Rotatable Magnetron Research Articles

Comparison of magnetron sputtering systems for high-rate deposition of thick copper layers for microelectronic applications

Objectives. When designing production equipment for the implementation of metal film deposition processes, the selection of technological sources for providing the required quality (structure, appearance), maximum process efficiency, and productivity, poses a challenging task. Since laboratory results often differ from issues faced in production processes, this choice becomes even more difficult under real production conditions due to a lack of sources for comparison. The purpose of the present work is therefore to compare magnetron deposition methods under real industrial conditions (planar extended magnetron, liquid-phase magnetron and cylindrical magnetron with a rotating cathode), identify their advantages and disadvantages along with features of thus-formed metal films, analyze the economic feasibility of each variant, and give practical recommendations for selecting a source when implementing the described process.Methods. Films were deposited using magnetron sputtering system. Roughness was measured using a MarSurf PS1 profilometer. The structure of the films was studied using a Hitachi SU1510 scanning electron microscope. Film thicknesses were measured by X-ray fluorescence analysis using a Fisherscope X-RAY XDV-SDD measuring instrument.Results. Sources of magnetron sputtering for the high-rate deposition of metallization layers under industrial conditions are considered. Obtained samples were compared according to the following criteria: deposition rate while maintaining the required quality, surface defects, film grain size, roughness, uniformity of the deposited layer, deposition efficiency (the ratio of the metal deposited directly onto the substrate to the amount of metal produced during the process). A comparison of the characteristics showed that the deposition rate for the liquid-phase magnetron is commensurate with the similar parameter for the cylindrical magnetron, exceeding the rate for the classical planar magnetron by about 4 times while maintaining the uniform appearance of the samples. The samples deposited with a liquid-phase magnetron had the highest roughness and the largest grain size. Although the cheapest method, liquid-phase magnetron sputtering achieved the lowest sputtering efficiency.Conclusions. The choice of the deposition method depends on the problem to be solved. The rotatable magnetron system can be considered optimal in terms of cost, deposition rate, and quality of the deposited layers. Liquid-phase magnetron sputtering is recommended for low-cost high-speed deposition where there are no strict requirements for appearance, or in case of operation of small-sized equipment.

Transfer of the sputter technique for deposition of strongly thermochromic VO2-based coatings on ultrathin flexible glass to large-scale roll-to-roll device

The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. We report on transfer of the sputter technique for deposition of strongly thermochromic ZrO2/W-doped VO2/ZrO2 coatings on ultrathin (0.1 mm) flexible glass from a laboratory-scale device with three (V, W and Zr) planar magnetron targets to a large-scale roll-to-roll device with two (W-doped V and ZrO2) rotatable magnetron targets. The depositions were performed at a relatively low substrate surface temperature (330–350 °C) and without any substrate bias voltage. The W-doped VO2 layers were deposited using a reactive high-power impulse magnetron sputtering with a pulsed O2 flow control. We compare the process parameters used in both deposition devices and explain the basic principle of this sputter technique using the discharge characteristics measured during a large-scale roll-to-roll deposition. We characterize the design, structure (X-ray diffraction) and optical properties (spectrophotometry and spectroscopic ellipsometry) of the three-layer coatings. The coatings prepared on ultrathin flexible glass using the large-scale roll-to-roll device at a temperature close to 350 °C exhibit a low transition temperature of 22 °C, an integral luminous transmittance over 45% and a modulation of the solar energy transmittance approaching 10%. This is a promising first step to a cost-effective and high-rate preparation of large-area thermochromic VO2-based coatings for future smart-window applications.

Development of rotational maze-shaped RF magnetron plasma for successful target utilization and thin-film preparation

A rotational maze-shaped RF magnetron sputtering plasma has been developed by combining three kinds of rod magnets for improving target utilization. The maze-shaped plasma is produced to perform the closed form along the magnetron motion predicted by the magnet arrangement. The radial profile of a copper target erosion has two peaks and the pattern is based on rotating the maze-shaped plasma. A target utilization rate has attained approximately 64.8%, which is to two to three times higher than that of conventional stable magnetron sputtering. Al-doped ZnO deposited thin films have shown resistivity of 1.5–2.6 × 10−4 Ω cm under a substrate at room temperature and the transmittance gets to approximately 90% in the visible region. It is found from X-ray diffraction pattern that the diffraction peak of AZO films is 33.97° and the grains exhibit a preferential orientation along the (002) axis.

Novel nanostructured electron transport compact layer for efficient and large-area perovskite solar cells using acidic treatment of titanium layer

A new method for the deposition of a pinhole-free compact layer of TiO2 is introduced for the development of efficient perovskite solar cells. Acidic treatment of titanium layer (ATTL), deposited by rotational magnetron sputtering, presents a compact pinhole-free TiO2 thin film. Deposition of a compact TiO2 thin film on fluorine-doped tin oxide layers by ATTL did not change the surface roughness. To compare the introduced method, perovskite solar cell devices were fabricated and studied using different methods for the deposition of the TiO2 compact layers, which were used as common compact layer deposition methods. The ATTL method proposed considerable photovoltaic enhancement of perovskite solar cell performance (at least 22% enhancement in this work) by reducing the pinholes and sheet resistance of the TiO2 thin film. The improvement in the open-circuit voltage and the fill factor of the prepared devices using the ATTL method strongly confirmed the nature of the deposited pinhole-free TiO2 thin film. This method is shown to be an appropriate route for the reliable large-scale deposition of TiO2 compact layers.

Roll-to-roll deposition of silicon oxynitride layers on polymer films using a rotatable dual magnetron system

High performance permeation barrier coatings are usually multilayer stacks consisting of inorganic and organic layers. Besides the water vapor transmission rate, the optical properties of such layers have a high importance. This contribution focuses on the deposition of silicon oxynitride as an inorganic layer. This material attracts a widespread interest due to its varying refractive index depending on its oxygen and nitrogen content. The experiments were carried out in a roll-to-roll coating machine using a rotatable magnetron system. The layers were deposited by reactive pulse magnetron sputtering using targets of 1m length. It was established that the ratio of oxygen to nitrogen in the layer was not only determined by the reactive gas mixture but also by the chosen set point of the closed loop control. Both the Secondary Ion Mass Spectrometry and the Glow Discharge Optical Emission Spectroscopy measurements revealed a vertically different composition of the SiOxNy layers. This could be supported by the simulation of the optical properties of the layers.

Review Article: Tracing the recorded history of thin-film sputter deposition: From the 1800s to 2017

Thin films, ubiquitous in today's world, have a documented history of more than 5000 years. However, thin-film growth by sputter deposition, which required the development of vacuum pumps and electrical power in the 1600s and the 1700s, is a much more recent phenomenon. First reported in the early 1800s, sputter deposition already dominated the optical-coating market by 1880. Preferential sputtering of alloys, sputtering of liquids, multitarget sputtering, and optical spectroscopy for process characterization were all described in the 1800s. Measurements of threshold energies and yields were carried out in the late 1800s, and yields in reasonable agreement with modern data were reported in the 1930s. Roll-to-roll sputter coating on flexible substrates was introduced in the mid-1930s, and the initial demonstration of sustained self-sputtering (i.e., sputtering without gas) was performed in 1970. The term magnetron dates to 1921, and the results of the first magnetron sputtering experiments were published in the late 1930s. The earliest descriptions of a parallel-plate magnetron were provided in a patent filed in 1962, rotatable magnetrons appeared in the early 1980s, and tunable “unbalanced” magnetron sputtering was developed in 1992. Two additional forms of magnetron sputtering evolved during the 1990s, both with the goal of efficiently ionizing sputter-ejected metal atoms: ionized-magnetron sputtering and high-power impulse magnetron sputtering, with the latter now being available in several variants. Radio frequency (rf) glow discharges were reported in 1891, with the initial results from rf deposition and etching experiments published in the 1930s. Modern capacitively-coupled rf sputtering systems were developed and modeled in the early 1960s, and a patent was filed in 1975 that led to pulsed-dc and mid-frequency-ac sputtering. The purposeful synthesis of metal-oxide films goes back to at least 1907, leading to early metal-oxide and nitride sputtering experiments in 1933, although the term “reactive sputtering” was not used in the literature until 1953. The effect of target oxidation on secondary-electron yields and sputtering rates was reported in 1940. The first kinetic models of reactive sputtering appeared in the 1960s; high-rate reactive sputtering, based on partial-pressure control, was developed in the early 1980s. While abundant experimental and theoretical evidence already existed in the late 1800s to the early 1900s demonstrating that sputtering is due to momentum transfer via ion-bombardment-induced near-surface collision cascades, the concept of sputtering resulting from local “impact evaporation” continued in the literature into the 1960s. Modern sputtering theory is based upon a linear-transport model published in 1969. No less than eight Nobel Laureates in Physics and Chemistry played major roles in the evolution of modern sputter deposition.

Low Inductance Antenna (LIA) plasma source and plasma-enhanced dual rotatable magnetron sputter assisted with LIA

In recent years, both low plasma damage and low temperature deposition technic for polymer substrates (e.g. PCB, films and etc.) are often required. We have developed a plasma enhanced dual rotatable magnetron sputter source assisted with inductively coupled plasma (ICP) using low inductance antenna (LIA). LIA has same unique characteristics, a)low voltage high density plasma, b)well controllability of plasma profile to ensure uniformity over large area, c)ionization of sputtered particle and etc. when in being used as a plasma assistant, and besides, LIA can be used as a ICP source for polymer surface modification. We introduce a variety of the possibilities of whether this sputter source is usable for the process of the fabrication of PCB.

Comparison of the large-area reactive sputter processes of ZnO:Al and ITO using industrial size rotatable targets

Abstract The most commonly sputtered transparent conductive oxide (TCO) materials are aluminum doped zinc oxide (ZnO:Al) and indium tin oxide (ITO). The deposition of these TCO materials is complex as it involves optimizing conductivity, transparency, and thickness over a large substrate area. Although compound ceramic sputter targets are the standard in the Solar and Display industries, exploring reactive sputtering from metallic targets is interesting in that it may substantially reduce the target cost. This paper compares the reactive sputter deposition of ZnO:Al and ITO from an industrial scale rotatable single magnetron (RSM) with a tube length of 1.7 m. It will be shown that both processes are very distinct and thus different control mechanisms have to be chosen in order to control the working point of the reactive process. Whereas the global working point of the reactive ZnO:Al process can be controlled by parameters of the power supply only, this is not possible for the reactive ITO process. Here, the partial pressures or optical emissions have to be controlled as well. Suitable tools for the basic characterization of the reactive processes are the well-known hysteresis and voltage–current characteristics at different reactive gas flows. The properties of the deposited thin films will be linked to the chosen control parameters.

Progress on optical coatings deposited with dual rotatable magnetrons in a sputter up system

A turntable magnetron sputter system based on cylindrical magnetrons was used to investigate particles and uniformity profiles of different processes and coatings. The sputter system is based on a dynamic deposition employing a high-speed turntable and a double cylindrical pulsed magnetron discharge for the deposition of low and high index layers. Contamination by particles was investigated for different processes. Very clean coatings could be obtained for single layers as well as for multilayers. The thickness uniformity was investigated and optimized. In partial reactive mode, the oxygen partial pressure distribution is influenced by getter effects of the different surfaces in the sputter compartment, which makes the optimization of the uniformity more difficult. After suitable conditioning of the coater, a reproducible uniformity of 99.6% overall the substrate area was observed. The slope of the non-uniformity can be modified by changing the angle of the magnet bars of the magnetrons. The deposition of an optical multilayer system with around 60 layers and a total thickness of 8μm was demonstrated and also a uniformity of 99.6% could be determined on different 200mm glass substrates perpendicular and parallel to the arc of motion.

Rotatable magnetron sputtering of aluminium in continuous and high power pulse modes using different strength magnetic arrays

This paper reports preliminary results of industrial size (152 mm target O.D.) rotatable magnetron sputtering of Al target in direct current (DC) and High Power Impulse Magnetron Sputtering (HIPIMS) modes using two standard commercially available magnetic arrays: standard strength array (as used for DC and AC processing) and a lower strength ‘RF’ array [i.e. as used for radio frequency (RF) magnetron sputtering]. A comparison of processes resulted in by combining the different magnetic arrays and power modes is made in terms of magnetic field distribution on the cathode surface, magnetron characteristics, process characteristics and deposition rates. Optical emission spectroscopy (OES) revealed enhanced sputtered Al flux ionisation in the HIPIMS discharge monitored 64 mm away from the target surface when using the ‘RF’ array. Importantly, the results of this work (at the processing conditions investigated) demonstrate that at the same average power the deposition rate of Al using HIPIMS in conjunction with the ‘RF’ array is substantially the same as that obtained for the ‘standard’ strength balanced array and DC power. This indicates that the magnetic field design of the ‘RF’ magnetic array affects favourably the sputtered flux transport perpendicular to the target surface by altering mass transport direction and minimising effects that reduce deposition rate (e.g. ion return effect). Arc rate is also reduced significantly (approximately ten times) if the low strength ‘RF’ array is used.

WITHDRAWN: Rotatable Magnetron Sputtering of Aluminium in Continuous and High Power Pulse Modes Using Different Strength Magnetic Arrays

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Low-cost ZnO:Al transparent contact by reactive rotatable magnetron sputtering for Cu(In,Ga)Se 2 solar modules

Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu(In,Ga)Se 2 (CIGS) module manufacturing. Although innovative concepts like rotatable magnetron sputtering from ceramic targets have been realised, costs are still high due to expensive ceramic targets. Significant cost reductions are expected by using reactive sputtering of metallic targets. Therefore, ZSW and industrial partners investigated the reactive sputtering of Al-doped zinc oxide (ZAO) as TCO on CIGS absorbers of high quality and industrial relevance. The reactive DC sputtering from rotatable magnetron targets is controlled in the transition mode by adjusting oxygen flow and discharge voltage. Optimisation leads to ZAO films with a TCO quality nearly comparable to standard films deposited by DC ceramic sputtering. Scanning electron microscopy, X-ray diffraction, and Hall analyses of the ZAO films are performed. Medium-size CIGS modules are coated with reactively sputtered ZAO, resulting in 12.8% module efficiency and surpassing the efficiency of the ceramic witness device. Cd-free buffered devices are also successfully coated with reactive TCO. Damp heat stability according to IEC61646 is met by all reactively sputtered devices.

Rotatable magnetron sputtering: downscaling for better understanding

<title/>In coating applications, magnetron sputtering is frequently the technology of choice. In industrial continuous in-line sputtering processes, such as web coating and glass coating, rotatable magnetrons have, to a large extent, supplanted the more classic rectangular sputter magnetrons and constitute the heart of many coating systems with target lengths up to 4 m. However, for many people in the coating business, rotatable magnetrons are quite unknown. When comparing the two types, it looks as if rotatable magnetrons offer significant advantages over planars, as long as the required cylindrical targets are available. Rotabable magnetrons are still a relatively new technology, and have not been fully investigated on a lab scale due to the lack of availability of small systems. Experiments with an in house developed downscaled rotatable magnetron have allowed some of their typical characteristics to be identified. Especially in reactive sputtering, rotatable magnetrons exhibit unusual properties. In this article, it is shown that this peculiar behaviour can be understood as the result of redeposition of previously sputtered material back on the target outside the current discharge plasma zone. This redeposition is, to a large extend, also responsible for the poisoning characteristics as a function of rotation speed of the cathode cylinder. It is also shown that in reactive sputtering, rotatable magnetrons generate two beams of high energy and negatively charged particles which seriously influence the morphology of the growing layer. In between both beams, there is a zone of silence where only sputtered low energy material is deposited and in which fragile materials, such as perovskites can be grown.

High power impulse magnetron sputtering using a rotating cylindrical magnetron

Both the industrially favorable deposition technique, high power impulse magnetron sputtering (HIPIMS), and the industrially popular rotating cylindrical magnetron have been successfully combined. A stable operation without arcing, leaks, or other complications for the rotatable magnetron was attained, with current densities around 11 A cm−2. For Ti and Al, a much higher degree in ionization in the plasma region was observed for the HIPIMS mode compared to the direct current mode.

Ion energy distributions in AZO magnetron sputtering from planar and rotatable magnetrons

Ion energy distribution functions (IEDFs) have been measured at the substrate position in magnetron sputtering of an aluminium doped zinc oxide (AZO) target in argon and/or oxygen atmosphere. The IEDFs have been obtained against ground potential with an energy-dispersive ion mass spectrometer which was facing the target surface. Two different magnetron configurations have been investigated: a circular planar magnetron on laboratory scale and an industrial scale rotatable cylindrical magnetron. They were operated with asymmetric-bipolar pulsed d.c. power. Positive ions of the working gas as well as Al +, Zn +, and AlO + were observed, which show a low-energy peak in their IEDF from the plasma potential of the “on” phase and a high-energy peak of several 10 eV which is formed during the “off” phase of the pulsed d.c discharge. Negative ions, being mainly O − from the target, exhibit a strong peak in their IEDF at several 100 eV corresponding to the negative target voltage. With strongly varying target voltage in the “on” phase the IEDF may extend to very high energies. Maximum and average energy of both positive and negative ions depend on the discharge power as the voltage in the “on” and “off” phases governing the high-energy ions changes with power. The differently sized planar and rotatable magnetrons exhibit very similar IEDFs for positive as well as negative ions proving that basic physical processes are essentially the same.

Aluminium doped zinc oxide sputtered from rotatable dual magnetrons for thin film silicon solar cells

This study addresses the electrical and optical properties as well as the surface structure after wet-chemical etching of mid-frequency magnetron sputtered aluminium doped zinc oxide (ZnO:Al) films on glass substrates from rotatable ceramic targets. Etching of an as-deposited ZnO:Al film in acid leads to rough surfaces with various feature sizes. The influence of working pressure and substrate temperature on the surface topography after etching was investigated. It was found that the growth model which Kluth et al. applied to films sputtered in radio frequency mode from planar ceramic target can be transferred to film growth from tube target. Furthermore, the influence of Ar gas flow and discharge power on the film properties was investigated. We achieved low resistivity of about 5.4 × 10 − 4 Ω·cm at high growth rates of 120 nm·m/min. Finally, surface textured ZnO:Al films were applied as substrates for microcrystalline silicon solar cells and high efficiencies of up to 8.49% were obtained.

New target materials for innovative applications on glass

In the new emerging markets of flat panel display, photovoltaic and optical coating applications, the introduction of cylindrical rotating magnetron technology can accommodate the needs for faster, better and cheaper coating processes. Recent developments of hardware (compact end blocks, etc.) and target materials for rotatable magnetron technology offer a total solution to the innovative thin film applications.

Observation of hysteresis in a non-reactive magnetron discharge

Current–voltage (I–V) characteristics of a rotatable cylindrical magnetron were measured. The balancing of the magnetic field was varied by changing the height of the central magnets. At a certain level of unbalancing, the discharge current displayed bistable behavior with respect to the discharge voltage. The state of the system depended on its history and the argon pressure. This could be attributed to a negative differential resistance of the discharge. A simple model is used to interpret the results. The observed behavior might compromise process stability of large area coaters when a high energy flux to the substrate is mandatory.

Investigation of the sustaining mechanisms of dc magnetron discharges and consequences for I–V characteristics

The influence of the starting conditions and sheath thickness on the magnetron discharge is investigated using a Monte Carlo program. The average number of ionizations caused by an electron emitted from the cathode is calculated. It is shown that the sheath thickness plays a crucial role in the generation of ions and the sustainment of the discharge. An analytical formula is obtained which relates discharge voltage, sheath thickness and ion-induced secondary electron coefficient. From it, a natural explanation for the very steep current–voltage (I–V) characteristic in magnetron discharges follows. Comparison with experiment suggests an anomalous diffusion of electrons across the sheath. The simulations were done for a rotatable cylindrical magnetron, but the results should be valid for planar magnetrons as well.

A comparison of the characteristics of planar and cylindrical magnetrons operating in pulsed DC and AC modes

The deposition of functional films onto both polymeric web and large area glass substrates has been a major area of growth in recent years. The key to this growth has been the development of the mid-frequency (20–350 kHz) dual bipolar pulsed magnetron sputtering process, which now permits complex, multi-layer structures with specific properties to be routinely deposited in high throughput systems. There are, though, several competing variants of the dual bipolar process currently employed, with each variant imposing its own set of criteria in terms of cost, process stability, throughput and product performance. Commercially available coating systems utilise both planar and cylindrical rotatable magnetrons, driven by AC, or pulsed DC power supplies. Few direct comparisons, though, have been made of these alternative approaches. Consequently, selection of equipment and operating procedures are being made largely on an empirical basis, potentially leading to non-optimal deposition conditions, or reduced film functionality. In this study, therefore, titania and silica coatings have been deposited by reactive magnetron sputtering onto glass substrates in both magnetron configurations and power delivery modes. Film structures have been analysed by SEM and the operating characteristics of the competing technologies have also been studied in terms of deposition rates, hysteresis behaviour and thermal flux at the substrate. The results to date of this study are reported here.