METHOD FOR STUDYING THE GROWN-IN DEFECT DENSITY SPECTRA IN CZOCHRALSKI SILICON-WAFERS

We have developed a method for studying the as-grown defect density sp ectra of Czochralski silicon wafers by infrared light scattering tomog raphy These spectra show the defect density vs. size or stability temp erature. Different annealing procedures were used to reveal both parts of the spectra, one stable at high (1000 to 1280 degrees C) and the o ther at low temperature (500 to 1000 degrees C). The studies were perf ormed on wafers grown in the vacancy-rich regime and on wafers with a stacking fault ring 150 and 200 mm in diam. In the as-grown state, onl y a very small part of the defect spectrum lies above the detection li mit. In general, three main peaks appear in the spectrum. Their total height and exact positions are determined by the growth and cooling ra tes of the crystal, and by the initial concentration of interstitial o xygen. Due to the different locations of the maxima in the low tempera ture spectra, standard precipitation tests can be misleading for the e stimation of the oxygen precipitation capability. A high temperature p reanneal at 1000 or 1100 degrees C shifts the low temperature part of the spectrum to smaller sizes. However, a dissolution of the grown-in defects was never detected. We conclude that during the nucleation ann eals for internal gettering, only existing as-grown nuclei grow except under conditions when a time lag in nucleation is observed. The defec t spectra provide a unique basis for the simulation of defect generati on during wafer processing, and facilitate the selection of wafer mate rial for a given technology. Furthermore, they provide the basis for e ffective generation of a bulk defect zone for internal gettering.