On positive charge formed under negative bias temperature stress

As nitrogen concentration in silicon oxynitride (SiON) increases, negative bias temperature instability (NBTI) becomes a limiting factor for device lifetime. Despite recent efforts, there are confusions and issues remaining unsolved. One of them being how important positive charge formation in SiON is for NBTI and whether all positive charges are the same type. The objective of this work is to investigate positive charge formed in SiON during negative bias temperature stress (NBTS). In comparison with the positive charge formed during substrate hole injection where interface state generation is negligible, it will be shown that NBTS can induce three different types of positive charges: as-grown hole trapping, antineutralization positive charge (ANPC), and cyclic positive charge. Efforts have been made to search for the feature of NBTI, which cannot be explained without involving positive charge. It is unambiguously identified that the impact of measurement temperature on NBTI originates from only one type of defect: ANPC. By using the “on-the-fly” measurement technique, the positive charge density observed in a 2.7nm SiON can reach to the upper half of 1012cm−2, which is comparable with the positive charge reported for relatively thick SiO2 (>5nm). The relative importance of positive charge formation depends on measurement interruption time. The shorter the interruption, the more important positive charge becomes for NBTI.