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

•A new crucible free method to grow low dislocation density, single crystalline Si crystals without cone is proposed.•It is characterized by growth on large diameter seeds without using the Dash-technique.•A combination of RF- and MF heated susceptor (side heater) reduces the thermal stresses.•Single crystalline growth could be preserved for a length up to 90 mm. 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.