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

This publication describes the detection of buried defects in 3D NAND flash. It will first explain and motivate the use of negative mode voltage contrast electron beam inspection and then present recent use cases. Negative mode is able to generate a higher electrical field compared to conventional positive mode. A first use case shows that this high field can damage devices during inspection. Careful recipe development is necessary to find the correct dose that allows detection without damaging the device. In the second use case the electric breakthrough is necessary to detect certain defects. 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. The higher electrical field, sufficient to break through the damaged insulator makes the defects electrically active and detectable. It 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 in this case activates only pre-existing defects and does not affect healthy devices.