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Gregory M. Johnson
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Proceedings Papers
Gregory M. Johnson, Andreas Rummel, Pietro Paolo Barbarino, Giuseppe Sciuto, Massimiliano Astuto ...
ISTFA2024, ISTFA 2024: Conference Proceedings from the 50th International Symposium for Testing and Failure Analysis, 463-468, October 28–November 1, 2024,
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An innovative method of characterizing p/n junctions and finding defects in SiC MOSFETs is discussed. First, a baseline technique is considered, which involves OBIRCH analysis of shorting paths after etching off the surface metal. The resolution, however, is not satisfactory. Top surface EBIC and EBIRCH results are then presented. Single-probe imaging with EBIC on gates with a 25 kV SEM (Scanning Electronic Microscopy) is shown to be able to image sub-surface depletion zones in the sample. Further measurements by EBIRCH isolated the precise spot of the defect.
Proceedings Papers
ISTFA2024, ISTFA 2024: Conference Proceedings from the 50th International Symposium for Testing and Failure Analysis, 478-484, October 28–November 1, 2024,
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The effects of sample prep with a Ga + -ion Focused Ion Beam (Ga-FIB) on measurements of electron beam induced current (EBIC) were studied. Concerns have been occasionally raised about amorphization from the beam, or even Ga + implantation ruining the ability to make useful measurements for purposes of either failure analysis or device tailoring. To understand the magnitude of any deleterious effects, two different lamellae from a 5 nm SRAM sample were prepared with different areas of increasingly improved polish, as indicated by decreasing, cumulative, FIB beam energy, followed by EBIC measurements at 1 or 2 kV beam landing energy. A first experiment looked at the ability to generate EBIC measurements from depletion zones and found no difference across the various beam polish cells. A second experiment considered leakage and/or shorts and found little problematic currents, within standard deviations.
Proceedings Papers
ISTFA2024, ISTFA 2024: Conference Proceedings from the 50th International Symposium for Testing and Failure Analysis, 485-491, October 28–November 1, 2024,
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Milling experiments were undertaken with an AFM-in-SEM system to examine various layers in the SRAMs of a 3 nm finFET node technology chip. The simultaneous Conductive AFM and tomographic milling operation provided feedback as to the exact state of delayering in the sample. Despite the relatively rough appearance of some areas of the chip, the milling by the AFM tip was able to create local areas with high planarity. The AFM measurement provided the exact moment certain structures were polished through. Discussion of various electrical modes in the analysis that might provide clearer indications of breakthrough is also undertaken in this paper.
Proceedings Papers
ISTFA2023, ISTFA 2023: Conference Proceedings from the 49th International Symposium for Testing and Failure Analysis, 509-518, November 12–16, 2023,
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A commercially available 4H-SiC power device and a GaN on SiC HEMT were examined with Ga-FIB sectioning and various junction analysis techniques. The impact of Ga-FIB on the electronic properties of such power devices is observed to be less significant than anticipated. A field of view was FIB-milled into the structure, exposing a row of devices. In this window, p/n junctions were evaluated by Passive Voltage Contrast (PVC), Electron Beam Induced Current (EBIC), and Kelvin Force Probe Microscopy (KFPM). Results showed excellent fidelity to expectations and each technique brought out new insights. In further work, the gate voltage was varied and the changing of depletion zones upon device turn-on was observed. This work: 1) Demonstrates complete sufficiency of Ga-FIB cross sections for regular cross-sectional work. 2) Demonstrates a novel method for investigating junction properties from Ga-FIB sections of power devices which largely leaves the rest of the device intact. 3) Provides some assurance that the Ga-FIB does not severely impact the evaluation of junction properties in some power semiconductors. 4) Points to alternative mechanism for device turn-on.
Proceedings Papers
ISTFA2023, ISTFA 2023: Conference Proceedings from the 49th International Symposium for Testing and Failure Analysis, 561-566, November 12–16, 2023,
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A commercially available 6T SRAM was examined with an AFM-in-SEM system. A conductive AFM measurement was taken using an AC bias on the backside of the sample with a linear amplifier on the data. Then using a cone-shaped, diamond AFM tip, subsequent scans were made over the field of view at increasingly higher downforce until areas of the chip were worn away. The results provide a survey of implants and structure milling from contact level through the wells of the device. An additional experiment was performed with EBAC.
Proceedings Papers
ISTFA2022, ISTFA 2022: Conference Proceedings from the 48th International Symposium for Testing and Failure Analysis, 81-85, October 30–November 3, 2022,
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Power devices are now ubiquitous and integral in control of systems across various sectors of the economy. Silicon-based power devices still dominate in most of the applications although new materials and device architectures are becoming common in the next generation of devices. While several techniques to characterize the overall device properties are necessary, the fundamentals in several of these power devices such as Insulated Gate Bipolar Transistors (IGBTs) still rely on healthy junctions for optimal device performance. The technique of Electron Beam Induced Current (EBIC) is used to examine the depletion zones of the p/n junctions between drift and body regions of the device. Simple sample preparation methods such as cleaving the device allows quick cross-section evaluation of the device structure and electrical characterization using EBIC yields good data. The role of acceleration potential on depletion zone thickness is considered during the analysis of intact die and cross-sections. While low voltage EBIC provides images of the p/n junctions in cross-sections, it is found that high voltage (30 kV) EBIC images can also be used to image these same p/n junctions and therefore may point to a very quick line monitor or means for early failure analysis of these devices.
Proceedings Papers
ISTFA2022, ISTFA 2022: Conference Proceedings from the 48th International Symposium for Testing and Failure Analysis, 262-268, October 30–November 3, 2022,
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In prior work, it was demonstrated that information about device turn-on can be obtained in a nanoprobing setup which involves no applied bias across the channel. This was performed on nFET logic devices in 7 nm technology and attributed to the Seebeck effect, or heating from the SEM beam. In this work, the experiments are continued to both nFET and pFET devices and on both 22 nm and 5 nm devices. Further discussion about the opportunities and evidence for Seebeck effect in nanoprobing are discussed.
Proceedings Papers
ISTFA2022, ISTFA 2022: Conference Proceedings from the 48th International Symposium for Testing and Failure Analysis, 438-444, October 30–November 3, 2022,
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The results of analyses on a commercially available 7 nm SRAM, using an in-situ AFM inside a SEM, are presented. In addition to typical results for conductive AFM, a novel method is described that uses the SEM beam to prepare a region for additional material removal, thus bringing out clearer electrical data. This would be of exceptional value for technology nodes using cobalt as a contact material. Finally, techniques making use of the current from the SEM beam as the source of current during the measurement are described. The technique may have value for well resistance measurements using in-situ structures on live product, a survey of junction health, or the localization of point defects.
Proceedings Papers
ISTFA2021, ISTFA 2021: Conference Proceedings from the 47th International Symposium for Testing and Failure Analysis, 253-257, October 31–November 4, 2021,
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An experimental study was undertaken to determine the minimum level of leakage or shorting current that could be detected by electron-beam induced resistance change (EBIRCH) analysis. A 22-nm SRAM array was overstressed with a series of gradually increasing voltage biases followed by EBIRCH scans at 1 V and 2-kV SEM imaging until fins were observed. It was found that the fins of a pulldown device could be imaged by EBIRCH at just 12 nA of shorting current, representative of a soft failure. Stressing the sample at higher voltages eventually created an ohmic short, which upon further investigation, strongly suggested that the Seebeck effect plays a significant role in EBIRCH analysis.
Proceedings Papers
ISTFA2019, ISTFA 2019: Conference Proceedings from the 45th International Symposium for Testing and Failure Analysis, 192-196, November 10–14, 2019,
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The examination of partially deprocessed ICs for well imaging has been investigated. First it has been shown [1] that Ga+ FIB imaging can readily and strongly highlight the N-well / P-well boundary in an IC as shown again here. Second, a model which only considers secondary electron creation and scattering [2] is confirmed to be sufficient for understanding these imaging effects. Heavy Ga doping provides no marked change in PVC (passive voltage contrast). Then comparisons in the same field of view between optimized He+ and Ga+ imaging, has shown that He+ provides much greater PVC contrast when looking through deep oxide, and much better resolution on shallow surfaces. The quantitative model Stopping and Range of Ions in Matter (SRIM) [3] was consulted and confirmed these expectations for resolution and depth superiority of the He+ beam. According to the SRIM, there may even be less damage from the He+ beam. Yet these known effects of Ga+ damage has not prevented its widespread use in semiconductor FA and process monitoring. Thus, the use of GFIS (Gas field ion source) He+ beam for voltage contrast and junction imaging warrants further exploration.
Proceedings Papers
ISTFA2018, ISTFA 2018: Conference Proceedings from the 44th International Symposium for Testing and Failure Analysis, 115-120, October 28–November 1, 2018,
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Massively parallel test structures, based on looking for shorts between certain design elements in the SRAM cells, are becoming increasingly relied upon in yield characterization. The localization of electrical shorts in these structures has posed significant challenges in advanced technology nodes, due to the size, and design complexity. Several of the traditional methods (nanoprobing, OBIRCH, etc.) are shown to be inadequate to find defects in SRAM cells, either due to resolution, or time required. In recent years, the Electron Beam Induced Resistance Change (EBIRCH) technique has increasingly been utilized for failure analysis. Combining EBIRCH with other techniques, such as SEM based nanoprobing system and PVC, allows not only direct electrical characterization of suspicious bridging sites but also allows engineers to pinpoint the exact location of defects with SEM resolution. This paper will demonstrate the several cases where SRAM-like test structures provided extreme challenges, and EBIRCH was the key technique towards finding the fail. A node to node, node to wordline, and ground-ground contact fails are presented. A combination of EBIRCH with the more traditional techniques in advanced technology node is key to timely and accurate determination of shorting mechanisms in our test structures.
Proceedings Papers
ISTFA2018, ISTFA 2018: Conference Proceedings from the 44th International Symposium for Testing and Failure Analysis, 169-175, October 28–November 1, 2018,
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Electron-Beam Induced Resistance CHange (EBIRCH) is a technique that makes use of the electron beam of a scanning electron microscope for defect localization. The beam has an effect on the sample, and the resistance changes resulting from that effect are mapped in the system. This paper explores the beam-based nature of the technique and uses understanding from another beam-based technique, Optical Beam Induced Resistance CHange (OBIRCH), to propose a dominant mechanism. This mechanism may explain the widely different success rates between different types of samples observed after six month’s use of the technique for isolations on large health of line structures in a failure analysis lab.
Proceedings Papers
ISTFA2017, ISTFA 2017: Conference Proceedings from the 43rd International Symposium for Testing and Failure Analysis, 155-159, November 5–9, 2017,
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The timely and accurate imaging of problems in p/n junctions is increasingly important. Scanning Capacitance Microscopy is a current standard for precise 2D-mapping of carrier profiles, but care must be taken to choose the correct field of view because of the slow scan time. This paper provides commentary on the usefulness and possible pitfalls of a wide range of techniques available to the modern FA analyst, with examples from problem solving in a process development environment. SEM passive voltage contrast may provide imaging of junctions, but may be limited to N-well / P-well after special sample prep. OBIRCH provides reliable information on any current flows, but may not be selective specifically to those involving junction problems. Electron Beam Induced Current provides junction information at SEM resolution, but it may be hard for subtle problems to not be swamped out by massive signals. Multi-photon OBIC shows promise for high-resolution laser-based imaging, but may require highly special wiring. Photon Emission is an old standby. A case study is given which shows that one must be careful to match camera type and defect mechanism type in order to be able to see actual junction leakage.
Proceedings Papers
ISTFA2016, ISTFA 2016: Conference Proceedings from the 42nd International Symposium for Testing and Failure Analysis, 112-117, November 6–10, 2016,
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Semiconductor Test Site structures were analyzed using an EBIRCH (Electron Beam Induced Resistance CHange) system. Localization of a RX (active area) to PC (gate) short was achieved with resolution that surpassed that of OBIRCH (Optical Beam Induced Resistance CHange). A voltage breakdown test structure at Metal 1 was stressed in the system, giving isolation to the specific contact. A five-fin diode macro was examined, and it is believed that the electrically active diffusions were imaged as individual fins from Metal 1. A series of ring oscillator devices were examined in steady state condition, and careful consideration of the image supports a hypothesis that Seebeck effect, from heating material interfaces in an EBIRCH system, is the reason for the “dipoles” reported in earlier literature.
Proceedings Papers
ISTFA2016, ISTFA 2016: Conference Proceedings from the 42nd International Symposium for Testing and Failure Analysis, 533-539, November 6–10, 2016,
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Applications of MpOBIC (Multi-photon Optical Beam Induced Current) are discussed for use in defect localization. The MpOBIC signals in a ring oscillator under static conditions are examined and demonstrate the superior optical resolution of the system over traditional OBIRCH. A 5-fin diode test structure is examined under passive conditions, demonstrating that true multi-photon OBIC has occurred from the backside. The same diode is examined in forward bias, and the resulting discussion concludes that both OBIC and OBIRCH signals are present in the sample. Thus, we claim that both OBIC and OBIRCH signals can provide device characterization information from an MpOBIC system.