Golovko O. Improving the technology of growing monocrystalline silicon for electronic and photovoltaic devices

To improve the technology of growing silicon monocrystals by the Czochralski method under conditions of mass production, scientific understanding of the processes occurring at the atomic level in the melt and single crystal of silicon during growth have been supplemented and developed. It is shown the lifetime of non-equilibrium charge carriers increases with an increase in the ratio of the concentrations of two complexing impurities – oxygen and carbon. It was found that to ensure the level of the lifetime of nonequilibrium charge carriers above 20 μs, it is necessary to maintain the ratio of the concentrations of oxygen and carbon impurities in silicon single crystals at least 20. It is shown that an increase in the diameter of the quartz crucible leads to a decrease in the oxygen concentration in the upper half of the silicon single crystal. Using the developed mathematical model, the concentration of electrically inactive boron atoms in silicon single crystals doped with boron was estimated. It is shown that the concentration of electrically inactive boron atoms decreases along the length of the silicon single crystal. Boron complexes are formed not during crystallization, but during cooling of those parts of the single crystal that move away from the crystallization front in the process of pulling the single crystal out of the melt. Using the developed mathematical model for volatile impurities in silicon (phosphorus, oxygen), the ratio of the concentrations of electrically inactive and active phosphorus atoms in single crystals of silicon doped with phosphorus was estimated. It was shown that complexes with the participation of phosphorus are formed at high temperatures near the crystallization front. Evaluation of the ratio of the concentrations of optically inactive and active oxygen atoms showed that complexes with the participation of oxygen are formed predominantly at high temperatures near the crystallization front. It is shown that if the fraction of electrically inactive phosphorus atoms is above 8%, then a second phase is formed in the silicon wafer during the technological operation of thermal oxidation. An additional requirement for the quality of silicon single crystals is proposed: the fraction of electrically inactive phosphorus atoms should not exceed 8%. A mathematical model has been developed that makes it possible to optimize the duration of the technological operation of homogenization of silicon melt before the start of growing a single crystal. The use of the proposed model makes it possible to increase the yield of a suitable product by the parameter «oxygen concentration». The possibility of the presence of microclusters in the form of atomic chains with covalent bonds in the silicon melt is substantiated. For the first time, a probabilistic model of the size distribution of such microclusters has been developed. Gamma distribution suggested. For the construction of the distribution shape parameter, the dynamic viscosity was used for the first time, which is a structurally sensitive parameter of the melt. The distribution function of the probability density of microclusters in a silicon melt has been calculated by the number of atoms in a cluster for temperatures typical for the practice of growing single crystals from a melt by the Czochralski method. The results agree with the literature data for a germanium melt obtained from experimental data on X-ray diffraction scattering. The cluster component of the total entropy of the silicon melt has been defined under the assumption of the gamma distribution of microclusters in the form of chains with covalent interatomic bonds. The technology of monocrystalline silicon growing has been improved, which due to the use of the ratio of oxygen and carbon impurities in single crystals not less than 20, crucible of appropriate diameter and changes in the temperature program allowed to increase the part of silicon single crystal that meets technical requirements.