Papers by Keyword: Micropipe

Abstract: The growing demand for wide-bandgap (WBG) materials in the microelectronics industry has led to increased investment in medium- and high-voltage power products based on SiC technology. SiC offers an excellent balance between high voltage blocking capability, high temperature operation and high switching frequencies [1]. One key step in preparing high-performance devices is improving the growth process of SiC ingot material by Physical Vapor Transport (PVT). Epitaxial growth occurs through the chemical vapor deposition (CVD) method [2]. However, this method is reported to generate extended defects such as Complex Stacking Faults (formerly referred to as carrots) and Polytype Inclusions (formerly referred to as triangles or comets) and propagate defects pre-existing in the bulk material, such as micropipes (MPs) and threading screw dislocations (TSDs), which have a very high killer ratio in SiC devices [3, 4]. In this work, the KOH molten etching method was used to investigate the nature of the defects that caused device failures; Raman spectroscopy was also employed to identify the spectroscopic correspondence of the peaks of interest.

Abstract: Micropipe defects in silicon carbide (SiC) materials significantly degrade the performance of SiC materials and their applications in semiconductor devices. In this study, systematic methods were utilized to characterize different micropipes in 4H-SiC. X-ray topography was employed to investigate the morphology of micropipe defects in SiC substrates and quantify their associated lattice distortion fields. Meanwhile, white light interferometry mode microscopy and inner stain were utilized to thoroughly characterize their properties. It was found that micropipes were accompanied with different size and distortion areas in SiC substrate. This work will be served as a refined characterization of micropipes and give guidance for device application for SiC substrate.

Abstract: In this study, high current stress was applied to the body diode of SiC-MOSFETs, and chips exhibiting leakage current degradation due to the bipolar degradation phenomenon were analyzed to identify the crystal defects responsible for the abnormal leakage current. Failure analysis and defect inspection during the device fabrication process revealed that abnormal leakage occurred at the periphery of extended stacking faults originating from or near the micropipe itself. As these extended stacking faults also increase the forward voltage drop of MOSFETs, these results suggest that micropipe are critical defects in SiC-MOSFETs inducing both forward voltage and leakage current degradation in the bipolar degradation phenomenon.

Abstract: This paper details the defect inspection and characterization of the 200 mm 4H-SiC (0001) n-type substrate pre-and post-epitaxy. The findings in this paper focus on the characterization of the micropipes (MPs) present in the 200 mm SiC substrate. Following epitaxy, the observations include how the micropipes were propagated from the substrate to the epilayer. This study explores the closing of micropipes during epitaxial growth. As a part of our efforts to better understand the crystal structure and elemental composition of the micropipes in the epilayer, we have conducted SAED and EDX experiments. To the best of our knowledge, it is the first report to demonstrate the region near the micropipe sidewall surface, is remarkably Si-rich (~ 9:1) than in the region towards the bulk (~1:1) after SiC epitaxial growth.

Abstract: Several defects were analyzed through the manufacturing chain along with their impact on devices. High kill rate of micropipes were seen on both Diodes and MOSFETs as expected. The purity of micropipe detection was found to be affected by the presence of inclusions. Inclusions were successfully sub-classified and separated out from micropipes, based on their location depth from the wafer surface. The effect on devices was found to relate to how deep the inclusion was located, with the ones at the surface having the biggest impact. Various sources of Stacking Faults (SFs) were reported, with Basal Plane Dislocations (BPDs) in the crystal being a major contributor. Higher local densities of BPDs were found to have a more detrimental effect. SFs were sub-classified using the wavelength of each peak. The effect of both overall SFs and each SF sub-type on devices was determined, each sub-type having different effect on the device. Various ways of mitigating the effects of defects and dislocations are demonstrated. Reducing killer defects, SF nucleation probability, and BPDs propagation by epitaxial process optimizations are shown. Resilience up to 3500A/cm² against bipolar degradation is demonstrated by using an engineered buffer layer. Process and device design optimizations show high resiliency against crystal and epi defects and dislocations, with improved yield and lower leakage.

Abstract: We have developed a process that is able to detect, count, and map micropipes on SiC substrates. This process uses a polarized light microscope to scan the wafer. The pictures taken are analyzed with a program that produces a micropipe map as well as numerical defect distribution data in a text file. The results of the process were validated with x-ray topography measurement. The repeatability of this process is also studied and reported.

Abstract: The distribution of extended defects in silicon carbide (SiC) crystals grown on profiled seeds by the sublimation (physical vapor transport) method has been studied by optical microscopy in combination with chemical etching. It is established that free lateral growth on protruding relief elements (mesas) is accompanied by a sharp decrease in the density of threading dislocations and micropipes. The decreased density of dislocations is retained after growing a thick layer that involves the overgrowth of grooves that separated individual mesas.

Abstract: Understanding the growth and propagation of defects in SiC remains of interest in an effort to continue to improve device performance. A post-growth boule heat-treatment revealed to form micropipe pairs from apparent single screw dislocations is reviewed. In the treated samples almost no 1c threading screw dislocations were found. Instead, micropipe pairs were observed in similar densities to 1c threading screw dislocations in non-heat treated samples. It is hypothesized that the elevated temperatures allowed for enhanced dislocation mobility, enabling the transition.

Abstract: The commercial availability of high quality 150 mm 4H SiC wafers has aided in the growth of SiC power device fabrication. The progress of 150 mm 4H SiC wafer development at Dow Corning is reviewed. Defect densities compare well to those typical for 100 mm wafers, with even lower threading screw dislocation densities observed in 150 mm wafers. Resistivity data shows a comparable range from 0.012 – 0.025 ohm.cm, and excellent shape control is highlighted for wafer thicknesses of 350 μm and 500 μm.

Abstract: — The distribution of extended defects in silicon carbide (SiC) crystals grown on profiled seeds by the sublimation (physical vapor transport) method has been studied by optical microscopy in combination with chemical etching and AFM. It is established that free lateral growth on protruding relief elements (mesas) is accompanied by a sharp decrease in the density of threading dislocations and micropipes. The decreased density of dislocations is retained after growing a thick layer that involves the overgrowth of grooves that separated individual mesas.