Research On Purification Effect For Cold Plasma Etching Silicon

Owing to high cost of silicon materials, the wide application of solar cell is restricted extremely in the world. A lot of researches show that the efficiency can reach 80% of single crystal silicon, by using solar grade silicon with purity of 4N to 6N for solar cell fabrication,but the cost only a quarter of that. So, research on preparation of solar grade silicon is of great importance.In this thesis, firstly, the domestic and foreign new processes and methods for preparation of solar grade silicon is introduced. And then, the mechanism for cold plasma etching silicon is discussed in brief.On account of that in plasma sheath particles have enough energy, the silicon powders have to be located in the sheath to get better purification effect. The cold plasma sheath is analyzed and caculated.And the relation of the sheath thickness to current density, voltage on the cathode, pressure in chamber will serve as theoretical guide for increasing sheath thickness. A motional model for silicon particulates is developed to investigate the drop time. After analyzing in detail, the drop time in sheath for silicon particulates was demonstrated obviously. And when the size of silicon powder is about 100μm ,the purification effect and yield will give a good performance. Employing 1D model, toward the heavy particles in cathode sheath ,the velocity and energy distribution functions are deduced, the expression for neutral and ionic fluxes are obtained, and the etching rate is formed based on hydrodynamics. These results will guide the experiment for technical parameters regulation.Lastly, the experiment of physical etching silicon powders to remove surface impurities is carried out, with Ar as dominant gas in the chamber. And the experiment results show that impurities percentage decreases obviously from 97.66% to 98.47%.