Correlation between the reliability of ultra-thin ISSG SiO₂ and hydrogen content

The electrical characteristics of NMOS capacitors fabricated using high quality, ultra-thin (20-25 angstroms) SiO₂, grown by in-situ steam generation (ISSG) in a rapid thermal processing system, and a clustered amorphous Si gate electrode is reported. The results show that, in addition to the enhanced growth rate of ISSG oxides, the lower stress-induced leakage current (SILC) and significantly improved reliability of ISSG SiO₂, such as a longer time-to-breakdown (T_BD) under a constant voltage stress and larger charge-to-breakdown (Q_BD) characteristics, as compared to SiO₂ of similar equivalent oxide thickness (EOT) grown by rapid thermal oxidation (RTO). In addition, it is also found that the reliability of ISSG oxide is considerably improved as the H₂ percentage increases. The result of Fourier-transformed infrared (FT-IR) spectroscopy indicates that ISSG oxides exhibit lower compressive strain than RTO oxides. Such appreciably improved reliability of ISSG oxide and reduced compressive strain may be explained by the reduction of defects within the structural transition layer (STL) between SiO₂ and Si substrate, such as weak Si-Si bonds (oxygen vacancies) and strained Si-O bonds, by highly reactive oxygen atoms which are hypothesized to be dissociated from the molecular oxygen due to the presence of hydrogen.