Effects of melt depth on oxygen transport in silicon crystal growth by continuous-feeding Czochralski method

Abstract

The continuous-feeding Czochralski method (CCz) is an effective and promising way for the high-quality and large-weight monocrystalline silicon growth. In the CCz technology, the inner crucible is employed to prevent unmelted silicon granules from being transported to the melt-crystal interface, which introduces a new source of oxygen impurities and makes the temperature and flow distribution in the melt complicated. So it is challenging to regulate the oxygen impurities at the m-c interface in the CCz process. The melt depth stays constant during the CCz process, and it determines the crucible area where oxygen impurities are dissolved. Therefore, in order to manage and minimize the oxygen impurities at the m-c interface, controlling the melt depth may be a good way. In the study, the influence of melt depth on oxygen impurity distribution at the melt-crystal interface is investigated using a series of global simulations coupled with the transport of oxygen and carbon impurities. The findings indicate that as melt depth increases, the temperature of the crucible wall inside the inner crucible drops, and oxygen impurities transported from the melt between the inner and outer crucibles to the interior of the inner crucible likewise decrease in content. However, the rate of SiO evaporation at the free melt surface inside the inner crucible essentially stays the same. Therefore, the oxygen impurity content at the melt-crystal (m-c) interface decreases with the increase of melt depth. The paper also suggests that while constructing the scheme for lowering oxygen content, it is necessary to take into account the position relation between the heater and the crucible, the height of the crucible above the free melt surface, and the rotation of the inner crucible.