Mechanism of biaxial alignment in thin films, deposited by magnetron sputtering

Biaxially aligned TiN layers have been deposited by reactive unbalanced magnetron sputtering. In this work, a mechanism for the resulting microstructure and biaxial alignment of the deposited TiN layers will be discussed. According to the described model, the resulting biaxial alignment is caused by an overgrowth mechanism (zone T) due to an anisotropy in growth rate of the different oriented grains towards the incoming material flux. Hence, the in-plane alignment will mainly depend on two parameters: the mobility during the growth (zone T condition) and the spread on the incoming material flux. This spread on the incoming material flux has been calculated by an earlier published Monte Carlo simulation program of the transport of sputtered particles towards the substrate. The model for the mechanism of biaxial alignment is validated by comparing the experimental and theoretical influence of target-substrate distance and working pressure on the resulting in-plane alignment.     

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.     

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.     

Comparison of chromium nitride coatings deposited by DC and RF magnetron sputtering

Chromium nitride coatings were deposited by DC and RF reactive magnetron sputtering on AISI 304 stainless steels without substrate heating. A Cr₂N phase was formed in the RF sputtered coatings with a low N₂ flow content ranging within 30-50%. A NaCl type CrN_x phase was obtained by DC magnetron sputtering with different N₂ flow contents. The coating hardness increased with the increase of the N₂ flow content. When the coatings deposited with the same N₂ flow content were compared, the hardness of the RF sputtered CrN_x was higher than that of the DC sputtered CrN_x, which was mainly due to the distinct difference between the dense structure (RF process) and the porous structure (DC process). The RF sputtered CrN_x coatings showed an excellent adhesion strength as compared to the DC sputtered coatings. By selecting the deposition method and optimizing the N₂ flow content, CrN_x coatings with a preferred microstructure could be obtained, which would be a candidate material for research and applications in nano-science.     

Atomic force microscopy and X-ray photoelectron spectroscopy evaluation of adhesion and nanostructure of thin Cr films

Chromium (Cr) thin films were deposited on float glass using electron beam (e-beam) physical vapor deposition and radio frequency (RF) magnetron sputtering techniques. Surface morphology of these Cr films was studied using atomic force microscopy (AFM). The e-beam deposited Cr films consisted of isolated surface mounds while in RF sputtered samples, these mounds combined to form larger islands. Lower surface adhesive properties were observed for e-beam deposited films, as determined from AFM force-distance curves, presumably due to the nanostructural differences. Similar amounts of adsorbed atmospheric carbonaceous contaminants and water vapor were detected on samples deposited using both methods with e-beam deposited samples having additional carbide species, as determined by X-ray photoelectron spectroscopy data. The dominant crystallographic plane in both e-beam deposited and RF sputtered Cr thin films was (110) of body-centered cubic Cr metal structure as determined from X-ray diffraction data. Weak (211) reflection was also observed in RF sputtered samples and was attributed to a different thin Cr film condensation and growth mechanism which resulted in nanostructural differences between films deposited using two different methods.     

Application of magnetron sputtering for producing bioactive ceramic coatings on implant materials

Radio frequency (RF) magnetron sputtering is a versatile deposition technique that can produce thin, uniform, dense calcium phosphate coatings. In this paper, principle and character of magnetron sputtering is introduced, and development of the hydroxyapatite and its composite coatings application is reviewed. In addition, influence of heat treatment on magnetron sputtered coatings is discussed. The heat treated coatings have been shown to exhibit bioactive behaviour both in vivo and in vitro. At last, the future application of the bioactive ceramic coating deposited by magnetron sputtering is mentioned.     

Effect of flux clusterization on the thickness of films deposited by magnetron and pulsed laser sputtering of metal oxides

We have studied the relation between clusterization in the flux of a substance and the thickness of deposited films obtained by the magnetron and pulsed laser sputtering of La_0.7Sr_0.3MnO₃ and YBa₂Cu₃O_{7 − δ} targets, respectively. No cluster formation has been observed in the case of magnetron sputtering, which is explained by a low concentration of atoms (ions) in the sputtered material flux. In accordance with calculations for the flux of non-interacting atoms, the deposited film thickness (h) exhibits exponential decrease with increasing distance (L) from the target. In the case of pulsed laser sputtering, for which the concentration of sputtered substance in the plasma is four orders of magnitude higher, the h(L) curve sharply deviates from the calculated dependence for the distances L > 6.2 cm, which is explained by the onset of intense clusterization in the laser plasma flux.     

Annealing dependence of residual stress and optical properties of TiO2 thin film deposited by different deposition methods

Titanium oxide (TiO(2)) thin films were prepared by different deposition methods. The methods were E-gun evaporation with ion-assisted deposition (IAD), radio-frequency (RF) ion-beam sputtering, and direct current (DC) magnetron sputtering. Residual stress was released after annealing the films deposited by RF ion-beam or DC magnetron sputtering but not evaporation, and the extinction coefficient varied significantly. The surface roughness of the evaporated films exceeded that of both sputtered films. At the annealing temperature of 300 degrees C, anatase crystallization occurred in evaporated film but not in the RF ion-beam or DC magnetron-sputtered films. TiO(2) films deposited by sputtering were generally more stable during annealing than those deposited by evaporation.     

Influence of AlN buffer layer thickness and deposition methods on GaN epitaxial growth

A gallium nitride (GaN) epitaxial layer was grown by metal-organic chemical vapor deposition (MOCVD) on Si (111) substrates with aluminum nitride (AlN) buffer layers at various thicknesses. The AlN buffer layers were deposited by two methods: radio frequency (RF) magnetron sputtering and MOCVD. The effect of the AlN deposition method and layer thickness on the morphological, structural and optical properties of the GaN layers was investigated. Field emission scanning electron microscopy showed that GaN did not coalesce on the sputtered AlN buffer layer. On the other hand, it coalesced with a single domain on the MOCVD-grown AlN buffer layer. Structural and optical analyses indicated that GaN on the MOCVD-grown AlN buffer layer had fewer defects and a better aligned lattice to the a- and c-axes than GaN on the sputtered AlN buffer layer.     

Effect of LP-buffer on the structure of ZnO thin films prepared on glass substrate using RF magnetron sputtering

The ZnO thin films with preferential C-orientation and smooth surface have been prepared using an RF magnetron sputtering method by the insertion of low-power (LP) sputtered ZnO buffer. The XRD results show that the C-orientation of the ZnO buffer layer deposited under the RF power of 30 W is much better than that deposited under higher RF power. With the increase of the LP-buffer thickness, the C-orientation as well as the crystal quality of ZnO films improves, the surface becomes smooth and the RMS roughness decreases from 88.4 Å to 38.5 Å. The ZnO lattice is independent of the insertion of LP buffer.     

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.     

The use of camera obscura in sputter deposition

Camera obscura or pinhole camera is an optical device where object is recorded through a small pinhole. A similar experiment was performed in a sputter deposition system. A shield with small aperture (1 mm in diameter) was positioned between the target and the glass substrate. Only the material sputtered in direction of the aperture was deposited on the substrate. In this way a direct image of the target was recorded (similar to a camera obscura). The thickness profile of the image made by the camera obscura is proportional to the flux of emitted particles from the target. Experiments were conducted in a triode sputtering system and in a magnetron sputtering system. The camera obscura was used to study sputtering from different two-element segmental targets: Ti-Al, Al-W, Al-Cu, Ti-W, Ni-C. The thickness profiles of deposits were measured by profilometer. These simple experiments were performed to give a better understanding of the sputtering process.     

射频磁控溅射TiO2/HA复合生物膜的制备与表征

将水热合成的羟基磷灰石(HA)粉与20 wt%Ti粉混合,冷压烧结成靶材。采用射频磁控溅射方法,在工业纯钛基体上沉积TiO₂/HA生物薄膜,通过扫描电镜(SEM)及其能谱(EDS)、X射线衍射(XRD)和差热分析仪(TDA)对膜层进行了表征,探讨了溅射膜的晶化工艺。结果表明:由于选择溅射和OH-损失,溅射膜由TiO₂晶体颗粒和非晶钙磷化合物组成,且其Ca/P比降低。经700℃,0.5 h水蒸气处理,非晶钙磷化合物结晶度大大提高,并部分转化为HA晶体,且处理后的溅射膜与基体间无裂纹。     

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.     

Residual stress in polytetrafluoroethylene-metal nanocomposite films prepared by magnetron sputtering

In the present research we have evaluated residual stress as well as thermal stability of polytetrafluoroethylene (PTFE) and PTFE-based silver (Ag) nanocomposite films fabricated by dual magnetron sputtering. We used a RF magnetron system for sputtering PTFE, and a DC magnetron sputter source for metal. We have demonstrated that thin nanocomposite films of Ag/sputtered PTFE (thickness 800 to 1100 nm, Ag concentration 3.5 to 24.5%) deposited on silicon are stressed (6.24 to 12.2 MPa). The residual stress depends on the concentration of the nanoparticles. Pure sputter deposited PTFE films are under a small tensile stress, which becomes increasingly more compressive upon increasing the filling factor of the metallic nanoparticles. Depending on the concentration of nanoparticles, the residual stress is determined by a thermal component that is sensitive to temperature variation, even in the range of room temperature. In the evaluation of the thermal response of the nanocomposite-silicon system, both the changes in the thermal expansion coefficient as well as the elastic modulus of the nanocomposite with the concentration should be taken into account.     

溅射镀铝碳纤维质量的研究

针对制取C／Al复合材料、C／Al间润湿与结合牢固度问题，以及CVD法涂Al在高温损伤碳纤维等难题，采用磁控溅射镀加溅射离子镀膜方法，在碳纤维表面镀Al膜。系统地研究了碳纤维镀Al的界面变化、组分分布、受热强度变化等内容，讨论C／Al复合材料的复合工艺问题。研究结果表明，磁控溅射法碳纤维镀Al膜表面光洁、均匀、规整、C／Al润湿、结合牢固，无化学反应损伤碳纤维现象。镀铝碳纤维受热后拉伸强度稍有降低，但无化学反应及生成Al4C3的现象。研究结果能给C／Al复合材料的制备创造工艺条件。     

Production of solar absorbing cermet films by dual cathode d.c. magnetron sputtering

A technique using d.c. reactive sputtering from two cathodes for the production of graded-index solar selective cermet films is described. Two variations are presented, one in which the grading is carried out by changing the electrical inputs alone, and the other in which the substrate is translated through a flux of sputtered material that is constant in time. The second variation employs a magnetron source. The coatings produced are iron-silicon oxide and copper-aluminium oxide. The annealing behaviour of the films was studied and the iron-silicon oxide film was found to be stable in vacuum up to 400°C.     

ZnO transparent thin films for gas sensor applications

Zinc oxide (ZnO) transparent thin films were deposited onto silicon and Corning glass substrates by dc magnetron sputtering using metallic and ceramic targets. Surface investigations carried out by Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) have shown a strong influence of deposition technique parameters on film surface topography. Film roughness (RMS), grain shape and dimensions are correlated with the deposition technique parameters as well as with the target material. XRD measurements have proven that the dc sputtered films are polycrystalline with the (002) as preferential crystallographic orientation. AFM analysis of thin films sputtered from a ceramic target has shown a completely different surface behavior compared with that of the films grown from a metallic target. This work demonstrates that the target material and the growth conditions determine the film surface characteristics. The gas sensing characteristics of these films are strongly influenced by surface morphology. Thus correlating the optical and electrical film properties with surface parameters (i.e. RMS and Grain Radius) can lead to an enhancement of the material's potential for gas sensing applications.     

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.     

Microstructures using RF sputtered PSG film as a sacrificial layer in surface micromachining

In this paper, we explore RF magnetron sputtered Phosphor-silicate-glass (PSG) film as a sacrificial layer in surface micromachining technology. For this purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by conventional solid-state reaction route using P₂O₅ and SiO₂ powders. The PSG films were prepared in a RF (13·56 MHz) magnetron sputtering system at 300 watt RF power, 20 mTorr pressure and 45 mm target-to-substrate spacing without external substrate heating. Microstructures of sputtered silicon dioxide film were fabricated using sputtered PSG film as sacrificial layer in surface micromachining process.