Integration and reliability of CVD Ru cap for Cu/Low-k development

Abstract

Selective CVD Ru cap deposition process has been developed for BEOL Cu/Low-k integration. Selectivity of CVD Ru deposition between Cu and dielectrics is investigated. Electrical performance, electromigration (EM) lifetime, voltage ramp (I-V), and time -dependent-dielectric-breakdown (TDDB) are also characterized for Cu interconnects capped with CVD Ru. This selective CVD Ru cap process is a good candidate for 22nm and beyond technology nodes. IntroductionAs Cu interconnect feature sizes continue to shrink, current density is increasing, creating greater risk of EM failure [1]. The interface between dielectric capping layer and Cu has been shown to be the dominant Cu diffusion path and the weakest site in resisting EM failure [2,3]. It has also been observed that a metallic capping layer is an effective method to slows the diffusion and enhance electromigration resistance [4,5]. While various approaches have been proposed to reduce Cu transport and void growth by adding a metal cap layer on Cu interconnects, most have an undesirable impact on line-to-line leakage, Cu resistance, and interconnect capacitance [6,7]. For instance, the implementation of a selective metal cap via electroless deposition technique is challenge due to difficulty in preventing contamination of the dielectric surface from the plating bath. In addition to line-toline leakage yield degradation and other reliability related issues, a contaminated dielectric surface could also impact overall interconnect capacitance. This electroless plating approach also entails added processing steps, for example pre and post deposition treatments, and increased cost.

Formation of highly reliable Cu/low-k interconnects by using CVD Co barrier in dual damascene structures

“…Most voids are commonly generated at the interface between a top of Cu line and an upper capping dielectric due to the lowest activation energy for Cu diffusion (0.9eV). Thus, a number of studies have been published that selective deposition of thin metal on Cu lines can prevent this movement [8][9][10].…”