Application of FIB/TEM to Failure Analysis of Liquid Crystal Displays

The fragile locations of process-induced defects in hydrogenated amorphous silicon thin-film transistors (a-Si : H TFTs), which are used as elements of active-matrix liquid crystal displays, are investigated by combining focused ion beam (FIB) techniques with cross-sectional transmission electron microscopy (X-TEM). This article also describes how an array can be characterized by using a TFT array tester and a scanning force microscope that can detect, accurately locate, and identify pixel faults. The rapid FIB technique is applied to TFT failure analysis problems which require very localized etching without inducing mechanical stress. We demonstrate how these techniques are used to characterize TFT defects such as portions of the TFT multilayer damaged by micro-scratch and foreign materials. These layers cause short-circuit failures. These observations lead to identification of the fault and analysis of its cause, which in turn lead to a marked yield improvement.