Light Emission Microscopy Research Articles

Metabolic light absorption, scattering, and emission (MetaLASE) microscopy.

Optical imaging of metabolism can provide key information about health and disease progression in cells and tissues; however, current methods have lacked gold-standard information about histological structure. Conversely, histology and virtual histology methods have lacked metabolic contrast. Here, we present metabolic light absorption, scattering, and emission (MetaLASE) microscopy, which rapidly provides a virtual histology and optical metabolic readout simultaneously. Hematoxylin-like nucleic contrast and eosin-like cytoplasmic contrast are obtained using photoacoustic remote sensing and ultraviolet reflectance microscopy, respectively. The same ultraviolet source excites endogenous Nicotinamide adenine dinucleotide (phosphate), flavin adenine dinucleotide, and collagen autofluorescence, providing a map of optical redox ratios to visualize metabolic variations including in areas of invasive carcinoma. Benign chronic inflammation and glands also are seen to exhibit hypermetabolism. MetaLASE microscopy offers promise for future applications in intraoperative margin analysis and in research applications where greater insights into metabolic activity could be correlated with cell and tissue types.

Evaluation of electron radiation damage to green fluorescent protein

Green fluorescent protein (GFP) emits light when irradiated by not only light but also electrons. This electron-induced light emission called cathodoluminescence (CL) can be used to realize a high-resolution light emission microscopy based on the irradiation of a very narrow electron beam. To implement CL mapping in life sciences the investigation of the damage resistance of GFP to electron irradiation needs to be clarified. In this study, we investigated the electron radiation damage to GFP by analyzing the change in the CL intensity during electron beam irradiation. Since some of the CL spectra changed in shape during electron irradiation, the change in the intensity between 585 and 605 nm were measured. The characteristic doses at different electron current densities and electron energies were investigated. The characteristic dose of EGFP is much larger than that of coronene, which is one of the stable organic molecules against the electron beam irradiation.

TIM, EMMI and 3D TCAD analysis of discrete-technology SCRs

Transient interferometric mapping (TIM) and backside light emission microscopy (EMMI) are applied to study the trigger behavior and on-state spreading in discrete-technology electrostatic discharge (ESD) protection silicon controlled rectifier (SCR) test-structures without and with trigger taps. The trigger taps or device corners are clearly identified as regions where the avalanche breakdown and SCR action are initiated. The regions relevant to the holding current can be identified by EMMI. In SCR mode the injection regions from the npn and pnp emitters have been localized by TIM. The on-state spreading (OSS) speed of 1–4μm/ns obtained from TIM is consistent with the results of 3D TCAD simulations. The driving force of the OSS is discussed on the basis of TCAD results.

Signal noise perturbation on automotive mixed-mode semiconductor device generated by graded substrate defect

The semiconductor technologies evolution allows greatly reducing noise impact on products and many structures have been created to reduce its effect. However, this paper presents the apparition of a noise issue during the production of a mixed-mode device dedicated to automotive applications. The research investigations concerned the fact that failure was not detected at test level but at customer level; therefore, it was determinant to understand the root cause of this failure mode to drive corrective actions in order to secure customer. The challenge was to analyse noise in Failure Analysis (FA) without fault spatial localization results. Indeed, Light Emission Microscopy (EMMI) and Thermal Laser Stimulation (ex: Soft Defect Localization – SDL) were unable to provide any defective area in the product. The lack of failing device identification led us to combine electrical and design analyses in order to define hypothesis on the failure origin. It was then possible to drive physical investigations through different approaches, using physical cross-section, Secondary Ion Mass Spectrometry (SIMS) and Scanning Capacitance Microscopy (SCM) techniques. Finally, the obtained complementary results will be discussed and an explanation of the failure mechanism will be presented as the root cause issue, allowing defining the defective step in production process.

SiPM Avalanche Size and Crosstalk Measurements with Light Emission Microscopy

Diodes operating in reverse bias emit visible light. This light emission process is important in silicon photomultipliers where microcells, arranged in a matrix, can trigger avalanches in adjacent microcells. One of the main goals toward improving silicon photomultipliers as light detectors is to design sensors with significantly higher photon detection efficiency than the classical photomultipliers. To achieve this goal, one needs to operate the silicon photomultiplier under a high relative overvoltage, saturating its Geiger efficiency. This means operating it under high gain and a correspondingly high level of optical crosstalk. In this paper, we describe a new and precise visual method for measuring the crosstalk as well as the transverse size of avalanches in a silicon photomultiplier microcell. This size turns out to be significantly smaller than the usually used microcell size, practically independent from the overvoltage or type. It also has implications for designing small, fast microcells that could reach a naturally lower size limit.

Performance improvement of Si-CCD detector based backside reflected light and photon emission microscopy by FIB ultimate substrate thinning

In FA laboratories a significant number of photon emission microscopy (PEM) systems are equipped with the most common detector, namely cooled Si-CCD camera. Backside reflected light microscopy (RLM) and photon emission microscopy (PEM) using this detector are possible but strongly limited by the interaction of light with silicon substrate. In this work, we show the improvement of the RLM and PEM performed from the chip backside using standard cooled Si-CCD camera by localized focused-ion-beam (FIB) assisted silicon substrate removal. Thinning down the silicon substrate significantly improves signal-to-noise ratio of the techniques as well as their resolving properties. It also enables extended spectral analysis, also in the visible regime of the light spectrum. This study has been done using 120nm technology process test structures.

Mucosal delivery of human papillomavirus pseudovirus-encapsidated plasmids improves the potency of DNA vaccination

Mucosal immunization may be important for protection against pathogens whose transmission and pathogenesis target the mucosal tissue. The capsid proteins of human papillomavirus (HPV) confer tropism for the basal epithelium and can encapsidate DNA during self-assembly to form pseudovirions (PsVs). Therefore, we produced mucosal vaccine vectors by HPV PsV encapsidation of DNA plasmids expressing an experimental antigen derived from the M and M2 proteins of respiratory syncytial virus (RSV). Intravaginal (IVag) delivery elicited local and systemic M–M2-specific CD8+ T-cell and antibody responses in mice that were comparable to an ∼10,000-fold higher dose of naked DNA. A single HPV PsV IVag immunization primed for M–M2-specific-IgA in nasal and vaginal secretions. Based on light emission and immunofluorescent microscopy, immunization with HPV PsV-encapsidated luciferase- and red fluorescent protein (RFP)-expressing plasmids resulted in transient antigen expression (<5 days), which was restricted to the vaginal epithelium. HPV PsV encapsidation of plasmid DNA is a novel strategy for mucosal immunization that could provide new vaccine options for selected mucosal pathogens.

A new method to quantify retention-failed cells of an EEPROM CAST

The cell array stress test (CAST) is a very simple tool to study one of the main issues of Non Volatile Memory reliability: data retention. However, it is not possible to easily quantify and localise the retention-failed cells of a CAST. Thus, a new experimental technique to localize and to quantify retention-failed EEPROM cells into a CAST is presented in this paper. This new technique is based on light emission microscopy; the aim is to observe light emission coming from cells and to localize their position with accuracy on CAST area. It is a visual and non destructive method which validity has been shown on cycled cells after a retention test.

Issues for single-event proton testing of SRAMs

The impact of total ionizing dose and displacement damage on single-event upset and single-event latchup hardness assurance testing of present-day commercial SRAMs is studied over a wide range of proton energies and fluence levels. Commercial SRAMs from six different vendors were irradiated at proton energies from 8 to 500 MeV and at total doses from 0 to 100 krad(Si) using multiple radiation sources. For some SRAMs, the single-event upset cross section increased with total dose. The amount of increase in SEU cross section strongly depended on the bias configuration during total dose irradiation and single-event upset characterization. For most of the SRAMs that showed an increase in single-event upset cross section with total dose, the static power supply leakage current also increased. Light emission microscopy photographs identified the source of the increase in power supply leakage current for these SRAMs as originating in peripheral transistors outside the memory array. This suggests a new single-event upset mechanism for present-day devices, which may be due to a reduction in the internally supplied memory array bias level with total dose, increasing memory cell sensitivity to single-event upset. The proton energy at which the single-event latchup cross section saturated varied considerably between devices. For one technology, the single-event latchup cross section did not saturate until the proton energy was increased to 200 MeV. These data indicate that single-event latchup hardness assurance testing should be performed at high proton energies (>100 MeV). For fluence levels less than 10/sup 11/ protons/cm/sup 2/ at a proton energy of 105 MeV, proton-induced displacement damage had no observable affect on single-event latchup cross section. The implications of these effects on single-event upset and latchup hardness assurance testing are discussed.

Identification of radiation-induced parasitic leakage paths using light emission microscopy

Eliminating radiation-induced parasitic leakage paths in integrated circuits (ICs) is key to improving their total dose hardness. Semiconductor manufacturers can use a combination of design and/or process techniques to eliminate known radiation-induced parasitic leakage paths. However, unknown or critical radiation-induced parasitic leakage may still exist on fully processed ICs and it is extremely difficult (if not impossible) to identify these leakage paths based on radiation induced parametric degradation. We show that light emission microscopy can be used to identify the location of radiation-induced parasitic leakage paths in ICs. This is illustrated by using light emission microscopy to find radiation-induced parasitic leakage paths in partially-depleted silicon on insulator static random-access memories (SRAMs). Once leakage paths were identified, modifications were made to the SRAM design to improve the total dose radiation hardness of the SRAMs. Light emission microscopy should prove to be an important tool for the development of future radiation hardened technologies and devices.

Characteristics of Oxide Breakdown and Related Impact on Device of Ultrathin (2.2 nm) Silicon Dioxide

The oxide breakdown characteristics of ultrathin oxide (2.2 nm) have been studied in this paper. Light emission microscopy (EMMI) analysis shows that each breakdown has a specific failure location with a random distribution. Gate leakage current increases for all soft breakdown events are similar. After soft breakdown, the I–V curve still shows the representative direct tunneling characteristics and can be fitted using a dual direct tunneling (DDT) model. Soft breakdown has no effect on the drain current of long-channel devices. Breakdown at the polyedge appears to be of the hard-breakdown mode and results in an abrupt increase in gate current. For short-channel devices, the polyedge is always within the damaged region of an oxide because the channel is shorter than the damaged region of the oxide. Hence, only hard breakdown resulting in permanent damage is observed in short-channel devices.

絶縁体上のシリコン層（ＳＯＩ）に形成したデバイスにおけるタングステンコンタクト不良の構造解析

We analyzed the leakage current failure in the silicon (Si) on insulator devices. The failure sites were detected by light emission microscopy, and they were found to be tungsten (W) contacts. The cross section of the failed W contact was processed by focused ion beam, and it was observed by scanning ion and transmission electron microscopes. The defect goes the through active Si and buried SiO2 layer from the buried W and arrives at the Si substrate. Our Auger electron spectroscopy analysis and energy-dispersive x-ray spectroscopy analysis identified that the defect included W, and that the active Si layer included a slight crystal defect. Our analysis suggests that the failure mechanism is over-etching of reactive ion etching (RIE) and a crystal defect of active Si layer. If the etching speed of the defective crystal is faster than the normal Si, a void is formed in the SiO2 layer. Currently, the RIE process was improved, the crystal defect decreased, and the leakage current failure mode in the W contact decreased.

Light emission microscopy for reliability studies

Light emission microscopy is now recognized as a powerful technique for failure analysis and reliability studies in Integrated Circuits. In this paper, the light emission technique is presented with a critical analysis of the different elements that may improve its detection level. The different sources of light emission in Integrated Circuits are reported and the origin of light emission with a review of the different proposed mechanisms is discussed. The influence of the silicon substrate and poly silicon layers on electro-luminescence sensitivity is highlighted. The main applications of light emission microscopy to reliability in VLSI circuits are also reviewed, including hot carrier effects, thin oxide reliability, ESD, latch-up. Finally, the latest innovations in light emission microscopy are presented.

Probeless voltage contrast using a focused ion beam for opens and shorts defect isolation of ultralarge scale integration technologies

Defect isolation in large yield mazes for accurate and timely physical analysis continues to be a critical part of process development for 0.4 and 0.25 μm technologies. Shrinking dimensions have challenged common approaches such as light emission microscopy (LEM), optical beam induced current (OBIC), liquid crystal, and mechanical probing to the point where alternate techniques are needed. This article describes simple but powerful defect isolation techniques using probeless voltage contrast in a focused ion beam (FIB) tool. Fail modes to which the techniques are applicable include deep trench capacitor polysilicon to substrate leakage, gate conductor to self-aligned contact shorts, metal line opens, via chain opens, and metal line to line shorts. When possible, OBIC or LEM are initially used to determine the approximate fail location followed by precise isolation using the FIB. Typical examples of each fail mode will be shown. The basic principle employs the positive focused ion beam to charge floating structures which tend to attenuate the secondary electron image. This provides a suitable potential difference between grounded and ungrounded structures which can be easily observed in the electron imaging mode. Using this phenomenon along with leveraging the ability of the FIB to cut and deposit replaces the need for a probe. In addition, once a defect is isolated it can be precisely marked and then unlayered or cross sectioned in situ. This technique has provided the only practical solution to isolate defects in some situations while reducing the average turn around time for feedback to process engineering.

Light emission microscopy for thin oxide reliability analysis

We present a wide analysis of light emission phenomenon in thin gate oxide. For thickness ranging from 45 to 230Å, we study the dependence of photon emission rate with gate oxide thickness and gate materials. Soft breakdown occurring in ultra thin oxide is also analysed.

IC failure analysis: techniques and tools for quality reliability improvement

The role of failure analysis is discussed. Failure analysis techniques and tools, including electrical measurements, optical microscopy, thermal imaging analysis, electron beam techniques, light emission microscopy, ion beam techniques, and scanning probe microscopy, are reviewed. Opportunities for advances in the field of IC failure analysis are considered.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Explanation of current crowding phenomena induced by impact ionization in advanced Si bipolar transistors by means of electrical measurements and light emission microscopy

This paper analyzes impact ionization phenomena in advanced polysilicon emitter bipolar transistors. Two intrinsic limitations affecting multiplication coefficient at high electric fields are discussed. Emission microscopy is adopted to directly investigate and observe current crowding effects at the basis of the first kind of instability, which takes place when the device is driven at constant emitter current I E . The second kind of instability consists in the snap-back of the collector current I c when the device is driven at constant emitter-base voltage V EB and can be explained by a simple model which takes into account the voltage drop induced by negative base current on the base spreading resistance.