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Analysis of dynamic parameters of sapphire crystallization by the Kyropulos method

Ievgenii V. Kryvonosov 1,  Dmitrii I. Kryvonosov ,  Pavel V. Konevskyi 1,  Leonid Lytvynov 1

1. Institute for Single Crystals NAS of Ukraine (ISC), 60 Lenin Ave., Kharkov 61001, Ukraine

Abstract
The Kyropoulos method is the technique most widely used for the growth of large-size sapphire crystals. The shape and quality of the crystals are defined by the thermal field configuration, the shape of the crystallization front (CF), the rates of crystallization and crystal pulling from the melt. The main problem to be solved in the process of crystal growth by the said method is the control of the growth dynamics from the changes of the weight sensor readings. The change of the CF shape in the process of crystal growth depends on the configuration of the thermal field of the used setup and the conditions of heat removal. The value of the increase of the crystal mass per unit of time and, consequently, the crystal’s homogeneity, also change. Degradation of the thermal unit elements in the process of operation may modify the character of the change of the CF from process to process. Therefore, the crystallization conditions require correction each 5 or 6 crystallization processes.

There has been proposed a method for the determination, optimization and control of the main dynamic parameters of the crystallization process. This method implies the use of the computer program for the dynamic calculator developed in cooperation with Alyuda Research [1]. The program makes it possible to calculate the main crystal growth parameters and simulate the dynamic parameters of the crystallization process (the size and shape of the crucible, the quantity of the starting material, the CF shape, the rates of crystallization and crystal pulling from the melt), for different crystallization conditions. The program “SK Analysis” allows to analyze the dynamics of the change of the CF shape (Fig.), the shape and weight of the crystal, as well as the dynamics of the change of the weight sensor readings. By analyzing the dynamic characteristics one can virtually optimize the technological parameters using the program “SK Forecast”, and establish the optimum dynamics of the increase of the crystal weight. Such a characteristic in the form of a time function is introduced into the program of a real crystallization process as a parameter of the heater power regulator.

Fig. Simulation of the dynamics of CF shape for the grown crystal

Successive regular computer analysis, control and correction of the main dynamic crystallization parameters makes it possible to timely monitor and correct the changes in the thermal field during the growth equipment operation. Such a low-cost, on-line and addressed technological operation raises the efficiency of the growth process.

[1] Alyuda Research www.alyuda.com

 

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  1. The study of heat transfer processes in the system shaper-melt-crystal in the process of growing massive sapphire profiles by Stepanov/EFG method

Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Ievgenii V. Kryvonosov
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-03-25 15:02
Revised:   2013-03-25 15:23