Diffusion furnaces employing ultra low mass transport systems and methods of wafer rapid diffusion processing

摘要

Multi-zone, solar cell diffusion furnaces having a plurality of radiant element (SiC) or/and high intensity IR lamp heated process zones, including baffle, ramp-up, firing, soaking and cooling zone(s). The transport of solar cell wafers, e.g., silicon, selenium, germanium or gallium-based solar cell wafers, through the furnace is implemented by use of an ultra low-mass, wafer transport system comprising laterally spaced shielded, synchronously driven, metal bands or chains carrying non-rotating alumina tubes suspended on wires between them. The wafers rest on raised circumferential standoffs spaced laterally along the alumina tubes, which reduces contamination. The high intensity IR flux rapidly photo-radiation conditions the wafers so that diffusion occurs 3× faster than conventional high-mass thermal furnaces. Longitudinal side wall heaters comprising coil heaters in Inconel sheaths inserted in carrier tubes are employed to insure even heating of wafer edges adjacent the side walls.