Reactive Ion Implantation Research Articles

On the role of chemisorption in the formation of the target surface compound layer during reactive magnetron sputtering

Modeling of the reactive sputter processes requires a description of the target processes which results in the formation of a compound layer on the target. The sputter removal of the formed compound is balanced by compound formation mechanisms. Chemisorption of reactive gas atoms and molecules was initially identified as one of these processes. Further improvement of these chemisorption based models was achieved by the inclusion of processes such direct reactive ion implantation, knock-on implantation of chemisorbed species, and the redeposition of sputtered material on the target. In a recent study, the importance of ion implantation was questioned and an alternative model proposed. The results of this model are confronted with existing literature to investigate its validity.

Influence of chemisorption on the double hysteresis phenomenon during reactive sputtering

Process curves that are obtained during reactive magnetron sputtering can exhibit a double S-shape, also termed a double hysteresis. A previous study mainly focused on the relationship between the double shape behavior and the reaction kinetics of implanted reactive ions, although chemisorption also defines the target condition. As a follow-up study, the influence of chemisorption on double hysteresis is computationally studied by high-throughput calculations using a state-of-the-art model for reactive sputtering. The analysis reveals that the magnitude of the double hysteresis is a conserved quantity for the chemisorption driven reactions at the substrate level. At the target level, a balance between compound formation by direct reactive ion implantation and chemisorption is established. A minimal condition for double hysteresis is derived and process conditions are identified for which the double hysteresis can be measured for target materials prone to strong chemisorption of the reactive gas. The condition can assist to further explore the close interplay between chemisorption and implantation during reactive sputtering.

Properties of millisecond-scale modulated pulsed power magnetron discharge applied for reactive sputtering of zirconia

The electrical properties of a modulated pulsed power (MPP) magnetron discharge were experimentally and theoretically studied in case of reactive sputtering of metallic zirconium target in argon/oxygen mixtures. The high-power pulsing was assisted by pre-ionization provided by a low-power direct current (DC) magnetron discharge filling the pulse-off period. The ranges of stable discharge operation parameters (applied voltage and oxygen flow rate) were determined for pulse-on time of 3 ms and pulse-off time 100–1000 ms. The maximum stable peak power density was 2.1 kW cm−2. Strong dependence of the MPP discharge current waveforms on the pulse-off time was found, indicating the important role of the pre-ionizing DC discharge. In presence of oxygen, discharge peak current was observed with characteristic width up to 1.5 ms, followed by non-reactive-like plateau region. For theoretical treatment of the observed discharge current behavior, we modified the well-known Berg model of reactive sputtering by introducing the terms required for adequate description of time-dependent poisoning and sputtering processes. The reactive ion implantation term was also transformed to account for the process saturation at high ion current densities. Calculation results from the modified Berg model demonstrated good agreement between our experimental observations of discharge current evolution and target poisoning dynamics in the timescale of milliseconds.

Rotating cylindrical magnetron sputtering: Simulation of the reactive process

A rotating cylindrical magnetron consists of a cylindrical tube, functioning as the cathode, which rotates around a stationary magnet assembly. In stationary mode, the cylindrical magnetron behaves similar to a planar magnetron with respect to the influence of reactive gas addition to the plasma. However, the transition from metallic mode to poisoned mode and vice versa depends on the rotation speed. An existing model has been modified to simulate the influence of target rotation on the well known hysteresis behavior during reactive magnetron sputtering. The model shows that the existing poisoning mechanisms, i.e., chemisorption, direct reactive ion implantation and knock on implantation, are insufficient to describe the poisoning behavior of the rotating target. A better description of the process is only possible by including the deposition of sputtered material on the target.

Nano-patterning of perpendicular magnetic recording media by low-energy implantation of chemically reactive ions

Magnetic nano-patterning of perpendicular hard disk media with perpendicular anisotropy, but preserving disk surface planarity, is presented here. Reactive ion implantation is used to locally modify the chemical composition (hence the magnetization and magnetic anisotropy) of the Co/Pd multilayer in irradiated areas. The procedure involves low energy, chemically reactive ion irradiation through a resist mask. Among N, P and As ions, P are shown to be most adequate to obtain optimum bit density and topography flatness for industrial Co/Pd multilayer media. The effect of this ion contributes to isolate perpendicular bits by destroying both anisotropy and magnetic exchange in the irradiated areas. Low ion fluences are effective due to the stabilization of atomic displacement levels by the chemical effect of covalent impurities.

Studies on the structure and electrical characteristics of oxide layers synthesized by reactive ion implantation into tantalum

High purity (99.9%), 0.25 mm thick, tantalum samples were implanted with oxygen reactive ions ( 16O +) at 100 keV energy at fluence levels ranging from 1 × 10 16 to 5 × 10 17 ions-cm − 2 to synthesize tantalum oxide layers. The structure of the ion beam synthesized layers was analyzed by FTIR spectroscopy studies. The electrical characteristics were investigated on Al/ Tantalum oxide/Ta (MIM) structures by current–voltage (I–V) and capacitance/dielectric loss-frequency measurements. The FTIR studies show the formation of amorphous tantalum oxide layers of complex structures- tantalum pentaoxide (Ta 2O 5) and suboxides of tantalum depending on the implantation and post annealing conditions. The I–V studies show ohmic conduction for low voltages and space charge limited conduction (SCLC) at high voltages. The leakage current density of the samples was found to depend on the processing conditions. The electrical resistivity of the tantalum after oxygen implantation is found to increase with ion fluence. The capacitance of the MIM devices fabricated with ion beam synthesized tantalum oxide layers show small variation with frequency. In general, an enhancement in the capacitance and reduction in the dielectric loss were observed upon annealing on samples synthesized with low fluence level indicating gradual transformation into good dielectric layer.

Towards a more complete model for reactive magnetron sputtering

Using an analytical model, the effect of reactive ion implantation on the state of the target surface during magnetron sputtering is studied. To describe the substrate condition during reactive sputter deposition, the model uses the well-known Berg model approach. However, the target condition is modelled differently, i.e. besides chemisorption the model includes reactive ion implantation. To test this latter modification, the simulation results are compared with the results of oblique reactive ion beam experiments. The good agreement forms the basis of using the model for reactive magnetron sputtering. It is shown that the well-known hysteresis behaviour of the deposition parameters can be described. Although at first sight the model is comparable to other models, it is shown that the kinetics are clearly different. A good description of the kinetics during reactive magnetron sputtering is essential to model, for example, the reactive sputter process using a rotating cylindrical magnetron.

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.

Modeling of the target surface modification by reactive ion implantation during magnetron sputtering

The erosion rate of an aluminum target bombarded with Ar+ and O2+ ions was simulated using TRIDYN. An abrupt change of the erosion rate is noticed at a critical mole fraction of O2+ ions. This target behavior can also be described by a simple analytical model showing that the abrupt change finds its origin in an avalanche induced by reaction ion implantation. Indeed, by the reduction of the average sputter yield by compound formation, more reactive ions become implanted into the target as the number of implanted ions depends inversely on the average sputter yield. As such, an avalanche situation can develop which finally results in a completely oxidized target. It is also shown that the critical mole fraction depends linearly on the sputter yield of the target material and that target poisoning induced by ion implantation can result in a hysteresis behavior for the target condition.

Investigation of defects in reactive ion-implanted silicon

The reactive ion implantation in silicon at different fluence levels varying from 5 × 10 16 to 1 × 10 18 ions cm −2 was carried out at 30 keV to synthesize silicon dioxide (SiO 2), silicon nitride (Si 3N 4) and silicon oxynitride (Si x O y N z ) layers at room temperature. The electron spin resonance (ESR) measurements were performed on these samples to study the defects. The rapid thermal annealing (RTA) behaviour of defects in nitrogen ambient was also studied. The room temperature ESR studies show a defect center related to silicon dangling bonds at g∼2.0040–2.0051. This defect center almost disappears after RTA at 1073 K for 5 min. The spin density is found to depend strongly on the ion-fluence. The low temperature studies indicate the presence of an additional center associated with interface defects at g∼1.999 for low fluence implanted samples. However, this defect center was not observed for samples implanted with high fluence levels (⩾5 × 10 17 ions cm −2).

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.

Target poisoning during reactive magnetron sputtering: Part I: the influence of ion implantation

Gettering plays a minor role during reactive sputtering of silicon in a nitrogen/argon mixture. However, an abrupt increase of the target voltage as a function of the nitrogen mole fraction is noticed which is not expected from the classical models explaining reactive magnetron sputtering. To explain the target voltage behaviour during DC magnetron sputtering of silicon in an argon/nitrogen mixture, a model is proposed which is based on the reactive ion implantation into the subsurface region of the silicon target. The model calculates the concentration of the nitrogen ions implanted into the target and assumes three possible pathways for these implanted ions. A first pathway is the chemical reaction between the implanted nitrogen ions and the target material to form silicon nitride. The implanted nitrogen can also remain in the target as non-reacted nitrogen atoms. Or, the nitrogen atoms can recombine in the target and diffuse from the target. The compound formation results in a decrease of the target surface recession speed or target erosion rate. As the surface concentration of the implanted ions is inversely proportional to the surface recession speed, an avalanche situation becomes possible. This abrupt transition in recession speed is accompanied with a sudden increase of the concentration of non-reacted nitrogen atoms in the target. In this way, the abrupt target voltage change, noticed at a given mole fraction of nitrogen in the plasma, can be understood.

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.

Target voltage behaviour during DC sputtering of silicon in an argon/nitrogen mixture

On addition of nitrogen to an argon plasma, the silicon target voltage changes. By following the target voltage during the addition and removal of the reactive gas, the influence of the plasma condition was separated from the influence of the target condition on the target voltage. In this way, we were able to investigate the target surface modification during reactive sputtering. The target surface modification seems to be induced by reactive ion implantation. The target surface modification is not stable and N 2 desorption from a silicon target after reactive sputtering is noticed.

Deoxygenation of Y-Ba-Cu-O thin films by reactive ion implantation

Thin films of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO), grown by pulsed laser deposition, were implanted with Si/sup +/ ions at energies of 30,60, and 90 keV and at doses ranging from 1/spl times/10/sup 13/ cm/sup -2/ to 3/spl times/10/sup 11/ cm/sup -2/. X-ray diffraction techniques were used to investigate the structural dependence on implant parameters and annealing conditions, while d.c. magnetization was measured to characterize superconducting properties. By implanting only the upper portion of the film, implanted Si/sup +/ ions, near the surface, inhibit the superconductivity by removing oxygen from the bottom YBCO lattice which still retains its original crystal structure.

Ion implantation in high temperature superconducting films

Reactive ion implantation (RII) has been used to inhibit superconductivity in oxide superconductor materials. By introducing ions which are chemically reactive with oxygen into a high temperature superconductor (HTS) oxide film, the conductivity of the material may be inhibited by the interaction of the implanted ions with the oxygen in the oxide. Both Si and B ions, with doses ranging from 1/spl times/10/sup 15/-1/spl times/10/sup 17//cm/sup 2/, were implanted into epitaxial YBCO films with injection energies ranging from 20-180 keV, depending on the film thickness. The implanted ions do not alter the overall crystal structure of the HTS film, but do inhibit the electrical conductivity and diamagnetism. Multiple ion implantations have also been employed to achieve uniform ion distributions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adherent Zirconia Films by Reactive Ion Implantation

Conventional methods of forming ceramic coatings on metal substrates, such as CVD or plasma spray, typically retain a sharp interface and may have adhesion problems. In order to produce a completely mixed interface for better adhesion, a method using reactive ion implantation was used which can grow a thick stoichiometric film of an oxide ceramic starting from inside the substrate. Zirconium oxide ceramic films have been produced by this technique using a high‐energy zirconium ion beam in an oxygen gas ambient. Compositional data are shown based on Auger electron spectroscopy of the film. Tribological properties of the layer were determined from wear and friction measurements using a pin‐on‐disk test apparatus. The adhesion was measured both by a scratch technique as well as by thermal shock. Results show an extremely adherent ZrO2 film with good tribological properties.