It was recalled that defects in p- polished wafers obtained from Czochralski-type crystals were usually revealed by hot SCl, using immersion times ranging from 1200s to 4h. This removed 20 to 200nm. This could not be done when the wafers had defect densities that were orders of magnitude lower. Instead, a low defect-density could be investigated by sequentially treating wafers several times in the hot solution so that the overall duration was of the order of 20h; resulting in the removal of about 1μm. The defects which were delineated by hot etching could also be investigated by means of atomic force microscopy. In the case of homo-epitaxial layers, these defects were identified as being single as well as dual pits with a morphology that was characteristic of so-called crystal-originated particles. These were related to voids which were generated by vacancy agglomeration in the growing ingot. The morphology of the delineated defects indicated that such voids also existed in homoepitaxial layers. The O back-pressure during homo-epitaxial growth was negligible. Therefore, the formation of voids in the epitaxial layer was not affected by O when an O-free substrate, such as a wafer cut from a float-zone crystal, was used.

Observation of Extremely Low Defect Densities in Silicon Wafers R.Schmolke, D.Graf, R.Kirchner, R.Schader, N.Werner, E.P.Mayer, P.Wagner: Japanese Journal of Applied Physics - 1, 1999, 38[4A], 1852-7