Comparison of the Ti/TiN/AlCu/TiN stack with TiN/AlCu/Ti/TiN stack for application in ULSI metallization

The relative advantages and disadvantages of the two ULSI metallization stacks viz., Ti/TiN/AlCu/TiN and TiN/AlCu/Ti/TiN are described. The electromigration and thermal stability characteristics are compared using grain size of the Al metal, the XRD rocking curve peak and FWHM of the Al (111) orientation, SWEAT lifetime and electrical characteristics before and after thermal cycling of the test structures. In the literature, there exists work that report an improvement in the electromigration lifetime in the situation where Ti is in direct contact with Al due to the formation of TiAl 3 . The results for submicron dimensions presented in this paper clearly point to very important requirements for those results to hold and highlight the danger in assuming its validity for submicron lines. The W- plug via schemes resulting from use of both these metallization stacks will be compared from both the electrical and reliability standpoint. The conflict arising between the functionality and reliability of the vias with the reliability of the metallization lines is discussed.