The assumed impact of Ge doping on void formation during Czochralski-growth of silicon single crystals, is studied using scanning infrared microscopy. It has been reported that Ge doping leads to a reduction in the flow pattern defect density and of the crystal originated particle size, both suggesting an effect of Ge on vacancy concentration and void formation during crystal growth. The present study however reveals only a marginal-if any-effect of Ge doping on grown-in single void size and density. Double and multiple void formation might however be suppressed partially by Ge doping leading to the observed decrease in flow pattern defect density. The limited effect of Ge doping on single void formation is in agreement with earlier findings that Ge atoms are only a weak trap for vacancies at higher temperatures and therefor should have a smaller impact on the vacancy thermal equilibrium concentration and on single void nucleation than, e.g., interstitial oxygen and nitrogen.

During the last decade the 300 mm Si wafer has been optimized and one is already studying 450 mm crystals and wafers. The in­creasing silicon crystal diameter shows two important trends with respect to substrate characteristics: the interstitial oxygen concen­tration is decreasing while the size of grown in voids (COP's) in vacancy-rich crystals is increasing. The first effect is due the suppression of melt movements by the use of magnetic fields leading to a more limited transport of oxy­gen to the crystal. This and the decreasing thermal budget of ad­vanced device processing leads to reduced internal gettering capa­city. The increasing COP size is due to the combination of decreas­ing pulling rate and thermal gradient leading to a decreased void nucleation and increased thermal budget for void growth. The ef­fect of Ge doping in the range between 1E16 cm^-3 and 1E19 cm^-3 on both COP's and oxygen precipitation will be discussed.

A dislocation-free silicon single crystal doped with 10 20 cm -3 germanium (Ge) has been grown using the Czochralski (CZ) growth technique. The Ge concentration in the seed-end and tang-end of the crystal was 8×1019 cm -3 and 1.6×10 20 cm -3 , respectively. The effective segregation coefficient of Ge, the distribution of flow pattern defects (FPDs) and the wafer warpage have been characterized. Both the effective segregation coefficient and the equilibrium segregation coefficient of Ge in silicon were evaluated. Then, the density of FPDs was traced from seed-end to tang-end of the ingot, a suppression of FPDs by Ge doping was shown. That is probably because the Ge atoms consume free vacancies and thus a higher density of smaller voids is formed. Furthermore, the mechanical strength of wafers has also been characterized by batch warpage analysis. The warpage in the seed-end was larger than that in the tang-end of the ingot, showing that the mechanical strength of wafers is enhanced by Ge doping. Such improvement is interpreted by an enhanced dislocation pinning effect associated with the enhanced nucleation of grown-in oxygen precipitates in the Gedoped silicon wafers.

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