Effect of Ag content on the microstructure development of Sn-Ag-Cu interconnects

The impact of the Ag content on the microstructure development of the Sn-xAg-Cu (x= 0.0, 1.2, 2.6, 3.0, 3.5 and 3.9) interconnects was studied in detail by using surface microetching microscopy, cross section microscopy, differential scanning calorimetry and shear test. The thermal treatment was realized by conducting isothermal aging (150 ^sup ^C/1000 hrs). i) Ag content had a clear effect on the interconnect microstructure evolution. ii) Ag^sub 3^Sn intermetallic compound (IMC) plates were sophisticated microtextures with various morphologies and the basic microstructure of the Ag^sub 3^Sn plates had a morphology of a strengthened fan. iii) The Ag^sub 3^Sn plates grew in central symmetry. iv) The Cu-Sn IMC microstructures were also influenced by the Ag content, but to a lesser degree. iv) The occurrence of the Ag^sub 3^Sn plates did not exactly follow the trend of Ag content increase, but was governed more by the alloy undercooling. For the given Cu content, the undercooling of the alloy groups demonstrated a quasi-parabolic behavior with a minimum apex. vi) After aging, there were size recession and sharp edge smoothening for the Ag^sub 3^Sn plates after aging. These phenomena are explained by edge spheroidization and cylinderization of the Ag^sub 3^Sn plates during the aging. vii) The corresponding macro-mechanical performance of the LF interconnects did not degrade after the aging, independent to the Ag content.[PUBLICATION ABSTRACT]