Papers by Author: William M. Vetter

Abstract: The interactions between basal plane dislocations (BPDs) and threading screw and edge dislocations (TSDs and TEDs) in hexagonal SiC have been studied using synchrotron white beam x-ray topography (SWBXT). TSDs are shown to strongly interact with advancing basal plane dislocations (BPDs) while TEDs do not. A BPD can cut through an individual TED without the formation of jogs or kinks. The BPDs were observed to be pinned by TSDs creating trailing dislocation dipoles. If these dipoles are in screw orientation segments can cross-slip and annihilate also potentially leaving isolated trailing loops. The three-dimensional (3D) distribution of BPDs can lead to aggregation of opposite sign edge segments leading to the creation of low angle grain boundaries (LAGBs) characterized by pure basal plane tilt of magnitude determined by the net difference in densities of the opposite sign dislocations. Similar aggregation can also occur against pre-existing prismatic tilt boundaries made up of TED walls with the net difference in densities of the opposite sign dislocations contributing some basal plane tilt character to the LAGB.

Abstract: Micropipe density (MPD) is a crucial parameter for silicon carbide (SiC) substrates that determines the quality, stability and yield of the semiconductor devices built on these substrates. The importance of MPD is underscored by the fact that all existing specifications for 6H- and 4H-SiC substrates set upper limits for it. Several methods for measuring the MPD are known, however, their reliability and applicability to various types of substrates (e.g. semiinsulating, conducting, etc.) has not been systematically studied. The subject of this paper is a comparative study of various techniques used for the MPD measurement accompanied by statistical analysis of the results. The study was initiated by several organizations working in the immediate field of silicon carbide or in closely related fields and included SiC substrate manufacturers, substrate consumers, equipment manufacturers and universities. The study represented a round robin experiment in which MPD was measured on thirty SiC wafers of various pedigrees. The values of MPD have been determined using both destructive and non-destructive techniques. The repeatability of each technique is analyzed and compared with that of other techniques.

Abstract: Among the types of dislocation seen in homo-epilayers of SiC grown upon 4H-SiC wafers with an 8° surface offcut are basal plane dislocations propagated into the epilayer at an 8° inclination, and threading edge dislocations. These types may be imaged by monochromatic synchrotron x-ray topography in the grazing-incidence reflection geometry using the 11 2 8 reflection. Equations needed to apply the ray-tracing method of computer simulating x-ray topographic defect images in this experimental geometry were derived and used to simulate images of the threading edge dislocations. Simulations of the threading edge dislocations showed 4 μm wide white ovals with narrow arcs of dark contrast at their ends, inclined relative to the g-vector of the topograph according to the sign of their Burgers vector. These resembled the experimental topographs, inasmuch as was possible at the maximum resolution of x-ray topographs.

Abstract: Synchrotron white-beam x-ray topographs taken in the back-reflection mode have proved a powerful tool in the study of defects in semiconductor-grade silicon carbide crystals. Capable of mapping the distribution of axial dislocations across a wafer's area (notably the devastating micropipe defect), it can also provide information on their natures. Under favorable conditions, various other types of defect may be observed in back-reflection topographs of SiC, among which are subgrain boundaries, inclusions, and basal plane dislocations. Observed defect images in backreflection topographs may be simulated using relatively simple computer algorithms based on ray tracing. It has been possible to use back-reflection topographs of SiC substrates with device structures deposited upon them to relate the incidence of defects to device failure.