Aluminum Sputtering Research Articles

Advanced process control of metal sputter deposition using a time series analysis

Using a time series model, we constructed a disturbance model for the aluminum sputter deposition process, and derived an autoregressive integrated moving average and recursive least-squares (ARIMA-RLS) controller based on this new disturbance model. Experimental results revealed that the ARI(3,1) model appropriately characterized the dynamic behavior of the disturbance for this process. The ARIMA-RLS controller, which includes information on process noise, is able to automatically regulate the model coefficients as the target is replaced or degrades. In this paper, the d-EWMA controller, the age-based d-EWMA controller, and the ARIMA-RLS controller were applied to aluminum sputter deposition processes in order to predict deposition rates and compare their performances. Application of the ARIMA-RLS controller is proven herein to significantly improve the estimation accuracy of the aluminum sputter deposition process, regardless of whether or not deposition rates are measured for each run.

Characteristics of low K thin film microstrip line on standard lossy silicon substrate for radio frequency integrated circuits

AbstractIn this paper, effective dielectric constant, line attenuation, and characteristic impedance of thin film microstrip line (TFML) on polyimide dielectric as interconnection for radio frequency integrated circuits is investigated. The TFML is fabricated on low cost low resistivity silicon substrate (ρ≤10 Ω cm) by incorporating a spin‐on dielectric polyimide and sputtering of aluminum. An accurate on‐wafer‐procedure for extracting the microwave characteristics of TFML up to 50 GHz is described and the method is successfully applied to low‐K polyimide deposited on the silicon. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 79–83, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22052

Hysteresis behavior during reactive magnetron sputtering of Al2O3 using a rotating cylindrical magnetron

Rotating cylindrical magnetrons are used intensively on industrial scale. A rotating cylindrical magnetron on laboratory scale makes it possible to study this deposition technique in detail and under well controlled conditions. Therefore, a small scale rotating cylindrical magnetron was designed and used to study the influence of the rotation speed on the hysteresis behavior during reactive magnetron sputtering of aluminum in Ar∕O2 in dc mode. This study reveals that the hysteresis shifts towards lower oxygen flows when the rotation speed of the target is increased, i.e., target poisoning occurs more readily when the rotation speed is increased. The shift is more pronounced for the lower branch of the hysteresis loop than for the upper branch of the hysteresis. This behavior can be understood qualitatively. The results also show that the oxidation mechanism inside the race track is different from the oxidation mechanism outside the race track. Indeed, outside the race track the oxidation mechanism is only defined by chemisorption while inside the race track reactive ion implantation will also influence the oxidation mechanism.

Effects of Substrate Temperature and Argon Gas Pressure on the Properties of dc Magnetron Sputtered Aluminum Doped Zinc Oxide

not Available.

Developing an analytic methodology to accurately predict probing depth in integrated circuit structures

This work designs an analytic methodology for applying the probe-before-bump procedure to predict probing depth and proposes feasible probing design parameters to avoid excessive probing of the bump pad. Two kinds of multi-level wafers were used to implement the probing experiment, with a single touch down, and an overdrive of 70 µm, 100 µm, 130 µm, and 150 µm by using a vertical probe card. The Young’s modulus and hardness of the two multilevel structures are measured on which the first bump pads are produced by sputtering aluminum onto the SiO2, while the second bump pads are produced by sputtering aluminum onto the copper, creating a pad metal of approximately 1-µm thickness by using the nanoindenter. The test results indicate that the Young’s modulus of the thin film material exceeds that of bulk material by 20–30 GPa. The difference between analytic and experimental probing depth ranges from 2.3% to 8.9%, revealing that the proposed novel analytic model is extremely accurate. Engineers or researchers can use the analytic methodology to accurately predict probing depth and acquire probing parameters that are accurate, cost effective, and efficient, thus eliminating the need to use focused ion beam (FIB) or other measurement instruments to determine the probing depth.

Mechanisms for the enhancement of the thermal stability of organic thin films by aluminum oxide capping layers

We present a detailed study of the thermal stability of organic thin films of diindenoperylene encapsulated by sputtered aluminum oxide layers. We studied the influence of capping layer thickness, stoichiometry, and heating rate on the thermal stability of capped films and their eventual breakdown. Under optimized encapsulation conditions (thick and stoichiometric capping layer), the organic films desorb only at temperatures 200 °C above the desorption of the uncapped film. Moreover, the capped organic films retain their crystalline order at these elevated temperatures, whereas they would normally (i.e., uncapped) be in the gas phase. This study therefore also shows a way of studying organic materials under temperature conditions normally inaccessible. Considering results from complementary techniques, we discuss possible scenarios for the eventual breakdown. The results have implications for the performance and long-term stability of organic devices for which stability against elevated temperatures as well as against exposure to ambient gases is crucial.

Crystal growth and superhardness effects of ZrN/AlON nanomultilayers synthesized by reactive magnetron sputtering

Two series of ZrN/AlON nanomultilayers were synthesized by reactively sputtering zirconium and aluminum oxide targets in the gaseous mixture of argon and nitrogen. The thickness of ZrN layers was fixed in one of the series and the thickness of AlON layers in the other. The composition, microstructure and mechanical properties of films were characterized by X-ray energy dispersive spectroscopy, X-ray diffraction, high resolution transmission electron microscopy and nanoindentation. The investigation results indicate that during the process of Al2O3 target sputtering in the mixed atmosphere, part of oxygen atoms in Al2O3 were replaced by nitrogen atoms, leading to the formation of aluminum oxynitride, AlON. Under the influence of the “template effects” of ZrN layers, the AlON layers that used to exist as amorphous under sputtering conditions were forced to crystallize and grew epitaxially with the ZrN layers when the thickness of AlON was limited to less than 0.9 nm. Correspondingly, the hardness of multilayers was remarkably enhanced to its maximum value of 33.0GPa. A further increase in the thickness of AlON layers led to the crystalline AlON layers transforming into amorphous. The epitaxial growth of multilayers was blocked, accompanied by the decline of hardness.

Structure of superhard nanocrystalline (Ti,Al)N layers deposited by reactive pulsed magnetron sputtering

Stoichiometric Ti 1 − x Al x N layers with 0.55 < x < 0.57 have been deposited by adjusting working point and pulse times for reactive pulsed magnetron sputtering of aluminum and titanium target. By variation of the substrate bias voltage between floating potential and 100 V, the hardness of the layers is drastically raised up to 38 GPa. The aim of the present work is the identification of structural reasons for the achievement of these very high hardness values. XRD investigations with grazing angle of incidence have revealed that the layers consist of two phases with predominantly cubic rock salt and minor amounts of hexagonal wurtzite structure, respectively. The structure of the layer with the maximum hardness has been additionally investigated by cross-section TEM. It can be shown that the microstructure consists of repeatedly interrupted columns with a lateral size of about 25 nm. Within these columns, globulitic nanocrystallites with a grain size between 6 and 12 nm are present. In addition the TEM investigations have revealed that the layer is composed of alternating aluminum rich and titanium rich layers with a period of about 2.9 nm. It is concluded that the maximum hardness values are mainly caused by the presence of this defined superlattice structure, which hinders the formation and movement of dislocations. By GD-OES depth profiling of the chemical composition it can be shown that the layers possess a good oxidation, by the formation of a thin aluminum oxide passivation layer.

Vertically Aligned Nanopillar Arrays with Hard Skins Using Anodic Aluminum Oxide for Nano Imprint Lithography

Master molds with nano-pillar structures were fabricated by using anodic aluminum oxide (AAO) for nano-imprint lithography (NIL). The proposed method consists of (1) AAO fabrication, (2) transfer of the thin AAO layer onto a substrate, (3) aluminum sputtering, (4) aluminum melting, and (5) removal of the thin AAO layer. Since the sputtered aluminum penetrated into the porous alumina walls of the AAO template during the melting step, the pillars had skin layers of aluminum/alumina composite which added additional mechanical strength and chemical resistance. The diameter of a pillar in the nano-pillar master mold was larger than that of the hole diameter of the original AAO template because of the hard skin of aluminum/alumina composite layer which covers the pillar surface. The pillar structure could be used as a mold for NIL, resulting in a regular pore array on a polymer film.

Deposition of Ni–Al–Y alloy films using a hybrid arc ion plating and magnetron sputtering system

The rare-earth ternary additions to Ni–Al alloys can improve their mechanical and thermal properties as well as their operation in more extreme environmental conditions. In this study, Ni–Al–Y films are deposited using a hybrid system consisting of a NiAl arc source and an yttrium magnetron sputtering source. The effects of substrate bias on the crystal structure and composition of the Ni–Al–Y films are studied. The sputtering of the yttrium target is enhanced by ions emitted from the NiAl arc source in the experimental arrangement. The decrease in yttrium concentration from the sputtering target is found to be far more pronounced when the substrates are biased at − 100 V than grounded. The increased energy of the ions bombarding the higher biased substrates is considered to enhance the sputtering of yttrium and aluminum and thereby decrease their concentration in the films. As well as sputtering effects, the reduced aluminum concentration in the deposited films, compared to that of the source material, is attributed to the incident angle of arc-emitted aluminum species as well as their scattering by heavier vapor species. It is found that the B2 structure is stabilized by doping a small amount of yttrium into nickel-rich Ni–Al films. Moreover, the addition of yttrium enhances nucleation of Al 2O 3 growth during the high temperature oxidation tests.

Sputtering-induced nanometre hole formation in Ni3Al under intense electron beam irradiation

The irradiation damage of polycrystalline Ni3Al thin foils of stoichiometric composition by a stationary nanoscale 200 keV field emission gun (FEG) electron probe in a FEI Tecnai F20 (S)TEM has been investigated. At current densities greater than 107 A/m2, nanometre holes are produced quickly with both ⟨001⟩ and ⟨110⟩ incident electron beam directions. EDX spectra from the irradiated volume have been collected simultaneously during the hole forming process. From the EDX results, preferential surface sputtering of aluminium from Ni3Al has been demonstrated. To understand the underlying physical process of sputtering, modelling based on a combination of molecular dynamics and Monte Carlo simulation has been performed. It appears to reproduce faithfully the overall film sputtering and hole formation processes, but is not capable of predicting the detailed geometry of the hole. It predicts that the sputtering cross-section of Al atoms is much higher than that of Ni atoms, resulting in a very small concentration of Al at the surface. This, together with the increase of surface area during hole formation, explains the preferential Al loss observed from the specimen. Calculated sputtering rates agree well with experiment, and are of the order of magnitude of 10−8 atoms/electron.

Intermetallic products formed by joint cold cathode vacuum arc sputtering of titanium and aluminium

Abstract The results of investigation of coatings formed by means of dual cold cathode vacuum arc sputtering are presented. In cathode sputtering, using a plasma accelerator one usually try to diminish the liquid drops fraction in the accelerated plasma. Here deposited species include droplets, vapour and ions. Products of Ti and Al sputtering on cold and hot copper alloy and steel substrates have been investigated. The deposited layers have been characterised by X-ray diffraction and the morphology of surfaces has been studied by optical metallography. Characteristics of layers formed by participation of quenched droplets versus “pure” ion sputtering have been compared. Feasibility of vacuum arc plasma accelerator to form nanocrystalline and amorphous coatings is discussed. Layers consisting of Ti, Al, intermetallics TIAl3, TiAl2 and TiAl have been obtained.

Electrical properties of thin rf sputtered aluminum oxide films

Thin films of aluminum oxide (Al2O3) were fabricated by rf magnetron sputtering. Different sputter conditions, e.g., composition of the sputter gas (Ar:O2), sputter gas pressure, deposition rate, and preparation of the Al2O3 sputter target before deposition were investigated with the aim to achieve good insulating films with high electrical breakdown fields. The Al2O3 films had a thickness of 160nm and were deposited on ITO covered glass. By evaporation of Au electrodes on top of the Al2O3 films thin film capacitors were fabricated. Current voltage (I–V) measurements were performed under high vacuum and temperatures between 4 and 300K. Significant scattering of the I–V curves and “burn-in” effects are observed. We find that an admixture of 1% of O2 in the sputter gas improves the electrical properties, but higher breakdown fields and smaller leakage currents are obtained for sputtering in pure Ar, using a sputter target conditioned in an Ar:O2 mixture. Impedance spectra, revealed a dielectric constant of ∼7 for all Al2O3 films. Atomic force microscopy experiments reveal that the surfaces are rather rough with grain sizes in the order of 0.3–0.5μm.

Target poisoning during reactive magnetron sputtering: Part II: the influence of chemisorption and gettering

As generally accepted gettering of the reactive gas by the sputtered target material plays an important role for most reactive gas/target combinations. The influence of the gettering process and the chemisorption of reactive gas on the target have been modelled by Berg et al. (J. Vac. Sci. Technol. A 5(2) (1987) 202–207). However, in this model the effect of ion implantation was not included. Therefore, a model is proposed which takes ion implantation into account. The model is used to understand the target voltage behaviour during reactive sputtering of aluminium in an argon/oxygen mixture. At high pumping speed or low current, a target voltage increase is noticed before the critical point. This can be attributed to chemisorption of oxygen on the aluminium target. Chemisorption of oxygen reduces the erosion rate of the target, which enhances the poisoning of the aluminium target by reactive ion implantation. At low pumping speed or high current, i.e. when gettering dominates the reactive sputtering process, the effect of chemisorption on the target voltage is less pronounced due to the competition between reactive ion implantation and chemisorption.

The effect of ratio of deposition times and via density on via fill in aluminum multilayer metallization

The effect of sub micron device via density on via fills was studied. A two-step cold/hot aluminum sputtering process was used to evaluate the effect of via density and ratio of deposition times on via fills. As via density increases, via fill becomes more challenging with a two-step cold/hot aluminum sputtering process. The via fill percentage was increased by changing the ratio of cold/hot deposition times. Results show that denser via structures require extended cold deposition times to compensate for higher via density. For a successful via fill, a conformal nucleation layer of aluminum must be formed with cold deposition, which acts as a seed and wetting layer to promote aluminum reflow into vias during subsequent hot deposition. It was found that by changing the ratio of cold/hot deposition times from 60:40 to 79:21 on dense via structure, the via fill was improved by 30%.

The structure of co-deposited aluminium–titanium alloy coatings

Aluminium–titanium alloy coatings are attractive materials for a wide range of applications from aerospace and high performance engine applications to solar absorbers, depending on the alloy deposited and its corresponding properties. Consequently, a detailed study of the Al–Ti alloy system has been carried out, and the results to date are presented here. In this study, Al–Ti films have been prepared by physical vapour deposition using two planar unbalanced magnetrons in a closed field configuration, with a biased substrate. Pure aluminium and pure titanium sputtering targets were used for the co-deposition of coatings with compositions varying throughout the full binary range from pure aluminium to pure titanium. The coatings were deposited onto glass substrates. The deposited films were analysed by EDX, XRD and SEM processes in the as-deposited state and after high temperature annealing, to investigate changes in structure and phase composition. The as-deposited coatings contain only aluminium and titanium phases but after the annealing process, stable intermetallic phases are formed. Attempts have been made to relate these changes to specific process and geometrical factors within the deposition system. The tribological properties of these coatings were reported in a companion paper (The tribological properties of co-deposited aluminium–titanium alloy coatings, presented at ICMCTF 2003, San Diego, April 28th–May 2nd, 2003).

The structure of co-deposited aluminium–titanium alloy coatings

Aluminium–titanium alloy coatings are attractive materials for a wide range of applications from aerospace and high performance engine applications to solar absorbers, depending on the alloy deposited and its corresponding properties. Consequently, a detailed study of the Al–Ti alloy system has been carried out, and the results to date are presented here. In this study, Al–Ti films have been prepared by physical vapour deposition using two planar unbalanced magnetrons in a closed field configuration, with a biased substrate. Pure aluminium and pure titanium sputtering targets were used for the co-deposition of coatings with compositions varying throughout the full binary range from pure aluminium to pure titanium. The coatings were deposited onto glass substrates. The deposited films were analysed by EDX, XRD and SEM processes in the as-deposited state and after high temperature annealing, to investigate changes in structure and phase composition. The as-deposited coatings contain only aluminium and titanium phases but after the annealing process, stable intermetallic phases are formed. Attempts have been made to relate these changes to specific process and geometrical factors within the deposition system. The tribological properties of these coatings were reported in a companion paper (The tribological properties of co-deposited aluminium–titanium alloy coatings, presented at ICMCTF 2003, San Diego, April 28th–May 2nd, 2003).

Dynamic Monte Carlo simulation for reactive sputtering of aluminium

We have applied TRIDYN to simulate the transition from the metallic sputtering to the reactive sputtering mode during magnetron sputtering for an Al target when oxygen is added to argon plasma. Changes in the thickness and composition of multicomponent targets are investigated. The results basically confirm the reactive ion implantation mechanism together with chemical reaction in the subsurface. When oxygen mole fraction x<0.14, the target surface never becomes fully oxidized, even for very long sputtering times. When x>0.14 the target surface can be more or less fully oxidized. Furthermore, an abrupt change in the surface erosion rate at x=0.03 is observed. This corresponds to the avalanche phenomenon indicating the sputtering mode transition.

Preparation of Fe-Pt Nanowires through Anodic Oxidation of Sputtered Aluminum on Glass Surface

ABSTRACTNew process for the preparation of Fe-Pt nanowires has been developed through anodic oxidation and electro deposition technique. Aluminum thin film sputtered on ITO thin film on a glass surface was decomposed into alumina by anodic oxidation technique. The anodic alumina layer possessed nanometer size pore array standing on the glass surface. The barrier layer at the bottom of nanopores was removed by acid etching to attain DC field smooth electro deposition. Fe-Pt components were introduced into nanopores of anodic alumina by electro deposition. The magnetization of Fe-Pt nanowires was investigated. The magnetization perpendicular to the glass surface was very strong and the in-plane magnetization was very small, indicating that the magnetic Fe-Pt nanowires could be potentially applied to ultra high density magnetic recording. The density of the nanowires was estimated to be about 1T bits /inch2.

An Approach to Nanoglasses through Anodic Oxidation of Sputtered Aluminum on Glass Surface

ABSTRACTThe new processes for the preparation of nanoglasses have been developed through anodic oxidation. The aluminum thin film sputtered on the ITO thin film on the glass surface was decomposed into alumina by anodic oxidation technique. The alumina layer possessed nanometer size pore array standing on the glass surface. The sizes of the pore was widened by acid etching from 10∼20nm to a few hundred nm. The glass substrate having the alumina nanostructures on the surface could transmit the UV and visible light at the wavelength range of 200 ∼ 800nm. The TiO2 sol was impregnated into the pores of alumina layer and the sample was heated at ∼ 400 °C for 2 hr, converted into TiO2 nanotubes of anatase phase. The acid etching could remove the alumina skeletons, leaving the TiO2 nanotube array on the glass surface. These glasses were transparent to the light in UV-visible region. The electro deposition technique was applied to the introduction of Ni metal into pores, giving Ni nanorod array on the glass surface. The glass samples possessing TiO2 nanotube array showed very good catalytic function on the decomposition of acetaldehyde gas under the irradiation of UV light. The effect of the dimensions of the Ni nanorods on the magnetization was investigated.