Reactive Ac Magnetron Sputtering Research Articles

Highly Oriented and Stress Modified Thick AlN Films Deposited on Low Thermal Expansion Alloy Substrates for Flexible Electronics in Harsh Environment

Highly oriented and stress-modified thick aluminium nitride (AlN) films were deposited by reactive AC magnetron sputtering on 4 inch substrates and foils made of the low thermal expansion alloy “42Alloy” for flexible electronics in harsh environment. As a result of modification of film depositing conditions for reducing residual stress, a flat three micrometer thick AlN film was deposited successfully on the 50 μm thick 42Alloy foil, and its full width at half maximum of AlN(002) was 5.00 degree. And, it was confirmed that the AlN films on 42Alloy foils have piezoelectricity by measurement of a tip displacement of the cantilever-shape test structure.

Sputtered cobalt doped CuO nano-structured thin films for photoconductive sensors

Pure and cobalt (Co) doped CuO thin films have been deposited by DC and AC reactive magnetron sputtering technique. The doping ratio has been controlled by the RF power of the AC sputtering unit. The sputtering power ranges from 0 to 50 W. The crystal structure of the films has been identified by X-ray diffraction. One of the peaks has been shifted toward the high diffraction angle. Energy dispersive analysis shows cationic deficiency of the pure and doped samples. Morphology of the films has been investigated by atomic force microscopy. Film roughness decrease with the increase of sputtering power. Spectrophotometry studies reveal that films darken with the increase of sputtering power. The current–voltage curves show Ohmic contacts and an enhancement in the conductivity with the increase of Co concentrations. Photoresponse measurements have shown that the film doped at 50 W is the best photodetector sensor.

Spectrally selective Al/AlN/Al/AlN tandem solar absorber by inline reactive ac magnetron sputtering

Spectrally selective Al/AlN/Al/AlN tandem solar absorbers were deposited onto soda lime glass substrates using inline ac magnetron sputtering in a reactive atmosphere containing argon and nitrogen. To achieve a reproducible and homogenous deposition process, the deposition of multilayer Al/AlN/Al/AlN films under different process conditions was investigated. Two main variables, ac power and the speed of substrate movement in the chamber, were varied in the ranges of 1–10 kW and 10·47–31·4 mm s−1 respectively to obtain films with high absorption and low emittance. The effects of film thickness of different layers and deposition conditions on the optical performance of selective coatings were also studied. Structural features and surface morphology of the films were investigated by X-ray diffraction and field emission scanning electron microscopy analyses respectively. In the present study, tandem solar absorber films deposited onto glass substrate with optimised sputtering parameters can consistently achieve solar absorptance α of 0·864 and thermal emittance ϵ of 0·03 at 80°C.

Microstructure and chemical wet etching characteristics of AlN films deposited by ac reactive magnetron sputtering

The influence of the surface morphology of a molybdenum underlayer on the crystallinity and etchability of reactively sputtered c-axis oriented aluminum nitride thin films was investigated. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, high resolution x-ray diffraction, and defect selective chemical etching were used to characterize the microstructure of the Mo and AlN films. 1000nm thick films of AlN with a full width at half maximum (FWHM) of the x-ray rocking curve ranging from 1.1° to 1.9° were deposited on 300nm thick Mo underlayers with a FWHM of around 1.5°. The Ar pressure during the Mo deposition had a critical effect on the Mo film surface morphology, affecting the structure of the subsequently deposited AlN films and, hence, their wet etching characteristics. AlN films deposited on Mo sputtered at a relatively high pressure could not be etched completely, while AlN films deposited on low pressure Mo etched more easily. Postdeposition etching of the Mo surface in Ar rf discharge prior to deposition of the AlN film was found to influence the formation of AlN residuals that were difficult to etch. Optimal rf plasma etching conditions were found, which minimized the formation of these residuals.

Microtribological rating of transparent conducting oxide for thin film solar cells

In this study, the mechanical properties of transparent conducting oxide (TCO) deposited on glass substrates, namely, aluminium doped zinc oxide (ZnO:Al) and fluorine doped tin oxide (SnO2:F) for the application of amorphous or amorphous/microcrystalline silicon solar cells, were investigated. The ZnO : Al thin films were deposited by either inline reactive ac magnetron sputtering or radio frequency magnetron sputtering utilising ceramic targets. The SnO2:F thin films were prepared using either inline or offline chemical vapour deposition (CVD). The micromechanical properties such as elastic and permanent deformation, microtribological properties and scratch resistance were measured to assess the film properties. The micro-structure-analysis method (MISTAN) was used to characterise those properties in situ with high local resolution. The inline reactive ac magnetron sputtered ZnO:Al films show relatively good scratch resistance. The surface structure of ZnO:Al films can be roughened by an etching process in order to enhance the scattered light into the cells. At the same time, the microfriction of the ZnO:Al films under the same load is higher after the etching process. Also the elastic and permanent deformation of inline reactive ac magnetron sputtered ZnO:Al films are increased after etching. The etching process has a significant impact on the radio frequency magnetron with ceramic targets deposited ZnO:Al films, since the scratch resistance of these films can be significantly improved by the etching process. The results show that the SnO2:F films possess poor mechanical resistance and planar surface structure.

Comment on “CrNx and Cr1−xAlxN as template films for the growth of α-alumina using ac reactive magnetron sputtering,” [J. Vac. Sci. Technol. A 25, 1367 (2007)

Comment on “CrNx and Cr1−xAlxN as template films for the growth of α-alumina using ac reactive magnetron sputtering,” [J. Vac. Sci. Technol. A 25, 1367 (2007)

Mechanical and tribological properties of compositionally graded CrAlN films deposited by AC reactive magnetron sputtering

In this work, CrAlN films with Al/Cr atomic ratios between 0.02 and 1.4 were deposited on tool inserts by AC magnetron sputtering at 5 kW for three different Ar/N 2 flow rates. The unique configuration of the inverted cylindrical magnetron sputtering (ICM-10) system enables the deposition of compositionally graded Cr–Al–N coatings under a single deposition condition. The effect of aluminum on the structural, mechanical and tribological properties of (Cr,Al)N coatings are reported and compared with ALCRONA and CrN coatings from Balzers. Mechanical properties have been evaluated by the microhardness indentation technique, and the hardness is 18 and 15 GPa for CrN and CrAlN films, respectively. The tribological tests have been performed using the pin-on-disc method at room temperature and 700 °C. The results indicate that the coefficient of friction at room temperature and 700 °C for all the deposited coatings, Balzers-ALCRONA and CrN fall between 0.4–0.6. The wear volume at high temperature (700 °C) decreases with increase in Al incorporation. Auger Electron Spectroscopy reveals that all films have about 10 at.% of oxygen. Atomic Force Microscopy showed that our films had roughness ranging from 80 to 150 nm. X-ray mapping on (Cr, Al)N coatings for different Ar/N 2 gas compositions showed transitions from cubic to hexagonal with decreasing nitrogen.

Cr N x and Cr1−xAlxN as template films for the growth of α-alumina using ac reactive magnetron sputtering

Crystalline alumina thin films were deposited on WC–Co substrates using a reactive inverted cylindrical ac magnetron sputtering technique with a chromium oxide prelayer. The interfacial prelayer of chromium oxide was prepared by controlled oxidation of CrNx and Cr1−xAlxN films deposited previously using the same ac reactive magnetron configured with one Cr and Al target. The oxidation was carried out by annealing CrNx and Cr1−xAlxN films in air at 973 and 1373K, respectively. Scanning electron microscopy and energy dispersive x-ray microanalysis were carried out to investigate the thin film surface morphology and composition. The alumina coatings obtained on oxidized CrNx films (templates) were smooth and consisted primarily of κ and α phases. The diffraction peaks from the γ phase were not observed in any of the alumina coatings. The morphology and phase composition of the alumina coatings on the oxidized Cr1−xAlxN films (templates) were strongly dependent on the aluminum content in the films.

Effect of substrate orientation on film properties using AC reactive magnetron sputtering

CrN coatings were prepared by magnetron sputtering with target-substrate orientations varying between 0° and 90° and N 2 flow rates of 43, 40 and 30 sccm. The coatings were deposited on (111) Si wafers at a chamber pressure of 0.2 Pa for 1 h. Initial results indicate that the target-substrate orientation to the incoming flux of ionized species affects the microstructure, phase and preferred orientation of the crystallites in Cr–N coatings. The SEM studies of the film morphology showed a distinct change from coarser, less dense coatings to smooth, dense and fine-grained morphologies as a function of the changing orientation of the substrate, while the cross-sectional micrographs showed a columnar growth of the crystallites independent of substrate orientation. When the target-substrate angle was varied from 0° to 90°, the average roughness (Ra) decreased from 78 to 23 nm. We report on the details of the microstructural and chemical characterization of the films deposited in this study.

Effects of deposition parameters on the structure of AlN coatings grown by reactive magnetron sputtering

AlN films were deposited on microscopy glass slide and silicon (111 orientation) substrates by reactive ac magnetron sputtering using two nitrogen concentrations and three discharge powers of 1.5, 2.5, and 5.0kW. X-ray diffraction studies showed that films prepared on glass and Si substrates were of hexagonal wurtizite phase. Films on Si substrates also contained small amounts of the cubic phase of AlN besides the predominantly hexagonal wurtizite phase. AlN coatings on glass substrates were textured towards the (00∙2) plane; this preferred orientation of crystals was found to decrease with increase in sputtering power. Scanning electron microscopy studies showed that AlN films prepared at higher nitrogen concentration have a microstructure consisting of pebblelike crystals, some of which were hexagonal in shape. The crystal size in the coatings increased with sputtering power and was in the range of 70–230nm.

Crystalline alumina coatings by reactive ac magnetron sputtering

Alumina coatings were deposited on silicon (111 orientation) substrates by reactive ac magnetron sputtering. Film deposition was done using Al targets and three O2∕Ar gas flow rate ratios at 5kW power. X-ray diffraction studies showed that films were crystalline and contained several phases of alumina. Secondary ion mass spectroscopy analyses were used to measure O∕Al atomic ratio and Ar and H concentrations in the films. Hydrogen content in the coatings depended on the O2 partial pressure used during sputtering and also on the arrival rate of Al and O species on the substrates and seemed to influence the crystallinity of the coatings.

A study of AC reactive magnetron sputtering technique for the deposition of compositionally graded coating in the Cr–Al–N system

Cr 1− x Al x N coatings were deposited on various substrates using an inverted cylindrical AC magnetron sputtering system with chromium and aluminum targets, at a chamber pressure of 0.2 Pa (1.5 mTorr) for 1.5 h. The present study focuses on the effect of various deposition parameters, such as the N 2/Ar ratio and the target power on the properties of the coatings obtained. Some of the samples were subjected to oxidation in still air at 900 °C. The morphology and structure of these coatings were investigated by various analytical techniques such as XRD, SEM, EDAX and EDS. We report on the effect of processing parameters on the morphology, orientation, composition and oxidation behavior of the compositionally graded (Cr 1− x Al x )N coatings.

Growth and characterization of chromium oxide thin films prepared by reactive ac magnetron sputtering

Cr O x thin films were prepared on single crystal silicon (111 orientation) and glass substrates by midfrequency (41kHz) ac sputtering technique in an Isoflux ICM-10 sputter deposition system consisting of two hollow cylindrical targets of Cr in an argon-oxygen plasma at a discharge power of 5kW and without any deliberate substrate heating. X-ray diffraction studies showed that the coatings were of hcp rhombohedral α-phase chromium oxide. CrOx coating samples were found to grow preferentially towards the (110) crystal orientation of α-Cr2O3. Texturing was found to depend on the orientation of the substrates relative to the targets and also on the nature of substrates. One coating sample grown on Si substrate was annealed in air up to 1173K. Whereas heat treatment increased the crystallite size, CrOx coating was thermally stable and did not show any structural transformations. Scanning electron microscopy studies showed differences in the surface morphology of the coatings grown on glass and silicon substrates. Dynamic secondary ion mass spectrometry measurements performed on one CrOx coating deposited on silicon showed that the O∕Cr ratio in the films was 1.38. Ar and H impurity concentrations were also measured in this coating as a function of film thickness. Alumina coatings were prepared on Si substrates by reactive sputtering technique using CrOx coating as template layers. X-ray diffraction studies showed that CrOx template layers improved the crystallinity of alumina coatings grown on top of it and also facilitated the formation of the thermodynamically stable α-alumina phase.

Structure-property correlations in aluminum oxide thin films grown by reactive AC magnetron sputtering

Crystalline alumina thin films were deposited on glass, silicon and WC-Co substrates by reactive inverted cylindrical AC magnetron sputtering technique both with and without aluminum precoating at two working pressures. Coatings prepared on Si wafers with Al precoating were found to be γ-phase of aluminum oxide. However alumina coatings prepared on Si wafer without Al precoating showed evidence for the presence of δ and θ-phases besides the γ-phase. Two coating samples grown on Si substrates with Al prelayer were annealed at 400 and 900 °C for 8 h under flowing oxygen conditions. Annealing at 400 °C increased the grain size for γ-alumina phase while annealing to 900 °C formed δ and κ-phases in the coatings. Scanning electron microscopy and energy dispersive X-ray microanalysis were carried out to investigate the thin film surface morphology and composition. While γ-alumina coatings were ultrafine grained, coatings containing δ- and κ-phases showed large size grains. Nanoindentation and nanoscratch tests were performed on all samples to determine the thin film hardness and scratch resistant properties. Higher working pressure during film deposition seemed to lower film hardness values. Significant differences were observed in the mechanical properties of alumina thin films grown with Al precoating on silicon substrates. While the Al precoating improves thin film adhesion and leads to less severe failure, it significantly decreased the thin film hardness as measured by nanoindentation technique.

ZnO:Al films deposited by in-line reactive AC magnetron sputtering for a-Si:H thin film solar cells

Throughout the last years strong efforts have been made to use aluminium doped zinc oxide (ZnO:Al) films on glass as substrates for amorphous or amorphous/microcrystalline silicon solar cells. The material promises better performance at low cost especially because ZnO:Al can be roughened in order to enhance the light scattering into the cell. Best optical and electrical properties are usually achieved by RF sputtering of ceramic targets. For this process deposition rates are low and the costs are comparatively high. Reactive sputtering from metallic Zn/Al compound targets offers higher rates and a comparable high film quality in respect to transmission and conductivity. In the presented work the process has been optimised to lead to high quality films as shown by reproducible cell efficiencies of around 9% initial for single junction amorphous silicon solar cells on commercial glass substrates. The crucial point for achieving high efficiencies is to know the dependency of the surface structure after the roughening step, which is usually performed in a wet etch, on the deposition parameters like oxygen partial pressure, aluminium content of the targets and temperature. The most important insights are discussed and the process of optimisation is presented.

Investigation of SiO2 optical films produced by reactive ac magnetron sputtering

This paper presents the results of experimental studies of the optical constants and growth rate of SiO2 films fabricated by the magnetron sputtering of a Si target in an Ar:O2 medium by ultrasonic-frequency current. The resulting SiO2 films are similar in optical parameters to SiO2 films fabricated by ion-assisted electron-beam evaporation. © 2004 Optical Society of America

Transparent and conductive ZnO:Al films deposited by large area reactive magnetron sputtering

A new coating technology has been developed for large area deposition of transparent and conductive ZnO:Al films. Reactive AC magnetron sputtering from metallic Zn:Al has been performed at low substrate temperature below 200 °C using the new CleanMag technology of applied films based on moving magnets for layers with low defect density and with conventional reactive AC magnetron sputtering using static magnets (Applied Films TwinMag). Process stabilization at non-stable process conditions in transition mode has been achieved using closed loop control of discharge power according to fast oxygen partial pressure measurements taken by a lambda probe. Films with film thickness of 800–1000 nm deposited with dynamic deposition rate of a D>60 nm m/min exhibit low resistivity of ρ<270 μΩ cm and small absorption ( k<2×10 −3) in the visible range. The homogeneity of sheet resistance on float glass substrates with dimension of 600×1000 mm 2 is better than ±6%. Film properties such as etching characteristics and haze can be controlled due to adjustment of total pressure and substrate temperature for large are a-Si:H thin film photovoltaic applications [1].

Obtaining TiO2 optical films by reactive ac magnetron sputtering

Obtaining TiO2 optical films by reactive ac magnetron sputtering

Optical and electrical properties of doped zinc oxide films prepared by ac reactive magnetron sputtering

Aluminum-doped and indium-doped zinc oxide films have been prepared by reactive ac magnetron sputtering (twin-cathode arrangement with ac plasma excitation at frequency of 40 kHz) from metallic targets with different dopant concentrations at substrate temperature of about 573 K. The optical, electrical and structural properties of the sputtered ZnO:Al and ZnO:In thin films have been investigated by optical spectroscopy (UV-IR), X-ray diffraction, Hall-mobility and conductivity measurements. For aluminum-doped ZnO films a minimum resistivity of 4.0 × 10 −4 Ω cm at high transparency (larger than 89% at film thickness of 530 nm) has been obtained at Al concentration in the target material of 1.2 wt%. Higher resistivity of 8.7 × 10 −4 Ω cm (85% transmission at film thickness of 400 nm) has been observed for indium-doped zinc oxide films at dopant concentration of about 2 wt% In in the target material.

Equivalent circuit model for large-area ac magnetron sputtering of dielectrics

Some important circuit considerations for ac reactive magnetron sputtering of dielectrics are addressed. We start with a simplified circuit model of a discharge appropriate to the ultrasonic frequency range. The model predicts that a power supply with sufficient secondary leakage inductance acts as a constant current source. The model accurately represents the wave form of the current observed in practice. A large spike observed on the rising edge of the voltage waveform is not predicted by the model. Results are presented for reactive sputtering of silicon-dioxide thin films from cylindrical silicon targets employing a dual magnetron rotatable cathode powered with an ac power supply operating at about 30 kHz. Single layer SiO 2 films produced over a period of more than 150 h. The lateral film thickness variation was less than ±3% and refractive index stability was ±0.004 at 545 nm. Samples coated after 150 h of continuous cathode operation exhibited small densities of arc-related film inclusions.