In the field of failure analysis (FA) for semiconductor devices, the transmission electron microscope (TEM) as an analytical tool is integral to finding visible evidence of defects and their root cause. Especially as device features shrink, imaging and analyzing increasingly subtle defects requires detailed elemental analysis. In this work, elemental analysis using an aberration-corrected TEM at different accelerating voltages (200 kV and 80 kV) is discussed. The impact of accelerating voltage on elemental analysis with regards to Electron Energy Loss Spectroscopy (EELS) and Energy Dispersive X-Ray Spectroscopy (EDS) is of central focus. Two case studies involving TEM samples of different thicknesses are presented that clearly indicate important differences in the analytical data collected at different accelerating voltages. The work revealed that for elemental analysis of thick TEM samples (100 nm and over) 200 kV is preferred, and for thin samples, 80 kV provides superior signal in EDS and EELS.

As integrated circuit (IC) feature dimensions have shrunk, the need for precise and repeatable sample preparation techniques has increased. In this work, the process of preparation of ultrathin planar-to-cross-section conversion transmission electron microscopy (TEM) samples using a gallium dual-column focused ion beam (FIB)/scanning electron microscope (SEM) system is examined. Sample preparation technique in this paper is aimed at repeatably isolating features in the 5-30 nm range, while limiting common issues such as amorphization, lamella warpage, and the curtain effect (or “curtaining”). This can be achieved through careful selection of FIB parameters including ion beam energy, ion beam current, stage tilt, and deposited protective layer materials and thicknesses, which are all discussed in this work.

Visualization of dopant related anomalies in integrated circuits is extremely challenging. Cleaving of the die may not be possible in practical failure analysis situations that require extensive electrical fault isolation, where the failing die can be submitted of scanning probe microscopy analysis in various states such as partially depackaged die, backside thinned die, and so on. In advanced technologies, the circuit orientation in the wafer may not align with preferred crystallographic direction for cleaving the silicon or other substrates. In order to overcome these issues, a focused ion beam lift-out based approach for site-specific cross-section sample preparation is developed in this work. A directional mechanical polishing procedure to produce smooth damage-free surface for junction profiling is also implemented. Two failure analysis applications of the sample preparation method to visualize junction anomalies using scanning microwave microscopy are also discussed.

Transmission electron microscope based elemental analysis techniques utilize X-ray photons in EDS and inelastically scattered electrons or the energy-loss electrons in electron energy-loss spectroscopy and energy-filtered transmission electron microscopy (EFTEM). This paper discusses the applications of EFTEM to visualize polysilicon defects, gate dielectric and silicon nanocrystals using inelastically scattered low energy-loss electrons. It focuses on features that are primarily composed of silicon and silicon-oxide. Various benefits of using plasmon energy-loss electrons to image silicon nanocrystals layer in thin film storage device are also outlined. Even though this work has focused on low-loss imaging of features and defects in the front-end of the process based on silicon/silicon-oxide integrated circuits, these techniques can also be applied to technologies based on other materials by selecting appropriate plasmon peaks corresponding to those materials.

The aggressive scaling of metal oxide semiconductor field effect transistor (MOSFET) device features, including gate dielectrics, silicides, and strained Si channels, presents unique metrology and characterization challenges to control electrical properties such as reliability and leakage current. This paper describes challenges faced in measuring the thickness of thin gate oxides and interfacial layers found in high-K gate dielectrics, determining Ni silicide phase in devices, and characterizing strain in MOSFETs with SiGe stressors. From case studies, it has been observed that thin layers (gate oxide, high-K film thickness, and interfacial layer) can be measured using high-resolution transmission electron microscopy (HRTEM) with good accuracy but there are some challenges in the form of sample thickness, damage-free samples, and precise sectioning of the sample for site-specific specimens. Complementary information based on HRTEM, annular dark field, and image simulation should be used to check the accuracy of thin gate dielectric measurements.

The identification of foreign material at metal-oxide interface or at the poly-substrate interface by means energy dispersive spectroscopy (EDS) is very difficult. Auger depth profiling can be used as an alternative method to cross-section EDS analysis for the identification of very thin layers of foreign material in semiconductor devices. This article presents a sample preparation method adapted from a planar transmission electron microscopy sample preparation method so that Auger depth profiling can be used as a practical tool for identifying very thin layers of foreign materials at interfaces buried deep within semiconductor devices. The discussion covers the advantages, applications, and the procedure for performing the analysis. The high degree of control provided by the method gives an analyst the ability to easily thin down material layers to less than 100nm of a target layer, thereby significantly reducing sample preparation time as well as analysis time on the Auger tool.

Conventional focused ion beam (FIB) based specific area transmission electron microscopy (TEM) sample preparation techniques usually requires complex grinding and gluing steps before final FIB thinning of the sample to electron transparency (<0.25 μm). A novel technique known as lift-out, plucking or pullout method that eliminates all the pre-FIB sample preparation has been developed for specific area TEM sample preparation by several authors. The advantages of the lift-out procedure include reduced sample preparation time and possibility of specific area TEM sample preparation of most components of integrated circuit with almost no geometric or dimensional limitations. In this paper, details of liftout method, developed during the present work, for site specific x-sectional and a new site specific planar sample preparation are described. Various methodologies are discussed to maximize the success rate by optimizing the factors that affect the technique. In failure analysis, the geometric and dimensional flexibility offered by the lift-out technique can be used to prepare specific area TEM sample of back thinned die, small particles and packaged parts. Such novel applications of lift-out technique in failure analysis are discussed with the examples of TEM results obtained from GaAs and Si based devices. Importantly, it was possible to obtain high resolution lattice images from the lift-out samples transferred on holey carbon supported 3mm copper grids.