Grain boundary void growth in bamboo interconnect under thermal residual stress field

Abstract

An analytic expression is developed to predict grain boundary void growth in bamboo interconnect under thermal residual stress field. The rate process is controlled by grain boundary and interconnect/passivation interface diffusions. The thermal residual stress field relaxes during void growth. Based on the present analysis, the behaviors of the void growth and the stress redistribution are characterized as a function of the microstructure of the interconnect, the state of the thermal residual stress, the initial size of the void, as well as the diffusivity ratio between the interface and the grain boundary.

Local distribution of residual stress of Cu in LSI interconnect

“…Such circuits require a highly reliable Cu line and Cu/dielectric interface [1,2]. Their reliability is influenced by failure mechanisms such as stressinduced voiding, electromigration, and interfacial delamination [2][3][4], which in turn are caused by tensile stress due to thermal treatment in LSI interconnect fabrication [2]. Therefore, the distribution of the residual stress in the Cu lines and interface influences where failure occurs in LSIs.…”

Electromigration-induced stress in a confined bamboo interconnect with randomly distributed grain sizes

“…[2]. There has been much work on the interaction between stresses and the change in matter distribution along the interfaces (including IF and GB) based a rigid grain model [9,18,20,27,28]. This model assumes that diffusion is fast enough along the interfaces so that shear stresses acting on interfaces are relaxed and material inserted into interfaces is uniformly placed.…”

“…High tensile stress induced by EM facilitates void nucleation and growth, which can eventually cause failure of devices. The stress-induced void dynamics has been extensively studied [7,10,14,18,26]. Therefore, understanding the stress field in bamboo interconnects prior to void initiation is essential for the failure analysis.…”

“…Interconnects with bamboo microstructures have been shown to have drastically increased lifetimes because of the absence of high diffusivity GB paths along the length of the lines. In the confined bamboo interconnect, deposited on an oxidized silicon substrate and covered by dielectric passivation layer, the coupling of the GB diffusion with the line/passivation interface (IF) diffusion is the dominant mass transport mechanism [17][18][19][20][21][22], where the major mass transport path is a network consisting of the GB and the IF. Consequently, the model with 1D simplification fails to describe the stress evolution in bamboo interconnects.…”

The Thermal Residual Stress Redistribution in a Bamboo Interconnect

“…However, the stress does not remain constant but varies with time. In general, the stress in interconnects can be redistributed and partially released by several mechanisms, such as the diffusion through grain boundaries (GB) and interconnect-passivation interface (IF), and voiding and cracking [12][13][14][15][16][17]. Experimental evidence [13,14] indicates that the coupling of the GB diffusion and IF diffusion is the dominant stress relaxation mechanism in passivated Cu films.…”