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E-beam voltage contrast inspection is a very common method for in-line detection of many key defect types for rapid yield learning during technology development. Generally, the wafer surface is charged positive, but sometimes charging the wafer surface negative makes more sense. This paper reviews four advantages that negative charging may provide. Switching from positive to negative charging is typically achieved using landing energy and/or extraction voltage. A third control knob is introduced and demonstrated using three common inspection layers, contact chemical mechanical polish (CMP), 3D NAND wordline shorts and 3D NAND wordline opens. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is frequently used to monitor phosphorylated peptides or protein kinase activities. However, few reports have compared a radioactivity assay with MALDI-TOF-MS analysis. We analyzed the phosphorylation ratios of 23 peptide substrates for G protein-coupled receptor kinase 2 (GRK2) with different lengths and numbers of negatively charged amino acids by MALDI-TOF-MS. We then examined the correlations between the phosphorylation ratios determined by MALDI-TOF-MS and the radioactivity levels (counts per minute, CPM) determined using a radioactive assay. Using MALDI-TOF-MS, the phosphorylation ratios were greater in the negative mode than in the positive mode. The phosphorylation ratio measured in the negative mode was strongly correlated with the CPM ( r = 0.86). The number of acidic amino acids was related to the phosphorylation of peptide substrates by GRK2 ( r = 0.53 and 0.46 for the phosphorylation ratio and CPM, respectively). These results suggest that MALDI-TOF-MS is an alternative to radioactive assays for monitoring phosphorylated peptides. [ABSTRACT FROM AUTHOR]