Papers by Keyword: Thickness Uniformity

Abstract: Vacuum Assisted Resin Infusion (VARI) process has known significant industrial and scientific attentions due to its ability to manufacture large composite structures with a relatively high fiber volume fraction and low cost. However, it suffers simultaneously from long processing time and non-uniformity in part thickness along the part length due to respectively low pressure gradient between inlet and outlet, and the flexible nature of the vacuum bag. One approach to improve the part thickness uniformity is by allowing the excess resin to be drained out through the vent. This phase is called post infusion stage and has major influence on the quality of the part and production time. Therefore, the objective of the present study is to provide semi-analytical solution for resin pressure distribution, fiber volume fraction and part thickness during resin infusion and post-infusion phases in vacuum assisted resin infusion. The results show that the post filling constitutes a major part of the total process time and optimizing this stage can reduce the resin waste and process time and improve the composite part thickness uniformity.

Abstract: In this paper, the performance of a new CVD reactor (called PE1O8) designed by LPE and developed in the European project REACTION to process uniform 4H-SiC homoepitaxy on 200 mm substrate is reported. Its tunable multi-zone injection system and new gas delivery configuration ensure the uniform gas distribution throughout the substrate. Excellent thickness and doping uniformity on 200 mm substrates are achieved with run-to-run variation less than 1.4% and 5.6% respectively.

Abstract: In order to analysis the effect of the sheet metal postures on the forming thickness, the horizontal sheet posture, the multidirectional sheet postures with the inclined angle of , and the multidirectional sheet postures obtained after optimization were respectively used for comparative analysis through the numerical simulation against the same model. The result shows that the optimized multidirectional sheet metal postures can reduce the overall thickness difference of the formed part and realize the thickness uniformity.

Abstract: N-type 4H-SiC homo-epitaxial films were grown by high speed wafer rotation vertical CVD tool, and effect of surface C/Si ratios on in-wafer uniformity and lower limit of carrier concentration of the SiC films on 150 mm diameter wafers was investigated. From analysis of in-wafer distribution by mapping of whole wafers, it was found that high in-wafer thickness uniformity was obtained for the films grown both at lower introduced C/Si ratio of about 1.35, which corresponds to surface C/Si ratio is lower than 1.0, and at higher introduced C/Si ratio of about 1.80, which corresponds to surface C/Si ratio is higher than 1.0. However, larger fluctuation of the carrier concentration at wafer edge was observed for the film grown at lower introduced C/Si ratio, compared with the film grown at higher introduced C/Si ratio. Lower fluctuation of the carrier concentration for the film grown at higher introduced C/Si ratio is thought to be due to lower sensitivity of carrier concentration on growth temperature, which is observed for the film grown at surface C/Si ratio higher than 1.0. Also, the film grown at higher introduced C/Si ratio showed longer carrier lifetime with higher uniformity, although the film grown at lower introduced C/Si ratio indicated shorter carrier lifetime with lower uniformity. The mean carrier concentration of the films grown at higher introduced C/Si ratio was reduced by two digits compared with those grown at lower introduced C/Si ratio, and low carrier concentration of 1.7 x 10¹⁴ cm^-3 with high in-wafer uniformity for intentionally doped SiC film grown at higher introduced C/Si ratio was achieved. Based on the results mentioned above, fabrication of thick and low-doped epi layer on 150 mm diameter wafer with high in-wafer uniformity was demonstrated.

Abstract: N-type 4H-SiC homo-epitaxial films were grown on 150 mm diameter wafers by high speed wafer rotation vertical CVD tool, and effect of surface C/Si ratio on short-term and long-term repeatability of the SiC films was investigated. By tuning of growth condition, high uniform SiC film with in-wafer thickness uniformity of ±2.8 % (1.6 % σ/mean) and carrier concentration uniformity of ±3.1 % (1.9 % σ/mean) was successfully grown at higher introduced C/Si ratio of about 1.80, which corresponds to surface C/Si ratio higher than 1.0 on the whole wafer. This result was comparable to the film grown at lower introduced C/Si ratio of about 1.35, which corresponds to surface C/Si ratio lower than 1.0 on the whole wafer. On the other hand, the films on 13 wafers successively grown at higher introduced C/Si ratio indicated low fluctuation from 1.85 to 3.09 % (σ/mean), and the short-term repeatability of the in-wafer carrier concentration uniformity of the films grown at higher introduced C/Si ratio was improved compared with the films grown at lower introduced C/Si ratio. Additionally, in-wafer carrier concentration uniformity of the films on 171 wafers grown at higher introduced C/Si ratio showed 75 % quartile of 4.26 % (σ/mean), and this result was greatly superior to that of 8.21 % (σ/mean) for the films on 130 wafers grown at lower introduced C/Si ratio.

Abstract: Due to the optimization problem of coating thickness uniformity for two times spray technology, an optimization method of coating thickness uniformity for two times spray technology was proposed based on the optimized spray trajectory of one time. Based on the established tool model and complex curved surface was partitioned into several plane patches, the model of coating thickness was established for two times spray on the plane. The optimization model of coating uniformity was given and the golden section method was used to solve it. Simulation result show that the feasibility and availability of optimization model; the coating uniformity was improved effectively after optimization for two times spray trajectory.

Abstract: Large variations have been observed in the uniformity and carrier concentration of epitaxial graphene grown on SiC by sublimation for samples grown under identical conditions and on nominally on-axis hexagonal SiC (0001) substrates. We have previously shown that these issues are both related to the morphology of the graphene-SiC surface after sublimation growth. Here we present a study on how the substrate polytype, substrate surface morphology and surface restructuring during sublimation growth affect the uniformity and carrier concentration in epitaxial graphene on SiC. These issues were investigated employing surface morphology mapping by atomic force microscopy coupled with local surface potential mapping using Scanning Kelvin probe microscopy.

Abstract: Ti₃Al intermetallic alloy is a hard formed material with many advantages for aviation and aerospace applications. Superplastic forming (SPF) is an ideal process for Ti₃Al alloy to form sheet metal component. The thickness distribution of U cross-section circular parts, which were superplastically formed in two different female die cavity, were predicted by FEM software. According to female die forming thickness distribution, preforming die cavity was designed and was optimized by FEM software. Superplastic bugling tests with and without preforming were carried out. The thickness of parts were measured and compared with predictions by FEM software. The results showed that preforming can promote thickness uniformity efficiently in female die forming. In this experiment, the thickness difference range of the part formed with preforming reduced 75.8% compared with part formed without preforming.

Abstract: A new type of multi-site magnetron sputtering system has been researched, which has more than one workbench. Based on the operating principle of the magnetron sputtering system which with a circular plane target, a mathematical model has been developed to simulate and discuss the influencing factors on the film thickness uniformity. The results showed that when the substrates were rotating axially and eccentrically, the film thickness distribution were affected by both the target-substrate distance and the eccentricity. If the eccentricity was constant, the film thickness would become thinner when the target-substrate distance increased, and the thickness uniformity tended to be improved. If the target-substrate distance was constant, the thickness uniformity would become better when the eccentricity increased. Moreover, if the substrate rotated axially and revolved around the target simultaneously, the thickness uniformity would become better when velocity ratio of axial rotation to revolution increased. And the effect of the thickness uniformity became small gradually if the ratio increases to a certain degree. In addition, increasing the etching area properly not only could conduct the film distribution to better, and improve the substrate film thickness uniformity also. Finally, taking a series of experiments, and analyzing the experimental data, the conclusion of the study results in the paper had been verified.

Abstract: In this paper, an effective method is presented to improve thickness uniformity in nickel electroforming process. In most electroforming processes, thickness ratio of edge to center is 2.5~4 and the shape of the electroforming zone is naturally a concave. Dividing conductive zone of electroforming structure to redistribute current density was applied to improve electroforming uniformity. Theoretical analysis and experimental results verify that a proper dividing method can improve the electroforming uniformity effectively. In the experiment, the thickness ratio of edge to center decreases from 2.91 to 1.88.