Papers by Author: Hele Savin

Abstract: Low temperature boron and phosphorous diffusion gettering (BDG and PDG) of iron in Czochralski-grown silicon were experimentally studied. Differences and similarities between the gettering techniques were clarified by using intentionally iron contaminated wafers emphasizing especially the effect of oxygen. Experiments showed that the surprisingly high gettering effects of BDG could be explained by B-Si precipitates. Oxygen precipitation was seen to decrease minority carrier diffusion length after long gettering at low temperatures in both BDG and PDG. In the case of BDG oxygen precipitation affected more as a higher thermal budget was needed to obtain similar sheet resistance to that of PDG. According to experiments the efficiency of BDG can not be concluded from the sheet resistance, whereas the efficiency of PDG can. This has practical influences in a process control environment.

Abstract: Iron precipitation in multicrystalline silicon has been modeled aiming at the optimization of intrinsic gettering of iron in multicrystalline silicon. Iron precipitation during both crystal growth and following phosphorus diffusion gettering (PDG) are simulated and compared to experimental results as the iron precipitate density after these processes is essential in the modeling of intrinsic gettering in multicrystalline silicon solar cell processing. The PDG decreases the density of iron precipitates compared to the as-grown state and as expected the effect is larger at lower initial iron concentrations. Due to this effect the iron precipitation is significantly reduced almost throughout the whole ingot height and it can be concluded that intrinsic gettering has a beneficial effect only in the case of high initial iron concentration, in accordance with the experimental results. The simulated change in interstitial iron concentration as a function of intrinsic gettering temperature suggests the same optimum intrinsic gettering temperature as the experiments. With the given model it is however much easier to find optimal parameters compared to expensive and time consuming experiments.

Abstract: The impact of nickel on minority carrier recombination lifetime has been studied in ptype CZ silicon using SPV and μ-PCD techniques. The results show that small oxide precipitates can be used to improve drastically the detection limit of nickel. This is explained by the decoration of oxide precipitates by nickel, which results in the enhanced recombination activity. In the absence of oxide precipitates or other related bulk microdefects nickel precipitates preferably to wafer surfaces, which does not have such a high impact on the measured recombination lifetime, at least on a low concentration level. Low temperature anneal at 180°C or light illumination of the wafers after nickel in-diffusion did not reveal any further change in lifetime in any of the wafers, which may indicate that nickel precipitates efficiently during air-cooling from high temperature.

Abstract: We compare SPV technique with µ−PCD for the determination of recombination activity of copper precipitates in p-Si. The copper precipitates were formed in bulk silicon through illumination at room temperature. We observed that the recombination activities of copper precipitates measured with SPV are higher than the ones measured with µ−PCD technique. However, it seems that the copper detection sensitivity is about the same with SPV and µ−PCD techniques.