An optical study on dislocation clusters in a slowly pulled silicon crystal

Since the defect density of slowly pulled Czochralski (CZ) Si crystals is f airly low, determination of the surveillance volume is very important to ge t correct information about defects in the crystals. Here, the volume is de fined as that to be searched by a single surveillance trial from a viewpoin t of economical quality control of the crystals and should be equal to or a little larger than the reciprocal density of the defects. The following tw o-step investigation resulted in successful and novel use of an ordinary IR light scattering tomograph (LST) instrument for this purpose. (1) The surv eillance thickness of photoluminescence (PL) due to carriers optically inje cted by a laser beam for LST is estimated as 300 mu m in the crystal, becau se the carriers diffuse out emitting PL about 150 mu m from the position il luminated by the laser beam. Thus PL mapping is very effective to search fo r low defect density silicon crystals since defects such as dislocations ac t as PL killer centers. (2) The dark positions in the PL mapping were caref ully surveyed by layer-by-layer tomography using the light scattered by def ects, where a beam of 1.06 mu m radiation from a Nd-YAG laser was focused i nto about 5 mu m in diameter to scan inside the crystal. By complimentary c ombination of the above two methods, large entangled dislocation loops were clearly confirmed in a slowly pulled p-type CZ Si crystal. (C) 1999 Americ an Institute of Physics. [S0021-8979(99)05823-5].