Evolution and distribution of thermal stress during the shouldering stage of Czochralski silicon growth: Effects on defect dynamics and strategies for process optimization

The shouldering stage in the Czochralski (CZ) method, a critical unsteady phase preceding constant-diameter growth, has received limited research attention. In this work, the evolution of thermal stress and defect distribution during the shouldering stage are comprehensively evaluated for 300 mm CZ silicon, and the effects of key process parameters are thoroughly elucidated. Transient simulations based on the finite-volume method are performed to capture dynamic processes, with the accuracy verified by comparisons with experimental measurements. It is found that shouldering is a critical stage to prevent structure loss as it gives rise to the peak value of thermal stress at the solid–liquid interface during the whole CZ process due to the substantial change in the interface shape. Increasing shoulder height effectively reduces interfacial stress as a result of more stable melt convection and a flatter interface, thereby suppressing dislocation multiplication and vacancy accumulation. Consequently, larger shoulder heights can improve the success rate of single-crystal growth, in agreement with our experimental data. Meanwhile, higher pulling rates reduce thermal gradients and consequently lower interfacial stress. In contrast, rotation rates of the crystal and crucible exhibit only minor effects during shouldering. These findings highlight the significance of shouldering in terms of stress and defect control, and provide practical strategies for optimizing large-diameter single-crystal growth through adjustable parameters.