Abstract Aluminum Nitride Thin Films Research Articles

Structural and Optical Properties of Aluminium Nitride Thin Films Fabricated Using Pulsed Laser Deposition and DC Magnetron Sputtering on Various Substrates

Abstract Aluminium nitride thin films were fabricated using pulsed laser deposition and DC magnetron sputtering. Different technological parameters and the effects of different substrates on the optical and structural parameters of AlN samples were studied. An X-ray diffraction study was performed for the layer deposited on the Si3N4 substrate. A high-energy electron diffraction study was also carried out for the layer deposited on a KCl substrate. Transmission spectra of layers on quartz, sapphire, and glass substrates were obtained. An evaluation of the optical band gap of the obtained layers was carried out (Eg form 3.81 to 5.81 eV) and the refractive index was calculated (2.58). The relative density of the film (N1TN-AlN sample) is 1.26 and was calculated using the Lorentz-Lorentz relationship. Layers of aluminium nitride show an amorphous character with a polycrystalline region. It was shown that the properties of AlN films strongly depend on the method, growth conditions, and substrate used.

Substrate Heating Effect on c-Axis Texture and Piezoelectric Properties of AlN Thin Films Deposited by Unbalanced Magnetron Sputtering

Aluminum nitride (AlN) thin films with highly preferred (002) orientations have been reactively deposited by a pulsed-closed field unbalanced magnetron sputtering system using TiN/Ti as the seed/adhesion layer with various substrate temperatures. The texture, orientation and piezoelectric properties of AlN films were characterized by means of x-ray diffraction, rocking curves and laser interferometry. A Michelson laser interferometer was designed and built to obtain the converse piezoelectric response of the deposited AlN thin films. It was found that a slight substrate temperature increase would significantly affect the (002) orientation and the piezoelectric coefficient of AlN thin films compared to the coating obtained with no intentional substrate heating, while higher temperature applications on substrate deteriorated the c-axis texture of the coatings without significant improvement in the piezoelectric response of AlN films.

Deposition and characterization of AlN thin films obtained by radio frequency reactive magnetron sputtering

Aluminum nitride (AlN) thin films were deposited by reactive radio frequency magnetron sputtering from pure aluminum target, onto Si (100), ultra dense flat carbon, and quartz. Series of samples were obtained varying the Ar and N2 gaseous mixture. The characterizations performed were Fourier transform infrared (FTIR), X-ray diffraction, high resolution transmission electron microscopy, visible optical absorption, Rutherford backscattering spectrometry, and residual stress measurements by Stoney’s equation. In this paper we report on the Ar/N2 ratio needed to produce preferential (002) AlN growth. Correlations between X-ray diffraction and FTIR are made for highly oriented (002) AlN films.

AlN thin films prepared by ArF plasma assisted PLD. Role of process conditions on electronic and chemical–morphological properties

Aluminium nitride thin films were deposited on n-Si substrates by RF plasma activated reactive pulsed laser deposition (PLD). An ArF excimer pulsed laser, 10 Hz and 2.5 J/cm2 energy fluence, has been used to ablate a pure Al target in a reactive atmosphere of N2 plasma (generated by a RF source), at varying processing parameters (substrate temperature, time, and N2 plasma configuration). We studied the dependence and correlation of structural and electronic properties with the experimental conditions. The chemical composition of deposited material has been determined by both Raman and X-ray photoelectron spectroscopy (XPS). Electrical resistivity has been evaluated by the sheet resistance method. Both spectroscopic characterizations (Raman and XPS) show a strong dependence in the formation of AlN on the deposition temperature. At low temperatures, there is little formation of nitride, with a prevalence of aluminium oxide, while at higher temperatures the N uptake increases, with AlN formation. Raman analysis also highlights the formation of nano-structures, for temperatures ≥400∘C. These material characteristics have a fundamental influence on the electronic properties. Indeed, electrical resistivity properties have been found to be strongly dependent on the film structure, nitrogen incorporation, and presence of mixed oxide compounds, closely related to deposition temperature.

Deposition of Transparent AlN Thin Film on SiALON Substrate by Reactive Magnetron Sputtering

Aluminum nitride thin film has been deposited on transparent SiAlON substrate by reactive magnetron sputtering. X-ray photoelectron spectroscopy patterns and raman spectra were used to analysis the phase composition of the thin film, and the surface morphology of the thin film was observed by atomic force microscope, which reveal that AlN thin film with smooth surface and columniform microstructure was formed. The fourier transform infrared spectral of the SiAlON substrate and SiAlON/AlN composition structure indicate that the AlN thin film has high transmittance above 99%, it is to say that the AlN thin film is transparent, and it nearly have no affect on the infrared transmittance of the SiAlON substrate.

Study of Deposition of Aluminum Nitride Thin Films by Hollow Cathode Electron Beam Vapor Deposition Method

Aluminum nitride (AlN) thin films were deposited on (100) oriented silicon wafers substrates by Hollow Cathode Electron Beam Vapor Deposition system (HCEBVD) under various Ar/N2 mass flow ratio. The films were characterized by Atomic Force Microscopy (AFM), Glancing Incident X-ray Diffraction (GIXRD) techniques and Ultraviolet/Visible Spectrophotometer (UV/VIS). It was found that the thin films are polycrystalline and have a hexagonal wurtzite structure with (002) preferred orientation, as revealed by GIXRD. AFM analysis indicates that the surface of the thin films is smooth, with average RMS (Root Mean Square) roughness Ra of 0.7nm, which is suitable for application in surface acoustic wave devices. The film thickness and optical refractory properties of the AlN thin films were investigated.

Synthetic Properties of the <i>c</i>-Axis Tilted AlN Thin Films

Aluminum nitride (AlN) is one of the most popular piezoelectric materials for high frequency resonators, filters and sensors. The piezoelectric property, i.e. electromechanical coupling coefficient, of AlN thin film is highly related to its crystalline orientation. AlN thin films with various c-axis-tilted angles can be fabricated by the RF sputtering technique. The crystallization and grain growth orientations of AlN thin film are examined by XRD, SEM, and TEM, while the bonding condition and nano-mechanical properties are investigated by a raman system and a nano-indentation technique.

Optical properties of pulse laser deposited AlN thin films on silicon

Aluminium-nitride thin films were deposited on silicon Si(111) substrate with pulsed laser deposition in a Riber LDM-32 system. The optical properties of the films were studied by means of optical spectroscopy with an incoherent light source mainly covering the visible range. It is demonstrated that, in comparison with an aluminium mirror, under certain deposition conditions, the film may behave as a metallic thin film as far as the optical reflection is concerned. In this case, there is an enhanced plasmonic reflection peak in the optical spectrum and the peak may be modified according to the degree of the phase transition. The microscopic structures as well as the surface topographies of the films were also studied with X-ray photoelectron spectroscopy and scanning electron microscopy. It turns out that the density and the size of the microscopic domains in the film determine whether the film remains dielectric or becomes metallic. The diamagnetic effect in the enhanced plasma increases in the process when the sample is smoothed out with the optimized nitrogen gas pressure. The nitrogen pressure is thus identified as the most influential deposition condition to the phase transition.

Preparation of AlN thin films for film bulk acoustic resonator application by radio frequency sputtering

Aluminum nitride (AlN) thin films with high c-axis orientation have been prepared on a glass substrate with an Al bottom electrode by radio frequency (RF) reactive magnetron sputtering. Based on the analysis of Berg’s hysteresis model, the improved sputtering system is realized without a hysteresis effect. A new control method for rapidly depositing highly c-axis oriented AlN thin films is proposed. The N2 concentration could be controlled by observing the changes in cathode voltage, to realize the optimum processing condition where the target could be fixed stably in the transition region, and both stoichiometric film composition and a high deposition rate could be obtained. Under a 500 W RF power of a target with a 6 cm diameter, a substrate temperature of 450°C, a target-substrate distance of 60 mm and a N2 concentration of 25%, AlN thin film with preferential (002) orientation was deposited at 2.3 μm/h which is a much higher rate than previously achieved. Through X-ray diffraction (XRD) analysis, the full width at half maximum (FWHM) of AlN (002) was shown to be about 0.28°, which shows the good crystallinity and crystal orientation of AlN thin film. With other parameters held constant, any increase or decrease in N2 concentration results in an increase in the FWHM of AlN.

CMOS-compatible light-emitting devices based on thin aluminum nitride film containing Al nanocrystals

Aluminum nitride (AlN) films have attractive physical properties, such as wide bandgap (6.2 eV), high thermal conductivity (320 W/mK), and good match of both thermal expansion coefficient and lattice constant to those of Si substrate . Based on these properties, AlN films can be applied in surface acoustic wave (SAW) devices, memories devices, and optoelectronic devices. It has been reported in our recent studies that amorphous AlN thin films containing aluminum nanocrystals (nc-Al) deposited on Si substrate by radio-frequency (rf) magnetron sputtering possess memory effect and exhibit interesting current conduction behaviors.

Effects of 3C-SiC Intermediate Layer on the Properties of AlN Films Grown on SiO<sub>2</sub>/Si Substrate

Aluminum nitride thin films were deposited on polycrystalline 3C-SiC intermediate layer by pulsed reactive magnetron sputtering system. Characteristics of AlN/SiC structures were investigated experimentally by means of FE-SEM, AFM, X-ray diffraction, and FT-IR. The columnar structure of AlN thin films was observed by FE-SEM. The surface roughness of AlN films on 3C-SiC layer was measured using AFM. X-ray diffraction pattern of AlN films on SiC layers highly were oriented as (002). Full width of half maximum (FWHM) of the rocking curve around (002) reflections was 1.3°. It was determined from infrared absorbance spectrum that the residual stress of AlN thin films grown on SiC layers was almost free. The presented results show that AlN thin films on 3C-SiC buffer layers can be used for various applications.

Deposition of AlN thin films on Si substrates using 3C-SiC as buffer layer by reactive magnetron sputtering

Aluminium nitride (AlN) thin films were deposited on a polycrystalline (poly) 3C-SiC layer by a pulsed reactive magnetron sputtering system. The columnar structure of AlN thin films was observed by FE-SEM. The surface roughness of AlN films on the 3C-SiC layer was 9.3 nm. The X-ray diffraction pattern of AlN films on SiC buffer layers was highly oriented at (002). Full width at half maximum of the rocking curve near (002) reflections was 1.3°. The infrared absorbance spectrum indicated that the residual stress of AlN thin films grown on SiC buffer layers was nearly negligible. The 3C-SiC intermediate layers are promising for the realisation of nitride based electronic and mechanical devices.

Surface Morphology Studies of Sub-Ps Pulsed-Laser-Deposited AlN Thin Films

Aluminum nitride thin films were deposited by multipulse KrF* (λ = 248 nm, τ∼450 fs) excimer laser ablation of AlN targets in low-pressure nitrogen. We investigated the morphology of the deposited films by scanning as well as transmission electron microscopy, as a function of laser fluence and ambient nitrogen pressure. The AlN films entirely consist of grains (clusters) with average diameters of a few tens of nanometers. In addition, particulates several hundreds of nanometers in diameter (spherical droplets) were observed on the surfaces of the deposited films. Besides these particulates, we noticed the presence of micrometer-size whiskers, or dendritic- and wave-like structures, consisting of agglomerates of nanoparticles. The particulates density decreases with the decrease of the laser fluence, or with the increase of the ambient nitrogen pressure, while their average size increases. This indicates that clustering is the dominant particulates formation mechanism, as a result of the enhanced number of collisions in the fs laser generated ablation plasma.

Element composition and electrochemical behaviour of polycrystalline AlN thin films

Abstract Aluminium nitride (AlN) thin films were deposited under different nitrogen partial and total pressures by means of reactive d.c. magnetron sputtering. The investigated films had polycrystalline structure, revealed by electron beam diffraction (EBD). The depth profiles of Al, N and C distributions were registered by a direct emission layer-by-layer analysis in a hollow cathode glow discharge. All data indicated that there are no peculiarities of the element depth profiles in our films. The X-ray photoelectron spectroscopy (XPS) spectrum was used to determine the composition of the films. The spectrum clearly showed peaks from Al, N, O and C atoms present in the films. The electrochemical behaviour of the films was investigated using a d.c. electrochemical test in a 3% NaCl solution. The AlN films grown at a higher nitrogen partial pressure performed with a better electrochemical behaviour. A strong IR absorption band was obtained around 670 cm −1 , which confirmed that the deposited films were AlN.

Changes in optical transmittance and surface morphology of AlN thin films exposed to atmosphere

Aluminum nitride (AlN) thin films have been prepared by the ion-beam assisted deposition (IBAD) method, and the influence of exposure to different atmosphere on optical transmittance and surface morphology has been studied. AlN films have been prepared with the nitrogen ion beam energy of 0.1, 0.2, or 1.5 keV. Synthesized films have been exposed to the following conditions: (i) laboratory air (RT and 40–60% RH), (ii) saturated humidity air (RT and 80–90% RH), and (iii) elevated temperature air (100 °C and 10–20% RH). Optical transmission spectrum in the wavelength region from 190 to 2200 nm has been measured by a UV-visible spectrometer every week. Surface morphology of the films has been observed with an optical microscope (OM), and phase identification has been performed by thin film x-ray diffraction (TFXRD). The optical transmittance has not changed drastically after exposure both to the laboratory air and the saturated humidity air for 60 weeks and after exposure to the elevated temperature air for 48 weeks. Observations by OM showed that round-shaped substances were formed on the film surfaces after exposure to the atmosphere, and the size of the substances on the film surface exposed to saturated humidity air is much larger than those on the surface exposed to other atmosphere. The results of TFXRD revealed that the AlN diffraction peaks have gradually decreased with exposure time, but any new phase due to reaction products has not been detected for the samples exposed to the laboratory air, the saturated humidity air, or the elevated temperature air. From the present results, it is concluded that the IBAD AlN films can be applied in low humidity air without losing high transparency up to 60 weeks, and the films prepared with 1.5 keV ion beam show better durability than the films prepared with 0.1 or 0.2 keV ion beam for exposure to the saturated humidity air.

Aluminium nitride thin films prepared by ion beam assisted deposition method

Aluminium nitride thin films were prepared by ion beam assisted deposition (IBAD) and the influenceof nitrogen ion beam energy on the microstructure, orientation, surface morphology, optical properties, and durability of the thin films was studied. In the case of synthesis with a low energy ion beam, the films showeda c axis oriented state with a columnar structure and an extremely smooth surface, but the durability against water was weak. In the case of synthesis with a high energy ion beam, the films showed a multioriented state with a granular structure, a roughened surface, and an improved durability against water. It is concluded that the nitrogen ion beam energy plays an important role in synthesising AIN films by the IBAD method, andthat the film structure and properties can be controlled by regulating the ion beam energy.

X-ray Photoelectron Spectroscopy Depth Profiling of Aluminium Nitride Thin Films

Aluminium nitride thin films grown at room temperature on degenerate silicon (conducting) substrates have been studied using XPS. The hydrolysis layer at the surface of the AIN was examined using valence band measurements, and the effect of 5 kV argon ion milling used to remove the hydrolysis layer was scrutinized using angle-resolved XPS. The N/Al ratios found from the angle-resolved measurements indicate nitrogen depletion from the surface of the milled samples, whereas O/Al ratios indicate no such depletion of oxygen. After argon ion milling, carbon uptake from the ultrahigh vacuum analysis chamber was found to be significant.

Effect of negative bias voltage on the microstructures of AlN thin films fabricated by reactive r.f. magnetron sputtering

Aluminium nitride thin films have been fabricated on silicon wafers by reactive r.f. magnetron sputtering in mixed Ar-N2 discharge with variation of negative bias voltage. The effect of negative bias voltage on the microstructures of AlN thin films have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), stress measurement, Auger electron spectroscopy (AES), etc. While the negative bias voltage was varied in the range 0 to −45 V, highly c-axis oriented film can be fabricated at −30 V, and the grain size and compressive stress increase with the negative bias voltage. From the plasma analysis, the dominant positive chemical species is identified as N+2 ions. The above results can be understood considering that at the kinetic energy transfer and flux of N+2 ions increase with increasing negative bias voltage.

Effects of ion beam irradiation on the properties and epitaxial growth of aluminium nitride film by the ion beam assisted deposition process

Aluminium nitride thin films were grown on Si(111) substrates by ion beam assisted deposition. Epitaxial growth of the AIN films was obtained at the low temperature of 450 °C. Characterization of the AIN epitaxial layer was carried out by grazing-incidence diffraction (GID) and high resolution transmission electron microscopy (HRTEM). GID analysis showed two kinds of epitaxial orientation between AIN epitaxial layer and Si substrate. An amorphous layer was observed at the interface between AIN film and Si by cross-sectional HRTEM analysis. The amorphous layer could release the misfit strain between the AIN film and the Si substrate in an early stage of growth. The AIN epitaxial layer formed despite the large lattice mismatch. In addition, the optical properties of AIN films including transmittance, energy band gap, and refractive index were determined and discussed.

Preparation of AlN thin films by reactive sputtering and optical emission spectroscopy during sputtering

Abstract Aluminum Nitride (AlN) thin films were prepared by reactive rf-magnetron sputtering in a mixed gas atmosphere composing of argon and nitrogen. The deposition rate, electrical resistivity and crystal structure were studied as a function of partial pressure of nitrogen (P N2). Total pressure(P N2+Ar) was controlled to maintain a constant pressure of 6.0 ×10−2 Pa. The structure of as-prepared films can be divided into three regions from X-ray diffraction analysis: (1) P N2 ≤ 6.0 ×10−3 Pa, Al, (2) P N2 = 1.2 ×10−2 Pa ∼ 2.4 ×10−2 Pa, a mixed phase of Al and AlN, (3) P N2 ≥ 3.0 ×10−2 Pa, AlN. With increase of P N2, the deposition rate of the films decreased drastically around P N2 = 2.4 ×10−2 Pa, and finally approached to a constant value of 25 A/min around P N2 = 6.0 ×10−1 Pa. This is proved from the measurement of optical emission spectroscopy to occur by the formation of nitride on the surface of aluminum target. AlN thin films deposited in higher P N2 exhibited a higher crystallity and a higher ref...