Papers by Keyword: Silicon Nitride

Abstract: Nano-Si₃N₄ has been synthesized by the thermal plasma with silicon tetrachloride (SiCl₄) as the Si source, liquid ammonia (NH₃) as the N source, and silane (SiH₄) as the catalyst. And the prepared Nano-Si₃N₄was heat-treated atfour different temperatures of 1350°C, 1400°C, 1450°C, 1500°C. The as-prepared samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). The results showed that the particle size of the nano-Si₃N₄ powder was less than 100 nm and it was amorphous when the temperature below 1450°C. At 1500°C, the synthesized Si₃N₄ powder with the grain size of 10 nm was crystallized, and the α-phase Si₃N₄ reached more than 90%.

Abstract: AISI 1020 steel is considered to be one of the most applicable structural steels, in particular in the cold drawn form. Heating of this grade of steel prior to A_C1 must have been applied to spheroidize the lamellar cementite, and consequently enhances the cold formability character of the steel. Si₃N₄ nanoinoculation of this grade of steel has been used in this study, where it is added to the molten steel, in order to avoid the high cost long term heat treatment process prior to cold deformation process. Optical microscopy and SEM have been used to evaluate the morphology of cementite after nanoinoculation process with Si₃N₄. Tensile properties of nanoinoculated steels have been investigated. Finally, wear adhesive resistance of investigated samples has been evaluated. The obtained results showed a great enhancement in the mechanical properties, strength, ductility and adhesive wear resistance, as a result of the nucleation of cementite into a new spheroidal phase and grain refinement by Si₃N₄ inoculation and allow usage of AISI 1020 steels inoculated by nanoinoculant Si₃N₄ in further technological applications.

Abstract: This paper describes both aqueous and solvent-based formulations aimed at etching silicon oxide (SiO_x) with etching rates (E/R) of the order of 10-20 A/min with selectivity greater than 5 with respect to silicon nitride (SiN_x) . Diluted hydrofluoric acid (dHF) with very low pH was tried first but the selectivity was found to increase only with higher SiO_x E/R. Solvent-based formulations derived from previous work also behaved in a similar way, however its SiO_x E/R could be reduced by modifying the total fluoride concentration inside formulation. Finally, we found that low SiO_x E/R could also be implemented in the diluted buffer-oxide etch (BOE) solution and the selectivity could be adjusted by addition of a specific surfactant at a very low concentration level.

Abstract: For technology nodes beyond 14nm silicon nitride spacer etching has become a major challenge. Conventional plasma etching techniques based on CHF₃/O₂ cannot achieve thorough nitride removal on horizontal surfaces without inducing either CD loss or Si/SiGe source/drain recess. This leads to either gate leakage increase or poor raised source/drain epitaxy. To overcome atomic scale control issues faced with continuous plasma processes, several techniques aiming at achieving atomic layer etching or thin layer etching were recently described [1]. An original etching approach has been reported which consists in modifying the silicon nitride through H₂ ion implantation by plasma (ICP or CCP) and then selectively removing the modified fraction of the layer thanks to chemical etching [2]. Layer modification depth is controlled thanks to plasma parameters (bias voltage and process time). This unconventional technique was demonstrated on 14nm FDSOI logic device and showed less than 1nm spacer CD loss, less than 0.6nm SiGe recess which enabled defect-free source/drain epitaxy [2]. Mechanisms for silicon nitride modifications and selective removal are discussed in this article by comparing downstream plasma, liquid-phase HF and gas-phase HF as removal techniques.

Abstract: The etching of silicon nitride using phosphoric acid with silicon dioxide as a mask is an important process step used in the production of 3D NAND devices. This paper examines the theory of formation of a silica film onto the silicon dioxide surface during this etching step by performing a shell balance analysis of silica species in the etched out liquid volume of the 3D NAND structures. The method of moments is used to solve for the moments of the distribution of particle sizes, and this is used to solve for the potential energy barrier for silica particles to adhere to the silicon dioxide surface.

Abstract: We discuss several mechanistic approaches and experimental data for improving post-CMP cleaning of W plugs with TiN as barrier liner, and dielectric substrates SiO₂ and Si₃N₄ for use at the 10 nm technology node (metal pitch of 40 nm). Particle charge in the low pH, W CMP slurries are usually positive, and the W surface is always negatively charged at pH >3. Therefore, a strong electrostatic attraction is expected to occur between the W surface and the residual particles during post-CMP cleaning. Two main approaches were chosen to break down the strong particles-W surface post-CMP electrostatic interactions, as well as particles dispersion and prevention of redeposition: (1) using cleaning additives able to adsorb at the W surface and reverse the W surface charge; (2) using organic additives to reverse the particle charge. The latter approach results in two strongly negative charged surfaces, which are able to repulse each other, and leads to the best cleaning.

Abstract: This study reports on effect of boron and carbon addition on the phase transformations during ball milling and subsequent sintering of Si₃N₄+B and Si₃N₄+C powder mixtures. Ball milling at room temperature was conducted using stainless steel vials (225 mL) and balls (19mm diameter), 300 rpm and a bal-to-powder weight ratio of 10:1. The as-milled powders were uniaxially compacted in order to obtain cylinder samples with 10 mm diameter, which were subsequently sintered under nitrogen atmosphere at 1500°C for 1h. Characterization of the as-milled powders and sintered samples was performed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. Only peaks of Si₃N₄ were identified in X-ray diffractograms of as-milled Si₃N₄+B and Si₃N₄+C powders, suggesting that metastable structures were found during milling. After sintering at 1500°C for 1h, the Si₃N₄+BN and Si₃N₄+SiC ceramic composites were formed from the mechanically alloyed Si₃N₄+B and Si₃N₄+C powders.

Abstract: The wettability and mechanical properties of solder the joint of Sn-Cu-Ni-xSi₃N₄ had been investigated. In this study, five different silicon nitride (Si₃N₄) percentage addition were chosen (0 wt. %, 0.25 wt. %, 0.5 wt. %, 0.75 wt. %, and 1.0 wt. %). Contact angle measurement demonstrated that with Si₃N₄ addition, the wetting perfomances had been improved with the decrease of wettability contact angle. It is believed that the Si₃N₄ particles suppresses the interfacial IMC growth and thus improves the shear strength. Interfacial IMC thickness measurement and shear strength results showed that with thinner IMC layer (by increasing amount of wt.% of Si₃N₄), the higher the shear strength of the joint. Fracture surface of sheared samples shows a combination of both brittle and ductile fracture.

Abstract: The influence of 1 wt.% and 2 wt.% of graphene platelets (GPLs) addition on indentation fracture toughness (IF) of aluminium oxide (Al₂O₃) and silicon nitride (Si₃N₄) based composites has been investigated and compared to the monoliths. Ceramic composites reinforced with GPLs were prepared using hot-press processing technology. Microstructures were observed at fracture surfaces by scanning electron microscopy (SEM). Crack type identification was performed by gradually polishing of the indentation surface and mechanical properties of both systems were measured. Indentation fracture toughness was calculated by various methods and R-curves were prepared. The main activated toughening mechanisms, responsible for the increased fracture toughness are crack deflection, crack branching and crack bridging in the forms of graphene sheet pull-out or graphene necking.

Abstract: BN-Si₃N₄ composite ceramic wave-transparent materials with excellent mechanical properties were prepared by spark plasma sintering (SPS) using h-BN and α-Si₃N₄ powders as raw materials, Al₂O₃ and Y₂O₃ as sintering aids. The influence of sintering pressure on density and mechanical properties of BN-Si₃N₄ composite ceramics were studied. The phases were observed by X-ray diffraction (XRD), and the microstructures were identified by scanning electron microscopy (SEM). The results showed that with the sintering pressure increases, the relative density, bending strength and fracture toughness of the composite ceramics were significantly increased, and the porosity decreased rapidly. The effects of pressure on the properties of the composite ceramics was not significant at >40MPa, so 40MPa is optimal for the composite ceramics to gain good overall performance, i.e. the relative density was 89.1%, the porosity was 2.3%, the bending strength reached 215.4 MPa, and the fracture toughness was 3.1/MPa·m^1/2.