Presentation slides for the ISTFA 2024 Tutorial session “Review of Scanning Probe Microscopy Methods for Failure Analysis (2024 Update).”

An approach to overcome barriers to practical Compressed Sensing (CS) implementation in serial scanning electron microscopes (SEM) or scanning transmission electron microscopes (STEM) is presented which integrates scan generator hardware specifically developed for CS, a novel and generalized CS sparse sampling strategy, and an ultra-fast reconstruction method, to form a complete CS system for 2D or 3D scanning probe microscopy. The system is capable of producing a wide variety of highly random sparse sampling scan patterns with any fractional degree of sparsity from 0- 99.9% while not requiring fast beam blanking. Reconstructing a 2kx2k or 4kx4k image requires ~150-300ms. The ultra-fast reconstruction means it is possible to view a dynamic reduced raster reconstructed image based upon a fractional real-time dose. This CS platform provides a framework to explore a rich environment of use cases in CS electron microscopy that benefit from the combination of faster acquisition and reduced probe interaction.

Presentation slides for the ISTFA 2023 Tutorial session “SEM Based EBIC, EBAC, and E-Beam Probing Techniques.”

Presentation slides for the ISTFA 2023 Tutorial session “Review of Scanning Probe Microscopy Methods for Failure Analysis (2023 Update).”

In recent years, scanning probe microscopy (SPM) has drawn substantial attention for subsurface imaging, since the ultrasharp AFM tip (≈ 10 nm in radius) can deliver and detect, mechanical and electrical signals right above the material’s 3D volume with which it is directly interacting. Electrostatic force microscopy, or EFM, is one of the most common atomic force microscopy (AFM) variants for electrical property characterization. In this work, we demonstrate a method to significantly improve EFM’s subsurface imaging capability. Unlike conventional EFM, where an AC bias is applied to the cantilever, we applied two out of phase AC biases to adjacent subsurface lines and image the resulting cantilever response at the surface. The resulting remote bias induced EFM (RB-EFM) amplitude shows decent contrast of metal lines with a 2.4 μm spacing buried up to 4 μm beneath the surface. This novel method may resolve lines with a horizontal spacing of less than 130 nm at such depth and wider lines to at least 6 μm in depth. In addition, the results are compared with conventional EFM and KPFM that detects subsurface structure with two independent DC biases. A COMSOL simulation model has been developed that reproduces the essential features of the measurement and explains the improvement of subsurface imaging with RB-EFM compared to other electrostatic force imaging techniques. We show, that by biasing independent lines at a small delta in frequency from the cantilever resonance, multiple line traces can be differentiated in the RB-EFM image.

This presentation provides an introduction to atomic force microscopy (AFM) and its many uses in semiconductor failure analysis. It provides examples showing how AFM is used to obtain information on electric fields, surface potential, current, resistance, capacitance, impedance, carrier concentration, mechanical contact (height and energy dissipation), temperature, and composition. It also addresses a number of related issues including the use of external stimuli, sample preparation requirements, and probe tip selection.

This paper discusses the steps involved in the failure analysis of power semiconductor devices in which leakage currents are observed and can be traced to doping-profile variations in ion-implanted layers. The discovery and assessment of such defects takes knowledge and skill in sample preparation, fault isolation, and the use of advanced inspection techniques, particularly scanning capacitance microscopy, as explained in the paper. Several diodes, MOSFETs, and IGBTs were examined using the proposed approach and the results are presented along with SCM images showing incomplete and poorly shaped ion-implanted structures determined to be the root cause of failure in each case.

This paper discusses advancements that have been made in scanning microwave impedance microscopy (sMIM) and how they are being used to measure various electrical properties in semiconductor devices. It explains that sMIM has a sensitivity of less than 0.1 aF and can measure minute changes in dielectric constant (k-value) and distinguish dopant levels over a wide range of concentrations with a spatial resolution of a few nm. For dielectric films and dopant levels, measurements are conveniently given in log-linear form with a repeatability well within the typical requirements for process monitoring. This, in turn, has enabled reliable quantification, where once only qualitative information was provided. The paper presents real-device results representing a wide range of measurement scenarios.

This work highlights the unique capabilities of time-resolved scanning nonlinear dielectric microscopy as demonstrated in the study of SiO 2 /SiC interfaces. Scanning nonlinear dielectric microscopy (SNDM) is a microwave-based scanning probe technique with high sensitivity to variations in tip-sample capacitance. Time-resolved SNDM, a modified version, is used in this study because it allows simultaneous nanoscale imaging of interface defect density ( D it ) and differential capacitance (d C /d V ), lending itself to correlation analysis and a better understanding of the relationships that influence interface quality. Through cross-correlation analysis, it is shown that D it images are not strongly correlated with simultaneously obtained d C /d V images, but rather with difference images derived from d C /d V images recorded with different voltage sweep directions. The results indicate that the d C /d V images visualize the nonuniformity of the total interface charge density and the difference images reflect that of D it at a particular energy range.

Three-dimensional device (FinFET) doping requirements are challenging due to fin sidewall doping, crystallinity control, junction profile control, and leakage control in the fin. In addition, physical failure analyses of FinFETs can frequently reach a “dead end” with a No Defect Found (NDF) result when channel doping issues are the suspected culprit (e.g., high Vt, low Vt, low gain, sub-threshold leakage, etc.). In new technology development, the lack of empirical dopant profile data to support device and process models and engineering has had, and continues to have, a profound negative impact on these emerging technologies. Therefore, there exists a critical need for dopant profiling in the industry to support the latest technologies that use FinFETs as their fundamental building block [1]. Here, we discuss a novel sample preparation method for cross-sectional dopant profiling of FinFET devices. Our results show that the combination of low voltage (<500eV), shallow angle (~10 degree) ion milling, dry etching, and mechanical polishing provides an adequately smooth surface (Rq<5Å) and minimizes surface amorphization, thereby allowing a strong Scanning Capacitance Microscopy (SCM) signal representative of local active dopant (carrier) concentration. The strength of the dopant signal was found to be dependent upon mill rate, electrical contact quality, amorphous layer presence and SCM probe quality. This paper focuses on a procedure to overcome critical issues during sample preparation for dopant profiling in FinFETs.

A novel method of fabrication of all-metal probes for scanning probe microscopy was developed. The motivation for this work was to develop probes and a method of fabricating them, which can be applied to measure friction of pairs of many different materials at the nanoscale. The main process of the presented manufacturing technique is nickel electrodeposition. The other steps are similarly simple and cheap. Moreover, the technique can be easily modified to manufacture probes of different materials and with different tip shapes.

In 1986 the Atomic Force Microscope (AFM) was invented by Gerd Binnig, Christoph Gerber, and Calvin Quate [1]. Since then, numerous analytical techniques have been developed and implemented on the AFM platform, evolving into what is collectively called the Scanning Probe Microscope (SPM). The SPM has since become well established as a mainstream analytical instrument with a continually increasing role in the development of nanoscale semiconductor technologies providing critical data from initial concept to technology development to manufacturing to failure analysis [2]. Scanning Capacitance Microscopy (SCM) has a longstanding, well-established track record for detecting dopant-related mechanisms that adversely affect device performance on planar (Field Effect Transistor) FETs as well as other structures (e.g., diodes, capacitors, resistors). The semiconductor industry’s transition to three dimensional FinFET devices has resulted in many challenges with regard to device analysis. This is especially true when it is necessary to perform detailed dopant analysis on a specific device; the device may be comprised of a single or multiple fins that have been called out specifically through traditional fault localization techniques. Scanning Capacitance Spectroscopy (SCS) is an analytical method, implemented on the SCM platform in which a series of DC bias conditions is applied to the sample and the carrier response is recorded using SCM [3]. SCS has a proven history of highlighting dopant related anomalies in semiconductor devices, which, in some instances, might not otherwise be “visible”. This paper describes successful application of SCM and SCS in showing, in full detail, a dopant-related failure mechanism on an individual, location-specific 14 nm FinFET.

In this paper, the authors report their successful attempt to acquire the scanning nonlinear dielectric microscopy (SNDM) signals around the floating gate and channel structures of the 3D Flash memory device, utilizing the custom-built SNDM tool with a super-sharp diamond tip. The report includes details of the SNDM measurement and process involved in sample preparation. With the super-sharp diamond tips with radius of less than 5 nm to achieve the supreme spatial resolution, the authors successfully obtained the SNDM signals of floating gate in high contrast to the background in the selected areas. They deduced the minimum spatial resolution and seized a clear evidence that the diffusion length differences of the n-type impurity among the channels are less than 21 nm. Thus, they concluded that SNDM is one of the most powerful analytical techniques to evaluate the carrier distribution in the superfine three dimensionally structured memory devices.

Two-dimensional semiconductors such as atomically-thin MoS2 have recently gained much attention because of their superior material properties fascinating for the future electronic device applications. Here we investigate the nanoscale dominant carrier distribution on atomically-thin natural and Nbdoped MoS2 mechanically exfoliated on SiO2/Si substrates by using scanning nonlinear dielectric microscopy. We show that a few-layer natural MoS2 sample is an n-type semiconductor, as expected, but Nb-doped MoS2, normally considered as a p-type semiconductor, can unexpectedly become an n-type semiconductor due to strong unintentional electron doping.

Dopants imaging using scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy are used for identifying doped areas within a device, the latter being analyzed either in a top view or in a side view. This paper presents a sample preparation workflow based on focused ion beam (FIB) use. A discussion is then conducted to assess advantages of the method and factors to monitor vigilantly. Dealing with FIB machining, any sample preparation geometry can be achieved, as it is for transmission electron microscopy (TEM) sample preparation: cross-section, planar, or inverted TEM preparation. This may pave the way to novel SCM imaging opportunities. As FIB milling generates a parasitic gallium implanted layer, a mechanical polishing step is needed to clean the specimen prior to SCM imaging. Efforts can be conducted to reduce the thickness of this layer, by reducing the acceleration voltage of the incident gallium ions, to ease sample cleaning.

The carrier distribution in solar cell is important evaluation target. Scanning nonlinear dielectric microscopy is applied to the cross section of phosphorus implanted emitter in monocrystalline silicon solar cell and visualizes the carrier distribution quantitatively. The effective diffusivities of phosphorus are estimated from the experimental results. Then, the three-dimensional carrier distribution is simulated. The experimental and simulation results show good correlation.

High resolution observation of density of interface states (Dit) at SiO2/4H-SiC interfaces was performed by time-resolved scanning nonlinear dielectric microscopy (tr-SNDM). The sizes of the non-uniform contrasts observed in the map of Dit were in the order of several tens of nanometers, which are smaller than the value reported in the previous study (>100 nm). The simulation of the tr-SNDM measurement suggested that the spatial resolution of tr-SNDM is down to the tip radius of the cantilever used for the measurement and can be smaller than the lateral spread of the depletion layer width.

It is widely acknowledged that Atomic force microscopy (AFM) methods such as conductive probe AFM (CAFM) and Scanning Capacitance Microscopy (SCM) are valuable tools for semiconductor failure analysis. One of the main advantages of these techniques is the ability to provide localized, die-level fault isolation over an area of several microns much faster than conventional nanoprobing methods. SCM, has advantages over CAFM in that it is not limited to bulk technologies and can be utilized for fault isolation on SOI-based technologies. Herein, we present a case-study of SCM die-level fault isolation on SOI-based FinFET technology at the 14nm node.

The transistor structure of memory devices and other cutting-edge semiconductor devices has become extremely minute and complicated owing primarily to advances in process technology and employment of three-dimensional structures. Among the various approaches to improve the device performance and functionality, optimizing the carrier distribution is considered to be quite effective. This study focuses on scanning nonlinear dielectric microscopy (SNDM), a capacitance-based scanning probe microscopy technique. First, to evaluate SNDM's potential for high-resolution measurement, the most commonly used metal coated tip with a tip radius of 25 nm was used to measure a quite low-density impurity distribution. Then, after confirming that the SNDM's S/N ratio was sufficiently high for the smaller probe tip, an ultra-fine diamond probe tip with a nominal tip radius of lesser than 5nm as an SNDM probe tip to measure sub-20 nm node flash memory cell transistors was employed. Successful results were obtained and are reported.

Scanning Microwave Impedance Microscopy (sMIM) can be used to characterize dielectric thin films and to quantitatively discern film thickness differences. FEM modeling of the sMIM response provides understanding of how to connect the measured sMIM signals to the underlying properties of the dielectric film and its substrate. Modeling shows that sMIM can be used to characterize a range of dielectric film thicknesses spanning both low-k and medium-k dielectric constants. A model system consisting of SiO2 thin films of various thickness on silicon substrates is used to illustrate the technique experimentally.