Micropipe-induced birefringence in 6H silicon carbide

Abstract

International audienceThe micropipe-induced birefringence of 6H silicon carbide (SiC) is measured and quantitatively modelled. A good agreement can be obtained between theory and experiment, provided that background residual stress is added to the local dislocation-induced stress. Observations are compatible with or predictable from the Burgers vector values, and birefringence is shown to be an interesting tool for probing the nature of the dislocations associated with e. g. micropipes; it is also faster than and complementary to the more involved techniques of transmission electron microscopy or X-ray topography

Critical assessment of birefringence imaging of dislocations in 6H silicon carbide

“…In a former publication [11], we showed that a close agreement could be obtained between experimental and simulated birefringence patterns induced by micropipes. However, since those micropipes are associated with large Burgers vector length, they cannot give the limit of detection of the method.…”

“…We use Zeiss Neofluar objectives with a magnification ranging from  2.5 to  100, and polarized green light with wavelength l¼540 nm. The measurement principles and modeling have already been thoroughly discussed in [11], so that they will not be repeated here. The reader can consult this reference for calculation details.…”

“…In the case of single crystals and wafer characterization, this method has now a long history (see, e.g., [13][14][15][16]), and both experimental and modeling data have accumulated. In particular, the influence of residual stress on the birefringence pattern induced by a dislocation is a well known fact [11,15]. In the case of silicon carbide, it was proposed by Ma to use this technique as a reliable method for detecting micropipes [9,10], which consists in dislocations with a very large Burgers vector, leading to the formation of a hollow core along the dislocation line as explained by Frank many decades ago [17].…”

“…Birefringence microscopy is an additional, nondestructive technique which was proposed by Kato et al [8] and then by Ma et al in the case of SiC [9,10], and subsequently developed by others (see, e.g., [11,12] as well as the Refs. collected in [11]). It puts to good use the fact that the strain induced by a dislocation extends over large distances.…”

“…They thus have to routinely identify and count linear defects in SiC wafers and crystals, a task which can be conveniently achieved through the use of X-ray topography [5], transmission electron microscopy (TEM) [6] or KOH etching [7]. Birefringence microscopy is an additional, nondestructive technique which was proposed by Kato et al [8] and then by Ma et al in the case of SiC [9,10], and subsequently developed by others (see, e.g., [11,12] as well as the Refs. collected in [11]).…”