Presentation slides for the ISTFA 2024 Tutorial session “Correlative Microscopy: In-Situ AFM-in-SEM Introduction, Capabilities, and Case Studies Semiconductor Materials and Batteries.”

We present a study of dislocation conductivity under forward bias in p-GaN/AlGaN/GaN heterojunctions on a GaN-on-Si substrate, which are part of every p-GaN HEMT structure. Conductive atomic force microscopy (C-AFM) is combined with structural analysis by scanning transmission electron microscopy (STEM) and defect selective etching (DSE). The density of conductive TDs was found to be 5 × 10 6 cm -2 , using semi-automatic measurements to gather larger statistics on a delayered HEMT sample. IV measurements show a shift in turn-on voltage at the leakage positions. To characterize the type of the conductive TDs, DSE with a KOH/NaOH melt was used. Three distinct etch pit sizes were observed after 5 s etch time, with large, medium and edge pits according to STEM characterization seemingly corresponding to screw, mixed and edge TDs, respectively. However, characterization by DSE etch pit size alone was found to be unreliable, as STEM TD typing of seven conductive TDs using two-beam diffraction conditions revealed mostly pure screw and mixed-type dislocations with medium-sized etch pits as origin of the observed leakage current. Our work highlights the limitations of DSE as a characterization method and recommends additional validation by STEM for each new material system, investigated layer, and etching setup. The implications of finding conductive TDs with screw-component under low forward bias conditions on device behavior and the limitations of the C-AFM method are discussed. Based on the results, it is not anticipated that the identified conductive TDs will have a substantial effect on a GaN HEMT device. Overall, this study provides important insights into the electrical properties of TDs and offers useful recommendations for future research in this area.

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.

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.

Presentation slides for the ISTFA 2023 Tutorial session “In-situ Correlative AFM-SEM Characterization for Failure Analysis.”

Presentation slides for the ISTFA 2023 Tutorial session “On the Impact of Artificial Intelligence in Electrical Modes for Atomic Force Microscopies.”

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.

This presentation provides an overview of nanoprobe systems and what they reveal about defects and abnormalities in semiconductor device structures and materials. The presentation covers the basic operating principles, implementation, and capabilities of atomic force probe and beam-based imaging techniques, including AFP pico-current contrast and scanning capacitance imaging, SEM/FIB active voltage contrast imaging, and SEM/FIB electron-beam absorbed current (EBAC), induced current (EBIC), and induced resistance change (EBIRCH) imaging. It also includes guidelines for probing transistors and copper metallization and case studies in which nanoprobing was used to analyze gate oxide and substrate defects, intermittent bit cell failures, threshold voltage shifts, and time-domain popcorn noise.

This presentation is a pictorial guide to the selection and application of measurement methods for defect localization. The presentation covers passive voltage contrast (PVC), nanoprobing, conductive atomic force microscopy, and photon emission microscopy (PEM). It describes signal types, how the measurements are made, the sensing mechanisms involved, and the output that can be expected.

This paper explains how nanoprobe analysis was used to determine the cause of data retention failures in nonvolatile memory (NVM) bitcells. The challenge with such memory cells is that they consist of two transistors with a single control gate in series with a programmable floating gate connected by a shared source/drain active area. With such a layout, there is no way to isolate the control gate from the floating gate, meaning that characterization must be performed simultaneously on both transistors. Having to characterize two transistors connected in series increases the number of potential electrical signature effects not by a factor of two, but rather the power of two, which makes interpreting the results much more difficult. As discussed in the paper, however, the authors used an atomic force probe to verify the bit map of the faulty device and then analyze the failing bit to confirm the programming error and reveal the possible failure mechanism. The failure mechanism was determined based on its electrical signature and a physical analysis of the bitcell location.

This paper presents a number of case studies in which various methods and tools are used to localize resistive open defects, including two-terminal IV, two-terminal electron-beam absorbed current (EBAC), electron beam induced resistance change (EBIRCH), pulsed IV, capacitance-voltage (CV) measurements, and scanning capacitance microscopy (SCM). It also reviews the advantages and limitations of each technique.

This paper demonstrates a novel defect localization approach based on EBIRCH isolation conducted from the backside of flip chips. It discusses sample preparation and probing considerations and presents a case study that shows how the technique makes it possible to determine the root cause of subtle defects, such as bridging, in flip chip failures.

This paper explains how tunneling atomic force microscopy (AFM) was used to determine the cause of leakage in FinFETs along the boundary of SRAM cells. The leaking devices were electrically isolated using photoemission microscopy, but conventional FA techniques, including SEM and TEM imaging, found no structural abnormalities. Suspecting that the failures may be due to dopant-related issues, the authors obtained cross sections of both good and bad devices and scanned them in a tunneling AFM. The paper describes the sample preparation process and includes cross-sectional images showing the difference between good and bad transistors. In SRAM areas where no leakage occurred, the fins are well defined and evenly spaced. However, in the area where an emission spot was observed, two of the fins appear to be overlapping, the result of n-well implants that merged.

This presentation provides an overview of nanoprobe systems and what they reveal about defects and abnormalities in semiconductor device structures and materials. The presentation covers the basic operating principles, implementation, and capabilities of atomic force probe and beam-based imaging techniques, including AFP pico-current contrast and scanning capacitance imaging, SEM/FIB active voltage contrast imaging, and SEM/FIB electron-beam absorbed current (EBAC), induced current (EBIC), and induced resistance change (EBIRCH) imaging. It also includes guidelines for probing transistors and copper metallization and case studies in which nanoprobing was used to analyze gate oxide and substrate defects, intermittent bit cell failures, threshold voltage shifts, and time-domain popcorn noise.

This presentation is a pictorial guide to the selection and application of measurement methods for defect localization. The presentation covers electron beam absorbed current (EBAC), electron beam induced current (EBIC), passive voltage contrast (PVC), optical and electron beam induced resistance change methods (OBIRCH and EBIRCH), lock-in thermography, photon emission microscopy (PEM), and nanoprobing. It describes how the measurements are made, the sensing mechanisms involved, and the output that can be expected.

Passive voltage contrast (PVC) is widely used to detect underlying connectivity issues between metals based on the brightness of upper metals using scanning electron microscopy (SEM) or focused ion beam (FIB). [1] However, it cannot be applied in all cases due to the uniqueness of each case where brightness alone is insufficient to tell leakage location. In this study, propose a simple technique using platinum (Pt) marking as a circuit edit (CE) technique to alter metal PVC to identify the actual leakage location. Conventional SEM and PVC contrast imaging are unable to pinpoint exact defects without data confirming the leakage from nano-probing such as Atomic Force Probing (AFP) or SEM base nano-probing (NP) [2]. Using this method, we can improve the analysis cycle time by direct analysts the defective location in SEM, while also saving tool cost.

This paper discusses the implementation of GHz-Scanning Acoustic Microscopy (GHz-SAM) into a wafer level scanning tool and its application for the detection of delamination at the interface of hybrid bonded wafers. It is demonstrated that the in-plane resolution of the GHz-SAM technique can be enhanced by thinning the sample. In the current study this thinning step has been performed by the ion beam of a ToF-SIMS tool containing an in-situ AFM, which allows not only chemical analysis of the interface but also a well-controlled local thinning (size, depth and roughness).

This research sets up failure analysis flow to verify failure mechanisms and root causes of different kinds of contact leakage. This flow mainly uses EBIC, C-AFM and nano-probing to do fault isolation and confirm electrical failure mechanisms. Appropriate sample preparation is also mandatory for FIB, SEM and TEM inspection.

Scanning nonlinear dielectric microscopy is continuously developed as an AFM-derived method for 2D dopant profiling of semiconductor devices. In this paper, the authors apply 2D carrier density mapping to Si and SiC and succeed a high resolution observation of the SiC planar power MOSFET. Furthermore, they develop software that combines dC/dV and dC/dz images and expresses both density and polarity in a single distribution image. The discussion provides the details of AFM experiments that were conducted using a Hitachi environmental control AFM5300E system. The results indicated that the carrier density decreases in the boundary region between n plus source and p body. The authors conclude that although the resolutions of dC/dV and dC/dz are estimated to be 20 nm or less and 30 nm or less, respectively, there is a possibility that the resolution can be further improved by using a sharpened probe.

With decreasing device sizes, nanometer-sized defects on the wafer substrates can already limit the performance of the devices. The detection and precise classification of these defects requires additional characterization methods with a resolution in the nanometer range. It is well known that AFM can measure not only surface morphology but also mechanical and electrical properties. However, the versatility of AFM is not fully utilized in industrial applications due to the various limitations. Various limitations include low throughput and tip life in addition to the laborious efforts for finding the defects in inline automated defect review (ADR). In this paper we introduce the ADR AFM with mechanical and electrical characterization capability of defects in addition to high throughput, high resolution, and non-destructive means for obtaining 3D information for nm-scale defect review and classification.