Tunable composition and properties of Al-O-N films prepared by reactive deep oscillation magnetron sputtering

Journal Pre-proof Tunable composition and properties of Al-O-N films prepared by reactive deep oscillation magnetron sputtering

A. Belosludtsev, J. Vlček, J. Houška, S. Haviar, R. Čerstvý PII:

S0257-8972(20)30385-6

DOI:

https://doi.org/10.1016/j.surfcoat.2020.125716

Reference:

SCT 125716

To appear in:

Surface & Coatings Technology

Please cite this article as: A. Belosludtsev, J. Vlček, J. Houška, et al., Tunable composition and properties of Al-O-N films prepared by reactive deep oscillation magnetron sputtering, Surface & Coatings Technology (2018), https://doi.org/10.1016/j.surfcoat.2020.125716

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© 2018 Published by Elsevier.

Journal Pre-proof Tunable composition and properties of Al-O-N films prepared by reactive deep oscillation magnetron sputtering

A. Belosludtseva, J. Vlček*, J. Houška, S. Haviar, R. Čerstvý

Department of Physics and NTIS – European Centre of Excellence, University of West Bohemia, Univerzitní 8, 306 14 Plzeň, Czech Republic Corresponding author. Tel.: +420 377 632 200; Fax: +420 377 632 202.

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Present address: Center for Physical Sciences and Technology, Savanoriu Ave. 231, Vilnius,

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E-mail address: [email protected] (J. Vlček)

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02300, Lithuania

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Abstract

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We report a low-temperature deposition of Al-O-N films in a wide range of compositions. We use and explain the advantages of reactive deep oscillation magnetron sputtering (leading

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to suppressed arcing on the Al target) with a pulsed reactive gas flow control and optimized reactive gas inlet position (leading to a very smooth composition control, despite the different reactivities of O2 and N2). Next, we focus on the relationships between film composition, structure and functional properties. We demonstrate a smoothly controlled refractive index at a very low extinction coefficient, and identify the Al-O-N composition leading to the highest hardness, elastic recovery and elastic strain to failure. We discuss some of the technological applications which these properties are useful for.

Keywords: Aluminium oxynitrides; Reactive DOMS; Tunable composition; Optical properties; Mechanical properties

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Journal Pre-proof 1. Introduction Besides the polycrystalline aluminium oxynitride (Al-O-N) bulk material with a cubic spinel structure, which is produced at very high temperatures (see, for example, reviews [1, 2] and the works cited therein), the Al-O-N films of various structures and elemental compositions have become very important for a large variety of applications from microelectronic [3-6] and optical [6-13] applications, gas barrier films [14], multilayer capacitors [15], oxidation resistant coatings on space-grade epoxy [16] to protective coatings

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[17, 18].

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Reactive magnetron sputtering is a suitable method to prepare Al-O-N films [5, 10, 13-16,

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18, 19] in a one-step process allowing a direct incorporation of nitrogen into the materials. In addition, magnetron sputtering can be easily scaled up from small-sized laboratory deposition

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systems to large-scale industrial devices. However, the processes at both the target surface

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and the growing film surface are affected by a much higher affinity of Al to oxygen than to nitrogen. Let us recall the standard Gibbs free energy of formation of -791.2 kJ per mole of Al

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atoms for Al2O3 and -287.0 kJ per mole of Al atoms for AlN [20]. Thus, smooth control of the composition of Al-O-N (as well as many other metal oxynitrides) constitutes a big challenge of a high current interest.

In our recent papers [21, 22], we reported on high-rate reactive sputtering of Ta-O-N films [21] and Hf-O-N films [22] with smoothly controlled compositions. They were prepared using a standard (the voltage pulse duration of 50 µs and 200 µs, respectively) high-power impulse magnetron sputtering (HiPIMS) with a feedback pulsed reactive gas flow control (RGFC) and a reactive gas (oxygen and nitrogen) injection into the high-density plasma in front of the sputtered metal target.

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The pulsed RGFC makes it possible to deliver a high power into the discharge pulses without arcing on the target and to utilize exclusive benefits of the reactive HiPIMS deposition [23]. The advantages of the used pulsed RGFC method are: (i) very high process stability (no problems with inertia of the inlet system, delay of valves and sensors, and hysteresis effects) as the controller does not keep one working point but an interval in accordance with the control-theory literature dealing with the control of non-linear systems

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[24], (ii) simplicity as no additional measurement devices (such as a plasma emission

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monitoring system, mass spectrometer or Lambda sensor) are needed, and (iii) applicability

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to large-area coaters as a multi-segment RG injection control can be used.

The RG injection into the high-density plasma in front of the sputtered target leads to a

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high degree of dissociation of both O2 and N2 molecules, and consequently to a replacement

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of the aforementioned different reactivities of the O2 and N2 molecules by similar (high)

discharge.

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reactivities of O and N atoms, and many O+ and N+ ions which are produced in the HiPIMS

The present paper is focused on the structure, and optical and mechanical properties of Al-O-N films with tunable composition, prepared by a reactive deep oscillation magnetron sputtering (DOMS) with RGFC. The DOMS is a modified version of HiPIMS with packages (macropulses) of short high-power micropulses [25, 26]. Our motivation to apply this highpower discharge with short voltage pulses was to avoid problems with arcing on the Al target during a standard (voltage pulses longer than 40 µs) HiPIMS deposition.

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2. Experimental details 2.1. Al-O-N preparation The films were deposited using a strongly unbalanced magnetron source with a directly water-cooled planar aluminium target (99.98 % Al purity, diameter of 100 mm and thickness of 6 mm) in a standard stainless-steel vacuum chamber (diameter of 507 mm and length of 520 mm), which was evacuated by a diffusion pump (2 m3s-1) backed up with a rotary pump

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(30 m3h-1). The base pressure before deposition was 10-3 Pa. A detailed characterization of the

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magnetic field and the degree of its unbalance is given in [27].

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The magnetron was driven by a DOMS power supply (HIPIMS Cyprium plasma generator, Zpulser Inc.). In this work, the macropulse (composed of 10 micropulses) duration

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was 500 µs at a repetition frequency of 350 Hz. The micropulse on-time was 20 µs at a

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repetition frequency of 20 kHz within a macropulse (Fig. 1). The deposition-averaged target

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power density (averaged over the total target area) was approximately 8 Wcm-2.

The Al-O-N films were deposited onto Si(100) substrates located 100 mm from the target and held at a floating potential. The substrate surface temperature reached during the depositions (without any external heating) was less than 120 °C.

During deposition, the argon partial pressure was kept constant at 2 Pa (a flow rate of 25 sccm). This rather higher pressure value was used to avoid process instabilities in our deposition system with the strongly unbalanced magnetron source [23] applied to the Al target at high target power densities. Reactive gases (oxygen and nitrogen) were admitted into the vacuum chamber from their sources via individual synchronized mass flow controllers and

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Journal Pre-proof were mixed in two conduits. Both RG inlets with a diameter of 1 mm were placed symmetrically above the target racetrack at the same distance of 20 mm from the target surface and oriented toward the substrate (following the discussion in Refs. [23, 28]). It should be noted that the to-substrate RG injection into the dense plasma in front of the sputtered target is very suitable for reactive HiPIMS deposition of dielectric films. It leads to a substantial increase in the local RG partial pressure [28] at a very high RG dissociation in the high-density plasma. As a consequence, the RG partial pressure in the vacuum chamber,

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pRG, needed for preparation of stoichiometric films, can be very low [29]. This is of key

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importance for process stability, for an increased deposition rate of films and for a decreased

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production of high-energy O- ions (in case of preparation of oxide films) owing to a low

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compound fraction in the target surface layer [23, 28].

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The total pressure of the Ar + O2 + N2 gas mixtures and the fixed Ar partial pressure of 2

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Pa were measured at a point on the chamber wall of 270 mm from the target-substrate axis [21-23]. We used a high-stability capacitance manometer (Baratron, type 627, MKS

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Instruments) with the accuracy better than 1 %.

The total flow rate of reactive gases, ΦRG, was not fixed but pulsing between 0 and 5 sccm (see Fig. 1) in all depositions and the duration of the ΦRG pulses (injecting oxygen and nitrogen in front of the sputtered Al target) was determined during the deposition by a programmable logic controller [30] using a pre-selected critical value of the average discharge _

current on Al target in a period (2857 µs) of the power supply (I d ) cr = 2.1 A. The process controller provided a control feedback signal to both synchronized RG mass flow controllers in order to adjust the duration of the simultaneous O2 and N2 pulses. The N2 fraction in the

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Journal Pre-proof total RG flow is denoted by [N2] from now. The Al-O-N depositions were performed for [N2] in the range from O to 100 %.

The basic principle of the RGFC is illustrated in Fig. 1, which shows the time evolution of the magnetron voltage, Ud(t), and the target current density, Jt(t), averaged over the total _

target area, for the minimum and maximum I d during the deposition at [N2] = 0. As can be

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seen in Fig. 1, the waveforms of Ud(t) and Jt(t) oscillate between the curves measured at the _

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minimum and maximum I d which correlate with the minimum and maximum pRG,

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respectively, during the deposition (see Table 1). The time between the minimum and maximum pRG is on a level of seconds. Note that the pRG oscillations don´t result in any

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vertical inhomogeneties in the films prepared using this deposition technique [31]. This can

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be explained by the opposite effects of the changes in pRG on the individual processes on the

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target surface and in a discharge plasma, discussed in [32].

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The same value of (I d ) cr = 2.1 A, which was optimized for the deposition of stoichiometric Al2O3 films at the micropulse voltage on-time t'on = 6 µs and the micropulse voltage off-time t'off = 44 µs defined by the power-supply software (see Fig. 1), resulted in a gradual increase of the pRG with an increasing [N2], see Table 1. However, the actual micropulse on-time ton = 20 µs was the same in all cases investigated. As can be seen in Table 1, the maximum value of the target power density, max Sd, during a micropulse cannot be expressed as a product of the max ǀUdǀ and the max Jt owing to a delay in the max Jt compared to the max ǀUdǀ, see Fig. 1.

2.2. Al-O-N characterization

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Journal Pre-proof The Al, O and N contents in the films (given in at. % and referred to as [Al], [O] and [N], respectively, from now on) were measured by energy dispersive (EDS) and wave dispersive (WDS) spectroscopies carried out in a scanning electron microscope (Hitachi, SU-70) equipped with EDS (Thermo Scientific, UltraDry) and WDS (Thermo Scientific, MagnaRay) detectors. The spectra were obtained using a primary energy of 10 kV. The Proza matrix correction was done using standard reference samples of pure Al, SiO2 and AlN (Astimex Scientific Ltd.). The maximum error of measured compositions, estimated on the basis of

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WDS and EDS analyses from multiple measurements but also taking into account the limited

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trueness of the method itself, is 1%, 2% and 3% for [Al], [O] and [N], respectively.

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The X-ray diffraction (XRD) measurements were performed using the PANalytical X'Pert PRO diffractometer working in the Bragg-Brentano geometry using a CuKα (40 kV, 40 mA)

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radiation. To avoid a strong reflection from the Si (100) substrate, a slightly asymmetrical

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diffraction geometry with an ω-offset of 1.5° was used. The results were collected over the

relevant peaks.

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2θ-range from 8° to 108°, and are shown over the range from 20° to 62° which includes all

The optical properties (refractive index, n, and extinction coefficient, k) and the thickness of the films (1.0-1.3 m) were determined by spectroscopic ellipsometry using a J.A. Woollam Co. instrument. The measurements were performed using angles of incidence of 65°, 70° and 75° in reflection. The optical data were fitted in the wavelength, , range 2502000 nm using the WVASE software and an optical model consisting of a crystalline Si substrate, a Al-O-N layer represented by the Cauchy dispersion formula and a surface roughness layer. Below we also discuss n and k values at specific wavelengths, e.g. n550 and k550 for  = 550 nm.

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The Fourier transform infrared spectroscopy (FTIR) measurements were performed in transmission using the Vertex 80v (Bruker Optics) instrument. The absorption coefficient was obtained using the measured film transmittance, the film thickness measured at the same location by ellipsometry, and the same WVASE software which was used for ellipsometry. The light absorption was represented by a combination of Gaussian oscillators.

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The film hardness, H, elastic recovery, We, and effective Young's modulus E* = E/(1-2)

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where E and  are the Young's modulus and the Poisson's ratio, respectively, were determined

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using an ultramicroindenter (Fischerscope H-100B) according to the ISO 14577-1:2002E

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standard. The measurements were performed with a preset maximum load of 20 mN (leading to indentation depths below 10% of the film thickness) at 25 different positions. The residual

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macrostress, σ, was determined using the Stoney’s formula (see e.g. [33]) from the bending of

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3. Results and discussion

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Si(100) stripes (5x35x0.38 mm3) measured by profilometry (Dektak 8 Stylus Profiler, Veeco).

3.1. Elemental composition and deposition rate The elemental composition of Al-O-N films is shown in Fig. 2. The first thing to note is that [N] increases and [O] decreases with [N2] almost linearly, at almost the same [N] and [O] at [N2] = 50%. In other words, there is no fingerprint of higher reactivity of oxygen compared to that of nitrogen, which is indicated e.g. by the aforementioned (Sec. 1) Gibbs energies and which may complicate the composition control in a case of conventional sputtering. This can be explained by the high degree of dissociation of O2 and N2 molecules injected into the highdensity plasma, leading to the film growth predominantly from isolated atoms. Thus, the different sticking coefficients of O2 and N2 molecules are replaced by about the same (high)

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Journal Pre-proof sticking coefficients of O and N atoms, and O+ and N+ ions which are produced very effectively in the DOMS discharge and strike the growing films. Here, it should be mentioned that the same sticking coefficients (equal to 1) are used for O atoms [28,34] and N atoms [35] on the metal fraction of the substrate surface in surface models. This achievement is similar to that reported in our previous work dealing with Ta-O-N [21]. Second, Fig. 2 shows that in agreement with different stoichiometries of the binary phases (40% of Al in Al2O3, 50% of Al in AlN), an increasing [N2] leads to increasing [Al] from 40 to 47%. This kind of

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electroneutral substitution (instead of 1:1 substitution), indicated by the present results for

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mostly amorphous Al-O-N, is similar to that reported e.g. in [36] for crystalline Ti-Al-O-N.

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Third, the aforementioned high reactivities of atomic O and especially atomic N even led to

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slightly overstoichiometric films. This can be quantified in terms of the content of Al vacancies, calculable as 2/3[O]+[N]-[Al], which is positive for all compositions and

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increases from less than 1 per 100 film atoms for [N2] = 0% to more than 4 per 100 film

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atoms for [N2] = 100% (not shown graphically). The O content, especially that in the film prepared at [N2] = 100%, is slightly affected also by the release of adsorbed and subplanted

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oxygen from the chamber walls and the sputter target.

Figure 3 shows the deposition rate of the Al-O-N films. The relatively high value aD = 27 nm/min, achieved for the stoichiometric Al2O3 film at the relatively low depositionaveraged target power density close to 8 Wcm-2, decreases gradually to aD = 14 nm/min for the Al47O5N48 film at the same target power density. This can be explained not only (i) by an increasing compound fraction in the target surface layer with the increasing pRG in the vacuum chamber (see Table 1), but also (ii) by the aforementioned increasing Al incorporation (at the decreasing RG incorporation) into the films. Here, it should be _

mentioned that the pRG increases with an increasing [N2] to keep a constant (I d ) cr = 2.1 A

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Journal Pre-proof during depositions in spite of the slightly higher secondary electron emission yield of 0.22 for AlN than 0.19 for Al2O3 [37].

3.2. Al-O-N structure The structure of Al-O-N films is shown in complementary Figs. 4 (XRD) and 5 (FTIR). Figure 4 shows that the O-rich films with [N] up to 9% (prepared at [N2] up to 20%) are amorphous, except a trace amount of metallic Al nanoparticles (indicated by a small but

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certain XRD peak, and observable also in terms of extinction coefficient, see Sec. 3.3).

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The films with [N] of 21-30% ([N2] of 40-60%) are fully amorphous. Note the advantages of

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stable amorphous Al-O-N as a gate insulator for high-power AlGaN-based electronics, as

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discussed e.g. in [5] in comparison with N-free Al2O3 (sharper interfaces and comparable or lower - depending on the gate voltage - leakage current despite the narrower band gap). This

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is combined with industry-friendly sputtering of amorphous films, compared to e.g. atomic

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layer deposition of defect-free crystals. The N-rich films with [N] of 37-48% ([N2] of 70-100%) exhibit formation of hexagonal (wurtzite) AlN crystals, with a possible small

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amount of O atoms in their lattice. There is a preferential orientation characterized by (100) planes parallel to the film surface (2 = 33.22°) followed by (110) planes (2 = 59.35°). At the highest N content there is also a contribution of (002) and (101) planes (2 = 36.04° and 37.92°, respectively)

Figure 5 confirms, despite the overlaps of individual peaks, the transition from films dominated by Al-O bonds (Al-O stretching around 800 cm-1 with a contribution of O-Al-O bending around 675 cm-1 [39]) to films dominated by Al-N bonds (frequently reported transverse vibrations close to 670 cm-1 [40], with a contribution of longitudinal vibrations at higher frequencies, around 865 cm-1 according to [41]). Note also the peak around 2140 cm-1

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Journal Pre-proof (weak but not overlapping with the others), present in all spectra obtained at non-zero [N2] and corresponding to N-Al-N according to [40]. The main part of the spectra (below 1000 cm-1) is getting narrower with an increasing [N2], which may be not only due to a dominance of a single vibrational mode but also due to the better crystallinity (Fig. 4).

3.3. Al-O-N properties Figure 6 shows the optical constants of Al-O-N films in the range up to 600 nm where

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they exhibit the most pronounced changes (not in the whole measurement range up to 2000

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nm). Figure 6a shows that all films exhibit decreasing n(), which is an usual feature of

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transparent materials. At any given , the refractive index monotonically increases with [N],

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e.g. at  = 550 nm from 1.69 to 1.95. The former value, n550 = 1.69 for Al40O59N1, very well

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corresponds to the upper bound of values achieved for Al2O3 (except the corundum phase) [42] and indicates that the films are very well densified. The latter value, n550 = 1.95 for

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Al47O5N48, is slightly below the upper bound of values reported for pure AlN [43], at least partially due to the O content. Note that the width of the aforementioned n range and the

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industry-friendly technique allowing one to smoothly tune n in this range make the Al-O-N system interesting e.g. for rugate filters [8]. The upper bound of the n range, close to the square root of n of Si, makes it interesting e.g. for antireflective layers in photovoltaic applications. Fig. 6b confirms that all films are very well transparent in the whole range of interest. The films prepared at [N2] = 0-20% exhibit (compared to idealized Al2O3) slightly enhanced k, slowly decreasing e.g. from k300 of 110-2 to k550 of 410-3 (still sufficiently low for transparency at a micrometer thickness). This is a fingerprint of the fact that while the deposition technique used did not lead to any macroparticles, the O-rich films include a trace amount of Al nanoparticles (Fig. 4). The films prepared at [N2] = 20-100% exhibit a steeply

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Journal Pre-proof decreasing k() (the exponential Urbach tail), e.g. from k300 on the order of 10-2 to k550 on the order or well below 10-4.

The mechanical properties of Al-O-N films are shown in Fig. 7. The hardness (Fig. 7a) of amorphous compositions monotonically increases with [N], from H = 10 GPa for Al40O59N1 to H = 14 GPa for Al44O26N30. The crystallization (Fig. 4) leads to even steeper increase of the hardness (significantly beyond the error bars based on multiple measurements), up to 19 GPa

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for Al47O11N42 ([N2] = 80%). A case can be made that this is not only due to the crystallinity

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in itself, but also due to a formation of a nanocomposite structure consisting of the AlN-based

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crystals in an O-rich amorphous matrix. Indeed, the transition from [N2] = 80% to [N2] =

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100% leads to a slightly softer film Al47O5N48 possibly due to a too low volume fraction of the amorphous matrix. The enhanced hardness of the N-rich crystalline oxynitrides based on

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h-AlN is consistent with the enhanced hardness of another N-rich crystalline oxynitride based

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on h-Al10O3N8 [17]. This phase in itself was not detected in our case, but its composition Al48O14N38 is very similar to the two our hardest compositions Al46O17N37 and Al47O11N42. In

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parallel, the compressive stress in the films is very low (||<0.3 GPa) and not correlated with H. The low values measured for the residual stress in the films are in agreement with the works [44,45]. The comparison of Figs. 7a and 7b reveals that the evolution of H is well correlated with that of H/E* (measure of the elastic strain to failure; increasing from 0.07 for Al40O59N1 to 0.12 for Al47O11N42) and We (increasing from 44% for Al40O59N1 to 71% for Al47O11N42). The properties of the two hardest compositions fulfill the required properties of materials resistant to cracking as defined e.g. in [46].

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Journal Pre-proof 4. Conclusions Aluminium oxynitride films were prepared by reactive deep oscillation magnetron sputtering with a pulsed reactive gas flow control at a temperature below 120 °C. The deposition technique used made it possible to smoothly control the film composition, from an almost pure Al2O3 through Al45O27N28, prepared at equal flows of O2 and N2 despite their different reactivities, to an almost pure AlN. The film structure changes from amorphous at high O contents to wurtzite AlN-based at high N contents, at a trace amount of Al

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nanoparticles only at the highest O contents and no Al macroparticles. The films are highly

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optically transparent and exhibit a refractive index monotonically increasing with the

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N content, e.g. from 1.69 to 1.95 at the wavelength of 550 nm. The film hardness changes

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non-monotonically and reaches the highest value of 19 GPa for the composition Al47O11N42. The results are important for the design of Al-O-N coatings, and industry-friendly pathways

Acknowledgment

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for their preparation in a wide range of compositions, for various technological applications.

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This work was supported by the European structural and investment funds under project no. CZ.02.1.01/0.0/0.0/17_048/0007267.

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Journal Pre-proof References 1

N.D. Corbin, Aluminum oxynitride spinel: a review, J. Eur. Ceram. Soc. 5 (1989) 143159. doi: 10.1016/0955-2219(89)90030-7

2

J.W. McCauley, P. Patel, M. Chen, G. Gilde, E. Strassburger, B. Paliwal, K.T. Ramesh, D.P. Dandekar, AlON: A brief history of its emergence and evolution, J. Eur. Ceram. Soc. 29 (2009) 223-236. doi: 10.1016/j.jeurceramsoc.2008.03.046

3

G.W. Soares, K.P. Bastos, R.P. Pezzi, L. Miotti, C. Driemeier, I.J.R. Baumvol, C. Hinkle,

D.J. Lee, J.W. Lim, J.K. Mun, S.J. Yun, Improved stability of electrical properties of

-p

4

ro

Lett. 84 (2004) 4992-4994. doi: 10.1063/1.1763230

of

G. Lucovsky, Nitrogen bonding, stability, and transport in AlON films on Si, Appl. Phys.

re

nitrogen-added Al2O3 films grown by PEALD as gate dielectric, Mater. Res. Bull. 83 (2016) 597-602. doi: 10.1016/j.materresbull.2016.07.008 R. Asahara, M. Nozaki, T. Yamada, J. Ito, S. Nakazawa, M. Ishida, T. Ueda, A. Yoshigoe,

lP

5

na

T. Hosoi, T. Shimura, H. Watanabe, Effect of nitrogen incorporation into Al-based gate insulators in AlON/AlGaN/GaN metal-oxide-semiconductor structures, Appl. Phys.

6

Jo ur

Express 9 (2016) 101002. doi: 10.7567/APEX.9.101002 H.-Y. Chen, H.-L. Lu, J.-X. Chen, F. Zhang, X.-M. Ji, W.-J. Liu, X.-F. Yang, D.W. Zhang, Low-temperature one-step growth of AlON thin films with homogenous nitrogendoping profile by plasma-enhanced atomic layer deposition, ACS Appl. Mater. Interfaces 44 (2017) 38662-38669. doi: 10.1021/acsami.7b12262 7

H. Demiryont, L.R. Thomson, G.J. Collins, Optical properties of aluminum oxynitrides deposited

by

laser-assisted

CVD,

Appl.

doi: 10.1364/ao.25.001311

- 14 -

Opt.

25

(1986)

1311-1318.

Journal Pre-proof 8

C.K. Hwangbo, L.J. Lingg, J.P. Lehan, H.A. Macleod, F. Suits, Reactive ion assisted deposition of aluminum oxynitride thin films, Appl. Opt. 28 (1989) 2779-2784. doi: 10.1364/AO.28.002779

9

W. Dehuang, G. Liang, An aluminum oxynitride film, Thin Solid Films 198 (1991) 207210. doi: 10.1016/0040-6090(91)90339-Y

10 S. Dreer, R. Krismer, P. Wilhartitz, G. Friedbacher, Statistical evaluation of refractive index, growth rate, hardness and Young´s modulus of aluminium oxynitride films, Thin

of

Solid Films 354 (1999) 43-49. doi: 10.1016/S0040-6090(99)00564-7

ro

11 W. Xiao, X. Jiang, Optical and mechanical properties of nanocrystalline aluminum

deposition,

J.

Cryst.

doi: 10.1016/j.jcrysgro.2004.01.019

Growth

264

(2004)

165-171.

re

vapor

-p

oxynitride films prepared by electron cyclotron resonance plasma enhanced chemical

lP

12 Y.-H. Lin, J.-C. Hsu, Y. Ding, P.W. Wang, Optical properties of high transmittance

na

aluminum oxynitride thin films for spectral range from near ultraviolet to visible, Opt. Rev. 16 (2009) 400-403. doi: 10.1007/s10043-009-0076-6

Jo ur

13 A. Belosludtsev, N. Kyzas, A. Selskis, R. Narbutiene, Design, preparation and characterization of antireflective coatings using oxynitride films, Opt. Mater. 98 (2019) 109430. doi: 10.1016/j.optmat.2019.109430 14 A.G. Erlat, B.M. Henry, J.J. Ingram, D.B. Mountain, A. McGuigan, R.P. Howson, C.R.M. Grovenor, G.A.D. Briggs, Y. Tsukahara, Characterization of aluminium oxynitride gas barrier films, Thin Solid Films 388 (2001) 78-86. doi: 10.1016/S0040-6090(01)00836-7 15 K.R. Bray, R.L.C. Wu, S. Fries-Carr, J. Weimer, Aluminum oxynitride dielectrics for multilayer capacitors with higher energy density and wide temperature properties, Thin Solid Films 518 (2009) 366-371. doi: 10.1016/j.tsf.2009.06.052

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Journal Pre-proof 16 N.J. Ianno, H. Enshashy, R.O. Dillon, Aluminum oxynitride coatings for oxidation resistance of epoxy films, Surf. Coat. Technol. 155 (2002) 130-135. doi: 10.1016/S02578972(02)00051-8 17 J.S. Zabinski, J.J. Hu, J.E. Bultman, N.A. Pierce, A.A. Voevodin, Stoichiometry and characterization of aluminum oxynitride thin films grown by ion-beam-assisted pulsed laser deposition, Thin Solid Films 516 (2008) 6215-6219. doi: 10.1016/j.tsf.2007.11.120 18 J. Musil, R. Jílek, T. Meissner, T. Tölg, R. Čerstvý, Two-phase single layer Al-O-N

of

nanocomposite films with enhanced resistance to cracking, Surf. Coat. Technol. 206

ro

(2012) 4230-4234. doi: 10.1016/j.surfcoat.2012.04.028

-p

19 J. Borges, F. Vaz, L. Marques, AlNxOy thin films deposited by DC reactive magnetron

re

sputtering, Appl. Surf. Sci. 257 (2010) 1478-1483. doi: 10.1016/j.apsusc.2010.08.076 20 J.A. Dean, Lange´s Handbook of Chemistry, 15th ed. McGraw-Hill, Inc., New York,

lP

1999.

na

21 J. Rezek, J. Vlček, J. Houška, R. Čerstvý, High-rate reactive high-power impulse magnetron sputtering of Ta-O-N films with tunable composition and properties, Thin

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Solid Films 566 (2014) 70-77. doi: 10.1016/j.tsf.2014.07.033 22 A. Belosludtsev, J. Houška, J. Vlček, S. Haviar, R. Čerstvý, J. Rezek, M. Kettner, Structure and properties of Hf-O-N films prepared by high-rate reactive HiPIMS with smoothly

controlled

composition,

Ceram.

Int.

43

(2017)

5661-5667.

doi:

10.1016/j.ceramint.2017.01.102 23 J. Vlček, J. Rezek, J. Houška, T. Kozák, J. Kohout, Benefits of the controlled reactive high-power impulse magnetron sputtering of stoichiometric ZrO2 films, Vacuum 114 (2015) 131-141. doi: 10.1016/j.vacuum.2014.12.004 24 J. Bechhoefer, Feedback for physicists: A tutorial essay on control, Rev. Mod. Phys. 77 (2005) 783-836. doi: 10.1103/RevModPhys.77.783

- 16 -

Journal Pre-proof 25 F. Ferreira, C. Sousa, A. Cavaleiro, A. Anders, J. Oliveira, Phase tailoring of tantalum thin films deposited in deep oscillation magnetron sputtering mode, Surf. Coat. Technol. 314 (2017) 97-104. doi: 10.1016/j.surfcoat.2016.08.017 26 J. Lin, High rate reactive sputtering of Al2O3 coatings by HiPIMS, Surf. Coat. Technol. 357 (2019) 402-411. doi: 10.1016/j.surfcoat.2018.10.024 27 P. Kudláček, J. Vlček, K. Burcalová, J. Lukáš, Highly ionized fluxes of sputtered titanium

(2008) 025010. doi: 10.1088/0963-0252/17/2/025010

of

atoms in high-power pulsed magnetron discharges, Plasma Sources Sci. Technol. 17

ro

28 T. Kozák, J. Vlček, A parametric model for reactive high-power impulse magnetron

-p

sputtering of films, J. Phys. D: Appl. Phys. 49 (2016) 055202. doi: 10.1088/0022-

re

3727/49/5/055202

29 J. Vlček, D. Kolenatý, T. Kozák, J. Houška, J. Čapek, Š. Kos, Ion-flux characteristics

lP

during low-temperature (300 °C) deposition of thermochromic VO2 films using controlled

6463/aae9c6

na

reactive HiPIMS, J. Phys. D: Appl. Phys. 52 (2019) 025205. doi: 10.1088/1361-

Jo ur

30 J. Vlček, J. Rezek, J. Houška, R. Čerstvý, R. Bugyi, Process stabilization and a significant enhancement of the deposition rate in reactive high-power impulse magnetron sputtering of ZrO2 and Ta2O5 films, Surf. Coat. Technol. 236 (2013) 550-556. doi: 10.1016/j.surfcoat.2013.10.052

31 N.-W. Pi, M. Zhang, J. Jiang, A. Belosludtsev, J. Vlček, J. Houška, E.I. Meletis, Microstructure of hard and optically transparent HfO2 films prepared by high-power impulse magnetron sputtering with a pulsed oxygen flow control, Thin Solid Films 619 (2016) 239-249. doi: 10.1016/j.tsf.2016.10.059

- 17 -

Journal Pre-proof 32 A.D. Pajdarová, J. Vlček, J. Rezek, Optical emission spectroscopy during the deposition of zirconium dioxide films by controlled reactive high-power impulse magnetron sputtering, J. Appl. Phys. 121 (2017) 171908. doi: 10.1063/1.4977822 33 J. Gunnars, U. Wiklund, Determination of growth-induced strain and thermo-elastic properties of coatings by curvature measurements, Mater. Sci. Eng. A. 336 (2002) 7-21. doi: 10.1016/S0921-5093(01)01979-7 34 T. Kubart, O. Kappertz, T. Nyberg, S. Berg, Dynamic behaviour of the reactive sputtering

of

process, Thin Solid Films 515 (2006) 421-424. doi: 10.1016/j.tsf.2005.12.250

ro

35 W. Möller, D. Güttler, Modelling of plasma-target interaction during reactive magnetron

-p

sputtering of TiN, J. Appl. Phys. 102 (2007) 094501. doi: 10.1063/1.2800262

re

36 M. Hans, M. to Baben, D. Music, J. Ebenhöch, D. Primetzhofer, D. Kurapov, M. Arndt, H. Rudigier, J.M. Schneider, Effect of oxygen incorporation on the structure and elasticity

lP

of Ti-Al-O-N coatings synthesized by cathodic arc and high power pulsed magnetron

na

sputtering, J. Appl. Phys. 116 (2014) 093515. doi: 10.1063/1.4894776 37 D. Depla, X.Y. Li, S. Mahieu, R. DeGryse, Determination of the effective electron

Jo ur

emission yields of compound materials, J. Phys. D: Appl. Phys. 41 (2008) 202003. doi: 10.1088/0022-3727/41/20/202003 38 JCPDS-ICDD, PDF-4+ Database, International Centre for Diffraction Data, Newton Square, PA, USA, 2015.

39 A.R. Chowdhuri, C.G. Takoudis, Investigation of the aluminum oxide / Si(100) interface formed by chemical vapor deposition, Thin Solid Films 446 (2004) 155-159. doi: 10.1016/S0040-6090(03)01311-7 40 A.V. Singh, S. Chandra, G. Bose, Deposition and characterization of c-axis oriented aluminum nitride films by radio frequency magnetron sputtering without external substrate heating, Thin Solid Films 519 (2011) 5846-5853. doi: 10.1016/j.tsf.2011.02.074

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Journal Pre-proof 41 A. Raveh, M. Weiss, M. Pinkas, D.Z. Rosen, G. Kimmel, Graded Al–AlN, TiN, and TiAlN multilayers deposited by radio-frequency reactive magnetron sputtering, Surf. Coat. Technol. 114 (1999) 269-277. doi: 10.1016/S0257-8972(99)00054-7 42 J. Houska, J. Blazek, J. Rezek, S. Proksova, Overview of optical properties of various modifications of Al2O3 films prepared by various techniques, Thin Solid Films 520 (2012) 5405-5408. doi: 10.1016/j.tsf.2012.03.113 43 F. Natali, F. Semond, J. Massies, D. Byrne, S. Laugt, O. Tottereau, P. Vennegues, E.

of

Dogheche, E. Dumont, Correlation between threading dislocation density and the

-p

82 (2003) 1386-1388. doi: 10.1063/1.1558217

ro

refractive index of AlN grown by molecular-beam epitaxy on Si(111), Appl. Phys. Lett.

re

44 J. Kohout, E. Bousser, T. Schmitt, R. Vernhess, O. Zabeida, J. Klemberg-Sapieha, L. Martinu, Stable reactive deposition of amorphous Al2O3 films with low residual stress

lP

amd enhanced toughness using pulsed dc magnetron sputtering with very low duty cycle,

na

Vacuum 124 (2016) 96-100. doi: 10.1016/j.vacuum.2015.11.017 45 J. Kohout, J. Qian, T. Schmitt, R. Vernhess, O. Zabeida, J. Klemberg-Sapieha, L. Martinu,

Jo ur

Hard AlN films prepared by low duty cycle magnetron sputtering and by other deposition techniques, J. Vac. Sci. Technol. A35 (2017) 061505. doi: 10.1116/1.4999460 46 J. Musil, Flexible hard nanocomposite coatings, RSC Adv. 5 (2015) 60482-60495. doi: 10.1039/C5RA09586G

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Journal Pre-proof Table 1 Process parameters of Al-O-N films for two nitrogen fractions in the total flow rate of reactive gases at a preset deposition-averaged target power density close to 8 Wcm-2, an argon partial preasure of 2 Pa and the same voltage pulse durations. Here, pRG is the total partial pressure of reactive gases, and max |Ud|, max Jt and max Sd are the corresponding maximum values of the magnetron voltage, the target current density and the target power density, respectively, _

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achieved during depositions at the same pre-selected value (I d ) cr = 2.1 A and the total flow

Process parameters

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rate of reactive gases, ΦRG, pulsing between 0 and 5 sccm (Fig. 1).

max Jt (Acm-2)

max Sd (Wcm-2)

pRG (Pa)

max |Ud| (V)

0

0.02-0.05

850-740

0.6-1.4

370-675

100

0.05-0.10

780-770

0.7-1.1

440-580

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N2 fraction (%)

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Journal Pre-proof Figure captions

Fig. 1. Waveforms of the magnetron voltage, Ud, and the target current density, Jt, for a 500 µs macropulse composed of 10 micropulses (panel a) and for a micropulse with the pulse-on time ton = 20 µs (panel b) during a deposition of Al2O3 films at a preset deposition-averaged target power density close to 8 Wcm-2 (Table 1). Time evolution of the average discharge _

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current I d on Al target in a period of the power supply (2857 µs) during the deposition is _

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shown in the inset of the panel a. A pre-selected critical value (I d ) cr = 2.1 A determining the

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switching-on and switching-off of the total flow rate of reactive gases ΦRG = 5 sccm is

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marked by dots. In the main panels, the dashed (blue) and full (red) lines represent the _

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waveforms (both Ud anf Jt) measured at the minimum (indicated in panel a) and maximum I d during the deposition, respectively. The micropulse voltage-on time t'on = 6 µs and the

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the panel b.

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micropulse voltage-off time t'off = 44 µs as defined by the power-supply software are given in

Fig. 2. Elemental composition of Al-O-N films prepared at various N2 fractions in the RG flow.

Fig. 3. Deposition rate of Al-O-N films prepared at various N2 fractions in the RG flow.

Fig. 4. X-ray diffraction patterns taken from Al-O-N films prepared at various N2 fractions in the RG flow. The relevant diffraction peaks of cubic (fcc) Al (Card No. 00-004-0787) and hexagonal (wurtzite) AlN (Card No. 00-025-1133), taken from [38], are marked.

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Journal Pre-proof Fig. 5. FTIR spectra taken from Al-O-N films prepared at various N2 fractions in the RG flow. The individual vibrational modes are marked according to [39-41] and further described in the text.

Fig. 6. Dispersion of the refractive index (panel a) and extinction coefficient (panel b) of Al-O-N films prepared at various N2 fractions in the RG flow.

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Fig. 7. Hardness and residual macrostress (panel a), and hardness to effective Young’s

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modulus ratio, H/E*, and elastic recovery (panel b) of Al-O-N films prepared at various N2

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fractions in the RG flow.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Credit Author Statement Alexander Belosludtsev: Investigation, Data curation, Visualization Jaroslav Vlček: Conceptualization, Methodology, Writing Jiří Houška: Investigation, Writing Stanislav Haviar: Investigation Radomír Čerstvý: Investigation

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Journal Pre-proof Highlights Al-O-N films by low-temperature deep oscillation magnetron sputtering Amorphous or wurtzite AlN-based, without Al macroparticles (only nanoparticles) Linear composition-gas mixture dependence despite different reactivities of O2 and N2 Refractive index follows compositional changes, at a very low extinction coefficient

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Composition Al47O11N42 identified as the hardest one (19 GPa)

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