The Effect of Deep N+ Well on Single-Event Transient in 65 nm Triple-Well NMOSFET

In a triple-well NMOSFET, a deep n+ well (DNW) is buried in the substrate to isolate the substrate noise. The presence of this deep n+ well leads to changes in single-event transient effects compared to bulk NMOSFET. In space, a single cosmic particle can deposit enough charge in the sensitive volume of a semiconductor device to cause a potential change in the transient state, that is, a single-event transient (SET). In this study, a quantitative characterization of the effect of a DNW on a SET in a 65 nm triple-well NMOSFET was performed using heavy ion experiments. Compared with a bulk NMOSFET, the experimental data show that the percentages of average increase of a SET pulse width are 22% (at linear energy transfer (LET) = 37.4 MeV·cm2/mg) and 23% (at LET = 22.2 MeV·cm2/mg) in a triple-well NMOSFET. This study indicates that a triple-well NMOSFET is more sensitive to a SET, which means that it may not be appropriate for radiation hardened integrated circuit design compared with a bulk NMOSFET.

Case Study on Abnormal Electron-Optical Frequency Mapping Phenomena in Failure Analysis

In recent years, laser reflectance modulation measurements are widely used in failure analysis. Among them, EOFM (Electron-Optical Frequency Mapping) technique is easy to operate and very practical. In this article, some images with abnormal EOFM phenomena and their corresponding defects are showing up, the causes of those abnormal EOFM phenomena are also pointed out. They prove that EOFM function is very effective for discovering open or high-impedance defects on metal trace and pinpointing short-circuit defects. In addition to the two aspects above, there are also some abnormal EOFM phenomena we couldn’t explain perfectly. We studied one of them and proposed two possible causes of the anomaly. After simulation experiment and calculation, it could be basically determined that the abnormal EOFM phenomenon was caused by the substrate noise current.