Effects of texture, microstructure, and alloy content on electromigration of aluminum-based metallization

Abstract

The role of microstructure is becoming increasingly important as minimum feature sizes decrease in succeeding generations of devices. To insure reliability, advances have been made in aluminum-based interconnects in the form of new metallurgies and multilayer metal structures. The interplay of metallurgy and microstructure now must be understood in lines with widths less than 0.5 μm. This paper will analyze the texture effects on electromigration behavior in pure Al, AlCu, and multilayer Ti/AlCu/Ti metallurgies being mindful that the texture is inseparable from other aspects of microstructure such as grain size and grain size distribution. An increasingly strong (111) texture shows higher mean time to failure and lower dispersion. Preliminary results indicate that narrow line widths produce higher dispersion of failure times regardless of the texture. The texture depends on deposition conditions, annealing conditions, and type of substrate (amorphous or oriented crystalline) whereas alloy content alone has not been found to have a measurable effect on the texture. In general, sputtered textures are sharper (lower spread of the (111) fiber distribution) than evaporated textures. Annealing at temperatures sufficiently high to induce grain growth sharpens the (111) texture and/or decreases the fraction of randomly oriented grains. Finally, deposition on a thin, highly textured titanium underlayer sharpens the subsequent aluminum alloy texture.