CROSS-SECTIONAL CHARACTERIZATION OF THIN-FILM TRANSISTORS WITH TRANSMISSION ELECTRON-MICROSCOPY

The nanometer-scale multilayered structure of hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) used as elements for active matrix liquid crystal displays was characterized by means of cross-sectional transmission electron microscopy (TEM). This article describes how an array can be characterized by using a TFT array tester that can detect, accurately locate, and identify pixel faults. Cross-sectional TEM was used to investigate the discrete layer construction of a faulty TFT and the generation of defects during manufacturing processes. Two types of faulty TFTs are examined in this study: (1) those in which gross defects such as contamination are readily detectable and (2) those in which no significant anomalies are detectable under an optical microscope inspection. Cross-sectional results were obtained by TEM for both types of faulty TFTs. Contamination layers composed of silicon oxide were observed in the same location in both cases, with a thickness of 10-30 nm. These layers caused contact failures. This observation led to identification of the fault and analysis of its cause, which in turn led to a marked yield improvement. An a-Si layer was crystallized as an artifact during TEM observation. Electron irradiation damage is also discussed.