Materials Science and Engineering B61–62 (1999) 63–67 Coherent X-ray imaging investigation of macrodefects and micropipes on SiC S. Milita a, *, R. Madar b , J. Baruchel a , M. Anikin b , T. Argunova c a E.S.R.F. BP 220, Aenue des Martyrs, F -38043 Grenoble Cedex, France b LMGP-UMR 5628 INPG/CNRS, ENSPG, B.P. 46, F -38402 St Martin d’He `res, France c IOFFE Physico -Technical Institute, 194021 St. Petersburg, Russia Abstract We describe an X-ray phase imaging technique able to detect micro and macrodefects on SiC. This technique enables investigation of thick samples, not accessible to light transmission microscopy and provides additional information on the defects. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Defects on SiC; X-ray phase image 1. Introduction A big effort is addressed to produce large-area single crystalline wafers of SiC free from structural defects to fulfil the requirements for high power, high temperature and high frequency devices. The outstanding properties of this material appear to be very sensitive to the crystalline quality of the wafers. Actually micropipes and macro-defects are known to reduce the device performances and reliability. Therefore it seems essen- tial to study the nature and the evolution of these defects during the growth process by means of a high sensitive and non-destructive technique. X-ray diffraction topography is well suited to study defects like dislocations and inclusions in high quality SiC crystals [1,2]. But in the case of very deformed crystals, the images of the individual defects superim- pose and are not anymore distinguishable. This is the case of many of the presently produced SiC wafers. The reduced focus length when performing high mag- nification (about 100 times) optical microscopy, to de- tect small defects, limits the possibilities of conventional transmission light imaging to thin samples. Therefore we decided to take advantage of the unique properties of a third generation synchrotron radiation facility like the ESRF and to use a simple X-ray phase imaging technique. Subsequently thick samples can be investi- gated when defects density is low enough to avoid overlapping of their projected images. We started working with relatively thin slices that can be observed both by using X-ray and optical mi- croscopy in order to establish the actual correspon- dence between the defects detected by the two techniques and to investigate to which extent X-ray phase imaging enables a more complete description of the defects (sizes and shapes). 2. Sample preparation 6H–SiC ingots have been grown by the modified Lely Method with an in situ sublimation etching [3,4]. The graphite crucible was designed in order to allow lateral enlargement of the ingot during the growth. These technical improvements are based on both theo- retical and experimental approaches of the profile of the thermal field inside the growth cavity as function of the crucible shape and overall set up. Beginning from the top of the boule, three slices were cut perpendicular to the growth direction at a distance of 1 mm from each other, corresponding to three different moments of the growth. The cut was done with a 4° miscut with respect to the c -axis. * Corresponding author. Fax: +33-4-76882542. E-mail address: milita@esrf.fr (S. Milita) 0921-5107/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0921-5107(98)00446-2