On surface temperatures during high power pulsed magnetron sputtering using a hot target

A study of temperature of a magnetron target was performed for the case of high power pulsed magnetron sputtering (HPPMS) of titanium thin films, using a water-cooled target and a hot target. Temporal evolution and spatial distribution of surface temperature were investigated. Temperature measurements were made by an infrared camera for target diameter of 100 mm, pulse repetition frequencies of 1 and 10 kHz, and discharge average pulse currents of from 2.5 to 35 A. For the case of hot target, surface temperature of the erosion zone increased up to 1750 °C and melting occurred. Temporal evolution of temperature after the end of deposition revealed phase change in solid-state from β-Ti to α-Ti at 882 °C and, for the case of high average pulse currents, also solidification at 1670 °C. The solid state phase transformation plateau was used to determine an emissivity of Ti target for the present case, and therefore precisely calibrate infrared camera measurements. The target melting was analysed in detail. The dependencies of maximum temperature on average pulse current and on average target power density for the case of hot target revealed the existence of heat losses other than radiation (i.e. enhanced sputtering, sublimation, electron emission and evaporation) at temperatures above 1500 °C, which correlates with higher erosion and deposition rates shown in another work.     

Modeling reactive sputter deposition of titanium nitride in a triode magnetron sputtering system

In this paper, the so-called Berg's model was successfully employed in order to model the reactive sputter deposition of titanium nitride (TiN) by a triode magnetron sputtering (TMS) system. Such system consists of a grounded grid introduced between the target and the substrate. The grid acts as the anode, and the glow discharge is formed between the target and grid. The qualitative model was compared to experimental data. In addition, results from a conventional MS system were also compared to the ones from the modified TMS system. It was possible to observe that (a) the width of the hysteresis region is narrower for TMS for all modeled conditions; (b) the hysteresis width increases as a function of grid-to-target distance.     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process: Part III: The particular case of exponential pulses

A new and original method, namely the reactive gas pulsing process (RGPP), was optimised to deposit titanium oxynitride thin films by dc reactive magnetron sputtering. Pure titanium target was sputtered in a reactive atmosphere composed of argon, nitrogen and oxygen. Argon and nitrogen gases were injected with a constant mass flow rate whereas oxygen was periodically supplied into the sputtering chamber. An exponential signal was generated to the oxygen mass flow meter with a constant pulsing period T = 45 s. During the injection time of the oxygen gas (t_ON time), the exponential shape was systematically modified in order to better control the amount of reactive gas introduced. Duty cycle was also changed and led to an extended alternation of the process between the nitrided and oxidised sputtering mode. Speed of poisoning of the titanium target surface by oxygen was calculated assuming real time measurements of the target potential. It was clearly shown that duty cycle and shape of the exponential signals used during oxygen injection are fundamental pulsing parameters. Both parameters must be taken into account in order to adjust and improve the monitoring of RGPP system for the deposition of titanium oxynitride coatings. Such approach prevents the full poisoning of the target surface by oxygen or nitrogen, and consequently, a wide range of oxynitride compounds can be easily reached.     

反应溅射制备AlN薄膜中沉积速率的研究

通过对浅射过程中辉光放电现象及薄膜沉积速率的研究，发现随着氮浓度的增大，靶面上形成一层不稳定的AlN层，由于AlN的溅射速率远小于Al，从而使薄膜的沉积速率显著下降。同时还研究了其它溅射参数对薄膜沉积速率的影响。结果表明：随靶基距的增大靶功率的减小，不同程度引起沉积速率的下降；随着溅射气压的增大，最初沉积速率不断增大，当溅射气压增大到一定程度时，沉积速率达到最大值，之后随溅射气 压的增大，又不断减小。     

Deposition of copper oxide by reactive magnetron sputtering

Copper oxide films were deposited on silicon substrates by direct current magnetron sputtering of Cu in a mixture of O₂ and Ar gases. Oxidation of the target as a result of adsorption or ion-plating of the reactive gases directly affects the discharge current and composition of the deposited films. We propose a kinetic model that relates the target oxidation to the discharge current, showing a one-to-one relationship between the discharge current characteristics and composition of the deposited films.     

Modelling of the hysteresis effect of target voltage in reactive magnetron sputtering process by using neural networks

Reactive sputtering process is very non-linear and usually exhibits hysteresis behaviour with respect to the reactive gas flow. Most of the problems encountered in the preparation of non-stoichiometric compound films by reactive sputtering are due to the hysteresis effect. Therefore, a considerable amount of effort has been devoted to find means for its elimination or ensuring a stable sputtering in the transition mode. This paper presents a new approach based on Artificial Neural Networks (ANNs) for modelling of the hysteresis effect of target voltage at different target power levels and reactive gas flow rates in reactive sputtering. Based on this model, it is possible to predict the target voltage in reactive magnetron sputtering processes, when the target power level, reactive gas flow rate and its direction are used as inputs to the artificial neural network (ANN). The proposed ANN is trained in different structures with the use of learning algorithms to obtain better performance and faster error convergence. Broyden–Fletcher–Goldfarb Shanno (BFGS) algorithm gives the best result among other learning algorithms used in the analysis. The training and test data required to develop the ANN model are obtained from the experimental studies. Both the training and the test results are in very good agreement with the experimental results obtained in this work.     

Microstructural and photocatalytic properties distribution of TiO2 coatings reactively sputtered as a function of the substrate position relatively to the Ti target

Amorphous and porous TiO₂ coatings were deposited by reactive magnetron sputtering at high pressure (3.4 Pa) on cold soda-lime glass placed at different positions relatively to the magnetron target, which corresponds to different impingement angles and target-to-substrate distances. The as-deposited coatings were heated at 450 °C under ambient air to crystallise into the photoactive anatase phase. The structural analyses combined with AFM experiments have shown a reduction of the crystallites and the lateral grain size with the removal of the substrate from the target axis inducing a specific area rise. Moreover, the stress state is all the less as compressive as the substrates are far away from the target. As a result, the photocatalytic properties are improved with the decrease of the incidence angle and with the target-to-substrate distance rise.     

Application of optical transmission interferometry for in-situ structural investigations of titanium dioxide sputter-deposited coatings

Titanium dioxide coatings (from 0.1 to 1.5 μm thick) have been dc sputter-deposited on glass slides from titanium targets in various Ar-O₂ reactive gas mixtures. Deposition rate and optical properties were controlled in-situ by optical transmission interferometry (OTI) with an optical fibre located behind the glass substrate in order to perform a real-time control of transmittance of the growing film. Thus, it is possible to determine in-situ the optical indices (n, k) and the thickness of the as-deposited film by using a simple simulation, developed on Matlab software. The optical properties of the films were investigated in relation to their structure, which depends on the sputtering conditions adopted. In particular, the effects of the sputtering pressure (working pressure and oxygen partial pressure), the discharge power and the substrate location into the reactor are investigated in detail. Films structure is assessed by standard grazing incidence X-ray diffraction (XRD).     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process. Part I: Pattern and period of pulses

Titanium oxynitride thin films were deposited by dc reactive magnetron sputtering. A metallic titanium target was sputtered in argon, nitrogen and oxygen reactive atmosphere. Argon and nitrogen gases were continuously injected into the process whereas oxygen mass flow rate was pulsed during the deposition. By means of a home made pulsing technique, the oxygen gas was introduced using various modulation patterns of the mass flow rate: rectangle, exponential, sine, isosceles triangle, mounting and descending triangles. The period T of the pulse length was systematically changed from 10 to 400 s. Similarly, kinetics and poisoning phenomena of the titanium target by nitrogen and oxygen were investigated from real time measurements of the target potential and total sputtering pressure. Such diagnostics allowed understanding the advantageous role of the reactive gas pulsing process (RGPP) to synthesize titanium oxynitride compounds. Some requirements, especially the shape of the pulses and the period length were established to alternate the process between the oxidised and nitrided sputtering mode. With suitable and reversible operating conditions, the RGPP led to deposit tuneable titanium oxynitride coatings, usually difficult to reach by conventional reactive sputtering.     

磁控溅射Ti靶镀料热发射脱靶的机理研究

高功率脉冲磁控溅射技术虽能实现提高镀料离化率以增强镀层力学性能的设计初衷,但其极低的沉积速率降低了工作效率,阻碍了该技术产业化的成功推广。因此,期望在达到镀料高离化率的同时,兼顾高速沉积是本研究的主要目的,为此本文提出一种创新性的研究思路,利用自主研发的双级脉冲电场,通过分别调控两个脉冲阶段的电场参量引发阴极靶面气体放电由辉光向弧光转变,借助弧光放电产生的高密度等离子体,增强靶面氩离子的碰撞动能和金属靶材产生的焦耳热,诱发镀料以高离化率、高产额的热发射方式脱离靶材。实验结果表明：在持续提高铜靶和钛靶的靶电流密度时,阴极靶材与阳极腔体间的伏安特性会由正比例的递增关系转变为反比例的递减关系,这说明气体放电会由辉光放电向弧光放电转变,并以此诱发镀料由碰撞溅射脱靶转变为溅射+热发射脱靶。实验以钛靶作为研究对象,采用双级脉冲电场在提高钛靶电流密度时,靶面形貌由具有阶梯状直线条纹的多边形凹坑结构转变为具有直线条纹的多边形凹坑和水流波纹状的圆形凹坑的混合结构,说明此时靶面镀料的脱靶方式除典型的碰撞溅射外,已逐渐向碰撞溅射加热发射双重脱靶方式转变,镀层的沉积速率也由6 nm/min大幅增大至26 nm/min。     

The effect of Ti sputter target oxidation level on reactive High Power Impulse Magnetron Sputtering process behaviour

This paper investigates the effect of sputter target oxidation level on reactive process behaviour during High Power Impulse Magnetron Sputtering of transition metal target (Ti) in Ar/O₂ atmosphere. It was found by this study that the sputter target state depends on the history of its use in reactive HIPIMS mode. The effect appears to be pronounced strongly due to the significance of ion irradiation induced effects leading to enhanced sputter target oxidation. The target sputter cleaning times (e.g. after a reactive deposition run) are long (compared to DC sputtering) due to the same reason. The abovementioned effect has serious implications for the hysteresis behaviour and reactive deposition process window. It is shown in this paper that the hysteresis loop can be artificially suppressed or even eliminated and the reactive deposition process window can be reduced a number of times if the starting target surface is not a clean metal surface but a partially oxidised metal surface. Such target surface condition is readily obtainable for the targets that have a history of prolonged use in reactive HIPIMS mode. Processing parameters, such as pulse frequency and peak voltage pulse values are shown to have influence on the degree to what the abovementioned effects occur.     

Modelling of sputtering yield amplification in serial reactive magnetron co-sputtering

Serial magnetron co-sputtering can be used to increase the deposition rate in reactive deposition of thin films. The increase in deposition rate is achieved by sputtering yield amplification through doping the sputtering target by a heavy element. The dopant is introduced by means of sputtering from an auxiliary target onto a rotating primary magnetron. During sputtering of the primary target, the dopant is implanted into the target surface. Here we present a model describing the serial co-sputtering technique. The model is based on the binary collision approximation and takes into account the dynamical sputtering and mixing at the target surface. As an example, W and Bi doping in reactive sputter deposition of Al₂O₃ is analyzed. W is shown to be very efficient dopant which can increase the deposition rate for oxide up to 100% with 1.6 at.% of W in the resulting coating. Doping by Bi is not very effective due to the low surface binding energy of Bi. The simulations show that sputtering yield amplification can be realized in the serial co-sputtering setup with rotating magnetrons.     

Use of a theoretical model to investigate RF and DC reactive sputtering of titanium and chromium oxide coatings

An analysis of RF and DC reactive sputtering techniques is presented. The transition between a metal sputtering mode and a compound sputtering mode is usually noticed with a metallic target and an argon+oxygen gas mixture. The so-called hysteresis effect often observed for small amounts of reactive gas is explained in recent models. By considering gas kinetics parameters, it is possible to evaluate quite simple relationships between the main processing parameters. These theoretical calculations enable the prediction and aid the understanding of instability phenomena observed in reactive sputtering. In this paper, the effects of some parameters on the position and size of instability regions are discussed, and the difference between DC and RF reactive deposition is investigated. Simulations and experimental results are compared for the case of titanium and chromium oxide thin films prepared by DC and RF reactive sputtering. The influence of sputtering power on the position of the hysteresis loop is analysed theoretically and experimentally, and the changes observed between the reactive sputtering of titanium and chromium oxide materials are also discussed.     

基于硅靶和碳化硅靶的碳化硅薄膜磁控溅射工艺对比

目的 通过基于碳化硅陶瓷靶的直接溅射和基于硅靶与甲烷的反应溅射,在Si(100)基底上沉积碳化硅薄膜,对比两种工艺制备碳化硅薄膜的异同.方法 采用直接磁控溅射与反应磁控溅射工艺制备碳化硅薄膜,通过白光干涉仪、轮廓仪、X光电子能谱仪(XPS)分析薄膜粗糙度、厚度、沉积速率、组分,通过X射线衍射仪和扫描电子显微镜分析薄膜的物相结构和形貌.结果 基于硅靶和甲烷的反应溅射工艺,甲烷流量百分比为20％～70％时,沉积速率从11.3 nm/min升高到36.5 nm/min.甲烷流量百分比为20％～60％时,表面粗糙度Rq值变化不大;甲烷流量百分比为70％时,Rq值有增大的趋势.对于甲烷反应溅射工艺,硅碳元素比例可调,但甲烷气体不易控制.基于碳化硅陶瓷靶工艺,随沉积时间(即膜层沉积厚度)的增加,表面粗糙度Rq变化不大,硅碳原子比接近1:1.两种工艺制备的薄膜均为晶态,且为8H-SiC.结论 比较两种工艺,相同靶功率下,硅靶反应溅射的沉积速率明显快于碳化硅陶瓷靶.硅靶反应溅射的元素比例可调,但甲烷气体不易控制;碳化硅陶瓷靶的沉积过程稳定,硅碳原子比接近1:1.     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process: Part II: The role of the duty cycle

The reactive gas pulsing process (RGPP) was used to deposit titanium oxynitride thin films by dc reactive magnetron sputtering. A titanium target was sputtered in a reactive atmosphere composed of Ar + O₂ + N₂. Argon and nitrogen gases were continuously introduced into the sputtering chamber whereas oxygen was injected with a well-controlled pulsing flow rate following a rectangular and periodic signal. A constant pulsing period T = 45 s was used for every deposition and the duty cycle α = t_ON/T was systematically changed from 0 to 100%. The operating conditions were investigated taking into account the poisoning phenomena of the target surface by oxygen and nitrogen. Kinetics of poisoning were followed from measurements of the total sputtering pressure and titanium target potential during the depositions. Deposition rate and optical transmittance of titanium oxynitride coatings were also analysed and correlated with the process parameters. Pulsing the oxygen flow rate with rectangular patterns and using suitable duty cycles, RGPP method allows working according to reversible nitrided-oxidised target conditions and leads to the deposition of a wide range of TiO_xN_y thin films, from metallic TiN to insulating TiO₂ compounds.     

Applications of combined ion implantation for improved tribological performance

Ion implantation set-up on the base of ion gun with target sputtering by Penning discharge plasma was created. The set-up allows to conduct implantation of ions of various materials with an implantation current of 100 μA/cm² at acceleration voltage of up to 30 kV. Combined implantation of TiB₂ compound and Argon or Nitrogen were applied for surface properties modification of WC-Co hard alloy and SKD11 steel. The effect of implantation on mechanical and tribological properties has been studied and discussed with respect to implantation fluence. It was shown that the main effect of implantation is the modification of thin surface layer with formation of Ti, B, N₂ — base compounds, which leads to modification of surface adhesion interaction and wear resistance improvement. Examples of application to real products are presented.     

Modelling of sputtering yield amplification effect in reactive deposition of oxides

Many reactive sputter deposition applications require high deposition rates. The primary limiting parameters in magnetron sputtering are the target power dissipation and sputtering yields of the target elements. In reactive deposition of oxides, the deposition rate is of particular interest due to the low sputtering yield of most commonly used oxides. Traditional high rate techniques rely on a feedback control of the oxygen partial pressure to prevent formation of oxide on the target and hence enable operation in the transition area. An alternative approach, based on target doping, is presented in this paper.By doping the sputtering target with heavy elements, it is possible to substantially enhance the sputtering yield and hence the deposition rate. Simulations of the partial sputtering yield values for aluminium from doped targets sputtered in reactive atmosphere have been carried out. The Monte Carlo based TRIDYN computer code has been used for simulations. The program has been used to find out optimum alloying conditions to obtain maximum partial sputtering yield for deposition of Al₂O₃. Our simulations indicate that the sputtering yield amplification in reactive sputtering may lead to much higher relative deposition rate increase than in a nonreactive case. The highest relative increase may be achieved in the transition region but substantial increase is predicted also in the oxide mode.     

Investigation of reactive high power impulse magnetron sputtering processes using various target material-reactive gas combinations

The two most important issues limiting reactive high power impulse magnetron sputtering (HIPIMS) process applicability until recently were the absence of suitable reactive HIPIMS control means and the limited capability of HIPIMS power supplies in terms of arc handling. The significant advancement has been made recently by the development of the optical plasma monitoring (PM)-based process control technology for reactive HIPIMS [Surface & Coatings Technology 204 (2010) 2159-2164]. The initial studies of reactive HIPIMS processes however have only covered Ti-O₂ target material-reactive gas system.In this paper the recently developed PM-based active feedback control technology was applied to explore further reactive HIPIMS processes now using a variety of different target material and reactive gas combinations. Data for hysteresis behaviour and process control using either PM or constant gas flow methods for Ti-O₂, Ti-CO₂, Cr-O₂, Cr-C₂H₄, Al-O₂, and Zn:Al-O₂ material-gas systems is presented and compared. In all cases the processes were found to exhibit hysteresis behaviour. The magnitude and features of the hysteresis loop were found to depend strongly on a particular metal-reactive gas pair. Similar to AC and DC reactive sputtering processes the hysteresis behaviour in reactive HIPIMS was found to be more pronounced for the gases that have high chemical affinity for a metal sputter target. The PM-based process control technology monitoring either metal or gas plasma emissions was shown to provide accurate control and stable operation of reactive HIPIMS discharges.     

反应磁控溅射MgO薄膜溅射模式的分形维表征

用反应磁控溅射的方法制备了MgO薄膜，基于原子力显微镜观测，并借助Fourier变换，计算了薄膜表面形貌的分形维数。发现分形维数变化对应于薄膜溅射模式的变化，二者之间有相关性，氧分压30％的分形维数是一个临界点，分形维数若发生明显跌落，意味着溅射模式发生变化，界于临界值两侧的分形维数，分别对应两种截然不同的溅射模式，与临界值对应的溅射状态则处于金属模式和氧化物模式的混和状态。