Towards high-bandwidth scanning impedance imaging

Abstract

Contact-less, three-dimensional scanning is a highly important field for the semiconductor industry. By using a system of high-bandwidth impedance sensors and drive electronics, the physical constituents of ICs such as buried/surface dielectrics, buried/surface conductors and PN junctions could be detected. This thesis takes an initial step toward high-bandwidth electroquasistatic (EQS) imaging by exploring the use of high-frequency imaging. When combined with impedance sensors having a high spatial density, it could be possible to develop a very-high-bandwidth scanning imaging system. The system explored here uses a capacitively-coupled electrode array in order to distinguish various features such as a dielectric layer or a variable air gap based on measured electrode impedance. The frequency at which the impedance is measured is near 500 MHz. Also, this system can be potentially used to image depth information and dielectric composition by using multi-wavelength electrode arrays. This thesis presents the selection and layout for the high-speed drive electronics and the construction and modeling of the driven electrode arrays. Validation experiments to illustrate capacitive sensing ability are also performed. The system is able to identify surface topography, distinguish surface dielectrics from metals, and discern changes in bulk conductivity.