Papers by Keyword: Defect Reduction

Abstract: Silicon Carbide (SiC) is a pivotal wide-bandgap semiconductor for high-power and high-frequency electronics. However, crystalline defects, particularly Basal Plane Dislocations (BPDs), severely degrade the performance and reliability of bipolar devices by nucleating stacking faults that cause fatal forward voltage drift. This work presents the successful growth of 8-inch, 4° off-axis, n-type 4H-SiC single crystals with significantly reduced BPD density via the Physical Vapor Transport (PVT) method using an improved reactor design. The key innovation involves replacing traditional graphite components with single or polycrystalline SiC for the seed holder and guide tube, subsequently coated with a thin (10 µm) tantalum carbide (TaC) film. This design ensures thermal expansion coefficient matching and reduces thermal radiation emissivity. Etch pit density analysis revealed that the improved design reduced the overall BPD density from over 1027 cm⁻² to a remarkably low 78 cm⁻². Furthermore, it drastically improved the radial uniformity of BPD distribution by stabilizing the thermal gradient and suppressing parasitic polycrystalline nucleation, marking a critical advancement towards high-yield production of high-quality, large-diameter SiC substrates.

Abstract: In this paper, we have investigated the influence of growth-interruption during buffer layer growth on killer defect density in SiC epilayer grown over 4H-SiC (0001) substrates. We have observed that the growth-interruption method reduces total killer defect density by ~45(±5)%. Implementing growth-interruption in the buffer layer is a novel approach to mitigate epitaxial defects such as in-grown stacking faults (SFs), triangular defects, and basal plane dislocations (BPDs) in the drift layer and provide an extra margin to bipolar degradation by terminating BPDs early in the heavily doped buffer layer. The defect reduction mechanism in the presence of hydrogen has been simulated using Kinetic Monte Carlo (KMC) simulations.

Abstract: This work studies the variation of the defects density of in situ doped 3C-SiC layers during heteroepitaxial Chemical Vapour Deposition (CVD). A review on the evolution of defects density as a function of 3C-SiC grown thickness, for different N doping concentrations is offered. The doping range spanned in the experiment suits the realization of power devices.The outcome of this work provides an explanatory picture of the significant drop in stacking faults density by roughly an order of magnitude through the N doping at concentrations of the order of ~2.9×10¹⁹ cm^-3 during the growth. Conversely, N doping shows to favor the development of dislocation-like defects within the crystalline matrix. However, in few um, the crystal is able to display an effective dislocation closure mechanism, which rapidly recovers crystal quality.

Abstract: Seven quality tools are one method or tool that is often used in problems solving. Seven quality tools are developed and introduced in Japan by some quality originators such as Deming and Juran. Any organizations that cannot manage the quality of its methods and products have a tendency to fall apart. Quality is crucial to sales, price control, productivity, risk control and compliance. Productivity improvement is one of the core strategies closer to production excellence and it is also necessary to achieve correct monetary and operational performance. It enhances client delight and decrease time and cost to expand, produce and deliver merchandise and carrier. Productivity has a positive and big relationship to performance measurement for manner utilization, system output, product costs, and work-in-process stock tiers and on-time shipping. development can be in the form of elimination, correction (restore) of ineffective processing, simplifying the procedure, optimizing the machine, decreasing variant, maximizing throughput, reducing fee, enhancing high-quality or responsiveness and lowering set-up time. Hydraulic systems are widely employed in most of industries like for rollers, cement industries equipment’s etc. used for high force movements to obtain motion in the process. And in the large scale industries all the facilities are provided for maintaining the efficiency of the hydraulic system, since they have investments and experienced personals. In this study elimination of major dismantling at sick bay at Eicher Tractor, Bhopal was done by applying seven quality tools. The main aim of this thesis is to provide an application of seven QC tools to improve the quality level. QC tools are the means for Collecting data, analysing data, identifying root causes and obtaining the results. All of these tools together can provide great process tracking and analysis that can be very helpful for quality improvements. These tools make quality improvements easier to see, implement and track. Findings revealed that 150 pieces of ADDC cylinder checked after action implementation and found no leakage during testing and 129 cylinders fitted in ADDC housing, where no droppage was observed at load testing machine and 86% productivity improved.

Abstract: The objective of this research was to reduce defects in the forming process of fired clay floor tiles by modifying the parameter settings of the influential factors using the Six Sigma approach. The current process had 152,871.16 DPPM (Defect Parts per Million). The main cause of this problem was the rough surface problem in the forming process. The five steps of the Six Sigma quality improvement approach were exercised in this research, i.e. define, measurement, analysis, improvement, and control phases, respectively. This research started by studying in details of the production process to find relevant factors that could cause a rough surface defect. The main factors were selected and analyzed by Failure Mode and Effect Analysis (FMEA). After that, the settings of each factor were discovered by applying the Design of Experiment (DOE) approach. The results showed that the appropriate settings were the sieve size of pan mill setting to 18 Mesh and the size of sieve holes at pan mill setting to be uniformly distributed. It is found that the defect was reduced to 49,151.14 DPPM, which is 67.85% of the defect before the improvement.

Abstract: High Quality Cost Effective Die Castings rely to a large extent on successful, effective and practical die design. A review is carried out of some runner and gate designs which resulted in successful high quality castings. Some High Pressure and Gravity cast casting are evaluated. Simulation results for evaluating the impact on the flow during filling due to Runner Geometries, Gate Geometries and positions as well as venting, overflows or risers are discussed. Thermal intervention through the use of internal thermal channels are also evaluated through the use of simulation results. The paper centres on a discussion of analysis of simulation results, predicting defects which impact on some aspects of surface finish and porosity. A case study is presented showing the value of following and taking heed of lessons learnt from simulation results, to carry out die designs with reduced reliance on simulation. Index Terms: South African Foundries, High Pressure Die Casting, Computerised Fluid Dynamics Simulation, Die Design, Defect Reduction.

Abstract: The objective of this research is to reduce the defective rate from bending defects in media disks of hard disk drives by finding an optimal machine setting in the assembly process. The Six Sigma method was applied to find out the factors which statistically affected the bending value and to obtain the optimal setting of those factors. It was found that a minimal bending value was achieved with the setting of the clamp screw torque at 3.25 in-lb, the screw bit height at 3.00 mm., and the vertical force on the disk clamp and the motor at 2.50 lbs. With this optimal setting, the process capability index C_pk increased from 0.69 to 1.39, the mean bending value decreased from 5.12% to 3.43%, and the defective rate reduced from 32,219 ppm to 39 ppm.

Abstract: Basal Plane Dislocations (BPD) were reduced in 4H-SiC epilayers by high temperature annealing in the range of 1600 °C to 1950 °C using two annealing techniques. Samples annealed at > 1750 °C showed almost complete elimination of BPDs propagating from the substrate. However, surface morphology was degraded for MW annealed samples above 1800 °C, with new BPDs being generated from the surface. A new capping technique was developed along with application of high N₂ overpressure to preserve the surface morphology and avoid formation of new BPDs.

Abstract: In this work a new approach for the production of freestanding cubic silicon carbide (3C SiC) in (001) orientation is presented which is based on the combination of chemical vapor deposition (CVD) and the fast sublimation growth process (FSGP). Fast homoepitaxial growth of 3C SiC using sublimation epitaxy on a template created by CVD growth on silicon substrates allows to obtain thick freestanding material with low defect densities. Using standard silicon wafers as substrate material permits a cost efficient process and the applying of wafers with different orientations. The (001) orientation used in this work will potentially allow further heteroepitaxial growth of other cubic semiconductors, like e.g. gallium nitride (GaN).