Ion beam reactively sputtered silicon nitride coatings

An ion beam source was used to deposit silicon nitride films by reactive sputtering a silicon target with an Ar+N₂ beam. The nitrogen fraction in the sputtering gas was 0.05 to 0.80 at a total pressure of 6 to 20×10^?5 torr. The ion beam current was 50 mA at 500 V. A rate of deposition of about 2 nm min^?1 (0.12 μm h^?1) was found, and the spectra indicated that Si₃N₄ was obtained for a fraction of nitrogen higher than 0.50. However, the AES spectra also indicated that the sputtered silicon nitride films were contaminated with oxygen and carbon and contained significant amounts of iron, nickel, and chromium, most probably sputtered from the holder of the substrate and target.     

Effect of oxygen plasma treatment on bonding states for columnar structured a-CNx thin films prepared by reactive sputtering

Amorphous carbon nitride (a-CN) thin films were deposited on silicon single crystal substrates by rf-reactive sputtering method using a graphite target and nitrogen gas. The substrate temperature was varied from room temperature (RT) to 853 K. After deposition, the effect of oxygen plasma treatment on bonding structures of the film surface has been studied by using an oxygen discharge at 16 Pa and rf power of 85 W. The chemical bonding states and film composition were analyzed by X-ray photoelectron spectroscopy (XPS), while film thickness was obtained from scanning electron microscopy (SEM) and ellipsometer. XPS study revealed that the films have NO₂ and NO₃ bonding structures when the films are deposited at temperatures higher than 673 K. After exposure to oxygen plasma, carbon in the film surface was etched selectively and this phenomenon was observed in all films. In contrast, the surface concentration of nitrogen was ket at constant values before and after oxygen plasma treatment. The NO₃ bonding state had dramatically increased after oxygen plasma treatment for films deposited at higher deposition temperatures. The film surfaces have been observed to change the function from hydrophobic to hydrophilic after oxygen plasma treatment.     

Enhancement of the crystalline quality of reactively sputtered yttria-stabilized zirconia by oxidation of the metallic target surface

Yttria-stabilized zirconia (YSZ) thin films were fabricated on glass substrates by direct current magnetron reactive sputtering. We found out that the crystalline quality of the YSZ film was improved by an oxidation process of the metallic target surface prior to the sputtering deposition process. It is speculated that, at the initial stage of the sputtering, the sputtered particles from the oxidized target surface form a layer with higher degree of crystallization on the substrate, compared with those particles from the metallic target surface. This crystallized layer can enhance the crystallization of the film deposited subsequently. Other sputtering conditions such as sputtering pressure, oxygen flow rate, substrate temperature, and Y₂O₃ content in the film were investigated, for optimization of the crystalline quality of the deposited YSZ film.     

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.     

Silicon nitride films prepared by reactive plasma sputtering

Silicon nitride films were prepared by reactive plasma sputtering in nitrogen at a pressure of 2×10^-4 Torr. The residual gas in the reactor during film sputtering was analysed. The chemical composition of the films was determined from infrared absorption spectra in the wavelength region 2.0–15.0 μm and by the elastic scattering of ³He particles.The best quality silicon nitride films were obtained in pure nitrogen at the minimum residual gas pressures. An absorption minimum at 11.0 μm in the infrared spectra, corresponding to the Si-N chemical bond in the Si₃N₄ molecule, was observed in our films, indicating that their composition was close to stoichiometric.With a residual hydrogen pressure above 10% or a residual oxygen pressure above 2% the generation of new chemical bonds Si-H, N-H and Si-O respectively was observed in the silicon nitride films.     

The use of novel PtSi thin film structures in preferential sputtering measurements

The yields of silicon and platinum from the argon sputtering of PtSi films were measured by Rutherford backscattering techniques. Novel thin film structures of Al₂O₃ (substrate)/W/PtSi were employed to facilitate the measurements. Before steady state was reached, more silicon than platinum was sputtered off, in good agreement with platinum enrichment measurements in the sputtered samples. At steady state the silicon and platinum sputtering yields were equal.     

氮化硅介质薄膜内应力的实验研究

研究了等离子体增强化学气相沉积氮化硅介质薄膜的内应力。采用钠光平面干涉测量了氮化硅薄膜内应力,通过改变薄膜沉积时的工艺参数,考察了反应气体流量比、沉积温度、射频功率密度等因素对氮化硅薄膜内应力的影响。在此基础上,对氮化硅介质薄膜本征应力的形成机制进行了分析讨论。     

气体流量比对反应溅射Si3N4薄膜的影响

利用射频磁控反应溅射法，以高纯Si为靶材，高纯N2气为反应气体，在Si衬底上制备出了Si3N4薄膜，研究了气体流量比对薄膜质量的影响。结果表明，薄膜的沉积速率主要与气体的流量比有关，随着气体流量比的增加，沉积速率下降，靶面的溅射由金属模式过渡到氮化物模式；薄膜中N／Si的原子比增加；红外吸收谱的Si—N键的振动峰向标准峰逼近。     

Pre-cracking technique for fracture mechanics experiments along interface between thin film and substrate

Utilizing the difference in interface strength due to fabrication process, a technique for producing a sharp pre-crack between a thin film and a substrate is proposed. A cracked specimen for examining fracture toughness of interface between a sputtered copper (Cu) thin film and silicon (Si) is made by the method. A vacuum-evaporated Cu thin film, which has poor adhesion to Si, is inserted between the sputtered Cu thin film and the Si substrate as a release layer. The release layer debonds from the Si substrate at very low load, and the sharp pre-crack is successfully introduced along the interface. Using the pre-cracked specimen, the interface fracture toughness test is conducted and the critical J-integral, J_C, is evaluated as about 1 J/m² for the sputtered Cu/Si interface.     

The surface modification of polymers to modulate endothelial cell growth

The effect of nitrogen ion implantation or ion-assisted film deposition on the growth of human endothelial cells in vitro on a substrate has been studied. It was shown that the largest change occurs when TiO₂ films were reactively sputtered onto the substrates, while the most passive surface was reactively sputtered SiO₂. SEM pictures of the cells adhering to the various treated surfaces show that the cells were healthy. Future studies on the effect of alloy films and their oxides and nitrides are proposed.     

Interface instability of r.f. sputtered silicon nitride films on silicon

Silicon nitride films have been deposited on sputter-etched silicon by r.f. sputtering. The quality of the sputtered nitride films was demonstrated by infrared spectrum analysis and measurement of the refractive index and dielectric constants. The interface instability of the Si₃N₄Si structure was investigated by MNS (metal-nitride-silicon) techniques. The C-V measurements revealed that Si injection (injection and/or extraction from the silicon side) is the dominating factor causing trapping instability in the MNS devices and that the application of positive or negative bias voltages is equally effective in producing Si injection. Little ion movement or polarization effect was observed under bias-and-temperature stresses. C-V traces were also plotted at liquid nitrogen temperature and the effect of Si injection was found to be the same as at room temperature. The commonly used tunneling model is employed to account for the temperature-insensitive instability at the Si₃N₄Si interface.     

Formation of a silicate layer between lead oxide and a silicon-wafer surface during heat treatment

PbO thin films were deposited on a silicon substrate by plasma-enhanced chemical vapour deposition (PECVD) using Pb(C₂H₅)₄ and oxygen at 250°C. The interdiffusion reaction phenomena between the PbO thin film and the silicon substrate during heat treatments were investigated in a horizontal furnace in the temperature range between 350 and 650°C under a nitrogen ambient for 1 h. The PECVD PbO film deposited on the silicon substrate at 250°C, was amorphous and contained carbon-related contaminants which could almost be removed by heat treatment at 350°C. The PbO on the silicon substrate initially participated in the interdiffusion reaction in the temperature range between 400 and 450°C. This produced a silicate layer containing lead components. The lead content in the film varied with the depth of film and heat-treatment temperature. Metallic lead was observed as a cluster in the specimen heated at 550°C. This cluster was produced by the agglomeration of metallic lead originating from PbO decomposition. The oxygen source for silicate formation was not ambient oxygen coming from the decomposition of Pb–O bonding. The metallic lead clusters dissolved as weakly bound metallic lead or as an unbound nanosized metal particle in the silicate layer at 650°C. This revised version was published online in November 2006 with corrections to the Cover Date.     

Interface structure of sputter deposited CNx film on silicon substrate

Amorphous carbon nitride (CN_x, x = 0.05) films were reactively sputtered on Si(100) substrate, and the interface structure was studied by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In cross-sectional TEM a gray interlayer about 5 nm thick between the bulk CN_x film and silicon substrate is observed, and the interface is dense. A little Si impurity (< 1 at.%) is revealed in the films deposited for short time (7 s and 17 s) by XPS measurement. The in-depth XPS analyses indicate that there exists an interlayer with Si impurity above, and a sub-surface layer with C and N below the original surface of silicon substrate. The two layers have different chemical composition and bonding state.     

Room-temperature crystallization of amorphous films by RF plasma treatment

The crystallization of amorphous thin films was achieved by 13.56 MHz RF (radio frequency) plasma treatment. This crystallization process has a strong advantage that the sample temperature is lower than 120 °C during the plasma treatment even without compulsory cooling and various amorphous films are crystallized after 2 min or so. This treatment works on amorphous films of various materials, independently of the film preparation method and substrate materials. Crystallization has been confirmed on amorphous thin films of sputtered ITO (tin doped indium oxide) deposited on soda-lime glass and PET (polyethylene terephthalate), of sputtered TiO₂ on soda-lime glass, of sol-gel derived TiO₂ on silicon wafer and of sputtered hydrogen-doped silicon on soda-lime glass.The plasma gas pressure was found to be the key parameter in the plasma crystallization process. The appropriate gas pressure depends on the plasma gas species and not on film or substrate materials. A Cu electrode, attached to the backside of the substrate and is electrically floated from the electric ground, was found to enhance the plasma crystallization performance.     

New approach in depositing thick, layered cubic boron nitride coatings by oxygen addition—structural and compositional analysis

Cubic boron nitride (c-BN) can be produced by PVD and PA-CVD techniques by intensive ion bombardment leading to highly stressed films limiting its use in industrial applications. Various attempts have been undertaken to reduce the compressive stress of c-BN thin films. A significant reduction in compressive stress and a substantially improved adhesion was achieved by a new coating concept consisting of a two-step adhesion-promoting base layer, a compositional-graded nucleation layer obtained by a stepwise decrease of the oxygen content in the Ar/N₂/O₂ atmosphere and a low-stressed c-BN:O top layer with controlled oxygen addition. The four-layer c-BN:O film with a thickness of 3 μm was deposited by unbalanced radio frequency magnetron sputtering of a hot-pressed hexagonal boron nitride target on silicon substrates. The adhesion layer was deposited in a mixed Ar/O₂ atmosphere of 0.26 Pa with a stepwise increased nitrogen gas flow and a subsequent increase of the ion energy by increasing the substrate bias from 0 to − 250 V. The c-BN nucleation was gradually initiated by decreasing the O₂ gas flow. The present study was focused on the investigation of the morphology, the microstructure on the nanoscale, and the bonding structure using scanning electron microscopy (SEM), Fourier-Transmission infra-red spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) employing analytical scanning transmission electron microscopy (ASTEM). The HRTEM images revealed a four-layer coating consisting of a gradual nucleation of t-BN, on which a gradual nucleation of c-BN was achieved by decreasing the oxygen gas flow.     

Reactive ion beam sputtering of thin films of lead,zirconium and titanium

Thin films of lead, zirconium and titanium were reactively sputtered in an oxygen atmosphere by a focused ion beam sputtering technique. With this technique, the plasma is contained in the ion gun so that neither the target nor the substrate is in a plasma environment. As a result, several factors which can interfere with the interpretation of the mechanism of compound formation (high energy secondary electron bombardment, high substrate temperature, high deposition pressure) are virtually eliminated.Properties such as deposition rate, resistivity and internal stress as a function of the partial pressure of oxygen were investigated. A decrease in the deposition rate was observed as the partial pressure of oxygen was increased from 1 × 10^-6 to 2 × 10^-4 Torr. This decrease was attributed to a build-up of a surface layer of adsorbed oxygen on the target. A model is proposed to predict the partial pressure of oxygen at which a dielectric film forms, based on the thermodynamic properties of the compound formed. All films deposited are in tensile stress. This suggests that compound formation occurs at the target and that the oxide is sputtered in the collision process.     

Effect of plasma treatment on the microstructure and electrical properties of MIM capacitors with PECVD silicon oxide and silicon nitride

Metal–insulator–metal (MIM) capacitors with plasma enhanced chemical vapor deposited (PECVD) nitride exhibit trap-induced dispersive behavior and electrical hysteresis, which lead to degradation in capacitor linearity at low frequencies. The dominant defect was suggested to be silicon dangling bonds originated from nitrogen deficiency. Previous methods to eliminate the dispersive behavior and electrical hysteresis include use of oxide–nitride–oxide (ONO) stacks and/or plasma pre-treatment of silicon substrate before nitride deposition [Van Huylenbroeck S, Decoutere S, Venegas R, Jenei S, Winderickx G (2002) IEEE Electron Device Lett 23:191; Lau WS (1990) Jpn J Appl Phys 29:L690]. In this study, the plasma post-treatment method was employed; MIM capacitors with PECVD oxide and nitride were treated with N₂O and SiH₄/NH₃ plasma, respectively, after deposition of the dielectric layer. No apparent change in film microstructure is observed after plasma treatment. Plasma post-treatment is effective in eliminating the electrical hysteresis shift of the nitride capacitors. Fourier transform infrared (FTIR) absorption spectra suggest an increase of the Si–H bond after SiH₄/NH₃ plasma bombardment of the nitride films. Auger depth profiling indicates a slight increase of nitrogen to silicon ratio after plasma treatment. The increase of the Si–H bonds as well as the raise of nitrogen to silicon ratio are two possible causes for the elimination of the hysteresis shift of the plasma-treated nitride capacitors. The time dependent dielectric breakdown testing indicates a decrease in both the leakage current and the lifetime of the MIM capacitors treated with plasma. Possible dielectric degradation mechanism is explored.     

Effects of the Ar–N2 sputtering gas mixture on the preferential orientation of sputtered Ru films

We have investigated the influence of N₂ addition to the Ar sputtering gas on the crystal orientation of sputtered Ru films. An rf magnetron sputtering apparatus with a Ru target (99.9%) and a glass substrate heated to 100 °C or 300 °C was used for the deposition. The crystal structure, chemical composition and electrical properties of the resultant films were investigated. X-ray diffraction (XRD) revealed the dominant orientation at 0% N₂ to be the c-axis. With increasing proportion of N₂ in the sputtering gas at a substrate temperature of 100 °C, the intensity of the (002) peak decreased, finally disappearing at 50% N₂. This c-axis-suppressed Ru film sputtered at 50% N₂ was found to contain nitrogen by Auger electron spectroscopy (AES), but by annealing the film in vacuum at 400 °C, the nitrogen in the film was completely removed. The film orientation remained the same as before annealing. Thus, we have demonstrated a new method for depositing Ru films with a controlled preferential orientation of either c-axis oriented or c-axis suppressed.     

Chemical vapour deposition of silicon nitride in a microwave plasma assisted reactor

Microwave plasma assisted chemical vapour deposition was used to produce silicon nitride films on silicon substrates from mixtures of methane and nitrogen. Deposition temperatures varied from 800 to 1000°C and pressure varied from 53.2 to 79.8×10²Pa. Gas mixtures with low methane content resulted in no reaction. Gas mixtures with high methane content produced an amorphous carbon film on the silicon wafer surface. At intermediate methane contents, the process produces a mixture of and silicon nitride. A mechanism is proposed according to which the silicon surface is chemically etched by the activated methyl radicals forming Si(CH₃)₄, which then reacts with nitrogen atoms (or ions) to form the silicon nitride. The morphology of the individual crystals evolves from platelets to needle-like depending on the deposition conditions, and on the surface coverage of the silicon surface.     

Transport of sputtered atoms investigated by Monte Carlo method

Increasing attention has been paid to the sputtering process as a tool to deposit films and to the study of the interaction between the film properties and the deposition parameters. It is obvious that the energy and direction of these particles arriving at the substrate is in close relation with the transport process from the target to the substrate. This work deals with the computer simulation of the sputtered Ag atoms trajectories through the background gas in a diode-sputtering configuration. For that, we have developed a numerical model to simulate the transport process. We followed the three-dimensional trajectory of each sputtered atom separately and calculated the scattering angle and the energy loss if a collision took place. A statistical method, Monte Carlo simulations is used. The model predicts the flux of Ag atoms arriving at the substrate, their energies and angular distribution. The dependence of the deposition rates of Ag atoms on the gas pressure and the distance between target to substrate were investigated.