Application of cross-sectional transmission electron microscopy to thin-film-transistor failure analysis

The 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, were investigated by combining focused ion beam (FIB) techniques with cross-sectional transmission electron microscopy (X-TEM), The 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 thin layers formed from etching residue, microvoids in the multilayers, fragile aluminum whisker protrusions on the electrodes, or portions of the TFT multilayer damaged by mechanical stress.