(612c) A Cellular Automata Approach for Simulation of Crystal Growth
The aim of the current paper is to consider the application of CA to the Horizontal Ribbon Growth (HRG) process. HRG was proposed by Shockley for producing single crystalline silicon sheets . It is a continuous process and it has potential to overcome the limitations of traditional batch-scale wafer processes based on Czochralski crystallization and wire sawing. In HRG, a thin silicon solid sheet is produced and extracted continuously from a molten silicon pool, minimizing in this way material losses. In order to achieve fast production speed, the pulling rate has to be determined in conjunction with proper cooling set up and the presence of impurities may introduce defects and other instabilities that must be controlled.
Many technical challenges have been encountered in the effort to stable and fast ribbon production in the HRG process. Experiments show that sudden dendritic growth occurs at the crystal front when the pulling speed exceeds a threshold which depends on a number of parameters in the system including the accumulation of impurities . Experimental results have shown cases of non-smooth and unstable solid-liquid interface and sharp wedge has occurred .
In the current paper we develop the CA approach for thin film crystal growth and show how the models can be used to derive stability/instability boundaries and control strategies to suppress these. We show results that demonstrate computational tractability and we present parametric tests to show how different cooling conditions, impurity concentrations, and other process related parameters relate to process stability. A method to control the process is proposed and it shown how model results relate to experimental results reported in the open literature.
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