Investigation Of Damage And Reliability Of Metal Films Under Mechanical/Thermal Cyclic Loading

With the rapid development of integrated circuits,the characteristic length scale of metal interconnect lines in the microelectronic devices is being reduced down to submicrometer-scale and even nanometer-scale.Since metal interconnect lines inside microchips are unavoidably subjected to electrical,thermal and mechanical load:ing during the fabrication and service of the metal lines,an investigation of mechanical fatigue and thermal fatigue properties and damage behavior of metal interconnect lines is of the great significance.In this work,metal interconnect lines,Cu and Au films,were studied as research subjects.The reliability of the Cu films before and after annealing treatment under fatigue loading were investigated systematically.While,the damage behaviors of the Au films were also investigated under independent thermal cyclic loading at the same time.The investigation of fatigue properties of the Cu films indicates that under the same strain amplitude the fatigue life of the Cu films whether as-deposited or annealed increases with decreasing the film thickness from 250 nm to 25 nm.There is a size effect on the fatigue life of the Cu films.Such size effect is attributed to the decrease in both the geometrical scale and grain size and the increase in constraint effect on dislocation motion with decreasing the film thickness.Under the same strain amplitude,the fatigue performance of the annealed Cu film is better than that of the as-deposited one.Fatigue loading can induce grain growth of the as-deposited and annealed Cu films,but in the same condition,the extent of fatigue-induced grain growth of the as-deposited Cu films is evidently higher than that of fatigue-induced grain growth of the annealed Cu films,indicating annealing treatment can evidently suppress the extent of the fatigue-induced grain growth.The extent of fatigue-induced grain growth of the as-deposited Cu films is evidently higher than that of the annealing-induced grain growth of the Cu films,revealing that the grain growth results from mechanical driving,rather than thermal activation.Furthermore,Fatigue loading can induce deformation twinning of Cu films.The investigation of damage behavior of the Au films under thermal cyclic loading indicates that circular buckling form at the the Au film surface under thermal cyclic loading.With increasing thermal cycles,the size of buckling first increases then keeps intact.This is attributed to the critical buckling stress first increases and then remains with the decrease in the half-width of buckling.