Papers by Keyword: TaC

Abstract: Tantalum carbide (TaC) coating, produced in an ultrahigh temperature chemical vapor deposition (CVD) process, exhibited high thermal and chemical stabilities, low emissivity, and high purity. Low emissivity of 0.3~0.43 was measured on TaC coating at 1000°C and compared with the one of SiC coating. As revealed in both simulation and experiment, the low emissivity of TaC coatings not only improves temperature uniformity in the SiC PVT process, but also reduces power consumption in both SiC crystal growth and GaN epitaxial deposition. The results provide important guidance to process tuning when switching from a conventional graphite or SiC-coated component to its TaC-coated counterpart.

Abstract: Tantalum carbide (TaC) coating, produced in an ultrahigh temperature chemical vapor deposition (CVD) process, exhibited high thermal and chemical stabilities, low emissivity, and high purity. The present research investigated through modeling the TaC emissivity and reactivity impacts on the temperature, C/Si ratio and growth rate in SiC physical vapor transport (PVT) process. The TaC coating effect was further validated by SiC crystal shape and quality through a series of growth experiments. As our study revealed, TaC coating can act as a protection and isolation layer to extend graphite component life, improve radial temperature uniformity, maintain SiC sublimation stoichiometry, suppress impurity migration, and reduce energy consumption. Ultimately a TaC-coated graphite crucible set is expected to improve SiC PVT process control and product quality.

Abstract: We propose the Si-vapor ambient anneal as a cap-free activation annealing (A/A) method for Silicon Carbide (SiC) using Tantalum Carbide / Tantalum composite materials (TaC/Ta). This method prevents the roughening of SiC surface by controlling the process function without conventional Carbon (C)-cap [1,2]. In this report, we evaluated the warping behavior of SiC wafer to confirm the effect of ion implantation (I/I) temperature (T_I/I) and epi-ready treatment using Si-vapor ambient anneal. Wafer warp suppressing effect of high temperature I/I was confirmed and large wafer warpage occurred due to thinning of the wafer thickness. Furthermore we also observed the simultaneous improvement of the sharp edge shape and sidewall roughness of the trench under the appropriate conditions of the Si-vapor ambient anneal. It is possible to shape the round shape of the trench edge and to improve the roughness of trench sidewall by Si-vapor ambient anneal simultaneously with activation annealing process.

Abstract: As a new thinning and surface planarizing process of Silicon Carbide (SiC) wafer, we propose the completely thermal-chemical etching process; Si-vapor etching (Si-VE) technology. In this work, the effects of mechanical strength and surface step-terrace structure by Si-VE are investigated on the 4° off-axis 4H-SiC (0001) Si-face substrates. The indentation hardness of Si-VE surface is superior to the conventional chemo-mechanical polishing (CMP) surface even after epitaxial growth. The transverse strength of thinned Si-VE substrate is also superior to the conventional mechanically ground substrate. The surface step-terrace structures are observed by the low energy electron channeling contrast (LE-ECC) imaging technique. The latent scratch causes bunched step lines (BSLs) with various inhomogeneous step morphologies only on the CMP surface.

Abstract: We propose the thermal chemical etching process for Silicon Carbide (SiC) under the Si-vapor ambient using Tantalum Carbide / metal Tantalum composite materials (TaC/Ta). In this process, the high-rate “Si-vapor etching” method is applied to the removal of the surface damage and the formation of epi-ready surface. Over 10μm of “Si-vapor etching” provides smooth surface without latent scratch and low stacking faults density as same as on the CMP after epitaxial growth, which are observed by confocal microscope with differential interference contrast (C-DIC) microscope and Photo-Luminescence (PL) imaging measurement. Furthermore, the low-rate Si-vapor etching method, “Si-vapor ambient annealing” is applied to post-implantation activation annealing process without conventional C-cap. “Si-vapor ambient annealing” provides lower sheet resistance and smoother surface than the C-cap annealing after very high temperature annealing up to 2000 °C.

Abstract: Tantalum carbide (TaC) gradient composites were fabricated via in-situ fabrication method from the tantalum plate and gray cast iron. The morphology, phase constituents, micro-hardness, and relative abrasion resistance of the composites were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-hardness tester and abrasive wear testing machine. The surface layer, which was ~160μm thick, was dense ceramic layer composed by ~90% submicron TaC particulates. The highest micro-hardness value of the dense ceramic layer was 13.84 GPa. In the sub-layer, the gradient distribution of TaC particulates reflected in the volume fraction decreased from 90% to 0%. While the micro-hardness value decreased from 10.81 GPa to 4.10 GPa. The metallurgical combination of the interface between the composites and matrix was perfect. The wear resistance of TaC reinforced iron matrix surface gradient composites increased significantly.

Abstract: As a new post-implantation activation annealing of Silicon Carbide (SiC), we propose the Si-vapor ambient anneal using Tantalum Carbide / metal Tantalum composite materials (TaC/Ta). In this technique, semi-closed TaC/Ta container which can supply Si-vapor ambient is used, and Si vapor compensates thermal desorption Si atoms from the SiC surface above 1500°C and can maintain the original surface morphology by controlling a process temperature and Ar back pressure. Therefore the Si-vapor ambient anneal is able to simplify the process of conventional activation anneal methods using refractory cap-layers for protecting SiC surface from thermal damage of Si-atom desorption. Experiments were performed under Ar 1.3kPa at 1600/1700°C for 5min optimized conditions in a 6inch TaC/Ta container, and the Al⁺ ion-implanted 4H-SiC properties after annealing were characterized by atomic force microscopy (AFM), Rutherford Back-scattering Spectrometry (RBS) channeling method, and four-point probe method. According to evaluation, there was no roughening of SiC surface from AFM topographic images and recovery of crystallinity at the ion-implanted layer was equivalent to by the conventional cap-layer method from RBS channeling measurement. The sheet resistance of 12kΩ/ at 1700°C equal to the typical Al⁺ ion implanted p-type SiC is confirmed by four-point probe method.

Abstract: Agile supply chain must possess the ability of utilizing alliance corporations’ production capacity fully in a systematic view, in order to meet the market demands and its changes quickly and economically. Powerful scheduling techniques are the key support for supply chains’ agility. Based on the discontinuous schedulable periods of suppliers, an agile supply chain static scheduling under schedulable periods (ASCSSSP) of multiple optional suppliers for each part is studied. According to the final product’s supplying BOM, this paper sets up a structural framework model for agile supply chains firstly, then analyzes and builds a mathematic model for the task assignment and schedule optimization of ASCSSSP with the supply-demand time and quantity constraints, and especially designs a novel heuristic algorithm of Task Adjusted by Cost (TAC) to solve the model. Finally, by some numerical experiments, the efficiency and practicability of the model and algorithm is verified by contrasting analysis.

Abstract: Mechanical properties of ferritic-marensitic steels can be improved through dispersion of fine particles with large industrial applications like nuclear, military and aeronautic areas. Steels used at nuclear reactors suffer some damage when exposure to various kinds of radiation such as gamma, plasma, neutrons among others. Special steels have been studied to resist these processes in which cause a significant degradation of these materials. Reduced activation ferritic/martensitic steels (RAFM) are used for fusion structural materials with the substitution of some alloying elements such as Mo, Nb and Ni present in the commercial martensitic steels by other elements which exhibit faster decay of induced radioactivity, such as Ta, W and V. This present work study the development of EUROFER97 steel reinforced with 3wt% of tantalum carbide (TaC).

Abstract: Gamma irradiation crosslinking of nylon6 fibers with and without the presence of triallyl cyanurate(TAC) was studied, XRD、DSC、IR and TG were used to analyze the effects of irradiation crosslinking on structure and properties of PA6 fibers. The melt-drip performance of PA6 fibers was improved after irradiation crosslinking. The breaking strength increased first then decreased as a function of absorbed dose, while elongation at break decreased. The melting temperature and crystallinity decreased with increasing the dose. Besides, the onset temperature of degradation fell slightly and the amount of non-volatile residue at 600oC increased as the irradiation dosage increased.