HIGH PHOSPHORUS GETTERING EFFICIENCY IN POLYCRYSTALLINE SILICON BY OPTIMIZATION OF CLASSICAL THERMAL ANNEALING CONDITIONS

The external gettering effect by phosphorus diffusion is used to impro ve the minority carrier diffusion length of polycrystalline silicon. L arge grain silicon wafers are exposed to a POCl3, source at different temperatures and durations and are afterwards post-annealed in a conve ntional diffusion furnace in a pure argon atmosphere. The influence of the starting and quenching temperatures of the post-annealing step on the gettering efficiency is investigated. The optimisation of the the rmal annealing cycle parameters, i.e. the determination of the best co mbination of starting temperature of post-annealing, heating and cooli ng rates, post-annealing temperature and duration, pull-out temperatur e of the wafers, and POCl3 diffusion conditions, results in a large im provement of the minority carrier diffusion length in comparison to th e starting material. A further advantage of this post-annealing is the improvement of the homogeneity of the active phosphorus distribution and of the electrical properties.