Titanium film deposition by high-power impulse magnetron sputtering: Influence of pulse duration

Surface modification with high-power glow discharges is a promising physical vapor deposition (PVD) technology for industrial usage. A metal ion density higher than 10¹⁸ m⁻³ can be obtained due to a high-power input in the plasma. In the present paper, titanium films were deposited on Si (100) substrates using high-power impulse magnetron sputtering (HIPIMS). The pulse duration was varied to investigate the deposition rate and the titanium film structure. The plasma source was an unbalanced magnetron sputtering (UBMS) discharge generation system. The deposition rate was correlated to the electrical characteristics. There was an instantaneous power threshold of approximately 36 kW to significantly increase the deposition rate by 4-5 times. The deposition rate increased linearly with respect to the average power until the average power reached 5.6 kW (about 30 W/cm² for a total area of the target), and an 83% increase of the deposition rate from the linear relationship was observed. The increase of the deposition rate was possibly closely related to the so-called thermal spike, where the target temperature increases due to a high power input to the target. The surface morphology and the crystalline structure of the films were studied for a variety of pulse durations, and the results were compared to the case of the direct-current magnetron sputtering (dcMS) process. The titanium films at an average power of 1.2 kW and a pulse duration of 50 μs have a smaller crystalline size and a smoother surface than those at an average power of 825 W by dcMS. The crystal orientation (101) was dominated when the pulse duration was lengthened to 180 μs, although the (002) orientation was dominant in dcMS. The crystal size and the surface roughness increased significantly when the pulse duration was increased from 50 μs to 180 μs in HIPIMS. The consumed power in the plasma by HIPIMS can be an important parameter for the crystal size and the structure.     

Thin polymer films from polyimide vacuum thermal degradation with and without a glow discharge

Polyimide-like thin films were deposited by thermal degradation of polyimide with and without simultaneous activation by a glow discharge excited using an r.f. planar magnetron. The films deposited without discharge are similar in composition to conventional polyimide, whereas the deposition with plasma results in cross-linked coatings with composition typical for plasma polymers e.g. prepared by r.f. sputtering of polyimide. AFM reveals rough surface topography for the films evaporated without plasma. The application of plasma leads to very smooth plasma polymer films.     

Reactive deposition of Al-N coatings in Ar/N2 atmospheres using pulsed-DC or high power impulse magnetron sputtering discharges

In this paper, the metal to ceramic transition of the Al-N₂ system was investigated using classical reactive pulsed-DC magnetron sputtering and HIgh Power Impulse Magnetron Sputtering (HIPIMS) at a constant average current of 3 A. Optical emission spectroscopy measurements revealed more ionised aluminium species in the HIPIMS discharge compared to pulsed-DC sputtering. It also showed excited N⁰ and ionised N⁺ species in reactive Ar/N₂ HIPIMS discharges. The corresponding evolution of the consumed nitrogen flow as a function of the N₂ partial pressure revealed that a higher amount of reactive gas is needed to achieve stoichiometric AlN with HIPIMS. Electron probe micro-analysis and X-ray diffraction measurements confirmed that a partially poisoned aluminium target is enough to allow the deposition of stoichiometric hcp-AlN thin films via HIPIMS. To go further in the comparison of both processes, two stoichiometric hexagonal aluminium nitride thin films have been deposited. High power impulse magnetron sputtered hcp-AlN exhibits a higher nano-hardness (18 GPa) than that of the coating realised with conventional pulsed-DC sputtering (8 GPa).     

Some remarks on Ag/C:H nanocomposite films

Nanocomposite films Ag/C:H were prepared using DC unbalanced magnetron sputtering operated in Ar and n-hexane mixture. Optical emission spectroscopy was used to monitor deposition process as witnessed by XPS quantitative analysis. UV-vis transmittance of Ag/C:H films as a function of Ag content show well-known anomalous optical absorption. FTIR (SEIRA) spectroscopy and HRTEM images were used to reveal an interface region between plasma polymer C:H and Ag nanocluster surface.     

Plasma polymers prepared by RF sputtering of polyethylene

Hydrocarbon plasma polymer thin films were deposited by means of magnetron sputtering of polyethylene (PE) using Ar as the working gas. AFM, ESCA, FTIR techniques were applied to investigate the films properties and composition. The films sputtered at Radio frequency (RF) power up to 100 W have a plasma polymer structure whereas further increase of RF power results in hydrocarbon plasma polymers more resembling conventional PE.     

Structure and properties of high power impulse magnetron sputtering and DC magnetron sputtering CrN and TiN films deposited in an industrial scale unit

Deposition of complex shaped or round-symmetric samples requires multi-fold substrate rotations during deposition or multiple cathode arrangements. The present paper investigates the influence of the high power impulse magnetron sputtering (HIPIMS) and DC magnetron sputtering (DCMS) process on the mechanical and tribological properties as well as the resulting structure of CrN and TiN coatings using static (0-fold) and dynamic (1-, 2- and 3-fold) depositions in an industrial scale unit. Furthermore, to increase the deposition rate without losing the high ion density in the plasma a hybrid HIPIMS/DCMS deposition technique is investigated. The results demonstrate the advantage of the HIPIMS technique when using multi-fold substrate rotation during deposition as it enables depositions of CrN_HIPIMS and TiN_HIPIMS coatings with hardness values around 23 and 35 GPa, respectively, compared with around 15 GPa for CrN_DCMS and TiN_DCMS coatings. Hardness values of 35 GPa for TiN_DCMS coatings prepared with substrate rotations could only be obtained when introducing an additional anode or using a multilayered CrN_HIPIMS/TiN_DCMS base layer as a template.Based on our results we can conclude that especially for up-scaling and multi-fold substrate rotations the HIPIMS process offers an improved performance as compared to DCMS.     

ZnO 薄膜包装材料溅射制备工艺与阻隔性能研究

目的为了解决普通聚合物包装塑料对水、氧的阻隔能力不足,以及包装内容物货架时间短等问题,研究氧化锌(ZnO)沉积复合薄膜制备工艺与阻隔性能之间的关系,探索其应用于包装材料的可行性。方法采用射频磁控溅射技术(RF),以ZnO为靶材,在PET塑料表面沉积制备氧化锌薄膜包装材料,并详细分析射频溅射功率、沉积时间与工作气压对ZnO复合薄膜微观形貌、沉积速率以及阻隔性能的影响。结果当溅射功率为150 W,沉积时间为30 min,工作气压为0.8 Pa时,ZnO薄膜均匀且致密,阻隔能力最强,其氧气透过率(OTR)降低为1.23 m L/(m2·d),水蒸汽透过率(WVTR)降低为0.382 g/(m2·d)。与相同厚度下的PET原膜相比,所制备的ZnO高阻隔薄膜的透氧率降低了49.5倍,透湿率降低了17.6倍。结论射频溅射参数通过影响复合薄膜的微观形貌、致密程度、沉积速率以及沉积层厚度等方面对其阻隔能力会产生较大影响。     

High-power impulse magnetron sputtering of Ti-Si-C thin films from a Ti3SiC2 compound target

We have deposited Ti-Si-C thin films using high-power impulse magnetron sputtering (HIPIMS) from a Ti₃SiC₂ compound target. The as-deposited films were composite materials with TiC as the main crystalline constituent. X-ray diffraction and photoelectron spectroscopy indicated that they also contained amorphous SiC, and for films deposited on inclined substrates, crystalline Ti₅Si₃C_x. The film morphology was dense and flat, while films deposited with direct-current magnetron sputtering under comparable conditions were rough and porous. We show that, due to the high degree of ionization of the sputtered species obtained in HIPIMS, the film composition, in particular the C content, depends on substrate inclination angle and Ar process pressure.     

Plasma polymer films from sputtered polyimide

Deposition of plasma polymer films by r.f. magnetron sputtering of polyimide in an atmosphere of argon, nitrogen and in a self-sputtering mode is studied. In situ analytical techniques are applied to monitor the composition of both plasma and growing film during the deposition. A co-evaporation regime is observed at higher applied powers. Such a regime is characterized by a significant increase in deposition rate of plasma polymer films. In addition CO-based groups appear in the plasma volume and in the resulting films. The films deposited in a pulsed mode are similar in composition to those deposited in the continuous regime at equivalent power. The plasma polymer films are found to be stable to short-term oxidation in air.     

等离子体源增强磁控溅射沉积Al2O3薄膜研究

采用电子回旋共振微波等离子体源增强磁控溅射沉积氧化铝薄膜.X射线光电子谱和X射线衍射分析表明,在600℃沉积温度下,Si（100）基片上获得了亚稳的具有化学计量配比成分、面心立方结构的γ-Al₂O₃薄膜.薄膜的折射率为1.7,与稳定的α-Al₂O₃体材料相当.     

The preparation of permalloy 80/20 thin films using a pulsed DC discharge in a hollow cathode

Permalloy thin films have many applications as sensors and actuators but the preparation of magnetic films by magnetron sputtering is problematic since the target material reduces or changes the magnetic configuration of the magnetron. Hollow cathode discharges can produce similar or greater plasma densities to that found in magnetron sputtering and can therefore be operated over a similar pressure range. Pulsed DC sputtering has been seen to have some advantages compared to DC or RF sputtering. In this paper we report the use of a combination of pulsed DC sputtering with a hollow cathode system to prepare thin films of Permalloy. The deposition rate was found to strongly depend on the gas flow used to prepare the thin films. Combinations of the experimental conditions were found to produce films with a (111) preferential crystal orientation and that the grain size of the crystals was mainly determined by the deposition rate. Furthermore, changes in the degree of ion bombardment did not appear to have any significant affect on the structure of the deposit.     

Oxidation behaviour of TiAlYN/CrN and CrAlYN/CrN nanoscale multilayer coatings with Al2O3 topcoat deposited on γ-TiAl alloys

Abstract

TiAlYN/CrN and CrAlYN/CrN nanoscale multilayer coatings were deposited on γ-TiAl specimens using magnetron sputtering techniques. The nitride layers were manufactured by unbalanced magnetron sputtering (UBM) and high power impulse magnetron sputtering (HIPIMS). The CrAlYN/CrN coatings had an oxy-nitride overcoat. On some of the coated samples an additional alumina topcoat was deposited. The oxidation behaviour of the different coatings was investigated at 750 and 850°C performing quasi-isothermal oxidation tests in laboratory air. Mass change data were measured during exposure up to failure or the maximum exposure length of 2500 h. When exposed to air at 750°C, the Ti-based nitride films exhibited higher oxidation resistance than the Ti – 45Al –8Nb substrate material. The alumina topcoat enhanced the oxidation protection of this coating system, acting as diffusion barrier to oxygen penetration. At 850°C, the TiAlYN/CrN films exhibited poor stability and rapidly oxidised, and therefore were not applicable for long-term protective coatings on γ-TiAl alloys. The beneficial effect of the additional Al₂O₃ layer was less pronounced at this exposure temperature. The Cr-based nitride films exhibited high oxidation resistance during exposure at 850°C. HIPIMS deposition improved the oxidation behaviour of the CrAlYN/CrN nanoscale multilayer coatings in comparison to UBM coatings. For these coatings, the decomposed and partially oxidised nitride films were an effective barrier to oxygen inward diffusion. The alumina topcoat did not significantly increase the oxidation resistance of the γ-TiAl alloy coated with Cr-based nitride films.     

Heating of polymer substrate by discharge plasma in radiofrequency magnetron sputtering deposition

The substrate used for the thin film deposition in a radiofrequency magnetron sputtering deposition system is heated by the deposition plasma. This may change drastically the surface properties of the polymer substrates. Deposition of titanium dioxide thin films on polymethyl methacrylate and polycarbonate substrates resulted in buckling of the substrate surfaces. This effect was evaluated by analysis of atomic force microscopy topography images of the deposited films. The amount of energy received by the substrate surface during the film deposition was determined by a thermal probe. Then, the results of the thermal probe measurements were used to compute the surface temperature of the polymer substrate. The computation revealed that the substrate surface temperature depends on the substrate thickness, discharge power and substrate holder temperature. For the case of the TiO₂ film depositions in the radiofrequency magnetron plasma, the computation indicated substrate surface temperature values under the polymer melting temperature. Therefore, the buckling of polymer substrate surface in the deposition plasma may not be regarded as a temperature driven surface instability, but more as an effect of argon ion bombardment.     

Comparison of microstructure and mechanical properties of chromium nitride-based coatings deposited by high power impulse magnetron sputtering and by the combined steered cathodic arc/unbalanced magnetron technique

Sliding, abrasive, and impact wear tests were performed on chromium nitride (CrN)-based coatings deposited on mirror-polished M2 high speed steel substrates by the novel high power impulse magnetron sputtering (HIPIMS) utilising high peak cathode powers densities of 3000 W cm⁻². The coatings were compared to single layer CrN and multilayer superlattice CrN/NbN coatings deposited by the arc bond sputtering (ABS) technique designed to improve the coating substrate adhesion by a combined steered cathodic arc/unbalanced magnetron (UBM) sputtering process. The substrates were metal ion etched using non-reactive HIPIMS or steered cathodic arc at a substrate bias voltage of −1200 V. Subsequently a 2- to 3-μm thick CrN or CrN/NbN coating was deposited by reactive HIPIMS or UBM. No bias was used during the HIPIMS deposition, while the bias during UBM growth was in the range 75-100 V. The ion saturation current measured by a flat electrostatic probe reached values of 50 mA cm⁻² peak for HIPIMS and 1 mA cm⁻² continuous during UBM deposition. The microstructure of the HIPIMS coatings observed by transmission electron microscopy was fully dense in contrast to the voided columnar structure observed in conventional UBM sputtered CrN and CrN/NbN. The sliding wear coefficients of the HIPIMS CrN films of 2.3×10⁻¹⁶ m³ N⁻¹ m⁻¹ were lower by a factor of 4 and the roughness of the wear track was significantly reduced compared to the UBM-deposited CrN. The abrasive wear coefficient of the HIPIMS coating was 2.2×10⁻¹³ m³ N⁻¹ m⁻¹ representing an improvement by a factor of 3 over UBM deposited CrN and a wear resistance comparable to that of the superlattice CrN/NbN. The adhesion of the HIPIMS deposited CrN was comparable to state-of-the-art ABS technology.     

Deposition rate characteristics for steady state high power impulse magnetron sputtering (HIPIMS) discharges generated with a modulated pulsed power (MPP) generator

High power impulse magnetron sputtering (HIPIMS) pulses have been of great interest over the last decade. With such sputtering techniques a substantial amount of target material can be ionized and used for the engineering of surfaces and coatings. Depending on voltage, system configuration and target material, such discharges can be either transient or reach steady state currents during the pulse. The used HIPIMS power supply was a constant voltage supplies. Similarly, HIPIMS pulses with multiple steady state current phases can be generated using a modulated pulsed power (MPP) generator. A typical pulse consists of an ignition, low current and high current phase. The contribution of these phases to the deposition rate is presented. The ionization rate of single charge chromium ions has been found to increase linearly with increasing peak current density. An increase in deposition rate with lower magnetic field strength at the target surface can be attributed to a higher sputter yield due to a higher cathode voltage due to increasing system impedance in HIPIMS case, weaker trapping of deposition flux and to enhanced ion flux towards the substrate.     

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.     

直流磁控溅射研究进展

直流磁控溅射是重要的物理气相沉积技术,广泛应用在工业生产和科学研究中.主要评论了近年来直流磁控溅射技术在溅射机理和非平衡闭合磁控靶等方面取得的重要进展,并评述了脉冲磁控模式和基于闭合磁场直流磁控溅射沉积涂层的结构区域模型.直流非平衡磁控溅射是直流磁控溅射技术中的重要里程碑,使磁控溅射技术直接过渡到离子镀阶段,而脉冲磁控溅射技术为稳定沉积高质量的非导电涂层作出了重要的贡献.     

Hysteresis behaviour of reactive high power impulse magnetron sputtering

Hysteresis behaviour during reactive High Power Impulse Magnetron Sputtering (HIPIMS) has been investigated in detail. Such analysis has been made possible by the recently developed plasma emission monitoring based reactive HIPIMS monitoring and control technology. Hysteresis curves were recorded at frequencies of 300, 450 and 600 Hz at an average power of 3.0 kW during reactive HIPIMS of Ti in Ar/O₂ atmosphere. It is shown that the target pulsing parameters, such as frequency, pulse voltage, and duty cycle do affect the overall shape of the hysteresis loop. Analysis of the hysteresis behaviour at different target pulsing parameters reveals how different regions of the hysteresis loop are affected by different pulsing parameters. The outcomes of this work demonstrate trends and explain relationships between the pulsing parameters and the hysteresis behaviour. Although the overall picture is rather complicated, it is quite clear that the hysteresis effect is induced by the same processes as in direct current magnetron sputtering, while the influence of the reactive ion implantation oxidation mechanism appears to be far more significant in reactive HIPIMS.     

Defect passivation by O2 plasma treatment on high-k dielectric HfO2 films at room temperature

Oxygen plasma treatment process was used to passivate the non-stoichiometric HfO₂ films deposited by magnetron sputtering. After optimal oxygen plasma treatment, the gate leakage of HfO₂ films would be reduced and dielectric breakdown voltage would be improved to 30 percentage. XPS spectrum was used to analysis the non-stoichiometric HfO₂ films after oxygen plasma treatment which demonstrate a higher concentration of incorporated oxygen atoms at the surface in comparison to the bulk HfO₂. This simple method can maintain high-k dielectric deposition process at room temperature by sputtering. It would be useful for fabrication thin film transistor on polymer based substrate in the future.