Dear Hossein Shanehsaz, from my humble point of view, the answer to your question cannot fit in the format of the answers here. The mechanism of growth of ice crystals is still not fully understood, depending on a large number of environmental parameters, such as: temperature, humidity, pressure, air and water dustiness and much more. To understand the mechanism of ice crystal formation, I advise you to read specialized glaciological literature, for example, the work of Dr. G.L. Kenneth: Physical Dynamics of Ice Crystal Growth. You can also find information of interest to you in the monumental book The Physics of Glaciers by Kurt M. Cuffey and W. S. B. Paterson.