Silicon crystal growth by the modified FZ technique

Abstract

An additional heater, similar to the axial heating process setup (AHP heater), was used in crystal growth of Si and its compound with 20% at Ge by the Floating Zone (FZ) method with the purpose of controlling both the shape of the melt–crystal interface and the thermal conditions at the interfaces during the run. The heater shapes the melt zone around itself by surface tension forces, being suspended between the growing crystal and feed rod. To protect the graphite casing of the heater against the aggressive action of molten silicon, the casing surface was coated with SiC having a special nano-crystalline structure. The range of the melt layer thickness, which one could establish as high as possible for the stability of the shaping process, was found to be up to 20 mm. Grown As- doped Si single crystals with a diameter of up to 15 mm was shown to have strong twinning directly caused by presence of the SiC inclusions revealed in the bulk of a crystal. The possibility of reducing the convexity and produce an interface close to a flat shape by means of the AHP heater was proved. Faceted growth of Si was found to be present in crystal growth on [111]-oriented seeds, with the faceted area occupying almost all of the cross section of the crystal under certain conditions.