Papers by Keyword: Uniformity

Abstract: It is shown that new methods of severe plastic deformation design require combining different methods of plastic deformation. As for carbon steel wire, using drawing as a basic operation is obvious. The combination of drawing with bending and twisting was estimated by the stress-strain uniformity complex. It allows choosing the deformation processing conditions which ensure the uniform stress-strain state in each point of the carbon steel wire cross section. Based on such combination, a new method for manufacturing of semi-products with ultra fine grain structure by drawing with torsion was developed. The combination of wire drawing in two consecutively arranged dies with simultaneous bending and torsion allows achieving complex stress-strain state of the processed metal and ensure the share stresses. Metallographic investigation shows that such scheme of combined plastic deformation provides the uniformity of metal microstructure in its cross section.

Abstract: This paper reports on recent advances in 4H-SiC epitaxial growth toward high-throughput production of high-quality and uniform 150 mm-diameter 4H-SiC epilayers by enhancing of growth rates, improving uniformity and reducing defect densities. A vertical single-wafer type SiC epitaxial reactor is employed and high-speed wafer rotation is confirmed as effective, not only for enhancing growth rates without increasing the source gas supply but also improving thickness and doping uniformities. The current levels of reducing particle-induced defects, in-grown stacking faults, basal plane dislocations and the Z_1/2 center (carbon vacancies) are reviewed.

Abstract: For the popularization of SiC power device, improvement on both productivity and quality of 150 mm diameter SiC epitaxial wafer is inevitable. With highly productive 8x150-mm CVD reactor, we have grown epitaxial layer on 4° off 4H-SiC wafer Si-and C-face. Modifying some reactor parts and optimizing growth conditions enabled us to achieve a good balance between high uniformity and smooth surface.

Abstract: In the paper a new method has been proposed for the determining of the very fine machining uniformity over the elaborated surface and could be applied to different machined materials and machining procedures. The proposed methodology is relatively simple and is essentially formulated in the few subsequent steps: taking surface roughness 3D profile accordingly proposed scheme; estimation of the roughness statistical parameters: R_p, R_v, R_t, R_a, R_q, R_skew, R_kurt, and if need be – surface rugosity Ru; calculation of the centroid of the obtained data due to the measurement fields, calculation of the barycentre of the obtained data with the weighting variable chosen for the appropriate evaluation of the surface machining uniformity. As the main Cartesian coordinates of the centroid calculation we propose (R_skew, R_kurt), although other data organization schemes have also been provided as the example solutions. The final evaluation of the surface machining uniformity is based upon the Euclidean distance between the centroid and barycentre of the surface roughness data. The proposed method has been applied to experimental results obtained with the AFM technique used on samples of the polished AZ31 magnesium alloy. The surface machining procedure comprised of four stages performed with using different abrasive media, finally lead to the highest grade of the surface roughness.

Abstract: 7050aluminum alloy billets processed by semi-continuous casting were studied using conventional casting (N-EMS), conventional electromagnetic stirring casting (EMS) and annulus electromagnetic stirring casting (AEMS), respectively. Adopting the method of mathematical statistics, Zn, Mg, Cu chemical component uniformity and the microstructure of 7050 aluminum alloy billets were analyzed. The results showed that the high chemical component uniformity of the AEMS billets were obtained compared with N-EMS and EMS. The Zn, Mg, Cu element component variance was reduced 26% compared with EMS. And the A-EMS process exhibited superior grain refinement and remarkable structure homogeneity, which mainly consisted of rosaceous and nearly globular structure. The average grain size for AEMS sample was 42μm, and the grain shape factor was about 0.68.

Abstract: In the present study, high-quality chemical vapor deposition (CVD) micro-crystalline diamond (MCD) film was successfully deposited on the surface of the Φ0.5 mm×120 mm tungsten wire using a special designed graphitic jig for supporting the substrate and a two-step deposition procedure for guaranteeing the uniformity of as-deposited diamond film. It is proved that as-deposited film indeed presented much more uniform thickness than that obtained using a conventional jig described in the previous literature, and a very thick WC interlayer spontaneously formed between the substrate and the diamond film, which together with as-deposited MCD film have significant effects on mechanical properties of the wire. Generally speaking, the coated wire remains extremely high surface hardness of the MCD film and considerable toughness of the substrate, along with favorable film-substrate adhesion. It is recognized that these the coated tungsten wires have broad application prospects, but the technologies for depositing diamond films that are thick enough on even longer and thinner wires still need further investigation.

Abstract: This paper presents the current performance of 150mm SiC epitaxy on state-of-the-art 150mm substrates. Excellent on-wafer uniformity has been achieved with mean thickness uniformity at 1.8% and mean doping uniformity at 5.4%. The epilayer surface is smooth across wafer diameter with a typical defect density below 1 cm^-2. Within a run, wafer-to-wafer variation of 0.7 % for thickness and 5% for doping is demonstrated. The mean values of warp and bow after epitaxy are 35 um 15 μm, respectively. The above metrics are critical to enable cost effective production of 150mm SiC epiwafers suited for device fabrication.

Abstract: The guidelines necessary to improve the n-type doping uniformity on C-face epitaxial growth of 4H-SiC have been examined as far as the practical throughput is maintained, e.g. 3×150 mm wafers with the growth rate higher than 20 μm/h. The flow-channel enlargement was carried out and the effect was estimated by temperature distribution estimation performed by hydrogen etching. Also, effective C/Si was simulated with the temperature distribution obtained from the hydrogen etching experiments. As a result, positional agreement was found between the region where carrier concentration begins to increase and the drastic drop in temperature and the effective C/Si ratio.

Abstract: Silicon dioxide film has been used as the gate dielectric material in MOS device technology for decades. The film is normally grown in a diffusion furnace using a dry thermal oxidation process. As the device is scaled down to nanometer dimensions, the SiO₂ film uniformity requirement is more stringent than ever. In this paper, the effect of furnace temperature and the flow rate of oxygen gas on wafer temperature distribution was investigated. The result was recorded by using the Infrared Thermometer with Dual Laser Targeting device (IRT5000). We have found that the uniformity of temperature distribution on the wafer is almost directly proportional to the O₂ flow rate for the entire furnace temperature range (900 - 1050°C). On the other hand, the effect of O₂ flow rate on wafer temperature distributions clearly shows two distinct regions; for furnace temperatures of less than 1000 °C, the higher the O₂ flow rate, the better the uniformity. For the furnace temperatures of more than 1000 °C, we did not observe any clear dependency of wafer temperature distribution on O₂ flow rate.

Abstract: As for the impinging jets of single group slot nozzles, the heat transfer of the top and bottom strip surface is uneven which is mainly caused by the various jet distances of the top and bottom nozzle to the strip surface and the effect of gravity. In this study, the convective heat transfer process of the top and bottom strip surface due to single group slot nozzles in the ultra-fast cooling (UFC) system was studied by the fluid-structure interaction finite element method. The distributions of the flow field and heat transfer for the top and bottom strip surfaces were obtained under the various parameters. The results showed that, the difference value of the average Nusselt numbe for the top and bottom strip surface was decreased with the increase of the jet velocity, but when the jet velocity was up to 5m/s it remained almost the same. The uniformity of the top and bottom surface was improved by the jet impingement height (h) for the h <45mm. It was found that for h =25mm, the heat transfers of the top and down surfaces were more evenly, and the different value of average Nusselt number for the decreased by about 12.6%-28% as the jet impingement height increased from 25mm to 45mm when the slot width was 5mm.