Katsuhiro Tsujimoto

Relationship of grain nanostructure and orientation in whisker growth on aluminum thin films on glass substrates

Abstract The mechanism and characteristics of aluminum whisker generation were studied by using pure-aluminum (pure-Al) thin film sputterdeposited on glass substrate. The experiments revealed that whisker generation is accelerated at thermal stress temperatures above 270 °C as the exposure time at the maximum temperature becomes longer, and that the potential for whisker generation increases as the margin between the deposition and the thermal stress temperatures is increased. Plan-view TEM and electron diffraction analyses of whiskers also revealed that an Al film with a large proportion of (111) texture shows strong resistance to whisker generation, and that no whiskers grow from the (111)-oriented grain.

Transmission electron microscopy of thin-film transistors on glass substrates

Abstract The recent attention paid to sample preparation of multilayered structure on glass substrates indicates that cross-sectional transmission electron microscopy (X-TEM) are of considerable interest for their potential effectiveness in thin-film transistor liquid crystal display (TFT-LCD) application. We describe the significant features of our failure analysis problem which involves some difficulties: fragile location, anomalous, and rare defect. An application of focused ion beam (FIB) etching to specimen preparation for X-TEM observation is introduced. We demonstrated that the FIB technique, which allows very localized etching without inducing mechanical stress to thin TEM sample, is very convenient for this delicate location. We also demonstrate that our FIB etching technique is capable of high thinning rates, which allows rapid production of high-quality TEM specimen. Finally, we demonstrate how faulty TFTs including long and fragile protrusions such as whiskers, can be characterized by means of FIB and X-TEM combination.

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.

Investigation of thin-film transistors using a combination of focused ion beam etching and cross-sectional transmission electron microscopy observation

Abstract 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 is investigated using a combination of focused ion beam (FIB) etching and cross-sectional transmission electron microscopy (X-TEM). This paper presents how faulty TFTs fabricated on a glass substrate can be characterized by X-TEM to achieve pinpoint accuracy. X-TEM specimens are prepared by FIB etching from TFTs including relatively large microvoids in their multilayers, without dropping of delicate edges. Cross-sectional bright-field TEM micrographs clearly show the details around the microvoids. This pinpoint X-TEM identifies faults and gives an analysis of their causes. In this paper, conventional low-angle ion milling and FIB etching are compared, Ion irradiation damage during FIB etching is also discussed.

Electron microscopy observation of whiskers and hillocks formed on an Al film deposited on to a glass substrate

Abstract Hillocks and whiskers formed on an Al film deposited on to a glass substrate have been characterized by plan-view as well as cross-sectional transmission electron microscopy. Most of the hillocks and whiskers were nucleated in the middle of the bottom grains and few dislocations were observed inside the bottom grains. Hillocks inherit the orientations from the bottom grains, while whiskers do not. A new formation mechanism of hillocks and whiskers where surface diffusion and impurity-enhanced grain-boundary diffusion play important roles has been proposed.

Effects of surface damaging and overcoating on the formation of hillocks and whiskers on pure Al films deposited on to a glass substrate

Abstract Conditions of the outermost surfaces of Al films deposited on to a glass substrate were modified systematically in two different ways. In one, the surfaces of the Al films were indented by a Vickers indenter with different loads. In the other, overcoating layers with different thicknesses were deposited on to the original Al films. The effects of the Vickers indentation and the overcoating layer on the formation of hillocks and whiskers were studied systematically. Modification of the outermost surfaces leads to both suppression and enhancement of formation of hillocks and whiskers. It is concluded that the strength of the natural oxide layer governs whether or not whiskers and hillocks are formed.

Transmission electron microscopy of whiskers and hillocks formed on Al films deposited onto a glass

Whiskers and hillocks formed on an Al film deposited onto a glass substrate have been observed by means of a variety of transmission electron microscopy technique.

Nanostructural investigation of whiskers and hillocks of Al-based metallization in thin-film transistor liquid crystal displays

Nanostructure of whiskers and hillocks in various aluminum (Al)-based thin films for thin-film transistor (TFT) on glass substrates has been investigated. We developed a novel technique to fabricate whiskers and hillocks artificially, using nanoindentation technique and annealing in a vacuum furnace. During the annealing, some Al whiskers and hillocks are formed, particularly on the edges of indentation marks. The high degree of whisker formation in this technique correlated to the weak hillock formation resistance in actual TFT arrays. Nanostructure of these thin films was investigated by cross-sectional transmission electron microscopy (X-TEM). The surface morphology of as-deposited films was also investigated by atomic force microscopy (AFM).