Silicon Oxynitride Materials Research Articles

Luminescence Mechanism in Amorphous Silicon Oxynitride Films: Band Tail Model or N-Si-O Bond Defects Model

Silicon oxynitride films are one kind of important gate dielectric materials for applications in the fabrication of silicon CMOS integrated circuits (ICs), which have been widely and deeply studied. However, with the significant demand of the technologies for Si-based monolithic optoelectronic ICs, the research efforts on the optoelectronic applications of these materials have been continually increasing, particularly in the study of light emission properties and recombination mechanisms. In this paper, we first briefly outline the present photoluminescence (PL) mechanisms in amorphous silicon oxynitride (a-SiOxNy) films. Since the PL properties and recombination processes are affected by both structural disorder and chemical disorder, the PL mechanism has been still unclear and even controversial until now. Among these various PL recombination models, the band tail states and defect states models have gained general consensus. Recently a N-Si-O bond defect model has been reported, which depends on relative atom concentration of oxygen and nitrogen in the silicon oxynitride materials. It has been revealed that oxygen bonding plays a key role not only in reducing the structural disorder, but also in creating N-Si-O (Nx) defect states in the band gap. The characteristics of two models, namely band tail and N-Si-O bond defects, have been discussed in detail. Finally it has been shown that by controlling the chemical composition of these non-stoichiometric silicon oxynitride materials, the optical and electronic properties can be improved.

Incorporation of europium(II) nanostructures into the channels of mesoporous silicon oxy-nitride for enhanced photoluminescence

Divalent europium(II)-doped mesoporous silicon oxy-nitride materials, as a novel type of nanoscopic photoluminescent material, are studied in which the optically active luminescent centers are isolated within the pores. Colorless and transparent blue emitting luminous Eu2+-doped mesoporous silicon oxy-nitride materials were prepared from mesoporous silica via impregnation, nanocasting and nitrogen-assisted carbothermal reduction and nitridation method. The morphology and porosity of the silica remain unchanged during the synthesis process as revealed by SEM images and by nitrogen sorption studies. Photoluminescence studies reveal a strong blue emission band for Eu2+ centered at 425 nm with a quantum efficiency of 47%. The luminescent intensity is greatly influenced by the amount of co-dopant, Al3+ ions.

Linearly combined optical structures based on SiON

We investigate an optical structure that results from a linear combination of two periodic, multilayer dielectric functions of slightly different periodicities. By solving the corresponding Maxwell's equation, we show that such linearly combined optical structure supports a dense number of localized (slow) modes. For a practical implementation of the linear combination of the dielectric functions, we make use a silicon oxynitride (SiON) material platform where the refractive index of SiON can be tuned over a continuous range, by changing the percentage of oxygen. The proposed optical structure works, despite a system of low refractive index contrast, and can be effectively used to create efficient polychromatic slow light systems and devices.

Formation of Mach angle profiles during wet etching of silica and silicon nitride materials

In integrated circuit technology peeling of masking photoresist films is a major drawback during the long-timed wet etching of materials. It causes an undesired film underetching, which is often accompanied by a formation of complex etch profiles. Here we report on a detailed study of wedge-shaped profile formation in a series of silicon oxide, silicon oxynitride and silicon nitride materials during wet etching in a buffered hydrofluoric acid (BHF) solution. The shape of etched profiles reflects the time-dependent adhesion properties of the photoresist to a particular material and can be perfectly circular, purely linear or a combination of both, separated by a knee feature. Starting from a formal analogy between the sonic boom propagation and the wet underetching process, we model the wedge formation mechanism analytically. This model predicts the final form of the profile as a function of time and fits the experimental data perfectly. We discuss how this knowledge can be extended to the design and the realization of optical components such as highly efficient etch-less vertical tapers for passive silicon photonics.

Fabrication and properties of GeSi and SiON layers for above-IC integrated optics

A study is presented on silicon oxynitride material for waveguides and germanium–silicon alloys for p-i-n diodes. The materials are manufactured at low, CMOS-backend compatible temperatures, targeting the integration of optical functions on top of CMOS chips. Low-temperature germanium–silicon deposition, crystallization and doping are studied for integrated photo detection up to ∼1500nm wavelength. An investigation of the process window for laser crystallization is presented aiming toward the localization control of crystal boundaries and the achievement of crystals larger than 2μm. Further, an inductively-coupled-plasma chemical vapor deposition process is presented for silicon oxynitride manufacturing at 150°C wafer temperature, yielding low-loss material in a wide optical spectral range. Integration schemes for an optical plane on top of CMOS using these materials are discussed.

Bright red, orange-yellow and white switching photoluminescence from silicon oxynitride films with fast decay dynamics

Strong tunable photoluminescence (PL) from silicon oxynitride materials have been demonstrated by modulating the oxygen content. The increase of oxygen content in the films from 8% to 61% results in red, orange-yellow and white switching PL. The change in PL characteristics of these films is ascribed to the variation of defect luminescent centers as well as the evolution of dominant phase structures changing from silicon nitride to silicon oxynitride and silicon oxide. The intense PL intensity is suggested from the nanoseconds recombination lifetime as well as the alleviation of internal stress in silicon oxynitride.

Synthesis of porous spherical silicon oxynitride material and evaluation of its properties in reversed-phase chromatographic separation

Silica has been widely used as HPLC column packing material. However, the fact that base can attack the silanol and dissolve the silica embarrasses the utilization of silica stationary phase in high pH mobile phases (pH >8). In our previous research, the use of porous spherical silicon oxynitride (sph-SiON) material from high temperature nitridation of silica microspheres as stationary phase for HPLC has been explored, and the sph-SiON is stable to alkaline mobile phases and demonstrates excellent separation of a variety of polar compounds in hydrophilic interaction liquid chromatography (HILIC) mode. Herein, the degree of nitridation was studied as a function of temperature of nitridation at 750-1 050 degrees C, yielding the silicon oxynitride with 0.40%-12.0% (mass fraction) nitrogen from elemental analysis. At the temperature of 1 050 degrees C, the nitrogen content increased from 12.0% to 24.5% with the nitridation time increasing from 20 h to 120 h. The sph-SiON is stable when disposed in different pH aqueous solutions for one week. The sph-SiON material can be modified to give hydrophobic surface through the reaction of surface Si-NHx with dimethyloctadecylchlorosilane. Elemental analysis and 13C cross-polarization magic-angle spinning (CP/MAS) NMR spectrum of C18-sph-SiON prove the integration of C18 alkyl groups attached onto the sph-SiON surface. The chromatographic evaluation of C18-sph-SiON in reversed-phase separation mode was performed with alkylbenzenes as hydrophobic probes. Three alkylbenzene compounds can be separated and retained well on C18-sph-SiON even in the mobile phase of methanol/H2O (70/30, v/v) with 78 507 plates/m, and an excellent tailing factor (0.95) can be obtained for ethylbenzene. In comparison with C18-SiO2, C18-sph-SiON shows distinct differences with respect to different classes of analytes, i. e. neutral analyte naphthalene, acidic analyte ibuprofen, and basic analyte amitriptyline.

Silicon oxynitride microspheres as stationary phase for high performance liquid chromatography

Porous spherical silicon oxynitride material exhibits much improvement of chemical stability under high pH mobile phase condition, which can be used as the stationary phase in hydrophilic interaction chromatography mode, and modified to give hydrophobic surface through the interaction of surface Si–NH2 and Si–NH–Si groups with functionalized reagents.

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 (SiH 4), ammonia (NH 3) and nitrogen protoxide (N 2O) 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.

Influences of silicon nano-crystallized structures on the optical performance of silicon oxynitride rib-type waveguides

Silicon oxynitride (SiON) films were deposited on p-type (100) silicon substrates by plasma enhanced chemical vapor deposition (PECVD), at the temperature of 300 °C, using silane (SiH 4), nitrogen (N 2), ammonia (NH 3) and laughing gas (N 2O) as gas precursors. The effects of the processing gas ratio of N 2O/(N 2 + NH 3) on the optical properties, microstructure and chemical bonding evolutions of SiON material, and the influences of silicon nano-crystallized structures on the optical performance of SiON-based rib-type optical waveguides were studied. Microstructure evolutions analysis and optical measurements indicated that the refractive index and the extinction coefficient could be precisely determined by controlling the N 2O/(N 2 + NH 3) ratio and the thermal annealing process. A greater density and dimension of silicon nano-crystallized structures resulted in more optical scattering effect phenomena occurring between the interface of silicon nano-crystallized structure and SiON matrix and more optical propagation loss.

High Efficiency Nitride Based Phosphors for White LEDs

In this overview paper, novel rare-earth doped silicon nitride based phosphors for white LEDs applications have been demonstrated. The luminescence properties of orange-red-emitting phosphors (M2Si5N8:Eu2+) and green-to-yellow emitting phosphors (MSi2N2O2:Eu2+, M = Ca, Sr, Ba) are discussed in detail with a focus on the relationship between the properties and structures. With high conversion efficiency in the near UV/blue region, along with high chemical/physical stability, Eu2+ - and Ce3+ - activated alkaline-earth silicon nitride and oxynitride materials are excellent wavelength-conversion phosphors for white LEDs.

Nitridation mechanism of mesoporous silica: SBA-15

Mesoporous silicon oxynitride materials (NSBA-15) are prepared by the thermal treatment of mesoporous silica (SBA-15) in NH 3 flow at various temperatures (between 873 and 1273 K), and are characterized by FT-IR, elemental analysis, ESR, XRD, 29Si MAS NMR, and N 2 adsorption/desorption. The nitridation routes were determined through the investigation on surface defect species and N distribution around the tetrahedral site of Si as well as the surface groups of NSBA-15. The structural changes by nitridation are also investigated through the study on the changes in porosity under thermal treatments in NH 3 or N 2 flow. Our investigations have revealed the role of surface defect species as well as surface groups and NH 3 in the nitridation. The nitridation proceeds through the radical reaction of NH 3 with Si–O and Si species below 973 K. N-related defects are produced through the open reaction of siloxane bridging bonds by H atoms generated from NH 3 on the surface above 1073 K. Nitridation is enhanced by the condensation of SiNH 2 species and the radical reaction of NH 3 with N-related defects. Based on the understanding of the factors that are effective in the nitridation, the nitridation mechanism of mesoporous silica is proposed.

Nitrogen Loss and Structural Change of Nitrogen-incorporated SBA-15 Mesoporous Materials Under Different Treatment Conditions

Work on nitrogen loss and structural change of nitrogen-containing SBA-15 mesoporous materials after heat treatment in air or water treatment is described herein. The nitrogen-containing SBA-15 lost nitrogen after being treated in air at high temperature or in water, the mesoporous structure of which was very well maintained and did not collapse. HRTEM, N2 sorption, powder XRD, and SEM were used to study the structural ordering and morphology of the mesoporous silicon oxynitride materials before and after treatment. FTIR and C/N/H elemental analysis confirmed that nitrogen loss occurred after the mesoporous silicon oxynitride material was treated. Nitrogen was lost via hydrolysis of ammonium groups when mesoporous silicon oxynitride material was treated in water and by being substituted by oxygen from air when it was heated in air at high temperature.

Ordered mesoporous MCM-41 silicon oxynitride solid base materials with high nitrogen content: synthesis, characterisation and catalytic evaluation

We present here the synthesis, physicochemical characterisation and catalytic evaluation of mesoporous silicon oxynitride materials. The solid base catalytic materials were prepared by subjecting pure silica MCM-41 mesoporous molecular sieves to nitridation, i.e., treatment with ammonia at high temperature. The mesoporous MCM-41 silicon oxynitride materials are well ordered and possess high surface area and pore volume. The nitrogen content was controlled within the range 8.6 to 25.1 wt% by simply changing the nitridation temperatures (between 850 and 1150 °C) or the time allowed for nitridation (from 20 to 80 hours). The nitrogen is incorporated onto the MCM-41 framework in the form of various NHx species, including terminal NH2 and bridging NH groups as well as adsorbed ammonium ions. The oxynitride materials were found to exhibit considerable catalytic activity for the Knoevenagel condensation reaction. The catalytic activity was correlated to the nitrogen content and was therefore highest for materials nitrided at high (1150 °C) temperature. In all cases, the nitrided materials were found to be generally stable with respect to storage and they suffered no significant structural degradation over a period of a few months. Oxynitride materials with the highest nitrogen content (i.e., those nitrided at temperatures ≥1050 °C) were found to be more susceptible to loss of surface area and pore volume after storage under ambient conditions for 6 months. The ease of preparation and control of the nitrogen content of mesoporous oxynitride materials and their stability makes them attractive as alternative solid base catalysts especially for large molecule transformations.

Highly ordered mesoporous silicon oxynitride materials as base catalysts.

Highly ordered mesoporous silicon oxynitride materials as base catalysts.

Highly Ordered Mesoporous Silicon Oxynitride Materials as Base Catalysts

Highly Ordered Mesoporous Silicon Oxynitride Materials as Base Catalysts

Synthesis of Highly Ordered Mesoporous Silicon Oxynitride with High Nitrogen Content

Abstract Mesoporous silicon oxynitride materials, which were highly ordered and had high nitrogen content, were prepared by heat treatment of fresh SBA15 precursors in flowing ammonium at high temperatures.

Small-size silicon-oxynitride AWG demultiplexer operating around 725 nm

We present experimental results of very compact, high /spl Delta/n, five-channel arrayed waveguide gratings (AWGs) with 5 nm-channel-spacing fabricated in the silicon-oxynitride material system. The on-chip insertion loss is about 5 dB and the crosstalk is -30 dB around 725 nm wavelength. The uniformity of the waveguide layers is better than /spl plusmn/1%,.

Application of in situ ellipsometry in the fabrication of thin-film optical coatings on semiconductors

Thin-film interference filters, suitable for use on GaAs- and InP-based lasers, have been fabricated by use of the electron-cyclotron resonance plasma-enhanced chemical vapor deposition technique. Multilayer film structures composed of silicon oxynitride material have been deposited at low temperatures with an in situ rotating compensator ellipsometer for monitoring the index of refraction and thickness of the deposited layers. Individual layers with an index of refraction from 3.3 to 1.46 at 633 nm have been produced with a run-to-run reproducibility of 0.005 and a thickness control of 10 A. Several filter designs have been implemented, including high-reflection filters, one- and two-layer anitreflection filters, and narrow-band high-reflection filters. It is shown that an accurate measurement of the filter optical properties during deposition is possible and that controlled reflectance spectra can be obtained.

Silicon-Oxynitride (SiON) for Photonic Integrated Circuits

AbstractWe report on the fabrication and analysis of silicon-oxynitride (SiON) as core material for silicon-based planar photonic waveguide circuits. Features of devices made of this particular SiON material are: (1) a silicon-compatible technology (low-cost perspective), (2) a waveguide structure with high dielectric index contrast, allowing a very compact device layout (approximately 10× smaller radius of curvature than conventional doped SiO2 technology), (3) a low optical loss < 0.15 dB/cm, in the 1550 nm telecommunication window and (4) a negligible polarization dependence. The materials aspects and resulting analyses of the SiON layers as well as particular device properties are described.