Showing papers by "Carl V. Thompson published in 2001"

The dynamic competition between stress generation and relaxation mechanisms during coalescence of Volmer–Weber thin films

Abstract: Real-time measurements of stress evolution during the deposition of Volmer–Weber thin films reveal a complex interplay between mechanisms for stress generation and stress relaxation. We observed a generic stress evolution from compressive to tensile, then back to compressive stress as the film thickened, in amorphous and polycrystalline Ge and Si, as well as in polycrystalline Ag, Al, and Ti. Direct measurements of stress relaxation during growth interrupts demonstrate that the generic behavior occurs even in the absence of stress relaxation. When relaxation did occur, the mechanism depended sensitively on whether the film was continuous or discontinuous, on the process conditions, and on the film/substrate interfacial strength. For Ag films, interfacial shear dominated the early relaxation behavior, whereas this mechanism was negligible in Al films due to the much stronger bonding at the Al/SiO2 interface. For amorphous Ge, selective relaxation of tensile stress was observed only at elevated temperatures...

Electromigration in Cu interconnects with very different grain structures

Abstract: To determine the effects of grain structures on the rate of electromigration-induced failure of Cu interconnects, scanned laser annealing (SLA) has been used to produce Cu interconnects with very different grain structures. SLA, in which a moving hot-zone induces local grain growth, can be used to produce interconnects with fully bamboo grain structures that have bamboo grain lengths up to ten times the interconnect width. Electromigration experiments have been carried out on interconnects with very-long-grained bamboo structures, as well as on interconnects with polygranular structures in which the average grain size is less than the linewidth. Such differences are known to lead to orders of magnitude changes in lifetimes for Al-based interconnects. However, no significant differences in the failure rates were found for these Cu interconnects. This result supports earlier work that suggested that electromigration in Cu interconnects with now-standard liners and interlevel diffusion-barrier layers occurs ...

Effect of current direction on the lifetime of different levels of Cu dual-damascene metallization

Abstract: Electromigration in the lower metal (M1) and the upper metal (M2) of Cu dual-damascene interconnections has been studied. The failure times of M2 test structures are significantly longer than those of identical M1 structures. It is proposed that this asymmetry is the result of a difference in the location of void formation and growth, which is believed to be related to the ease of electromigration-induced void nucleation and growth at the Cu/Si3N4 interface. Asymmetric via reliability is therefore an intrinsic characteristic of current Cu interconnect technology.

Grain growth and evolution of other cellular structures

Abstract: Publisher Summary This chapter discusses grain growth and evolution of other cellular structures. The properties of polycrystalline materials are strongly affected by the average size of their grains, and by the nature of the distribution of their grain sizes. This is especially true of the mechanical properties of materials, but also holds true for the electrical, optical, and magnetic properties. While the initial grain size distribution of a material is controlled by the nucleation of its constituent crystals and by subsequent growth and impingement processes, further evolution often occurs through motion of the grain boundaries that form when crystals impinge. Grain boundary motion results in the growth of some grains, and the shrinkage and disappearance of others, with the average grain size increasing. This process, which occurs in fully crystalline materials, is generally referred to as grain growth. To understand how the distribution of grain sizes evolves during grain growth it is necessary to go beyond the phenomenological model. This has been accomplished with greatest success for 2D systems, for which some relatively simple but powerful topological rules are known. Many of the concepts discussed here in the context of grain growth apply to the evolution of other cellular systems such as magnetic domains and froths or foams.

Experimental characterization and modeling of the reliability of interconnect trees

Abstract: Interaction of the segments of interconnect trees during electromigration experiments has been studied using several simple tree structures. It is demonstrated that the reliability of a segment can not be predicted without knowledge of the conditions for stress migration and electromigration in connecting segments. Simulations of stress evolution during electromigration in interconnect trees have also been developed, and have been shown to predict behavior consistent with experimental results. Based on experiments and simulations, an analytic model for estimating the reliability of interconnect trees is developed. This analysis is based on calculations of the lifetimes of individual nodes within a tree, by estimating the times for void nucleation, void growth to failure, and formation of extrusions, using current density information for all of the segments connecting at a node. Models, simulations and experimental results on the reliability of interconnect trees are shown to yield mutually consistent resu...

Diffusional creep in damascene Cu lines

Abstract: Damascene Cu lines are increasingly being used as electrical interconnects in microelectronic integrated circuits. During the manufacturing process, Cu interconnects are subjected to thermal cycling that leads to complex stress states, which affect their reliability. While a realistic assessment of the impact of thermal stresses on the reliability should take into account the inelastic behavior of the damascene Cu lines, unfortunately, little is known about their mechanical behavior. The goal of this work was to identify the physical mechanisms responsible for the inelastic behavior of damascene Cu lines, and to assess the effects of the varied dimensions and passivation layers. The curvature changes caused by thermal cycling of wafers with damascene Cu lines were measured in the temperature range from −80 to 450 °C. At low temperatures, the deformation in the lines is predominantly elastic, but becomes inelastic above 200 °C. Our experimental results indicate that diffusion-controlled creep is the domina...

Simulation of microstructural evolution induced by scanned laser annealing of metallic interconnects

Abstract: Through modeling and simulations, we have determined the mechanisms that lead to the observed microstructural evolution induced by the scanned laser annealing (SLA) of interconnects. We found that higher laser powers and lower scan rates lead to greater transformation to bamboo microstructures, as well as to longer average bamboo grain lengths. The thermal profile along the interconnect length is shown to have a weak effect on the fraction transformed to bamboo, but a strong effect on the average bamboo grain length. Additionally, using simulations, we have determined SLA conditions that should lead to the development of single crystal structures, which are velocities of 1 μm/s or lower, laser powers 9.7 mW or higher, and steep thermal profiles.

Modeling of the effects of crystallographic orientation on electromigration-limited reliability of interconnects with bamboo grain structures

Abstract: We presented a model for the line-width-dependent grain structure statistics in bamboo interconnects. We then showed, using an electromigration simulation, that grain orientation-dependent interface diffusivities constitute a likely mechanism contributing to the variabilities in lifetimes observed in experiments.