POLARITY ASYMMETRY OF OXIDES GROWN ON POLYCRYSTALLINE SILICON

The quality of oxide thermally grown on polycrystalline silicon, commonly referred to as polyoxide, is strongly dependent on polysilicon doping processes and polyoxide growth conditions. The electrical properties of polyoxides using different polysilicon doping processes (in situ, ion implanted, and POCl//3) and different oxidation processes (dry, wet, and LPCVD) have been studied. The emphasis is on the dependence of the polarity asymmetry of leakage current, critical electric field histogram, electron trapping rate, and charge to breakdown. Polyoxides with in situ doped polysilicon exhibit an unusual polarity asymmetry, i. e. , higher field enhancement and charge to breakdown are observed when the upper electrode is biased negative. This is the opposite of the asymmetry reported for polyoxides before. High-temperature annealing of the polysilicon films prior to oxidation reduces this asymmetry.