Optimizing seeded casting of mono-like silicon crystals through numerical simulation

Recently, silicon ingots produced by typical multicrystalline casting systems but having monocrystalline features are entering the photovoltaic market. In order to look into the particular properties of this novel method, the normal silicon casting process is numerically simulated, and compared to an optimized mono-like casting process, based on the use of oriented monocrystalline silicon seeds. The seeding process was optimized by reducing the time spent in the melt in order to reduce the back diffusion of harmful non-feedstock metal impurities such as iron, reducing the thermomechanical stress to avoid dislocation multiplication, and decreasing the overall interface curvature. Additionally, the growth conditions in the zone just above the seeds were fine-tuned to increase the production of vacancy point defects, in the hope of achieving “vacancy passivation” of harmful interstitial iron by moving it to substitutional position.

► Casting of seeded mono-like silicon was numerically simulated and optimized.
► The melt time was reduced to prevent the back-diffusion of Fe.
► Vacancy formation encouraged to achieve “vacancy passivation” of Fe.
► Stress and interface curvature reduced to prevent dislocation multiplication.
► G/V parameter monitored to avoid the incorporation of SiC inclusions.