INFRARED STUDIES OF DEFECTS FORMED DURING POSTIRRADIATION ANNEALS OF CZOCHRALSKI SILICON

This article reports on defect studies of neutron-irradiated Czochrals ki-grown silicon (Cz-Si) material by means of infrared spectroscopy. I n particular, the investigation was focused on the evolution of the 82 8 cm(-1) well-known band of A-center, due to isochronal anneals from r oom temperature (RT) up to approximate to 700 degrees C. The strength of the VO band begins to increase above approximate to 200 gradually u p to 300 degrees C (stage I); then, it begins to decrease up to approx imate to 400 degrees C (stage II), where upon it stabilizes up to appr oximate to 550 degrees C (stage III). Upon re-irradiation under exactl y the same conditions and repeating the annealing process, the increas e of the VO signal in stage I disappears. The phenomenon is ascribed t o the existence of defect aggregates labeled as X-i centers which are correlated with (impurity-defect) clusters that compete with O-i in ca pturing vacancies. The presence of X-i centers is related to the therm al annealings performed. Comparison of the evolution of VO (828 cm(-1) ) and VO2 (887 cm(-1)) bands between irradiated and re-irradiated mate rials, during stage II, is made and the results are discussed in the f ramework of established reaction patterns. The stabilization of the am plitude of the 828 cm(-1) line in stage III is examined. The prevailin g aspect is that a portion of A-centers in neutron-irradiated Si acqui res larger thermal stability by relaxing in the vicinity of larger def ects. (C) 1998 American Institute of Physics. [S0021-8979(98)1119-0].