In-Situ Tem Characterization of Whiskers on Al Electrodes for Thin-Film Transistors

Abstract

AbstractThe recent attention paid to stress migration of aluminum (Al) electrodes in thin-film transistor liquid crystal display (TFT-LCD) applications indicates that wiring materials with low electrical resistivities are of considerable interest for their potential use in higher-resolution displays. In this paper, we firstly describe how as-grown Al whiskers on Al electrodes fabricated on a LCD-grade glass substrate can be characterized by means of a high-voltage transmission electron microscope (HV-TEM) operated at 1 MV. The whiskers ranging from 300 to 400 nm in diameter are sufficient to be transparent to high-voltage electrons. This allows detailed observation of whisker characteristics such as its morphology and crystallography. In most cases, the as-grown Al whiskers in our study had straight rod shapes, and could be regarded as single crystals. Secondly, we report on the in-situ fabrication and observation of Al whiskers at elevated temperature with the HV-TEM. Since relatively thick TEM samples (up to about 1 mm) can be set on a sample holder in the HV-TEM, various growth stages of Al whiskers can be investigated under various heating conditions. Finally, we demonstrate a TEM sample preparation method for the cross-section of an individual Al whisker, using focused ion beam (FIB) etching. This technique makes it possible to reduce the thickness of an Al whisker close to the root. Both bright- and dark-field TEM images provide nanostructural information on the whisker/Al thin-film interface.