Anselm Loges

Scanning electron and polarization microscopy study of the variability and character of hollow macro-defects in silicon carbide wafers

Polarization microscopy is a suitable tool for studying strain in appropriately cut SiC single crystals. The outline shape examined by electron microscopy and the induced interference pattern observed by polarization microscopy were both used to study the variation and character of macro-defects present in SiC wafers. While voids are usually in a relaxed state, hollow-core dislocations are characterized by large interference halos up to ∼100 µm in diameter. Conoscopy, i.e. evaluation of the interference pattern created by inserting an Amici Bertrand lens, is used to examine these optical phenomena in more detail and gain additional knowledge on the inclination of wafers cut towards the c-axis. The discrepancy between the simulated and observed interference patterns for (0001)-SiC strongly indicates that pipes are not pure screw dislocations, as commonly thought, but have an edge component.

A Novel Approach for Oxide Scale Growth Characterization: Combining Etching with Atomic Force Microscopy

The combination of atomic force microscopy (AFM) analysis of oxide scales before and after chemical etching is presented as a fast, powerful method to gain information on oxide scale growth kinetics. While not limited to the field of ceramics, we chose the thermal oxidation of silicon carbide at high temperatures (1, 400 ∘ C) as an example for the potential of the AFM/etching method. SiC is a promising semiconductor material with many high-temperature applications during which not only simple oxidation, but also crystallization of the initially vitreous silica scale occurs. We demonstrate how AFM/etching analysis of crystalline areas (radialites) yields valuable information on the growth rate of the crystalline and amorphous silica scale. This can be directly translated into a statement on the oxidation passivation potential of a certain oxide scale state/morphology with important consequences for the actual high-temperature application. Also, the influence of impurities is addressed as this is an essential aspect for real-world application of silicon carbide (both, as a refractory and ceramic material).