dc.description.abstract | Silicon single crystal is the substrate of silicon based solar cell, semiconductor and so on. The oxygen impurity in the silicon single crystal is the main effect factor for solar cell lifetime and the efficiency of semiconductor devices. In Czochralski silicon crystal growth, it can change flow convection to control oxygen impurity transportation by following ways like crystal/crucible rotation control, argon flowrate and install heat shield. Because silicon is magnetic, the silicon melt flow convection can effect by Lorentz force which produce from additional magnetic. This grown silicon crystal under magnetic field can get lower oxygen concentration than traditional Czochralski method. This thesis use numerical simulation to analysis the mechanism under cusp magnetic field in silicon melt convection of crystal growth. Under the adjust of growth parameter or magnetic factor, we investigate the distribution of thermal, temperature and oxygen impurity to grow lower oxygen concentration content silicon single crystal.
First, through simulation to understand the principle of cusp magnetic field in silicon melt. Magnetic field and magnetic silicon can produce Lorentz force. The flow convection suppressed by counter Lorentz force become stable and restrain oxygen impurity on crucible wall. Second, we investigate the effect of growth parameter under cusp magnetic field. Crucible rotation changes flow pattern obviously than crystal rotation and get lower oxygen concentration. To shrink the stress flow which effects the evaporation of oxygen, we change the gap of heat shield and melt free surface, heat shield shape and argon flowrate, to increase SiO transmission rate where above melt surface. We found stress flow and secondary flow are adverse effects on flow convection and impurity transportation for oxygen impurity control. We also discuss Zero Gauss Plane, a characteristic of cusp magnetic field; the best position in this furnace is under melt surface 25mm. The magnetic influent flow structure makes the oxygen distribution at a best state. Final, discuss the grown silicon single crystal axial oxygen concentration uniformity under cusp magnetic field. We found through adjust of crucible rotation together with magnetic strength can get more homogeneous crystal axial oxygen concentration distribution.
This thesis analysis silicon single crystal growth mechanism under magnetic Czochralski method, find the effects of crystal growth, impurity distribution by magnetron parameter and by the control of growth parameters. Using cusp magnetic field is helpful to control oxygen impurity concentration and improve magnetron method crystal growth process. Magnetic Czochralski method increase the production yield and reach the aim of low oxygen concentration content silicon single crystal. | en_US |