Formation of vacancy and oxygen containing complexes in Cz-Si by rapid thermal annealing

Changes of the oxygen (O) state in Czochralski silicon (Cz Si) caused by rapid thermal annealing (RTA) were studied by means of Fourier transform infrared spectroscopy (FTIR) in a highly sensitive mode. The formation of vacancy (V) and O containing complexes VO4, previously known only from radiation experiments was observed as a result of RTA of Si wafers under clean room conditions without applying any irradiation. The use of half wafers during RTA processing and the use of the second untreated part of the same wafer as a reference during precise differential FTIR measurements allowed us to reveal, quite reproducibly, the small RTA induced changes in the absorbance in the level of ≈10−5 in absorbance units. Special attention was paid to separate the real contribution from the bulk from a possible surface related contribution in the recorded differential absorbance spectra. As a result, the quantitatively reproducible vibrational absorption band 985 cm−1 at room temperature known of VO4 was revealed in each of the examined wafers after RTA. The concentration of the observed complexes was approximately 1.4×1013 cm−3 as estimated from the integrated calibration factor for interstitial oxygen (Oi). No traces of VO, VO2, VO3, VO5 and VO6 were found in a similar level. A moderate decrease, in the level of 1013-1014 cm−3, of the content of oxygen dimers (O2i, 1012 cm−1) and trimers (O3i, 1005 cm−1) in as-grown Si was observed after RTA. Changes in the concentration of Oi did not exceed approximately 0.5%. Possible reasons for the preferential formation of VO4 by RTA are briefly discussed.