Cu/low-k BEOL Process Integration of 90 nm NOR Flash and Their Effect on Cell Characteristic, RC delay and Prevention of Cu diffusion

摘要

In this paper, the result of successful process integration for the development of 90 nm NOR flash device, which adopted Cu and low-k material in BEOL (Back End Of Line) process is discussed. We focused on the effect of Cu integration on the flash cell characteristic, RC delay and the prevention of Cu diffusion. Our BEOL process met electrical target specification of 90 nm NOR flash device such as via resistance (Rc) and sheet resistance (Rs), and showed no shrinkage or bowing of low-k film in the trench pattern. Simulated data demonstrated that our BEOL process improved RC delay. However, we found that Cu diffusion into upper Al pad could affect the poor endurance characteristic. Our new pad condition satisfied endurance property of 90 nm NOR flash device as well as Rs. This study demonstrates that our new BEOL structure is compatible with conventional NOR flash process and will be expected to meet the requirements of high performance NOR flash device beyond sub-65 nm technology node.