Transmission Electron Microscopy of Semiconductor Based Products

Abstract

AbstractThe demand for increasingly higher performance semiconductor products has stimulated the semiconductor industry to respond by producing devices with increasingly complex circuitry, more transistors in less space, more layers of metal, dielectric and interconnects, more interfaces, and a manufacturing process with nearly 1,000 steps. As all device features are shrunk in the quest for higher performance, the role of Transmission Electron Microscopy as a characterization tool takes on a continually increasing importance over older, lower-resolution characterization tools, such as SEM. The Ångstrom scale imaging resolution and nanometer scale chemical analysis and diffraction resolution provided by modem TEM's are particularly well suited for solving materials problems encountered during research, development, production engineering, reliability testing, and failure analysis. A critical enabling technology for the application of TEM to semiconductor based products as the feature size shrinks below a quarter micron is advances in specimen preparation. The traditional 1,000Å thick specimen will be unsatisfactory in a growing number of applications. It can be shown using a simple geometrical model, that the thickness of TEM specimens must shrink as the square root of the feature size reduction. Moreover, the center-targeting of these specimens must improve so that the centertargeting error shrinks linearly with the feature size reduction. To meet these challenges, control of the specimen preparation process will require a new generation of polishing and ion milling tools that make use of high resolution imaging to control the ion milling process. In addition, as the TEM specimen thickness shrinks, the thickness of surface amorphization produced must also be reduced. Gallium focused ion beam systems can produce hundreds of Ångstroms of amorphised surface silicon, an amount which can consume an entire thin specimen. This limitation to FIB milling requires a method of removal of amorphised material that leaves no artifact in the remaining material.