A study of silicon oxynitride film prepared by ion beam assisted deposition

A SOI-based optoelectronic device needs a high-quality antireflection coating on both faces of the device to minimize the optical reflectance from the face. In this work amorphous silicon oxynitride films were deposited on silicon substrates by ion beam assisted deposition (IBAD). The main purpose was to use silicon oxynitride film as single layer anti-reflection coating for SOI-based optoelectronic devices. This application is primarily based on the ability to tune the silicon oxynitride optical functions to the optimal values by changing deposition parameters. The chemical information was measured by X-ray photoelectron spectroscopy (XPS). Spectroscopic ellipsometry (SE) was applied to measure the refractive index and thickness. Single-side polished silicon substrate that was coated with silicon oxynitride film exhibited low reflectance. Double-side polished silicon substrate that was coated with silicon oxynitride film exhibited high transmittance. In addition, the Fresnel losses could be reduced to 0.08 dB by depositing silicon oxynitride films onto double-side polished silicon substrates. The results suggested silicon oxynitride film was a very attractive single layer anti-reflection coating for SOI-based optoelectronic device.     

Low refractive index silicon oxide coatings at room temperature using atmospheric-pressure very high-frequency plasma

Low refractive index silicon oxide films were deposited using atmospheric-pressure He/SiH₄/CO₂ plasma excited by a 150-MHz very high-frequency power. Significant increase in deposition rate at room temperature could prevent the formation of dense SiO₂ network, decreasing refractive index of the resulting film effectively. As a result, a silicon oxide film with the lowest refractive index, n = 1.24 at 632.8 nm, was obtained with a very high deposition rate of 235 nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave anti-reflection coating of a glass substrate.     

自组装法制备中空二氧化硅纳米粒子减反射薄膜

以正硅酸乙酯(TEOS)为壳层材料, 聚丙烯酸(PAA)为核材料, 以传统的Stöber水解法为基础制备得到结构规整的中空二氧化硅纳米粒子, 并采用自组装法制备单层减反射薄膜和宽波段双层减反射薄膜。主要研究中空二氧化硅纳米粒子的结构调控方法; 自组装次数和中空二氧化硅纳米粒子分散液的pH值对减反射薄膜透光率的影响规律, 以及具有渐变折射率的双层减反射薄膜的制备。研究结果表明: 通过调节PAA和TEOS的用量可精确调控中空二氧化硅纳米粒子的粒径和空腔体积分率, 进而可精确调控减反射薄膜的厚度和折射率; 通过酸洗工艺, 将自组装次数由10次减少为2次, 简化了涂膜的工艺条件, 在最佳工艺条件下所制备的单层减反射薄膜在350~800 nm波长范围内可显著提高玻璃的透光率, 在最佳波长(λ=520 nm)处将玻璃的透光率由91.6%提高至98.1%; 双层减反射薄膜可在更宽的波段范围内提高基材的透光率, 在400~1500 nm波长范围内将玻璃的透光率提高了5%以上。     

SiOxNy Films deposited with SiCl4 by remote plasma enhanced CVD

Silicon oxynitride films have been deposited with SiCl₄ by remote-plasma enhanced chemical vapor deposition (PECVD) at a substrate temperature of 250°C. Different mixtures of O₂ and NH₃ were used to obtain different oxynitride compositions ranging from SiO₂ to an stoichiometry close to that of silicon nitride. Rutherford backscattering spectrometry was used to determine the chemical composition of the SiO_xN_y films. The behavior of the IR absorption spectra as well as the refractive index measured by ellipsometry were used to estimate the effect of the different deposition parameters. It was found that the IR spectra show a shift of the characteristic peak associated with the stretching vibration mode of the Si-O-Si bonds towards lower wavenumbers as the relative concentration of ammonia was increased with respect oxygen. No double peaks associated with silicon oxide and silicon nitride were observed, indicating the formation of an homogeneous alloy. The IR spectra did not show any presence of water or hydrogen related impurities in the film. Also the effect of a hydrogen flow added during the deposition process on the structural characteristics of the deposited films was studied using dielectric spectroscopy and atomic force microscopy measurements showing that the hydrogen flow added during deposition results in a reduction of the film roughness and a planarization effect, which is very interesting for the application of these films in microelectronics devices.     

Room-temperature formation of low refractive index silicon oxide films using atmospheric-pressure plasma

This study aims to apply atmospheric-pressure (AP) plasma to the fabrication of single-layer anti-reflection (AR) coatings with porous silicon oxide. 150 MHz very high-frequency (VHF) excitation of AP plasma permits to enhance the chemical reactions both in the gas phase and on the film-growing surface, increasing deposition rate significantly. Silicon oxide films were prepared from silane (SiH4) and carbon dioxide (CO2) dual sources diluted with helium. The microstructure and refractive index of the films were studied using infrared absorption and ellipsometry as a function of VHF power density. It was shown that significant increase in deposition rate at room temperature prevented the formation of a dense SiO2 network, decreasing refractive index of the resulting film effectively. As a result, a porous silicon oxide film, which had the lowest refractive index of 1.24 at 632.8 nm, was obtained with a very high deposition rate of 235 nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave AR coating of a glass plate.     

Optical properties of LPCVD silicon oxynitride

Low pressure chemical vapour deposition (LPCVD) silicon oxynitride films of various compositions (from pure SiO₂ to pure Si₃N₄) were deposited by changing the relative gas flow ratio. The effects of oxygen on the physical properties of the films were studied by spectroellipsometry (using Bruggeman approximation and Wemple Di Domenico model) and infrared spectroscopy. Refractive index measured by spectroellipsometry method is studied as a function of some deposition parameters: temperature of deposition, gases fluxes ratio. The high value of deposition temperature means low values in refractive index. More oxygen into films decreases the refractive index. The refractive index dispersion is studied by single-oscillator Wemple Di Domenico model. The optical band gap varies monotonically from 5 eV for silicon nitride, to 9eV for HTO LPCVD silicon dioxide and for the studied silicon oxynitride was found to be between 5 and 6 eV.     

Dual-band windows (DBW) transparent for fundamental and second harmonic generation frequencies

Using the known “looking glass” transformation property (z → 2π − z, y → 2π − y) of the optical phase thickness z and y of matching layers of two-layer anti-reflection coating, together with the fact that optical characteristics of any film do not change after addition of a half-wavelength layer, we designed dual-band anti-reflection coatings transparent at any preset wavelengths λ₁ and λ₂. On the basis of this result common fractional anti-reflection coatings for second and higher harmonics generation using dispersionless coating materials are developed. Explicit analytical relationships between refractive indices of the layers and substrate are deduced. Since for second harmonic generation the dispersion of materials may be a factor we show how to compensate the known dispersion of the coating materials by special choice of dispersion of a suitable substrate.     

Structural and optical properties of yttrium trioxide thin films prepared by RF magnetron sputtering

Yttrium trioxide (Y₂O₃) thin films have been deposited on silicon (111) at different RF powers and the sputtering pressures by RF magnetron sputtering. The influences of the RF power and the sputtering pressures on the structural and optical properties of Y₂O₃ thin films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscope (AFM) and spectroscopic ellipsometer (SE). The results show that chemical composition of as-deposited Y₂O₃ film is apparently close to the stoichiometric ratio and it is crystallized but crystallinity is poor. The monoclinic and cubic fluorite-like structure can coexist in as-deposited Y₂O₃ film. A four-layer-structured optical model consisting of silicon substrate, silicon dioxide (SiO₂) interlayer, Y₂O₃ layer and a surface roughness (SR) layer is built for interpreting preferably the results measured by spectroscopic ellipsometry. With the increase of RF power or decrease of sputtering pressure, the refractive index and optical bandgap of sputtered Y₂O₃ film is increased and the extinction coefficients is decreased.     

Structural and optical properties of yttrium trioxide thin films prepared by RF magnetron sputtering

Yttrium trioxide (Y₂O₃) thin films have been deposited on silicon (111) at different RF powers and the sputtering pressures by RF magnetron sputtering. The influences of the RF power and the sputtering pressures on the structural and optical properties of Y₂O₃ thin films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscope (AFM) and spectroscopic ellipsometer (SE). The results show that chemical composition of as-deposited Y₂O₃ film is apparently close to the stoichiometric ratio and it is crystallized but crystallinity is poor. The monoclinic and cubic fluorite-like structure can coexist in as-deposited Y₂O₃ film. A four-layer-structured optical model consisting of silicon substrate, silicon dioxide (SiO₂) interlayer, Y₂O₃ layer and a surface roughness (SR) layer is built for interpreting preferably the results measured by spectroscopic ellipsometry. With the increase of RF power or decrease of sputtering pressure, the refractive index and optical bandgap of sputtered Y₂O₃ film is increased and the extinction coefficients is decreased.     

Characterization of silicon oxynitride thin films deposited by electron beam physical vapor deposition technique

Thin films of silicon oxynitride (SiO_xN_y) were deposited successfully on silicon wafer substrates using electron beam physical vapor deposition (EB-PVD) technique by varying the substrate temperature (T=100–450 °C) and deposition time (t=0.5–2.5 min). The films were characterized by UV–Visible and X-ray photoelectron spectroscopy (XPS), Tally step measurement and Ellipsometry. The minimum reflectivity R=1.72% is obtained for the films deposited under the conditions of T=350 °C, t=1.5 min at λ=548 nm. Further, the characterization results revealed that the refractive index (RI) of the films increases with increase in the substrate temperature due to increase in silicon nitride content. The refractive index and the thickness of the films were found to be in the range of n=1.72–1.90 and d=40–138 nm, respectively. The values n=1.88 and d=79 nm observed corresponding to the minimum reflectivity R=1.72% satisfy the condition of near quarter wavelength single layer antireflection coating. Thus, the above films might have the tremendous potential for antireflective coating applications.     

Design of multi-layer anti-reflection coating for terrestrial solar panel glass

To date, there is no ideal anti-reflection (AR) coating available on solar glass which can effectively transmit the incident light within the visible wavelength range. However, there is a need to develop multifunctional coating with superior anti-reflection properties and self-cleaning ability meant to be used for solar glass panels. In spite of self-cleaning ability of materials like TiO₂ and ZnO, these coatings on glass substrate have tendency to reduce light transmission due to their high refractive indices than glass. Thus, to infuse the anti-reflective property, a low refractive index, SiO₂ layer needs to be used in conjunction with TiO₂ and ZnO layers. In such case, the optimization of individual layer thickness is crucial to achieve maximum transmittance of the visible light. In the present study, we propose an omni-directional anti-reflection coating design for the visible spectral wavelength range of 400–700 nm, where the maximum intensity of light is converted into electrical energy. Herein, we employ the quarter wavelength criteria using SiO₂, TiO₂ and ZnO to design the coating composed of single, double and triple layers. The thickness of individual layers was optimized for maximum light transmittance using essential Mcleod simulation software to produce destructive interference between reflected waves and constructive interference between transmitted waves.     

Chemical, optical, vibrational and luminescent properties of hydrogenated silicon-rich oxynitride films

X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Fourier transform infrared and room temperature photoluminescence spectroscopy has been used to investigate the chemical, optical, vibrational and luminescent properties of Plasma Enhanced Chemical Vapor Deposited SiO_xN_y/H (0.17≤x≤0.96; 0.07≤y≤0.27), hydrogenated silicon-rich oxynitride (SRON). The linear dependence of the refractive index of the SRON films on the O/Si ratio was established. The photoluminescence from the SRON films were attributed to the embedded amorphous silicon clusters in the films. The dependence of luminescence maximum values on the O/Si and O/N ratios has been explored. We postulate that at O/Si ratio of 0.18 and an O/N ratio of 2.0 (SiO_0.18N_0.09) the film underwent a transformation from silicon-rich oxynitride to a-Si/H film with oxygen and nitrogen impurities.     

Optical and structural properties of silicon oxynitride deposited by plasma enhanced chemical vapor deposition

We present an overview of the properties of silicon oxynitride material (SiON) deposited by plasma enhanced chemical vapor deposition (PECVD) for photovoltaic applications. SiON films were deposited using silane (SiH₄), ammonia (NH₃) and nitrogen protoxide (N₂O) as precursor gases in a low frequency PECVD. Varying the gas flow mixture leads to a whole range of SiON layers starting from the silicon oxide to the silicon nitride with unique stoichiometries and properties. Thanks to spectroscopic ellipsometry measurements we have confirmed the suitability of SiON for antireflection coating layers due to the range of the refractive indexes attainable. SiON structure was analyzed by X-ray photo-electron spectroscopy. We have thus highlighted the critical role of oxygen behavior on the SiON network and the progressive replacement of nitrogen by oxygen atoms when the oxygen precursor increases. The type of chemical bonds present in SiON layers was also investigated by infrared spectroscopy. The SiON layers also contain a non-negligible amount of hydrogen which might be useful for passivation applications. The behavior of hydrogen content was thus analyzed by elastic recoil decay analysis and desorption characterization. A typical rapid thermal annealing was performed on the SiON samples in order to simulate the solar cells contact annealing and to investigate its impact on the dielectric film properties. It was found that hydrogen becomes weakly bonded to the films and strongly decreases in quantity with the annealing. The surface passivation effect is presented in the last part of this paper. The trend before and after a rapid thermal annealing showed opposite results which could be explained by the high porosity of the layers and the formation of Si-O bonds.     

Plasma-enhanced deposition of silicon oxynitride films

Optical, mechanical and chemical properties of plasma-enhanced chemically vapor-deposited silicon oxynitride films were investigated for the SiH₄ (10% in helium), NH₃ and N₂O system at 13.56 MHz. The film composition was varied by changing the ratio of N₂O to NH₃ in the gas phase. The deposition rate, refractive index and stress were observed to be linear functions of the mole fraction of N₂O in the feed gases. The ratio of oxygen to nitrogen in the film, determined by Rutherford backscattering spectrometry, was found to be a linear function of the ratio of N₂O to NH₃. The relative hydrogen content of the films was found to decrease as the N₂O concentration increased. Film structure and composition were also varied by changing the total pressure.     

Double layer SiNx:H films for passivation and anti-reflection coating of c-Si solar cells

In this report, we present a cost effective simple innovative approach to fabricate double layer anti-reflection (DLAR) coatings using a single material which can provide high qualities of passivation and anti-reflection property. Two layers of SiN_x:H films with different refractive indices were deposited onto p-type c-Si wafer using plasma enhanced chemical vapor deposition reactor by controlling the NH₃ and SiH₄ gas ratio. Refractive indices of top and bottom layers were chosen as 1.9 and 2.3 respectively. The effect of passivation at the interface was investigated by effective carrier lifetime, hydrogen concentration and interface trapped density (D_it) measurements. The optical characteristic was analyzed by reflectance and transmittance measurements. A superior efficiency of 17.61% was obtained for solar cells fabricated with DLAR coating when compared to an efficiency of 17.24% for cells with SLAR coating. Further, J_sc and V_oc of solar cell with DLAR coating is increased by a value of ~ 1 mA/cm² and 4 mV respectively than cell with SLAR coating.     

Optische und mechanische Eigenschaften von RLVIP HfO2‐Schichten

Optical and mechanical properties of RLVIP HfO₂ films In this paper HfO₂‐films were deposited on unheated fused silica, borosilicate glass, and silicon wafer substrates by reactive low voltage ion plating (RLVIP). Optical film properties, i. e. refractive index and absorption as well as mechanical properties, particularly film stress, were investigated. Their dependence on deposition parameters, i. e. arc current and oxygen partial pressure was studied. The film refractive index was calculated from spectrophotometric measurements. The low absorption was determined by photothermal deflection spectrometry. Stress measurements were performed by bending disc method with uncoated and coated silicon wafer substrates.     

A novel magnetron sputtering for flexible coatings as a function for production of high quality films

A novel sputtering technique combining the symmetric compressive magnets with cylindrical cathode has been developed to mass produce high-quality oxide and nitride films on plastic sheets. The discharge characteristics of our sputtering can supply about three times larger power efficiencies than that of the conventional magnetron sputtering. Moreover, in continuous dielectric sputtering experiments, the substrate temperature was kept lower than 60 °C. The refractive index of SiN_X and SiO₂ thin film at 500 nm is 1.86 and 1.46 respectively. Moreover, 4 layered anti-reflection coatings of silicon nitride and oxide films deposited on both sides of the PET sheet is achieved to fabricate, and the reflection less than 1% is realized in the range from 420 to 680 nm.     

Thin films of boron nitride grown by CVD

For the first time, thin films of boron nitride were deposited by chemical vapour deposition on to polished silicon and other metal substrates using the inorganic compound H₃BNH₃ (aminodiborane) and ammonia as carrier gas. The substrate temperature was varied from 400 to 600°C. The films were chemically inert and adherent to the substrates. The FTIR spectrum of the film showed B-N-B absorption at 800 cm⁻¹, B-N stretching at 1056 cm⁻¹, and also a weak absorption at 1340cm⁻¹ corresponding to B-N-B bending vibration. Deposited films also exhibited X-ray diffraction pattern with interplanar spacing with (002) plane of hexagonal boron nitride.     

太阳电池组件上纳米多孔SiO_2减反射膜的制备和增透性能研究

采用溶胶-凝胶法制备纳米多孔SiO_2减反射薄膜,通过对不同制备工艺的探索(如陈化时间、提拉速度)以及所制备的纳米SiO_2薄膜的微观结构的研究,探究SiO_2溶胶特性对薄膜结构的影响以及薄膜纳米结构对其光透过率的影响,寻找最优化的制备工艺制备纳米多孔SiO_2减反射薄膜,进一步提高太阳电池组件上超白玻璃的透过率问题. 结果表明以氨水为催化剂、陈化时间为4天、提拉速度为1.25mm/s的工艺制备减反射薄膜效果最好. 在超白玻璃盖板上镀减反射膜后, 透过率 (400～1100nm)由90%提高到96%,对太阳电池组件应用可进一步增加6%左右的可见光利用.     

Effect of the substrate temperature on the properties of Ga-doped ZnO films for photovoltaic cell applications deposited by a pulsed DC magnetron sputtering with a rotating cylindrical target

Effect of substrate temperature on the properties of Ga-doped ZnO (GZO) films was investigated by pulsed DC magnetron sputtering with a rotating cylindrical target with an aim to establish suitable process conditions for their photovoltaic (PV) cell applications. Without formation of undesirable secondary oxide phases such as Ga₂O₃ and ZnGa₂O₄, the GZO film having mixed orientation at lower deposition temperature evolved into the c-axis oriented one with increasing deposition temperature to 230 °C, which accompanied morphological evolution to vertically oriented dense columnar structure and improved doping efficiency. Correlated with this, crater-like surface texturing was possible only on the sample deposited at 230 °C. Electrical resistivity and diffuse surface reflectance over the spectral range of 200-1200 nm of this GZO film after surface texturing were 8.73 × 10⁻⁴ Ω cm and 3.32%, respectively, indicating that the film has application potential as anti-reflection coating and front electrode of PV cells. Morphological features, surface texturing behavior, electrical and optical properties of the GZO films in this study suggest that this novel technique would be applicable to the fabrication of anti-reflection coating and front electrode of PV cells only when substrate temperature is sufficiently high.