edfas.org 25 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 25 NO. 4 capability of RPM-3D. 3D NAND memory has represented the most striking demonstration of the impact on performance, cost, and scaling of vertical device integration.[8] While 3D NAND is currently stacking more than 100 layers to provide increasingly higher storage capacity, the gatefirst and channel-last fabrication flow of these devices is limiting the formation of single-crystal vertical silicon channel. As a result, electron conduction is dominated by scattering at grain boundaries and interface defects of the polycrystalline (poly-Si) channel material, with negative impact on the drive current for the read operation.[9] The structure used in this work replicates a vertical poly-Si channel for 3D NAND based on a macaroni geometry reported elsewhere.[6,9] The test vehicle is a dense array of hollow poly-silicon tubes, embedded in oxide. The outer device diameter is 80 nm, the poly-Si width is 11 nm, and the channel height is 300 nm. After the poly-Si is formed the remaining space is filled with SiO2, thus creating a structure where the poly-Si is entirely embedded within SiO2. Using probe alteration technique, RPM-3D precisely scalpels layer-by-layer using a diamond probe and current sensing with Pt-Ir to a depth of 100 nm for this case. Combining all the layer-by-layer 2D conductive data together, the 3D conductive tomogram is reconstructed (Fig. 5d). Samples are placed on the sample stage with a thin coating of silver epoxy on the bottom side to provide stable adhesion along with excellent electrical contact for C-AFM measurements. CONCLUSIONS This article discussed recent advances in tomographic sensing using scanning probe microscopy with scalpel SPM. Starting from the baseline hardware of the rapid probe microscope, the authors developed a sensing configuration that overcomes the limitation of using a single tip for both material removal and sensing and/or eliminates the time delays required to change tips between these steps. Automation of the multi-probe material removal process, capable of maintaining a user-defined rate for hundreds of nm of material erosion in various types of samples and for different kind of probes was reported. The new multi-probe removal functionality, where the fast and accurate estimate of the trench step height during the scalpel SPM removal phase is used to feedback the load force to the multi-probe head. This defines a possible pathway for automation in the control of removal rate for a wide variety of material systems. Furthermore, the benefit of probe switching in the suppression of tipinduced artifacts for tomographic dataset collection with electrical AFM modes was demonstrated. This is reported with the use of high-aspect ratio conductive probes for the recovery of the electrical fidelity/sensitivity when studying densely integrated structures with C-AFM. As a result, this shows how the rapidly switchable, multi-probe hardware can demonstrate the analytical capability for densely integrated MIM structures based on thin oxides. All combined, this makes the RPM-3D the first multi-mode and multi-probes microscope for the generation of tomographic AFM with ample range of application in materials research and failure analysis. REFERENCES 1. N.G. Orji, et al.: “Metrology for the Next Generation of Semiconductor Devices,” Nat. Electron, 2018, 1, p. 532. 2. U. Celano: Metrology and Physical Mechanisms in New Generation Ionic Devices, Springer International Publishing, 2016, doi.org/ 10.1007/978-3-319-39531-9. 3. U. Celano, et al.: “Metrology, Inspection, and Process Control for Semiconductor Manufacturing XXXV,” Proc. SPIE 2021, 2021, 116110J, doi.org/10.1117/12.2583065. 4. J. Song, et al.: “3D Structure-property Correlations of Electronic and Energy Materials by Tomographic Atomic Force Microscopy,” Appl. Phys. Lett., 2021, 118, p. 080501, doi.org/10.1063/5.0040984. 5. U. Celano, et al.: “Non-filamentary (VMCO) Memory: A Two-and Three-dimensional Study on Switching and Failure Modes,” 2017 IEEE International Electron Devices Meeting (IEDM), 2017, p. 204, doi. org/10.1109/IEDM.2017.8268519. 6. C. O’Sullivan, et al.: “Improving Tomographic Sensing of Scalpel SPM with Multi-Probe Functionality and Automatic Removal Rate Extraction,” 2021 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA), 2021, p. 1–4, doi. org/10.1109/IPFA53173.2021.9617432. 7. A. Humphris, et. al.: “Probe Microscopy for Metrology of Next Generation Devices,” Proc. SPIE 9778, Metrology, Inspection, and Process Control for Microlithography, 2016, doi.org/10.1117/12.2219035. 8. S.-H. Lee: “Technology Scaling Challenges and Opportunities of Memory Devices,” 2016 IEEE International Electron Devices Meeting (IEDM), 2016, p. 1.1.1-1.1.8, doi.org/10.1109/IEDM.2016.7838026. 9. D. Verreck, et al.: “Quantitative 3-D Model to Explain Large Single Trap Charge Variability in Vertical NAND Memory,” 2019 IEEE International Electron Devices Meeting (IEDM), 2019, p. 32.1.1-32.1.4, doi.org/10.1109/IEDM19573.2019.8993552. ABOUT THE AUTHORS Deepanjan Sharma received a M.S. degree in physics from Ulm University, Germany in 2017. After that he worked as a research fellow in AFM lab at International Iberian Nanotechnological Laboratory, Portugal, and pursued a Ph.D. from the University of Duisburg-Essen in 2021. He is presently employed as an R&D engineer in Infinitesima Pvt Ltd and posted as a project manager in IMEC. He is working on the development of next generation high speed automated SPM capable of generating 3D volumetric data.
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