Effect of high-energy electron-beam irradiation on the optical properties of ion-beam-sputtered silicon oxynitride thin films

Silicon oxynitride thin films are prepared by ion-beam sputtering, and the optical properties and surface chemical composition are studied by spectrophotometric and x-ray photoelectron spectroscopy, respectively. It is seen that the films sputtered by use of nitrogen alone as the sputtering species from a silicon nitride target are completely transparent (k < 0.005) and have a refractive-index dispersion from 1.85 to 1.71 over the visible and near-infrared spectral regions, and the films show distinct spectral lines that are due to silicon, Si(2s), nitrogen, N(1s), and oxygen, O(1s). Sputter deposition of argon and of argon and nitrogen produces silicon-rich silicon oxynitride films that are absorbent and have high refractive indices. These films have a direct electronic transition, with a threshold energy of 1.75 eV. Electron irradiation transforms optically transparent silicon oxynitride films into silicon-rich silicon oxynitride films that have higher refractive indices and are optically absorbing owing to the presence of nonsaturated silicon in the irradiated films. The degradation in current responsivity of silicon photodetectors, under electron irradiation, is within 3% over the wavelength region from 450 to 750 nm, which is entirely due to the degradation of optical properties of silicon oxynitride antireflection coatings.     

氮氧化硅薄膜的研究进展

氮氧化硅薄膜材料具有优异的热力学、介电及光学性能,在微电子、光学器件等方面有着重要应用.其主要制备方法包括化学气相沉积、溅射、直接氮化/氧化及离子植入.综述了该类材料的制备方法和应用研究进展,并指出了制备方法和应用研究的发展方向.     

氮化硼光电薄膜材料的制备及其性能研究

本文通过热丝辅助等离子体增强化学气相沉积法 (HF PECVD)在单晶硅片和石英片衬底上分别成功生长了氮化硼薄膜材料。用X射线衍射 (XRD和傅立叶变换红外光谱 (FTIR)分析了薄膜样品的结构和组成 ,用扫描电镜 (SEM)观察了薄膜样品的表面形态 ,用紫外—可见光分光光度计 (UV)研究了薄膜样品的紫外吸收特征 ,并确认薄膜样品的光学能隙。此外 ,本文还探讨了衬底的超声预处理在薄膜材料生长中所起的作用     

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.     

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.     

CHEMICAL VAPOR DEPOSITION OF SEVERAL SILICON-BASED DIELECTRIC FILMS

Thin films of dielectric materials are used extensively in the semiconductor and microelectronics industries, and a number of techniques are used to prepare them. Both conventional chemical vapor deposition and plasma-enhanced chemical vapor deposition of silicon dioxide, silicon nitride, and silicon oxynitride are discussed in this review. The effect of process parameters on the properties of these films is discussed.     

Low temperature silicon nitride by hot wire chemical vapour deposition for the use in impermeable thin film encapsulation on flexible substrates

High quality non porous silicon nitride layers were deposited by hot wire chemical vapour deposition at substrate temperatures lower than 110 degrees C. The layer properties were investigated using FTIR, reflection/transmission measurements and 1:6 buffered HF etching rate. A Si-H peak position of 2180 cm(-1) in the Fourier transform infrared absorption spectrum indicates a N/Si ratio around 1.2. Together with a refractive index of 1.97 at a wavelength of 632 nm and an extinction coefficient of 0.002 at 400 nm, this suggests that a transparent high density silicon nitride material has been made below 110 degrees C, which is compatible with polymer films and is expected to have a high impermeability. To confirm the compatibility with polymer films a silicon nitride layer was deposited on poly(glycidyl methacrylate) made by initiated chemical vapour deposition, resulting in a highly transparent double layer.     

IR transmittance studies of hydrogen-free and hydrogenated silicon nitride and silicon oxynitride films deposited by reactive sputtering

Amorphous silicon nitride and silicon oxynitride films were deposited by reactive r.f. sputtering in various reactive ambients of nitrogen, oxygen and hydrogen of different compositions. The IR transmittance of the films was studied as a function of their hydrogen content and the oxygen:nitrogen ratio. The results were discussed in terms of compensation of gap states by hydrogenation. The microscopic structure of the silicon oxynitride films is believed to depend on the oxygen:nitrogen atomic ratio.     

Properties of Si3N4 and AIN Films Produced by Reactive Ion Plating and Gas Discharge Sputtering

Thin films of Silicon- and Aluminiumnitride were produced by Reactive Low Voltage Ion Plating and low pressure dc-Magnetron Sputtering. The films show excellent adherence, high hardness and abrasion resistance, and are dense and homogeneous. Both processes, applied at optimum conditions, enable the production of films with nearly identical optical properties. Such optimized deposition conditions in both processes yielded a mean refractive index of n₅₅₀ = 2.05 ± 0.03 for Si₃N₄ and of n₅₅₀ = 2.12 ± 0.01 for AIN films. The region of high optical transmission was found to be between 0.23 and 9.5μm (Si₃N₄) and between 0.2 and 12.5 μm (AIN). In the visible range both metal nitride films are free of optical absorption (k <10^?3). These materials, together with their oxynitride phases, offer interesting applications for the deposition of optical multilayer systems with very high spectral stability.     

Silicon nanostructured layers for improvement of silicon solar cells' efficiency: A promising perspective

The photovoltaics industry is dominated by silicon solar cells technology mainly because of the low manufacturing cost. However, these solar cells show an important limiting factor on conversion efficiency due to the inefficient absorption of high energy photons as a consequence of the indirect bandgap structure of bulk silicon. In this article, we discuss about different possibilities to improve the efficiency of solar cells and we propose the use of silicon nanostructured layers to achieve this goal. We present the fabrication methods as well as the characterization results of two kinds of layers which can be used for solar cells' efficiency improvement, namely non-stoichiometric silica layers (SiO_x) and non-stoichiometric silicon nitride layers (SiN_x). We demonstrate that the photoluminescence (PL) properties and/or the increased photocurrent (PC) signal at high-energy photon could be used to improve this efficiency. Finally, the major asset of these methods lies in their possibility to be incorporated to the solar cell processing for an insignificant cost.     

Characterization of silicon oxynitride films prepared by the simultaneous implantation of oxygen and nitrogen ions into silicon

Silicon oxynitride films about 5 nm in thickness were prepared by simultaneously implanting 5 keV oxygen and nitrogen ions into silicon at room temperature up to saturation. These films with concentrations ranging from pure silicon oxide to silicon nitride were characterized using Auger electron spectroscopy, electron energy loss spectroscopy and depth-concentration profiling. The different behaviour of the silicon oxynitride films compared with those of silicon oxide and silicon nitride with regard to thermal stability and hardness against electron and argon ion irradiation is pointed out.     

Concurrent bandgap narrowing and polarization enhancement in epitaxial ferroelectric nanofilms

Perovskite-type ferroelectric (FE) crystals are wide bandgap materials with technologically valuable optical and photoelectric properties. Here, versatile engineering of electronic transitions is demonstrated in FE nanofilms of KTaO₃, KNbO₃ (KNO), and NaNbO₃ (NNO) with a thickness of 10–30 unit cells. Control of the bandgap is achieved using heteroepitaxial growth of new structural phases on SrTiO₃ (001) substrates. Compared to bulk crystals, anomalous bandgap narrowing is obtained in the FE state of KNO and NNO films. This effect opposes polarization-induced bandgap widening, which is typically found for FE materials. Transmission electron microscopy and spectroscopic ellipsometry measurements indicate that the formation of higher-symmetry structural phases of KNO and NNO produces the desirable red shift of the absorption spectrum towards visible light, while simultaneously stabilizing robust FE order. Tuning of optical properties in FE films is of interest for nanoscale photonic and optoelectronic devices.     

BN薄膜的制备及BPXN1-X薄膜的紫外光敏特性

采用热丝和射频等离子体辅助化学气相沉积方法(HF-PECVD),以单晶硅为衬底在低温(< 500℃)条件下沉积氮化硼(BN)薄膜材料.通过傅立叶变换红外光谱(FTIR)、 X射线衍射(XRD)及扫描电镜(SEM)对薄膜样品的组成和结构进行了分析,探讨了温度和等离子体对沉积BN薄膜的影响.此外,用紫外-可见光分光光度计(UV)测试了石英衬底上生长磷掺杂氮化硼(BPXN1-X)薄膜样品的紫外吸收特征,分析了磷掺杂对 BN光学能隙的调节作用以及 BPXN1-X薄膜在紫外空间探测领域的应用前景.结果表明,以单晶硅和光学石英玻璃为衬底在低温条件下用 HF-PECVD方法可以沉积较高质量的 BN薄膜,BN的光学能隙宽度通过磷的掺杂可以得到连续调节,在紫外空间光探测领域具有很大的应用潜力.     

Red spectral shift and enhanced quantum efficiency in phonon-free photoluminescence from silicon nanocrystals

Crystalline silicon is the most important semiconductor material in the electronics industry. However, silicon has poor optical properties because of its indirect bandgap, which prevents the efficient emission and absorption of light. The energy structure of silicon can be manipulated through quantum confinement effects, and the excitonic emission from silicon nanocrystals increases in intensity and shifts to shorter wavelengths (a blueshift) as the size of the nanocrystals is reduced. Here we report experimental evidence for a short-lived visible band in the photoluminescence spectrum of silicon nanocrystals that increases in intensity and shifts to longer wavelengths (a redshift) with smaller nanocrystal sizes. This higher intensity indicates an increased quantum efficiency, which for 2.5-nm-diameter nanocrystals is enhanced by three orders of magnitude compared to bulk silicon. We assign this band to the radiative recombination of non-equilibrium electron-hole pairs in a process that does not involve phonons.     

Surface acoustic wave characterization of PECVD films on galliumarsenide

Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelectric films. Such films can be used for the development of semiconductor-integrated microwave-frequency surface and bulk acoustic wave devices. The acoustic properties of silicon nitride, silicon oxynitride, silicon carbide, and TEOS glass, deposited by plasma-enhanced chemical-vapor-deposition (PECVD) on GaAs, have been characterized using linear arrays of SAW interdigital electrodes operating in the harmonic mode over the frequency region from 30 MHz to above 1.0 GHz. The elastic constants of these amorphous films have been determined by fitting theoretical dispersion curves to the measured SAW velocity characteristics. Frequency-dependent SAW propagation-loss values have been determined from the observed linear change in loss as a function of transducer separation. Preliminary measurements of the temperature coefficient of frequency (TCF) for SAW propagation of the films on GaAs are also given     

Concurrent bandgap narrowing and polarization enhancement in epitaxial ferroelectric nanofilms

Abstract

Perovskite-type ferroelectric (FE) crystals are wide bandgap materials with technologically valuable optical and photoelectric properties. Here, versatile engineering of electronic transitions is demonstrated in FE nanofilms of KTaO₃, KNbO₃ (KNO), and NaNbO₃ (NNO) with a thickness of 10–30 unit cells. Control of the bandgap is achieved using heteroepitaxial growth of new structural phases on SrTiO₃ (001) substrates. Compared to bulk crystals, anomalous bandgap narrowing is obtained in the FE state of KNO and NNO films. This effect opposes polarization-induced bandgap widening, which is typically found for FE materials. Transmission electron microscopy and spectroscopic ellipsometry measurements indicate that the formation of higher-symmetry structural phases of KNO and NNO produces the desirable red shift of the absorption spectrum towards visible light, while simultaneously stabilizing robust FE order. Tuning of optical properties in FE films is of interest for nanoscale photonic and optoelectronic devices.     

Novel process for low temperature crystallization of a-SiC:H for optoelectronic applications

Metal-induced crystallization (MIC) process was employed to crystallize hydrogenated amorphous silicon carbide (a-SiC:H) films deposited by PECVD on n-type Si substrate. To optimize the crystallization process, Aluminum thin films of different thicknesses were deposited on a-SiC:H films which were then annealed at 600 °C in N₂ environment for 1 h. UV–visible spectrophotometer, atomic force microscopy (AFM) and hall measurement system were used to characterize the films. It was observed from the UV–visible spectrum that the films crystallized using higher Al thickness show absorption in the visible range whereas the samples crystallized with lower Al thickness did not show absorption in the visible range but shows large absorption above the bandgap of the material. Considering UV–visible and Hall measurement data it can be concluded that the sample crystallized with 50 nm of Al can be a good candidate for SiC–Si hetero-junction solar cells.     

A carpet cloak for visible light

We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nanoporous silicon oxide substrate with a very low refractive index (n<1.25). The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale creating a local effective medium index. The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequencies.     

Optical properties of amorphous silicon nitride thin-films prepared by VHF-PECVD using silane and nitrogen

Hydrogenated amorphous silicon nitride (a-Si_1-x N _x :H) thin-films with x between 0.42 and 0.58 were deposited from silane diluted in nitrogen gas by VHF PE-CVD using a novel method for impedance matching. We determine the refractive index dispersion relations and the optical absorption edge information from the transmission spectra and report on the changes in the optical properties as the composition is varied. The optical properties of these films are similar to those of silicon nitride deposited using the more conventional silane-ammonia mixtures.