Crystal twisting in Cz Si growth

• Crystal twisting during Czochralski growth of silicon crystals is sometimes observed at increased pulling rates.
• Details of heat transfer in the crystal and in Si melt can be comprehensively studied by computer modeling within 2D and 3D, quasi-steady and unsteady approximations.
• For varying growth conditions, we have observed correlation between melt supercooling over the free surface and the start of crystal twisting.

Crystal twisting during Czochralski growth of silicon crystals is sometimes observed at increased pulling rates. Crystal twisting with spatial fluctuations of the crystal surface and diameter may result in losing growth control or in the need of lowering the pulling speed. There are many ideas in the literature about reasons of spiral growth or twisting during Cz crystal growth of oxides and other materials. We contribute to this research, analyzing large scale Cz Si growth. For varying growth conditions, we have observed correlation between melt supercooling over the free surface and the start of crystal twisting. These findings support the idea that crystal twisting is closely related to a temperature distribution along the melt free surface near the tri-junction point. Correlations of melt supercooling with crystal twisting have favored developments of a predictive criterion of crystal twisting, which can be used to find the maximal stable crystallization rate by computer modeling for a particular hot zone design.