Effects of texture and grain structure on electromigration lifetime of Al−Cu interconnects

Abstract

The effects of Ti underlayer (collimated Ti vs. standard Ti) and Al deposition power (12 KW vs. 6 KW) on the electromigration (EM) lifetime of Ti/Al-0.5 wt. %Cu/Ti/TiN stack films were investigated The. (002) texture of standard Ti (s-Ti) was stronger than that of collimated Ti (c-Ti), and the Al (111) texture, grain size distribution, and EM lifetime of Al stack prepared with s-Ti underlayer were also better than those with c-Ti underlayer independent of the Al deposition power. The low power (6 KW) deposition led to better Al (111) texture, larger median grain size, and longer EM lifetime than did high power (12 KW) deposition independent of the type of Ti underlayer. Longer deposition time for low power sputtering allowed more time for the deposited Al atoms to be rearranged at more stable sites and to react with Ti, which resulted in a stronger Al (111) texture, larger median grain size, and a more uniform Ti−Al reaction layer. The (002) texture of the Ti underlayer is closely related to the Al (111) texture which is a major factor affecting EM lifetime.