Surface Pretreatments of Silicon Nitride for CVD Diamond Deposition

The efficiency of different surface pretreatments (four standard chemical etchings and four diamond powder abrasive procedures) on silicon nitride (Si₃N₄) substrates for chemical vapor deposition (CVD) of diamond has been systematically investigated. Blank Si₃N₄ samples were polished with colloidal silica (∼0.25 μm). Diamond nucleation and growth runs were conducted in a microwave plasma chemical vapor deposition apparatus for 10 min and 6 h, respectively. Superior results concerning nucleation density ( N _d∼ 10¹⁰ cm⁻² after 10 min), film uniformity, and grain size (below 2 μm after 6 h) were obtained for the mechanically microflawed samples, revealing that chemical etchings (hot and cold strong acids, molten base or CF₄ plasma) are not crucial for good CVD diamond quality on Si₃N₄.     

High-Temperature Passive Oxidation of Chemically Vapor Deposited Silicon Carbide

The oxidation behavior of chemically vapor deposited (CVD) SiC at high temperature was investigated using a thermogravimetric technique in the temperatures range of 1823 to 1948 K. The specimens were prepared by chemical vapor deposition using SiCl₄, C₃H₈, and H₂ as source gases. The oxidation behavior of the CVD-SiC indicated "passive" oxidation and a two-step parabolic oxidation kinetics over the entire temperature range. The crystallization of the SiO₂ film formed may have caused this two-step parabolic behavior. The parabolic oxidation rate constant ( K _p) varied with the square root of the oxygen partial pressure ( P ^1/2_O2). The activation energy for the oxidation was determined to be 345 and 387 kJ · mol⁻¹. These values suggest that the diffusion process of the oxygen ion which passes through the SiO₂ film is rate-controlling.     

Optimization of Chemical Vapor Deposition Parameters for Fabrication of Oxidation-Resistant Mullite Coatings on Silicon Nitride

Fabrication of mullite (3Al₂O₃·2SiO₂) coatings by chemical vapor deposition (CVD) using AlCl₃–SiCl₄–H₂–CO₂ gas mixtures was studied. The resultant CVD mullite coating microstructures were sensitive to gas-phase composition and deposition temperature. Chemical thermodynamic calculations performed on the AlCl₃–SiCl₄–H₂–CO₂ system were used to predict an equilibrium CVD phase diagram. Results from the thermodynamic analysis, process optimization, and effects of various process parameters on coating morphology are discussed. Dense, adherent crystalline CVD mullite coatings ∼2 μm thick were successfully grown on Si₃N₄ substrates at 1000°C and 10.7 kPa total pressure. The resultant coatings were 001 textured and contained well-faceted grains ∼0.3–0.5 μm in size.     

Low-Temperature Metal-Organic Chemical Vapor Deposition of Silicon Nitride

Amorphous silicon nitride films have been deposited on single-crystal silicon from the gas mixture of methylsilazane and ammonia at 873 to 1073 K. The films have been characterized by ellipsometry, Fourier transform infrared spectroscopy, and Auger electron spectroscopy. The Si-C, Si-H, and C-H bonds in methylsilazane can be effectively cleaved and the associated C and H species removed. The structure and composition of the films do not show any apparent dependence on the deposition temperature.     

Some New Perspectives on Oxidation of Silicon Carbide and Silicon Nitride

This study provides new perspectives on why the oxidation rates of silicon carbide and silicon nitride are lower than those of silicon and on the conditions under which gas bubbles can form on them. The effects on oxidation of various rate-limiting steps are evaluated by considering the partial pressure gradients of various species, such as O₂, CO, and N₂. Also calculated are the parabolic rate constants for the situations when the rates are controlled by oxygen and/or carbon monoxide (or nitrogen) diffusion. These considerations indicate that the oxidation of silicon carbide and silicon nitride should be mixed controlled, influenced both by an interface reaction and diffusion.     

Oxidation Studies of Aluminum-Implanted NBD 200 Silicon Nitride

The effects of aluminum-ion-implantation on the oxidation behavior of NBD 200 Si₃N₄ were investigated over an implant concentration range of 0–30 at.%, at 800°–1100°C, in 1 atm dry O₂. Oxidation of both unimplanted and implanted samples follows a parabolic rate law. The parabolic rate constant decreases and the activation energy increases with aluminum concentration. Smooth and crack-free oxides are formed under the combination of high implant concentrations and low oxidation temperatures. Outward diffusion of Mg²⁺ from the bulk of NBD 200 to the oxide layer remains the rate-limiting step for aluminum-implanted samples. The enhancement of the oxidation resistance of NBD 200 by aluminum implantation is attributed to the retardation of the outward diffusion of Mg²⁺.     

High-Temperature Oxidation of Chemically Vapor-Deposited Silicon Carbide in Wet Oxygen at 1823 to 1923 K

The oxidation of chemically vapor-deposited SiC in wet O₂ (water vapor partial pressure = 0.01 MPa, total pressure = 0.1 MPa) was examined using a thermogravimetric technique in the temperature range of 1823 to 1923 K. The oxidation kinetics follow a linear-parabolic relationship over the entire temperature range. The activation energies of linear and parabolic rate constants were 428 and 397 kJ · mol⁻¹, respectively. The results suggested that the rate-controlling step is a chemical reaction at an SiC/SiO₂ interface in the linear oxidation regime, and the rate-controlling step is an oxygen diffusion process through the oxide film (cristobalite) in the parabolic oxidation regime.     

Thermodynamic Calculations on the Chemical Vapor Deposition of Silicon Nitride and Silicon from Silane and Chlorinated Silanes

After a discussion of the thermochemical values of the Si–H–Cl–N system which occur in the literature, CVD phase diagrams are presented which include contours of constant deposition efficiency. The temperature range considered is from 800 to 2600 K. A number of chlorinated silanes as well as silane can be used as a silicon source, while ammonia is used as the nitrogen source. The effects of pressure variation and dilution by nitrogen and hydrogen are also included. Some initial calculations concerning silicon diimide are made. The CVD phase diagrams are used to describe several mechanisms occurring during the formation of silicon nitride from the gas phase.     

多孔石英基体上CVD法沉积氮化硅涂层的工艺、结构与性能研究

以甲硅烷(20％甲硅烷+80％氢气)和氨气作为反应前驱体,选择孔隙率为20％左右的多孔石英陶瓷基体,采用CVD法在多孔石英基体表面制备了氮化硅涂层.研究了沉积反应温度、反应压力、反应气体配比以及沉积时间等工艺参数对附着力的影响,确定了CVD法制备氮化硅涂层的最佳工艺参数,通过对所得涂层及复合材料进行抗弯强度和介电性能的表征,探讨了氮化硅涂层对多孔石英基体力学性能和介电性能的影响.     

High-Temperature Active Oxidation of Chemically Vapor-Deposited Silicon Carbide in an Ar─O2 Atmosphere

Active oxidation behavior of chemically vapor-deposited silicon carbide in an Ar─O₂ atmosphere at 0.1 MPa was examined in the temperature range between 1840 and 1923 K. The transition from active oxidation (mass loss) to passive oxidation (mass gain) was observed at certain distinct oxygen partial pressures ( P _O2^t). The values of P _O2^t increased with increasing temperature and with decreasing total gas flow rates. This behavior was well explained by Wagner's model and thermodynamic calculations. Active oxidation rates ( k _a) increased with increasing O₂ partial pressures and total gas flow rates. The rate-controlling step of the active oxidation was concluded to be O₂ diffusion through the gaseous boundary layer.     

Paralinear Oxidation of Silicon Nitride in a Water-Vapor/Oxygen Environment

Three Si₃N₄ materials were exposed to dry oxygen flowing at 0.44 cm/s at temperatures between 1200° and 1400°C. Weight change was measured using a continuously recording microbalance. Parabolic kinetics were observed. When the same materials were exposed to a 50% H₂O–50% O₂ gas mixture flowing at 4.4 cm/s, all three types exhibited paralinear kinetics. The material was oxidized by water vapor to form solid SiO₂. The protective SiO₂ was in turn volatilized by water vapor to form primarily gaseous Si(OH)₄. Nonlinear least-squares analysis and a paralinear kinetic model were used to determine parabolic and linear rate constants from the kinetic data. Volatilization of the protective SiO₂ scale could result in accelerated consumption of Si₃N₄. Recession rates under conditions more representative of actual combustors were compared with the furnace data.     

Improved Oxidation Resistance of Silicon Nitride by Aluminum Implantation: II, Analysis and Optimization

In the preceding paper, it was shown that aluminum ion implantation significantly improves the oxidation resistance of Si₃N₄ ceramics under the influence of sodium. Not only is the oxidation rate reduced by up to an order of magnitude, the phase and morphological characteristics of the oxides grown on aluminum-implanted samples are improved as well. The role of aluminum in negating the detrimental effect of sodium on the oxidation resistance of Si₃N₄ ceramics can be interpreted on the basis of network modification of the oxide layers by sodium and aluminum cations. The degree of improvement in the oxidation resistance does not, however, necessarily increase with the aluminum concentration. A simple quantitative analysis is presented which correlates the optimum aluminum implant concentration and the sodium content in the gas phase for the optimization of the oxidation resistance of Si₃N₄ ceramics.     

氮化硅薄膜制备方法现状综述

氮化硅薄膜是一种多功能材料，在许多领域有着广泛的应用。本文系统综述氮化硅薄膜的性质、结构、应用及各种制备方法，并对今后的研究作了展望。     

Volatility Diagrams for Silica, Silicon Nitride, and Silicon Carbide and Their Application to High-Temperature Decomposition and Oxidation

Volatility diagrams—isothermal plots showing the partial pressures of two gaseous species in equilibrium with the several condensed phases possible in a system—are discussed for the Si-O and Si-N systems, and extended to the Si-N-O and Si-C-O systems, in which the important ceramic constituents SiO₂, Si₃N₄, Si₂N₂O, and SiC appear as stable phases. Their use in understanding the passiveactive oxidation transitions for Si, Si₃N₄, and SiC are demonstrated.     

Improved Oxidation Resistance of Silicon Nitride by Aluminum Implantation: I, Kinetics and Oxide Characteristics

Hot-isostatically-pressed, additive-free Si₃N₄ ceramics were implanted with aluminum at multi-energies and multidoses to achieve uniform implant concentrations at 1, 5, and 10 at.% to a depth of about 200 nm. The oxidation behavior of unimplanted and aluminum-implanted Si₃N₄ samples was investigated in 1 atm flowing oxygen entrained with 100 and 220 ppm NaNO₃ vapor at 900–1100°C. Unimplanted Si₃N₄ exhibits a rapid, linear oxidation rate with an apparent activation energy of about 70 kJ/mol, independent of the sodium content in the gas phase. Oxides formed on the unimplanted samples are rough and are populated with cracks and pores. In contrast, aluminum-implanted Si₃N₄ shows a significantly reduced, parabolic oxidation rate with apparent activation energies in the range of 90–140 kJ/mol, depending on the sodium content as well as the implant concentration. The oxides formed on the implanted samples are glassy and mostly free from surface flaws. The alteration of the oxidation kinetics and mechanism of Si₃N₄ in a sodium-containing environment by aluminum implantation is a consequence of the effective modification of the properties of the sodium silicates through aluminum incorporation.     

氮化硅薄膜生长随时间演化过程及其特性研究

氮化硅SiN_x薄膜凭借介电常数高和稳定性好的特点而被广泛应用于光电器件中,但薄膜的厚度对器件的性能有重要影响。针对此问题采用等离子体化学气相沉积技术,以高纯NH₃、N₂和SiH₄为反应气体,优化其他沉积参数,通过改变沉积时间来生长SiN_x薄膜。用X射线衍射谱(XRD),紫外-可见光光谱(UV-VIS)、傅里叶变换红外光谱(FTIR)和扫描电镜(SEM)对薄膜结构进行表征,详细研究了沉积时间与薄膜厚度的关系以及沉积时间对薄膜性能的影响。试验结果表明:所制备的样品为非晶SiN_x薄膜结构,薄膜厚度随沉积时间均匀增加;薄膜折射率随沉积时间的增加而增大,光学带隙基本不随时间变化。SEM测试结果表明,随着沉积时间增加,薄膜致密性与均匀性越来越好,氧含量也越来越少,说明薄膜致密性提高可以有效阻挡O原子进入薄膜,阻止后氧化现象的发生。     

Si3N4及其复合材料强韧化研究进展

简述了氮化硅陶瓷的结构、性能和制备工艺，并分别通过自增韧补强、纤维／晶须强韧化、层状结构强韧化、相变强韧化以及颗粒弥散强韧化等方法对氮化硅陶瓷的强韧化研究进行了分类叙述。     

Sol-Gel Alumina Coating for Improved Cyclic Oxidation Resistance of Silicon Nitride

A 25 nm thick α-alumina layer was deposited on a turbine-grade silicon nitride by sol-gel dip coating and subsequent heat treatment in air at 1200°C. This layer had a nanometer grain structure. Silicon nitride protected by this thin layer showed a significant improvement in oxidation resistance over its uncoated counterpart after 200 cyclic exposures in air at 1250°C. The oxide layer grown on the coated silicon nitride also exhibited superior surface morphology, compared with the uncoated silicon nitride.     

Oxidation Behavior of Silver- and Copper-Based Brazing Filler Metals for Silicon Nitride/Metal Joints

The oxidation behavior of reactive-element-containing brazing filler metals at 600°C was studied. Weight-gain measurements coupled with scanning electron microscopy and energy dispersive X-ray analysis indicated the formation of a nonprotective oxide on the following three ternary alloys: (i) Cu-80%, Sn-10%, Ti-10%; (ii) Ag–Cu eutectic + 5% Ti; and (iii) Ag–Cu eutectic + 5% Zr. Additions of Ni and Si to these alloys failed to reduce spallation. However, a protective oxide was formed by adding Al. The resultant quaternary alloys possessed excellent flow properties on silicon nitride.     

Composition and Microstructure of Chemically Vapor-Deposited Boron Nitride, Aluminum Nitride, and Boron Nitride + Aluminum Nitride Composites

The composition and microstructure of dispersed-phase ceramic composites containing BN and AIN as well as BN and AIN single-phase ceramics prepared by chemical vapor deposition have been characterized using X-ray diffraction, scanning electron microscopy, electron microprobe, and transmission electron microscopy techniques. Under certain processing conditions, the codeposited coating microstructure consists of small single-crystal AIN fibers (whiskers) surrounded by a turbostratic BN matrix. Other processing conditions resulted in single-phase films of AIN with a fibrous structure. The compositions of the codeposits range from 2 to 50 mol% BN, 50 to 80 mol% AIN with 7% to 25% oxygen impurity as determined by electron microprobe analysis.