A two-step growth route of ternary aluminium doped zirconium oxide film on silicon

Accepted Manuscript A two-step growth route of ternary aluminium doped zirconium oxide film on silicon Hock Jin Quah, Zainuriah Hassan, Way Foong Lim PII:

S0925-8388(18)34058-1

DOI:

https://doi.org/10.1016/j.jallcom.2018.10.359

Reference:

JALCOM 48177

To appear in:

Journal of Alloys and Compounds

Received Date: 29 May 2018 Revised Date:

21 October 2018

Accepted Date: 27 October 2018

Please cite this article as: H.J. Quah, Z. Hassan, W.F. Lim, A two-step growth route of ternary aluminium doped zirconium oxide film on silicon, Journal of Alloys and Compounds (2018), doi: https:// doi.org/10.1016/j.jallcom.2018.10.359. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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A Two-Step Growth Route of Ternary Aluminium Doped Zirconium Oxide Film on Silicon

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Hock Jin Quah1, Zainuriah Hassan1, Way Foong Lim1,* Institute of Nano Optoelectronic Research and Technology (INOR), Universiti Sains Malaysia,

11800 Penang, Malaysia.

*Corresponding author: [email protected]/ [email protected] (W. F. Lim)

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Tel: +604-6535637; Fax: +604-6535639

Abstract

Co-sputtering and post-sputter oxidation were incorporated as a two-step growth route for the formation of ternary aluminium doped zirconium oxide (AlxZryOz) films on silicon (Si) substrate using Al-Zr alloy film as the template film. Post-sputter oxidation at 400, 600, 800, and 1000˚C

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has transformed the amorphous as-deposited Al-Zr film to crystalline AlxZryOzfilms. A mixed monoclinic-tetragonal phase of AlxZryOz films was formed at 400 and 600˚C, while above which, tetragonal phase was obtained. The increase of oxidation temperature has also encouraged the

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formation of aluminium zirconium silicate (Al-Zr-Si-O) interfacial layer (IL), owing to an

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increase in the adsorption and diffusion of oxygen molecules from the ambient. The presence of excess oxygen in the film oxidized at the highest temperature (1000˚C) has translated into the formation of oxygen interstitials residing in the lattice, which have induced mid-gap states at the band gap of the film. As a result, a degradation in leakage current density-voltage (J-V) characteristic was obtained and the corresponding structural, optical, and capacitance-voltage characteristics were presented in comparison to the films oxidized at lower temperatures.

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Keywords: Co-sputtering; Growth; AlxZryOz; oxygen interstitials; vacancies; metal-oxide-

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semiconductor

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1. Introduction A barrier to unremitting scaling of silicon (Si)-based metal-oxide-semiconductor (MOS) devices has long been underpinned to its gate oxide material. A further reduction of silicon

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dioxide (SiO2) thickness to approximately 1 nm thick would trigger quantum mechanical tunneling issue and that gives rise to gate leakage current. Although SiO2 has been the materialof-choice for Si-based MOS devices, an intolerable increase of gate leakage current

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exponentially with the scaling of oxide thickness would prompt pre-mature breakdown of the MOS devices. A revolution of the Si technology by shifting to the employment of a physically

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thicker gate oxide material with a dielectric constant (k) value higher than that of the SiO2 (k= 3.9) would mitigate the aforementioned issue [1-4]. Hence, the technology has been ensued with the advent of various high k gate oxide materials, which include but are not limited to the binary Al2O3 [5], Y2O3 [1-2, 6], ZrO2 [7], La2O3 [8], CeO2 [9-10], and ternary La-doped ZrO2 [11],

Y2O3-doped HfO2 [17].

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LaAlO3 [12], DyScO3 [13], La-doped CeO2 [4, 14-15], GdScO3 [13], Sm-doped CeO2 [16], and

Amongst the investigated gate oxide materials, remarkable footprint has been dedicated

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to zirconium oxide (ZrO2), owing to its high k (k = 23-29) and wide band gap (Eg) (5-7 eV) [1819]. In addition, its defect chemistry associated with intrinsic defects (Zr vacancies, interstitial Zr,

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O vacancies, and interstitial O) would also either create acceptor or donor level in the Eg of ZrO2 [20]. Nonetheless, low crystallization temperature (500˚C) as well as permeability of ZrO2 towards oxygen may hamper its MOS characteristics. Leakage current may happen along grain boundaries of the crystalline phases while residual oxygen present in the oxide could seep through the ZrO2 layer to the substrate surface, encouraging interfacial layer growth that would eventually deplete the purpose of using the high k ZrO2 as a substitutional oxide for SiO2 [21].

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In comparison to ZrO2, the emergence of aluminium oxide (Al2O3) has sparked a significant breakthrough amongst the gate oxide materials for its low oxygen diffusivity and ability to remain amorphous at temperature up to 1000˚C [21-22] not withstanding its high k

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value (k = 8-10) and wide Eg (7-9 eV) [23-24]. Inevitably, Al2O3 has been deployed either as an interlayer, sandwiched between ZrO2 and n-GaAs substrate [25] and between Y2O3 and GaN substrate [23-24], or as a dopant in the ZrO2 layer to produce a hybrid Al2O3-ZrO2 oxide layer

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[21, 26]. Based on a study that reported about ultra high vacuum electron-beam evaporated Al2O3-ZrO2 film subjected to rapid thermal annealing from 800 to 1100˚C for 2 min, the

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presence of Al2O3 in the film was capable to assist in decreasing the formation of interfacial layer at the ZrO2-Si interface apart from increasing crystallization temperature of the ZrO2 (up to 1000˚C) [21]. As a consequence, a relatively low leakage current [~10-7A/cm2 at gate voltage (Vg) = 1] and high k (k = 20.1) value were obtained by the Al2O3-ZrO2 film [21]. Another study

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reported that instead of including the Al2O3 film as an interlayer at the interface of ZrO2 and underlying substrate, positioning the Al2O3 film above the ZrO2 layer would serve as a permeation barrier to suppress the formation of microscopic voids and grain boundaries that may

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exist in the Al2O3 or ZrO2 single layer [27]. Moreover, an additional phase allied with ternary ZrAlxOy, which has been deemed to be more thermodynamically stable and possesses a higher

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packing density than the single layers will be also formed at the interface between the Al2O3 and ZrO2 layers [28].

Nevertheless, according to a binary diagram of Al-Zr, a phase separation is favourable to

take place in the mixed Al2O3-ZrO2 layer, attributable to the absence of a mutual solubility between Al2O3 and ZrO2 from room temperature to Eutectic temperature of 1130˚C [29]. Unsurprisingly, the previous works regarding the attempts of doping Al2O3 into ZrO2 layer have

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resulted in the formation of hybrid Al2O3-ZrO2 oxide layer [21, 26], except for a thermodynamic study in recent time that divulged a successful transformation of 4-160 nm thick of an initially direct current (DC) sputtered 2 µm thick Al-Zr alloy film to amorphous ternary AlxZr1-xOy film

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on Si3N4/SiO2/Si substrate after thermal oxidation at 350-560˚C for a dwell time of 60-600 min in a quartz ampoule (filled with oxygen partial pressure) placed in a preheated sand bath [30]. Keeping pace with the previous studies about the hybrid Al2O3-ZrO2 oxide formation, the aspect

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of MOS characteristics brought by the oxide remains lacking as the prior matters for discussion were closely related with phase transformation and stability of the resulting ZrO2 crystal

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structure. It was conveniently deduced from the literature that thin film comprising of crystalline Al2O3-ZrO2 mixed phases has been successfully grown on 450˚C and 750˚C-heated Si substrates after radio frequency (RF) sputtering from Al and Zr targets under the flow of high purity argonoxygen gas [26]. Similar finding was obtained by switching to using Al2O3 and ZrO2 targets

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under argon gas flow [31].

The other study reported that tetragonal and monoclinic ZrO2 phases were attained via annealing of the amorphous films grown via reactive DC magnetron sputtering from metal

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targets [32-34]. A transformation of the tetragonal ZrO2 to monoclinic phase was observed upon reaching a steady-state condition during in-situ growth of approximately 3 at.% Al2O3 mixed into

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ZrO2 on ~300˚C-heated Si substrate using the same technique [35]. Nonetheless, the growth of monoclinic phase was disrupted, leading to the formation of amorphous phase as more Al2O3 was added to the ZrO2 lattice [26]. It was concluded that amorphous Al2O3 phase was present in the mixed film when the atomic ratio of Al:Zr was lower than 6:1 [36]. In another work, an enhancement in crystallinity of the film was reported for pulsed reactive magnetron sputtered

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Al2O3-ZrO2 film, provided that the atomic content of either the Al2O3 or ZrO2 being the second oxide doped into the host lattice did not exceed 10 at.% [37]. Dissimilar from the previous reported studies, the present research strives to employ a

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two-step growth route by initially depositing Al-Zr alloy film on non-heated Si substrate using simultaneous RF-DC magnetron co-sputtering under high purity argon gas flow, followed by post-sputter oxidation in an oxidizing ambient to transform the alloy film to a ternary oxide.

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Feasibility of this work is originated from Ellingham diagrams that deduce an almost identical Gibbs free energy (∆G) for the reaction of Al and Zr with oxygen. A close affinity possessed by

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Al and Zr towards oxygen indicates that both the Al and Zr could be readily oxidized simultaneously [29]. Although the similar approach has been initiated via thermodynamic study [30], higher temperatures (400-1000˚C) are incorporated in this work during post-deposition annealing of ~150 nm thick Al-Zr alloy film for a constant duration of 60 min, aiming to obtain

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crystalline phases of ternary AlxZr1-xOy film on Si substrate for systematic investigation in the aspects of structural, morphological, chemical, optical, and MOS characteristics, which have thus

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far not been reported in the literature.

2. Experimental procedures

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N-type Si (100) substrates were diced into smaller dimension of 1 x 1 cm2 prior to Radio

Corporation of America (RCA) cleaning. These cleaned samples were dipped into a 1:50 volume ratio of hydrofluoric acid (HF):distilled water (H2O) solution to strip native oxide of SiO2 away. These samples were immediately loaded into dual magnetron sputtering machine (HVV AUTO A500) with the sputtering chamber being pumped down to 4 x 10-5 mbar to create a high vacuum environment for subsequent film growth using co-sputtering approach. Plasma cleaning was

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performed on both zirconium and aluminum metal targets for 5 min before the commencement of co-sputtering process. The co-sputtering process was carried out simultaneously using DC and RF magnetron sputtering of the pure Zr and Al targets, respectively, at a chamber pressure of 2.0

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x 10-2 mbar, subjected to argon gas flow at a rate of 12 sccm. DC and RF power were adjusted to 160W and 100 W, respectively for the deposition of approximately 150 nm thick Al-Zr alloy film on Si substrate, in which thickness of the deposited film was monitored using a quartz

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crystal monitor (SQM-160). After that, the sample was placed in a horizontal tube furnace for post-sputter oxidation in oxygen gas ambient at different temperatures (400, 600, 800, and

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1000˚C) for 60 min. A heating rate of approximately 10˚C/min was used to achieve the desired oxidation temperatures. In order to fabricate metal-oxide-semiconductor (MOS) test structures, thermal evaporator (AUTO 306) was used to deposit Al electrodes with diameter of 0.08 cm on the oxidized films using a shadow mask. A blanket of Al was subsequently deposited on the

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backside of the Si substrates using the similar technique.

High resolution X-ray diffraction (HRXRD) modeled Panalytical X’Pert PRO MRD PW3040 operated using Cu Kα radiation (λ= 1.5406 Å) under 40 kV and 30 mA in a scan range

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of 2θ = 20–80°, a step time of 2.0 s, and a step size of 0.05° was utilized in characterizing crystalline phases and orientations of the as-deposited and post-sputter oxidized films. Surface

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morphologies and cross-sectional images of the investigated samples were characterized using field-emission scanning electron microscopy (FESEM; FEI Nova NanoSEM 450). 3-dimensional surface topographies and root-mean-square (RMS) roughness of the investigated films were acquired using atomic force microscopy (AFM; Dimension Edge, Bruker). Horiba Jobin Yvon HR800UV system operated at 514.5 nm argon ion laser was utilized to obtain Raman spectra of the investigated samples at room temperature. Optical band gap of the investigated samples was

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estimated from diffuse reflectance spectra measured using a Cary 5000 ultraviolet (UV)-visible spectrophotometer. MOS characteristics of the investigated samples were studied by performing

using Keithley 4200-SCS parameter analyzer.

3. Results and Discussion

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current-voltage (I-V) and high frequency (1 MHz) capacitance-voltage (C-V) measurements

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Fig. 1 depicts HRXRD patterns of as-deposited Al-Zr alloy film and AlxZryOz films obtained after post-sputter oxidation from 400 to 1000°C in oxygen ambient for 60 min. A

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relatively broad diffraction peak was perceived by the as-deposited Al-Zr film, suggesting the presence of amorphous phase in the film. Post-sputter oxidation at various temperatures has successfully oxidized the Al-Zr alloy film to AlxZryOz films as well as transforming the amorphous film to crystalline phases. As the as-deposited Al-Zr film was subjected to oxidation

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temperature at 400˚C, a narrowing of the broad diffraction peak (ranging from 28.5˚ to 32.0˚) could be observed when compared with the as-deposited Al-Zr film. The narrowing effect of diffraction peak due to the oxidation at 400˚C suggested that an onset crystallization of the

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AlxZryOz film has taken place. Therefore, the AlxZryOz film formed at 400˚C might comprise of a mixture of amorphous and crystalline phase of AlxZryOz. Owing to the absence of International

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Centre for Diffraction Data (ICDD) information of AlxZryOz, the detectable diffraction peaks were confirmed by comparing with ICDD details of tetragonal phase of ZrO2 (ICDD file no. of 00-050-1089). Apparently, at the lowest temperature (400°C), tetragonal phases of AlxZryOz oriented in (011) and (110) planes were detected at a larger diffraction angle as compared to tetragonal phase of ZrO2. This finding was an indication that a decrease in lattice parameter (lattice contraction) could have happened as a result of incorporating Al3+ with a smaller ionic

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radius (0.39 Å or 0.52 Å) [38-39] than that of Zr4+ (0.72 Å) [38] into the ZrO2 lattice. As the temperature was increased to 600°C, the (110) plane subsided along with the emergence of AlxZryOz peak oriented in (002) and (112) planes as well as an increase in the intensity of peaks

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related to AlxZryOz phase oriented in (011) plane. A further increase of the temperature to 800°C has continuously enhanced intensity of the peaks, accompanied with the re-appearance of (110) plane and the detection of additional diffraction peaks associated with tetragonal phases of

became the strongest at the highest temperature (1000°C).

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AlxZryOz to be oriented in (020), (013), and (121) planes. Intensities of the AlxZryOz peaks

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In addition, a progressive shift of the AlxZryOz peaks to lower diffraction angles could be discerned from the HRXRD patterns to have taken place as the temperature was increased from 400 to 1000°C. The peak position, though getting closer to tetragonal phase of ZrO2, remained larger in diffraction angle. It was believed that the peak shift of AlxZryOz to lower angles could

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be originated from an expansion [40-41] of the AlxZryOz lattice that became increasingly prominent with the rise of oxidation temperature. Nevertheless, it was rather elusive for lattice expansion to take place in the AlxZryOz lattice since literature unveiled that oxygen vacancies

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would be generated to maintain local charge balance in the lattice as a result of the substitution of tetravalent Zr4+ cations for the trivalent Al3+ cations, in which the presence of oxygen

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vacancies would in turn bring a contraction to the lattice [26, 40, 42]. An incongruity of the present work suggested that oxygen ambient during post-sputter oxidation could have provided a large stream of oxygen, especially at higher temperatures to oxidize the Al-Zr alloy film until an extent that any excess oxygen would reside in the AlxZryOz lattice as oxygen interstitials. The formation of oxygen interstitials would likely result in lattice expansion and the likelihood of

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having the excess oxygen to reside as interstitials was closely related to the presence of Al-O network in the lattice that would favour the capture of oxygen to the interstitial sites [24]. The increase in lattice expansion was further confirmed through the calculation of lattice

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parameters c and a for the AlxZryOz films using the following equations [43-46]:


 = 2 sin

   

+





(2)

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= 

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(1)

where λ is wavelength of X-ray radiation (0.15406 nm), n is order of diffraction, dhkl is interplanar spacing, (hkl) is Miller’s indexes, and θ is diffraction angle. It could be ascertained from Fig.2 that an increasing trend in c in opposition to a with the increase of post-sputter

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oxidation temperature from 400 to 800˚C was obtained for the AlxZryOz films. Further increase of temperature to 1000˚C has led to a minute decrease of c and increase of a as compared to that obtained at 800˚C. The changes in c and a could be corroborated with the changes of oxygen

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interstitials present in the films that have resulted in lattice expansion as a consequence of the

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capturing of excess oxygen coming from the ambient to interstitial sites of the lattice. According to the calculated cell volume (V = a2c) [46] for the investigated films, the acquisition of an increasing trend in the V from 65.058 (Å)3 to 65.515 (Å)3 with the increase of temperature from 400 to 1000˚C was an indication to support the occurrence of volume expansion in the lattice as a result of increasing oxygen composition in the films. In addition, it could be noted from the ratio of cell parameters (c/a√2) for the tetragonality [46] of the films, in which any value superior to 1.010 would show the presence of tetragonal phase distinguishable from the metastable 10

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tetragonal phase that would show the value smaller than 1.010 (Fig. 2). The acquisition of (c/a√2) value smaller than 1.010 for the films obtained at 400 and 600˚C might be caused by the occurrence of slight distortion of the lattice by the oxygen network, which could not be

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distinguished by HRXRD but might be pointed out by Raman spectroscopy [46-47].

Coefficient of texture, Thkl for the investigated AlxZryOz films (Fig. 3) was calculated

 () " ()

÷ ∑$ $

 () " ()

(3)

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T =

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using the subsequent equation [48]:

where Im (hkl) is the measured relative intensity of reflection from the (hkl) plane, Io (hkl) is the intensity from the same plane in a standard t-ZrO2 reference sample, and n is the number of AlxZryOz reflection peaks. The attainment of Thkl value exceeding 1 was an indication to show a

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preferred orientation in a specific plane [49]. Results revealed that the films oxidized at 400˚C and 600˚C have demonstrated a preferred orientation in (110) and (002) plane, respectively while

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further increase of the oxidation temperature to 800 and 1000˚C has favoured the growth of the films in two orientations, ascribed to (002) and (110) planes at 800˚C and (002) and (020) planes

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at 1000˚C. The existence of a mixed preferred orientation in the films oxidized at 800 and 1000˚C was owing to the attainment of Thkl value greater than 1 for both the planes, as depicted in Fig. 3. In contrast, a larger Thkl value was acquired for the (002) plane, surpassing that for the (110) or (020) plane, indicating a dominant growth of the film along the (002) plane in both the films obtained by oxidation at 800 and 1000˚C. Williamson-Hall (W-H) approach [50] was employed to calculate crystallite size (D) and microstrain (ε) present in the investigated films after considering line broadening (β) effect 11

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caused by lattice domain and lattice deformation, as conveniently expressed via the following relationship:

,

= + -

./ *0$ +'

(4)

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&' ()* +'

,

where λ is the wavelength of X-rays, θi is the diffraction angle, βi is the integral breath (in radius

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2θ) of the ith Bragg reflection positioned at 2θi, and ε is the elastic strain. Based on the intercept

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and slope of the W-H plot (not shown), the D and ε of the AlxZryOz films obtained at different oxidation temperatures were extracted, respectively. As the post-sputter oxidation temperature was increased from 400 to 1000˚C, an upward trend was obtained for the D values (3.9 to 35.4 nm) in opposition to that for the ε values (Fig. 4).

A simple mechanism elaborating about a transformation of the Al-Zr alloy to AlxZryOz

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film via post-sputter oxidation process was proposed. Generally, the process would start off with an adsorption of ambient oxygen molecules on the amorphous Al-Zr alloy surface via diffusion [51]. The oxygen molecules would initially become physisorbed and the energy liberated from

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the physisorption process would be subsequently absorbed by the Al-Zr lattice. The gain of

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energy by the lattice would relax the Al-Zr lattice atoms and thereafter promoting electron transfer to happen between the adsorbed oxygen molecules and Al-Zr atoms. The Al-Zr atoms that have gained sufficient energy would lose electrons and become positively charged while the oxygen molecules would be dissociated into oxygen anions. A reaction between the oxygen anions and Al-Zr cations would yield the formation of AlxZryOz along with oxygen vacancies for charge balance.

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The absence of detecting diffraction peak associated with Al-Zr by HRXRD indicated that adequate time and temperature have been allocated during post-sputter oxidation to transform the amorphous Al-Zr alloy to AlxZryOz film. In fact, the reaction between adsorbed

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oxygen molecules with the amorphous Al-Zr alloy should result in amorphous AlxZryOz film in the initial stage before nucleation. Nonetheless, the detection of tetragonal AlxZryOz phase after post-sputter oxidation at 400˚C in the present case revealed that a barrier for the nucleation has

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been surmounted at 400˚C. As the oxidation temperature was increased to greater than 400˚C, surface of the Al-Zr film would be getting hotter, and thereafter enhancing the adsorption of

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oxygen molecules. Besides, the increase of temperature would also accelerate diffusion of the adsorbed oxygen into the film. Hence, the increase in both adsorption and diffusion process would inevitably facilitate the formation of AlxZryOz. Continuous addition of oxygen to the lattice with respect to temperature did not seem to alter crystal structure of the film as the excess

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oxygen was incorporated into the interstitial sites [52]. An expansion of the tetragonal structure was thus expected and the enrichment of oxygen contents in the lattice would continuously trigger nucleation and growth of the AlxZryOz film, in which the D was increasing with declining

observed.

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ε. Eventually, an enhancement in intensity of the diffraction peaks of tetragonal AlxZryOz was

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Further investigation was carried out using Raman spectroscopy to determine the

presence of any amorphous or crystalline phases not detectable by HRXRD in the investigated samples [53]. Raman spectra present in the as-deposited amorphous Al-Zr alloy film and AlxZryOz films obtained by post-sputter oxidation at various temperatures are depicted in Fig. 5a. In contrast, all the investigated samples provided Raman signals, except for the as-deposited sample, in which no evidence of Raman spectrum was being noticed, indicating the absence of

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Raman signals from both the amorphous Al-Zr alloy film and underlying Si substrate. It was conceivable that the Al-Zr alloy film was highly opaque and thus the underlying Si substrate would not give detectable contribution to the Raman signal [54-56]. De-convolution using

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Gaussian fitting was employed for analysis of Raman spectra acquired for the dissimilar AlxZryOz films obtained after post-sputter oxidation. It was noteworthy from Fig.5b for the Raman spectra extracted within wavelength range of 120-220 cm-1 that, monoclinic phase of

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ZrO2 was detected at peak around ~178 cm-1 [57-58] in the film obtained by post-deposition oxidation at 400˚C. The increase of oxidation temperature to 600˚C has resulted in additional

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monoclinic phases detected at ~194 cm-1 [57] and 215 cm-1 [58], accompanied with tetragonal phase of ZrO2 at ~145 cm-1 [57-58]. The monoclinic (~327, 382, 472, 505, 544, and 553 cm-1) [58] and tetragonal (317 cm-1) [58-59] phases of ZrO2 were also detected in the wavelength ranges of 220-400 cm-1 (Fig. 5c) and 460-580 cm-1 (Fig. 5d) for both the films annealed at 400

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and 600˚C. As the oxidation temperature was increased beyond 600˚C, Raman peaks corresponding to monoclinic phases of ZrO2 subsided, leaving only tetragonal phases of ZrO2 detectable at ~145 [57-58], 280 [59-60], and 317 cm-1 [58-59] (Fig. 5b and 5c). The presence of

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tetragonal phases of ZrO2 has been supported using HRXRD but not for the monoclinic phases of ZrO2. This circumstance might be plausibly due to the incidence of monoclinic distortion in

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the AlxZryOz lattice, in which a displacement of oxygen not detectable by the HRXRD could have taken placeduring monoclinic-tetragonal transitionin the lattice [46-47]. Findings from Raman spectroscopy evidenced that the introduction of oxygen to as-deposited Al-Zr film has led to the formation of monoclinic-tetragonal mixed phases in the AlxZryOz films obtained at 400 and 600˚C, while continually addition of oxygen has transformed the mixed phases film to tetragonal phase at temperatures greater than 600˚C. Apart from detecting the presence of

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monoclinic and tetragonal phases of ZrO2, Raman spectroscopy has also identified features allied with aluminium zirconium silicate (Al-Zr-Si-O) (~358 cm-1) (Fig. 5c), which were blue-shifted as compared to ZrSiO4 (353 cm-1) [60], as well as amorphous SiOx matrix containing Si

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nanocrystals (~484 cm-1) [61] (Fig. 5d) for the films post-sputter oxidized at 400 and 600˚C, but not for the films oxidized at 800 and 1000˚C. The detection of these features at lower

the AlxZryOz film and underlying Si substrate.

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temperatures might be caused by the presence of an interfacial layer (IL) at the interface between

Whilst the IL formation was envisioned to take place only in the films oxidized at 400

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and 600˚C using Raman spectroscopy, Fourier Transformed Infrared (FTIR) spectroscopy divulged the formation of IL between the AlxZryOz film and underlying Si substrate in all of the investigated films via the detection of absorption peaks of Zr-O-Si at 416 cm-1 [62] (Fig. 6) as well as Al-O-Si absorption bands at 729 cm-1 [63]. The emergence of these absorption peaks was

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accompanied with asymmetric Si-O-Si stretching vibration of transverse-optical and longitudinal-optic mode for amorphous SiOx, respectively detected at 1078 [64] and 1260 cm-1 [65]. The existence of amorphous SiOx was detected along with amorphous ZrO2 (389 cm-1) [62]

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and amorphous AlO4 tetrahedral (446 cm-1) [66], which could be supporting evidence to show the presence of amorphous Al-Zr-O-Si IL layer in the investigated films. Besides, the detection

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of absorption band at 976 cm-1 revealed the presence of stretching vibration originating from a disruption of Si-O network upon forming alloy with ZrO2 [64], which was referred to the formation of Zr-O-Si composition with a terminal O atom being covalently bonded to a Si network while making a more ionic bond with Zr4+ ion [67]. Besides, it could be observed for the existence of absorption feature at 1112 cm-1, ascribed to oxygen interstitials (Oi) [68], in which the peak became more intensified in the sample obtained by post-sputter oxidation at the highest

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temperature (1000˚C). This finding supported the prediction that was made regarding the formation of oxygen-rich AlxZryOz film at higher temperatures by having the excess oxygen to reside in the interstitial sites.

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In addition, absorption bands designated to Zr-O bonding of tetragonal phases of ZrO2 (tZrO2) were revealed at 403 [69], 473 [62], 501 [69], 542 [62], and 670 cm-1 [70] while the bandscentered at 430 [62] and 454 cm-1 [69] were attributed to monoclinic phases of ZrO2 (m-

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ZrO2) (Fig. 6). It was noticeable that the absorption bands of m-ZrO2 diminished when the temperature was varied to 800 and 1000˚C. This observation was in agreement with Raman

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findings concerning about the existence of monoclinic phases along with tetragonal phases in the AlxZryOz films obtained at lower temperatures (Fig. 5). In all of the investigated films, it could be observed that absorption spectrum corresponding to Al-O was also detected at 1034 cm-1[71], revealing the existence of Al-O network in the AlxZryOz films.

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Fig.7 depicts typical surface morphology of the investigated AlxZryOz film obtained at 1000˚C examined using field-emission scanning electron microscopy (FESEM). Noticeable formation of voids or cracks was not detected. Further investigation was carried out by assessing

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topography of the films using three-dimensional (3-D) atomic force microscopy (AFM) (Fig. 8a to 8e). It was deduced that an increase in oxidation temperature from 400 to 800˚C has improved

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surface topography of the films, which in turn caused a reduction in the surface roughness from 1.13 nm at 400˚C to 0.74 nm at 800˚C (Fig. 8f). By further enhancing the temperature to 1000˚C, protrusions with dissimilar heights were seen to form (Fig. 8e), and thus leading to the acquisition of a larger RMS roughness (0.917 nm) (Fig.8f). UV-visible spectroscopy was carried in a diffuse reflectance mode in order to extract band gap (Eg) of the investigated AlxZryOz films using Kubelka-Munk (KM) function. The KM

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function would allow optical absorption of a sample to be approximated from its diffuse reflectance spectrum, according to the following equation [72-73]:

( 34)

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F(R) =

(5)

54

where R is the diffuse reflectance and the F(R) function can be multiplied by hv using

SC

corresponding coefficient (n), which can be 1/2 and 2 for direct-band and indirect-band transition,

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respectively. A plot of (F(R) x hv)2 (not shown) or (F(R) x hv)1/2 vs hv (not shown) would give a straight line, from which, upon extrapolation to (F(R) x hv)2 or (F(R) x hv)1/2 = 0, direct Eg (Ed) and indirect Eg (Eid) values could be obtained. Three direct and indirect-band transition regions were exhibited by the film obtained at 400˚C, yielding Ed values of 2.19, 3.45, and 4.24 eV and Eid values of 1.11, 2.74, and 3.61 eV. The presence of multiple direct-band transitions could be

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related to competing absorption process, originating from a hybridization between the Zr and Al orbitals with oxygen, which would form the valence and conduction bands [74]. The detection of indirect-band transition region, which was continuously followed by direct-band transition

EP

suggested that the indirect-band transition was caused by folded conduction and valence bands attributable to substantial amount of oxygen vacancies in the film [73]. As the temperature was

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increased to 600˚C, the Ed values were increased to 2.47, 3.63, and 4.81 eV along with the increase of Eid values to 1.40, 2.97, and 3.93 eV. Further increase of the temperature to 800˚C has resulted in Ed of 3.98, 4.92, and 5.56 eV as well as Eid of 3.84, 4.75, and 5.51 eV. As the temperature reached 1000˚C, a decrease in the Ed values were observed (3.95, 4.83, and 5.50 eV). The decrease in the Ed value might be related to an increase in oxygen contents (interstitial

17

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oxygen) in the film, which would interrupt the inter-band transitions [73]. Schematic energy band diagrams showing direct and indirect band transitions are presented in Fig. 9. Further analyses were carried out by calculating energy difference between the direct and

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indirect-band transitions for each film to be compared with the reported value for tetragonal ZrO2 without oxygen vacancies (0.17 eV) [75]. It was noticeable that the largest energy difference (~0.63-1.08 eV) was present for the film oxidized at 400˚C, followed by 600˚C (~0.66-1.07 eV),

SC

800˚C (~0.05-0.17 eV), and 1000˚C (~0.06-0.16 eV). The acquisition of a larger energy difference at 400 and 600˚C (> 0.17 eV) in comparison to that at 800 and 1000˚C (≤ 0.17 eV)

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indicated that more remarkable folded bands were found at lower temperatures, resulting from different fates of oxygen vacancies [73]. The decrease in energy difference at higher temperatures on the other hand resembled a decrease in the amount of oxygen vacancies present in the film. Apart from the energy difference between direct and indirect band transitions, the

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energy difference between direct and direct band transitions could be used to predict the presence of mid-gap states related to oxygen interstitials in the films. It was determined that the energy difference between two direct band gaps (∆E) was 0.79-1.26 eV for 400˚C, 1.16-1.18 eV for

EP

600˚C, 0.64-0.94 eV for 800˚C, and 0.59-0.88 eV for 1000˚C. The attainment of a smaller deviation in the energy of direct-to-direct band transitions at 800 and 1000˚C, closer to that of

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the reported energy gap between the oxygen interstitials related states and valence band (0.8 eV) [76] confirmed that oxygen interstitials have formed the mid-gap states in the films. Hence, the detectable direct band transition occurring at lower energy side was attributed to the mid-gap states caused by the presence of oxygen interstitials in the films. In comparison, the formation of mid-gap states was more pronounced at 1000˚C, leading to a decrease in the Ed, as aforementioned.

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Fig.

10

illustrates

bi-directional

capacitance-voltage

(C-V)

characteristics

of

Al/AlxZryOz/Si MOS capacitors under high frequency (1 MHz) measurement from -4 V to +4 V. Positive flatband voltage shift (∆VFB) was observed for the sample obtained by post-sputter

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oxidation at 400˚C, denoting the presence of negatively charged traps in the film. Conversely, positively charged traps were found in the other samples obtained at higher temperatures (6001000˚C), owing to the opposite ∆VFB demonstrated. The types of charged traps present in the

SC

films could be quantified via the calculation ofeffective oxide charge (Qeff) (Fig. 11) using the

Q788 =

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following equation [77-79]:

∆:;< ="> ?@

(6)

where Cox is maximum accumulation capacitance, q is the electronic charge, and A is the

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capacitor area. In fact, the formation of AlxZryOz film would generate oxygen vacancies for charge balance, which would in turn provide positive Qeff to the lattice. As per discussed in preceding section with regards to volume expansion for the AlxZryOz films as a function of post-

EP

sputter oxidation temperature, the increase in temperature has prepared an oxygen-rich

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environment for oxidation to take place and that the excess oxygen have resided as oxygen interstitials in the lattice. Some of the excess oxygen could have occupied the oxygen vacancies sites and thus contributing to a decrease in the calculated energy difference between direct and indirect band transition at higher temperatures. As a consequence, owing to charge compensation effect, the increase in oxygen interstitials coupled with a decrease in oxygen vacancies would provide more negatively charged traps to the lattice to surpass positively charged traps brought by the oxygen vacancies [30]. Therefore, inexorably, either a declining trend for the positive Qeff 19

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or an increasing trend for the negative Qeff was expected. Neither trend was however truly complied by the samples, as shown in Fig. 11, except that the film oxidized at 400˚C has been ruled out from consideration. The decreasing trend in positive Qeff as the temperature was

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changed from 600 to 1000˚C matched well with the anticipation pertaining to the decrease in positively charged traps as a consequence of charge compensation in the films yet it would remain vague for the acquirement of negative Qeff at the temperature lower than 600˚C. The

SC

elusiveness might occur if there were remaining Al-Zr atoms that have not reacted with incoming oxygen from the ambient to form the AlxZryOz film, and thus leaving behind Al-Zr dangling

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bonds. The presence of Al-Zr dangling bonds would serve as negatively charged traps [80] and thus yielding the acquisition of negative Qeff in the film obtained at 400˚C. Furthermore, the anticipation of having the dangling bonds in the film also explained the detection of a rather broad and obscure AlxZryOz diffraction peak for the sample in comparison to those oxidized at

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higher temperatures (Fig. 1).

In addition, it could be elucidated from the bi-directional C-V measurements for clockwise and anti-clockwise hysteresis behaviours of the samples. In comparison, clockwise

EP

hysteresis behaviour was exhibited by the samples oxidized at lower temperatures (400 and 600˚C) while anti-clockwise hysteresis behaviour was demonstrated at higher temperatures (800

AC C

and 1000˚C). It was noteworthy that scattering centre was the contributing factor that was responsible for the clockwise hysteresis characteristics shown by the former samples [9]. It was foreseeable that the presence of negatively charged traps at 400˚C would induce greater repulsive forces towards incoming electrons from the Si substrate and hence scattering effect would be significantly higher than that happening at 600˚C. The enhancement in scattering effect would bring deleterious impacts onto trapping and de-trapping phenomenon in the AlxZryOz film during

20

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forward and reverse biases, in which the electrons that were trapped in the films would encounter greater difficulties to be de-trapped due to the collision of scattered electrons. Therefore, the

STD =

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corresponding slow trap density (STD) (Fig. 11) estimated using the following equation [77-79]:

C:=">

(7)

?@

SC

where ∆V is the difference between forward- and reverse-bias flatband voltage was larger at

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400˚C. The decrease in STD at 600˚C was closely related to the existence of oxygen vacancies in the films as positively charged traps to capture incoming electrons and became neutral, lessening the scattering effects. Further increase of the oxidation temperature to 800˚C has trimmed down the STD value to the lowest comparing to the other samples. Nonetheless, the STD value did not continuously decrease as the temperature approached 1000˚C. Instead, the STD value was

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increased to become greater than that obtained at 600˚C and 800˚C. This circumstance might plausibly develop from the mid-gap states created by the oxygen interstitials, in which majority of the incoming electrons could have been trapped in the states, which were located

EP

approximately 0.8 eV from valence band of the film. Hence, a larger bias was required during

AC C

reverse bias in order to have the electrons de-trapped to conduction band of the film. In addition, dissimilar C-V accumulation capacitance level was observed for the

investigated samples. In comparison, the highest accumulation capacitance level was exhibited by the film oxidized at 400˚C, followed by 600, 800, and 1000˚C. The decrease in accumulation capacitance level with respect to the oxidation temperature could be either caused by changes in the total oxide thickness (AlxZryOz + IL) or IL thickness for the samples. According to crosssectional studies of the investigated samples using FESEM, as depicted in Fig. 12, a decrease in 21

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the total oxide thickness from 158.5 nm to 147.9 nm (Fig. 13) was obtained as the post-sputter oxidation temperature was increased from 400 to 800˚C. However, the total oxide thickness was increased to 198.7 nm as the temperature reached 1000˚C. The acquisition of decreased total

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oxide thickness as the temperature was varied from 400 to 800˚C as compared to the asdeposited Al-Zr film (162.0 nm) suggested the occurrence of film densification. Nonetheless, film densification did not take place as the temperature was increased to 1000˚C.

SC

In fact, the acquisition of a declining trend for the total oxide thickness as the temperature was varied from 400 to 800˚C would in turn give rise to an increasing trend in the accumulation

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capacitance level. The opposite (decreasing) trend demonstrated for the accumulation capacitance level has hence ruled out the effects brought by total oxide thickness and purported that the overall capacitance of the samples was greatly dominated by the IL thickness instead. The attainment of the lowest accumulation capacitance level at 1000˚C proposed that the thickest

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IL was formed at the interface of AlxZryOz and Si substrate in comparison to the other samples. The decrease in C-V accumulation capacitance level as well as the changes in total oxide thicknesses were used to estimate the k value obtained for each of the investigated samples. A

EP

reduction in the k value from 23.2 (400˚C) to 17.7 as the temperature was increased from 400 to 800˚C was attained while the k value was slightly increased to 17.8 when the temperature

AC C

approached 1000˚C. The similar trend established by k and total oxide thickness indicated that the changes in total oxide thickness was responsible for the k reduction. In this work, the likeliness of IL growth could be caused by the diffusion of adsorbed

oxygen molecules to the Si surface for oxidation to take place. As the temperature was increased in diffusivity of adsorbed oxygen molecules along with the increase of temperature would accelerate the formation of AlxZryOz with oxygen vacancies. However, at the lowest temperature

22

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(400˚C), the adsorbed oxygen molecules would preferably bond to Zr atoms before bonding to Al atoms, owing to a greater affinity of Zr towards oxygen as compared to Al. The formation of ZrOx that was pervious to oxygen [21] would allow the passage of other adsorbed oxygen

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molecules to be bonded to Al atoms and subsequently formed AlxZryOz accompanied with oxygen vacancies formation. The oxygen vacancies would serve as hopping sites for additional adsorbed oxygen molecules to diffuse to the Si surface for oxidation to take place [40, 81]. The

SC

oxidation process would initially form SiOx intermediate layer, which would subsequently react with AlxZryOz composition nearer to the Si surface to yield the formation of Al-Zr-Si-O IL. As a

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consequence of the consumption of AlxZryOz, a film densification of the AlxZryOz layer was said to happen.

Owing to a slower diffusivity of adsorbed oxygen molecules at 400˚C, the amount of oxygen that was able to reach Si surface for oxidation within the allocated oxidation time would

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be limited and thus the acquired IL thickness would be the lowest. The increase of temperature to 600˚C and 800˚C would enhance the adsorption of oxygen molecules in addition to accelerating the diffusion process. With these, IL growth was facilitated and an increase in the IL formation

EP

was obtained while continuous film densification was also achieved. Nevertheless, further increase of the temperature to 1000˚C has however led to an increase in the total oxide thickness

AC C

to become greater (198.7 nm) than that of 400˚C (158.5 nm), 600˚C (157.5 nm), and 800˚C (147.9 nm) without the occurrence of film densification although continuous increase in IL thickness was suggested based on the lowest C-V accumulation capacitance level obtained (Fig. 10). This phenomenon might happen when the enhancement in adsorption of oxygen molecules as well as diffusivity of the oxygen at the highest temperature has provided excess oxygen to reside as oxygen interstitials in the lattice. The lattice might have become saturated with oxygen

23

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to an extent that a kick-off mechanism of the excess oxygen would likely happen, in which the excess oxygen would be pushed further inward to the Si surface. An increase in oxygen accumulation on the Si surface would accelerate the formation of SiOx intermediate layer. Owing

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to the saturation of lattice, the consumption of AlxZryOz layer to react with the SiOx intermediate layer for the formation of Al-Zr-Si-O IL would be trimmed down, and thus the film densification would be lessen. The occurrence of this might eventually result in the formation of Al-Zr-Si-O

SC

IL that was more prominent in SiOx composition in the sample oxidized at 1000˚C.

Interface trap density (Dit) present at the interface of Al-Zr-Si-O IL and underlying Si

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substrate was estimated using Terman’s method that takes into consideration the following equation [77-79]:

="> EFC:G H ?@E(IJ )

(8)

TE D

D0D =

where ∆Vg = Vg – Vg(ideal) is the voltage shift of the experimental curve from the ideal curve, Vg is the experimental gate voltage, and Φs is the surface potential of GaN at a specific gate voltage.

EP

The calculated Dit values were plotted as a function of energy trap level (Ec-Et), as shown in Fig.

AC C

14. Total interface trap density (Dtotal) of the investigated samples was also calculated from the area under Dit-(Ec-Et) plot (inset of Fig. 14) for comparison. In comparison, the lowest Dtotal value was perceived by the film oxidized at 400˚C while the highest Dit was obtained by the film oxidized at 600˚C. An improvement in the Dtotal was demonstrated as the temperature was increased from 600 to 1000˚C. It was believed that the attainment of the lowest Dtotal value at 400˚C was associated with the formation of Al-Zr-Si-O IL, which was deemed to be the lowest in thickness as compared to the other samples. Whilst this finding might suggest that the increase 24

ACCEPTED MANUSCRIPT

in the formation of Al-Zr-Si-O IL with the increase of oxidation temperature might degrade the interface quality, and thus leading to higher Dit values at higher temperatures, the acquisition of a decreasing trend in the Dtotal values at temperatures beyond 600˚C has eradicated the hypothesis.

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Instead, the improvement in interface quality as the temperature was increased to 800˚C and 1000˚C could be caused by the increase in SiOx composition in the Al-Zr-Si-O IL.

Typical leakage current density-voltage (J-V) characteristics of the investigated samples

SC

are presented in Fig. 15. It could be observed that an improvement in electric breakdown voltage (VB) as well as a reduction in J was obtained for the samples obtained by post-sputter oxidation

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at higher temperatures (800 and 1000˚C) in comparison to the samples oxidized at lower temperatures (400 and 600˚C). VB is defined as an instantaneous increment in the J at a specific E, in which the film would experience a breakdown. It was believed that the changes in the J-V characteristics were largely dependent on the type of traps and density of traps present in the

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samples. Regardless of the lowest Dit value or the highest k value acquired by the 400˚Coxidized sample, a degradation in the J-V characteristic was observed. This could be influenced by the presence of negative Qeff that served as the scattering centre, in which the injected

EP

electrons at a relatively low V were sufficient to break the bonding of AlxZryOz film, leading to a breakdown. The increase of oxidation temperature to 600˚C, which has resulted in the formation

AC C

of positive Qeff might require higher V in order to contribute to a breakdown of the sample, owing to the trapping of injected electrons by the positively charged traps to form neutral traps. Therefore, a better J-V characteristic was exhibited at 600˚C. An improvement in J-V characteristic at 800˚C could be related to the lowest STD and the existence of a lesser density of positive Qeff as a consequence of charge compensation by the excess oxygen residing as oxygen interstitials, which in turn gave rise to the formation of oxygen-rich AlxZryOz film with a better

25

ACCEPTED MANUSCRIPT

quality. Continuous increase of adsorption and diffusion of adsorbed oxygen molecules at 1000˚C has significantly increased the amount of oxygen interstitials and thus further decreasing the positive Qeff present in the sample. Nevertheless, the large amount of oxygen interstitials

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could have created mid-gap states, whereby the injected electrons would be trapped in the states until forming a leakage current path detrimental to breakdown of the sample. Therefore, the corresponding J-V characteristic at 1000˚C was not better than that obtained at 800˚C.

SC

Further analysis was carried out by performing C-V measurement on the AlxZryOz film subjected to oxidation at 800˚C using different frequencies (1 MHz, 100kHz, and 10 kHz) (Fig.

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16). A relationship of the C-V frequencies and k values has been studied. The calculated k value was decreased from 18.8 to 17.7 with the increased of frequency from 10 kHz to 1 MHz. The decrease of k with respect to the frequency might be due to the presence of orientation polarization effect in the sample, which usually would take place when the C-V measurement

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was carried out in frequencies less than 1 MHz [82]. The dipoles in the oxide might not be

observed [83].

4. Conclusion

EP

completely aligned with respect to the electric field and thus a decrease in the k value was

AC C

A two-step growth route encompassing co-sputtering and post-sputter oxidation of Al-Zr

alloy films was attempted in the present work to explore the formation of ternary-based AlxZryOz films on Si substrate. The as-deposited Al-Zr alloy film was determined to be in amorphous phase by HRXRD, in which post-sputter oxidation at various temperatures, ranging from 400 to 1000˚C was successful to transform the amorphous Al-Zr alloy film to crystalline AlxZryOz films. Depending on the oxidation temperature, phase transformation of the crystalline films was

26

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observed. HRXRD, Raman, and FTIR studies have evidenced the formation of monoclinictetragonal mixed phases of AlxZryOz at lower temperatures (400 and 600˚C) while beyond which, tetragonal AlxZryOz films were obtained. On top of the successful formation of AlxZryOz films

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from the Al-Zr alloy films via post-sputter oxidation treatment, additional amorphous compound was confirmed to exist in the investigated samples via the detection of Raman peaks ascribed to Al-Zr-Si-O and amorphous SiOx in addition to FTIR absorption bands attributable to Al-O-Si,

SC

Zr-O-Si, amorphous SiOx, amorphous ZrO2, and amorphous AlO4 tetrahedral. The formation of amorphous Al-Zr-Si-O compound was believed to originate from an interfacial layer (IL) that

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could have formed at the interface between the AlxZryOz film and underlying Si substrate, following the post-sputter oxidation process in oxygen ambient at high temperatures. The influence brought by the IL formation was reflected through a decrease in the accumulation capacitance level for high frequency capacitance-voltage (C-V) measurement with respect to the

TE D

oxidation temperature, in which the IL formation was deemed to be the highest at 1000˚C. The effects of IL formation towards interface quality were assessed through the attainment of interface trap density (Dit). The lowest Dit value detected for the sample oxidized at 400˚C

EP

suggested that the formation of Al-Zr-Si-O IL has led to an improvement in the interface quality yet continuous increase in the IL formation at 600˚C has however degraded the interface quality.

AC C

Further increase of the temperature to 800 and 1000˚C has however improved the interface quality, owing to an increase of SiOx composition in the Al-Zr-Si-O IL. In addition, it was deduced from the direct and indirect band transitions estimated using Kubelka-Munk function for a decrease in oxygen vacancies as a function of temperature. The presence of oxygen interstitials in the investigated films was also figured out via the supporting evidence from FTIR showing the corresponding absorption band. The existence of oxygen vacancies and interstitials has

27

ACCEPTED MANUSCRIPT

contributed to a charge compensation, wherein a decrease in positive Qeff was obtained as the temperature was increased from 600 to 1000˚C, except for the sample subjected to oxidation at 400˚C, which possessed negative Qeff. Owing to the existence of negatively charged traps in the

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sample, J-V characteristic was the lowest at 400˚C. The presence of positively charged traps that could capture injected electrons from Si substrate to form neutral traps on the other hand has led to an improvement in the J-V characteristic at higher temperatures (600-1000˚C). Nonetheless, in

SC

comparison, J-V characteristic of the sample subjected to 1000˚C could not surpass that of 800˚C. This was primarily caused by the oxygen interstitials at the highest temperature (1000˚C) with

corresponding J-V characteristic.

Acknowledgement

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prominence of inducing mid-gap states in the band gap of the AlxZryOz film, degrading the

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The authors would like to acknowledge Universiti Sains Malaysia and Long Term Research

AC C

EP

Grant (LRGS; 203/CINOR/6720013), for their financial support.

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Figure Captions:

Fig. 1. High resolution X-ray diffraction (HRXRD) patterns of as-deposited Al-Zr alloy film and

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AlxZryOz films obtained by post-sputter oxidation at different temperatures (400-1000˚C).

Fig. 2. A relationship between lattice parameters c and a, cell volume, and ratio of cell parameters for AlxZryOz films obtained by post-sputter oxidation at different temperatures (400-

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1000˚C).

different temperatures (400-1000˚C).

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Fig. 3. Coefficient of texture, Thkl for AlxZryOz films obtained by post-sputter oxidation at

Fig. 4. Crystallite size (D) and microstrain (ε) determined for AlxZryOz films obtained by postsputter oxidation at different temperatures (400-1000˚C) using Williamson-Hall approach. Fig. 5. (a) Raman spectra and de-convoluted Raman spectra within (b) 120-220 cm-1, (c) 220-

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400 cm-1, and (d) 460-580 cm-1 for AlxZryOz films obtained by post-sputter oxidation at different temperatures (400-1000˚C).

Fig. 6. Fourier Transformed Infrared (FTIR) absorption spectra for AlxZryOz films obtained by

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post-sputter oxidation at different temperatures (400-1000˚C). Fig. 7. Typical field emission scanning electron microscopy (FESEM) image of AlxZryOz film

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subjected to post-sputter oxidation at 1000˚C Fig. 8. Three-dimensional (3D) atomic force microscopy surface topography images of AlxZryOz films obtained by post-sputter oxidation at different temperatures (400-1000˚C). Fig. 9. Schematic energy band diagrams showing direct (a-d) and indirect (e-h) band transitions for AlxZryOz films obtained by post-sputter oxidation at 400˚C (a-e), 600˚C (b-f), 800˚C (c-g), and 1000˚C (d-h).

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Fig. 10. High frequency (1 MHz) capacitance-voltage (C-V) curves of Al/AlxZryOz/Si/Al metaloxide-semiconductor structures for the films obtained by oxidation at different temperatures. Fig. 11. Calculated effective oxide charges (Qeff) and slow trap density (STD) present in the

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AlxZryOz films obtained by post-sputter oxidation at different temperatures (400-1000˚C).

Fig. 12. FESEM cross-sectional images for (a) as-deposited Al-Zr films as well as AlxZryOz films obtained by post-sputter oxidation at (b) 400, (c) 600, (d) 800 and (e) 1000˚C.

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Fig. 13. A relationship between total oxide thickness obtained for AlxZryOz films and postsputter oxidation temperature.

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Fig. 14. Interface trap density (Dit) and total interface trap density (Dtotal) (inset) calculated for Al/AlxZryOz/Si/Al metal-oxide-semiconductor structures.

Fig. 15. Leakage current density-gate voltage (J-Vg) characteristics of Al/AlxZryOz/Si/Al metaloxide-semiconductor structures for the films obtained by oxidation at different temperatures.

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Fig. 16. Capacitance-voltage (C-V) curves for AlxZryOz film subjected to oxidation at 800˚C that were measured using different frequencies of 1 MHz, 100 kHz, and 10 kHz (line in grey colour

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Figures:

Fig. 1. High resolution X-ray diffraction (HRXRD) patterns of as-deposited Al-Zr alloy film and

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AlxZryOz films obtained by post-sputter oxidation at different temperatures (400-1000˚C).

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Fig. 2. A relationship between lattice parameters c and a, cell volume, and ratio of cell

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1000˚C).

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parameters for AlxZryOz films obtained by post-sputter oxidation at different temperatures (400-

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Fig. 3. Coefficient of texture, Thkl for AlxZryOz films obtained by post-sputter oxidation at

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different temperatures (400-1000˚C).

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Fig. 4. Crystallite size (D) and microstrain (ε) determined for AlxZryOz films obtained by post-

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sputter oxidation at different temperatures (400-1000˚C) using Williamson-Hall approach.

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Fig. 5. (a) Raman spectra and de-convoluted Raman spectra within (b) 120-220 cm-1, (c) 220400 cm-1, and (d) 460-580 cm-1 for AlxZryOz films obtained by post-sputter oxidation at different

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temperatures (400-1000˚C).

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Fig. 6. Fourier Transformed Infrared (FTIR) absorption spectra for AlxZryOz films obtained by

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Fig. 7. Typical field emission scanning electron microscopy (FESEM) image of AlxZryOz film

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subjected to post-sputter oxidation at 1000˚C

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Fig. 8. Three-dimensional (3D) atomic force microscopy surface topography images of AlxZryOz

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Fig. 9. Schematic energy band diagrams showing direct (a-d) and indirect (e-h) band transitions for AlxZryOz films obtained by post-sputter oxidation at 400˚C (a-e), 600˚C (b-f), 800˚C (c-g),

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and 1000˚C (d-h).

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Fig. 10. High frequency (1 MHz) capacitance-voltage (C-V) curves of Al/AlxZryOz/Si/Al metal-

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Fig. 11. Calculated effective oxide charges (Qeff) and slow trap density (STD) present in the

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Fig. 12. FESEM cross-sectional images for (a) as-deposited Al-Zr filmsas well as AlxZryOz films

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Fig. 13. A relationship between total oxide thickness obtained for AlxZryOz films and post-

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Fig. 14. Interface trap density (Dit) and total interface trap density (Dtotal) (inset) calculated for

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Al/AlxZryOz/Si/Al metal-oxide-semiconductor structures.

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Fig. 15. Leakage current density-gate voltage (J-Vg) characteristics of Al/AlxZryOz/Si/Al metal-

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Fig. 16. Capacitance-voltage (C-V) curves for AlxZryOz film subjected to oxidation at 800˚C that were measured using different frequencies of 1 MHz, 100 kHz, and 10 kHz (line in grey colour

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Highlights Formation of ternary aluminium doped zirconium oxide film via two-step growth.

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Transformation from amorphous Al-Zr alloy films to crystalline AlxZryOz films.

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Oxygen interstitials induced mid-gap states in the band gap of AlxZryOz film.

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Metal-oxide-semiconductor characteristics of AlxZryOz film on silicon substrate.

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