Facet growth kinetics and diameter fluctuations in molten zone Si crystal growth

• Growth of < 111 > silicon crystals by float zone and zone melting technique. • Investigation of facet size by Secco etching and of dislocations by x-ray topography. • Kinetic coefficients for dislocation-free and dislocated growth were identified. • Introduction of geometrical model to explain facet diameter fluctuations. • Fluctuations likely caused by individual dislocations passing the facet. Several <111> oriented silicon single crystals have been grown in ellipsoid mirror furnaces at various growth rates by the zone melting technique. The crystals grown with initial necking show no dislocation and large (111) facets perpendicular to the growth axis. Measurements of facet growth rate and undercooling allowed selecting the applicable kinetic coefficients in case of facets growing through 2D-seed nucleation mode. Crystals grown without necking exhibit dislocations and show smaller stable facets, allowing the determination of the kinetic coefficient in case of dislocation-driven facet growth. Among these crystals, those grown at lower velocity, with a lower temperature gradient, show a decrease of dislocation density with length of the crystal and an increase of facet diameter fluctuations. A geometric model of dislocation-facet interaction suggests that these diameter fluctuations are due to the effect of individual dislocations crossing the facet, which increase when the dislocation density decreases.