ANALYSIS OF GRAIN-BOUNDARY STRUCTURE IN AL-CU INTERCONNECTS

The role of crystallographic texture in electromigration resistance of interconnect lines is well documented. The presence of a strong (111) fiber texture results in a more reliable interconnect structure. It i s also generally accepted that grain-boundary diffusion is the primary mechanism by which electromigration failures occur. It has been diffi cult to this point, however, to obtain statistically reliable informat ion of grain-boundary structure in these materials as transmission ele ctron microscopy investigations are limited by tedious specimen prepar ation and small, nonrepresentative, imaging regions. The present work focuses upon characterization of texture and grain-boundary structure of interconnect lines using orientation imaging microscopy, and partic ularly, upon the linewidth dependence of these measures. Conventionall y processed Al-1%Cu lines were investigated to determine the affects o f a postpatterning anneal on boundary structure as a function of linew idth. It was observed that texture tended to strengthen slightly with decreasing linewidth subsequent to the anneal procedure. Grain morphol ogy changed substantially as the narrow lines became near bamboo in ch aracter and the crystallographic character of the boundary plane chang ed as a function of linewidth. These results are contrasted with those obtained from Al-1%Cu lines, which were fabricated using the damascen e process, The damascene lines show a marked weakening in texture as t he linewidth decreases, accompanied by a more random misorientation di stribution. A description of the competing energetics, which result in the observed microstructures, is included. (C) 1997 American Institut e of Physics.