Effect of a Funnel-Shaped Radiation Shield on the Characteristics of a Silicon CZ Furnace

For the 6″ silicon CZ system, effects of a funnel-shaped radiation shield on the temperature profiles in the melt and crystal, the melt/crystal interface shape and also the distribution of the thermal stresses were investigated theoretically by the finite element analysis based on the conduction-dominated model. It is found that a funnel-shaped radiation shield can make the melt/crystal interface less convex to the crystal (relatively flatter), providing a higher pull rate and smaller thermal stresses in the crystal compared with other radiation shield geometries, such as a doughnut (torus) shape. Also, the principal operating conditions in the CZ system, such as the crucible temperature, can be changed widely by selecting the emissivity and/or thickness of the shield.