Study Of Defects In Germanium-doped Czochralski Silicon

The development of integrated circuits led to the decrease of the device feature size, and it is therefore important to control the size and the density of microdefects in silicon. However with the increase diameter of silicon and with the application of magnetic CZ (MCZ) method, the initial oxygen concentration becomes lower.So it is more difficult to form oxygen precipitates and create gettering sites in the bulk silicon, Meanwhile, it is also well known that Voids, especially those located in the near-surface of a wafer, can deteriorate gate oxide integration (GOI) and increase the leakage current of metal-oxide-semiconductor (MOS) devices. Using the co-doping technology to control the microdefects will be the important direction of the study of silicon material.In this thesis, a heavily germanium-doped CZ silicon crystal has been grown. Moreover, the void defect in germanium-doped CZ silicon has been investigated. Furthermore, the effect of irradiation on the oxygen precipitation in germanium-doped silicon has been discussed. Listed below are the most important results achieved in this work.(1) A dislocation-free silicon single crystal doped with 1020 cm-3 Ge has been grown using the CZ growth technique. The concentration of germanium was measured by secondary ion mass spectrometry (SIMS). The effective segregation coefficient of Ge was calculated according to the parameters of crystal growth. Then, the density of FPDs was traced from seed-end to tang-end of the ingot and a suppression of FPDs by Ge doping was shown. 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.(2) The distribution of the flow pattern defects (FPDs) in germanium-doped CZ silicon wafers with lightly and heavily dopants have been investigated. In the lightly doped 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 they reverse in the heavily P-doped GCZ Si and CZ Si crystals. 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.(3) The effect of irradiation on oxygen precipitation has been investigated. The oxygen precipitates can be enhanced by electron irradiation. The larger the irradiation dose is, the more the oxygen precipitates are. Furthermore, the oxygen precipitates can be formed when the nucleation temperature is 450℃in neutron irradiated GCZ silicon, while the nucleation temperature should come to 650℃C in neutron irradiated GCZ silicon. In the non-irradiated CZ and GCZ silicon, the nucleation temperature should come to 800℃.