The high power impulse magnetron sputtering discharge as an ionized physical vapor deposition tool

Various magnetron sputtering tools have been developed that provide a high degree of ionization of the sputtered vapor referred to as ionized physical vapor deposition (IPVD). The ions can be controlled with respect to energy and direction as they arrive to the growth surface which allows for increased control of film properties during growth. Here, the design parameters for IPVD systems are briefly reviewed. The first sputter based IPVD systems utilized a secondary plasma source between the target and the substrate in order to generate a highly ionized sputtered vapor. High power impulse magnetron sputtering (HiPIMS) is a recent sputtering technique that utilizes IPVD where a high density plasma is created by applying high power pulses at low frequency and low duty cycle to a magnetron sputtering device. A summary of the key experimental findings for the HiPIMS discharge is given. Measurements of the temporal and spatial behavior of the plasma parameters indicate electron density peak, that expands from the target with a fixed velocity. The discharge develops from an inert sputtering gas dominated to a sputtered vapor dominated during the pulse. The high electron density results in a high degree of ionization of the deposition material.     

Studies of medium frequency high power density magnetron sputtering discharges

Optical emission spectroscopy and Langmuir probe have been used to study the power dependence of medium frequency, 100 kHz, pulsed magnetron sputtering discharge. Copper target was sputtered in the argon atmosphere. The examined power ranged from 0.5 to 4.5 kW which gave an average power density on target surface from 25 to 115 W/cm². Optical spectroscopy did not reveal any significant changes of copper ion contribution to the sputtering process. The electron temperature and plasma potential changed a little with applied power. The electron density depended linearly on the sputtering power.     

高功率脉冲磁控溅射制备ZnO薄膜的研究进展

氧化锌薄膜材料由于具有高电导率、良好的光学透过率、原料储存丰富、成本低廉的特点,被认为是最具有潜力的透明导电薄膜.特别是其宽禁带(3.37eV)和高达60meV的激子束缚能,使其在环境温度制备同质结发光器件、太阳能电池电子传输层具有巨大的应用前景.然而,传统制备方法难以实现薄膜质量的综合调控,存在p-ZnO稳定性差、制...     

Fully dense, non-faceted 111-textured high power impulse magnetron sputtering TiN films grown in the absence of substrate heating and bias

We demonstrate the deposition of fully dense, stoichiometric TiN films on amorphous SiO₂ by reactive high power impulse magnetron sputtering (HiPIMS) in the absence of both substrate heating and applied bias. Contrary to the highly underdense layers obtained by reactive dc magnetron sputtering (dcMS) under similar conditions, the film nanostructure exhibits neither intra- nor intergrain porosity, exhibiting a strong 111 preferred orientation with flat surfaces. Competitive grain growth occurs only during the early stages of deposition (< 100 nm). The strong differences in the kinetically-limited nanostructural evolution for HiPIMS vs. dcMS are explained by high real-time deposition rates with long relaxation times, high ionization probabilities for Ti, and broad ion energy distributions.     

Medium frequency magnetron self-sputtering of copper

It is well known that the magnetron self-sustained sputtering (SSS) process can be achieved in the direct current (DC) operation mode (DC-SSS) if certain conditions are fulfilled: high self-sputtering yield of the target material (theoretically Y>1), appropriate magnetron source design, high target power density to ensure high ionization level of the sputtered material. The main disadvantage of the DC-SSS process is the instability related to possibility of an arc formation. The author postulates that magnetron plasma pulsing can minimize this problem.In this paper, voltage and current waveforms of medium frequency (MF) powered magnetron source are analysed. A simple electrical model, explaining dynamics of MF magnetron discharge is presented. The method to achieve MF magnetron SSS process is proposed and experimentally verified. The results of MF magnetron SSS (MF-SSS) process are presented for the first time (to the author's knowledge). The experiments were performed using a planar magnetron source equipped with a copper target of 50 mm in diameter and 6 mm thick. The magnetron source was powered by a resonant (110 kHz) power supply. The target power density during MF-SSS process was about 490 W/cm².     

Modulated pulse power sputtered chromium coatings

Cr coatings were deposited using continuous dc magnetron sputtering (dcMS) and modulated pulse power sputtering (MPP) techniques in a closed field unbalanced magnetron sputtering system at equivalent average target powers. It was found that MPP sputtering exhibited higher deposition rates than in dcMS when the average target power density was above 14 W cm^− 2 for the Cr coating depositions. Plasma diagnostics confirmed a significant increase in the numbers of both target material (Cr) and gas (Ar) ions in the MPP plasma as compared to the dc plasma. The substrate peak current densities measured in the MPP depositions (104-324 mA cm^− 2) have been increased by over a factor of 50 to those in the dcMS conditions (2-5.5 mA cm^− 2). The enhanced ion flux bombardment from the highly ionized MPP plasma led to the formation of denser microstructure and finer grain size in the MPP Cr coatings than in the dcMS Cr coatings. In addition, MPP sputtered Cr coatings exhibited improved hardness and adhesion.     

Reactive sputtering of magnesium oxide thin film for plasma display panel applications

A magnesium oxide thin film deposition process based on reactive magnetron sputtering for plasma display panel applications has been developed. The sputtering system was manufactured with a vertical In-Line type of 1067 mm, which has a length of 563 mm and a width of 982 mm. Reactive magnetron discharge was generated using a 7.5 kW unipolar pulsed power supply. The power supply was operated at a maximum constant voltage of 500 V and a constant current of 15 A. The frequency and the duty were changed 10–100 kHz and 10–60%, respectively. Magnesium oxide films were prepared using various deposition conditions: 0.4–1.33 Pa pressure, the ratio of O₂/(O₂+Ar)=0.1–0.5, 50% duty and 0.5–1.7 kW peak power. The deposition rates of a static state and a moving state were measured to be approximately 45 nm/min and 6 nm/min at the distance of 50 mm between the target and the substrate, respectively. The texture of the sputtered magnesium oxide thin film was characterized by X-ray diffraction. Secondary electron emission coefficient was measured to be 0.1 at 100 V of ion acceleration voltage. The transmittance was observed to be approximately 90% at the wavelength of 300–800 nm. The density and hardness were measured as 93.2%, and 800–900 kg/mm², respectively. When the prepared magnesium oxide film applied to the 6-inch plasma display panel, discharge phenomena of the plasma display panel occurred at 200 V.     

Influence of additional magnetic field on plasma parameters in magnetron sputtering

With three additional magnetic rings being assembled outside the discharge room and connected with the magnetic field of the conventional unbalanced magnetron sputtering, a closed magnetic field configuration distribution had been formed in the whole discharge room and which can confine discharge plasma more effectively. The spatial distribution of the newly designed magnetic field configuration was simulated using the ANSYS software. Plasma potential, electron temperature, electron density and ion density in the discharge plasma were diagnosed by Langmuir probe and the optical emission line intensity ratios of Ar⁺/Ar and Cu⁺/Cu were studied by optical emission spectroscopy. The structure and morphology of the Cu films are measured by scanning electron microscopy. A comparative study of the new magnetic field configuration with the conventional unbalanced magnetic field configuration was conducted. The results showed that the application of the additional magnetic field can increase the plasma density, enhance the ionization degree of the sputtered Cu and decrease the plasma potential effectively. The characteristics of the deposited Cu film were also influenced by the new magnetic field configuration greatly.     

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.     

The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharge

The energy distribution of sputtered and ionized metal atoms as well as ions from the sputtering gas is reported for a high power impulse magnetron sputtering (HIPIMS) discharge. High power pulses were applied to a conventional planar circular magnetron Ti target. The peak power on the target surface was 1-2 kW/cm² with a duty factor of about 0.5%. Time resolved, and time averaged ion energy distributions were recorded with an energy resolving quadrupole mass spectrometer. The ion energy distributions recorded for the HIPIMS discharge are broader with maximum detected energy of 100 eV and contain a larger fraction of highly energetic ions (about 50% with E_i > 20 eV) as compared to a conventional direct current magnetron sputtering discharge. The composition of the ion flux was also determined, and reveals a high metal fraction. During the most intense moment of the discharge, the ionic flux consisted of approximately 50% Ti¹⁺, 24% Ti²⁺, 23% Ar¹⁺, and 3% Ar²⁺ ions.     

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.     

Synthetic simulation of plasma formation,target erosion,and film deposition in a large magnetron sputtering apparatus

Examples of simulations of all relevant sputtering processes are described in this paper. Processes include plasma formation, target erosion, emission of sputtered atoms, and deposition of sputtered atoms for two types of magnetron sputtering apparatuses. One is axisymmetric and the other is three-dimensional.     

Hysteresis and process stability in reactive high power impulse magnetron sputtering of metal oxides

In the further development of reactive sputter deposition, strategies which allow for stabilization of the transition zone between the metallic and compound modes, elimination of the process hysteresis, and increase of the deposition rate, are of particular interest. In this study, the hysteresis behavior and the characteristics of the transition zone during reactive high power impulse magnetron sputtering (HiPIMS) of Al and Ce targets in an Ar-O₂ atmosphere as a function of the pulsing frequency and the pumping speed are investigated. Comparison with reactive direct current magnetron sputtering (DCMS) reveals that HiPIMS allows for elimination/suppression of the hysteresis and a smoother transition from the metallic to the compound sputtering mode. For the experimental conditions employed in the present study, optimum behavior with respect to the hysteresis width is obtained at frequency values between 2 and 4 kHz, while HiPIMS processes with values below or above this range resemble the DCMS behavior. Al-O films are deposited using both HiPIMS and DCMS. Analysis of the film properties shows that elimination/suppression of the hysteresis in HiPIMS facilitates the growth of stoichiometric and transparent Al₂O₃ at relatively high deposition rates over a wider range of experimental conditions as compared to DCMS.     

Titanium oxide thin films deposited by high-power impulse magnetron sputtering

Ionized physical vapor deposition processes are of great interest for surface modification because the flexibility of the thin film deposition process can be increased by ionizing the metallic vapor. Recently, high-power impulse magnetron discharges have been implemented to achieve high ionization rates.Thin films of titanium oxide have been deposited on glass and steel substrates using 450 × 150 mm rectangular titanium target in argon-oxygen atmosphere. The average power delivered to the plasma is ranging between 1.5 and 2 kW and peak current and voltage are respectively 200 A and 900 V.Films are characterized using Scanning Electron Microscopy, Grazing Incidence X-ray Diffraction and Optical Transmission Spectroscopy. One of the major findings is the presence of rutile deposited on steel substrate (even for 0 V bias grounded substrate) and the significant increase of the refractive index of the films deposited on glass compared to thin films deposited via conventional direct current bipolar pulsed magnetron sputtering. Films synthesized by high-power impulse magnetron sputtering are denser.     

The physical reason for the apparently low deposition rate during high-power pulsed magnetron sputtering

In high-power pulsed magnetron sputtering, a large power density is applied giving rise to a high degree of ionization. From an application point of view, the major drawback of this technology is the considerably lower deposition rate as compared to DC magnetron sputtering. Using transport-of-ions-in-matter simulations, we show that the apparently low deposition rate can be understood based on the non-linear energy dependence of the sputtering yields. Our calculations are consistent with deposition-rate measurements on Cu films as well as with published deposition-rate data for Ti [Konstantinidis S, Dauchot JP, Ganciu M, Ricard A, Hecq M. J Appl Phys 2006;99:013307].     

Prozesse mit hoher Plasmastromdichte und unterschiedlichen Verdampfungsquellen

The hot filament supported high current discharge can be used with various process steps. During the heating cycle, intense electron bombardment provides a soft and efficient energy source. In triode etching the high plasma density improves the throwing power and reduces the arcing problem on oxide inclusions from preceding grinding steps. For the coating cycle the high current density can be fitted into different deposition processes. Activated reactive ion plating is done with a high voltage electron beam gun. But one can also combine the high current density plasma with a magnetron to produce a high plasma density on the substrate and solve the problems of reactivity of this vapor source. Alternatively the high current density plasma can also be used to drive a CVD-reaction. Several of these processes can be combined to hybrid deposition technologies. A few examples of coating realisations and performance in the different processes will be given.     

The effect of external cusp magnetic field on Ar ICP characteristics

In this paper, three permanent magnet rings, which were placed alternatively between the three antenna coils of a cylindrical inductively coupled radio frequency (rf) argon plasma for rf enhanced ionized magnetron sputtering system, were used to produce a closed magnetic field distribution with the magnetic field of the unbalanced magnetron sputtering to confine discharge plasma. Langmuir probe measurement was used to study the effect of the magnetic field on the plasma characteristics and their spatial distribution. The results show that the presence of the closed magnetic field leads to the increase of the ion density and the decrease of electron temperature and plasma potential. With the closed magnetic field, the plasma density distribution in radial direction will become more uniform.     

Deposition of photocatalytic titania coatings on polymeric substrates by HiPIMS

Titania coatings have been deposited onto PET substrates by reactive magnetron sputtering in the HiPIMS (high power impulse magnetron sputtering) mode and for comparison, pulsed DC mode. In the latter case, the substrate showed evidence of melting, but the HiPIMS results were dependent on the characteristics of the power supply when operating under nominally identical conditions. A coating deposited by one of the HiPIMS supplies was found to have a mixed phase structure and to demonstrate a level of photocatalytic activity comparable to conventional coatings which had been post-deposition annealed.     

Characteristics of DLC films by DC magnetron sputtering incorporated with cesium

Diamond-like carbon films were deposited by planar DC magnetron sputtering with cesium vapor. The electrical properties of the plasma were investigated by the I-V measurement of the discharge. The increase in the plasma density and the generation of the negative carbon ions were observed from the I-V curves and deposition rate with different substrate biases. The deposited DLC films were examined by Raman spectroscopy and plasmon energy loss analysis in order to assess their structures. The DLC film obtained with Cs vapor contained a higher sp³ fraction than that without Cs vapor. This result implied that the negative carbon ions produced by Cs vapor participated in the deposition through the subplantation process. From experimental results, it is expected that Cs vapor addition to conventional magnetron sputtering system makes possible the deposition of higher quality DLC as well as large area deposition.