Nitridation Kinetics of Silicon Monocrystal and Morphology of Nitride Film

Basing on TGA (thermal gravimetric analysis) of thermal nitridation at l200, l250, l300℃, respectively,analysis of high temperature kinetics for nitridation of silicon monocrystal has been carried out. According tothe theory for kinetics of reaction of vapour with solid phase a nitridation kinetic model, from which it can beshown thal the rate of nitridation reaction of silicon crystal should be controlled by three stage limiting factors,was proposed. These limiting factors are chemical reaction, chemical reaction mixed with diffusion and diffu-sion. Using this model to treat our experimental data, satisfactory correlation coefficient and apparentactivation energy of nitridation of p-type (lll) silicon crystal have been obtained. The nitride film was identi'fied to be a-Si_3N_4 (Hexagonal, a=0.7758nm,c_o=0.5623nm) by X-ray diffraction analysis. Morphology ofthe nitride films formed in different nitridation duration was observed in both planar andcross-sectional viewsby SEM (scanning electron microscope).     

Effects of residual radicals on compositional and structural stability of silicon nitride fibers

In this study, amorphous silicon nitride fibers were prepared through the nitridation of cured polycarbosilane fibers. It was observed that their composition and properties can be controlled by adjusting the flow of NH₃ during the nitridation process. Based on their compositional and structural stability, the samples could be divided into two classes: stable fibers and unstable fibers. As indicated by the electron spin resonance spectra, the amount of the residual free radicals in the unstable fibers was significantly higher than that in the stable fibers. Because of the reactions of the radicals with the moisture in the air, the oxygen content of the unstable fibers increased day by day until the residual radicals were exhausted. Thus, to develop silicon nitride fibers with both low oxygen content and low carbon content, the amount of NH₃ used should be optimized to eliminate the free radicals. These results suggest that it is possible to tailor the nitridation conditions for preparing high-purity silicon nitride materials so that they exhibit desirable properties, such as compositional and structural stability, good mechanical properties, and high electrical resistivity.     

Structure and property changes of ZrO2/Al2O3/ZrO2 laminate induced by low-temperature NH3 annealing applicable to metal-insulator-metal capacitor

Phase transformation and morphology evolution of ZrO₂/Al₂O₃/ZrO₂ laminate induced by the post-deposition NH₃ annealing at 480 °C were studied and the effect on the electrical property of the TiN/ZrO₂/Al₂O₃/ZrO₂/TiN capacitor module was evaluated in dynamic random access memory cell. Experimental results indicated N could indeed be incorporated into the dielectric laminate by the low-temperature NH₃ annealing, resulting in tetragonal-to-cubic phase transformation and small crystallites in the ZrO₂ layers. The C residue and Cl impurity in the ZrO₂/Al₂O₃/ZrO₂ laminate, which derived from the dielectric film formation and capping TiN layer deposition, respectively, could also be reduced by the nitridation process. As a result of the better surface morphology and less impurity content, lower dielectric leakage current and longer reliability lifetime were observed for the nitrided ZrO₂/Al₂O₃/ZrO₂ capacitor. This study demonstrates the low-temperature NH₃ annealing on ZrO₂/Al₂O₃/ZrO₂ dielectric can be applicable to the metal-insulator-metal capacitor structure with nitride-based electrode, which brings advantages over mass production-wise property improvements and extends the practical applicability of the ZrO₂/Al₂O₃/ZrO₂ dielectric.     

Rapid thermal nitridation of thin SiO2 films

An alternative to SiO₂ for gate dielectric applications in MIS devices is nitrided silicon dioxide. A study of this material is presented in this paper. Thin SiO₂ layers (10 nm minimum thickness) were grown on silicon substrates and subsequently nitrided in ammonia at 1 atm using a rapid thermal processing system. Nitridation times ranged from 3 sec to 60 sec at temperatures from 900 to 1200‡ C. The resulting films were then characterized using a variety of techniques including high resolution TEM, XPS, AES, SIMS, and electrical measurements (C-V). Higher temperatures and longer processing times resulted in the accumulation of nitrogen at the film surface and at the Si/SiO₂ interface. As expected, the electrical characteristics of the nitrided films were strongly influenced by the processing conditions. The morphology of the interface, as revealed by high-resolution TEM, was also altered by the nitridation process, especially for high processing temperatures (>1000° C).     

Preparation of H-bar cross-sectional specimen for in situ TEM straining experiments: A FIB-based method applied to a nitrided Ti-6Al-4V alloy

The in situ tensile straining of cross-sectional specimens inside a TEM is intrinsically very difficult to perform despite its obvious interest to study interfaces of surface treated materials. We have combined a FIB-based method to produce H-bar specimens of a nitrided Ti-6Al-4V alloy and in situ TEM straining stage, to successfully study the plastic deformation mechanisms that are activated close to the nitrided surface in the Ti-based alloy.     

Impact of preanneal process on threshold voltage of MOS transistors for trench DRAM

As the first step of DRAM manufacture, preanneal process plays an important role in determining the threshold voltage variation. It is found that the higher trans-1,2-dichloroethene flow in pad oxide growth and the higher nitrogen flow in high-temperature annealing step would respectively engender a lower boron segregation coefficient and higher nitridation of the oxide, both modify the boron distribution in the substrate and consequently the behavior of the threshold voltage. As the feature size of DRAM devices enter nanometer regime, besides gate oxidation, ion implantation and related thermal processes, the impact of preanneal process condition should be prudentially taken into consideration for rigorous control of the threshold voltage in the advanced DRAM production.     

A novel family of solid basic catalysts obtained by nitridation of crystalline microporous aluminosilicates and aluminophosphates

Novel basic catalysts are obtained by ammonia treatment of crystalline, microporous aluminosilicates (zeolites) and aluminophosphates at temperatures above 800°C. The resulting materials are active catalysts in the Knoevenagel condensation of benzaldehyde with malononitrile, presumably due to the presence of nitrogen-containing species bound to the crystalline framework. While nitridation of zeolite NaY at temperatures around or below 800°C does not result in an increase of the catalytic activity, ammonia treatment at 850–875°C produces a significantly more active material. Further typical experimental results are presented which suggest that the activity gain seems to depend not only on the temperature of ammonia treatment but also on the structure and the chemical composition of the parent material. The novel microporous catalysts with their reasonable base strength offer the principle possibility to perform base catalyzed reactions in a shape selective manner.     

Room temperature deposition of self-assembled Al nanoclusters on stepped sapphire (0001) surface and subsequent nitridation

Self-assembled growth and nitridation of ultrathin Al nanoclusters on a stepped sapphire (0001) surface were studied by high-resolution X-ray photoemission spectroscopy, atomic force microscopy and low-energy electron diffraction (LEED). Upon room temperature deposition, in the coverage range of ∼ 0.79 to 2.3 monolayer (ML), Al nanoclusters were uniformly nucleated over the entire surface of defect-free atomically smooth terraces as well as step edges. Subsequent nitridation at elevated temperatures by ammonia did not alter the morphology of the nanoclusters. The global morphology of the stepped sapphire (0001) surface such as terrace width, step height and facet orientation had no obvious influence on the nucleation morphology of the nanoclusters in the given Al coverage range. However, local structural defects at the joints of short facets and step edges played a noticeable role on the local morphology of the nanoclusters and subsequently the nitridation chemistry. The Al nanoclusters were uniformly nitridated from surface and downwards through the 3D structures. The LEED pattern indicated a certain degree of crystallinity on the nitridated surface at a nominal Al coverage less than 2 ML, whereas at 2.3 ML Al coverage, the nitridated surface became amorphous. Thus there is a critical coverage for good surface order.     

Sialon-SiC材料的氮化热力学研究

以金属Al粉、Si粉、SiO2 粉及SiC颗粒为原料 ,在常压氮气及 14 5 0℃～ 15 5 0℃的氮化烧结条件下 ,可获得以 β Sialon为结合相的Sialon SiC复相材料。研究结果表明 :凝胶注模坯体经脱脂处理后可形成贯通的微小孔隙 ,提供了氮气进入坯体的通道 ,使氮化反应充分进行。控制氮化温度为 14 5 0℃～ 15 5 0℃及氧分压PO2 为 10 - 1 8.8～ 10 - 1 7.6 MPa,可使金属Al形成AlN及Al2 O3,成为β Sialon物相组成Si3N4 Al2 O3 AlN SiO2 所需的成分。尽管氮化试验的气体中氧分压远大于 10 - 1 7.6 MPa ,使部分AlN氧化为Al2 O3和N2 ,但氧化过程产生的N2 又使坯体该部位孔隙中的氮分压提高、氧分压降低 ,使Al2 O3与AlN达到热力学共存状态。     

水蒸气对氮化烧成制品的影响

利用硅和氮直接合成氮化硅,并用其作为结合相生产氮化硅-碳化硅制品时,氮化炉中水蒸气浓度过大（＞0．7％）的话,对制品的质量会产生诸多不良影响。