Papers by Keyword: Non-Destructive Characterization

Abstract: Accurate characterization of dislocations is crucial for optimizing the performance of SiC-based power devices. The traditional way to measure dislocation density in SiC industry is KOH etching, a destructive approach that makes the wafer no longer available for epitaxial growth. Another major limitation of this technique is the accuracy of the data since some dislocations can be hardly recognized. For example, the etch pit of threading screw dislocation is similar to that of threading edge dislocation, both of which are usually in hexagonal shape while the primary difference is the size. However, those challenges and limitations in KOH etching do not exist in X-ray topography. In this paper, the non-destructive approach, X-ray topography, is introduced to characterize dislocations in 4H-SiC industry. Threading screw dislocations were measured by both KOH etching and X-ray topography, the result of which indicates that some threading screw dislocations clearly visible in X-ray topograph are not recognizable in KOH etching image. In addition, some 60° prismatic dislocations not recognized in KOH etching image can be observed in X-ray topographs. Moreover, unlike destructive KOH etching, wafers measured by X-ray topography can be further used for annealing, epitaxial growth, ion implantation and etc., which is beneficial to SiC fundamental research.

Abstract: The objective of this study is to realize a non-destructive characterization of cementitious materials using ultrasonic method. The motivation of our work is to show that the ultrasound can be applied not only in medical imaging but also in the assessment of construction materials, which is not widely known in this domain. In order to solve the problem, the ultrasonic velocity measurement was performed on the samples before and after carbonation of a standardized mortar at different periods. The results offer the possibility to determine the mechanical properties such as Young modulus E, shear modulus G and Poisson's ratio. This is an advantage for in-situ structures in comparison with destructive methods that require destroying the samples. The main contributions of this study are: 1) Ultrasonic occultation of cement materials is a reliable method with a small margin of error; 2) The values ​​of mechanical properties found by ultrasonic method are consistent with theoretical values ​​found in the literature; 3) The evolution of these mechanical properties is consistent with the densification of the microstructure during carbonation due to the formation of CaCO₃.

Abstract: The quality of the interfaces in multilayer composites is a critical issue in the reliability testing of the composite product during the manufacturing process and in-service. Weak interfaces have often gone undetected and may become potentially defective at a later stage. One example is the interface between mold compound and silicon (MC/Si) in IC packaging. There is a desire to study the interface quality quantitatively, so the potential defective area can be evaluated and identified early. In this paper, a nondestructive evaluation methodology is proposed to measure the available strength of the interface by using ultrasonic reflection coefficients. It is known that interface degradation can be either due to poor manufacturing process and stress loading. Characterization of the interface quality of the MC/Si interface is first conducted by measuring longitudinal ultrasonic wave reflections from the interface samples fabricated under varying conditioning processes that simulate the degradation. A combined test that measures the reflection coefficient of the interface under stress load has also been conducted to quantify the effect of the load. Finally, it is shown that the overall effect on the reflection coefficient and available strength of the interface is derived and can be used as a quantitative indicator.