Long term reliability of SiO/sub 2//SiN/SiO/sub 2/ thin layer insulator formed in 9 mu m deep trench on high boron concentrated silicon

摘要

The SiO/sub 2//SiN/SiO/sub 2/ (ONO) capacitor formed in the 9 mu m-deep trench is investigated in terms of leakage current and long-term reliability. The leakage current and time-dependent dielectric breakdown (TDDB) characteristics are comparable for both planar and trench type ONO structures. Therefore the test results are not specific to trench structures only but are common characteristics of ONO films. Breakdown voltage of the ONO film is dependent on gate bias polarity and the ratio of bottom-oxide to top-oxide thicknesses. In general, the current is controlled by the exit-oxide thickness for electron current in the ONO film. The mean time to failure becomes longer as the nitride thickness increases. This characteristic is most prominent in the nitrogen annealed samples. The behavior of electric-field factor beta was investigated for variations in nitride thickness. From these results it is concluded that nitride-dominant ONO film is better for long-term reliability.