Defect formation in Si-crystals grown on large diameter bulk seeds by a modified FZ-method

The crucible free growth of dislocation free respectively low defect single crystals on large diameter silicon seeds without using the common Dash technique was investigated. A promising concept to reach this aim was to reduce the thermal gradients and stresses. Therefore, a combination of RF- and MF heating, additionally to the standard FZ setup, was used by implementation of a further coil which is surrounding the 4 inch diameter seeds. The heat dissipation conditions, the growth velocity and the ratio between RF- and MF power were varied. Crystals were grown with a total length up to 120 mm. After 90 mm of single crystalline growth the crystals became polycrystalline. All grown crystals, independent of the seed structure or preparation procedure, developed a dislocation network during heating already before melting the seed surface and growth start. By noticeable reduction of the thermal stresses the single crystalline status could be maintained for a certain distance and an immediate transition to the polycrystalline growth could be avoided.