磁控溅射法制备铁氧体薄膜的界面结合强度研究

利用磁控溅射法在单硅晶基底和玻璃基底上沉积铁氧体薄膜,采用AFM观察薄膜的微观形貌,采用划痕法测试薄膜的界面结合强度,测试结果表明:由于两种不同材质上沉积的薄膜粗糙度缘故,硅晶/铁氧体薄膜的临界载荷为19.7N,其划痕形貌为裂纹状扩展,玻璃/铁氧体薄膜的临界载荷为5.3N,其划痕形貌为剥落状。     

Chemical vapor deposition of aluminum from methylpyrrolidine alane complex

Chemical vapor deposition of aluminum from a recently developed precursor, methylpyrrolidine alane complex, has been studied. Aluminum films deposited on conducting surfaces (titanium nitride, copper, gold), but not on insulating surfaces (silicon, silicon dioxide, glass) at low substrate temperatures, showing deposition selectivity, while the deposition selectivity was lost at high substrate temperatures (> 210 °C). Al deposition rates on TiN and Cu were very close, but much higher than on Au. Deposition rates on all conducting substrates increased with the temperature and reached maximum at 180 °C. Al films deposited on as-sputtered TiN or Cu have no preferred orientations. Al–Au alloys and intermetallics were observed in the films deposited on Au. Surface morphology observation revealed that the film growth on TiN or Cu is different from that on Au. The surface roughness of Al films increased with the deposition time or the film thickness.     

An evaluation of metal and semiconductor films formed by ionized-cluster beam deposition

The mechanism of film formation and the properties of films deposited by the ionized-cluster beam technique were investigated. In this technique, strong adhesion of the film to the substrate and good crystalline deposition are expected.A high adhesive strength of over 100 kg cm^-2 for Cu films on glass substrates was obtained in the experiments. The migration of adatoms consisting of ionized and neutral clusters was observed on the substrte surface. This effect, called the migration effect, can be considered to characterize film formation by cluster beam deposition and to produce good crystalline films. Si single crystals were obtained on Si substrates. A p-n junction photodiode was fabricated by the deposition of n-type Si on a p-type substrate. The diode shows improved spectral sensitivity in the UV region compared with that of commercially available solar cells.     

Effect of angle of incidence during deposition on Ti-Pd-Au conductor film adhesion

The influence of a number of the preparation conditions on the adhesive properties of the Ti-Pd-Au metallization on Ta₂N film resistors was investigated. Test samples consisted of a filament-evaporated conductor film on an unpatterned Ta₂N film on glass, sapphire and Al₂O₃ ceramic substrates. The adhesive properties of the Ti-Pd-Au films were examined as a function of the angle of incidence at which the Ti and Pd atoms were deposited. In addition the adhesive properties were examined after heat treatment in air and after electroplating gold. Transmission electron microscopy and density measurements established that at higher angles of incidence (>60°) Ti and Pd films became increasingly porous and that adhesion at the Ti-Pd interface degraded rapidly upon exposure to air. Both evaporated and plated Au layers appear to offer little protection for films evaporated under these conditions. Good adhesion was found to be independent of the substrate material and of the method used for gold deposition when the Ti-Pd films were evaporated at angles of incidence of 48° or less.     

Microstructural characterization of thin gold films on a polyimide substrate

The study of thin metal films on flexible substrates is of interest for manufacture of many devices, such as implantable electrode arrays consisting of gold film on polyimide substrates. Adhesion of the film to the substrate is of utmost importance for device durability. Gold adhesion to a polyimide has previously been shown to increase when a variety of substrate treatments are performed prior to gold sputter deposition, but little microstructural analysis has been made to complete the process-structure-properties relationship. Here, the grain size is shown to increase slightly but statistically significantly if an oxygen plasma etch and adhesion layer treatment of the film is performed prior to deposition of the gold. A log-normal grain size distribution is found for gold on each sample, and the grains are shown to be columnar. Gold deposited on non-treated polyimide shows a strong {111} texture, but a random texture is seen in both pretreated systems, indicating that the pretreatment affects the surface energy of the polyimide and alters the gold film growth.     

A comparison of TiN films produced by reactive d.c. sputtering and ion-assisted deposition

The properties of TiN films produced by reactive d.c. sputtering have been compared with those formed by deposition during irradiation by 10 keV nitrogen ions. Films were deposited on aluminium, nickel, molybdenum, silicon and titanium substrates which were chosen because they have a range of mechanical properties. The composition of the films has been studied by Rutherford backscattering, nuclear reaction analysis and transmission electron microscopy and data concerning their hardness and adhesion are also presented. It was found that the films produced by ion-assisted deposition (IAD) were nearly stoichiometric TiN with a predominant (100) orientation while the reactively sputtered films were less crystalline and contained a significant amount of oxygen and carbon throughout the film. There was also considerable improvement in the adhesion of the IAD films but their hardness was only marginally improved.     

Characterization of iridium oxide thin films deposited by pulsed-direct-current reactive sputtering

Thin films of iridium oxide were deposited on silicon and borosilicate glass substrates by pulsed-direct-current (pulsed-DC) reactive sputtering of iridium metal in an oxygen-containing atmosphere. Optimum deposition conditions were identified in terms of plasma pulsing conditions, oxygen partial pressures, and substrate temperature. The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and Rutherford backscattering spectroscopy. According to the results, it was possible to obtain films that are near-stoichiometric, smooth and uniform in texture. The films deposited without substrate heating were amorphous, and those deposited at substrate temperatures above 300 °C were found to have a homogeneous polycrystalline structure. The results also showed that pulsed-DC sputtered iridium oxide films were smoother and had lower micro-inclusions density than DC-sputtered films obtained under otherwise similar deposition conditions. This improvement in the film quality is at the expense of a tolerable decrease in the deposition rate.     

Micro-scratch analysis and mechanical properties of plasma-deposited silicon-based coatings on polymer substrates

Advanced optical applications require multifunctional coatings with specific mechanical properties, such as resistance to damage and good adhesion to different types of substrates, including polymers. In the present study we deposited amorphous hydrogenated silicon nitride (SiN_1.3) and oxide (SiO₂) films on polycarbonate and on silicon substrates by plasma enhanced chemical vapor deposition (PECVD), using a dual-mode microwave/radio frequency plasma system. The film adhesion was determined by the micro-scratch test. Depth-sensing indentation and substrate curvature measurements were used to evaluate the microhardness. Young's modulus and residual stresses of the films. The adhesion strength, represented by the critical load, L_c, when the film starts to delaminate, was determined as a function of the substrate material and the energy of bombarding ions. A direct correlation between the L_c values and the mechanical properties of the films was found. The formation of different crack patterns in the coatings during the scratch procedure is explained in terms of stress release mechanism depending on the mechanical properties of the film, the substrate and the interface region. In addition, different models applicable to the evaluation of the work of adhesion in the case of hard coatings on soft substrates are critically reviewed.     

Ultrasonic cavitation test applied to thin metallic films for assessing their adhesion with mercaptosilanes and surface roughness

Evaluating the adhesion of micrometer or nanometer thick coatings is a challenging question which concerns many application fields. This is especially true for thin films deposited on a substrate of elastic modulus higher than that of the film, or for granular coatings, that do not allow the use of common adhesion tests. Usually, applied to characterize the wear resistance of bulk materials or thick coatings, the ultrasonic cavitation test is applied here to evaluate the adhesion strength of gold and copper thin films (~200 nm) that are evaporated on a silicon substrate. The test is shown to be sensitive enough to discriminate the influence of the surface chemistry on the adhesion strength of gold and copper films. Particularly, the role of (3-mercaptopropyl)triethoxysilane as an effective adhesion promotor is demonstrated. Furthermore, the role of surface roughness of the substrate is characterized and discussed in order to get further insights on the way this parameter interferes with the ultrasonic test and determines the adhesive strength of the coating. An estimate of the adhesive strength is given on the basis of the coating delamination kinetics.     

Improvement of adhesion of DLC coating on nitinol substrate by hybrid ion beam deposition technique

Diamond-like carbon (DLC) films were prepared for a protective coating on nitinol substrate by hybrid ion beam deposition technique with an acetelene as a source of hydrocarbon ions. An amorphous silicon (a-Si) interlayer was deposited on the substrates to ensure better adhesion of the DLC films followed by Ar ion beam treatment. The film thickness increased with increase in ion gun anode voltage. The residual stresses in the DLC films decreased with increase in ion gun anode voltage and film thickness, while the stress values were independent of the radio frequency (RF) bias voltage. The adhesion of the DLC film was improved by surface treatment with argon ion beam for longer time and by increasing the thickness of a-Si interlayer.     

Effect of the initial structure on the electrical property of crystalline silicon films deposited on glass by hot-wire chemical vapor deposition

Crystalline silicon films on an inexpensive glass substrate are currently prepared by depositing an amorphous silicon film and then crystallizing it by excimer laser annealing, rapid thermal annealing, or metal-induced crystallization because crystalline silicon films cannot be directly deposited on glass at a low temperature. It was recently shown that by adding HCI gas in the hot-wire chemical vapor deposition (HWCVD) process, the crystalline silicon film can be directly deposited on a glass substrate without additional annealing. The electrical properties of silicon films prepared using a gas mixture of SiH4 and HCl in the HWCVD process could be further improved by controlling the initial structure, which was achieved by adjusting the delay time in deposition. The size of the silicon particles in the initial structure increased with increasing delay time, which increased the mobility and decreased the resistivity of the deposited films. The 0 and 5 min delay times produced the silicon particle sizes of approximately 10 and approximately 28 nm, respectively, in the initial microstructure, which produced the final films, after deposition for 300 sec, of resistivities of 0.32 and 0.13 Omega-cm, mobilities of 1.06 and 1.48 cm2 V(-1) S(-1), and relative densities of 0.87 and 0.92, respectively.     

In-situ X-ray investigations of quench-condensed thin gold films

Thin gold films were deposited on float glass substrates held at cryogenic temperatures down to 77 K and investigated in-situ using X-ray reflectometry and surface sensitive reflection mode X-ray absorption spectroscopy (XAFS). The combination of these in-situ X-ray methods with simultaneous electrical resistivity measurements yields information about the surface and volume microstructure of the deposited films as a function of the deposition temperature and their changes induced by a subsequent annealing treatment. The surface sensitive XAFS experiments clearly proved that the films exhibit a polycrystalline structure throughout the temperature range studied here. The data were fitted using a correlated Debye-model. The results show that for film deposition at low substrate temperatures < 130 K, a significantly decreasing Debye-temperature was found, reaching values of about 100 K in comparison to 165 K for the polycrystalline bulk material. This decrease was interpreted to be predominantly related to defective film regions with an increased static disorder.     

N-type crystalline silicon films free of amorphous silicon deposited on glass by HCl addition using hot wire chemical vapour deposition

Since n-type crystalline silicon films have the electric property much better than those of hydrogenated amorphous and microcrystalline silicon films, they can enhance the performance of advanced electronic devices such as solar cells and thin film transistors (TFTs). Since the formation of amorphous silicon is unavoidable in the low temperature deposition of microcrystalline silicon on a glass substrate at temperatures less than 550 degrees C in the plasma-enhanced chemical vapour deposition and hot wire chemical vapour deposition (HWCVD), crystalline silicon films have not been deposited directly on a glass substrate but fabricated by the post treatment of amorphous silicon films. In this work, by adding the HCl gas, amorphous silicon-free n-type crystalline silicon films could be deposited directly on a glass substrate by HWCVD. The resistivity of the n-type crystalline silicon film for the flow rate ratio of [HCl]/[SiH4] = 7.5 and [PH3]/[SiH4] = 0.042 was 5.31 x 10(-4) ohms cm, which is comparable to the resistivity 1.23 x 10(-3) ohms cm of films prepared by thermal annealing of amorphous silicon films. The absence of amorphous silicon in the film could be confirmed by high resolution transmission electron microscopy.     

Preparation and investigation of VOx thin films of n- and p-types

In this work we present first results on the synthesis of vanadium oxide semi-transparent conducting thin films of p- and n-types. The films were deposited by thermal evaporation method in vacuum, on: silicon, glass, sapphire, and gold substrates. Temperature of substrate during deposition was set around 250 °C. As deposited films were of a p-type of conductivity. Thermal annealing at 420 °C of as-deposited films in air at atmospheric pressure resulted in a change in the conductivity type.Optical, electrical and thermal properties of the deposited films were studied. The topography of the films was studied using AFM microscope. P-N structures were created using VO_x films on silicon and glass substrates. Electrical measurements had shown a non-linear behaviour of the samples.     

Electrical characterization of amorphous silicon carbide thin films deposited via polymeric source chemical vapor deposition

Polymeric source chemical vapor deposition (PS-CVD) was used to synthesize amorphous silicon carbide (a-SiC) thin films. The PS-CVD process was conducted at temperatures between 750 and 1000 °C. The substrates used were silicon single crystal wafers of p-type and n-type, and thermally grown silicon dioxide substrates. The chemical and electrical properties of the films were studied by various techniques, including Fourier transform infrared spectroscopy, elastic recoil detection (ERD), and capacitance-voltage technique. A correlation was observed between the average concentration of oxygen in the films and the deposition temperature, linking a low oxygen concentration to a high deposition temperature. However, the concentration of oxygen in the films deposited at the same temperature is independent of the substrate. The thin films deposited at low temperature showed insulating behaviour, while the semiconducting behaviour is obtained at high deposition temperatures. Ohmic contacts were obtained on the deposited semiconductor thin film by evaporating nickel contacts, followed by annealing of the sample at 800 °C for 2 min.     

Cat-CVD-prepared oxygen-rich μc-Si:H for wide-bandgap material

Microcrystalline phase-involved oxygen-rich a-Si:H (hydrogenated amorphous silicon) films have been obtained using catalytic chemical vapor deposition (Cat-CVD) process. Pure SiH₄ (silane), H₂ (hydrogen), and O₂ (oxygen) gases were introduced in the chamber by maintaining a pressure of 0.1 Torr. A tungsten catalyzer was fixed at temperatures of 1750 and 1950 °C for film deposition on glass and crystalline silicon substrates at 200 °C. As revealed from X-ray diffraction spectra, the microcrystalline phase appears for oxygen-rich a-Si:H samples deposited at a catalyzer temperature of 1950 °C. However, this microcrystalline phase tends to disappear for further oxygen incorporation. The oxygen content in the deposited films was corroborated by FTIR analysis revealing SiOSi bonds and typical SiH bonding structures. The optical bandgap of the sample increases from 2.0 to 2.7 eV with oxygen gas flow and oxygen incorporation to the deposited films. In the present thin film deposition conditions, no strong tungsten filament degradation was observed after a number of sample preparations.     

Control of the bias voltage in d.c. PVD processes on insulator substrates

In plasma-PVD processes, ion bombardment during the growth of thin films has a strong influence on films properties such as morphology, composition, structure, stress, electrical conductivity, and others. Therefore, an accurate control of substrate bias voltage is needed in order to deposit films with the desired properties. For insulator substrates, dc biasing the substrate holder is useless, since the surface shall not follow the applied bias but it will be at the non-controlled floating potential.In this work we present a simple method for the effective control of the substrate bias in dc PVD processes with insulator substrates, based on placing a metallic grid at a certain distance from the non-conductive surfaces to be coated. The desired negative bias is applied to this metallic grid which accelerates ions from the plasma and directs them to the surface to cover. This method has been successfully applied to the deposition of TiN coatings on glass and decorative ceramics by Cathodic Arc Deposition. The deposited films showed good adhesion and gold color, in contrast with the bad adhered and brownish films deposited without the grid. The dependencies on the color and on the mechanical properties of our TiN films deposited on insulating substrates with the value of the bias voltage applied to the substrate are similar to those typically reported in the literature when conductive substrates are used.     

Microstructure of interface for high-adhesion DLC film on metal substrates by plasma-based ion implantation

The diamond-like carbon (DLC) film was prepared on various metal substrates with a plasma-based ion implantation and deposition using superimposed RF and negative high-voltage pulses. The adhesion strength of DLC film was enhanced above the epoxy resin strength by implantation of carbon ions or mixed ions of carbon and silicon to the substrate surface before DLC deposition. In order to clarify the mechanism for improvement in adhesive strength, the microstructure of an interface between DLC film and substrate was examined in detail by transmission electron microscopy (TEM) observations in combination with EDS analysis. As a result, the enhancement in adhesion strength of DLC film by C ion implantation resulted from the formation of amorphous-like phase in the ion-implanted region of substrate, the production of carbon-component graded interface, the destruction of the oxide layer on the top surface of substrate, and the reduction of residual stress in DLC film by ion implantation during the deposition. The production of stress-free DLC film allowed us to demonstrate a supra-thick DLC film of more than 400 μm in thickness.     

Adhesion enhancements and internal stress in MgF2 films deposited with ion beam assistance

We performed adhesion measurements using a dynamically loaded scratch tester to evaluate MgF₂ coatings deposited onto heated and unheated fused silica substrates. Resistance evaporation at 5 Å s^-1 with Ar⁺ ion beam assistance improved the relative adhesive strength of films deposited onto unheated substrates by over an order of magnitude compared with the results for heated substrates without ion beam assistance. Additional experiments were performed to measure internal stress in MgF₂ films on specially masked BK-7 glass substrates using modulated transmission ellipsometry. We found that ion-assisted deposition can reduce internal stress to approximately 450 kgf cm^-2 (tensile) in films 2300 Å thick. The great potential for stress relaxation in MgF₂ films deposited with ion assistance is suggested by these measurements, but additional work with films of higher purity may be required to identify the relative contributions of stress relief, substrate cleaning and chemical bonding to improved adhesion.