Electrical properties of thin PECVD silicon oxynitride films

Thin silicon oxynitride films with excellent uniformity were prepared by plasma enhanced CVD. Oxygen incorporation leads to improved breakdown behavior and to reduction of the film conductivity compared to PECVD silicon nitride layers. Thin PECVD silicon oxynitride films deposited on single crystal and poly-Si exhibit good insulation properties in both cases.     

Evolution of stress in evaporated silicon dioxide thin films

The evolution of stress in evaporated SiO2, used as optical coatings, is investigated experimentally through in situ stress measurement. A typical evolution pattern consisting of five subprocedures （thin film deposition, stopping deposition, cooling, venting the vacuum chamber, and exposing coated optics to the atmosphere） is put forward. Further investigations into the subprocedures reveal their features. During the deposition stage, the stresses are usually compressive and reach a stable state when the deposited film is thicker than 100 nm. An increment of compressive stress value is observed with the decrease of residual gas pressure or deposition rate. A very low stress of-20 MPa is formed in SiO2 films deposited at 3×10^-2 Pa. After deposition, the stress increases slightly in the compressive direction and is subject to the stabilization in subsequent tens of minutes. In the process of venting and exposure, the compressive component increases rapidly with the admission of room air and then reaches saturation, followed by a logarithmic decrement of the compressive state in the succeeding hours. An initial discussion of these behaviors is given.     

Thickness dependent studies of dielectric breakdown in Langmuir thin molecular films

The usefulness of Langmuir thin molecular films for making devices has made it necessary to study their dielectric breakdown behaviour. Study of thickness dependence of the breakdown field in these films is important from the point of view of device applications as well as the understanding of breakdown phenomenon. In the present paper, thickness dependence of two breakdown events corresponding to ‘onset breakdown’ and ‘maximum breakdown’ voltages have been reported for the ‘build-up’ Langmuir films of barium palmitate, margarate and behenate in the thickness ranges (23–300 Å) and (370–2400 Å), respectively. These two events are of particular interest because the former determines the permissible operating voltage and the latter leads to the ‘practically’ important ultimate dielectric strength of the film. The Langmuir films have been chosen because of their accurately known and controllable uniform thickness, high dielectric strength and high structural perfection. The onset breakdown strength of all the substances is found to vary as d^-1 (d being film thickness) in the ultra-thin range which have been explained qualitatively in terms of boundary effects. The maximum breakdown strength is also found to be almost inversely proportional to the film thickness but the results remain inexplicable because the actual mechanism of destructive breakdown is not yet fully understood. The typical J-V characteristics in the ‘non-destructive’ phase have also been given.     

Laser annealing study of PECVD deposited hydrogenated amorphous silicon carbon alloy films

The influence of carbon content on the crystallization process has been investigated for the excimer laser annealed hydrogenated amorphous silicon carbon alloy films deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique, using silane methane gas mixture diluted in helium, as well as for the hydrogenated microcrystalline silicon carbon alloy films prepared by PECVD from silane methane gas mixture highly diluted in hydrogen, for comparison. The study demonstrates clearly that the increase in the carbon content prevents the crystallization process in the hydrogen diluted samples while the crystallization process is enhanced in the laser annealing of amorphous samples because of the increase in the absorbed laser energy density that occurs for the amorphous films with the higher carbon content. This, in turn, facilitates the crystallization for the laser annealed samples with higher carbon content, resulting in the formation of SiC crystallites along with Si crystallites.     

碳化硅薄膜脉冲激光晶化特性研究

采用XeCl准分子激光对非晶碳化硅(a-SiC)薄膜的脉冲激光晶化特性进行了研究.通过原子力显微镜（AFM）和Raman光谱技术对退火前后薄膜样品的形貌、结构及物相特性进行了分析.结果表明，选用合适的激光能量采用激光退火技术能够实现a-SiC薄膜的纳米晶化.退火薄膜中的纳米颗粒大小随着激光能量密度的增加而增大；Raman谱分析结果显示了退火后的薄膜的晶态结构特性并给出了伴随退火过程存在的物相分凝现象.根据以上结果并结合激光退火特性，对a-SiC的脉冲激光晶化机理进行了讨论. 关键词： 激光退火 晶化 碳化硅     

Low-temperature PECVD of silicon dioxide on polymeric hydrogels

In this work, a complex investigation of the film surface composition and nanoscale mechanical properties, i.e. hardness and elastic modulus, of plasma-modified and silica-coated hydrogel thin films was carried out. Plasma treatment was performed in a reactive ion etching chamber (SF₆, CHF₃) at radio frequency (rf, 13.56 MHz) and in a plasma-enhanced chemical vapor deposition chamber (SiH₄/N₂, NH₃, N₂O) at radio frequency and dual frequency (13.56 MHz/100 kHz), respectively. The use of the dual-frequency configuration comprising two power supplies and operated in a switched mode enabled the investigation of the ion-bombardment influence on the polymer properties. For the application in silicon micromachined sensors best results were obtained by using a NH₃ or SiH₄/N₂ low-pressure plasma modification and a silica coating of the sensitive hydrogel film. PACS 81.05.Lg; 81.15.Gh; 81.65.Cf; 81.70.Bt     

Density-fluctuation-induced swelling of polymer thin films in carbon dioxide

We report an anomalous swelling of polymer thin films in carbon dioxide (CO(2)) which is associated (in both locus and form) with the density fluctuation ridge that forms along the extension of the coexistence curve of gas and liquid in the P-T phase diagram. Neutron reflectivity results showed that CO(2) could be sorbed to a large extent ( approximately 60%) in thin polymer films even when the bulk miscibility of the polymer with CO(2) is very poor. The anomalous swelling is found to scale with the polymer radius of gyration (R(g)) and extends to a distance approximately 10 R(g).     

The Rayleigh law in silicon doped hafnium oxide ferroelectric thin films

A wealth of studies have confirmed that the low‐field hysteresis behaviour of ferroelectric bulk ceramics and thin films can be described using Rayleigh relations, and irreversible domain wall motion across the array of pining defects has been commonly accepted as the underlying micro‐mechanism. Recently, HfO₂ thin films incorporated with various dopants were reported to show pronounced ferroelectricity, however, their microscopic domain structure remains unclear till now. In this work, the effects of the applied electric field amplitude, frequency and temperature on the sub‐coercive polarization reversal properties were investigated for 10 nm thick Si‐doped HfO₂ thin films. The applicability of the Rayleigh law to ultra‐thin ferroelectric films was first confirmed, indicating the existence of a multi‐domain structure. Since the grain size is about 20–30 nm, a direct observation of domain walls within the grains is rather challenging and this indirect method is a feasible approach to resolve the domain structure. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

高压PECVD技术沉积硅基薄膜过程中硅烷状态的研究

采用高压射频等离子体增强化学气相沉积(RF-PECVD)方法在不同功率下制备了一系列硅薄膜材料，研究了材料晶化率和生长速度随功率变化的规律， 进而研究PECVD方法沉积硅薄膜过程中的硅烷反应状态，并提出可以根据硅烷耗尽程度的不同将硅烷反应状态分为未耗尽、耗尽和过耗尽三种.然后，对不同硅烷反应状态下的材料结构、光电性能以及相应的电池进行了研究，并指出适合于太阳电池本征层的高质量微晶硅材料应该沉积在硅烷耗尽状态. 关键词： 耗尽状态 微晶硅 光发射谱     

Characterization of LPCVD and PECVD silicon oxynitride films

The chemical composition and structure of silicon oxynitrides, deposited in low pressure and plasma enhanced chemical vapour deposition processes are discussed. From an extrapolation of the characteristics of plasma grown oxynitrides a model for the deposition of LPCVD material is derived. A main conclusion of this model is that Si-Si bonds have a larger tendency to occur in this material than Si dangling bonds.     

A reassessment of electron escape depths in silicon and thermally grown silicon dioxide thin films

The escape depths of electrons with kinetic energies of approximately 1150 and 1380 eV in Si and thermally grown SiO₂ thin films have been calculated, using three methods, from X-ray photoelectron spectra of samples which have been characterized by high resolution transmission electron microscopy (HRTEM). The most reliable and reproducible escape depths derived in this study are significantly less than the average of those reported in the literature. It is believed that this is due principally to inaccurate characterization of the samples previously used for escape depths measurements.     

Defect sites in thin films of germanium dioxide irradiated with silicon ions

Optical transmission spectra of GeO₂ films irradiated with silicon ions and subjected to postimplantation annealing in the regime of silicon nanocrystal formation are analyzed. It is shown that point defects form in the films after irradiation with doses D ～ 10²⁰ m^?2: germanium electron centers, neutral oxygen vacancies, and Ge²⁺ centers, which have been annealed at a temperature of 1000°C for an hour. At D ≥ 1 × 10²¹ m^?2, more complex defects arise in the films, which are only partially annealed under the same conditions.     

Thermally stimulated currents in thin films of silicon monoxide doped with metallic impurities

We have determined the median values of the relaxation time and activation energy of thermally stimulated charges in silicon monoxide doped with metallic impurities. The results are compared with those obtained from alternating current experiments.     

Electrical breakdown of thin polymer films

Data are presented on the dielectric strength of thin polymer films. The conclusion is drawn that the electron avalanche concept is inapplicable to the breakdown of thin films. It is proposed to consider electrical breakdown as a consequence of an abrupt local field enhancement induced by evolution of the space charge injected into the polymer from electrodes. It is shown that the lifetime of polymer films depends exponentially on electric field strength.     

Raman characterization of the structural evolution in amorphous and partially nanocrystalline hydrogenated silicon thin films prepared by PECVD

Hydrogenated silicon (Si:H) thin films were obtained by plasma‐enhanced chemical vapor deposition (PECVD). Raman spectroscopy was used to investigate the structural evolution in phosphor‐doped n‐type amorphous hydrogenated silicon thin films, which were prepared under different substrate temperatures and gas pressures. Meanwhile, the effect of nitrogen doping on the structure of P‐doped thin films was also investigated by Raman spectroscopy. Moreover, the transition from the amorphous state to the nanocrystalline state of undoped Si:H films deposited through low argon dilution was studied by Raman spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that Raman spectroscopy can sensitively detect the structural evolution in hydrogenated silicon thin films deposited under different conditions in a PECVD system. Copyright © 2010 John Wiley & Sons, Ltd.     

Submillimeter wave-guiding on thin dielectric films

The excitation and propagation of guided submillimeter waves (λ = 0.337 mm) is demonstrated on stretched, self-supporting sheets of polyethylene (PET) and polyterephthalate (PTER). Prism-film couplers serve for input and output. The PTER films show negative birefringence (n₀ = 1.76, n_e = 1.68). An attenuation of 0.25 dB/cm was measured for the TM₀ mode on a 12 μm thick PTER film.