edfas.org 27 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 26 NO. 4 ELECTRONICALLY VIABLE TEM SAMPLES WITH PFIB AND STEM EBIC William A. Hubbard NanoElectronic Imaging, Riverside, California bhubbard@nanoelectronicimaging.com EDFAAO (2024) 4:27-34 1537-0755/$19.00 ©ASM International® INTRODUCTION Transmission electron microscopy (TEM) is a standard technique for imaging microelectronics at high resolution. Despite exceptional spatial resolution, the information provided by TEM, and its common accessories, is related primarily to the physical structure and composition of samples. TEM is insensitive to electronic and thermal changes, which often play a more central role in device operation and degradation. Scanning TEM electron beaminduced current (STEM EBIC) imaging is a promising technique for providing high-resolution electronic and thermal contrast as a complement to TEM’s physical contrast. As ion beam (FIB) to prepare thin, electrically contacted cross-section samples for STEM EBIC imaging and in situ biasing. Techniques involving both standard Ga+ FIB and Xe+ plasma FIB (PFIB) are described. STEM EBIC results on example devices are presented, including a simple capacitor structure, under bias, and an off-the-shelf high electron-mobility transistor (HEMT). The ability to routinely observe, via STEM EBIC, electronic and thermal signals in “live” devices, especially while operating or under stress, could considerably improve our understanding of defects and the electronic and thermal dynamics that cause them. EBIC IN SEM AND STEM EBIC imaging in the scanning electron microscope (SEM) has been a mainstay of the failure analysis toolkit since it was introduced in the 1960s.[3] EBIC current generated by the separation of beam-induced electron-hole pairs (EHPs) can produce contrast related to electric fields and carrier mobility. EBIC from absorption of beam electrons, or electron beam-absorbed current (EBAC),[4] can generate resistance contrast to, for example, map connectivity in electrical leads. Electron beam-induced resistance change (EBIRCH), which maps beam-induced changes in current flow of a biased sample, is an emerging technique that has proven effective at locating defects.[5,6] While these SEM-based EBIC techniques are limited in their spatial resolution compared to TEM-based techniques, they are often capable of large-scale electronic characterization of intact components, providing a straightforward method for locating and understanding faults. The standard mode of EBIC, field separation of EHPs, is also accessible with STEM EBIC,[7] where it may or may not provide higher resolution than SEM EBIC. The resolution of this mode is often limited by the minority carrier diffusion length, or how far from a region of electric field "SCANNING TEM ELECTRON BEAMINDUCED CURRENT (STEM EBIC) IMAGING IS A PROMISING TECHNIQUE FOR PROVIDING HIGH-RESOLUTION ELECTRONIC AND THERMAL CONTRAST AS A COMPLEMENT TO TEM’S PHYSICAL CONTRAST." discussed in previous articles for this magazine,[1,2] STEM EBIC has potential to reveal the subtle electronic changes that precede physical degradation, but sample preparation has been a major bottleneck to its more widespread implementation to study microelectronics. Because the sample requirements for STEM EBIC, namely electron transparency and electrical connection, are effectively identical to samples for in situ biasing, sample preparation challenges also contribute to a disproportionately low instance of operando studies of electronic devices. This article presents recent progress in using the focused (continued on page 30)
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