselected nanometers. area electron The selected diffraction area pattern electron exhibited diffraction CrN pattern (111) exhibitedand (200) CrN spots.(111) andFigure (200) 3b spots.shows Figurelattice 3fringesb shows of 0.236 lattice and fringes 0.207 of nm 0.236 belonging and 0.207 to d-spacings nm belonging of to CrNd-spacings (111) and of (200), CrN (111)respectively. and (200), Figure respectively. 4 depicts Figurethe Ra 4and depicts Rq values the Rofa theand CrWNRq values coat- of the ings.CrWN Ra coatings.and Rq exhibitedRa and Rconstantq exhibited values constant of 2.4–3.0 values and of 3.1–3.8 2.4–3.0 nm, and respectively. 3.1–3.8 nm, respectively. These roughnessThese roughness values were values low were compared low compared to those (R toa: those2.3–6.1 (R nm,a: 2.3–6.1 Rq: 2.9–7.6 nm, nm)Rq: 2.9–7.6of CrWN nm) of coatingsCrWN coatingsprepared preparedthrough DCMS through accompanied DCMS accompanied with an atomic with ratio an Cr/W atomic > 1 ratio and an Cr/W fcc > 1 phaseand an [15,18]. fcc phase These [15 results,18]. These indicate results that indicatethe films that fabricated the films by fabricatedHiPIMS/RFMS by HiPIMS/RFMS formed a denseformed structure a dense and structure a smooth and surface. a smooth The surface.films with The a columnar films with structure a columnar could structure promote could Cupromote diffusion Cu diffusionthrough the through grain theboundaries grain boundaries [27]; therefore, [27]; therefore, the characteristics the characteristics of the of Coatings 2021, 11, x FOR PEER REVIEWCrthe51 W Cr2N47W coatingsN coatings when whenused as used a diffusion as a diffusion barrier barrier were werefurther further investigated investigated5 andof 14 are and are 51 2 47 discusseddiscussed in in the the next next section. section.

Figure 2. Cross-sectional FE-SEM images of (a) Cr65W4N31, (b) Cr62W3N35, (c) Cr58W2N40, and (d) Figure 2. Cross-sectional FE-SEM images of (a) Cr65W4N31,(b) Cr62W3N35,(c) Cr58W2N40, and Cr51W2N47 coatings. (d) Cr51W2N47 coatings.

Figure 3. (a) XTEM and (b) HRTEM images of the Cr51W2N47 coatings.

Figure 4. Surface roughness values of the CrWN coatings.

Coatings 2021, 11, x FOR PEER REVIEW 5 of 14

Coatings 2021, 11, 690 Figure 2. Cross-sectional FE-SEM images of (a) Cr65W4N31, (b) Cr62W3N35, (c) Cr58W 2N40, and 5(d of) 14 Cr51W2N47 coatings. Figure 2. Cross-sectional FE-SEM images of (a) Cr65W4N31, (b) Cr62W3N35, (c) Cr58W2N40, and (d) Cr51W2N47 coatings.

Figure 3. (a) XTEM and (b) HRTEM images of the Cr51W2N47 coatings. Figure 3. (a) XTEM and (b) HRTEM images of the Cr51W2N47 coatings. Figure 3. (a) XTEM and (b) HRTEM images of the Cr51W2N47 coatings.

FigureFigureFigure 4. Surface 4. 4.Surface Surface roughness roughnessroughness values values of of ofthe the the CrWN CrWN CrWN coatings. coatings. coatings. Figure5 shows the mechanical properties of the CrWN coatings. The variation in mechanical properties with N content revealed the combined effects of the phase and residual stress. Figure6 displays the residual stress of CrWN coatings, which shows a tendency to vary from tensile (1.30 GPa) to compressive stress (−0.53 GPa) when the N content is increased. Compressive residual stress was beneficial for increasing the hardness [18,51,52]. Figure7a shows the relationship between the hardness and the residual stress of CrWN coatings. Selected data from a previous study [15] on DCMS-prepared CrWN coatings dominated by a Cr2N or CrN phase are shown in Figure7a for comparison. The hardness and residual stress reveal a linear fitting trend. Figure7b shows the relationship between Young’s modulus and residual stress, and reveals a lower fitting slope compared to those shown in Figure7a. Therefore, the Cr62W3N35 coatings showed higher H and E values than those of the Cr65W4N31 coatings, whereas the Cr51W2N47 coatings exhibited higher H and E values than those of the Cr58W2N40 coatings. However, the H values of the Cr62W3N35 and Cr51W2N47 coatings were 20.2 and 19.7 GPa, respectively, implying that the H was affected by their phase structures. The Cr62W3N35 coatings crystallized into a Cr2N phase, whereas the Cr51W2N47 coatings formed a CrN phase. Previous studies [53–55] have reported that Cr2N is harder than CrN, both in bulk and film form, because of the higher covalent bonding character of Cr2N. Hirota et al. [53] reported hardness values of 14.5 and 11.2 GPa for ceramic Cr2N and CrN, respectively. Hones et al. [54] reported values of 28 and 18 GPa for sputtered Cr2N and CrN films, respectively, whereas 16.1 and 12.5 GPa were obtained in the work of Wei et al. [55]. In a previous study [15], CrWN coatings with a high W content of 31–57 at.% and fabricated through DCMS revealed an fcc structure and high compressive residual stress in the range from −2.1 to −3.0 GPa, accompanied by a high H of 21.1–27.1 GPa and a high E of 241–310 GPa. By contrast, the Cr51W2N47 coatings prepared through DCMS exhibited a columnar structure accompanied by a low H of 10.8 GPa, a low E of 168 GPa, a high Ra of 6.1 nm, a high Rq of 7.6 nm, and a tensile stress of 0.54 GPa [18]. The DCMS–Cr51W2N47 Coatings 2021, 11, x FOR PEER REVIEW 6 of 14

Figure 5 shows the mechanical properties of the CrWN coatings. The variation in mechanical properties with N content revealed the combined effects of the phase and residual stress. Figure 6 displays the residual stress of CrWN coatings, which shows a tendency to vary from tensile (1.30 GPa) to compressive stress (−0.53 GPa) when the N content is increased. Compressive residual stress was beneficial for increasing the hardness [18,51,52]. Figure 7a shows the relationship between the hardness and the residual stress of CrWN coatings. Selected data from a previous study [15] on DCMS-prepared CrWN coatings dominated by a Cr2N or CrN phase are shown in Figure 7a for comparison. The hardness and residual stress reveal a linear fitting trend. Figure 7b shows the relationship between Young’s modulus and residual stress, and reveals a lower fitting slope compared to those shown in Figure 7a. Therefore, the Cr62W3N35 coatings showed higher H and E values than those of the Cr65W4N31 coatings, whereas the Cr51W2N47 coatings exhibited higher H and E values than those of the Cr58W2N40 coatings. However, the H values of the Cr62W3N35 and Cr51W2N47 coatings were 20.2 and 19.7 GPa, respectively, implying that the H was affected by their phase structures. The Cr62W3N35 coatings crystallized into a Cr2N phase, whereas the Cr51W2N47 coatings formed a CrN phase. Previous studies [53–55] have reported that Cr2N is harder than CrN, both in bulk and film form, because of the higher covalent bonding character of Cr2N. Hirota et al. [53] reported hardness values of 14.5 and 11.2 GPa for ceramic Cr2N and CrN, respectively. Hones et al. [54] reported values of 28 and 18 GPa for sputtered Cr2N and CrN films, respectively, whereas 16.1 and 12.5 GPa were obtained in the work of Wei et al. [55]. In a previous study [15], CrWN coatings with a high W content of 31–57 at.% and fabricated through DCMS revealed an fcc structure and high compressive residual stress in the range from −2.1 to −3.0 GPa, accompanied by a high H of 21.1–27.1 GPa and a high E of 241–310 GPa. By contrast, the Cr51W2N47 coatings Coatings 2021, 11, 690 prepared through DCMS exhibited a columnar structure accompanied by a low H6 ofof 14 10.8 GPa, a low E of 168 GPa, a high Ra of 6.1 nm, a high Rq of 7.6 nm, and a tensile stress of 0.54 GPa [18]. The DCMS–Cr51W2N47 coatings exhibited a loose and columnar structure, with a (111) orientation [18], whereas the HiPIMS/RFMS-Cr51W2N47 coatings revealed a densecoatings and exhibited granular astructure loose and (Figure columnar 3) with structure, a weak with (200) a (111)orientation orientation (Figure [18], 1). whereas Hones theet al.HiPIMS/RFMS-Cr [11] suggested a51 smallW2N47 quantitycoatings of revealed W stabilized a dense CrWN and granular coatings structure with a (Figure similar3) withweak a (200)weak orientation. (200) orientation Martine(Figure et al.1). [2]Hones reported et al. that [11] CrN suggested films awith small (200) quantity and (111) of W orienta- stabilized tionsCrWN demonstrated coatings with hardness a similar weaklevels (200) of 18 orientation. and 12–14 Martine GPa, respectively. et al. [2] reported The thathybrid CrN films with (200) and (111) orientations demonstrated hardness levels of 18 and 12–14 GPa, HiPIMS/RFMS process in this study enhanced the mechanical properties of the Cr51W2N47 respectively. The hybrid HiPIMS/RFMS process in this study enhanced the mechanical coatings, even though the W content was low. properties of the Cr51W2N47 coatings, even though the W content was low.

CoatingsCoatings 2021 2021, 11,, 11x FOR, x FOR PEER PEER REVIEW REVIEW 7 of7 of14 14

FigureFigure 5. 5. HH andand E Elevelslevels of of CrWN CrWN coatings. coatings.

FigureFigureFigure 6. 6. Residual6.Residual Residual stresses stresses stresses of of CrWNof CrWN CrWN coatings. coatings. coatings.

3 2 FigureFigureFigure 7. 7. Relationship7.Relationship Relationship between between between (a (a )( )ahardness hardness) hardness and and and HH /E3H/E3/E 2levels2levels levels and and and (b ( b)( )bYoung’s Young’s) Young’s modulus modulus modulus against against against residual residual residual stresses stresses stresses of of ofthe the the CrWN coatings. CrWNCrWN coatings. coatings.

FigureFigure 8 shows8 shows the the H/E H/E and and H 3H/E32/E ratios2 ratios of ofthe the CrWN CrWN coatings. coatings. H/E H/E represents represents the the indicatorindicator of ofelastic elastic strain strain to tofailure failure [56], [56], whereas whereas H 3H/E32/E denotes2 denotes the the resistance resistance against against plasticplastic deformation deformation [57]. [57]. The The H 3H/E32/E and2 and residual residual stress stress exhibi exhibitedted a lineara linear fitting fitting trend trend (Figure(Figure 7a) 7a) similar similar to tothose those of ofH andH and H/E H/E (not (not shown shown in inthis this paper) paper) against against residual residual stress. stress. H/EH/E and and H3 H/E32/E were2 were suggested suggested as aspointers pointers for for fracture fracture toughness, toughness, which which affected affected the the wear wear resistanceresistance [58]. [58]. However, However, such such correlations correlations between between H/E H/E and and H 3H/E32/E for2 for toughness toughness were were compatiblecompatible with with hard hard coatings coatings with with low low plasti plasticitycity [59]. [59]. Figure Figure 9 shows9 shows the the wear wear scars scars of of thethe CrWN CrWN coatings. coatings. Chippings Chippings marks marks were were observed observed along along the the wear wear track track of ofthe the CrCr65W654WN431N coatings.31 coatings. The The elemental elemental mapping mapping of ofCr Cr and and N Nindicated indicated that that the the coating coating was was wornworn out, out, whereas whereas the the Fe Fe signal signal revealed revealed th eth exposuree exposure of ofthe the SUS420 SUS420 substrate. substrate. Similar Similar wearwear behavior behavior was was shown shown for for the the Cr Cr62W623WN335N and35 and Cr Cr58W582WN240N coatings40 coatings with with narrow narrow wear wear widths.widths. The The results results of ofwear wear tests tests indicated indicated that that the the Cr Cr65W654WN431N, 31Cr, Cr62W623WN335N, 35and, and Cr Cr58W582WN240N 40 coatingscoatings were were exhausted exhausted with with a weara wear length length of of200 200 m, m, whereas whereas the the Cr Cr51W512WN247N coatings47 coatings exhibitedexhibited a low a low wear wear rate rate of of1.4 1.4 × 10 × −106 mm−6 mm3·N3·N−1·m−1·m−1 with−1 with a coefficient a coefficient of offriction friction of of0.60. 0.60. The The DCMS-preparedDCMS-prepared CrWN CrWN coatings coatings with with an an H ≤H19.1 ≤19.1 GPa GPa were were worn worn through through after after wear wear tests, tests, andand the the coatings coatings with with H valuesH values of 20.3–27.0of 20.3–27.0 GPa GPa exhibited exhibited wear wear rates rates of 3.1–12of 3.1–12 × 10 × −106 mm−6 mm3·N3−·N1·m−1·m−1 −1 [15].[15]. Figure Figure 10 10shows shows the the scratch scratch scars scars of ofthe the CrWN CrWN coatings. coatings. LC1 L andC1 and LC2 L presentedC2 presented loads loads inducinginducing cohesive cohesive failure failure and and exposing exposing the the substrate, substrate, respectively respectively [60]. [60]. The The Cr Cr65W654WN431N 31 coatingscoatings exhibited exhibited the the lowest lowest LC1 L andC1 and LC2 L valuesC2 values among among the the tested tested samples, samples, implying implying their their brittleness.brittleness. Severe Severe chippi chippingng was was observed observed for for the the Cr Cr65W654WN431N coatings31 coatings after after the the normal normal load load reachedreached the the LC1 L. C1Slight. Slight chipping chipping was was found found on on the the Cr Cr62W623WN335N and35 and Cr Cr58W582WN240N coatings,40 coatings,

Coatings 2021, 11, 690 7 of 14

Figure8 shows the H/E and H3/E2 ratios of the CrWN coatings. H/E represents the indicator of elastic strain to failure [56], whereas H3/E2 denotes the resistance against plastic deformation [57]. The H3/E2 and residual stress exhibited a linear ﬁtting trend (Figure7a) similar to those of H and H/E (not shown in this paper) against residual stress. H/E and H3/E2 were suggested as pointers for fracture toughness, which affected the wear resistance [58]. However, such correlations between H/E and H3/E2 for toughness were compatible with hard coatings with low plasticity [59]. Figure9 shows the wear scars of the CrWN coatings. Chippings marks were observed along the wear track of the Cr65W4N31 coatings. The elemental mapping of Cr and N indicated that the coating was worn out, whereas the Fe signal revealed the exposure of the SUS420 substrate. Similar wear behavior was shown for the Cr62W3N35 and Cr58W2N40 coatings with narrow wear widths. The results of wear tests indicated that the Cr65W4N31, Cr62W3N35, and Cr58W2N40 coatings were exhausted with a wear length of 200 m, whereas the Cr51W2N47 coatings exhibited a low wear rate of 1.4 × 10−6 mm3·N−1·m−1 with a coefﬁcient of friction of Coatings 2021, 11, x FOR PEER REVIEW0.60. The DCMS-prepared CrWN coatings with an H ≤ 19.1 GPa were worn through 8 of 14 after wear tests, and the coatings with H values of 20.3–27.0 GPa exhibited wear rates of 3.1–12 × 10−6 mm3·N−1·m−1 [15]. Figure 10 shows the scratch scars of the CrWN coatings. LC1 and LC2 presented loads inducing cohesive failure and exposing the substrate, whereasrespectively almost [60]. The no Cr chipping65W4N31 coatings was detected exhibited on the the lowest Cr51LC1Wand2N47L C2coatings.values among The distinct devia- tionsthe tested in wear samples, and implying scratch their tests brittleness. could be Severeattrib chippinguted to wasthe observedeffect of forresidual the stress. The Cr65W4N31 coatings after the normal load reached the LC1. Slight chipping was found Cr65W4N31 coatings exhibited a high tensile residual stress (1.30 GPa), whereas the on the Cr62W3N35 and Cr58W2N40 coatings, whereas almost no chipping was detected Cron51 theW2 CrN5147W coatings2N47 coatings. demonstrated The distinct a deviationscompressive in wear residual and scratch stress tests (−0.53 could GPa). be The LC1 was 2attributed N for the to the Cr effect65W4N of31 residual coatings stress. and The 5–7 Cr65 NW 4forN31 thecoatings other exhibited three coatings. a high tensile The LC1 and H/E residual stress (1.30 GPa), whereas the Cr W N coatings demonstrated a compressive values of these CrWN coatings exhibited51 2 47 similar trends. The LC2 increased from 6 N for residual stress (−0.53 GPa). The LC1 was 2 N for the Cr65W4N31 coatings and 5–7 N the Cr65W4N31 coatings to 15, 22, and 25 N for the Cr62W3N35, Cr58W2N40, and Cr51W2N47 for the other three coatings. The LC1 and H/E values of these CrWN coatings exhibited 51 2 47 coatings,similar trends. respectively, The LC2 increased implying from that 6 N the for Cr the CrW65NW4N coatings31 coatings possessed to 15, 22, andthe highest adhe- sion25 N forstrength, the Cr62 Wagreeing3N35, Cr58 withW2N 40a ,high and Cr wear51W2 Nresistance.47 coatings, respectively,The Cr51W implying2N47 coating that exhibited the superiorthe Cr51W 2mechanicalN47 coatings possessedproperties the highestand tribological adhesion strength, characteristics agreeing with among a high the surveyed CrWNwear resistance. coatings. The Cr51W2N47 coating exhibited the superior mechanical properties and tribological characteristics among the surveyed CrWN coatings.

Figure 8. H/E and H3/E2 ratios of CrWN coatings. Figure 8. H/E and H3/E2 ratios of CrWN coatings.

Figure 9. Wear scars and elemental mapping of (a) Cr65W4N31, (b) Cr62W3N35, (c) Cr58W2N40, and (d) Cr51W2N47 coatings.

Coatings 2021, 11, x FOR PEER REVIEW 8 of 14

whereas almost no chipping was detected on the Cr51W2N47 coatings. The distinct devia- tions in wear and scratch tests could be attributed to the effect of residual stress. The Cr65W4N31 coatings exhibited a high tensile residual stress (1.30 GPa), whereas the Cr51W2N47 coatings demonstrated a compressive residual stress (−0.53 GPa). The LC1 was 2 N for the Cr65W4N31 coatings and 5–7 N for the other three coatings. The LC1 and H/E values of these CrWN coatings exhibited similar trends. The LC2 increased from 6 N for the Cr65W4N31 coatings to 15, 22, and 25 N for the Cr62W3N35, Cr58W2N40, and Cr51W2N47 coatings, respectively, implying that the Cr51W2N47 coatings possessed the highest adhesion strength, agreeing with a high wear resistance. The Cr51W2N47 coating exhibited the superior mechanical properties and tribological characteristics among the surveyed CrWN coatings.

Coatings 2021, 11, 690 8 of 14

Figure 8. H/E and H3/E2 ratios of CrWN coatings.

Coatings 2021, 11, x FOR PEER REVIEW 9 of 14 FigureFigure 9. 9. WearWear scars scars and and elemental elemental mapping mapping of of (a (a) )Cr Cr6565WW4N431N, 31(b,() bCr)62 CrW623NW353,N (c35) ,(Crc58)W Cr258NW40, 2andN40 (,d and) Cr(d51)W Cr251NW47 2coatings.N47 coatings.

FigureFigure 10. 10. ScratchScratch scars scars of of the the CrWN CrWN coatings. coatings. 3.2. Diffusion Barriers 3.2. Diffusion Barriers Table2 lists the atomic compositions of the two CrWN films prepared at a thickness of Table 2 lists the atomic compositions of the two CrWN films prepared at a thickness approximately 100 nm and used as diffusion barriers for Cu metallization. In Section 3.1, the of approximately 100 nm and used as diffusion barriers for Cu metallization. In Section coatings prepared using WCr = 500 W, WW = 50 W, f N2 = 0.4, and a deposition time of 85.6 min 3.1, the coatings prepared using WCr = 500 W, WW = 50 W, fN2 = 0.4, and a deposition time exhibited a composition of Cr51W2N47, whereas the composition became Cr59W2N39 as the of 85.6 min exhibited a composition of Cr51W2N47, whereas the composition became deposition time was reduced to 6.7 min. This result can be attributed to the overestimation Cr59W2N39 as the deposition time was reduced to 6.7 min. This result can be attributed to of Cr content because of a low thickness of 108 nm for the CrWN films accompanied by a the overestimation of Cr content because of a low thickness of 108 nm for the CrWN films Cr interlayer of 10 nm. In addition, the Cr54W6N40 samples were prepared using a higher accompanied by a Cr interlayer of 10 nm. In addition, the Cr54W6N40 samples were pre- WW of 100 W. Figure 11 shows the sheet resistance of the Cu/CrWN/Cr/Si samples. The pared using a higher WW of 100 W. Figure 11 shows the sheet resistance of the 550 ◦C annealed samples exhibited lower sheet resistances than those at the as-deposited Cu/CrWN/Cr/Si samples. The 550 °C annealed samples exhibited lower sheet resistances state, which was attributed to the defect annihilation and grain growth of Cu films [29,61]. than those at the as-deposited state, which was attributed to the defect annihilation and The sheet resistance increased slightly when the samples were annealed at 600 and 650 ◦C, grain growth of Cu films [29,61]. The sheet resistance increased slightly when the samples whereas an abrupt increase was observed when the annealing temperature was set to 700 ◦C, were annealed at 600 and 650 °C, whereas an abrupt increase was observed when the which implied the formation of Cu3Si [61]. Figures 12 and 13 show the GIXRD patterns of annealing temperature was set to 700 °C, which implied the formation of Cu3Si [61].◦ the Cu/Cr59W2N39/Cr/Si and Cu/Cr54W6N40/Cr/Si samples annealed at 550–650 C, re- Figures 12 and 13 show the GIXRD patterns of the Cu/Cr59W2N39/Cr/Si and spectively, and no reflection from Cu-silicide is observed. The as-deposited samples exhibited Cu/Cr54W6N40/Cr/Si samples annealed at 550–650 °C, respectively, and no reflection from◦ CrN and Cu phases, whereas a Cr2N phase was observed after annealing at 550–650 C. Cu-silicide is observed. The as-deposited samples exhibited CrN and Cu phases, whereas The diffusion barrier performance of the Cu/CrWN/Cr/Si samples was further examined a Cr2N phase was observed after annealing at 550–650 °C. The diffusion barrier perfor- through the AES depth profiles of the annealed samples. mance of the Cu/CrWN/Cr/Si samples was further examined through the AES depth profiles of the annealed samples.

Table 2. Co-sputtering parameters, atomic compositions, and thicknesses of CrWN films.

WCr 1 WW 2 Atomic Compositions (at.%) Thickness Sample fN2 (W) (W) Cr W N O (nm) Cr59W2N39 500 50 0.4 57.5 ± 0.5 2.3 ± 0.0 37.8 ± 0.5 2.4 ± 0.0 108 Cr54W6N40 500 100 0.4 52.8 ± 0.5 6.5 ± 0.2 39.1 ± 0.8 1.6 ± 0.2 103 1 WCr: power on Cr target; 2 WW: power on W target.

Coatings 2021, 11, 690 9 of 14

Table 2. Co-sputtering parameters, atomic compositions, and thicknesses of CrWN ﬁlms.

W 1 W 2 Atomic Compositions (at.%) Thickness Sample Cr W f (W) (W)N2 Cr W N O (nm) Cr W N 500 50 0.4 57.5 ± 0.5 2.3 ± 0.0 37.8 ± 0.5 2.4 ± 0.0 108 CoatingsCoatings59 202120212 39,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 1010 ofof 1414 Cr54W6N40 500 100 0.4 52.8 ± 0.5 6.5 ± 0.2 39.1 ± 0.8 1.6 ± 0.2 103 1 2 WCr: power on Cr target; WW: power on W target.

FigureFigureFigure 11.11. 11. SheetSheetSheet resistanceresistance resistance ofof of thethe the annealedannealed annealed Cu/CrWN/Cr/SiCu/CrWN/Cr/Si samples.samples. samples.

FigureFigureFigure 12.12. 12. GIXRDGIXRDGIXRD patternspatterns patterns ofof of (( (aaa))) as-depositedas-deposited as-deposited andand and (( (bb–––dd))) annealedannealed annealed Cu/CrCu/Cr Cu/Cr595959WWW22NN239N39/Cr/Si/Cr/Si39/Cr/Si samples.samples. samples.

FigureFigureFigure 13.13. 13. GIXRDGIXRDGIXRD patternspatterns patterns ofof of (( (aaa))) as-depositedas-deposited as-deposited andand and (( (bb–––dd))) annealedannealed annealed Cu/CrCu/Cr Cu/Cr545454WWW66NN640N40/Cr/Si/Cr/Si40/Cr/Si samples.samples. samples.

FiguresFigures 1414 andand 1515 showshow thethe AESAES depthdepth profprofilesiles ofof thethe as-depositedas-deposited andand annealedannealed Cu/CrCu/Cr5959WW22NN3939/Cr/Si/Cr/Si andand Cu/CrCu/Cr5454WW66NN4040/Cr/Si/Cr/Si samples,samples, respectively.respectively. TheThe mainmain variationvariation be-be- tweentween thethe as-depositedas-deposited andand annealedannealed samplessamples occurredoccurred atat thethe interlayer.interlayer. TheThe originaloriginal CrCr interlayerinterlayer evolvedevolved intointo anan interdiffusioninterdiffusion zonezone consistingconsisting ofof Cr,Cr, N,N, andand Si.Si. TheThe interdiffu-interdiffu- sionsion betweenbetween Si/CrSi/Cr interfaceinterface waswas reportedreported atat 450450 °C°C [62].[62]. CuCu diffuseddiffused intointo aa shallowshallow depthdepth ofof thethe CrWNCrWN filmsfilms atat 650650 °C.°C. ThThee CrWNCrWN filmsfilms playedplayed thethe rolerole ofof aa diffusiondiffusion barrierbarrier upup toto 650650 °C°C afterafter annealingannealing forfor 11 h.h.

Coatings 2021, 11, 690 10 of 14

Figures 14 and 15 show the AES depth profiles of the as-deposited and annealed Cu/Cr59W2N39/Cr/Si and Cu/Cr54W6N40/Cr/Si samples, respectively. The main variation between the as-deposited and annealed samples occurred at the interlayer. The original Cr interlayer evolved into an interdiffusion zone consisting of Cr, N, and Si. The interdiffusion between Si/Cr interface was reported at 450 ◦C[62]. Cu diffused into a ◦ CoatingsCoatings 20212021,, 1111,, xx FORFOR PEERPEER REVIEWREVIEWshallow depth of the CrWN films at 650 C. The CrWN films played the role of a diffusion1111 ofof 1414

barrier up to 650 ◦C after annealing for 1 h.

◦ ◦ Figure 14. AES depth proﬁles of (a) as-deposited, (b) 600 C, and (c) 650 C annealed Cu/Cr59W2N39/Cr/Si samples. FigureFigure 14.14. AESAES depthdepth profilesprofiles ofof ((aa)) as-deposited,as-deposited, ((bb)) 600600 °C,°C, andand ((cc)) 650650 °C°C annealedannealed Cu/CrCu/Cr5959WW22NN3939/Cr/Si/Cr/Si samples.samples. (Annealed(Annealed(Annealed in inin vacuum vacuumvacuum for forfor 1 11 h). h).h).

Figure 15. Cont.

FigureFigure 15.15. AESAES depthdepth profilesprofiles ofof ((aa)) as-deposited,as-deposited, ((bb)) 600600 °C,°C, andand ((cc)) 650650 °C°C annealedannealed Cu/CrCu/Cr5454WW66NN4040/Cr/Si/Cr/Si samples.samples. (Annealed(Annealed inin vacuumvacuum forfor 11 h)h)

Coatings 2021, 11, x FOR PEER REVIEW 11 of 14

Figure 14. AES depth profiles of (a) as-deposited, (b) 600 °C, and (c) 650 °C annealed Cu/Cr59W2N39/Cr/Si samples. (Annealed in vacuum for 1 h).

Coatings 2021, 11, 690 11 of 14

◦ ◦ FigureFigure 15. 15.AES AES depthdepth proﬁles profiles of of ( a()a as-deposited,) as-deposited, (b ()b 600) 600C, °C, and and (c )(c 650) 650C °C annealed annealed Cu/Cr Cu/Cr54W54W6N6N4040/Cr/Si/Cr/Si samples. (Annealed(Annealed in in vacuum vacuum for for 1 h).1 h)

4. Conclusions CrWN coatings were successively fabricated through a hybrid HiPIMS/RFMS process. The N content of the CrWN coatings increased when the f N2 was increased, accompanied by structural variation from the Cr2N to CrN phase. The principal conclusions of this study can be summarized as: 1. The hybrid HiPIMS/RFMS process formed CrWN coatings with a dense structure and a smooth surface. 2. The mechanical properties, hardness and Young’s modulus, of the CrWN coatings were affected by the crystalline phase and residual stress. The Cr51W2N47 coatings exhibited a granular structure, revealing enhanced mechanical properties (H: 19.7 GPa, E: 296 GPa) and reduced surface roughness values (Ra: 2.6 nm, Rq: 3.3 nm), accompanied by a compressive residual stress of −0.53 GPa. 3. The tribological characteristics, wear resistance, and scratch behavior of the CrWN coatings were affected by residual stress. The Cr51W2N47 coatings with a compressive residual stress exhibited superior tribological characteristics compared to those CrWN coatings revealing tensile residual stresses. 4. The application of CrWN ﬁlms as a diffusion barrier on Cu metallization was practiced by annealing up to 650 ◦C in a vacuum for 1 h.

Author Contributions: Conceptualization, L.-C.C.; validation, L.-C.C.; investigation, C.-E.W. and T.-Y.O.; resources, L.-C.C.; writing-original draft preparation, L.-C.C.; project administration, L.-C.C. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Ministry of Science and Technology, Taiwan, grant numbers 108-2221-E-131-012 and 109-2622-E-131-003-CC3. The APC was funded by Ming Chi University of Technology. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Acknowledgments: The technical support of the Instrumentation Center at the National Tsing Hua University with the AES and EPMA analyses is greatly appreciated. Conﬂicts of Interest: The authors declare no conﬂict of interest. Coatings 2021, 11, 690 12 of 14

References

1. Shin, C.S.; Gall, N.; Hellgren, N.; Patscheider, J.; Petrov, I.; Greene, J.E. Vacancy hardening in single-crystal TiNx (001) layers. J. Appl. Phys. 2003, 93, 6025–6028. [CrossRef] 2. Martinez, E.; Sanjinés, R.; Banakh, O.; Lévy, F. Electrical, optical and mechanical properties of sputtered CrNy and Cr1−xSixN1.02 thin films. Thin Solid Films 2004, 447, 332–336. [CrossRef] 3. Kong, J.Z.; Xu, P.; Cao, Y.Q.; Li, A.D.; Wang, Q.Z.; Zhou, F. Improved corrosion protection of CrN hard coating on steel sealed with TiOxNy–TiN composite layers. Surf. Coat. Technol. 2020, 381, 125108. [CrossRef] 4. Liu, X.; Ma, G.J.; Sun, G.; Duan, Y.P.; Liu, S.H. Effect of deposition and annealing temperature on mechanical properties of TaN film. Appl. Surf. Sci. 2011, 258, 1033–1037. [CrossRef] 5. Liu, K.Y.; Lee, J.W.; Wu, F.B. Fabrication and tribological behavior of sputtering TaN coatings. Surf. Coat. Technol. 2014, 259, 123–128. [CrossRef] 6. Hones, P.; Martin, N.; Regula, M.; Lévy, F. Structural and mechanical properties of chromium nitride, molybdenum nitride, and tungsten nitride thin films. J. Phys. D Appl. Phys. 2003, 36, 1023–1029. [CrossRef] 7. Lou, B.S.; Moirangthem, I.; Lee, J.W. Fabrication of tungsten nitride thin films by superimposed HiPIMS and MF system: Effects of nitrogen flow rate. Surf. Coat. Technol. 2020, 393, 125743. [CrossRef] 8. Zhou, M.; Makino, Y.; Nose, M.; Nogi, K. Phase transition and properties of Ti–Al–N thin films prepared by r.f.-plasma assisted magnetron sputtering. Thin Solid Films 1999, 339, 203–208. [CrossRef] 9. Aouadi, S.M.; Filip, P.; Debessai, M. Characterization of tantalum zirconium nitride sputter-deposited nanocrystalline coatings. Surf. Coat. Technol. 2004, 187, 177–184. [CrossRef] 10. Chang, L.C.; Chang, C.Y.; Chen, Y.I. Mechanical properties and oxidation resistance of reactively sputtered Ta1–xZrxNy thin films. Surf. Coat. Technol. 2015, 280, 27–36. [CrossRef] 11. Hones, P.; Consiglio, R.; Randall, N.; Lévy, F. Mechanical properties of hard chromium tungsten nitride coatings. Surf. Coat. Technol. 2000, 125, 179–184. [CrossRef] 12. Wu, F.B.; Tien, S.K.; Duh, J.G. Manufacture, microstructure and mechanical properties of CrWN and CrN/WN nanolayered coatings. Surf. Coat. Technol. 2005, 200, 1514–1518. [CrossRef] 13. Yao, S.H.; Su, Y.L.; Kao, W.H.; Cheng, K.W. Evaluation on wear behavior of Cr–Ag–N and Cr–W–N PVD nanocomposite coatings using two different types of tribometer. Surf. Coat. Technol. 2006, 201, 2520–2526. [CrossRef] 14. Wu, W.Y.; Wu, C.H.; Xiao, B.H.; Yang, T.X.; Lin, S.Y.; Chen, P.H.; Chang, C.L. Microstructure, mechanical and tribological properties of CrWN films deposited by DC magnetron sputtering. Vacuum 2013, 87, 209–212. [CrossRef] 15. Chang, L.C.; Zheng, Y.Z.; Gao, Y.X.; Chen, Y.I. Mechanical properties and oxidation resistance of sputtered Cr–W–N coatings. Surf. Coat. Technol. 2017, 320, 196–200. [CrossRef] 16. Lin, C.H.; Duh, J.G.; Yau, B.S. Processing of chromium tungsten nitride hard coatings for glass molding. Surf. Coat. Technol. 2006, 201, 1316–1322. [CrossRef] 17. Lin, T.N.; Han, S.; Weng, K.W.; Lee, C.T. Investigation on the structural and mechanical properties of anti-sticking sputtered tungsten chromium nitride films. Thin Solid Films 2013, 529, 333–337. [CrossRef] 18. Chen, Y.I.; Cheng, Y.R.; Chang, L.C.; Lee, J.W. Chemical inertness of Cr–W–N coatings in glass molding. Thin Solid Films 2015, 593, 102–109. [CrossRef] 19. Huang, A.; Xie, Z.; Li, K.; Chen, Q.; Chen, Y.; Gong, F. Thermal stability of CrWN glass molding coatings after vacuum annealing. Coatings 2020, 10, 198. [CrossRef] 20. Nitta, T.; Ohmi, T.; Hoshi, T.; Sakai, S.; Sakaibara, K.; Imai, S.; Shibata, T. Evaluating the large electromigration resistance of copper interconnects employing a newly developed accelerated life-test method. J. Electrochem. Soc. 1993, 140, 1131–1137. [CrossRef] 21. McBrayer, J.D.; Swanson, R.M.; Sigmon, T.W. Diffusion of Metals in Silicon Dioxide. J. Electrochem. Soc. 1986, 133, 1242–1246. [CrossRef] 22. Istratov, A.A.; Flink, C.; Hieslmair, H.; Weber, E.R. Intrinsic diffusion coefficient of interstitial copper in silicon. Phys. Rev. Lett. 1998, 81, 1243–1246. [CrossRef] 23. Ono, H.; Nakano, T.; Ohta, T. Diffusion barrier effects of transition metals for Cu/M/Si multilayers (M = Cr, Ti, Nb, Mo, Ta, W). Appl. Phys. Lett. 1994, 64, 1511–1513. [CrossRef] 24. Shang, J.; Hao, J.X.; Hang, T.; Li, M. Diffusion barrier effect of Ta/Ti bilayer in organic dielectric/Cu interconnects. Thin Solid Films 2018, 653, 113–118. [CrossRef] 25. Wang, H.W.; Chiou, B.S. Barrier layer effect of titanium-tungsten on the electromigration in sputtered copper films on polyimide. J. Mater. Sci. Mater. Electron. 2000, 11, 17–24. [CrossRef] 26. Fugger, M.; Plappert, M.; Schäffer, C.; Humbel, O.; Hutter, H.; Danninger, H.; Nowottnick, M. Comparison of WTi and WTi(N) as diffusion barriers for Al and Cu metallization on Si with respect to thermal stability and diffusion behavior of Ti. Microelectron. Reliab. 2014, 54, 2487–2493. [CrossRef] 27. Takeyama, M.B.; Sato, M.; Aoyagi, E.; Noya, A. Preparation of ultrathin TiNx films by radical assisted low temperature deposition and their barrier properties against Cu diffusion. Vacuum 2016, 126, 10–15. [CrossRef] 28. Chen, S.F.; Wang, S.J.; Yang, T.H.; Yang, Z.D.; Bor, H.Y.; Wei, C.N. Effect of nitrogen flow rate on TaN diffusion barrier layer deposited between a Cu layer and a Si-based substrate. Ceram. Int. 2017, 43, 12505–12510. [CrossRef] Coatings 2021, 11, 690 13 of 14

29. Kim, J.B.; Nandi, D.K.; Kim, T.H.; Jang, Y.; Bae, J.S.; Hong, T.E.; Kim, S.H. Atomic layer deposition of WNx thin films using a F-free tungsten metalorganic precursor and NH3 plasma as a Cu-diffusion barrier. Thin Solid Films 2019, 685, 393–401. [CrossRef] 30. Suh, B.S.; Lee, Y.J.; Hwang, J.S.; Park, C.O. Properties of reactively sputtered WNx as Cu diffusion barrier. Thin Solid Films 1999, 348, 299–303. [CrossRef] 31. Wojcik, H.; Kaltofen, R.; Merkel, U.; Krien, C.; Strehle, S.; Gluch, J.; Knaut, M.; Wenzel, C.; Preusse, A.; Bartha, J.W.; et al. Electrical Evaluation of Ru–W(–N), Ru–Ta(–N) and Ru–Mn films as Cu diffusion barriers. Microelectron. Eng. 2012, 92, 71–75. [CrossRef] 32. Wang, Q.X.; Liang, S.H.; Wang, X.H.; Fan, Z.K. Diffusion barrier performance of amorphous W–Ti–N films in Cu metallization. Vacuum 2010, 84, 1270–1274. 33. Lee, J.; Duh, J.G. Structural evolution of Zr–Cu–Ni–Al–N thin film metallic glass and its diffusion barrier performance in Cu-Si interconnect at elevated temperature. Vacuum 2017, 142, 81–86. [CrossRef] 34. Hsiao, Y.T.; Tung, C.H.; Lin, S.J.; Yeh, J.W.; Chang, S.Y. Thermodynamic route for self-forming 1.5 nm V–Nb–Mo–Ta–W high- entropy alloy barrier layer: Roles of enthalpy and mixing entropy. Acta Mater. 2020, 199, 107–115. [CrossRef] 35. Chang, J.C.; Tu, S.L.; Chen, M.C. Sputtered Cr and reactively sputtered CrNx serving as barrier layers against copper diffusion. J. Electrochem. Soc. 1998, 145, 4290–4296. [CrossRef] 36. Marulanda, D.M.; Lousa, A.; Martinez-de-Olcoz, L.; Olaya, J.J. Microstructure characterization of nano-structured Cr/Cr2N multilayer films produced through radio frequency magnetron sputtering. Thin Solid Films 2014, 550, 272–277. [CrossRef] 37. Lu, F.H.; Chen, H.Y. Phase changes of CrN films annealed at high temperature under controlled atmosphere. Thin Solid Films 2001, 398, 368–373. [CrossRef] 38. Kouznetsov, V.; Macák, K.; Schneider, J.M.; Helmersson, U.; Petrov, I. A novel pulsed magnetron sputter technique utilizing very high target power densities. Surf. Coat. Technol. 1990, 122, 290–293. [CrossRef] 39. Helmersson, U.; Lattemann, M.; Bohlmark, J.; Ehiasarian, A.P.; Gudmundsson, J.T. Ionized physical vapor deposition (IPVD): A review of technology and applications. Thin Solid Films 2006, 513, 1–24. [CrossRef] 40. Gudmundsson, J.T.; Brenning, N.; Lundin, D.; Helmersson, U. High power impulse magnetron sputtering discharge. J. Vac. Sci. Technol. A Vac. Surf. Films 2012, 30, 030801. [CrossRef] 41. Ehiasarian, A.P. High-power impulse magnetron sputtering and its applications. Pure Appl. Chem. 2010, 82, 1247–1258. [CrossRef] 42. Sarakinos, K.; Alami, J.; Konstantinidis, S. High power pulsed magnetron sputtering: A review on scientific and engineering state of the art. Surf. Coat. Technol. 2010, 204, 1661–1684. [CrossRef] 43. Purandare, Y.P.; Ehiasarian, A.P.; Hovsepian, P.E. Structure and properties of ZrN coatings deposited by high power impulse magnetron sputtering technology. J. Vac. Sci. Technol. A 2011, 29, 011004. [CrossRef] 44. Ehiasarian, A.P.; Münz, W.-D.; Hultman, L.; Helmersson, U.; Petrov, I. High power pulsed magnetron sputtered CrNx films. Surf. Coat. Technol. 2003, 163, 267–272. [CrossRef] 45. Chang, L.C.; Chang, C.Y.; You, Y.W. Ta–Zr–N thin films fabricated through HIPIMS/RFMS co-sputtering. Coatings 2017, 7, 189. [CrossRef] 46. Chang, L.C.; Zheng, Y.Z.; Chen, Y.I. Mechanical properties of Zr–Si–N films fabricated through HiPIMS/RFMS co-sputtering. Coatings 2018, 8, 263. [CrossRef] 47. Oliver, W.C.; Pharr, G.M. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. J. Mater. Res. 1992, 7, 1564–1583. [CrossRef] 48. Janssen, G.C.A.M.; Abdalla, M.M.; van Keulen, F.; Pujada, B.R.; van Venrooy, B. Celebrating the 100th anniversary of the Stoney equation for film stress: Developments from polycrystalline steel strips to single crystal silicon wafers. Thin Solid Films 2009, 517, 1858–1867. [CrossRef] 49. Barin, I. Thermochemical Data of Pure Substances, 3rd ed.; VCH: New York, NY, USA, 1995. 50. Lin, J.; Sproul, W.D.; Moore, J.J.; Lee, S.; Myers, S. High rate deposition of thick CrN and Cr2N coatings using modulated pulse power (MPP) magnetron sputtering. Surf. Coat. Technol. 2011, 205, 3226–3234. [CrossRef] 51. Bielawski, M. Residual stress control in TiN/Si coatings deposited by unbalanced magnetron sputtering. Surf. Coat. Technol. 2006, 200, 3987–3995. [CrossRef] 52. Tan, S.; Zhang, X.; Wu, X.; Fang, F.; Jiang, J. Effect of substrate bias and temperature on magnetron sputtered CrSiN films. Appl. Surf. Sci. 2011, 257, 1850–1853. [CrossRef] 53. Hirota, K.; Takano, Y.; Yoshinaka, M.; Yamaguchi, O. Hot isostatic pressing of chromium nitrides (Cr2N and CrN) prepared by self-propagating high-temperature synthesis. J. Am. Ceram. Soc. 2001, 84, 2120–2122. [CrossRef] 54. Hones, P.; Sanjines, R.; Lévy, F. Characterization of sputter-deposited chromium nitride thin films for hard coatings. Surf. Coat. Technol. 1997, 94, 398–402. [CrossRef] 55. Wei, G.; Rar, A.; Barnard, J.A. Composition, structure, and nanomechanical properties of DC-sputtered CrNx (0 ≤ x ≤ 1) thin films. Thin Solid Films 2001, 398, 460–464. [CrossRef] 56. Pogrebnjak, A.D.; Beresnev, V.M.; Bondar, O.V.; Postolnyi, B.O.; Zaleski, K.; Coy, E.; Jurga, S.; Lisovenko, M.O.; Konarski, P.; Rebouta, L.; et al. Superhard CrN/MoN coatings with multilayer architecture. Mater. Des. 2018, 153, 47–59. [CrossRef] 57. Tsui, T.Y.; Pharr, G.M.; Oliver, W.C.; Bhatia, C.S.; White, R.L.; Anders, S.; Anders, A.; Brown, I.G. Nanoindentation and nanoscratching of hard carbon coatings for magnetic disks. Mater. Res. Soc. Symp. Proc. 1995, 383, 447–452. [CrossRef] 58. Li, H.; Liu, Z.; Li, J.; Huang, J.; Kong, J.; Wu, Q.; Xiong, D. Effects of Hf addition on the structure, mechanical and tribological properties of CrN film. Surf. Coat. Technol. 2020, 397, 126067. [CrossRef] Coatings 2021, 11, 690 14 of 14

59. Chen, X.; Du, Y.; Chung, Y.W. Commentary on using H/E and H3/E2 as proxies for fracture toughness of hard coatings. Thin Solid Films 2019, 688, 137265. [CrossRef] 60. Odén, M.; Ericsson, C.; Håkansson, G.; Ljungcrantz, H. Microstructure and mechanical behavior of arc-evaporated Cr–N coatings. Surf. Coat. Technol. 1999, 114, 39–51. [CrossRef] 61. Meng, Y.; Song, Z.X.; Li, Y.H.; Qian, D.; Hu, W.; Xu, K.W. Thermal stability of ultra thin Zr–B—N ﬁlms as diffusion barrier between Cu and Si. Appl. Surf. Sci. 2020, 527, 146810. [CrossRef] 62. Zalar, A.; Hofmann, S.; Panjan, P. Characterization of chemical interdiffusivities at silicon/metal interfaces in initial reaction stages. Vacuum 1997, 48, 625–627. [CrossRef]