In-Situ Observation and Quantitative Analysis of Electromigration Void Dynamics

Abstract

Electromigration (EM) void nucleation and growth is a failure mechanism of integrated circuit (IC) metallization. The time-to-failure of interconnect lines depends on the void nucleation time and the void growth time. While much work has been done to model the void nucleation stage, the current understanding of the void growth stage is minimal. Characterizing the void growth and interaction dynamics is essential to further explaining EM performance of IC interconnects.

EM-induced void behavior has been previously studied in-situ, however these studies have been exclusively phenomenological in nature. Void dynamics have been observed to be complex, exhibiting growth, movement, and interaction. This chapter describes work using high-resolution electron-beam lithography to define sub-micrometer pre-patterned voids and hillocks of various sizes and shapes into gold lines in order to observe and quantify void growth, void-void interactions and void-hillock interactions. The EM-induced dynamics of these pre-patterned void systems were measured in a field-emission scanning electron microscope in-situ. Results indicate that growth dynamics can be quantified in terms of void aspect ratios. Long-range void-void interactions can be quantitatively analyzed in terms of secondary, induced void formation, while short-range interactions are best analyzed in terms of direct pre-patterned void shape changes. Dynamics for void-hillock interaction were not found, leading to the conclusion that hillocks do not affect the damage formation as do voids. The quantitative techniques developed and described in this chapter indicate void growth and interaction can be measured.