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The distribution and etching rate of flow pattern defects (FPDs) in germanium- doped Czochralski (GCZ) silicon (Si) wafers with light and heavy dopants—either boron (B) or phosphorus (P)—have been investigated. In the lightly doped (both B and P) Czochralski (CZ) Si crystals, the FPD densities in GCZ Si decrease with the increase of Ge concentration. In the heavily B-doped GCZ Si crystals, the FPDs are denser compared with the heavily B-doped CZ Si, whereas the reverse is true in the heavily P-doped GCZ Si and CZ Si crystals. It is also shown that the etching rates in the lightly doped CZ Si crystals can be slightly enlarged by the Ge doping. It is proposed that, in lightly doped GCZ Si, Ge doping could consume free vacancies and thus form high-density but small-sized voids, while the stress compensation induced by B and Ge atoms could increase the vacancy concentration in heavily B-doped GCZ Si, leading to sparse and large-sized voids.

A dislocation-free silicon single crystal doped with 1020 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 8×1019cm-3and 1.6×1020 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 Ge-doped silicon wafers. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.