Mechanism of reliability failure in Cu interconnects with ultralow-κ materials

Abstract

This letter presents evidence of an oxidation-driven failure mechanism in Cu interconnects integrated with ultralow-κ materials. It is found that the open pore structure of ultralow-κ materials allows oxidants in the ambient to reach the interconnect structure and induce oxidation of Cu. In contrast to a normal oxidation process where Cu is in contact with the oxidant, oxidation is controlled by the outdiffusion of Cu through the barrier layers, Ta and SiCN, to form Cu oxide in the pores of the dielectric material. The loss of Cu by outdiffusion induces extensive voiding and subsequent failure in Cu interconnects.

Copper diffusion barrier properties of CVD boron carbo-nitride

“…Metal ion diffusion through insulating films is facilitated by the presence of oxygen through an oxidation pathway, 7,8,20,21 and a higher level of surface oxidation may enhance Cu + ion injection into the barrier. Two possible factors, which may be B-B composition dependent, are BCN film oxidation upon ambient exposure and the variable bond lengths within the film.…”

Failure mechanism analysis and process improvement on time-dependent dielectric breakdown of Cu/ultra-low-k dielectric based on complementary Raman and FTIR spectroscopy study

“…Although Ta/TaN barrier metal provides better migration resistance than Copper, 24 the problem is that the pores in ultra-low-k materials can be highly connected and provide migration paths for processing gases and moistures. 25,26 That path similar to capping layer, which normally observed from copper migration provides a leakage path from one conductor to an adjacent conductor, and the current conduction mechanism is assumed to be Poole-Frenkel (PF). After the migration of Ta ions, the dielectric gap between Cu lines decreased, and degradation of the ultra-low-k materials be accelerated and the device doesn't went to break down.…”

Electrical Breakdown in Advanced Interconnect Dielectrics

“…Trench-only test structure with alternating biases (8) Similarly, metal barrier thickness reduction will affect the thickness of metal barrier sidewalls (and bottom) within vias, thus potentially worsening the reliability margin for vias against Cu out-diffusion failures (regardless of whether new advanced barrier metallizations are used) [21][22][23][24][25].…”