Stress migration lifetime for Cu interconnects with CoWP-only cap

Stress migration lifetime is characterized for a CoWP-only cap process (i.e., no dielectric cap) and a CoWP + SiN cap process. For the CoWP-only process, the stress migration lifetime depends on the CoWP thickness. In order to achieve a long stress migration lifetime, the CoWP must be sufficiently thick to protect the Cu during the via etch and strip processes. The data suggests that CoWP removal is enhanced beneath partially landed vias, resulting in reduced stress migration lifetime.