Investigation of the rf and dc hollow cathode plasma-jet sputtering systems for the deposition of silicon thin films

Both rf and dc hollow cathode plasma-jet sputtering systems have been investigated for thin film semiconductor deposition. These systems were studied as a modification of the well-known rf hollow cathode plasma jet system. The aim of this modification was to provide low temperature deposition of semiconductor silicon and silicon-based alloys as thin films with these plasma jet systems. As a first step, the deposition of an already well explored, hydrogenated amorphous silicon material, a-Si:H, was chosen for experimentation. Plasma erosion of single crystal silicon nozzles in an Ar and H₂ working gas mixture was utilized for this purpose. A comparison of both dc and rf hollow cathode plasma jets has been made and correlated to the a-Si:H thin film properties. As a preliminary result, large differences between the properties of a-Si:H thin films deposited using dc and rf plasmas have been found. Monohydride Si:H composition was found for a-Si:H films fabricated using the dc plasma jet system under certain experimental conditions. However, predominantly di-hydride and multi-hydride structures and strong oxidization were found for the a-Si:H films deposited using rf plasma excitation. The sputtering efficiencies of both the rf and dc jet sources for silicon films have been found to be similar.     

The effect of disturbed PECVD electrode surfaces on the homogeneity of microcrystalline silicon films

In this work we present a novel electrode design for the plasma enhanced chemical vapor deposition of microcrystalline silicon thin films that enables optical access to the growing layer under normal incidence. The optical access is realized by piercing the electrode with a conical feed through of 10 mm diameter at the electrode side facing the plasma. The influence of the feed through on deposition homogeneity is studied in different pressure regimes from 8 mbar to 24 mbar on intrinsic layers optimized for state of the art thin-film silicon solar cells. The homogeneity of the layers was determined by spatially resolved thickness measurements and evaluation of the crystalline volume fraction by Raman spectroscopy. With the aim to minimize the influence of the disturbance of the electrode surface the effect of different insets in the feed through on the homogeneity is studied. To find a maximum in optical transmission of the insets at optimal film homogeneity different designs of metallic grids were tested. We show that using the modified electrode it is possible to deposit microcrystalline silicon layers which are comparable in homogeneity to those fabricated with an unchanged standard electrode. This was achieved by covering only 19% of the area of the feed through by a metallic inset.     

HWCVD与RF-PECVD复合技术制备微晶硅薄膜的性能*

采用热丝化学气相沉积(HWCVD)和射频等离子体化学气相沉积(RF-PECVD)相结合的技术,在普通载玻片和聚酰亚胺衬底上沉积制备微晶硅薄膜。系统考查了热丝到衬底的距离对沉积薄膜结构和性能的影响规律,用拉曼光谱仪、X-射线衍射仪(XRD)、紫外可见光纤光谱仪对薄膜的晶化率、微观结构和光学性能进行研究。结果表明:薄膜沉积速率最高可达到0.73nm/s,晶化率和禁带宽度分别可以在0%～78%和0.86～1.28eV变化,射频等离子体的引入有助于多晶硅薄膜的(220)择优生长,HWCVD的引入有助于薄膜晶化。     

Spatially resolved Langmuir probe measurements of a magnetically enhanced hollow cathode arc plasma

Hollow cathode arc discharges are efficient plasma sources and are applied in substrate pretreatment or plasma-activated deposition processes. In order to generate large volume homogeneous plasmas to guarantee uniformity of plasma activation and coating properties, in the presented configuration a ring-shaped anode is positioned coaxially around the hollow cathode tube. A magnetic field is applied, which is axial within the cathode tube and spreads out in the deposition chamber. In order to characterize the hollow cathode plasma, spatially resolved Langmuir probe measurements have been carried out. The charge carrier density maximum on the cathode tube axis reaches values up to 10¹³ cm^? 3. With increasing distance from the plasma source, the plasma density decreases and shows a smoother lateral profile. Maxwellian electron energy distribution functions are observed with spatially homogeneous electron temperatures in the range 1–4 eV. Increasing the chamber pressure leads to higher plasma densities and lower electron temperatures. Reduction of the gas flow through the hollow cathode tube results in a strong rise of the plasma density over two orders of magnitude. The magnetic field supports the low gas flow mode and leads to higher plasma densities, too. The results of the Langmuir probe measurements are discussed by means of the active zone model and are further related to optical emission measurements performed in the vicinity of the hollow cathode orifice.     

Influence of substrate pre-treatments on the growth of SixNyHz thin films by plasma enhanced chemical vapor deposition

A two-step plasma enhanced chemical vapor deposition procedure has been developed to produce high quality Si_xN_yH_z films for quantum cascade laser applications. The procedure consists in exposing the GaAs substrate to a controlled N₂ plasma previous to the silicon nitride film deposition. The pre-treatment causes the formation of a thin GaN film that passivates the GaAs wafer. The method has been optimized varying RF power, N₂ flow rate and process time of the pre-treatments and monitoring their effects on the resulting chemical composition and dielectric properties of the nitride overlayers, by means of infrared spectroscopy, X-ray photoelectron spectroscopy and electric characterizations. A narrow window in the pre-treatment RF power, N₂ flux and time values, improves the composition, structural and dielectric properties of the silicon nitride overlayers. The best result has been found depositing the silicon nitride films on GaAs wafer after 2 min of N₂ plasma treatment with a power of 20 W and a 50 cm³/min flow rate.     

Growth kinetics of plasma deposited microcrystalline silicon thin films

A continuum model for the nucleation and growth of microcrystalline silicon thin films from SiH₄/H₂ discharges is presented. The simulation considers mass balances and surface coverage with adspecies and silicon clusters up to the size where they can be considered as thermodynamically stable. The model is combined to a plasma gas phase simulator and a simulator of thin film morphology and is used for studying the growth differences in two different regions, the center and the edge of a 30 × 30 cm² substrate. The predictions for the film growth rate, film crystallinity and surface roughness in both regions are presented and discussed together with the main processes governing nucleation and growth and the slow step for stable nanocrystal formation.     

Influence of ion bombardment on the surface functionalization of plasma deposited coatings

This paper investigates the influence of ion bombardment on surface functionalization of hybrid organic-inorganic coatings deposited by plasma enhanced chemical vapor deposition. The experiment involves simultaneous deposition of silicon based coatings on Si substrates at the live and a floating electrode of 13.56 MHz asymmetric capacitive coupled plasma. The films were characterized using Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, which shows the presence of both inorganic Si-O-Si and organic Si-OH groups. By increasing the RF power we observe a consistent increase in nano-hardness of the film at the powered electrode, however the OH functional group is found to reduce drastically. In contrast, the nano-hardness of the films deposited at the floating electrode remains constant throughout the range of the applied RF power and it also retains the OH functional groups. At a typical RF power, above 200 W, we observe a decrease in deposition rate at the powered electrode. This is attributed to film densification by ion bombardment in conjunction with sputtering. Based on these observations, a qualitative discussion is presented to account for the differences in the chemical and mechanical properties of the films deposited at the floating and the live electrodes.     

Optical properties of Se or S-doped hydrogenated amorphous silicon thin films with annealing temperature and dopant concentration

We report the effects of the thermal annealing and dopant concentration on the optical properties of Se or S-doped hydrogenated amorphous silicon thin films. The Se and S-doped a-Si:H (a-Si,Se:H and a-Si,S:H) thin films were prepared by glow discharge plasma enhanced chemical vapor deposition (GD-PECVD) on 7059 corning glass. The films were subsequently annealed in vacuum in the temperature range from 100 to 500 °C. Influence of doping and annealing was examined by means of optical transmission spectroscopy of the films in the wavelength range of 300-1100 nm taken at room temperature. The absorption coefficients and refractive indices decreased as the annealing temperature increased from 100 to 300 °C and then increased again as the annealing temperature further increased to 500 °C, while the highest bandgap was observed at 300 °C for all of the samples. For a given dopant concentration bandgap was observed to be higher in a-Si,S:H than a-Si,Se:H thin films.     

Fabrication and characterization of ITO thin films on heat-resistant transparent flexible clay films

Transparent conductive indium tin oxide (ITO) thin films were deposited on transparent flexible clay films with heat resistant and high gas barrier properties by rf magnetron sputtering. The electrical, structural, and optical properties of these films were examined as a function of deposition temperature. A lowest resistivity of 4.2 × 10^− 4 Ωcm and an average transmittance more than 90% in the visible region were obtained for the ITO thin films fabricated at deposition temperatures more than 300 °C. It was found that ITO thin films with low resistivity and high transparency can be achieved on transparent flexible clay film using conventional rf magnetron sputtering at high temperature, those characteristics are comparable to those of ITO thin films deposited on a glass substrate.     

Combination of zinc alloy coating with thin plasma polymer films for novel corrosion protective systems on coated steel

Steel sheet used in automotive applications has to be corrosion protected effectively, which is usually realized by zinc or zinc alloy coatings with a thickness range of 5–10 μm. Steel sheet for areas of a car body which are exceptionally stressed by corrosion, e.g. cavity flanges or joints, may be protected additionally by a thin weldable organic coating with a thickness of 2–4 μm. A very promising approach to a significantly reduced use of resources is the combination of zinc alloy coatings with thin plasma polymer films deposited by means of plasma-enhanced chemical vapour deposition (PECVD). Such plasma polymer films of just a few 100 nm thickness show excellent barrier and adhesion properties as well as a high mechanical stability.Within this work thin plasma polymer films were deposited on zinc alloy coated steel substrates using the strip hollow cathode (SHC) method, which was modified for application on grounded substrates. A pulsed DC glow discharge in a mixture of argon and an organosilane precursor was used for the deposition of films with a thickness of 100–500 nm.The chemical compositions of the coatings were determined by means of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The morphologies of the coating systems were studied by means of scanning electron microscopy. The performance of the coating systems has been studied in different specific tests of corrosion and processing behaviour. The investigated coating systems show a corrosion resistance comparable to reference samples of electro-galvanised steel sheet with additional organic coating even with a coating thickness less of half of the reference samples.     

Fabricating TiO2 Photocatalysts by rf Reactive Magnetron Sputtering at Varied Oxygen Partial Pressures

Titanium dioxide (TiO₂) thin films were fabricated onto non-alkali glass substrates by rf reactive magnetron sputtering at room temperature using Ti-metal target at varied oxygen partial pressure [O₂/(Ar + O₂)]. The sputtering deposition was performed under an rf power of 200 W. The target to substrate distance was kept at 80 mm, and the total gas pressure was 10 mTorr after 2 h of deposition. It was found that the crystalline structure, surface morphology, and photocatalytic activities of the TiO₂ thin films were affected by the oxygen partial pressure during deposition. The XRD patterns exhibited a broad-hump shape indicating the amorphous structure of TiO₂ thin films. The thin films deposited at a relatively high value of oxygen partial pressure (70%) had a good photo-induced decomposition of methylene blue (MB), photo-induced hydrophilicity, and had a small grain size.     

Duplex treatment of AISI 304 austenitic stainless steel using rf nitriding and dc reactive magnetron sputtering of titanium

In this work, duplex treatment has been carried out using radio frequency (rf) plasma nitriding process and direct current (dc) magnetron sputtering of titanium. Nitriding of AISI 304 stainless steel, using rf plasma technique, created a thick modified layer of approximately 20 μm for short plasma processing time of 10 min. After nitriding process, a thin titanium nitride film has been deposited using dc magnetron sputtering of titanium for different nitrogen/argon gas pressure ratios. The treated samples were characterized via glow discharge optical spectroscopy, X-ray diffractometry, scanning electron microscopy, profile meter and Vickers microhardness tester. The elemental composition, thickness and microhardness values of the duplex treated layers are found to be gas composition dependent. The data shows that the microhardness of the duplex treated layer increases to 1.42 fold relative to the associate value of the nitrided one. Moreover, high deposition rate of 110 nm/min is obtained.     

Surface morphology of nanostructured anatase thin films prepared by pulsed liquid injection MOCVD

Nanostructured anatase thin films were prepared by chemical vapor deposition feeding a metal organic precursor in a pulsed liquid injection mode. The films were deposited at 500 °C on stainless steel substrates using a single molecular titanium isopropoxide liquid solution as the precursor, without any reactant gas. An effective pulsing injection mechanism for the precursor supply provides uniform concentration of the precursor in the vapor phase, allowing the formation of titanium dioxide layers from small micro-doses of the metal organic precursor. Energy-dispersive spectroscopy, scanning electron microscopy and X-ray diffraction studies show the formation of crack-free nanostructured anatase thin films, highly oriented, formed basically by stepwised nanostructures with a uniform coverage and no detectable carbon contamination. Surface crystallinity, composition, nanostructure and morphology are discussed in terms of the experimental parameters used in the deposition process.     

Atmospheric pressure barrier torch discharge and its optimization for flexible deposition of TiO2 thin coatings on various surfaces

This paper reports on the preparation of titanium (IV) oxide films via the improved atmospheric pressure barrier torch discharge (BTD) deposition. This approach is a modification of the atmospheric pressure glow discharges (APGDs) ranking among plasma enhanced chemical vapor deposition (PECVD) techniques. These methods are based on plasma–chemical reactions of the precursors' vapors occurring in the active plasma environment. The layers are produced in terms of heterogeneous recombination reactions of the high active species on the supporting surface. The major treated topic comprises the influence of the used support on the physical properties of the layers. A set of three different supports was used including quartz slides (non-conducting, dielectric), silicon discs (semi-conducting) and polished Ni sheets (conducting). Crystallographic structure, surface roughness, surface wettability and the film thickness were assessed and used as a set of physical properties to be discussed and compared for each of the films and mutually. In parallel the qualitative analysis of the emission spectra of the barrier torch discharge during the deposition process was also presented. Different conductive connection of plasma stream with the substrate crucially influences the temperature of this substrate. It has a direct effect mainly on the crystallinity and morphology of the films and also on the plasma parameters. This knowledge might be used as a tool for the optimization of deposition conditions. Photocatalytic functionality of the layers was quantified in a simple test based on the photocatalytic oxidation of Rhodamine B (C₂₈H₃₁ClN₂O₃) under UV radiation.     

刻蚀工艺对四面体非晶碳膜生长及其性能的影响

目的研究不同等离子体刻蚀工艺对基体和四面体非晶碳膜(ta-C)的影响,并进一步考察不同电弧等离子体刻蚀时间对ta-C薄膜结构的影响。方法采用自主设计研制的45°单弯曲磁过滤阴极真空电弧镀膜设备,进行不同等离子体刻蚀以及ta-C薄膜的沉积。使用等离子体发射光谱仪表征离子种类及其密度,使用椭偏仪表征薄膜厚度,原子力显微镜表征刻蚀后的基体粗糙度,拉曼光谱仪和XPS表征薄膜结构,TEM分析薄膜的膜基界面结构。结果辉光刻蚀工艺中,作用的等离子体离子以低密度的Ar离子为主;而电弧刻蚀时,作用的等离子体离子为高密度的Ar离子和少量的C离子,并且能够在基体表面形成约15 nm的界面层,并实现非晶碳膜(a-C)的预沉积。随电弧等离子体刻蚀时间增加,ta-C薄膜的sp3含量有所降低。结论相比于辉光刻蚀,电弧刻蚀利于制备较厚的ta-C薄膜。这主要是因为电弧刻蚀时,基体表面形成良好的界面混合层,并预沉积了非晶碳膜,形成a-C/ta-C的梯度结构,有助于增强膜基结合力。     

Study on Ti/BDD Film Electrode with Ta Interlayer

Boron doped diamond(BDD)thin films have been deposited on Ti substrate with Ta interlayer by MP-CVD(microwave plasma chemical vapor deposition),and Ta interlayer was deposited by magnetron sputtering.The physical and electrochemical behaviors of the Ti/Ta/BDD electrode and its application in electrochemical oxidation of wastewater containing 2,4-dichlorophenol were studied.Raman spectroscopy and field emission scanning electron microscopy(FESEM)demonstrates that the films obtained exhibit well-defined diamond features.XRD spectroscopy shows no TiC in the BDD film with Ta interlayer.Electrochemical measurement shows the BDD electrode behaves low background current and wide working potential window up to 4 V.Further,the removal efficiency of chemical oxygen demand(COD)of the BDD electrodes were evaluated by the electrochemical oxidation of 2,4-dichlorophenol.     

Characteristics of copper oxide films deposited by PBII&D

Copper oxide films were deposited by plasma based ion implantation and deposition using a copper antenna as rf sputtering ion source. A gas mixture of Ar + O₂ was used as working gas. During the process, copper that was sputtered from the rf antenna reacted with oxygen and was deposited on a silicon substrate. The composition and the chemical state of the deposited films were analyzed by XPS. The structure of the films was detected by XRD. It is observed that Cu₂O film has been prepared on the Si substrate. It is found that the microstructure of the deposited film is amorphous for the applied voltage of − 5 kV. The surface layer of the deposited films is CuO. This is because the surface layer absorbs the oxygen from ambient air after the treated sample was removed from the vacuum chamber. An appropriate applied voltage, 2 kV under the present conditions, brings the lowest resistance. It is also seen that the maximum absorbance of the deposited films moves to a lower wavelength with increased applied voltage.     

Adhesion improvement of hydrogenated diamond-like carbon thin films by pre-deposition plasma treatment of rubber substrate

For reduction of friction and enhancement of wear resistance of dynamic rubber seals, thin films of hydrogenated diamond-like carbon (DLC) have been deposited on hydrogenated nitrile butadiene rubber (HNBR) via magnetron-enhanced plasma chemical vapor deposition (ME-PCVD). Pre-deposition plasma treatment of HNBR substrate is proved to be crucial for the improvement of film performance due to enhanced interfacial adhesion. The columnar structure and the crack network formed during deposition enhance the flexibility of DLC thin films and exhibit strain tolerance up to 5%. Below 50% stretch strain and after unloading, thin DLC films of ∼ 300 nm thickness still adhere on the rubber substrates and no spallation or delamination is observed. The thin DLC film deposited on Ar-plasma pre-treated rubber at − 400 V substrate bias potential exhibits a very low coefficient of friction of 0.175 (compared to > 1 of uncoated HNBR rubber). After tribotests even under high normal load of 3 N, almost no wear can be seen on the films. Such tribological property is even better than that of 1 µm thick DLC or Me-DLC coated rubbers.     

Structural and electronic properties of Si nanocrystals embedded in amorphous SiC matrix

Si-rich hydrogenated amorphous silicon carbide thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited films were subsequently annealed at 900 °C and 1000 °C to form Si nanocrystals embedded in amorphous SiC matrix. Raman spectra demonstrate the formation of Si nanocrystals with size around 7–9 nm. For the sample annealed at 1000 °C, the crystallinity can be reached to 70%. As increasing the annealing temperature, the dark conductivity is increased accompanying with the increase of crystallinity of the film. The dark conductivity reaches to 1.2 × 10^?6 S cm^?1 for the sample annealed at 1000 °C, which is 4 orders of magnitude higher than that of as-deposited film. It is found that the carrier transport process is dominated by the thermally activated transport process according to the temperature-dependent conductivity results.     

Influence of substrate bias on the composition of SiC thin films fabricated by PECVD and underlying mechanism

The influence of the substrate bias on the composition of SiC thin films synthesized by plasma-enhanced chemical vapor deposition was studied. Our results indicate that the ratio of Si to C in the thin films is almost stoichiometric at a bias of − 300 V, whereas excessive carbon is observed in the films if the bias is lower or higher. Very little oxygen can be detected in the film produced without biasing. The effects of the bias on the composition of the thin films can be attributed to the interaction between the positive ions in the plasma and the surface atoms. The underlying mechanism is also discussed.