Search

The formation of n+-p or n+-p-p+ junctions by rapid thermal diffusion of phosphorus or co-diffusion of phosphorus and aluminum into silicon is opening new possibilities for low-cost and environmentally safe solar cell production. In this work, we analyze the influence of the higher energetic part of the lamp spectrum on phosphorus diffusion, and the impact of evaporated aluminum for back surface field formation during a P-Al co-diffusion step. The diffusion of phosphorus from doped glass films spun onto monocrystalline silicon material in various furnace configurations with front, back, or double sided heating is studied to investigate the influence of the radiation spectra on the dopant profiles. The experiments reveal a relation of the dopant profile to the amount of ultraviolet radiation reaching the surface. Therefore, a modified RTP-System is used for further investigations to demonstrate the influence of the ultraviolet (UV) light on the diffusion profiles. These experiments clearly show that the influence of the UV light is mainly on the densification of the spin-on-glass and not on diffusion kinetics in silicon. Furthermore, the simultaneous formation of a back surface field is of special interest for solar cells. Earlier studies of the simultaneous diffusion of phosphorus and aluminum in order to form a n+-p-p+ structure show (compared to a single phosphorus diffusion) deeper n+ emitters. Using glass densification experiments on such samples, a correlation was found between the decrease in emissivity on the aluminum-coated part of the wafer and the increase in temperature, which seems to be responsible for the deeper profiles. [ABSTRACT FROM AUTHOR]