Process design of Cu(Sn) alloy deposition for highly reliable ultra large-scale integration interconnects

Cu(Sn) alloys were studied as possible candidates for highly reliable interconnects. For conformational deposition of Cu(Sn) alloy seed layer, the effect of Sn doping and the deposition sequence of Cu(Sn) alloy on Cu wettability were investigated by evaluating the agglomeration behavior of Cu(Sn) seed layers on a TaN barrier. Two different sputter-deposited stacked layers were studied; Cu/Sn/TaN/SiO2/Si and Sn/Cu/TaN/SiO2/Si structure. Cu(Sn) alloy layers with 5 at.% Sn were agglomerated more than a pure Cu layer due to the lower melting point of Cu by Sn doping. The agglomeration behavior depended on the deposition sequence; Cu/Sn/TaN/SiO2/Si structure was agglomerated more than Sn/Cu/TaN/SiO2/Si structure because Cu atoms on liquid Sn layer can diffuse easily. Consequently, for continuous, thin seed-layer deposition, Sn atoms as an alloy element should be deposited after a continuous Cu layer is formed.