Activation and Detection of Buried Defects by Negative Mode E-Beam Inspection

This publication describes the detection of buried defects in 3D NAND flash. Although not electrically active, they are a reliability risk and therefore detection is very important for process improvement. Negative mode electron beam inspection must be used to activate and detect these defects. Negative mode is able to generate a higher electrical field compared to conventional positive mode, sufficient to break through the damaged insulator making the defects electrically active and detectable. Negative mode inspection also makes the defects visible to electrical test, which is not the case when positive mode inspection is used. Further investigation shows that the breakthrough activates only pre-existing defects and does not affect healthy blocks.