Method for improving crystallinity of semiconductor ribbon

Abstract

A method is disclosed for improving the crystallinity of semiconductor ribbon material while increasing the material throughput and decreasing energy requirements. The crystallinity of a ribbon of semiconductor material can be improved by forming a localized molten zone in the material and sweeping this molten zone along the length of the material. As the molten zone refreezes, the material is locally recrystallized with enhanced grain size. In accordance with the invention, two ribbons are positioned back-to-back with a slight spacing between the ribbons. Energy sources are focused on the outer surfaces of the two ribbons to create a molten zone in each of the ribbons. Because of the close proximity between the ribbons, much of the energy reradiated from each molten zone is absorbed by the adjacent ribbon. The molten zones are then swept along both of the ribbons to simultaneously cause crystal improvement in both ribbons. The total energy input required for recrystallizing two ribbons is only slightly greater than the energy required to recrystallize one ribbon. Further improvements in the process are achieved by positioning a thermal diffuser between the two ribbons and/or staggering the relative positions of the molten zones.