Characteristics of the inter-poly Al₂O₃ dielectrics on NH₃-nitrided bottom poly-Si for next-generation flash memories

The effects of surface NH₃ nitridation of the bottom poly-Si film, and post-deposition annealing (PDA) temperature, on the electrical properties and reliability characteristics of aluminum oxide (Al ₂O₃) inter-poly capacitors, were evaluated in this study. The polarity-dependent dielectric properties of Al₂O₃ inter-poly dielectrics (IPDs) were strongly affected by both surface nitridation and the annealing temperature. For positive gate bias, IPDs with NH₃ surface nitridation significantly suppressed the formation of an additional layer with a lower dielectric constant, during the post-annealing process, and obtained a smoother interface, compared to those without nitridation treatment. Furthermore, the presence of a thin Si-N layer made the PDA more effective in eliminating the traps existing in the as-deposited films, and improved dielectric characteristics, under negative polarity. As a result, the smoother interface and smaller electron trapping rate contributed to the drastically reduced leakage current, enhanced breakdown field, and charge to breakdown (Q_bd) of the Al₂O₃ inter-poly capacitors with surface NH₃ nitridation. Moreover, the electrical properties of Al₂O₃ IPD were heavily dependent upon the PDA temperature. The sample exhibited optimal quality in terms of leakage current, electron trapping rate and Q_bd when annealed at 900°C. X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses have shown that this occurrence arises from various compositions, under different annealing conditions and excess oxygen, which can act as an electron trapping center, playing an important role in determining IPD electrical properties.