Arrival Rate Ratio Research Articles

The effect of bias power on some properties of titanium and titanium oxide films prepared by r.f. magnetron sputtering

Titanium and titanium oxide thin films have been deposited on (100) silicon wafers and glass substrates by r.f. reactive sputtering magnetron. Substrates have been r.f. biased during the growth of the film and the influence of the bias power on some properties of the coatings has been investigated. The results of the deposition rate measurements show that this is weakly affected when bias power is low. As the r.f. bias power increases, the deposition rate decreases strongly due to an increase of the layer density and resputtering phenomena. Atomic force microscopy showed that the surface morphology of metallic and oxide films can be modified using bias treatment. Roughness analyses exhibited a similar evolution as the deposition rate and surface topography when bias power changes. Optical properties like refractive index followed the same variations as previous results. So, when r.f. bias power increases, various phenomena take place and different zones can be defined from these investigations. Argon ion to atom arrival rate ratio and average energy per deposited atom have been calculated from experimental values of current density applied to the substrate and energy of argon ions impinging on the growing film. Their evaluations have been discussed for metallic and oxide materials.

Nanoindentation hardness, abrasive wear, and microstructure of TiN/NbN polycrystalline nanostructured multilayer films grown by reactive magnetron sputtering

TiN, NbN, and TiN/NbN polycrystalline nanostructured multilayer films were deposited on high-speed steel substrates by unbalanced reactive magnetron sputtering of Ti and Nb targets in Ar–N2 discharges. Two techniques were used for obtaining a series of multilayers with compositional modulation period, Λ, in the range 3.8–100 nm; rotation of a cylindrical substrate holder between two opposing cathodes or by positioning inclined cathodes above the substrate and using shutters. For the two setups, ions were accelerated from the discharge by a negative substrate bias Vs=120–150 V and Vs=100 V, respectively, with an ion-to-metal arrival rate ratio of ∼1. The nanoindentation hardness and abrasive wear resistance by dimple grinding test of the coatings were compared between the sample series and related to the microstructure, phase composition, and residual stress σres obtained by transmission electron microscopy, x-ray diffraction, and substrate curvature technique, respectively. All films exhibited a dense and columnar microstructure with 20–90 nm grain sizes. Nanoindentation test of the high-Vs series showed similar hardness for TiN/NbN nanostructured multilayers and homogeneous films in the range of 32–34 GPa. For the low-Vs series, mixed-phase hexagonal β-Nb2N/cubic δ-NbN films exhibited the highest hardness of 39 GPa, TiN had the lowest hardness with 26 GPa, and TiN/NbN multilayers had values in between. The absence of superlattice hardening in the polycrystalline TiN/NbN nanostructured multilayer is suggested to be due to microcracking at grain boundaries under the indentor tip. For both series, σres was lower for the multilayers than the corresponding homogeneous films. The low-Vs multilayers exhibited σres⩽1.6 GPa for Λ⩽16.6 nm, more than a factor of 2 smaller than for homogeneous TiN, NbN, and TiNbN-alloy films. High-Vs multilayers had σres∼4 GPa. The abrasive wear resistance of films between sample series showed a negative correlation with grain size. Films of the high-Vs series exhibited higher wear resistance compared to the corresponding films of the low-Vs series. Wear constants of high-Vs β-Nb2N films and TiN/NbN multilayers were as low as 28 and 40 μm3 mm−1 N−1, respectively.

Measurement of the niobium/sapphire interface toughness via delamination

Niobium films were deposited on sapphire substrates using both physical vapor deposition (PVD) and ion beam assisted deposition (IBAD) at an ion energy of 1000 eV and an ion-to-atom arrival rate ratio of 0.4. The interface between the niobium film and the sapphire substrate was doped with up to 7.6 monolayers of silver. The films were patterned into fine lines using photolithography. During the photolithography process curling and buckling were observed. The curling indicated a stress gradient in which the top of the film is tensile with respect to the bottom of the film, while buckling demonstrated that a portion of the film thickness must have been in compression. An analysis of the delamination showed that the critical energy release rate for the interface was on the order of 1 J/m 2, and that the compressive stress is of the order 1 GPa. The higher energy release rate of the IBAD samples confirmed that the stronger interface is due either to the orientation relationship between the ion beam textured niobium film and the (0001) sapphire surface or the interface mixing caused by ion bombardment.

Structural characteristics and hardness of zirconium carbide films prepared by tri-ion beam-assisted deposition

Zirconium carbide (ZrC) films were prepared by using two Ar+ beams to sputter a zirconium target and a graphite target separately, and a third Ar+ beam to simultaneously bombard the growing film. The effects of the arrival rate ratio of zirconium to carbon (Zr/C) and the bombarding Ar+ energies of 0.1–15 keV on the formation, structure and properties of the films were investigated. It was found that although the Zr/C atomic ratio could be varied within a range of 0.45–1.26 without inhibiting the formation of crystalline ZrC, the increase of Zr/C will reduce the hardness and enhance the (220) orientation of ZrC films. The energy of bombarding Ar+ ions substantially influenced the crystallographic orientation and morphology of the deposited films. The experimental results disclosed that the ZrC films prepared by 800–1000 eV Ar+-assisted bombardment with a Zr/C ratio of 0.78–0.97 have a fine and compact structure, and hardness as high as 2800–3150 kgf mm−2.

Ion beam assisted deposition of AlN monolithic films and Al/AlN multilayers: a comparative study

Monolithic AlN films and Al/AlN multilayers with periodic thickness ranging from 6 to 24 nm were synthesized by ion beam assisted deposition (IBAD) from electron beam evaporated aluminum and a nitrogen ion beam. During deposition of the multilayers, the nitrogen ion beam was alternately switched on and off, corresponding to AlN and Al sublayer deposition periods, respectively. A comparative study, with respect to microstructure and mechanical properties, was conducted both between the monolithic AlN films prepared with varied IBAD process parameters, and between the Al/AlN multilayers and their constituent monolithic AlN films. Two fundamental IBAD parameters of ion energy (100–500 eV) and ion-to-atom arrival rate ratio (1.45–3.60) were found to play important roles in the properties of the monolithic AlN films. Some contradictions in this respect appearing in the literature are discussed. When comparing the Al/AlN multilayers with their constituting monolithic AlN films, a substantial improvement of the mechanical properties has been observed only at low ion energies and ion-to-atom arrival rate ratios. Possible reasons are discussed.

Modeling of the deposition of stoichiometric Al2O3 using nonarcing direct current magnetron sputtering

dc sputter deposition of stoichiometric Al2O3 is usually difficult due to the formation of an oxidized layer on the target surface, which reduces the deposition rate drastically and causes charge buildup and arcing at the target. To avoid this situation the arrival rate ratio O2/Al must be high enough at the substrate position that a stoichiometric film can form but low enough at the target that a conducting target surface is maintained. We have utilized Monte Carlo simulations to estimate the flux distribution of sputtered particles for different geometries. These results, supplemented by Bergs’ standard steady state model for the reactive sputtering process, made it possible to predict the composition at different surfaces in the processing chamber. Experimental studies were carried out for several different target-to-substrate distances and a range of sputtering gas pressures. The results show that the process can be tailored to achieve stoichiometric Al2O3 at the substrates while keeping the target in the metallic state. This is achieved by providing a high enough inert gas pressure or large enough target-to-substrate distance. Thick stoichiometric Al2O3 films were successfully deposited at these conditions with low or no arcing during deposition. A considerable back-deposition of Al on to the noneroded part of the target keeping the surfaces conducting is the key factor for the reduction of arcing.

High rate reactive dc magnetron sputter deposition of Al2O3 films

Aluminum oxide films were produced by reactive dc magnetron sputtering of Al in Ar+O2. The composition of the films was characterized by Rutherford backscattering measurements. Stoichiometric films possessed excellent optical properties with a refractive index of ∼1.6 for visible and near-infrared light. It was possible to produce stoichiometric films while keeping the target in the metallic mode of operation; the resulting deposition rate was 23 nm min−1, as compared to 0.95 nm min−1 for films grown from an oxidized target. An O/Al arrival rate ratio exceeding ∼17 was required for stoichiometric films to be grown at room temperature. The success of the present high-rate deposition strategy hinges on the use of a suitable deposition system geometry — including a large target-to-substrate distance and a small target size — and on the use of sufficient Ar pressure. Monte Carlo simulations are presented; they can be reconciled with our empirical data.

Modeling of the deposition of stoichiometric Al2O3 using non-arcing dc magnetron sputtering

dc sputter deposition of stoichiometric Al2O3 is usually difficult due to the formation of an oxidized layer on the target surface, which reduces the deposition rate drastically and causes charge buildup and arcing at the target. To avoid this situation the arrival rate ratio O2/Al must be high enough at the substrate position that a stoichiometric film can form but low enough at the target that a conducting target surface is maintained. We have utilized Monte Carlo simulations to estimate the flux distribution of sputtered particles for different geometries. These results, supplemented by Bergs’ standard steady state model for the reactive sputtering process, made it possible to predict the composition at different surfaces in the processing chamber. Experimental studies were carried out for several different target-to-substrate distances and a range of sputtering gas pressures. The results show that the process can be tailored to achieve stoichiometric Al2O3 at the substrates while keeping the target in the metallic state. This is achieved by providing a high enough inert gas pressure or large enough target-to-substrate distance. Thick stoichiometric Al2O3films were successfully deposited at these conditions with low or no arcing during deposition. A considerable back-deposition of Al on to the noneroded part of the target keeping the surfaces conducting is the key factor for the reduction of arcing. (Less)

Design and analysis of a replicated server architecture for supporting IP-host mobility

Mobility support in IP networks requires servers to forward packets to mobile hosts and to maintain information pertaining to a mobile host’s location in the network. In the mobile Internet Protocol (mobile-IP), location and packet forwarding functions are provided by servers referred to as home agents. These home agents may become the bottleneck when there are a large number of mobile hosts in the network. In this paper, we consider the design and analysis of a replicated server architecture in which multiple home agents are used to provide mobility support. In order to minimize the delay across the home agents, one of the key aspects is the design of load balancing schemes in which a home agent may transfer the control of a mobile host to another home agent in the same network. The methods for triggering the transfer and the policy for selecting the next home agent define various load balancing schemes which have different performance characteristics. In this paper, we design a protocol that forms the building block for implementing such load balancing schemes, and we then study the performance characteristics of three selection schemes, namely, random, round-robin, and join the shortest queue (JSQ), and three transfers policies, namely, timer-, counter- and threshold-based. The key results of this study are as follows: (1) The results show that both random and round-robin selection policies can yield modest load balancing gains, and that these gains increase when the traffic is more bursty (burstiness is defined as the ratio of the peak arrival rate to the mean arrival rate) as well as when there are more home agents. (2) The threshold-based transfer policy performs better than timer-based and counter-based policies, since in threshold-based policies transfers are made only when the queue is overloaded, unlike counter- and timer-based policies in which transfers can be made from an unloaded home agent to an overloaded home agent.

Nickel metallization of Si by dynamic ion-beam mixing

Thin Ni films were prepared at room temperature by Ni metal vapor deposition on Si substrates and simultaneous irradiation by Ar ions with an energy of 2–20 keV. The reaction of Ni and Si during dynamic ion-beam mixing was studied. The fluences of the ion beam were 4.7 × 1017 and 8.9 × 1017 cm−2, and arrival rate ratios Ni/Ar were 9.7 and 5.1. Concentration profiles of Ni, Si, Ar, C, and O were analyzed with Auger electron spectroscopy; the surface morphology and the crystalline structure were investigated with a cross-sectional scanning electron microscope and X-ray diffractometry. The theoretical profiles were calculated with the dynamic Monte-Carlo simulation code T-DYN for comparison with the experimentally obtained profiles. It was possible to observe the ballistic mixing effects and also thermally activated formation of nickel silicide.

Nickel metallisation of Si by dynamic ion-beam mixing

Thin Ni films were prepared at room temperature by Ni metal vapour deposition and simultaneous irradiation by Ar ions with an energy of 2–20 keV. The reaction of Ni with Si during dynamic ion-beam mixing was studied. The fluences of the ion beam were 4.7 × 1017 and 8.9 × 1017 cm−2, and arrival rate ratios Ni/Ar were 9.7 and 5.1. Concentration profiles of Ni, Si, C, and O were analysed with Auger electron spectroscopy; the surface morphology and the crystalline structure were investigated with a cross-sectional scanning electron microscope and X-ray diffractometry. The theoretical profiles were calculated with the dynamic Monte Carlo simulation T-DYN for comparison with the experimentally obtained profiles. It was possible to observe the ballistic mixing effects and also thermally activated formation of nickel silicide.

An experimental comparison of capacity rationing models

In this paper, we evaluate two approaches to capacity rationing to manage demand in make-to-order manufacturing firms that face seasonal demand in excess of installed capacity. We assume that the firms produce two classes of products, one having a higher profit contribution per unit of capacity than the other. In the first approach, capacity is reserved for the higher profit class in a dynamic fashion using an expected value analysis each time an order is received for the lower profit class. In the second approach, the amount of capacity reserved for the higher profit class is set at the beginning of the planning horizon and never changed. The two approaches are evaluated relative to the case with no capacity rationing (i.e. orders are accepted as they arrive as long as capacity is available) for a wide array of experimental situations by varying the ratio of unit profit contributions for the two product classes, the ratio of total available capacity to total expected demand, the ratio of order arrival rates and order sizes for the two classes, and variability in demand for each class. The results show that both rationing models produce significantly higher levels of profit than the model with no capacity rationing.

Effect of ion bombardment on in-plane texture, surface morphology, and microstructure of vapor deposited Nb thin films

Niobium films were deposited by physical vapor deposition (PVD) and ion-beam-assisted deposition (IBAD) using ion energies of 0, 250, 500 and 1000 eV, and R ratios (ion-to-atom arrival rate ratio) of 0, 0.1, and 0.4 on (100) silicon, amorphous glass, and (0001) sapphire substrates of thickness 50–1000 nm. Besides a {110} fiber texture, an in-plane texture was created by orienting the ion beam with respect to the substrate. The in-plane texture as measured by the degree of orientation was strongly dependent on both ion-beam energy and the R ratio. In fact, the degree of orientation in the films followed a linear relationship with the energy per deposited atom, En. The grain structure was columnar and the column width increased with normalized energy. The surface morphology depended on both the normalized energy of the ion beam and the film thickness. All films had domelike surface features that were oriented along the ion-beam incident direction. The dimension of these features increased with normalized energy and film thickness. Surface roughness also increased with normalized energy and film thickness, with the root-mean-square roughness increasing from 1.6 nm for the PVD sample (100 nm thick) to 36.7 nm for the IBAD film (1000 eV, R=0.4, 800 nm thick). Both the surface morphology evolution and in-plane texture development in these films were the result of the different ion sputter rates among differently oriented grains.

Microstructure and mechanical properties of IBAD niobium films on sapphire substrates

The effect of ion bombardment during film deposition on the microstructure, surface morphology, residual stress, hardness and interfacial fracture energy was determined for Nb films on sapphire substrates. In the present study, niobium films of nominal thickness 100 nm were deposited on (0001) sapphire substrates by Physical Vapor Deposition (PVD) and by Ion Beam Assisted Deposition (IBAD) at an ion energy E = 1000 eV and an ion-to-atom arrival rate ratio R = 0.4. The microstructures of the PVD and IBAD films were very similar, but the IBAD film had a much rougher surface. Ion bombardment also changed the residual stress state from tensile (224 MPa) for the PVD film to compressive (−400 MPa) for the IBAD film. The IBAD film had a lower hardness (5.7 GPa) than the PVD film (10.9 GPa) as determined by nanoindentation. An attempt was made to measure the fracture energy of both the PVD niobium-sapphire and IBAD niobium-sapphire interfaces by scratch test and nanoindentation. The PVD sample failed in a brittle manner in both tests and interfacial fracture energies were able to be estimated. By contrast, the IBAD sample failed in a ductile manner in both tests, precluding the determination of the interfacial fracture energy.

Effects of Ar bombardment on magnetic properties of Fe films deposited by double-ion-beam sputtering

The microstructure and magnetic properties of polycrystalline Fe films have been investigated in detail by controlling the condition of ion-beam sputtering with an Ar bombardment with a constant ratio of arrival rate of Fe to Ar. To control the Fe crystallite size, Fe films have been deposited at an Ar bombardment voltage VA in the range of 80–2000 V with the condition that the ratios of the arrival rate RA (atoms of Fe/atoms of Ar) were 1 to 1 (RA of 1) and 1 to 0.1 (RA of 0.1). Fe films with excellent soft magnetic characteristics for 4πMs of about 21.5 kG and HC of 2.5 Oe were deposited on the substrate bombarded by Ar ions with VA of 200 V at Rs of 1 and 400 V at RA of 0.1. The Ar bombardment had the two effects of raising the local temperature of the film surface and decreasing the Fe crystallite size. The orientation of crystals in the films may be related to the bombardment energy and amount of Ar ions. The high-energy bombardment formed a mixing layer between the deposited film and the surface of the substrate. These results imply that Ar bombardment by the proper energy and amount of Ar ions assists in improving the soft magnetic properties in the films.

Structures and properties of copper thin films prepared by ion beam assisted deposition

Copper thin films were prepared by ion beam assisted deposition (IBAD) technique, to perform a systematic investigation on the effect of ion bombardment with respect to the structural modification and the electrical properties of the films. The films were deposited under the argon ion bombardment with energies between 75 and 675 eV. The atomic density of the films deposited on Si substrates strongly depeded on the deposition rate rather than the energy or the current on beams. Under the same deposition rate, the atomic density gradually decreased with an increase of the ion energy. As for the films on SiO 2 substrates, however, the atomic densities were improved with increasing the arrival rate ratio and the ion energy. X-ray diffraction analysis showed that the film structures were modified to have (111) preferred orientation and the films had larger vertical grain sizes with increasing the arrival rate ratio and the ion energy. These modifications were also most significant for the films deposited on SiO 2 substrates. Electrical resistivity strongly depended on the argon concentration in the films, while less depended on the crystallinity. The increase of the electrical resistivity for the films on Si substrates was larger than those on SiO 2 substrates. It was suggested that the lateral grain size, which dominates the electrical resistivity, reduced with an increase of the arrival rate ratio and the ion energy. The results could be summarized as the structure of the films prepared by IBAD technique became columnar and the electrical resistivity had a strong correlation with the argon concentration.

Low-temperature deposition of cubic BN:C films by unbalanced direct current magnetron sputtering of a B4C target

Controllable-unbalanced dc magnetron sputtering of a B4C target in mixed Ar–N2 discharges has been used to deposit BN:C thin films with carbon concentrations in the range of 5–21 at. % on Si(001) substrates. The variation of the nitrogen gas consumption with nitrogen partial pressure was used to determine the sorption capacity of the sputtering source and was then correlated to the film elemental composition. An additional axially symmetric magnetic field was used to vary the discharge plasma density near the substrate in a wide range. Hence, the ion flux Ji of primary Ar+ and N+2 ions accelerated to the substrate by an applied negative substrate bias could be varied while keeping the deposition flux Jn (the sum of film building species, B, C, and N atoms) near constant. BN:C films were grown at large ion-to-neutral flux ratios 3≤Ji/Jn≤24, ion energies Ei≤500 eV, and substrate temperatures 150≤Ts≤350 °C. The phase and elemental composition of as-deposited BN:C films were characterized by Fourier transform infrared spectroscopy and wavelength dispersive x-ray spectroscopy, respectively. Deposition of cubic phase c-BN:C containing 5–7 at. % of C is demonstrated under conditions of low energy (110 eV) ion bombardment, a high ion-to-atom arrival rate ratio (Ji/Jn∼24), and low growth temperatures (∼150 °C).

Effects of ion energy and arrival rate on the composition of zirconium oxide films prepared by ion-beam assisted deposition

Thin zirconium oxide films were grown using the ion-beam assisted deposition method. Zirconium metal was evaporated by an electron beam and condensed on a Si substrate, while oxygen ions were directed simultaneously onto the substrate, allowing the fundamental deposition parameters of ion energy and arrival rate ratio ARR(O/Zr) to be measured and controlled easily. X-ray photoelectron spectroscopy (XPS) was used to study the oxidation and the composition of the films. XPS analyses indicated the presence of four oxidation states of zirconium (Zr4+−Zr1+) in Zr 3d spectra and two peaks in O 1s spectra; Zr4+ is a predominant ion in all the films and the two peaks in O 1s spectra are related to the oxide and to hydroxyl groups and/or carbonates, respectively. Composition analyses of the films suggested that these oxygen-associated species may be bound to zirconium. The variation of composition as a function of ion energy (from 2 to 20 keV) and ARR(O/Zr) (at 0.54 and 1.09) could be explained with the preferential sputtering of zirconium from the growing film by incoming oxygen ions and the incorporation of oxygen ions into the film.

Surface Morphology of Nb Films by Ion Beam Assisted Deposition

AbstractNiobium films of thickness 50 nm to 1000 nm were deposited by ion beam assisted deposition (IBAD) using ion energies of 0, 500 and 1000 eV, and R ratios (ion-to-atom arrival rate ratio) of 0, 0.1, and 0.4 on (100) silicon and (0001) sapphire substrates. The films have columnar structures and the column width increases with normalized energy (En = E × R). The surface morphology depends on both the normalized energy of the ion beam, En, and the film thickness. All films have dome-like surface features that are oriented along the ion beam incident direction. The dimension of these features increases with normalized energy and film thickness. Surface roughness also increases with normalized energy and film thickness, with the root mean square (rms) roughness increasing from 1.6 nm for the PVD sample (100 nm thick) to 36.7 nm for the IBAD film (1000 eV, R = 0.4, 800 nm thick). The surface morphology of IBAD films is the result of a combination of channeling and shadowing effects.

Synthesis and Mechanical Properties of Niobium Films by Ion Beam Assisted Deposition

AbstractMechanical properties of niobium thin films are studied by controlling the microstructure, texture and residual stress of the films using ion beam assisted deposition (IBAD). Niobium films were deposited onto (100) Si substrates and their microstructure, texture and residual stress were measured as a function of ion energy and R ratio (ion to atom arrival rate ratio). The grain sizes of these films ranged from 20 nm to 40 nm and no effect of ion bombardment was observed. All the films have strong (110) fiber texture, but the in-plane texture is a strong function of the incident angle, energy and flux of the ion beam. Results show that while the degree of the texture increases with increasing ion energy and flux, it is also a strong linear function of the product of the two. The residual stress of the films was measured by a scanninglaser reflection technique. As a function of normalized energy, the stress is tensile for En < 30 eV/atom with a maximum of 400 MPa at about 15 eV/atom. It becomes compressive with increasing normalized energy and saturates at - 400 MPa for En > 50 eV/atom. Both PVD (physical vapor deposition) and IBAD films have a hardness of about 6 GPa at shallow depth measured by nanoindentation. The different stress state may be responsible for the 15%difference on hardness observed between the PVD and IBAD films.