Research Of Internal Radiation During Semitransparent Crystal Growth Process And Experimental Measurement Of Crystal Products

Sapphire crystal is widely used in many fields such as microelectronics,optoelectronics, medical, etc., and plays an important role in modern science andtechnology. Czochralski method is currently one of the most popular techniques forsapphire growth. To satisfy the quality requirements of sapphire crystal, the improvementof the growth technology has been an important research topic. The interface shape duringthe crystal growth is closely related to quality of sapphire crystals.This paper focuses on the internal radiation during Czochralski sapphire crystalgrowth process, including the effects of internal radiation model and different types ofinclusions (mainly iridium and bubbles) on the interface shape. With a computational fluiddynamics software (Fluent), two-dimensional and three-dimensional numericalsimulations of Czochralski sapphire growth process are conducted. Interface shapes underdifferent growth conditions are obtained. For internal radiation, this thesis examinesdifferent radiation models, and finally chooses discrete ordinates model for internalradiation calculation. The purpose is to obtain the growth interface shape accurately. Forinclusions, simplified model is adopted for qualitative analysis according to the actualsituations. Through changing optical properties at the local position during the calculationof the radiation, interface shapes with the presence of the various inclusions are obtained.The results show that, the predicted convexity of the interface increases after taking intoaccount internal radiation. Increase of the absorption coefficient of the crystal and meltleads to a larger interface convexity. Inclusions at the center of the crystal or at the regionclose to the crystal surface make the corresponding parts of interface distorted. Opaqueinclusions make local interface distorted up, while transparent inclusions cause localinterface distorted down. It is further found that three-dimensional effects causenon-axisymmetric temperature distribution and fluid flow in the growth furnace.Integrated study of internal radiation and inclusions can provide significant information of crystal imperfection due to inclusions in actual manufacturing process.Furthermore, this thesis also summarizes methods and instruments for crystal qualityinspection. The purpose is to provide measuring techniques to monitor the quality ofsapphire products.