Direct comparison of the electrical properties in metal/oxide/nitride/oxide/silicon and metal/aluminum oxide/nitride/oxide/silicon capacitors with equivalent oxide thicknesses

We examine the electrical properties of metal/oxide/nitride/oxide/silicon (MONOS) capacitors with two different blocking oxides, SiO₂ and Al₂O₃, under the influence of the same electric field. The thickness of the Al₂O₃ layer is set to 150 Å, which is electrically equivalent to a thickness of the SiO₂ layer of 65 Å, in the MONOS structure for this purpose. The capacitor with the Al₂O₃ blocking layer shows a larger capacitance-voltage memory window of 8.6 V, lower program voltage of 7 V, faster program/erase speeds of 10 ms/1 μs, lower leakage current of 100 pA and longer data retention than the one with the SiO₂ blocking layer does. These improvements are attributed to the suppression of the carrier transport to the gate electrode afforded by the use of an Al₂O₃ blocking layer physically thicker than the SiO₂ one, as well as the effective charge-trapping by Al₂O₃ at the deep energy levels in the nitride layer.     

Refraction properties of PECVD of silicon nitride film

Using a neural network, the refractive index of a film deposited in a plasma enhanced chemical vapor deposition is characterized. The deposition process was characterized by a 2^6-1 fractional factorial experiment. Experimental variables and ranges include 20-40 W radio frequency (RF) power, 80-160 Pa pressure, 180-260 sccm SiH₄ flow rate, 1-1.4 sccm NH₃ flow rate, 0-1000 sccm N₂ flow rate, and 200-300°C substrate temperature. To examine the effect of the interaction between variables on the refractive index, a predictive neural network model was constructed. Prediction accuracy was optimized as a function of training factors. Model predictions were certified experimentally. Many complex interactions between the variables not reported previously were revealed. The power effect was transparent only in such plasma conditions as high SiH₄ or NH₃ flow rate. The temperature effect was conspicuous under high pressure. Deposition mechanisms were qualitatively estimated in conjunction with the reported linear dependency of refractive index on SiH/NH ratio.     

Improved electrical and reliability characteristics in metal/oxide/nitride/oxide/silicon capacitors with blocking oxide layers formed under the radical oxidation process

We propose a Metal-Oxide-Nitride-Oxide-Silicon (MONOS) structure whose blocking oxide is formed by radical oxidation on the silicon nitride (Si3N4) layer to improve the electrical and reliability characteristics. We directly compare the electrical and reliability properties of the MONOS capacitors with two different blocking oxide (SiO2) layers, which are called a "radical oxide" grown by the radical oxidation and a "CVD oxide" deposited by chemical vapor deposition (CVD) respectively. The MONOS capacitor with a radical oxide shows a larger C-V memory window of 3.6 V at sweep voltages from 9 V to -9 V, faster program/erase speeds of 1 micros/1 ms at bias voltages of -6 V and 8 V, a lower leakage current of 7 pA and a longer data retention, compared to those of the MONOS capacitor with a CVD oxide. These improvements have been attributed to both high densification of blocking oxide film and increased nitride-related memory traps at the interface between the blocking oxide and Si3N4 layer by radical oxidation.     

Electrical characterization of MIS capacitors fabricated from ECR-PECVD silicon oxide and silicon nitride bilayer films

In this study, a comparative electrical characterization of Al/SiN _x /Si and Al/SiN _x /SiO₂/Si MIS structures has been carried out. Both SiO₂ and SiN _x films have been deposited by using electron-cyclotron resonance plasma-enhanced chemical vapor deposition method. C–V results show that samples without SiO₂ have more defects than those with SiO₂. Deep-level transient spectroscopy and conductance transient measurements demonstrate that as for the samples containing the SiO₂ film, these defects are mostly concentrated in the insulator/semiconductor interface, whereas in the other case defects are spatially distributed into the insulator.     

Sintering and microstructure of silicon nitride prepared by plasma CVD

Ultrafine Si₃N₄ powder with average particle size of 30 nm prepared by a thermal plasma CVD was sintered at 1750 °C in nitrogen for 1 h. The sintering behaviour of the powder was characterized by the crystallization of the powder and the resultant sintered bodies were observed with microscopes. It was found that the sinterability depended strongly on the green density and the degree of crystallization. If the powder was homogeneously mixed with sintering additives, it sintered to 98% density at 1750 °C in a nitrogen atmosphere. The microstructure of the sintered bodies observed by SEM indicated that they consist of needle-like grains with an aspect ratio of about 4. The microstructure of a thin film of the sintered body observed by TEM indicated that the grains with crystal habits were wet with liquid phase. TEM also clarified that two kinds of grain boundaries were present; one was wet with liquid phase along a grain boundary and the other was a coincident one without liquid phase. The lattice fringes of liquid phase suggested the presence of Y-apatite which would be generated during cooling.     

Effect of oxide additive in silicon nitride on interfacial structure and strength of silicon nitride joints brazed with aluminium

Silicon nitride ceramics with Y₂O₃ and Al₂O₃ as sintering additives were brazed with aluminium, and the brazed strength and the interfacial structure of the joints were compared with those of the joints made of additive-free silicon nitride ceramics. It is concluded that the additives in silicon nitride ceramics take part in the interfacial reaction, make the reaction layer thicker, and hence increase the brazed strength greatly.     

Effect of microstructure on electrical properties of Li and Cr substituted nickel oxide

LCNO (Li_0.35Cr_0.10Ni_0.55O) sample was prepared by modified sol–gel method and annealed at different temperatures (400, 800 and 1000 °C) in order to have variation in the size of grains and grain boundaries. The crystallinity and phase purity have been studied by employing the X-ray diffraction (XRD) technique. All the samples are crystallize to cubic symmetry with \(Fm\overline 3 m\) space group and, XRD patterns could be analysed by employing the Rietveld method. The microstructural and elemental analysis of the sample has been carried out by using the field emission scanning electron microscopy (FESEM). The grain size increases with the increase in annealing temperature which leads to increase the dielectric constant with the grain size. Interestingly, the enhancement of dielectric constant with the increase in grain size could be explained by the Barrier Layer Capacitances (BLCs) model. The frequency dispersion of dielectric constant could be explained by the Maxwell Wagner relaxation model. Furthermore, it is also observed that the activation energy obtained from dielectric relaxation analysis is comparable with the activation energy obtained by impedance analysis (Cole–Cole). In addition, the correlation between microstructure (grains and grain boundaries) with electrical transport properties of LCNO has been reported.     

Doping-induced modulation of electrical and optical properties of silicon nitride

This work presents first-principle calculations of electronic structure and optical properties of doped α-Si₃N₄. It is found that B and P impurities form shallow acceptor and deep donor bands, respectively, in the band gap of α-Si₃N₄. Analysis of the charge neutrality level indicates that bipolar doping of α-SiN_x is possible and that both n- and p-type electrical conductivity can be expected. This result can be helpful to extend the list of device applications of SiN_x. Furthermore, it is shown that upon heavy doping with these impurities, the optical properties of the material are modified by doping. Both the refractive index and extinction coefficients are increased over the photon energy range 0-4 eV as a result of the doping.     

Effect of spark plasma sintering on microstructure and electrical properties of ZnO-based varistors

Conditions for the elaboration of varistors by spark plasma sintering (SPS) are investigated, using 70 nm zinc oxide nano-particles. For this purpose, the system constituted of zinc oxide, bismuth oxide and other metal oxide is used. Material sintering has been performed by SPS at various temperatures and dwell times. Determination of the microstructure and chemical composition of the as-prepared ceramics are characterized by scanning electron microscopy and X-ray diffraction analysis. Micro-structural analysis revealed the presence of ZnO, spinel and bismuth rich phases. ZnO based Varistor samples sintered within climb speeds 100 and 400 °C/min are compared. The nonlinear electrical characteristics, current–voltage, are measured. The breakdown voltage of the varistors strongly depends on grain sizes. The results show that the best varistors are obtained by SPS at sintering temperatures ranging from 900 to 1200 °C.     

Effect of microstructure on the erosion and impact damage of sintered silicon nitride

The erosion rates and impact damage of two sintered silicon nitride materials with identical compositions but different microstructures were determined as a function of impacting particle (SiC) kinetic energy and temperature (25–1000° C) using a slinger-type erosion apparatus. The coarse-grained silicon nitride had significantly better resistance to impact damage than the fine-grained material. Crack-microstructure interactions were characterized using scanning electron microscopy and showed that crack-bridging was an important toughening mechanism in the coarse-grained material. Post-impact strength data were significantly less than those predicted from the indentation-strength data, due to impact flaws linking up prior to fracture. Consistent with its greater fracture resistance, the erosion rate of the coarse-grained material was less than that of the fine-grained material for erosion at 25 deg, and was independent of erosion temperature.     

Effect of phase composition and microstructure on the thermal diffusivity of silicon nitride

The effects of compositional and microstructural variables and processing conditions on the room temperature thermal diffusivity of hot-pressed and reaction-sintered silicon nitride were determined. The thermal diffusivity for hot-pressed silicon nitride increases with-content. Maximum thermal diffusivity is reached at about 3 wt % MgO. The higher thermal diffusivity of the -phase is attributed to its higher purity level and the less distorted crystal structure compared to the-phase. In reaction-sintered nitride the thermal diffusivity is strongly influenced by the relative amount and needle-like morphology of the-phase. Correlations of the thermal diffusivity with mechanical properties are discussed.     

PECVD法生长氮化硅工艺的研究

采用了等离子体增强化学气相沉积法(plasma-enhanced chemical vapor deposition,PECVD)在聚酰亚胺(polyimide,PI)牺牲层上生长氮化硅薄膜,讨论沉积温度、射频功率、反应气体流量比等工艺参数对氮化硅薄膜的生长速率、氮硅比、残余应力等性能的影响,得到适合制作接触式射频MEMS开关中悬梁的氮化硅薄膜的最佳工艺条件.     

Effects of additive amount on microstructure and mechanical properties of silicon carbide-silicon nitride composites

Powder mixtures of -SiC--Si₃N₄ in a weight ratio of 1 : 1 containing 5–20 wt% Y-Mg-Si-Al-O-N oxynitride as a sintering additive were liquid-phase sintered at 1800°C for 3 h by hot-pressing. These materials had a microstructure of in situ-toughened composites as a result of the phase transformation of Si₃N₄ during sintering. The introduction of larger amount of additives accelerated the grain growth of elongated -Si₃N₄ grains with higher aspect ratio, resulting in the improved fracture toughness and strength. Typical flexural strength and fracture toughness of SiC-Si₃N₄ composites containing 15 wt% oxynitride glass were 860 MPa and 5.7 MPa · m^1/2, respectively.     

Effects of plasma treatments on structural and electrical properties of methyl-doped silicon oxide low dielectric constant film

In this article, a methyl-doped silicon oxide low k film for use in inter-level dielectric application has been characterized. The structural and electrical properties of films prepared by chemical vapor deposition before and after different etching and photo-resist stripping (PRS) plasma treatments were studied. Structural properties of the low k film with various extents of forming gas and O₂ plasma treatments were reflected by the contents of Si-CH₃ and Si-H bonds. Surface roughness of films with plasma treatments was closely linked to the ratios of the cage- and network-structures of Si-O. Electrical properties of plasma-treated films were dependent on the applications of both etching and PRS plasma chemistries. Forming gas PRS caused the least low k film structural change and electrical deterioration compared with O₂ treatment. Moreover, E_bd of films decreased significantly by CH₂F₂ versus C₄F₈ etch. The best electrical properties of the film was obtained with a leakage current density of < 1 × 10^− 8 A/cm² and a dielectric breakdown strength of ∼3.2 MV/cm after being subjected with C₄F₈ / N₂ / Ar trench etch and forming gas PRS treatment.     

Relationships between processing,microstructure and properties of dense and reaction-bonded silicon nitride

Some aspects of processing, microstructure and properties of the various types of silicon nitride are discussed. Special emphasis is placed on the relationships between powder properties, process conditions, densification and microstructure, as well as the interdependence between microstructure and properties. After summarizing the areas of crystal structure and thermodynamic properties, and processing of the different types of Si₃N₄, the state-of-the-art of dense and reaction-bonded silicon nitride is given. For both types the formation mechanisms and microstructure, relationships between powder properties, additives (in the case of dense Si₃N₄), process conditions, and densification and microstructure, as well as data and microstructural effects of various mechanical, thermal and thermo-mechanical properties, are outlined. Advanced processing techniques, such as sintering, gas-pressure sintering, post-sintering, and the different routes of hot-isostatic pressing (starting with powder compacts, reaction-bonded Si₃N₄ or pre-sintered Si₃N₄ and the resulting properties, are discussed.     

Effect of microstructure on the high temperature strength of nitride bonded silicon carbide composite

Four compositions of nitride bonded SiC were fabricated with varying particle size of SiC of ∼ 9.67, ∼ 13.79, ∼ 60 μ and their mixture with Si of ∼ 4.83 μ particle size. The green density and hence the open porosity of the shapes were varied between 1.83 to 2.09 g/cc and 33.3 to 26.8 vol.%, respectively. The effect of these parameters on room temperature and high temperature strength of the composite up to 1300°C in ambient condition were studied. The high temperature flexural strength of the composite of all compositions increased at 1200 and 1300°C because of oxidation of Si₃N₄ phase and blunting crack front. Formation of Si₃N₄ whisker was also observed. The strength of the mixture composition was maximum.     

Effect of powder thermal treatment on the microstructure and electrical properties of doped ceria ceramics

Ce_0.8Sm_0.2O_2 − δ electrolytes were prepared by sol-gel methods with different thermal treatment conditions. It was found that the particle size of the powders thermally treated in N₂ could be controlled less than 10 nm, due to the fact that carbons that enwrapped the precursors could inhibit their crystallization. At the same time, the nano-sized precursors could form larger nuclei at the initial stage of sintering, resulting in the formation of electrolyte with higher density and larger grain size. At the same consent of oxygen vacancies, the enhancement of electrical properties for the electrolyte was correlated to its microstructure obtained by the N₂ thermal treatment.