STRUCTURE ENGINEERING FOR HILLOCK-FREE PURE ALUMINUM SPUTTER-DEPOSITION FOR GATE AND SOURCE LINE FABRICATION IN ACTIVE-MATRIX LIQUID-CRYSTAL DISPLAYS

In this article we present the results of a study aimed at developing hillock-free, pure-Al thin-film material suitable for the fabrication of gate and source lines in thin film transistor active-matrix liquid crystal displays. Strong Al(111) texture was shown to be a key attribu te for achieving good resistance to hillock formation. To obtain this strong Al(111) texture, we explored the incorporation of a thin metal layer, under the Al film, and we showed that Ti could be an appropriat e candidate for further optimization. Key variables affecting the qual ity of Al were found to be the roughness of the glass substrate, the t hickness of the titanium, the background vacuum quality, and the sputt ering temperature. By optimizing the deposition process for both Al an d Ti layers, we showed that aluminum films with very strong (111) text ure (rocking curve full width at half maximum 0.86 degrees), very smoo th surface (root mean square surface roughness 1.8 nm), and a uniform, columnar grain size (0.3-0.5 mu m) could be deposited by de magnetron sputtering. In addition to improving the aluminum microstructure, opt imization of the gate dielectric process was also performed with the a im of reducing hillock formation. Combined optimization of the sputter ing and gate dielectric deposition processes yielded an overall reduct ion in hillock density of 3.5-4 orders of magnitude, without the need for anodic oxidation or other means of capping the aluminum film. By c ombining Al/Ti de sputtering, dry-etching technology for one-step patt erning of the composite Al/Ti film, and gate insulator deposition at 3 00 degrees C we demonstrated, for the first time, gate metallization t echnology based on pure Al with excellent step coverage and ultralow h illock density (< 10(3) cm(-2)). (C) 1998 American Vacuum Society. [S0 734-2101(98)03004-8].